PhD, The University of Tokyo

LED

Ultrafast Laser spectroscopy

Photoexcited Carrier Dynamics

高速レーザー分光

光励起キャリアダイナミクス

Perovskite Solar Cell

ペロブスカイト太陽電池

Quantum Dot Solar Cell

Quantum Dot Solar Cell

solar cells

metal nanoparticles

semiconductor quantum dots

Thermal properties of condensed matter

Energy conversion

Optical properties

熱物性

光電エネルギー変換

光物性

金属ナノ粒子

半導体ナノ粒子

有機・無機ハイブリット太陽電池

Nanotechnology/Materials, Applied physics - general

Nanotechnology/Materials, Nanomaterials

Mar. 1995
The University of Tokyo, Graduate School, Division of Engineering, 応用化学専攻

Jul. 1989
中国南京大学, 情報物理学研究科, 音響学専攻, China

Jul. 1987
中国南京大学, Faculty of Science, 物理学科, China

Apr. 2022 - Mar. 2024
理事, 応用物理学会

Mar. 2014
Japan Society of Applied Physics
Excellent Women Scientist Award of The Japan Society of Applied Physics

Nov. 2003
Young Scientist Award of The Symposium on Ultrasonic Electronics

Oct. 2003
Best Paper Award of The Japan Society of Thermophysical Properties

Oct. 1997
Young Scientist Award of The Japan Society of Applied Physics

Carboxylate Pseudo-Halide-Assisted crystallization and antioxidant strategy for stable wide bandgap tin perovskite photovoltaics
Sung Won Cho; Hochan Song; Padmini Pandey; Seong Chan Cho; Saemon Yoon; Woo Hyeon Jeong; Hyungju Ahn; Seojun Lee; Jeong Yeon Lee; Qing Shen; Sang Uck Lee; Hyosung Choi; Dong Won Kang
Chemical Engineering Journal, 497, 01 Oct. 2024, The facile oxidation of Sn2+ to Sn4+ and uncontrolled crystal growth are significant challenges in the development of wide-bandgap (WBG) tin perovskite solar cells (TPSCs), affecting their performance and stability. This study introduces three strategically synthesized carboxylate pseudo-halides—3,3-diphenylpropylammonium trifluoroacetate (D-TFA), 3,3-diphenylpropylammonium acetate (D-Ac), and 3,3-diphenylpropylammonium formate (D-Fo), —as additives to mitigate Sn2+/Sn4+ oxidation in WBG TPSCs. These pseudo-halides coordinate with Sn2+, reducing electron density at the carboxylate carbon and forming robust bonds with SnI2(DMSO)3, thus impeding Sn2+ oxidation through oxygen adsorption. Among them, the formate ion (Fo-) in D-Fo exhibited the most significant deshielded peak, indicating the strongest coordination with Sn2+ and superior antioxidation effects by reducing reactivity with ambient oxygen. These interactions, along with 3,3-diphenylpropylammonium (DPA+), aid in controlling crystal growth, enhancing the formation of highly crystalline thin films, and improving overall stability. Consequently, D-Fo-assisted WBG tin perovskites demonstrated strong suppression of phase segregation under prolonged illumination of the air mass 1.5 spectrum, retaining 90 % of their initial characteristics. Ultimately, the D-Fo-enhanced WBG TPSC achieved an exemplary power conversion efficiency of 10.69 % with minimal hysteresis, surpassing the control cell's 7.43 %. Furthermore, the unencapsulated D-Fo device maintained nearly 87 % of its initial performance after 960 h under ambient conditions.
Scientific journal

The Application of Metallic Sn in Sn-Based Perovskite Solar Cells
Liang Wang; Hong Zhang; Qing Shen; Shuzi Hayase
ChemNanoMat, 10, 10, Oct. 2024, Nontoxic Sn-based perovskite solar cells (PSCs) represent a promising alternative to Pb-based PSCs, given their similar electronic properties and an ideal bandgap, accompanied by the highest theoretical efficiency (>33%). However, the performance of Sn-based PSCs lags significantly behind their Pb-based counterparts. This disparity arises from the susceptibility of Sn2+ to easy oxidation to Sn4+, an energy level mismatch, and fast crystilization. It is widely acknowledged that the oxidation of Sn2+ to Sn4+ results in severe P-type doping, leading to increased recombination, which is a primary factor contributing to the lower device performance. In this perspective article, we summarized the utilization of metallic Sn in Sn-based PSCs to facilitate the reduction of Sn4+ back to Sn2+. This approach is preferred due to its effectiveness, simplicity in process, and the absence of introducing additional impurities. Moreover, metallic Sn can serve as a source for synthesizing SnI2 and act as hole transport material through transformation from Sn to SnOx. We hope this article serve as a valuable reference for the ongoing development of Sn-based materials in PSCs technology.
Scientific journal

Enhanced Electron Transport in Heterojunction Sn-Perovskite Solar Cells Assisted by [6,6]-Phenyl-C61-butyric Acid Methyl Ester as a Dopant
Ajay Kumar Baranwal; Huan Bi; Gaurav Kapil; Takeshi Kitamura; Liang Wang; Jiaqi Liu; Qing Shen; Shuzi Hayase
ACS Energy Letters, 9, 8, 4119-4126, 09 Aug. 2024, Tin halide perovskite (THP) possesses p-type semiconducting properties owing to innate Sn oxidative defect states. These defect states create imbalance in charge collection at the interfaces, which hinders overall solar cell efficiency. To effectively harness THP’s potential, we introduced a strategic n-type commonly used material, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), as a dopant, which has rarely been discussed. The coupling of PCBM and THP, validated through experimental and density functional theory methods, effectively targeted Sn defect states and transformed the THP semiconducting nature from p-type to intrinsic. Furthermore, strategically positioned PCBM at the grain boundaries offered multiple benefits, including improved adhesion between grains, leading to reduced lattice strain, enhanced energetic matching, and efficient charge transfer. This positing effectively harnessed electron collection due to PCBM’s n-type electronic properties, leading to an enhanced PCE. This blend strategy, broadly followed in organic solar cells, led to the development of PCBM-THP heterojunction solar cells, achieving a record efficiency of 12.68%.
Scientific journal

Double side passivation of phenylethyl ammonium iodide for all perovskite tandem solar cell with efficiency of 26.8%
Huan Bi; Jiaqi Liu; Liang Wang; Zheng Zhang; Gaurav Kapil; Shahrir Razey Sahamir; Ajay Kumar Baranwal; Yuyao Wei; Yongge Yang; Dandan Wang; Takeshi Kitamura; Hiroshi Segawa; Qing Shen; Shuzi Hayase
EcoEnergy, Wiley, 02 Jul. 2024, Abstract

All‐perovskite tandem solar cells are regarded as the next generation of devices capable of enhancing the solar energy utilization rate. Unlike single‐junction perovskite solar cells (PSCs), the efficacy of tandem cells is contingent upon the performance of both the top and bottom cells. In this study, we employed a simultaneous co‐modification strategy to incorporate phenylethylammonium iodide (PEAI) at both the top and bottom interfaces of the perovskite film, aiming to boost the top cell's performance. Both experimental and theoretical findings indicate that PEAI not only elevates the perovskite film quality through chemical interactions but also mitigates nonradiative recombination within the device. Consequently, the efficiency of the wide‐bandgap (1.77 eV) PSCs based on nickel oxide (NiO_x) attained a level of 16.5%. Simultaneously, the all‐perovskite tandem solar cells achieved an efficiency of 26.81% and demonstrated superior stability.
Scientific journal

Restraining Photocurrent Loss of Lead-Free Perovskite Solar Cells by Regulating Surficial Hydroxyl of Fluorine-Doped Tin Oxide
Jiaqi Liu; Huan Bi; Zheng Zhang; Yasuhiro Fujiwara; Yoshitaka Sanehira; Gaurav Kapil; Takeshi Kitamura; Shahrir Razey Sahamir; Ajay Kumar Baranwal; Liang Wang; Qing Shen; Shuzi Hayase
ACS Applied Energy Materials, 7, 11, 4779-4785, 10 Jun. 2024, The surface treatment of transparent conducting oxide substrates constitutes the initial step in fabricating solar cells. However, the specifics of this process are often oversimplified. This study delves into the impact of surface treatment on fluorine-doped tin oxide (FTO) substrates on the performance of Sn perovskite solar cells. Varied thicknesses of the coated poly(3,4-ethylenedioxythiophene)polystyrenesulfonate (PEDOT:PSS) layer were achieved by regulating the quantity of hydroxyl on FTO substrates. The investigation reveals that the thickness of the PEDOT:PSS layer directly influences the photoluminescence intensity and carrier lifetime, irrespective of the perovskite crystal quality. Thinner PEDOT:PSS layers are observed to mitigate shallow-level defects, thereby enhancing the short-circuit current density of solar cell devices. This study underscores the significance of controlling the heterostructure properties for improving solar cell performance.
Scientific journal

Midgap states and energy alignment at interconnect are crucial for perovskite tandem solar cells
Gaurav Kapil; Yasuhiro Fujiwara; Huan Bi; Ajay Kumar Baranwal; Shahrir Razey Sahamir; Jiaqi Liu; Liang Wang; Daisuke Hirotani; Qing Shen; Hiroshi Segawa; Shuzi Hayase
Cell Reports Physical Science, Elsevier BV, 5, 7, 102060-102060, Jun. 2024, Monolithic, two-terminal stacking of wide and narrow band-gap perovskite absorbers can overcome the single-junction efficiency limitations. Empirically, two subcells need to be electrically coupled via an interconnecting layer (IL) where the majority charge carriers need to be recombined efficiently, avoiding minority recombination. This study explores how increasing the density of states (DOS) in the IL can encourage majority recombination and, hence, improve the open-circuit voltage (Voc). By using indium oxide doped with zinc oxide (IZO) in the IL, we found that adjusting film formation techniques can tune DOS and other properties. Additionally, higher in-plane resistance at the interconnect and favorable energy alignment across ILs are crucial for improving the power conversion efficiency (PCE). Compared to commonly used Au nanoparticles, the optimized ILs improved the PCE from 22.32% to 26.39%, the Voc from 1.84 to 1.94 V, and the short circuit current density from 15.42 to 17.18 mA/cm2.
Scientific journal

Elucidating the Mechanisms of the Large Stokes Shift in Isolated and Coupled PbS Quantum Dots
Hua Li; Chao Ding; Naoki Oguri; Yuuya Makino; Dong Liu; Yao Guo; Yuyao Wei; Yusheng Li; Yongge Yang; Dandan Wang; Shikai Chen; Taizo Masuda; Shuzi Hayase; Tomah Sogabe; Qing Shen
Journal of Physical Chemistry C, 128, 21, 8732-8740, 30 May 2024, Despite much effort being made, the origin of Stokes shift in colloidal quantum dot (CQD) solutions is still debatable to date, particularly in the case of QD films, which are typically used as active layers in the optoelectronic devices but have been rarely explored. Herein, we demonstrate that for QD solutions, the main origin contribution to the Stokes shift is the confined electron state (CES). In the case of QD films, in addition to the aforementioned CES, for the first time, we found that the Stokes shift is also affected by the electronic coupling strength between adjacent QDs. Overall, an improved understanding of the origin of the Stokes shift in lead sulfide (PbS) QD solutions and films can provide the key fundamental knowledge for realizing efficient optoelectronic devices.
Scientific journal

Photoexcited Carrier Dynamics in Iodine-Doped CH3NH3PbBr3 Single Crystals
Dong Liu; Chao Ding; Yao Guo; Hua Li; Yusheng Li; Dandan Wang; Yongge Yang; Yuyao Wei; Shikai Chen; Guozheng Shi; Taro Toyoda; Dong Won Kang; Shuzi Hayase; Qing Shen
Journal of Physical Chemistry Letters, 15, 21, 5618-5624, 30 May 2024, Iodine-doped bromide perovskite single crystals (IBPSCs) have important applications in optoelectronic fields, such as in solar cells. Currently, much research has aimed to study the phase separation phenomenon and device performance improvements in IBPSCs. However, important intrinsic photoexcited carrier dynamics are often overlooked in IBPSCs. Here, we explored the photoexcited carrier dynamics in typical iodine-doped MAPbBr3 single crystals using the excitation intensity-dependent steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) technique. We found that the trap state density changes with an increase in the amount of doped iodine. Further, we noticed that there is an influence of carrier diffusion on the photoexcited carrier dynamics, and then, we evaluated the carrier diffusion coefficients and recombination constants via numerical simulations of the PL kinetics. Consequently, we found that the electron shallow trap-related carrier behaviors substantially impacted the PL kinetics. Our results greatly facilitate a deeper understanding of the fundamental characteristics of mixed halide perovskite material.
Scientific journal

Stronger Coupling of Quantum Dots in Hole Transport Layer Through Intermediate Ligand Exchange to Enhance the Efficiency of PbS Quantum Dot Solar Cells
Yuyao Wei; Chao Ding; Guozheng Shi; Huan Bi; Yusheng Li; Hua Li; Dong Liu; Yongge Yang; Dandan Wang; Shikai Chen; Ruixiang Wang; Shuzi Hayase; Taizo Masuda; Qing Shen
Small Methods, Wiley, 12 Apr. 2024, Abstract

Nowadays, the extensively used lead sulfide (PbS) quantum dot (QD) hole transport layer (HTL) relies on layer‐by‐layer method to replace long chain oleic acid (OA) ligands with short 1,2‐ethanedithiol (EDT) ligands for preparation. However, the inevitable significant volume shrinkage caused by this traditional method will result in undesired cracks and disordered QD arrangement in the film, along with adverse increased defect density and inhomogeneous energy landscape. To solve the problem, a novel method for EDT passivated PbS QD (PbS‐EDT) HTL preparation using small‐sized benzoic acid (BA) as intermediate ligands is proposed in this work. BA is substituted for OA ligands in solution followed by ligand exchange with EDT layer by layer. With the new method, smoother PbS‐EDT films with more ordered and closer QD packing are gained. It is demonstrated stronger coupling between QDs and reduced defects in the QD HTL owing to the intermediate BA ligand exchange. As a result, the suppressed nonradiative recombination and enhanced carrier mobility are achieved, contributing to ≈20% growth in short circuit current density (J_sc) and a 23.4% higher power conversion efficiency (PCE) of 13.2%. This work provides a general framework for layer‐by‐layer QD film manufacturing optimization.
Scientific journal

Highly Luminescent Phase-Stable Hybrid Manganese Halides for Efficient X-ray Imaging
Sujun Ji; Yihang Liu; Yulong Wang; Hongyuan Zhao; Qiujie Wang; Qichao Meng; Yunfei Bai; Junke Jiang; Qing Shen; Feng Liu
Crystal Growth and Design, 24, 5, 2094-2103, 06 Mar. 2024, Mn(II)-based organic-inorganic hybrid metal halides have garnered considerable attention for their potential use in X-ray imaging due to their cost-effective solution processability and remarkable radioluminescence efficiency. However, achieving a photoluminescence quantum yield (PLQY) close to 100% across all compositions containing Cl-, Br-, and I- has been a challenge. Here, we introduce an efficient spacer cation, BDPA+ (C15H18N+), which enables all halide compounds to achieve high PLQYs of 95-98%. The high fluorescence efficiency is attributed to the passivation effect provided by π-conjugated aromatic groups and the long distance between emissive centers afforded by the periodic bulk structures of BDPA+. This effectively reduces energy transfer between Mn2+ ions, resulting in enhanced luminescence. Additionally, the strong hydrophobic nature of the organic component ensures that the resulting crystals maintain their stability for over 2 months in ambient air, making them suitable for a wide range of applications. A representative scintillator prepared from (BDPA)2MnBr4 exhibits impressive X-ray imaging performance with a high light yield of 44,000 ph/MeV and a low detection limit of 0.32 μGy/s, comparable to those of commercial LuAG:Ce scintillator crystals (25,000 ph/MeV, 2.32 μGy/s). These findings hold great promise for the future development of this class of materials, particularly for stable high-energy radiation detection.
Scientific journal

Achieving High Efficiency and Enhanced Thermal Stability in Germanium-Encapsulated Tin–Lead Perovskite Solar Cells
Shahrir Razey Sahamir; Gaurav Kapil; Takeru Bessho; Hiroshi Segawa; Qing Shen; Shuzi Hayase
ACS Materials Letters, American Chemical Society (ACS), 6, 4, 1241-1246, 04 Mar. 2024, The efficiency and the thermal stability enhancement in tin-lead (SnPb)-based perovskite solar cells (PSCs) was investigated in this study by employing germanium iodide (GeI2) as a doping agent. The incorporation of GeI2 enhanced the performance of GeI2-doped SnPb PSCs with the highest efficiency of 21.9%. The XPS depth profiling showed unique observation; the Ge layer was only formed on the surface of the SnPb films. This layer encapsulated the SnPb films and thus prevented the perovskite films from extreme oxidation and structural and morphological degradations. An interlayer engineering approach was adopted in order to prove the PSCs by employing MeO2PACz monolayer as the hole extraction layer, while the tin oxide (SnOx) layer fabricated via atomic layer deposition (ALD) was applied near the electron transport layer. More than 94% of the initial efficiency was retained after 1000 h of a thermal stability test conducted at 85 °C in nitrogen atmosphere in the champion device.
Scientific journal

Adhesion, stability, structural and electronic properties of perovskite/BaWO₄ heterostructures: first-principles and experimental characterizations
Yao Guo; Shiding Zhang; Zhaoyu Zhang; Yuanbin Xue; Jianxin Li; Haixiang Song; Yuhua Wang; Qing Shen
Inorganic Chemistry Frontiers, Royal Society of Chemistry (RSC), 11, 9, 2661-2671, Mar. 2024, The interfacial behavior and mechanism of the CsPbBr₃/BaWO₄ and MAPbBr₃/BaWO₄ heterostructures have been extensively investigated by a combined first-principles and experimental analysis.
Scientific journal

Over 14% efficiency of highly reproducible Sn perovskite solar cell via defect passivation and morphology repairment
Zheng Zhang; Jiaqi Liu; Huan Bi; Liang Wang; Qing Shen; Shuzi Hayase
Chemical Engineering Journal, Elsevier BV, 483, 149345-149345, Mar. 2024, As a safer and more environmentally friendly alternative to lead-based perovskite, lead-free tin halide perovskite solar cells (PSCs) have gained significant attention. However, these cells have faced challenges, including poor quality from easy oxidation and fast crystallization, resulting in a rough surface morphology with numerous defects. To address these issues, we developed a strategy utilizing polysilanes, specifically polymethyl-phenyl-silane (PMPS) and deca-phenyl-penta-silane (DPPS), to enhance the quality of tin perovskite. Various modification methods, such as precursor doping, antisolvent modification, and surface passivation, were attempted. A promising 14.18 % efficiency of Tin PSC with better stability was achieved through surface passivation of PMPS. Further characterization showed that PMPS could work as a bifunctional molecule: smooth surface morphology and enlarge grain size (short-circuit current (Jsc) enhancement) as well as reductant for Sn4+ and regulator of surface energy level (open-circuit voltage (Voc) enhancement).
Scientific journal

Tandem Synergistic Effect of Cu-In Dual Sites Confined on the Edge of Monolayer CuInP2S6 toward Selective Photoreduction of CO2 into Multi-Carbon Solar Fuels
Wa Gao; Li Shi; Wentao Hou; Cheng Ding; Qi Liu; Ran Long; Haoqiang Chi; Yongcai Zhang; Xiaoyong Xu; Xueying Ma; Zheng Tang; Yong Yang; Xiaoyong Wang; Qing Shen; Yujie Xiong; Jinlan Wang; Zhigang Zou; Yong Zhou
Angewandte Chemie - International Edition, 63, 9, 26 Feb. 2024, One-unit-cell, single-crystal, hexagonal CuInP2S6 atomically thin sheets of≈0.81 nm in thickness was successfully synthesized for photocatalytic reduction of CO2. Exciting ethene (C2H4) as the main product was dominantly generated with the yield-based selectivity reaching ≈56.4 %, and the electron-based selectivity as high as ≈74.6 %. The tandem synergistic effect of charge-enriched Cu−In dual sites confined on the lateral edge of the CuInP2S6 monolayer (ML) is mainly responsible for efficient conversion and high selectivity of the C2H4 product as the basal surface site of the ML, exposing S atoms, can not derive the CO2 photoreduction due to the high energy barrier for the proton-coupled electron transfer of CO2 into *COOH. The marginal In site of the ML preeminently targets CO2 conversion to *CO under light illumination, and the *CO then migrates to the neighbor Cu sites for the subsequent C−C coupling reaction into C2H4 with thermodynamic and kinetic feasibility. Moreover, ultrathin structure of the ML also allows to shorten the transfer distance of charge carriers from the interior onto the surface, thus inhibiting electron-hole recombination and enabling more electrons to survive and accumulate on the exposed active sites for CO2 reduction.
Scientific journal

Classifying the Role of Surface Ligands on the Passivation and Stability of Cs2NaInCl6 Double Perovskite Quantum Dots
Keita Tosa; Chao Ding; Shikai Chen; Shuzi Hayase; Qing Shen
Nanomaterials, MDPI AG, 14, 4, 376-376, 17 Feb. 2024, Cs2NaInCl6 double perovskites, which have excellent photoelectric conversion properties and are non-toxic and lead-free, have recently gained significant attention. In particular, double-perovskite quantum dots (QDs) are viewed as a promising material for optoelectronic device applications. Ligands such as oleic acid (OA) and oleylamine (OAm) are essential for the synthesis of perovskite QDs, but their specific roles in double-perovskite QDs remain unclear. In this study, we have investigated the binding of OA and OAm to Cs2NaInCl6 QDs through FTIR and NMR and their effects on the surface defect reduction and stability improvement for Cs2NaInCl6 QDs. We found that only OAm was bound to the QD surfaces while OA was not. The OAm has a significant effect on the photoluminescence quantum yield (PLQY) improvement by passivating the QD surface defects. The stability of the QDs was also evaluated, and it was observed that OA played a significant role in the stability of the QDs. Our findings provide valuable insights into the roles of ligands in influencing the photophysical properties and stability of lead-free double-perovskite QDs.
Scientific journal

In situ synergistic halogen passivation of semiconducting PbS quantum dot inks for efficient photovoltaics
Xiaobo Ding; Xin Wen; Yuto Kawata; Yang Liu; Guozheng Shi; Refka ben Ghazi; Xiang Sun; Yujie Zhu; Hao Wu; Haotian Gao; Qing Shen; Zeke Liu; Wanli Ma
Nanoscale, Royal Society of Chemistry (RSC), 16, 10, 5115-5122, Feb. 2024, An in situ mixed halogen passivation (MHP) strategy is reported in the direct synthesis of semiconducting PbS CQD inks, resulting in the optimal surface configuration and passivation.
Scientific journal

Stable Inorganic Colloidal Tin and Tin–Lead Perovskite Nanocrystals with Ultralong Carrier Lifetime via Sn(IV) Control
Yusheng Li; Dandan Wang; Yongge Yang; Chao Ding; Yuyu Hu; Feng Liu; Yuyao Wei; Dong Liu; Hua Li; Guozheng Shi; Shikai Chen; Hongshi Li; Akihito Fuchimoto; Keita Tosa; Unno Hiroki; Shuzi Hayase; Huiyun Wei; Qing Shen
Journal of the American Chemical Society, American Chemical Society (ACS), 146, 5, 3094-3101, 25 Jan. 2024, Inorganic tin (Sn) perovskite nanocrystals offer a promising solution to the potential toxicity concerns associated with their established lead (Pb)-based counterparts. Yet, achieving their superior stability and optoelectronic properties remains an ongoing challenge. Here, we report a synthesis of high-symmetry α-phase CsSnI3 nanocrystals with an ultralong 278 ns carrier lifetime, exceeding previous benchmarks by 2 orders of magnitude through meticulous Sn(IV) control. The nanocrystals demonstrate excellent colloidal stability, uniform monodispersity, and a distinct exciton peak. Central to these outcomes is our designed solid-liquid antioxidation suspension of tri-n-octylphosphine (TOP) and zerovalent tin (Sn(0)) that fully addresses the unique coexisting oxygen-driven and solvent-driven Sn oxidation mechanisms in Sn perovskite nanocrystal synthesis. We uncover the largely undervalued function of TOP in mitigating oxygen-driven Sn oxidation and introduce Sn(0) powder to generate a synergistic antioxidation function with TOP, significantly reducing Sn(IV)-induced defects and distortions and contributing to enhanced optoelectronic properties. Strikingly, this approach also profoundly impacts inorganic Sn-Pb perovskite nanocrystals, boosting lifetimes by 2 orders of magnitude and increasing photoluminescence quantum yield over 100-fold to 35%. Our findings illuminate the potential of Sn-based nanocrystals for optoelectronic applications.
Scientific journal

Deciphering the Atomic-Scale Structural Origin for Photoluminescence Quenching in Tin-Lead Alloyed Perovskite Nanocrystals
Dandan Wang; Yusheng Li; Yongge Yang; Yao Guo; Huiyun Wei; Feng Liu; Chao Ding; Yuyao Wei; Dong Liu; Hua Li; Guozheng Shi; Shikai Chen; Hongshi Li; Akihito Fuchimoto; Jing Xia; Shuzi Hayase; Qing Shen
ACS Nano, 2024, The development of tin-lead alloyed halide perovskite nanocrystals (PNCs) is highly desirable for creating ultrastable, eco-friendly optoelectronic applications. However, the current incorporation of tin into the lead matrix results in severe photoluminescence (PL) quenching. To date, the precise atomic-scale structural origins of this quenching are still unknown, representing a significant barrier to fully realizing the potential of these materials. Here, we uncover the distinctive defect-related microstructures responsible for PL quenching using atomic-resolution scanning transmission electron microscopy and theoretical calculations. Our findings reveal an increase in point defects and Ruddlesden-Popper (RP) planar faults with increasing tin content. Notably, the point defects include a spectrum of vacancies and previously overlooked antisite defects with bromide vacancies and cation antisite defects emerging as the primary contributors to deep-level defects. Furthermore, the RP planar faults exhibit not only the typical rock-salt stacking pattern found in pure Pb-based PNCs but also previously undocumented microstructures rich in bromide vacancies and deep-level cation antisite defects. Direct strain imaging uncovers severe lattice distortion and significant inhomogeneous strain distributions caused by point defect aggregation, potentially breaking the local force balance and driving RP planar fault formation via lattice slippage. Our work illuminates the nature and evolution of defects in tin-lead alloyed halide perovskite nanocrystals and their profound impact on PL quenching, providing insights that support future material strategies in the development of less toxic tin-lead alloyed perovskite nanocrystals.
Scientific journal

Energetic disorder dominates optical properties and recombination dynamics in tin-lead perovskite nanocrystals
Dandan Wang; Yusheng Li; Yongge Yang; Chao Ding; Yuyao Wei; Dong Liu; Hua Li; Huan Bi; Shikai Chen; Sujun Ji; Boyu Zhang; Yao Guo; Huiyun Wei; Hongshi Li; Shuzi Hayase; Qing Shen
eScience, 2024, Tin-lead alloyed perovskite nanocrystals (PNCs) offer a promising pathway toward low-toxicity and air-stable light-emitting devices. However, substantial energetic disorder has thus far hindered their lighting applications compared to pure lead-based PNCs. A fundamental understanding of this disorder and its impact on optical properties is crucial for overcoming this limitation. Here, using temperature-dependent static and transient absorption spectroscopy, we meticulously distinguish the contributions of static disorder (including defects, impurities, etc.) and dynamic disorder (carrier–phonon interactions). We reveal how these disorders shape band-tail structure and ultimately influence inter-band carrier recombination behaviors. Surprisingly, we find that static and dynamic disorder primarily control band-tail defect states and bandgap renormalization, respectively, which together modulate fast carrier trapping and slow band-band recombination rates. Furthermore, we link these disorders to the tin-induced symmetry-lowering distortions in tin-lead alloyed PNCs. These findings illuminate critical design principles for highly luminescent, low-toxicity tin-lead PNCs, accelerating their adoption in optoelectronic applications.
Scientific journal

Ternary Passivation for Enhanced Carrier Transport and Recombination Suppression in Highly Efficient Sn-Based Perovskite Solar Cells
Liang Wang; Qingqing Miao; Dandan Wang; Zheng Zhang; Mengmeng Chen; Huan Bi; Jiaqi Liu; Ajay Kumar Baranwal; Gaurav Kapil; Yoshitaka Sanehira; Takeshi Kitamura; Qing Shen; Tingli Ma; Shuzi Hayase
Small, 2024, The exploration of nontoxic Sn-based perovskites as a viable alternative to their toxic Pb-based counterparts has garnered increased attention. However, the power conversion efficiency of Sn-based perovskite solar cells lags significantly behind their Pb-based counterparts. This study presents a ternary passivation strategy aimed at enhancing device performance, employing [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM), poly(3-hexylthiophene) (P3HT), and indene C60 bisadduct (ICBA). These components play crucial roles in managing energy levels and enhancing carrier transportation, respectively. The results reveal that the introduction of the ternary system leads to improvements in carrier collection and transportation, accompanied by a suppression of the recombination process. Ultimately, the champion device achieves a remarkable performance with an efficiency of 14.64%. Notably, the device also exhibits robust operational and long-term stored stability.
Scientific journal

Photoacoustic Characterization of Photovoltaic Materials
Taro TOYODA; Qing SHEN
The Journal of The Institute of Electrical Engineers of Japan, Institute of Electrical Engineers of Japan (IEE Japan), 144, 1, 14-17, 01 Jan. 2024
Scientific journal

In Situ Room-Temperature Synthesis of All-Colloidal Quantum Dot CsPbBr₃–PbS Heterostructures
Yongge Yang; Dandan Wang; Yusheng Li; Jing Xia; Huiyun Wei; Chao Ding; Yuyu Hu; Yuyao Wei; Hua Li; Dong Liu; Guozheng Shi; Yaohong Zhang; Huan Bi; Shikai Chen; Hongshi Li; Xiang-Min Meng; Shuzi Hayase; Qing Shen
ACS Photonics, American Chemical Society (ACS), 10, 12, 4305-4314, 20 Nov. 2023
Scientific journal

Anchoring self-assembled monolayer at perovskite/hole collector interface for wide bandgap Sn-based solar cells with a record efficiency over 12%
SungWon Cho; Padmini Pandey; Saemon Yoon; Jun Ryu; Dong-Gun Lee; Qing Shen; Shuzi Hayase; Hochan Song; Hyosung Choi; Hyungju Ahn; Chang-Mok Oh; In-Wook Hwang; Jung Sang Cho; Dong-Won Kang
Surfaces and Interfaces, Elsevier BV, 42, 103478-103478, Nov. 2023
Scientific journal

Ferrocene Derivatives for Improving the Efficiency and Stability of MA‐Free Perovskite Solar Cells from the Perspective of Inhibiting Ion Migration and Releasing Film Stress
Huan Bi; Jiaqi Liu; Zheng Zhang; Liang Wang; Gaurav Kapil; Yuyao Wei; Ajay Kumar Baranwal; Shahrir Razey Sahamir; Yoshitaka Sanehira; Dandan Wang; Yongge Yang; Takeshi Kitamura; Raminta Beresneviciute; Saulius Grigalevicius; Qing Shen; Shuzi Hayase
Advanced Science, Wiley, 10, 35, 22 Oct. 2023, Abstract

Further improvement of the performance and stability of inverted perovskite solar cells (PSCs) is necessary for commercialization. Here, ferrocene derivative dibenzoylferrocene (DBzFe) is used as an additive to enhance the performance and stability of MA‐ and Br‐ free PSCs. The results show that the introduction of DBzFe not only passivates the defects in the film but also inhibits the ion migration in the film. The final device achieves a power conversion efficiency (PCE) of 23.53%, which is one of the highest efficiencies currently based on self‐assembled monolayers (SAMs). Moreover, it maintains more than 96.4% of the original efficiency when running continuously for 400 h at the maximum power point.
Scientific journal

All-Perovskite Tandem Solar Cells Approach 26.5% Efficiency by Employing Wide Bandgap Lead Perovskite Solar Cells with New Monomolecular Hole Transport Layer
Huan Bi; Jiaqi Liu; Zheng Zhang; Liang Wang; Raminta Beresneviciute; Daiva Tavgeniene; Gaurav Kapil; Chao Ding; Ajay Kumar Baranwal; Shahrir Razey Sahamir; Yoshitaka Sanehira; Hiroshi Segawa; Saulius Grigalevicius; Qing Shen; Shuzi Hayase
ACS Energy Letters, American Chemical Society (ACS), 8, 9, 3852-3859, 24 Aug. 2023
Scientific journal

Efficiency Enhancement of Wide Bandgap Lead Perovskite Solar Cells with PTAA Surface-Passivated with Monomolecular Layer from the Viewpoint of PTAA Band Bending
Huan Bi; Jiaqi Liu; Raminta Beresneviciute; Daiva Tavgeniene; Zheng Zhang; Liang Wang; Gaurav Kapil; Chao Ding; Shahrir Razey Sahamir; Yoshitaka Sanehira; Ajay Kumar Baranwal; Takeshi Kitamura; Dandan Wang; Yuyao Wei; Yongge Yang; Dong-Won Kang; Saulius Grigalevicius; Qing Shen; Shuzi Hayase
ACS Applied Materials & Interfaces, 22 Aug. 2023
Scientific journal

14.31 % Power Conversion Efficiency of Sn‐Based Perovskite Solar Cells via Efficient Reduction of Sn4+
Liang Wang; Qingqing Miao; Dandan Wang; Mengmeng Chen; Huan Bi; Jiaqi Liu; Ajay Kumar Baranwal; Gaurav Kapil; Yoshitaka Sanehira; Takeshi Kitamura; Tingli Ma; Zheng Zhang; Qing Shen; Shuzi Hayase
Angewandte Chemie, 14 Aug. 2023
Scientific journal

Enhancement of Efficiency and Stability for Tin Halide Perovskite Solar Cells by Using Improved Doping Method
Zheng Zhang; Liang Wang; Huan Bi; Ajay Kumar Baranwal; Gaurav Kapil; Yoshitaka Sanehira; Jiaqi Liu; Dong Liu; Qing Shen; Shuzi Hayase
Advanced Optical Materials, Wiley, 12, 2, 13 Aug. 2023, Abstract

In recent years, tin halide perovskite solar cells (PKSCs) have emerged as a promising alternative to lead‐PKSCs. However, due to defects such as Sn⁴⁺ and iodide vacancies, their efficiency is lower than lead‐PKSCs. To address this issue, various strategies are proposed to improve the quality of perovskite, including copper iodide (CuI) doping. Unfortunately, the conventional solvent composition of DMF:DMSO = 4:1 has limited the solubility of CuI, resulting in inconsistent results and limited efficiency improvements. However, this research proposed a preprocessing method of CuI to decrease the defects and improve the perovskite layer's morphology. As a result, the efficiency of tin‐PKSCs with both P‐I‐N and hole transport layer (HTL) free structures is enhanced, increasing from 9.8% to 13.1% and 9.4% to 10.5%, respectively. Moreover, the doped tin‐PKSCs have exhibited better stability, retaining 75% of their initial power conversion efficiency (PCE) after being stored in a glovebox for 102 days.
Scientific journal

Sn Perovskite Solar Cells with Tin Oxide Nanoparticle Layer as Hole Transport Layer
Takeshi Kitamura; Liang Wang; Zheng Zhang; Ajay Kumar Baranwal; Gaurav Kapil; Shahrir Razey Sahamir; Yoshitaka Sanehira; Huan Bi; Tingli Ma; Qing Shen; Shuzi Hayase
ACS Energy Letters, American Chemical Society (ACS), 8, 8, 3565-3568, 31 Jul. 2023
Scientific journal

How to minimize voltage and fill factor losses to achieve over 20% efficiency lead chalcogenide quantum dot solar cells: Strategies expected through numerical simulation
Dandan Wang; Yusheng Li; Yongge Yang; Shuzi Hayase; Haifeng Wu; Ruixiang Wang; Chao Ding; Qing Shen
Applied Energy, Elsevier BV, 341, 121124-121124, Jul. 2023
Scientific journal

Enhanced Hot-Phonon Bottleneck Effect on Slowing Hot Carrier Cooling in Metal Halide Perovskite Quantum Dots With Alloyed A-Site.
Hua Li; Qing Wang; Yusuke Oteki; Chao Ding; Dong Liu; Yao Guo; Yusheng Li; Yuyao Wei; Dandan Wang; Yongge Yang; Taizo Masuda; Mengmeng Chen; Zheng Zhang; Tomah Sogabe; Shuzi Hayase; Yoshitaka Okada; Satoshi Iikubo; Qing Shen
Advanced materials (Deerfield Beach, Fla.), e2301834, 13 Jun. 2023, True, A deep understanding of the effect of the A-site cation cross-exchange on the hot-carrier relaxation dynamics in perovskite quantum dots (PQDs) has profound implications on the further development of disruptive photovoltaic technologies. In this study, we investigated the hot carrier cooling kinetics of pure FAPbI3 , MAPbI3 , CsPbI3 and alloyed FA0.5 MA0.5 PbI3 , FA0.5 Cs0.5 PbI3 , and MA0.5 Cs0.5 PbI3 QDs using ultrafast transient absorption (TA) spectroscopy. The lifetimes of the initial fast cooling stage (<1 ps) of all the organic cation-containing PQDs were shorter than those of the CsPbI3 QDs, as verified by the electron-phonon coupling strength extracted from the temperature-dependent photoluminescence spectra. The lifetimes of the slow cooling stage of the alloyed PQDs were longer under illumination greater than 1 sun, which was ascribed to the introduction of co-vibrational optical phonon modes in the alloyed PQDs. This facilitated efficient acoustic phonon upconversion and enhanced the hot-phonon bottleneck effect, as demonstrated by first-principles calculations. This article is protected by copyright. All rights reserved.
Scientific journal, English

Low-Temperature Growth of ZnMgO Thin Films by Atmospheric Spin-Coating Using Diethylzinc Solution
Kenji Yoshino; Himeka Tominaga; Yuta Komaki; Masato Imai; Tomohiro Higashi; Takashi Minemoto; Qing Shen; Shuzi Hayase
Journal of Electronic Materials, Springer Science and Business Media LLC, 12 May 2023
Scientific journal

Perovskite Solar Cells Consisting of PTAA Modified with Monomolecular Layer and Application to All‐Perovskite Tandem Solar Cells with Efficiency over 25%
Huan Bi; Yasuhiro Fujiwara; Gaurav Kapil; Daiva Tavgeniene; Zheng Zhang; Liang Wang; Chao Ding; Shahrir Razey Sahamir; Ajay Kumar Baranwal; Yoshitaka Sanehira; Kitamura Takeshi; Guozheng Shi; Takeru Bessho; Hiroshi Segawa; Saulius Grigalevicius; Qing Shen; Shuzi Hayase
Advanced Functional Materials, Wiley, 33, 32, 26 Apr. 2023, Abstract

This study is on the enhancement of the efficiency of wide bandgap (FA_0.8Cs_0.2PbI_1.8Br_1.2) perovskite solar cells (PSCs) used as the top layer of the perovskite/perovskite tandem solar cell. Poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) and the monomolecular layer called SAM layer are effective hole collection layers for APbI₃ PSCs. However, these hole transport layers (HTL) do not give high efficiencies for the wide bandgap FA_0.8Cs_0.2PbI_1.8Br_1.2 PSCs. It is found that the surface‐modified PTAA by monomolecular layer (MNL) improves the efficiency of PSCs. The improved efficiency is explained by the improved FA_0.8Cs_0.2PbI_1.8Br_1.2 film quality, decreased film distortion (low lattice disordering) and low density of the charge recombination site, and improves carrier collection by the surface modified PTAA layer. In addition, the relationship between the length of the alkyl group linking the anchor group and the carbazole group is also discussed. Finally, the wide bandgap lead PSCs (E_g = 1.77 eV) fabricated on the PTAA/monomolecular bilayer give a higher power conversion efficiency of 16.57%. Meanwhile, all‐perovskite tandem solar cells with over 25% efficiency are reported by using the PTAA/monomolecular substrate.
Scientific journal

A multifunctional additive strategy to stabilize the precursor solution and passivate film defects for MA-free perovskite solar cells with an efficiency of 22.75%
Huan Bi; Mengna Guo; Chao Ding; Shuzi Hayase; Qing Shen; Gaoyi Han; Wenjing Hou
Materials Today Energy, Elsevier BV, 33, 101269-101269, Apr. 2023
Scientific journal

Reduced interfacial recombination losses and lead leakage in lead-based perovskite solar cells using 2D/3D perovskite engineering
Huan Bi; Yao Guo; Mengna Guo; Chao Ding; Shuzi Hayase; Hanjun Zou; Qing Shen; Gaoyi Han; Wenjing Hou
Journal of Power Sources, Elsevier BV, 563, 232825-232825, Apr. 2023
Scientific journal

Efficient Charge Transfer in MAPbI₃ QDs/TiO₂ Heterojunctions for High-Performance Solar Cells
Hua Li; Chao Ding; Dong Liu; Shota Yajima; Kei Takahashi; Shuzi Hayase; Qing Shen
Nanomaterials, Apr. 2023
Scientific journal

Open‐Shell Diradical‐Sensitized Electron Transport Layer for High‐Performance Colloidal Quantum Dot Solar Cells
Shiwen Fang; Jiaxing Huang; Ran Tao; Qi Wei; Xiaobo Ding; Shota Yajima; Zhongxin Chen; Weiya Zhu; Cheng Liu; Yusheng Li; Ni Yin; Leliang Song; Yang Liu; Guozheng Shi; Hao Wu; Yiyuan Gao; Xin Wen; Qi Chen; Qing Shen; Youyong Li; Zeke Liu; Yuan Li; Wanli Ma
Advanced Materials, Wiley, 35, 21, 30 Mar. 2023, Abstract

The zinc oxide (ZnO) nanoparticles (NPs) are well‐documented as an excellent electron transport layer (ETL) in optoelectronic devices. However, the intrinsic surface flaw of the ZnO NPs can easily result in serious surface recombination of carriers. Exploring effective passivation methods of ZnO NPs is essential to maximize the device's performance. Herein, a hybrid strategy is explored for the first time to improve the quality of ZnO ETL by incorporating stable organic open‐shell donor‐acceptor type diradicaloids. The high electron‐donating feature of the diradical molecules can efficiently passivate the deep‐level trap states and improve the conductivity of ZnO NP film. The unique advantage of the radical strategy is that its passivation effectiveness is highly correlated with the electron‐donating ability of radical molecules, which can be precisely controlled by the rational design of molecular chemical structures. The well‐passivated ZnO ETL is applied in lead sulfide (PbS) colloidal quantum dot solar cells, delivering a power conversion efficiency of 13.54%. More importantly, as a proof‐of‐concept study, this work will inspire the exploration of general strategies using radical molecules to construct high‐efficiency solution‐processed optoelectronic devices.
Scientific journal

Pb-free perovskite solar cells composed of Sn/Ge(1:1) alloyed perovskite layer prepared by spin-coating
Huan Bi; Mengmeng Chen; Liang Wang; Zheng Zhang; Chao Ding; Gaurav Kapil; Shahrir Razey Sahamir; Yoshitaka Sanehira; Ajay Kumar Baranwal; Takeshi Kitamura; Guozheng Shi; Qing Shen; Shuzi Hayase
Applied Physics Express, IOP Publishing, 16, 3, 036501-036501, 01 Mar. 2023, Abstract

Since the DMSO seriously oxidizes the GeI₂ which is one of the ingredients for the Sn/Ge perovskite, it was difficult to make high-quality films by using the conventional DMSO/DMF solvent. We now first report the MASn_0.5Ge_0.5I₃ perovskite solar cells (PSCs) prepared by a simple spin-coating technology. We found that triethanolamine (TEA)/n-methyl pyrrolidone (NMP) does not oxidize the GeI₂ and improves the stability of the precursor. The precursor solution with TEA/NMP/DMF gave high-quality perovskite films. The cell gave a power conversion efficiency of 2.18%. This is the first report proving that Sn/Ge PSCs are fabricated by a conventional solution process.
Scientific journal

Room-temperature photosynthesis of propane from CO2 with Cu single atoms on vacancy-rich TiO2
Yan Shen; Chunjin Ren; Lirong Zheng; Xiaoyong Xu; Ran Long; Wenqing Zhang; Yong Yang; Yongcai Zhang; Yingfang Yao; Haoqiang Chi; Jinlan Wang; Qing Shen; Yujie Xiong; Zhigang Zou; Yong Zhou
Nature Communications, Springer Science and Business Media LLC, 14, 1, 27 Feb. 2023, Abstract

Photochemical conversion of CO₂ into high-value C₂₊ products is difficult to achieve due to the energetic and mechanistic challenges in forming multiple C-C bonds. Herein, an efficient photocatalyst for the conversion of CO₂ into C₃H₈ is prepared by implanting Cu single atoms on Ti_0.91O₂ atomically-thin single layers. Cu single atoms promote the formation of neighbouring oxygen vacancies (V_Os) in Ti_0.91O₂ matrix. These oxygen vacancies modulate the electronic coupling interaction between Cu atoms and adjacent Ti atoms to form a unique Cu-Ti-V_O unit in Ti_0.91O₂ matrix. A high electron-based selectivity of 64.8% for C₃H₈ (product-based selectivity of 32.4%), and 86.2% for total C₂₊ hydrocarbons (product-based selectivity of 50.2%) are achieved. Theoretical calculations suggest that Cu-Ti-V_O unit may stabilize the key *CHOCO and *CH₂OCOCO intermediates and reduce their energy levels, tuning both C₁-C₁ and C₁-C₂ couplings into thermodynamically-favourable exothermal processes. Tandem catalysis mechanism and potential reaction pathway are tentatively proposed for C₃H₈ formation, involving an overall (20e⁻ – 20H⁺) reduction and coupling of three CO₂ molecules at room temperature.
Scientific journal

Accelerating defect analysis of solar cells via machine learning of the modulated transient photovoltage
Yusheng Li; Yiming Li; Jiangjian Shi; Licheng Lou; Xiao Xu; Yuqi Cui; Jionghua Wu; Dongmei Li; Yanhong Luo; Huijue Wu; Qing Shen; Qingbo Meng
Fundamental Research, Elsevier BV, Feb. 2023
Scientific journal

Simultaneous Characterization of Optical, Electronic, and Thermal Properties of Perovskite Single Crystals Using a Photoacoustic Technique
Dong Liu; Hua Li; Yusheng Li; Taro Toyoda; Koji Miyazaki; Shuzi Hayase; Chao Ding; Qing Shen
ACS Photonics, American Chemical Society (ACS), 10, 1, 265-273, 06 Jan. 2023
Scientific journal

Merging Passivation in Synthesis Enabling the Lowest Open‐Circuit Voltage Loss for PbS Quantum Dot Solar Cells
Yang Liu; Hao Wu; Guozheng Shi; Yusheng Li; Yiyuan Gao; Shiwen Fang; Haodong Tang; Wei Chen; Tianshu Ma; Irfan Khan; Kai Wang; Changlei Wang; Xiaofeng Li; Qing Shen; Zeke Liu; Wanli Ma
Advanced Materials, Wiley, 35, 5, 20 Dec. 2022, Abstract

The high open‐circuit voltage (V_oc) loss arising from insufficient surface passivation is the main factor that limits the efficiency of current lead sulfide colloidal quantum dots (PbS CQDs) solar cell. Here, synergistic passivation is performed in the direct synthesis of conductive PbS CQD inks by introducing multifunctional ligands to well coordinate the complicated CQDs surface with the thermodynamically optimal configuration. The improved passivation effect is intactly delivered to the final photovoltaic device, leading to an order lower surface trap density and beneficial doping behavior compared to the control sample. The obtained CQD inks show the highest photoluminescence quantum yield (PLQY) of 24% for all photovoltaic PbS CQD inks, which is more than twice the reported average PLQY value of ≈10%. As a result, a high V_oc of 0.71 V and power conversion efficiency (PCE) of 13.3% is achieved, which results in the lowest V_oc loss (0.35 eV) for the reported PbS CQD solar cells with PCE >10%, comparable to that of perovskite solar cells. This work provides valuable insights into the future CQDs passivation strategies and also demonstrates the great potential for the direct‐synthesis protocol of PbS CQDs.
Scientific journal

Unveiling of efficiency limit to fabricate high-performance PbSe quantum dot solar cells
Dandan Wang; Yusheng Li; Yongge Yang; Chao Ding; Qing Shen
SOLAR ENERGY, PERGAMON-ELSEVIER SCIENCE LTD, 247, 432-440, Nov. 2022, Lead selenide quantum dots (PbSe QDs), as promising active absorbers, have received considerable attention in solar cells. However, the performance of PbSe QD-based solar cells (PbSe QDSCs) still lags behind that of c-Si and perovskite solar cells mainly due to non-radiative and resistive losses. To investigate the limitation of PbSe QDSCs, we established a theoretical model based on the performance of the state-of-the-art PbSe QDSCs through diffusion-drift theory and systematically discussed the optional strategies for optimizing the efficiency of PbSe QDSCs. The optimizations were initially carried out in term of absorber layer thickness, defect densities in absorber layer and interface defect layer (IDL), thus yielding a power conversion efficiency (PCE) of 15.25% with open-circuit voltage (Voc) of 0.64 V and fill factor (FF) of 74.49% in PbSe QDSCs. After the modifications of the doping concentrations of charge transport layers and the band alignment in solar device, the PbSe QDSCs can achieve over 30% efficiency with a-80% and 32 % improvement in Voc and FF, respectively. Our findings gained here provide effective experimental guidelines and pave the way for PbSe QDSCs to approach their theoretical efficiency limit.
Scientific journal, English

Ultrafast inverse design of quantum dot optical spectra via a joint TD-DFT learning scheme and deep reinforcement learning
Hibiki Yoshida; Katsuyoshi Sakamoto; Naoya Miyashita; Koichi Yamaguchi; Qing Shen; Yoshitaka Okada; Tomah Sogabe
AIP Advances, AIP Publishing, 12, 11, 115316-115316, Nov. 2022, Peer-reviwed, Here, we report a case study on inverse design of quantum dot optical spectra using a deep reinforcement learning algorithm for the desired target optical property of semiconductor Cd _xSe _yTe _{x− y} quantum dots. Machine learning models were trained to predict the optical absorption and emission spectra by using the training dataset by time dependent density functional theory simulation. We show that the trained deep deterministic policy gradient inverse design agent can infer the molecular structure with an accuracy of less than 1 Å at a fixed computational time of milliseconds and up to 100–1000 times faster than the conventional heuristic particle swam optimization method. Most of the effective inverse design problems based on the surrogate machine learning and reinforcement learning model have been focused on the field of nano-photonics. Few attempts have been made in the field of quantum optical system in a similar manner. For the first time, our results, to our knowledge, provide concrete evidence that for computationally challenging tasks, a well-trained deep reinforcement learning agent can replace the existing quantum simulation and heuristics optimization tool, enabling fast and scalable simulations of the optical property of nanometer sized semiconductor quantum dots.
Scientific journal

SnOx as Bottom Hole Extraction Layer and Top In Situ Protection Layer Yields over 14% Efficiency in Sn-Based Perovskite Solar Cells
Liang Wang; Mengmeng Chen; Shuzhang Yang; Namiki Uezono; Qingqing Miao; Gaurav Kapil; Ajay Kumar Baranwal; Yoshitaka Sanehira; Dandan Wang; Dong Liu; Tingli Ma; Kenichi Ozawa; Takeaki Sakurai; Zheng Zhang; Qing Shen; Shuzi Hayase
ACS Energy Lett., 8, 3703-3708, 03 Oct. 2022, Peer-reviwed
Scientific journal, English

Sequential Passivation for Lead-Free Tin Perovskite Solar Cells with High Efficiency
Zheng Zhang; Muhammad Akmal Kamarudin; Ajay Kumar Baranwal; Gaurav Kapil; Shahrir Razey Sahamir; Yoshitaka Sanehira; Mengmeng Chen; Liang Wang; Qing Shen; Shuzi Hayase
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, WILEY-V C H VERLAG GMBH, 61, 42, Oct. 2022, Lead-free tin perovskite solar cells (PKSCs) have attracted tremendous interest as a replacement for toxic lead-based PKSCs. Nevertheless, the efficiency is significantly low due to the rough surface morphology and high number of defects, which are caused by the fast crystallization and easy oxidization. In this study, a facile and universal posttreatment strategy of sequential passivation with acetylacetone (ACAC) and ethylenediamine (EDA) is proposed. The results show that ACAC can reduce the trap density and enlarge the grain size (short-circuit current (J(sc)) enhancement), while EDA can bond the undercoordinated tin and regulate the energy level (open-circuit voltage (V-oc) enhancement). A promising 13 % efficiency is achieved with better stability. In addition, other combinations of diketones or amines are selected, with similar effects. This study provides a universal strategy to enhance the crystallinity and passivate defects while fabricating stable PKSCs with high efficiency.
Scientific journal, English

How to get high-efficiency lead chalcogenide quantum dot solar cells?
Chao Ding; Qing Shen
Science China Physics, Mechanics & Astronomy volume, 66, 217303, 16 Sep. 2022, Peer-reviwed
Scientific journal, English

Efficient Exciton Dislocation and Ultrafast Charge Extraction in CsPbI3 Perovskite Quantum Dots by Using Fullerene Derivative as Semiconductor Ligand
Yusheng Li; Dandan Wang; Shuzi Hayase; Yongge Yang; Chao Ding; Qing Shen
Nanomaterials, 12, 18, 3101-3109, 07 Sep. 2022, Peer-reviwed
Scientific journal, English

Sequential Passivation for Lead-Free Tin Perovskite Solar Cells with High Efficiency
Dr. Zheng Zhang; Dr. Muhammad Akmal Kamarudin; Dr. Ajay; Kumar Baranwal; Dr. Gaurav Kapil; Dr. Shahrir; Razey Sahamir; Dr. Yoshitaka Sanehira; Dr. Mengmeng Chen; Dr. Liang Wang; Prof. Qing Shen; Prof. Shuzi Hayase
Angew. Chem., e202210101, 1-7, 02 Sep. 2022, Peer-reviwed
Scientific journal, English

Efficient Exciton Dislocation and Ultrafast Charge Extraction in CsPbI₃ Perovskite Quantum Dots by Using Fullerene Derivative as Semiconductor Ligand
Yusheng Li; Dandan Wang; Shuzi Hayase; Yongge Yang; Chao Ding; Qing Shen
Nanomaterials, Sep. 2022
Scientific journal

Polar Bear Hair Inspired Supra-Photothermal Promoted Water Splitting
Yuan Cao; Linfeng Gao; Bing Wang; Yingfang Yao; Congping Wu; Qing Shen; Jianyong Feng; Yong Zhou; Zhaosheng Li; Zhigang Zou
ACS Materials Lett., 4, 10, 1912-1920, 01 Sep. 2022, Peer-reviwed
Scientific journal, English

Suppression of Defect and Trap Density through Dimethylammonium-Substituted Tin Perovskite Solar Cells
Muhammad Akmal Kamarudin; Shahrir Razey Sahamir; Kohei Nishimura; Satoshi Iikubo; Kenji Yoshino; Takashi Minemoto; Qing Shen; Shuzi Hayase
ACS Materials Lett., 4, 9, 1855-1862, 24 Aug. 2022, Peer-reviwed
Scientific journal, English

Unveiling the Role of the Metal Oxide/Sn Perovskite Interface Leading to Low Efficiency of Sn-Perovskite Solar Cells but Providing High Thermoelectric Properties
Ajay Kumar Baranwal; Shrikant Saini; Yoshitaka Sanehira; Gaurav Kapil; Muhammad Akmal Kamarudin; Chao Ding; Shahrir Razey Sahamir; Tomohide Yabuki; Satoshi Iikubo; Qing Shen; Koji Miyazaki; Shuzi Hayase
ACS Applied Energy Materials, 5, 8, 9750-9758, 22 Aug. 2022, Tin halide perovskites (THPs) have appealing optoelectronic properties similar to lead halide perovskites (LHPs). However, THPs coated on metal oxide electrodes in normal-structure perovskite solar cells exhibit poor diode rectification, resulting in poor efficiency. This poor photoelectric performance in n-i-p-based THP solar cells is in contrast with LHP solar cells. We report that this deficient performance of THP solar cells is triggered by the defect states of the metal oxide layer. The defect states of the metal oxide can trap the electrons from the THP, leading to the prompt formation of Sn(IV), which will increase the carrier density and lead to poor photoelectric performance. This observation was supported by the ultraviolet-photoelectron spectroscopic measurements of inorganic thin films Al2O3, SnO2, TiO2, ZnO, and ZrO2. However, this self-doping phenomenon resulting in the increase in carrier density can be applied to thermoelectric studies. Using CsSnI3/ZrO2 nanocomposites as thermoelectric active layers, we report a power factor of 186.58 μW/mK2 measured at room temperature, which is better than the 148.61 μW/mK2 of the original CsSnI3 thin film.
Scientific journal

Indent-Free Vapor-Assisted Surface Passivation Strategy toward Tin Halide Perovskite Solar Cells
Zheng Zhang; Muhammad Akmal Kamarudin; Ajay Kumar Baranwal; Liang Wang; Gaurav Kapil; Shahrir Razey Sahamir; Yoshitaka Sanehira; Mengmeng Chen; Qing Shen; Shuzi Hayase
ACS Applied Materials and Interfaces, AMER CHEMICAL SOC, 14, 31, 36200-36208, 10 Aug. 2022, Sn halide perovskite solar cells (PKSCs) are the most promising competitors to conventional lead PKSCs. Nevertheless, defects at the surfaces and grain boundaries hinder the improvement of the PKSCs' performance. Liquid surface passivation on the perovskite layer is commonly used to decrease these defects. In the case of tin perovskite solar cells, the liquid passivation improved the open-circuit voltage (Voc). However, this decreased the short-circuit current density (Jsc). We found that this Jsc loss is brought about by the thickness loss after the liquid passivation because tin perovskite layers are partially soluble in common solvents, and the calculated impact pressure was up to 155.4 kPa. Here, we introduce new vapor passivation including solvent and passivation molecules and report efficiency enhancement without decreasing Jsc. The vapor-passivated film showed longer time-resolved photoluminescence decay, smoother morphology, and lower defect densities. Most importantly, the vapor passivation method significantly enhanced the efficiency from 9.41 to 11.29% with Jsc increasing from 22.82 to 24.05 mA·cm-2. On the contrary, the corresponding liquid passivation method gave an efficiency of 10.90% with a decreased Jsc from 22.82 to 22.38 mA·cm-2. A commonly used and simple indent-free surface passivation strategy is proposed to enhance the efficiency and stability of PKSCs.
Scientific journal, English

Indent-Free Vapor-Assisted Surface Passivation Strategy toward Tin Halide Perovskite Solar Cells
Zheng Zhang; Muhammad Akmal Kamarudin; Ajay Kumar Baranwal; Liang Wang; Gaurav Kapil; Shahrir Razey Sahamir; Yoshitaka Sanehira; Mengmeng Chen; Qing Shen; Shuzi Hayase
ACS APPLIED MATERIALS & INTERFACES, AMER CHEMICAL SOC, 14, 31, 36200-36208, Aug. 2022, Sn halide perovskite solar cells (PKSCs) are the most promising competitors to conventional lead PKSCs. Nevertheless, defects at the surfaces and grain boundaries hinder the improvement of the PKSCs' performance. Liquid surface passivation on the perovskite layer is commonly used to decrease these defects. In the case of tin perovskite solar cells, the liquid passivation improved the open-circuit voltage (V-oc). However, this decreased the short-circuit current density (J(sc)). We found that this J(sc) loss is brought about by the thickness loss after the liquid passivation because tin perovskite layers are partially soluble in common solvents, and the calculated impact pressure was up to 155.4 kPa. Here, we introduce new vapor passivation including solvent and passivation molecules and report efficiency enhancement without decreasing J(sc). The vapor-passivated film showed longer time-resolved photo-luminescence decay, smoother morphology, and lower defect densities. Most importantly, the vapor passivation method significantly enhanced the efficiency from 9.41 to 11.29% with J(sc) increasing from 22.82 to 24.05 mAmiddotcm(-2). On the contrary, the corresponding liquid passivation method gave an efficiency of 10.90% with a decreased J(sc) from 22.82 to 22.38 mAmiddotcm(-2). A commonly used and simple indent-free surface passivation strategy is proposed to enhance the efficiency and stability of PKSCs.
Scientific journal, English

Enhanced efficiency and stability in Sn-based perovskite solar cells by trimethylsilyl halide surface passivation
Zheng Zhang; Liang Wang; Ajay Kumar Baranwal; Shahrir Razey Sahamir; Gaurav Kapil; Yoshitaka Sanehira; Muhammad Akmal Kamarudin; Kohei Nishimura; Chao Ding; Dong Liu; Yusheng Li; Hua Li; Mengmeng Chen; Qing Shen; Teresa S. Ripolles; Juan Bisquert; Shuzi Hayase
JOURNAL OF ENERGY CHEMISTRY, ELSEVIER, 71, 604-611, Aug. 2022, Lead free tin perovskite solar cells (PKSCs) are the most suitable alternative candidate for conventional lead perovskite solar cells. However, the efficiency and the stability are insufficient, mainly because of the poor film quality and numerous defects. Here we introduce an efficient strategy based on a simple trimethylsilyl halide surface passivation to increase the film quality and reduce the defect density. At the same time, a hydrophobic protective layer on the perovskite surface is formed, which enhanced the PKSCs' stability. The efficiency of the solar cell after the passivation was enhanced from 10.05 % to 12.22% with the improved open-circuit voltage from 0.57 V to 0.70 V. In addition, after 92 days of storage in N2 filled glove box, the modified T-PKSCs demonstrated high stability maintaining 80% of its initial efficiency. This work provides a simple and widely used strategy to optimize the surface/interface optoelectronic properties of perovskites for giving more efficient and stable solar cells and other optoelectronic devices. (C) 2022 Published by Elsevier B.V. on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Scientific journal, English

Multistrategy Preparation of Efficient and Stable Environment-Friendly Lead-Based Perovskite Solar Cells
Huan Bi; Gaoyi Han; Mengna Guo; Chao Ding; Hanjun Zou; Qing Shen; Shuzi Hayase; Wenjing Hou
ACS Appl. Mater. Interfaces, 14, 31, 35513-35521, 30 Jul. 2022, Peer-reviwed
Scientific journal, English

Over 15% Efficiency PbS Quantum-Dot Solar Cells by Synergistic Effects of Three Interface Engineering: Reducing Nonradiative Recombination and Balancing Charge Carrier Extraction
Chao Ding; Dandan Wang; Dong Liu; Hua Li; Yusheng Li; Shuzi Hayase; Tomah Sogabe; Taizo Masuda; Yong Zhou; Yingfang Yao; Zhigang Zou; Ruixiang Wang; Qing Shen
Adv. Energy Mater., 12, 15, 1-16, 28 Jul. 2022, Peer-reviwed
Scientific journal, English

Unraveling the Organic and Inorganic Passivation Mechanism of ZnO Nanowires for Construction of Efficient Bulk Heterojunction Quantum Dot Solar Cells
Yuyao Wei; Mako Nakamura; Chao Ding; Dong Liu; Hua Li; Yusheng Li; Yongge Yang; Dandan Wang; Ruixiang Wang; Shuzi Hayase; Taizo Masuda; Qing Shen
ACS Appl. Mater. Interfaces, 14, 31, 36268-36276, 27 Jul. 2022, Peer-reviwed
Scientific journal, English

The Effect of PbS Colloidal Quantum Dots with CdS and ZnS Coating on Photovoltaic Properties
Napasuda Wichaiyo; Mettaya Kitiwan; Qing Shen; Witoon Yindeesuk
Current Applied Science and Technology, King Mongkut's Institute of Technology Ladkrabang, 23, 2, 19 Jul. 2022, In this research, we used the co-precipitation method to fabricate lead sulfide colloidal quantum dots (PbS CQDs) for photovoltaic cells. PbS CQDs were deposited uniformly on a titanium dioxide electrode by the dip-coating method. Photoelectrodes were prepared by coating layers using the successive ionic layer adsorption and reaction (SILAR) method. A solar simulation was used to investigate the photovoltaic properties of photoelectrodes under one sun illumination (100 mW/cm2) at room temperature (AM 1.5 G). The photovoltaic measurements demonstrated that TiO2/PbS CQDs with CdS and ZnS coating electrodes had a maximum power conversion efficiency (PCE) of 1.01 %. The crystallite size of PbS CQDs with different coating layers was analyzed using X-ray diffraction (XRD), and the crystallite size range was 6-7 nm. The existence of PbS CQDs and coating layers on the TiO2 electrodes was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). UV-visible spectroscopy was used to obtain the optical properties of the photoelectrodes. The optical band gap was 0.72-0.75 eV.
Scientific journal

Unraveling the Organic and Inorganic Passivation Mechanism of ZnO Nanowires for Construction of Efficient Bulk Heterojunction Quantum Dot Solar Cells
Yuyao Wei; Mako Nakamura; Chao Ding; Dong Liu; Hua Li; Yusheng Li; Yongge Yang; Dandan Wang; Ruixiang Wang; Shuzi Hayase; Taizo Masuda; Qing Shen
ACS APPLIED MATERIALS & INTERFACES, AMER CHEMICAL SOC, Jul. 2022, Zinc oxide (ZnO) nanowire (NW) based lead sulfide (PbS) quantum dot solar cells (QDSCs), i.e., bulk heterojunction QDSCs, have been widely investigated because of the excellent photoelectronic properties of PbS QDs and ZnO NWs. To further improve the efficiency of this type of QDSCs, various passivation methods are applied to ZnO NWs to suppress interface recombination caused by trap defects. However, the comparison among passivation using organic, inorganic, and inorganic-organic hybrid materials with different properties has been less studied. In this work, the effect of passivation with inorganic Mg-doped ZnO (ZMO), organic 1,2-ethanedithiol (EDT) and both of them on ZnO NWs and PbS QDSCs are investigated. As a result, ZnO NWs purely passivated by organic material EDT show the best performance with fewer surface defects and better matched energy level with the PbS QD layer. A nearly 1.7 times larger power conversion efficiency (PCE) of 6.9% is achieved for the solar device using ZnO NW @EDT, compared with that (4.1%) of the untreated one. The work provides a promising way to impede interlayer charge recombination and facilitate carrier transport, thus enhancing the photovoltaic performance of the device.
Scientific journal, English

Influence of charge transport layer on the crystallinity and charge extraction of pure tin-based halide perovskite film
Yaohong Zhang; Muhammad Akmal Kamarudin; Qiao Li; Chao Ding; Yong Zhou; Yingfang Yao; Zhigang Zou; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Shuzi Hayase; Qing Shen
JOURNAL OF ENERGY CHEMISTRY, ELSEVIER, 69, 612-615, Jun. 2022, Tin-based halide perovskite have emerged as a promising alternative to toxic lead-based halide perovskite for next generation photovoltaic device. In order to reveal the effect of charge transport layers (CTLs) on the crystallinity and charge extraction of tin-based halide perovskite film, here we employ different electron transport materials and hole transport materials as CTLs used for perovskite film growth. The tin-based halide perovskite films grown on organic CTLs exhibit better crystallization, lower lattice strain and have less defect states than those grown on inorganic CTLs, and photogenerated hole seems easier to be extracted than electrons in tin-based halide perovskite films.The former one can explain very well why the inverted structure tin-based perovskite solar cells show much higher power conversion efficiency (PCE) compared to the regular structure device. The later one suggests balanced electron and hole extraction are needed for enhancing the photovoltaic performance of the tin-based perovskite solar cell. Furthermore, the carrier extraction rate at CTLs/perovskite interface not only depends on the band offset of the CTLs/perovskite interface but also can be affected by the free energy of coulombic interaction at the interface. These finding would shed light on the further improvement of tin-based perovskite solar cells. (C) 2022 Published by ELSEVIER B.V. and Science Press on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Scientific journal, English

Top-Contacts-Interface Engineering for High-Performance Perovskite Solar Cell With Reducing Lead Leakage
Huan Bi; Gaoyi Han; Mengna Guo; Chao Ding; Shuzi Hayase; Hanjun Zou; Qing Shen; Yao Guo; Wenjing Hou
Sol. RRL, 6, 2200352-1, 01 Jun. 2022, Peer-reviwed
Scientific journal, English

Exponential optical absorption edge in PbS quantum dot-ligand systems on single crystal rutile-TiO2 revealed by photoacoustic and absorbance spectroscopies
Taro Toyoda; Qing Shen; Naoki Nakazawa; Yasuha Yoshihara; Keita Kamiyama; Shuzi Hayase
Materials Research Express, IOP Publishing, 9, 2, 1-13, 20 Apr. 2022, Peer-reviwed
Scientific journal, English

Enhancing the Electronic Properties and Stability of High-Efficiency Tin-Lead Mixed Halide Perovskite Solar Cells via Doping Engineering.
Shahrir Razey Sahamir; Muhammad Akmal Kamarudin; Teresa S Ripolles; Ajay Kumar Baranwal; Gaurav Kapil; Qing Shen; Hiroshi Segawa; Juan Bisquert; Shuzi Hayase
The journal of physical chemistry letters, 13, 13, 3130-3137, 07 Apr. 2022, True, Overcoming Voc loss to increase the efficiency of perovskite solar cells (PSCs) has been aggressively studied. In this work, we introduce and compare rubidium iodide (RbI) and potassium iodide (KI) alkali metal halides (AMHs) as dopants in a tin-lead (SnPb)-based perovskite system to improve the performance of PSCs by enhancing their Voc. Improvement in terms of surface morphology, crystallinity, charge transfer, and carrier transport in the SnPb perovskites was observed with the addition of AMH dopants. Significant power conversion efficiency improvement has been achieved with the incorporation of either dopant, and the highest efficiency was 21.04% in SnPb mixed halide PSCs when the RbI dopant was employed. In conclusion, we can outline the enhancement strategy that yields a remarkable efficiency of >20% with a smaller Voc loss and improved storage, light, and thermal stability in SnPb PSCs via doping engineering.
Scientific journal, English

A highly efficient and stable perovskite cathode with in situ exsolved NiFe alloy nanoparticles for CO2 electrolysis
Mengmeng Wang; Naizhi Li; Qing Shen; Zhongliang Zhan; Chusheng Chen
SUSTAINABLE ENERGY & FUELS, ROYAL SOC CHEMISTRY, 6, 8, 2038-2044, Apr. 2022, Perovskite structured oxides are promising candidate cathode materials for solid oxide electrolysis cells (SOECs) due to their better redox stability and coking resistance than nickel-yttria stabilized zirconia. The present study aimed at improving the CO2 electrolysis performance of the lanthanum chromium ferrite cathode through modification with metal nanoparticle catalysts. NiFe nanoparticles were exsolved from (La0.75Sr0.25)(0.95)Cr0.5Fe0.35Ni0.15O3-delta (LSCrFN) upon exposure to hydrogen at 800 degrees C. For comparison, NiFe nanoparticles were also deposited on La0.75Sr0.25Cr0.5Fe0.5O3-delta (LSCrF) using the infiltration method. When used as a supporting cathode for SOECs, the one with the exsolved nanoparticles exhibited a higher CO2 electrolysis current density than the one with the infiltrated nanoparticles and the one without the nanoparticles, e.g., their corresponding current densities at 1.5 V and 800 degrees C were 1.15, 0.80, and 0.59 A cm(-2). The electrode with the exsolved nanoparticles also demonstrated much better durability than that with the infiltrated nanoparticles. When tested at 1 V and 800 degrees C, the current density of the former decreased from 0.66 to 0.63 A cm(-2) during a period of 260 h, i.e., 0.012% h(-1), and the nanoparticles remained well dispersed after the test. In contrast, for the latter, the current density dropped from 0.33 to 0.29 A cm(-2) within 26 h, i.e., 0.15% h(-1), and severe agglomeration of the nanoparticles occurred. It is concluded that perovskite oxides modified with the exsolved metal nanoparticles possess both high electrocatalytic activity and stability, promising for use as the supporting cathode for SOECs.
Scientific journal, English

Relationship between Carrier Density and Precursor Solution Stirring for Lead-Free Tin Halide Perovskite Solar Cells Performance
Baranwal A. K; Nishimura K; Liu D; Kamarudin M. A; Kapil G; Saini S; Yabuki T; Iikubo S; Minemoto T; Yoshino K; Miyazaki K; Shen Q; Hayase S
ACS Appl. Energy Mater., American Chemical Society, x, 4, 4002-4007, 01 Apr. 2022, Peer-reviwed, The oxidation of tin halide perovskite precursor (THP) with the solvent dimethyl sulfoxide (DMSO) has intriguing drawbacks. We found that THP oxidation under progressive stirring can be hindered by the addition of GeI2. Subsequently, the stirring time of the precursor solution affects the carrier density and semiconducting properties of fabricated films, because DMSO can increase the oxidation induced carrier density. On the other hand, dimethylformamide (DMF) can suppress the oxidation induced carrier density. After 24 h, an efficiency of 10.26% is found when DMF is used and 7.12% is found when DMSO is used as a stirring solvent.
Scientific journal, English

Highly efficient and low hysteresis methylammonium-free perovskite solar cells based on multifunctional oteracil potassium interface modification
Huan Bi; Yao Guo; Mengna Guo; Chao Ding; Shuzi Hayase; Tao Mou; Qing Shen; Gaoyi Han; Wenjing Hou
Chemical Engineering Journal, Elsevier B.V., 439, 125671, 09 Mar. 2022, Peer-reviwed
Scientific journal, English

Structural stability and optical properties of tin-based iodide perovskite
de A; Iikubo S; Yamamoto K; Shen Q; Yoshino K; Minemoto T; Hayase S
Japanese Journal of Applied Physics, Japanese Journal of Applied Physics, 61, 3, 03 Mar. 2022, Peer-reviwed
Scientific journal, English

Tin–Lead Perovskite Solar Cells Fabricated on Hole Selective Monolayers
Gaurav Kapil; Takeru Bessho; Yoshitaka Sanehira; Shahrir R. Sahamir; Mengmeng ChenMengmeng Chen; i-Powered Energy; System Research Center (i-PERC; The University of Electro-Communications; Chofugaoka; Chofu, Toky; Japan; More by Mengmeng Chen; Ajay Kumar Baranwal; Dong Liu; Yuya Sono; Daisuke Hirotani; Daishiro Nomura; Kohei Nishimura; Muhammad Akmal Kamarudin; Qing Shen; Hiroshi Segawa; Shuzi Hayase
ACS Energy Lett., American Chemical Society, 7, 3, 966-974, 11 Feb. 2022, Peer-reviwed
Scientific journal, English

High performance wide bandgap Lead-free perovskite solar cells by monolayer engineering
Mengmeng Chen; Gaurav Kapil; Liang Wang; Shahrir Razey Sahamir; Ajay K. Baranwal; Kohei Nishimura; Yoshitaka Sanehira; Zheng Zhang; Muhammad Akmal Kamarudin; Qing Shen; Shuzi Hayase
Chemical Engineering Journal, Elsevier B.V., 436, 135196, 11 Feb. 2022, Peer-reviwed
Scientific journal, English

Large synergy effects of doping, a site substitution, and surface passivation in wide bandgap Pb-free ASnI2Br perovskite solar cells on efficiency and stability enhancement
Mengmeng Chen; Gaurav Kapil; Yusheng Li; Muhammad Akmal Kamarudin; Ajay K. Baranwal; Kohei Nishimura; Shahrir Razey Sahamir; Yoshitaka Sanehira; Hua Li; Chao Ding; Zheng Zhang; Qing Shen; Shuzi Hayase
Journal of Power Sources, 520, 01 Feb. 2022, Peer-reviwed, Tin (Sn) based perovskite solar cells (PSCs) are rapidly getting attention due to their relatively less toxic nature compared to lead-PSCs. However, Sn perovskites previously reported are narrow-bandgap materials. Wide-bandgap perovskites, which are the key materials for the top layer of lead-free tandem solar cells, are rarely researched up to now. Here, it is demonstrated that optoelectronic properties of the GA0.06(FA0.8Cs0.2)0.94SnI2Br based wide-bandgap perovskite can be improved by exploring (1) Germanium (II) Iodide (GeI2) doping, (2) incorporation of Ethylenediamine Bromide (EDABr2) at A site, (3) EDA passivation. The incorporation of big organic cation EDABr2 in the wide-bandgap tin perovskite crystal structure together with GeI2 doping made the carrier lifetime of perovskite absorber increase from 1.1 ns to 22.8 ns and the power conversion efficiency (PCE) was enhanced from 2.55% to 4.86% with an increment of Voc ˃ 100 mV. Further, we achieved the balanced charge transfer by using EDA passivation on the optimized perovskite surface film. As a result, the efficiency was improved from 4.86% to 7.50%, which is the highest efficiency among lead-free wide bandgap PSCs. This enhanced photovoltaic performance of the wide-bandgap tin perovskite device presents a wide application in lead-free tandem towards commercial development.
Scientific journal, English

Influence of charge transport layer on the crystallinity and charge extraction of pure tin-based halide perovskite film
Yaohong Zhang; Muhammad Akmal Kamarudin; Qiao Li; Chao Ding; Yong Zhou; Yingfang Yao; Zhigang Zou; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Shuzi Hayase; Qing Shen
Journal of Energy Chemistry, Elsevier B.V., 69, 612-615, 15 Jan. 2022, Peer-reviwed
Scientific journal, English

Molybdenum Sulfide Quantum Dots Decorated on TiO2 for Photocatalytic Hydrogen Evolution
Tianyang Qiu; Lu Wang; Boye Zhou; Yanjun Zhu; Chen Zhuang; Qi Liu; Qing Shen; Yujie Xiong; Yong Zhou; Zhigang Zou
ACS Appl. Nano Mater., ACS Appl. Nano Mater., 5, 1, 702-709, 28 Dec. 2021, Peer-reviwed
Scientific journal, English

Bismuth Vacancy-Induced Efficient CO2 Photoreduction in BiOCl Directly from Natural Air: A Progressive Step toward Photosynthesis in Nature
Wang L; Wang R; Qiu T; Yang L; Han Q; Shen Q; Zhou X; Zhou Y; Zou Z
Nano Lett., American Chemical Society, 21, 24, 10260-10266, 12 Nov. 2021, Peer-reviwed
Scientific journal, English

Large Grain Growth and Energy Alignment Optimization by Diethylammonium Iodide Substitution at A Site in Lead-Free Tin Halide Perovskite Solar Cells
Zheng Zhang; Ajay Kumar Baranwal; Shahrir Razey Sahamir; Gaurav Kapil; Yoshitaka Sanehira; Mengmeng Chen; Kohei Nishimura; Chao Ding; Dong Liu; Hua Li; Yusheng Li; Muhammad Akmal Kamarudin; Qing Shen; Teresa S. Ripolles; Juan Bisquert; Shuzi Hayase
SOLAR RRL, WILEY-V C H VERLAG GMBH, 5, 11, Nov. 2021, Environment-friendly tin perovskite solar cells (T-PKSCs) are the most suitable alternative candidate for lead-free PKSCs. However, the photovoltaic performance of such T-PKSCs is far below those of lead-based perovskite solar cells due to an energetic mismatch between the perovskite layer and charge transport layers. Herein, it is shown that, by partial substitution of the A-site cation using diethylammonium iodide (DEAI) substitution, deeper energy levels are obtained. At the same time, the trap density is reduced and the grain size is significantly improved. The fabricated solar cell shows much enhanced efficiency from 7.31% to 10.28%, short-circuit current density from 18.68 to 21.69 mA cm(-2), open-circuit voltage from 0.59 to 0.67 V, and fill factor from 0.67 to 0.71 after DEAI substitution. Such an efficiency improvement can be explained by matching energy levels at the interfaces between perovskite layer and the charge transport layers. In addition, after 50 days of storage, the modified T-PKSCs demonstrate high stability maintaining 78% of its initial efficiency, whereas the reference device degrades to 68% during 28 days storage.
Scientific journal, English

Preparation of nanocomposites of PbS quantum dots dispersed in MAPbI3matrix from precursor solution of Pb xanthate
Daisuke Hirotani; Kohei Nishimura; Yaohong Zhang; Qing Shen; Shuzi Hayase
Advances in Natural Sciences: Nanoscience and Nanotechnology, IOP Publishing Ltd, 12, 3, 01 Sep. 2021, Organic-inorganic hybrid perovskites attract attentions because of their unique electro-optical properties which are expected to be applied to various devices. The perovskite compounds are generally prepared from precursor solutions consisting of two materials, AX and BX2 for ABX3. Generally, methylammonium lead triiodide (MAPbI3) perovskite is formed from the precursor solution consisting of methylammonium iodide (MAI) and lead iodide (PbI2). In this report, we select Pb(-S-C(S)-OR)2 (lead xanthate, abbreviated as Pb(XT)2) as the perovskite precursor instead of PbI2. We found that the precursor solutions consisting of the MAI and the Pb(XT)2 give nanocomposites consisting of MAPbI3 and PbS nanomaterials including PbS quantum dot without changing the MAPbI3 bandgap. In this report, nanocomposites prepared from precursors consisting of Pb(XT)2/MAI with various ratios are analysed by using XRD, XPS, TG-DTA, TEM and UV/VIS spectroscopy.
Scientific journal, English

Electrocatalytic fixation of N2into NO3-: Electron transfer between oxygen vacancies and loaded Au in Nb2O5-: Xnanobelts to promote ambient nitrogen oxidation
Yintong Zhang; Feng Du; Ruyi Wang; Xintong Ling; Xiaoyong Wang; Qing Shen; Yujie Xiong; Tao Li; Yong Zhou; Zhigang Zou
Journal of Materials Chemistry A, Royal Society of Chemistry, 9, 32, 17442-17450, 28 Aug. 2021, The electrocatalytic nitrogen oxidation reaction (NOR) is a promising alternative to the industrial synthesis of nitrate. However, with the enhancement of NOR activity by modification methods, the competitive oxygen evolution reaction (OER) is always improved simultaneously. Here, a hybrid electrocatalyst composed of Au nanoparticles and oxygen vacancy-enriched niobium oxide nanobelts (Au-Nb2O5-x) was prepared on niobium foil for N2 fixation into NO3-. The results of X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) demonstrate that electron transfer occurs between Au nanoparticles and the oxygen vacancies in Nb2O5-x nanobelts, which adjusts the electronic structures of oxygen vacancies near the Au/Nb2O5-x interface. Electrochemical and N2 temperature-programmed desorption (TPD) tests indicate that the optimization of the electronic structure suppresses the activity of the competitive OER on oxygen vacancy sites and facilitates nitrogen adsorption on the surface of Au-Nb2O5-x, which significantly enhances the NOR performance of the electrocatalyst.
Scientific journal, English

Hollow InVO4 Nanocuboid Assemblies toward Promoting Photocatalytic N2 Conversion Performance
Qiutong Han; Xiaowan Bai; Jingming Chen; Shengnan Feng; Wa Gao; Wenguang Tu; Xiaoyong Wang; Jinlan Wang; Bi Jia; Qing Shen; Yong Zhou; Zhigang Zou
Advanced Materials, 33, 2006780, 1-9, 15 Aug. 2021, Peer-reviwed
Scientific journal, English

Colloidal quantum-dot bulk-heterojunction solar cells
Chao Ding; Lixiu Zhang; Qing Shen; Liming Ding
Journal of Semiconductors, 42, 11, 110203-110206, 09 Aug. 2021, Peer-reviwed
Scientific journal, English

Matrix Manipulation of Directly-Synthesized PbS Quantum Dot Inks Enabled by Coordination Engineering
Li, F; Liu, Y; Shi, G; Chen, W; Guo, R; Liu, D; Zhang, Y; Wang, Y; Meng, X; Zhang, X; Lv, Y; Deng, W; Zhang, Q; Shi, Y; Chen, Y; Wang, K; Shen, Q; Liu, Z; Müller-Buschbaum, P; Ma, W
Adv. Funct. Mater., John Wiley & Sons, Inc., 31, 2104457, 06 Aug. 2021, Peer-reviwed
Scientific journal, English

Matrix Manipulation of Directly-Synthesized PbS Quantum Dot Inks Enabled by Coordination Engineering
Fei Li; Yang Liu; Guozheng Shi; Wei Chen; Renjun Guo; Dong Liu; Yaohong Zhang; Yongjie Wang; Xing Meng; Xuliang Zhang; You Lv; Wei Deng; Qing Zhang; Yao Shi; Yifan Chen; Kai Wang; Qing Shen; Zeke Liu; Peter Müller-Buschbaum; Wanli Ma
Advanced Functional Materials, 2021, 2104457, 1-9, 06 Aug. 2021, Peer-reviwed
Scientific journal, English

acancy-defect modulated pathway of photoreduction of co2 on single atomically thin aginp2s6 sheets into olefiant gas.
Gao W; Li S; He H; Li X; Cheng Z; Yang Y; Wang J; Shen Q; Wang X; Xiong Y; Zhou Y; Zou Z
Nat Commun, 12, 4747, 1-8, 06 Aug. 2021, Peer-reviwed
Scientific journal, English

The effect of water on colloidal quantum dot solar cells
Guozheng Shi; Chen Cheng; Tianshu Zhai; Botong Chen; Xinnan Mao; Yang Liu; Xuliang Zhang; Xufeng Ling; Yannan Zhang; Xing Meng; Yifan Chen; Steffen Duhm; Liang Zhang; Lu Wang; Shiyun Xiong; Zeke Liu; Wanli Ma
Nature Communications, NATURE RESEARCH, 12, 4381, 1-12, 19 Jul. 2021, Peer-reviwed, Almost all surfaces sensitive to the ambient environment are covered by water, whereas the impacts of water on surface-dominated colloidal quantum dot (CQD) semiconductor electronics have rarely been explored. Here, strongly hydrogen-bonded water on hydroxylated lead sulfide (PbS) CQD is identified. The water could pilot the thermally induced evolution of surface chemical environment, which significantly influences the nanostructures, carrier dynamics, and trap behaviors in CQD solar cells. The aggravation of surface hydroxylation and water adsorption triggers epitaxial CQD fusion during device fabrication under humid ambient, giving rise to the inter-band traps and deficiency in solar cells. To address this problem, meniscus-guided-coating technique is introduced to achieve dense-packed CQD solids and extrude ambient water, improving device performance and thermal stability. Our works not only elucidate the water involved PbS CQD surface chemistry, but may also achieve a comprehensive understanding of the impact of ambient water on CQD based electronics. Surface of colloidal quantum dot is sensitive to water, and the interaction could potentially alter its chemical environments. Here, Shi et al. investigate how the interaction effects the nanostructures and carrier dynamic in CQDs, and subsequently introduce meniscus-guided coating technique to mitigate CQD fusion triggered by water adsorption.
Scientific journal, English

Erratum: Bimetallic oxyhydroxidein situderived from an Fe2Co-MOF for efficient electrocatalytic oxygen evolution (J. Mater. Chem. A (2021) 9 (13271-13278) DOI: 10.1039/D1TA02159A)
Xintong Ling; Feng Du; Yintong Zhang; Yan Shen; Wa Gao; Bo Zhou; Zhiyuan Wang; Guoling Li; Tao Li; Qing Shen; Yujie Xiong; Xiaoyong Wang; Yong Zhou; Zhigang Zou
Journal of Materials Chemistry A, Royal Society of Chemistry, 9, 25, 14607, 07 Jul. 2021, The email address of one of the corresponding authors, Guoling Li (guoling.li@gmail.com), was omitted from the published article. The correct affiliations, including email addresses, are as shown here. This correction therefore includes addition of the email address of one of the corresponding authors, Guoling Li (guoling.li@gmail.com). The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.
Scientific journal, English

Analysis of ion implanted diamond-like-carbon films using laser-induced transient reflecting grating technique
Q. Shen; A. Harata; T. Sawada
Journal De Physique. IV : JP, 4, 7, Jul. 2021, Laser-induced transient reflecting grating (TRG) technique was applied to measure both nitrogen-ion-implanted and nonimplanted thin-film coatings (thickness, 40nm) of diamond-like-carbon (DLC). Different TRG responses corresponding to the different samples with a variety of nitrogen-ion implantation doses were observed and the hypersonic surface acoustic wave velocities were obtained with a variety of wavelengths. A phenomenon was observed that the SAW velocity of the implanted DLC coating with higher dose became larger than that of the nonimplanted sample.
Scientific journal

Bimetallic oxyhydroxidein situderived from an Fe2Co-MOF for efficient electrocatalytic oxygen evolution
Xintong Ling; Feng Du; Yintong Zhang; Yan Shen; Wa Gao; Bo Zhou; Zhiyuan Wang; Guoling Li; Tao Li; Qing Shen; Yujie Xiong; Xiaoyong Wang; Yong Zhou; Zhigang Zou
Journal of Materials Chemistry A, Royal Society of Chemistry, 9, 22, 13271-13278, 14 Jun. 2021, Metal-organic frameworks (MOFs) have received extensive attention as a research hotspot in the field of electrocatalytic water splitting. However, the study of electrochemicalin situformation of catalysts to improve the activity for the OER is far from being satisfactory. In this work, we prepared a Fe2Co-MIL-88B MOF on nickel foam (Fe2Co MOF/NF) through a solvothermal process. Fe0.67Co0.33OOH wasin situformed on the surface of an Fe2Co MOF during the OER, which is confirmed as the real active species. The electrocatalytic performance is significantly improved due to the electron transfer between Fe and Co, which is confirmed to be related to the positive coupling effect between Co and Fe and the change of the electronic structure caused by the replacement of Co by Fe metal ions in the MOF. Meanwhile, density functional theory calculations reveal that the OER on Fe0.67Co0.33OOH follows the Mars-van-Krevelen mechanism. The electrochemical test results show the superior OER activity of the catalyst with a low overpotential of 224 mV at a current density of 10 mA cm−2, a low Tafel slope of 45.3 mV dec−1, and excellent stability for 50 hours in 1 M KOH. This study provides a simple and effective strategy for the rational design and structural evolution of MOF-derived materials to achieve inexpensive and effective electrocatalysis.
Scientific journal, English

High-Efficiency Lead-Free Wide Band Gap Perovskite Solar Cells via Guanidinium Bromide Incorporation
Mengmeng Chen; Muhammad Akmal Kamarudin; Ajay K. Baranwal; Gaurav Kapil; Teresa S. Ripolles; Kohei Nishimura; Daisuke Hirotani; Shahrir Razey Sahamir; Zheng Zhang; Chao Ding; Yoshitaka Sanehira; Juan Bisquert; Qing Shen; Shuzi Hayase
ACS Applied Energy Materials, AMER CHEMICAL SOC, 4, 6, 5615-5624, 08 Jun. 2021, Peer-reviwed, Despite lead halide perovskite(top)/silicon(bottom) tandem solar cell achieving >29% efficiency, the toxicity of lead limits the adoption of perovskites in electronic devices. To solve this problem, tin perovskite has been suggested as an alternative candidate to be used as the top cell. However, most of the reports on tin perovskite solar cells are based on narrow band gap materials (band gap: 1.20-1.40 eV), which are not suitable to be used as the tandem top cell. In addition, the efficiency of the previously reported wide band gap lead-free perovskites is not satisfactory, shown to be less than 2.00%. This study explores the fabrication of the wide band gap (1.61 eV) ASnI(2)Br perovskite solar cells through the optimization of formamidinium and guanidinium content to improve the efficiency from 1.68 to 7.00%. Substituting the A site with larger cation results in a larger crystal size, which translated into higher device stability. Better energy-level alignment within the device significantly enhanced the charge injection and extraction, which translated into higher open-circuit voltage. This work provides proof that tin-halide perovskite solar cells have the potential in the fabrication of lead-free all-perovskite tandem solar cells.
Scientific journal, English

Passivating Quantum Dot Carrier Transport Layer with Metal Salts
Zihan Chen; Yaohong Zhang; Zhi Li Teh; Jianfeng Yang; Lin Yuan; Gavin J. Conibeer; Robert J. Patterson; Qing Shen; Shujuan Huang; Zhilong Zhang
ACS Applied Materials & Interfaces, 13, 24, 28679-28688, 08 Jun. 2021, Peer-reviwed
Scientific journal, English

Tin-Lead Perovskite Fabricated via Ethylenediamine Interlayer Guides to the Solar Cell Efficiency of 21.74%
Gaurav Kapil; Takeru Bessho; Takatoshi Maekawa; Ajay Kumar Baranwal; Yaohong Zhang,Muhammad Akmal Kamarudin; Daisuke Hirotani; Qing Shen; Hiroshi Segawa; Shuzi Hayase
Advanced Energy Materials, 11, 2101069, 1-9, 28 May 2021, Peer-reviwed
Scientific journal, English

Ultra-Halide-Rich Synthesis of Stable Pure Tin-Based Halide Perovskite Quantum Dots: Implications for Photovoltaics
Feng Liu; Junke Jiang; Taro Toyoda; Muhammad Akmal Kamarudin; Shuzi Hayase; Ruixiang Wang; Shuxia Tao; Qing Shen
ACS Appl. Nano Mater., 1-11, 30 Mar. 2021, Peer-reviwed
Scientific journal, English

Elegant Construction of ZnIn2S4/BiVO4 Hierarchical Heterostructures as Direct Z-Scheme Photocatalysts for Efficient CO2 Photoreduction
Qiutong Han; Liang Li; Wa Gao; Yan Shen; Lu Wang; Yintong Zhang; Xiaoyong Wang; Qing Shen; Yujie Xiong; Yong Zhou; Zhigang Zou
ACS Appl. Mater. Interfaces, 13, 13, 15092-15100, 24 Mar. 2021, Peer-reviwed
Scientific journal, English

The role of sodium in stabilizing tin–lead (Sn–Pb) alloyed perovskite quantum dots
Junke Jiang; Feng Liu; Qing Shen; Shuxia Tao
Journal of Materials Chemistry A, The Royal Society of Chemistry 2021, 19 Mar. 2021, Peer-reviwed
Scientific journal, English

Impact of Auger recombination on performance limitation of perovskite solar cell
JakapanChantana; YuKawano; TakahitoNishimur; AbdurashidMavlonov; QingShen; KenjiYoshino; SatoshiIikubo; ShuziHayase; TakashiMinemoto
Solar Energy, Elsevier Ltd, 217, 342-353, 15 Mar. 2021, Peer-reviwed, Theoretical limit (or detailed balance limit) of photovoltaic performances of single-junction solar cell was estimated under consideration of radiative recombination, where the solar cell was assumed as blackbody with temperature (T) of 298.15 K. The detailed balance limit of the perovskite solar cell is furthermore calculated under considerations of not only radiative recombination but also Auger recombination. It is revealed that open-circuit voltage (VOC) is primarily reduced with increasing the intrinsic density (ni) and Auger recombination coefficient (Cp), thus decreasing the conversion efficiency (η). Under the Eg of 1.55 eV and ni of 1 × 107 cm−3, the η of perovskite solar cell is reduced from 31.41% (without Auger recombination consideration) to 28.92% with the increased Cp to 1 × 10−29 cm6.s−1. According to the result, the Cp should be lower than 1 × 10−31 cm6.s−1 to avoid the impact of Auger recombination for the improved performances of perovskite solar cells, where it is suggested that the Cp can be reduced through band-structure engineering and alloying with other halide perovskites, thereby providing the avenues for material design. Furthermore, the effect of Shockley-Read-Hall recombination in the perovskite solar cell on its efficiency limit is discussed.
Scientific journal, English

Study of open circuit voltage loss mechanism in perovskite solar cells
Yulu He; Imane Abdellaoui; M. Abdel-Shakour; Towhi; Hossain Chowdhury; Muhammad Akmal Kamarudin; Ana Flávia Nogueira; Qing Shen; Shuzi Hayase; Ashraful Islam; Takeaki Sakurai
Japanese Journal of Applied Physics, 60, SBBF13, 1-6, 26 Feb. 2021, Peer-reviwed
Scientific journal, English

Relationship between perovsktie solar cell efficiency and lattice disordering
Daisuke Hirotani; Kohei Nishimura; Kengo Hamada; Muhammad Akmal Kamarudin; Satoshi Iikubo; Qing Shen; Taro Toyoda; Shuzi Hayase
Japanese Journal of Applied Physics, IOP Publishing, 60, 3, 035001-035001, 15 Feb. 2021, Abstract

Multi-cations lead perovskite solar cells have shown higher performance than single-cation perovskite solar cells. This compositional engineering of perovskite material retains the optimum tolerance factor while allowing the tuning of the band gap in addition to the enhanced stability of cubic phase perovskite. However, no in-depth explanation has been provided on the relationship between crystal structure of the perovskite and the solar cell efficiency. In this report, we investigate the effect of lattice disordering of FA_xMA_1−xPbI₃ perovskite on the tolerance factor and solar cell efficiency. The lattice disordering estimated using Williamson–Hall plot of XRD analysis revealed that the disordering is lowest when x = 0.2 and highest when x = 1.0. Correspondingly, x = 0.2 showed the highest solar cell performance and long carrier lifetime Our results show that the disordering in α phase of FA_xMA_1−xPbI₃ layer causes lattice deformation which affects the carrier lifetime and solar cell efficiency, instead of the defects on constituent elements.
Scientific journal

Modeling of Nucleation and Growth in the Synthesis of PbS Colloidal Quantum Dots Under Variable Temperatures
Dandan Wang; Meibo Xing; Yuyao Wei; Longxiang Wang; Ruixiang Wang; Qing Shen
ACS Omega, American Chemical Society, 6, 5, 3701-3710, 29 Jan. 2021, Peer-reviwed
Scientific journal, English

Mg-doped ZnO layer to enhance electron transporting for PbS quantum dot solar cells
Meibo Xing; Yuyao Wei; Dandan Wang; Qing Shen; Ruixiang Wang
CURRENT APPLIED PHYSICS, ELSEVIER, 21, 14-19, Jan. 2021, In this work, the effect of Mg doping on the performance of PbS quantum dot (QD) solar cells (QDSCs) is investigated. To elucidate that, PbS QDSCs with pristine ZnO and Mg-doped ZnO (ZMO) as electron transporting layers (ETLs) are fabricated, respectively. The current density-voltage (J-V) measurements are performed. The results show that the cell efficiency of the device with ZMO as an ETL is 9.46%, which increases about 75% compared to that of the pristine ZnO based device (5.41%). Enhanced short current density (Jsc) and fill factor (FF) are observed. It is demonstrated that Mg doping could passivate the surface defects and suppress the carrier recombination in ZnO ETL, thus resulting in larger bandgap and higher Fermi level (EF). The strategy of Mg doped ZnO ETL provides a promising way for pushing solar cell performance to a high level.
Scientific journal, English

Photoexcited carrier dynamics in colloidal quantum dot solar cells: insights into individual quantum dots, quantum dot solid films and devices
Zhang, Y; Wu, G; Liu, F; Ding, C; Zou, Z; Shen, Q
Chemical Society Reviews, Royal Society of Chemistry, 49, 1, 49-84, 11 Dec. 2020, Peer-reviwed, The certified power conversion efficiency (PCE) record of colloidal quantum dot solar cells (QDSCs) has considerably improved from below 4% to 16.6% in the last few years. However, the record PCE value of QDSCs is still substantially lower than the theoretical efficiency. So far, there have been several reviews on recent and significant achievements in QDSCs, but reviews on photoexcited carrier dynamics in QDSCs are scarce. The photovoltaic performances of QDSCs are still limited by the photovoltage, photocurrent and fill factor that are mainly determined by the photoexcited carrier dynamics, including carrier (or exciton) generation, carrier extraction or transfer, and the carrier recombination process, in the devices. In this review, the photoexcited carrier dynamics in the whole QDSCs, originating from individual quantum dots (QDs) to the entire device as well as the characterization methods used for analyzing the photoexcited carrier dynamics are summarized and discussed. The recent research including photoexcited multiple exciton generation (MEG), hot electron extraction, and carrier transfer between adjacent QDs, as well as carrier injection and recombination at each interface of QDSCs are discussed in detail herein. The influence of photoexcited carrier dynamics on the physiochemical properties of QDs and photovoltaic performances of QDSC devices is also discussed.
Scientific journal, English

Atomistic and Electronic Origin of Phase Instability of Metal Halide Perovskites
Junke Jiang; Feng Liu; Ionut Tranca; Qing Shen; Shuxia Tao
ACS Applied Energy Materials, 2020 American Chemical Society, 3, 12, 11548-11558, 22 Nov. 2020, Peer-reviwed
Scientific journal, English

Passivation Strategy of Reducing Both Electron and Hole Trap States for Achieving High-Efficiency PbS Quantum-Dot Solar Cells with Power Conversion Efficiency over 12%
Chao Ding; Feng Liu; Yaohong Zhang; Shuzi Hayase; Taizo Masuda; Ruixiang Wang; Yong Zhou; Yingfang Yao; Zhigang Zou; Qing Shen
ACS Energy Letters, ACS Publications, 5, 10, 3224-3236, 18 Sep. 2020, Peer-reviwed
Scientific journal, English

Inverted CsPbI2Br perovskite solar cells with enhanced efficiency and stability in ambient atmosphere via formamidinium incorporation, Solar Energy Materials and Solar Cells
Mengmeng Chen; Shahrir R. Sahamir; Gaurav Kapil; Ajay K. Baranwal; Muhammad Akmal Kamarudin; Yaohong Zhang; Kohei Nishimura; Chao Ding; Dong Liu; Daisuke Hirotani; Qing Shen; Shuzi Hayase
Solar Energy Materials and Solar Cells, Elsevier, 218, 110741-110749, 06 Sep. 2020, Peer-reviwed, CsPbI2Br is one of candidates of the top layer for the all perovskite tandem solar cells. However, the perovskite is prone to change the phase from α (black) to δ (yellow) type. In this research, Cs1-xFAxPbI2Br perovskites were fabricated in an ambient atmosphere, and their properties immediately after the fabrication and the phase stability were investigated. The quality of the perovskite films was enhanced and the trap density was reduced after the incorporation of the FA cations. The phase stability of the Cs1-xFAxPbI2Br perovskite was effectively enhanced. Consequently, the highest power conversion efficiency of 12.28% with open-circuit voltage (Voc) of 1.09 V, current intensity (Jsc) of 15.65 mA cm−2, and fill factor of 72% in the planar solar cell based on Cs0.7FA0.3PbI2Br perovskite is reported. The bandgap was optimized to be about 1.82 eV suitable for all perovskite tandem top layer. Most importantly, all the photovoltaic parameters of Cs0.7FA0.3PbI2Br perovskite solar cells showed ignorable decay after 2 months’ measurement in an ambient atmosphere with the presence of air and humidity without encapsulation.
Scientific journal, English

A New Strategy for Increasing the Efficiency of Inverted Perovskite Solar Cells to More than 21%: High-Humidity Induced Self-Passivation of Perovskite Films
Fan Zhang; Qingxun Huang; Jun Song; Shuzi Hayase; Junle Qu; Qing Shen
SOLAR RRL, WILEY-V C H VERLAG GMBH, 4, 9, Sep. 2020, The performance of perovskite solar cells (PSCs) is known to be extremely sensitive to humidity in the preparation environment. However, the main mechanism by which the moisture influences the quality of the perovskite film and the device performance is not yet fully understood. Herein, a new strategy is established to obtain inverted PSCs with a remarkabll high V-OC by including a high-humidity treatment and sufficient DMSO-atmosphere annealing in the preparation process. It is found that the lattice distortion on the surface of perovskite grains caused by the high-humidity treatment plays a key role in the self-passivation of perovskite. Inverted (p-i-n) PSCs based on the self-passivated perovskite films show effective suppression of nonradiative recombination, which increase the device V-OC to 1.17 V and achieve the highest efficiency of 21.38%. It is expected that the findings of this work shed more light on the currently proposed mechanism governing the action of moisture on the performance of the PSCs.
Scientific journal, English

Dependence of the optical properties and carrier dynamics of CsSn_xPb_1-xBr₃ Perovskite nanocrytal on the ratio of tin to lead
Kawabata Kentaro; Liu Feng; Zhang Yaohong; Shen Qing; Toyoda Taro; Hayase Shuzi
JSAP Annual Meetings Extended Abstracts, The Japan Society of Applied Physics, 2020.2, 1937-1937, 26 Aug. 2020
Japanese

Relationship between Built-in Potential and Open-circuit Voltage in Tin-based Perovskite Solar Cells
Hirotani Daisuke; Kamarudin Akmal; Nishimura Kohei; Qing Shen; Taro Toyoda; Hayase Shuzi
JSAP Annual Meetings Extended Abstracts, The Japan Society of Applied Physics, 2020.2, 1650-1650, 26 Aug. 2020
Japanese

Efficiency improvement of Sn-perovskite solar cells by A-site multicationization
Nishimura Kohei; Akmal Kamarudin Muhammad; Hirotani Daisuke; Hamada Kengo; Iikubo Satoshi; Shen Qing; Minemoto Takashi; Yoshino Kenji; Hayase Shuzi
JSAP Annual Meetings Extended Abstracts, The Japan Society of Applied Physics, 2020.2, 1653-1653, 26 Aug. 2020
Japanese

Stability Improvement of Perovskite Solar Cells by Adding Sb‐Xanthate to Precursor Solution
Kyung-Su Nam; Suvratha Krishnamurthy; Shen Qing; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Tingli Ma; Shyam Pandey; Shuzi Hayase
Phys. Status Solidi A, John Wiley & Sons, Inc, 217, 18, 2000144 -1-2000144 -5, 08 Jul. 2020, Peer-reviwed
Scientific journal, English

Synthesis of Pb-doped CdS quantum dot using SILAR method on mesoporous TiO2 layer
Yosita Sudswasd; Feng Liu; Taro Toyoda; Qing Shen; Witoon Yindeesuk
Journal of Physics: Conference Series, 1719, 012063, 05 Jul. 2020, Peer-reviwed
Scientific journal, English

In-Depth Exploration of the Charge Dynamics in Surface-Passivated ZnO Nanowires
Yaohong Zhang; Shuhei Ozu; Guohua Wu; Chao Ding; Feng Liu; Dong Liu; Takashi Minemoto; Taizo Masuda; Shuzi Hayase; Taro Toyoda; Qing Shen
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 124, 29, 15812-15817, Jul. 2020, One-dimension ZnO nanowires (NWs) are widely used in many optoelectronic devices owing to their high optical transparency and excellent electron-transporting property. Unfortunately, there are various shallow-level and deep-level states in ZnO NWs, which usually act as the charge recombination centers of the devices. Surface passivation is an effective way to reduce deep-level states in ZnO NWs. However, how the surface passivation affects the charge dynamic process in ZnO NWs is still unclear. Herein, we carried out an in-depth study of the charge dynamics in surface-passivated ZnO NWs by using time-resolved photoluminescence and transient absorption spectroscopy techniques. The results show that the percentage of nonradiative recombination in ZnO NWs is efficiently reduced, and the lifetime of photoexcited carrier is increased after surface passivation. The introduction of a thin passivation layer like SnO2 can effectively reduce the rate of interfacial charge recombination without any adverse effect on the electron injection process.
Scientific journal, English

In-Depth Exploration of the Charge Dynamics in Surface-Passivated ZnO Nanowires
Yaohong Zhang; Shuhei Ozu; Guohua Wu; Chao Ding; Feng Liu; Dong Liu; Takashi Minemoto; Taizo Masuda; Shuzi Hayase; Taro Toyoda; Qing Shen
The Journal of Physical Chemistry C, ACS Publications, 124, 29, 15812-15817, 26 Jun. 2020, Peer-reviwed
Scientific journal, English

All-inorganic cesium lead halide perovskite nanocrystals for solar-pumped laser application
T. Masuda; Y. Zhang; C. Ding; F. Liu; K. Sasaki; Q. Shen; M. Endo
Journal of Applied Physics, AIP Publishing, 127, 243104, 1-9, 24 Jun. 2020, Peer-reviwed, We demonstrate a low-concentrated solar-pumped laser (SPL) with natural sunlight by using an all-inorganic cesium lead halide perovskite (CsPbBrxI3-x) nanocrystal (NC) dispersed in toluene as a sensitizer. The perovskite NCs exhibit substantial advantages for SPL applications because of their broad absorption and narrow photoluminescence (PL) spectra with high quantum yield using inexpensive commercial precursors. We successfully synthesized CsPbBrxI3-x NCs with precisely tuned PL wavelengths from 581 to 612 nm by altering the I/Br ratio to achieve spectral overlap with Nd3+ ions, which have been widely used as a laser medium for SPLs. The measurement results show that the laser output power is highly sensitive to the peak PL wavelength of the NCs, and the highest laser output was obtained at the peak wavelength of 595 nm. Although the synthesized NCs have a wider absorption band, the laser output power obtained was much less than that of an organic dye of rhodamine 6G (R6G). The numerical analyses show that the optimal peak PL wavelength is 10 nm shorter than the absorption peak of Nd3+ ions because of the reflection property of the dichroic mirror coated on the input window. Moreover, we found that the concentration of NCs needs to be optimized in response to the peak PL wavelength. The calculations show that a laser output power 2.7 times greater than that of R6G can be obtained under an optimal peak PL wavelength of 575 nm and a concentration of 24 g/l for the CsPbBrxI3-x NCs.
Scientific journal, English

Exquisite Design of Porous Carbon Microtubule-Scaffolding Hierarchical In2O3-ZnIn2S4 Heterostructures toward Efficiently Photocatalytic Conversion of CO2 into CO
Wa Gao; Lu Wang; Chao Gao; Jinqiu Liu; Yong Yang; Liuqing Yang; Qing; Shen, Congping Wu; Yong Zhou; Zhigang Zou
Nanoscale, Royal Society of Chemistry, 12, 14676-14681, 17 Jun. 2020, Peer-reviwed
Scientific journal, English

Pb free perovskite solar cells with over 13 % efficiency-Direction to high efficiency-Pb free solar cells
Kohei Nishimura; Muhammad Akmal Kamarudin; Daisuke Hirotani; Shen Qing; Takashi Minemoto; Satoshi Iikubo; Kengo Yoshino; Shuzi Hayase
Conference Record of the IEEE Photovoltaic Specialists Conference, Institute of Electrical and Electronics Engineers Inc., 2020-, 0661-0663, 14 Jun. 2020, This is a report on Pb free perovskite solar cells. Direction to enhancing efficiency for Sn-perovskite solar cells are discussed. In order to decrease carrier density and defect density in Sn-perovskite layers, Ge ion doping, surface and grain boundary passivation, decrease in lattice strain, and band alignment are proved to be effective. Ge doped Sn-perovskite solar cells with 13% efficiency is reported.
International conference proceedings, English

The effect of p/n junction position on perovskite solar cell efficiency by changing polarity of the perovskite layer
Daisuke Hirotani; Yuta Maeda; Muhammad Akmal Kamarudin; Shen Qing; Taro Toyoda; Shuzi Hayase
Japan Society of Applied Physics, IOP SCIENCE, 59, 6, 061005-1-061005-7, 01 Jun. 2020, Peer-reviwed
Scientific journal, English

In situ preparation of Bi2S3 nanoribbon-anchored BiVO4 nanoscroll heterostructures for the catalysis of Cr(vi) photoreduction
Jianqiang Hu; Fen Zhang; Yong Yang; Qiutong Han; Zhaosheng Li; Qing Shen; Yongcai Zhang; Yong Zhou; Zhigang Zou
Catalysis Science & Technology, Royal Society of Chemistry, 10, 3843-3847, 25 May 2020, Peer-reviwed, Novel BiVO4/Bi2S3 heterostructures were fabricated simply by growing Bi2S3 nanoribbons on the surface of BiVO4 nanoscrolls, in situ, using pre-synthesized BiVO4 and bismuth(III) dimethyldithiocarbamate (Bi(dedc)3) as precursors. The length and density of the anchored Bi2S3 nanoribbons were controlled by tuning the amount of Bi(dedc)3 reacted with BiVO4 nanoscrolls. Compared to pure BiVO4, the prepared BiVO4/Bi2S3 heterostructures showed enhanced photocatalytic activity for Cr(VI) reduction under UV-visible light illumination, mainly due to the extended range of visible light absorption and the improved separation efficiency of photoinduced electrons and holes.
Scientific journal, English

Artificial Trees for Artificial Photosynthesis: Construction of Dendrite-Structured α-Fe2O3/g-C3N4 Z-Scheme System for Efficient CO2 Reduction into Solar Fuels
Yan Shen; Qiutong Han; Jianqiang Hu; Wa Gao; Lu Wang; Liuqing Yang; Chao Gao; Qing Shen; Congping Wu; Xiaoyong Wang; Xin Zhou; Yong Zhou; Zhigang Zou
ACS Applied Energy Materials, ACS Publications, 3, 7, 6561-6572, 20 May 2020, Peer-reviwed, A direct all-solid-state Z-scheme heterojunction photocatalyst of a g-C3N4-coated tree-like α-Fe2O3 was rationally constructed toward CO2 conversion. The so-called artificial tree shows excellent performance and stability for CO production (17.8 μmol g–1 h–1), almost 3 times that of pristine g-C3N4. Density functional theory computations explain the intrinsic cause for the formation of the Z-scheme structure. The enhanced photocatalytic performance can be attributed to a synergistic effect of the following factors: (1) the combination of α-Fe2O3 with g-C3N4 helps to promote light harvesting and CO2 adsorption; (2) the hybridization effectively enhances the spatial separation of photogenerated electrons and holes, suppressing the undesirable recombination of charge carriers; (3) the dendritic structure of α-Fe2O3 provides ample active sites with considerable steps, edges, and kinks along the twigs, and meanwhile, the exposed (001) facet with high electron conduction facilitates photoelectrons’ transportation to the interface. This work provides new insight into constructing Z-scheme photocatalysts for CO2 conversion.
Scientific journal, English

Surface-Modified Graphene Oxide/Lead Sulfide Hybrid Film-Forming Ink for High-Efficiency Bulk Nano-Heterojunction Colloidal Quantum Dot Solar Cells
Yaohong Zhang; Guohua Wu; Chao Ding; Feng Liu; Dong Liu; Taizo Masuda; Kenji Yoshino; Shuzi Hayase; Ruixiang Wang; Qing Shen
Nano-Micro Letters, Springer Nature, 12, 111, 1-14, 16 May 2020, Peer-reviwed, True, Solution-processed colloidal quantum dot solar cells (CQDSCs) is a promising candidate for new generation solar cells. To obtain stable and high performance lead sulfide (PbS)-based CQDSCs, high carrier mobility and low non-radiative recombination center density in the PbS CQDs active layer are required. In order to effectively improve the carrier mobility in PbS CQDs layer of CQDSCs, butylamine (BTA)-modified graphene oxide (BTA@GO) is first utilized in PbS-PbX2 (X = I-, Br-) CQDs ink to deposit the active layer of CQDSCs through one-step spin-coating method. Such surface treatment of GO dramatically upholds the intrinsic superior hole transfer peculiarity of GO and attenuates the hydrophilicity of GO in order to allow for its good dispersibility in ink solvent. The introduction of BTA@GO in CQDs layer can build up a bulk nano-heterojunction architecture, which provides a smooth charge carrier transport channel in turn improves the carrier mobility and conductivity, extends the carriers lifetime and reduces the trap density of PbS-PbX2 CQDs film. Finally, the BTA@GO/PbS-PbX2 hybrid CQDs film-based relatively large-area (0.35 cm2) CQDSCs shows a champion power conversion efficiency of 11.7% which is increased by 23.1% compared with the control device.
Scientific journal, English

Surface-Modified Graphene Oxide/Lead Sulfide Hybrid Film-Forming Ink for High-Efficiency Bulk Nano-Heterojunction Colloidal Quantum Dot Solar Cells
Yaohong Zhang; Guohua Wu; Chao Ding; Feng Liu; Dong Liu; Taizo Masuda; Kenji Yoshino; Shuzi Hayase; Ruixiang Wang; Qing Shen
NANO-MICRO LETTERS, SHANGHAI JIAO TONG UNIV PRESS, 12, 1, May 2020, Solution-processed colloidal quantum dot solar cells (CQDSCs) is a promising candidate for new generation solar cells. To obtain stable and high performance lead sulfide (PbS)-based CQDSCs, high carrier mobility and low non-radiative recombination center density in the PbS CQDs active layer are required. In order to effectively improve the carrier mobility in PbS CQDs layer of CQDSCs, butylamine (BTA)-modified graphene oxide (BTA@GO) is first utilized in PbS-PbX2 (X = I-, Br-) CQDs ink to deposit the active layer of CQDSCs through one-step spin-coating method. Such surface treatment of GO dramatically upholds the intrinsic superior hole transfer peculiarity of GO and attenuates the hydrophilicity of GO in order to allow for its good dispersibility in ink solvent. The introduction of BTA@GO in CQDs layer can build up a bulk nano-heterojunction architecture, which provides a smooth charge carrier transport channel in turn improves the carrier mobility and conductivity, extends the carriers lifetime and reduces the trap density of PbS-PbX2 CQDs film. Finally, the BTA@GO/PbS-PbX2 hybrid CQDs film-based relatively large-area (0.35 cm(2)) CQDSCs shows a champion power conversion efficiency of 11.7% which is increased by 23.1% compared with the control device.
Scientific journal, English

Lead-free tin-halide perovskite solar cells with 13% efficiency
Kohei Nishimura; Muhammad Akmal Kamarudin; Daisuke Hirotani; Kengo Hamada; Qing Shen; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Shuzi Hayase
Nano Energy, Elsevier Ltd., 74, 104858, 1-10, 28 Apr. 2020, Peer-reviwed, Despite the similarities of the optoelectronic properties between tin halide and lead halide perovskites, the performance of tin perovskite solar cells (PSCs) is still far below that of lead PSCs with highest reported efficiency to date of around 10%. This is due to the chemical instability of tin halide perovskite crystals and the energy band levels mismatch between the perovskite and charge transport layers. In this work, tin halide PSCs with efficiency of more than 13% has been fabricated by regulating the A site cation to achieve a tolerance factor of nearly 1. The partial substitution of formamidinium cation with ethylammonium cation affords a more stable tin perovskite crystal and at the same time suppresses the trap density by as much as 1 order of magnitude. Furthermore, the more favourable energy levels of the EA-substituted tin perovskites enhanced the charge extraction process into the charge transport layers and thus reducing the charge carrier recombination. This work provides a proof that tin-halide PSCs has the potential to compete with more toxic lead-based PSCs, and hopefully will pave the future direction for fabricating more efficient and stable lead-free PSCs.
Scientific journal, English

A New Strategy for Increasing the Efficiency of Inverted Perovskite Solar Cells to More than 21%: High‐Humidity Induced Self‐Passivation of Perovskite Films
Fan Zhang; Qingxun Huang; Jun Song; Shuzi Hayase; Junle Qu; Qing Shen
Solar RRL, WILEY‐VCH Verlag GmbH & Co. KGaA, 4, 9, 2000149-2000158, 15 Apr. 2020, Peer-reviwed, The performance of perovskite solar cells (PSCs) is known to be extremely sensitive to humidity in the preparation environment. However, the main mechanism by which the moisture influences the quality of the perovskite film and the device performance is not yet fully understood. Herein, a new strategy is established to obtain inverted PSCs with a remarkabll high VOC by including a high‐humidity treatment and sufficient DMSO‐atmosphere annealing in the preparation process. It is found that the lattice distortion on the surface of perovskite grains caused by the high‐humidity treatment plays a key role in the self‐passivation of perovskite. Inverted (p‐i‐n) PSCs based on the self‐passivated perovskite films show effective suppression of nonradiative recombination, which increase the device VOC to 1.17 V and achieve the highest efficiency of 21.38%. It is expected that the findings of this work shed more light on the currently proposed mechanism governing the action of moisture on the performance of the PSCs.
Scientific journal, English

Improvement of conversion efficiency of SnGe-perovskite solar cell by ethylammonium substitution
Nishimura Kohei; Muhammad Akmal Kamarudin; Hirotani Daisuke; Hamada Kengo; Iikubo Satoshi; Shen Qing; Minemoto Takashi; Yoshino Kenji; Hayase Shuzi
JSAP Annual Meetings Extended Abstracts, The Japan Society of Applied Physics, 2020.1, 2403-2403, 28 Feb. 2020
Japanese

Optical absorption of PbS quantum dots with ligands on single crystal TiO₂ - Comparative study of photoaocoustic and absorbance spectroscopies -
Toyoda Taro; Shen Qing; Nakazawa Naoki; Yoshihara Yasuha; Kamiyama Keita; Hayase Shuzi
JSAP Annual Meetings Extended Abstracts, The Japan Society of Applied Physics, 2020.1, 2400-2400, 28 Feb. 2020
Japanese

Photoexcited carrier dynamics of PbS/CdS core-shell quantum dots
Oguri Naoki; Ding Chao; Yoshida Koji; Zhang Yaohong; Hayase Shuzi; Toyoda Taro; Shen Qing
JSAP Annual Meetings Extended Abstracts, The Japan Society of Applied Physics, 2020.1, 2879-2879, 28 Feb. 2020
Japanese

Reducing trap density and carrier concentration by a Ge additive for an efficient quasi 2D/3D perovskite solar cell
Chi Huey Ng; Kengo Hamada; Gaurav Kapil; Muhammad Akmal Kamarudin; Zhen Wang; Satoshi Likubo; Qing Shen; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Journal of Materials Chemistry A, 8, 6, 2962-2968, 14 Feb. 2020, Peer-reviwed, © 2020 The Royal Society of Chemistry. We report that doping with hydrophobic bulky 2D phenylethylammonium (PEA+) is desirable to stabilize the perovskite matrix and enhance its stability. The addition of PEA+ alters the crystal growth orientation and improves the connectivity of the crystal grains. However, solely adding the PEA+ material cannot fully passivate the severe bulk recombination sites/interior defects due to Sn vacancies, leading to an efficiency of 3.96% (Voc of 0.36 V) for a Ge-free device. In contrast, we find that the addition of smaller-sized Ge ions with an optimum doping concentration effectively reduces the leakage current and suppresses the carrier density of the perovskite material. From the perspective of traps, the addition of Ge reduces the traps, typically deep traps, and its effectiveness (Ge) in trap passivation is further deduced from the thermally stimulated current (TSC) profile. The total trap density was doubly reduced to 4.14 × 1020 cm-3 when 7.5 mol% Ge was added, which led to a photo-conversion efficiency of 7.45% with a high Voc of 0.46 V. In addition, defect healing by the Ge additive significantly enhanced the stability of the unencapsulated device for 192 h. This work shows that Ge is an effective additive to suppress the recombination sites (trap state passivation), leading to the establishment of an efficient tin-based perovskite solar cell.
Scientific journal

Growth of Amorphous Passivation Layer Using Phenethylammonium Iodide for High-Performance Inverted Perovskite Solar Cells
Fan Zhang; Qinxun Huang; Jun Song; Yaohong Zhang; Chao Ding; Feng Liu; Dong Liu; Xiaobin Li; Hironobu Yasuda; Koji Yoshida; Junle Qu; Shuzi Hayase; Taro Toyoda; Takashi Minemoto; Qing Shen
SOLAR RRL, WILEY-V C H VERLAG GMBH, 4, 2, Feb. 2020, Organic-inorganic lead halide perovskite solar cells have realized a rapid increase of power conversion efficiency (PCE) in the past few years. However, their performance still suffers trap-assisted decline due to defects at the surface and grain boundaries of the perovskite film. Herein, a phenethylammonium iodide-lead iodide (PEAI-PbI2) passivation layer is formed on the CH3NH3PbI3 perovskite film. The characterization results indicate that the PEAI covering layer leads to the reduction of surface defects and suppression of nonradiative recombination. By manipulating this surface passivation method, a remarkably improved V-OC of 1.16 V and an enhanced PCE of 20.8% are achieved.
Scientific journal, English

Temperature dependent photovoltaic performance of TiO2/PbS heterojunction quantum dot solar cells
Meibo Xing; Yaohong Zhang; Qing Shen; Ruixiang Wang
SOLAR ENERGY, PERGAMON-ELSEVIER SCIENCE LTD, 195, 1-5, Jan. 2020, A planner heterojunction quantum dot solar cells (QDSCs) structure of FTO/TiO2/PbS-EMII/PbS-EDT/Au is fabricated via layer-by-layer spin coating method, and then the temperature dependent photovoltaic performance of QDSCs is studied. The results indicate that the environment temperature has great influence on the current density-voltage (J-V) characteristics of quantum dot solar cell. The short-circuit photocurrent density (J(SC)), open-circuit voltage (V-OC) and fill factor (FF) are all increased when the temperature decreases from 353 K to 253 K. A top value of power conversation efficiency (PCE, 9.78%) is obtained for the QDSCs when the environment temperature is lowered to 253 K, with a V-OC of 0.63 V, J(SC) of 33.1 mA/cm(2) and FF of 0.47, which is 33% above the PCE at room temperature (7.34%). In conclusion, it is necessary to cool the device for keeping the high efficiency operation of solar cell.
Scientific journal, English

Photoexcited hot and cold electron and hole dynamics at FAPbI3 perovskite quantum dots/metal oxide heterojunctions used for stable perovskite quantum dot solar cells
Ding, C; Liu, F; Zhang, Y; Hirotani, D; Rin, X; Hayase, S; Minemoto, T; Masuda, T; Wang, R; Shen, Q
Nano Energy, Elsevier, 67, 104267, 2020, Peer-reviwed
Scientific journal, English

Temperature dependent photovoltaic performance of TiO2/PbS heterojunction quantum dot solar cells
Xing, M; Zhang, Y; Shen, Q; Wang, R
Solar Energy, Elsevier, 195, 1-5, 2020, Peer-reviwed
Scientific journal, English

Boosting Photocatalytic CO2 Reduction on CsPbBr3 Perovskite Nanocrystals by Immobilizing Metal Complexes
Zhoujie Chen; Yangguang Hu; Jin Wang; Qing Shen; Yaohong Zhang; Chao Ding; Yu Bai; Guocan Jiang; Zhengquan Li; Nikolai Gaponik
Chem. Mater., ACS, 2020, Peer-reviwed
Scientific journal, English

Trioctylphosphine Oxide Acts as Alkahest for SnX2/PbX2: A General Synthetic Route to Perovskite ASnxPb1-xX3 (A= Cs, FA, MA; X= Cl, Br, I) Quantum Dots
Feng Liu; Yaohong Zhang; Chao Ding; Kentaro Kawabata; Yasuha Yoshihara; Taro Toyoda; Shuzi Hayase; Takashi Minemoto; Ruixiang Wang; Qing Shen
Chem. Mater., ACS, 32, 3, 1089-1100, 2020, Peer-reviwed
Scientific journal, English

Boosting Photocatalytic CO2 Reduction on CsPbBr3 Perovskite Nanocrystals by Immobilizing Metal Complexes
Zhoujie Chen; Yangguang Hu; Jin Wang; Qing Shen; Yaohong Zhang; Chao Ding; Yu Bai; Guocan Jiang; Zhengquan Li; Nikolai Gaponik
Chemistry of Materials, ACS, 32, 4, 1517-1525, 2020, Peer-reviwed
Scientific journal, English

Theoretical analysis of band alignment at back junction in Sn–Ge perovskite solar cells with inverted pin structure
Takashi Minemoto; Yu Kawano; Takahito Nishimura; Qing Shen; Kenji Yoshino; Satoshi Iikubo; Shuzi Hayase; Jakapan Chantana
Solar Energy Materials and Solar Cells, Elsvier, 206, 110268, 2020, Peer-reviwed
Scientific journal, English

Near-Infrared Emission from Tin–Lead (Sn–Pb) Alloyed Perovskite Quantum Dots by Sodium Doping
Feng Liu; Junke Jiang; Yaohong Zhang; Chao Ding; Taro Toyoda; Shuzi Hayase; Ruixiang Wang; Shuxia Tao; Qing Shen
Angewandte Chemie., 59, 22, 8421-8424, 2020, Peer-reviwed, True, Phase-stable CsSnx Pb1-x I3 perovskite quantum dots (QDs) hold great promise for optoelectronic applications owing to their strong response in the near-infrared region. Unfortunately, optimal utilization of their potential is limited by the severe photoluminescence (PL) quenching, leading to extremely low quantum yields (QYs) of approximately 0.3 %. The ultra-low sodium (Na) doping presented herein is found to be effective in improving PL QYs of these alloyed QDs without alerting their favourable electronic structure. X-ray photoelectron spectroscopy (XPS) studies suggest the formation of a stronger chemical interaction between I- and Sn2+ ions upon Na doping, which potentially helps to stabilize Sn2+ and suppresses the formation of I vacancy defects. The optimized PL QY of the Na-doped QDs reaches up to around 28 %, almost two orders of magnitude enhancement compared with the pristine one.
Scientific journal, English

Super stable CsPbBr3@SiO2 tumor imaging reagent by stress-response encapsulation
Wentao Song; Yiming Wang; Bing Wang; Yingfang Yao; Wenguang Wang; Jinhui Wu; Qing Shen; Wenjun Luo; Zhigang Zou
Nano Research, 1-7, 2020, Peer-reviwed
Scientific journal, English

Enhanced device performance with passivation of the TiO2 surface using a carboxylic acid fullerene monolayer for a SnPb perovskite solar cell with a normal planar structure
Kengo Hamada; Ryo Tanaka; Muhammad Akmal Kamarudin; Qing Shen; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Taro Toyoda; Tingli Ma; Dong-won Kang; Shuzi Hayase
ACS Appl. Mater. Interfaces, 12, 15, 17776-17782, 2020, Peer-reviwed, True, Research on tin-lead (SnPb) perovskite solar cells (PSCs) has gained popularity in recent years because of their low band gap, which could be applied to tandem solar cells. However, most of the work is based on inverted PSCs using PEDOT:PSS as the hole-transport layer as normal-structure PSCs show lower efficiency. In this work, the reason behind the low efficiency of normal-structure SnPb PSCs is elucidated and surface passivation has been tested as a method to overcome the problem. In the case of normal PSCs, at the interface between the titania layer and SnPb perovskite, there are many carrier traps observed originating from Ti-O-Sn bonds. In order to avoid the direct contact between titania and the SnPb perovskite layer, the titania surface is passivated with carboxylic acid C60 resulting in an efficiency increase from 5.14 to 7.91%. This will provide a direction of enhancing the efficiency of the normal-structure SnPb PSCs through heterojunction engineering.
Scientific journal, English

Thiourea-assisted coating of dispersed copper electrocatalysts on Si photocathodes for solar hydrogen production
Pin Wang; Ziyu Yin; Linfeng Gao; Hui Li; Tongyu Zhang; Qing Shen; Jun Lv; Yingfang Yao; Wenjun Luo; Zhigang Zou
Journal of Energy Chemistry, 40, 75-80, Jan. 2020, Peer-reviwed
Scientific journal, English

Suppression of Charge Carrier Recombination in Lead-Free Tin Halide Perovskite via Lewis Base Post-treatment
Muhammad Akmal Kamarudin; Daisuke Hirotani; Zhen Wang; Kengo Hamada; Kohei Nishimura; Qing Shen; Taro Toyoda; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Shuzi Hayase
The Journal of Physical Chemistry Letters, American Chemical Society ({ACS}), 10, 17, 5277-5283, 05 Sep. 2019, Peer-reviwed
Scientific journal, English

Relationship between Lattice Strain and Efficiency for Sn-Perovskite Solar Cells
Kohei Nishimura; Daisuke Hirotani; Muhammad Akmal Kamarudin; Qing Shen; Taro Toyoda; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Shuzi Hayase
ACS Applied Materials & Interfaces, American Chemical Society ({ACS}), 11, 34, 31105-31110, 28 Aug. 2019, Peer-reviwed
Scientific journal, English

Strain Relaxation and Light Management in Tin–Lead Perovskite Solar Cells to Achieve High Efficiencies
Gaurav Kapil; Takeru Bessho; Chi Huey Ng; Kengo Hamada; Manish Pandey; Muhammad Akmal Kamarudin; Daisuke Hirotani; Takumi Kinoshita; Takashi Minemoto; Qing Shen; Taro Toyoda; Takurou N. Murakami; Hiroshi Segawa; Shuzi Hayase
ACS Energy Letters, American Chemical Society ({ACS}), 4, 8, 1991-1998, 09 Aug. 2019, Peer-reviwed
Scientific journal, English

Growth of Amorphous Passivation Layer Using Phenethylammonium Iodide for High‐Performance Inverted Perovskite Solar Cells
Zhang, F; Huang, Q; Song, J; Zhang, Y; Ding, C; Liu, F; Liu, D; Li, X; Yasuda, H; Yoshida, K; Qu, J; Hayase, S; Toyoda, T; Minemoto, T; Shen, Q
Sol. RRL, Wiley, 4, 2, 1900243, 02 Jul. 2019, Peer-reviwed, Organic-inorganic lead halide perovskite solar cells have realized a rapid increase of power conversion efficiency (PCE) in the past few years. However, their performance still suffers trap-assisted decline due to defects at the surface and grain boundaries of the perovskite film. Herein, a phenethylammonium iodide-lead iodide (PEAI-PbI2) passivation layer is formed on the CH3NH3PbI3 perovskite film. The characterization results indicate that the PEAI covering layer leads to the reduction of surface defects and suppression of nonradiative recombination. By manipulating this surface passivation method, a remarkably improved V-OC of 1.16 V and an enhanced PCE of 20.8% are achieved.
Scientific journal, English

Growth of Amorphous Passivation Layer Using Phenethylammonium Iodide for High‐Performance Inverted Perovskite Solar Cells
Zhang, F; Huang, Q; Song, J; Zhang, Y; Ding, C; Liu, F; Liu, D; Li, X; Yasuda, H; Yoshida, K; Qu, J; Hayase, S; Toyoda, T; Minemoto, T; Shen, Q
Sol. RRL. doi:10.1002/solr.201900243, WILEY-V C H VERLAG GMBH, 3, 5, 1900243-1-1900243-8, 02 Jul. 2019, Peer-reviwed, Organic-inorganic lead halide perovskite solar cells have realized a rapid increase of power conversion efficiency (PCE) in the past few years. However, their performance still suffers trap-assisted decline due to defects at the surface and grain boundaries of the perovskite film. Herein, a phenethylammonium iodide-lead iodide (PEAI-PbI2) passivation layer is formed on the CH3NH3PbI3 perovskite film. The characterization results indicate that the PEAI covering layer leads to the reduction of surface defects and suppression of nonradiative recombination. By manipulating this surface passivation method, a remarkably improved V-OC of 1.16 V and an enhanced PCE of 20.8% are achieved.
Scientific journal, English

Prussian blue analogue-derived Ni and Co bimetallic oxide nanoplate arrays block-built from porous and hollow nanocubes for the efficient oxygen evolution reaction
Shen, Y; Guo, S.-G; Du, F; Yuan, X.-B; Zhang, Y; Hu, J; Shen, Q; Luo, W; Alsaedi, A; Hayat, T; Wen, G; Li, G.-L; Zhou, Y; Zou, Z
Nanoscale, Royal Society of Chemistry, 11, 11765-11773, 01 Jun. 2019, Peer-reviwed
Scientific journal, English

Template deposition of Sb2S3 for solid-state sensitized solar cells
Yafeng Xu; Wenyong Chen; Linhua Hu; Xu Pan; Shangfeng Yang; Qing Shen; Jun Zhu
Journal of Alloys and Compounds, Elsevier, 784, 947-953, 05 May 2019, Peer-reviwed
Scientific journal, English

BiVO4 tubular structures: oxygen defect-rich and largely exposed reactive {010} facets synergistically boost photocatalytic water oxidation and the selective N=N coupling reaction of 5-amino-1H-tetrazole
Hu, J; He, H; Zhou, X; Li, Z; Shen, Q; Luo, W; Alsaedi, A; Hayat, T; Zhou, Y; Zou, Z
Chemical Communications, Royal Society of Chemistry, 55, 39, 5635-5638, 12 Apr. 2019, Peer-reviwed
Scientific journal, English

Role of GeI2 and SnF2 additives for SnGe perovskite solar cells
Chi Huey Ng; Kohei Nishimura; Nozomi Ito; Kengo Hamada; Daisuke Hirotani; Zhen Wang; Fu Yang; Satoshi likubo; Qing Shen; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Nano Energy, Elsevier BV, 58, 130-137, Apr. 2019, Peer-reviwed
Scientific journal, English

Highly symmetrical, 24-faceted, concave BiVO4 polyhedron bounded by multiple high-index facets for prominent photocatalytic O2 evolution under visible light
Zhou, Yong; Zou, Zhigang; Li, Zhaosheng; Shen, Qing; Wu, Congping; Zhou, Xin; Luo, Wenjun; Asiri, Abdullah M; He, Huichao; Hu, Jianqiang
Chemical Communications, 0, 0-0, 26 Mar. 2019, Peer-reviwed
Scientific journal, English

Highly symmetrical, 24-faceted, concave BiVO4 polyhedron bounded by multiple high-index facets for prominent photocatalytic O2 evolution under visible light
Zhou, Yong; Zou, Zhigang; Li, Zhaosheng; Shen, Qing; Wu, Congping; Zhou, Xin; Luo, Wenjun; Asiri, Abdullah M; He, Huichao; Hu, Jianqiang
Chemical Communications, 55, 33, 4777-4780, 26 Mar. 2019, Peer-reviwed
Scientific journal, English

Thiourea-assisted coating of dispersed copper electrocatalysts on Si photocathodes for solar hydrogen production
Pin Wang; Ziyu Yin; Linfeng Gao; Hui Li; Tongyu Zhang; Qing Shen; Jun Lv; Yingfang Yao; Wenjun Luo; Zhigang Zou
Journal of Energy Chemistry, 40, 75-80, 06 Mar. 2019, Peer-reviwed
Scientific journal, English

GeI2 Additive for High Optoelectronic Quality CsPbI3 Quantum Dots and Their Application in Photovoltaic Devices
Feng Liu; Chao Ding; Yaohong Zhang; Taichi Kamisaka; Qian Zhao; Joseph M. Luther; Taro Toyoda; Shuzi Hayase; Takashi Minemoto; Kenji Yoshino; Bing Zhang; Songyuan Dai; Junke Jiang; Shuxia Tao; Qing Shen
Chemistry of Materials, 31, 3324-3326, 14 Jan. 2019, Peer-reviwed
Scientific journal, English

Surface coatings for improving solar cell efficiencies
Qing Shen; Chao Ding; Yaohong Zhang; Feng Liu; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Optics InfoBase Conference Papers, OSA - The Optical Society, 2019, 2019, The efficiencies of the next generation solar cells such as quantum dot (QD)-based solar cells and perovskite solar cells can be improved largely through surface coating on the interfaces and the mechanism have been investigated.
International conference proceedings, English

Solar-pumped fiber laser with all-inorganic cesium lead halide perovskite quantum dots
Taizo Masuda; Mitsuhiro Iyoda; Yuta Yasumatsu; Kiyoto Sasaki; Yaohong Zhang; Chao Ding; Feng Liu; Qing Shen; Masamori Endo
Proceedings of SPIE - The International Society for Optical Engineering, 10897, 2019, We demonstrate a low-concentrated solar-pumped fiber laser with all-inorganic cesium lead halide perovskite quantum dots (QDs), which function as a sensitizer. The perovskite QDs exhibit substantial advantages for solarpumped laser applications because of their broad absorption and narrow emission spectra with high quantum yield. We successfully tuned the peak emission wavelength of the perovskite QDs by altering the I/Br ratio in order to achieve spectral overlap with Nd3+ ions, which have been widely used as a laser medium for solar-pumped lasers. The measurement results show that the laser output power is highly sensitive to the peak emission wavelength of the QDs. Although our synthesized QDs have a quantum yield of approximately 65%, which is less than that of conventional organic dyes, the laser performance was comparable because the fluorescence spectrum is tailored to the Nd3+ absorption band.
International conference proceedings

Effect of Precursor Solution Aging on the Thermoelectric Performance of CsSnI3 Thin Film
Ajay Kumar Baranwal; Shrikant Saini; Zhen Wang; Kengo Hamada; Daisuke Hirotani; Kohei Nishimura; Muhammad Akmal Kamarudin; Gaurav Kapil; Tomohide Yabuki; Satoshi Iikubo; Qing Shen; Koji Miyazaki; Shuzi Hayase
Journal of Electronic Materials, 2019, Peer-reviwed, © 2019, The Minerals, Metals & Materials Society. Inorganic CsSnI3 based perovskite crystals are interesting thermoelectric materials, owing to their unusual electronic properties. Here we report the thermoelectric power performance of a solution-coated CsSnI3 thin film from the viewpoint of carrier concentration optimizations. It was found that the carrier concentration can be changed by altering the aging time of the precursor solution. X-ray photoelectron spectroscopy analysis showed that the concentration of metallic Sn4+ increased as the solution aging time increased. This made possible to explore the relationship between carrier concentration and thermoelectric power factor. After controlling Sn4+ concentrations, we report a power factor of 145.10 μW m−1 K−2 , along with electrical conductivity 106 S/cm and Seebeck coefficient of 117 μV/K, measured at room temperature.
Scientific journal

The effect of transparent conductive oxide substrate on the efficiency of snge-perovskite solar cells
Kengo Hamada; Muhammad Akmal Kamarudin; Wang Zhen; Daisuke Hirotani; Qing Shen; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Taro Toyoda; Shuzi Hayase
Journal of Photopolymer Science and Technology, 32, 4, 597-602, 2019, Peer-reviwed, © 2019 SPST. The efficiency of Sn-perovskite solar cells has been dramatically improved by adopting the inverted structure solar cells and is expected to reach the efficiency of lead-based perovskite solar cell. We have observed fluctuations in the efficiency of the same perovskite material due to the type of TCO substrates. In this study, we investigated the influence of TCO substrates on the solar cell characteristics of SnGe-perovskite solar cells. It was found that the efficiency of the SnGe-perovskite solar cell is better with fluorine-doped tin oxide (FTO) substrate (9.24%) than indium-doped tin oxide (ITO) substrate (7.72%). The improvement of the efficiency of the cell with FTO substrate is contributed by the improvement in the short-circuit current Jsc and Voc. The high transmittance of FTO substrate enhanced the Jsc while the Voc is influenced by the Fermi level of the transparent conductive oxide film. Although there is a difference in the surface roughness between TCO substrates, there is no direct influence on the device performance that can be observed.
Scientific journal

Role of GeI2 and SnF2 additives for SnGe perovskite solar cells
Ng, Chi Huey; Nishimura, Kohei; Ito, Nozomi; Hamada, Kengo; Hirotani, Daisuke; Wang, Zhen; Yang, Fu; likubo, Satoshi; Shen, Qing; Yoshino, Kenji; Minemoto, Takashi; Hayase, Shuzi
Nano Energy, Elsevier BV, 58, 130-137, 2019, Peer-reviwed
Scientific journal, English

Determination of iron species, including biomineralized jarosite, in the iron-hyperaccumulator moss Scopelophila ligulata by Mössbauer, X-ray diffraction, and elemental analyses
Nakajima, Hiromitsu; Okazawa, Atsushi; Kubuki, Shiro; Shen, Qing; Itoh, Kiminori
Biometals, 32, 1, 171-184, 2019, Peer-reviwed, Scopelophila ligulata is an Fe-hyperaccumulator moss growing in acidic environments, but the mechanism of Fe accumulation remains unknown. To understand the mechanism, we determined Fe species in S. ligulata samples. The moss samples were collected from four sites in Japan. The concentrations of Fe, P, S, Cl, and K in them were measured by induced coupled plasma mass spectrometry. Fe species in some of them were determined by Mössbauer spectroscopy and were confirmed by X-ray diffraction analysis. Fe species in S. ligulata samples were determined to be jarosite, ferritin, high-spin Fe(II) species, and akaganeite. To our knowledge, this is the first report on the biomineralization of jarosite in mosses. This result, combined with the fact that bacteria, a fungus, and a grass mineralize jarosite, suggests that its biomineralization is a common characteristic in a wide variety of living organisms. These findings indicate that the biomineralization of jarosite occurs not only in the region-specific species but in species adapted to a low-pH and metal-contaminated environment in different regions, provide a better understanding of the mechanism of Fe accumulation in the Fe-hyperaccumulator moss S. ligulata, and offer new insights into the biomineralization of jarosite.
Scientific journal, English

Improving Photovoltaic Performance of ZnO Nanowires Based Colloidal Quantum Dot Solar Cells via SnO2 Passivation Strategy
Shuhei Ozu; Yaohong Zhang; Hironobu Yasuda; Yukiko Kitabatake; Taro Toyoda; Masayuki Hirata; Kenji Yoshino; Kenji Katayama; Shuzi Hayase; Ruixiang Wang; Qing Shen
Front. Energy Res., 7, 11, 2019, Peer-reviwed, Invited
Scientific journal, English

Pb-free Sn perovskite solar cells doped with samarium iodide
Kengo Hamada; Daisuke Hirotani; Muhammad Akmal Kamarudin; Kohei Nishimura; Qing Shen; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Taro Toyoda; Shuzi Hayase
Chemistry Letters, The Chemical Society of Japan, 48, 8, 836-839, 2019, Peer-reviwed, © 2019 The Chemical Society of Japan. The efficiency of Sn-perovskite solar (Sn-PVK) cells was enhanced by adding 1% Samarium iodide (SmI2). Increase in Jsc and FF is associated with the enhancement of efficiency and and explained by lower series resistance. SmI2 is known as a strong reducing agent and is oxidized to Sm3+ by reducing a substrate. By adding 1 and 5% SmI2, the carrier concentration of Sn-perovskite layer due to the presence of Sn4+ was decreased from 4.8 © 1022/cm3 to 1.2 © 1019/cm3 and 6.1 © 1018/cm3 respectively, because of the suppression of the oxidation from Sn2+ to Sn4+ by the strong reducing properties of SmI2. The low charge carrier concentration is also associated with the enhanced solar cell efficiency.
Scientific journal, English

Improving Photovoltaic Performance of ZnO Nanowires Based Colloidal Quantum Dot Solar Cells via SnO2 Passivation Strategy
Shuhei Ozu; Yaohong Zhang; Hironobu Yasuda; Yukiko Kitabatake; Taro Toyoda; Masayuki Hirata; Kenji Yoshino; Kenji Katayama; Shuzi Hayase; Ruixiang Wang; Qing Shen
Front. Energy Res, 7, 11-19, 2019, Peer-reviwed, Invited
Scientific journal, English

Two-Step Synthesis of Laminar Vanadate via a Facile Hydrothermal Route and Enhancing the Photocatalytic Reduction of CO2 into Solar Fuel through Tuning of the Oxygen Vacancies by in Situ Vacuum Illumination Treatment
Xingyu Chen; Chen Zhuang; Xiaoqi Wang; Aizhen Liao; Liang Li; Qi Liu; Ying Tang; Congping Wu; Qing Shen; Zhentao Yu; Yong Zhou; Zhigang Zou
ACS Applied Energy Materials, American Chemical Society, 1, 12, 6857-6864, 24 Dec. 2018, Monoclinic LaVO4, tetragonal CeVO4 and monoclinic Pb2V2O7 with laminar structures composed of nanosheets have been successfully fabricated using a two-step facile hydrothermal route. The narrow-bandgap LaVO4, CeVO4 and Pb2V2O7 vanadate exhibited photocatalytic activity toward the photoreduction of CO2 into C2H5OH in the liquid phase. The existence of oxygen vacancies on LaVO4 surface further enhanced the photocatalytic activity for photoreduction of CO2 into CO in gas phase, which can be easily obtained using a vacuum illumination treatment. The EPR, PL and FTIR results indicated that oxygen vacancies are beneficial to the separation of electrons by prolonging the lifetime of the photogenerated electrons and enhancing the chemisorption of CO2 on the photocatalyst surface.
Scientific journal, English

The Interparticle Distance Limit for Multiple Exciton Dissociation in PbS Quantum Dot Solid Films
Naoki Nakazawa; Yaohong Zhang; Feng Liu; Chao Ding; Kanae Hori; Taro Toyoda; Yingfang Yao; Yong Zhou; Shuji Hayase; Ruixiang Wang; Zhigang Zou; Qing Shen
Nanoscale Horizons, 4, 2, 445-451, 20 Dec. 2018, Peer-reviwed, True, Understanding the behaviour of multiple exciton dissociation in quantum dot (QD) solid films is of fundamental interest and paramount importance for improving the performance of quantum dot solar cells (QDSCs). Unfortunately, the charge transfer behaviour of photogenerated multiple exciton in QD solid films is not clear to date. Herein, we systematically investigate the multiple exciton charge transfer behaviour in PbS QD solid films by using ultrafast transient absorption spectroscopy. We observe that the multiple exciton charge transfer rate within QD ensembles is exponentially enhanced as the interparticle distance between the QDs decreases. Biexciton and triexciton dissociation between adjacent QDs occurs via a charge transfer tunneling effect just like single exciton, and the charge tunneling constants of the single exciton (β1: 0.67 ± 0.02 nm-1), biexciton (β2: 0.68 ± 0.05 nm-1) and triexciton (β3: 0.71 ± 0.01 nm-1) are obtained. More importantly, for the first time, the interparticle distance limit (≤4.3 nm) for multiple exciton charge transfer between adjacent QDs is found for the extraction of multiple excitons rapidly before the occurrence of Auger recombination. This result points out a vital and necessary condition for the use of multiple excitons produced in PbS QD films, especially for their applications in QDSCs.
Scientific journal, English

New Tin(II) Fluoride Derivative as a Precursor for Enhancing the Efficiency of Inverted Planar Tin/Lead Perovskite Solar Cells
Teresa S. Ripolles; Daiki Yamasuso; Yaohong Zhang; Muhammad Akmal Kamarudin; Chao Ding; Daisuke Hirotani; Qing Shen; Shuzi Hayase
Journal of Physical Chemistry C, 122, 48, 27284-27291, 06 Dec. 2018, Peer-reviwed, © 2018 American Chemical Society. Hybrid organic-inorganic lead halide perovskite has become one of the most attractive materials for future low-cost and high-efficiency solar technology. However, serious concern about the content of toxic lead in photovoltaic devices emphasizes the mixture of tin/lead. Here, we synthesized and fully characterized tin(II) fluoride with a molecule of dimethyl sulfoxide such as a [SnF2(DMSO)]2 complex to be used as an additive in the Sn-Pb perovskite precursor for photovoltaic applications. Once the concentration of the SnF2 complex has been optimized to be 10 mol %, the highest efficiency achieved in the inverted architecture was 15.93% with an open circuit voltage of 0.77 V, short circuit current of 26.53 mA cm-2, and fill factor (FF) of 0.78. Transient absorption and impedance spectroscopy corroborated that this complex reduces the trap states and improves the transport recombination at the interface compared with solar cells without additives or with the SnF2 additive, in which the latter is widely used. Here, we suggest an alternative method to control the Sn+2 reaction in Sn-Pb perovskite devices.
Scientific journal

Three-dimensional Bi2MoO6/TiO2 array heterojunction photoanode modified with cobalt phosphate cocatalyst for high-efficient photoelectrochemical water oxidation
Wang, Lu; Wang, Ruyi; Zhou, Yong; Shen, Qing; Ye, JinHua; Wu, Congping; Zou, Zhigang
Catalysis Today, 0, 0-0, 28 Nov. 2018, Peer-reviwed
Scientific journal, English

Enhanced performance of ZnO based perovskite solar cells by Nb2O5 surface passivation
Putao Zhang; Fu Yang; Gaurav Kapil; Qing Shen; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
ORGANIC ELECTRONICS, ELSEVIER SCIENCE BV, 62, 615-620, Nov. 2018, TiO2 has been extensively utilized as bottom electron transporting scaffold for perovskite solar cells (PSCs) but need for its high processing temperature (> 450 degrees C) hinders its applicability for the flexible plastic substrates. Use of the low temperature processed ZnO is one of the probable solutions as electron transport layer (ETL) in PSCs owing to its high electron mobility. An amicable solution for the instability of the perovskite absorber layers fabricated on to ZnO leading resulting in to poor power conversion efficiency (PCE) and long-term stability is necessary for to harness the benefit of ZnO as ETL in PSCs. Herein, we modified the ZnO surface by spin-coating an ultrathin Nb2O5 as surface passivation layer. In this work, both of the ZnO and Nb2O5 were fabricated by spin coating and sintered at relatively lower temperature of 200 degrees C. Utilizing this Nb2O5 surface passivated and low temperature processed ZnO as ETL, dramatically enhanced stability of perovskite film over 20 days under ambient condition has been clearly demonstrated. This bilayer of Nb2O5 surface passivated ZnO scaffold used for fabrication of the planer heterojunction PSCs based on CH3NH3PbI3, led to the maximum PCE of 14.57% under simulated solar irradiation for an optimized ZnO thickness of 42 nm. Moreover, implication of the surface passivation of ZnO by Nb2O5 leading to the formation of highly crystalline, stable and dense perovskite film has been probed by SEM and XRD investigations.
Scientific journal, English

Enhancement of charge transport in quantum dots solar cells by N-butylamine-assisted sulfur-crosslinking of PbS quantum dots
Zhen Wang; Zhaosheng Hu; Muhammad Akmal Kamarudin; Gaurav Kapil; Atul Tripathi; Qing Shen; Kenji Yoshino; Takashi Minemoto; Sham S. Pandey; Shuzi Hayase
SOLAR ENERGY, PERGAMON-ELSEVIER SCIENCE LTD, 174, 399-408, Nov. 2018, A novel and facile strategy to realize selective inorganic ligand (S2-) exchange on Pb-rich surface of PbS colloidal quantum dots (QDs) has been demonstrated. This was achieved via xanthate ligand decomposition at room temperature without damaging the QDs surface. This proposed method offers an amicable solution for the limitation that inorganic-terminated colloidal QDs are restricted by the specific requirement to solvents with high dielectric constant. Furthermore, Introduction of S2- to form sulfur-crosslinking PbS QDs enables reaction force-induced QDs arrays and smooth surface morphology of the spin-coated QDs film as evidenced by atomic force microscopy. Passivation of QDs by bromide combined with sulfur led to stronger electronic coupling between adjacent QDs as compared to bromide-only passivated QDs counterparts. Bromide and sulfur hybrid-capped QDs exhibited remarkably enhanced carrier mobility from 1.66 x 10(-4) cm(2)/V s to 5.0 x 10(-1) cm(2)/V s as evidenced by the Hall- Effect measurement. The smooth QDs film morphology and higher charge transport contributed to the boost in the power conversion efficiency of QDs solar cells up 4.96% compared that using only CTAB passivated PbS QDs solar cells (3.04%). This controlled sulfurization approach paves a potential way for improved optoelectronic properties and devices based on QDs.
Scientific journal, English

Addition Effect of Pyreneammonium Iodide to Methylammonium Lead Halide Perovskite-2D/3D Heterostructured Perovskite with Enhanced Stability
Yang, F; Hirotani, D; Kapil, G; Kamarudin, A. M; Ng, H. C; Zhang Y; Shen, Q; Hayase, S
Advanced Functional Materials, 57, 39, 122745-12749, Nov. 2018, Peer-reviwed
Scientific journal, English

Enhancement of charge transport in quantum dots solar cells by N-butylamine-assisted sulfur-crosslinking of PbS quantum dots
Zhen Wang; Zhaosheng Hu; Muhammad Akmal Kamarudin; Gaurav Kapil; Atul Tripathi; Qing Shen; Kenji Yoshino; Takashi Minemoto; Sham S. Pandey; Shuzi Hayase
Solar Energy, 174, 399-408, Nov. 2018, Peer-reviwed
Scientific journal, English

All-Inorganic CsPb1−xGexI2Br Perovskite with Enhanced Phase Stability and Photovoltaic Performance
Fu Yang; Daisuke Hirotani; Gaurav Kapil; Muhammad Akmal Kamarudin; Chi Huey Ng; Yaohong Zhang; Qing Shen; Shuzi Hayase
Angewandte Chemie - International Edition, 57, 39, 12745-12749, 24 Sep. 2018, Peer-reviwed, © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Compared with organic-inorganic perovskites, all-inorganic cesium-based perovskites without volatile organic compounds have gained extensive interests because of the high thermal stability. However, they have a problem on phase transition from cubic phase (active for photo-electric conversion) to orthorhombic phase (inactive for photo-electric conversion) at room temperature, which has hindered further progress. Herein, novel inorganic CsPb1−xGexI2Br perovskites were prepared in humid ambient atmosphere without a glovebox. The phase stability of the all-inorganic perovskite was effectively enhanced after germanium addition. In addition, the highest power conversion efficiency of 10.8 % with high open-circuit voltage (VOC) of 1.27 V in a planar solar cell based on CsPb0.8Ge0.2I2Br perovskite was achieved. Furthermore, the highest VOC up to 1.34 V was obtained by CsPb0.7Ge0.3I2Br perovskite, which is a remarkable record in the field of all-inorganic perovskite solar cells. More importantly, all the photovoltaic parameters of CsPb0.8Ge0.2I2Br perovskite solar cells showed nearly no decay after 7 h measurement in 50–60 % relative humidity without encapsulation.
Scientific journal, English

All-Inorganic CsPb1-xGexI2Br Perovskite with Enhanced Phase Stability and Photovoltaic Performance
Fu Yang; Daisuke Hirotani; Gaurav Kapil; Muhammad Akmal Kamarudin; Chi Huey Ng; Yaohong Zhang; Qing Shen; Shuzi Hayase
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, WILEY-V C H VERLAG GMBH, 57, 39, 12745-12749, Sep. 2018, Compared with organic-inorganic perovskites, all-inorganic cesium-based perovskites without volatile organic compounds have gained extensive interests because of the high thermal stability. However, they have a problem on phase transition from cubic phase (active for photo-electric conversion) to orthorhombic phase (inactive for photo-electric conversion) at room temperature, which has hindered further progress. Herein, novel inorganic CsPb1-xGexI2Br perovskites were prepared in humid ambient atmosphere without a glovebox. The phase stability of the all-inorganic perovskite was effectively enhanced after germanium addition. In addition, the highest power conversion efficiency of 10.8% with high open-circuit voltage (V-OC) of 1.27V in a planar solar cell based on CsPb0.8Ge0.2I2Br perovskite was achieved. Furthermore, the highest V-OC up to 1.34V was obtained by CsPb0.7Ge0.3I2Br perovskite, which is a remarkable record in the field of all-inorganic perovskite solar cells. More importantly, all the photovoltaic parameters of CsPb0.8Ge0.2I2Br perovskite solar cells showed nearly no decay after 7h measurement in 50-60% relative humidity without encapsulation.
Scientific journal, English

Lead Selenide Colloidal Quantum Dot Solar Cells Achieving High Open-Circuit Voltage with One-Step Deposition Strategy
Yaohong Zhang; Guohua Wu; Chao Ding; Feng Liu; Yingfang Yao; Yong Zhou; Congping Wu; Naoki Nakazawa; Qingxun Huang; Taro Toyoda; Ruixiang Wang; Shuzi Hayase; Zhigang Zou; Qing Shen
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 9, 13, 3598-3603, Jul. 2018, Lead selenide (PbSe) colloidal quantum dots (CQDs) are considered to be a strong candidate for high-efficiency colloidal quantum dot solar cells (CQDSCs) due to its efficient multiple exciton generation. However, currently, even the best PbSe CQDSCs can only display open-circuit voltage (V-oc) about 0.530 V. Here, we introduce a solution-phase ligand exchange method to prepare PbI2-capped PbSe (PbSe-PbI2) CQD inks, and for the first time, the absorber layer of PbSe CQDSCs was deposited in one step by using this PbSe-PbI2 CQD inks. One-step-deposited PbSe CQDs absorber layer exhibits fast charge transfer rate, reduced energy funneling, and low trap assisted recombination. The champion large-area (active area is 0.35 cm(2))PbSe CQDSCs fabricated with one-step PbSe CQDs achieve a power conversion efficiency (PCE) of 6.0% and al V-oc of 0.616 V which is the highest V-oc among PbSe CQDSCs reported to date.
Scientific journal, English

Ultrafast selective extraction of hot holes from cesium lead iodide perovskite films
Qing Shen; Teresa S. Ripolles; Jacky Even; Yaohong Zhang; Chao Ding; Feng Liu; Takuya Izuishi; Naoki Nakazawa; Taro Toyoda; Yuhei Ogomi; Shuzi Hayase
Journal of Energy Chemistry, Elsevier B.V., 27, 4, 1170-1174, 01 Jul. 2018, Peer-reviwed, Lead halide perovskites have some unique properties which are very promising for optoelectronic applications such as solar cells, LEDs and lasers. One important and expected application of perovskite halide semiconductors is solar cell operation including hot carriers. This advanced solar cell concept allows overcoming the Shockley–Queisser efficiency limit, thereby achieving energy conversion efficiency as high as 66% by extracting hot carriers. Understanding ultrafast photoexcited carrier dynamics and extraction in lead halide perovskites is crucial for these applications. Here, we clarify the hot carrier cooling and transfer dynamics in all-inorganic cesium lead iodide (CsPbI3) perovskite using transient absorption spectroscopy and Al2O3, poly(3-hexylthiophene-2,5-diyl) (P3HT) and TiO2 as selective contacts. We find that slow hot carrier cooling occurs on a timescale longer than 10 ps in the cases of CsPbI3/Al2O3 and CsPbI3/ TiO2, which is attributed to hot phonon bottleneck for the high photoexcited carrier density. An efficient ultrafast hole transfer from CsPbI3 to the P3HT hole extracting layer is observed. These results suggest that hot holes can be extracted by appropriate selective contacts before energy dissipation into the halide perovskite lattice and that CsPbI3 has a potential for hot carrier solar cell applications.
Scientific journal, English

Lead selenide colloidal quantum dot solar cells achieving high open-circuit voltage with one-step deposition strategy
Yaohong Zhang; Guohua Wu; Chao Ding; Feng Liu; Yingfang Yao; Yong Zhou; Congping Wu; Naoki Nakazawa; Qingxun Huang; Taro Toyoda; Ruixiang Wang; Shuzi Hayase; Zhigang Zhou; Qing Shen
The Journal of Physical Chemistry Letter, 9, 13, 3598-3603, 15 Jun. 2018, Peer-reviwed, True, Lead selenide (PbSe) colloidal quantum dots (CQDs) are considered to be a strong candidate for high-efficiency colloidal quantum dot solar cells (CQDSCs) due to its efficient multiple exciton generation. However, currently, even the best PbSe CQDSCs can only display open-circuit voltage ( Voc) about 0.530 V. Here, we introduce a solution-phase ligand exchange method to prepare PbI2-capped PbSe (PbSe-PbI2) CQD inks, and for the first time, the absorber layer of PbSe CQDSCs was deposited in one step by using this PbSe-PbI2 CQD inks. One-step-deposited PbSe CQDs absorber layer exhibits fast charge transfer rate, reduced energy funneling, and low trap assisted recombination. The champion large-area (active area is 0.35 cm2) PbSe CQDSCs fabricated with one-step PbSe CQDs achieve a power conversion efficiency (PCE) of 6.0% and a Voc of 0.616 V, which is the highest Voc among PbSe CQDSCs reported to date.
Scientific journal, English

Highly Efficient 17.6% Tin-Lead Mixed Perovskite Solar Cells Realized through Spike Structure
Gaurav Kapil; Teresa S. Ripolles; Kengo Hamada; Yuhei Ogomi; Takeru Bessho; Takumi Kinoshita; Jakapan Chantana; Kenji Yoshino; Qing Shen; Taro Toyoda; Takashi Minemoto; Takurou N. Murakami; Hiroshi Segawa; Shuzi Hayase
Nano Letters, 18, 6, 3600-3607, 13 Jun. 2018, Peer-reviwed, © 2018 American Chemical Society. Frequently observed high Voc loss in tin-lead mixed perovskite solar cells is considered to be one of the serious bottle-necks in spite of the high attainable Jsc due to wide wavelength photon harvesting. An amicable solution to minimize the Voc loss up to 0.50 V has been demonstrated by introducing an n-type interface with spike structure between the absorber and electron transport layer inspired by highly efficient Cu(In,Ga)Se2 solar cells. Introduction of a conduction band offset of ∼0.15 eV with a thin phenyl-C61-butyric acid methyl ester layer (∼25 nm) on the top of perovskite absorber resulted into improved Voc of 0.75 V leading to best power conversion efficiency of 17.6%. This enhancement is attributed to the facile charge flow at the interface owing to the reduction of interfacial traps and carrier recombination with spike structure as evidenced by time-resolved photoluminescence, nanosecond transient absorption, and electrochemical impedance spectroscopy measurements.
Scientific journal, English

Interface Passivation Effects on the Photovoltaic Performance of Quantum Dot Sensitized Inverse Opal TiO₂ Solar Cells
Qing Shen
Nanomaterials, Jun. 2018
Scientific journal

Hindered Formation of Photoinactive δ-FAPbI3 Phase and Hysteresis-Free Mixed-Cation Planar Heterojunction Perovskite Solar Cells with Enhanced Efficiency via Potassium Incorporation
Disheng Yao; Chunmei Zhang; Ngoc Duy Pham; Yaohong Zhang; Vincent Tiing Tiong; Aijun Du; Qing Shen; Gregory J. Wilson; Hongxia Wang
Journal of Physical Chemistry Letters, American Chemical Society, 9, 8, 2113-2120, 19 Apr. 2018, Peer-reviwed, Organic-inorganic hybrid lead halide perovskite solar cells have demonstrated competitive power conversion efficiency over 22%
nevertheless, critical issues such as unsatisfactory device stability, serious current-voltage hysteresis, and formation of photo nonactive perovskite phases are obstacles for commercialization of this photovoltaics technology. Herein we report a facial yet effective method to hinder formation of photoinactive δ-FAPbI3 and hysteresis behavior in planar heterojunction perovskite solar cells based on Kx(MA0.17FA0.83)1-xPbI2.5Br0.5 (0≤ x ≤ 0.1) through incorporation of potassium ions (K+). X-ray diffraction patterns demonstrate formation of photoinactive δ-FAPbI3 was almost completely suppressed after K+ incorporation. Density functional theory calculation shows K+ prefers to enter the interstitial sites of perovskite lattice, leading to chemical environmental change in the crystal structure. Ultrafast transient absorption spectroscopy has revealed that K+ incorporation leads to enhanced carrier lifetime by 50%, which is also confirmed by reduced trap-assisted recombination of the perovskite solar cells containing K+ in photovoltage decay. Ultraviolet photoelectron spectroscopy illustrates that K+ incorporation results in a significant rise of conduction band minimum of the perovskite material by 130 meV, leading to a more favorable energy alignment with electron transporting material. At the optimal content of 3% K+ (molar ratio, relative to the total monovalent cations), nearly hysteresis-free, enhanced power conversion efficiencies from 15.72% to 17.23% were obtained in this solar cell.
Scientific journal, English

Mixed Sn–Ge Perovskite for Enhanced Perovskite Solar Cell Performance in Air
Nozomi Ito; Muhammad Akmal Kamarudin; Daisuke Hirotani; Yaohong Zhang; Qing Shen; Yuhei Ogomi; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Shuzi Hayase
The Journal of Physical Chemistry Letters, American Chemical Society ({ACS}), 9, 7, 1682-1688, 05 Apr. 2018, Peer-reviwed
Scientific journal, English

Hindered Formation of Photoinactive delta-FAPbl(3) Phase and Hysteresis Free Mixed-Cation Planar Heterojunction Perovskite Solar Cells with Enhanced Efficiency via Potassium Incorporation
Disheng Yao; Chunmei Zhang; Ngoc Duy Pham; Yaohong Zhang; Vincent Tiing Tiong; Aijun Du; Qing Shen; Gregory J. Wilson; Hongxia Wang
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 9, 8, 2113-2120, Apr. 2018, Organic-inorganic hybrid lead halide perovskite solar cells have demonstrated competitive power conversion efficiency over 22%; nevertheless, critical issues such as unsatisfactory device stability, serious current-voltage hysteresis, and formation of photo nonactive perovskite phases are obstacles for commercialization of this photovoltaics technology. Herein we report a facial yet effective method to hinder formation of photoinactive delta-FAPbI(3) and hysteresis behavior in planar heterojunction perovskite solar cells based on K-x(MA(0.17)FA(0.83))(1-x)PbI2.5Br0.5 (0 <= x <= 0.1) through incorporation of potassium ions (K+). X-ray diffraction patterns demonstrate formation of photoinactive delta-FAPbI(3) was almost completely suppressed after K+ incorporation. Density functional theory calculation shows K+ prefers to enter the interstitial sites of perovskite lattice, leading to chemical environmental change in the crystal structure. Ultrafast transient absorption spectroscopy has revealed that K+ incorporation leads to enhanced carrier lifetime by 50%, which is also confirmed by reduced trap-assisted recombination of the perovskite solar cells containing K+ in photovoltage decay. Ultraviolet photoelectron spectroscopy illustrates that K+ incorporation results in a significant rise of conduction band minimum of the perovskite material by 130 meV, leading to a more favorable energy alignment with electron transporting material. At the optimal content of 3% K+ (molar ratio, relative to the total monovalent cations), nearly hysteresis-free, enhanced power conversion efficiencies from 15.72% to 17.23% were obtained in this solar cell.
Scientific journal, English

Understanding charge transfer and recombination by interface engineering for improving the efficiency of PbS quantum dot solar cells
Chao Ding; Yaohong Zhang; Feng Liu; Yukiko Kitabatake; Shuzi Hayase; Taro Toyoda; Ruixiang Wang; Kenji Yoshino; Takashi Minemoto; Qing Shen
Nanoscale Horizons, 3, 4, 417-429, 26 Mar. 2018, Peer-reviwed, True, In quantum dot heterojunction solar cells (QDHSCs), the QD active layer absorbs sunlight and then transfers the photogenerated electrons to an electron-transport layer (ETL). It is generally believed that the conduction band minimum (CBM) of the ETL should be lower than that of the QDs to enable efficient charge transfer from the QDs to the collection electrode (here, FTO) through the ETL. However, by employing Mg-doped ZnO (Zn1-xMgxO) as a model ETL in PbS QDHSCs, we found that an ETL with a lower CBM is not necessary to realize efficient charge transfer in QDHSCs. The existence of shallow defect states in the Zn1-xMgxO ETL can serve as additional charge-transfer pathways. In addition, the conduction band offset (CBO) between the ETL and the QD absorber has been, for the first time, revealed to significantly affect interfacial recombination in QDHSCs. We demonstrate that a spike in the band structure at the ETL/QD interface is useful for suppressing interfacial recombination and improving the open-circuit voltage. By varying the Mg doping level in ZnO, we were able to tune the CBM, defect distribution and carrier concentration in the ETL, which play key roles in charge transfer and recombination and therefore the device performance. PbS QDHSCs based on the optimized Zn1-xMgxO ETL exhibited a high power conversion efficiency of 10.6%. Our findings provide important guidance for enhancing the photovoltaic performance of QD-based solar cells.
Scientific journal, English

Octadecylamine-Functionalized Single-Walled Carbon Nanotubes for Facilitating the Formation of a Monolithic Perovskite Layer and Stable Solar Cells
Vincent Tiing Tiong; Ngoc Duy Pham; Teng Wang; Tianxiang Zhu; Xinluo Zhao; Yaohong Zhang; Qing Shen; John Bell; Linhua Hu; Songyuan Dai; Hongxia Wang
Advanced Functional Materials, Wiley-VCH Verlag, 28, 10, 1705545, 07 Mar. 2018, Peer-reviwed, Organic–inorganic lead halide perovskites have shown great future for application in solar cells owing to their exceptional optical and electronic properties. To achieve high-performance perovskite solar cells, a perovskite light absorbing layer with large grains is desirable in order to minimize grain boundaries and recombination during the operation of the device. Herein, a simple yet efficient approach is developed to synthesize perovskite films consisting of monolithic-like grains with micrometer size through in situ deposition of octadecylamine functionalized single-walled carbon nanotubes (ODA-SWCNTs) onto the surface of the perovskite layer. The ODA-SWCNTs form a capping layer that controls the evaporation rate of organic solvents in the perovskite film during the postthermal treatment. This favorable morphology in turn dramatically enhances the short-circuit current density of the perovskite solar cells and almost completely eliminates the hysteresis. A maximum power conversion efficiency of 16.1% is achieved with an ODA-SWCNT incorporated planar solar cell using (FA0.83MA0.17)0.95Cs0.05Pb(I0.83Br0.17)3 as light absorber. Furthermore, the perovskite solar cells with ODA-SWCNT demonstrate extraordinary stability with performance retention of 80% after 45 d stability testing under high humidity (60–90%) environment. This work opens up a new avenue for morphology manipulation of perovskite films and enhances the device stability using carbon material.
Scientific journal, English

Octadecylamine-Functionalized Single-Walled Carbon Nanotubes for Facilitating the Formation of a Monolithic Perovskite Layer and Stable Solar Cells
Vincent Tiing Tiong; Ngoc Duy Pham; Teng Wang; Tianxiang Zhu; Xinluo Zhao; Yaohong Zhang; Qing Shen; John Bell; Linhua Hu; Songyuan Dai; Hongxia Wang
ADVANCED FUNCTIONAL MATERIALS, WILEY-V C H VERLAG GMBH, 28, 10, Mar. 2018, Organic-inorganic lead halide perovskites have shown great future for application in solar cells owing to their exceptional optical and electronic properties. To achieve high-performance perovskite solar cells, a perovskite light absorbing layer with large grains is desirable in order to minimize grain boundaries and recombination during the operation of the device. Herein, a simple yet efficient approach is developed to synthesize perovskite films consisting of monolithic-like grains with micrometer size through in situ deposition of octadecylamine functionalized single-walled carbon nanotubes (ODA-SWCNTs) onto the surface of the perovskite layer. The ODA-SWCNTs form a capping layer that controls the evaporation rate of organic solvents in the perovskite film during the postthermal treatment. This favorable morphology in turn dramatically enhances the short-circuit current density of the perovskite solar cells and almost completely eliminates the hysteresis. A maximum power conversion efficiency of 16.1% is achieved with an ODA-SWCNT incorporated planar solar cell using (FA(0.83)MA(0.17))(0.95)Cs0.05Pb(I0.83Br0.17)(3) as light absorber. Furthermore, the perovskite solar cells with ODA-SWCNT demonstrate extraordinary stability with performance retention of 80% after 45 d stability testing under high humidity (60-90%) environment. This work opens up a new avenue for morphology manipulation of perovskite films and enhances the device stability using carbon material.
Scientific journal, English

Growth Mechanism of ZnO Thin Films Grown by Spray Pyrolysis Using Diethylzinc Solution
Masato Imai; Marin Watanabe; Himeka Tominaga; Kenji Yoshino; Yuhei Ogomi; Qing Shen; Taro Toyoda; Takashi Minemoto; Shuzi Hayase
Physica Status Solidi (A) Applications and Materials Science, Wiley-VCH Verlag, 215, 4, 1700406, 21 Feb. 2018, Peer-reviwed, Non-doped ZnO thin films are deposited on glass by spray pyrolysis using Diethylzinc diluted with diisopropyl ether. The droplet impacts are observed and the structural properties of films are studied as deposition temperature dependence. The shape of a droplet impacts changes from a hemisphere to a flat plane with increasing the deposition temperature. The images of cross sectional transmittance electron microscopy show granular non-crystalline for RT (room temperature) sample and columnar polycrystalline for 150 °C sample as shown on the right-side. The growth mechanism of ZnO thin films is discussed by considering the relationship between the shape of droplet impacts and the morphology of the deposited films. Also, the presence of the crystal formed by precursor is suggested for the films deposited at lower temperature.
Scientific journal, English

Charge carrier kinetics in hematite with NiFeOx coating in aqueous solutions: Dependence on bias voltage
Woon Yong Sohn; James E. Thorne; Yaohong Zhang; Shota Kuwahara; Qing Shen; Dunwei Wang; Kenji Katayama
Journal of Photochemistry and Photobiology A: Chemistry, Elsevier B.V., 353, 15, 344-348, 15 Feb. 2018, Peer-reviwed, Charge carrier dynamics of hematite with and without an amorphous NiFeOx coating were investigated in aqueous solution, depending on bias voltage. We found three different components in the μs − s time region from both samples, arising from trapped electrons and holes at surface states and long-lived holes driven into the interface between hematite surface and the electrolyte, respectively. When a bias voltage of over 0.5 V was applied, the intensity of both the components arising from the trapped electrons and holes were increased due to the improvement of the charge separation efficiency. In addition, the component arising from the long-lived holes appeared, which has been assigned to the charge transfer kinetics taking place at the interface. We demonstrated that, in the case of the coated one, all the above-mentioned changes of the dynamics occured under lower applied potentials than applied to the bare sample. In addition, we found that the decay of the electron/hole recombination dynamics was retarded by the NiFeOx coating, meaning that the surface defects of hematite, the recombination centers, were passivated by the coating. It implies that the amorphous NiFeOx coating plays a crucial role in improving the charge transfer kinetics of hematite by decreasing in the charge carrier recombination, which is beneficial for water oxidation.
Scientific journal, English

Ultrafast Electron Injection from Photoexcited Perovskite CsPbI3 QDs into TiO2 Nanoparticles with Injection Efficiency near 99%
Feng Liu; Yaohong Zhang; Chao Ding; Taro Toyoda; Yuhei Ogomi; Teresa S. Ripolles; Shuzi Hayase; Takashi Minemoto; Kenji Yoshino; Songyuan Dai; Qing Shen
Journal of Physical Chemistry Letters, American Chemical Society, 9, 2, 294-297, 18 Jan. 2018, Peer-reviwed, Photoexcited electron injection dynamics from CsPbI3 quantum dots (QDs) to wide gap metal oxides are studied by transient absorption spectroscopy. Experimental results show under a low excitation intensity that ∼99% of the photoexcited electrons in CsPbI3 QDs can be injected into TiO2 with a size-dependent rate ranging from 1.30 × 1010 to 2.10 × 1010 s-1, which is also ∼2.5 times faster than that in the case of ZnO. A demonstration QD-sensitized solar cell based on a CsPbI3/TiO2 electrode is fabricated that delivers a power conversion efficiency of 5%.
Scientific journal, English

Interface passivation effects on the photovoltaic performance of quantum dot sensitized inverse opal TiO2
Kanae Hori; Yaohong Zhang; Pimsiri Tusamalee; Naoki Nakazawa; Yasuha Yoshihara; Ruixiang Wang; Taro Toyoda; Shuzi Hayase; Qing Shen
Nanomaterials, 8, 460, 2018, Peer-reviwed
Scientific journal, English

Enhanced performance of ZnO based perovskite solar cells by Nb2O5 surface passivation
Putao Zhang; Fu Yang; Gaurav Kapil; Qing Shen; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
Organic Electronics, ELSEVIER SCIENCE BV, 62, 615-620, 2018, Peer-reviwed, TiO2 has been extensively utilized as bottom electron transporting scaffold for perovskite solar cells (PSCs) but need for its high processing temperature (> 450 degrees C) hinders its applicability for the flexible plastic substrates. Use of the low temperature processed ZnO is one of the probable solutions as electron transport layer (ETL) in PSCs owing to its high electron mobility. An amicable solution for the instability of the perovskite absorber layers fabricated on to ZnO leading resulting in to poor power conversion efficiency (PCE) and long-term stability is necessary for to harness the benefit of ZnO as ETL in PSCs. Herein, we modified the ZnO surface by spin-coating an ultrathin Nb2O5 as surface passivation layer. In this work, both of the ZnO and Nb2O5 were fabricated by spin coating and sintered at relatively lower temperature of 200 degrees C. Utilizing this Nb2O5 surface passivated and low temperature processed ZnO as ETL, dramatically enhanced stability of perovskite film over 20 days under ambient condition has been clearly demonstrated. This bilayer of Nb2O5 surface passivated ZnO scaffold used for fabrication of the planer heterojunction PSCs based on CH3NH3PbI3, led to the maximum PCE of 14.57% under simulated solar irradiation for an optimized ZnO thickness of 42 nm. Moreover, implication of the surface passivation of ZnO by Nb2O5 leading to the formation of highly crystalline, stable and dense perovskite film has been probed by SEM and XRD investigations.
Scientific journal, English

Solution-Processed Air-Stable Copper Bismuth Iodide for Photovoltaics
Zhaosheng Hu; Zhen Wang; Gaurav Kapil; Tingli Ma; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Taro Toyoda; Qing Shen; Shuzi Hayase
ChemSusChem, 11, 17, 2930-2935, 2018, Peer-reviwed, True, Bismuth-based solar cells have been under intensive interest as an efficient non-toxic absorber in photovoltaics. Within this new family of semiconductors, we herein report a new, long-term stable copper bismuth iodide (CuBiI4 ). A solutionprocessed method under air atmosphere is used to prepare the material. The adopted HI-assisted dimethylacetamide (DMA) co-solvent can completely dissolve CuI and BiI3 powders with high concentration compared with other organic solvents. Moreover, the high vapor pressure of tributyl phosphate, selected for the solvent vapor annealing (SVA), enables complete low-temperature (≤70 °C) film preparation, resulting in a stable, uniform, dense CuBiI4 film. The average grain size increases with the precursor concentration, greatly improving the photoluminescence lifetime and hall mobility; a carrier lifetime of 3.03 ns as well as an appreciable hall mobility of 110 cm2  V-1 s-1 were obtained. XRD illustrates that the crystal structure is cubic (space group Fd3m) and favored in the [1 1 1] direction. Moreover, the photovoltaic performance of CuBiI4 was also investigated. A wide bandgap (2.67 eV) solar cell with 0.82 % power conversion efficiency is presented, which exhibits excellent long-term stability over 1008 h under ambient conditions. This air-stable material may give an application in future tandem solar cells as a stable short-wavelength light absorber.
Scientific journal, English

Effect of the conduction band offset on interfacial recombination behavior of the planar perovskite solar cells
Chao Ding; Yaohong Zhang; Feng Liu; Yukiko Kitabatake; Shuzi Hayase; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Kenji Katayama; Qing Shen
Nano Energy, 53, 17-26, 2018, Peer-reviwed
Scientific journal, English

Construction of Al-ZnO/CdS Photoanodes Modified with Distinctive Alumina Passivation Layer for Improvement of Photoelectrochemical Efficiency and Stability
Yong Zhou; Zhigang Zou; Ruyi Wang; Dong Li; Lu Wang; Xirui Zhao; Guangcheng Yang; Ai-Dong Li; Congping Wu; Qing Shen
Nanoscale, 10, 19621-19627, 2018, Peer-reviwed
Scientific journal, English

Anisotropic Crystal Growth, Optical Absorption, and Ground-​State Energy Level of CdSe Quantum Dots Adsorbed on the (001) and (102) Surfaces of Anatase-​TiO2: Quantum Dot-​Sensitization System
Toyoda, Taro; Shen, Qing; Hironaka, Motoki; Kamiyama, Keita; Kobayashi, Hisayoshi; Hirose, Yasushi; Hayase, Shuzi
Journal of Physical Chemistry C, 122, 29200-29209, 2018, Peer-reviwed
Scientific journal, English

Crystal Growth, Exponential Optical Absorption Edge, and Ground State Energy Level of PbS Quantum Dots Adsorbed on the (001), (110), and (111) Surfaces of Rutile-TiO2
Taro Toyoda; Qing Shen; Kanae Hori; Naoki Nakazawa; Keita Kamiyama; Shuzi Hayase
The Journal of Physical Chemistry C, 122, 25, 13590-13599, 2018, Peer-reviwed
Scientific journal, English

Dependences of the Optical Absorption, Ground State Energy Level, and Interfacial Electron Transfer Dynamics on the Size of CdSe Quantum Dots Adsorbed on the (001), (110), and (111) Surfaces of Single Crystal Rutile TiO2
Taro Toyoda; Qing Shen; Keita Kamiyama; Kenji Katayama; Shuzi Hayase
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 121, 45, 25390-25401, Nov. 2017, Peer-reviwed, Quantum dots (QDs) provide an attractive alternative sensitizer to organic dyes. However, there have been few reports on QD-sensitized solar cells (QDSCs) that have photovoltaic conversion efficiencies exceeding those of dye-sensitized solar cells. This is because of the lack of fundamental studies of QDs on conventional nanocrystalline metal oxide electrodes which possess much amount of heterogeneity. An important first step is an investigation of the dependences of the optical absorption, the ground state energy level, and the interfacial electron transfer (IET) on the size of QDs deposited on well characterized single crystal oxides. The present study focuses on a system of CdSe QDs adsorbed on the (001), (110), and (111) surfaces of single crystal rutile-TiO2. The optical absorption spectra, characterized using photoacoustic spectroscopy, were found to be independent of the surface orientation concerning the optical absorption edge. The exponential optical absorption tail (Urbach tail) suggests that the disorder decreases with the increasing size of the QDs and is independent of the surface orientation. The ground state energy levels of the QDs were characterized using photoelectron yield spectroscopy. That on the (001) surface shifts upward, while that on the (110) surface shifts downward with increasing QD size. That on the (111) surface is independent of the QD size, indicating the difference of the influence of the surface orientation on adsorption of the QDs. The IET rate constant and the relaxation component were characterized. The JET rate constant was found to decrease as the size of the QDs increases and depends on the surface orientation, indicating the differences in the decrease of the free energy change and lower coupling between the excited state of CdSe QDs and the Ti 3d orbitals in rutile-TiO2. The relaxation component increases with increasing QD size and depends on the surface orientation, correlating with the density of states in the conduction band of rutile-TiO2.
Scientific journal, English

Colloidal Synthesis of Air-Stable Alloyed CsSn1-xPxI3 Perovskite Nanocrystals for Use in Solar Cells
Feng Liu; Chao Ding; Yaohong Zhang; Teresa S. Ripolles; Taichi Kamisaka; Taro Toyoda; Shuzi Hayase; Takashi Minemoto; Kenji Yoshino; Songyuan Dai; Masatoshi Yanagida; Hidenori Noguchi; Qing Shen
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, AMER CHEMICAL SOC, 139, 46, 16708-16719, Nov. 2017, Peer-reviwed, Organic-inorganic hybrid perovskite solar cells have demonstrated unprecedented high power conversion efficiencies in the past few years. Now, the universal instability of the perovskites has become the main barrier for this kind of solar cells to realize commercialization. This situation can be even worse for those tin-based perovskites, especially for CsSnI3, because upon exposure to ambient atmosphere the desired black orthorhombic phase CsSnI3 would promptly lose single crystallinity and degrade to the inactive yellow phase, followed by irreversible oxidation into metallic Cs2SnI6. By alloying CsSnI3 with CsPbI3, we herein report the synthesis of alloyed perovskite quantum dot (QD), CsSn1-xPbxI3, which not only can be phase-stable for months in purified colloidal solution but also remains intact even directly exposed to ambient air, far superior to both of its parent CsSnI3 and CsPbI3 QDs. Ultrafast transient absorption spectroscopy studies reveal that the photoexcited electrons in the alloyed QDs can be injected into TiO2 nanocrystals at a fast rate of 1.12 X 10(11) S-1 which enables a high photocurrent generation in solar cells.
Scientific journal, English

Copper deficient Zn-Cu-In-Se quantum dot sensitized solar cells for high efficiency
Linlin Zhang; Zhenxiao Pan; Wei Wang; Jun Du; Zhenwei Ren; Qing Shen; Xinhua Zhong
JOURNAL OF MATERIALS CHEMISTRY A, ROYAL SOC CHEMISTRY, 5, 40, 21442-21451, Oct. 2017, Peer-reviwed, Improving the intrinsic optoelectronic properties of quantum dots (QDs) is essential to tap their potential as light-harvesting materials in QD sensitized solar cell (QDSC) applications. High quality composition controllable Zn-Cu-In-Se (ZCISe) QDs were synthesized, and the influence of non-stoichiometry on the optoelectronic properties, as well as on the photovoltaic performance of the resulting QDSCs, was investigated systematically. Experimental results revealed that the Cu content in the ZCISe QDs can remarkably influence the optical properties of QDs as well as the resultant photovoltaic performance of solar cells. The power conversion efficiency (PCE) can be distinctly improved with the use of Cu-deficient ZCISe QDs as a sensitizer regardless of the compromised light harvesting capability. Transient absorption (TA) and open-circuit voltage decay (OCVD) measurements demonstrated that the defect state-related donor-acceptor pair (DAP) in the ZCISe QDs was favorable for the enhancement of the lifetime of photogenerated electrons in the ZCISe QDSCs. The long-lived electrons in the Cu-deficient ZCISe QDs benefit the improvement of the photovoltaic performance of the resultant cell devices by suppressing charge recombination. Electrochemical impedance spectroscopy (EIS) results illustrated that the charge recombination process at the photoanode/electrolyte interfaces can be effectively inhibited in Cu-deficient ZCISe QD based cells. Finally, a highest PCE of 12.57% (J(sc) = 25.97 mA cm(-2), V-oc = 0.752 V and FF = 0.644) was achieved employing ZCISe QDs with a Cu/In molar ratio of 0.7 under AM 1.5 G one full sun illumination. This is one of the highest efficiencies in QDSCs.
Scientific journal, English

Highly Luminescent Phase-Stable CsPbl(3) Perovskite Quantum Dots Achieving Near 100% Absolute Photoluminescence Quantum Yield
Feng Liu; Yaohong Zhang; Chao Ding; Syuusuke Kobayashi; Takuya Izuishi; Naoki Nakazawa; Taro Toyoda; Tsuyoshi Ohta; Shuzi Hayase; Takashi Minemoto; Kenji Yoshino; Songyuan Dai; Qing Shen
ACS NANO, AMER CHEMICAL SOC, 11, 10, 10373-10383, Oct. 2017, Peer-reviwed, Perovskite quantum dots (QDs) as a new type of colloidal nanocrystals have gained significant attention for both fundamental research and commercial applications owing to their appealing optoelectronic properties and excellent chemical processability. For their wide range of potential applications, synthesizing colloidal QDs with high crystal quality is of crucial importance. However, like most common QD systems such as CdSe and PbS, those reported perovskite QDs still suffer from a certain density of trapping defects, giving rise to detrimental nonradiative recombination centers and thus quenching luminescence. In this paper, we show that a high room-temperature photoluminescence quantum yield of up to 100% can be obtained in CsPbI3 perovskite QDs, signifying the achievement of almost complete elimination of the trapping defects. This is realized with our improved synthetic protocol that involves introducing organolead compound trioctylphosphinePbI(2) (TOP-PbI2) as the reactive precursor, which also leads to a significantly improved stability for the resulting CsPbI3 QD solutions. Ultrafast kinetic analysis with time-resolved transient absorption spectroscopy evidence the negligible electron or hole-trapping pathways in our QDs, which explains such a high quantum efficiency. We expect the successful synthesis of the "ideal" perovskite QDs will exert profound influence on their applications to both QD-based light-harvesting and -emitting devices.
Scientific journal, English

Slow hot carrier cooling in cesium lead iodide perovskites
Qing Shen; Teresa S. Ripolles; Jacky Even; Yuhei Ogomi; Koji Nishinaka; Takuya Izuishi; Naoki Nakazawa; Yaohong Zhang; Chao Ding; Feng Liu; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Kenji Katayama; Shuzi Hayase
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 111, 15, 153903, Oct. 2017, Peer-reviwed, Lead halide perovskites are attracting a great deal of interest for optoelectronic applications such as solar cells, LEDs, and lasers because of their unique properties. In solar cells, heat dissipation by hot carriers results in a major energy loss channel responsible for the Shockley-Queisser efficiency limit. Hot carrier solar cells offer the possibility to overcome this limit and achieve energy conversion efficiency as high as 66% by extracting hot carriers. Therefore, fundamental studies on hot carrier relaxation dynamics in lead halide perovskites are important. Here, we elucidated the hot carrier cooling dynamics in all-inorganic cesium lead iodide (CsPbI3) perovskite using transient absorption spectroscopy. We observe that the hot carrier cooling rate in CsPbI3 decreases as the fluence of the pump light increases and the cooling is as slow as a few 10 ps when the photoexcited carrier density is 7 x 10(18) cm(-3), which is attributed to phonon bottleneck for high photoexcited carrier densities. Our findings suggest that CsPbI3 has a potential for hot carrier solar cell applications. Published by AIP Publishing.
Scientific journal, English

Hole-Transport Materials Containing Triphenylamine Donors with a Spiro[fluorene-9,9 '-xanthene] Core for Efficient and Stable Large Area Perovskite Solar Cells
Guohua Wu; Yaohong Zhang; Ryuji Kaneko; Yoshiyuki Kojima; Kosuke Sugawa; Towhid H. Chowdhury; Ashraful Islam; Qing Shen; Md. Akhtaruzzaman; Takeshi Noda; Joe Otsuki
SOLAR RRL, WILEY-V C H VERLAG GMBH, 1, 9, Sep. 2017, Three low-cost triphenylamine-based hole-transport materials (HTMs) with spiro[fluorene-9,9-xanthene] (SFX) skeleton are synthesized through a facile three-step procedure. The effect of the chemical structure of the HTMs on the optical property, energy levels, H2O/HTM interface, as well as the perovskite solar cell performance are studied. With the increasing bulkiness of attached groups on the SFX skeleton, the charge recombination resistance at the TiO(2)perovskite/HTMs interfaces is gradually increased, leading to increased open-circuit voltages. The device based on the bulkiest HTM (named BTPA-6) exhibits a better solar cell performance (11.57%, area: 1.02 cm(2)) than those with BTPA-4 and BTPA-5 in the forward scan. BTPA-6 also exhibits a power conversion efficiency of 14.4% (area: 0.375 cm(2)) which nearly matches spiro-OMeTAD (15.0%) in the reverse scan. Furthermore, all the three cost-effective (similar to 1/3 of that of spiro-OMeTAD) HTMs exhibit better long-term stabilities than spiro-OMeTAD.
Scientific journal, English

Anomalous enhancement by alkylamine of the dye-sensitized solar cells using TEMPO redox
Taisei Nishimura; Woon Yong Sohn; Qing Shen; Shota Kuwahara; Kenji Katayama
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 346, 281-286, Sep. 2017, Peer-reviwed, It has been believed that the TEMPO redox cannot be used for the dye-sensitized solar cells (DSCs) using a ruthenium dye as a sensitizer. However, we found that the photovoltaic performance of DSCs was gradually improved just by keeping them in dark, and it took more than 3 weeks until the performance was saturated. We identified the reason for it; 2,2,6,6-tetramethylpiperidine (TMP) molecule, which was generated during the aging, prevented the reverse charge transfer. This was caused by the molecular interaction of TMP either with the ruthenium dyes or TEMPO redox or both. We found that the freshly prepared DSCs with a ruthenium dye can give a photovoltaic performance just by adding the piperidine additives. Furthermore, we found that not only heterocyclic amine molecules but also alkylamine molecules which do not include the ring structure show the similar effect. This result will pave the way for a novel interfacial control for the charge transfer. (C) 2017 Elsevier B.V. All rights reserved.
Scientific journal, English

Optimization of Experimental Parameters for the Performance of Solid-state Dye-sensitized Solar Cells
Miki Yamaguchi; Taisei Nisimura; Woon Yong Sohn; Qing Shen; Shota Kuwahara; Kenji Katayama
ANALYTICAL SCIENCES, JAPAN SOC ANALYTICAL CHEMISTRY, 33, 9, 1041-1046, Sep. 2017, Peer-reviwed, The effects of various sample parameters for solid-state dye sensitized solar cells were studied with carrier dynamics measurements and electrochemical measurements. Although many parameters and processes have been decided based on the experience of researchers, the chemical and physical reasons for the selections have not been clarified. We studied the effect of the generally utilized materials and processing such as the blocking layer, titanium oxide thickness, surface treatment, and the selection of dyes and hole transfer materials. Based on our findings, we were able to rationally optimize the structure of the solid-state dye sensitized solar cells in terms of cell performance or the lifetime of charge carriers.
Scientific journal, English

Electron transport properties in dye-sensitized solar cells with {001} facet-dominant TiO2 nanoparticles
M. M. Maitani; K. Tanaka; Q. Shen; T. Toyoda; Y. Wada
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 19, 33, 22129-22140, Sep. 2017, Peer-reviwed, Dye-sensitized solar cells (DSSCs) with reactive {001} facet-dominant TiO2 have attracted a great deal of attention owing to their high solar cell performance, despite the origin and the variation of the results being controversial. Here, we report the characteristic charge transport properties of DSSCs composed of {001} and {101} facet-dominant TiO2 nanoparticles in order to explain the origin of solar cell performance. Based on transient photocurrent and photovoltage measurements and transient absorption spectroscopy, the energetics of TiO2 semiconductors and dye sensitizers are utilized to understand the electron diffusion, recombination, and injection kinetics to determine solar cell performance. Novel strategies to improve DSSC performance by utilizing the characteristics of {001} facet-dominant TiO2 nanoparticles are proposed, which are (1) enhancement of electron injection and (2) reduction of carrier recombination for J(SC) and V-OC improvement, despite the drawback of slower electron diffusion in the mesoporous network of {001} facet-dominant TiO2.
Scientific journal, English

Recombination Suppression in PbS Quantum Dot Heterojunction Solar Cells by Energy-Level Alignment in the Quantum Dot Active Layers
Chao Ding; Yaohong Zhang; Feng Liu; Naoki Nakazawa; Qingxun Huang; Shuzi Hayase; Yuhei Ogomi; Taro Toyoda; Ruixiang Wang; Qing Shen
ACS Appl. Mater. Interfaces, 10, 31, 26142-26152, 01 Sep. 2017, Peer-reviwed, True, Using spatial energy-level gradient engineering with quantum dots (QDs) of different sizes to increase the generated carrier collection at the junction of a QD heterojunction solar cell (QDHSC) is a hopeful route for improving the energy-conversion efficiency. However, the results of current related research have shown that a variable band-gap structure in a QDHSC will create an appreciable increase, not in the illumination current density, but rather in the fill factor. In addition, there are a lack of studies on the mechanism of the effect of these graded structures on the photovoltaic performance of QDHSCs. This study presents the development of air atmosphere solution-processed TiO2/PbS QDs/Au QDHSCs by engineering the energy-level alignment (ELA) of the active layer via the use of a sorted order of differently sized QD layers (four QD sizes). In comparison to the ungraded device (without the ELA), the optimized graded architecture (containing the ELA) solar cells exhibited a great increase (21.4%) in short-circuit current density ( Jsc). As a result, a Jsc value greater than 30 mA/cm2 has been realized in planar, thinner absorption layer (∼300 nm) PbS QDHSCs, and the open-circuit voltage ( Voc) and power-conversion efficiency (PCE) were also improved. Through characterization by the light intensity dependences of the Jsc and Voc and transient photovoltage decay, we find that (i) the ELA structure, serving as an electron-blocking layer, reduces the interfacial recombination at the PbS/anode interface, and (ii) the ELA structure can drive more carriers toward the desirable collection electrode, and the additional carriers can fill the trap states, reducing the trap-assisted recombination in the PbS QDHSCs. This work has clearly elucidated the mechanism of the recombination suppression in the graded QDHSCs and demonstrated the effects of ELA structure on the improvement of Jsc. The charge recombination mechanisms characterized in this work would be able to shed light on further improvements of QDHSCs, which could even benefit other types of solar cells.
Scientific journal, English

A 2,1,3-Benzooxadiazole Moiety in a D-A-D-type Hole-Transporting Material for Boosting the Photovoltage in Perovskite Solar Cells
Guohua Wu; Yaohong Zhang; Ryuji Kaneko; Yoshiyuki Kojima; Qing Shen; Ashraful Islam; Kosuke Sugawa; Joe Otsuki
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 121, 33, 17617-17624, Aug. 2017, Peer-reviwed, A donor acceptor donor molecule with a 2,1,3-benzooxadiazole moiety, named BTPA-3, was successfully synthesized and employed as a hole transporting material (HTM) for, Cs-0.05(MA(0.17)FA(0.83))(0.95)Pb(I0.83Br0.17)(3)- and CH3NH3PbBr3-based perovskite solar cells (PSCs). The best CH3NH3PbBr3-based PSC with BTPA-3 exhibited a superior efficiency (5.91%) compared to the cell with spiro-OMeTAD (5.61%), even an 80 mV higher open-circuit voltage (V-oc) being recorded in the reverse scan (average V-oc: 1.41 V for BTPA-3 and 1.33 V for spiro-OMeTAD). The higher V-oc is attributed to larger recombination resistance and the resulting longer photovoltage lifetimes in the cells with BTPA-3. In the meantime, for the Cs-0.05(MA(0.17)FA(0.83))(0.95)Pb(I0.83Br0.17)(3)-based PSC, BTPA-3 exhibited a much lower conversion efficiency (9.81%) compared with the cell with spiro-OMeTAD (13.2%) due to a small driving force for the hole injection. The morphologies and conductivities of the hole-transport layers were also investigated, and the results are discussed in relation to the performances of the PSCs, Finally, PSCs with BTP4-3 as an HTM based on both perovskite lead halide materials exhibited good long-term stabilities.
Scientific journal, English

High Efficiency Quantum Dot Sensitized Solar Cells Based on Direct Adsorption of Quantum Dots on Photoanodes
Wenran Wang; Guocan Jiang; Juan Yu; Wei Wang; Zhenxiao Pan; Naoki Nakazawa; Qing Shen; Xinhua Zhong
ACS APPLIED MATERIALS & INTERFACES, AMER CHEMICAL SOC, 9, 27, 22549-22559, Jul. 2017, Peer-reviwed, Unambiguously direct adsorption (DA) of initial oil -soluble quantum dots (QDs) on TiO2 film electrode is a convenient and simple approach in the construction of quantum dot sensitized solar cells (QDSCs). Regrettably, low QD loading amount and poor reproducibility shadow the advantages of DA route and constrain its practical application. Herein, the influence of experimental variables in DA process on QD loading amount as well as on the photovoltaic performance of the resultant QDSCs was investigated and optimized systematically, including the choice of solvent, purification of time, as well as concentration. Experimental results demonstrated that it is essential to choose appropriate solvent as well as control purification cycles of original QD suspensions so as to realize satisfactory QD loading amount and ensure the high reproducibility. In addition, DA mode renders efficient electron injection from QD to TiO2, yet low QD loading amount and adverse QD agglomeration in comparison with the well-developed capping ligand induced self-assembly (CLIS) deposition approach. Mg2+ treatment on TiO2 photoanodes can promote the QD loading amount in DA mode. The optimized QDSCs based on DA mode exhibited efficiencies of 6.90% and 9.02% for CdSe and Zn Cu In Se QDSCs, respectively, which were comparable to the best results based on CLIS mode (6.88% and 9.56%, respectively). QDs, solvent optimization and sensitization
Scientific journal, English

Investigation of Interfacial Charge Transfer in Solution Processed Cs2SnI6 Thin Films
Gaurav Kapil; Ttakeshi Ohta; Tsuguo Koyanagi; Murugan Vigneshwaran; Yaohong Zhang; Yuhei Ogomi; Shyam S. Pandey; Kenji Yoshino; Qing Shen; Taro Toyoda; Md. Mijanur Rahman; Takashi Minemoto; Takurou N. Murakami; Hiroshi Segawa; Shuzi Hayase
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 121, 24, 13092-13100, Jun. 2017, Peer-reviwed, Cesium tin halide based perovskite Cs2SnI6 has been subjected to in-depth investigations owing to its potentiality toward the realization of environment benign Pb free and stable solar cells. In spite of the fact that Cs2SnI6 has been successfully utilized as an efficient hole transport material owing to its p-type semiconducting nature, however, the nature of the majority carrier is still under debate. Therefore, intrinsic properties of Cs2SnI6 have been investigated in detail to explore its potentiality as light absorber along with facile electron and hole transport. A high absorption coefficient (5 x 10(4) cm(-1)) at 700 nm indicates the penetration depth of 700 nm light to be 0.2 mu m, which is comparable to conventional Pb based solar cells. Preparation of pure and CsI impurity free dense thin films with controllable thicknesses of Cs2SnI6 by the solution processable method has been reported to be difficult owing to its poor solubility. An amicable solution to circumvent such problems of Cs2SnI6 has been provided utilizing spray-coating in combination with spin-coating. The presence of two emission peaks at 710 and 885 nm in the prepared Cs2SnI6 thin films indicated coexistence of quantum dot and bulk parts which were further supported by transmission electron microscopy (TEM) investigations. Time-resolved photoluminescence (PL) and transient absorption spectroscopy (TAS) were employed to investigate the excitation carrier lifetime, which revealed fast decay kinetics in the picoseconds (ps) to nanoseconds (ns) time domains. Time-resolved microwave photoconductivity decay (MPCD) measurement provided the mobile charge carrier lifetime exceeding 300 ns, which was also in agreement with the nanosecond transient absorption spectroscopy (ns-TAS) indicating slow charge decay lasting up to 20 mu s. TA assisted interfacial charge transfer investigations utilizing Cs2SnI6 in combination with n-type PCBM and p-type P3HT exhibited both intrinsic electron and hole transport.
Scientific journal, English

Atmospheric growth of ZnO films deposited by spray pyrolysis using diethylzinc solution
Masato Imai; Marin Watanabe; Akiko Mochihara; Himeka Tominaga; Kenji Yoshino; Qing Shen; Taro Toyoda; Shuzi Hayase
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 468, 473-476, Jun. 2017, Peer-reviwed, Non-doped ZnO thin films are deposited on glass substrates by spray pyrolysis using diethylzinc solution at a range from a room temperature to 150 degrees C while making N-2 gas flow in atmospheric pressure. The morphology, the structural property, the density and the optical band gap are studied. As the deposition temperature is increasing, the overall density and the optical band gap approach to the values of ZnO single crystal. The quality of ZnO thin film deposited at 150 degrees C becomes near ZnO single crystal.
Scientific journal, English

Fabrication, characterization and application of fully green superhydrophilic lignosulfonate multilayer films
Li Chen; Di-lai Lu; Jia-Ru Ye; Qing Shen
MATERIALS LETTERS, ELSEVIER SCIENCE BV, 194, 217-219, May 2017, Peer-reviwed, A fully green superhydrophilic lignosulfonate (LGS) film was prepared by the layer-by-layer electric assembly (LBLEA). Experimentally, the voltage was varied from zero to 4 kV, and the electrostatic interaction (EI) was controlled in enhancement or reduction. Results showed that the surface of LGS film formed by common condition was in hydrophilic and formed by LBLEA corresponding to the 4 kV plus El-enhancement was in superhydrophilic. FESEM images comparison found that the superhydrophilic LGS film has smooth surface than that of the hydrophilic sample and ATR-FTIR spectra comparison found that the formation of superhydrophilic LGS film is due to the 4 kV El-enhancement-based LBLEA process caused the sulfonate groups moving from the bulk LGS to its surface. This superhydrophilic LGS film showed enhanced adsorption of copper (II) ions about 47% than that of the common LGS film. (C) 2017 Elsevier B.V. All rights reserved.
Scientific journal, English

Improvement of Photovoltaic Performance of Colloidal Quantum Dot Solar Cells Using Organic Small Molecule as Hole-Selective Layer
Yaohong Zhang; Guohua Wu; Ivan Mora-Sero; Chao Ding; Feng Liu; Qingxun Huang; Yuhei Ogomi; Shuzi Hayase; Taro Toyoda; Ruixiang Wang; Joe Otsuki; Qing Shen
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 8, 10, 2163-2169, May 2017, Peer-reviwed, A novel organic small molecule bis-triphenylamine with spiro(fluorene-9,9'-xanthene) as the conjugated system, named BTPA-4, is successfully synthesized and employed as the hole-selective layer (HSL) in colloidal quantum dots solar cells (CQDSCs). The introduction of BTPA-4 layer can significantly prolong effective carrier lifetime (tau(eff)), increase charge recombination resistance (R-rec), and thus diminish the interfacial charge recombination at the PbS-QDs/Au electrode interface. The effect of BTPA-4 as HSL in the device performance is especially significant for the open-circuit voltage (V-oc) and power conversion efficiency (PCE), with a similar to 10% and 15% enhancement respectively, comparing with those of device without the HSL. Furthermore, the PbS CQDSCs with BTPA-4 possessed a noticeably stable property for over 100 days of storage under ambient atmosphere.
Scientific journal, English

Photoelectrochemical water reduction over wide gap (Ag,Cu)(In,Ga)S-2 thin film photocathodes
Wilman Septina; Minori Sugimoto; Ding Chao; Qing Shen; Shigeru Nakatsuka; Yoshitaro Nose; Takashi Harada; Shigeru Ikeda
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 19, 19, 12502-12508, May 2017, Peer-reviwed, The effects of partial replacement of Cu with Ag in a Cu(In,Ga) S-2 (CIGS) thin film on its structural, optical, electrostructural, and photoelectrochemical (PEC) properties were investigated, in order to improve its performance for PEC water reduction under sunlight illumination. Results from X-ray diffraction (XRD) analyses revealed the successful partial replacement of Cu with Ag to form solid-solutions with different Ag/(Ag + Cu) ratios (A(x)CIGS, x = Ag/(Ag + Cu) = 0.1, 0.2, 0.3 and 0.4), as confirmed by a gradual change in the (112) reflections to smaller 2 theta angles with increasing Ag/(Ag + Cu) ratio. Analyses of the photoabsorption properties of the materials using photoacoustic spectroscopy indicated changes in the band gap energies associated with increasing the Ag/(Ag + Cu) ratio. In addition, valence band maximum potentials of A(x) CIGS were deepened gradually with increasing Ag/(Ag + Cu) ratio. After modifying these A(x) CIGS films with a CdS ultrathin (ca. 70 nm) layer and a Pt catalyst, the PEC water reduction properties were evaluated in an electrolyte solution with the pH adjusted to 6.5, under simulated sunlight (AM 1.5G) radiation. Compared to the CdS- and Pt-modified Ag-free A(x) CIGS (A(0) CIGS) films, appreciable enhancements in the PEC properties were observed for electrodes based on A(x) CIGS (x 4 0) films, and the best PEC performance was obtained for the electrode based on the A(0.2) CIGS film. However, the electrode derived from the A(x) CIGS film with Ag/(Ag + Cu) ratios higher than 0.3 showed diminished PEC properties due to the partial conversion of its semiconducting properties from p-type to n-type.
Scientific journal, English

Ligand-dependent exciton dynamics and photovoltaic properties of PbS quantum dot heterojunction solar cells
Jin Chang; Yuhei Ogomi; Chao Ding; Yao Hong Zhang; Taro Toyoda; Shuzi Hayase; Kenji Katayama; Qing Shen
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 19, 9, 6358-6367, Mar. 2017, Peer-reviwed, The surface chemistry of colloidal quantum dots (QDs) plays an important role in determining the photoelectric properties of QD films and the corresponding quantum dot heterojunction solar cells (QDHSCs). To investigate the effects of the ligand structure on the photovoltaic performance and exciton dynamics of QDHSCs, PbS QDHSCs were fabricated by the solid state ligand exchange method with mercaptoalkanoic acid as the cross-linking ligand. Temperature-dependent photoluminescence and ultrafast transient absorption spectra show that the electronic coupling and charge transfer rate within QD ensembles were monotonically enhanced as the ligand length decreased. However, in practical QDHSCs, the second shortest ligand 3-mercaptopropionic acid (MPA) showed higher power conversion efficiency than the shortest ligand thioglycolic acid (TGA). This could be attributed to the difference in their surface trap states, supported by thermally stimulated current measurements. Moreover, compared with the non-conjugated ligand MPA, the conjugated ligand 4-mercaptobenzoic acid (MBA) introduces less trap states and has a similar charge transfer rate in QD ensembles, but has poor photovoltaic properties. This unexpected result could be contributed by the QD-ligand orbital mixing, leading to the charge transfer from QDs to ligands instead of charge transfer between adjacent QDs. This work highlights the significant effects of ligand structures on the photovoltaic properties and exciton dynamics of QDHSCs, which would shed light on the further development of QD-based photoelectric devices.
Scientific journal, English

Alloying Strategy in Cu-In-Ga-Se Quantum Dots for High Efficiency Quantum Dot Sensitized Solar Cells
Wenxiang Peng; Jun Du; Zhenxiao Pan; Naoki Nakazawa; Jiankun Sun; Zhonglin Du; Gencai Shen; Juan Yu; Jin-Song Hu; Qing Shen; Xinhua Zhong
ACS APPLIED MATERIALS & INTERFACES, AMER CHEMICAL SOC, 9, 6, 5328-5336, Feb. 2017, Peer-reviwed, I-III-VI2 group "green" quantum dots (QDs) are attracting increasing attention in photoelectronic conversion applications. Herein, on the basis of the "simultaneous nucleation and growth" approach, Cu-In-Ga-Se (CIGSe) QDs with light harvesting range of about 1000 nm were synthesized and used as sensitizer to construct quantum dot sensitized solar cells (QDSCs). Inductively coupled plasma atomic emission spectrometry (ICP-AES), wild-angle X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses demonstrate that the Ga element was alloyed in the Cu-In-Se (CISe) host. Ultraviolet photoelectron spectroscopy (UPS) and femtosecond (fs) resolution transient absorption (TA) measurement results indicate that the alloying strategy could optimize the electronic structure in the obtained CIGSe QD material, thus matching well with TiO2 substrate and favoring the photogenerated electron extraction. Open circuit voltage decay (OCVD) and impedance spectroscopy (IS) tests indicate that the intrinsic recombination in CIGSe QDSCs was well suppressed relative to that in CISe QDSCs. As a result, CIGSe based QDSCs with use of titanium mesh supported mesoporous carbon counter electrode exhibited a champion efficiency of 11.49% (J(sc) = 25.01 mA/cm(2), V-oc = 0.740 V, FF = 0.621) under the irradiation of full one sun in comparison with 9.46% for CISe QDSCs.
Scientific journal, English

Near IR sensitive Sn based perovskite solar cells with high current density reaching 30mA/cm2
Yuhei Ogomi; Daisuke Hirotani; Kosei Fujiwara; Keita Sakaguchi; Qing Shen; Taro Toyoda; Kenji Yoshino; Atsushi Wakamiya; Teresa S. Ripolles; Shuzi Hayase
2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017, Institute of Electrical and Electronics Engineers Inc., 2957-2962, 2017, Enhancing Jsc of solar cells consisting of mixed metal perovskite, MASn0.5Pb0.5I3 (SnPb PVK), is reported. The SnPb PVK was prepared from Pbk/SnL· mixture or SnI2(DMSO)2/PbI2(DMSO)2 mixture, where these PVK are abbreviated as SnPb-A PVK and SnPb-B PVK, respectively. Urbach energy's sharpness factor (σ) for SnPb-B PVK was 1.5 which was higher than 0.5 for SnPb-A PVK, suggesting that the SnPb-B PVK has less crystal disordering than the SnPb-A PVK. The Jsc of the SnPb-B PVK cell was improved to 30 mA/cm2, compared to 20 mA/cm2 for SnPb-A PVK cell. The carrier dynamics is discussed by transient spectroscopy studies.
International conference proceedings, English

Photovoltaic Properties of CdSe Quantum Dot Sensitized Inverse Opal TiO2 Solar Cells: The Effect of TiCl4 Post Treatment
Motoki Hironaka; Taro Toyoda; Kanae Hori; Yuhei Ogomi; Shuzi Hayase; Qing Shen
Journal of Modern Physics, 8, 522-530, 2017, Peer-reviwed
Scientific journal, English

Hole-Transport Materials Containing Triphenylamine Donors with a Spiro[fluorene-9,9'-xanthene] Core for Efficient and Stable Large Area Perovskite Solar Cells
Guohua Wu; Yaohong Zhang; Ryuji Kaneko; Yoshiyuki Kojima; Kosuke Sugawa; Towhid; H. Chowdhury; Ashraful Islam; Qing Shen; Md. Akhtaruzzaman; Takeshi Noda; Joe Otsuki
Solar RRL, WILEY-V C H VERLAG GMBH, 1, 9, 1700096, 2017, Peer-reviwed, Three low-cost triphenylamine-based hole-transport materials (HTMs) with spiro[fluorene-9,9-xanthene] (SFX) skeleton are synthesized through a facile three-step procedure. The effect of the chemical structure of the HTMs on the optical property, energy levels, H2O/HTM interface, as well as the perovskite solar cell performance are studied. With the increasing bulkiness of attached groups on the SFX skeleton, the charge recombination resistance at the TiO(2)perovskite/HTMs interfaces is gradually increased, leading to increased open-circuit voltages. The device based on the bulkiest HTM (named BTPA-6) exhibits a better solar cell performance (11.57%, area: 1.02 cm(2)) than those with BTPA-4 and BTPA-5 in the forward scan. BTPA-6 also exhibits a power conversion efficiency of 14.4% (area: 0.375 cm(2)) which nearly matches spiro-OMeTAD (15.0%) in the reverse scan. Furthermore, all the three cost-effective (similar to 1/3 of that of spiro-OMeTAD) HTMs exhibit better long-term stabilities than spiro-OMeTAD.
Scientific journal, English

Air Stable PbSe Colloidal Quantum Dot Heterojunction Solar Cells: Ligand-Dependent Exciton Dissociation, Recombination, Photovoltaic Property, and Stability
Yaohong Zhang; Chao Ding; Guohua Wu; Naoki Nakazawa; Jin Chang; Yuhei Ogomi; Taro Toyoda; Shuzi Hayase; Kenji Katayama; Qing Shen
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 120, 50, 28509-28518, Dec. 2016, Peer-reviwed, We fabricated the long-term air stable PbSe colloidal quantum dots (CQDs) based planar heterojunction solar cells (FTO/TiO2/PbSe/Au) with relatively larger active area (0.25 cm(2)) using tetrabutylammonium iodide (TBAI, I-) as ligand in solid state ligand-exchange process. For the first time, we have achieved the whole preparation process of the device in the ambient atmosphere from PbSe CQDs collection to PbSe colloidal quantum dot solar cells (CQDSCs) fabrication, then storage and in their following measurements. Especially, TBAI-treated PbSe CQDSCs exhibited a power conversion efficiency (PCE) of 3.53% under AM 1.5 G in air, and also a remarkable long-term stability (more than 90 days) of their storage in ambient atmosphere has been identified. By contrast, 1,2-ethanedithiol (EDT), 3-mercaptopropionic acid (MPA) and cetyltrimethylammonium bromide (CTAB, Br-) treated PbSe CQDSCs were further studied. The ligand-dependent exciton dissociation, recombination, energy level shift, and air stability of PbSe CQDs treated with these different ligands were systematically investigated. It was noted that TBAI-treated PbSe CQDSCs exhibited suppressed recombination, faster charge transfer rate, and longer carrier lifetimes, which resulted in a higher PCE and long-term air stability.
Scientific journal, English

Near IR sensitive Sn based perovskite solar cells with high current density reaching 30mA/cm²
Ogomi Y; Hirotani D; Fujiwara K; Sakaguchi K; Shen Q; Toyoda T; Yoshino K; Wakamiya A; Ripolles T; Hayase S
Conference Record of the IEEE Photovoltaic Specialists Conference, Conference Record of the IEEE Photovoltaic Specialists Conference, 2016-November, 808-811, 18 Nov. 2016, © 2016 IEEE. Enhancing Jsc of solar cells consisting of mixed metal perovskite, MASn0.5Pb0.5I3 (SnPb PVK), is reported. The SnPb PVK was prepared from Pbt/SnL· mixture or SnI2(DMSO)2/PbI2(DMSO)2 mixture, where these PVK are abbreviated as SnPb-A PVK and SnPb-B PVK, respectively. Urbach energy's sharpness factor (σ) for SnPb-B PVK was 1.5 which was higher than 0.5 for SnPb-A PVK, suggesting that the SnPb-B PVK has less crystal disordering than the SnPb-A PVK. The Jsc of the SnPb-B PVK cell was improved to 30 mA/cm2, compared to 20 mA/cm2for SnPb-A PVK cell. The carrier dynamics is discussed by transient spectroscopy studies.
Scientific journal, Japanese

Thiocyanate-free asymmetric ruthenium (II) dye sensitizers containing azole chromophores with near-IR light-harvesting capacity
Guohua Wu; Ryuji Kaneko; Ashraful Islam; Yaohong Zhang; Kosuke Sugawa; Liyuan Han; Qing Shen; Idriss Bedja; Ravindra Kumar Gupta; Joe Otsuki
Journal of Power sources, Elsevier, 331, 100-111, Nov. 2016, Peer-reviwed
Scientific journal, English

Recent progress on quantum dot solar cells: a review
Tomah Sogabe; Qing Shen; Koichi Yamaguchi
JOURNAL OF PHOTONICS FOR ENERGY, SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 6, 4, 040901, Oct. 2016, Peer-reviwed, Semiconductor quantum dots (QDs) have a potential to increase the power conversion efficiency in photovoltaic operation because of the enhancement of photoexcitation. Recent advances in self-assembled QD solar cells (QDSCs) and colloidal QDSCs are reviewed, with a focus on understanding carrier dynamics. For intermediate-band solar cells using self-assembled QDs, suppression of a reduction of open circuit voltage presents challenges for further efficiency improvement. This reduction mechanism is discussed based on recent reports. In QD sensitized cells and QD heterojunction cells using colloidal QDs well-controlled heterointerface and surface passivation are key issues for enhancement of photovoltaic performances. The improved performances of colloidal QDSCs are presented. (C) The Authors. Published by SPIE
Scientific journal, English

The effect of CdS on the charge separation and recombination dynamics in PbS/CdS double-layered quantum dot sensitized solar cells
Koki Sato; Keita Ono; Takuya Izuishi; Shota Kuwahara; Kenji Katayama; Taro Toyoda; Shuzi Hayase; Qing Shen
CHEMICAL PHYSICS, ELSEVIER SCIENCE BV, 478, 159-163, Oct. 2016, Peer-reviwed, Quantum dot sensitized solar cells (QDSSCs) have attracted much interest due to their theoretical efficiency, predicted to be as high as 44%. However, the energy conversion efficiency of QDSSCs is still a lot lower than the theoretical value, one reason for which is the number of surface defects on the QDs. In order to improve the conversion efficiency, surface passivation of the QDs has been applied to QDSSCs. Studying the mechanism of how the surface passivation influences the photoexcited carrier dynamics is very important. In this paper, we clarify the effects of CdS passivation on electron injection, trapping and recombination in CdS passivated PbS QDSSCs (called PbS/CdS double-layered QDSSCs). We found that electron trapping and recombination can be suppressed effectively, and that the electron injection efficiency can be increased significantly by surface passivation with CdS on PbS QDSSCs. Our findings provide a better understanding of the effects of surface passivation on QDSSCs, which will prove beneficial for making further improvements in the photovoltaic properties of QDSSCs. (C) 2016 Elsevier B.V. All rights reserved.
Scientific journal, English

Architecture of the Interface between the Perovskite and Hole-Transport Layers in Perovskite Solar Cells
Masahiro Moriya; Daisuke Hirotani; Tsuyoshi Ohta; Yuhei Ogomi; Qing Shen; Teresa S. Ripolles; Kenji Yoshino; Taro Toyoda; Takashi Minemoto; Shuzi Hayase
CHEMSUSCHEM, WILEY-V C H VERLAG GMBH, 9, 18, 2634-2639, Sep. 2016, Peer-reviwed, The interface between the perovskite (PVK, CH3NH3PbI3) and hole-transport layers in perovskite solar cells is discussed. The device architecture studied is as follows: F-doped tin oxide (FTO)-coated glass/compact TiO2/mesoporous TiO2/PVK/2,2,7,7-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9-spirobifluorene (Spiro-MeOTAD)/Au. After a thin layer of 4,4,4-trifluorobutylammonium iodide (TFBA) was inserted at the interface between PVK and Spiro-MeOTAD, the photovoltaic efficiency increased from 11.6-14.5% to 15.1-17.6%. TFBA (10ppm) was added in the PVK solution before coating. Owing to the low surface tension of TFBA, TFBA rose to the surface of the PVK layer spontaneously during spin-coating to make a thin organic layer. The PVK grain boundaries also seemed to be passivated with the addition of TFBA. However, large differences in Urbach energies and valence band energy level were not observed for the PVK layer with and without the addition of TFBA. The charge recombination time constant between the PVK and the Spiro-MeOTAD became slower (from 8.4 to 280sec) after 10ppm of TFBA was added in the PVK. The experimental results using TFBA conclude that insertion of a very thin layer at the interface between PVK and Spiro-MeOTAD is effective for suppressing charge recombination and increasing photovoltaic performances.
Scientific journal, English

Facile Synthesis and Characterization of Sulfur Doped Low Bandgap Bismuth Based Perovskites by Soluble Precursor Route
Murugan Vigneshwaran; Takeshi Ohta; Satoshi Iikubo; Gaurav Kapil; Teresa S. Ripolles; Yuhei Ogomi; Ting Ma; Shyam S. Pandey; Qing Shen; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
CHEMISTRY OF MATERIALS, AMER CHEMICAL SOC, 28, 18, 6436-6440, Sep. 2016, Peer-reviwed, The bismuth based perovskite with the structure (CH3NH3)(3)Bi2I9 (MBI) is rapidly emerging as eco-friendly and stable semiconducting material as a substitute for the lead halide perovskites. A relatively higher bandgap of MBI (about 2.1 eV) has been found to be a bottleneck in realizing the high photovoltaic performance similar to that of lead halide based perovskites. We demonstrate the bandgap engineering of novel bismuth based perovskites obtained by in situ sulfur doping of MBI via the thermal decomposition of Bi(xt)(3) (xt = ethyl xanthate) precursor. Colors of the obtained films clearly changed from orange to black when annealed from 80 to 120 degrees C. Formation of sulfur doped MA(3)Bi(2)I(9) was confirmed by XRD and the presence of sulfur was confirmed through XPS. In this work, obtained sulfur doped bismuth perovskites exhibited a bandgap of 1.45 eV which is even lower than that of most commonly used lead halide perovskites. Hall-Effect measurements showed that the carrier concentration and mobility are much higher as compared to that of undoped MA(3)Bi(2)I(9).
Scientific journal, English

Novel Y doped BiVO4 thin film electrodes for enhanced photoelectric and photocatalytic performance
Yaohong Zhang; Zhiguo Yi; Guohua Wu; Qing Shen
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 327, 25-32, Aug. 2016, Peer-reviwed, Y3+ doped BiVO4 powder has been shown the potential to be an efficient photocatalyst for water splitting and hydrocarbon gas degradation. However, the photoelectric property of YxBi1-xVO4 has not been investigated. What's more, in some special fields, it is vital to apply thin film and it is electrode instead of powder due to some kind of necessity, such as thin film solar cell and photoelectrocatalysis. Also, there is less report on the photoelectric and photocatalytic properties of Y3+ doped BiVO4 thin film. Here, relatively dense and flat YxBi1-xVO4 thin film was in-situ fabricated on FTO substrate by using a solution polymeric method. It was found that by increasing Y3+ content, the crystalline phase of the YxBi1-xVO4 thin film changed from monoclinic and tetragonal mixture phase to tetragonal solid solution phase, and the conduction band of YxBi1-xVO4 film showed more negatively shift. For the first time, we extensively investigated the photocurrent, incident photon to current efficiency (IPCE) and photoinduced hydrophilicity properties of YxBi1-xVO4 thin film electrode. Their corresponding electrochemical impedance spectroscopy, which revealed charge transfer characteristics were studied simultaneously. Due to the excellent photoelectric performance, the Y0.05Bi0.95VO4 (composite of monoclinic BiVO4 and tetragonal YVO4) thin film electrode exhibited the best photocatalytic activity to degrade Rhodamine B in water than other thin film electrodes. (C) 2016 Elsevier B.V. All rights reserved.
Scientific journal, English

Adsorption and Electronic Structure of CdSe Quantum Dots on Single Crystal ZnO: A Basic Study of Quantum Dot-Sensitization System
Taro Toyoda; Witoon Yindeesuk; Keita Kamiyama; Shuzi Hayase; Qing Shen
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 120, 30, 16367-16376, Aug. 2016, Peer-reviwed, We describe the morphology and consider the optical absorption and the ground state energy level of CdSe quantum dots (QDs) on single crystal ZnO substrates with various crystal orientations. The morphologies and crystal growth of CdSe QDs were analyzed by atomic force microscopy photoacoustic (PA) spectroscopy for the optical absorption measurements, and photoelectron yield (PY) spectroscopy to evaluate the ground state energy level. The adsorption and crystal growth of CdSe QDs depend on both the adsorption time and the surface orientation of the ZnO substrate. The change in average diameter of the QDs on ZnO with adsorption. time is not related to the crystal surface orientation, and the growth is a two-step process, different from that on single crystal rutile-TiO2. This is characteristic of the difference between CdSe QDs grown on ZnO and those grown on rutile-TiO2. The crystal quality of the QDs on ZnO is poorer than those grown on rutile-TiO2, indicating that the reaction for crystal growth on ZnO is different from that on rutile-TiO2. The energy level of the valence band maximum (VBM) for the (0001) single crystal ZnO surface is higher than those for the (1010) and (1110) surfaces. The ground state energy level of CdSe QDs on single crystal ZnO depend's On both the adsorption time and the surface orientation, which is indicative of the effect of the loss of solvation energy due to the dielectric polarization of the surroundings.
Scientific journal, English

Neutral and anionic tetrazole-based ligands in designing novel ruthenium dyes for dye-sensitized solar cells
Guohua Wu; Ryuji Kaneko; Yaohong Zhang; Yoshinao Shinozaki; Kosuke Sugawa; Ashraful Islam; Liyuan Han; Idriss Bedja; Ravindra Kumar Gupta; Qing Shen; Joe Otsuki
JOURNAL OF POWER SOURCES, ELSEVIER SCIENCE BV, 307, 18, 416-425, Mar. 2016, Peer-reviwed, Two novel thiocyanate-free Ru(II) complexes have been synthesized, characterized and evaluated as dyes for dye-sensitized solar cells. Both complexes have two tridentate ligands: one is the tricarboxyterpyridine as an anchoring ligand and the other is one of the two bis(tetrazolyl)pyridine derivatives. One of the bis(tetrazolyl)pyridine ligand coordinates to the Ru(II) ion as a doubly deprotonated tetrazolate anion with a formal charge of 2 to form a neutral complex, which is coded as BTP dye, while the other bis(methyltetrazolyl)pyridine ligand coordinates to the Ru(II) ion as a neutral ligand forming a divalent cationic complex, coded as BMTP dye. Unexpectedly, the oxidation potentials for these two compounds are similar, implying similar electron-donating effects of the anionic tetrazolate ligand and the neutral methyltetrazole ligand to the Ru(II) ion. Despite similar HOMO/LUMO levels, BTP dye performs much better, recording 6.10% efficiency, than BMTP dye for DSSCs. Electrochemical impedance spectroscopy as well as nanosecond transient absorption spectroscopy indicates that the differences in the electron injection and electron recombination processes, which may be the consequences of the difference in the localization of LUMO as suggested by DFT calculations, are the main causes for the differences in performance. (C) 2015 Elsevier B.V. All rights reserved.
Scientific journal, English

Zn-Cu-In-Se Quantum Dot Solar Cells with a Certified Power Conversion Efficiency of 11.6%
Jun Du; Zhonglin Du; Jin-Song Hu; Zhenxiao Pan; Qing Shen; Jiankun Sung; Donghui Long; Hui Dong; Litao Sun; Xinhua Zhong; Li-Jun Wan
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, AMER CHEMICAL SOC, 138, 12, 4201-4209, Mar. 2016, Peer-reviwed, The enhancement of power conversion efficiency (PCE) and the development of toxic Cd-, Pb-free quantum dots (QDs) are critical for the prosperity of QD-based solar cells. It is known that the properties (such as light harvesting range, band gap alignment, density of trap state defects, etc.) of QD light harvesters play a crucial effect on the photovoltaic performance of QD based solar cells. Herein, high quality similar to 4 nm Cd-, Pb-free Zn-Cu-In-Se alloyed QDs with an absorption onset extending to similar to 1000 nm were developed as effective light harvesters to construct quantum dot sensitized solar cells (QDSCs). Due to the small particle size, the developed QD sensitizer can be efficiently immobilized on TiO2 film electrode in less than 0.5 h. An average PCE of 11.66% and a certified PCE of 11.61% have been demonstrated in the QDSCs based on these Zn-Cu-In-Se-QDs. The remarkably improved photovoltaic performance for Zn-Cu-In-Se QDSCs vs Cu-In-Se QDSCs (11.66% vs 9.54% in PCE) is mainly derived from the higher conduction band edge, which favors the photogenerated electron extraction and results in higher photocurrent, and the alloyed structure of Zn-Cu-In-Se-QD light harvester, which benefits the suppression of charge recombination at photoanode/electrolyte interfaces and thus improves the photovoltage.
Scientific journal, English

Low-temperature Growth of Porous and Dense ZnO Films for Perovskite Solar Cells on ITO Substrate
Kenji Yoshino; Akiko Ide; Akiko Mochihara; Yuhei Ogomi; Qing Shen; Taro Toyoda; Shuzi Hayase
CHEMISTRY LETTERS, CHEMICAL SOC JAPAN, 45, 2, 176-178, Feb. 2016, Peer-reviwed, A novel precursor with zinc oxide (ZnO) structure was synthesized for ZnO film deposition using diethylzinc in some solvents. Non-doped ZnO films on a glass substrate were successfully grown by conventional spin coating using the non doped novel precursor solution. Highly porous and dense ZnO thin films were obtained at 150 degrees C using the novel precursor with chlorobenzene and toluene, respectively.
Scientific journal, English

The Electronic Structure and Photoinduced Electron Transfer Rate of CdSe Quantum Dots on Single Crystal Rutile TiO2: Dependence on the Crystal Orientation of the Substrate
Taro Toyoda; Witoon Yindeesuk; Keita Karniyama; Kenji Katayama; Hisayoshi Kobayashi; Shuzi Hayase; Qing Shen
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 120, 4, 2047-2057, Feb. 2016, Peer-reviwed, Semiconductor quantum dots (QDs) have many desirable characteristics for use as sensitizers, such as enabling tuning of the band gap on the basis of the quantum confinement effect, a higher extinction coefficient, and facilitating charge injection as a result of the large dipole moment. Despite these potential advantages, no major advance in the efficiency of quantum-dot-sensitized solar cells (QDSCs) has yet been reported. The poor efficiency can be attributed to electron-transfer (ET) reactions that compete with the ideal energy generation cycle in QDSCs. Despite the great technological significance, the interfacial ET between QDs and inorganic species remains poorly understood. In this paper, we describe the electronic structure and the interactions between multiple sized CdSe QDs and single crystal rutile TiO2 with (001), (110), and (111) orientations. Single crystal TiO2 is well characterized and is not only ideal for comparing the amount and the structure of the QDs but is also useful for studying ET reactions. The rate of adsorption of CdSe QDs depends on the crystal orientation, although the average increase in diameter of the QDs is independent of the crystal orientation. The highest occupied molecular orbital (HOMO) level is independent of the adsorption time. On the other hand, the value of the HOMO level depends on the crystal orientation of the R-TiO2 substrate. The ET rate constant increases as the change in free energy increases and depends on the crystal orientation. This suggests that the mixing of the wave functions between the conduction band in the R-TiO2 and the lowest unoccupied molecular orbital (LUMO) level in the CdSe QDs depends on the crystal orientation.
Scientific journal, English

Mn doped quantum dot sensitized solar cells with power conversion efficiency exceeding 9%
Jin Wang; Yan Li; Qing Shen; Takuya Izuishi; Zhenxiao Pan; Ke Zhao; Xinhua Zhong
JOURNAL OF MATERIALS CHEMISTRY A, ROYAL SOC CHEMISTRY, 4, 3, 877-886, 2016, Peer-reviwed, Transition metal ion (especially Mn2+) doping has been proven to be an effective approach to modify the intrinsic photo-electronic properties of semiconductor quantum dots (QDs). However, previous works to directly grow Mn doped QDs on TiO2 film electrodes at room temperature resulted in the potential of the Mn dopant not being fully demonstrated in quantum dot sensitized solar cells (QDSCs). Herein, Mn doped CdSe0.65Te0.35 QDs (simplified as Mn : QD) were pre-synthesized via a "growth doping" strategy at high temperature. A QD-sensitized photoanode with the configuration TiO2/Mn : QD/Mn : ZnS/SiO2 was prepared and corresponding cell devices were constructed using Cu2S/brass counter electrodes and polysulfide electrolyte, together with reference cells with the photoanode configurations TiO2/Mn : QD/ZnS/SiO2, TiO2/QD/Mn : ZnS/SiO2, and TiO2/QD/ZnS/SiO2. The photovoltaic performance results indicate that TiO2/Mn : QD/Mn : ZnS/SiO2 cells exhibit the best photovoltaic performance among all the studied cell devices with a power conversion efficiency (PCE) for the champion cell of 9.40% (J(sc) = 20.87 mA cm(-2), V-oc = 0.688 V, FF = 0.655) under AM 1.5 G one full sun illumination, which is among the best results for QDSCs. The open circuit voltage decay (OCVD), impedance spectroscopy (IS) and transient absorption (TA) measurements confirm that the Mn2+ dopant can suppress charge recombination and improve the photovoltage and PCE of the resulting cells.
Scientific journal, English

Surface engineering of PbS quantum dot sensitized solar cells with a conversion efficiency exceeding 7%
Shuang Jiao; Jin Wang; Qing Shen; Yan Li; Xinhua Zhong
JOURNAL OF MATERIALS CHEMISTRY A, ROYAL SOC CHEMISTRY, 4, 19, 7214-7221, 2016, Peer-reviwed, The power conversion efficiencies (PCEs) of PbS quantum dot sensitized solar cells (QDSCs) reported are typically below 6%. This poor efficiency is mainly derived from the serious charge recombination in internal QDs and at the interface of QDs/TiO2/electrolyte. In this work, PbS/CdS QDs with a core/shell structure, which were used as the photosensitizer to fabricate sensitized solar cells, were prepared through the ion exchange method. With the reduced trapping state defects on the surface of the PbS QDs and resulting effective suppression of adverse charge recombination, the PbS/CdS QD-based cells have been improved remarkably in comparison with the pristine PbS-based QDSCs. By optimization of the thickness of the CdS shell, a PCE of 7.19% under one full sun illumination was obtained on the fabricated devices, which is among the best performances for liquid-junction PbS QDSCs.
Scientific journal, English

CdSeTe/CdS Type-I Core/Shell Quantum Dot Sensitized Solar Cells with Efficiency over 9%
Junwei Yang; Jin Wang; Ke Zhao; Takuya Izuishi; Yan Li; Qing Shen; Xinhua Zhong
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 119, 52, 28800-28808, Dec. 2015, Surface trap defects are the limited factor for quantum dots (QDs) application in solar cells. The trapping states can be efficiently suppressed by coating a shell of wider band gap material around the core QDs. We choose CdSe0.65Te0.35 (simplified as CdSeTe) as a model core material, and CdS shell was then overcoated around the CdSeTe core QD to decrease surface defect density and to increase the stability of the core QDs. By optimizing the thickness of the CdS shell, the power conversion efficiency (PCE) of the CdSeTe/CdS quantum dots sensitized solar cells (QDSCs) is enhanced by 13% in comparison with that of plain CdSeTe QDSCs. Transient absorption (TA), incident-photo-to-carrier conversion efficiency (IPCE), open-circuit voltage decay (OVCD), and electrochemical impedance spectroscopy (EIS) measurements confirmed the suppressed charge recombination process in internal QDs and QD/TiO2/electrolyte interfaces with the overcoating of CdS shell around CdSeTe core QDs. With the further overcoating of a-TiO2 and SiO2 barrier layers around the QD-sensitized photoanode, the PCE of champion CdSeTe QDSCs achieved 9.48% (Jsc = 20.82 mA/cm(2), V-oc = 0.713 V, FF = 0.639) with average PCE 9.39 + 0.09% under AM 1.5 G one full sun illumination.
Scientific journal, English

Uncovering the charge transfer and recombination mechanism in ZnS-coated PbS quantum dot sensitized solar cells
Jin Chang; Takuya Oshima; Sojiro Hachiya; Konki Sato; Taro Toyoda; Kenji Katayama; Shuzi Hayase; Qing Shen
SOLAR ENERGY, PERGAMON-ELSEVIER SCIENCE LTD, 122, 307-313, Dec. 2015, Peer-reviwed, Invited, In this work, the charge transfer and recombination mechanism is uncovered for the PbS/ZnS quantum dot sensitized solar cells (QDSSCs) based on nanoporous TiO2 electrodes. PbS quantum dots (QDs) were in-situ grown on TiO2 nanoparticles through the successive ionic absorption and reaction (SILAR) method, followed by the surface passivation of ZnS for the sensitized electrodes. It was observed that the ZnS coating cycles play a significant role in determining the photovoltaic parameters. The highest power conversion efficiency of 1.4% was achieved by coating 13 cycles of ZnS on TiO2/PbS electrode. It is essential to understand why and how ZnS passivation layers improve the photovoltaic performance of PbS QDSSCs. All obtained solar cells were characterized thoroughly by optical and electrical techniques. The open-circuit voltage decay technique and electrochemical impedance measurements indicated that the ZnS passivation layers significantly suppressed the charge recombination at the TiO2/electrolyte and TiO2/QD interfaces. The transient grating measurements suggested that the electron injection from PbS QDs to TiO2 was obviously enhanced by the ZnS coating layers. This could be attributed to the reduction of carrier trapping and recombination in PbS QDs after surface passivation. These beneficial effects of ZnS layers, therefore, resulted in the improved photovoltaic performances of PbS QDSSCs. This work provides better understanding on the passivation effect of ZnS layers in PbS QDSSCs, which would be beneficial for the further improvement of QDSSCs. (C) 2015 Elsevier Ltd. All rights reserved.
Scientific journal, English

Effects of different chloride precursors on crystal growth of lead halide perovskites
Vigneshwaran Murugan; Yuhei Ogomi; Shyam S. Pandey; Taro Toyoda; Qing Shen; Shuzi Hayase
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 8, 12, 125501, Dec. 2015, Peer-reviwed, The optimized quantity and nature of a chloride precursor used for the formation of large perovskite crystals with minimal disorder were explored. The effect of the alkyl chain length of an alkyl ammonium chloride precursor on the crystal growth of CH3NH3PbI3 was systematically investigated. It was found that the addition of ethyl ammonium chloride (EACl) increased the crystal size, which is almost twice (88 nm) the size of standard perovskite crystals (47 nm) having a preferential orientation towards the (110) plane. Photoacoustic studies demonstrated that the disorder in the perovskite crystals was highly reduced by the addition of the EACl precursor. (C) 2015 The Japan Society of Applied Physics
Scientific journal, English

CdSeTe/CdS Type-I Core/Shell Quantum Dot Sensitized Solar Cells with Efficiency over 9%
Junwei Yang; Jin Wang; Ke Zhao; Takuya Izuishi; Yan Li; Qing Shen; Xinhua Zhong
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 119, 52, 28800-28808, Dec. 2015, Peer-reviwed, Surface trap defects are the limited factor for quantum dots (QDs) application in solar cells. The trapping states can be efficiently suppressed by coating a shell of wider band gap material around the core QDs. We choose CdSe0.65Te0.35 (simplified as CdSeTe) as a model core material, and CdS shell was then overcoated around the CdSeTe core QD to decrease surface defect density and to increase the stability of the core QDs. By optimizing the thickness of the CdS shell, the power conversion efficiency (PCE) of the CdSeTe/CdS quantum dots sensitized solar cells (QDSCs) is enhanced by 13% in comparison with that of plain CdSeTe QDSCs. Transient absorption (TA), incident-photo-to-carrier conversion efficiency (IPCE), open-circuit voltage decay (OVCD), and electrochemical impedance spectroscopy (EIS) measurements confirmed the suppressed charge recombination process in internal QDs and QD/TiO2/electrolyte interfaces with the overcoating of CdS shell around CdSeTe core QDs. With the further overcoating of a-TiO2 and SiO2 barrier layers around the QD-sensitized photoanode, the PCE of champion CdSeTe QDSCs achieved 9.48% (Jsc = 20.82 mA/cm(2), V-oc = 0.713 V, FF = 0.639) with average PCE 9.39 + 0.09% under AM 1.5 G one full sun illumination.
Scientific journal, English

Characterization of hot carrier cooling and multiple exciton generation dynamics in PbS Qps using an improved transient grating technique
Qing Shen; Kenji Katayama; Taro Toyoda
JOURNAL OF ENERGY CHEMISTRY, ELSEVIER SCIENCE BV, 24, 6, 712-716, Nov. 2015, Peer-reviwed, Multiple exciton generation (MEG) dynamics in colloidal PbS quantum dots (QDs) characterized with an improved transient grating (TG) technique will be reported. Only one peak soon after optical absorption and a fast decay within 1 ps can be observed in the TG kinetics when the photon energy of the pump light hv is smaller than 2.7E(g) (E-g: band gap between LUMO and HOMO in the QDs), which corresponds to hot carrier cooling. When hv is greater than 2.7E(g), however, after the initial peak, the TG signal decreases first and soon increases, and then a new peak appears at about 2 to 3 ps. The initial peak and the new peak correspond to hot carriers at the higher excited state and MEG at the lowest excited state, respectively. By proposing a theoretical model, we can calculate the hot carrier cooling time constant and MEG occurrence time constant quantitatively. When MEG does not happen for hv smaller than 2.7E(g), hot carrier cools with a time constant of 400 fs. When MEG occurs for by larger than 2.7E(g), hot carrier cools with a time constant as small as 200 fs, while MEG occurs with a time constant of 600 fs. The detailed hot carrier cooling and MEG occurrence dynamics characterized in this work would shed light on the further understanding of MEG mechanism of various type of semiconductor QDs. (C) 2015 Science Press and Dalian Institute of Chemical Physics. All rights reserved.
Scientific journal, English

Blocking Effect for Carrier Transfer to Triiodide in Alkyl-Functionalized Dyes in Dye-Sensitized Solar Cell
Keita Omata; Shota Kuwahara; Ryo Hosokawa; Taisei Nishimura; Qing Shen; Taro Toyoda; Kenji Katayama
BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, CHEMICAL SOC JAPAN, 88, 9, 1308-1313, Sep. 2015, Peer-reviwed, A blocking effect on the approach of electron acceptors into a dye/TiO2 electrode in a dye-sensitized solar cell was confirmed by the observation of charge dynamics at the interface when an alkyl-functionalized dye was used. It was found that the density of the adsorbed MK-2 on the TiO2 surface affected the ionic motion in an electrolyte at the interface, and that electron electrolyte recombination was suppressed with a high density of adsorbed MK-2 molecules, causing prevention of the approach of the redox ions.
Scientific journal, English

Effect of defects in TiO2 nanotube thin film on the photovoltaic properties of quantum dot-sensitized solar cells
Masaya Akimoto; Taro Toyoda; Tsuyoshi Okuno; Shuji Hayase; Qing Shen
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 590, 90-97, Sep. 2015, Peer-reviwed, In the liquid-phase-deposition (LPD) method, the deposition temperature is considered to be one of the most important factors in TiO2 nanotube crystal growth. We investigated the effects of the deposition temperature on the surface morphology and defects in TiO2 nanotube (NT-TiO2) thin film electrodes utilizing scanning-electron-microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL), together with the effects of these on the photovoltaic characteristics of CdSe quantum dot (QD)-sensitized NT-TiO2 solar cells. In addition, we studied the effect of these defects on the physical properties, such as the carrier recombination and electron transport at the TiO2 and TiO2/QD interface. NT-TiO2 electrodes prepared at low temperatures have a more uniform surface and lower defects than those prepared at high temperatures. From the PL measurements and the photovoltaic characterization such as shunt resistance (R-sh) and open circuit voltage decay (OCVD), these defects can act as carrier recombination centers. The defect density increases with increasing deposition temperature, leading to an increase in carrier recombination. Series resistances (R-s) of the solar cells with NT-TiO2 electrodes prepared at high temperatures were larger than those of the solar cells with NT-TiO2 electrodes prepared at low temperatures, suggesting that the defects can also affect the carrier transport characteristics. Eventually, CdSe QD-sensitized NT-TiO2 solar cells employing NT-TiO2 prepared at low temperatures showed higher conversion efficiencies than those prepared at high temperatures. (C) 2015 Elsevier B.V. All rights reserved.
Scientific journal, English

Upconversion Luminescence of Er3+/Yb3+ Co-doped La2O3-TiO2-ZrO2 Glasses Prepared by Containerless Processing
Zhu Mei-Juan; Yu Jian-Ding; Zhang Ming-Hui; Gu Yan-Jing; Li Qin; Fang Bi-Jun; Zhao Hong-Yang; Shen Qing
JOURNAL OF INORGANIC MATERIALS, SCIENCE PRESS, 30, 4, 391-396, Apr. 2015, Peer-reviwed, Sphere transparent titanate glasses (La0.94-xEr0.06Ybx)(Ti0.95Zr0.05)(2.25)O-6 (x=0-0.24, in steps of 0.04) were prepared by containerless processing. The DTA curve shows that the glass(x=0) has high glass transition temperature(T-g=818 degrees C) and onset temperature of crystallization(T-o=906 degrees C). The thermal stability and the glass forming ability decrease with the Yb3+ concentration increasing. Strong absorption bands at 975 um are observed, showing effective absorption of Yb3+ at 975 nm. The transmittance is almost 70% in 300-3000 nm except characteristic absorption of Er3+ and Yb3+. Three emission bands centered at 535, 554, 672 nm are obtained at the excitation of 980 nm laser. When the Yb3+ concentration x is 0.16, the glass sample performs the strongest upconversion luminescence, which emission intensity at 672 nm is almost 130 times as high as that of Er3+-doped glass at room temperature.
Scientific journal, Chinese

Infrared light sensitive Sn/Pb binary perovskite solar cells with improved stability in air and organic amine-free perovskite solar cells with improved stability against light exposure
Yuhei Ogomi; Qing Shen; Koji Nishinaka; Teresa S. Ripolles; Kosei Fujiwara; Keita Sakaguchi; Taro Toyoda; Shuzi Hayase
2015 IEEE 42ND PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC), IEEE, 2015, Peer-reviwed, We found that the Sn halide perovskite became stable in air when Pb halide perovskite was added. In this report we discuss photovoltaic performances for the binary MASnPbI (MA: methylammonium) perovskite solar cells (4.2% efficiency) with gradient structure from the bottom to the top. In addition, we also reported organic amine free-CsPbI solar cells with about 2-4 % efficiency. Urbach energy measurement suggested that lowering defect density of the binary MASnPbI and CsPbI perovskite solar cells are needed for enhancing the efficiency.
International conference proceedings, English

The cause for the low efficiency of dye sensitized solar cells with a combination of ruthenium dyes and cobalt redox
Keita Omata; Shota Kuwahara; Kenji Katayama; Shen Qing; Taro Toyoda; Kun-Mu Lee; Chun-Guey Wu
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 17, 15, 10170-10175, 2015, Peer-reviwed, It has been a concern that the cobalt redox cannot give a good performance for the dye-sensitized solar cells when it is used with ruthenium dyes. The electron dynamics measurements clarified the electron loss processes, and clarified the cause. The result indicated the direct interaction between the ruthenium dyes with the cobalt redox, and it reduced the charge injection from the triplet state of the dyes to the titanium oxide, and also it increased the electron recombination process with the cobalt redox species. Both the problems of injection and recombination were solved by using the ruthenium dye with alkyl chains keeping a distance between the dye and the cobalt redox.
Scientific journal, English

Electronic structures of two types of TiO2 electrodes: inverse opal and nanoparticulate cases
Taro Toyoda; Witoon Yindeesuk; Tsuyoshi Okuno; Masaya Akimoto; Keita Kamiyama; Shuzi Hayase; Qing Shen
RSC ADVANCES, ROYAL SOC CHEMISTRY, 5, 61, 49623-49632, 2015, Peer-reviwed, We present a comparison between the electronic structures of inverse opal (IO) and nanoparticulate (NP)-TiO2 electrodes. The electronic structure details were obtained from optical absorption, fluorescence, and valence band studies in order to clarify the nature of the higher photovoltaic performance observed in sensitized solar cells using IO-TiO2 electrodes. We used photoacoustic (PA) and photoluminescence (PL) spectroscopy to characterize the optical absorption and fluorescence properties, respectively. Photoelectron yield (PY) spectroscopy was applied to characterize the position of the valence band maximum (VBM) of the IO- and NP-TiO2 electrodes. The PA spectrum for IO-TiO2 is different to that for NP-TiO2, indicating differences in the exciton-phonon interactions and the density of states in the conduction band. PL measurements showed that the curvature of the valence band structure of IO-TiO2 is different to that of NP-TiO2. Also, PL measurements showed that the oxygen vacancy in IO-TiO2 is different to that in NP-TiO2. Moreover, PY measurements showed VBM in IO-TiO2 to be at a higher position than that in NP-TiO2, suggesting a correlation with the increased open circuit voltage (V-oc) in sensitized solar cells.
Scientific journal, English

Band Engineering in Core/Shell ZnTe/CdSe for Photovoltage and Efficiency Enhancement in Exciplex Quantum Dot Sensitized Solar Cells
Shuang Jiao; Qing Shen; Ivan Mora-Sero; Jin Wang; Zhenxiao Pan; Ke Zhao; Yuki Kuga; Xinhua Zhong; Juan Bisquert
ACS NANO, AMER CHEMICAL SOC, 9, 1, 908-915, Jan. 2015, Peer-reviwed, Even though previously reported CdTe/CdSe type-II core/shell QD sensitizers possess intrinsic superior optoelectronic properties (such as wide absorption range, fast charge separation, and slow charge recombination) in serving as light absorbers, the efficiency of the resultant solar cell is still limited by the relatively low photovoltage. To further enhance photovoltage and cell efficiency accordingly, ZnTe/CdSe type-II core/shell QDs with much larger conduction band (CB) offset in comparison with that of CdTe/CdSe (1.22 eV vs 0.27 eV) are adopted as sensitizers in the construction of quantum dot sensitized solar cells (QDSCs). The augment of band offset produces an increase of the charge accumulation across the QD/TiO2 interface under illumination and induces stronger dipole effects, therefore bringing forward an upward shift of the TiO2 CB edge after sensitization and resulting in enhancement of the photovoltage of the resultant cell devices. The variation of relative chemical capacitance, C mu, between ZnTe/CdSe and reference CdTe/CdSe cells extracted from impedance spectroscopy (IS) characterization under dark and illumination conditions clearly demonstrates that, under light irradiation conditions, the sensitization of ZnTe/CdSe QDs upshifts the CB edge of TiO2 by the level of similar to 50 mV related to that in the reference cell and results in the enhancement of Voc of the corresponding cell devices. In addition, charge extraction measurements have also confirmed the photovoltage enhancement in the ZnTe/CdSe cell related to reference CdTe/CdSe cell. Furthermore, transient grating (TG) measurements have revealed a faster electron injection rate for the ZnTe/CdSe-based QDSCs in comparison with the CdSe cells. The resultant ZnTe/CdSe QD-based QDSCs exhibit a champion power conversion efficiency of 7.17% and a certified efficiency of 6.82% under AM 1.5G full one sun illumination, which is, as far as we know, one of the highest efficiencies for liquid-junction QDSCs.
Scientific journal, English

High reduction of interfacial charge recombination in colloidal quantum dot solar cells by metal oxide surface passivation
Jin Chang; Yuki Kuga; Ivan Mora-Sero; Taro Toyoda; Yuhei Ogomi; Shuzi Hayase; Juan Bisquert; Qing Shen
NANOSCALE, ROYAL SOC CHEMISTRY, 7, 12, 5446-5456, 2015, Peer-reviwed, Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar cells (CQDSCs). By coating thin TiO2 layers onto ZnO-NW surfaces, the open-circuit voltage and power conversion efficiency have been improved by over 40% in PbS CQDSCs. Characterization by transient photovoltage decay and impedance spectroscopy indicated that the interfacial recombination was significantly reduced by the surface passivation strategy. An efficiency as high as 6.13% was achieved through the passivation approach and optimization for the length of the ZnO-NW arrays (device active area: 16 mm(2)). All solar cells were tested in air, and exhibited excellent air storage stability (without any performance decline over more than 130 days). This work highlights the significance of metal oxide passivation in achieving high performance BHJ solar cells. The charge recombination mechanism uncovered in this work could shed light on the further improvement of PbS CQDSCs and/or other types of solar cells.
Scientific journal, English

Optical absorption, charge separation and recombination dynamics in Sn/Pb cocktail perovskite solar cells and their relationships to photovoltaic performances
Qing Shen; Yuhei Ogomi; Jin Chang; Taro Toyoda; Kosei Fujiwara; Kenji Yoshino; Koki Sato; Kohei Yamazaki; Masaya Akimoto; Yuki Kuga; Kenji Katayama; Shuzi Hayase
JOURNAL OF MATERIALS CHEMISTRY A, ROYAL SOC CHEMISTRY, 3, 17, 9308-9316, 2015, Peer-reviwed, Invited, The interest in organometal trihalide perovskite (CH3NH3PbI3)-based solid-state hybrid solar cells has increased in recent years due to the high efficiencies achieved, with a record of over 20%, and the simple low temperature preparation method. Further improvements in the photovoltaic performance can be obtained by increasing the light harvesting in the NIR region up to 1000 nm. Recently, successful energy harvesting up to a wavelength of 1060 nm using Sn/Pb cocktail halide based perovskite materials has been achieved. However, the energy conversion efficiency of such solar cells (less than 10%) is much lower than that of CH3NH3PbI3 based solar cells, which is due to their lower open circuit voltage (V-oc) and fill factor (FF). In order to improve this, we need to have a good understanding of the key factors governing the photovoltaic performance of these solar cells, i.e., the optical absorption, the charge separation and the recombination dynamics. Therefore, for this study, we characterized the optical absorption properties, including the bandgap and the Urbach energy, clarified the photoexcited carrier recombination dynamics in Sn/Pb cocktail perovskite (CH3NH3Sn0.5Pb0.5I3) and the charge separation and recombination dynamics at each interface in TiO2/Sn/Pb perovskite/P3HT solar cells, and lastly investigated the relationships between these and the photovoltaic performance.
Scientific journal, English

Photoacoustic spectroscopy of TiO2 nanotube electrode adsorbed with CdSe quantum dots and its photovoltaic properties
Masaya Akimoto; Qing Shen; Shuji Hayase; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 53, 7, 07KB08-1-07KB08-8, Jul. 2014, Peer-reviwed, We report on the optical absorption properties and photovoltaic characteristics of nanotube (NT) TiO2 electrodes adsorbed with CdSe quantum dots (QDs), and compared them with those of nanoparticle (NP) TiO2 electrodes adsorbed with CdSe QDs. The CdSe QDs were grown directly on the TiO2 electrodes by the successive ionic layer adsorption and reaction (SILAR) method. The width of the exponential tail (E-U) of the photoacoustic (PA) spectra of the NT-TiO2 electrodes without CdSe QDs was more than 3 times lower than that of NP-TiO2. The results imply that the surface defects and disorder in NT-TiO2 are fewer than those in NP-TiO2. From the photovoltaic characteristics, we found that the shunt resistance (R-sh) of the CdSe-QD-sensitized NT-TiO2 solar cell was much higher than that of the CdSe-QD-sensitized NP-TiO2 solar cell, indicating the surface defects and disorder in NT-TiO2 were fewer than those in NP-TiO2. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English

Effect of TiO2 Crystal Orientation on the Adsorption of CdSe Quantum Dots for Photosensitization Studied by the Photoacoustic and Photoelectron Yield Methods
Taro Toyoda; Witoon Yindeesuk; Keita Kamiyama; Shuzi Hayase; Qing Shen
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 118, 30, 16680-16687, Jul. 2014, Peer-reviwed, We describe the adsorption and growth of CdSe quantum dots (QDs) on single crystals of rutile TiO2 with different crystal orientations. We used atomic force microscopy (AFM) to characterize the morphology of the QDs and photoacoustic (PA) spectroscopy to measure the optical absorption. Photoelectron yield (PY) spectroscopy was applied to characterize the valence band maximum (VBM) of the single crystal TiO2. The AFM images and the absorbance measurements showed that the number of CdSe QDs grown on the (111) surface was larger than those grown on the (110) and (001) surfaces. The absorbance measurements showed that the adsorption becomes linearly proportional to the adsorption time. However, the rate of adsorption is different for each crystal orientation. The crystals grow higher on (111) surfaces than on (110) and (001) surfaces. The position of the VBM for the (111) surface is higher than those for the (110) and (001) surfaces. Hence, the formation and growth of CdSe QDs on (111) surfaces is more active than on the other orientations. The increase in the average diameter of CdSe QDs with adsorption time is independent of the crystal orientation. Although the growth rate of CdSe QDs on (001) surfaces is lower than on (110) and (111) surfaces, the crystal quality is better on the former.
Scientific journal, English

All-Solid Perovskite Solar Cells with HOCO-R-NH3+I- Anchor-Group Inserted between Porous Titania and Perovskite
Yuhei Ogomi; Atsushi Morita; Shota Tsukamoto; Takahiro Saitho; Qing Shen; Taro Toyoda; Kenji Yoshino; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 118, 30, 16651-16659, Jul. 2014, Peer-reviwed, HOCO-R-NH3+I monolayer working as an anchor for perovskite (CH3NH3PbI3 (abbreviation: PEROVI3)) was inserted between the surface of porous metal oxide (titania or alumina) and the PEROVI3. Power conversion efficiency (PCE) of PEROVI3 solar cells increased from 8% to 10% after the HOCO-R-NH3+I- monolayer was inserted. Moreover, PCE of 12% was achieved for cells fabricated at optimized conditions. This increase in the efficiency was explained by retardation of charge recombination, and better PEROVI3 crystal growth, which improves PEROVI3 network on these porous metal oxides. It was proved that PEROVI3 crystal growth can be controlled by HOCO-R-NH3+I- on these porous metal oxides.
Scientific journal, English

Photoacoustic spectroscopy of TiO
Akimoto Masaya; Shen Qing; Hayase Shuji; Toyoda Taro
Jpn. J. Appl. Phys., Institute of Physics, 53, 7, 07KB08, 17 Jun. 2014
English

High-Efficiency "Green" Quantum Dot Solar Cells
Zhenxiao Pan; Ivan Mora-Sero; Qing Shen; Hua Zhang; Yan Li; Ke Zhao; Jin Wang; Xinhua Zhong; Juan Bisquert
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, AMER CHEMICAL SOC, 136, 25, 9203-9210, Jun. 2014, Peer-reviwed, Semiconductor quantum dots (QDs) are extremely interesting materials for the development of photovoltaic devices, but currently the present the drawback is that the most efficient devices have been prepared with toxic heavy metals of Cd or Pb. Solar cells based on "green" QDs-totally free of Cd or Pb-present a modest efficiency of 2.52%. Herein we achieve effective surface passivation of the ternary CuInS2 (CIS) QDs that provides high photovoltaic quality core/shell CIS/ZnS (CIS-Z) QDs, leading to the development of high-efficiency green QD solar cells that surpass the performance of those based on the toxic cadmium and lead chalcogenides QDs. Using wide absorption range QDs, CIS-Z-based quantum dot sensitized solar cell (QDSC) configuration with high QD loading and with the benefit of the recombination reduction with type-I core/shell structure, we boost the power conversion efficiency of Cd- and Pb-free QDSC to a record of 7.04% (with certified efficiency of 6.66%) under AM 1.5G one sun irradiation. This efficiency is the best performance to date for QDSCs and also demonstrates that it is possible to obtain comparable or even better photovoltaic performance from green CIS QDs to the toxic cadmium and lead chalcogenides QDs.
Scientific journal, English

Control of Charge Dynamics through a Charge-Separation Interface for All-Solid Perovskite-Sensitized Solar Cells
Yuhei Ogomi; Kenji Kukihara; Shen Qing; Taro Toyoda; Kenji Yoshino; Shyam Pandey; Hisayo Momose; Shuzi Hayase
CHEMPHYSCHEM, WILEY-V C H VERLAG GMBH, 15, 6, 1062-1069, Apr. 2014, Peer-reviwed, The relationship between the structure of the charge-separation interface and the photovoltaic performance of all-solid dye-sensitized solar cells is reported. This cell is composed of porous a TiO2/perovskite (CH3NH3PbIxCl3-x)/p-type organic conductor. The porous titania layer was passivated with Al2O3 or Y2O3 to remove surface traps of the porous titania layer. Both passivations were effective in increasing the efficiency of the solar cell. Especially, the effect of Y2O3 passivation was remarkable. After passivation, the efficiency increased from 6.59 to 7.5%. The increase in the efficiency was discussed in terms of the electron lifetime in TiO2, the thermally stimulated current, the measurement of the microwave refractive carrier lifetime, and transition absorption spectroscopy. It was proven that surface passivation resulted in retardation of charge recombination between the electrons in the porous titania layers and the holes in the p-type organic conductors.
Scientific journal, English

CH3NH3SnxPb(1-x)I3 Perovskite Solar Cells Covering up to 1060 nm
Yuhei Ogomi; Atsushi Morita; Syota Tsukamoto; Takahiro Saitho; Naotaka Fujikawa; Qing Shen; Taro Toyoda; Kenji Yoshino; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 5, 6, 1004-1011, Mar. 2014, Peer-reviwed, We report photovoltaic performances of all-solid state Sn/Pb halide-based perovskite solar cells. The cell has the following composition: F-doped SnO2 layered glass/compact titania layer/porous titania layer/CH3NH3SnxPb(1-x)I3/regioregular poly(3-hexylthiophene-2,5-diyl). Sn halide perovskite itself did not show photovoltaic properties. Photovoltaic properties were observed when PbI2 was added in SnI2. The best performance was obtained by using CH3NH3Sn0.5Pb0.5I3 perovskite. 4.18% efficiency with open circuit voltage 0.42 V, fill factor 0.50, and short circuit current 20.04 mA/cm(2) are reported. The edge of the incident photon to current efficiency curve reached 1060 nm, which was 260 nm red-shifted compared with that of CH3NH3PbI3 perovskite solar cells.
Scientific journal, English

Light trapping considerations in self-assembled ZnO nanorod arrays for quantum dot sensitized solar cells
Chun Yan Luan; King Tai Cheung; Yishu Foo; Li Yu Yu; Qing Shen; Juan Antonio Zapien
OXIDE-BASED MATERIALS AND DEVICES V, SPIE-INT SOC OPTICAL ENGINEERING, 8987, 2014, Peer-reviwed, We study light absorption in ZnO nanorod arrays sensitized with CdSe quantum dots as one of the factors affecting solar cell performance in need of improvement given their current performance well below expectations. Light trapping in nanorod arrays (NRAs) as it relates to array density and length as well as quantum dot (QD) loading is studied using the Finite Difference Time Domain model. It is shown that light absorption in such solar cell architecture is a sensitive function of the morphological dimensions and that a higher NRA density does not necessarily correspond to large absorption in the solar cell. Instead, light trapping efficiency depends significantly on the array density, QD axial distribution and refractive index contrast between NR and QDs thus suggesting strategies for improved quantum dot solar cell (QDSC) fabrication. In addition, we present experimental data showing dramatic improvement in photo conversion efficiency performance for relatively short ZnO NRAs (similar to 1 mu m) of low NRA density, but whose efficiency improvement can not be solely explained based on our current light trapping estimates from the numerical simulations.
International conference proceedings, English

Sn halide based perovskite sensitized solar cells covering up to 1060 nm
Yuhei Ogomi; Atsushi Morita; Shota Tsukamoto; Takahiro Saito; Naotaka Fujikawa; Shen Qing; Taro Toyoda; Kenji Yoshino; Shyam S. Pandey; Tingli Ma; Shuzi Shuzi Hayase
ORGANIC PHOTOVOLTAICS XV, SPIE-INT SOC OPTICAL ENGINEERING, 9184, 2014, Peer-reviwed, We have succeeded in harvesting energy in the NIR region by using Sn halide based perovskite materials. The cell has the following composition: F-doped SnO2 layered glass/compact titania layer/porous titania layer/Sn based perovskite material/ p-type polymer semiconductor. The edge of the incident photon to current efficiency (IPCE) edge reached 1040 nm. 4.18 % efficiency with open circuit efficiency (Voc): 0.42 V, fill factor (FF): 0.5, short circuit current (Jsc): 20.04 mA/cm2 is reported.
International conference proceedings, English

Ex Situ CdSe Quantum Dot-Sensitized Solar Cells Employing Inorganic Ligand Exchange To Boost Efficiency
Feng Liu; Jun Zhu; Junfeng Wei; Yi Li; Linhua Hu; Yang Huang; Oshima Takuya; Qing Shen; Taro Toyoda; Bing Zhang; Jianxi Yao; Songyuan Dai
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 118, 1, 214-222, Jan. 2014, Peer-reviwed, We present an effective way to boost the as-synthesized CdSe quantum dot-sensitized solar cells (QDSSCs) performance by introducing an inorganic ligand exchange strategy into this traditional system. Inorganic ligand exchange, to the best of our knowledge, is designed for the first time for CdSe-based QDSSCs, and it features low-cost, easy operation, and repeatable process. The route involves the direct deposition of the CdSe quantum dots (QDs), which were initially capped with trioctylphosphine (TOP) ligands onto mesoporous TiO2 nanocrystalline electrodes and followed by a post-treatment of the sensitized photoanode films with sulfur ions (S2-) solution. Here, changes in surface chemical status of CdSe QDs during the inorganic ligand exchange process and the influence of ligand exchange on the electron's ultralfast transfer between nanoparticles were investigated through XPS and femtosecond transient grating techniques,. respectively. With the inorganic ligand passivated CdSe QDs, the QDSSCs exhibited a power conversion efficiency of 3.17% (AM1.5G, 100 mW/cm(2)), 65% higher than that of the organic ligands capped QDSSCs.
Scientific journal, English

All-solid Sn/Pb halide perovskite sensitized solar cells
Yuhei Ogomi; Atsushi Morital; Shota Tsukamotol; Takahiro Saithol; Naotaka Fujikawal; Shen Qing; Taro Toyoda; Kenji Yoshino; Shyam S. Pandeyl; Tingli Mal; Shuzi Hayase
2014 IEEE 40TH PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC), IEEE, 147-151, 2014, We have succeeded in harvesting energy in near infrared region (NIR) by using air stable Sn doped metal halide perovskite materials. The edge of the incident photon to current efficiency (IPCE) edge reached 1060 nm. 4.18 % efficiency is reported. The photovoltaic performance was compared with Pb halide perovskite solar cell with 14.4% efficiency, leading to the conclusion that the low FF and Voc are associated with low shunt resistance (Rsh). One of the methods to suppress the charge recombination will be reported, which includes passivation of porous titania surface states with aminoacid HI salts. The relationship among the surface states of titaniaor alumina, and crystallinity of the perovskites induced by surface passivation molecules, and photovoltaic performances are discussed.
International conference proceedings, English

Effect of electrolyte constituents on the motion of ionic species and recombination kinetics in dye-sensitized solar cells
Shota Kuwahara; Soichiro Taya; Naoya Osada; Qing Shen; Taro Toyoda; Kenji Katayama
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 16, 11, 5242-5249, 2014, Peer-reviwed, The dynamic motion of ions in electrolyte solutions and its effect on recombination was investigated by the heterodyne transient grating method in addition to transient absorption and transient photocurrent methods in dye sensitized solar cells. Realignment of ionic species at the electrode/electrolyte interface was observed after the electron injection in TiO2 on the order of ms. The process was affected by the total quantity of ionic species as well as cation species in the electrolyte. The recombination processes of the electrons were also affected by the constituents; the probability of the electron-electrolyte recombination decreased with decrease in I-2 concentration; the dominant recombination process changed from the electron-electrolyte to the electron-dye recombination by decreasing I- concentration. It is concluded that sufficient I- is necessary for the suppression of the electron-dye recombination and that sufficient I-2 is necessary for an efficient redox cycle, while low concentration of I-3(-) ions at the electrolyte/TiO2 interface is preferable to suppress the electron-electrolyte recombination. The effect of the cation size in an electrolyte solution on the charge dynamics was also investigated, and it was revealed that the steric hindrance of cations changed the penetration of ionic species into the nanoporous dye/TiO2 electrode, causing a change in the electrostatic properties at the interface. The cation dependence indicated that the presence of large-sized cations suppressed the electron-electrolyte recombination by disturbing the approach of I-3(-) paired with the cations.
Scientific journal, English

Photoexcited carrier dynamics of double-layered CdS/CdSe quantum dot sensitized solar cells measured by heterodyne transient grating and transient absorption methods
N. Osada; T. Oshima; S. Kuwahara; T. Toyoda; Q. Shen; K. Katayama
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 16, 12, 5774-5778, 2014, Peer-reviwed, The charge dynamics in the double-layered quantum dot sensitized solar cell (QDSSC) was studied to clarify the reason why the cell performance was much improved by a double-layer coating, by using the heterodyne transient grating (HD-TG) and transient absorption methods, based on a previous study for a conventional QDSSC (N. Maeda et al., Phys. Chem. Chem. Phys., 2013, 15, 11006.) In the double-layered QDSSC, the layer order of CdS and CdSe affected the cell performance. When CdS is in between TiO2 and CdSe, the conversion efficiency was enhanced by 70%, while it was lowered by 50% in the opposite order. From the information on charge dynamics, it was found that electrons were efficiently injected to TiO2 by appropriate band alignment of CdS and CdSe, while only a part of the electrons were transferred to the TiO2 when the layer order was opposite. Furthermore, the reverse electron transfer does not matter for the conversion efficiency, because the process increased even for the appropriate layer order.
Scientific journal, English

Role of lithium and co-existing cations in electrolyte to improve performance of dye-sensitized solar cells
Soichiro Taya; Shota Kuwahara; Qing Shen; Taro Toyoda; Kenji Katayama
RSC ADVANCES, ROYAL SOC CHEMISTRY, 4, 41, 21517-21520, 2014, Peer-reviwed, The performance of dye-sensitized solar cells (DSSCs) with an electrolyte including mixed cations was evaluated, and the relevant carrier dynamics were investigated by the heterodyne transient grating method. The performance of the DSSCs showed maximum conversion efficiency for an Li+ cation ratio of 75% with 25% other cations.
Scientific journal, English

Multiple exciton generation in cluster-free alloy CdxHg1-xTe colloidal quantum dots synthesized in water
Stephen V. Kershaw; Sergii Kalytchuk; Olga Zhovtiuk; Qing Shen; Takuya Oshima; Witoon Yindeesuk; Taro Toyoda; Andrey L. Rogach
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 16, 47, 25710-25722, 2014, Peer-reviwed, Invited, A number of different composition CdxHg1-xTe alloy quantum dots have been synthesized using a modified aqueous synthesis and ion exchange method. The benefits of good stoichiometric control and high emission quantum yield were retained whilst also ensuring that the tendency to form gel-like clusters and adsorb excess cations in the stabilizing ligand shells was mitigated using a sequestering method to remove excess ionic material during and after the synthesis. This was highly desirable for ultrafast carrier dynamics measurements, avoiding strong photocharging effects which may mask fundamental carrier signals. Transient grating measurements revealed a composition dependent carrier multiplication process which competes with phonon mediated carrier cooling to deplete the initial hot carrier population. The interplay between these two mechanisms is strongly dependent on the electron effective mass which in these alloys has a marked composition dependence and may be considerably lower than the hole effective mass. For a composition x = 0.52 we measured a maximum carrier multiplication quantum yield of 199 +/- 19% with pump photon energy 3 times the bandgap energy, E-g, whilst the threshold energy is calculated to be just 2.15E(g). There is some evidence to suggest an impact ionization process analogous to the inverse Auger S mechanism seen in bulk CdxHg1-xTe.
Scientific journal, English

Charge transfer and recombination at the metal oxide/CH3NH3PbClI2/spiro-OMeTAD interfaces: uncovering the detailed mechanism behind high efficiency solar cells
Qing Shen; Yuhei Ogomi; Jin Chang; Syota Tsukamoto; Kenji Kukihara; Takuya Oshima; Naoya Osada; Kenji Yoshino; Kenji Katayama; Taro Toyoda; Shuzi Hayase
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 16, 37, 19984-19992, 2014, Peer-reviwed, In recent years, organometal halide perovskite-based solid-state hybrid solar cells have attracted unexpected increasing interest because of their high efficiency (the record power conversion efficiency has been reported to be over 15%) and low fabrication cost. It has been accepted that the high efficiency was mainly attributed to the strong optical absorption (absorption coefficient: 15 000 cm(-1) at 550 nm) over a broader range (up to 800 nm) and the long lifetimes of photoexcited charge carriers (in the order of 10 ns - a few 100 ns) of the perovskite absorbers. However, much of the fundamental photophysical properties of perovskite relating to the high photovoltaic performance are remained to be investigated. The charge separation and recombination processes at the material interfaces are particularly important for solar cell performances. To better understand the high efficiency of perovskite solar cells, we systematically investigated the charge separation (electron and hole injection) and charge recombination dynamics of CH3NH3PbClI2 hybrid solar cells employing TiO2 nanostructures as the electron transfer material (ETM) and spiro-OMeTAD as the hole transfer material (HTM). The measurements were carried out using transient absorption (TA) techniques on a time scale from sub-picoseconds to milliseconds. We clarified the timescales of electron injection, hole injection, and recombination processes in TiO2/CH3NH3PbClI2/spiro-OMeTAD solar cells. Charge separation and collection efficiency of the perovskite-based solar cells were discussed. In addition, the effect of TiO2 size on the charge separation and recombination dynamics was also investigated. It was found that all TiO2-based perovskite solar cells possessed similar charge separation processes, but quite different recombination dynamics. Our results indicate that charge recombination was crucial to the performance of the perovskite solar cells, which could be effectively suppressed through optimising nanostructured TiO2 films and surface passivation, thus pushing these cells to even higher efficiency.
Scientific journal, English

Influence of linker molecules on interfacial electron transfer and photovoltaic performance of quantum dot sensitized solar cells
Junwei Yang; Takuya Oshima; Witoon Yindeesuk; Zhenxiao Pan; Xinhua Zhong; Qing Shen
JOURNAL OF MATERIALS CHEMISTRY A, ROYAL SOC CHEMISTRY, 2, 48, 20882-20888, 2014, Peer-reviwed, The charge transfer rate between QD sensitizer/TiO2 interfaces in quantum dot sensitized solar cells (QDSCs) is one of the most important criteria determining the photovoltaic performance of cells. To investigate the influence of linker molecules on the electron transfer rate at the QD-linker-TiO2 interface and the final performance of the resultant QDSCs, colloidal QDs capped with thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), and cysteine (Cys), which also serve as molecular linkers between QDs and TiO2 nanoparticles, were self-assembled on a TiO2 mesoporous film electrode from the corresponding QD aqueous dispersions. The influence of the studied linker molecules (TGA, MPA, and Cys) on the loading amount of QD sensitizer on the TiO2 mesoporous film, the electron injection rate from QDs to the TiO2 matrix, the incident photon to charge carrier generation efficiency (IPCE), and the corresponding photovoltaic performance of the resultant QDSCs were systematically studied. CdSe and CdSexTe(1-x) QD sensitized solar cells were selected as a model cell to evaluate the influence of the adopted linker molecules. Under AM 1.5G full one sun intensity illumination, the power conversion efficiency (PCE) of TGA-capped QDs (5.40% for CdSe, and 6.68% for CdSexTe(1-x)) was 7-14% greater than those of MPA- and Cys-capped QDs. Similarly, the absorbed photon-to-current efficiency was 8-13% greater. These differences arise from linker molecule-dependent variations of the electron-injection rate. Transient grating measurements indicate that the electron injection rate constant from TGA-capped CdSe (8.0 x 10(9) s(-1)) was greater than from MPA- and Cys-capped CdSe (2.6-2.9 x 10(9) s(-1)). Thus, TGA-capped QDs are readily attached to the TiO2 substrate and exhibit better electronic properties and desirable electron-transfer rate, and therefore bring forward better photovoltaic performance in the resultant solar cells.
Scientific journal, English

Optical absorption of CdSe quantum dots on electrodes with different morphology
Witoon Yindeesuk; Qing Shen; Shuzi Hayase; Taro Toyoda
AIP ADVANCES, AMER INST PHYSICS, 3, 10, Oct. 2013, We have studied the optical absorption of CdSe quantum dots (QDs) adsorbed on inverse opal TiO2 (IO-TiO2) and nanoparticulate TiO2 (NP-TiO2) electrodes using photoacoustic (PA) measurements. The CdSe QDs were grown directly on IO-TiO2 and NP-TiO2 electrodes by a successive ionic layer adsorption and reaction (SILAR) method with different numbers of cycles. The average diameter of the QDs was estimated by applying an effective mass approximation to the PA spectra. The increasing size of the QDs with increasing number of cycles was confirmed by a redshift in the optical absorption spectrum. The average diameter of the CdSe QDs on the IO-TiO2 electrodes was similar to that on the NP-TiO2 ones, indicating that growth is independent of morphology. However, there were more CdSe QDs on the NP-TiO2 electrodes than on the IO-TiO2 ones, indicating that there were different amounts of active sites on each type of electrode. In addition, the Urbach parameter of the exponential optical absorption tail was also estimated from the PA spectrum. The Urbach parameter of CdSe QDs on IO-TiO2 electrodes was higher than that on NP-TiO2 ones, indicating that CdSe QDs on IO-TiO2 electrodes are more disordered states than those on NP-TiO2 electrodes. The Urbach parameter decreases in both cases with the increase of SILAR cycles, and it tended to move toward a constant value. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Scientific journal, English

Optical absorption of CdSe quantum dots on electrodes with different morphology
Witoon Yindeesuk; Qing Shen; Shuzi Hayase; Taro Toyoda
AIP ADVANCES, AMER INST PHYSICS, 3, 10, 1021115-1021119, Oct. 2013, Peer-reviwed, We have studied the optical absorption of CdSe quantum dots (QDs) adsorbed on inverse opal TiO2 (IO-TiO2) and nanoparticulate TiO2 (NP-TiO2) electrodes using photoacoustic (PA) measurements. The CdSe QDs were grown directly on IO-TiO2 and NP-TiO2 electrodes by a successive ionic layer adsorption and reaction (SILAR) method with different numbers of cycles. The average diameter of the QDs was estimated by applying an effective mass approximation to the PA spectra. The increasing size of the QDs with increasing number of cycles was confirmed by a redshift in the optical absorption spectrum. The average diameter of the CdSe QDs on the IO-TiO2 electrodes was similar to that on the NP-TiO2 ones, indicating that growth is independent of morphology. However, there were more CdSe QDs on the NP-TiO2 electrodes than on the IO-TiO2 ones, indicating that there were different amounts of active sites on each type of electrode. In addition, the Urbach parameter of the exponential optical absorption tail was also estimated from the PA spectrum. The Urbach parameter of CdSe QDs on IO-TiO2 electrodes was higher than that on NP-TiO2 ones, indicating that CdSe QDs on IO-TiO2 electrodes are more disordered states than those on NP-TiO2 electrodes. The Urbach parameter decreases in both cases with the increase of SILAR cycles, and it tended to move toward a constant value. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Scientific journal, English

Ultrafast characterization of the electron injection from CdSe quantum dots and dye N719 co-sensitizers into TiO2 using sulfide based ionic liquid for enhanced long term stability
Victoria Gonzalez-Pedro; Qing Shen; Vasko Jovanovski; Sixto Gimenez; Ramon Tena-Zaera; Taro Toyoda; Ivan Mora-Sero
ELECTROCHIMICA ACTA, PERGAMON-ELSEVIER SCIENCE LTD, 100, 35-43, Jun. 2013, Peer-reviwed, Combination of inorganic quantum dots (QDs) and organic/metallorganic dyes as supracollectors nanocomposites could have an important role on the development of efficient photovoltaic devices based on the synergistic action of the hybrid-sensitizers. Here we have analyzed the combination of CdSe QDs and polypyridil N719 ruthenium dye. By ultrafast transient grating measurements we show that the cascading structure (type 11) of this system takes full advantage to augment electron injection and hole regeneration efficiencies. Co-sensitized TiO2 electrodes lead to an improvement in charge separation, increasing the number of injected electrons from the CdSe QDs to the TiO2 as a consequence of the suppression of back reaction, by fast regeneration of holes by the dye action. The potentiality of this supracollector system has been verified in a complete cell configuration. Sulfide/polysulfide based ionic liquid in which both sensitizers (QD and dye) are stable has been employed as hole conducting media. In spite of the limited efficiencies of the analyzed cells, the higher photocurrents measured for CdSe/N719 co-sensitization compared to the cells sensitized using a single sensitizer constitutes a valid proof of the concept. Impedance spectroscopy unveiled the recombination limitation of the analyzed cells. On the other hand, ionic liquid exhibits an enhanced cell stability maintaining cell efficiency after one week and keeping it at 80% after 21 days. The reported results highlight a huge potential of the synergetic combination of QD and dyes for improving solar cell performance and of novel sulfide/polysulfide ionic liquid-based electrolytes for enhancing long term stability and sustainability of QD sensitizers. (C) 2013 Elsevier Ltd. All rights reserved.
Scientific journal, English

先進理工学科における2年次専門実験（電気・電子回路実験）の準備と実施について
奥野剛史; 大家明広; 山崎典昌; 高橋光生; 早川義彦; 矢崎和幸; 和田紀子; 藁科崇; 坂本克好; Choo Cheow Keong; 永井豊; 守屋雅隆; 沈青; 島田宏; 林茂雄
電気通信大学紀要 vol25, no1 (2013.2) pp.73-78, 25, 1, 73-78, Feb. 2013, Peer-reviwed
Research institution, Japanese

High performance PbS Quantum Dot Sensitized Solar Cells exceeding 4% efficiency: the role of metal precursors in the electron injection and charge separation
Victoria Gonzalez-Pedro; Cornelia Sima; Gabriela Marzari; Pablo P. Boix; Sixto Gimenez; Qing Shen; Thomas Dittrich; Ivan Mora-Sero
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 15, 33, 13835-13843, 2013, Peer-reviwed, Here we report the preparation of high performance Quantum Dot Sensitized Solar Cells (QDSCs) based on PbS-CdS co-sensitized nanoporous TiO2 electrodes. QDs were directly grown on the TiO2 mesostructure by the Successive Ionic Layer Absorption and Reaction (SILAR) technique. This method is characterized by a fast deposition rate which involves random crystal growth and poor control of the defect states and lattice mismatch in the QDs limiting the quality of the electrodes for photovoltaic applications. In this work we demonstrate that the nature of the metallic precursor selected for SILAR has an active role in both the QD's deposition rate and the defect's distribution in the material, with important consequences for the final photovoltaic performance of the device. For this purpose, acetate and nitrate salts were selected as metallic precursors for the SILAR deposition and films with similar absorption properties and consequently with similar density of photogenerated carriers were studied. Under these conditions, ultrafast carrier dynamics and surface photovoltage spectroscopy reveal that the use of acetate precursors leads to higher injection efficiency and lower internal recombination due to contribution from defect states. This was corroborated in a complete cell configuration with films sensitized with acetate precursors, achieving unprecedented photocurrents of similar to 22 mA cm(-2) and high power conversion efficiency exceeding 4%, under full 1 sun illumination.
Scientific journal, English

Dye sensitized solar cells consisting of metallophthalocyanine axially anchored on metal oxide nanoparticles through metal-O-metal linkages-difference in photovoltaic performances between TiO2 and SnO2 electrode
B. Park; Q. Shen; Y. Ogomi; S. S. Pandey; T. Toyoda; S. Hyayse
ECS J. Solid State Sci. Technol., Vol. 2,, Q6-Q11, Jan. 2013, Peer-reviwed
Scientific journal, English

Detection of non-absorbing charge dynamics via refractive index change in dye-sensitized solar cells
Shota Kuwahara; Hiroaki Hata; Soichiro Taya; Naotaka Maeda; Qing Shen; Taro Toyoda; Kenji Katayama
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 15, 16, 5975-5981, 2013, Peer-reviwed, The carrier dynamics in dye-sensitized solar cells was investigated by using the transient grating, in addition to the transient absorption method and transient photocurrent method on the order of microseconds to seconds. The signals for the same sample were obtained under a short-circuit condition to compare the carrier dynamics via refractive index change with the transient photocurrent measurement. Optically silent carrier dynamics by transient absorption have been successfully observed via a refractive index change. The corresponding signal components were originated from the charge dynamics at the solid/liquid interface, especially on the liquid side; rearrangement or diffusion motion of charged redox species occurred when the injected electrons were trapped at the TiO2 surface and when the electron-electrolyte recombination occurred at the interface. The assignments were confirmed from the dependence on the viscosity of the solvent and the presence of 4-tert-butyl pyridine. As the viscosity of the solvent increased, the rearrangement and the motion of the charged redox species were delayed. Since the rearrangement dynamics was changed by the presence of 4-tert-butyl pyridine, it affected not only the TiO2 surface but also the redox species close to the interface.
Scientific journal, English

Carrier dynamics in quantum-dot sensitized solar cells measured by transient grating and transient absorption methods
Naotaka Maeda; Hiroaki Hata; Naoya Osada; Qing Shen; Taro Toyoda; Shota Kuwahara; Kenji Katayama
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 15, 26, 11006-11013, 2013, Peer-reviwed, Carrier dynamics in quantum-dot sensitized solar cells (QDSSCs) was clarified by combining the information obtained by the heterodyne transient grating (HD-TG), transient absorption (TA) and transient photocurrent (TP) measurements under the short circuit conditions in the time range from microseconds to seconds. The HD-TG signal is sensitive to the ionic species at the electrode/electrolyte interface, and the electrons in the titanium oxide layer injected from quantum dots (QDs) were monitored by the TA signal, and the photocurrent as a final output was monitored by the TP signal. By using the compensating information, the whole picture of the charge dynamics was obtained in the time region after the initial electron injection from QDs into the titanium oxide layer. In the former part of this paper, the assignment of the responses for each measurement was clarified based on the previous paper on dye sensitized solar cells (S. Kuwahara, et al. Phys. Chem. Chem. Phys., 2013, 15(16), 5975-5981). In the latter part, the effect of the device parameters for actual QDSSCs, such as electrolyte concentrations, and coating times of surface passivation of QDs were investigated.
Scientific journal, English

Huge suppression of charge recombination in P3HT-ZnO organic-inorganic hybrid solar cells by locating dyes at the ZnO/P3HT interfaces
Qing Shen; Yuhei Ogomi; Sandeep K. Das; Shyam S. Pandey; Kenji Yoshino; Kenji Katayama; Hisayo Momose; Taro Toyoda; Shuzi Hayase
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 15, 34, 14370-14376, 2013, Peer-reviwed, The charge separation and charge recombination dynamics in P3HT-ZnO and P3HT-dye-ZnO bulk heterojunction organic-inorganic hybrid solar cells (OIHSCs) prepared by a one-pot method were studied using a transient absorption (TA) method, both for optical absorption of P3HT in the visible region and for optical absorption of SQ36 in the NIR region. In the case of P3HT-ZnO, the charge separation was very fast, occurring within 1 ps. On the other hand, high charge recombination between electrons in the surface states and/or the conduction band of ZnO and holes in P3HT was observed. In the case of P3HT-dye-ZnO, we found that the charge recombination could be greatly suppressed by locating the dye at the P3HT/ZnO interfaces while maintaining a fast charge separation rate (a few ps to 10 ps). Our findings provide one methodology for the design of OIHSCs for improving their conversion efficiency, which is to position the dye at the appropriate BHJ interfaces.
Scientific journal, English

Photovoltaics and photoexcited carrier dynamics of double-layered CdS/CdSe quantum dot-sensitized solar cells
T. Toyoda; Y. Onishi; K. Katayama; T. Sawada; S. Hayase; Q. Shen
J. Mater. Sci. Eng. A&B, 3, 601-608, 2013, Peer-reviwed
Scientific journal, English

Relationship between the catalytic activity of Pt/alumina and the relaxation process of the photoexcited electrons
J. Ito; Y. Hanaki; Q. Shen; T. Toyoda
Appl. Surf. Sci., 268, 230-235, Nov. 2012, Peer-reviwed
Scientific journal, English

Quantum-Dot-Sensitized Solar Cells: Effect of Nanostructured TiO2 Morphologies on Photovoltaic Properties
Taro Toyoda; Qing Shen
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 3, 14, 1885-1893, Jul. 2012, Peer-reviwed, There is a great deal of interest in dye-sensitized solar cells (DSCs) fabricated with nanostructured TiO2 electrodes. Many different dye molecules have been designed and synthesized to achieve high photovoltaic conversion efficiency. Recently, as an alternative to organic dyes, semiconductor quantum dots (QDs) have been studied for their light-harvesting capability compared with other sensitizers. Accordingly, an attractive configuration to exploit these fascinating properties of semiconductor QDs is the quantum-dot-sensitized solar cell (QDSC) due to their high photoactivity, process realization, and low cost of production. The morphology of TiO2 electrodes included with surface orientation is important for satisfactory assembly of QDSCs in order to improve the efficiency. Breakthroughs allowing an increase in efficiency will advance on two areas of electrode morphology control, namely, (A) TiO2 nanotube electrodes and (B) inverse opal TiO2 electrodes.
Scientific journal, English

Effect of nanostructured electrode architecture and semiconductor deposition strategy on the photovoltaic performance of quantum dot sensitized solar cells
Mahmoud Samadpour; Sixto Gimenez; Pablo P. Boix; Qing Shen; Mauricio E. Calvo; Nima Taghavinia; Azam Iraji Zad; Taro Toyoda; Hernan Miguez; Ivan Mora-Sero
ELECTROCHIMICA ACTA, PERGAMON-ELSEVIER SCIENCE LTD, 75, 139-147, Jul. 2012, Peer-reviwed, Here we analyze the effect of two relevant aspects related to cell preparation on quantum dot sensitized solar cells (QDSCs) performance: the architecture of the TiO2 nanostructured electrode and the growth method of quantum dots (QD). Particular attention is given to the effect on the photovoltage. V-oc, since this parameter conveys the main current limitation of QDSCs. We have analyzed electrodes directly sensitized with CdSe QDs grown by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR). We have carried out a systematic study comprising structural, optical, photophysical and photoelectrochemical characterization in order to correlate the material properties of the photoanodes with the functional performance of the manufactured QDSCs. The results show that the correspondence between photovoltaic conversion efficiency and the surface area of TiO2 depends on the QDs deposition method. Higher V-oc values are systematically obtained for TiO2 morphologies with decreasing surface area and for cells using CBD growth method. This is systematically correlated to a higher recombination resistance of CBD sensitized electrodes. Electron injection kinetics from QDs into TiO2 also depends on both the TiO2 structure and the QDs deposition method, being systematically faster for CBD. Only for electrodes prepared with small TiO2 nanoparticles SILAR method presents better performance than CBD, indicating that the small pore size disturb the CBD growth method. These results have important implications for the optimization of QDSCs. (C) 2012 Elsevier Ltd. All rights reserved.
Scientific journal, English

Ultrafast carrier dynamics in PbS quantum dots
Qing Shen; Kenji Katayama; Tsuguo Sawada; Sojiro Hachiya; Taro Toyoda
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 542, 89-93, Jul. 2012, Peer-reviwed, Ultrafast carrier dynamics in PbS quantum dots (QDs) is characterized using a transient grating technique. In addition to an initial peak, a new peak appears at about 3 ps when the excitation photon energy is greater than 2.7E(g) (E-g: band gap between LUMO and HOMO in the QDs). The first peak is considered to be related to hot carriers and the second one is believed to result from multiple exciton generation (MEG). We found that MEG began in as fast as 200 fs and complete around 3 ps. We succeeded in observing the dynamics of MEG occurrence in PbS QDs. (C) 2012 Elsevier B. V. All rights reserved.
Scientific journal, English

Effect of ZnS coatings on the enhancement of the photovoltaic properties of PbS quantum dot-sensitized solar cells
Sojiro Hachiya; Qing Shen; Taro Toyoda
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 111, 10, 104315 - 104315-4, May 2012, Peer-reviwed, We have studied the effect of ZnS coatings on the photovoltaic properties of PbS quantum dot-sensitized solar cells (QDSSCs). PbS QDs are suitable materials for QDSSCs because of their wide tight absorption range; however, their high photochemical reactivity is a problem that needs to be overcome for solar cell applications. In this paper, a ZnS passivation layer was applied to PbS QDs adsorbed onto electrodes using a successive ionic layer adsorption and reaction (SILAR) method for different numbers of cycles in both aqueous and methanol solutions. It was demonstrated that, as a consequence of the low viscosity of methanol, the performance of the PbS QDSSCs was greatly enhanced when a methanol, rather than aqueous, solution was used in the SILAR method. The optical absorption properties of PbS QDs adsorbed on TiO2 electrodes with or without ZnS surface passivation were studied. An increase in size of the PbS QDs after coating with ZnS was confirmed by a red shift in the optical absorption spectra measured using photoacoustic spectroscopy. The photovoltaic properties of a sandwich structure of PbS QDSSCs were studied under "one sun" illumination using a polysulfide (S/S2-) redox system as the electrolyte and Cu2S on brass as the counter electrode. The short-circuit current density dramatically increased from 0.50 mA/cm(2) to 11.2 mA/cm(2) after the electrodes were modified with the ZnS coating. The maximum conversion efficiency that was achieved for PbS QDSSCs with a ZnS coating under one sun illumination was 1.92%. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4720468]
Scientific journal, English

Characterization of Photoexcited Carriers and Thermal Properties of Nanoparticulate TiO2 Film Using Heterodyne Transient Grating Method
Hiroaki Hata; Kenji Katayama; Qing Shen; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 51, 4, 042601, Apr. 2012, Peer-reviwed, Diffusion of photoexcited carriers and the subsequent thermal diffusion by photoexcitation of a nanoparticulate TiO2 thin film were observed by the heterodyne transient grating (HD-TG) method. The observed HD-TG signal showed that the photoexcited carriers were generated inhomogeneously in the depth direction and they diffused both in the depth and parallel directions of the film. The diffusion processes were analyzed using a two-dimensional diffusion model. The thermal profile generated by the relaxation of the photoexcited carriers was treated by the same model. It was found that the effective diffusivities of the photoexcited carriers and heat decreased as the size of the nanoparticles in the film increased. It is suggested that the transport properties of the photoexcited carriers and heat are dominated by the inter-particulate resistance. (C) 2012 The Japan Society of Applied Physics
Scientific journal, English

Semiconductor quantum dot-sensitized solar cells employing TiO2 nanostructured photoanodes with different morphologies
Qing Shen; Taro Toyoda
Quantum Dot Devices, Springer New York, 317-350, 01 Jan. 2012, Peer-reviwed, CdSe quantum dot (QD)-sensitized solar cells (QDSCs) were synthesized by adsorbing CdSe QDs onto TiO2 nanostructured electrodes with different morphologies, i.e., nanoparticles, nanotubes, and inverse opals. The optical absorption, photoelectrochemical, and photovoltaic properties of the QDSCs were characterized and the dependences of these properties on the QD deposition time and the TiO2 nanostructure are discussed. To improve the photovoltaic performance of the CdSe QDSCs, surface passivation with a ZnS coating was introduced and Cu2S counter electrodes were applied. All aspects of the photovoltaic performance, including the short-circuit photocurrent density, open-circuit voltage, fill factor, and efficiency, were found to be significantly improved by the surface modification with ZnS. For the counter electrode, the Cu2S electrode was demonstrated to be more efficient than platinum against the polysulfide electrolytes usually used as redox couples in CdSe QDSCs. Moreover, CdS QD adsorption on the TiO2 electrodes prior to CdSe QD adsorption also resulted in better solar cell performance. In addition, we found that the morphology of the TiO2 electrodes had a great influence on the photovoltaic properties of the QDSCs. Finally, a power conversion efficiency as high as 4.9% was achieved for a combined CdS/CdSe QDSC under solar illumination of 100 mW/cm2.
In book, English

Multiple electron injection dynamics in linearly-linked two dye co-sensitized nanocrystalline metal oxide electrodes for dye-sensitized solar cells
Qing Shen; Yuhei Ogomi; Byung-wook Park; Takafumi Inoue; Shyam S. Pandey; Akari Miyamoto; Shinsuke Fujita; Kenji Katayama; Taro Toyoda; Shuzi Hayase
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 14, 13, 4605-4613, 2012, Peer-reviwed, Understanding the electron transfer dynamics at the interface between dye sensitizer and semiconductor nanoparticle is very important for both a fundamental study and development of dye-sensitized solar cells (DSCs), which are a potential candidate for next generation solar cells. In this study, we have characterized the ultrafast photoexcited electron dynamics in a newly produced linearly-linked two dye co-sensitized solar cell using both a transient absorption (TA) and an improved transient grating (TG) technique, in which tin(IV) 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (NcSn) and cis-diisothiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II) bis(tetrabutylammonium) (N719) are molecularly and linearly linked and are bonded to the surface of a nanocrystalline tin dioxide (SnO2) electrode by a metal-O-metal linkage (i.e. SnO2-NcSn-N719). By comparing the TA and TG kinetics of NcSn, N719, and hybrid NcSn-N719 molecules adsorbed onto both of the SnO2 and zirconium dioxide (ZrO2) nanocrystalline films, the forward and backward electron transfer dynamics in SnO2-NcSn-N719 were clarified. We found that there are two pathways for electron injection from the linearly-linked two dye molecules (NcSn-N719) to SnO2. The first is a stepwise electron injection, in which photoexcited electrons first transfer from N719 to NcSn with a transfer time of 0.95 ps and then transfer from NcSn to the conduction band (CB) of SnO2 with two timescales of 1.6 ps and 4.2 ps. The second is direct photoexcited electron transfer from N719 to the CB of SnO2 with a timescale of 20-30 ps. On the other hand, back electron transfer from SnO2 to NcSn is on a timescale of about 2 ns, which is about three orders of magnitude slower compared to the forward electron transfer from NcSn to SnO2. The back electron transfer from NcSn to N719 is on a timescale of about 40 ps, which is about one order slower compared to the forward electron transfer from N719 to NcSn. These results demonstrate that photoexcited electrons can be effectively injected into SnO2 from both of the N719 and NcSn dyes.
Scientific journal, English

Dependences of the optical absorption and photovoltaic properties of CdS quantum dot-sensitized solar cells on the CdS quantum dot adsorption time
Sojiro Hachiya; Yohei Onishi; Qing Shen; Taro Toyoda
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 110, 5, 054319-1~5, Sep. 2011, Peer-reviwed, We have studied the optical absorption properties of CdS quantum dots (QDs) adsorbed on TiO(2) electrodes and the photovoltaic properties of CdS quantum dot-sensitized solar cells (QDSSCs). CdS QDs were grown directly on a nanostructured TiO(2) surface by a chemical bath deposition method for different adsorption times from 30 min to 8 h. The growing size of CdS QDs on the TiO(2) electrodes with increasing adsorption time was confirmed by a redshift in the optical spectra, measured using photoacoustic (PA) spectroscopy. The steepness factor, which reflects the amount of disorder and the number of defects, was also estimated from the PA spectrum. The steepness factor decreased sharply at 1 h adsorption time when the CdS QDs commenced aggregating. Subsequently, the steepness factor increased for longer adsorption times, indicating that the density of surface states of the CdS QDs had decreased due to a decrease in the ratio of surface area to volume with the growth in average size. The photovoltaic properties of sandwich structure solar cells were studied under an illumination of air mass (AM) 1.5 using Cu(2)S on brass as a counter electrode and a polysulfide (S/S(2-)) redox system as the electrolyte. The maximum photovoltaic conversion efficiency obtained was 1.22%, which was for the device that had 2 h CdS adsorption. The variations in series resistance and shunt resistance were estimated from the slopes of photocurrent density-photovoltage curves near the short circuit and open circuit conditions, respectively. With increasing adsorption time, both resistances decreased until 2 h adsorption when the maximum photoconversion efficiency was observed. These results indicate that the CdS adsorption time is closely correlated with the photovoltaic properties of CdS QDSSCs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3626061]
Scientific journal, English

Multiple electron injection from dyes to titania layer for high efficiency-dye-sensitized solar cells
Byung-Wook Park; Kengo Sadamasu; Yuhei Ogomi; Akari Miyamoto; Shinsuke Fujita; Shyam S. Pandey; Qing Shen; Taro Toyoda; Shuzi Hayase
Conference Record of the IEEE Photovoltaic Specialists Conference, 001187-001191, 2011, We report two kinds of dye-sensitized solar cells where multiple electron injection mechanism is used. One is multiple electron injection consisting of linearly linked two dye molecules. Tin(IV) 2,11,20,29-tetra-tert-butyl-2,3- naphthalocyanine (NcSn) was adsorbed on a SnO 2 surface by a Sn(p)-O-Sn(n) linkage, where Sn(p) and Sn(n) stand for a Sn atom on a Sn nanoparticle surface and that at the center of NcSn, respectively. Cis-diisothiocyanato- bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II) bis(tetrabutylammonium), known as N719, was bonded to NcSn by a-Sn(n)-O-CO-linkage. The incident photon to photocurrent efficiency (IPCE) curve of the cell (DD-cell) suggested that electrons are injected from both N719 and NcSn to SnO 2 nanoparticles. The mechanism was supported by transient absorption spectra studies. The other is multiple electron injection from double titania layer (top and bottom layers). The top and bottom electrodes were stained with different dyes having different λ max. A top layer fabricated on a glass was mechanically pressed with a bottom layer fabricated on a glass cloth to fabricate an anode. The glass cloth acts as a supporter of a porous titania layer as well as a holder of electrolyte. The incident photon to current efficiency (IPCE) curve had two peaks corresponding to those of the two dyes, which demonstrates that electrons are collected from both the top and bottom layers. © 2011 IEEE.
International conference proceedings, English

A flexible photoelectrode for CdS/CdSe quantum dot-sensitized solar cells (QDSSCs)
Xiaoming Huang; Shuqing Huang; Quanxin Zhang; Xiaozhi Guo; Dongmei Li; Yanhong Luo; Qing Shen; Tara Toyoda; Qingbo Meng
CHEMICAL COMMUNICATIONS, ROYAL SOC CHEMISTRY, 47, 9, 2664-2666, 2011, Peer-reviwed, We, for the first time, prepared a flexible photoelectrode for CdS/CdSe quantum dot-sensitized solar cells (QDSSCs). A power conversion efficiency of 3.47% was achieved under AM 1.5G illumination for a sandwich type QDSSC consisting of this flexible photoelectrode, Cu(2)S counter electrode and polysulfide electrolyte between the electrodes.
Scientific journal, English

Highly efficient CdS/CdSe-sensitized solar cells controlled by the structural properties of compact porous TiO2 photoelectrodes
Quanxin Zhang; Xiaozhi Guo; Xiaoming Huang; Shuqing Huang; Dongmei Li; Yanhong Luo; Qing Shen; Taro Toyoda; Qingbo Meng
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 13, 10, 4659-4667, 2011, Peer-reviwed, At present, the photovoltaic performance of quantum dot-sensitized solar cells (QDSCs) is still much lower than conventional DSCs. Appropriate porous TiO2 photoanodes for QDSCs need to be further investigated, and optimization of the nanoparticle-based photoanodes is highly desirable as well. In this article, the influence of the structural properties of various TiO2 photoanodes on CdS/CdSe-sensitized solar cells have been systematically studied. Quantitative analyses of light-harvesting efficiency (LHE) and electron-transfer yield (Phi(ET)) for the QDSCs are investigated for the first time. It is revealed that the LHE increases in the long wavelength region with the addition of large size TiO2 particles to the transparent film. In the meantime, the balance between the light scattering and surface area also needs to be controlled, which can significantly restrain the dark current of the device. A double-layer photoanodic structure can give 4.92% of light-to-electricity conversion efficiency with a photoactive area of 0.15 cm(2)
Scientific journal, English

Uncovering the role of the ZnS treatment in the performance of quantum dot sensitized solar cells
Nestor Guijarro; Jose M. Campina; Qing Shen; Taro Toyoda; Teresa Lana-Villarreal; Roberto Gomez
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 13, 25, 12024-12032, 2011, Peer-reviwed, Among the third-generation photovoltaic devices, much attention is being paid to the so-called Quantum Dot sensitized Solar Cells (QDSCs). The currently poor performance of QDSCs seems to be efficiently patched by the ZnS treatment, increasing the output parameters of the devices, albeit its function remains rather unclear. Here new insights into the role of the ZnS layer on the QDSC performance are provided, revealing simultaneously the most active recombination pathways. Optical and AFM characterization confirms that the ZnS deposit covers, at least partially, both the TiO(2) nanoparticles and the QDs (CdSe). Photoanodes submitted to the ZnS treatment before and/or after the introduction of colloidal CdSe QDs were studied by electrochemical impedance spectroscopy, cyclic voltammetry and photocurrent experiments. The corresponding results prove that the passivation of the CdSe QDs rather than the blockage of the TiO(2) surface is the main factor leading to the efficiency improvement. In addition, a study of the ultrafast carrier dynamics by means of the Lens-Free Heterodyne Detection Transient Grating technique indicates that the ZnS shell also increases the rate of electron transfer. The dual role of the ZnS layer should be kept in mind in the quest for new modifiers for enhancing the performance of QDSCs.
Scientific journal, English

Highly efficient quasi-solid-state quantum-dot-sensitized solar cell based on hydrogel electrolytes
Zhexun Yu; Quanxin Zhang; Da Qin; Yanhong Luo; Dongmei Li; Qing Shen; Taro Toyoda; Qingbo Meng
ELECTROCHEMISTRY COMMUNICATIONS, ELSEVIER SCIENCE INC, 12, 12, 1776-1779, Dec. 2010, Chemically crosslinked polyacrylamide-based hydrogel has been first used as the polymer matrix to prepare quasi-solid-state polysulfide electrolyte for CdS/CdSe co-sensitized solar cells (QDSCs). The room temperature ionic conductivity of the gel electrolyte reaches 0.093 S.cm(-1). QDSCs based on this quasi-solid-state electrolyte can present up to 4.0% of light-to-electricity conversion efficiency. Meanwhile, the interfacial recombination at TiO2/electrolyte interface of the cell is also investigated by Electrochemical Impedance Spectroscopy (EIS). (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English

Direct Correlation between Ultrafast Injection and Photoanode Performance in Quantum Dot Sensitized Solar Cells
Nestor Guijarro; Qing Shen; Sixto Gimenez; Ivan Mora-Sero; Juan Bisquert; Teresa Lana-Villarreal; Taro Toyoda; Roberto Gomez
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 114, 50, 22352-22360, Dec. 2010, Peer-reviwed, The performance of quantum dot (QD) sensitized solar cells depends mainly on both electron injection from the QDs to the oxide matrix and recombination rates. Here we show a direct correlation between ultrafast carrier dynamics and photoanode (and complete solar cell) performance. TiO(2) nanoparticulate electrodes sensitized with colloidal CdSe QDs are prepared by either direct or linker-assisted adsorption (using cysteine, p-mercaptobenzoic acid, and mercaptopropionic acid). These electrodes are examined by ultrafast carrier dynamics, photopotential, and incident photon-to-current efficiency measurements to unravel factors controlling the efficiency in a closed solar cell. Subpicosecond time-resolved measurements are carried out by means of a lens-free heterodyne transient grating technique. In general, faster electron injection is observed for QDs directly adsorbed on TiO(2), which correlates with a better cell performance. Otherwise, increasingly faster electron injection is obtained as QD size decreases, regardless the mode of attachment. Photopotential measurements are performed in either sulfite or polysulfide solutions, in order to isolate different recombination pathways. The slowest recombination is reported for direct adsorption, whereas cysteine-mediated adsorption shows faster recombination. This study stresses the utility of ultrafast kinetic characterization in the development of efficient photoconverter devices.
Scientific journal, English

Photoacoustic and photoelectrochemical current spectra of combined CdS/CdSe quantum dots adsorbed on nanostructured TiO2 electrodes, together with photovoltaic characteristics
Taro Toyoda; Keita Oshikane; Dongmei Li; Yanhong Luo; Qingbo Meng; Qing Shen
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 108, 11, 114304-1~7, Dec. 2010, Peer-reviwed, We describe the performance of quantum dot (QD)-sensitized solar cells based on CdSe QD sensitizer on a preadsorbed layer of CdS QDs (combined CdS/CdSe QDs) together with the basic studies of optical absorption and photoeletrochemical current characteristics. It can be observed from optical absorption measurements using photoacoustic spectroscopy that the CdSe QDs on the nanostructured TiO2 electrodes preadsorbed with CdS QDs grow more rapidly during the initial adsorption process than those without preadsorption. The maximum incident photon-to-current conversion efficiency (IPCE) value of the CdSe QDs on the nanostructured TiO2 electrodes preadsorbed with CdS QDs is higher than that without preadsorption, indicating the possibilities of decreases in recombination centers, interface states, and inverse transfer rate. Short-circuit current (J(sc)) in combined CdS/CdSe QD-sensitized solar cells shows maximum with the increase in CdSe QDs adsorption times between 2 and 24 h. The other parameters, open-circuit voltage (V-oc) and fill factor, is independent of adsorption time. Therefore, the photovoltaic conversion efficiency (eta) of combined CdS/CdSe QD-sensitized solar cell shows a maximum value of 3.5%. (c) 2010 American Institute of Physics. [doi:10.1063/1.3517066]
Scientific journal, English

Highly efficient quasi-solid-state quantum-dot-sensitized solar cell based on hydrogel electrolytes
Zhexun Yu; Quanxin Zhang; Da Qin; Yanhong Luo; Dongmei Li; Qing Shen; Taro Toyoda; Qingbo Meng
ELECTROCHEMISTRY COMMUNICATIONS, ELSEVIER SCIENCE INC, 12, 12, 1776-1779, Dec. 2010, Peer-reviwed, Chemically crosslinked polyacrylamide-based hydrogel has been first used as the polymer matrix to prepare quasi-solid-state polysulfide electrolyte for CdS/CdSe co-sensitized solar cells (QDSCs). The room temperature ionic conductivity of the gel electrolyte reaches 0.093 S.cm(-1). QDSCs based on this quasi-solid-state electrolyte can present up to 4.0% of light-to-electricity conversion efficiency. Meanwhile, the interfacial recombination at TiO(2)/electrolyte interface of the cell is also investigated by Electrochemical Impedance Spectroscopy (EIS). (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English

Separation of ultrafast photoexcited electron and hole dynamics in CdSe quantum dots adsorbed onto nanostructured TiO2 films
Qing Shen; Yasumasa Ayuzawa; Kenji Katayama; Tsuguo Sawada; Taro Toyoda
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 97, 26, 263113-1~3, Dec. 2010, Peer-reviwed, The ultrafast photoexcited electron and hole dynamics of CdSe quantum dots (QDs) deposited onto nanostructured TiO2 films were studied using an improved transient grating (TG) technique. By comparing the TG responses measured in air and in a Na2S solution (holeacceptor), we succeeded in separating the dynamic characteristics of photoexcited electrons and holes in the CdSe QDs. We found that charge separation in the CdSe QDs occurred over a very fast time scale from a few hundreds of femtoseconds in the Na2S solution via hole transfer to S2- ions to a few picoseconds in air via hole trapping. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3533374]
Scientific journal, English

Screen-printed Cu2S-based Counter Electrode for Quantum-dot-sensitized Solar Cell
Minghui Deng; Shuqing Huang; Quanxin Zhang; Dongmei Li; Yanhong Luo; Qing Shen; Taro Toyoda; Qingbo Meng
CHEMISTRY LETTERS, CHEMICAL SOC JAPAN, 39, 11, 1168-1170, Nov. 2010, Peer-reviwed, Cu2S-based counter electrodes screen-printed on different substrates for CdS/CdSe quantum-dot-sensitized solar cells are reported The photovoltaic conversion efficiency of 3 71% was obtained with Cu2S counter electrode deposited on conductive substrate due to low charge-transfer resistance By addition of conductive carbon material, a cell with Cu2S/C composite counter electrode screen-printed on insulated glass substrate displayed an efficiency of 3 37% These results showed the potential application of such Cu2S-based counter electrode for large-scale quantum-dot-sensitized solar cells in the future
Scientific journal, English

CdSe quantum dot-sensitized solar cell employing TiO2 nanotube working-electrode and Cu2S counter-electrode
Qing Shen; Akari Yamada; Satoru Tamura; Taro Toyoda
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 97, 12, 123107, Sep. 2010, Peer-reviwed, We proposed a CdSe quantum dot (QD)-sensitized solar cell (QDSSC), which is constructed with a CdSe QD adsorbed TiO2 nanotube working electrode on a Ti substrate, a ring shaped Cu2S counter electrode, prepared on a brass substrate having a glass window, and polysulfide electrolyte. The light was incident from the counter electrode. An incident photon to current conversion efficiency as high as 65% and a photovoltaic conversion efficiency as high as 1.8% under one sun have been achieved. We have demonstrated less costly QDSSC, without the requirement for both a transparent conductive electrode or a platinum film. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3491245]
Scientific journal, English

Fibrous CdS/CdSe quantum dot co-sensitized solar cells based on ordered TiO2 nanotube arrays
Shuqing Huang; Quanxin Zhang; Xiaoming Huang; Xiaozhi Guo; Minghui Deng; Dongmei Li; Yanhong Luo; Qing Shen; Taro Toyoda; Qingbo Meng
NANOTECHNOLOGY, IOP PUBLISHING LTD, 21, 37, 375201, Sep. 2010, Peer-reviwed, A new kind of fibrous quantum dot sensitized solar cell has been designed and fabricated by using CdS and CdSe co-sensitized TiO2 nanotubes on Ti wire as the photoanode and highly active Cu2S as the counter electrode. By optimizing the CdSe deposition time and the length of the nanotube, a power conversion efficiency of 3.18% has been obtained under AM 1.5 illumination (100 mW cm(-2)). The potential application of this kind of solar cell has also been discussed in this paper.
Scientific journal, English

Low-Cost Flexible Nano-Sulfide/Carbon Composite Counter Electrode for Quantum-Dot-Sensitized Solar Cell
Minghui Deng; Quanxin Zhang; Shuqing Huang; Dongmei Li; Yanhong Luo; Qing Shen; Taro Toyoda; Qingbo Meng
NANOSCALE RESEARCH LETTERS, SPRINGER, 5, 6, 986-990, Jun. 2010, Peer-reviwed, Cu(2)S nanocrystal particles were in situ deposited on graphite paper to prepare nano-sulfide/carbon composite counter electrode for CdS/CdSe quantum-dot-sensitized solar cell (QDSC). By optimization of deposition time, photovoltaic conversion efficiency up to 3.08% was obtained. In the meantime, this composite counter electrode was superior to the commonly used Pt, Au and carbon counter electrodes. Electrochemical impedance spectra further confirmed that low charge transfer resistance at counter electrode/electrolyte interface was responsible for this, implied the potential application of this composite counter electrode in high-efficiency QDSC.
Scientific journal, English

Sensitization of Titanium Dioxide Photoanodes with Cadmium Selenide Quantum Dots Prepared by SILAR: Photoelectrochemical and Carrier Dynamics Studies
N. Guijarro; T. Lana-Villarreal; Q. Shen; T. Toyoda; R. Gó mez
J. Phys. Chem. C, 114, 21928-21937, May 2010, Peer-reviwed
Scientific journal, English

Comparative study of by near-field heterodyne transient grating and continuously variable spatial frequency transient grating methods for measurements of terahertz reflection responses
H. Inoue; K. Katayama; Q. Shen; T. Toyoda; K. A. Nelson
15TH INTERNATIONAL CONFERENCE ON PHOTOACOUSTIC AND PHOTOTHERMAL PHENOMENA (ICPPP15), IOP PUBLISHING LTD, 214, 012123, 2010, Peer-reviwed, We measured terahertz reflection responses utilizing a propagating phonon polariton wave, which was generated and detected by two different methods: the near-field heterodyne transient grating and the continuously variable spatial frequency transient grating method. The obtained results were compared for the purpose of clarifying which of both methods is better for measurements of terahertz reflection responses. The phonon polariton wave is propagated and reflected at a ferroelectric crystal edge. From the viewpoint of the separation between the excited and reflected phonon polariton waves, the latter method is better for measurements of reflection responses.
International conference proceedings, English

Recombination in Quantum Dot Sensitized Solar Cells
Ivan Mora-Sero; Sixto Gimenez; Francisco Fabregat-Santiago; Roberto Gomez; Qing Shen; Taro Toyoda; Juan Bisquert
ACCOUNTS OF CHEMICAL RESEARCH, AMER CHEMICAL SOC, 42, 11, 1848-1857, Nov. 2009, Peer-reviwed, Quantum dot sensitized solar cells (QDSCs) have attracted significant attention as promising third-generation photovoltaic devices. In the form of quantum dots (QDs), the semiconductor sensitizers have very useful and often tunable properties; moreover, their theoretical thermodynamic efficiency might be as high as 44%, better than the original 31% calculated ceiling. Unfortunately, the practical performance of these devices still lags behind that of dye-sensitized solar cells. In this Account, we summarize the strategies for depositing CdSe quantum dots on nanostructured mesoporous TiO2 electrodes and discuss the methods that facilitate improvement in the performance and stability of QDSCs.
One particularly significant factor for solar cells that use polysulfide electrolyte as the redox couple, which provides the best performance among QDSCs, is the passivation of the photoanode surface with a ZnS coating, which leads to a dramatic increase of photocurrents and efficiencies. However, these solar cells usually show a poor current-potential characteristic, so a general investigation of the recombination mechanisms is required for improvements. A physical model based on recombination through a monoenergetic TiO2 surface state that takes into account the effect of the surface coverage has been developed to better understand the recombination mechanisms of QDSCs. The three main methods of QD adsorption on TiO2 are (i) in situ growth of QDs by chemical bath deposition (CBD), (ii) deposition of presynthesized colloidal QDs by direct adsorption (DA), and (iii) deposition of presynthesized colloidal QDs by linker-assisted adsorption (LA).
A systematic investigation by impedance spectroscopy of QDSCs prepared by these methods showed a decrease in the charge-transfer resistance and increased electron lifetimes for CBD samples; the same result was found after ZnS coating because of the covering of the TiO2 surface. The increase of the lifetime with the ZnS treatment has also been checked independently by open-circuit potential (V-OC) decay measurements. Despite the lower recombination rates by electron transfer to electrolyte as well as the higher light absorption of CBD samples, only a moderate increase of photocurrent compared with colloidal QD samples is obtained, indicating the presence of an additional, internal recombination pathway in the closely packed QD layer.
Scientific journal, English

Electron dynamics in GaN wafers with an inhomogeneous distribution of defects in the depth direction
Yuji Ohashi; Kenji Katayama; Qing Shen; Taro Toyoda
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 106, 6, 063515, Sep. 2009, Peer-reviwed, The dynamics of photoexcited electrons in a GaN wafer with an inhomogeneous dislocation density distribution in the depth direction was measured by the near-field heterodyne transient grating method. We investigated the dependence of the interfaces with different dislocation densities, the dependence on the pump wavelength for a sample with a decaying distribution of dislocation density, which gives information on the depth dependence on the carrier dynamics. In the latter experiment, the observed depth region was continuously changed by tuning the wavelength around the band gap of GaN. The responses of the electron dynamics can be fitted with the sum of two exponential decays for all the experiments and only the slower component decayed faster as the dislocation density increased. It was concluded that the faster component corresponded to the trap process of electrons by deep states due to inherent defects in the GaN wafer and the slower component corresponded to the recombination of the trapped electrons at the defect states by dislocation defects. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3197281]
Scientific journal, English

Improving the performance of colloidal quantum-dot-sensitized solar cells
Sixto Gimenez; Ivan Mora-Sero; Lorena Macor; Nestor Guijarro; Teresa Lana-Villarreal; Roberto Gomez; Lina J. Diguna; Qing Shen; Taro Toyoda; Juan Bisquert
NANOTECHNOLOGY, IOP PUBLISHING LTD, 20, 29, 295204 (1-6), Jul. 2009, Peer-reviwed, Solar cells based on a mesoporous structure of TiO(2) and the polysulfide redox electrolyte were prepared by direct adsorption of colloidal CdSe quantum dot light absorbers onto the oxide without any particular linker. Several factors cooperate to improve the performance of quantum-dot-sensitized solar cells: an open structure of the wide bandgap electron collector, which facilitates a higher covering of the internal surface with the sensitizer, a surface passivation of TiO(2) to reduce recombination and improved counter electrode materials. As a result, solar cells of 1.83% efficiency under full 1 sun illumination intensity have been obtained. Despite a relatively large short circuit current (J(sc) = 7.13 mA cm (2)) and open circuit voltage (V(oc) = 0.53 V), the colloidal quantum dot solar cell performance is still limited by a low fill factor of 0.50, which is believed to arise from charge transfer of photogenerated electrons to the aqueous electrolyte.
Scientific journal, English

Terahertz reflection response measurement using a phonon polariton wave
Hayato Inoue; Kenji Katayama; Qing Shen; Taro Toyoda; Keith A. Nelson
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 105, 5, 054902, Mar. 2009, Peer-reviwed, We developed a new technique for the measurement of terahertz reflection responses utilizing a propagating phonon polariton wave. Frequency tunable phonon polariton waves were generated by the recently developed continuously variable spatial frequency transient grating method [K. Katayama, H. Inoue, H. Sugiya, Q. Shen, T. Taro, and K. A. Nelson, Appl. Phys. Lett. 92, 031906 (2008)]. The phonon polariton wave traveled in a ferroelectric crystal in an in-plane direction with an inclined angle of 26 degrees, and the wave reflected at the crystal edge where a sample was positioned. The reflected polariton wave was detected by the same method as that used for the generation of the polariton waves. By comparing the reflection intensities in the presence and absence of the sample, reflectivity of the polariton wave was calculated, and the refractive index and absorption in the terahertz region were obtained.
Scientific journal, English

Electric Characteristics of Li2O-Doped TiO2 Nanocrystalline Film and Its Application to Dye-Sensitized Solar Cells
Masahiro Nada; Tomohiro Gonda; Qing Shen; Hiroshi Shimada; Taro Toyoda; Naoki Kobayashi
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 48, 2, 025505, Feb. 2009, Peer-reviwed, The effects of Li2O doping on TiO2 nanocrystalline film are investigated to improve the conversion efficiency of dye-sensitized solar cells (DSC), while considering the mechanism of electric conduction in the TiO2 nanocrystalline film. The temperature dependence of carrier concentration and electric conductivity of Li2O-doped TiO2 nanocrystalline film are determined by Hall effect and high-impedance conductivity measurements. At the doping condition of 4.5 x 10(-5) molar ratio of Li2O to TiO2, the electric conductivity at room temperature is maximum, which is almost two orders of magnitude higher than that of the undoped sample. The conduction type and carrier concentration at 500 K are n-type and 1.75 x 10(13) cm(-3), respectively. From the temperature dependence of the electron concentration, the donor depth is estimated as 1.0 eV. By applying Li2O doping to DSC, the conversion efficiency and open-circuit voltage are maximum at the highest conductivity of the Li2O-doped TiO2 layer. (C) 2009 The Japan Society of Applied Physics
Scientific journal, English

Photoacoustic spectra of Au quantum dots adsorbed on nanostructured TiO2 electrodes together with the photoelectrochemical current characteristics
Taro Toyoda; Sae Tsugawa; Qing Shen
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 105, 3, 034314, Feb. 2009, Peer-reviwed, The optical absorption of Au quantum dots (QDs) was studied by applying the photoacoustic (PA) spectroscopic technique, which is useful for optically opaque samples. The characteristic bands of Au QDs were observed at around 2.4 eV for electrodes consisting of 15 nm TiO2 nanoparticles and at around 2.3 eV for those consisting of 37 nm ones, which correspond to the characteristic surface plasmon resonance bands in the visible region. The electrode thickness dependence of the PA signal intensity around the characteristic band showed a tendency toward saturation in both cases. There was a great difference in the saturation characteristics of the PA signal intensity between the electrodes made with different sized TiO2 nanoparticles, even though the preparation conditions for the Au QDs were the same. The saturation time for electrodes made with 37 nm TiO2 nanoparticles was shorter than those made with 15 nm particles, indicating that the penetration of the QDs into the electrodes made with 37 nm nanoparticles was less than those made with 15 nm nanoparticles, although the porous area observed was high. Also, the PA signal intensity around the peak of electrodes with 15 nm nanoparticles is larger than that with 37 nm ones, indicating a higher adsorption rate for the smaller nanoparticles due to the lower surface activation energy of larger nanoparticles. There was no photoelectrochemical current response although the characteristic optical absorption bands of the Au QDs were observed by surface plasmon resonance.
Scientific journal, English

Room-Temperature Absorption Edge of InGaN/GaN Quantum Wells Characterized by Photoacoustic Measurement
Yosuke Takeda; Daigo Takagi; Tatsuji Sano; Shin Tabata; Naoki Kobayashi; Qing Shen; Taro Toyoda; Jun Yamamoto; Yuzaburo Ban; Kou Matsumoto
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 47, 12, 8805-8807, Dec. 2008, Peer-reviwed, The absorption edges of five periods of InxGa1-xN (3nm)/GaN (15mn) (x = 0.07-0.23) quantum wells (QWs) are characterized by photoacoustic (PA) measurement at room temperature. The absorption edge is determined by differentiating the PA signal Curve to obtain the inflection point on the assumption that the signal curve consists of Urbach tail in the low-energy region and Elliott's equation in the high-energy region. The constant absorption edge of GaN is observed at 3.4 eV and an absorption edge redshift with increasing In composition is observed for InGaN QWs. As a result, the Stokes shift increases with In composition and the highest shift of 435 meV is observed at x = 0.23. From the energy calculation of optical transition in the InGaN/GaN QWs under an internal polarization field, the transition between the ground states confined in the well with it triangular potential causes a low-energy shift in the photoluminescence peak from the bulk band-gap energy, and the excited bound states whose wave functions are confined by the step-linear potential extending over the GaN barrier lead to the high-energy shift in the, absorption edge. [DOI: 10.1143/JJAP.47.8805]
Scientific journal, English

Characterization of electron transfer from CdSe quantum dots to nanostructured TiO2 electrode using a near-field heterodyne transient grating technique
Qing Shen; Kenji Katayama; Tsuguo Sawada; Taro Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 516, 17, 5927-5930, Jul. 2008, Peer-reviwed, The ultrafast carrier dynamics of the CdSe QDs adsorbed on a nanostructured TiO2 electrode and on a glass substrate were studied using a near-field heterodyne detection transient grating (NF-HD-TG) method. Two decay processes were observed in the TG responses. The fast decay time constants tau(1) were the same (2.3 ps) for these two kinds of substrates, corresponding to the photoexcited hole relaxation in the CdSe QDs. However, the slow decay time constants tau(2) were very different for these two kinds of substrates, reflecting the photoexcited electron relaxation (i.e., trapping and/or transfer). Since no electron transfer from the CdSe QDs to the glass substrate could occur, we could estimate the electron transfer rate from the CdSe QDs into the nanostructured TiO2 electrode to be approximately 5.4 x 10(9) s(-1) using the values of tau(2) detected for these two kinds of substrates. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English

Effect of ZnS coating on the photovoltaic properties of CdSe quantum dot-sensitized solar cells
Qing Shen; Junya Kobayashi; Lina J. Diguna; Taro Toyoda
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 103, 8, 084304, Apr. 2008, Peer-reviwed, CdSe quantum dots (QDs) were adsorbed onto nanostructured TiO(2) films for different times by using a chemical bath deposition method in order to produce QD-sensitized solar cells (QDSSCs). Surface modification was done by coating ZnS onto the CdSe QDs. The optical absorption and current-voltage characteristics of these devices were studied. The size of the CdSe QDs increased with increasing adsorption time, and there was an optimum CdSe adsorption time for achieving the best photovoltaic conversion efficiency. The photovoltaic properties of short-circuit current density, open-circuit voltage, and photovoltaic conversion efficiency were significantly improved after modifying the surface with ZnS. Under a solar illumination of 100 mW/cm(2), an efficiency as high as 2.02% was achieved for the CdSe QDSSCs that were made by using this method. (C) 2008 American Institute of Physics.
Scientific journal, English

Correlation between crystal growth and photo sensitization of nanostructured TiO2 electrodes using supporting Ti substrates by self-assembled CdSe quantum dots
Taro Toyoda; Junya Kobayashi; Qing Shen
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 516, 9, 2426-2431, Mar. 2008, Peer-reviwed, Crystal growth of semiconductor quantum dots (QDs) adsorbed on nanostructured TiO2 electrodes is important not only for crystallographic studies but also for improving the photovoltaic efficiency of semiconductor-sensitized solar cells. In this study, nanostructured TiO2 electrodes using supporting Ti substrates were prepared. These electrodes are then adsorbed with self-assembled Use QDs as photosensitizers to investigate the crystal growth and photoelectrochemical current properties. Average diameters of the Use QDs can be estimated from optical absorption spectra by using photoacoustic (PA) technique. PA technique is a powerful tool for evaluating the optical absorption of opaque and scattered samples because of the detection by photothermal phenomenon. When the adsorption time increases, the CdSe QDs diameter increases and then shows saturation for all the cases. Normal solution growth plus suppression (negative growth) contributions can be derived by PA spectroscopic analysis. Both of them depend on adsorption temperatures for CdSe QDs formation. Photosensitization of the nanostructured TiO2 electrodes in the visible region resulting from Use QDs deposition can be clearly observed. Incident photon to current conversion efficiency (IPCE) of Use QDs adsorbed at high temperature formation is smaller than that adsorbed at low temperature one, indicating the increase of recombination centers with increasing adsorption temperature. This implies that negative growth, or dissolving effect, produces much more recombination centers inside of Use QDs and/or interface between the QDs and TiO2. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English

A device-independent design scheme on interactive animation and game
Li Xin-yu; Song Ying; Huang Xia; Xiang Li-sheng; Shen Qing
WORLD CONGRESS ON ENGINEERING 2008, VOLS I-II, INT ASSOC ENGINEERS-IAENG, 265-269, 2008, Today, there are almost 136 million Internet users and 500 million mobile users in China. Wireless networks are striding toward wide band service. Animations and games are urgent to seize hold of both Internet and wireless market simultaneously, i.e., to attract more users. However, this is a difficult task indeed, because animation and game designers must take environments of both Internet and wireless network and consistency across devices in consideration. A scheme to solve above design problems with minimum labor cost is proposed. Also, many practical solutions to problems posed by limit physical resources of mobile are discussed.
International conference proceedings, English

Generation and detection of tunable phonon polaritons using a single transmission grating
Kenji Katayama; Hayato Inoue; Hisashi Sugiya; Qing Shen; Taro Toyoda; Keith A. Nelson
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 92, 3, 031906, Jan. 2008, Peer-reviwed, Frequency tunable phonon polariton waves were generated and detected using an original optical configuration of the transient grating method. In this technique, the excitation beam was shone onto a transmission grating after being transmitted through a lens, and a lithium niobate wafer located at a defocus position of the lens was irradiated by an expanded or reduced image of the transmission grating, causing excitation of phonon polaritons. Because the magnification of the light intensity pattern can be controlled by the sample-grating distance, the wavelength of the phonon polaritons, which is equal to the optical fringe spacing, can be continuously varied.
Scientific journal, English

Optical absorption and ultrafast carrier dynamics characterization of CdSe quantum dots deposited on different morphologies of nanostructured TiO2 films
Lina J. Diguna; Qing Shen; Akira Sato; Kenji Katayama; Tsuguo Sawada; Taro Toyoda
MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, ELSEVIER SCIENCE BV, 27, 5-8, 1514-1520, Sep. 2007, Peer-reviwed, in this study, CdSe QDs were chemically adsorbed onto the inverse opal TiO2 film as well as the common nanocrystalline TiO2 film. The optical absorption studied by using photoacoustic (PA) spectroscopy implies the growing and larger amount of CdSe QDs onto inverse opal TiO2 by increasing deposition time. For the same deposition time, the growth of CdSe QD size are independent on TiO2 matrixes, but largely deposited on the common nanocrystalline TiO2 film than the inverse opal TiO2. Ultrafast carrier dynamics shows a fast (hole) decay process and a slow (electron) decay process with lifetimes of a few ps and a few tens to hundreds ps, respectively. With increasing deposition time, regarding larger size and amount of CdSe QDs, the time constant of these two processes become longer for CdSe deposited inverse opal TiO2 samples. However, for the same deposition time, CdSc deposited inverse opal TiO2 have the shorter lifetime of both hole and electron decay processes compared to one on nanocrystalline TiO2, showing that the amount of CdSe QDs, the interfaces between CdSe QDs, play important role in carrier relaxation. (C) 2006 Elsevier B.V All rights reserved.
Scientific journal, English

Effect of Fe doping on photoluminescence of yttria-stabilized zirconia
H. Nakajima; H. Ishihara; Q. Shen; T. Toyoda; K. Itoh; H. Kaneko; Y. Tamaura
JOURNAL OF ALLOYS AND COMPOUNDS, ELSEVIER SCIENCE SA, 441, 1-2, 255-258, Aug. 2007, Peer-reviwed, Photoluminescence (PL) spectra of yttria-stabilized zirconia (YSZ) samples with different Fe mole fractions were measured to study the influence of Fe doping on their spectra. The PL spectra of all the samples can be decomposed into two Gaussian bands centered around 440 and 510 nm, and the two bands can be attributed to oxygen vacancy states in the bulk and the surface of the samples. We found that the intensity ratio of the PL band around 440 nm to that around 510 nm increases as the Fe mole fraction increases. This can be explained by considering the distribution of Fe-associated defects (bulk or surface) and the PL quenching by the defects. These results show that PL spectroscopy can be used to study properties of Fe dopant in YSZ. Moreover, photoacoustic spectra of the samples were measured to characterize defects in the samples. (C) 2006 Elsevier B.V. All rights reserved.
Scientific journal, English

Crystal growth. of CdSe quantum dots adsorbed on nanoparticle, inverse opal, and nanotube TiO2 photoelectrodes characterized by photoacoustic spectroscopy
Taro Toyoda; Terumasa Uehata; Rihito Suganuma; Satoru Tamura; Akira Sato; Kana Yamamoto; Qing Shen; Naoki Kobayashi
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 46, 7B, 4616-4621, Jul. 2007, Peer-reviwed, The crystal growth of semiconductor quantum dots (QDs) adsorbed on nanostructured TiO2 photoelectrodes is important not only for crystallographic studies but also for improving the photovoltaic efficiency of semiconductor-sensitized solar cells. In this study, nanoparticle, inverse opal, and nanotube TiO2 electrodes are prepared. These electrodes are then adsorbed with CdSe QDs as photosensitizers to investigate crystal growth. The average diameters of the CdSe QDs can be estimated from the photoacoustic (PA) spectra. When the adsorption time increases, the CdSe QD diameter increases and then shows saturation. Normal solution growth plus suppression (negative growth) can be obtained by PA analysis. Both of them depend on the morphology of TiO2 electrodes and the final solution concentration for the CdSe QD preparation.
Scientific journal, English

High efficiency of CdSe quantum-dot-sensitized TiO2 inverse opal solar cells
Lina J. Diguna; Qing Shen; Junya Kobayashi; Taro Toyoda
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 91, 2, 023116, Jul. 2007, Peer-reviwed, The authors have demonstrated an approach to sensitized-type solar cells, based on TiO2 inverse opal and the use of CdSe quantum dots (QDs) as sensitizers. CdSe QDs were grown in situ on TiO2 inverse opal electrodes, utilizing a chemical bath deposition method. All of the photovoltaic performances, including short circuit photocurrent density, open circuit voltage, fill factor, and efficiency, were significantly improved by surface modification with ZnS and fluoride ions. A power conversion efficiency of about 2.7% has been attained, under solar illumination of 100 mW/cm(2). This value is relatively high for metal oxide solar cells, sensitized with semiconductor QDs. (C) 2007 American Institute of Physics.
Scientific journal, English

Optical absorption, photosensitization, and ultrafast carrier dynamic investigations of CdSe quantum dots grafted onto nanostructured SnO2 electrode and fluorine-doped tin oxide (FTO) glass
Qing Shen; Makoto Yanai; Kenji Katayama; Tsuguo Sawada; Taro Toyoda
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 442, 1-3, 89-96, Jul. 2007, Peer-reviwed, CdSe quantum dots (QDs) are adsorbed onto nanostructured SnO2 and planar FTO electrodes by a chemical adsorption technique. Optical absorption and the incident-photon-to-current conversion efficiency (IPCE) are studied by using photoacoustic and photoelectrochemical methods. The growth rate of the CdSe QDs depends on the morphology of the substrate. Larger IPCE peak values and larger integrated area for the IPCE spectra are obtained for the nanostructured SnO2 electrodes. The ultrafast carrier dynamics of the CdSe QDs are studied using a transient grating technique. It is found that the electron relaxation of the CdSe QDs depends strongly on the morphology of the substrate. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English

Phonon polariton generation and detection using near-field heterodyne transient grating method
Kenji Katayama; Qing Shen; Taro Toyoda; Keith A. Nelson
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 90, 17, 171117, Apr. 2007, Peer-reviwed, A technique for the generation and detection of phonon polariton was developed based on the near-field heterodyne transient grating method. It features a compact and simple optical setup and easy wavelength tuning ability of the phonon polariton. The wavelength was tuned by changing the grating spacing of a transmission grating positioned in front of a sample, and this was performed by sliding a glass plate with transmission gratings with many different grating spacings along the glass plate surface. (c) 2007 American Institute of Physics.
Scientific journal, English

Characterization of carrier dynamics in semiconductor nanomaterials using near-field heterodyne transient grating method
Q. Shen; K. Katayama; T. Sawada; T. Toyoda
MICROPROCESSES AND NANOTECHNOLOGY 2007, DIGEST OF PAPERS, JAPAN SOCIETY APPLIED PHYSICS, 34-+, 2007, Peer-reviwed
International conference proceedings, English

Carrier dynamics in porous silicon studied with a near-field heterodyne transient grating method
Masahiro Yamaguchi; Kenji Katayama; Qing Shen; Taro Toyoda; Tsuguo Sawada
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 427, 1-3, 192-196, Aug. 2006, Peer-reviwed, The dynamics of excited carriers in porous silicon were investigated using the near-field heterodyne transient grating method, and the fundamental processes related to light emission were determined. The processes include trapping to surface states and two-body recombination of excited carriers, with trapping being the dominant source of light emission. Since nonlinear processes, namely two-body recombination, are included, it is necessary to measure the pump intensity dependence of the transient responses and to analyze them with a nonlinear differential equation in order to obtain accurate decay times. (c) 2006 Elsevier B.V. All rights reserved.
Scientific journal, English

Optical absorption, photoelectrochemical, and ultrafast carrier dynamic investigations of TiO2 electrodes composed of nanotubes and nanowires sensitized with CdSe quantum dots
Qing Shen; Kenji Katayama; Tsuguo Sawada; Masahiro Yamaguchi; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 45, 6B, 5569-5574, Jun. 2006, Peer-reviwed, TiO2 electrodes composed of nanotubes and nanowires are prepared from TiO2 gels using a surfactant-assisted self-assembly method reported earlier. CdSe quantum dots (QDs) are adsorbed onto the. TiO2 electrodes by chemical deposition (CD). Their average size increases from 4 to 6nm with increasing deposition time from 3 to 82h. The optical absorption and incident photon-to-current conversion efficiency (IPCE) of the electrodes are studied by photoacoustic (PA) and plIiotoelectrochemical (PEC) methods. The photosensitization of the TiO2 electrodes by CdSe QDs is demonstrated by both PA and IPCE spectra. The ultrafast carrier dynamics of the CdSe-sensitized TiO2 electrodes composed of nanotubes and nanowires is studied using a lens-free heterodyne detection transient grating (LF-HD-TG) technique.,Fast and slow decay processes with lifetimes of about 3 ps and 60-130 ps, respectively, are observed.
Scientific journal, English

Photoacoustic and photoelectrochemical characterization of inverse opal TiO2 sensitized with CdSe quantum dots
Lina J. Diguna; Motonobu Murakami; Akira Sato; Yuki Kumagai; Taishi Ishihara; Naoki Kobayashi; Qing Shen; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 45, 6B, 5563-5568, Jun. 2006, Peer-reviwed, Inverse opal TiO2 may offer a novel and promising solution for enhancing the light harvesting efficiency of dye-sensitized solar cells (DSSCs). Its large interconnected pores enable a better penetration of the dye sensitizers via the matrix pores, making this material surpasses the efficiency of conventional TiO2 electrodes. Moreover, it also exhibits a photonic band gap that may enable a significant change in its dye absorbance by the adjustment of the photon localization near the red edge of the photonic band gap to the position of dye absorption. In this study, we report a simple method of fabrication of inverse opal TiO2, wherein the voids in artificial opal latex are filled with nanosized TiO2 particles by adding a drop of TiCl4 into the latex matrix, hydrolyzing, and heating. In this process, we investigate the effect of different heat treatment times on the properties of inverse opal TiO2. Photoacoustic (PA) characterization shows that longer heat treatment times could produce more defect sites. The presence of defects causes the inhibition of electron transfer and results in a decrease in incident photon-to-current conversion efficiency (IPCE). CdSe quantum dots were adsorbed onto inverse opal TiO2 by chemical deposition. The blue shift of PA spectra relative to the bulk CdSe and the gain in IPCE were clearly observed. This result indicates the quantum confinement effect and photosensitization of CdSe quantum dots.
Scientific journal, English

The effect of ultraviolet irradiation on the photothermal, photo luminescence and photo luminescence excitation spectra of Mn-doped ZnS nanoparticles
AB Cruz; Q Shen; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 499, 1-2, 104-109, Mar. 2006, Peer-reviwed, Research involving Mn doped nanocrystalline ZnS (ZnS:Mn) has grown in recent years, partly due to the high quantum luminescence efficiencies that have been reported. We measured the photoacoustic (PA), the photoluminescence (PL) and the photoluminescence excitation (PLE) spectra of surface-passivated and unpassivated ZnS:Mn. The effects of UV irradiation on the PL and PLE spectra were also studied. A decrease in the PA intensity after UV exposure was observed for the ZnS:Mn, indicating a decrease in the nonradiative relaxation probability. The observed increase in PL intensity indicates a corresponding increase in the radiative transition probability. For the PLE spectra, possible aggregation of the primary particles could have resulted in the lower measured energy of the PLE peak compared to the value predicted by the effective mass approximation theory. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

The influence of chemical post-etching and UV irradiation on the optical absorption and thermal diffusivity of porous silicon studied by photoacoustic technique
Q Shen; M Inoguchi; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 499, 1-2, 161-167, Mar. 2006, Peer-reviwed, We applied a photoacoustic (PA) technique to study the optical absorption and thermal diffusivity of porous silicon (Psi) samples. The Psi layers were formed on p-type Si wafers in an HF electrolyte. Three kinds of Psi samples that had undergone chemical post-etching were studied before and after UV irradiation for 2 h. We observed that a strong confinement effect occurred in all of the Psi samples from the blue shift of the band gap energy compared with that of crystalline Si, while the effective thermal diffusivities were almost two orders of the magnitude smaller than that of conventional Si crystals. The band gap shifted to higher energy and the effective thermal diffusivity decreased as the post-etching time increased. In the case of a Psi sample that was not chemically post-etched, the optical absorption and effective thermal diffusivity before and after UV irradiation were almost unchanged. However, for the Psi samples that were chemically post-etched, the optical absorption decreased and the effective thermal diffusivity increased after UV irradiation. This indicates that Psi samples that are post-etched are more readily affected by UV irradiation, i.e., oxidized by replacing Si-H, bonds by Si-O-x, than those that do not undergo post-etching. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

Photoacoustic and photo electrochemical characterization of CdSe-sensitized TiO2 electrodes composed of nanotubes and nanowires
Q Shen; T Sato; M Hashimoto; CC Chen; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 499, 1-2, 299-305, Mar. 2006, Peer-reviwed, Morphology of titanium dioxide (TiO2) electrodes and the choice of the sensitizers have been important factors for the improvement of dye-sensitized solar cell (DSSC) efficiency. TiO2 electrodes, having a higher degree of order than random fractal-like assemblies of nanoparticles, are desirable for the improvement of the electron transport characteristics. In recent years, semiconductor quantum dots (QDs) have attracted much attention as sensitizers, replacing organic dyes in DSSCs. In this study, TiO2 electrodes, composed of nanotubes and nanowires, were prepared from TiO2 gels using a surfactant-assisted self-assembling method reported recently. Since use of semiconductor QDs as sensitizers has some advantages in solar cell applications, CdSe QDs were adsorbed onto the TiO2 electrodes as a sensitizer. The photoacoustic (PA) and the incident photon-to-current conversion efficiency (IPCE) spectra were measured for the TiO2 electrodes, both with and without CdSe QD deposition to evaluate their optical absorption property and photon-to-electron conversion efficiencies. Dependencies of the optical absorption and the IPCE on the TiO2 electrode thickness (0.7 mu m-2.8 mu m) were studied. It was found that the IPCE peak value and the integrated area of the IPCE spectra for the TiO2 electrodes with CdSe deposition increased as the electrode thickness increased. The highest IPCE value of about 45% was obtained from an electrode with a thickness of 2.8 mu m. This value is as high as those obtained from CdSe QD-sensitized TiO2 electrodes made from nanoparticles, of which the thicknesses were 10 mu m. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

Photoexcited hole dynamics in TiO2 nanocrystalline films characterized using a lens-free heterodyne detection transient grating technique
Q Shen; K Katayama; T Sawada; M Yamaguchi; Y Kumagai; T Toyoda
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 419, 4-6, 464-468, Feb. 2006, Peer-reviwed, A lens-free heterodyne detection transient grating (LF-HD-TG) technique has been applied to study the ultrafast carrier dynamics of anatase and rutile TiO2 films made from TiO2 nanoparticles. The decay of photoexcited hole concentrations in TiO2 films can be directly detected using the technique, since the effective mass of holes in TiO2 is much smaller than that of electrons. We find that the relaxation of holes in anatase occurs via first-order kinetics as fast as 1 ps, which is attributed to a hole trapping process. However, the lifetimes of holes in rutile are found to be longer than hundreds of ps. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

Studies on the effect of UV irradiation on Mn-doped ZnS nanoparticles
AB Cruz; Q Shen; T Toyoda
MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, ELSEVIER SCIENCE BV, 25, 5-8, 761-765, Dec. 2005, Peer-reviwed, With the advent of the increased attraction in compound semiconductors, attention has been focused on the research involving nanocrystalline Mn2+ doped ZnS (ZnS: Mn). In this paper, nano-scaled ZnS: Mn (both unpassivated and pasivated samples) was synthesized and we report the photoacoustic (PA) as well as photo luminescence (PL) properties upon exposure to ultraviolet (UV) light. It was found that passivation with acrylic acid (AA) yielded higher photoluminescence intensity. UV exposure caused a decrease in the PA intensity observed owing to a decrease in the nonradiative processes during exposure. A corresponding increase in the radiative processes was verified with the increase in the PL intensity during UV exposure. These experimental results suggest the possibility of UV curing for the passivating AA monomer and photochemical reactions around the nanocrystals, indicating the increase of the fluorescence quantum efficiency. Luminescent time decay measurements for the sample without AA showed a lengthening in the time decay constant after UV exposure. On the other hand, for the sample with AA, no change in the time decay constants was observed. This further strengthens the theory that during UV exposure, different luminescent decay mechanisms exist for the unpassivated and passivated samples. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

Effect of rutile-type content on nanostructured anatase-type TiO2 electrode sensitized with CdSe quantum dots characterized with photoacoustic and photoelectrochemical current spectroscopies
T Toyoda; Tsuboya, I; Q Shen
MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, ELSEVIER SCIENCE BV, 25, 5-8, 853-857, Dec. 2005, Peer-reviwed, Two types of nanostructured. TiO2 electrodes were prepared without rutile-type (100% anatase-type) and with rutile-type (12%) content. CdSe quantum dots (QDs) were adsorbed onto each of the two types of TiO2 electrodes using a chemical deposition (CD) technique. Optical absorption and photoelectrochemical properties were characterized with photoacoustic (PA) and photoelectrochemical current (PEC) methods. The redshift of the PA and PEC spectra with increasing CdSe sizes were clearly observed, indicating quantum confinement effects and photosensitization. It was found that the PA and PEC spectra in the visible region were different for the two types of TiO2 electrodes for the same deposition time. The PA and PEC intensities of TiO2 electrodes with rutile-type content were larger than those without rutile-type content, indicating that adsorbed CdSe QDs in the TiO2 electrodes with rutile-type content might be higher than those without rutile-type content. Moreover, the transport properties in the TiO2 electrodes with rutile-type content might be improved. These results suggest that the rutile-type content is advantageous to increase the photoelectrochemical properties of TiO2 electrodes. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

Study of ultrafast carrier dynamics of nanostructured TiO2 films with and without CdSe quantum dot deposition using lens-free heterodyne detection transient grating technique
Q Shen; K Katayama; M Yamaguchi; T Sawada; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 486, 1-2, 15-19, Aug. 2005, Peer-reviwed, Ultrafast carrier dynamics of nanostructured TiO2 films with and without Use quantum dot (QD) deposition were studied using a lensfree heterodyne detection transient grating (LF-HD-TG) technique. The natiostructured TiO2 films were prepared with anatase TiO2 nanoparticles with an average diameter of 27 nm. Use quantum dots with an average size of 5 nm were adsorbed onto the TiO2 films by a chemical deposition (CD) technique. The relaxation processes of the photoexcited electrons and holes can be detected separately using the LF-HD-TG technique. For the TiO2 film without CdSe deposition, it was found that the photoexcited holes relaxed within 2 ps. For the Use QD deposited nanostructured TiO2 film, two decay processes with time constants of 2 ps (tau(1)) and 16 PS (tau(2)) were detected. The fast decay process was attributed to photoexcited hole relaxation due to trapping in Use QDs. The slow decay process mainly reflected photoexcited electron transfer from Use QDs to TiO2. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

Lens-free heterodyne transient grating technique
K Katayama; Q Shen; T Toyoda; M Yamaguchi; T Sawada
JOURNAL DE PHYSIQUE IV, EDP SCIENCES S A, 125, 349-353, Jun. 2005, Peer-reviwed, Recently developed lens-free heterodyne transient grating technique was applied to samples with rough surfaces on the order of several microns and photo-induced transient responses were successfully obtained on the temporal order of picoseconds. It was shown that the limitation of the sample roughness considerably reduced, compared with other conventional ultrafast methods. Theoretically the sample roughness was allowed on the order of 100 microns under our experimental condition, while it is on the order of several hundreds nanometers using a transient grating method.
Scientific journal, English

Photoluminescence study of mixtures of anatase and rutile TiO2 nanoparticles: Influence of charge transfer between the nanoparticles on their photo luminescence excitation bands
H Nakajima; T Mori; Q Shen; T Toyoda
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 409, 1-3, 81-84, Jun. 2005, Peer-reviwed, We have measured photoluminescence (PL) excitation spectra of TiO2 powders with various rutile phase contents, and have found a correlation between the energy level of the PL excitation band (E-PLE) and the rutile phase content. The EPLE of the mixture and its band-gap energy were redshifted compared to those expected from its rutile phase content. We can explain this correlation by considering the charge transfer between the anatase and rutile TiO2 nanoparticles of the mixture. These results suggest that the extent of charge transfer can be estimated by PL spectroscopy. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

Photoacoustic and photoluminescence characterization of passivated and unpassivated Mn-doped ZnS nanoparticles
AB Cruz; Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, JAPAN SOC APPLIED PHYSICS, 44, 6B, 4354-4357, Jun. 2005, Peer-reviwed, In this study, passivated and unpassivated nanocrystalline ZnS with varying Mn(2+) concentrations (ZnS:Mn) were synthesized and their photoacoustic (PA) and photoluminescence (PL) characteristics were studied. The PA intensity peak for the nanocrystalline ZnS was found to be blue-shifted compared with that for the bulk material due to quantum confinement effects. The difference of the PA signals of doped ZnS and undoped ZnS yielded the Mn(2+) optical absorption spectra. The intensity of the PA peak increased linearly with Mn concentration. The PL spectra showed a peak position at 2.08eV corresponding to the d-d transition of Mn(2+). For the unpassivated sample, a decrease in the PL intensities for higher Mn concentrations was observed. This could be attributed to concentration quenching. Addition of acrylic acid as a passivator led to an increase in PL intensity for all Mn concentrations and prevented the decrease in the PL intensity for higher Mn concentrations. These could be attributed to the surface passivation, which reduces the nonradiative recombination probabilities, thus increasing PL intensities.
Scientific journal, English

Photoacoustic and photoelectrochemical characterization of CdSe quantum dots grafted onto fluorine-doped tin oxide (FTO) substrate
T Toyoda; D Arae; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, JAPAN SOC APPLIED PHYSICS, 44, 6B, 4465-4468, Jun. 2005, Peer-reviwed, We report on the optical absorption properties, measured by the photoacoustic (PA) method, and photoelectrocheinical current (PEC) characteristics (including transient measurements) of CdSe quantum dots (Q-dots) grafted onto a planar fluorine-doped SnO2 (FTO) substrate. CdSe Q-dots were fabricated by the chemical solution deposition (CD) technique. With increasing deposition time, the redshift of the PA spectra can be clearly observed and optical absorption in the visible region due to CdSe Q-dots can be demonstrated. The average diameters of the CdSe Q-dots for each deposition time can be estimated using an effective mass approximation producing diameters of 5.1 not to 5.6 nm for deposition times of 5 h to 25 It, respectively. Thus, PA spectroscopy is useful in obtaining the Q-dots sizes even though there is no use of a high-resolution scanning electron microscope (SEM). An increase in PEC and the clear shift of the spectra to the lower energy region are observed with increasing deposition time, indicating the photosensitization of the FTO electrodes in the visible region resulting from CdSe Q-dots. It can be seen that the maximum value of incident photon to current conversion efficiency (IPCE) is similar to 10%, which is higher than that previously reported (similar to 6%). Transient PEC measurements show that electron recombination in a smaller amount of CdSe Q-dots is lower than that in a higher amount of Q-dots.
Scientific journal, English

Effect of ligand carboxylation on adsorption and photosensitization in Ru(II)-complex dye-sensitized nanocrystalline TiO(2) solar cell
T Ishihara; J Tokue; T Sano; Q Shen; T Toyoda; N Kobayashi
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, JAPAN SOC APPLIED PHYSICS, 44, 4B, 2780-2782, Apr. 2005, Peer-reviwed, The kinetics of dye adsorption onto a mesoporous TiO(2) film is compared between Ru(II) complex dyes with and without carboxy groups in the bipyridyl ligand, by diffuse reflectance spectroscopy at room temperature. Both dyes show adsorption saturation, and the dye without carboxy groups simply obeys the Langmuir isotherm equation. The dye with carboxy groups exhibits the same kinetics as the dye without carboxy groups in the period up to 20 min. However, in contrast to the latter, it increases its adsorption rate after this time, suggesting a change of the adsorption mode from physisorption to chemisorption. The carboxy group in the dye-sensitized solar cell is assumed to play a role in the chemical modification of the TiO(2) surface via a two-step adsorption from physisorption to chemisorption.
Scientific journal, English

Optical absorption, photoelectrochemical, and ultrafast carrier dynamic investigations of CdSe quantum dot sensitized TiO2 electrodes composed of nanotubes and nanowires
Q. Shen; K. Katayama; M. Yamaguchi; T. Sawada; K. Sato; T. Toyoda
Digest of Papers - Microprocesses and Nanotechnology 2005: 2005 International Microprocesses and Nanotechnology Conference, 2005, 184-185, 2005
International conference proceedings, English

Effect of rutile-type content on optical absorption and photoelectrochemical properties of nanostructured anatase-type TiO2 electrodes sensitized with CdSe quantum dots
H. Otsuka; Q. Shen; T. Toyoda
Digest of Papers - Microprocesses and Nanotechnology 2005: 2005 International Microprocesses and Nanotechnology Conference, 2005, 182-183, 2005, Interest in the study of dye-sensitized nanocrystalline TiO2 has grown considerably in recent years.1) In this study, two types of nanostructured TiO2 electrodes were prepared without rutile-type (100% anatase-type) and with rutile-type (12%) content. CdSe quantum dots (QDs) were adsorbed onto each of the two types of TiO2 electrodes as photosensitizer using a chemical deposition technique.2) Optical absorption and photoelectrochemical properties were characterized with photoacoustic (PA) and incident photon to current conversion efficiency (IPCE) methods, respectively. PA and IPCE spectra indicate the redshift with increasing CdSe adsorption time. It was found that the PA and IPCE spectra in the visible region were different for the two types of TiO2 electrodes for the same deposition time. Figs.1 and 2 show the PA and the IPCE spectra of TiO 2 electrodes without (a) and with (b) rutile-type content in different CdSe adsorption times, respectively. The PA and the IPCE intensities of TiO2 electrodes with rutile-type content were higher than those without rutile-type content, indicating that adsorbed CdSe QDs in the TiO 2 electrodes with rutile-type content might be higher than those without rutile-type content. Hence, the optical absorption and the transport properties in the TiO2 electrodes with rutile-type content might be improved. These results suggest that the rutile-type content is advantageous to increase the optical absorption and the photoelectrochemical properties of TiO2 electrodes.
International conference proceedings, English

Synthesis and characterization of nano honeycomb TiO2 electrodes
L. J. Diguna; M. Murakami; A. Sato; Y. Kumagai; T. Ishihara; N. Kobayashi; Q. Shen; T. Toyoda
Digest of Papers - Microprocesses and Nanotechnology 2005: 2005 International Microprocesses and Nanotechnology Conference, 2005, 96-97, 2005
International conference proceedings, English

Carrier dynamics of anatase and rutile TiO2 nanostructured electrodes adsorbed with CdSe quantum dots
Qing Shen; Yoki Kumagai; Kenji Katayama; Masahiro Yamaguchi; Tsuguo Sawada; Taro Toyoda
IQEC, International Quantum Electronics Conference Proceedings, 2005, 781-782, 2005, Peer-reviwed, Ultrafast carrier dynamics of anatase and rutile TiO2 nanostructured electrodes deposited with CdSe quantum dots (QDs) are studied using lens-free heterodyne detection transient grating (LF-HD-TG) technique. We find that the relaxation time of the photoexcited holes is as long as a few hundreds ps for rutile TiO2, but is smaller than 2 ps for anatase TiO2. Two decay processes with time scales of 2 ps (τ1) and a few tens ps or hundreds ps (τ2) are observed for CdSe QDs. The fast decay process is considered as photoexcited hole relaxation owing to trapping by the surface states of CdSe QDs. While the slow decay process reflects photoexcited electron relaxation processes, and mainly electron transfer from CdSe QDs to TiO2. We find that relaxation time of electrons (τ2) depends greatly on the crystal structure of TiO2.
International conference proceedings, English

Effect of UV exposure on the photoluminescence characteristics of nanocrystalline Mn-doped ZnS
Almira B. Cruz; Shen Qing; Taro Toyoda
IQEC, International Quantum Electronics Conference Proceedings, 2005, 777-778, 2005, Peer-reviwed, Upon UV exposure for the unpassivated and passivated Mn doped nanocrystalline ZnS we find increase in the PL intensity, corresponding to an increase in the radiative transition probability. The measured decay times for the unpassivated samples before and after UV exposure became shorter with higher Mn concentration. In the passivated samples, the measured decay time constant became longer with higher Mn concentrations. Over all the decay time constant for the passivated samples were shorter compared to the unpassivated samples.
International conference proceedings, English

Photoexcited carrier dynamic characterization of TiO2 electrodes composed of different size mixture of nanoparticles sensitized with CdSe quantum dots
Taro Toyoda; Yuki Kumagai; Qing Shen; Masahiro Yamaguchi; Tsuguo Sawada; Kenji Katayama
IQEC, International Quantum Electronics Conference Proceedings, 2005, 253-254, 2005, Peer-reviwed, We investigate the effect of different size mixture of TiO2 nanoparticles (15 and 27 nm) in anatase-type electrodes sensitized with CdSe quantum dots on excited carrier dynamics. The decay time of excited electrons in CdSe quantum dots decreases with the increase of 27 nm nanoparticles mixture.
International conference proceedings, English

Photosensitization of nanostructured TiO2 with CdSe quantum dots: effects of microstructure and electron transport in TiO2 substrates
Q Shen; D Arae; T Toyoda
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 164, 1-3, 75-80, Jun. 2004, Four sample types of nanostructured titanium dioxide (TiO2) electrodes were studied, variously prepared with TiO2 nanocrystalline particles of different sizes (15 and 27 nm in diameter) and with the addition of polyethylene glycol (PEG) binders having two different molecular weights (MW) (20,000 and 500,000). CdSe nanoparticles (CdSe quantum dots: CdSe QDs) were adsorbed on to each of the four types of TiO2 electrode using a chemical deposition technique. Photoacoustic (PA) and photoelectrochemical (PEC) current spectra were measured, together with the incident photon to current conversion efficiency (IPCE). The photosensitization by the CdSe QDs was confirmed. It was found that the PEC current and IPCE are strongly dependent on the TiO2 nanoparticle size and the MW of PEG in the TiO2/water paste. The correlation of the PEC and IPCE with the microstructure and the electron diffusion coefficient for each of TiO2 nanostructured electrode type are discussed, providing information which could lead to the optimization of dye-sensitized solar cells (DSSC). (C) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English

Characterization of nanostructured TiO2 electrodes sensitized with CdSe quantum dots using photoacoustic and photoelectrochemical current methods
Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 43, 5B, 2946-2951, May 2004, Two types of nanostructured titanium dioxide (TiO2) electrodes were prepared with anatase TiO2 nanoparticles of different sizes (average diameters of 15 and 27 nm). CdSe quantum dots were adsorbed onto each of the two types of TiO2 electrodes, by a chemical deposition (CD) technique, the average sizes of which increased to 7 nm on increasing the deposition time. Optical absorption and photoelectrochemical properties were characterized by using photoacoustic (PA) and photoelectrochemical (PEC) current methods. Redshift of the PA and PEC current spectra with increasing CdSe sizes was clearly observed, which indicates quantum confinement effects and photosensitization by the CdSe quantum dots. It was found that the PEC current spectra in the visible region were quite different for the two types of TiO2 electrodes for the same deposition time, although the PA spectra were very similar to each other. The correlation of the PEC current spectra with the microstructures of the two types of TiO2 electrodes was discussed, which provided information that could lead to the optimization of dye-sensitized solar cells (DSSC).
Scientific journal, English

Studies of optical absorption and electron transport in nanocrystalline TiO2 electrodes
Q Shen; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 438, 167-170, Aug. 2003, Four kinds of nanostructured titanium dioxide (TiO2) electrodes were prepared by changing the sizes of the TiO2 nanocrystalline particles (15 urn and 27 nm in diameter) and the molecular weight (MW) of the polyethylene glycol (PEG) (MW: 20 000 and 500 000) in TiO2/water paste, which was used for sample preparation. The effects of the sizes of the TiO2 particles and MW of the PEG on the microstructure, optical absorption, photoelectrochemical current (PEC) and electron transport properties of the resultant electrodes were studied. When the size of the TiO2 nanocrystalline particles used in the paste is larger, the porosity and the sizes of the TiO2 nanocrystals produced in the resultant electrodes increases. The TiO2/water paste with different MW of the PEG has different viscosity resulting to different microstructure and electron transport property of the TiO2 electrodes. It was found that the largest PEC current intensity and best electron transport property was obtained when the TiO2 electrode was prepared with the smaller TiO2 nanocrystals (15 nm) and the PEG with MW of 500 000. (C) 2003 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Photoacoustic and photoelectrochemical current response of nanostructured TiO2 electrodes
T Toyoda; M Hayashi; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 42, 5B, 3036-3040, May 2003, We report the effect of voltage in a concentrated KCl electrolyte applied to nanostructured TiO2 electrodes during their final preparation processes on photoacoustic (PA) and photoelectrochemical (PEC) current spectra and their modulation frequency dependence to clarify their response characteristics. The PA signal intensities of the TiO2 electrodes with different applied voltage treatments are higher than that without the treatments below the fundamental absorption edge. These results suggest an inner-band transition due to an increase in carrier concentration owing to donor levels formed by partially reduced Ti ions (Ti4+ --> Ti3+) following the applied voltage treatments. The PEC spectra for the applied voltage treatments above -1.5 V show broad bands at approximately 3.3 and 3.8 eV. The intensities of all peaks increase rapidly at an applied voltage above -1.5V, which is similar to that of the PA intensity at a photon energy of 2.0eV. The increase in the PEC intensity with different applied voltage treatments implies an increase in carrier concentration due to donor level formation by the treatments. The modulation frequency dependence of the PA signal intensity is related to the applied voltage treatments below a frequency of 60 Hz. This indicates the increase in the interfacial thermal resistance to prevent heat diffusion at the interface between the nanostructured TiO2 film and the Ti substrate with the increase in applied voltage. The modulation frequency dependence of PEC current also depends on the applied voltage treatments, indicating the enhancement of the photoexcited electron diffusion response with the increase in applied voltage.
Scientific journal, English

Effect of sensitization by quantum-sized CdS on photoacoustic and photoelectrochemical current spectra of porous TiO2 electrodes
T Toyoda; J Sato; Q Shen
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 74, 1, 297-299, Jan. 2003, Peer-reviwed, We report the optical absorption characteristics of highly porous, polycrystalline TiO2 electrodes, on which CdS nanocrystal particles are adsorbed, measured by the photoacoustic (PA) method together with the photoelectrochemical (PEC) current characteristics. The PA spectrum shifts to the lower photon energy region and the intensity below the band-gap energy of TiO2 increases rapidly with an increase in the number of CdS coating layers to 20 and becomes almost constant at more than 20 layers, indicating the possibility of the growth of CdS coated layers. The increase in PEC current intensity and a clear shift of spectra to the lower photon energy region are observed with the increased number of CdS coated layers, indicating the possibility of the transfer of photoexcited electrons of the CdS nanocrystals to the TiO2 conduction band. The PEC current spectrum shifts to the lower photon energy region and the intensity below the band-gap energy of TiO2 increases rapidly with an increase of in the number of CdS coating layers to 20 and decreases with a further increase in the number of layers coated to 40. Thus, nanocrystals of low-band-gap semiconductors are suitable for the sensitization of TiO2 PEC solar cells as well as dye sensitization. (C) 2003 American Institute of Physics.
Scientific journal, English

Photoacoustic spectroscopy of CdTe nanocrystals doped in a GeO2 glass matrix.
I.Tsuboya; D.Arae; Q.Shen; T.Toyoda
Review of Scientific Instruments, 74, 792, Jan. 2003, Peer-reviwed
Scientific journal, English

Mn ion concentration dependence of the photoacoustic and photoluminescence spectra of ZnS:Mn nanocrystals.
T.Toyoda; J.Matsuzawa; A.B.Cruz; Q.Shen
Review of Scientific Instruments, 74, 793, Jan. 2003, Peer-reviwed
Scientific journal, English

Exposure time dependence of the photoacoustic and photoluminescence intensities of porous silicon with different wavelengths of excitation light
T Toyoda; T Yamazaki; Q Shen
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 74, 1, 869-871, Jan. 2003, Peer-reviwed, We report the exposure time dependence of the photoacoustic (PA) intensities of porous silicon (PS) with different excitation wavelengths together with that of the photoluminescence (PL). Although the PA intensity decreases somewhat slowly with exposure time, the PL intensity undergoes significant degradation at a first stage until 50 min. The exposure time dependencies of PA and PL show the combinations of two exponential decays. Fast decay time in the PA intensity decreases with the increase of the excitation wavelength. On the other hand, that in the PL intensity increases with the increase of the excitation wavelength. In the shorter wavelength excitation, the degradation at first stage in PL is faster than that in PA. However, in the larger wavelength excitation, the degradation at first stage in PL is slower than that in PA. Slow decay times in PA and PL increase with the increase of the excitation wavelength. These experimental results suggest that the change of the optical absorption center is different from that of luminescent center. The former is related to the formation of oxides inside PS layers although the latter relates to the surface of PS. (C) 2003 American Institute of Physics.
Scientific journal, English

Dependence of thermal conductivity of porous silicon on porosity characterized by photoacoustic technique
Q Shen; T Toyoda
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 74, 1, 601-603, Jan. 2003, We have applied a photoacoustic (PA) technique to study the thermal properties of porous silicon (PS) films formed on p-type Si substrates by electrochemical anodic etching with greatly different porosities (20%-60%). From the dependence of the PA signals on the modulation frequency of excitation light measured under a transmission detection configuration, the effective thermal diffusivities for the two-layer PS on Si samples were determined. Using a two-layer model, the thermal conductivity of the PS films was evaluated and found to decrease greatly as the porosity is larger than 30%, which was two or three orders of magnitude lower than that reported for monocrystalline silicon. The results demonstrate that the thermal conductivity of PS films depends strongly on its structure. (C) 2003 American Institute of Physics.
Scientific journal, English

Effect of sensitization by quantum-sized CdS on photoacoustic and photoelectrochemical current spectra of porous TiO2 electrodes
T Toyoda; J Sato; Q Shen
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 74, 1, 297-299, Jan. 2003, We report the optical absorption characteristics of highly porous, polycrystalline TiO2 electrodes, on which CdS nanocrystal particles are adsorbed, measured by the photoacoustic (PA) method together with the photoelectrochemical (PEC) current characteristics. The PA spectrum shifts to the lower photon energy region and the intensity below the band-gap energy of TiO2 increases rapidly with an increase in the number of CdS coating layers to 20 and becomes almost constant at more than 20 layers, indicating the possibility of the growth of CdS coated layers. The increase in PEC current intensity and a clear shift of spectra to the lower photon energy region are observed with the increased number of CdS coated layers, indicating the possibility of the transfer of photoexcited electrons of the CdS nanocrystals to the TiO2 conduction band. The PEC current spectrum shifts to the lower photon energy region and the intensity below the band-gap energy of TiO2 increases rapidly with an increase of in the number of CdS coating layers to 20 and decreases with a further increase in the number of layers coated to 40. Thus, nanocrystals of low-band-gap semiconductors are suitable for the sensitization of TiO2 PEC solar cells as well as dye sensitization. (C) 2003 American Institute of Physics.
Scientific journal, English

Photoacoustic Spectroscopy of CdTe Nanocrystals Doped in GeO2 Glass Matrix
I. Tsuboya; D. Arae; Q. Shen; T. Toyoda
Rev. Sci. Instrum., 74, 792, 2003
Scientific journal, English

Mn Ion Concentration Dependence of the Photoacoustic and Photoluminescence Spectra of ZnS:Mn Nanocrystals
T. Toyoda; J. Matsuzawa; A. B. Cruz; Q. Shen
Rev. Sci. Instrum., 74, 793, 2003
Scientific journal, English

Pressure dependence of Brillouin scattering spectra in semiconductors CdSxSe1-x doped glasses.
Y.Takagi; N.Sato; Q.Shen; T.Toyoda
Journal of Non-Crystalline Solids, 307-310, 785-789, Dec. 2002, Peer-reviwed
Scientific journal, English

Porosity dependence of thermal conductivity for porous silicon characterized by photoaccoustic technique.
Q.Shen; T.Toyoda
Proceedings of the International Workshop on Modern Science and Technology, 79-82, Sep. 2002
International conference proceedings, English

Pressure dependence of Brillouin scattering spectra in semiconductors CdSxSe1-x doped glasses
Y Takagi; N Sato; Q Shen; T Toyoda
JOURNAL OF NON-CRYSTALLINE SOLIDS, ELSEVIER SCIENCE BV, 307, 785-789, Sep. 2002, In the glasses doped with semiconductors CdSxSe1-x (low-pass sharp-cut filters), the semiconductors in the glass matrix are developed by thermal treatments with various annealing times (t(a)) and temperatures (T-a). No size effects were previously obtained for Brillouin shifts of these samples. Therefore, Brillouin scattering of the samples with various, and T-a = 700 degreesC have been investigated under pressure. Any heat treatments made samples slightly soft and the internal strain inside the samples almost vanished. The slopes, d log omega/dP, were plotted as a function of t(a)(1/3), respectively. It was possible that the slopes indicated a linear increase. This result revealed that the semiconductor micro-crystals in the glasses contributed to the stiffening of the glasses. There seems to be some kind of size effect. (C) 2002 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO2 films fabricated with different applied voltage treatments
T Toyoda; M Hayashi; J Sato; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 41, 5B, 3367-3370, May 2002, Peer-reviwed, We report the effect of voltage in a concentrated KCl electrolyte applied to highly porous, polycrystalline TiO2 films during their final preparation processes on photoacoustic (PA) and photoelectrochemical (PEC) current spectra. The PA signal intensities of the TiO2 films with different applied voltage treatments are higher than those without the treatments below the band-gap region, suggesting an inner-band transition due to an increase in carrier concentration by the voltage treatments. The PA intensity below the band-gap region increases with the increase of the applied voltage, indicating the increase in the carrier concentration due to the formation of donor levels by partially reduced Ti ions (Ti4+ --> Ti3+). The PEC spectra for the applied voltage treatments with -1.5 V and without the treatments show broad bands at approximately 3.31 eV. The PEC spectra for the applied voltage treatments over -1.5 V show two peaks at approximately 3.31 eV and 3.88 eV. The PEC intensities at each peak position increase rapidly above the applied voltage of -1.5 V (eight times larger for the voltage of -3.5 V than those without the treatments), which is similar to that of the PA intensity at a photon energy of 2.0 eV. The increase of the PEC intensity with different applied voltage treatments implies an increase in carrier concentration due to the formation of donor levels by the treatments. These results suggest that TiO2 electrodes suitable for the sensitization by dyes or quantum-sized semiconductors can be obtained by applying the voltage treatments.
Scientific journal, English

Photoacoustic and photoluminescence spectra of ZnS : Mn nanocrystals
T Toyoda; J Matsuzawa; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 41, 5B, 3383-3386, May 2002, Peer-reviwed, The optical absorption spectra of ZnS:Mn nanocrystals can be obtained by applying photoacoustic (PA) spectroscopy, which is a powerful technique for detecting small amounts of highly scattered materials. The peak position in PA difference spectra increases linearly within experimental accuracy with the decrease of Mn2+ ion concentration. These results correspond to the following possibilities, (1) the increase of the higher excited energy states relative to the ground state of (6)A(1), (2) the increase of state density for the higher excited states and (3) the increase of transition probability from the (6)A(1) state to the higher excited states. These possibilities suggest the hybridization of the s-p states of the ZnS nanocrystal host and the d state of the Mn2+ ion impurity. The peak position of the PL spectrum (the transition from T-4(1) to (6)A(1) states) is similar to2.08 eV with a half width of 0.24 eV, similar to that of the bulk ZnS:Mn, and it is independent of the Mn2+ ion concentration. This result might be attributed to the fact that the Mn2+ emission is due to phonon assisted transition. Hence, there might be a slight shift of the peak position with increase of Mn2+ ion concentration due to hybridization of the s-p states of the ZnS nanocrystal host and the d state of the Mn2+ ion impurity. The peak intensity of the PL spectrum shows a maximum at a certain value of Mn2+ ion concentration and it decreases with the increase of concentration of Mn2+ ion impurities (concentration quenching).
Scientific journal, English

Effect of size confinement on CdSe nanocrystals in a GeO2 glass matrix characterized by photoacoustic spectroscopy
T Toyoda; D Arae; Q Shen
PHYSICA B-CONDENSED MATTER, ELSEVIER SCIENCE BV, 316, 476-478, May 2002, Peer-reviwed, Change in the electronic states due to quantum confinement effect was studied for CdSe nanocrystals in a GeO2 glass matrix by photoacoustic (PA) spectroscopy. The PA technique is a photothermal method which is useful for optical absorption characterization of opaque samples. In the PA method, one can detect an acoustic energy directly proportional to the thermal energy induced by nonradiative processes. The lowest excited energy of CdSe nanocrystals in a GeO2 glass by quantum confinement effect shifts to lower energy region with the increase of annealing time and temperature, indicating the increase of nanocrystal size. The nanocrystal growing is a diffusion process and the thermal activation energy of ion diffusion during nanocrystal growth is determined to be 1.7eV. (C) 2002 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Effect of size confinement on CdSe nanocrystals in a GeO2 glass matrix characterized by photoacoustic spectroscopy
T Toyoda; D Arae; Q Shen
PHYSICA B-CONDENSED MATTER, ELSEVIER SCIENCE BV, 316, 476-478, May 2002, Change in the electronic states due to quantum confinement effect was studied for CdSe nanocrystals in a GeO2 glass matrix by photoacoustic (PA) spectroscopy. The PA technique is a photothermal method which is useful for optical absorption characterization of opaque samples. In the PA method, one can detect an acoustic energy directly proportional to the thermal energy induced by nonradiative processes. The lowest excited energy of CdSe nanocrystals in a GeO2 glass by quantum confinement effect shifts to lower energy region with the increase of annealing time and temperature, indicating the increase of nanocrystal size. The nanocrystal growing is a diffusion process and the thermal activation energy of ion diffusion during nanocrystal growth is determined to be 1.7eV. (C) 2002 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO2 films fabricated with different applied voltage treatments
T Toyoda; M Hayashi; J Sato; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 41, 5B, 3367-3370, May 2002, We report the effect of voltage in a concentrated KCl electrolyte applied to highly porous, polycrystalline TiO2 films during their final preparation processes on photoacoustic (PA) and photoelectrochemical (PEC) current spectra. The PA signal intensities of the TiO2 films with different applied voltage treatments are higher than those without the treatments below the band-gap region, suggesting an inner-band transition due to an increase in carrier concentration by the voltage treatments. The PA intensity below the band-gap region increases with the increase of the applied voltage, indicating the increase in the carrier concentration due to the formation of donor levels by partially reduced Ti ions (Ti4+ --> Ti3+). The PEC spectra for the applied voltage treatments with -1.5 V and without the treatments show broad bands at approximately 3.31 eV. The PEC spectra for the applied voltage treatments over -1.5 V show two peaks at approximately 3.31 eV and 3.88 eV. The PEC intensities at each peak position increase rapidly above the applied voltage of -1.5 V (eight times larger for the voltage of -3.5 V than those without the treatments), which is similar to that of the PA intensity at a photon energy of 2.0 eV. The increase of the PEC intensity with different applied voltage treatments implies an increase in carrier concentration due to the formation of donor levels by the treatments. These results suggest that TiO2 electrodes suitable for the sensitization by dyes or quantum-sized semiconductors can be obtained by applying the voltage treatments.
Scientific journal, English

Photoacoustic and photoluminescence spectra of ZnS : Mn nanocrystals
T Toyoda; J Matsuzawa; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 41, 5B, 3383-3386, May 2002, The optical absorption spectra of ZnS:Mn nanocrystals can be obtained by applying photoacoustic (PA) spectroscopy, which is a powerful technique for detecting small amounts of highly scattered materials. The peak position in PA difference spectra increases linearly within experimental accuracy with the decrease of Mn2+ ion concentration. These results correspond to the following possibilities, (1) the increase of the higher excited energy states relative to the ground state of (6)A(1), (2) the increase of state density for the higher excited states and (3) the increase of transition probability from the (6)A(1) state to the higher excited states. These possibilities suggest the hybridization of the s-p states of the ZnS nanocrystal host and the d state of the Mn2+ ion impurity. The peak position of the PL spectrum (the transition from T-4(1) to (6)A(1) states) is similar to2.08 eV with a half width of 0.24 eV, similar to that of the bulk ZnS:Mn, and it is independent of the Mn2+ ion concentration. This result might be attributed to the fact that the Mn2+ emission is due to phonon assisted transition. Hence, there might be a slight shift of the peak position with increase of Mn2+ ion concentration due to hybridization of the s-p states of the ZnS nanocrystal host and the d state of the Mn2+ ion impurity. The peak intensity of the PL spectrum shows a maximum at a certain value of Mn2+ ion concentration and it decreases with the increase of concentration of Mn2+ ion impurities (concentration quenching).
Scientific journal, English

Photothermal characterization of highly porous, polycrystalline TiO2 electrodes fabricated by chemical synthesis
T Toyoda; M Hayashi; J Sato; Q Shen
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, KLUWER ACADEMIC PUBL, 69, 3, 1037-1044, 2002, Peer-reviwed, We report the optical absorption characteristics of highly porous, polycrystalline TiO2 electrodes and the influence of hydrolysis period for the preparation processes by photoacoustic (PA) spectroscopy together with photoelectrochemical (PEC) current ones. The PA spectra show peaks which are attributed to the lowest transition energy due to the quantum confinement effect. The peak intensity decreases with the increase of hydrolysis periods, indicating the possibilities of the changes in the thermal properties and the densities due to hydrolysis processes. The PEC spectra indicate that the photocurrent intensity also show peak and that of the longer hydrolysis periods is somewhat smaller than others, indicating the increase of interface states due to the formation of grain boundaries with the increase of hydrolysis processes.
Scientific journal, English

Characterization of thermal properties of porous silicon film/silicon using photoacoustic technique
Q Shen; T Toyoda
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, SPRINGER, 69, 3, 1067-1073, 2002, Peer-reviwed, We have applied photoacoustic (PA) technique to study the thermal properties of porous silicon (PS) films formed on p-type Si substrates by electrochemical anodic etching. Four PS samples with close thicknesses but greatly different porosities (from 20 to 60%) were examined. From the dependences of the PA signals on the modulation frequency of excitation light measured under a transmission detection configuration (TDC), effective thermal diffusivities for the two-layered PS/Si samples were determined and found to decrease greatly from 0.095 to 0.020 cm(2) s(-1) as the porosity increased from 20 to 60%.
Scientific journal, English

Pressure Dependence of Brillouin Scattering Spectra in Semiconductors CdSxSe1-x doped glasses
Y. Takagi; N. Sato; Q. Shen; T. Taro
J. Non-crystalline Solids, 307-310, 785-789, 2002
Scientific journal, English

Effect of Voltage Treatment on the Photoacoustic and Photoelectrochemical Current Spectra of Highly Porous, Polycrystalline TiO2 electrodes
J. Sato; M. Hayashi; Q. Shen; T. Toyoda
Anal. Sci., 17, i1153-i1155, 2002
Scientific journal, English

Photoacoustic Spectra of CdSe Nanocrystals in a GeO2 Glass Matrix
D. Arae; Q. Shen; T. Toyoda
Anal. Sci., 17, i1149-i1152, 2002
Scientific journal

Photothermal characterization of highly porous, polycrystalline TiO2 electrodes fabricated by chemical synthesis
T Toyoda; M Hayashi; J Sato; Q Shen
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, KLUWER ACADEMIC PUBL, 69, 3, 1037-1044, 2002, We report the optical absorption characteristics of highly porous, polycrystalline TiO2 electrodes and the influence of hydrolysis period for the preparation processes by photoacoustic (PA) spectroscopy together with photoelectrochemical (PEC) current ones. The PA spectra show peaks which are attributed to the lowest transition energy due to the quantum confinement effect. The peak intensity decreases with the increase of hydrolysis periods, indicating the possibilities of the changes in the thermal properties and the densities due to hydrolysis processes. The PEC spectra indicate that the photocurrent intensity also show peak and that of the longer hydrolysis periods is somewhat smaller than others, indicating the increase of interface states due to the formation of grain boundaries with the increase of hydrolysis processes.
Scientific journal, English

Characterization of thermal properties of porous silicon film/silicon using photoacoustic technique
Q. Shen; T. Toyoda
Journal of Thermal Analysis and Calorimetry, 69, 3, 1067-1073, 2002, We have applied photoacoustic (PA) technique to study the thermal properties of porous silicon (PS) films formed on p-type Si substrates by electrochemical anodic etching. Four PS samples with close thicknesses but greatly different porosities (from 20 to 60%) were examined. From the dependences of the PA signals on the modulation frequency of excitation light measured under a transmission detection configuration (TDC), effective thermal diffusivities for the two-layered PS/Si samples were determined and found to decrease greatly from 0.095 to 0.020 cm2 s-1 as the porosity increased from 20 to 60%.
Scientific journal, English

Photoacoustic spectra of mixed TiO2 ultrafine powders with rutile and anatase structures
T Toyoda; R Taira; Q Shen; M Ohmori
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 40, 5B, 3587-3590, May 2001, We have measured the optical absorption of mixed TiO2 ultrafine powders with rutile and tanatase structures by photoacoustic (PA) spectroscopy, which is a powerful technique for detecting small amounts of strongly scattered materials. The values of band-gap energies, E-g, of the TiO2 ultrafine powders with different rutile contents were determined by the theory of interband transition in semiconductors. The values of E-g of rutile and anatase structures of TiO2 ultrafine powders are 3.00 CV and 3.20 eV. respectively, obtained from FA intensity and PA phase spectra, indicating the usefulness of PA spectroscopy. Mixed TiO2 ultrafine powders with rutile and anatase structures (20-140 nm diameters) were obtained by thermal oxidation of TiCl4. Rutile structure contents depend on the thermal oxidation temperature. The value of E-g of a mixed TiO2 ultrafine powder with rutile and anatase structures decreases continuously with the increase of the rutile content. This indicates that the apparent E-g can be controlled by mixing the nanometer-sized TiO2 powders with rutile and anatase structures, hence, we can control and obtain TiO2 materials with an arbitrary apparent E-g between rutile and anatase structures.
Scientific journal, English

ZnOセラミックス中のCo不純物の光音響スペクトル
豊田太郎; 海野 誠; 沈 青
電子情報通信学会技術研究報告, The Institute of Electronics, Information and Communication Engineers, 100, 640, 17-22, 2001, Photoacoustic(PA) spectroscopy is applied to study the optical absorption of ZnO ceramics doped with 0-2.0 mol% CoO impurities sintered at 1200℃. PA spectroscopy is useful for scattering materials such as ceramics to get the optical absorption characteristics. Both of PA intensity and phase spectra showed the optical absorption peaks by Co impurities which were interpreted in terms of the inner transition of the(3d)^7 electrons in Co^<2+>(crystal field splitting). These signal intensities increase linearly with the increase of Co impurities at the low concentration region. At higher concentration region, they showed the constant values. These nonlinearlity of the PA intensities suggest the increase of magnetic interaction between Co impurities, and, hence, the PA intensities are saturated with the increase of Co impurities.
Japanese

Effect of size confinement on CdSe nanocrystals in a GeO_2_ glass matrix characterized by photoacoustic spectroscopy
T. Toyoda; D. Arae; T. Iio; Q. Shen
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 238-239, 2001
English

Optical absorption characteristics and modulation frequency dependence of the photoelectrochemical current spectra of highly porous，polycrystalline TiO_2_ electrodes
T. Toyoda; J. Sato; Q. Shen
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 240-241, 2001
English

Influence of anodization period on the photoacoustic spectra of poros silicon
T. Toyoda; R. Torai; Q. Shen
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 242-243, 2001
English

Photoacoustic spectra of mixed TiO_2_ ultrfine powders with rutile and anatase types
T. Toyoda; R. Taira; Q. Shen
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 244-245, 2001
English

ポーラスSiの光音響スペクトルの陽極化成電流時間依存性
虎井礼司; 沈 青; 豊田太郎
第48回応用物理学関係連合講演会講演予稿集, 812, 2001
Japanese

光音響分光法によるGeO_2_ガラス中に分散したCdSeナノクリスタル野評価
新江 大; 沈 青; 豊田太郎
第48回応用物理学関係連合講演会講演予稿集, 1419, 2001
Japanese

フラクタル状ポーラスTiO_2_電極の光吸収と光電流スペクトルの変調周波数依存性
佐藤 淳; 沈 青; 豊田太郎
第48回応用物理学関係連合講演会講演予稿集, 1420, 2001
Japanese

ルチル型とアナターゼ型のTiO_2_混合微粒子系の光音響法による評価
豊田太郎; 平 梨恵; 沈 青
第48回応用物理学関係連合講演会講演予稿集, 1420, 2001
Japanese

透過型光音響分光法による半導体の熱物性と電子物性の評価
沈 青; 豊田太郎
熱物性, 15, 15-22, 2001
Japanese

Photoacoustic spectra of mixed ceramics of Al2O3 and Cr2O3
T Toyoda; H Yamamoto; M Togashi; Q Shen
ANALYTICAL SCIENCES, JAPAN SOC ANALYTICAL CHEMISTRY, 17, S43-S46, 2001, Qualitative investigation of Cr3+ ion concentration dependence of the optical absorption characteristics in mixed ceramic Al2-xCrxO3 (0 less than or equal tox less than or equal to2) measured by photoacoustic (PA) spectroscopy have been carried out. Two peaks which correspond to U- and Y-bands ((4)A(2) --> T-4(2) and (4)A(2) --> T-4(1) transitions, respectively) can be observed up to the mole fraction x of 2.0. The peak positions of U- and Y-bands shift to lower photon energy region with the increase of mole fraction x. However, the decreasing rate of the Y-band is more rapid than that of the U-band, indicating the difference of the formation of electronic structures between U-band and Y-band with the increase of mole fraction x. The widths of U- and Y-bands increase with the increase of mole fraction x. The increase of the Y-band is slightly larger than that of the U-band (similar to 0.05 eV), indicating the difference between U-band and Y-band formation of the influence of the increase of mole fraction x.
Scientific journal, English

Photoacoustic spectra of low-dimensional magnet of VOMoO4
T Toyoda; Q Shen; Shiozaki, I
ANALYTICAL SCIENCES, JAPAN SOC ANALYTICAL CHEMISTRY, 17, S47-S49, 2001, Crystal of VOMoO4 is constituted from linear chains of VO6 octahedra along the c-axis. Every chain is connected with each other through MoO4 tetrahedra. The temperature dependent behavior of magnetic susceptibility shows a broad maximum around 100 K. That suggests a characteristic of one-dimensional antiferromagnet. Although optical absorption measurements are important to investigate electronic structure of materials at first step, few investigations on its characteristics have been carried out. In this paper, we report on the optical absorption properties of VOMoO4 by photoacoustic (PA) spectroscopy. It is useful to obtain absorption characteristics for strongly scattering media such as small sized crystals of VOMoO4 because its signal is less sensitive to light scattering effects. Although there were no dearly predominant interband transition, the optical absorption edge of VOMoO4 is assumed to be direct allowed transition because the square of the PA signal intensities are proportional to photon energy. Thus, the direct allowed band-gap energy for VOMoO4 is obtained as 1.6 eV for the first time by PA spectroscopic technique.
Scientific journal, English

Ultrafast dynamics of CdSxSe1-x nanocrystals doped in glasses studied by ultrafast transient lensing effect
Q Shen; T Toyoda; Y Hirose; K Katayama; H Yui; M Fujinami; T Sawada; A Harata
ANALYTICAL SCIENCES, JAPAN SOC ANALYTICAL CHEMISTRY, 17, S241-S244, 2001, Ultrafast dynamics of CdSxSe1-x (x=0.26) nanocrystals doped in glasses was studied using a femtosecond ultrafast transient lensing (UTL) technique. Three kinds of samples with different average diameters (5.3 nm, 6.5 nm and 9.4 nm, respectively) of CdSxSe1-x(x=0.26) nanocrystals were measured after photodarkened by irradiation of a pulsed laser light with a peak power density of 3 GW/cm(2) for 2 minutes. The UTL signals showed tri-exponential behaviors and three decay times were estimated to be about 1ps, 9 ps and > 300 ps. The three decay components were considered to be attributed to the direct recombination and trapping by some trapping states from the excited states, and subsequently radiative and nonradiative recombination processes through two kinds of trapping states at the nanocrystal-glass interfaces for the photo-excited carriers. It was found that as the averaged size of CdSxSe1-x (x=0.26) nanocrystals in the glasses decreased, the relative intensity of the 3rd component increased while that of the 2nd component decreased.
Scientific journal, English

Effect of size confinement on photoacoustic spectra and photothermal response of CdSxSe1-x (0 <= x <= 1) nanocrystals in a glass matrix
T Toyoda; Q Shen
ANALYTICAL SCIENCES, JAPAN SOC ANALYTICAL CHEMISTRY, 17, S259-S261, 2001, Photoacoustic (PA) spectroscopy is applied to study an optical absorption of CdSxSe1-x.(x=0.26) nanocrystals in a glass matrix annealed at 700 degreesC for different time duration. As the annealing time increases, a shift of the absorption peak due to the quantum confinement effect to lower energy is observed. The average diameters increases from 4.6 to 9.4 nm as the annealing time increases from 0 to 120 min. The PA signal intensities plotted in the semilogarithmic scale vary linearly below the fundamental absorption edges. The steepness factor (slope of exponential optical absorption) of the PA spectra increases with increasing annealing time. The ultrafast transient lensing (UTL) effect signals showed tri-exponential behavior in the order of 1 ps (A), a few ten ps (B), and more than a few hundred ps (C). It was found that the relative of component C increased while that of component B decreases as the size of nanocrystals in a glass matrix decreased.
Scientific journal, English

Characterization of optical and thermal properties of porous silicon using photoacoustic technique
Q Shen; T Takahashi; T Toyoda
ANALYTICAL SCIENCES, JAPAN SOC ANALYTICAL CHEMISTRY, 17, S281-S283, 2001, Optical and thermal properties of porous silicon (PS) performed on p-type Si substrates by anodic etching were studied using photoacoustic technique. Four kinds of PS samples with different thicknesses (1.1, 1.76, 1.87 and 2.54 mu m) were detected. In the PA spectra under a modulation frequency of 993 Hz, the PA signal intensity became larger as the thickness of the PS layer increased but the optical gaps were almost the same (similar to1.9 eV) for the all samples. From the frequency dependences of the PA signals under a transmission detection configuration (TDC) at an excitation wavelength of 360 nm, minima of the PA intensities appeared at frequencies f(min) and moved to lower frequency region with the increase of the PS thickness. Under TDC, thermal diffusion and carrier diffusion processes contributed to the PA signals and they could be separated by the analysis of frequency dependence. Effective thermal diffusivities for the two-layered PS/Si samples were estimated to be 0.034, 0.029, 0.018 and 0.016 cm(2)/s from f(min) for the four samples, respectively.
Scientific journal, English

Effect of voltage treatment on modulation frequency dependence of the photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO2 electrodes
T. Toyoda; J. Sato; Q. Shen
Jpn. J. Appl. Phys., The Japan Society of Applied Physics, 40, 5, 3853-3856, 2001, We report the effect of voltage on a concentrated KCl electrolyte applied to a highly porous TiO₂ electrode during its final preparation process on the photoelectrochemical current (PEC) spectra. Optical absorption measurements were monitored by a photoacoustic (PA) method. The PA spectrum of the TiO₂ electrode with the voltage treatment is similar to that without the treatment above the band-gap region. Below the band-gap region, the intensities of the PA spectrum of the TiO₂ electrode with the voltage treatment are higher than those without the treatment, suggesting an increase of carrier concentration by the voltage treatment. The PEC spectra without the voltage treatment show a monotonic increase with the photon energy above the band-gap region. The PEC intensity with the voltage treatment increases rapidly immediately above the band-gap region and shows saturated values. The PEC intensity of the TiO₂ electrode with the voltage treatment is approximately twice that without the treatment above the band-gap region. The increase of the PEC intensity implies an increase of carrier concentration due to partially reduced Ti ions. The modulation frequency dependence of the PEC intensity of TiO₂ electrodes with and without the voltage treatment shows two types of exponential decay. The decay rate in the TiO₂ electrode with the voltage treatment is slower than that without the treatment below the modulation frequency of 100 Hz. The decay rate with the voltage treatment agrees with that without the treatment above the modulation frequency of 100 Hz.
English

ポーラスSiの光音響スペクトルと蛍光スペクトルに及ぼす化学エッチング効果
豊田太郎; 高橋徹治; 沈 青
日本分光学会平成13年度春季講演会講演要旨集, 60, 2001
Japanese

Photo-acoustic spectra of CdSe nanocrystals in a GeO2 glass matrix
T. Toyoda; D. Arae; Q. Shen
Abstracts of the International Congress on Analytical Sciences 2001, 277, 2001
English

Effect of voltage treatments on the photoacoustic and photoelectrochemical current spectra highly porous, polycrystalline TiO2 electrodes
T. Toyoda; J. Sato; Q. Shen
Abstracts of the International Congress on Analytical Sciences 2001, 277, 2001
English

Photo- acoustic and photoluminescence spectra of porous silicon with different anodization period
T. Toyoda; R. Torai; Q. Shen
Abstracts of the International Congress on Analytical Science 2001, 278, 2001
English

Influence of anodization period on the photoacoustic spectra of porous silicon
T. Toyoda; R. Torai; Q. Shen
Abstracts of the 10th International Conference on Phonon Scattering in Condensed Matter, 216, 2001
English

Effect of size confinement on CdSe nanocrystals in a GeO2 glass matrix characterized by photoacoustic spectroscopy
T. Toyoda; D. Arae; Q. Shen
Abstracts of the 10th International Conference on Phonon Scattering in Condensed Matter, 218, 2001
English

ポーラスSiの光吸収と発光の時間依存性
虎井礼司; 沈 青; 豊田太郎
第62回応用物理学会学術講演会講演予稿集, 1076, 2001
Japanese

フラクタル状TiO2膜の光音響スペクトル
佐藤 淳; 林 雅; 沈 青; 豊田太郎
第62回応用物理学会学術講演会講演予稿集, 1082, 2001
Japanese

Photoacoustic, photoelectrochemical current, and photoluminescence spectra of highly porous, polycrystalline TiO2 electrodes fabricated by chemical synthesis
Taro Toyoda; Tomoya Hayakawa; Qing Shen
Materials Science and Engineering B: Solid-State Materials for Advanced Technology, Elsevier Sequoia SA, 78, 2-3, 84-89, 15 Dec. 2000, We report the effect of the application of a voltage in a concentrated KCl electrolyte on photoacoustic (PA), photoelectrochemical current (PEC), and photoluminescence (PL) spectra for the preparation of highly porous, polycrystalline TiO2 electrodes. The intensities of the PA spectra of the TiO2 electrode with the voltage treatments are larger than those without the treatments below the bandgap region, suggesting a decrease of scattering and/or an increase of the carrier concentration by the voltage treatments. The modulation frequency dependence of the PA intensity above the bandgap of the former is different from the latter in the low-frequency region, indicating a good contact (namely, the reduction of interface states) between the TiO2 film and the substrate (Ti metal). Also, the modulation frequency dependence of the PA phase above the bandgap region of the former is different from the latter, suggesting larger thermal conductivity of the TiO2 electrode with the voltage treatments than that without treatments. The intensity of the PEC spectrum of the TiO2 electrode with the voltage treatments is threefold that without the treatments above the bandgap region, also suggesting good contact (namely, the reduction of interface states). Although the peak positions in the PL spectra are in agreement with each other, the PL intensity of the TiO2 electrode with the voltage treatments is higher, suggesting the increase of the radiative recombination center owing to the increase of donor levels formed by partially reduced Ti ions.
Scientific journal, English

Photoacoustic, photoelectrochemical current, and photoluminescence spectra of highly porous, polycrystalline TiO2 electrodes fabricated by chemical synthesis
T Toyoda; T Hayakawa; Q Shen
MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, ELSEVIER SCIENCE SA, 78, 2-3, 84-89, Dec. 2000, We report the effect of the application of a voltage in a concentrated KCI electrolyte on photoacoustic (PA), photoelectrochemical current (PEC), and photoluminescence (PL) spectra for the preparation of highly porous, polycrystalline TiO2 electrodes. The intensities of the PA spectra of the TiO2 electrode with the voltage treatments are larger than those without the treatments below the bandgap region, suggesting a decrease of scattering and/or an increase of the carrier concentration by the voltage treatments. The modulation frequency dependence of the PA intensity above the bandgap of the former is different from the Latter in the low-frequency region, indicating a good contact (namely, the reduction of interface states) between the TiO2 film and the substrate (Ti metal). Also, the modulation frequency dependence of the PA phase above the bandgap region of the former is different from the latter, suggesting larger thermal conductivity of the TiO2 electrode with the voltage treatments than that without treatments. The intensity of the PEC spectrum of the TiO2 electrode with the voltage treatments is threefold that without the treatments above the bandgap region, also suggesting good contact (namely, the reduction of interface states). Although the peak positions in the PL spectra are in agreement with each other, the PL intensity of the TiO2 electrode with the voltage treatments is higher, suggesting the increase of the radiative recombination center owing to the increase of donor levels formed by partially reduced Ti ions. (C) 2000 Elsevier Science S.A. All rights reserved.
Scientific journal, English

Photoacoustic and photoluminescence studies of porous silicon etched by low-concentration hydrofluoric acid
T Toyoda; T Takahashi; Q Shen
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 88, 11, 6444-6450, Dec. 2000, We applied photoacoustic (PA), photoluminescence (PL), photoluminescence excitation (PLE), and atomic force microscopy (AFM) techniques on porous silicon (PS) layers to study the influence of chemical etching by low-concentration hydrofluoric acid. The chemical etching reveals the formation of PS layers of small dimensions by AFM observations, indicating the possibility of a strong quantum confinement effect. PA spectroscopy is useful to obtain the optical absorption characteristic for strongly scattering media such as PS and it helps to confirm the above speculation by indicating the blueshift of the fundamental absorption edge for the PS layer with chemical etching. PL spectroscopy also confirms the possibility of a quantum confinement effect by revealing the strong intensity and blueshift for the PS layer with chemical etching. PLE measurements suggest that the site for the radiative processes is different from that for the recombination of carriers and the PL of PS layers were dominated only by small crystallites in various size distributions. (C) 2000 American Institute of Physics. [S0021-8979(00)02919-4].
Scientific journal, English

Photoluminescence and photoacoustic investigations of the photodarkening effect in CdSxSe1-x nanocrystal-doped glasses
Q Shen; K Abe; T Shigenari; T Toyoda
JOURNAL OF LUMINESCENCE, ELSEVIER SCIENCE BV, 87-9, 444-446, May 2000, Photoluminescence (PL) and Photoacoustic (PA) techniques were applied to study photodarkening phenomena in CdSxSe1-x (x = 0.26) nanocrystal-doped glasses. We found that the PL intensities decreased greatly after undergoing darkening and the PA signal intensities became higher( similar to 3-6%). The PA signal intensities exponentially decay below the fundamental absorption edges, of which the logarithmic slope decreases after undergoing photodarkening. This implies an increase of the effective number of the surface states of the CdSxSe1-x nanocrystals due to darkening. These results can be explained well by a model according to which nonradiative recombination centers were activated at the semiconductor nanocrystal and glass interfaces by the darkening. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Scientific journal, English

Photoacoustic and photoluminescence characterization of highly porous, polycrystalline TiO2 electrodes made by chemical synthesis
T Toyoda; T Hayakawa; K Abe; T Shigenari; Q Shen
JOURNAL OF LUMINESCENCE, ELSEVIER SCIENCE BV, 87-9, 1237-1239, May 2000, We report the effect of the application of a voltage in a concentrated electrolyte on photoacoustic (PA) and photoluminescence (PL) spectra for the preparation of porous TiO2 electrodes. The intensities of the PA spectrum of the TiO2 electrode with the treatments are larger than those without the treatments below the band-gap region, indicating the formation of defect states at the surface. The modulation frequency dependence of the PA intensity of the former is different from the latter in the low-frequency region, indicating good contact and/or the reduction of the interface states between TiO2 film and substrate. The PL spectrum of the former shows more intense signal intensities than the latter, indicating the increase of recombination processes by the defect states at the surface. These states might aid in the formation of a good Schottky barrier. (C) 2000 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Photoacoustic characterization of thermal and electronic transport properties of CdInGaS4 in a transmission detection configuration
Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 39, 5B, 3164-3168, May 2000, Photoacoustic (PA) measurement under a transmission detection configuration (TDC) was applied to study the thermal and electronic transport properties of CdIaGaS(4). It was shown that the PA signal in the TDC originated from both electronic transport process and heat transport process in the semiconductor sample, and these could be separated by changing the modulation frequency of the elicited light. By fitting the theoretically calculated PA signal amplitudes as a function of the modulation frequence to the experimental ones for a variety of thicknesses, the values of the excess-carrier lifetime, carrier diffusivity, surface recombination velocity, and thermal diffusivity of the CdInGaS4 were determined. The contributions of three heat sources to the PA signals were investigated. We found that the PA signals of CdInGaS4 mainly resulted from nonradiative surface recombination under our experimental conditions.
Scientific journal, English

Characterization of electronic states of TiO2 powders by photoacoustic spectroscopy
T Toyoda; H Kawano; Q Shen; A Kotera; M Ohmori
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 39, 5B, 3160-3163, May 2000, We have measured the optical absorption of TiO2 powders by photoacoustic (PA) spectroscopy, which is powerful for detecting small amounts of strongly scattering materials. The band-gap energies E-g of rutile and anatase types of TiO2 powders with particle radii of 40nm are 3.06eV and 3.20eV, respectively, from PA intensity and PA phase spectra, indicating the usefulness of PA spectroscopy. The PA intensity and phase spectra show that the E-g of anatase-type TiO2 powders with a particle radius of 11 nm is 3.25 eV (blue shift) within the experimental accuracy, indicating the possible onset of a quantum size effect with decreasing particle size. The PA intensities plotted semilogarithmically vary linearly with photon energy immediately below the band-gap, in accordance with Urbach's rule (exponential tail). The slope of the exponential absorption of rutile-type TiO2 powders is larger than that of the anatase, indicating that the anatase-type has increasing energy from the displacement of atoms specifically due to oxygen vacancies and/or chlorine impurities in the production processes of the powders.
Scientific journal, English

Dependence of the photoacoustic signal intensity on modulation frequency for CdInGaS4 crystals under a transmission detection configuration
Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 39, 2A, 511-512, Feb. 2000, Dependence of the photoacoustic (PA) signals on the modulation frequency was measured for CdInGaS4 crystals in the reflection and transmission detection configurations (RDC and TDC). The PA signals originate from both the thermal diffusion and photo-excited carrier diffusion processes under TDC. The two processes can be separated by changing the modulation frequency of the excited light. The experimental results show the possibility of characterizing the thermal and electronic properties of CdInCaS4 crystals by the PA technique in TDC.
Scientific journal, English

Photoacoustic, Electrochemical Photocurrent, and Photoluminescence Spectra of Highly Porous, Polycrystalline TiO_2_ electrodes Fabricated by Chemical Synthesis
T. Toyoda; T. Hayakawa; Q. Shen
Extended Abstracts of the 3rd NIMC International Symposium on Photoreaction Control and Phtofunctional Materials, 256-257, 2000
English

Characterization of Electronic States for TiO_2_ Powders by Photoacoustic Spectroscopy
T. Toyoda; H. Kawano; Q. Shen; A. Kotera; M. Ohmori
Extended Abstracts of the 3rd NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 258-259, 2000
English

CdSeをドープしたGeO_2_ガラスの作製と光音響分光法による評価
沈 青; 飯尾能将; 豊田太郎
第47回応用物理学関係連合講演会講演予稿集, 1366, 2000
Japanese

Al_2_O_3_とCr_2_O_3_との結晶セラミックスの光音響スペクトル
豊田太郎; 山本洋秀; 富樫昌美; 沈 青
第47回応用物理学関係連合講演会講演予稿集, 1366, 2000
Japanese

TiO_2_膜の光音響ならびにフォトルミネッセンススペクトルに及ぼす電圧印加処理効果
豊田太郎; 早川智也; 沈 青
第47回応用物理学関係連合講演会講演予稿集, 1366, 2000
Japanese

TiO_2_膜の光音響ならびに光電流スペクトルに及ぼす電圧印加処理効果
豊田太郎; 早川智也; 沈 青
第47回応用物理学関係連合講演会講演予稿集, 1367, 2000
Japanese

Modulation Frequency Dependence of the Photoacoustic Signal Intensities for Multinary Compound CdInGaS4 with a DC Electric Field
Taro Toyoda; Masamichi Yamamuro; Qing Shen
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 39, 1, 457-458, 2000, Photoacoustic (PA) spectroscopy is used to study the heat generated by nonradiative processes of CdInGaS4 with an external dc electric field transverse to the light path in order to study the correlation between earner diffusion processes and nonradiative processes. Maxima are observed on PA spectra at 2.7 and 2.3 eV, the amplitude of which values are proportional to the square of the applied voltage. The peak at 2.7 eV shifted toward higher energy region when the modulation frequency increased. That at 2.3 eV did not shift. The PA signal intensity at 2.7 eV changes from f(-1.0) to f(-1.5), with the increase of de electric field. On the contrary, that at 2.3 eV changes suddenly from f(-1.5) to f(-2.0) with the increase of dc electric field.
Scientific journal, English

Modulation Frequency Dependences of Photoacoustic Signal Intensity and Phase for CdInGaS4
Qing Shen; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 39, 1, 459-460, 2000, Modulation frequency dependences of photoacoustic (PA) signal intensity and phase in a transmission geometry were experimentally measured and theoretically calculated for CdInGaS4. It was shown that the PA signal originated from both the electronic transport process and the heat diffusion process in the sample, which could be separated at a characteristic frequency f(min). It was found that the PA signal phase reversed and the PA signal intensity showed a minimum at the frequency f(min).
Scientific journal, English

Brillouin scattering of glasses doped with semiconductors CdS_x_Se_1-x_
Y. Takagi; N. Sato; Q. Shen; T. Toyoda
Trans. Mater. Res. Sco. Jpn., 25, 951-954, 2000
English

Effect of size confinement on photoacoustic spectra and photothermal response of CdS_x_Se_1-x_（0≦x≦1）nanocrystals in a glass matrix
T. Toyoda; Q. Shen
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, A-26-p1, 2000
English

Effect of chemical etching on photoacoustic and photocurrent spectra of highly porous, polycrystalline TiO_2_ electrodes,
T. Toyoda; T. Hayakawa; H. Kawano; Q. Shen
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, A-26-p4, 2000
English

Photoacoustic spectra of mixed ceramics of Al_2_O_3_ and Cr_2_O_3_
T. Toyoda; H. Yamamoto; M. Togashi; Q. Shen
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-01-11, 2000
English

Photoacoustic spectra of low-demensional magnet of VOMoO_4_
T. Toyoda; Q. Shen; I. Shiozaki
Abstracts of the 11th International Conference on Photoacoustic and Photohermal Phenomena, P-01-12, 2000
English

Photoacoustic studies of thermal and electronic properties of CdInGaS_4_
Q. Shen; T. Toyoda
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-03-25, 2000
English

Photoacoustic and photolmminescence studies of porous silicon etched by low-concentration HF
T. Toyoda; T. Takahashi; M. Yammamuro; Q. Shen
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-06-12, 2000
English

Chracterization of thermal and electronic properties of porous silicon using photoacoustic technique
Q. Shen; T. Takahashi; T. Toyoda
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-06-14, 2000
English

ポーラス化TiO_2_電極の，光音響ならびに光電流スペクトルに及ぼす電圧印加処理効果
豊田太郎; 早川智也; 河野 寛; 沈 青
第8回「高効率太陽電池および太陽光発電システム」ワークショップ予稿集, 155-158, 2000
Japanese

Chracterization of thermal and electronic properties of CdInGaS_4_ by photoacoustic technique
Q. Shen; T. Toyoda
Abstracts Book of the 1st Asian Conference on Crystal Growth and Crystal Technology, 427, 2000
English

Photoacoustic spectra of CdSe nenocrystals grown in a GeO_2_ glass mitrix
T. Toyoda; Q. Shen
Abstracts Book of the 1st Asian Conference on Crystal Growth and Crystal Technology, 428, 2000
English

Optical absorption characterization of low-dimensional magnet of VOMoO_4_ by photoacoustic spectroscopy
T. Toyoda; Q. Shen; I. Shiozaki
Abstracts Book of the 1st Asian Conference on Crystal Growth and Crystal Technology, 497, 2000
English

Effect of size confinement on ultrafast relaxation dynamics of CdS_x_Se_1-x_（x=0.26） nanocrystals in a glass matrix investigated by ultrafast lensing effect
T. Toyoda; Q. Shen; Y. Hirose; K. Katayama; M. Fujinami; T. Sawada; A. Harata
Abstracts of the 25th International Conference on the Physics of Semiconductors, 535, 2000
English

光音響法によるルチル型成分含有率の異なるTiO_2_微粒子の評価
豊田太郎; 平 梨恵; 河野 寛; 沈 青; 大森将弘
第21回日本熱物性シンポジウム講演論文集, 138-140, 2000
Japanese

光音響法によるポーラスシリコンの熱物性評価
沈 青; 高橋徹治; 豊田太郎
第21回日本熱物性シンポジウム講演論文集, 157-159, 2000
Japanese

Dependence of the photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO_2_ electrodes on mudulation frequency
J. Sato; Q. Shen; T. Toyoda
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 86, 2000
English

Photoacoustic spectra of mixed TiO_2_ powders with rutile and anatase types
R. Taira; Q. Shen; T. Toyoda
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 87, 2000
English

Photoacoustic spectra of CdS nanocrystals in a GeO_2_ glass matrix
D. Arae; Q. Shen; T. Toyoda
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 88, 2000
English

Photoacoustic spectra of ternarhy and multinary semiconducting compound CdIn_2_S_4_ with different stoichiometric ratio
N. Nakajima; T. Takizawa; Q. Shen; T. Toyoda
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 89, 2000
English

フラクタル状ポーラス化TiO_2_膜の光音響・光電流スペクトル変調周波数依存性
佐藤 淳; 沈 青; 豊田太郎
第21回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 109-110, 2000
Japanese

ルチル型とアナターゼ型のTiO_2_混合微粒子系の光音響スペクトル
豊田太郎; 平 梨恵; 沈 青
第21回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 111-112, 2000
Japanese

Brilouin Scattering of Glasses Doped with Semiconducters CdS_x_Se_1-x_
Yasunari Takagi; Naoko Sato; Qing Shen; Taro Toyoda
第11回日本MRS学術シンポジウム予稿集，（KSP 神戸サイエンスパーク）, 221, Dec. 1999
English

半導体（CdS_x_Se_1-x_）ドープガラスの顕微ブリルアン散乱
佐藤真子; 高木康成; 沈 青; 豊田太郎
日本物理学会講演概要集４，（岩手大), 620, Sep. 1999
Japanese

Photoacoustic studies of annealed CdSxSe1-x (x=0.26) nanocrystals in a glass matrix
Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 38, 5B, 3163-3167, May 1999, Photoacoustic (PA) spectroscopy is applied to study an optical absorption of CdSxSe1-x (s = 0.26) nanocrystals in a glass matrix annealed at 700 degrees C for different time durations. As the annealing lime increases, a shift of the absorption peak (due to the quantum confinement effect) to lower energy is observed in the PA spectra at room temperatures. The observed absorption peak shifts are used to evaluate the average size of CdSxSe1-x nanocrystals in terms of a simple model. The average radius increases from 2.3 to 4.7 nm as the annealing time increases from 0 to 120 min. The PA signal intensities plotted in the semilogarithmic scale vary linearly below the fundamental absorption edges in accordance with the Urbach rule for the optical absorption coefficient. The steepness factor (slope of exponential optical absorption) of the PA spectra increases with increasing annealing time. The change of the electronic states by annealing is explained by considering that the contribution of the surface states decreases with the increase of the nanocrystal size.
Scientific journal, English

Photoacoustic and photocurrent studies of highly porous TiO2 electrodes sensitized by quantum-sized CdS
T Toyoda; K Saikusa; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 38, 5B, 3185-3186, May 1999, Photoacoustic (PA) and photocurrent (PC) spectra of highly porous TiO2 have been measured. The PA spectrum shifts to the lower energy region and the PA intensity below the fundamental absorption edge of TiO2 increases rapidly with an increase in the number of CdS coating layers to seven and becomes almost constant at more than seven layers. The increase in PC intensity and a clear shift of spectra to the lower energy region are observed with increasing number of CdS layers coated, indicating the possibility of the transfer of photoexcited electrons of CdS nanocrystals to the conduction band of TiO2.
Scientific journal, English

CdS_x_Se_1-x_（x＝0.26）ドープガラスの光音響スペクトル
豊田太郎; 沈 青
電子情報通信学会技術研究報告（超音波）, US98-1～9, 23-28, Apr. 1999
Japanese

光音響を用いた，ポーラス化TiO_2_に吸着したCdSナノクリスタルの評価
豊田太郎; 七種耕治; 沈 青
日本音響学会1999年春季研究発表講演論文集, 1999, 1, 819-820, Mar. 1999
Japanese

光音響分光法によるCdInGaS_4_電子輸送と熱物性の評価
沈 青; 豊田太郎
第46回応用物理学会連合講演会講演予稿集, 1342, Mar. 1999
Japanese

光音響分光法によるphotodarkeningしたCdS_x_Se_1-x_ドープガラスの評価
沈 青; 豊田太郎
第46回応用物理学会連合講演会講演予稿集, 1342, Mar. 1999
Japanese

フラクタル化多結晶TiO_2_の光音響ならびに光電流スペクトル
早川智也; 沈 青; 豊田太郎
第46回応用物理学会連合講演会講演予稿集, 1343, Mar. 1999
Japanese

Photoacoustic spectra of CdInGaS4 with a dc electric field
T Toyoda; M Yamamuro; Q Shen
PHOTOACOUSTIC AND PHOTOTHERMAL PHENOMENA, AMER INST PHYSICS, 463, 274-276, 1999, Photoacoustic (PA) spectroscopy is used to study the heat generated by nonradiative processes of CdInGaS4, with an external de electric field transverse to the light path in order to stud! the correlation between carrier diffusion effects and nonradiative processes. Maxima are observed in PA spectra at 2.7 and 2.3 eV, the amplitude of which values are proportional to the square of the applied voltage. The peak at 2.7 eV shifted toward higher energy when the modulation frequency increased. That at 2.3 eV did not shift. The PA signal intensity at 2.7 eV changes from f(-1.0) to f(-1.5) with the increase of de electric field. On the contrary, that at 2.3 eV changes suddenly from f(-1.0) to f(-2.0) with the increase of de electric field.
International conference proceedings, English

Photoacoustic spectroscopy of annealed CdSxSe1-x (x = 0.26) nanocrystal doped glasses
Q Shen; T Toyoda
PHOTOACOUSTIC AND PHOTOTHERMAL PHENOMENA, AMER INST PHYSICS, 463, 494-496, 1999, Photoacoustic method has been applied to study the optical absorption properties of CdSxSe1-x (x=0.26) nanocrystals in a glass matrix annealed at 700 degrees C for different times. As the annealing time increases, the absorption peak in the PA spectra shifts to lower energies. The PA signal intensities exponentially decal below the fundamental absorption edges, of which the logarithmic dope increases with the increasing annealing time. It can be explained by decrease of the surface states relative to the whole electronic states due to the increase of radii and/or the increase of uniformity of the distribution of the nanocrystal sizes due to the annealing effect.
International conference proceedings, English

Photothermal applications of lasers: Study of fast and ultrafast photothermal phenomena at metal-liquid interfaces
A Harata; Q Shen; T Sawada
ANNUAL REVIEW OF PHYSICAL CHEMISTRY, ANNUAL REVIEWS INC, 50, 193-219, 1999, Recent studies on fast (<10 ns) and ultrafast (<10 ps) photothermal and photoacoustic phenomena occurring at solid-liquid interfaces are discussed, including related topics, with emphasis placed on interfaces between aqueous solutions and metals under electrochemical potential control. Details of transient reflecting grating measurements for metal-liquid interfaces are considered as they relate to mesoscopic interface structures and nano-environments. Dependencies of fast photothermal phenomena on the electrochemical potential and types of anions in the solutions are shown. Ultrafast photothermal phenomena observed by transient reflectivity measurements are considered in connection with interface femtochemistry and hot electron reactions. Technical progress in measuring fast and ultrafast photothermal phenomena is reviewed for solid-liquid interfaces, including colloidal solutions.
English

ポーラスSiの光音響スペクトルと発光特性
高橋 徹治; 山室正倫; 沈 青; 豊田太郎
電子情報通信学会技術研究報告（超音波）, The Institute of Electronics, Information and Communication Engineers, 99, 32, 7-12, 1999, Porous silicon,which can be prepared by electrochemical method on the Si surface, shows photoluminesoence in visible region at room temperature. So it has attracted much attention for application to optical devices. Although the optical absorption properties are very important for basic and applied studies,these properties can not be measured using the conventional method because of the light scattering and the opaque substrate. It is well known that photoacoustic (PA) method is useful for studying the optical absorption on those samples. In this work, the chemical etching effects of porous silicon are studied using photoacoustic, photoluminescence (PL) and photoluminescence excitation (PLE) methods. The PA signal intensity above the fundamental absorption edge of porous silicon with chemical etching is smaller than that without etching, indicating the larger fluorescence quantum efficiency in porous silicon with chemical etching than that without etching.
Japanese

光音響法による四元化合物半導体CdInGaS_4_の電子物性と熱物性の評価
沈 青; 豊田太郎
電子情報通信学会技術研究報告（超音波）, 99, 132, 9-14, 1999
Japanese

光音響法によるポーラス化フラクタル状TiO_2_の電圧印加処理の評価
豊田太郎; 早川智也; 沈 青
電子情報通信学会技術研究報告（超音波）, The Institute of Electronics, Information and Communication Engineers, 99, 132, 15-20, 1999, TiO_2 is one of the candidates for photoanode materials that split water in solar energy conversion cells because of its high chemical and photoelectrochemical durability. In order to increase solar energy conversion efficiency, the preparation of highly porous, polycrystalline TiO_2 to increase surface area by chemical synthesis has been proposed. In the present paper, we report the optical absorption spectra by photoacousric (PA) method of the materials to show the effect of applying voltage in electrolyte for final preparation processes. Although the PA spectrum of TiO_2 with applying voltage treatments is similar to that wihout the treatments above the band gap, the former below the band gap shows larger singal intensities than the latter, indicating the possibility of the formation of defect states by applying voltage treatments.
Japanese

Photoluminescence and Photoacoustic Study on Laser-Induced Darkening in CdS_x_Se_1-x_ Nanocrystal-Doped Glasses
Q. Shen; K. Abe; T. Shigenari; T. Toyoda
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 122, 1999
English

Photoacoustic and Photoluminescence Characterization of Highly Porous, Polycrystalline TiO_2_ electrodes made by Chemical Synthesis
T. Toyoda; T. Hayakawa; K. Abe; T. Shigenari; Q. Shen
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 176, 1999
English

Influence of Chemical Etching for Porous Silicon on Photoacoustic, Photoluminescence, and Photoluminescence Excitation Spectra
T. Toyoda; T. Takahashi; M. Yamamuro; K. Abe; T. Shigenari; Q. Shen
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 224, 1999
English

Nonradiative Character of Ceramic Al_2-x_Cr_x_O_3_（0.002＜■.―.x＜■.―.1.0）by Means of Photoacoustic Measurements
T. Toyoda; M. Togashi; Q. Shen
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 248, 1999
English

Photothermal Investigation of CdS_x_Se_1-x_（x＝0.26）Nanocrystals in a Glass Matrix（Annealing and Temperature Effect）
T. Toyoda; Q. Shen
Abstracts of the 15th European Conference on Thermophysical Properties, 324, 1999
English

Photothermal Investigation of Highly Porous, Polycrystalline TiO_2_ electrodes
T. Toyoda; T. Hayakawa; Q. Shen
Abstracts of the 15th European Conference on Thermophysical Properties, 325, 1999
English

Photothermal Investigation of P-Type Si with an Apllied DC-Electric Field
T. Toyoda; M. Ishida; T. Takahashi; Q. Shen
Abstracts of the 15th European Conference on Thermophysical Properties, 326, 1999
English

化学エッチングしたポーラスシリコンの発光と光音響スペクトル
高橋徹治; 沈 青; 豊田太郎
第60回応用物理学会学術講演会講演予稿集, 658, 1999
Japanese

光音響分光法によるCdInGaS_4_の電子物性と熱物性の評価（Ⅱ）
沈 青; 豊田太郎
第60回応用物理学会学術講演会講演予稿集, 658, 1999
Japanese

光音響法によるTiO_2_微粒子の評価
豊田太郎; 河野 寛; 沈 青; 小寺昭彦; 大森将弘
第20回日本熱物性シンポジウム講演論文集, 70-73, 1999
Japanese

光音響法によるポーラス化TiO_2_とその表面に吸着したCdSナノクリスタルの評価
豊田太郎; 七種耕治; 早川智也; 沈 青
第20回日本熱物性シンポジウム講演論文集, 74-77, 1999
Japanese

光音響分光法によるCdInGaS_4_の熱物性と電子物性の評価
沈 青; 豊田太郎
第20回日本熱物性シンポジウム講演論文集, 94-97, 1999
Japanese

CdSSe系ドープガラスの光音響スペクトル（アニール温度依存性）
沈 青; 飯尾能将; 豊田太郎
第20回日本熱物性シンポジウム講演論文集, 98-101, 1999
Japanese

ポーラスシリコンの光音響スペクトル
高橋徹治; 沈 青; 豊田太郎
第20回日本熱物性シンポジウム講演論文集, 106-109, 1999
Japanese

Al_2_O_3_とCr_2_O_3_との結晶セラミックスの光音響スペクトル
豊田太郎; 山本洋秀; 富樫昌美; 沈 青
第20回日本熱物性シンポジウム講演論文集, 110-113, 1999
Japanese

Al_2_O_3_とCr_2_O_3_との結晶セラミックスの光音響スペクトルと発光特性
豊田太郎; 山本洋秀; 高橋徹治; 沈 青
第19回電子材料研究討論会講演論文集, 62, 1999
Japanese

ポーラス化TiO_2_膜の光音響法による電子状態評価
豊田太郎; 早川智也; 河野 寛; 沈 青
第19回電子材料研究討論会講演論文集, 63, 1999
Japanese

TiO_2_微粒子の光音響スペクトル
豊田太郎; 河野 寛; 沈 青; 小寺昭彦; 大森将弘
第20回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 91-91, 1999
Japanese

透過型光音響法による CdInGaS_4_の熱物性と電子物性の評価
沈 青; 豊田太郎
第20回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 93-94, 1999
Japanese

ガラス中のCdS_x_Se_1-x_（x＝0.26）マイクロクラスター粒径変化が光音響スペクトルに及ぼす効果
沈 青; 豊田太郎
第19回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 59-60, Nov. 1998
Japanese

溶液成長によるCdS薄膜と，ポーラス化TiO_2_に吸着したCdSナノクリスタルの光音響スペクトル
豊田太郎; 七種耕治; 山室正倫; 沈 青
第19回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 141-142, Nov. 1998
Japanese

Detection of photoinduced electronic, thermal, and acoustic dynamics of gold film using a transient reflecting grating method under three types of surface plasmon resonance conditions
K Katayama; T Sawada; Q Shen; A Harata
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 58, 13, 8428-8436, Oct. 1998, Mechanisms of unusual signal enhancement observed for transient reflecting grating (TRG) experiments are investigated under three types of surface plasmon resonance (SPR) conditions, where two pump beams only, a probe beam only, or two pump beams and a probe beam, excite surface plasmon. A gold thin film deposited on a glass prism is measured in the Kretschmann configuration with a temporal resolution of tens of picoseconds. The signal under each SPR condition exhibits different characteristic features in signal intensity and transient behavior unlike the usual non-SPR TRG experiments. Under SPR with pump beams, high conversion efficiency from Light to heat allows detection of a TRG signal 11 times larger in magnitude and much lower in background level than under a non-SPR with them. Under SPR with the probe beam, diffraction caused by heat-induced spatial modulation as described by complex reflection Fresnel coefficients is theoretically proved to enhance the TRG signal and to change transient behavior, which provides a way to get selective observation of heat diffusion near the surface. When both pump and probe beams excite surface plasmons, an additional signal is observed, almost at the same time as the optical pulse, having 100 times larger intensity than the other signals, which is due to electrons excited at the gold surface.
Scientific journal, English

CdS微粒子を吸着したポーラス化TiO_2_の光音響ならびに光電流スペクトル
豊田太郎; 七種耕治; 沈 青
第18回電子材料研究討論会講演予稿集, 69-70, Oct. 1998
Japanese

CdSSe系ドープガラスの光音響スペクトル
沈 青; 豊田太郎
第18回電子材料研究討論会講演予稿集, 71-72, Oct. 1998
Japanese

CdSSe系ドープガラスの光音響スペクトル（アニール時間依存性）
島本 聡; 沈 青
第59回応用物理学会学術講演会講演予稿集, 1141, Sep. 1998
Japanese

CdS微粒子を吸着したポーラス化TiO_2_の光音響ならびに光電流スペクトル
豊田太郎; 七種耕治; 沈 青
第59回応用物理学会学術講演会講演予稿集, 1141, Sep. 1998
Japanese

Photoacoustic spectra of CdS_x_Se_1-x_（x＝0.26）nanocrystals in a glas matrix
T. Toyoda; Q. Shen
Abstracts of the Oji International Seminar on Photothermal Phenomena and Their Applications (invited), 26-33, Aug. 1998
English

Analysis of thim films and solid-liquid interfaces using picosecond transient reflecting grating technique
Q. Shen; A. Harata; T. Sawada
Oji International Seminar on Photothermal and Their Applications (invited), 80-87, Aug. 1998
English

Photoacoustic spectra of CdInGaS_4_ with a dc electric field
T. Toyoda; M. Yamamuro; Q. Shen
Abstracts of the 10th International Conference on Photoacoustic and Photothermal Phenomena, 205-206, Aug. 1998
English

Photoacoustic studies annealed GdSxSe1-x（x＝0.26）nanocrystals in a glass matrix
Q. Shen; T. Toyoda
Abstracts of the 10th International Conference on Photoacoustic and Photothermal Phenomena, 391-392, Aug. 1998
English

Detection of Photo-Induced Electronic, Thermal and Acoustic Dynamics of a Gold Film Using a Transient Reflecting Grating Method under Three Types of Surace Plasmon Resonance Conditions
Kenji KATAYAMA; Tsuguo SAWADA; Qing SHEN; and Akira HARATA
Physical Review B, 58, 13, 8428-8436, 1998, True
English

Photoacoustic and photoluminescence studies of CdSxSe1-x doped glasses
Q Shen; Y Kato; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 36, 5B, 3297-3299, May 1997, Peer-reviwed, A series of CdSxSe1-x doped glasses with a mole fraction of sulfur in the range 0.68 less than or equal to x less than or equal to 0.91 is studied by photoacoustic (PA) and photoluminescence (PL) methods. Unlike the usual transmitted optical absorption measurement in which the samples have to be thin and have good quality surfaces, the photoacoustic spectroscopy (PAS) measurement yields relatively true optical spectra even if the glasses are quite thick. From the PA spectra, shifts in absorption bands due to the quantum confinement effect are observed in the glasses having larger x values. The quantum confinement effect becomes larger in glasses with larger mole fractions of sulfur. The sizes of the microcrystals are expected to be smaller in the glasses having larger x values. This is also consistent with the PL experimental results.
Scientific journal, English

Hypersonic investigation of electrochemical interfaces
A Harata; Q Shen; T Sawada
PHYSICA B-CONDENSED MATTER, ELSEVIER SCIENCE BV, 219-20, 629-631, Apr. 1996, Peer-reviwed, Evidence is presented that an electric double layer is observable with hypersonic waves. Potential-dependent behavior of hypersonic waves was investigated with the transient reflecting grating (TRG) method for a gold film (1 mu m) electrode supported on a substrate in acidic solutions. Shapes of initial parts of the TRG-responses were dependent on the potential and composition of the solution. Theoretical calculation showed that longitudinal hypersonic echoes and heat diffusion dominate the initial part for the gold film. The acoustic wavelength of 22 nm is comparable to the thickness of the electric double layer whose structure is potential-dependent. Reflectivity of the hypersonic echoes depends on the potential.
Scientific journal, English

Theory of transient reflecting grating in fluid/metallic thin film/substrate systems for thin film characterization and electrochemical investigation
Q Shen; A Harata; T Sawada
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 35, 4A, 2339-2349, Apr. 1996, Peer-reviwed, A general theory was developed to calculate the diffraction signals from a transient reflecting grating (TRG) at metallic thin film/substrate interfaces and liquid/solid interfaces. The TRG signals for an Au film/soda lime glass system were experimentally measured and theoretically calculated to examine their agreement. It was found theoretically and experimentally that longitudinal acoustic pulses and echoes with ultrahigh-frequency components (> 10 GHz) propagating normal to the sample surfaces are generated and can be detected at the surfaces of thin films, using the TRG technique, along with surface acoustic waves. By using the time intervals of two neighboring longitudinal acoustic echoes, thicknesses or longitudinal acoustic wave velocities for opaque thin films were determinable. Furthermore, it was shown that this method is applicable to the analysis of electrochemical interfaces in situ, through changes in the thermal and longitudinal acoustic properties of electric double layers with electrochemical potentials.
Scientific journal, English

Enhancement of transient reflecting grating amplitude under surface plasmon resonance
Q Shen; K Katayama; A Harata; T Sawada
9TH INTERNATIONAL CONFERENCE ON PHOTOACOUSTIC AND PHOTOTHERMAL PHENOMENA, CONFERENCE DIGEST, NANJING UNIVERSITY INSTITUTE ACOUSTICS, 345-346, 1996, Peer-reviwed
International conference proceedings, English

Theoretical and experimental analyses of transient reflecting grating (TRG) generation and detection of hypersonic longitudinal waves
Q Shen; A Harata; T Sawada
ACUSTICA, S HIRZEL VERLAG, 82, S207-S207, Jan. 1996, Peer-reviwed
Scientific journal, English

ANALYSIS OF ION-IMPLANTED DIAMOND-LIKE-CARBON FILMS USING LASER-INDUCED TRANSIENT REFLECTING GRATING TECHNIQUE
Q SHEN; A HARATA; T SAWADA
JOURNAL DE PHYSIQUE IV, EDITIONS PHYSIQUE, 4, C7, 233-236, Jul. 1994, Peer-reviwed, Laser-induced transient reflecting grating (TRG) technique was applied to measure both nitrogen-ion-implanted and nonimplanted thin-film coatings (thickness, 40nm) of diamond-like-carbon (DLC). Different TRG responses corresponding to the different samples with a variety of nitrogen-ion implantation doses were observed and the hypersonic surface acoustic wave velocities were obtained with a variety of wavelengths. A phenomenon was observed that the SAW velocity of the implanted DLC coating with higher dose became larger than that of the nonimplanted sample.
Scientific journal, English

TRANSIENT REFLECTING GRATING STUDY OF ION-IMPLANTED SEMICONDUCTORS
A HARATA; H NISHIMURA; Q SHEN; T TANAKA; T SAWADA
JOURNAL DE PHYSIQUE IV, EDITIONS PHYSIQUE, 4, C7, 159-162, Jul. 1994, Peer-reviwed, Surface modification of Si(100) wafers induced by argon-ion implantation (ion energy, 300keV; dose, 10(11) - 10(17) atoms/cm(2)) was investigated using a transient reflecting grating technique. Effects of the implantation on velocity, intensity and onset time of surface acoustic waves (SAW) were discussed accompanying the acoustic anisotropy. SAW velocity dispersion was also examined for one of the lightly ion-implanted sample (dose, 10(11) atoms/cm(2)).
Scientific journal, English

LASER-STIMULATED SCATTERING MICROSCOPE STUDY OF AN ION-IMPLANTED SILICON SURFACE
A HARATA; Q SHEN; T TANAKA; T SAWADA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, JAPAN SOC APPLIED PHYSICS, 32, 8, 3633-3638, Aug. 1993, Peer-reviwed, Surface modification of a silicon single crystal induced by argon ion implantation of a light dose condition (300 keV, 10(11) atoms/cm2) has been investigated using a laser-stimulated scattering microscope, whose operational principle is based on microscopic measurements of transient reflecting gratings (TRGs). One-dimensional distributions of various material parameters, velocity, onset time and attenuation coefficient of surface acoustic waves and parameters relating to thermal diffusion, thermal expansion and optical absorption, are determined by analyzing the TRG responses measured sequentially along a line across the implanted and unimplanted regions. Some theoretical aspects are presented for the empirical equation used in deducing these parameters from the TRG responses. The change in the anisotropic property of the acoustic velocity is also discussed.
Scientific journal, English

Super narrow bandgap (<1.2 eV) halide double perovskites: Recent advancements and future perspectives
Jeong Yeon Lee; Padmini Pandey; Seojun Lee; Qing Shen; Dong Won Kang
In recent years, the utilization of perovskite materials attracted significant attention in optoelectronics due to their promising efficiency and cost-effectiveness. Nevertheless, challenges persist in precisely engineering the bandgap of perovskites to below 1.2 eV, a critical requirement for their incorporation in optoelectronic devices spanning interdisciplinary device applications aimed at exploiting the infrared regions. This review suggests halide double perovskites (HDPs) as potential alternatives, offering a comprehensive overview of recent advancements in this field. The study covers both experimental and theoretical approaches. Experimentally, the various compositions, bandgaps, material properties, and diverse preparation techniques for developing super narrow-bandgap (NBG) HDPs are thoroughly discussed. Theoretical perspectives are also explored, examining compositions, bandgap properties, and computational methods. This review explores the defects and associated challenges inherent in super narrow bandgap (NBG) hybrid double perovskites (HDPs), along with their utilization in interdisciplinary applications. It also includes a discussion on strategies to overcome current challenges, suggesting directions for further research, and envisioning potential applications of these materials in optoelectronic devices. Undoubtedly, the in-depth study of super NBG (below 1.2 eV) HDPs is set to have a significant impact on the development of advanced materials for cross-disciplinary device applications., 01 Jul. 2024, Chemical Engineering Journal, 491, Book review, 1385-8947, 85192492672

Resilient Women and the Resiliency of Science
Niveen M. Khashab; Sara E. Skrabalak; Lihi Adler-Abramovich; Stacey F. Bent; Fedwa El-Mellouhi; Eugenia Kumacheva; Delia J. Milliron; Jennifer Neu; Elham Rezasoltani; Qing Shen; Sabrina Sicolo
American Chemical Society, 14 Sep. 2021, Chemistry of Materials, 33, 17, 6585-6588, English, Book review, 1520-5002, 85114613597

State-of-the-Art Progress in Diverse Black Phosphorus-Based Structures: Basic Properties, Synthesis, Stability, Photo- and Electrocatalysis-Driven Energy Conversion
Wa Gao; Yong Zhou; Xinglong Wu; Qing Shen; Jinhua Ye; Zhigang Zou
Over the past few decades, the design and development of advanced catalysts for efficient energy conversion technologies have undergone extensive study. Black phosphorus (BP) is considered to be one of the most promising catalysts, exhibiting remarkable performance and drawing significant attention, because of its extraordinary physicochemical properties: a unique layered structure, anisotropic structure, tunable direct bandgap, and ultrahigh charge mobility. In this review, the fundamentals of bulk BP, single- and few-layer phosphorene, and BP quantum dots are briefly introduced, along with their crystal structure, optical and electrical properties, stability, and synthetic methods. Furthermore, recent progress toward diverse BP-based materials for photo- and electrocatalysis for renewable energy is summarized, specifically focusing on water splitting, CO2 conversion, and nitrogen fixation. Finally, the challenges ahead for these BP-based catalysts are also emphasized, alongside and perspectives on their further development as part of the this fast-flourishing renewable energy field., Wiley-VCH Verlag, 01 Jan. 2021, Advanced Functional Materials, 31, 3, English, Book review, 1616-3028, 85091181349

Quantum dot size dependence of the photoexcited carrier dynamics in PbS quantum dot film
小栗直己; 朝倉良太; DING C.; 早瀬修二; 豊田太郎; SHEN Q.
2021, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 68th, 202102240201278386

Optical Properties and Photoexcited Carrier Dynamics and Stability of APbBr₃ Perovskite NCs
矢嶋祥太; 川畑健太郎; LIU Feng; ZHANG Yaohong; DING Chao; 豊田太郎; 早瀬修二; SHEN Qing
2021, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 68th, 202102247523145609

Synthesis of CsSn_xPb_1-xI₃ Perovskite QDs and Their Optical Properties
矢嶋祥太; DING Chao; 豊田太郎; 早瀬修二; SHEN Qing
2021, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 82nd, 202202231973950590

Improvement of conversion efficiency of Tin perovskite solar cells by Multi-anion substitution
西村滉平; KAMARUDIN Muhammad Akmal; SHEN Qing; 飯久保智; 峯元高志; 吉野賢二; 早瀬修二
2021, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 82nd, 202202232355408872

Photoexcited carrier dynamics of PbS/CdS quantum dots film
小栗直己; DING C.; 早瀬修二; 曽我部東馬; 豊田太郎; SHEN Q.
2021, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 82nd, 202202261214535291

Improvement of conversion efficiency for tin perovskite solar cells using bromide substitution
西村滉平; KAMARUDIN Muhammad Akmal; SHEN Qing; 飯久保智; 峯元高志; 吉野賢二; 早瀬修二
2021, 電気化学秋季大会講演要旨集(CD-ROM), 2021, 202202211209742915

Standardization of Perovskite Films Deposition Process by in-situ Observation
廣谷太佑; 濱田健吾; KAMARUDIN Akmal; QING Shen; 豊田太郎; 早瀬修二
2020, 日本化学会春季年会講演予稿集(CD-ROM), 100th, 202002289223150806

Improvement of conversion efficiency of SnGe-perovskite solar cell by ethylammonium substitution
西村滉平; KAMARUDIN Muhammad Akmal; 廣谷太佑; 濱田健吾; 飯久保智; SHEN Qing; 峯元高志; 吉野賢二; 早瀬修二; 早瀬修二
2020, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 67th, 202002236244675829

Optical Absorption of PbS Quantum Dots with Ligands on Single Crystal TiO₂-Comparative Study of Photoacoustic and Absorbance Spectroscopies-
豊田太郎; SHEN Qing; 中澤直樹; 吉原泰葉; 神山慶太; 早瀬修二
2020, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 67th, 202002282074647284

Photoexcited carrier dynamics of PbS/CdS core-shell quantum dots
小栗直己; DING C.; 吉田康二; ZHANG Y.; 早瀬修二; 豊田太郎; SHEN Qing
2020, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 67th, 202002287919157664

Conversion Efficiency Improvement of SnGe-perovskite Solar Cells by Ethylammonium Substitution
西村滉平; KAMARYDIN Muhamad Akmal; 廣谷太佑; 濱田健吾; SHEN Qing; 飯久保智; 峯元高志; 吉野賢二; 早瀬修二; 早瀬修二
2020, 電気化学会大会講演要旨集(CD-ROM), 87th, 202002229326764906

Dependence of the optical properties and carrier dynamics of CsSn_xPb_1-xBr₃ Perovskite nanocrytal on the ratio of tin to lead
川畑健大朗; LIU Feng; ZHANG Yaohong; DING Chao; 豊田太郎; 早瀬修二; SHEN Qing
2020, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 81st, 202102241986403657

Efficiency improvement of Sn-perovskite solar cells by A-site multicationization
西村滉平; KAMARUDIN Muhammad Akmal; 廣谷太佑; 濱田健吾; 飯久保智; SHEN Qing; 峯元高志; 吉野賢二; 早瀬修二; 早瀬修二
2020, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 81st, 202102276707607187

Relationship between Built-in Potential and Open-circuit Voltage in Tin-based Perovskite Solar Cells
廣谷太佑; KAMARUDIN Muhammad Akmal; 西村滉平; SHEN Qing; 豊田太郎; 早瀬修二
2020, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 81st, 202102283659058140

Micro-scale current path distributions of Zn 1-x Mg x O-coated SnO 2 :F transparent electrodes prepared by sol-gel and sputtering methods in perovskite solar cells
Jakapan Chantana; Teruaki Hirayama; Chao Ding; Yu Kawano; Qing Shen; Kenji Yoshino; Shuzi Hayase; Takashi Minemoto
© 2018 Elsevier B.V. Methylammonium lead iodide perovskite solar cells with Zn 1-x Mg x O buffers (hole-blocking layers) were fabricated to optimize conduction band offset (CBO) of buffer/perovskite absorber interface. The Zn 1-x Mg x O films were prepared by sol-gel and sputtering methods. It is disclosed that the Zn 1-x Mg x O buffers with increasing [Mg]/([Mg] + [Zn]) from 0 (pure ZnO) to 0.15 prepared by the sol-gel method lead to the enhancement of conversion efficiency (η) from 10.7 to 15.1%, attributed to the improvement of the CBO. However, the Zn 1-x Mg x O buffers with enhancing [Mg]/([Mg] + [Zn]) from 0 to 0.10 deposited by the sputtering method yield the decrease in η from 6.6 to 5.6%. The lower η in the case of the sputtering method is mainly caused by the lower short-circuit current density (J SC ). According to micro-scale current path distributions of ZnO-coated SnO 2 :F (FTO) substrates, local current easily flows in case of ZnO-coated FTO sample by sol-gel method. On the other hand, the local current hardly flows especially at peak regions of sample surface in case of ZnO-coated FTO sample by sputtering method. This is because ZnO (or Zn 1-x Mg x O with [Mg]/([Mg] + [Zn]) of 0) by sputtering has higher resistance than that by sol-gel method and tends to be formed on peak regions of the FTO surface. Consequently, the low J SC of the perovskite solar cells with the buffer by sputtering method is observed., 01 Jan. 2019, Thin Solid Films, 669, 455-460, 0040-6090, 85056826714

異なるTiO₂結晶面に吸着した半導体量子ドットの光吸収とUrbach則-光熱変換法と吸光度法による評価-
豊田太郎; SHEN Qing; 神山慶太; 早瀬修二
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902218315783788

Aサイト置換によるSn-Perovskite太陽電池特性と結晶歪みの相関
西村滉平; 廣谷太佑; KAMARUDIN Muhammad Akmal; 飯久保智; SHEN Qing; 豊田太郎; 峯元高志; 吉野賢二; 早瀬修二
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902238899556452

TiO₂単結晶基板上にPbS量子ドット間距離を制御吸着した系の光音響法と光電子収量法による評価:量子ドット増感系
豊田太郎; SHEN Qing; 中澤直樹; 吉原泰葉; 神山慶太; 早瀬修二
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902256643166828

PbS量子ドット薄膜における光励起キャリアダイナミクス-量子ドットサイズの依存性-
北畠有紀子; 北畠有紀子; 大図修平; DING C.; ZHANG Y.; 豊田太郎; 早瀬修二; 片山建二; SHEN Q.
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902268098357964

界面パッシベーションによるPbS量子ドット/ZnOナノワイヤヘテロ接合太陽電池の開放電圧の向上
中村眞子; DING C.; 大図修平; 吉田康二; 吉原泰葉; 豊田太郎; 早瀬修二; SHEN Q.
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902237334555263

逆オパール構造TiO₂光電極を用いたSb₂S₃固体型増感太陽電池
吉原泰葉; 豊田太郎; 早瀬修二; SHEN Qing
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902269007839710

CsSn_xPb_1-xBr₃ペロブスカイト量子ドットの合成と光学的特性
川畑健大朗; LIU Feng; 安田寛啓; 吉田康二; 豊田太郎; 早瀬修二; SHEN Qing
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902280478540183

塗布型Pb-ペロブスカイトの半導体特性と太陽電池性能評価
廣谷太佑; 前田優太; SUDHIR Pandey Shyam; QING Shen; 豊田太郎; 峯元高志; 吉野賢二; 早瀬修二; 早瀬修二
2019, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 80th, 201902235770180479

相安定性を持つCsSn_xPb_1-xBr₃ペロブスカイト量子ドットの光学的特性
川畑健大朗; LIU Feng; ZHANG Yaohong; DING Chao; 豊田太郎; 早瀬修二; SHEN Qing
2019, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 80th, 201902273298371572

界面パッシベーションによるPbS量子ドット/ZnOナノワイヤーヘテロ接合太陽電池の電荷再結合の抑制
中村眞子; DIMG C.; 豊田太郎; 早瀬修二; SHEN Q.
2019, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 80th, 201902285143814962

Silver Bismuth Halideを用いた鉛フリー太陽電池の研究
濱田健吾; 廣谷太佑; 西村滉平; KAMARUDIN Muhammad Akmal; SHEN Qing; 豊田太郎; MA Tingli; 早瀬修二
2019, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 80th, 201902220327459540

Sn-ペロブスカイト太陽電池の保管による結晶歪みと変換効率の関係
西村滉平; KAMARUDIN Munammad Akmal; 廣谷太佑; 濱田健吾; 飯久保智; SHEN Qing; 豊田太郎; 峯元高志; 吉野賢二; 早瀬修二; 早瀬修二
2019, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 80th, 201902283093521769

FAPbI₃ペロブスカイトナノ結晶の光学特性と半導体基板への光励起電子の移動ダイナミクス
LIN X.; DING C.; ZHANG Y.; LIU F.; CHANTANA Jakapan; 峯元高志; 豊田太郎; 早瀬修二; SHEN Q.
2019, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 80th, 201902232394378132

異なるTiO₂結晶面に吸着した半導体量子ドットの光吸収とUrbach則:光熱変換法と吸光度法による評価
豊田太郎; SHEN Qing; 神山慶太; 早瀬修二
2019, 光化学討論会要旨集(CD-ROM), 2019, 201902256188578166

ルチル型TiO₂単結晶に吸着したPbS量子ドットの結晶成長と電子構造
豊田太郎; SHEN Qing; 堀奏江; 中澤直樹; 神山慶太; 早瀬修二
2018, ナノ学会大会講演予稿集, 16th, 201902218891602106

ペロブスカイト太陽電池における電荷分離・電荷再結合ダイナミックスと光電変換特性との相関 (特集 ペロブスカイト太陽電池の概観と最前線)
沈 青; 尾込 裕平; 豊田 太郎; 吉野 賢二; 早瀬 修二
応用物理学会有機分子・バイオエレクトロニクス分科会, Nov. 2016, Molecular electronics and bioelectronics = 応用物理学会,有機分子・バイオエレクトロニクス分科会会誌, 27, 4, 263-266, Japanese, 2423-8805, 40021070563, AN10464559

Charge Separation, Recombination and the Mechanism of Improvement in Photovoltaic Properties in Perovskite Solar Cells
沈 青; 尾込 裕平; 豊田 太郎; 吉野 賢二; 早瀬 修二
シーエムシー出版, Jul. 2015, ファインケミカル : 調査・資料・報道・抄録, 44, 7, 26-33, Japanese, 0913-6150, 40021171781, AN00015672

Non-vacuum Process of CuInS2 Thin Films From Metal Xanthate Precursors
Mochihara Akiko; Yoshino Kenji; Kawano Minobu; Ogomi Yuhei; Pandey Shyam S.; Shen Qing; Toyoda Taro; Hayase Shuzi
Miyazaki University, 31 Jul. 2014, Memoirs of the Faculty of Engineering, Miyazaki University, 43, 81-84, Japanese, 0540-4924, 110009817985, AA00732558

3P1-2 Photoacoustic Spectroscopy of TiO_2 Nanotube Electrode Adsorbed with CdSe Quantum Dots(Poster Session)
Akimoto Masaya; Shen Qing; Hayase Shuji; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 20 Nov. 2013, Proceedings of Symposium on Ultrasonic Electronics, 34, 415-416, English, 1348-8236, 110009847177, AA1240726X

2P1-9 Photoacoustic characterization of CdSe quantum dots adsorbed on different morphologies of nanostructured TiO_2 for photovoltaic applications(Poster Session)
Yindeesuk Witoon; Akimoto Masaya; Tai Daiki; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 13 Nov. 2012, Proceedings of Symposium on Ultrasonic Electronics, 33, 165-166, English, 1348-8236, 110009619784, AA1240726X

Photoacoustic Spectra of Self-Assembled TiO_2 Nanotube Electrodes by Anodic Oxidation
OTA Tomoka; YAMADA Akari; SHEN Qing; TOYODA Taro
Dye-sensitized solar cells (DSSCs) have attracted much interest as a next generation solar cell. Conventional DSSCs are composed of working electrode made from TiO_2 nanoparticles. Studies on several nanostructured TiO_2 electrodes are in progress. One-dimensional structures of TiO_2such as nanowires and nanotubes are useful for transporting electrons to the substrates. In this study, we prepared self-assembled TiO_2 nanotube (NT) films on Ti substrates using an electrochemical anodizing method. We characterize the optical absorption of TiO_2 NTs by using a photoacoustic (PA) technique. The PA technique is able to measure optical absorption properties for opaque samples., The Institute of Electronics, Information and Communication Engineers, 21 Apr. 2011, IEICE technical report, 111, 21, 35-39, Japanese, 0913-5685, 110008688761, AN1001290X

1Pa-7 Photoacoustic Characterization of Porous Zinc Oxide Thin Films(Poster Session)
Yamada Shuzo; Hosono Eiji; Zhou Haoshen; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 06 Dec. 2010, Proceedings of Symposium on Ultrasonic Electronics, 31, 29-30, English, 1348-8236, 110008149768, AA1240726X

1Pa-6 Photoacoustic and Photoelectrochemical Characterization of Nanostructures TiO_2 Electrode Adsorbed with PbS Quantum Dots(Poster Session)
Hachiya Sojiro; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 06 Dec. 2010, Proceedings of Symposium on Ultrasonic Electronics, 31, 27-28, English, 1348-8236, 110008149767, AA1240726X

1Pa-5 Photoacoustic Spectra of Self-Assembled TiO_2 Nanotube Electrodes by Anodic Oxidation(Poster Session)
Yamada Akari; Ota Tomoka; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 06 Dec. 2010, Proceedings of Symposium on Ultrasonic Electronics, 31, 25-26, English, 1348-8236, 110008149766, AA1240726X

2P2-20 Application of photoacoustic technique for Characterization of thermal diffusivities of nanostructured TiO_2 films(Poster Session)
Nin Tomohiro; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 18 Nov. 2009, Proceedings of Symposium on Ultrasonic Electronics, 30, 263-264, English, 1348-8236, 110007721692, AA1240726X

1J1-2 Characterization of thermal properties of porous Si film adsorbed with CdSe quantum dots using photoacoustic technique(Ultrasonic properties of materials, Phonon physics)
Kogakura Jun; Kato Yushi; Shen Qing; Toyoda Taro
A strong interest has been attracted on nanocrystalline Si (NSi) since it was found to show efficient luminescence at room temperature. In addition, NSi has the thermal conductivity much smaller than that of Si. Therefore, the NSi has been expected to be applied to light emitting devices, thermal insulators, and optical devices. But there are few reports about the thermal property of NSi. In particular, the mechanism of thermal conductive process in the NSi adsorbed with molecules and/or quantum dots is not clear. In this paper, we report our experimental results on the measurements of thermal properties of NSi film adsorbed with CdSe quantum dots using photoacousic technique., Steering committee of symposium on ultrasonic electronics, 11 Nov. 2008, Proceedings of Symposium on Ultrasonic Electronics, 29, 3-4, Japanese, 1348-8236, 110007459278, AA1240726X

Photoacoustic and Photoelectrochemical current spectra of TiO_2 Nanotube Electrodes prepared with Anodic oxidation
TAMURA Satoru; YAMADA Akari; SHEN Qing; TOYODA Taro
08 Oct. 2008, Thermophysical properties, 29, 137-139, Japanese, 0911-1743, 10024651201, AN10370091

Characterization of thermal properties of porous Si film adsorbed with CdSe quantum dots using photoacoustic technique
KOGAKURA Jun; KATO Yushi; SHEN Qing; TOYODA Taro
08 Oct. 2008, Thermophysical properties, 29, 149-151, Japanese, 0911-1743, 10024651238, AN10370091

PHOTOACOUSTIC AND ULTRAFAST CARRIER DYNAMICS OF Au QUANTUM DOTS GRAFTED ONTO NANOSTRUCTURED TiO_2 ELECTRODES
SHEN Qing; SUGANUMA Rihito; KATAYAMA Kenji; SAWADA Tsuguo; TOYODA Taro
08 Oct. 2008, Thermophysical properties, 29, 140-142, Japanese, 0911-1743, 10024651208, AN10370091

PHOTOACOUSTIC AND REFLECTION SPECTRA OF TiO_2 INVERSE OPAL ELECTRODES ADSORBED WITH CdSe QUANTUM DOTS
DIGUNA Lina Jaya; AYUZAWA Yasumasa; SHEN Qing; TOYODA Taro
08 Oct. 2008, Thermophysical properties, 29, 152-154, English, 0911-1743, 10024651246, AN10370091

Characterization of thermal properties of porous Si film adsorbed with CdSe quantum dots using photoacoustic technique
KOGAKURA Jun; KATO Yushi; SHEN Qing; TOYODA Taro
A strong interest has been attracted on porous Si (PSi) since it was found to show efficient luminescence at room temperature. In addition, PSi has the thermal conductivity much smaller than that of Si. Therefore, the PSi has been expected to be applied to light emitting devices, thermal insulators, and optical devices. But there are few reports about the thermal property of PSi. In particular, the mechanism of thermal conductive process in the PSi adsorbed with molecules and/or quantum dots is not clear. In this paper, we report our experimental results on the measurements of thermal properties of PSi film adsorbed with CdSe quantum dots using photoacousic technique., The Institute of Electronics, Information and Communication Engineers, 25 Apr. 2008, IEICE technical report, 108, 19, 5-9, Japanese, 0913-5685, 110006874039, AN1001290X

1-04P-18 Photoacoustic Spectra and Photoexcited Carrier Dynamics of CdSe Quantum Dots Adsorbed on TiO_2 Nanotubes Electrodes(Poster session 1)
Yamamoto K.; Shen Q.; Katayama K.; Sawada T.; Toyoda T.
Steering committee of symposium on ultrasonic electronics, 14 Nov. 2007, Proceedings of Symposium on Ultrasonic Electronics, 28, 51-52, English, 1348-8236, 110007459058, AA1240726X

1-04P-17 Photoacoustic Spectra and Ultrafast Carrier Dynamics of Nanostructured TiO_2 Films Sensitized with CdS Quantum Dots(Poster session 1)
Sato Akira; Shen Qing; Katayama Kenji; Sawada Tsuguo; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 14 Nov. 2007, Proceedings of Symposium on Ultrasonic Electronics, 28, 49-50, English, 1348-8236, 110007459057, AA1240726X

1-04-03 Characterization of Thermal Properties of Nano-crystalline Si Films Using Photoacoustic Technique(Acousto-optics)
Shen Qing; Kato Yusi; Kogakura Jun; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 14 Nov. 2007, Proceedings of Symposium on Ultrasonic Electronics, 28, 11-12, English, 1348-8236, 110007459039, AA1240726X

1-04P-15 Photoacoustic Spectra of Au Quantum Dots Adsorbed on Nanostructured TiO_2 Films(Poster session 1)
Toyoda Taro; Tsugawa Sae; Shen Qing
Steering committee of symposium on ultrasonic electronics, 14 Nov. 2007, Proceedings of Symposium on Ultrasonic Electronics, 28, 45-46, English, 1348-8236, 110007459055, AA1240726X

Photoacoustic and Photoelectrochemical Current Spectra of TiO_2 Nanotube Electrodes Adsorbed with CdSe Quantum Dots
TAMURA Satoru; YAMAMOTO Kana; SHEN Qing; TOYODA Taro
Dye-sensitized solar cells (DSSCs) made from nanostructured TiO_2 electrodes have received considerable attention as future solar cells. The surface morphology optimization of TiO_2 electrodes is one of the factors for improving the DSSCs efficiency. Recently, it was reported that TiO_2 nanotube electrodes show higher short-circuit current than TiO_2 nanoparticle electrodes. This phenomena can be possibly applied for DSSCs to increase photovoltaic conversion efficiency. In this paper, we fabricated the TiO_2 nanotube electrodes, and CdSe quantum dots (QDs) were adsorbed as a sensitizer instead of organic dye. We report the experimental results on optical absorption and electron transfer from CdSe QDs to TiO_2 electrodes by using the photoacoustic (PAS) and incident photon to current conversion efficiency (IPCE) methods, respectively., The Institute of Electronics, Information and Communication Engineers, 23 May 2007, IEICE technical report, 107, 75, 1-4, Japanese, 0913-5685, 110006290582, AN1001290X

P3-38 Photoacoustic and Photoelectrochemical Characterization of CdSe Quantum Dots Grafted onto Fluorine-Doped Tin Oxide (FTO) Glass and Nanostructured SnO_2 Electrode(Poster session 3)
Toyoda Taro; Yanai Makoto; Shen Qing; Katayama Kenji; Sawada Tsuguo
Steering committee of symposium on ultrasonic electronics, 15 Nov. 2006, Proceedings of Symposium on Ultrasonic Electronics, 27, 449-450, English, 1348-8236, 110007458990, AA1240726X

P3-41 Photoacoustic Spectroscopy of CdSe Quantum Dots Adsorbed on Nanostructured TiO_2 Electrode(Poster session 3)
Toyoda Taro; Uehata Terumasa; Shen Qing
Steering committee of symposium on ultrasonic electronics, 15 Nov. 2006, Proceedings of Symposium on Ultrasonic Electronics, 27, 455-456, English, 1348-8236, 110007458993, AA1240726X

Photoacoustic and photoelectrochemical characterization of photonic TiO_2 electrodes sensitized with CdSe quantum dots
SATO Akira; DIGUNA Lina J.; SHEN Qing; ISHIHARA Taishi; KOBAYASHI Naoki; TOYODA Taro
Periodic dielectric arrays with lattice space of the order of wavelengths of light are termed as photonic crystals. Photonic crystals have a property that the group velocity of the specific light becomes small. This phenomena can be possibly applied for dye-sensitized solar cells (DSSC) to increase light harvesting efficiency. In this paper, we fabricated the TiO_2 photonic crystals electrodes, and adsorbed CdSe quantum dots (QDs) on the electrodes as a sensitizer instead of organic dye. We report the experimental results on light absorption and electron transfer from CdSe QDs to TiO_2 electrodes by using the photoacoustic (PA) method and incident photon to current conversion efficiency (IPCE) method, respectively., The Institute of Electronics, Information and Communication Engineers, 19 Apr. 2006, IEICE technical report, 106, 28, 31-34, Japanese, 0913-5685, 110004718814, AN1001290X

J-2 Photoacoustic and Photoelectrochemical Characterization of TiO_2 Nanotube and Nanowire Composite Electrodes Sensitized with CdSe Quantum Dots
Yamamoto Kana; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 16 Nov. 2005, Proceedings of Symposium on Ultrasonic Electronics, 26, 331-332, Japanese, 1348-8236, 110007458684, AA1240726X

P3-66 Photoacoustic and ohotoelectorochemical characterization of nhotonic TiO_2 electrodes sensitized with CdSe quantum dots
Sato Akira; Diguna Lina J.; Murakami Motonobu; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 16 Nov. 2005, Proceedings of Symposium on Ultrasonic Electronics, 26, 471-472, Japanese, 1348-8236, 110007458753, AA1240726X

P3-54 Dependence of HF concentration in anodization process on photoacoustic and photoluminescence spectra
Kumei M.; Inoguchi M.; Toyoda T.; Shen Q.
Steering committee of symposium on ultrasonic electronics, 16 Nov. 2005, Proceedings of Symposium on Ultrasonic Electronics, 26, 447-448, Japanese, 1348-8236, 110007458741, AA1240726X

P3-59 Photoacoustic and photoelectrochemical characterization of CdSe quantum dots grafted onto fluorine-doped tin oxide (FTO) glass and nanostructured SnO_2 electrodes
Yanai Makoto; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 16 Nov. 2005, Proceedings of Symposium on Ultrasonic Electronics, 26, 457-458, Japanese, 1348-8236, 110007458746, AA1240726X

Charactarization of Nanocrystalline Silicon using Photoacoustic Method
INOGUCHI Masashi; SHEN Qing; TOYODA Taro
We applied a photoacoustic (PA) technique to study the optical absorption and thermal diffusivity of nanocrystalline silicon (NSi) samples. The NSi layers were formed on p-type Si wafers in an HF electrolyte. Three kinds of NSi samples that had undergone chemical post-etching were studied before and after UV irradiation for 2 h. We observed that a strong confinement effect occurred in all of the NSi samples from the blue shift of the band gap energy compared with that of crystalline Si, while the effective thermal diffusivities were almost two orders of the magnitude smaller than that of conventional Si crystals. The band gap shifted to higher energy and the effective thermal diffusivity decreased as the post-etching time increased. In the case of a NSi sample that was not chemically post-etched, the optical absorption and effective thermal diffusivity before and after UV irradiation were almost unchanged. However, for the NSi samples that were chemically post-etched, the optical absorption decreased and the effective thermal diffusivity increased after UV irradiation. This indicates that NSi samples that are post-etched are more readily affected by UV irradiation, i.e., oxidized by replacing Si-Hx bonds by Si-Ox, than those that do not undergo post-etching., The Institute of Electronics, Information and Communication Engineers, 06 May 2005, IEICE technical report. Ultrasonics, 105, 44, 13-18, Japanese, 0913-5685, 110003204779, AN1001290X

P2-34 Photoacoustic and Photoluminescence Characterization of Mn-doped ZnS Nanoparticle : Study of UV Irradiation Effect(Short presentation for poster)
Cruz Almira B.; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 27 Oct. 2004, Proceedings of Symposium on Ultrasonic Electronics, 25, 225-226, English, 1348-8236, 110007458396, AA1240726X

P1-48 Photoacoustic and photoelectrochemical characterization of CdSe quantum dots grafted onto fluorine-doped tin oxide (FTO) glass
Toyoda Taro; Arae Dai; Shen Qing
Steering committee of symposium on ultrasonic electronics, 27 Oct. 2004, Proceedings of Symposium on Ultrasonic Electronics, 25, 107-108, Japanese, 1348-8236, 110007458338, AA1240726X

P1-47 Photoacoustic and Photoelectrochemical Current Characterization of Nanostractured TiO_2 Electrodes Composed with Different Size TiO_2 Nanoparticles
Kumagai Yuki; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 27 Oct. 2004, Proceedings of Symposium on Ultrasonic Electronics, 25, 105-106, Japanese, 1348-8236, 110007458337, AA1240726X

P1-46 Characterization of Optical Absorption and Thermal Diffusivity for Nanocrystaline Silicon
Inoguchi M.; Shen Q.; Toyoda T.
Steering committee of symposium on ultrasonic electronics, 27 Oct. 2004, Proceedings of Symposium on Ultrasonic Electronics, 25, 103-104, Japanese, 1348-8236, 110007458336, AA1240726X

P1-49 Photoacoustic and photoelectrochemical current characterization of nanostructured TiO_2 electrodes : annealing temperature dependence
Sato Tadakazu; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 27 Oct. 2004, Proceedings of Symposium on Ultrasonic Electronics, 25, 109-110, Japanese, 1348-8236, 110007458339, AA1240726X

P2-E-36 Photoacoustic and Photoelectrochecnical Current Spectra of Nanostructured TiO_2 Electrodes Composed with Different Size TiO_2 Nanoparticles
Kumagai Yuki; Qing Shen; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 12 Nov. 2003, Proceedings of Symposium on Ultrasonic Electronics, 24, 189-190, Japanese, 1348-8236, 110007458177, AA1240726X

P2-E-35 Characterization of Nanostructured TiO_2 Electrodes Sensitized with CdSe Quantum Dots Using Photoacoustic and Photoelectrochemical Current Methods
Qing Shen; Arae Dai; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 12 Nov. 2003, Proceedings of Symposium on Ultrasonic Electronics, 24, 187-188, Japanese, 1348-8236, 110007458176, AA1240726X

C-4 Photoacoustic and photoelectrochemical current response of nanostructured TiO_2 electrodes
Toyoda Taro; Hayashi Masashi; Shen Qing
Steering committee of symposium on ultrasonic electronics, 07 Nov. 2002, Symposium on ultrasonic electronics, 23, 125-126, Japanese, 110007464420, AN10578660

Photoacoustic Characterization of Highly Porous, Polycrystalline TiO_2 Electrodes Fabricated with Different Applied Voltage Treatments
HAYASHI M.; SHEN Q.; TOYODA T.
We report the effect of voltage on a concentrated KCI electrolyte applied to highly porous, polycrystalline TiC_2 films on the photoacoustic (PA) and photoelectrochemical (PEC) current spectra. The PA signal intensities of the TiO_2 films with the different applied voltage treatments are higher than that without the treatments below the band-gap region, suggesting an inner-band transition due to an increase of carrier concentration by the voltage treatments. The PA intensity below the band-gap region increases with the increase of the applied voltage, indicating the increase of the carrier concentration. The PEC spectra for the applied voltage treatments with -1.5 V and without the treatments show broad bands at approximately around 3.31 eV. The PEC spectra for the applied voltage treatments over -1.5 V show two peaks at approximately around 3.31 eV and 3.88 eV. The intensities of the each peak positions increase rapidly above the applied voltage of -1.5 V. The increase of the PEC intensity with the different applied voltage treatments implies an increase carrier concentration due to donor levels formation by the treatments., The Institute of Electronics, Information and Communication Engineers, 13 May 2002, IEICE technical report. Ultrasonics, 102, 67, 1-5, Japanese, 0913-5685, 110003188504, AN1001290X

Photoacoustic Characterization of Thermal Properties of Porous Silicon Films
SHEN Q.; TOYODA T.
Since porous silicon(PS)showed efficient luminescence at room temperature, a strong interest has been attracted on both the light emission mechanism and the applications of PS such as light emitting devices, thermal insulators, and optical devices. It is important to study the optical and thermal properties of PS for these applications. In particularly, it is desirable to measure the properties of PS without separating PS from a Si substrate. In this paper, we report our experimental results on the measurements of thermal diffusivities of PS samples with different porosities using the transmitted photoacoustic method. We will show how the thermal diffusivity of PS changes with the porosities of the PS., The Institute of Electronics, Information and Communication Engineers, 12 Dec. 2001, IEICE technical report. Ultrasonics, 101, 514, 7-13, Japanese, 0913-5685, 110003188471, AN1001290X

P1-28 Photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO_2 filmes
Hayashi Masashi; Sato Jun; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 07 Nov. 2001, Symposium on ultrasonic electronics, 22, 119-120, Japanese, 110007464207, AN10578660

P2-25 Photoacoustic spectra of ZnS:Mn Nanocrystals
Matsuzawa Juichiro; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 07 Nov. 2001, Symposium on ultrasonic electronics, 22, 221-222, Japanese, 110007464258, AN10578660

Photoacoustic Spectra of Low-Dimensional Magnet of VOMoO4 (Photoacoustic and Photothermal Phenomena--11th International Conference Kyoto, Japan June 2000)
Toyoda Taro; Shen Qing; Shiozaki Ikuyo
Japan Society for Analytical Chemistry, 2001, Analytical Sciences, 17, s47-49, English, 0910-6340, 40005335921, AA10500785

Optical absorption measurements by photothermal methods
TOYODA Taro; SHEN Qing
応用物理学会, Mar. 1998, 應用物理, 67, 3, 283-288, Japanese, 0369-8009, 10005093579, AN00026679

PA13 Photoacoustic and Photoconductive Spectra of CdInGaS_4
Yamamuro Masamichi; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 12 Nov. 1997, Symposium on ultrasonic electronics, 18, 143-144, Japanese, 110007461255, AN10578660

PD7 Photoacoustic Spectra for CdS_xSe_<1-x>(0≦x≦1) Doped Glass
Kato Yuichiro; Shen Qing; Toyoda Taro
Steering committee of symposium on ultrasonic electronics, 23 Oct. 1996, Symposium on ultrasonic electronics, 17, 29-30, Japanese, 110007461019, AN10578660

Unusual enhancement of transient reflecting grating signal under a surface plasmon resonance condition
K Katayama; Q Shen; A Harata; T Sawada
Subnanosecond time-resolved transient reflecting grating (TRG) measurements were carried out under resonance conditions of surface plasmon (SP) with a Kretschmann configuration using a 40-nm-thick gold film deposited on a hemicylindrical prism. The TRG was generated and detected with two pump beams and with one probe beam incident from the prism side, the angles of which for incidence and polarization were changed. When the pump beams resonantly excited SPs, the TRG signal amplitude was enhanced as expected. An unusual enhancement was observed when the probe beam excited SPs, i.e., the TRG signal amplitude was also enhanced strongly although reflecting diffraction was probed under the less reflective condition. This enhancement was accompanied by a transient wave form change. The mechanism of these phenomena is discussed. (C) 1996 American Institute of Physics., AMER INST PHYSICS, Oct. 1996, APPLIED PHYSICS LETTERS, 69, 17, 2468-2470, English, 0003-6951, 80009258212, WOS:A1996VN89800006

ANALYSIS OF THE THERMAL AND ACOUSTIC PROPERTIES OF ION-IMPLANTED DIAMOND-LIKE CARBON-FILMS USING THE TRANSIENT REFLECTING GRATING TECHNIQUE
Q SHEN; A HARATA; T SAWADA
AMER INST PHYSICS, Feb. 1995, JOURNAL OF APPLIED PHYSICS, 77, 4, 1488-1491, English, 0021-8979, 80008122330, WOS:A1995QG50000019

ANALYSIS OF METALLIC MULTILAYERS USING HYPERSONIC SURFACE-WAVES INDUCED BY TRANSIENT REFLECTING GRATINGS
Q SHEN; A HARATA; T SAWADA
Gigahertz surface acoustic waves (the Rayleigh-like modes) have been optically generated and detected on ultrathin (< 1 mum) metallic single-layer and multilayered films attached to glass substrates using the laser-induced transient reflecting grating (TRG) technique. The dispersion relations of the excited Rayleigh-like modes could be constructed experimentally and theoretically. By finding the best fitting of the theoretical dispersion curves to the experimental data, this method can be used to deduce the elastic constants of ultrathin multilayered films., JAPAN J APPLIED PHYSICS, Aug. 1993, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 32, 8, 3628-3632, English, 0021-4922, WOS:A1993LU48600057

Perovskite Materials and Devices
Yaohong Zhang; Yu Chen; Guohua Wu; Haizheng Zhong; Qing Shen
English, Contributor, Chapter 9 Halide Perovskite Nanocrystals and Applications to Solar Cells, Wiley‐VCH GmbH, 21 Jun. 2022

Perovskite Photovoltaics and Optoelectronics: From Fundamentals to Advanced Applications
Yaohong Zhang; Guohua Wu; Qing Shen
English, Contributor, Quantum Dots of Halide Perovskite, Wiley‐VCH Verlag GmbH & Co. KGaA, 07 Feb. 2022

Quantum Dots of Halide Perovskite
Yaohong Zhang; Guohua Wu; Qing Shen
English, Joint work, 07 Feb. 2022

Perovskite Materials - Synthesis, Characterisation, Properties, and Applications
Q.Shen; Y. Ogomi; T. Toyoda; K. Yoshino; S. Hayase
English, Joint work, Chapter 13 Optical Absorption, Charge Separation and Recombination Dynamics in Pb and Sn/Pb Cocktail Perovskite Solar Cells and Their Relationships to the Photovoltaic Properties, INTECH, Feb. 2016

太陽光と光電変換機能
Japanese, Joint work, 第3章「新規素子開発」、３半導体量子ドットの多重励起子生成と太陽電池への応用, シーエムシ―出版社, 28 Jan. 2016

Quantum Dot Solar Cells
Q. Shen; T. Katayama; T. Toyoda
English, Joint work, The dynamics of multiple exciton generation in semiconductor quantum dots, Springer, 2014

量子ドット太陽電池の最前線
Japanese, Joint work, 第2章 1 化学吸着法、第3章 1.2ショットキー太陽電池、1.3空乏ヘテロ型, シーエムシ―出版社, Oct. 2012

Quantum Dot Devices
Q. Shen; T. Toyoda
English, Joint work, Semiconductor Quantum Dot-Sensitized Solar Cells Employing Chapter 13 TiO2 Nanostructured Photoanodes with Different Morphologies, Springer, Apr. 2012

Trendsand Topics in Sensitized and Organic Solar Cells
Q. Shen; T. Toyoda
English, Joint work, Part II Chapter2 Semiconductor quantum dot-sensitized solar cells: effects of surface modification and photoanode morphology on photovoltaic properties, CMC, 2012

Solar Cells - New Aspects and Solutions
T. Toyoda; Q. Shen
English, Joint work, Chapter 22 Optical Absorption and Photocurrent Spectra of CdSe Quantum Dots Adsorbed on Nanocrystalline TiO2 Electrode Together with Photovoltaic Properties, INTECH, Nov. 2011

Solar Cells - New Aspects and Solutions
Q. Shen; T. Toyoda
English, Joint work, Chapter 13 Ultrafast Electron and Hole Dynamics in CdSe Quantum Dot Sensitized Solar Cells, INTECH, Nov. 2011

レーザー分光分析
Japanese, Joint work, 第３章 超高速分光 3.2節 固体と表面の分光１, 丸善株式会社, Jun. 2009

電子材料ハンドブック
Japanese, Joint work, 第７章「光機能材料」, 朝倉書店, Nov. 2006

Photoexcited Carrier Dynamics in Iodine-Doped CH3NH3PbBr3 Single Crystals
Dong Liu; Hua Li; Yusheng Li; Dandan Wang; Yongge Yang; Yuyao Wei; Shikai Chen; Guozheng Shi; Taro Toyoda; Shuzi Hayase; Qing Shen
The 85th JSAP Autumn Meeting 2024
19 Sep. 2024
16 Sep. 2024- 20 Sep. 2024

Colloidal Quantum Dots: Synthesis, Optical Property and Applicaiton to Solar Cells
Qing Shen
Public symposium, English, The 24th International Conference on Photochemical Conversion and Storage of Solar Energy (IPS-24) and the International Conference on Artificial Photosynthesis-2024 (ICARP2024), Invited
30 Jul. 2024
28 Jul. 2024- 02 Aug. 2024

Less defect and stable perovskite quantum dots for solar cell applications
Qing Shen
Nominated symposium, English, International Symposium on Solar Energy 2024, Invited
23 Jul. 2024
22 Jul. 2024- 23 Jul. 2024

The Effects of Perovskite Quantum Dot Additives on the Perovskite Film Property and the Photovolatic Conversion Efficiency Enhancement of Perovskite Solar Cells
Qing Shen
English, The 41st International Conference of Photopolymer Science and Technology, Invited
26 Jun. 2024
25 Jun. 2024- 28 Jun. 2024

Unraveling charge transport layer effects on thermal stability in mixed A-site tin-based halide perovskite films
Wang Dandan; Li Yusheng; Wang Liang; Liu Dong; Liu Jiaqi; Hayase Shuzi; Shen Qing
Oral presentation, The 71st JSAP Spring Meeting 2024
22 Mar. 2024- 25 Mar. 2024

Transport and Extraction of Photoexcited Charge Carriers in Tin Based Perovskites
Dong Liu; Yusheng Li; Dandan Wang; Liang Wang; Jiaqi Liu; Shuzi Hayase; Qing Shen
Oral presentation, 2024年 第71回 応用物理学会 春季学術講演会
22 Mar. 2024- 25 Mar. 2024

両性イオンをリガンドとした無機ハロゲン化スズペロブスカイト量子ドットの合成と光物性
海野 弘貴; 李 玉胜; 豊田 太郎; 早瀬 修二; 沈 青
Poster presentation, 2024年 第71回 応用物理学会 春季学術講演会
22 Mar. 2024- 25 Mar. 2024

p型とn型のPbS量子ドットの作製と光物性評価
金子 沙有里; 魏 玉瑶; ウィチャイヨ ナパスダ; 早瀬 修二; 豊田 太郎; 沈 青
Poster presentation, 2024年 第71回 応用物理学会 春季学術講演会
22 Mar. 2024- 25 Mar. 2024

Optical Property, Photoexcited Carrier Dynamics and Application to Solar cells of Perovskite Quantum Dots
Qing Shen
Australia-Japan Joint Conference on Perovskite Solar Cells, Invited
05 Jan. 2024- 05 Jan. 2024

Less Defect and Phase Stable Perovskite Nanocrystals
Qing Shen
Invited oral presentation, International Summit on Organic and Hybrid Photovoltaics Stability (ISOS-14) and Woman Leaders in Solar Energy, Invited
08 Nov. 2023- 10 Nov. 2023

Phase stable and less defect tin-based perovskite nanocrystals: synthesis, optical property and photoexcited carrier dynamics
Qing Shen
Invited oral presentation, The 34th International Photovoltaic Science and Engineering Conference (PVSEC34), Invited
05 Nov. 2023- 10 Nov. 2023

Cs2NaInCl6ダブルペロブスカイト量子ドットの表面リガンド
戸佐 圭汰; 丁 超; 早瀬 修二; 沈 青
Oral presentation, 2023年 第84回 応用物理学会 秋季学術講演会
19 Sep. 2023- 23 Sep. 2023

Photocurrent Enhancement in PbS Quantum Dot Solar Cells with PbS Hole Transport Layer Passivated by Short Organic Ligands through two-step ligand exchange method
Yuyao Wei; Chao Ding; Guozheng Shi; Shuzi Hayase; Qing Shen
Poster presentation, The 31th International Conference on Photochemistry
23 Jul. 2023- 28 Jul. 2023

Optical properties and photoexcited carrier dynamics of CH3NH3PbBrxI3-x single crystals
Dong Liu; Hua Li; Yusheng Li; Taro Toyoda; Shuzi Hayase; Chao Ding; Qing Shen
Poster presentation, The 31th International Conference on Photochemistry
23 Jul. 2023- 28 Jul. 2023

Organic solar cells with PbS quantum dots additives in the active layer
Kei Takahashi; Taiga Matsumoto; Yuyao Wei; Chao Ding; Taro Toyoda; Shuzi Hayase; Qing Shen
Poster presentation, The 31th International Conference on Photochemistry
23 Jul. 2023- 28 Jul. 2023

Optical property of blue photoluminescence perovskite quantum dots
Akihito Fuchimoto; Yongge Yang; Hua Li; Yusheng Li; Taro Toyoda; Shuzi Hayase; Chao Ding; Taizo Masuda; Qing Shen
Poster presentation, The 31th International Conference on Photochemistry
23 Jul. 2023- 28 Jul. 2023

Red Emission of Cs2NaInCl6 Double Perovskite Quantum Dots
Keita Tosa; Chao Ding; Shuzi Hayase; Qing Shen
Poster presentation, The 31th International Conference on Photochemistry
23 Jul. 2023- 28 Jul. 2023

界面修飾によるペロブスカイト量子ドット太陽電池の光電変換特性の向上
宝寺 峻吉; 丁 超; 李 花; 矢嶋 祥太; 豊田 太郎; 早瀬 修二; 沈 青
J-PVS第20回「次世代の太陽光発電システム」シンポジウム
29 Jun. 2023- 30 Jun. 2023

活性層にPbS量子ドットを添加した有機太陽電池
高橋 啓; 松本 大河; 魏 玉瑶; 丁 超; 豊田 太郎; 早瀬 修二; 沈 青
Poster presentation, J-PVS第20回「次世代の太陽光発電システム」シンポジウム
29 Jun. 2023- 30 Jun. 2023

Photocurrent Enhancement in PbS Quantum Dot Solar Cells with Quantum Dot Hole Transport Layer Passivated by Short Organic Ligands
Yuyao Wei; Chao Ding; Guozheng Shi; Shuzi Hayase; Qing Shen
Oral presentation, The 40th International Conference of Photopolymer Science and Technology
27 Jun. 2023- 30 Jun. 2023

Numerical optimizations of lead sulfide colloidal quantum dot solar cells
Wang Dandan,Li Yusheng; Ding Chao; Hayase Shuzi; Shen Qing
Poster presentation, The 70th JSAP Spring Meeting 2023
15 Mar. 2023- 18 Mar. 2023

Passivation on ZnO NWs to enhance the efficiency of PbS/ZnO NW QDSCs
Yuyao Wei; Chao Ding; Mako Nakamura; Shuzi Hayase; Qing Shen
Poster presentation, The 70th JSAP Spring Meeting 2023
15 Mar. 2023- 18 Mar. 2023

鉛錫ペロブスカイト単結晶の光学特性に関する研究
劉 東; 李 花; 李 玉勝; 豊田 太郎; 早瀬 修二; 丁 超; 沈 青
Poster presentation, 2023年 第70回 応用物理学会 春季学術講演会
15 Mar. 2023- 18 Mar. 2023

界面修飾によるペロブスカイト量子ドット太陽電池の光電変換特性の向上
宝寺 峻吉; 丁 超; 李 花; 矢嶋 祥太; 豊田 太郎; 早瀬 修二; 沈 青
Poster presentation, 2023年 第70回 応用物理学会 春季学術講演会
15 Mar. 2023- 18 Mar. 2023

活性層にPbS量子ドットを添加した有機太陽電池
高橋 啓; 松本 大河; 魏 玉瑶; 丁 超; 豊田 太郎; 早瀬 修二; 沈 青
Poster presentation, 2023年 第70回 応用物理学会 春季学術講演会
15 Mar. 2023- 18 Mar. 2023

Cs2NaInCl6ダブルペロブスカイトの赤色発光
戸佐 圭汰; 丁 超; 早瀬修二; 沈 青
２０２３年 第７０回応用物理学会 春季講演会
17 Mar. 2023

Hot Carrier Cooling and Extraction Dynamics of Perovskite Quantum Dots
Qing Shen; Yusheng Li; Hua Li; Shota Yajima; Chao Ding
Invited oral presentation, Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics, Invited
22 Jan. 2023- 24 Jan. 2023

Hot carrier cooling and extraction dynamics of perovskite quantum dots".
Qing Shen
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics （IPEROP23）, Invited
24 Jan. 2023

Protecting Hot Carriers by Introducing Inorganic Cations in Halide Perovskite Quantum Dots
Hua Li; Chao Ding; Qing Shen
The 4rd ASEAN-UEC Workshop on Informatics and Engineering
19 Dec. 2022

塩化ゲルマニウム前駆体を用いたCs2NaInCl6ペロブスカイト量子ドットの作製と光物性
戸佐 圭汰; 丁 超; 早瀬 修二; 沈 青
２０２２年 第８３回応用物理学会 秋季講演会
22 Sep. 2022

光音響法による MAPbX3 (X= Br, I) 単結晶 の 電子物性 と熱物性の研究
劉 東; 李 花; 李 玉勝; 豊田 太郎; 早瀬 修二; 丁 超; 沈 青
２０２２年 第８３回応用物理学会 秋季講演会
22 Sep. 2022

青色発光ペロブスカイト量子ドットの合成と光物性
淵本秋人; 丁 超; 矢嶋 祥太; 豊田 太郎; 早瀬 修二; 増田 泰三; 沈 青
２０２２年 第８３回応用物理学会 秋季講演会
22 Sep. 2022

ペロブスカイト太陽電池の光励起キャリアダイナミクスと光電変換特性に及ぼすペロブスカイト量子ドットの効果
長内 亮太; 丁 超; 李 花; 李玉勝; 早瀬 修二; 沈 青
２０２２年応用物理学会 秋季講演会, Peer-reviewed
22 Sep. 2022

有機無機ハロゲン化スズペロブスカイト量子ドットの合成と光物性
矢嶋祥太; 丁超; 李玉胜; 李 花; 豊田太郎; 早瀬修二; 沈青
第83回応用物理学会秋季学術講演会, Peer-reviewed
22 Sep. 2022

Synthesis, optical property and photoexcited carrier dynamics of phase stable and less-defect perovskite nanocrystals for application in solar cells
Qing Shen
The 39th International Conference of Photopolymer Science and Technology, Invited
30 Jun. 2022

Optical property, photoexcited carrier dynamics and application to solar cells of phase stable and less-defect perovskite nanocrystal
Qing Shen; Chao Ding; Hua Li; Yusheng Li; Shota Yajima
E-MRS WiRE 2022, Invited
02 Jun. 2022

Device simulations: Reducing non-radiative recombination losses for achieving >15% efficient lead sulfide quantum dot solar cells
Wang Dandan; Ding Chao; Xing Meibo; Wu Haifeng; Wang Ruixiang; Shen Qing
Applied Energy Symposium: Clean Energy Towards Carbon Neutrality
23 Apr. 2022

Optical property, photoexcited carrier dynamics and application to solar cells of perovskite nanocrystals
Qing Shen; Yusheng Li; Hua Li; Chao Ding
Invited oral presentation, English, Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22), Invited, International conference
20 Apr. 2022

Hot carrier cooling of CsSnxPb1-xBr3 quantum dots
S. Yajima; C. Ding; T. Toyoda; S. Hayase; Q. Shen; “Hot carrier cooling of CsSnxP; xBr; quantum dots”; Material Research Meati
13 Dec. 2021

CsSnxPb1-xI3ペロブスカイト量子ドットの合成と光物性
矢嶋祥太; 丁超; 豊田太郎; 早瀬修二; 沈青
矢嶋祥太, 丁超, 豊田太郎, 早瀬修二, 沈青, CsSnxPb1-xI3ペロブスカイト量子ドットの合成と光物性, 第82回応用物理学会秋季学術講演会, 2021年9月13日
13 Sep. 2021

APbBr3ペロブスカイトナノ結晶の光物性と光励起キャリアダイナミクスおよび安定性, 第68回応用物理学会春季学術講演会, 2021年3月17日
矢嶋祥太; 劉峰; 張耀紅; 丁超; 豊田太郎; 早瀬修二; 沈青
第68回応用物理学会春季学術講演会
17 Mar. 2021

Phase Stable and Less-Defect Perovskite Quantum Dots: Optical Property, Photoexcited Carrier Dynamics, and Application to Solar Cells
Invited oral presentation, English, ECS Meeting, International conference
05 Oct. 2020

Less-Defect Perovskite Quantum Dots: Synthesis, Optical Properties and Application to Optoelectronic Devices
Qing SHEN; Feng LIU; Yaohong ZHANG; Chao DING; Taro TOYODA; Shuzi HAYASE
Invited oral presentation, English, Materials research meeting 2019, Invited, YOKOHAMA,JAPAN, https://mrm2019.jmru.org/, International conference
10 Dec. 2019

Phase Stable and Less-Defect Perovskite Quantum Dots: Optical Property, Photoexcited Hot Carrier Dynamics, Charge Transfer and Application to Optoelectronic Devices
Qing Shen; Feng Liu; Chao Ding; Yaohong Zhang; Taro Toyoda; Shuzi Hayase
Invited oral presentation, English, Proceedings of nanoGe Fall Meeting19 (NGFM19), Invited, Berlin, Germany, https://www.nanoge.org/NGFM19/home, International conference
04 Nov. 2019

Surface Coatings for Improving Solar Cell Efficiencies
Qing Shen; Chao Ding; Yaohong Zhang; Feng Liu; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Invited oral presentation, English, 14th Topical Meeting on Optical Interference Coatings, Invited, New Mexico, USA, International conference
02 Jun. 2019

Less-Defect Perovskite Nanocrytals: Optical Properties and Application to Solar Cells
F. Liu; Y. Zhang; C. Ding; T. Toyoda; S. Hayase; Q. Shen
Invited oral presentation, English, The 6th Conference on Science and Technology of Emerging Solar Energy Materials, Invited, Beijing, China, http://solar.iphy.ac.cn/2019/solar_confen.html, International conference
25 May 2019

Phase-stable and high optoelectronic quality all-inorganic perovskite quantum dots and their application in optoelectronic devices
F. Liu; Y. Zhang; C. Ding; T. Toyoda; S. Hayase; Q. Shen
Invited oral presentation, English, 2019 MRS Spring Meeting & Exhibit, Phoenix, USA, https://www.mrs.org/spring2019, International conference
22 Apr. 2019

Colloidal Synthesis of Phase-Stable and Defect-Free Perovskite Nanocrystals for Use in Solar Cells
F. Liu; Y. Zhang; C. Ding; S. Hayase; T. Toyoda; Q. Shen
Invited oral presentation, English, the 11th International Summit on Organic and Hybrid Photovoltaics Stability (ISOS), Invited, Suzhou, China, International conference
22 Oct. 2018

Interface Engineering, Photoexcited Carrier Dynamics and Mechanism for Improving Photovoltaic Performance of Perovskite Solar Cells
Qing Shen; Chao Ding; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Invited oral presentation, English, The 5th Conference on New Generation Solar Cells, Invited, Beijing, China, International conference
27 May 2018

量子ドット太陽電池の電荷分離界面の構築と高効率化への道筋
沈 青
Invited oral presentation, Japanese, 第65回応用物理学会春季学術講演会, Invited, Domestic conference
19 Mar. 2018

量子ドット太陽電池の電荷分離界面の構築と高効率化への道筋
沈 青
Invited oral presentation, Japanese, 第65回応用物理学会春季学術講演会, Invited, 日本応用物理学会, 早稲田大学, Domestic conference
19 Mar. 2018

Charge Transfer Dynamics and Photovoltaic Properties of Perovskite Solar Cells: Effects of Interface Engineering on Photoexcited Carrier Dynamics and Photovoltaic Performance of Perovskite Solar Cells
Qing Shen; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Invited oral presentation, English, International Conference on Perovskite Thin Film Photovoltaics, Photonics and Optoelectronics (ABXPV18PEROPTO), Invited, Rennes, France, International conference
27 Feb. 2018

Charge Transfer Dynamics and Photovoltaic Properties of Perovskite Solar Cells: Effects of the Energy Level Alignment of Zn1-xMgxO Electron Selective Layer
Qing Shen; Chao Ding; Yaohong Zhang; Feng Liu; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Invited oral presentation, English, 2nd Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV18), Invited, Kitakyushu, Japan, International conference
18 Jan. 2018

Photoexcited Carrier Dynamics, Interface Passivation and Mechanism for Improving Photovoltaic Performance of Perovskite Solar Cell
Qing Shen; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Oral presentation, English, The 15th International Conference on Advanced Materials (IUMRS-ICAM 2017), Kyoto, Japan, International conference
27 Aug. 2017

量子ドット太陽電池の電荷分離界面の構築と高効率化への道筋
沈 青
Invited oral presentation, Japanese, 第14回「次世代の太陽光発電システム」－未来に向けた太陽光発電の新たな価値創出へー, Invited, 名古屋大学, Domestic conference
20 Jul. 2017

Size-dependent optical absorption, ground state energy, and interfacial electron transfer dynamics of CdSe quantum dots on single crystal rutile-TiO2 (001), (110), and (111) surfaces
Taro Toyoda; Qing Shen; Keita Kamiyama; Kenji Katayama; Shuzi Hayase
Oral presentation, English, 10th International Symposium on Transparent Oxide and Related Materials for Electronics and Optics, Tokyo, Japan, International conference
05 Jun. 2017

Effects of Interface passivation on Photoexcited Carrier Dynamics and Photovoltaic Performance in Perovskite Solar Cell
Qing Shen; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Invited oral presentation, English, The 4th Conference on New Generation Solar Cells, Invited, Rennes, France, International conference
27 May 2017

Slow Hot Carrier Cooling in Bulk CsPbI3 Perovskite and CsPbI3 Quantum Dots
Qing Shen; Feng Liu; Teresa S. Ripolles; Naoki Nakazawa; Yaohong Zhang; Yuhei Ogomi; Koji Nishinaka; Takuya Izuishi; Taro Toyoda; Shuzi Hayase
Oral presentation, English, International Conference on Hybrid and Organic Photovolatics (HOPV17), Lausanne, Switzerland, International conference
21 May 2017

Effects of Interface Engineering on Photoexcited Carrier Dynamics and Photovoltaic Performance in Perovskite Solar Cell
Qing Shen; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Invited oral presentation, English, 2017 China PV Technology International Conference, Invited, Xian, China, International conference
30 Mar. 2017

量子ドット太陽電池の電荷分離界面の構築と高効率化への道筋
沈 青
Invited oral presentation, Japanese, 日本化学会第97春季年会, Invited, 日本化学会, 慶応大学, Domestic conference
18 Mar. 2017

Charge Transfer Dynamics and Photovoltaic Properties of Perovskite Solar Cells: Effects of Interface Engineering on Photoexcited Carrier Dynamics and Photovoltaic Performance of Perovskite Solar Cells
Qing Shen; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Invited oral presentation, English, International Conference on Perovskite Thin Film Photovoltaics, Photonics and Optoelectronics (ABXPV18PEROPTO), Invited, Rennes, France, International conference
27 Feb. 2017

Photoexcited Carrier Dynamics, Interface Passivation and Mechanism for Improving Photovoltaic Performance in perovskite solar cells
Qing Shen; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Takashi Minemoto; Shuzi Hayase
Invited oral presentation, English, Asia Pacific Hybrid and Organic Photovoltaics Conferece (AP-HOPV17), Invited, Yokohama, International conference
03 Feb. 2017

Perovskite and Quantum Dot Solar Cells: Photoexcited Carrier Dynamics, Interface Engineering and Mechanism for Improving Photovoltaic Performance
Qing Shen; Taro Toyoda; Shuzi Hayase
Invited oral presentation, English, 12th China SoG Silicon and PV Power Conference, Invited, Jiaxing, China, International conference
24 Nov. 2016

Photoexcited Carrier Dynamics in Perovskite Solar Cells: Uncovering the Mechanism for Achieving High Efficiency
Qing Shen; Yuhei, Ogomi; Kenji Yoshino; Taro Toyoda; Shuzi Hayase
Invited oral presentation, English, The 10th Aseanian Conference on Nano-Hybrid Solar Cells, Invited, Beijing, International conference
22 Sep. 2016

高速レーザー分光法による太陽電池での光励起キャリアダイナミクスの解明－量子ドット太陽電池とペロブスカイト太陽電池について－
沈 青
Invited oral presentation, Japanese, 2016年応用物理学会秋季学術講演会, Invited, 応用物理学会, 新潟, Domestic conference
14 Sep. 2016

量子ドット太陽電池のナノ界面制御と高効率化
沈 青; 豊田太郎
Nominated symposium, Japanese, 2016年応用物理学会秋季学術講演会, Invited, 応用物理学会, 新潟, Domestic conference
13 Sep. 2016

Slow Hot Carrier Cooling and Fast Hole Transfer to P3HT in Cesium Lead Iodide (CsPbI3) Perovskite
Qing Shen; Teresa S. Ripolles; Yuhei Ogomi; Koji Nishinaka; Takuya Izuishi; Kenji Katayama; Taro Toyoda; Kenji Yoshino; Shuzi Hayase
Oral presentation, English, International Conference on Hybrid and Organic Photovolatics (HOPV16), International conference
28 Jun. 2016

Slow hot carrrier cooling and ultrafast hole transfer in CsPbI3 perovskite: potential for hot carrier solar cell application
Qing Shen; Teresa S. Ripolles; Yuhei Ogomi; Koji Nishinaka; Takuya Izuishi; Kenji Katayama; Taro Toyoda; Kenji Yoshino; Shuzi Hayase
Oral presentation, English, the 26th international symposium on photochemistry, International conference
03 Apr. 2016

Slow hot carrier cooling in caesium lead iodide (CsPbI3) perovskite
Qing Shen; Teresa S. Ripolles; Yuhei Ogomi; Koji Nishinaka; Taro Toyoda; Takuya Izuishi; Kenji Yoshino; Shuzi Hayase
Oral presentation, English, 2016 MRS Spring Meeting & Exhibit, Phoenix, USA, International conference
28 Mar. 2016

量子ドット太陽電池のナノ界面制御と高効率化
沈 青; 豊田太郎
Invited oral presentation, Japanese, 日本化学会第96春季年会, Invited, 日本化学会, 京都, Domestic conference
24 Mar. 2016

Quantum Dot and Perovskite Solar Cells: Interface Engineering, Photoexcited Carrier Dynamics and Mechanism for Improving Photovoltaic Performance
Q. Shen; T. Toyoda; S. Hayase
Nominated symposium, English, Japanese Swiss Energy Materials Workshop, Invited, International conference
Mar. 2016

Optical absorption, charge separation and recombination in perovskite solar cells and their relationships to photovoltaic performances
Qing Shen; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Shuzi Hayase
Nominated symposium, English, Organic/dye-sensitized/perovskite solar cell workshop, Invited, International conference
05 Dec. 2015

量子ドット太陽電池の多重励起子生成の解析
沈 青
Public discourse, Japanese, 応用物理学会有機分子・バイオエレクトロニクス分科講習会 「次世代太陽エネルギー変換デバイスの研究開発を支える先端計測」, Invited, Domestic conference
Nov. 2015

ペロブスカイト太陽電池の光励起キャリアダイナミクス
沈 青
Invited oral presentation, Japanese, 学振１７５委員会 有機系太陽電池分科会 第３回研究会, Invited, Domestic conference
Nov. 2015

ペロブスカイト系太陽電池の最前線I
沈 青
Invited oral presentation, Japanese, 第五回次世代太陽電池研究会, Invited, Domestic conference
Jun. 2015

Uncovering the Detailed Mechanism behind High Efficiency Perovskite Hybrid Solar Cells by Studying Charge Separation and Recombination Dynamics
Q. Shen; Y. Ogomi; K. Yoshino; T. Toyoda; S. Hayase
Invited oral presentation, English, The 2nd Conference on New Generation Solar Cells, Invited, International conference
23 May 2015

igh Reduction of Interfacial Charge Recombination in PbS Heterojunction Colloidal Quantum Dot Solar Cells by Metal Oxide Surface Passivation
J. Chang; Y. Kuga; I. Mora-Seró; T. Toyoda; Y. Ogomi; S. Hayase; J. Bisquert; Q. Shen
Oral presentation, English, The International Conference on Hybrid and Organic Photovoltaics (HOPV15), International conference
May 2015

ペロブスカイト型の電荷ダイナミクス
沈 青
Nominated symposium, Japanese, CiRfSEシンポジウム, Invited, Domestic conference
Mar. 2015

量子ドット太陽電池の光励起キャリアダイナミクスと界面制御による光電変換特性向上
沈 青
Invited oral presentation, Japanese, 第11回量子ナノ材料セミナー, Invited, Domestic conference
2015

Charge separation and recombination dynamics in Sn/Pb halide perovskite solar cell: uncovering the bottleneck of photovoltaic efficiency
Qing Shen; Yuhei Ogomi; Taro Toyoda; Kenji Yoshino; Shuzi Hayase
Oral presentation, English, The International Conference Solution processed Semiconductor Solar Cells, International conference
Sep. 2014

Uncovering the Mechanism of High Efficiency of Perovskite Solid-State Hybrid Solar Cells by Studying Charge Separation and Recombination
Q. Shen; Y. Ogomi; S. Tsukamoto; K. Kukihara; T. Oshima; N. Osada; K. Yoshino; K. Katayama; T. Toyoda; S. Hayase
Invited oral presentation, English, The 15th IUMRS-International Conference in Asia (IUMRS-ICA 2014), Invited, International conference
25 Aug. 2014

P1-49 Photoacoustic and photoelectrochemical current characterization of nanostructured TiO_2 electrodes : annealing temperature dependence
Sato Tadakazu; Shen Qing; Toyoda Taro
Japanese, Proceedings of Symposium on Ultrasonic Electronics, Steering committee of symposium on ultrasonic electronics
27 Oct. 2004
27 Oct. 2004- 27 Oct. 2004

P1-46 Characterization of Optical Absorption and Thermal Diffusivity for Nanocrystaline Silicon
Inoguchi M.; Shen Q.; Toyoda T.
Japanese, Proceedings of Symposium on Ultrasonic Electronics, Steering committee of symposium on ultrasonic electronics
27 Oct. 2004
27 Oct. 2004- 27 Oct. 2004

P1-47 Photoacoustic and Photoelectrochemical Current Characterization of Nanostractured TiO_2 Electrodes Composed with Different Size TiO_2 Nanoparticles
Kumagai Yuki; Shen Qing; Toyoda Taro
Japanese, Proceedings of Symposium on Ultrasonic Electronics, Steering committee of symposium on ultrasonic electronics
27 Oct. 2004
27 Oct. 2004- 27 Oct. 2004

P2-E-35 Characterization of Nanostructured TiO_2 Electrodes Sensitized with CdSe Quantum Dots Using Photoacoustic and Photoelectrochemical Current Methods
Qing Shen; Arae Dai; Toyoda Taro
Japanese, Proceedings of Symposium on Ultrasonic Electronics, Steering committee of symposium on ultrasonic electronics
12 Nov. 2003
12 Nov. 2003- 12 Nov. 2003

P2-E-36 Photoacoustic and Photoelectrochecnical Current Spectra of Nanostructured TiO_2 Electrodes Composed with Different Size TiO_2 Nanoparticles
Kumagai Yuki; Qing Shen; Toyoda Taro
Japanese, Proceedings of Symposium on Ultrasonic Electronics, Steering committee of symposium on ultrasonic electronics
12 Nov. 2003
12 Nov. 2003- 12 Nov. 2003

光音響法と光化学電流法によるナノ構造TiO2膜電極の評価
沈 青; 豊田太郎
Oral presentation, Japanese, 第50回応用物理学関係連合講演会講演予稿集
Mar. 2003

メゾポーラス化TiO2膜に固定化したCdSeナノ粒子の光音響・光化学電流スペクトル
豊田太郎; 山本浩之; 林 雅; 新江 大; 沈 青
Oral presentation, Japanese, 第50回応用物理学関係連合講演会講演予稿集
Mar. 2003

ナノ構造を有するTiO2膜電極の光音響・光電流応答特性
豊田太郎; 林 雅; 沈 青
Oral presentation, Japanese, 第50回応用物理学関係連合講演会講演予稿集
Mar. 2003

Mnを不純物として含むZnSナノ粒子の光音響・発光強度の紫外線照射効果
豊田太郎; A.B.Cruz; 沈 青
Oral presentation, Japanese, 第50回応用物理学関係連合講演会講演予稿集
Mar. 2003

Study of optical absorption and electron transport in nanoporous nanocrystalline TiO2 films.
Q.Shen; T.Toyoda
Oral presentation, English, Abstracs of the 5th International Conference on Nano-Molecular Electronics
Dec. 2002

C-4 Photoacoustic and photoelectrochemical current response of nanostructured TiO_2 electrodes
Toyoda Taro; Hayashi Masashi; Shen Qing
Japanese, Symposium on ultrasonic electronics, Steering committee of symposium on ultrasonic electronics
07 Nov. 2002
07 Nov. 2002- 07 Nov. 2002

ナノ構造を有するTiO2電極の光音響・光電流応答特性
豊田太郎; 林 雅; 沈 青
Oral presentation, Japanese, 第23回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集
Nov. 2002

光熱変換現象によるITOおよびメゾポーラス酸化チタンに固定化したCdSeナノ粒子の評価
新江 大; 沈 青; 豊田太郎
Oral presentation, Japanese, 第23回日本熱物性シンポジウム講演論文集
Nov. 2002

CdSナノ粒子を吸着したTiO2光電極の光音響スペクトルと光電変換
豊田太郎; 佐藤 淳; 林 雅; 沈 青
Oral presentation, Japanese, 第21回固体・表面光化学討論会講演要旨集
Nov. 2002

光音響法によるポーラスシリコンの熱伝導率の評価
沈 青; 豊田太郎
Oral presentation, Japanese, 第23回日本熱物性シンポジウム講演論文集
Nov. 2002

ナノ構造を有するTiO2電極の光音響ならびに光電流スペクトル
沈 青; 豊田太郎
Oral presentation, Japanese, 第40回粉体に関する討論会講演論文集
Nov. 2002

Porosity dependence of thermal conductivity for porous silicon characterized by photoaccoustic technique.
Q.Shen; T.Toyoda
Invited oral presentation, English, Proceedings of the International Workshop on Modern Science and Technology, International conference
Sep. 2002

Mn ion concentration dependence of the photothermal and photoluminescence spectra for ZnS:Mn nanocrystals.
T.Toyoda; J.Matsuzawa; A.B.Cruz; Q.Shen
Oral presentation, English, Abstracts of the 16th European Conference on Thermophysical Properties
Sep. 2002

Exposure time dependence of the photothermal and photoluminescence intensities for porous silicon with different wavelengths of excitation light
T.Toyoda; T.Yamazaki; R.torai; Q.Shen
Oral presentation, English, Abstracts of the 16th European Conference on Thermaphysical Properties
Sep. 2002

Efffect of applied voltage treatments on photothermal and photoelectrochemical current spectra in final preparation processes of porous TiO2 electrodes.
T.Toyoda; M.Hayashi; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 16th European Conference on Theermophysical Properties
Sep. 2002

Effect of sensitization by quantum-sized CdS on photothermal and photoelectrochemical current spectra of porous TiO2 electrodes.
T.Toyoda; J.Sato; Q.shen
Oral presentation, English, Abstracts of the 16th European Conference on Thermophysical Properties
Sep. 2002

Characterization of optical and thermal properties of porous silicon films on silicon substrate using photothermal technique.
Q.Shen; T.Toyoda
Oral presentation, English, Abstracts of the 16th European Conference on Thermophysical Properties
Sep. 2002

Apparent band-gap energies of mixed TiO2 nanoparticles with anatase and rutile structures characterized with photoacoustic intensity and phase spectra.
T.Toyoda; R.Taira; Q.Shen
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002

Effect of applied voltage treatments on photoacoustic and photoelectrochemical current spectra in final preparation processes of porous TiO2 electrodes.
T.Toyoda; M.Hayashi; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002

Mn ion concentration dependence of the photoacoustic and photoluminescence spectra for ZnS:Mn nanocrystals.
T.Toyoda; J.Matsuzawa; A.B.Cruz; Q.Shen
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002

Effect of sensitization by quantum-sized CdS on Photoacoustic and photoelectrochemical current spectra of porous TiO2.
T.Toyoda; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002

Efffect of applied voltage treatments on photoacoustic and photoelectrochemical current spectra in final preparation processes of porous TiO2 electrodes.
T.Toyoda; M.Hayashi; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacosutic and Photothermal Phenomena
Jun. 2002

Effect of sensitization by quantum-sied CdS on photoacoustic and photoelectrochemical current spectra of porous TiO2 electrodes.
T.Toyoda; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002

Dependence of the thermal conductivity of porous silicon on its porosity characterized by photoacoustic technique.
Q.Shen; T.Toyoda
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002

Apparent band-gap energies of mixed TiO2 nanoparticles with anatase and rutile structures characterized with photoacoustic intensity and phase spectra.
T.Toyoda; R.Taira; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena.
Jun. 2002

Mn ion concentration dependence and photoluminescence spectra of ZnS:Mn nanocrystals.
T.Toyoda; J.Matsuzawa; A.B.Cruz; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002

Photoacoustic spectroscopy of CdTe nanocrystals doped in a GeO2 glass matrix.
I.Tsuboya; D.Arae; Q.Shen; T.Toyoda
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002

Exposure time dependence of the photoacoustic and photoluminescence intensities of porous silicon with different wavelengths of excitation light.
T.Toyoda; T.Yamazaki; R.Torai; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002

Photoacoustic Characterization of Highly Porous, Polycrystalline TiO_2 Electrodes Fabricated with Different Applied Voltage Treatments
HAYASHI M.; SHEN Q.; TOYODA T.
Japanese, IEICE technical report. Ultrasonics, The Institute of Electronics, Information and Communication Engineers, http://id.ndl.go.jp/bib/6188122, We report the effect of voltage on a concentrated KCI electrolyte applied to highly porous, polycrystalline TiC_2 films on the photoacoustic (PA) and photoelectrochemical (PEC) current spectra. The PA signal intensities of the TiO_2 films with the different applied voltage treatments are higher than that without the treatments below the band-gap region, suggesting an inner-band transition due to an increase of carrier concentration by the voltage treatments. The PA intensity below the band-gap region increases with the increase of the applied voltage, indicating the increase of the carrier concentration. The PEC spectra for the applied voltage treatments with -1.5 V and without the treatments show broad bands at approximately around 3.31 eV. The PEC spectra for the applied voltage treatments over -1.5 V show two peaks at approximately around 3.31 eV and 3.88 eV. The intensities of the each peak positions increase rapidly above the applied voltage of -1.5 V. The increase of the PEC intensity with the different applied voltage treatments implies an increase carrier concentration due to donor levels formation by the treatments.
13 May 2002
13 May 2002- 13 May 2002

TiO2電極における電圧印加処理が光音響スペクトルに及ぼす効果
林 雅; 沈 青; 豊田太郎
Oral presentation, Japanese, 電子情報通信学会技術研究報告
May 2002

Characterization of optical and thermal properties of porous silicon films on silicon substrates using photoacoustic technique.
Qing Shen; Taro Toyoda
Oral presentation, English, Extended Abstracts of the 5th AIST International Symposium on Photoreaction Control and Photofunctional Materials
Mar. 2002

Photoacoustic Characterization of Thermal Properties of Porous Silicon Films
SHEN Q.; TOYODA T.
Japanese, IEICE technical report. Ultrasonics, The Institute of Electronics, Information and Communication Engineers, http://id.ndl.go.jp/bib/6043207, Since porous silicon(PS)showed efficient luminescence at room temperature, a strong interest has been attracted on both the light emission mechanism and the applications of PS such as light emitting devices, thermal insulators, and optical devices. It is important to study the optical and thermal properties of PS for these applications. In particularly, it is desirable to measure the properties of PS without separating PS from a Si substrate. In this paper, we report our experimental results on the measurements of thermal diffusivities of PS samples with different porosities using the transmitted photoacoustic method. We will show how the thermal diffusivity of PS changes with the porosities of the PS.
12 Dec. 2001
12 Dec. 2001- 12 Dec. 2001

P2-25 Photoacoustic spectra of ZnS:Mn Nanocrystals
Matsuzawa Juichiro; Shen Qing; Toyoda Taro
Japanese, Symposium on ultrasonic electronics, Steering committee of symposium on ultrasonic electronics
07 Nov. 2001
07 Nov. 2001- 07 Nov. 2001

P1-28 Photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO_2 filmes
Hayashi Masashi; Sato Jun; Shen Qing; Toyoda Taro
Japanese, Symposium on ultrasonic electronics, Steering committee of symposium on ultrasonic electronics
07 Nov. 2001
07 Nov. 2001- 07 Nov. 2001

Photoacoustic Spectra of Low-Dimensional Magnet of VOMoO4 (Photoacoustic and Photothermal Phenomena--11th International Conference Kyoto, Japan June 2000)
Toyoda Taro; Shen Qing; Shiozaki Ikuyo
English, Analytical Sciences, Japan Society for Analytical Chemistry, http://id.ndl.go.jp/bib/5769861
2001
2001 2001

Optical absorption measurements by photothermal methods
TOYODA Taro; SHEN Qing
Japanese, 應用物理, 応用物理学会, http://id.ndl.go.jp/bib/4423234
Mar. 1998
Mar. 1998 Mar. 1998

PA13 Photoacoustic and Photoconductive Spectra of CdInGaS_4
Yamamuro Masamichi; Shen Qing; Toyoda Taro
Japanese, Symposium on ultrasonic electronics, Steering committee of symposium on ultrasonic electronics
12 Nov. 1997
12 Nov. 1997- 12 Nov. 1997

PD7 Photoacoustic Spectra for CdS_xSe_<1-x>(0≦x≦1) Doped Glass
Kato Yuichiro; Shen Qing; Toyoda Taro
Japanese, Symposium on ultrasonic electronics, Steering committee of symposium on ultrasonic electronics
23 Oct. 1996
23 Oct. 1996- 23 Oct. 1996

Unusual enhancement of transient reflecting grating signal under a surface plasmon resonance condition
K Katayama; Q Shen; A Harata; T Sawada
English, APPLIED PHYSICS LETTERS, AMER INST PHYSICS, Subnanosecond time-resolved transient reflecting grating (TRG) measurements were carried out under resonance conditions of surface plasmon (SP) with a Kretschmann configuration using a 40-nm-thick gold film deposited on a hemicylindrical prism. The TRG was generated and detected with two pump beams and with one probe beam incident from the prism side, the angles of which for incidence and polarization were changed. When the pump beams resonantly excited SPs, the TRG signal amplitude was enhanced as expected. An unusual enhancement was observed when the probe beam excited SPs, i.e., the TRG signal amplitude was also enhanced strongly although reflecting diffraction was probed under the less reflective condition. This enhancement was accompanied by a transient wave form change. The mechanism of these phenomena is discussed. (C) 1996 American Institute of Physics.
Oct. 1996
Oct. 1996 Oct. 1996

ANALYSIS OF THE THERMAL AND ACOUSTIC PROPERTIES OF ION-IMPLANTED DIAMOND-LIKE CARBON-FILMS USING THE TRANSIENT REFLECTING GRATING TECHNIQUE
Q SHEN; A HARATA; T SAWADA
English, JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS
Feb. 1995
Feb. 1995 Feb. 1995

ANALYSIS OF METALLIC MULTILAYERS USING HYPERSONIC SURFACE-WAVES INDUCED BY TRANSIENT REFLECTING GRATINGS
Q SHEN; A HARATA; T SAWADA
English, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, Gigahertz surface acoustic waves (the Rayleigh-like modes) have been optically generated and detected on ultrathin (< 1 mum) metallic single-layer and multilayered films attached to glass substrates using the laser-induced transient reflecting grating (TRG) technique. The dispersion relations of the excited Rayleigh-like modes could be constructed experimentally and theoretically. By finding the best fitting of the theoretical dispersion curves to the experimental data, this method can be used to deduce the elastic constants of ultrathin multilayered films.
Aug. 1993
Aug. 1993 Aug. 1993

光工学実験第二
Apr. 2023 - Present
The University of Electro-Communications

基礎電子回路
Apr. 2020 - Present

物理学概論第二
Apr. 2019 - Present
The University of Electro-Communications

基 礎 電 子 回 路
The University of Electro-Communications

光工学実験第二
The University of Electro-Communications

基 礎 電 子 回 路
The University of Electro-Communications

基 礎 電 子 回 路
電気通信大学

光工学実験第二
電気通信大学

K課程卒研輪講
The University of Electro-Communications

K課程卒研輪講
電気通信大学

先進理工学専攻基礎
The University of Electro-Communications

先進理工学専攻基礎
電気通信大学

物理学概論第二
The University of Electro-Communications

物理学概論第二
電気通信大学

光エレクトロンニクス実験第二
The University of Electro-Communications

光エレクトロンニクス実験第二
The University of Electro-Communications

光エレクトロンニクス実験第二
電気通信大学

総合コミュニケーション科学
The University of Electro-Communications

総合コミュニケーション科学
電気通信大学

基礎数学演習第一（留学生）
The University of Electro-Communications

基礎数学演習第一（留学生）
The University of Electro-Communications

基礎数学演習第一（留学生）
電気通信大学

熱物性学会

分光学会

ナノ学会

電気化学会

光化学協会

学振第175委員会

日本化学会

応用物理学会

ナノｐｎ接合型量子ドット太陽電池の界面構築による高効率化と多重励起子の電荷分離
沈 青
日本学術振興会, 科学研究費助成事業, 電気通信大学, 基盤研究(B), 24K01295
01 Apr. 2024 - 31 Mar. 2027

タンデム太陽電池用鉛フリーワイドバンドギャップ錫ペロブスカイトの研究
Principal investigator
Apr. 2023 - Mar. 2025

Direction toward high-efficiency Sn perovskite solar cells analyzed by impedance
早瀬 修二; 沈 青; カマルディン ムハマドアクマル
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Fund for the Promotion of Joint International Research (Fostering Joint International Research (B)), 鉛を含まないペロブスカイト太陽電池の高効率化が望まれている。錫系ペロブスカイトがその最も期待される候補であるが効率が低いという問題点があった。錫系ペロブスカイト太陽電池の効率を向上するためには結晶欠陥に起因する電荷再結合サイト密度を低下させる必要がある。これまで我々はヨウ素イオン欠陥（undercordinated Sn ion）密度を低下させるために、エチレンジアミンによるパッシベーションが有効であることを示してきた。今回表面撥水性を有するハロゲン化ケイ素(Me3Si-Br)で表面をパッシベーションしたところ、耐久性、効率が向上することを見出した。効率は表面パッシベーション後に10.05%から12.22%に向上した。耐久性は未封止、窒素下で保存したところ、パッシベーション前には40日で30%の効率低下があったが、パッシベーション後は92日間で20%の低下に抑えることができた。ヨウ素イオン欠陥にBrイオンが配位しMe3Siグループが界面、粒界に吸着することにより、ヨウ素イオン欠陥密度を低下させるとともに、粒界を疎水性化し水分の侵入を防止していると推定された。Ms3SiXのXはClイオン=Iイオン 07 Oct. 2019 - 31 Mar. 2023

量子ドット増感系の光誘起電荷移動：基板結晶面の電子構造が増感機能に及ぼす効果
豊田 太郎; 沈 青
日本学術振興会, 科学研究費助成事業, 電気通信大学, 基盤研究(C), 半導体量子ドット(QD)は太陽電池の増感剤として、色素系を凌駕する特性を持つ。従来の増感型太陽電池ではQDの吸着面積を増大させるために、基板電極としてはナノ粒子集合体酸化物が対象となる(TiO2, ZnO等)。しかしこの電極系は乱雑な多結晶体のために、QDの電子状態や電子移動に関する評価が曖昧になる。本研究は物性が十分に判明されている単結晶基板を対象として、異なる面方位を持つ酸化物単結晶へQD吸着を行い、QDに対する基板の効果を明らかにすることを目的とする。今年度も引き続きルチル型TiO2単結晶の(001), (110), (111)面を対象基板として、さらに３種類の異なる配位子をPbS-QDに結合しQD-QD間の距離の制御を行い、昨年度に得られた結果の再現性について検討を行った。従来と同様に、(1)光音響法(PA)による脱励起状態、(2)吸光度法(Abs)による励起、(3)光電子収量法(PY)によるイオン化エネルギー、の一連の再現性評価を行った。その結果、PAスペクトルとAbsスペクトルの吸収端下の異なることが再確認された。特に(111)基板上ではQD-QD間隔の増大に大きな変化が生じた、これらの結果は脱励起に伴う無輻射緩和による熱生成効率がQD-QD間隔および基板結晶面により異なるという新しい発見につながった。これらの基板情報は、従来の酸化物ナノ粒子集合体電極に対して、増感型太陽電池のエネルギー変換効率向上化を考慮するデバイス設計に対して有用な情報を提供することが可能となると考えられる。, 17K04988
01 Apr. 2017 - 31 Mar. 2023

Elucidation of low efficiency for Sn perovskite solar cells and enhancement of efficiency by heteronanointerface architecture
Shuzi Hayase
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), The purpose of this research is to propose the way to enhance the efficiency of Pb free perovskite solar cells, namely, Sn PVK solar cells. Focus was put on decreasing defect density of PVK crystals including the grain boundary and the heterointerfaces. In order to make clear the performance of Sn PVK layer, no metal dopant was added in B site of ABX3 structure. We aimed at unveiling items retarding the efficiency-enhancement for the Sn-PVK. We found the following items for the efficiency enhancement. 1. Inverted structures are recommended to avoid the direct contact between Sn-PVK and inorganic oxide semiconductors, 2. To reduce the crystal lattice strain by optimizing the size of A site gives higher efficiency, 3. Grain boundary passivation is effective, 4. Addition of reducing agents, such as Sm ion, are useful because of the decrease in the defect density associated with Sn4+., 17H03106
01 Apr. 2017 - 31 Mar. 2020

Dependences of the optical absorption and interfacial electron transfer dynamics of quantum dots adsorbed on singlecrystal rutile TiO2.
Toyoda Taro
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Grant-in-Aid for Scientific Research (C), Quantum dots (QDs) provide an attractive alternative sensitizer to organic dyes. There is a lack of fundamental studies of QD on conventional nanocrystalline TiO2 electrodes with much amount of heteroigeneity. We have shown the dependences of the optical absorption, the ground state energy level, and interfacial electron transfer dynamics on the size of CdSe QDs on single crystal rutile-TiO2. The expenential optical absorption tail indicates a decrease in structural disorder with increasing size. The ground state energy level of the CdSe QDs shows anisotropic, depending on the surface orientation of TiO2. The interfacial electron transfer rate constant decreases with increasing size and depends on the surface orientation of TiO2., 26390016
01 Apr. 2014 - 31 Mar. 2018

Trap distribution analysis for thermal stimulation current of tin-based perovskite thin film
Ogomi Yuhei; SHEN Qing; IIKUBO Satoshi; HAYASE Shuzi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kyushu Institute of Technology, Grant-in-Aid for Young Scientists (B), Focus has been directed for tin-based perovskite films as a substitute for most widely studied lead halide perovskites. This research has investigated the relationship between crystal growth control of tin-based perovskite along with defect analysis and its implications on the solar cell performance. We have demonstrated a profound enhancement of the short circuit current from 20 mA/cm2 to 30 mA/cm2 using SnI2 complex for the fabrication of tin-halide perovskite as material. It has been found that when TiO2 as electron transporting material and SnI2 were chemically bonded, there was an increase in the TiO2 surface traps. Therefore, efforts were directed to prepare the tin-based perovskite solar cells without using TiO2 which led to the improved device performance. The absorption wavelength was changed by partially replacing the iodine by bromine. SnF2 was also doped in order to supplement metal defects. The conversion efficiency of the solar cell improved from 4.5% to 15.9%., 15K21224
01 Apr. 2015 - 31 Mar. 2017

Nano-interface engineering of heterojunction quantum dot solar cells and the effect on charge separation of multiple excitons
Shen Qing; HAYASE Shuzi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Grant-in-Aid for Scientific Research (B), As one candidate of the next generation solar cells, colloidal quantum dot (CQD) based solar cells (CQDSCs) have attracted considerable interest and developed rapidly during the last few years. CQDSCs have some unique advantages such as the band-gap tunability, high absorption coefficient, multiple exciton generation (MEG) possibility and low cost for preparation. Although theoretical energy conversion efficiency of CQDSCs has been predicted to be about 44% much higher than the Shockley-Queisser limit (33%), it is still about 8% at present time (2014). Therefore, fundamental studies on the mechanism for improving energy conversion efficiency of CQDSCs are very important. In this project, we focus on clarifying the photoexcited carrier dynamics, especially the dynamics of MEG and improving the charge separation and suppress recombination in QD heterojunction solar cells by controlling the interfaces of CQDSCs as well as the approaches to improving the energy conversion efficiency., 26286013
01 Apr. 2014 - 31 Mar. 2017

多重励起子生成と表面プラズモン効果による光励起キャリアダイナミクスと光電変換特性
豊田 太郎; 沈 青
日本学術振興会, 科学研究費助成事業, 電気通信大学, 特定領域研究, 近年Au量子ドットを吸着したTiO_2電極において、プラズモン共鳴に基づく光誘起電荷分離が発見されたため、新しい増感太陽電池への応用が注目されている。一方半導体量子ドットが多重励起子生成(MEG)を示すことから、従来の色素増感に代わる半導体量子ドット増感太陽電池が注目されている。本研究はAu量子ドットによる光局在場のMEG生成に与える効果について検討し、MEG生成増大条件を見出し半導体量子ドット増感太陽電池の光電変換向上を目的としている。半導体量子ドットとしてCdSeを、金属量子ドットとしてAuを対象とし、ナノ粒子TiO_2電極への複合化吸着を行った。この系に対して、光吸収特性評価、光電流特性評価を行った。その結果、CdSe量子ドットの平均粒径は作製吸着時間とともに増大し、光電流はある吸着時間で極大を示した。さらに太陽電池デバイスを形成し、光電変換特性評価を行った。その結果、開放電圧と曲線因子は、CdSe量子ドット単独吸着の場合もAu/CdSe複合化吸着も大きな違いは見られなかった。しかし短絡電流はCdSe量子ドットの吸着時間が短時間の場合には、複合化吸着では単独吸着に比べて約30%程増大することが見出された。この結果を反映して、光電変換効率も同様の増大と変化を示した。また太陽電池デバイスにおける並列抵抗成分は、複合吸着の場合に減少することがわかった。これはCdSe量子ドットとAu量子ドットの直接接触による影響と考えられる。他の評価として、単独吸着の場合と複合化吸着の場合の超高速過渡応答特性の検討を行った。その結果、複合化吸着の場合は単独吸着の場合と比較して、緩和時間が長くなる傾向が見られた。, 21020014
2009 - 2010

Production method of methylammonium lead halide perovskite quantum dots
Patent right, Taizo Masuda, Qing Shen, Chao Ding, Yaohong Zhang, Feng Liu, 特願17218681, 特開11479718, Date announced: 22 Sep. 2022, Taizo Masuda, Qing Shen, Chao Ding, Yaohong Zhang, Feng Liu

ホルムアミジニウムハロゲン化鉛ペロブスカイト量子ドットの調製方法
Patent right, 増田泰造, 佐々木清人, 沈青, 劉鋒, 張耀紅, 丁超, 201910427519.0, Date applied: 22 May 2019, Toyota Motor Corporation

量子ドット、これを用いた光デバイス、及び量子ドットの作製方法
Patent right, 劉鋒, 沈青, 張耀紅, 豊田太郎, 特願2017-057431, Date applied: 23 Mar. 2017, 国立大学法人電気通信大学

電通大など、量子ドット太陽電池で変換効率15%超
日経経済新聞, https://www.nikkei.com/prime/tech-foresight/article/DGXZQOUC10A2B0Q2A111C2000000
Nov. 2022

電通大、量子ドット太陽電池にて変換効率15.45％を達成
マイナビニュース, https://www.mapion.co.jp/news/column/cobs2498481-1-all/
Oct. 2022

電通大，量子ドット太陽電池で最高変換効率達成
Optronics online, https://optronics-media.com/news/20221019/78991/, Internet
Oct. 2022

電通大、量子ドット太陽電池にて変換効率15.45％を達成
TECH+ テクノロジー 環境技術, https://news.mynavi.jp/techplus/article/20221020-2485731/, Internet
Oct. 2022

Home»エネルギー»電通大、量子ドット太陽電池にて変換効率15.45％を達成 エネルギー 電通大、量子ドット太陽電池にて変換効率15.45％を達成
神奈川新聞(Kanagawa-ken), http://kanagawa-ken.com/energy/24071/

【ニュースリリース】硫化鉛量子ドット太陽電池の世界最高性能を達成
Internet

JSAP-MRS Joint Symposium: New direction of perovskite solar cells
Planning etc, 16 Sep. 2024 - 16 Sep. 2024