Doctor of Science, Osaka University

Thermoelectric devices

Electronic material (organic, Inorganic)

Solar cell (Photovoltaic devices)

Photoelectric conversion device

Manufacturing technology (mechanical, electrical/electronic, chemical engineering), Electric/electronic material engineering

Manufacturing technology (mechanical, electrical/electronic, chemical engineering), Electronic devices and equipment

Nanotechnology/Materials, Polymer materials

Nanotechnology/Materials, Organic functional materials

01 Apr. 2001 - 31 Mar. 2019
Kyushu Institute of Technology, Graduate School of Life Science and Systems Engineering, Professor

01 Apr. 1978 - 31 Mar. 2001
Toshiba Corporation, Research and Development Center, 退職時 研究主幹（部長）

Mar. 1983
Osaka University, 理学研究科

Mar. 1978
Osaka University, 理学研究科, 高分子化学

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

Direct measurement of electron affinity of carbazole-based self-assembled monolayer used as hole-selective layer in high-efficiency perovskite solar cells
Aruto Akatsuka; Makoto Miura; Gaurav Kapil; Shuzi Hayase; Hiroyuki Yoshida
Applied Physics Letters, AIP Publishing, 124, 24, 10 Jun. 2024, Carbazole-based self-assembled monolayers have received considerable attention as hole-selective layers (HSLs) in inverted perovskite solar cells. As an HSL, the electron-blocking capability is important and directly related to electron affinity (EA). Low-energy inverse photoelectron spectroscopy (LEIPS) is the most reliable method for EA measurement. However, the intense electron-impact-induced fluorescence from carbazole interferes with their measurement. By improving the photon detector, we were able to measure 2PACz and MeO-2PACz LEIPS spectra and determine their respective EAs of 1.72 and 1.48 eV. These small EA values ensure effective electron-blocking capability of HSLs regardless of the type of perovskite layer.
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, 102060-102060, Jun. 2024
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

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
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
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

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
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

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, 11 Aug. 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

Optimization of Device Parameters for Back Contact Transparent Conductive Oxide Less Dye Sensitized Solar Cells Fabrication
Md Zaman Molla; Ajay Kumar Baranwal; Shuzi Hayase; Shyam S. Pandey
Physica Status Solidi-A, 20 Jun. 2023, Peer-reviwed
Scientific journal, English

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

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, 01 Mar. 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

Cylindrical transparent conductive oxide-free dye-sensitized solar cells with treated flat titanium sheet
Azwar Hayat; Ajay Kumar Baranwal; Masaki Nakamura; Fujisawa Shigeki; Shyam S. Pandey; Shuzi Hayase
Journal of Phonics for Energy (SPIE), 12, 4, 045502, 02 Dec. 2022, Peer-reviwed
Scientific journal, English

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 LETTERS, AMER CHEMICAL SOC, 7, 10, 3703-3708, Oct. 2022, Sn-based perovskite solar cells (S-PSCs) are a promising candidate to replace toxic Pb-based PSCs. For promoting their industrial application, developing inorganic substitutions of unstable poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is also an important part due to its intrinsic stability and low cost. Here, we in situ prepared ambipolar SnOx by a simple and fast plasma-assistant strategy (P-SnOx). The as-prepared P-SnOx works as a hole transport layer directly, yielding a 10.89 +/- 0.51% power conversion efficiency (PCE) comparable to a PEDOT:PSS-based device (10.39 +/- 0.72%). The top SnOx (T-SnOx), composed of SnO2 and Sn metal, as a modifier and a protection layer of the perovskite by reducing Sn4+ to Sn2+, gives a 13.08 +/- 0.33% device performance. This in situ top protective strategy combined with P-SnOx as a hole transport layer further boosts the champion PCE of S-PSCs to 14.09% (13.5 +/- 0.32%).
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

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

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, 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

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

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

Use of anti-solvent to enhance thermoelectric response of hybrid halide perovskite thin films
Shrikant Saini; Izuki Matsumoto; Sakura Kishishita; Ajay Kumar Baranwal; Tomohide Yabuki; Shuzi Hayase; Koji Miyazaki
Japanese Journal of Applied Physics, 61, SE, 01 Jun. 2022, Hybrid halide perovskite research has recently been focused on thermoelectric energy harvesting due to the cost-effectiveness of the fabrication approach and to the ultra-low thermal conductivity. To achieve high performance, tuning of the electrical conductivity is a key parameter that is influenced by grain boundary scattering and charge carrier density. The fabrication process allows the tuning of these parameters. We report the use of anti-solvent to enhance the thermoelectric performance of lead-free hybrid halide perovskite (CH3NH3SnI3) thin films. Thin films with anti-solvent show higher connectivity in grains and higher Sn+4 oxidation states which result in the enhancement of the value of electrical conductivity. The thin films were prepared by a cost-effective wet process. Structural and chemical characterizations were performed using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The values of electrical conductivity and the Seebeck coefficient were measured near room temperature. A high value of the power factor (1.55 μW m-1 K-2 at 320 K) was achieved for thin films treated with anti-solvent.
Scientific journal

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, 436, 15 May 2022, 2PACz monolayer on PEDOT-PSS as the hole transport layer (HTL) was introduced to the inverted p-i-n Tin (Sn) based perovskite solar cells (PSCs) with 1.62 eV bandgap (Wide bandgap). 2PACz giving high efficiency to Pb perovskite solar cells was not effective at all for the Sn perovskite solar cells. We found that the efficiency was enhanced by synergistic effects of the 2PACz monolayer and PEDPT-PSS. The efficiency enhancement was explained by the compactness of the perovskite layer fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS, an energetically aligned interface of the HTL/Sn-based perovskite absorber, the lower lattice disordering and reduced non-radiative recombination of the perovskite layer. The cell stability was improved by the compact surface morphology of the Sn perovskite fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS and the suppression of direct contact between PEDOT-PSS and perovskite film. EDA0.01(GA0.06(FA0.8Cs0.2)0.94)0.98SnI2Br perovskite fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS, gave the power conversion efficiency (PCE) of 8.66%, which is the highest performance for wide bandgap Sn perovskite solar cells reported so far.
Scientific journal

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

Relationship between Carrier Density and Precursor Solution Stirring for Lead-Free Tin Halide Perovskite Solar Cells Performance
Ajay Kumar Baranwal; Kohei Nishimura; Dong Liu; Muhammad Akmal Kamarudin; Gaurav Kapil; Shrikant Saini; Tomohide Yabuki; Satoshi Iikubo; Takashi Minemoto; Kenji Yoshino; Koji Miyazaki; Qing Shen; Shuzi Hayase
ACS Applied Energy Materials, 5, 4, 4002-4007, Apr. 2022, 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

Tin-Lead Perovskite Solar Cells Fabricated on Hole Selective Monolayers
Gaurav Kapil; Takeru Bessho; Yoshitaka Sanehira; Shahrir R. Sahamir; 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 Letters, 7, 3, 966-974, 11 Mar. 2022, According to the detailed balanced limit for a single-junction solar cell, tin-lead (Sn-Pb) perovskite solar cells (PSCs) can achieve power conversion efficiencies (PCEs) more than Pb-PSCs. However, the rise in PCE of Sn-Pb PSCs is limited by the choice of hole transport layer to PEDOT:PSS only. Inspired by the use of hole selective monolayers (HSM) in Pb only PSCs, here, we employed 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz), leading to PCE (21.39%) comparable to PSCs fabricated on conventional PEDOT:PSS (21.37%). Moreover, we reported a small molecule, methyl phosphonic acid (MPA), employing which an equipotential performance (PCE= 21.08%) was obtained owing to its passivation effect on the transparent conducting oxide (TCO) layer. Furthermore, by taking motivation from the idea of cosensitization in dye sensitized solar cells, we explored the point that the coabsorption of 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz) and a small molecule MPA on TCO glass led to the Sn-Pb PSC (1.25 eV) with a PCE of 23.3% and open-circuit voltage of 0.88 V.
Scientific journal

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, 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

Electronic structure and thermal conductance of the MASnI3/Bi2Te3 interface: a first-principles study.
Masayuki Morimoto; Shoya Kawano; Shotaro Miyamoto; Koji Miyazaki; Shuzi Hayase; Satoshi Iikubo
Scientific reports, 12, 1, 217-217, 07 Jan. 2022, True, To develop high-performance thermoelectric devices that can be created using printing technology, the interface of a composite material composed of MASnI3 and Bi2Te3, which individually show excellent thermoelectric performance, was studied based on first-principles calculations. The structural stability, electronic state, and interfacial thermal conductance of the interface between Bi2Te3 and MASnI3 were evaluated. Among the interface structure models, we found stable interface structures and revealed their specific electronic states. Around the Fermi energy, the interface structures with TeII and Bi terminations exhibited interface levels attributed to the overlapping electron densities for Bi2Te3 and MASnI3 at the interface. Calculation of the interfacial thermal conductance using the diffuse mismatch model suggested that construction of the interface between Bi2Te3 and MASnI3 could reduce the thermal conductivity. The obtained value was similar to the experimental value for the inorganic/organic interface.
Scientific journal, English

Unravelling the bottleneck of phosphonic acid anchoring groups aiming toward enhancing the stability and efficiency of mesoscopic solar cells
Ajendra Kumar Vats; Pritha Roy; Linjun Tang; Shuzi Hayase; Shyam S. Pandey
Frontiers of Chemical Science and Engineering, Springer Science and Business Media LLC, 26 Nov. 2021
Scientific journal

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

Computational molecular design of NIR dyes with varying anchoring groups for improving the efficiency and stability of dye-sensitized solar cells
Pandey SHYAM; Ajendra Kumar Vats; Linjun Tang; Shuzi Hayase
Japanese Journal of Applied Physics, 61, SB, SB1021(1)-SB1021(11), 21 Sep. 2021, Peer-reviwed
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

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, 25, 08 Jul. 2021, Tin-lead perovskite solar cells (PSCs) show inferior power conversion efficiency (PCE) than their Pb counterparts mainly because of the higher open-circuit voltage (Voc) loss. Here, it is revealed that the p-type surface of perovskite transforms to n-type, based on post-treatment by a Lewis base, ethylenediamine. This approach forms a graded band structure owing to the rise of the Fermi-energy level at the surface of the perovskite layer, and increases the built-in potential from 0.56 to 0.76 V, which increases the Voc by more than 100 mV. It is demonstrated that EDA can lower the defect density (Sn4+ amount) by screening perovskite against oxygen, and by bonding with undercoordinated Sn on the surface. This study further explores the role of Br anion inclusion in the perovskite lattice from the viewpoint of reducing the lattice strain and Urbach energy. Finally, a high Voc of 0.86 V is obtained, corresponding to a voltage deficit of 0.39 V, using a perovskite absorber with a bandgap of 1.25 eV and the highest PCE (21.74%) reported so far for Sn-Pb PSCs is achieved.
Scientific journal

Study of open circuit voltage loss mechanism in perovskite solar cells
Yulu He; Imane Abdellaoui; M. Abdel-Shakour; Towhid Hossain Chowdhury; Muhammad Akmal Kamarudin; Ana Flávia Nogueira; Qing Shen; Shuzi Hayase; Ashraful Islam; Takeaki Sakurai
Japanese Journal of Applied Physics, IOP Publishing Ltd, 60, 01 May 2021, Open circuit voltage (V oc) loss within perovskite solar cells (PSCs) is undesirable as it reduces the power conversion efficiency of these devices. This report proposes a useful method to study V oc loss mechanisms based on experimental samples. V oc in the radiative limit (Vocrad) of devices is estimated by combining the detailed balance theory and the van Roosbroeck-Shockley relation. Furthermore, V oc loss from bulk recombination can be quantified by introducing the bulk lifetime. Thus, the V oc loss from bulk recombination of MAPbI3 and FASnI3 was estimated as 0.094 V and 0.061 V, respectively. The analysis helps distinguish and quantify the V oc loss of PSCs.
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 Applied Nano Materials, American Chemical Society, 4, 4, 3958-3968, 23 Apr. 2021, Tin (Sn)-based halide perovskites crystallized in the form of quantum dots (QDs) have attracted considerable attention due to their attractive features that are unique to the quantum realm. However, unlike those of their lead (Pb) counterparts, isolation and purification of the as-synthesized Sn-based QDs remain a challenge, as they undergo rapid decomposition in the most common antisolvents as well as in open air. Herein, we discover that CsSnX3 (X = Cl, Br, and I) QDs prepared under ultra-halide-rich conditions exhibit superior durability against the antisolvents even with high hydrophilicity like methyl acetate and can be thus readily purified under ambient conditions without the need for a strict inert atmosphere. First principles calculations reveal that halide-rich synthesis favors the formation of enhanced chemical bonds between QDs and their surface ligands and reduces ligand mobility. Both help to prevent structural decomposition and to preserve the perovskite composition. The successful synthesis of structurally stable Sn-based perovskite QDs accomplished without the use of any particular antioxidants or additional doping, provides alternative material design strategies for enhancing the stability of these fascinating yet fragile nanomaterials.
Scientific journal, English

Impact of Auger recombination on performance limitation of perovskite solar cell
Jakapan Chantana; Yu Kawano; Takahito Nishimura; Abdurashid Mavlonov; Qing Shen; Kenji Yoshino; Satoshi Iikubo; Shuzi Hayase; Takashi Minemoto
Solar Energy, Elsevier Ltd, 217, 342-353, 15 Mar. 2021, 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

Surface structure of quasi-2D perovskite PEA2mMAn−2mPbnI3n (n ≫ m)
Abduheber Mirzehmet; Tomoki Ohtsuka; Syed A. Abd. Rahman; Takumi Aihara; Muhammad Akmal Kamarudin; Shahrir Razey Sahamir; Shuzi Hayase; Tomoki Yuyama; Peter Krüger; Hiroyuki Yoshida
Applied Physics Express, IOP Publishing, 14, 3, 031006-031006, 01 Mar. 2021, Peer-reviwed
Scientific journal

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

Effect of impurity elements on the structural stability and electronic state in tin iodide perovskite
J. Yamasaki; S. Iikubo; K. Yamamoto; K. Tanaka; Y. Ogomi; S. Hayase
Journal of Solid State Chemistry, Academic Press Inc., 293, 01 Jan. 2021, Effect of impurity elements on the structural stability and electronic state in the tin iodide perovskite, which is useful for tuning carrier concentration to improve the thermoelectric performance, have been investigated using first-principles calculations. MASnI3 (MA ​= ​CH3NH3+) and CsSnI3 are considered as mother materials, and an impurity injection from three types of oxides—Al2O3, TiO2, and Y2O3— acting as scaffolds are considered. Three cations, Al3+, Ti3+, and Y3+, occupy the A or B sites, and one anion O2− occupies an I site. From the estimated formation energy Eform, Al and Ti impurities cause structural instability. In contrast, a Y impurity placed at a B site decrease Eform to −0.05 ​eV/atom and renders the perovskite structure more stable, while a Y impurity at an A site causes instability in the structure. For the calculated structural stability, the bonding analysis clearly explains the difference between the aforementioned sites. The Y–I covalent bonding around E ​= ​−4 ​eV is relatively strong when a Y is placed at a B site. Covalent bonding formed by the impurity elements has a finite contribution to the structural stability, even in the ionic crystal like an iodide perovskite.
Scientific journal, English

Inverted CsPbI2Br perovskite solar cells with enhanced efficiency and stability in ambient atmosphere via formamidinium incorporation
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, 218, Dec. 2020, 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

Inorganic narrow bandgap CsPb0.4Sn0.6I2.4Br0.6 perovskite solar cells with exceptional efficiency
Seojun Lee; Janghyuk Moon; Jun Ryu; Bhaskar Parida; Saemon Yoon; Dong-Gun Lee; Jung Sang Cho; Shuzi Hayase; Dong-Won Kang
Nano Energy, Elsevier Ltd, 77, 01 Nov. 2020, The instability of organic/inorganic hybrid perovskite solar cells (PSCs) has motivated the development of the inorganic halide PSCs. However, the representative inorganic CsPbI3 still suffers from phase instability in ambient air and an unfavorable wide bandgap (1.75 eV), thereby limiting its efficiency. In this study, a binary metal composition of Pb:Sn = 4:6 in CsPb1-xSnxI3 is found to stabilize the cubic CsPbI3 phase and reduce its bandgap. Based on the parental CsPb0.4Sn0.6I3, compositional engineering is further conducted for CsPb0.4Sn0.6I3-yBry perovskites. After introducing a suitable Br content (y = 0.6), there are remarkable improvements in the crystalline quality and a denser morphology in the perovskite films. Furthermore, in the novel inorganic CsPb0.4Sn0.6I2.4Br0.6 perovskite, trap-assisted recombination is effectively suppressed, with a desirable narrow bandgap of 1.35 eV. As a result, the corresponding PSC delivered an unprecedented efficiency of 12.34%, which is the highest among the inorganic Sn-rich (Sn >
50%) PSCs reported to date. Additionally, the unencapsulated PSC demonstrates impressive long-term air stability, which exceeds the performance of 100% Pb-based inorganic CsPbI3 and/or CsPbI2Br PSCs reported. This near-infrared absorbing (~930 nm) inorganic PSC with exceptional efficiency, durability and Pb-reduction generates a promising route for further progress of perovskite-based photovoltaics.
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, American Chemical Society, 5, 10, 3224-3236, 09 Oct. 2020, For the current passivation strategy, pure iodine passivation during solid-state ligand exchange (SSE) cannot completely passivate the entire surface of PbS colloidal quantum dots (CQDs). Here, a simple stepwise passivation strategy is proposed based on the postpassivation of PbS CQD films with a halogen (Cl, Br, or I) after iodine passivation through the SSE. This postpassivation could compensate for the missing ligands caused by the polar environment during the SSE. Thus, both electron-and hole-trapping states are greatly reduced, and the charge transport in the CQD film is significantly improved. The PbS CQD films post-treated with chlorine exhibit a carrier diffusion length increased by 70% when compared with that of control samples. We demonstrate the highest power conversion efficiency of 12.4% among the reported PbS CQD solar cells prepared with the SSE method to date. In addition, the unencapsulated device shows good stability in air.
Scientific journal, English

Effect of electrolyte for back contact transparent conducting oxide-less dye-sensitized solar cells: Iodine versus cobalt
Md Zaman Molla; Ajay K. Baranwal; Shuzi Hayase; Shyam S. Pandey
Journal of Photonics for Energy, 10, 4, 01 Oct. 2020, Grätzel solar cells are reported in a transparent conducting oxide-less (TCO-less) back-contact dye-sensitized solar cell (BC-DSC) architecture using a stainless steel mesh-protected working electrode along with nanoporous TiO2 semiconductor and metal-free D205 dye. Liquid electrolytes play a significant role for the dye regeneration in the working operation of TCO-less BC-DSCs; therefore, we report the effectiveness of two different commonly utilized electrolytes (iodine-and cobalt-based redox shuttles) for the construction and performance of TCO-less dye-sensitized solar cells (DSCs). Differential performance of DSCs thus fabricated was interpreted utilizing impedance spectral and lifetime analysis. It was found that although utilization of cobalt bipyridyl complex-based electrolyte was able to harvest higher photons in the lower wavelength region (330 to 430 nm) as compared to its iodine electrolyte counterparts, hampered dye regeneration due to reduced driving force and slower ion diffusion in combination with higher charge transport resistance at TiO2 / dye / electrolyte was responsible for relatively hampered photovoltaic performance at peak absorption.
Scientific journal

Boosting the Efficiency of Low-Cost T-C-O-Less Dye-Sensitized Solar Cells Employing Nanoparticle Spacers and Cobalt Complex Redox Shuttle
Md Zaman Molla; Ajay Kumar Baranwal; Shuzi Hayase; Shyam S. Pandey
ACS Applied Electronic Materials, 2, 9, 2721-2729, 22 Sep. 2020, A strategy has been explored to enhance the diffusion of Co2+/3+ species through the dye-stained nanoparticle spacer employed as an electrolyte absorbing layer with different nanoparticle sizes of TiO2 (30 and 20 nm) and ZrO2 (15 nm) films in transparent conducting oxide-less back-contact dye-sensitized solar cells (T-C-O-less B-C-DSCs). A dye-stained nanoparticle spacer with a relatively larger particle of the TiO2 (30 nm) film brought about easy diffusion of cobalt(II/III) complexes leading to an enhanced photoconversion efficiency (PCE) of 6.55% as compared to relatively smaller nanoparticle of the TiO2 (20 nm) film (4.95%) and ZrO2 (15 nm) film (2.03%). The T-C-O-less B-C-DSC exhibits a lower PCE of 6.55% relative to the T-C-O-based DSC (9.10%) owing to relatively hampered diffusivity of [Co(bpy)3]3+/2+ complexes through perforated holes of the SS-mesh as well as the nanoparticle spacer. A differential study reveals that the cobalt electrolyte exhibits much improved light accumulation in the range 330-430 nm relative to the iodine electrolyte counterpart. The corrosion study of the SS-mesh and Ti-protected SS-mesh reveals that stable T-C-O-less B-C-DSCs can be attained only by the cobalt electrolyte because of its mild nature toward the SS-mesh and Ti metal as compared to the iodine electrolyte.
Scientific journal

Parametric optimization of back-contact T-C-O-free dye-sensitized solar cells employing indoline and porphyrin sensitizer based on cobalt redox electrolyte
Md Zaman Molla; Ajay Kumar Baranwal; Gaurav Kapil; Shuzi Hayase; Shyam S. Pandey
Solar Energy, 208, 411-418, 15 Sep. 2020, Transparent-conductive-oxide-free (T-C-O-free) back-contact (B-C) dye-sensitized solar cell (DSC) utilizing flexible Stainless Steel (SS) mesh (SS-mesh) supported with mesoporous TiO2 as a photoanode employing cobalt electrolyte is being presented. A thin layer of Ti metal over the SS-mesh was ascertained to be essential to retard the back electron reaction, which was confirmed by the dark current measurements. The interfacial contact between the SS-mesh and nanoporous (NP) TiO2 of the photoanode of T-C-O-free B-C-DSC was driven to influence the photovoltaic performance greatly. It was confirmed by electrochemical impedance analysis that NP TiO2 of 30 nm exhibited less charge transfer impedance observed at TiO2-dye-electrolyte interface as compared to TiO2 of having particle size of 15–20 nm. T-C-O-free B-C-DSC employing dye mixer combination of indoline dyes D-131 and D-205 (1:1) with relatively larger NP of TiO2 (30 nm) as compared to TiO2 of 15–20 nm exhibited enhanced photoconversion efficiency (PCE) of 4.02%. To increase the PCE even further, T-C-O-free B-C-DSC with cobalt based electrolyte sensitized with porphyrin (YD2-o-C8)-dye bearing a larger optical window was investigated. An optimized 10 µm thickness of the TiO2 layer was found to be optimum leading to an enhanced PCE of 5.26%.
Scientific journal

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
Physica Status Solidi (A) Applications and Materials Science, Wiley-VCH Verlag, 217, 18, 01 Sep. 2020, Herein, it is reported that the stability of a halogenated perovskite (PVK) solar cell consisting of an fluorine-doped tin oxide (FTO) substrate/TiO2/CH3NH3PbI3/N2,N2,N2′,N2′,N7,N7,N7′,N7′-octakis(4-methoxyphenyl)-9,9′-spirobi[9H-fluorene]-2,2′,7,7′-tetramine/Ag/Au structure is improved by adding Sb-xanthate to the PVK layer without large loss of efficiency. The Sb-element-rich layer is observed on top of the PVK layer. From the X-ray photoelectron spectroscopy (XPS) study, it is concluded that an inorganic SbxOy passivation layer on the PVK layer is prepared by baking the solution of the Sb-xanthate and the PVK precursor. The inorganic layer prevents moisture and oxygen from penetrating into the PVK layer. This article provides a new method to obtain a passivation layer on a PVK layer by baking a mixture solution in one step for improving solar cell stability.
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

Synthesis of Sb(V) complexes with pyridyl cations and application for lead-free perovskite solar cells
Zhenhua Xu; Chu Zhang; Fengyang Yu; Yusuke Kamata; Shuzi Hayase; Tingli Ma
Chemistry Letters, Chemical Society of Japan, 49, 8, 944-946, 05 Aug. 2020, Lead halide perovskite has emerged as a promising photovoltaic material due to its excellent power conversion efficiency (PCE). However, the toxicity problem of lead-based perovskite hampers the commercialization of perovskite solar cells. Here, we develop several Sb(V) complexes with pyridyl cations and serve as absorber layer for lead-free perovskite solar cells. The designed complexes were based on 4-tert-butylpyridine (tBP) and N-ethylpyridinium (N-EtPy) cations with bandgaps of 2.01 eV and 1.95 eV, which showed their potential for solar cells and optoelectronic applications. We also found a chemical rule for stable Sb complexes in terms of the bond connectivity of pnictogen-antimony. Initial studies produce a solar cell with a PCE of 0.9% and offer inspiration for further exploration of environment-friendly perovskite families.
Scientific journal, English

Interdiffusion Stomatal Movement in Efficient Multiple-Cation-Based Perovskite Solar Cells.
Cong Li; Zhinan Zhu; Bingqiang Niu; Fu Yang; Xinpeng Chen; Yingke Ren; Peng Zhong; Shuzi Hayase; Tianhong Cui; Rusen Yang
ACS applied materials & interfaces, 12, 31, 35105-35112, 05 Aug. 2020, True, The composition and crystallization process are essential for high-quality perovskite films. Cesium (Cs) and methylammonium chlorine (MACl) were found to affect the crystallization kinetics of perovskite, and the performance and stability of corresponding devices were greatly improved. We adopted an ion exchange method to remove MACl vapor and add Cs to form a multiple-cation-based perovskite film. With the increase of annealing time, Cl- from cesium chloride (CsCl) and MA from methylammonium bromide (MABr) formed gradually MACl vapor, and the porosity of surface morphology improved accordingly. The highly crystallized and compact CsyMAx - yFA1 - xPbI3 - xBrx perovskite film with different compositions was eventually obtained. The effects of the amount of MABr on the property of perovskite films and on the performance of the corresponding perovskite solar cells (PerSCs) were systematically studied. The PerSCs derived from 12 mg of MABr exhibit the best photovoltaic performance with a power conversion efficiency of 21.57% under 1 sun illumination.
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 {BV}, 74, 104858-104858, Aug. 2020, Peer-reviwed
Scientific journal

Cesium Acetate-Induced Interfacial Compositional Change and Graded Band Level in MAPbI3 Perovskite Solar Cells.
Ajay Kumar Jena; Ayumi Ishii; Zhanglin Guo; Muhammad Akmal Kamarudin; Shuzi Hayase; Tsutomu Miyasaka
ACS applied materials & interfaces, 12, 30, 33631-33637, 29 Jul. 2020, True, Compositional engineering and interfacial modifications have played pivotal roles in the accomplishment of high-efficiency perovskite solar cells (PSCs). Different interfaces in the PSCs influence the performance remarkably either by altering the crystallization of the active material or shifting the energy levels or improving the electrical contact. This work reports how a thin layer of cesium acetate on the TiO2 electron transport layer (ETL) induces generation of a PbI2-rich methylammonium lead iodide (MAPbI3) composition at the ETL/MAPbI3 interface, which downshifts the conduction band level of MAPbI3 to create an energy level gradient favorable for carrier collection, resulting in higher photocurrent, fill factor, and overall power conversion efficiency.
Scientific journal, English

Interface engineering with a novel n-type small organic molecule for efficient inverted perovskite solar cells
Helin Wang; Fu Yang; Ning Li; Jun Song; Junle Qu; Shuzi Hayase; Wai-Yeung Wong
Chemical Engineering Journal, Elsevier B.V., 392, 15 Jul. 2020, Fullerene derivatives are promising electron transporting materials for low-temperature processed inverted perovskite solar cells (PSCs). However, fullerene derivatives have some disadvantages, e.g. [6,6]-phenyl C61 butyric acid methyl ester (PCBM) has unmanageable morphology, low electron mobility and easily generated non-radiative recombination, which restrict the performance of PSCs. Herein, a novel n-type small organic molecule, homologous perylene diimide tetramer (HPDT), is designed and synthesized in this work to engineer the interface properties by enhancing interface contact, decreasing energetic barrier and recombination losses. HPDT shows suitable energy levels and high electron mobility and thus will increase the electron mobility during interface engineering in the inverted PSCs. Moreover, coating HPDT on top of perovskite prior to the deposition of PCBM is helpful to achieve a homogeneous pinhole-free PCBM layer, leading to enhanced power conversion efficiency from 17.38% up to 19.75% for inverted MAPbI3 PSCs along with a negligible hysteresis. Significantly, our results undoubtedly provide new guidelines in exploring n-type organic small molecules for high-performance PSCs.
Scientific journal, 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
Japanese Journal of Applied Physics, Institute of Physics Publishing, 59, 6, 01 Jul. 2020, Four types of perovskite solar cells (PVK PV) were fabricated to investigate the effect of charge separation interface (p/n junction) for inverted and normal structures. For inverted structures, (1) TCO/p-type/p-PVK/n-type and (2) TCO/p-type/n-PVK/n-type, were prepared by changing the PVK composition. For normal structures, (3) TCO/n-type/n-PVK/p-type and (4) TCO/n-type/p-PVK/p-type structures were fabricated in the same way. The solar cell efficiency of (2) was better than that of (1), and (3) showed a higher efficiency than (4). In all cases, the cell in which the p/n junction is located at the back side of the PVK layer from the incident light direction gave higher efficiency. Band bending, Fermi level, and carrier mobility were measured for these PVK layers and solar cells. We concluded that the higher efficiency for (2) and (3), where both cells of the p/n junction are located on the bottom of the PVK layer, is explained by the higher mobility of minority carriers, respectively.
Scientific journal, English

Unileg thermoelectric module comprised by coated halide-perovskite thin film
Shrikant Saini; Ajay Kumar Baranwal; Tomohide Yabuki; Shuzi Hayase; Koji Miyazaki
Journal of Heat Transfer, 142, 7, Jul. 2020, The direct conversion of thermal energy into electricity is possible by thermoelectric effect. CsSnI3 perovskite has shown a way with its intrinsic ultralow thermal conductivity and large Seebeck coefficient. In this work, CsSnI3 thin films were optimized. Thin films were structurally and chemically characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). Thermoelectric properties such as electrical conductivity, Seebeck coefficient, and thermal conductivity were measured near room temperature (300 K). CsSnI3 thin films unileg thermoelectric modules were fabricated on a glass substrate. The maximum output power is obtained about 0.8 nW for five legs (25mm×3mm×600 nm) modules for the temperature difference of about 5 °C.
Scientific journal

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

Efficient Surface Passivation and Electron Transport Enable Low Temperature-Processed Inverted Perovskite Solar Cells with Efficiency over 20%
Helin Wang; Fu Yang; Ning Li; Muhammad Akmal Kamarudin; Junle Qu; Jun Song; Shuzi Hayase; Christoph J. Brabec
ACS Sustainable Chemistry & Engineering, American Chemical Society ({ACS}), 15 Jun. 2020, Peer-reviwed
Scientific journal

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

VOC Over 1.4 V for Amorphous Tin-Oxide-Based Dopant-Free CsPbI2Br Perovskite Solar Cells.
Zhanglin Guo; Ajay Kumar Jena; Izuru Takei; Gyu Min Kim; Muhammad Akmal Kamarudin; Yoshitaka Sanehira; Ayumi Ishii; Youhei Numata; Shuzi Hayase; Tsutomu Miyasaka
Journal of the American Chemical Society, 142, 21, 9725-9734, 27 May 2020, True, CsPbI2Br perovskite solar cells have attracted much attention because of the rapid development in their efficiency and their great potential as a top cell of tandem solar cells. However, the VOC outputs observed so far in most cases are far from that desired for a top cell. Up to now, with various kinds of treatments, the reported champion VOC is only 1.32 V, with a VOC deficit of 0.60 V. In this work, we found that aging of the SnCl2 precursor solution for the electron-transporting layer can promote the VOC of CsPbI2Br solar cells by employing a dopant-free-polymer hole transport material (HTM) over 1.40 V and efficiency over 15.5% with high reproducibility. With the champion VOC of 1.43 V, the VOC deficit was reduced to <0.50 V, which is achieved for the first time. This simple technique of SnCl2 solution aging forms a uniform and smooth amorphous SnOx film with pure Sn4+, elevates the conduction band of SnOx, and reduces the interfacial gaps and the trap state density of the device, resulting in enhancement in average VOC from ∼1.2 V in the nonaged case to ∼1.4 V in the aged case. Furthermore, the device using an aged SnCl2 solution also exhibits a much better long-term stability than that made of the fresh solution. These achievements in dopant/additive-free CsPbI2Br solar cells can be useful for future research on CsPbI2Br and tandem solar cells.
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 (International ed. in English), 59, 22, 8421-8424, 25 May 2020, 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

Boosting the Conversion Efficiency Over 20% in MAPbI3 Perovskite Planar Solar Cells by Employing a Solution-Processed Aluminum-Doped Nickel Oxide Hole Collector.
Bhaskar Parida; Saemon Yoon; Jun Ryu; Shuzi Hayase; Sang Mun Jeong; Dong-Won Kang
ACS applied materials & interfaces, 12, 20, 22958-22970, 20 May 2020, True, Recently, nickel oxide (NiOx) thin films have been used as an efficient and robust hole transport layer (HTL) in inverted planar perovskite solar cells (IP-PSCs) to replace costly and unstable organic transport materials. However, the power conversion efficiency (PCE) of most IP-PSCs using NiOx HTLs is rather limited below 20% due to insufficient electronic conductivity of the NiOx. In this work, solution-processed Al-doped NiOx (ANO) films are suggested as HTLs for low-cost and stable IP-PSCs. The electrical conductivity of the NiOx film is significantly enhanced by Al doping, which effectively reduces the nonradiative recombination losses at the HTL-perovskite interfaces and boosts hole extraction/transportation. The device with undoped NiOx shows the best PCE of 16.56%, whereas ANO HTL (5% doping) contributes to achieving a PCE of 20.84%, which outperforms other CH3NH3PbI3 IP-PSCs with NiOx-based HTLs reported to date. Moreover, a reliability test (1728 h storage) shows that the performance stability is enhanced by approximately 11% by employing ANO HTLs. This investigation into ANO HTLs provides a new guideline for the further development of highly efficient and reliable IP-PSCs using low-cost and robust metal oxide HTLs.
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, 111-111, 16 May 2020, 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

Synthesis, photophysical characterization and dye adsorption behavior in unsymmetrical squaraine dyes with varying anchoring groups
Ajendra Kumar Vats; Anusha Pradhan; Shuzi Hayase; Shyam S. Pandey
Journal of Photochemistry and Photobiology A: Chemistry, Elsevier B.V., 394, 01 May 2020, Four newly designed unsymmetrical squaraine dyes bearing different functional groups for their anchoring on the surface of mesoporous TiO2 were successfully synthesized aiming towards development of far-red sensitizers for dye-sensitized solar cells (DSSCs). The synthesized dyes were characterized by 1H NMR, fast ion bombardment mass, and subjected to photophysical investigations by electronic absorption/fluorescence emission spectroscopy and cyclic voltammetry. These dyes exhibited excellent solubility in a number of common organic solvents. Adsorption behavior of these dyes on the thin films of mesoporous TiO2 was investigated in detail and results indicated that rate of dye adsorption follows the order −COOH>
-PO3H2>
OH >
SO3H. At the same time, dye desorption studies demonstrated that stability of adsorbed dyes on the mesoporous TiO2 follows the order -PO3H2>
>
OH>
−COOH >
–SO3H. Further, implication of the nature of anchoring groups of dye molecules upon the energy levels of their highest occupied molecular orbital and lowest unoccupied molecular orbital was evaluated by both of the combined theoretical and experimental approaches. In spite of enhanced dye loading, very high binding strength and favorable energetic cascade, SQ-143 bearing Phosphonic acid exhibited hampered photovoltaic performance as compared to that of SQ-138 with carboxylic acid anchoring group. Amongst various sensitizers used for present investigation, SQ-138 exhibited best photovoltaic performance having short-circuit current density, open circuit voltage and fill factor of 12.49 mA/cm2, 0.60 V, and 0.53, respectively, leading to power conversion efficiency of 4.07 % after simulated solar irradiation.
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 applied materials & interfaces, 12, 15, 17776-17782, 15 Apr. 2020, 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

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

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
Chemistry of Materials, American Chemical Society, 32, 3, 1089-1100, 11 Feb. 2020, Bulk halide Sn-Pb alloyed perovskites show great promise as alternatives to lead counterparts with attractive properties such as extended spectral response and improved phase stability. However, until now there has been no efficient way of making such alloyed materials in quantum dots (QD) endowed with a full range of halide covering. Although a recently reported trioctylphosphine (TOP)-based technique demonstrates efficacy in synthesizing perovskite CsSnxPb1-xI3 QDs, it is incapable of producing those pure Br/Cl-based Sn-Pb alloyed QDs due to the insufficient solubility of PbBr2 and PbCl2 in TOP. Here, by taking advantage of the strong solvent ability of trioctylphosphine oxide (TOPO) for both SnX2 and PbX2 halide salts, we present the first synthesis of pure halogen-based prototype ASnxPb1-xX3 (A = Cs, FA, MA
X = Cl, Br, I) QDs, which exhibit distinctive structural and physicochemical features that can be facilely controlled by varying halide species and Sn/Pb ratios. TOPO plays a key role in delivering reactive precursors but NMR measurement suggests it is not present on the QD surface after a postwashing process. The successful making of halide-tunable Sn-Pb perovskite QDs has offered great material versatility for the perovskite QD family, which enables a more systematic investigation of their fundamental photoexcited charge carrier dynamics that have not been explored.
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
Chao Ding; Feng Liu; Yaohong Zhang; Daisuke Hirotani; Xing Rin; Shuzi Hayase; Takashi Minemoto; Taizo Masuda; Ruixiang Wang; Qing Shen
Nano Energy, Elsevier Ltd, 67, 01 Jan. 2020, Highly luminescent formamidinium lead iodide (FAPbI3) quantum dots (QDs) exhibit high stability and narrowest bandgap energy among lead halide perovskites, thus they have become one of the most promising materials for the development of perovskite QD-based light-harvesting and near infrared-emitting devices. However, little is known thus far about photoexcited carrier dynamics at the interface between FAPbI3 QDs and charge transport layers, which is very important for both fundamental studies and applications of the QD/charge transport layer heterojunctions. Here, we systematically investigate both hot and cold photoexcited carrier (electron and hole) dynamics including relaxation and transfer at the heterojunction interfaces between FAPbI3 QDs and two kinds of well used charge acceptors, i.e., TiO2 and NiOx. We find that (i) the hot carriers in the FAPbI3 QDs are cooled to cold carriers with a cooling rate in the order of 1011 s−1, and (ii) the cold-electron and -hole injection rates are size dependent and are 2.01–2.29 × 109 s−1 and 1.55–1.96 × 109 s−1 at the two types of FAPbI3 QD/MO (metal oxide) heterojunctions, respectively, which are in good agreements with Marcus theory of charge transfer. In addition, the photoexcited carrier injection efficiency at the two heterojunctions is found to be as high as over 99%, which is the most important key for achieving high photovoltaic performance of the FAPbI3 QD solar cells (QDSCs). Prototypes of the two types of heterojunction-based QDSCs, i.e., normal-structure solar cells based on FAPbI3 QD/TiO2 and inverted-structure solar cells based on FAPbI3 QD/NiOx, were developed and the power conversion efficiencies of more than 9% and 5% were obtained, respectively. Moreover, the photovoltaic performance showed a higher storage stability over 100 days. The photovoltaic performance would be improved largely by optimization of each parts in the QDSCs. Our results shed light on perovskite QD-based optoelectronic devices.
Scientific journal, English

Interface engineering using Y2O3 scaffold to enhance the thermoelectric performance of CsSnI3 thin film,
Ajay Kumar Baranwal; Shrikant Saini; Zhen Wang; Daisuke Hirotani; Tomohide Yabuki; Koji Miyazaki; Shuzi Hayase
Organic Electronics (Elsevier), 2020, 76, 105488. https://doi.org/10.1016/j.orgel.2019.105488, https://doi.org/10.1016/j.orge, 2020, Peer-reviwed, Solution processed Cesium Tin halide perovskites (CsSnI3) are inorganic crystal to be explored for thermoelectric applications. Here, we report a novel strategy using an inorganic Y2O3 scaffold to improve the thermoelectric performance. The additional Y2O3 influence the CsSnI3 crystal growth and favor more conducting behavior with intrinsic defects (Sn4+) formation. Therefore, the resulting solution processed composite film Y2O3/CsSnI3 show much improved electrical conductivity of ~310 S/cm as compared to ~98 S/cm of pristine CsSnI3 film. Under the influence of Y2O3, the resulting phonon scattering path was enhanced significantly due to formed defects/vacancy and reduced CsSnI3 crystal size, which showed a reduction in thermal conductivity from 0.74 W/mK to 0.28 W/mK. This work paves a new paradigm to improve the thermoelectric performance of solution based thermoelectric generator.
Scientific journal, English

Synthesis of monodispersed silver particles: Synthetic techniques to control shapes, particle size distribution and lightness of silver particles
Kanetaro Sannohe; Tingli Ma; Shuzi Hayase
Advanced Powder Technology, Elsevier B.V., 30, 12, 3088-3098, 01 Dec. 2019, The purpose of this paper is to give process for preparing monodispersed silver particles with round shape having aspect ratio of 1, because the shape is suitable for preparing silver grids with fine pattern size. We found that the combination of gelatin and hydrazine gave the monodispersed silver particles with the aspect ratio of 1. Presence of the high molecular compounds is crucial probably because they are adsorbed on the surface of growing silver particles and control the uniform crystal growth. In addition, the relationship between these reaction conditions and the particle shape are discussed in detail.
Scientific journal, English

La-doped SnO2 as ETL for efficient planar-structure hybrid perovskite solar cells
Zhenhua Xu; Siow Hwa Teo; Liguo Gao; Zhanglin Guo; Yusuke Kamata; Shuzi Hayase; Tingli Ma
ORGANIC ELECTRONICS, ELSEVIER, 73, 62-68, Oct. 2019, SnO2 has attracted considerable attention in perovskite solar cells (PSCs) due to its excellent optical and electrical properties. However, a poor surface morphology, specifically with the presence of pinholes after the annealing process, limits its application in PSCs. To overcome the drawback of fin oxide, lanthanum (La) is herein first to be doped into the layer, which is able to alleviate the SnO2 crystal aggregation and produce full-coverage and a uniform film. In addition, La:SnO2 can effectively reduce the band offset of the SnO2 layer, which results in the high Voc of 1.11 V. Systematic analyses revealed that the La:SnO2 layer enhances the electron extraction and suppresses charge recombination, leading to the power conversion efficiency (PCE) enhancement from 14.24% to 17.08%.
Scientific journal, English

Role of device architecture and AlO_X interlayer in organic Schottky diodes and their interpretation by analytical modeling
Nikita Kumari; Manish Pandey; Kengo Hamada; Daisuke Hirotani; Shuichi Nagamatsu; Shuzi Hayase; Shyam S. Pandey
Journal of Applied Physics, AIP Publishing, 126, 12, 125501-125501, 28 Sep. 2019
Scientific journal

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
Journal of Physical Chemistry Letters, 10, 17, 5277-5283, 05 Sep. 2019, Peer-reviwed, True, Copyright © 2019 American Chemical Society. Lead-free tin perovskite solar cells (PSCs) show the most promise to replace the more toxic lead-based perovskite solar cells. However, the efficiency is significantly less than that of lead-based PSCs as a result of low open-circuit voltage. This is due to the tendency of Sn2+ to oxidize into Sn4+ in the presence of air together with the formation of defects and traps caused by the fast crystallization of tin perovskite materials. Here, post-treatment of the tin perovskite layer with edamine Lewis base to suppress the recombination reaction in tin halide PSCs results in efficiencies higher than 10%, which is the highest reported efficiency to date for pure tin halide PSCs. The X-ray photoelectron spectroscopy data suggest that the recombination reaction originates from the nonstoichiometric Sn:I ratio rather than the Sn4+:Sn2+ ratio. The amine group in edamine bonded the undercoordinated tin, passivating the dangling bonds and defects, resulting in suppressed charge carrier recombination.
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 and Interfaces, 11, 34, 31105-31110, 28 Aug. 2019, Peer-reviwed, True, Copyright © 2019 American Chemical Society. In the composition of Q0.1(FA0.75MA0.25)0.9SnI3, Q is replaced with Na+, K+, Cs+, ethylammonium+ (EA+), and butylammonium+ (BA+), respectively, and the relationship between actually measured lattice strain and photovoltaic performances is discussed. The lattice strain evaluated by the Williamson-hall plot of X-ray diffraction data decreased as the tolerance factor was close to one. The efficiency of the Sn-perovskite solar cell was enhanced as the lattice strain decreased. Among them, EA0.1(FA0.75MA0.25)0.9SnI3 having lowest lattice strain gave the best result of 5.41%. Because the carrier mobility increased with a decrease in the lattice strain, these lattice strains would disturb carrier mobility and decrease the solar cell efficiency. Finally, the results that the efficiency of the SnGe-perovskite solar cells was gradually enhanced from 6.42 to 7.60% during storage, was explained by the lattice strain relaxation during the storage.
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, 4, 8, 1991-1998, 09 Aug. 2019, Peer-reviwed, © 2019 American Chemical Society. Tin-lead (Sn-Pb)-based perovskite solar cells (PSCs) still exhibit inferior power conversion efficiency (PCE) compared to their pure Pb counterparts because of high voltage loss (VL) and high photocurrent loss in the infrared region. This study explores that a small amount of cesium ion (Cs+) incorporation in the lattice of Sn-Pb perovskite can reduce the relative lattice strain, which in turn decreases the VL less than 0.50 V. Moreover, surface and bulk trap densities also seem to be reduced by Cs+ addition, as concluded by thermally stimulated current measurements and increased carrier lifetime by photoluminescence study. It was discovered that a small amount of Cs+ lowered the Urbach energy, which can be used as a signature to optimize the optoelectronic and the photovoltaic properties of multication perovskite materials. This study further demonstrates that a high external quantum efficiency (∼80% at 900 nm) can be obtained with fluorine-doped tin oxide (FTO) glass rather than frequently used indium tin oxide (ITO) glass. The strategies employed in the work improved the open-circuit voltage to 0.81 V and gave a photocurrent density of >30 mA/cm2 and a PCE of >20% using a band gap of 1.27 eV.
Scientific journal

Wide wavelength photon harvesting in dye-sensitized solar cells utilizing cobalt complex redox electrolyte: Implication of surface passivation
Anusha Pradhan; Maryala Sai Kiran; Gaurav Kapil; Shuzi Hayase; Shyam S. Pandey
Solar Energy Materials and Solar Cells, Elsevier B.V., 195, 122-133, 15 Jun. 2019, A combination of near infra-red (NIR) photon harvesting and cobalt electrolytes having deeper redox energy level are needed for the fabrication of high efficiency dye-sensitized solar cells (DSSCs). A logical molecular design of unsymmetrical squaraine dye (SQ-110) as a representative of NIR dyes has been demonstrated to function well in DSSC using cobalt complex redox electrolyte. Problem of mass transport limitations due to the bulky cobalt complex ions leading to relatively enhanced charge recombination was amicably solved by single as well as multiple compact metal oxide surface passivation on both of the transparent conducting oxide substrate as well as mesoporous TiO 2 . Complete absence of light absorption beyond 550 nm wavelength region by D-35 and utilization of a complementary light harvesting dye SQ-110 led to efficient wide wavelength photon harvesting. DSSC fabricated using a dye cocktail of D-35 and SQ-110 in 4:1 ratio resulted in to photoconversion efficiency (PCE) of 7.2%, which is much higher as compared to the constituent individual sensitizers D-35 (3.6%) and SQ-110 (1.9%). This synergistic enhancement in PCE by dye cocktail was associated with the mutual co-operation of respective dyes in terms controlling the dye aggregation and complementary photon harvesting. In this dye cocktail system, D-35 is involved in the prevention of dye aggregation, lower wavelength photon harvesting and energy transfer induced photocurrent enhancement.
Scientific journal, English

Niobium Incorporation into CsPbI2Br for Stable and Efficient All-Inorganic Perovskite Solar Cells.
Zhanglin Guo; Shuai Zhao; Anmin Liu; Yusuke Kamata; Siowhwa Teo; Shuzhang Yang; Zhenhua Xu; Shuzi Hayase; Tingli Ma
ACS applied materials & interfaces, 11, 22, 19994-20003, 05 Jun. 2019, True, All-inorganic perovskites are attracting increasing attention due to their superior thermal stability than that of the traditional CH3NH3PbI3, while their inferior phase stability in ambient conditions is still an unsolved issue. Here, for the first time, we report the incorporation of niobium (Nb5+) ions into the CsPbI2Br perovskite. Results indicate that Nb5+ can effectively stabilize the photoactive α-CsPbI2Br phase by the possible substitution of Pb2+. With 0.5% Nb doping, the carbon electrode-based all-inorganic perovskite solar cells achieved a high photoconversion efficiency value of 10.42%, 15% higher than that of the control device. The Nb5+ incorporation reduces the charge recombination in the perovskite, leading to a champion Voc value of 1.27 V and a negligible hysteresis effect. This work explicates the high compatibility of all-inorganic perovskite materials and unlocks the opportunities for the use of high-valence ions for perovskite property modification.
Scientific journal, English

2D positional profiling of orientation and thickness uniformity in the semiconducting polymers thin films
Nikita Kumari; Atul S.M. Tripathi; Shifumi Sadakata; Manish Pandey; Shuichi Nagamatsu; Shuzi Hayase; Shyam S. Pandey
Organic Electronics, Elsevier {BV}, 68, 221-229, May 2019, Peer-reviwed
Scientific journal

Xanthate-induced sulfur doped all-inorganic perovskite with superior phase stability and enhanced performance
Zhen Wang; Ajay K. Baranwal; Muhammad Akmal kamarudin; chi huey Ng; Manish Pandey; Tingli Ma; Shuzi Hayase
Nano Energy, 59, 258-267, May 2019, Peer-reviwed, © 2019 Elsevier Ltd Although the efficiency of perovskite-based solar cell has boosted up to 23%, their stability hinders the further development due to the volatile nature of organic components in conventional organic-inorganic hybrid perovskites. All-inorganic perovskites have been reported to achieve enhanced thermal stability. Herein we applied xanthate in all-inorganic perovskite to realize the sulfur-doped CsPbIBr 2 for superior phase stability. The additive cesium xanthate (CsXth) could be decomposed into cesium sulfides during annealing process. The divalent S 2- lies in the interstices of perovskite lattice and strongly coordinates with CsPbIBr 2 to stabilize the ɑ-phase, as a result, greatly enhanced stability was achieved at ambient air with 65% relative humidity (RH) compared with the reference film. Moreover, we obtained a champion efficiency of 9.78% with a high open-circuit voltage (V oc ) of 1.30 V based on 5% CsXth-CsPbIBr 2 under humid air. Performance of sulfur-doped perovskite device shows almost no decay in 10 h under humid air with 65% RH without encapsulation. These advantages provide an efficient way to prepare more efficient and superior stable perovskite device, which is beneficial toward commercialization in the future.
Scientific journal, English

Passivation of Grain Boundary by Squaraine Zwitterions for Defect Passivation and Efficient Perovskite Solar Cells
Zhen Wang; Anusha Pradhan; Muhammad Akmal kamarudin; Manish Pandey; Shyam S. Pandey; Putao Zhang; Chi huey Ng; Atul S.M. Tripathi; Tingli Ma; Shuzi Hayase
ACS Applied Materials & Interfaces, American Chemical Society ({ACS}), 11, 10, 10012-10020, 13 Mar. 2019, Peer-reviwed, True, Unavoidable defects in grain boundaries (GBs) are detrimental and critically influence the organometal halide perovskite performance and stability. To address this issue, semiconducting molecules have been employed to passivate traps along perovskite GBs. Here, we designed and synthesized three squaraine molecules (SQ) with zwitterionic structure to interact with under-coordinated Pb2+ and passivate Pb-I antisite defects. Density functional theory calculation shows symmetric O atoms could coordinate with perovskite grains simultaneously, resulting in continuous charge distribution at the SQ-perovskite interface. The energetic traps distribution in CH3NH3PbI3 perovskite is influenced significantly by the interaction between SQ and perovskite as analyzed by thermally stimulated current, in which the deep-level defects are considerably reduced due to efficient SQ passivation. In addition, we explore how SQ molecules with different energy offset affect the charge extraction, which is suggested to facilitate exciton separation at the perovskite-SQ interface. These benefits lead to enhanced perovskite efficiency from 15.77 to 18.83% with the fill factor approaching 80%, which is among the highest efficiency reported for MAPbI3 solar cells fabricated in an ambient environment at 60% relative humidity (RH). Considerable retardation of perovskite device degradation was achieved, retaining 90% of initial efficiency when kept 600 h at 60 ± 5% RH.
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; Shuzi Hayase; Ruixiang Wang; Zhigang Zou; Qing Shen
Nanoscale horizons, 4, 2, 445-451, 01 Mar. 2019, 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

GeI 2 Additive for High Optoelectronic Quality CsPbI 3 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, American Chemical Society, 31, 3, 798-807, 12 Feb. 2019, Trioctylphosphine (TOP)-based syntheses of CsPbI 3 perovskite quantum dots (QDs) yield unprecedented high photoluminescence quantum yield (PL QY), lower Stokes shifts, and longer carrier lifetimes due to their enhanced crystallinity. This synthetic route relies on a heavily Pb-rich condition or a large Pb:Cs molar ratio in precursor solution to produce QDs with appropriate stoichiometry as well as to guarantee a good colloidal stability. The high Pb condition is achieved by a high concentration of PbI 2 prepared in TOP. Here we find such Pb-rich strategies can be avoided by providing additional iodine ions using other metal halide salts. In particular GeI 2 , which contrary to PbI 2 , readily dissolves in TOP. CsPbI 3 QDs prepared using PbI 2 /GeI 2 combination show near-unity PL QY and improved chemical stability compared to the previous synthetic route. Furthermore, we find no sign of Ge incorporation in the QDs (compositionally or energetically). The ensuing QD solar cells deliver power conversion efficiency of 12.15% and retain 85% of its peak performance after storage over 90 days. The PbI 2 /GeI 2 dual-source iodine synthetic approach presented here represents a more rational and robust route to high-quality CsPbI 3 QDs.
Scientific journal, English

The Role of Lanthanum in a Nickel Oxide-Based Inverted Perovskite Solar Cell for Efficiency and Stability Improvement.
Siowhwa Teo; Zhanglin Guo; Zhenhua Xu; Chu Zhang; Yusuke Kamata; Shuzi Hayase; Tingli Ma
ChemSusChem, 12, 2, 518-526, 24 Jan. 2019, True, A high-performing inverted perovskite solar cell (PSC) always relies on the hole transporting layer (HTL) quality and its interfaces. This work investigates the impact of La incorporation within the NiOx matrix for defects passivation, thus leading to high charge extraction ability and stability without compromising its power conversion efficiency. In the presence of La, the La-NiOx quality is clearly improved; without the formation of pinholes. In addition, the inclusion of La alters the energy band alignment; consequently, enhancing the hole transportation and widening the Voc (>1 V), as compared to the pristine NiOx . The beneficial effect of La was further revealed through the photoluminescence measurement and density of states (DOS) analysis, in which trap states are passivated by La. More importantly, the perovskite solar cell, with La-NiOx as the HTL, exhibits 21 % enhancement in efficiency and a remarkable stability that is greater than that of pristine NiOx . This also unlocks an opportunity for commercialization.
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

Growth of halide perovskites thin films for thermoelectric applications
Shrikant Saini; Ajay Kumar Baranwal; Tomohide Yabuki; Shuzi Hayase; Koji Miyazaki
MRS Advances, Materials Research Society, 4, 30, 1719-1725, 2019, Thermoelectric materials can play an important role to develop a sustainable energy source for internet of things devices near room temperature. In this direction, it is important to have a thermoelectric material with high thermoelectric performance. Cesium tin triiodide (CsSnI3) single crystal perovskite has shown high value of Seebeck coefficient and ultra low thermal conductivity which are necessary conditions for high thermoelectric performance. Here, we report the thermoelectric response of CsSnI3 thin films. These films are prepared by cost effective wet spin coating process at different baking temperature. Films were characterized using X-ray diffraction and scanning electron microscopy. In our case, films baked at 130°C for 5 min have shown the best thermoelectric performance at room temperature with: Seebeck coefficient 115 μV/K and electrical conductivity 124 S/cm, thermal conductivity 0.36 W/m·K and figure of merit ZT of 0.137.
Scientific journal, English

Achievable high: V oc of carbon based all-inorganic CsPbIBr 2 perovskite solar cells through interface engineering
Zhanglin Guo; Siowhwa Teo; Zhenhua Xu; Chu Zhang; Yusuke Kamata; Shuzi Hayase; Tingli Ma
Journal of Materials Chemistry A, Royal Society of Chemistry, 7, 3, 1227-1232, 2019, In this work, a simple interface engineering process for SnO 2 electron selective layer (ESL) surface passivation employing a SnCl 2 solution is introduced, which has successfully reduced the energy loss for a high open-circuit voltage (V oc ) output and consequently improved the performance of all-inorganic CsPbIBr 2 perovskite solar cells (PSCs). It was found that surface passivation can effectively suppress the recombination process at the interface between the perovskite and SnO 2 due to higher recombination resistance. The shorter PL decay time is attributed to the excellent electron extraction from the perovskite film. After optimizing surface passivation, the power conversion efficiency (PCE) was enhanced from 4.73% to 7.00% and a high V oc of 1.31 V was achieved, which is one of the highest V oc values reported for inorganic Cs-based PSCs. More importantly, the passivated SnO 2 based device retains 95.5% of its initial performance at 90 °C in air without encapsulation. This work provides a simple and efficient interface engineering method to improve the V oc and efficiency of all-inorganic PSCs.
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

Hot-injection and ultrasonic irradiation syntheses of Cs2SnI6 quantum dot using Sn long-chain amino-complex
Tsuguo Koyanagi; Gaurav Kapil; Yuhei Ogomi; Kenji Yoshino; Qin Shen; Taro Toyoda; Takurou N. Murakami; Hiroshi Segawa; Shuzi Hayase
J Nanopart Res, 2020, 22:69 https://doi.org/10.1007/s11051-020-04787-w., SPRINGER, https://doi.org/10.1007/s11051, 3, 2019, Peer-reviwed, Lead (Pb) perovskites can be synthetically modified to form colloidal nanocrystals which exhibit remarkable optoelectronic properties in the various fields such as light-emitting devices, flexible electronics, and photodetectors. However, because of the toxicity issue of Pb, nanocrystals of Pb free such as tin (Sn)-based perovskites have got attention. In the present work, we have selected the Sn-based perovskite, Cs2SnI6, owing to the high air and thermal stability. Quantum dots of Cs2SnI6 were prepared by using two methods, namely the hot-injection method and the ultrasonic irradiation method. The difference between Cs2SnI6 particles generated by these two methods was discussed. The particles synthesized by using the hot-injection method were less than 10 nm in size and were aggregated structure due to particle tight-binding energy. On the other hand, the particles by using the ultrasonic irradiation method gave a mono-dispersed solution. The particle size was from several ten nanometers to several hundred nanometers.
Scientific journal, English

Hybrid-Halide Perovskite Thin Film Growth for Thermoelectric Applications,
SHRIKANT SAINI; AJAY KUMAR BARANWAL; TOMOHIDE YABUKI; SHUZI HAYASE; KOJI MIYAZAKI
Journal of ELECTRONIC MATERIALS https://doi.org/10.1007/s11664-020-07958-6., https://doi.org/10.1007/s11664, https://doi.org/10.1007/s11664, 2019, Peer-reviwed
Scientific journal, English

Theoretical analysis of band alignment at back junction in Sn-Ge perovskite solar cells with inverted p-i-n structure
Takashi Minemoto; Yu Kawano; Takahito Nishimura; Qing Shen; Kenji Yoshino; Satoshi Iikubo; Shuzi Hayase
SOLMAT, 10.1016/j.solmat.2019.110208., 10.1016/j.solmat.2019.110208., 2019, Peer-reviwed
Scientific journal, English

Delocalized Molecule Surface Electronic Modification for Enhanced Performance and High Environmental Stability of CsPbI2Br Perovskite Solar Cells
Zhen Wang; Ajay K. Baranwal; Muhammad Akmal kamarudin; Putao Zhang; Gaurav Kapil; Tingli Ma; Shuzi Hayase
Nano Energy, https://doi.org/10.1016/j.nanoen.2019.104180, https://doi.org/10.1016/j.nano, 2019, Peer-reviwed, All-inorganic perovskites have drawn tremendous attentions in view of their superb thermal stability. However, unavoidable defects near the perovskite surface seriously hampers carrier transport and easily results in ion accumulation at the interface of perovskite layer and charge transport layer. Herein, delocalized thiazole and imidazole derivatives iodide salts functionalized on perovskite surface have been investigated comprehensively. These two salts post-treatment on perovskite could efficiently passivate traps arising from Cs+ or I− vacancies. Additionally, these highly п-conjugated delocalized molecules can contribute to the efficient charge transport and prevent ions accumulation at the interface. As a result, sulfur-contained aminothiazolium iodide (ATI) post-treated CsPbI2Br devices showed simultaneous enhanced current density and voltage due to its higher interaction with perovskite lattice, this led to a champion efficiency of 13.91% with superb fill factor of more than 80%, which exhibited dramatic enhancement compared with the control samples (10.12%). Furthermore, surface passivation with delocalized molecules could effectively stabilize CsPbI2Br phase at room temperature or 80 °C annealing in ambient condition (65% RH). Equally important, this surface passivation allowed competitive efficiency of 11.26% with a large-area device (1.00 cm2). This high kill tolerant approach provide a new route to fabricate inorganic perovskite devices with higher efficiency and stability.
Scientific journal, English

12. 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
Sol. RRL 2019, 1900243, 1900243, WILEY-V C H VERLAG GMBH, Sol. RRL 2019, 1900243, 190024, 2, 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

Dependence of ITO-coated flexible substrates in the performance and bending durability of perovskite solar cells
Manish Pandey; Zhen Wang; Gaurav Kapil; Ajay K. Baranwal; Daisuke Hirotani; Kengo Hamada; Shuzi Hayase
Advanced Engineering Materials, 2019, 1900288, DOI:10.1002/adem.20190028., 8, 2019, Peer-reviwed, Flexible perovskite solar cells (PSCs) is being reported on different kinds of indium tin oxide (ITO)-coated flexible substrates such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) with varying sheet resistance. High sheet resistance and low transmittance of these substrates in comparison to glass-ITO based rigid substrate are among the major issues in achieving high power conversion efficiency (PCE), especially with large active area due to considerably low fill factor (FF) values. With a small active cell area of 0.1 cm2, it is found that sheet resistance of these substrates do not play a dominant role and the short circuit current density (JSC) depends on the transmittance of these conducting flexible substrates producing average PCE of 12.1% with PEN-ITO (12 Ω/□) and 11.74% for PET-ITO (49 Ω/□). When the active cell area is increased to 1 cm2, sheet resistance seems to play a major role to maintain JSC as well as FF of the flexible PSCs giving PCE of ∼10% with PEN-ITO (12 Ω/□) in comparison to 3.4% for PET-ITO (49 Ω/□). In contrast to PCE results, bending durability test for 1000 cycles showed that the flexible substrates with highest sheet resistance can retain maximum PCE.
Scientific journal, English

Efficient, Hysteresis Free, Inverted Planar Flexible Perovskite Solar Cells via Perovskite Engineering and Stability in Cylindrical Encapsulation,
Manish Pandey; Gaurav Kapil; Kazuhiko Sakamoto; Daisuke Hirotani; Muhammad Akmal Kamrudin; Zhen Wang; Kengo Hamada; Daishiro Nomura; Hyo-Gyoung Kang; Hideaki Nagayoshi; Masaki Nakamura; Masahiro Hayashi; Takatoshi Nomura; Shuzi Hayase
Sustainable Energy & Fuels, 2019,3, 1739-1748,, Royal Society of Chemistry (RSC), DOI:10.1039/c9se00153k, 7, 1739-1748, 2019, Peer-reviwed,

Efficient flexible perovskite solar cells were obtained by compositional engineering. Cylindrically encapsulated devices retained 90% of the device efficiency after 6000 h.

Scientific journal, English

Solution-processed intermediate-band solar cells with lead sulfide quantum dots and lead halide perovskites
Hiroji Hosokawa; Ryo Tamaki; Takuya Sawada; Akinori Okonogi; Haruyuki Sato; Yuhei Ogomi; Shuzi Hayase; Yoshitaka Okada; Toshihiro Yano
Nature Communications, Vol. 10,43, (2019), Nature Communications, Vol. 1, 1, 43-43, 2019, Peer-reviwed, True, The intermediate-band solar cell (IBSC) with quantum dots and a bulk semiconductor matrix has potential for high power conversion efficiency, exceeding the Shockley-Queisser limit. However, the IBSCs reported to date have been fabricated only by dry process and their efficiencies are limited, because their photo-absorption layers have low particle density of quantum dots, defects due to lattice strain, and low bandgap energy of bulk semiconductors. Here we present solution-processed IBSCs containing photo-absorption layers where lead sulfide quantum dots are densely dispersed in methylammonium lead bromide perovskite matrices with a high bandgap energy of 2.3 eV under undistorted conditions. We confirm that the present IBSCs exhibit two-step photon absorption via intermediate-band at room temperature by inter-subband photocurrent spectroscopy.
Scientific journal, English

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, 49, 5, 2698-2703, 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

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, 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

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

Structured crystallization for efficient all-inorganic perovskite solar cells with high phase stability
Zhen Wang; Ajay K. Baranwal; Muhammad Akmal Kamarudin; Yusuke Kamata; Chi Huey Ng; Manish Pandey; Tingli Ma; Shuzi Hayase
Journal of Materials Chemistry A, 7, 35, 20390-20397, 2019, Peer-reviwed, © The Royal Society of Chemistry 2019. All-inorganic perovskites suffer from a phase transition from a cubic α-phase to a tetragonal δ-phase in the ambient atmosphere, although they have the advantage of higher thermal stability. Here, we demonstrated that yttrium-induced perovskite crystallization results in significantly improved phase stability of perovskite even under humid air conditions. Yttrium in precursors was found to impede the crystal growth of perovskite film to stabilize the α-phase of a CsPbI2Br phase and was finally incorporated into the CsPbI2Br perovskite lattice. This structural crystallization process induced by yttrium incorporation gave rise to denser compact films with small grains and host lattice rearrangement by partial substitution for Pb. As a result, a 360-fold phase stability improvement was achieved in humid air with 65% RH compared with the reference film. The favorable electronic structure for efficient electron-hole dissociation and carrier transport to the cathode led to a much-enhanced power conversion efficiency (PCE) of 13.25% after yttrium incorporation compared with only 8.46% for the reference cells in humid air. Moreover, yttrium-incorporated perovskite solar cells (PSCs) without encapsulation exhibited superior long-term stability when stored in ambient air with 65% RH, showing nearly no degradation over 14 h.
Scientific journal

Vacuum deposition of CsPbI3 layers on textured Si for Perovskite/Si tandem solar cells
Keitaro Hamada; Kyosuke Yonezawa; Kohei Yamamoto; Tetsuya Taima; Shuzi Hayase; Noboru Ooyagi; Yuzo Yamamoto; Keisuke Ohdaira
Japanese Journal of Applied Physics 58, SBBF06, 2019., IOP PUBLISHING LTD, Japanese Journal of Applied Ph, SBBF06, 2019, Peer-reviwed, We attempt the conformal deposition of CsPbI3 layers on pyramidal-shaped textured crystalline Si (c-Si) surfaces, aiming at application to Perovskite/Si tandem solar cells. CsPbI3 layers are deposited through vacuum evaporation on textured c-Si surfaces with various pyramid sizes. Conformal CsPbI3 layers are formed on the textured c-Si, which is, in principle, difficult to be realized by conventional solution processes. We also confirmed a reduction in the optical reflectance ofCsPbI(3)/Si structures by similar to 10% (absolute) by using textured c-Si compared to the case of flat Si. A co-evaporation method can prevent the aggregation of Csl particles, which are seen when the films are formed by sequential evaporation. These results indicate the feasibility of Perovskite/c-Si tandem cells with textured c-Si, leading to low optical reflectivity and a high photocurrent. (C) 2019 The Japan Society of Applied Physics
Scientific journal, English

Role of GeI2 and SnF2 Additives for SnGe Perovskite Solar Cells
Ng, C.H; Nishimura K; Ito N; Hamada, K; Hirotani, D; Yang, F; Wang Z; likubo, S; Shen, Q; Yoshino K; Minemoto, T; Hayase, S
Nano Energy, Volume 58, April 2019, Pages 130-137,, Elsevier BV, https://doi.org/10.1016/j.nano, 130-137, 2019, Peer-reviwed
Scientific journal, English

Preparation of Perovskite Films under Liquid Nitrogen Atmosphere for High Efficiency Perovskite Solar Cells,
Zhang, P; Yang, F; Kapil, G; Ng, C. H; Ma, T; Hayase, S
ACS Sustainable Chem. Eng., 7, 3956-3961, 2019, AMER CHEMICAL SOC, ACS Sustainable Chem. Eng., 7,, 4, 3959-3961, 2019, Peer-reviwed, High-quality perovskite film with high coverage and tight grain arrangement is a key factor for obtaining high performance and stable perovskite devices. Herein, high-quality perovskite films were successfully prepared by a liquid nitrogen assisted method (LN method). Here, the vaporization of liquid nitrogen reduces the ambient temperature and absorbs thermal energy from the substrate surface to increase the nucleation speed of perovskite. The scanning electron microscopy results showed that CH3NH3PbI3 perovskite films prepared by the liquid nitrogen assisted method were dense and pinhole-free. The devices prepared by the LN method result in a high performance with the power conversion efficiency (PCE) up to 16.53%, and the performance could maintain more than 89% of the primary PCE after 30 days storage in a desiccator at room temperature.
Scientific journal, English

Melamine Hydroiodide Functionalized MAPbI3 Perovskite with Enhanced Photovoltaic Performance and Stability in Ambient Atmosphere
Yang, F; Kamarudin, A. M; Hirotani, D; Zhang, P; Kapil, G; Ng, C. H; Ma, T; Hayase, S
Solar RRL, 3, 1800275, Jan. 2019, Peer-reviwed
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
The Journal of Physical Chemistry C, American Chemical Society ({ACS}), 122, 48, 27284-27291, 06 Dec. 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
Taro Toyoda; Qing Shen; Motoki Hironaka; Keita Kamiyama; Hisayoshi Kobayashi; Yasushi Hirose; Shuzi Hayase
The Journal of Physical Chemistry C, American Chemical Society ({ACS}), Dec. 2018, Peer-reviwed

Interfacial Sulfur Functionalization Anchoring SnO2 and CH3NH3PbI3 for Enhanced Stability and Trap Passivation in Perovskite Solar Cells
Zhen Wang; Muhammad Akmal Kamarudin; Ng Chi Huey; Fu Yang; Manish Pandey; Gaurav Kapil; Tingli Ma; Shuzi Hayase
ChemSusChem, 11, 22, 3941-3948, 23 Nov. 2018, Peer-reviwed, True, © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Trap states at the interface or in bulk perovskite materials critically influence perovskite solar cells performance and long-term stability. Here, a strategy for efficiently passivating charge traps and mitigating interfacial recombination by SnO2 surface sulfur functionalization is reported, which utilizes xanthate decomposition on the SnO2 surface at low temperature. The results show that functionalized sulfur atoms can coordinate with under-coordinated Pb2+ ions near the interface. After device fabrication under more than 60 % humidity in ambient air, the efficiency of methylammonium lead iodide (MAPbI3) perovskite solar cells based on sulfur-functionalized SnO2 increased from 16.56 % to 18.41 % with suppressed hysteresis, which resulted from the accelerated interfacial charge transport kinetics and decreased traps in bulk perovskite by interfacial sulfur functionalization. Additionally, thermally stimulated current studies show the decreased trap density in the shallow trap area after interfacial sulfur functionalization. The interfacial sulfur functionalized solar cells without sealing also exhibited considerable retardation of solar cell degradation with only 10 % degradation after 70 days air storage. This work demonstrates a facile sulfur functionalization strategy by using xanthate decomposition on SnO2 surfaces to obtain highly efficient perovskite solar cells.
Scientific journal, English

High Electrical Conductivity 2D MXene Serves as Additive of Perovskite for Efficient Solar Cells.
Zhanglin Guo; Liguo Gao; Zhenhua Xu; Siowhwa Teo; Chu Zhang; Yusuke Kamata; Shuzi Hayase; Tingli Ma
Small (Weinheim an der Bergstrasse, Germany), 14, 47, e1802738, Nov. 2018, True, MXenes, a newly intriguing family of 2D materials, have recently attracted considerable attention owing to their excellent properties such as high electrical conductivity and mobility, tunable structure, and termination groups. Here, the Ti3 C2 Tx MXene is incorporated into the perovskite absorber layer for the first time, which aims for efficiency enhancement. Results show that the termination groups of Ti3 C2 Tx can retard the crystallization rate, thereby increasing the crystal size of CH3 NH3 PbI3 . It is found that the high electrical conductivity and mobility of MXene can accelerate the charge transfer. After optimizing the key parameters, 12% enhancement in device performance is achieved by 0.03 wt% amount of MXene additive. This work unlocks opportunities for the use of MXene as potential materials in perovskite solar cell applications.
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

Synthesis and Optoelectrical Characterization of Novel Squaraine Dyes Derived from Benzothiophene and Benzofuran.
G Hanumantha Rao; Manish Pandey; Kamatham Narayanaswamy; Ravulakollu Srinivasa Rao; Shyam S Pandey; Shuzi Hayase; Surya Prakash Singh
ACS omega, 3, 10, 13919-13927, 31 Oct. 2018, True, Synthesis and photophysical characterizations of two novel small molecules SQ-BEN-THI and SQ-BEN-FUR with D-A-D molecular structure consisting of squaraine as central unit and benzothiophene and benzofuran as end groups are being reported. Apart from very sharp and intense light absorption by these molecular sensitizers in near-infrared (NIR) wavelength region, their possibility as small molecular organic semiconductor was also explored after fabricating organic field-effect transistors (OFETs). Results obtained from photophysical, electrochemical, and quantum chemical studies were combined to elucidate the structural and optoelectronic properties. Electrical characterization pertaining to the charge-transport properties carried after OFET fabrication exhibited field-effect mobilities of 4.0 × 10-5 and 5.4 × 10-5 cm2/(V s) for SQ-BEN-THI and SQ-BEN-FUR, respectively. After thermal annealing at 130 °C, the field-effect mobility was found to increase for both squaraine dyes. Relatively facile carrier transport in SQ-BEN-FUR compared to that of SQ-BEN-THI could be attributed to relatively higher backbone planarity as indicated from optimized molecular structure obtained after density functional theory calculations. This work may guide for further molecular design and synthesis of novel squaraine dyes for high-performance OFET applications.
Scientific journal, English

Synthesis and Photophysical Characterization of Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells Utilizing Cobalt Electrolytes
Anusha Pradhan; Maryala Sai Kiran; Gaurav Kapil; Shuzi Hayase; Shyam S. Pandey
ACS Applied Energy Materials, American Chemical Society, 1, 9, 4545-4553, 24 Sep. 2018, Development of novel near-infrared (near-IR) dyes compatible with cobalt complex based redox shuttles for their utilization as sensitizer is inevitable for the fabrication of high-efficiency dye-sensitized solar cells (DSSCs). A series of newly designed unsymmetrical squaraine dyes as a model of near-IR sensitizer were synthesized and characterized for their application as far-red sensitizers of DSSCs utilizing Co(bpy)2+/3+ redox electrolyte. It was shown that logical molecular design led to not only energetic tunability of the sensitizers but also the possibility of good far-red photon harvesting up to 750 nm. One of the newly designed sensitizers, SQ-110, bearing two long alkyl substituents in combination with an electron donating methoxy group directly linked to the aromatic ring was par excellent in terms of its photoconversion efficiency among the dyes utilized in this work. DSSC fabricated using SQ-110 as sensitizer and Co(bpy)2+/3+ redox electrolyte furnished a photoconversion efficiency of 1.98% along with good photon harvesting mainly in the far-red wavelength region. It was further demonstrated that dye molecular structure plays a rather more prominent role than their energetics in controlling the overall device performance of the DSSCs.
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, German Chemical Society, 57, 39, 12745-12749, 24 Sep. 2018, Peer-reviwed, True, © 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

Performance Enhancement of Mesoporous TiO2-Based Perovskite Solar Cells by SbI3 Interfacial Modification Layer
Putao Zhang; Fu Yang; Muhammad Akmal Kamarudin; Chi Huey Ng; Gaurav Kapil; Tingli Ma; Shuzi Hayase
ACS Applied Materials & Interfaces, American Chemical Society ({ACS}), 10, 35, 29630-29637, 05 Sep. 2018, Peer-reviwed, True, TiO2 is commonly used as an electron-transporting material in perovskite photovoltaic devices due to its advantages, including suitable band gap, good photoelectrochemical stability, and simple preparation process. However, there are many oxygen vacancies or defects on the surface of TiO2 and thus this affects the stability of TiO2-based perovskite solar cells under UV light. In this work, a thin (monolayer) SbI3 modification layer is introduced on the mesoporous TiO2 surface and the effect at the interface between of TiO2 and perovskite is monitored by using a quartz crystal microbalance system. We demonstrate that the SbI3-modified TiO2 electrodes exhibit superior electronic properties by reducing electronic trap states, enabling faster electron transport. This approach results in higher performances compared with electrodes without the SbI3 passivation layer. CH3NH3PbI3 perovskite solar cells with a maximum power conversion efficiency of 17.33% in air, accompanied by a reduction in hysteresis and enhancement of the device stability, are reported.
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 applied materials & interfaces, 10, 31, 26142-26152, 08 Aug. 2018, 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

Magnesium-Doped MAPbI3 Perovskite Layers for Enhanced Photovoltaic Performance in Humid Air Atmosphere
Fu Yang; Muhammad Akmal Kamarudin; Gaurav Kapil; Daisuke Hirotani; Putao Zhang; Chi Huey Ng; Tingli Ma; Shuzi Hayase
ACS Applied Materials & Interfaces, American Chemical Society ({ACS}), 10, 29, 24543-24548, 25 Jul. 2018, Peer-reviwed, True, Despite the high efficiency of MAPbI3 perovskite solar cells, the long term stability and degradation in humid atmosphere are issues that still needed to be addressed. In this work, magnesium iodide (MgI2) was first successfully used as a dopant into MAPbI3 perovskite prepared in humid air atmosphere. Mg doping decreased the valence band level, which was determined from photoelectron yield spectroscopy. Compared to the pristine MAPbI3 perovskite film, the 1.0% Mg-doped perovskite film showed increased crystal grain size and formation of pinhole-free perovskite film. Performance of the solar cell was increased from 14.2% of the doping-free solar cell to 17.8% of 1.0% Mg-doped device. Moreover, 90% of the original power conversion efficiency was still retained after storage in 30-40% relative humidity for 600 h.
Scientific journal, English

Enhanced Crystallization by Methanol Additive in Antisolvent for Achieving High-Quality MAPbI3 Perovskite Films in Humid Atmosphere
Fu Yang; Muhammad Akmal Kamarudin; Putao Zhang; Gaurav Kapil; Tingli Ma; Shuzi Hayase
ChemSusChem, Wiley, 11, 14, 2348-2357, 20 Jul. 2018, Peer-reviwed, True, © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Perovskite solar cells have attracted considerable attention owing to their easy and low-cost solution manufacturing process with high power conversion efficiency. However, the fabrication process is usually performed inside a glovebox to avoid moisture, as organometallic halide perovskites are easily dissolved in water. In this study, we propose a one-step fabrication of high-quality MAPbI3 perovskite films in around 50 % relative humidity (RH) humid ambient air by using diethyl ether as an antisolvent and methanol as an additive into this antisolvent. Because of the presence of methanol, the water molecules can be efficiently removed from the gaps of the perovskite precursors and the perovskite film formation can be slightly controlled, leading to pinhole-free and low roughness films. Concurrently, methanol can be used to tune the DMSO ratio in the intermediate perovskite phase to regulate perovskite formation. Planar solar cells fabricated by using this method exhibited the best efficiency of 16.4 % with a reduced current density–voltage hysteresis. This efficiency value is approximately 160 % higher than the devices fabrication by using only diethyl ether treatment. From the impedance measurement, it is also found that the recombination reaction is suppressed when the device is prepared with methanol additive in the antisolvent. This method presents a new path for controlling the growth and morphology of perovskite films in humid climates and laboratories with uncontrolled environments.
Scientific journal, English

Minute quantities of hexagonal nanoplates PtFe alloy with facile operating conditions enhanced electrocatalytic activity and durability for oxygen reduction reaction
Nannan Wang; Yanqiang Li; Zhanglin Guo; Huan Li; Shuzi Hayase; Tingli Ma
Journal of Alloys and Compounds, Elsevier Ltd, 752, 23-31, 05 Jul. 2018, Peer-reviwed, Pt-based alloys have been explored as the most promising cathode catalyst for fuel cells due to their excellent electrocatalytic activity in oxygen reduction reaction (ORR). However, the long-term performance of Pt-based alloys is compromised owing to the de-alloying behavior under the corrosive circumstance. More importantly, the complicated synthesized methods have hindered their further practical application. In this report, a facile and effective operating conditions-assisted method has been developed to synthesize the stable hexagonal nanoplates PtFe alloy with a high electrocatalytic activity. In the three prepared PtM (M: Fe, Co, Ni) alloy samples, the PtFe alloy exhibits a superior catalytic activity, which improves by about 100 and 178 mV for half-wave potential in alkaline and acidic medium with the same Pt-loading amount, respectively. In addition, the PtFe alloy catalyst exhibits an electrochemical stability, compared to the conventional carbon-supported Pt catalysts. In view of the advantages of the facile operating preparation and the excellent electrocatalytic performance, we believe that the hexagonal nanoplates PtFe alloy holds great application as a promising electrocatalyst in polymer electrolyte membrane fuel cell (PEMFC).
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, ACS, 18, 6, 3600-3607, 13 Jun. 2018, Peer-reviwed, True, © 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

Anomalous Dielectric Behavior of a Pb/Sn Perovskite: Effect of Trapped Charges on Complex Photoconductivity
Kento Yamada; Ryosuke Nishikubo; Hikaru Oga; Yuhei Ogomi; Shuzi Hayase; Shohei Kanno; Yutaka Imamura; Masahiko Hada; Akinori Saeki
ACS Photonics, American Chemical Society ({ACS}), 5, 8, 3189-3197, Jun. 2018, Peer-reviwed
Scientific journal, English

Dependence of Acetate-Based Antisolvents for High Humidity Fabrication of CH3NH3PbI3 Perovskite Devices in Ambient Atmosphere
Fu Yang; Gaurav Kapil; Putao Zhang; Zhaosheng Hu; Muhammad Akmal Kamarudin; Tingli Ma; Shuzi Hayase
ACS Applied Materials & Interfaces, American Chemical Society ({ACS}), 10, 19, 16482-16489, 16 May 2018, Peer-reviwed, True, High-efficiency perovskite solar cells (PSCs) need to be fabricated in the nitrogen-filled glovebox by the atmosphere-controlled crystallization process. However, the use of the glovebox process is of great concern for mass level production of PSCs. In this work, notable efficient CH3NH3PbI3 solar cells can be obtained in high humidity ambient atmosphere (60-70% relative humidity) by using acetate as the antisolvent, in which dependence of methyl, ethyl, propyl, and butyl acetate on the crystal growth mechanism is discussed. It is explored that acetate screens the sensitive perovskite intermediate phases from water molecules during perovskite film formation and annealing. It is revealed that relatively high vapor pressure and high water solubility of methyl acetate (MA) leads to the formation of highly dense and pinhole free perovskite films guiding to the best power conversion efficiency (PCE) of 16.3% with a reduced hysteresis. The devices prepared using MA showed remarkable shelf life stability of more than 80% for 360 h in ambient air condition, when compared to the devices fabricated using other antisolvents with low vapor pressure and low water solubility. Moreover, the PCE was still kept at 15.6% even though 2 vol % deionized water was added in the MA for preparing the perovskite layer.
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
Journal of Physical Chemistry Letters, 9, 7, 1682-1688, Apr. 2018, Peer-reviwed, True, © 2018 American Chemical Society. Lead-based perovskite solar cells have gained ground in recent years, showing efficiency as high as 20%, which is on par with that of silicon solar cells. However, the toxicity of lead makes it a nonideal candidate for use in solar cells. Alternatively, tin-based perovskites have been proposed because of their nontoxic nature and abundance. Unfortunately, these solar cells suffer from low efficiency and stability. Here, we propose a new type of perovskite material based on mixed tin and germanium. The material showed a band gap around 1.4-1.5 eV as measured from photoacoustic spectroscopy, which is ideal from the perspective of solar cells. In a solar cell device with inverted planar structure, pure tin perovskite solar cell showed a moderate efficiency of 3.31%. With 5% doping of germanium into the perovskite, the efficiency improved up to 4.48% (6.90% after 72 h) when measured in air without encapsulation.
Scientific journal, English

Rapid Formation and Macroscopic Self-Assembly of Liquid-Crystalline, High-Mobility, Semiconducting Thienothiophene
Manish Pandey; Ashwathanarayana Gowda; Shuichi Nagamatsu; Sandeep Kumar; Wataru Takashima; Shuzi Hayase; Shyam S. Pandey
Advanced Materials Interfaces, Wiley-VCH Verlag, 5, 6, 1700875, 23 Mar. 2018, Peer-reviwed, A synergistic approach to enhance charge-carrier transport in organic semiconductors along with facile solution processing and high performance is crucial for the advancement of organic electronics. The floating film transfer method (FTM) is used as a facile and cost-effective method for the fabrication of large-scale, uniform, highly oriented poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (pBTTT C-14) films under ambient conditions. Utilization of such oriented films as the active semiconducting layer in organic field-effect transistors (OFETs) results in highly anisotropic charge-carrier transport. Highly oriented, FTM-processed pBTTT C-14 thin films are characterized by polarized electronic absorption and Raman spectroscopy, atomic force microscopy, out-of-plane X-ray diffraction, and grazing incident X-ray diffraction (GIXD) measurements. The GIXD data indicate an edge-on orientation, which is highly desirable for planar devices such as OFETs. OFETs built using the oriented films show a mobility anisotropy of 10 and the highest mobility is 1.24 cm2 V−1 s−1 along the backbone orientation, which is among the highest value reported for this class of materials using a similar device configuration.
Scientific journal, English

Anisotropic charge transport in highly oriented films of semiconducting polymer prepared by ribbon-shaped floating film
Atul S. M. Tripathi; Manish Pandey; Shifumi Sadakata; Shuichi Nagamatsu; Wataru Takashima; Shuzi Hayase; Shyam S. Pandey
Applied Physics Letters, American Institute of Physics Inc., 112, 12, 123301, 19 Mar. 2018, Peer-reviwed, Fabrication of large area and uniform thin films with preferred edge-on orientation is highly demanded for flexible organic electronic devices. In this work, utilization of a newly designed slider in the floating film transfer method to assist unidirectional film spreading led to the fabrication of uniform and macroscopically edge-on oriented ribbon-shaped floating films (15 cm × 2 cm) having very large optical anisotropy (>
20). The results pertaining to the in-plane grazing angle incident X-ray diffraction (GIXD) and φ-scan measurements revealed the well-stacked polymer backbone conformation with edge-on orientation without any inter-mixing of face-on oriented counterparts. Optical anisotropy dependent charge transport in organic field effect transistors using anisotropic poly(3,3‴-didodecyl-quaterthiophene) films has also been shown, and the results are supported by polarized electronic absorption and GIXD measurements.
Scientific journal, English

Piper Ornatum and Piper Betle as Organic Dyes for TiO2 and SnO2 Dye Sensitized Solar Cells
Azwar Hayat; A. Erwin E. Putra; Novriany Amaliyah; Shuzi Hayase; Shyam. S. Pandey
Journal of Physics: Conference Series, Institute of Physics Publishing, 979, 1, 13 Mar. 2018, Peer-reviwed, Dye sensitized solar cell (DSSC) mimics the principle of natural photosynthesis are now currently investigated due to low manufacturing cost as compared to silicon based solar cells. In this report, we utilized Piper ornatum (PO) and Piper betle (PB) as sensitizer to fabricate low cost DSSCs. We compared the photovoltaic performance of both sensitizers with Titanium dioxide (TiO2) and Tin dioxide (SnO2) semiconductors. The results show that PO and PB dyes have higher Short circuit current (Jsc) when applied in SnO2 compared to standard TiO2 photo-anode film even though the Open circuit voltage (Voc) was hampered on SnO2 device. In conclusion, from the result, higher electron injections can be achieved by choosing appropriate semiconductors with band gap that match with dyes energy level as one of strategy for further low cost solar cell.
International conference proceedings, 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

Effects of Temperature on Electrochemical Properties of Bismuth Oxide/Manganese Oxide Pseudocapacitor
Chi Huey Ng; Hong Ngee Lim; Shuzi Hayase; Zulkarnain Zainal; Suhaidi Shafie; Nay Ming Huang
Industrial and Engineering Chemistry Research, American Chemical Society, 57, 6, 2146-2154, 14 Feb. 2018, Peer-reviwed, In this study, a temperature investigation is conducted on a bismuth oxide/manganese oxide (Bi2O3/MnO2) supercapacitor to determine how temperature affects the performances of the supercapacitor. Energy and power densities of 9.5 Wh kg-1 and 102.6 W kg-1 are obtained at 60 °C, respectively, which are approximately twice the values for supercapacitors at 0 °C and 1.37-fold higher than those at 30 °C. Additionally, the supercapacitors achieve energy densities of 4.9 and 6.9 Wh kg-1, and power densities of 53.8 and 74.8 W kg-1 at 0 and 30 °C, respectively. Interestingly, the hybrid Bi2O3/MnO2 active materials exhibit superior stability and reversibility, retaining 95% of the original capacitance at 30 °C and >
75% at the high temperature of 60 °C. Although the cooler supercapacitor exhibits a slightly higher resistive performance, its excellent capacitance retention upon continuous charging/discharging measurement at 0 °C shows its potential for use as an all-weather compatible supercapacitor in the automotive sector.
Scientific journal, English

D–π–A Dyes that Contain New Hydantoin Anchoring Groups for Dye-Sensitized Solar Cells
Hisashi Masui; Masato M. Maitani; Shinichiro Fuse; Ayaka Yamamura; Yuhei Ogomi; Shuzi Hayase; Tatsuo Kaiho; Hiroshi Tanaka; Yuji Wada; Takashi Takahashi
Asian Journal of Organic Chemistry, Wiley-VCH Verlag, 7, 2, 458-464, 01 Feb. 2018, Peer-reviwed, The development of new anchoring groups is important to facilitate effective co-sensitization in dye-sensitized solar cells (DSSCs). Herein, stable organic D–π–A dyes that contain new heterocyclic hydantoin-based anchoring groups have been designed, synthesized, and used in DSSCs. These dye sensitizers were evaluated in terms of their absorption spectra, electrochemical properties, and performance in DSSC devices. Although only one-third of the amount of hydantoin-containing dyes adsorbed onto TiO2 relative to their cyanoacrylic-acid-containing analogues, they exhibited effective photoexcited electron-transfer properties. External quantum efficiencies of over 80 % was observed, which were comparable to those of the cyanoacrylic-acid-containing dyes. In addition, the new hydantoin-containing dyes exhibited significant robustness, which could allow improved stability of their corresponding photovoltaic devices under harsh conditions, such as high temperature and humidity.
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, True, 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

Synthesis of fe, co incorporated in p-doped porous carbon using a metal-organic framework (MOF) precursor as stable catalysts for oxygen reduction reaction
Nannan Wang; Yanqiang Li; Zhanglin Guo; Huan Li; Shuzi Hayase; Tingli Ma
Journal of the Electrochemical Society, Electrochemical Society Inc., 165, 12, G3080-G3086, 2018, Heteroatom-doped porous carbon materials have recently attracted significant attention due to their superior catalytic activities for an oxygen reduction reaction (ORR). Transition metals co-doped with heteroatom are considered to have positive effects on improving ORR catalytic activity and stability. We report a series of novel Fe, Co incorporated in P-doped carbon materials, which give high ORR performance by an in-situ carbonization method. The ratios of the two metals and the carbonization temperatures are the key factors for the electrocatalytic activity. Due to the synergistic effect of the two transition metals, the Fe, Co incorporated in P-doped porous carbon sample, carbonized at 900ºC, shows the highest catalytic activity and stability. Electrochemical measurements show that Fe, Co incorporated in P-doped porous carbon materials are promising electrocatalysts to substitute Pt-based catalysts for fuel cells application.
Scientific journal, English

Study To Observe the Effect of PbI2 Passivation on Carbon Electrode for Perovskite Solar Cells by Quartz Crystal Microbalance System
Putao Zhang; Gaurav Kapil; Kengo Hamada; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
ACS Sustainable Chemistry & Engineering, 6, 10221-10228, 2018., ACS, ACS Sustainable Chemistry & En, 8, 10221-10228, 2018, Peer-reviwed, A perovskite solar cell (PSC) utilizing a carbon electrode is a potential candidate for industrially viable, low-cost and highly stable photovoltaics. Therefore, it is important to understand the interface between perovskite layer and carbon electrode to achieve the improved performance of PSCs. We demonstrate an improvised two-step perovskite MAPbI(3) (methylammonium lead iodide) deposition method, involving a pretreatment of PbI2 on the porous structure of TiO2/ZrO2/Carbon, which led to the difference in performance. A PbI2 passivation layer at the interface between carbon electrode and perovskite resulted in the improved power conversion efficiency (PCE) of 7.30% from 2.21% compared to a one-step perovskite deposition with no pretreatment of PbI2. This study further explores that an enhanced PCE of 6.55% can be achieved with one-step fabrication while keeping the same perovskite. A fascinating methodology, utilizing quartz crystal microbalance (QCM), which involves the adsorption of PbI2 on the carbon surface, was employed to unravel this difference. QCM monitored adsorbed mass in real time and revealed that the mass of PbI2 on carbon layer increased with the increase in concentration of PbI2 in dimethylformamide (DMF). It was noticed that PbI2 was still adsorbed on the carbon surface even after rinsing with DMF, suggesting strong bonding of PbI2 with carbon. PbI2 presence after rinsing was also verified by X-ray photoelectron spectroscopy (XPS), which indicates that part of the Pb I reacts with the -OH on the carbon surface forming C-O-Pb linkages. Our study demonstrates that a carbon electrode passivated with PbI2 could reduce carrier recombination and improve performance of PSCs.
Scientific journal, English

Enhancement of Charge Ttransport in Quantum Dots Solar Cells by N-butylamine-Assisted Sulfur-crosslinking of PbS Quantum Dots
Zhen, W; Zhaosheng H; Muhammad A. K; Gaurav K; Atul T; Shen Q; Yoshino, K; Minemoto, T; Sham S. P; Hayase, S
Solar Energy, PERGAMON-ELSEVIER SCIENCE LTD, 174, 399-408, 2018, Peer-reviwed, 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

Solution‐Processed Air‐Stable Copper Bismuth Iodide CuBiI3 for Photovoltaics
Zhaoshung, H; Wang, Z; Kapil, G; Tingli Ma, T; Iikubo, S; Minemoto, T; Yopshino, K; Toyoda, T; Shen, Q; Hayase, S
ChemSusChem, Wiley, 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
Dinga, C; Zhang, Y; Liu, F; Kitabatake,Y; Hayase, S; Toyoda, T; Yoshino, K; Minemoto, T; Katayama, K; Shen, Q
Nano Energy, Elsevier, 53, 17-26, 2018, Peer-reviwed
Scientific journal, English

Tunable Open Circuit Voltage by Engineering Inorganic Cesium Lead Bromide/Iodide Perovskite Solar Cells,
Ng, C.H; Ripolles, T.S; Hamada, K; Teo, S.H; Lim, H.N; Bisquert, J; Hayase, S
Scientific reports, Nature, 8, 1, 2482-2482, 2018, Peer-reviwed, True, Perovskite solar cells based on series of inorganic cesium lead bromide and iodide mixture, CsPbBr3-xI x , where x varies between 0, 0.1, 0.2, and 0.3 molar ratio were synthesized by two step-sequential deposition at ambient condition to design the variations of wide band gap light absorbers. A device with high overall photoconversion efficiency of 3.98 % was obtained when small amount of iodide (CsPbBr2.9I0.1) was used as the perovskite and spiro-OMeTAD as the hole transport material (HTM). We investigated the origin of variation in open circuit voltage, Voc which was shown to be mainly dependent on two factors, which are the band gap of the perovskite and the work function of the HTM. An increment in Voc was observed for the device with larger perovskite band gap, while keeping the electron and hole extraction contacts the same. Besides, the usage of bilayer P3HT/MoO3 with deeper HOMO level as HTM instead of spiro-OMeTAD, thus increased the Voc from 1.16 V to 1.3 V for CsPbBr3 solar cell, although the photocurrent is lowered due to charge extraction issues. The stability studies confirmed that the addition of small amount of iodide into the CsPbBr3 is necessarily to stabilize the cell performance over time.
Scientific journal, English

Lead Selenide Colloidal Quantum Dot Solar Cells Achieving High Open-Circuit Voltage with One-Step Deposition Strategy
Zhang, Y; Wu, G; Ding, C; Liu, F; Yao, Y; Zhou, Y; Wu, C; Nakazawa, N; Huang, Q; Toyoda, T; Wang, R; Hayase, S; Zou, Z; Shen, Q
Journal of Physical Chemistry Letters, ACS, 9, 13, 3598-3603, 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

Understanding charge transfer and recombination by interface engineering for improving the efficiency of PbS quantum dot solar cells
Ding, C; Zhang, Y; Liu, F; Kitabatake, Y; Hayase, S; Toyoda, T; Wang, R; Yoshino, K; Minemoto, T; Shen, Q
Nanoscale Horizons, 3, p.417-429, 2018., RSC, 3, 4, 417-429, 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

Interface passivation effects on the photovoltaic performance of quantum dot sensitized inverse opal TiO2 solar cells
Hori, K; Zhang, Y; Tusamalee, P; Nakazawa, N; Yoshihara, Y; Wang, R; Toyoda, T; Hayase, S; Shen, Q
Nanomaterials, 8, p.460, 2018, MDPI, 8, 7, 460, 2018, Peer-reviwed, True, Quantum dot (QD)-sensitized solar cells (QDSSCs) are expected to achieve higher energy conversion efficiency than traditional single-junction silicon solar cells due to the unique properties of QDs. An inverse opal (IO)-TiO₂ (IO-TiO₂) electrode is useful for QDSSCs because of its three-dimensional (3D) periodic nanostructures and better electrolyte penetration compared to the normal nanoparticles (NPs)-TiO₂ (NPs-TiO₂) electrode. We find that the open-circuit voltages Voc of the QDSSCs with IO-TiO₂ electrodes are higher than those of QDSSCs with NPs-TiO₂ electrodes. One important strategy for enhancing photovoltaic conversion efficiency of QDSSCs with IO-TiO₂ electrodes is surface passivation of photoanodes using wide-bandgap semiconducting materials. In this study, we have proposed surface passivation on IO-TiO₂ with ZnS coating before QD deposition. The efficiency of QDSSCs with IO-TiO₂ electrodes is largely improved (from 0.74% to 1.33%) because of the enhancements of Voc (from 0.65 V to 0.74 V) and fill factor (FF) (from 0.37 to 0.63). This result indicates that ZnS passivation can reduce the interfacial recombination at the IO-TiO₂/QDs and IO-TiO₂/electrolyte interfaces, for which two possible explanations can be considered. One is the decrease of recombination at IO-TiO₂/electrolyte interfaces, and the other one is the reduction of the back-electron injection from the TiO₂ electrode to QDs. All of the above results are effective for improving the photovoltaic properties of QDSSCs.
Scientific journal, English

Photovoltaic performances of mono- and mixed-halide structures for perovskite solar cell
Ng, C.H; Lim, H.N; Hayase, S; Zainal, Z; Huang, N.M
Renewable and Sustainable Energy Reviews, 90, p.248-274, 2018, Elsevier, 90, 248-274, 2018, Peer-reviwed
Scientific journal, English

Ultrafast selective extraction of hot holes from cesium lead iodide perovskite films
Shen, Q; Ripolles, T.S; Even, J; Zhang, Y; Ding, C; Liu, F; Izuishi, T; Nakazawa, N; Toyoda, T; Ogomi, Y; Hayase, S
Journal of Energy Chemistry, Elsevier, 27, 1170-1174, 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
Toyoda, T; Shen, Q; Hori, K; Nakazawa, N; Kamiyama, K; Hayase, S
Journal of Physical Chemistry C, 122, p.13590-13599, 2018., ACS, 122, 13590-13599, 2018, Peer-reviwed
Scientific journal, English

First-principles study of electronic and optical properties of lead-free double perovskites Cs2NaBX6 (B = Sb, Bi; X = Cl, Br, I)
Zhao, S; Yamamoto, K; Iikubo, S; Hayase, S., Ma
Journal of Physics and Chemistry of Solids, Elsevier, 117, 117-121, 2018, Peer-reviwed, Organolead halide perovsklte is regarded as the most promising light-harvesting material for next-generation solar cells; however, the intrinsic instability and toxicity of lead are still of great concern. Bismuth is eco-friendly and has electronic properties similar to those of lead, which has gradually attracted interest for opto-electronic applications. However, the valence state of bismuth is different from that of lead, eliminating the possibility of replacing lead by bismuth in organolead halide perovskites. To address this matter, one feasible strategy is to construct B-site double perovskites by the combination of Bi3+ and B+ in 1:1 ratio. In this work, lead-free halide double perovsldtes of the form Cs2NaBX6 (B = Sb, Bi; X = Cl, Br, I) were investigated by first-principles calculations. The electronic properties, optical absorption coefficients, and thermodynamic stability of these compounds were investigated to ascertain their potential application in solar energy conversion. The results provide theoretical support for the exploration of lead-free perovskite materials in potential optoelectronic applications.
Scientific journal, English

Implications of doping and depletion on the switching characteristics in polymer-based organic field-effect transistors
Tiwari, S; Pandey, M; Takashima, W; Nagamatsu, S; Balasubramanian, S.K; Hayase, S; Pandey, S.S; Prakash, R
Organic Electronics: physics, materials, applications, Elsevier, 56, 152-158, 2018, Peer-reviwed
Scientific journal, English

Journal of Physical Chemistry Letters
Ito, N; Kamarudin, M.A; Hirotani, D; Zhang, Y; Shen, Q; Ogomi, Y; Iikubo, S; Minemoto, T; Yoshino, K; Hayase, S
Mixed Sn-Ge Perovskite for Enhanced Perovskite Solar Cell Performance in Air, ACS, 9, 1682-1688, 2018, Peer-reviwed
Scientific journal, English

Interparticle coupling effect of silver-gold heterodimer to enhance light harvesting in ultrathin perovskite solar cell
Zhaosheng Hu; Tingli Ma; Shuzi Hayase
Journal of Photonics for Energy, SPIE, 8, 1, 15502, 01 Jan. 2018, Peer-reviwed, Thin perovskite solar cells are under intensive interest since they reduce the amount of absorber layer, especially toxic lead in methylammonium lead iodide (MAPbI3) devices and have wide application in semitransparent and tandem solar cells. However, due to the decrease of the layer thickness, thin perovskite devices with weak light-harvesting have poor performance. Moreover, the performance of plasmonic thin perovskite devices by incorporating noncoupling metal NPs cannot give comparable performance with normal devices. In this perspective, we discuss the implication of employing random silver-gold heterodimers in MAPbI3 solar cells with the aim of establishing some guidelines for the efficient ultrathin perovskite solar cells. This method induces an extraordinarily high light-harvesting for ultrathin perovskite film. And the underlying physical mechanism behind the enhanced absorption is deeply investigated by plasmon hybridization, dipolar-dipolar coupling method and FDTD simulation. We notice that perovskite embedded silver-gold heterodimer overcomes the vanished antibonding plasmon resononse in nonjunction area of gold/silver homodimer. A 150-nm perovskite film with embedded random silver-gold heterodimers with 80 nm size and 25 nm gap distance processes 28.15% absorption enhancement compared to the reference film, which is higher than the reported 10% for gold homodimers. And we also predict a realistic solution-processed, easy, and low-cost fabrication method, which provide a means to realize highly efficient ultrathin perovskite solar cell including other absorber-based photovoltaics.
Scientific journal, English

Enhanced performance of ZnO based perovskite solar cells by Nb2O5 surface passivation
Zhang, P; Yang, F; Kapil, G; Shen, Q; Toyoda, T; Yoshino, K; Minemoto, T; Pandey, S.S; Ma, T; Hayase, S
Organic Electronics: physics, materials, applications, Elsevier, 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

Structural Stability of Iodide Perovskite: A Combined Cluster Expansion Method and First-Principles Study
K. Yamamoto; S. Iikubo; J. Yamasaki; Y. Ogomi; S. Hayase
Journal of Physical Chemistry C, American Chemical Society, 121, 50, 27797-27804, 21 Dec. 2017, To aid the development of Pb-free perovskite solar cells, the stability of the iodide perovskite structure ABI3 has been investigated by first-principles calculations, Bader charge analysis, and the cluster expansion method. At the A sites, methylammonium (MA, CH3NH3 +), formamidinium (FA, CH(NH2)2 +), and Cs+ were modeled, while at the B sites, one or two elements from Pb, Sn, Ge, In, Ga, Bi, and Sr were examined. For the partially substituted system A(B,B′)I3, we found that the stability strongly depends on the identity of the A-site cation. For example, Cs(B,B′)I3 structures are stabilized by a mixture of divalent cations, such as Pb, Sn, and Ge, at the B site. Concerning the stabilization mechanisms, Coulomb energy gain seems to be the origin of the structural stability in A = Cs structures. From our results, Cs(B,B′)I3, where the B site is occupied by divalent cations, are possible candidates for high stability, lead-free solar cell materials.
Scientific journal, English

Casting Control of Floating-films into Ribbon-shape Structure by modified Dynamic FTM
A Tripathi; M Pandey; S Nagamatsu; S S Pandey; S Hayase; W Takashima
Journal of Physics: Conference Series, {IOP} Publishing, 924, 012014-012014, Nov. 2017, Peer-reviwed
Scientific journal

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, True, 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

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

Investigation of the minimum driving force for dye regeneration utilizing model squaraine dyes for dye-sensitized solar cells
Anusha Pradhan; Takuya Morimoto; Maryala Saikiran; Gaurav Kapil; Shuzi Hayase; Shyam S. Pandey
JOURNAL OF MATERIALS CHEMISTRY A, ROYAL SOC CHEMISTRY, 5, 43, 22672-22682, Nov. 2017, Peer-reviwed, Combined theoretical and experimental approaches were implemented to design model far-red sensitive unsymmetrical squaraine dyes in order to estimate the minimum energy barrier required for dye regeneration. Our logical molecular design indicated that it is possible to have a fine control on the energetics within 0.2 eV only by the judicious selection of substituents and alkyl chain length keeping the main pi-molecular framework the same. The utilization of the LSDA functional under TD-DFT calculations offered an effective and economical computational method for the reliable prediction of the energetics as well as the absorption maximum of the sensitizers. Among the designed dyes under investigation, SQ-75 exhibited the best photovoltaic performance, having a short-circuit current density of 10.92 mA cm(-2), open circuit voltage of 0.57 V and a fill factor of 0.67, leading to a photoconversion efficiency of 4.25% despite having photon harvesting mainly in the far-red region. The best photon harvesting by SQ-75, even with an energy difference of only 0.12 eV between the energy of its highest occupied molecular orbital and redox energy level I-/I-3(-) electrolyte, corroborates the possibility for dye regeneration with such a small driving force.
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, True, 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, 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

Efficient near infrared fluorescence detection of elastase enzyme using peptide-bound unsymmetrical squaraine dye
Maryala Saikiran; Daisuke Sato; Shyam S. Pandey; Shuzi Hayase; Tamaki Kato
BIOORGANIC & MEDICINAL CHEMISTRY LETTERS, PERGAMON-ELSEVIER SCIENCE LTD, 27, 17, 4024-4029, Sep. 2017, Peer-reviwed, True, Extended wavelength analyte-responsive fluorescent probes are highly desired for the imaging applications owing to their deep tissue penetration, and minimum interference from autofluorescence by biomolecules. Near infra-red (NIR) sensitive and self-quenching fluorescent probe based on the dye-peptide conjugate (SQ I PC) was designed and synthesized by facile and efficient one-pot synthetic route for the detection of Elastase activity. In the phosphate buffer solution, there was an efficient quenching of fluorescence of SQ 1 PC (86%) assisted by pronounced dye-dye interaction due to H-aggregate formation. Efficient and fast recovery of this quenched fluorescence of SQ 1 PC (> 50% in 30 s) was observed on hydrolysis of this peptide-dye conjugate by elastase enzyme. Presently designed NIR sensitive self quenching substrate offers the potential application for the detection of diseases related to proteases by efficient and fast detection of their activities. (C) 2017 Elsevier Ltd. All rights reserved.
Scientific journal, English

Current Advancements in Material Research and Techniques Focusing on Lead-free Perovskite Solar Cells
Chu Zhang; Liguo Gao; Shuzi Hayase; Tingli Ma
CHEMISTRY LETTERS, CHEMICAL SOC JAPAN, 46, 9, 1276-1284, Sep. 2017, Organic-inorganic lead halide perovskite solar cells (PSCs) recently achieved a photo-to-electricity conversion efficiency (PCE) of 22.1%. They drew much attention as promising photovoltaic devices. However, the Pb-based PSCs face great challenges for commercial and industrial applications due to the instability and the toxicity of perovskite materials. Herein, we summarize the current development of various types of Pb-free perovskites, such as the Sn-, Bi-, Ge-, Sr-, and Cu-based perovskites and their devices. In addition, we will address some remaining issues and prospects of the Pb-free PSCs.
English

In Situ Fabrication of Integrated Electrode of Perovskite Solar Cells
Liguo Gao; Shuzhang Yang; Yanqiang Li; Erling Zhao; Likun Wang; Chuanlei Fu; Shuzi Hayase; Tingli Ma
CHEMISTRY LETTERS, CHEMICAL SOC JAPAN, 46, 11, 1687-1690, Sep. 2017, An integrated electrode has been in situ fabricated on a titanium substrate by a simple thermal oxidation method. The integrated electrodes can replace glass substrates, fluorine-doped tin oxide (FTO), and TiO2 compact and mesoporous layers in conventional perovskite solar cells (PSCs) with bilayer configuration. Under AM1.5 illumination, photon-to-electricity conversion efficiency (PCE) of the fabricated PSCs is 9.92%, which is higher than that of PSCs with bilayer configuration. Interestingly, photoluminescence (PL) measurements show a lower charge recombination in the integrated electrodes than normal TiO2 electrodes fabricated layer by layer, thereby suggesting that photoinduced electrons in integrated electrodes can be more efficiently extracted. We also found that our PSCs have high conductivity and excellent stability. Therefore, the developed technique is suitable for fabricating large area PSCs.
Scientific journal, English

In Situ Fabrication of Nanoepitaxial TiO2 Protection Layer on Si Substrate: Hole Chemical Conduction Instead of Tunneling Effect
Liguo Gao; Qun Li; Hanlin Chen; Shuji Hayase; Tingli Ma
Solar RRL, Wiley-VCH Verlag, 1, 8, 01 Aug. 2017, The efficiency of the Si photoanode of photoelectrochemical (PEC) cells in solar water splitting undergoes poor charge separation and transfer process through multiple interfaces. This phenomenon occurs mainly due to a recombination induced by interfacial defects and quantum tunneling effect caused by SiO2 layer insulation. In this study, the in situ fabrication of nanoepitaxial TiO2 on Si substrates in constructing TiO2/Si heterojunction is performed by combining a self-assembly process and a hydrothermal method. The nanoepitaxial growth process is conducted because of the crystal type and lattice matching between anatase-type TiO2 and Si substrate. Studies have shown that a minimal insulator SiO2 layer is left in the heterogeneous interface, which is contacted by a chemical bond. Therefore, a nearly defect-free heterojunction without a SiO2 insulator layer is obtained. After depositing the common catalyst Ni, a large saturated current density of Ni/TiO2/Si photoanode is achieved. This excellent property is caused by fast carrier transfer through the heterogeneous interface, resulting in the efficiency of injection and separation of fast carriers. In comparison with the traditional method, (i.e., the TiO2 protection film deposited by atom layer deposition (ALD)), the Ni/TiO2/Si photoanode fabricated by nanoepitaxial growth has a significantly lower onset potential and remarkably higher current density, which is 11-fold at 1.23 V bias potential. Results confirm that the nanoepitaxy of TiO2 on Si can improve the stability of Si substrates in an alkaline solution for more than 24 h.
Scientific journal, English

Improved Reproducibility and Intercalation Control of Efficient Planar Inorganic Perovskite Solar Cells by Simple Alternate Vacuum Deposition of PbI2 and CsI
Md. Shahiduzzaman; Kyosuke Yonezawa; Kohei Yamamoto; Teresa S. Ripolles; Makoto Karakawa; Takayuki Kuwabara; Kohshin Takahashi; Shuzi Hayase; Tetsuya Taima
ACS Omega, American Chemical Society ({ACS}), 2, 8, 4464-4469, Aug. 2017, Peer-reviwed, True, Vacuum deposition is a simple and controllable approach that aims to form higher-quality perovskite films compared with those formed using solution-based deposition processes. Herein, we demonstrate a novel method to promote the intercalation control of inorganic cesium lead iodide (CsPbI3) perovskite thin films via alternate vacuum deposition. We also investigated the effect of layer-by-layer deposition of PbI2/CsI to fabricate efficient planar heterojunction CsPbI3 thin films and solar cells. This procedure is comparatively simple when compared with commonly used coevaporation techniques; further, precise intercalation control of the CsPbI3 thin films can be achieved by increasing the number of layers in the layer-by-layer deposition of PbI2/CsI. The best control and the highest reproducibility were achieved for the deposition of four double layers owing to the precise intercalation control during the deposition of the CsPbI3 thin film. A power conversion efficiency of 6.79% was obtained via alternating vacuum deposition of two double layers with a short-circuit current density (J sc) of 12.06 mA/cm2, an open-circuit voltage (V oc) of 0.79 V, and a fill factor (FF) of 0.72. Our results suggest a route for inorganic precursors to be used for efficient perovskite solar cells via alternating vacuum deposition.
Scientific journal, English

Transparent Conductive Oxide-Less Dye-Sensitized Solar Cells Consisting of Dye-Cocktail and Cobalt Based Redox Electrolyte
Md. Zaman Molla; Ajay K. Baranwal; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, AMER SCIENTIFIC PUBLISHERS, 17, 7, 4748-4754, Jul. 2017, Thin Ti-metal protected stainless steel metal mesh coated with mesoporous TiO2 as flexible photoanode has been used to fabricate back contact transparent conductive oxide-less dye-sensitized solar cells. TiO2 nanoparticle having a particle size of 15-20 nm sensitized with dye cocktail of two indoline dyes D-205 and D-131 were first utilized owing to their complementary light harvesting properties. Short-circuit photocurrent density (J(sc)) for the dye cocktail combination of D-205 and D-131 (1: 1) was found to be increased due to the increased photon harvesting in the 400-500 nm mainly associated with the contribution from D-131 dye. In addition, the electron recombination was suppressed when dye cocktail was employed as confirmed by the dark current measurement leading to higher open-circuit voltage (V-oc). The enhanced J(sc) accompanied with increased V-oc resulted in to an improved efficiency of 3.59% for this cocktail combination. To enhance the efficiency even further, we have utilized TiO2 nanoparticle having a larger particle size of 30 nm facilitating the mass transport of the bulky [Co(bpy)(3)](3+/2+) redox species. In order to enhance the photon harvesting window TiO2 nanoparticles were sensitized with porphyrin dye (YD2-o-C8) along with different dye cocktail combinations with another complementary dye (Y123). Utilization of a dye cocktail of YD2-o-C8 and Y123 (4: 1) led to improved photoconversion efficiency of 5.25% under simulated solar irradiation.
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

Interplay of Orientation and Blending: Synergistic Enhancement of Field Effect Mobility in Thiophene-Based Conjugated Polymers
Manish Pandey; Shuichi Nagamatsu; Wataru Takashima; Shyam S. Pandey; Shuzi Hayase
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 121, 21, 11184-11193, Jun. 2017, Peer-reviwed, Trade-off between mechanical flexibility due to amorphicity and highly facile charge transport emanating from molecular crystallinity demands the orientation of conjugated polymers (CPs) for their utilization as active semiconducting material for flexible organic electronics. We have already demonstrated that it is rather easy to orient nonregiocontrolled poly(3-hexylthiophenes) (NR-P3HT) as compared to their highly regioregular counterparts due to very high alkyl chain interdigitation. To provide an amicable solution, efforts have been directed to orient blends of two CPs such as NR-P3HT (amorphous and flexible) and poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) (crystalline and facile charge transport) using a solution-based procedure floating film and transfer method (FTM). FTM-processed thin films of this blend system exhibited very high field effect transistor (FET) mobility reaching up to 0.1 cm(2)/V s, which is much higher than the corresponding individual CPs. In spite of only 10% incorporation of PBTTT in blend of NR-P3HT and PBTTT, there was a synergistically enhanced optical dichroic ratio (4.6 to 7.2) and FET mobility (8-fold) as compared to pristine NR-P3HT. At the same time, there was a 5-fold enhancement of FET mobility when 20% NR-P3HT was added in PBTTT as compared to that of PBTTT. This synergistic enhancement of charge carrier transport in the blend system has been explained by formation of oriented self-assembled fibrous domains of NR-P3HT and facile interdomain transport in crystalline PBTTT.
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

Photophysical characterization and BSA interaction of the direct ring carboxy functionalized unsymmetrical NIR cyanine dyes
Maryala Saikiran; Daisuke Sato; Shyam S. Pandey; Takeshi Ohta; Shuzi Hayase; Tamaki Kato
DYES AND PIGMENTS, ELSEVIER SCI LTD, 140, 6-13, May 2017, Peer-reviwed, Novel near infrared (NIR) sensitive unsymmetrical cyanine dyes bearing direct COOH functionalized indole ring were synthesized, characterized and subjected to photophysical investigations. These unsymmetrical cyanine dyes were then subjected to investigate their interaction with bovine serum albumin (BSA) as a model protein in Phosphate buffer solutions. Apart from NIR absorption and emission with high molar extinction coefficients they exhibit a blue shift in PBS solution owing to their enhanced dye aggregation. Interaction of these dyes with BSA leads to not only enhanced emission intensity but also bathochromically shifted absorption maximum due to formation of dye-BSA conjugate. These dyes bind strongly with BSA having about an order of magnitude higher binding constant as compared to the typical cyanine dyes. Amongst the unsymmetrical cyanine dyes investigated in this work one bearing substituents like Iodo and carboxylic acid in the terminal Indole rings (UCD-3) exhibited highest association with the BSA having very high binding constant of 1.01 x 10(7) M-1. (C) 2017 Elsevier Ltd. All rights reserved.
Scientific journal, English

Layer-by-layer coating of oriented conjugated polymer films towards anisotropic electronics
Manish Pandey; Shifumi Sadakata; Shuichi Nagamatsu; Shyam S. Pandey; Shuzi Hayase; Wataru Takashima
SYNTHETIC METALS, ELSEVIER SCIENCE SA, 227, 29-36, May 2017, Peer-reviwed, Dynamic casting of floating-film and transferring method for preparing oriented multilayer films of conjugated polymers is reported. This method is based on dynamic casting of a floating-film on liquid substrate to obtain oriented thin-film followed by its transfer on a desired solid substrate. The uniqueness in this method lies in the isolation of casting and coating procedures of oriented films, which enables us to fabricate the oriented multilayer with minimum interlayer interference. It provides a key-technology to build up the organic multi-layered architecture while preserving oriented morphologies. Several types of multilayer films have been prepared and investigated in detail in terms of their film characteristics. The layer-by-layer coating of oriented films demonstrated by this method is found to be a unique feature which overcomes cumbersome procedures in the conventional orientation methods. The coating procedure demonstrated in this study provides a facile methodology to construct anisotropic architectures. (C) 2017 Published by Elsevier B.V.
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, True, 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

Solvent driven performance in thin floating-films of PBITT for organic field effect transistor: Role of macroscopic orientation
Manish Pandey; Shyam S. Pandey; Shuichi Nagamatsu; Shuzi Hayase; Wataru Takashima
ORGANIC ELECTRONICS, ELSEVIER SCIENCE BV, 43, 240-246, Apr. 2017, Peer-reviwed, Considering the advantages of floating film transfer method (FTM), we have investigated the optical and electronic characteristics of PBTTT-C14 thin-films prepared by the static and the dynamic casting on liquid substrate. It has been demonstrated that judicious selection of solvents during FTM switches the casting mode from the static casting (S-FTM) using high boiling point solvent to the dynamic casting (D-FTM) from low boiling point solvent. Although both of the methods provide the edge-on oriented structure of PBTTT-C14 by XRD, the structural and the optical analyses reveal relatively extended pi-C conjugation length in parallel D-FTM film as compared to that of S-FTM. A high field-effect mobility (mu) of 0.11 cm(2)/V.s was exhibited by OFETs fabricated by parallel D-FTM film even without any high temperature post-annealing up to the liquid crystalline phase transition. This observed value of mu for parallel D-FTM is 4.7 and 12.8 times higher than the isotropic S-FTM and the perpendicular D-FTM films, respectively. (C) 2017 Elsevier B.V. All rights reserved.
Scientific journal, English

Effect of lead-free (CH3NH3)(3)Bi2I9 perovskite addition on spectrum absorption and enhanced photovoltaic performance of bismuth triiodide solar cells
Chunfeng Lan; Jingting Luo; Shuai Zhao; Chu Zhang; Weiguo Liu; Shuzi Hayase; Tingli Ma
JOURNAL OF ALLOYS AND COMPOUNDS, ELSEVIER SCIENCE SA, 701, 834-840, Apr. 2017, Active composite layers of bismuth triiodide (Bib) and lead-free (CH3NH3)(3)Bi2I9 (MBI) perovskite were prepared using a simple chemical solution method under ambient conditions for thin-film solar cells. Results of X-ray diffraction and scanning electron microscopy indicated that the crystallization and surface morphologies of the composite films varied with perovskite contents. Multi-absorption was observed in the composite films due to the bandgap difference between Bib and MBI perovsldte. Moreover, band bending at the BiI3-perovskite interfaces resulted in the realignment of energy levels in the composite films, and this phenomenon was beneficial to the efficient injection of excited electrons from the active layers into the TiO2 layers. Accordingly, due to the optimized crystallization and realigned energy level, when 20% of MBI perovskite was introduced into the active layers, the open-circuit voltage obviously increased from 0.44 V to 0.57 V in the (Bib)(0.8)(MBI)(0.2) composites solar cells, enhancing their power conversion efficiency by 67% compared with that in pure BiI3 solar cell. This study developed a new route for designing more efficient lead-free solar cells. (C) 2017 Elsevier B.V. All rights reserved.
Scientific journal, English

Annealing effects on CsPbI3-based planar heterojunction perovskite solar cells formed by vacuum deposition method
Kyosuke Yonezawa; Kohei Yamamoto; Md. Shahiduzzaman; Yoshikazu Furumoto; Keitaro Hamada; Teresa S. Ripolles; Makoto Karakawa; Takayuki Kuwabara; Kohshin Takahashi; Shuzi Hayase; Tetsuya Taima
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 56, 4, Apr. 2017, Peer-reviwed, Cesium iodide (CsI) is attracting attention as a substitute for organic materials such as CH3NH3I. In this work, we fabricated sequential-vacuum-deposited planar heterojunction (PHJ) cesium lead iodide (CsPbI3) perovskite solar cells with enhanced efficiencies by varying the annealing time (0.5, 1, 5, and 10 min). The effect of performance enhancement was investigated as a function of varying annealing time at 350 degrees C employing a hot plate. The best-performing device was obtained with an annealing time of 1 min, delivered photocurrent density (JSC) of 12.06 mA/cm(2), voltage (V-OC) of 0.71 V, and fill factor (FF) of 0.67, leading to a power conversion efficiency (PCE) of 5.71% at standard AM 1.5G solar illumination. (C) 2017 The Japan Society of Applied Physics
Scientific journal, English

Annealing effects on CsPbI
Yonezawa Kyosuke; Yamamoto Kohei; Shahiduzzaman Md.; Furumoto Yoshikazu; Hamada Keitaro; Ripolles Teresa; Karakawa Makoto; Kuwabara Takayuki; Takahashi Kohshin; Hayase Shuzi; Taima Tetsuya
Jpn. J. Appl. Phys., Institute of Physics, 56, 4, 04CS11, 24 Mar. 2017, Cesium iodide (CsI) is attracting attention as a substitute for organic materials such as CH3NH3I. In this work, we fabricated sequential-vacuum-deposited planar heterojunction (PHJ) cesium lead iodide (CsPbI3) perovskite solar cells with enhanced efficiencies by varying the annealing time (0.5, 1, 5, and 10 min). The effect of performance enhancement was investigated as a function of varying annealing time at 350 °C employing a hot plate. The best-performing device was obtained with an annealing time of 1 min, delivered photocurrent density (JSC) of 12.06 mA/cm², voltage (VOC) of 0.71 V, and fill factor (FF) of 0.67, leading to a power conversion efficiency (PCE) of 5.71% at standard AM 1.5G solar illumination.
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, True, 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

Controlling Factors for Orientation of Conjugated Polymer Films in Dynamic Floating-Film Transfer Method
Manish Pandey; Shyam S. Pandey; Shuichi Nagamatsu; Shuzi Hayase; Wataru Takashima
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, AMER SCIENTIFIC PUBLISHERS, 17, 3, 1915-1922, Mar. 2017, Peer-reviwed, Orientation in conjugated polymers is a unique phenomenon by the virtue of their one dimensionality leading to semiconductor performances in organic electronic devices. A unique, cost-effective and highly efficient method for the fabrication of oriented thin film consisted of non-regiocontrolled poly(3-hexylthiophene) (NR-P3HT) using dynamic floating-film transfer method (dynamic-FTM) hasbeen investigated. Orientation of NR-P3HT by dynamic-FTM has been quantitatively measured as the optical anisotropy represented by dichroic ratio (DR). Amongst several factors like concentration of polymer solution, temperature and viscosity ofliquid-substrate along with post-annealing temperature, viscosity of liquid-substrate plays a crucial role in controlling the molecular orientation. A judicious control and optimization of various underlying factors affecting the molecular orientation led to relatively high DR of 9.3 even in NR-P3HT films cast by dynamic-FTM.
Scientific journal, English

Transparent Conductive Oxide Layer and Hole Selective Layer Free Back-Contacted Hybrid Perovskite Solar Cell
Zhaosheng Hu; Gaurav Kapil; Hiromitsu Shimazaki; Shyam Sudhir Pandey; Tingli Ma; Shuzi Hayase
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 121, 8, 4214-4219, Mar. 2017, Back-contacted architectures have been under intensive investigation for that transparent conductive oxide (TCO) less solar cells (SCs) can be easily realized which avoid the transmission loss of light caused by TCO, typically comprised in conventional solar cells. Here, network-like porous Ti was first utilized as the back -contacted electrode, and a new design allows for a novel back contacted hybrid perovskite SC without TCO and hole selective layer, which shows a power output of 3.88% with long-term stability. In addition, it avoids limit available collection area of electrodes in the recent reported interdigitated electrode (IDE) based back-contacted TCO-less SCs.
Scientific journal, 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

Research following Pb Perovskite Solar Cells
HAYASE Shuzi
Electrochemistry, The Electrochemical Society of Japan, 85, 5, 222-225, 2017, Certified efficiency of Pb perovskite solar cells with mixed cations is reported to be 19.6% (1 cm²). One of the recent research interests is on enhancing the solar cell efficiency further. Band gap of the present Pb perovskite is about 1.55 eV. Supposing that Voc loss is 0.4 eV, the best efficiency is obtained by using perovskite with about 1.4 eV band gap. One of the candidates for the narrow band gap perovskite material is SnPb mixed metal perovskite. In this paper, the relationship between Voc losses and hetero-interface structures is discussed in detail, leading to the conclusion that hetero-interface structures give serious effects on the solar cell efficiency. It is reported that the efficiency was enhanced from about 5% to 16% after optimization of the hetero-interface structure. In addition, research trend on Pb free perovskite solar cells consisting of Sn or Bi, which is another recent research interest, is also reviewed.
English

Combined theoretical and experimental approaches for development of squaraine dyes with small energy barrier for electron injection
Shyam S. Pandey; Takuya Morimoto; Naotaka Fujikawa; Shuzi Hayase
SOLAR ENERGY MATERIALS AND SOLAR CELLS, ELSEVIER SCIENCE BV, 159, 625-632, Jan. 2017, Peer-reviwed, A series of far-red sensitizing squaraine dyes has been systematically designed and synthesized,in order to correlate the theoretically calculated values with their corresponding experimental parameters. Efforts have been directed towards determining the minimum thermodynamic energy barrier for the electron injection in the nanoporous TiO2 by logical molecular design. Theoretical calculations using Gaussian program package were performed for ground and excited states in both of the isolated gaseous state as well as in solution including the solvent effect using a self-consistent reaction field polarizable continuum model (PCM). Implementation of the PCM model or use of LSDA functional under TD-DFF calculations gives much better results for energetics as well as absorption maximum for all of the sensitizers used in this work. Newly designed symmetrical squaraine dye SQ-5 exhibits a minimum energy barrier of 0.16 eV for electron injection and shows photon harvesting behavior in far-red region with external photoconversion efficiency of 2.02% under simulated solar irradiation. (C) 2015 Elsevier B.V. All rights reserved.
Scientific journal, English

Transparent conductive oxide-less back contact dye-sensitized solar cells using flat titanium sheet with microholes for photoanode fabrication
Azwar Hayat; Ajay Kumar Baranwal; Masaki Nakamura; Fujisawa Shigeki; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
JOURNAL OF PHOTONICS FOR ENERGY, SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 7, 1, Jan. 2017, A flat titanium sheet with microholes (FTS-MH) has been utilized to fabricate transparent conductive oxide-less dye-sensitized solar cells (TCO-less DSSCs) in back contact device architecture. Utilization of FTS-MH to fabricate a TCO-less photoanode offers several advantages in terms of simplicity and ease of fabrication as compared with the TCO-less DSSCs structure reported previously. Hydrogen peroxide (H2O2) surface treatments on FTS-MH have shown important factors to enhance the photoanode properties. H2O2 surface treatment is able to change the surface morphology of FTS-MH, and the created anatase titanium dioxide (TiO2) nanostructures increase the surface contact between the FTS-MH and the coated mesoporous TiO2. Electrochemical impedance investigations reveled that improvements of the FTS-MH/TiO2 and TiO2/dye/electrolyte interface led to hampered charge recombination resulting in enhancement of both short-circuit current density and open-circuit voltage, respectively. Even after removal of both TCO layers, our complete TCO-less DSSCs exhibited a power conversion efficiency of 7.25% under simulated solar irradiation. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
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

Influence of backbone structure on orientation of conjugated polymers in the dynamic casting of thin floating-films
Manish Pandey; Shyam S. Pandey; Shuichi Nagamatsu; Shuzi Hayase; Wataru Takashima
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 619, 125-130, Nov. 2016, Peer-reviwed, Dynamic casting of conjugated polymer films on liquid-substrate is a unique method which provides thin floating-film and can be easily transferred on a desired substrate by stamping. The important feature in this procedure is associated with the formation of thin polymeric film during compression and solidification controlled by viscous drag of liquid substrate and solvent evaporation of the polymer, respectively. Lyotropic liquid-crystalline (LC) characteristics of conjugated polymer possibly assist to orient the polymer chain in one direction. It is found that this method produce highly oriented thin films (dichroic ratio >5) of thiophene-based conjugated polymers such as PBTTT-C14, PQT-C12 and non-regiocontrolled poly(3-hexylthiophene) NR-P3HT. On the other hand, weak orientation intensity in regioregular poly(3-hexylthiophene) RR-P3HT was found. The mechanism for this diverse orientation in thiophene-based conjugated polymers is discussed in correlation with the backbone chemical structure and lyotropic LC phase transition during the floating-film formation. (C) 2016 Elsevier B.V. All rights reserved.
Scientific journal, English

Enhancement of carrier mobility along with anisotropic transport in non-regiocontrolled poly (3-hexylthiophene) films processed by floating film transfer method
Manish Pandey; Shuichi Nagamatsu; Shyam S. Pandey; Shuzi Hayase; Wataru Takashima
ORGANIC ELECTRONICS, ELSEVIER SCIENCE BV, 38, 115-120, Nov. 2016, Peer-reviwed, A newly developed floating film transfer method (FTM) has been successfully utilized to fabricate oriented thin films of non-regiocontrolled poly (3-hexyl thiophene) (NR-P3HT) followed by the fabrication of organic field effect transistors (OFETs). AFM microstructural investigations demonstrate the facile molecular alignment of NR-P3HT by FTM leading to highly oriented macromolecular assemblies like fibrous domains with considerably enhanced pi-conjugation length. FTM thin films of NR-P3HT not only show enhanced optical anisotropy (dichroic ratio >8) but also significantly improved FET characteristics. FTM films in its parallel orientation exhibited a significant improvement (>2 orders) in the FET mobility as compared to its spin-coated device counterparts. (C) 2016 Elsevier B.V. All rights reserved.
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, ChemSusChem, 9, 18, 2634-2639, 22 Sep. 2016, True, The interface between the perovskite (PVK, CH3 NH3 PbI3 ) 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 (10 ppm) 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 280 μsec) after 10 ppm 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, Japanese

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

Mechanisms of charge accumulation in the dark operation of perovskite solar cells
Teresa S. Ripolles; Ajay K. Baranwal; Koji Nishinaka; Yuhei Ogomi; Germa Garcia-Belmonte; Shuzi Hayase
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 18, 22, 14970-14975, Jun. 2016, Peer-reviwed, In this work, a new current peak at forward bias in the dark current-voltage curves has been identified for standard mesoscopic perovskite solar cells. This characteristic peak appears only under some specific conditions, mainly in the reverse scan (RS) direction and when the solar cells were kept for several seconds under short-circuit conditions before starting the RS measurement. This peak disappears when the above experimental conditions are not applied. It is considered that this uncommon diode shape is obtained because shallow and/or deep trap states located at the interface between either perovskite/p-type or perovskite/n-type transport materials are dynamically filled during the RS voltage scan. To corroborate this hypothesis, the response of hole transport materials (HTMs), small molecule spiro-OMeTAD and polymer P3HT, as well as both HTMs with additives, was compared. Also perovskite absorbers such as CH3NH3PbI3 and all-inorganic perovskite based on cesium (CsPbI3) were also analyzed, achieving in all cases similar trends.
Scientific journal, English

Effect of Addition of KI on the Hydrothermal Growth of ZnO Nanostructures Towards Hybrid Optoelectronic Device Applications
Anubha Bilgaiyan; Tejendra Dixit; Gaurav Kapil; Shyam S. Pandey; Shuji Hayase; Iyamperumal Anand Palani; Vipul Singh
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, AMER SCIENTIFIC PUBLISHERS, 16, 4, 3301-3306, Apr. 2016, Peer-reviwed, We report the structural and optoelectronic properties of Zinc oxide (ZnO) nanostructures prepared by hydrothermal method. The morphological, structural and optical properties of the grown ZnO nanostructures were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectroscopy (PL) respectively. Upon addition of relatively small amount of KI during the in-situ hydrothermal growth the nanorods were formed, further increasing the concentration led to increased diameter of these nanorods and finally at relatively higher concentration of KI, ZnO nanosheets were formed. Later these structures were used to fabricate bi-layer ZnO/P3HT based hybrid photodiode. Subsequent hybrid photodiode measurement with ZnO nanorods and ZnO nanosheets indicated that the nanosheets exhibited improved photodiode response. Compared to the ZnO nanorod/P3HT devices, the optimized photodiode with the dense ZnO nanosheets/P3HT have shown significant increase in the rectification ratio and the photosenstivity from 3.21 to 1420 and from 5.85 to 1330 respectively. The enhanced photodiode response of bi-layered devices consisting of ZnO nanosheets indicated that optimizing the shape and size of ZnO nanostructures had a significant influence on the overall photocurrent and the observed results have been explained on the basis of reduction in the defect density with pronounced absorption in the UV region, thus leading to improved transmission of light in the visible range through these layers.
Scientific journal, English

Design of Far-Red Sensitizing Squaraine Dyes Aiming Towards the Fine Tuning of Dye Molecular Structure
Takuya Morimoto; Naotaka Fujikawa; Yuhei Ogomi; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, AMER SCIENTIFIC PUBLISHERS, 16, 4, 3282-3288, Apr. 2016, Model squaraine dyes having sharp and narrow absorptions mainly in the far-red wavelength region has been logically designed, synthesized and used for their application as sensitizer in the dye-sensitized solar cells (DSSC). In order to have fine control on energetics, dyes having same mother core and alkyl chain length varying only in molecular symmetry and position of substituent were designed. It has been found that even keeping all other structural factor constant, only positional variation of substituent leads to not only in the variation of energetics by 0.1 eV but affects the photovoltaic characteristics also. Optimum concentration of dye de-aggregating agent was found to be 100 times with respect to the sensitizing dye concentration. Amongst dyes utilized in this work best performance was obtained for unsymmetrical dye SQ-40 giving a photoconversion efficiency of 4.01% under simulated solar irradiation at global AM 1.5.
Scientific journal, English

Indoor Light Performance of Coil Type Cylindrical Dye Sensitized Solar Cells
Gaurav Kapil; Yuhei Ogomi; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, AMER SCIENTIFIC PUBLISHERS, 16, 4, 3183-3187, Apr. 2016, A very good performance under low/diffused light intensities is one of the application areas in which dye-sensitized solar cells (DSSCs) can be utilized effectively compared to their inorganic silicon solar cell counterparts. In this article, we have investigated the 1 SUN and low intensity fluorescent light performance of Titanium (Ti)-coil based cylindrical DSSC (C-DSSC) using ruthenium based N719 dye and organic dyes such as D205 and Y123. Electrochemical impedance spectroscopic results were analyzed for variable solar cell performances. Reflecting mirror with parabolic geometry as concentrator was also utilized to tap diffused light for indoor applications. Fluorescent light at relatively lower illumination intensities (0.2 mW/cm(2) to 0.5 mW/cm(2)) were used for the investigation of TCO-less C-DSSC performance with and without reflector geometry. Furthermore, the DSSC performances were analyzed and compared with the commercially available amorphous silicon based solar cell for indoor applications.
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

Effect of Varying Alkyl Chain Length on Thermal Decomposition Temperature of Zinc(II) Xanthates and its Impact on Curing of Epoxy Resin
Tarun Chand Vagvala; Shyam Sudhir Pandey; Suvratha Krishnamurthy; Shuzi Hayase
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, WILEY-V C H VERLAG GMBH, 642, 2, 134-139, Jan. 2016, Peer-reviwed, Linear and branched zinc(II) xanthates with varying alkyl chain length were synthesized and characterized by H-1 NMR, C-13 NMR, and IR spectroscopy, as well as elemental analysis. Zinc sulfide as the final decomposition product upon thermal annealing of zinc(II) xanthates was confirmed by XRD analysis. Cure time for epoxy resin composite at various temperatures was analyzed employing zinc(II) xanthates (5% mass) as latent cure catalysts. XRD investigation of the cured epoxy resin including zinc(II) xanthates upon thermal annealing revealed the presence of ZnS in-situ in the composite matrix, indicating the in-situ thermal decomposition of zinc(II) xanthates as probable mechanism for curing. Thermogravimetric analysis was performed to investigate the thermal decomposition temperature trend of zinc(II) xanthates. A parallel trend was observed correlating the thermal decomposition temperature trend of zinc(II) xanthates and the order of curing catalytic efficiency utilizing zinc(II) xanthates. In the case of linear alkylzinc(II) xanthates with an increase in the alkyl chain length, both thermal decomposition temperature and the cure time were enhanced. In contrast, in case of branched alkyl chain zinc(II) xanthates with increasing alkyl chain length show decreasing thermal decomposition temperature as well as cure time.
Scientific journal, English

Orientation Characteristics of Non-regiocontrolled Poly(3-hexyl-thiophene) Film by FTM on Various Liquid Substrates
M. Pandey; S. Nagamatsu; S. S. Pandey; S. Hayase; W. Takashima
INDIA-JAPAN EXPERT GROUP MEETING ON BIOMOLECULAR ELECTRONICS & ORGANIC NANOTECHNOLOGY FOR ENVIRONMENT PRESERVATION (IJEGMBE 2015), IOP PUBLISHING LTD, 704, 012005-1-012005-7, 2016, Peer-reviwed, Orientation characteristics of non-regiocontrolled poly(3-hexylthiophene) (NR-P3HT) films prepared by dynamic casting of floating film and transferring method (FTM) has been investigated. The film was first cast on liquid-substrate to obtain as a floating-film followed by its transfer on solid-substrate such as white-glass or Si-wafer in order to evaluate their optoelectronic characteristics. As a possible key-factor to generate the orientation of conjugated polymer in this method we focused on the components of liquid-substrate in this study. The orientation dependence upon various liquid-substrates reveals that dichroic ratio strongly changes with liquid-substrates. Pictures of floating-film show the change in size of floating-parts depending upon the liquid-substrate, representing the expansion length of casting solution upon the viscosity. These findings have indicated that spreading speed of polymer solution and solvent evaporation speed controls the size of floating-film leading to change in the orientation intensity. The multilayer coatings of oriented NR-P3HT films were used for polarized FTIR analysis exhibiting clear dichroism. The obtained dichroic characteristics were well corresponded with in-plane, out-of-plane and non-oriented vibronic modes of P3HT.
International conference proceedings, English

Parametric Optimization of Experimental Conditions for Dye-Sensitized Solar Cells based on Far-red Sensitive Squaraine Dye
Takuya Morimoto; Naotaka Fujikawa; Yuhei Ogomi; Shyam S. Pandey; Shuzi Hayase
INDIA-JAPAN EXPERT GROUP MEETING ON BIOMOLECULAR ELECTRONICS & ORGANIC NANOTECHNOLOGY FOR ENVIRONMENT PRESERVATION (IJEGMBE 2015), IOP PUBLISHING LTD, 704, 0120021-0120027, 2016, Peer-reviwed, A far-red sensitive unsymmetrical squaraine dye SQ-41 has been synthesized and subjected to the fabrication of dye-sensitized solar cells by varying the various parameters in order attain optimum photoconversion efficiency (eta). It has been demonstrated that an optimum ratio of dye to coadsorber, thickness of mesoporous TiO2 layer, redox electrolyte and surface treatment are necessary to enhance overall external eta. In the case of surface treatment, it has been shown to exhibit pronounced device performance when both of the FTO as well mesoporous TiO2 surfaces were treated with aqueous TiCl4. In spite of very high molar extinction coefficient of dye SQ-41, 10-12 mu m thickness of mesoporous TiO2 was found to be necessary to attain the maximum eta.
Scientific journal, English

Tandem Dye-Sensitized Solar Cells Based on TCO-less Back Contact Bottom Electrodes
Ajay K. Baranwal; Naotaka Fujikawa; Terumi Nishimura; Yuhei Ogomi; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
INDIA-JAPAN EXPERT GROUP MEETING ON BIOMOLECULAR ELECTRONICS & ORGANIC NANOTECHNOLOGY FOR ENVIRONMENT PRESERVATION (IJEGMBE 2015), IOP PUBLISHING LTD, 704, 1, 2016, Mechanically stacked and series connected tandem dye sensitized solar cells (TDSSCs) are fabricated in novel architectures. The architecture consist of TCO tandem DSSCs stacked with TCO-less back contact DSSCs as bottom electrodes (TCO-less tandem DSSCs). Resulting TCO-less tandem DSSCs architecture finds its usefulness in efficient photon harvesting due to improved light transmission and enhanced photons reaching to the bottom electrodes. The fabricated tandem performance was verified with visible light harvesting model dyes D131 and N719 as a proof of concept and provided the photoconversion efficiency (PCE) of 6.06 % under simulated condition. Introduction of panchromatic photon harvesting by utilizing near infrared light absorbing Si-phthalocyanine dye in combination with the modified tandem DSSC architecture led to enhancement in the PCE up to 7.19 %.
International conference proceedings, English

First principles analysis of oxygen vacancy formation and migration in Sr2BMoO6 (B = Mg, Co, Ni)
Shuai Zhao; Liguo Gao; Chunfeng Lan; Shyam S. Pandey; Shuzi Hayase; Tingli Ma
RSC ADVANCES, ROYAL SOC CHEMISTRY, 6, 38, 31968-31975, 2016, Molybdenum-based double perovskites have been extensively studied as electrode materials in solid oxide fuel cells (SOFCs) due to their mixed ionic/electronic conductivity (MIEC) characteristics. Since the ionic conductivity in perovskite crystals arises primarily from oxygen ion diffusion via a vacancy-hopping mechanism, both the formation energy of the oxygen vacancy and the migration energy barrier play an essential role in the MIEC performance. In this work, we present a detailed first-principles investigation on the stoichiometric and oxygen-deficient structures of double perovskites, Sr2BMoO6 (B = Mg, Co and Ni), using the density functional theory (DFT) method plus Hubbard U for Co and Ni. The electronic ground states of the oxygen-stoichiometric cells exhibited apparent eigenvalue gaps which are consistent with the measured insulating features. The oxygen-deficient structures were studied by removing a neutral oxygen atom according to SOFC working conditions, and the minimum energy path (MEP) of oxygen ion migration was optimized using the nudged elastic band (NEB) method which produced the theoretical migration energy barriers at the DFT+U level. The vacant oxygen sites released electrons to the adjacent cation d states, coupled with the delocalization characteristics of the Mo 4d state, which led eventually to the transition from an insulator to the electronic conductivity of the oxygen-deficient crystals. The electronic structure analysis suggested that the outer shell electrons of Mg, Co and Ni significantly affected the energies of oxygen vacancy formation and migration. Our results elucidate the effect of B-site substitution elements on the electronic properties and MIEC characteristics which provides theoretical support for the enhancement of the MIEC properties for these Mo-based double perovskites.
Scientific journal, English

Enhancing the performance of transparent conductive oxide-less back contact dye-sensitized solar cells by facile diffusion of cobalt species through TiO2 nanopores
Md. Zaman Molla; Minobu Kawano; Ajay K. Baranwal; Shyam S. Pandey; Yuhei Ogomi; Tingli Ma; Shuzi Hayase
RSC ADVANCES, ROYAL SOC CHEMISTRY, 6, 40, 33353-33360, 2016, We report a back contact (BC) transparent conductive oxide (TCO)-less dye-sensitized solar cell (DSSC) fabricated utilizing a Co2+/3+ redox shuttle based electrolyte. A new strategy has been proposed for the reduction of the electrolyte layer by coating with a TiO2 nanoparticle spacer (TN spacer) with controlled thickness. The negatively charged TN spacer was found to decrease the diffusion of cobalt species through the TN spacer due to electrostatic interactions leading to a hampered photoconversion efficiency of 4.41%. This sluggish diffusion of bulky cobalt ions was amicably facilitated by passivating the negatively charged TN spacer surface with dye molecules. Facile transport of electrolyte ions in the nanopores of the passivated TN spacer was further confirmed by electrochemical impedance spectroscopy and estimation of the diffusion of Co3+ species in the nanopores of the passivated TN spacer using cyclic voltammetry. The TCO-less BC-DSSC in combination with the cobalt electrolyte fabricated in this novel device architecture exhibits a significantly improved photoconversion efficiency of 6.42% after the TN spacer was passivated with the porphyrin-based dye YD2-o-C8.
Scientific journal, English

Near IR sensitive Sn based perovskite solar cells with high current density reaching 30mA/cm(2)
Yuhei Ogomi; Daisuke Hirotani; Kosei Fujiwara; Keita Sakaguchi; Qing Shen; Taro Toyoda; Kenji Yoshino; Atsushi Wakamiya; Teresa S. Ripolles; Shuzi Hayase
2016 IEEE 43RD PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC), IEEE, 808-811, 2016, Peer-reviwed, Enhancing J(sc) of solar cells consisting of mixed metal perovskite, MASn(0.5)Pb(0.5)I(3) (SnPb PVK), is reported. The SnPb PVK was prepared from PbI2/SnI2 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 (sigma) 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/cm(2), compared to 20 mA/cm(2) for SnPb-A PVK cell. The carrier dynamics is discussed by transient spectroscopy studies.
International conference proceedings, English

Concentration gradient controlled growth of large-grain CH3NH3PbI3 films and enhanced photovoltaic performance of solar cells in ambient conditions.
Chunfeng Lan; Shuai Zhao; Chu Zhang; Weiguo Liu; Shuzi Hayase; Tingli Ma
CrystEngComm, 18, 48, 9243-9251, 2016

Oxygen vacancy formation and migration in double perovskite Sr2CrMoO6: a first-principles study.
Shuai Zhao; Liguo Gao; Chunfeng Lan; Shyam S. Pandey; Shuzi Hayase; Tingli Ma
RSC Advances, ROYAL SOC CHEMISTRY, 2016, 49, 43034-43040, 2016, The perovskite-type oxide ABO(3) with mixed ionic and electronic conductivity (MIEC) is a promising candidate for electrode materials of the intermediate-temperature solid oxide fuel cells (IT-SOFCs). The strontium molybdate SrMoO3 shows high electrical conductivity but low oxygen ionic conductivity due to the stoichiometric features of oxygen. To enhance the oxygen ions diffusion rate, B-site Mo4+ cation was partially substituted by trivalent transition metals (TM) to generate the oxygen-deficient double perovskite Sr2BMoO6-delta. In this study, we present the theoretical investigation of the oxygen vacancy properties of Sr2CrMoO6 (SCM) using density functional theory (DFT) with on-site Coulomb potential U for the Cr 3d electrons. The oxygen vacancy formation and migration were investigated for the B-site-ordered SCM, as well as the SCM with Cr/Mo antisite defects (ADs). The oxygen ion migration was optimized by the climbing image nudged elastic band (CINEB) method to identify the minimum energy pathway. The B-site Cr/Mo ADs allow various TM-O bond types in the double perovskite SCM. The calculated formation energy and migration barrier suggests that the B-site Cr/Mo ADs are favorable to enhance the oxygen ionic conductivity of the SCM. These results elucidate the influence of B-site Cr and Mo cations on the oxygen vacancy formation and migration in the double perovskite SCM, which can be useful for investigating Cr-doped SrMoO3 as an IT-SOFCs anode.
Scientific journal, English

Investigation on structures, band gaps, and electronic structures of lead free La2NiMnO6 double perovskite materials for potential application of solar cell.
Chunfeng Lan; Shuai Zhao; Tingting Xu; Jie Ma; Shuzi Hayase; Tingli Ma
Journal of Alloys and Compounds, 655, 208-214, 2016

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, 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, 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

Transparent conductive oxide-less back contact dye-sensitized solar cells using cobalt electrolyte
Md. Zaman Molla; Norihiro Mizukoshi; Hiroaki Furukawa; Yuhei Ogomi; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
PROGRESS IN PHOTOVOLTAICS, WILEY-BLACKWELL, 23, 9, 1100-1109, Sep. 2015, Transparent conductive oxide-less (TCO-less) dye-sensitized solar cells (DSSCs) have been fabricated and characterized using nanoporous TiO2-coated stainless steel metal mesh as flexible photoanode and cobalt bipyridyl complex (Co(bpy))-based one electron redox shuttle electrolyte. Attempts have been made towards enhancing the efficiency of TCO-less DSSCs to match with their TCO-based DSSC counterparts. It has been found that surface protection of metal mesh is highly required for enhancing the efficiency of TCO-less DSSCs specially using cobalt electrolytes as confirmed by dark current-voltage characteristics. Photocurrent action spectra clearly reveal that TCO-based DSSCs using (Co(bpy)) electrolyte exhibits photon harvesting (incident photon to current conversion efficiency (IPCE) 52%) in the 370-450nm wavelength region as compared to photon harvesting at peak absorption of the dye (IPCE 56% at 550nm), which is almost the same (IPCE 47%) in the 400-610nm wavelength region for TCO-less DSSCs. Under similar experimental conditions, replacing indoline dye D-205 to porphyrin-based dye YD2-o-C8 led to the enhancement in the photoconversion efficiency from 3.33% to 4.84% under simulated solar irradiation. Copyright (c) 2014 John Wiley & Sons, Ltd.
Scientific journal, English

Investigation of metal xanthates as latent curing catalysts for epoxy resin via formation of in-situ metal sulfides
Tarun Chand Vagvala; Shyam Sudhir Pandey; Yuhei Ogomi; Tingly Ma; Shuzi Hayase
INORGANICA CHIMICA ACTA, ELSEVIER SCIENCE SA, 435, 292-298, Aug. 2015, Peer-reviwed, Cu(I), Pb(II), Sb(III), Zn(II), Cd(II), In(III), Ga(III) xanthates were synthesized and characterized by H-1 NMR, C-13 NMR, infrared spectroscopy and elemental analysis. The final product of decomposition of metal xanthates at 200 degrees C subjected to XRD and EDS analysis, confirmed generation of metal sulfides. The curing behavior was analyzed by performing curing time investigation of epoxy composite as a function of temperature employing 5% metal xanthates as catalysts. None of the metal xanthates demonstrated any significant curing of epoxy composite prior to 150 degrees C proving their latent curing potency. Ga(III) xanthate exhibited comparatively the most effective catalytic property. Thermogravimetric analysis utilized to examine the thermal behavior of metal xanthates indicated, metal xanthates which are air-stable at ambient temperatures undergo latent decomposition upon thermal annealing. The order of curing time at a given temperature and the trend of decomposition temperature of metal xanthate under consideration was observed to be similar. XRD and EDS study of epoxy composite consisting of metal xanthates cured by thermal annealing illustrated generation of metal sulfide in-situ in the matrix. It was presumed that the phenomena of metal xanthates under investigation yielding corresponding in-situ metal sulfides in the epoxy composite upon thermal annealing in a latent fashion is responsible for exhibiting latent curing catalytic activity. (C) 2015 Elsevier B.V. All rights reserved.
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; Shuzi Hayase; Qing Shen
Thin Solid Films, Elsevier, 590, 90-97, 21 Jul. 2015, Peer-reviwed
Scientific journal, English

Nonisothermal curing kinetics of epoxy resin composite utilizing Ga (III) xanthate as a latent catalyst
Tarun Chand Vagvala; Gaurav Kapil; Shyam S. Pandey; Yuhei Ogomi; Shuzi Hayase
JOURNAL OF APPLIED POLYMER SCIENCE, WILEY-BLACKWELL, 132, 26, Jul. 2015, Peer-reviwed, Cure kinetics and curing mechanism of epoxy resin composite utilizing gallium (III) xanthate as a latent catalyst was investigated and compared with the commercial latent catalyst UCAT3512T formulation. Nonisothermal differential scanning calorimetric technique at different heating rates was employed to investigate the kinetic parameters. Activation energy was determined using Kissinger's and Flynn-Wall-Ozawa methods. Ga (III) xanthate was found to possess superior latent properties compared with UCAT3512T since the activation energy value obtained was higher for epoxy resin composite consisting of Ga (III) xanthate than UCAT3512T. Friedman's isoconversional method was utlizied to for kinetic modeling. An autocatalytic model was found to be successful in describing the curing reaction for both of the formulations. The calculated conversion rate as a function of temperature obtained by solving the autocatalytic equation showed a very good fit with experimental values. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42149.
Scientific journal, English

Simple Metal-Free Dyes Derived from Triphenylamine for DSSC: A Comparative Study of Two Different Anchoring Group
K. Narayanaswamy; T. Swetha; Gaurav Kapil; Shyam S. Pandey; Shuzi Hayase; Surya Prakash Singh
ELECTROCHIMICA ACTA, PERGAMON-ELSEVIER SCIENCE LTD, 169, 256-263, Jul. 2015, Peer-reviwed, We synthesized two new organic dyes (KNS1 and KNS2) based on the triphenylamine (TPA) core structure. Both of the dyes contain triphenylamine and thiophene moieties as an electron donor and cyanoacrylic acid and rhodanine-3-acetic acid units as electron acceptors. Nanocrystalline TiO2 based dye-sensitized solar cells (DSSCs) were fabricated using these dyes to investigate the effect of two different anchoring groups on their photovoltaic performance. The DSSCs based on KNS1 and KNS2 showed power conversion efficiency (PCE) of about 2.01% and 2.95%, respectively. The PCE has been significantly improved upto 3.53% and 3.00%, upon addition of chenodeoxycholic acid (CDCA) to the dye solution. (C) 2015 Elsevier Ltd. All rights reserved.
Scientific journal, English

First principles study on the electronic and optical properties of B-site ordered double perovskite Sr2MMoO6 (M=Mg, Ca, and Zn)
Shuai Zhao; Chunfeng Lan; Jie Ma; Shyam S. Pandey; Shuzi Hayase; Tingli Ma
SOLID STATE COMMUNICATIONS, PERGAMON-ELSEVIER SCIENCE LTD, 213, 19-23, Jul. 2015, Electronic and optical properties of double perovskite Sr2MMoO6 (M=Mg, Ca, and Zn) were studied using density functional theory. The double perovskites Sr2MgMoO6 and Sr2CaMoO6 exhibited the direct band gap whereas Sr2ZnMoO6 was found to be indirect band gap material. The valence band maxima consisted mainly of oxygen 2p orbitals, whereas the conduction band minima was composed of hybridization between the B-site of Mo 4d and O 2p orbitals. The on-site Coulomb interaction was examined in terms of the influence of the transition metals' d orbitals on the electronic properties of the double perovskites. The dielectric functions and the absorption coefficients were studied from the ground electronic states. These results demonstrated that substituting the B-site elements in double perovskites is a potential method to tune the electronic structure for absorbing visible light for applications in inorganic perovskite solar cells. (C) 2015 Elsevier Ltd. All rights reserved.
Scientific journal, English

Dye-sensitized solar cells based on axially ligated phosphorus-phthalocyanine dyes
Azwar Hayat; Gururaj M. Shivashimpi; Terumi Nishimura; Naotaka Fujikawa; Yuhei Ogomi; Yoshihiro Yamaguchi; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 8, 4, Apr. 2015, Dye-sensitized solar cells with axially anchored phosphorous-phthalocyanine dyes were fabricated for the first time. Although the phosphorus-phthalocyanine dyes do not have a conventional anchoring group (-COOH), these dyes could be absorbed on a TiO2 semiconductor surface. After the optimization of energy levels, a 24% incident photon-to-current efficiency (IPCE) was observed at 710 nm with an IPCE curve edge of 800 nm. The efficiency was 2.67%, which was higher than those of previously reported dye-sensitized solar cells with axially anchored phthalocyanine dyes (less than 1%). (C) 2015 The Japan Society of Applied Physics
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

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, 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

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

Relationship between diffusion of Co3+/Co2+ redox species in nanopores of porous titania stained with dye molecules, dye molecular structures, and photovoltaic performances
Minobu Kawano; Tsubasa Nishiyama; Yuhei Ogomi; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
RSC ADVANCES, ROYAL SOC CHEMISTRY, 5, 102, 83725-83731, 2015, Diffusion of Co2+ and Co3+ in nanopores of porous titania stained with various dyes were evaluated and were compared with those of I-, and I-3(-). Diffusion of Co3+ in the bare nanopore was slower than that of I-3(-). Dyes adsorbed on the wall of nanopores affected these diffusion coefficients remarkably. The Co3+ diffusion in nanopores became faster when the nanopore wall was covered with dyes with long alkyl groups, probably because the long alkyl groups suppress the interaction between TiO2 surface and Co3+. Higher open circuit voltage (V-OC) was obtained for the DSSC with fast Co3+ diffusion in nanopores because the fast diffusion suppresses the charge recombination between electrons in titania and Co3+ remaining in the nanopores. The fast diffusion in nanopores was applied to thin nanoparticle spacer (th: 5 mu m) of DSSCs. After nanoparticle spacer was stained with dyes with long alkyl groups, the efficiency drastically increased from 2.8% to 5.3%.
Scientific journal, English

Combining novel device architecture and NIR dye towards the fabrication of transparent conductive oxide-less tandem dye sensitized solar cells
Ajay Kumar Baranwal; Naotaka Fujikawa; Azwar Hayat; Yuhei Ogomi; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
Applied Physics Express, Institute of Physics, 10, 8, 102301-102301, 2015, Tandem solar cells with different device architectures utilizing a back contact transparent conductive oxide-less bottom electrode (TCO-less tandem DSSC) that has better control of the optical transmission losses incurred by intermediate TCO layers with flexible Pt/tin-doped indium oxide (ITO)-polyethylene terephthalate film as an intermediate layer are reported. The proposed device architecture suppresses the optical loss to a greater extent (around 30%). Sensitizers were ruthenium-based N719 dye in the top electrode, while the newly synthesized phthalocyanine dye (PC25) corresponding to photon harvesting in the near infrared (NIR) region (up to 900 nm) was used in the TCO-less bottom cell. Open circuit voltage (Voc) ≥ 1.18 V (sum of top cell and bottom cell Voc) justifies the TCO-less tandem DSSC formation.
English

Complete Photodynamics of the Efficient YD2-o-C8 Based Solar Cell
Piotr Piatkowski; Cristina Martin; Maria Rosaria di Nunzio; Boiko Cohen; Shyam S Pandey; Shuzi Hayase; Abderrazzak Douhal
Journal of Physical Chemistry C, -sspandey, Nov. 2014, Peer-reviwed
Scientific journal, English

Titanium wire engineering and its effect on the performance of coil type cylindrical dye sensitized solar cells
Gaurav Kapil; Shyam S. Pandey; Yuhei Ogomi; Tingli Ma; Shuzi Hayase
ORGANIC ELECTRONICS, ELSEVIER SCIENCE BV, 15, 11, 3399-3405, Nov. 2014, This paper reports a comparative study of the photovoltaic characteristics of titanium (Ti) metal wires with different diameter and surface treatments towards their utilization as photoanodes for coil-based dye-sensitized solar cells. The surface property of the Ti wire, especially oxidized overlayer and surface treatments have been found to greatly influence the adhesion as well as optimum electrical contact between coated nanoporous titanium oxide (TiO2) and Ti-wires. Implication of adhesion of nanoporous TiO2 on the titanium wire and its influence on photovoltaic performance was analyzed using electrochemical impedance spectroscopy. Results of X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy reveals the formation of anatase TiO2 nanosheets after the H2O2 surface treatment on the titanium wire resulting into enhancement in the extent of dye loading leading to enhanced photoconversion efficiency of 4.71% under simulated solar irradiation. (C 2014 Elsevier B.V. All rights reserved.
Scientific journal, English

Template-Assisted Electrochemical Growth of Polypyrrole Nanotubes for Development of High Sensitivity Glucose Biosensor
Pragya Agar Palod; Shyam S. Pandey; Shuji Hayase; Vipul Singh
APPLIED BIOCHEMISTRY AND BIOTECHNOLOGY, HUMANA PRESS INC, 174, 3, 1059-1072, Oct. 2014, Peer-reviwed, In this paper, we report the growth of polypyrrole (PPy) nanotube arrays using template-assisted electrochemical polymerization to fabricate enzymatic glucose biosensors. The PPy nanotubes were grown on platinum-coated alumina membranes (Anodisc (TM) s). By varying the polymerization time during the potentiostatic electropolymerization, the size/diameter of the PPy nanotubes were controlled, leading to changes in the subsequent enzyme immobilization (via physical adsorption). Enzyme electrode thus fabricated resulted in to the optimum sensitivity of 18.6 mA cm(-2) M-1, a wide range of linear operation (0.25-20 mM) and the lowest detection limit of 0.25 mM glucose concentration for the biosensor with the polymerization time of 40 s. The effect of polymerization duration on the sensitivity has been explained on the basis of porosity and enzyme-loading capacity of polymerized electrodes.
Scientific journal, English

Graphene Oxide-Based Biosensor for Food Toxin Detection
Saurabh Srivastava; Md Azahar Ali; Sima Umrao; Upendra Kumar Parashar; Anchal Srivastava; Gajjala Sumana; B. D. Malhotra; Shyam Sudhir Pandey; Shuji Hayase
APPLIED BIOCHEMISTRY AND BIOTECHNOLOGY, HUMANA PRESS INC, 174, 3, 960-970, Oct. 2014, Peer-reviwed, We report results of the studies relating to the fabrication of a highly sensitive label free biosensor based on graphene oxide (GO) platform for the detection of aflatoxin B1 (AFB(1)) which is most toxic and predominant food toxin, using electrochemical impedance spectroscopy. The structural and optical characterization of GO/Au and anti-AFB(1)/GO/Au has been done by electron microscopy, Raman, X-ray diffraction (XRD), UV-vis and electrochemical impedance spectroscopy (EIS). The impedimetric sensing response of immunoelectrode as a function of AFB(1) concentration reveals wider linear detection range (0.5-5 ng/ml), high sensitivity (639 a"broken vertical bar ng(-1) ml), improved detection limit (0.23 ng ml(-1)) and good stability (5 weeks) for the label-free detection. Association constant (k (a)) for antigen-antibody interaction obtained as 0.46 ng ml(-1) indicates high affinity.
Scientific journal, English

Improved Understanding of the Electronic and Energetic Landscapes of Perovskite Solar Cells: High Local Charge Carrier Mobility, Reduced Recombination, and Extremely Shallow Traps
Hikaru Oga; Akinori Saeki; Yuhei Ogomi; Shuzi Hayase; Shu Seki
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, AMER CHEMICAL SOC, 136, 39, 13818-13825, Oct. 2014, Peer-reviwed, The intriguing photoactive features of organic-inorganic hybrid perovskites have enabled the preparation of a new class of highly efficient solar cells. However, the fundamental properties, upon which the performance of these devices is based, are currently under-explored, making their elucidation a vital issue. Herein, we have investigated the local mobility, recombination, and energetic landscape of charge carriers in a prototype CH3NH3PbI3 perovskite (PVK) using a laser-flash time-resolved microwave conductivity (TRMC) technique. PVK was prepared on mesoporous TiO2 and Al2O3 by one or two-step sequential deposition. PVK on mesoporous TiO2 exhibited a charge carrier mobility of 20 cm(2)V(-1)s(-1), which was predominantly attributed to holes. PVK on mesoporous Al2O3, on the other hand, exhibited a 50% lower mobility, which was resolved into balanced contributions from both holes and electrons. A general correlation between crystal size and mobility was revealed irrespective of the fabrication process and underlying layer. Modulating the microwave frequency from 9 toward 23 GHz allowed us to determine the intrinsic mobilities of each PVK sample (60-75 cm(2) V-1 s(-1)), which were mostly independent of the mesoporous scaffold. Kinetic and frequency analysis of the transient complex conductivity strongly support the superiority of the perovskite, based on a significant suppression of charge recombination, an extremely shallow trap depth (10 meV), and a low concentration of these trapped states (less than 10%). The transport mechanism was further investigated by examining the temperature dependence of the TRMC maxima. Our study provides a basis for understanding perovskite solar cell operation while highlighting the importance of the mesoporous layer and the perovskite fabrication process.
Scientific journal, English

Far-red sensitizing octatrifluorobutoxy phosphorous triazatetrabenzocorrole: Synthesis, spectral characterization and aggregation studies
Gururaj M. Shivashimpi; Shyam S. Pandey; Azwar Hayat; Naotaka Fujikawa; Yuhei Ogomi; Yoshihiro Yamaguchi; Shuzi Hayase
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 289, 53-59, Sep. 2014, Peer-reviwed, Novel phosphorous triazatetrabenzocorrole (4) bearing non-peripheral octatrifluorobutoxy groups was successfully synthesized, with an aim to develop potential far-red sensitizer for dye sensitized solar cells. The dye was characterized by H-1 NMR, IR, mass, and UV-vis spectral techniques. It showed excellent solubility in majority of common organic solvents. Aggregation behavior of the dye 4 was investigated in several solvents with increasing dielectric constants. This dye-4 was found to be adsorbed on the nanoporous TiO2 via axial ligation. Further implication of structure of dye due to incorporation of -CF3 group on the energy levels was evaluated by theoretical and experimental approaches. The intense far-red absorption of dye 4 including its excellent solubility and proper control of its energy levels makes it a promising candidate for its application as sensitizer in dye sensitized solar cells. (C) 2014 Elsevier B.V. All rights reserved.
Scientific journal, English

Molecular Structure and Crystal Packing of n-Type Semiconducting Material 3',3'-(1,4-Phenylene) bis {2'-(4-trifluoromethyl) phenyl} acrylonitrile
Moriguchi Tetsuji; Nagamatsu Shuichi; Okauchi Tatsuo; Tsuge Akihiko; Takashima Wataru; Hayase Shuji
Journal of Crystallography, Hindawi Publishing Corporation, 2014, 257249-1-257249-5, 19 Aug. 2014, The exact molecular structure and the crystal packing of the n-type semiconducting material 3′,3′-(1,4-phenylene)bis{2′-(4-trifluoromethyl)phenyl}acrylonitrile was determined by a single crystal X-ray diffraction with twin treatment technique. The air-stable product was crystallized from dichloromethane-hexane mixed solution. The solid-state structure is the example of a typical π-π stacking with side intermolecular CN–H short contact networks.
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

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, 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

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, 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

Reproducible Fabrication of Efficient Perovskite-based Solar Cells: X-ray Crystallographic Studies on the Formation of CH3NH3PbI3 Layers
Atsushi Wakamiya; Masaru Endo; Takahiro Sasamori; Norihiro Tokitoh; Yuhei Ogomi; Shuzi Hayase; Yasujiro Murata
CHEMISTRY LETTERS, CHEMICAL SOC JAPAN, 43, 5, 711-713, May 2014, Peer-reviwed, Lead halide complexes formed during the fabrication of perovslcite (CH3NH3PbI3)-based solar cells were examined by single-crystal X-ray diffraction analysis. Based on the observed results, the fabrication protocol using a sequential deposition method was optimized to reproducibly provide highly efficient solar cells with power conversion efficiencies of more than 10%.
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, 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

Tandem dye-sensitized solar cells with a back-contact bottom electrode without a transparent conductive oxide layer
A. K. Baranwal; T. Shiki; Y. Ogomi; S. S. Pandey; T. Ma; S. Hayase
RSC ADVANCES, ROYAL SOC CHEMISTRY, 4, 88, 47735-47742, 2014, Peer-reviwed, We report on the architecture of tandem dye-sensitized solar cells (DSSCs) with a back-contact bottom electrode without a transparent conductive oxide layer (TCO-less tandem DSSCs). The bottom electrode consists of glass/stained porous TiO2/back-contact porous metal. As the structure has fewer TCO layers than simple mechanical stack tandem DSSCs, more light reaches the bottom electrode. Two model dyes (D131 and N719) were used to confirm the tandem performance of the cells. The open-circuit voltage (V-oc) was the sum of the V-oc of the top cell and the V-oc of the TCO-less bottom cell, showing that the cell worked as a tandem cell. The power conversion efficiency of the TCO-less tandem DSSC (7.10%) was greater than that of the stack tandem DSSCs (6.28%).
Scientific journal, English

Gallium(III) xanthate as a novel thermal latent curing agent for an epoxy resin composite
Tarun Chand Vagvala; Shyam Sudhir Pandey; Yuhei Ogomi; Shuzi Hayase
RSC ADVANCES, ROYAL SOC CHEMISTRY, 4, 47, 24658-24661, 2014, Peer-reviwed, The latent thermal curing catalyst "Ga(III) xanthate" for an epoxy resin/phenol composite, and its curing behaviour are reported. Ga(III) xanthate swiftly cures the epoxy composite within 38.2 s at 200 degrees C. However the curing time of the epoxy composite with gallium(III) xanthate did not change after storage for six months unlike the commercially used catalyst.
Scientific journal, English

Improved Understanding of the Electronic and Energetic Landscapes of Perovskite Solar Cells: High Local Charge Carrier Mobility, Reduced Recombination, and Extremely Shallow Traps (vol 136, pg 13818, 2014)
Oga Hikaru; Saeki Akinori; Ogomi Yuhei; Hayase Shuzi; Seki Shu
Journal of the American Chemical Society, 136, 48, 16948, 2014, Peer-reviwed

Inhomogeneous deactivation with UV excitation in submicron grains of lead iodide perovskite-based solar cell as revealed by femtosecond transient absorption microscopy
Tetsuro Katayama; Akira Jinno; Eisuke Takeuchi; Syoji Ito; Masaru Endo; Atsushi Wakamiya; Yasujiro Murata; Yuhei Ogomi; Shuji Hayase; Hiroshi Miyasaka
Chemistry Letters, 43, 10, 1656-1658, 2014, Femtosecond transient absorption microscopy was applied to the elucidation of ultraf ast dynamics in a lead iodide perovskite solar cell. Space- and time-resolved detection revealed that rapid deactivation with a time constant of 0.7 ps took place without long-living species in submicron grains with the (CH3NH3)PbI3 capping layer, while the long-living component was detected in other areas.
Scientific journal

Effect of nature of anchoring groups on photosensitization behavior in unsymmetrical squaraine dyes
Gururaj M. Shivashimpi; Shyam S. Pandey; Rie Watanabe; Naotaka Fujikawa; Yuhei Ogomi; Yoshihiro Yamaguchi; Shuzi Hayase
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 273, 1-7, Jan. 2014, Peer-reviwed, A series of indole based unsymmetrical squaraine dyes bearing various anchoring groups such as carboxylate (SQ-A), cyanoacrylate (SQ-B) and thiophene-bridged cyanoacrylate (SQ-C) were synthesized and evaluated for their performance in dye sensitized solar cells (DSSCs) under similar experimental conditions. Electronic absorption spectral investigation on thin films of these dyes adsorbed on nanoporous TiO2 reveals relatively enhanced spectral broadening upon the incorporation of cyanoacrylate functionality as anchoring group. Incorporation of thiophene pi-bridge between the main chromophore and anchoring group (SQ-C) although resulted in to bathochromic shift in the far-red region but hampered photon harvesting due to relatively enhanced dye aggregation. Unsymmetrical squaraine dye (SQ-B) bearing cyanoacrylate anchoring group directly substituted and in conjugation with aromatic chromophore exhibited the best photovoltaic performance giving photoconversion efficiency of 5.03% under simulated solar irradiation. (C) 2013 Elsevier B.V. All rights reserved.
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

Low Temperature TiOx Compact Layer by Chemical Bath Deposition Method for Vapor Deposited Perovskite Solar cells.
Kouhei Yamamoto; Ying Zhou; Takayuki Kuwabara; Koshin Takahashi; Masaru Endo; Atushi Wakamiya; Yuhei Ogomi; Shuzi Hayase; Tetsuya Taima
2014 IEEE 40TH PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC), IEEE, 1573-1576, 2014, Peer-reviwed, In this paper, we try to fabricate the planer heterojunction (PHJ) perovskite solar cell based on low temperature TiOx compact layer by chemical bath deposition (CBD) method. We compared solar cell properties between compact-TiOx layer and compact-TiO2 layer, where CBD deposited films were heated at 250 degrees C in order to convert into TiO, amorphous state and 450 degrees C intoTiO(2) anatase state, respectively. Power conversion efficiency of PHJ perovskite solar cell based on our compact-TiO, shows almost same as that of TiO2 one. In addition, we discuss the origin of hysteresis of PHJ perovskite solar cell based on compact-TiO, and TiO2. We conclude that hysteresis of PHJ perovskite solar cell is heavily influenced by surface coverage and roughness of compact-TiOx or TiO2 layers on transparent conducting oxide.
International conference proceedings, 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, Peer-reviwed, 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

Fabrication and characterization of coil type transparent conductive oxide-less cylindrical dye-sensitized solar cells
Gaurav Kapil; Jin Ohara; Yuhei Ogomi; Shyam S. Pandey; Tingli Ma; Shuzi Hayase
RSC ADVANCES, ROYAL SOC CHEMISTRY, 4, 44, 22959-22963, 2014, Flexible metal wires were used to fabricate transparent conductive oxide (TCO)-less cylindrical dye-sensitized solar cells (DSSCs) with a very easy and fast fabrication process. The nature of the wire and interfacial contact between the metal wire and nanoporous TiO2 layer affected the charge transport giving the photoconversion efficiency of 3.88%.
Scientific journal, English

Transparent conductive oxide-less back contact dye-sensitized solar cells using Zinc porphyrin dye employing cobalt complex redox shuttle
Md. Zaman Molla; Shyam S. Pandey; Yuhei Ogomi; Tingli Ma; Shuzi Hayase
2014 IEEE 40TH PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC), IEEE, 1538-1542, 2014, A transparent conductive oxide-less (TCO-less) dye-sensitized solar cell (DSSC) consisting of back-contacted stainless steel metal mesh electrode has been fabricated. In this work, [Co(bpy)(3)](3+/2+) complex based redox electrolyte and porphyrin dye as sensitizer were utilized. Owing to relatively deeper redox energy level for cobalt based electrolytes as compared to I-3(-)/I- redox system, possibility of obtaining high open-circuit voltage was explored. Employing a thin film of Ti on the metal mesh as the charge recombination blocking layer resulted in enhanced photoconversion efficiency. TCO-less DSSC in combination with cobalt electrolyte gave the power conversion efficiency of 4.89% under simulated solar irradiation.
International conference proceedings, 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, 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

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
Phys. Chem. Chem. Phys., 15, 14370-14376, 01 Jul. 2013, Peer-reviwed
Scientific journal, English

Controlling the processable ZnO and polythiophene interface for dye-sensitized thin film organic solar cells
Sandeep K. Das; Katsunori Abe; Kenji Yoshino; Yuhei Ogomi; Shyam S. Pandey; Shuzi Hayase
Thin Solid Film, 536, 302-307, 01 Jul. 2013, Peer-reviwed
Scientific journal, English

Real-time photodynamics of squaraine-based dye-sensitized solar cells with iodide and cobalt electrolytes
María José Marchena; Gustavo De Miguel; Boiko Cohen; Juan Angel Organero; Shyam Pandey; Shuzi Hayase; Abderrazzak Douhal
Journal of Physical Chemistry C, 117, 23, 11906-11919, 13 Jun. 2013, Peer-reviwed, A series of dye-sensitized solar cells (DSSCs) has been prepared by using indole-based or quinoline-based squaraines (SQs) as the sensitizer and containing the commonly used I3-/I- redox pair or the lately employed cobalt complexes, [Co(dimethylbipyridine) 3]3+/2+, [Co(bipyridine)3]3+/2+, and [Co(phenanthroline)3]3+/2+ redox electrolytes. The photodynamics of the different electron transfer reactions have been investigated by means of the femto-to millisecond pump-probe techniques. In the femtosecond transient absorption experiments, the electron injection rate constants and efficiencies, kei and φei, were determined for each cell. Larger values of kei and φei for the indole-based (SQ 8) compared to the quinoline-based (SQ 12) squaraines were obtained (13.2 × 1010 s-1 and 0.95 × 1010 vs 6.9 × 1010 s-1 and 0.81 for SQ 8 or SQ 12 with the I3-/I- pair, respectively), despite the similar values of the electron injection driving forces (-ΔG0ei = 0.75 vs 0.76 eV). This is due to the lower electron density in the lowest unoccupied molecular orbital at the anchoring group (-COOH) in SQ 12 compared to SQ 8. However, the type of electrolyte did not affect the kinetics of the electron injection processes. In the flash photolysis experiments, the kinetic parameters of the electron recombination via dye or electrolyte and the cation regeneration were calculated from the decays of the transient absorption signals of the electrons (1550 nm) or the SQ cation (570 nm). It was found that the electron recombination with the oxidized redox species is faster with the Co-based compared to the I3 -/I- electrolytes for both SQs, τrec = 3 versus ∼0.5-1 ms. This proves that the steric hindrance in these SQs is not sufficient to avoid the approach of the Co3+ species to the surface of the TiO2 nanoparticle. Moreover, the regeneration rate constants and efficiencies, kreg and φreg, are considerably smaller for the cells with the different Co-based electrolytes compared to those with the I3-/I- pair (i.e., kreg = 30 × 104 vs 8 × 104 M-1s -1 and φreg = 0.96 vs 0.75 with the [Co(dmb) 3]3+/2+ for SQ 8). This is explained by the lower regeneration driving force, -ΔGreg, in the Co-based electrolytes (0.3-0.1 eV). Thus, the use of Co-based electrolytes in these two SQs is detrimental to the overall efficiency of the cell, since -ΔG reg values below 0.4 eV do not give complete regeneration efficiency. Finally, we have compared the measured photocurrent with the calculated electron injection and regeneration efficiencies, and we found a good correlation between both parameters. © 2013 American Chemical Society.
Scientific journal, English

Transparent conductive oxide-less three-dimensional cylindrical dye-sensitized solar cell fabricated with flexible metal mesh electrode
Jun Usagawa; Shyam S. Pandey; Yuhei Ogomi; Sho Noguchi; Yoshihiro Yamaguchi; Shuzi Hayase
Progress in Photovoltaics: Research and Applications, 21, 4, 517-524, Jun. 2013, Peer-reviwed, A cylindrical transparent conductive oxide-less dye-sensitized solar cell (DSSC) consisting of glass tube/stainless steel mesh-TiO2-dye/gel electrolytes/Pt-Ti rod having capability of self-light trapping is reported. Replacing the glass tube with heat-shrinkable tube to reduce electrolyte gap and optical loss due to light transmission and reflection led to the enhancement in the power conversion efficiency from 2.61% to 3.91%. Profiling of the current distribution measured by laser beam-induced current exhibited nearly the same current in the axial and radial directions, suggesting that light reflection on a cylindrical DSSC does not affect the efficiency seriously. Optimized best DSSC in this novel device architecture gave a short-circuit current density of 11.94 mA/cm2, an open-circuit voltage of 0.71 V and a fill factor of 0.66 leading to the power conversion efficiency of 5.58% at AM 1.5 under simulated solar irradiation. Copyright © 2011 John Wiley &
Sons, Ltd.
Scientific journal, English

Single-step fabrication of all-solid dye-sensitized solar cells using solution-processable precursor
Sandeep K. Das; Daiki Yamashita; Yuhei Ogomi; Shyam S. Pandey; Kenji Yoshino; Shuzi Hayase
Physica Status Solidi (A), 210, 1846-1850, 01 May 2013, Peer-reviwed
Scientific journal, English

Effect of extended pi-conjugation on photovoltaic performance of dye sensitized solar cells based on unsymmetrical squaraine dyes
Shyam S. Pandey; Rie Watanabe; Naotaka Fujikawa; Gururaj M. Shivashimpi; Yuhei Ogomi; Yoshihiro Yamaguchi; Shuzi Hayase
TETRAHEDRON, PERGAMON-ELSEVIER SCIENCE LTD, 69, 12, 2633-2639, Mar. 2013, Peer-reviwed, Aiming toward the far-red to near infra-red (NIR) photon harvesting, three new unsymmetrical squaraine dyes bearing direct ring carboxy functionalized indole as an anchoring moiety with varying donor groups with extended pi-conjugation have been successfully synthesized and utilized for dye sensitized solar cell fabrication. Under simulated solar irradiation, dye SQ-8 gave a photoconversion efficiency of 3.3% mainly harvesting photons in the far-red region between 500 and 700 nm. By extending the pi-conjugation of the donor moieties in the novel unsymmetrical squaraine dyes, it was possible to extend the light absorption from far-red to NIR wavelength region. In spite of good light absorption up to 900 nm and energetic matching, dye SQ-16 was found to exhibit the decreased photon harvesting, which was explained by the enhanced dye aggregation along with its difficulty in facile electron injection as indicated from electronic absorption spectroscopic and DFT calculation results, respectively. (C) 2013 Elsevier Ltd. All rights reserved.
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
Byung-wook Park; Qing Shen; Yuhei Ogomi; Shyam S. Pandey; Taro Toyoda; Shuzi Hayase
ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY, ELECTROCHEMICAL SOC INC, 2, 1, Q6-Q11, 2013, Peer-reviwed, High performance SnO2-based bottom electrodes are necessary for tandem dye-sensitized solar cells (DSSCs) harvesting infrared (IR) lights. Sensitizing dyes based on macrocyclic ligands are one of the candidates among the IR dyes. However, it is difficult to introduce anchoring groups such as carboxylic acid at the right position of macrocyclic rings where electron injection occurs. It was proved that axially anchored phthalocyanines (model compounds) bonded to SnO2 nanoparticle surfaces with short metal-O-metal linkage inject electrons from dyes to SnO2 layers spatially, because themacrocyclic rings are very close to SnO2 surfaces. TiO2 based DSSCs did not show photovoltaic properties because of very fast charge recombination between injected electrons and oxidized dyes which were measured by a transient absorption spectroscopy technique. In the case of SnO2-based DSSC, the charge recombination was slower than that of the TiO2-based DSSCs, which enabled the collection of electrons. Since this anchoring system can be prepared easily, it is a good strategy for use in the design of near-IR absorbing dye. (C) 2012 The Electrochemical Society. All rights reserved.
Scientific journal, English

Solution processable thin film organic photovoltaic cells based on far red sensitive soluble squaraine dyes
Shyam S. Pandey; Takafumi Mizuno; Sandeep Kumar Das; Yuhei Ogomi; Shuzi Hayase
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 522, 401-406, Nov. 2012, Peer-reviwed, Symmetrical squaraine (SQ) dyes with varying alkyl chain lengths have been synthesized towards their utilization as sensitizer for enhancing the photon harvesting in far-red region of solar spectrum. It has been observed that energy level of the SQ-dyes can be systematically tuned only by alkyl chain substitution. It has also been shown that SQ-dyes behave like p-type donors forming a p-n heterojunction with soluble fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) as n-type organic electron acceptor. Thin film organic photovoltaic p-n heterojunction devices have been fabricated using soluble SQ-dyes with PCBM without using any thermal evaporation technique for the active layers. A perusal of the photo-action spectra clearly corroborates that at least 0.25 eV energy barrier is necessary for the facile electron transfer from donor moiety to the acceptor after the photo-excitation. (C) 2012 Elsevier B.V. All rights reserved.
Scientific journal, English

Electrophoretic deposition onto an insulator for thin film preparation toward electronic device fabrication
Shougo Miyajima; Shuichi Nagamatsu; Shyam S. Pandey; Shuzi Hayase; Keiichi Kaneto; Wataru Takashima
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 101, 19, Nov. 2012, Peer-reviwed, An electrostatic film fabrication method utilizing the dielectric layer, entitled dielectric barrier electrophoretic deposition (DBEPD) has been proposed. We demonstrated the fabrication of uniform organic semiconductor thin film onto any kind of substrate by DBEPD. Optical absorption spectra of colloidal poly(3-hexylthiophene) (P3HT) film prepared by DBEPD exhibited the clear vibrational structure attributed to highly ordered domains. It was in contrast to the relatively disordered structure as shown in the case of P3HT film prepared by conventional electrophoretic deposition (EPD). Organic field effect transistors fabricated by each method showed similar organic field effect transistor characteristics, however, the uniformity of DBEPD film was superior to EPD film. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4766126]
Scientific journal, English

Relating the Photodynamics of Squaraine-Based Dye-Sensitized Solar Cells to the Molecular Structure of the Sensitizers and to the Presence of Additives
G. de Miguel; M. Marchena; B. Cohen; S. S. Pandey; S. Hayase; A. Douhal
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 116, 42, 22157-22168, Oct. 2012, Peer-reviwed, Dye-sensitized solar cells (DSSCs) fabricated with TiO2 nanoparticle thin films and sensitized with four types of indole-based squaraines, SQs (symmetric or asymmetric and varying the length and nature of the alkyl side chain substituents), have been prepared. We have studied the influence of the presence of different additives in the electrolyte solutions (tert-butyl pyridine and/or Li+ cations) on the electron transfer dynamics by means of femtosecond transient absorption spectroscopy and flash photolysis. We obtained the rate constants for the electron injection, k(ei) = 2, 3, 8, and 14 x 10(10) s(-1), for complete solar cells with an iodide-based electrolyte. The asymmetric SQ showed the largest k(ei), value, 14 x 10(10) s(-1), in line with a unidirectional flow of electrons from the lowest unoccupied molecular orbital (LUMO) orbital of the SQ to the sub-bandgap states of the TiO2, which leads to a more efficient electron injection than that in the symmetric SQs. Addition of tert-butyl pyridine to the electrolyte solution (I-/I-3(-) in acetonitrile) causes a 5-10-fold deceleration of the electron injection (for example, tau(obs) = 2-11 ps in SQ 41). When including the Li+ cation together with the tert-butyl pyridine, the injection is still slower than in cells without any additive (tau(obs) = 2-11 ps in SQ 41), which reflects a stronger influence of the tertbutyl pyridine in the electron injection process. The effective lifetimes for the charge regeneration reaction, tau(obs), range from 2 to 25 mu s for the complete cells with an iodide-based electrolyte. The fastest regeneration occurs in the SQs with the CF3-groups anchored to the side chains and, especially in SQ 26, with two CF3-groups. This result suggests that the inductive effect of the CF3- groups in the structure of SQ 26 and SQ 41 leads to a higher positive charge density in the pi-conjugated system, which promotes a higher local concentration of iodide near the oxidized dye and therefore faster regeneration kinetics. Moreover, addition of Li+ cations to the electrolyte accelerates the regeneration reaction, which is ascribed to its interaction with the backbone of the SQ, favoring the approach of the I- species. Using the transient absorption results, we calculated the electron injection efficiency phi(ei) and compared it with the short-circuit current density, J(sc), of the complete cells. Thus, in the complete cells sensitized with SQ 41 and SQ 4, (phi(ei) are the highest ones and present comparable values, 0.93 and 0.90, respectively. On the contrary, cells sensitized with SQ 26 and SQ 2 present lower values, 0.47 and 0.75, respectively. A similar tendency is observed for the values of J(sc). On the basis of this good correlation (phi(ei) vs J(sc)), we can suggest that the electron injection reaction is partially responsible for the photon losses and derive the reasons why this occurs.
Scientific journal, English

Dye Sensitized Solar Cells Based on Novel Far Red Sensitizing Unsymmetrical Squaraine Dye Containing Pyrroloquinoline Moiety
Shyam S. Pandey; Naotaka Fujikawa; Rie Watanabe; Yuhei Ogomi; Yoshihiro Yamaguchi; Shuzi Hayase
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 51, 10, Oct. 2012, Peer-reviwed, A novel far-red sensitive and direct aromatic ring carboxy functionalized unsymmetrical squaraine dye based on pyrroloquinoline moiety has been synthesized for the application as sensitizer of dye sensitized solar cells. This dye bearing the characteristics of both of indole and quinoline moieties exhibits the photon harvesting up to 820 nm. The enhancement in the photon harvesting window by the pyrroloquinoline based squaraine dye was attributed to the presence of increased pi-conjugation in its pyrroloquinoline donor part. This pyrroloquinoline bearing unsymmetrical squaraine dye exhibits a short circuit current density of 9.88 mA/cm(2), an open circuit voltage of 0.57 V and fill factor of 0.59 leading to the external power conversion efficiency of 3.33% under simulated solar irradiation of 100 mW/cm(2) at AM 1.5 condition. (C) 2012 The Japan Society of Applied Physics
Scientific journal, English

Differences in Dye-Sensitized Photovoltaic Behaviors between SnO2 and TiO2 Electrodes
Kengo Sadamasu; Yuhei Ogomi; Shyam S. Pandey; Shuzi Hayase
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 51, 10, Oct. 2012, Peer-reviwed, A SnO2 electrode is a promising candidate for a bottom electrode of dye-sensitized solar cells. One of the drawbacks is its low fill factor (FF). We clarified the cause of this low FF using our original hybrid cells consisting of carrier generation areas (a bottom layer consisting of TiO2/a dye layer) and carrier transport areas (a top layer consisting of SnO2 with and without a dye layer). A large decrease in FF was observed only when the SnO2 charge transport areas were covered by photo excited dyes, leading to the conclusion that back electron transfer reaction from SnO2 to oxidized dyes is a major route for the charge recombination. This was also confirmed by electron lifetime and dark current measurements. (C) 2012 The Japan Society of Applied Physics
Scientific journal, English

Novel unsymmetrical squaraine dye bearing cyanoacrylic acid anchoring group and its photosensitization behavior
Gururaj M. Shivashimpi; Shyam S. Pandey; Rie Watanabe; Naotaka Fujikawa; Yuhei Ogomi; Yoshihiro Yamaguchi; Shuzi Hayase
TETRAHEDRON LETTERS, PERGAMON-ELSEVIER SCIENCE LTD, 53, 40, 5437-5440, Oct. 2012, Peer-reviwed, Aiming toward the development of far-red sensitive organic dyes, unsymmetrical squaraine dye bearing direct cyanoacrylate functionalized indole ring has been synthesized and characterized along with its utilization as photosensitizer for dye-sensitized solar cells. Upon dye-sensitized solar cell fabrication, this sensitizer exhibits its potentiality as a good far-red sensitive dye having photoconversion efficiency of 5.03% under the simulated solar irradiation at AM 1.5 conditions. This opens up further possibility to design efficient far-red sensitive dyes by judicious implementation of suitable donor moieties with extended it-conjugation. (C) 2012 Elsevier Ltd. All rights reserved.
Scientific journal, English

Femto- to Millisecond Photophysical Characterization of Indole-Based Squaraines Adsorbed on TiO2 Nanoparticle Thin Films
G. de Miguel; M. Marchena; M. Ziolek; S. S. Pandey; S. Hayase; A. Douhal
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 116, 22, 12137-12148, Jun. 2012, Peer-reviwed, In this paper, we address femto- to millisecond transient absorption studies of TiO2 nanoparticle (NP) thin films sensitized with four squaraine (SQ) molecules, with and without a deaggregating agent, chenodeoxycholic acid (CDCA). On the femto- to picosecond time scale, we determined the presence of three transient species by using singular value decomposition (SVD) analysis, i.e., S-1 of the SQ monomers, S-1 of the SQ H-aggregates, and the SQ radical cation formed after the electron injection. Both monomers and H-aggregates are proven to inject electrons to the TiO2 conduction band, being 5 times faster in the monomers (e.g., k(ei)(mon) = 5.1 x 10(11) s(-1) and k(ei)(H-agg) = 1.1 x 10(11) s(-1) for SQ 41). Besides, the undesired singlet-singlet annihilation is an active process in these samples, constituting the drain of a high percentage of the absorbed photons. The coadsorption of CDCA on the TiO2 NP avoids the formation of H-aggregates, and therefore, only two transient species are present in these samples: S-1 of the monomer and the SQ radical cation with k(ei)(mon) = 6.7 x 10(11) s(-1) for SQ 41. On the microsecond scale, we only observed the transient feature of the radical cation of the SQ that permits one to study its recombination dynamics. Similar lifetimes (94-150 mu s) of the four SQ radial cations are obtained when only monomers are present in the sample. In the absence of CDCA, the presence of H-aggregates contributes to shorten the lifetime of the radical cation (e.g., from 110 to 45 mu s in the case of SQ 41). This fact can be explained by considering a stronger electronic coupling of H-aggregates/TiO2 surface with respect to the monomers. These results explore the photodynarnics of this family of SQs adsorbed on TiO2 NP in a very large time window and will enable a better understanding of the influence of aggregates in the kinetics of these SQ used as sensitizers in DSSCs.
Scientific journal, English

Photophysics of H- and J-Aggregates of Indole-Based Squaraines in Solid State
G. de Miguel; M. Ziolek; M. Zitnan; J. A. Organero; S. S. Pandey; S. Hayase; A. Douhal
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 116, 17, 9379-9389, May 2012, Peer-reviwed, The photodynamics of six types of indole-based squaraines (SQs) molecules deposited onto quartz substrates by using the spin-coating method have been studied by means of steady-state and time-resolved techniques. Enhanced scattering signal at the resonance wavelengths together with the broadening and shift of the absorption bands to the red side with respect to those in solution prove the formation of H- and J-aggregates in the thin film samples. Excited state deactivation dynamics were studied by the femtosecond (fs) transient absorption spectroscopy and nanosecond (ns) flash photolysis. Faster kinetics were obtained for the solid state samples as compared to those in solution. Singular value decomposition (SVD) analysis of the Is transient signal proves the presence of monomers and aggregates, enabling the separation of the kinetics for each one. For the SQ monomers, the dynamics of the singlet excited state does not depend on the pump fluence, and we thus propose that the quenching of the excited monomers is due to an energy transfer process to the aggregates. For the SQ aggregates, nonexponential fit of the experimental time profiles along with the power dependence of the transient absorption signal indicates a singlet-singlet annihilation process (gamma' approximate to 3 x 10(-15) cm(3) s(-1/2)). The combination of the long-range Forster-type mechanism and quantum delocalization is found to be the physical process that accounts for the singlet-singlet annihilation. In the flash photolysis experiments, we observed transient signals with a maximum intensity at 710 nm and lifetimes of 30 and 35 ns for SQ 41 and SQ 26, respectively. We have attributed these signals to the cis photoisomers of the aggregates deactivating to the trans photoisomers through the back photoisomerization reaction. These results provide information for a better understanding of the photodynamics of squaraines.
Scientific journal, English

Research Trend Aiming at High Efficiency Organic Solar Cells
HAYASE Shuzi
The Journal of Japan Institute for Interconnecting and Packaging Electronic Circuits, The Japan Institute of Electronics Packaging, 15, 3, 175-179, 01 May 2012
Japanese

Femto to millisecond observations of indole-based squaraine molecules photodynamics in solution
G. de Miguel; M. Marchena; M. Zitnan; S. S. Pandey; S. Hayase; A. Douhal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 14, 5, 1796-1805, 2012, Peer-reviwed, We present femto-to-millisecond studies of the photodynamics of seven types of indole-based squaraine molecules (SQs) in solvents of different H-bonding ability and viscosity. These SQs can be classified into two families: SQs with two carboxylic groups in the side indole groups (symmetrical SQs) and with only one carboxylic group (asymmetrical SQs). Steady-state absorption and fluorescence techniques show narrow absorption and emission bands, with a small Stokes shift (about 300 cm(-1)). The femtosecond transient absorption spectra give a very short (similar to 100 fs) dynamics (assigned to IVR) and the associated spectra show two excited species assigned to two stereoisomers. A trans-cis photoisomerization occurs in a very fast time through a conical intersection. Pico-to-nanosecond emission experiments also reveal the presence of two fluorescing trans stereoisomers whose lifetimes show similar sensitivities to the nature of solvent. For example, lifetimes of 1.72, 0.46 and 0.29 ns were determined for the trans photoisomer of the SQ 41 in triacetin, dichloromethane and acetonitrile, respectively, reflecting the short decay of the S-1 state in highly polar and low viscous solvents. Flash photolysis experiments gave the transient absorption signals of the cis photoisomer that is formed after the twisting process at S-1. The cis-to-trans photoisomerization at the ground state happens in the mu s time scale (1-4 mu s), and it depends on the H-bonding ability and viscosity of the solvent. Thus, combining fs-ns and ns-mu s experiments suggests that in the conical intersection region, only a small fraction of the twisted trans isomers are converted to the cis ones in the excited states. These results bring detailed and global insight into the large time window photodynamics of this family of SQs in solution.
Scientific journal, 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

Dye adsorption feature on titania surface and role of dye aggregation inhibitor monitored by quartz crystal microbalance (QCM)
Ryohei Hirota; Yuehi Ogomi; Shyam S. Pandey; Shuzi Hayase
ORGANIC PHOTOVOLTAICS XIII, SPIE-INT SOC OPTICAL ENGINEERING, 8477, 2012, Peer-reviwed
International conference proceedings, English

Flexible transparent conductive oxide-less flat and cylinder dye-sensitized solar cells
Jun Usagawa; Takeshi Kogo; Kengo Sadamasu; Shyam S. Pandey; Yuhei Ogomi; Shuzi Hayase
JOURNAL OF PHOTONICS FOR ENERGY, SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2, 2012, Peer-reviwed, Fabrication and photovoltaic performances for flexible transparent conductive oxide-less (TCO-less) flat and cylinder dye-sensitized solar cells (DSCs) are reported. The cylinder solar cell consists of a porous silicone tube, a protected stainless steel metal mesh (protected SUS mesh) working as a counter electrode, a gel electrolyte sheet, a dye/porous titania layer fabricated on a protected SUS mesh working as a anode, and a thermally shrinkable plastic tube, from the inside to the outside. The thermally shrinkable tube was used to reduce the gap between a cathode and an anode. In addition, a porous silicone tube was used for injecting electrolytes smoothly into the gel electrolyte layer. 5.08% efficiency (FF: 0.68; Voc: 0.68 V; Jsc: 11.07 mA/cm(2)) was observed. A flexible TCO-less flat DSCs with 6.1% efficiency which was improved by narrowing a gap between two electrodes is also reported. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JPE.2.021011]
Scientific journal, English

Aiming at High Efficiency Dye-Sensitized Solar Cells - From the View Point of Photoconversion Interface
Shuzi Hayase; Yuhei Ogomi; Shyam S. Pandey
ELECTROCHEMISTRY, ELECTROCHEMICAL SOC JAPAN, 79, 10, 761-767, Oct. 2011, Peer-reviwed, Researches aiming at high efficiency-dye-sensitized solar cells (DSC) are reviewed from the view point of photoconversion interfaces. Developments of dyes converting photons to electrons in near infrared regions are essential for increasing short circuit current (JSC). Hybrid cells consisting of double dye structures and double titania layer structures are proposed. Leak currents at photoconversion interfaces decrease open circuit voltage (VOC) and fill factor (FF). Therefore, strategies for decreasing leak currents are essential, especially for all-solid DSCs and I-/I-3(-) free DSCs. Structures of these interfaces are discussed in terms of surface passivation, self-organization. dye structures, interactions between dyes and I-3(-) in titania nanopores. Fundamental studies for tandem cells are also reported.
Scientific journal, English

Investigating the Role of Dye Dipole on Open Circuit Voltage in Solid-State Dye-Sensitized Solar Cells
Shyam S. Pandey; Kyung-Young Lee; Azwar Hayat; Yuhei Ogomi; Shuzi Hayase
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 50, 6, Jun. 2011, Peer-reviwed, To eliminate the possibility of perturbation caused by a liquid electrolyte and predict the role played by the nature of dipole of sensitizers with respect to the observed open circuit voltage (V-oc) in dye-sensitized solar cells (DSSCs) more precisely, solid-state DSSCs were fabricated using different sensitizing dyes. Results obtained by surface potential measurement indicate that increasing the alkyl chain length in symmetrical squaraine dyes leads to a relatively positive shift in surface potential. The use of dyes exhibiting higher surface potentials leads to the observation of increased V-oc, which has been explained by the dye dipole formation at the TiO2/hole transporting layer interface leading to an upward shift of the TiO2 conduction band. It is thus possible to obtain a high V-oc in DSSCs by designing new dyes either having long alkyl chains or a molecular structure having a higher dipole moment exhibiting a relatively positive shift in surface potential. (C) 2011 The Japan Society of Applied Physics
Scientific journal, English

Fabrication of Electron Passes in Nano-TiO2 Layer by High-Velocity Oxy-Fuel Method for Dye-Sensitized Solar Cells
Terumi Nishimura; Daishiro Nomura; Shohhei Sakaguchi; Hideaki Nagayoshi; Shuzi Hayase
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 50, 2, Feb. 2011, Peer-reviwed, Necking among titania nanoparticles in porous titania layers of dye-sensitized solar cells (DSC) was carried out by the collision of nanoparticles in a very fast gas flow of more than 1000-1500 m/s. where the substrate was held in an ambient atmosphere. The rapid gas flow was obtained by a high velocity oxy-fuel method (HVOF) operated at an intermediate temperature. The photovoltaic performance of a cell prepared by the HVOF method was slightly lower than that of DSCs fabricated by a conventional method involving coating-baking processes. The slightly low efficiency was explained by the small dye load and slightly lower electron diffusion coefficient in a porous titania layer. The time needed for fabricating a nanoporous titania layer (10 x 10 cm(2)) by the HVOF method was only a few minutes and was extremely shortened from the 2 h needed in the case of conventional coating and heating processes, which demonstrates that the HVOF method is useful for necking titania nanoparticles within an extremely short time. (C) 2011 The Japan Society of Applied Physics
Scientific journal, English

Hybrid Dye-Sensitized Solar Cells Consisting of Double Titania Layers for Harvesting Light with Wide Range of Wavelengths
Kengo Sadamasu; Takafumi Inoue; Yuhei Ogomi; Shyam S. Pandey; Shuzi Hayase
APPLIED PHYSICS EXPRESS, JAPAN SOC APPLIED PHYSICS, 4, 2, Feb. 2011, Peer-reviwed, We report a hybrid dye-sensitized solar cell consisting of double titania layers (top and bottom layers) stained with two dyes. A top layer fabricated on a glass was mechanically pressed with a bottom layer fabricated on a glass cloth. 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. (C) 2011 The Japan Society of Applied Physics
Scientific journal, English

One-Dimensional Nanostructure Arrays for Dye-Sensitized Solar Cells
Patcharee Charoensirithavorn; Takashi Sagawa; Shuzi Hayase; Susumu Yoshikawa
JOURNAL OF SOLAR ENERGY ENGINEERING-TRANSACTIONS OF THE ASME, ASME-AMER SOC MECHANICAL ENG, 133, 1, Feb. 2011, Peer-reviwed, This article reports the fabrication of ordered arrays of ZnO nanorods and TiO2 nanotubules by using a simple solution-based method and the application of these arrays as the working electrodes in dye-sensitized solar cells (DSCs) with an aim of offering superior electron transport conduits than in the conventional nanocrystalline nanoparticle films. The faster charge transport and lower recombination properties of one-dimensional (1D) nanostructure array electrodes as compared with those of the nanoparticle one observed and proved that such arrays of 1D nanostructure are the more promising electrode for DSCs in the future. [DOI: 10.1115/1.4001153]
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

Bis(alkyl-thiophene) thienothiophene as hole-transport organic semiconductor
Kazuhiro Takamiya; Shuhei Ishikawa; Daisuke Adachi; Shinya Oku; Shuichi Nagamatsu; Wataru Takashima; Shuzi Hayase; Keiichi Kaneto
9TH INTERNATIONAL CONFERENCE ON NANO-MOLECULAR ELECTRONICS, ELSEVIER SCIENCE BV, 14, 2011, Peer-reviwed, pi-conjugated low-molecules having the chemical structure of bis(alkyl-thiophene)thienothiophene, abbreviated as, C6-BTTT and C12-BTTT were synthesized and evaluated in their thermal, optical and electronic characteristics. Compounds were synthesized according with Suzuki reaction or Stille reaction. Thermal analysis represents both of C6- and C12-BTTTs did not possess liquid-crystalline phase. Comparison of hole transport characteristics shows a relative high hole transport in C6-BTTT and high air-stability in C12-BTTT, representing a contribution of alkyl-substituent. (C) 2010 Published by Elsevier B.V.
International conference proceedings, English

Transparent conductive oxideless tandem dye-sensitized solar cells consisting of light-splitting structures
Jun Usagawa; Masaki Kaya; Yuhei Ogomi; Shyam S. Pandey; Shuzi Hayase
JOURNAL OF PHOTONICS FOR ENERGY, SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 1, 2011, Peer-reviwed, Fiber and pillar tandem dye-sensitized solar cells (DSCs), which do not need transparent conductive oxideless layer tandem cells (TCO-less TAN), are fabricated and their fundamental tandem properties are evaluated. TCO-less TAN cells consist of a light-splitting waveguide and TCO-less DSCs. The TCO-less DSC is composed of a nanoporous titania back-contacted with a porous Ti electrode or a nanoporous titania sheet supported by a stainless steel mesh whose surface was protected with TiOx thin layers. Two kinds of light-splitting structures are introduced. One is a light-splitting structure in which polystyrene particles with different diameters are dispersed in water. The other consists of dichroic mirrors. These light-splitting structures are coupled with TCO-less DSCs stained with dyes absorbing light corresponding to these split lights. Open circuit voltages (V-oc) of these TCO-less tandem DSCs are two times (two tandem structure) or three times (three tandem structure) higher than those of the corresponding single cells, demonstrating that these structures work as tandem cells. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3555458]
Scientific journal, English

Fine tuning the structure of unsymmetrical squaraine dyes towards the development of efficient dye-sensitized solar cells
Shyam S. Pandey; Rie Watanabe; Naotaka Fujikawa; Yuhei Ogomi; Yoshihiro Yamaguchi; Shuzi Hayase
NEXT GENERATION (NANO) PHOTONIC AND CELL TECHNOLOGIES FOR SOLAR ENERGY CONVERSION II, SPIE-INT SOC OPTICAL ENGINEERING, 8111, 2011, Peer-reviwed, Creation of molecular asymmetry in the organic sensitizing dyes has been demonstrated for enhancing the photoconversion efficiency due to unidirectional flow of electron after the photoexcitation. Molecular structures for direct indole ring carboxy-functionalized unsymmetrical squaraine dyes have been optimized by fine tuning the molecular structures and judicious selection of the substituents to prevent the dye aggregation and electron recombination. Best efficiency of 4.42 % was achieved for unsymmetrical squaraine dye SQ-64 with a short circuit current density of 11.22 mA/cm2, a fill factor of 0.61 and an open circuit voltage of 0.64 V under standard AM 1.5 simulated solar irradiation.
International conference proceedings, English

Relationship Between I-3(-) Diffusion in Titania Nanopores Modified with Dyes and Open Circuit Voltage of Dye-Sensitized Solar Cell
Azwar Hayat; Shyam S. Pandey; Yuhei Ogomi; Shuzi Hayase
JOURNAL OF THE ELECTROCHEMICAL SOCIETY, ELECTROCHEMICAL SOC INC, 158, 7, B770-B771, 2011, Peer-reviwed, Relative diffusion rates (R-rel) of I-3(-) species in titania nanopores modified with various dye molecules were measured. Introduction of polar atoms such as O or F decreased R-rel and open circuit voltage (V-oc) of dye-sensitized solar cells (DSC). The results were explained by the fact that slow diffusion of I-3(-) species in nanopores increases opportunities of charge recombination between electrons in titania layer and I-3(-) existing in the titania nanopores. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3583638] All rights reserved.
Scientific journal, English

Electron Injection from Linearly Linked Two Dye Molecules to Metal Oxide Nanoparticles for Dye-Sensitized Solar Cells Covering Wavelength Range from 400 to 950 nm
Byung-wook Park; Takafumi Inoue; Yuhei Ogomi; Akari Miyamoto; Shinsuke Fujita; Shyam S. Pandey; Shuzi Hayase
APPLIED PHYSICS EXPRESS, JAPAN SOC APPLIED PHYSICS, 4, 1, Jan. 2011, Peer-reviwed, y We report a hybrid dye system, in which two dyes are linked linearly by a metal-O-metal linkage, for dye sensitized solar cells (cell-NcSn-N719). 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(2,20-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 cell-NcSn-N719 suggested that electrons are injected from both N719 and NcSn to SnO(2) nanoparticles. (C) 2011 The Japan Society of Applied Physics
Scientific journal, English

Tandem dye-sensitized solar cells consisting of floating electrode in one cell
Kenshiro Uzaki; Shyam S. Pandey; Shuzi Hayase
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 216, 2-3, 104-109, Dec. 2010, Peer-reviwed, Tandem dye-sensitized solar cells (Cell TAN) consisting of a floating electrode (bottom cell) and a TiO(2) electrode prepared on a F-doped SnO(2) glass (top cell) are reported. The floating electrode is a flexible and self-standing composite film consisting of a porous titania/dye layer supported by a mesh electrode. The floating electrode was inserted between the TiO(2) electrode and the counter electrode in a conventional single dye-sensitized solar cell to fabricate the Cell TAN. Therefore, the Cell TAN is completely different from previously reported tandem cells where two cells are merely accumulated and connected to each other. The Incident Photon to Current Conversion Efficiency (IPCE) curve for the Cell TAN had two peaks corresponding to those of the two single cells. The open circuit voltage (V(oc)) of the Cell TAN (0.88 V) was higher than that of the corresponding single cell (0.6-0.66 V). These two results strongly demonstrated that the Cell TAN has a potential for tandem cells. (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English

Probing mechanism of dye double layer formation from dye-cocktail solution for dye-sensitized solar cells
Yuhei Ogomi; Shyam S. Pandey; Shunta Kimura; Shuzi Hayase
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 519, 3, 1087-1092, Nov. 2010, Peer-reviwed, Absorption of photon in wide wavelength region is an important requirement for the enhancement of photoconversion efficiency of dye-sensitized solar cells (DSSC). Lack of photon absorption from visible to NIR wavelength region by a single dye requires the use of plural dyes for the panchromatic sensitization of nanoporous TiO(2). To our incredible surprise, when a dye cocktail of organic dye NK3705 and inorganic ruthenium based dye Z907 was implied for the dye adsorption, it led to the formation of dye double layer in spite of random arrangement of two dyes as evidenced from confocal laser microscopic investigations. Investigation pertaining to the evaluation of rate of dye adsorption and dye desorption for different organic and inorganic sensitizing dyes suggests that a combination of one dye with faster diffusion along with weak binding on TiO(2) surface and another dye with slow diffusion along with strong binding leads to the formation of dye double layer from a dye mixture by a simple dipping process. (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English

Alkyl and fluoro-alkyl substituted squaraine dyes: A prospective approach towards development of novel NIR sensitizers
Shyam S. Pandey; Takafumi Inoue; Naotaka Fujikawa; Yoshihiro Yamaguchi; Shuzi Hayase
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 519, 3, 1066-1071, Nov. 2010, Peer-reviwed, Alkyl and fluoroalkyl substituted symmetrical and unsymmetrical squaraine dyes have been synthesized for the fabrication of dye-sensitized solar cells (DSSC) based on nanoporous TiO(2). Results of DSSC performance clearly indicate that introduction of molecular asymmetry and increase in the alkyl chain length of the squaraine sensitizers leads to the enhancement in the photovoltaic performance. A perusal of photo-action spectra of squaraine sensitizer corroborates that introduction of molecular asymmetry and fluoroalkyl substitution leads to hampering of blue-shifted H-aggregate formation. Estimation of energy of HOMO and LUMO for these squaraine sensitizers used in the present investigation indicates that about 0.16 eV is sufficient for electron injection from photoexcited dye to TiO(2) conduction band and dye regeneration. (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English

Tandem Dye-Sensitized Solar Cells Consisting of Nanoporous Titania Sheet
Kenshiro Uzaki; Shyam S. Pandey; Yuhei Ogimi; Shuzi Hayase
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 49, 8, Aug. 2010, Peer-reviwed, Tandem dye-sensitized solar cells consisting of two electrodes in one cell are reported A tandem cell (Cell TAN OF or Cell TAN St) has a floating electrode (bottom cell) and a TiO(2) electrode prepared on a F-doped SnO(2) glass substrate (top cell) The floating electrode is a flexible and self-standing composite film consisting of a porous titania/dye layer supported by a glass mesh sheet or a stainless-steel mesh sheet The incident photon-to-current conversion efficiency (IPCE) curves for Cell TAN GF and Cell TAN St had two peaks corresponding to the visible absorption of the two dyes The open circuit voltages (V(oc)) of Cell TAN OF and Cell TAN St were 0 82 and 0 88 V. respectively, which were higher than that of the corresponding single cell (0 6-0 64V). These results demonstrated that both Cell TAN OF and Cell TAN St can be used as tandem cells The fact that the V(oc) of Cell TAN GF is almost the same as that of Cell TAN St leads to the conclusion that a conductive layer is not necessarily needed for the bottom electrode (C) 2010 The Japan Society of Applied Physics
Scientific journal, English

Substituent effect in direct ring functionalized squaraine dyes on near infra-red sensitization of nanocrystalline TiO2 for molecular photovoltaics
Shyam S. Pandey; Takafumi Inoue; Naotaka Fujikawa; Yoshihiro Yamaguchi; Shuji Hayase
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 214, 2-3, 269-275, Aug. 2010, Peer-reviwed, We have synthesized a series of novel blue colored symmetrical squaraine sensitizers with variable alkyl chain length for their application towards the fabrication of dye-sensitized solar cells (DSSCs). It has been found that an increase in the alkyl chain length substituted at N-position of indole ring exhibits enhanced electron diffusion length and electron life-time resulting in better passivation of nanocrystalline TiO2 surface leading to enhancement in the cell performance. Based on HOMO and LUMO energy measurement of squaraine dyes, it has been demonstrated that about 0.16 eV energy barrier is sufficient for electron injection from LUMO of dye to TiO2 conduction band and dye regeneration after photo-excitation. Performances of DSSCs using model squaraine dyes indicate that dodecyl alkyl substituent is optimum giving highest Voc and use of chenodeoxycholic acid along with the dye SQ-4 shows a photoconversion efficiency of 3.5% under AM 1.5 irradiation. (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English

Synthesis and characterization of squaric acid based NIR dyes for their application towards dye-sensitized solar cells
Takafumi Inoue; Shyam S. Pandey; Naotaka Fujikawa; Yoshihiro Yamaguchi; Shuji Hayase
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 213, 1, 23-29, Jun. 2010, Peer-reviwed, Synthesis of novel cyan-colored sensitizing dyes bearing squaric acid core and 2,3,3-trimethyl-indole as terminal moieties has been conducted in order to fabricate dye-sensitized solar cells based on nanoporous TiO(2). It has been found that position of COOH functionality utilized for anchoring with TiO(2) surface has a marked effect on solar cell performance. Carboxylic acid group directly substituted to indole ring gave about 5-fold higher conversion efficiency as compared to the dye when it was substituted in alkyl chain of the indole ring. Efficiency has been found to be hampered due to aggregation and enhancement in the efficiency was observed when dyes were used with chenodeoxycholic acid (CDCA). Using COCA and long alkyl substituent at the N-position of indole ring to prevent aggregation and enhanced TiO(2) surface passivation, respectively, has achieved a solar conversion efficiency of 3.15% with a short circuit current density of 7.26 mA/cm(2), an open circuit voltage of 0.64 V and a fill factor of 0.68 for SQ-5 under standard AM 1.5 solar irradiation. (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English

Dye-Sensitized Solar Cells Consisting of 3D-Electrodes-A Review: Aiming at High Efficiency From the View Point of Light Harvesting and Charge Collection
Kenshiro Uzaki; Terumi Nishimura; Jun Usagawa; Shuzi Hayase; Mitsuru Kono; Yoshihiro Yamaguchi
JOURNAL OF SOLAR ENERGY ENGINEERING-TRANSACTIONS OF THE ASME, ASME, 132, 2, May 2010, Peer-reviwed, Directions to high efficiency dye-sensitized solar cells (DSCs) are reviewed in terms of light harvesting and charge collection. Three dimensional DSCs characterized by a double dye layer electrode, a floating electrode, and a fiber type electrode are proposed. The potentiality of each structure was discussed by using each model cell. Transparent conductive layerless electrodes were the key structures in these cells. Fabrication processes and fundamental performances are reported. Finally, it is concluded that dyes having high photoconversion efficiency in the near IR and IR regions are essential for realizing these tandem and hybrid cells. [DOI: 10.1115/1.4001182]
Scientific journal, English

Influence of nature of surface dipoles on observed photovoltage in dye-sensitized solar cells as probed by surface potential measurement
Shyam S. Pandey; Shohei Sakaguchi; Yoshihiro Yamaguchi; Shuji Hayase
ORGANIC ELECTRONICS, ELSEVIER SCIENCE BV, 11, 3, 419-426, Mar. 2010, Peer-reviwed, A contact free method of surface potential measurement using scanning Kelvin-probe microscopy (SKPM) was conducted to probe the nature of nanocrystalline TiO(2)/dye interface. In combination with electrical measurements an effort has been made to establish a correlation between the nature of sensitizing dye and observed surface potential with open circuit voltage (Voc) after dye-sensitized solar cell (DSSC) fabrication. Effect of chenodeoxycholic acid (DCA) as co-adsorbent with dyes upon the enhancement of DSSC efficiency has been probed by SKPM, which revealed a positive shift of surface potential upon treatment of thin films of TiO(2) with DCA. The enhancement of DSSC performance upon DCA introduction has been explained by upward shift of TiO(2) conduction band edge leading to enhanced Voc along with the prevention of pi-stacked aggregation resulting in enhanced short-circuit current density. (C) 2009 Elsevier B.V. All rights reserved.
Scientific journal, English

TCO-less 3D-DYE-sensitized solar cells consisting of charge separation sheet and direction to high efficiency cells by using TCO-less structure
Jun Usagawa; Kenshiro Uzaki; Sham S. Pandey; Yuhei Ogomi; Yoshihiro Yamaguchi; Mitsuru Kono; Shuzi Hayase
Conference Record of the IEEE Photovoltaic Specialists Conference, 518-522, 2010, Three dimensional transparent conductive oxide-less dye-sensitized solar cells (3D-TCO-less DSCs) consisting of a flexible porous titania sheet are reported. The flexible titania sheet is composed of a dye stained porous titania layer and a mesh sheet acting as the backbone. Flexible TCO-less DSCs, tandem DSCs, TCO-less cylinder DSCs and TCO-Iess cubic DSCs are fabricated and their fundamental photovoltaic performances are reported. © 2010 IEEE.
International conference proceedings, English

TCO-less 3D dye-sensitized solar cells consisting of charge separation sheet -tandem, hybrid, cylinder and fiber cells-
Jun Usagawa; Kenshiro Uzaki; Masaki Kaya; Takeshi Kougo; Sham S. Pandey; Yuhei Ogomi; Yoshihiro Yamaguchi; Mitsuru Kono; Shuzi Hayase
2010 10th IEEE Conference on Nanotechnology, NANO 2010, 171-175, 2010, Peer-reviwed, Three dimensional transparent conductive oxide-less dye-sensitized solar cells (3D-TCO-less DSCs) consisting of a flexible porous titania sheet are reported. The flexible titania sheet is composed of a dye stained porous titania layer and a mesh sheet acting as the backbone. Flexible TCO-less DSCs, tandem DSCs, TCO-less cylinder DSCs and TCO-less cubic DSCs are fabricated and their fundamental photovoltaic performances are reported. ©2010 IEEE.
International conference proceedings, English

Improvement of Dye-Sensitized Solar Cell Through TiCl4-Treated TiO2 Nanotube Arrays
Patcharee Charoensirithavorn; Yuhei Ogomi; Takashi Sagawa; Shuzi Hayase; Susumu Yoshikawaa
JOURNAL OF THE ELECTROCHEMICAL SOCIETY, ELECTROCHEMICAL SOC INC, 157, 3, B354-B356, 2010, Peer-reviwed, Titania nanotube arrays have been fabricated on a fluoride-doped tin oxide substrate by liquid phase deposition using ZnO nanorod arrays as a template and have been applied as the electrode for dye-sensitized solar cells (DSCs). The performance of DSCs based on TiO2 nanotube electrodes can be improved by treating the TiO2 nanotube arrays with titanium tetrachloride (TiCl4). Both the short-circuit current density and the conversion efficiency increased almost 2 times after the TiCl4 treatment. The TiCl4 treatment not only increased the amount of absorbed dyes but also enhanced the electron transport in the TiO2 films. TiCl4-treated TiO2 nanotube arrays with 4 mu m thickness showed a short-circuit current density of 8.37 mA/cm(2), an open-circuit voltage of 0.80 V, a fill factor of 0.67, and an overall conversion efficiency (eta) of 4.53%.
Scientific journal, English

Ambipolar Transport in Bilayer Organic Field-Effect Transistor Based on Poly(3-hexylthiophene) and Fullerene Derivatives
Takeomi Morita; Vipul Singh; Shinya Oku; Shuichi Nagamatsu; Wataru Takashima; Shuzi Hayase; Keiichi Kaneto
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 49, 4, 2010, Peer-reviwed, Ambipolar characteristics in an organic field-effect transistor (FET) with a bilayer structure consisting of poly(3-hexylthiophene) (P3HT) and a fullerene derivative (PCBM) are reported. P3HT was deposited by a floating film transfer method (FTM) with toluene solution on spin-coated PCBM. The FTM-deposited film was found to show relatively high hole mobility even when cast using toluene solution. Even after coating P3HT on PCBM by FTM, a relatively high n-type transport was obtained. This indicates that FTM employed in this study is a mild way to coat an organic thin film on an organic semiconductor layer in terms of minimizing the effect of carrier transport in the underlayer. The transport characteristics have been discussed in comparison with those of ambipolar FETs prepared by other methods previously reported. (C) 2010 The Japan Society of Applied Physics
Scientific journal, English

A Steady Operation of n-Type Organic Thin-Film Transistors with Cyano-Substituted Distyrylbenzene Derivative
Shuichi Nagamatsu; Tetsuji Moriguchi; Toshiya Nagase; Shinya Oku; Kouji Kuramoto; Wataru Takashima; Tatsuo Okauchi; Katsuhiro Mizoguchi; Shuji Hayase; Keiichi Kaneto
APPLIED PHYSICS EXPRESS, JAPAN SOCIETY APPLIED PHYSICS, 2, 10, 101502, Oct. 2009, Peer-reviwed, A novel n-type organic semiconductor, cyano-substituted distyrylbenzene derivative, 1,4-bis{2-[4-(trifluoromethyl)phenyl]acrylonitorile}-benzene, was synthesized by Knoevenagel condensation with aldehyde and acetonitrile derivatives. Fabricated thin-film transistors (TFTs) exhibited high electron field-effect mobility of 10(-2)-10(-1) cm(2) V(-1) S(-1), on/off current ratio of 6 x 10(5). Hysteresis-free n-type transport characteristics observed in this device promises a steady operation of organic logic circuit. Almost same TFT characteristic was observed even after 1 month storage in ambient condition. The findings indicate that the material has a good resistance to atmospheric oxidants. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/APEX.2.101502
Scientific journal, English

Dye-Sensitized Solar Cells : Present and Future
HAYASE Shuzi
Journal of The Adhesion Society of Japan, The Adhesion Society of Japan, 45, 8, 313-320, 01 Aug. 2009
Japanese

Electrochemiluminescence Devices Consisting of ZnO Nanorods Vertically Grown on Substrate
Tomohito Tanaka; Hiroshi Takishita; Takashi Sagawa; Susumu Yoshikawa; Shuzi Hayase
CHEMISTRY LETTERS, CHEMICAL SOC JAPAN, 38, 7, 742-743, Jul. 2009, Peer-reviwed, Unique behaviors of electrochemiluminescence from a device consisting of ZnO nanorod (Cell-1) are reported. Cell-1 emitted more intense electrochemiluminescence than cell consisting of two flat electrodes (Cell-2). The onset potential at which the emission starts was 1.5 V for Cell-1, which was lower than 2.5 V for Cell-2. The unique behaviors were explained by asymmetric collision modes of emitting species (Ru-I and Ru-III) in the nanospace among ZnO nanorods and were characteristic to the ZnO nanorod array.
Scientific journal, English

Transparent conductive oxide layer-less three dimensional dye sensitized solar cells: Fabrication of ionic path in three dimensional Ti electrode
Takayuki Beppu; Yohei Kashiwa; Shuzi Hayase; Mitsuru Kono; Yoshihiro Yamaguchi
Japanese Journal of Applied Physics, 48, 6, Jun. 2009, A transparent conductive oxide-less dye-sensitized solar cell (TCO-less DSC) consisting of a thick and porous Ti electrode is reported. The Ti electrode was contacted with the back of a stained porous titania layer. A thick Ti electrode prepared by conventional sputtering prevented ionic diffusions through the Ti electrode and decreased photovoltaic performance. Tetrapod-shaped ZnO crystals were used to prepare straight and continuous nanopores in the Ti electrode to maintain the ionic diffusion. 8% efficiency of the TCO-less DSC is also reported. © 2009 The Japan Society of Applied Physics.
Scientific journal, English

Tandem Dye-Sensitized Solar Cells Fabricated on Glass Rod without Transparent Conductive Layers
Jun Usagawa; Shyam S. Pandey; Shuzi Hayase; Mitsuru Kono; Yoshihiro Yamaguchi
APPLIED PHYSICS EXPRESS, JAPAN SOCIETY APPLIED PHYSICS, 2, 6, Jun. 2009, Peer-reviwed, A tandem dye-sensitized solar cell was fabricated on a glass rod without a transparent conductive oxide layer (TCO-less GR-DSSC). Two model dyes having lambda(max) = 429 nm (Dye II) and lambda(max) = 646 nm (Dye I) respectively were used to examine the potential of the cell. The incident photon to current conversion efficiency (IPCE) curve of the TCO-less GR-DSSC had two peaks at around 490 and 600-650 nm. Open circuit voltage (V(oc)) of the TCO-less GR-DSSC was 1.13V which was the sum of the V(oc) (0.57 V) of each single cell. The results strongly demonstrate that the cell has a tandem character. (C) 2009 The Japan Society of Applied Physics
Scientific journal, English

Transparent conductive oxide layer-less dye-sensitized solar cells consisting of floating electrode with gradient TiOx blocking layer
Yoshikazu Yoshida; Shyam S. Pandey; Kenshiro Uzaki; Shuzi Hayase; Mitsuru Kono; Yoshihiro Yamaguchi
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 94, 9, Mar. 2009, Peer-reviwed, A transparent conductive oxide less dye-sensitized solar cell (TCO-less DSC) consisting of a glass/a floating electrode (FE)/a stained nanoporous titania layer/a gel electrolyte sheet/a Pt layer/a Ti sheet is reported. The FE is composed of a stainless mesh sheet covered with a gradient TiOx layer, which suppressed back-electron transfers from the stainless to electrolytes. The efficiency increased from 2.87% to 4.68% by replacing a conventional dense TiO2 blocking layer with the gradient TiOx layer. The cell in this architecture gave the efficiency of 5.56% after optimization.
Scientific journal, English

Preparation of Double Dye-Layer Structure of Dye-Sensitized Solar Cells from Cocktail Solutions for Harvesting Light in Wide Range of Wavelengths
Yusuke Noma; Keita Iizuka; Yuhei Ogomi; Shyam S. Pandey; Shuzi Hayase
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOCIETY APPLIED PHYSICS, 48, 2, Feb. 2009, Peer-reviwed, Dye-sensitized solar cells (DSCs) consisting of a double dye-layer structure of Ru dye (Z907) and organic dye (NK3705) were prepared by dipping porous titania substrates into dye mixture solutions. Dye structures such as NK3705 were crucial for realizing the double layer structure. A porous titania layer adsorbed NK3705 predominantly in the dye mixture. The adsorbed NK3705 was then replaced by Z907 from the top to the bottom of the porous titania surface as a function of dipping time. The DSCs based on the double dye-layer structure were able to harvest light in a wide range of wavelengths. (C) 2009 The Japan Society of Applied Physics
Scientific journal, English

Research Trends of Dye-Sensitized Solar Cells
Hayase Shuzi
Annals of the High Performance Paper Society, Japan, High Performance Paper Society, Japan, 48, 47-51, 2009, Dye-sensitized solar cell is expected as one of the next generation solar cells. Energy-conversion efficiency record reaches 10.4%, which is almost the same as that of amorphous silicone solar cells commercially available. This article summarizes the recent research trends of the solar cells from the viewpoint of high efficiency, low cost, solidification systems and module structures. Tandem cells with a floating electrode are described as one of our recent achievements. The demands for films and papers are also summarized.
Japanese

A facile route to TiO2 nanotube arrays for dye-sensitized solar cells
Patcharee Charoensirithavorn; Yuhei Ogomi; Takashi Sagawa; Shuzi Hayase; Susumu Yoshikawa
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 311, 3, 757-759, Jan. 2009, Peer-reviwed, Nanotube arrays of TiO2 were synthesized by using a template of ZnO nanorod arrays on fluorine-doped SnO2 (FTO) transparent conducting oxide glass substrate by liquid phase deposition (LPD) method. Dye (N719) sensitized solar cells (DSCs) comprising the TiO2 nanotube arrays were fabricated under the various conditions of the calcined temperature in the range of 300-500 C. The sintering temperature drastically affected the film crystallinity. Cell performances of the DSCs based on the TiO2 nanotube arrays with different cryatalinities were characterized and compared. It was found that the content of crystalline phase of anatase TiO2 nanotube arrays increased on raising the calcination temperature Lip to 500 C and resulting in enhancement of the cell performance of DSCs in terms of the short-circuit photocurrent density. (C) 2008 Published by Elsevier B.V.
Scientific journal, English

Effect of Heat-Treatment on Electron Transport Process in TiO2 Nanotube Arrays Prepared Through Liquid Phase Deposition for Dye-Sensitized Solar Cells
Patcharee Charoensirithavorn; Yuhei Ogomi; Takashi Sagawa; Shuzi Hayase; Susumu Yoshikawa
JOURNAL OF THE ELECTROCHEMICAL SOCIETY, ELECTROCHEMICAL SOC INC, 156, 11, H803-H807, 2009, Peer-reviwed, Nanotube arrays of TiO2 were synthesized by using a template of ZnO nanorod arrays on fluorine-doped SnO2 transparent conducting oxide glass substrate by liquid phase deposition method. Dye N719-sensitized photoelectrochemical cells comprising TiO2 nanotube arrays were fabricated and characterized. With an increase in the calcination temperature, the anatase content of the crystallized film increased and the conduction band of TiO2 shifted toward a negative potential, resulting in an increase in the cell performance in terms of the short-circuit photocurrent density and open-circuit voltage. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3211840] All rights reserved.
Scientific journal, English

Probing TiO2/Dye Interface in Dye Sensitized Solar Cells Using Surface Potential Measurement
Shohei Sakaguchi; Shyam S. Pandey; Keisuke Okada; Yoshihiro Yamaguchi; Shuji Hayase
APPLIED PHYSICS EXPRESS, JAPAN SOC APPLIED PHYSICS, 1, 10, Oct. 2008, Peer-reviwed, Surface potential measurement using scanning Kelvin-probe microscopy was conducted to investigate the relationship between dye characteristics and open circuit voltage (V-oc). It was observed that V-oc increased with the increase in surface potential of dye as compared to that of bare TiO2 giving increased efficiency of dye sensitized solar cells. Addition of chenodeoxycholic acid (DCA) as co-adsorbent caused positive shift of surface potential, which explained the increase of V-oc upon DCA incorporation. It was further explained by the negative shift of TiO2 conduction band edge in the presence of DCA. (c) 2008 The Japan Society of Applied Physics
Scientific journal, English

Direction to High Efficiency-dye-sensitized Solar Cells
HAYASE Shuzi
IEEJ Transactions on Fundamentals and Materials, The Institute of Electrical Engineers of Japan, 128, 9, 573-576, 01 Sep. 2008, The efficiency of dye-sensitized solar cells reached 11% which exceeded that of amorphous Si solar cells. The next target is 15 % efficiency. Focus is put on light harvesting and electron collecting performances to increase the efficiency. Tandem and hybrid cells have been reported to harvest light with wide range of wavelength. Electron collecting performances are improved by surface passivation of nano-titania particles. The research trends including our results are reported.
Japanese

I-2-Resistant TiOx/Ag Collector Fabricated by Arc Plasma Deposition for Dye-Sensitized Solar Cells
Yorikazu Yoshida; Yusuke Noma; Yohei Kashiwa; Shinichi Kojima; Takehito Katoh; Shuzi Hayase
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 47, 8, 6484-6487, Aug. 2008, Peer-reviwed, Dye-sensitized solar cells consisting of TiOx/Ag collectors resistant to I-2 are described. Ag collectors have to be protected against I-2 because Ag reacts with I-2 contained in electrolytes. Ag collectors merely covered with sputtered Ti layers (sputtered Ti/Ag) were eroded when the Substrate was dipped in electrolytes containing of I-2, because of the insufficient coverage of Ag collectors with sputtered Ti layers. When the sputtered Ti/Ag layers were passivated further with TiOx layers by arc plasma deposition (APD-TiOx/sputtered Ti/Ag), Ag erosion was totally suppressed. APD-TiOx/Ag collectors were not resistant to I-2 either. The combination Of Sputtered Ti layers and APD-TiOx layers was therefore necessary. The former was a kind of porous Ti layer in terms of iodide blocking but the coverage of the re-entrant areas of printed Ag was sufficient. The latter was pinhole-free but the coverage of re-entrant areas was not Sufficient. Both compensated for the shortcomings of pinhole and re-entrant coverage.
Scientific journal, English

Tio2 surface state control for dye sensitized solar cells with high efficiency and the solidification-fabrication of charge carrier path
Fumi Inakazu; Yuhei Ogomi; Yusuke Noma; Yoshihisa Fujita; Mitsuru Kono; Yoshihiro Yamaguchi; Yohie Kashiwa; Takeshi Kogo; Shuzi Hayase
Materials Research Society Symposium Proceedings, 1031, 43-48, 2008, Improvement of photovoltaic performance for dye sensitized solar cells (DSC) is discussed in terms of electron-path and ion-path. In order to make electron path, we focused on passivation of TiC>
2 surface states which are observed by thermally stimulated current (TSC). The TiC>
2 surface was well-passivated with dye molecules under pressurized CO2 atmosphere. It was found that DSC cells prepared by a CO2 process (Cell-CO 2) had higher efficiency than those prepared by a conventional dipping process (Cell-DIP) and the higher efficiency was associated with low TiO2-surface state, high electron diffusion coefficient and long electron life time in TiO2 for the Cell-CO2. In addition, dye-staining under pressurized CO2 atmosphere had advantages over a conventional dipping process on rapid dye-uptake and less dye aggregation. In order to fabricate ion-path in solidified electrolyte, we focused on surface modification of nano-materials. Surface of nano-materials such as TiO 2-nanoparticles and porous alumina films were modified with imidazolium iodide moieties consisting of long alkyl chains which render surface-molecules self-organized. Redox-species are concentrated on the self-organized molecules and make ion-path. We propose quasi-solid electrolyte system consisting of two layers having different charge carrier concentration to keep high photoconversion efficiencies even after solidification. © 2008 Materials Research Society.
International conference proceedings, English

Quasi-solid dye sensitized solar cells having straight ion paths: Proposal of high-efficiency QDSCs consisting of two carrier density layers
Takeshi Kogo; Shuzi Hayase; Tatsuo Kaiho; Mitsuru Taguchi
Journal of the Electrochemical Society, 155, 9, K166-K169, 2008, Peer-reviwed, Quasi-solid dye-sensitized solar cells (QDSCs) consisting of amylose/porous Al2O3 film/ionic liquid films (Am-Al/IL film) are reported. The surface of straight nanopores in the Al2O3 film was modified with amylose and these nanopores were filled with ionic-liquid-type electrolytes. The ionic liquid did not leak from these nanopores of the film. The photovoltaic performance of the QDSC consisting of Am-Al/IL films was almost the same as that before the solidification, despite that the film was occupied with 50% of electrochemically inactive Al 2O3 wall. It was found that the iodine was adsorbed on the straight wall of Am-Al films and the apparent diffusion coefficient of I 3- species was almost the same as that in the parent liquid electrolyte. From these results and our previous reports, we propose QDSC structures consisting of two-carrier-density layers (I-/I 3-) with low and high carrier concentrations for high-efficiency cells. A bulk area between a counter electrode and a TiO 2 electrode is occupied with a high-carrier-density medium (I -/I3-), and TiO2 nanopores are filled with a low-carrier-density medium (I-/I3 -). The former increases the conductivity and the latter suppresses the back electron transfer from the TiO2 layer to redox species. © 2008 The Electrochemical Society.
Scientific journal, English

Surface state passivation effect for nanoporous TiO2 electrode evaluated by thermally stimulated current and application to all-solid state dye-sensitized solar cells
Yuusuke Noma; Takashi Kado; Daisuke Ogata; Yoshitaka Hara; Shuzi Hayase
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 47, 1, 505-508, Jan. 2008, Peer-reviwed, The effect of surface state (trap) passivation of a nanoporous TiO2 electrode was examined by a thermally stimulated current method (TSC). TSC decreased after dye molecules were adsorbed or after Al2O3 thin layers were fabricated on the TiO2 electrode, suggesting that the surface trap of the TiO2 electrode was actually passivated following these surface modifications. Electron diffusion coefficient in the TiO2 electrode increased and electron recombination was retarded after the TSC peak decreased by the passivation. All-solid-type organic solar cells consisting of nanoporous TiO2/Al2O3/dye/polythiophene derivative (Cell 1) were prepared and the photovoltaic properties of Cell I were compared with those of Cell 2 consisting of TiO2/dye/polythiophene derivatives. By inserting the Al2O3 layer between the TiO2 layer and the dye molecule layer, we observed improvement of the photovoltaic properties.
Scientific journal, English

Influence of alkyl dihalide gelators on solidification of dye-sensitized solar cells
Shinji Murai; Satoshi Mikoshiba; Shuzi Hayase
SOLAR ENERGY MATERIALS AND SOLAR CELLS, ELSEVIER SCIENCE BV, 91, 18, 1707-1712, Nov. 2007, Peer-reviwed, Quasi-dye-sensitized solar cells were prepared by using ionic liquid-type electrolytes and gelators consisting of polyvinylpyridine and alkyl dihalides. Gelation occurred by the reaction of polyvinylpyridine and alkyl dihalides. When the chain length of the dihalides was varied, the short-circuit current (J(sc)) increased with an increase in the chain length. However, the open-circuit voltage (V-oc) and fill factor (ff) slightly decreased. The increase in J(sc) was brought about by the decrease in the interfacial resistances between the gel electrolyte and the counter electrode. In addition, the increase in the J(sc) was explained by increases in the apparent diffusion coefficient of I-/I-3(-) when the chain length increased. Decreases in V-oc and ff were explained by back-electron transfers from TiO2 to iodine in the electrolytes. V-oc of the cells solidified by alkyldiiodide was lower than that solidified by alkyldichloride or alkyldibromide. It was explained by negatively shifted redox potential of I-/I-3(-), compared with those for Cl-/Cl-2 or Br-/Br-2. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English

Quasi-solid dye sensitized solar cell with straight ion paths - Proposal of hybrid electrolytes for ionic liquid-type electrolytes
Takehito Kato; Shuzi Hayase
JOURNAL OF THE ELECTROCHEMICAL SOCIETY, ELECTROCHEMICAL SOC INC, 154, 1, B117-B121, 2007, Peer-reviwed, Quasi-solid dye sensitized solar cells (QDSC) with straight ion paths are reported. The cell consists of anodic oxidation Al2O3 films. Ionic liquid-type electrolyte is filled in the straight nanopores and they are sandwiched between a counter electrode and a TiO2 electrode. Even when electrochemically inactive Al2O3 wall occupies 50% of the electrolyte layer, the I-3(-) diffusion coefficient and solar cell performance are the same as those without the Al2O3 layers. This contrasts the results of cells filled with the mixture of Al2O3 nanoparticles and ionic liquid type electrolytes, where random ion paths are expected. In addition, when the inner wall of anodic oxidation Al2O3 films is chemically modified with long alkyl groups bearing methylimidazolium moieties, the increase in photovoltaic performance is observed. This is explained by the existence of ion paths along aligned methylimidazolium moieties in the surface-modified Al2O3 films, where I-2(I-3(-)) species are concentrated. The swift apparent I-3(-) diffusion coefficient is explained by Grotthuss mechanism. Because the I-2 species are concentrated in the straight pore of Al2O3 layers, the concentration of I-2(I-3(-)) species in TiO2 layers is reduced relatively. This increases light penetration depth at around 400 nm in the porous TiO2 layer and improves incident photon-to-current efficiency at around 400 nm. The hybrid electrolyte systems containing both of concentrated I-2(I-3(-)) in a porous Al2O3 layer and low concentration portions in nanopores in TiO2 are proposed to increase ionic liquid-type QDSC. (c) 2006 The Electrochemical Society.
Scientific journal, English

Dye-sensitized solar cells with high efficiency - From interface control to solidification - art. no. 665606
Yuhei Ogomi; Shohei Sakaguchi; Shuzi Hayase
ORGANIC PHOTOVOLTAICS VIII, SPIE-INT SOC OPTICAL ENGINEERING, 6656, 65606-65606, 2007, Peer-reviwed, Some items to increase photovoltaic performances of dye sensitized solar cells (DSC) are reported. Focus is put on the fabrication of the electron collection path and ionic path. In order to increase the surface coverage of TiO2 nano-particles with dye molecules, the dye adsorption on TiO2 layers was carried out under a pressurized CO2 atmosphere (CO2 process). The CO2 process promoted the dye adsorption and shortened the dye adsorption time to 1/10 - 1/100. In addition, solar cells prepared by the CO2 process had higher Voc and Jsc than those prepared by the conventional dipping process. The increase in the photovoltaic performance was explained by the large electron diffusion coefficient in TiO2 layers and by longer electron life time in TiO2 layers. Thermally stimulated current measurement (TSC) implied that the surface electron trap on the TiO2 nano-particle was passivated by the sufficient dye adsorptions on the TiO2 surfaces. In addition, it was found that the dye aggregation was prevented by the CO2 process, which increased the photovoltaic performances. Hybrid dye sensitized solar cells having two-dye-layer-structures were fabricated by the CO2 process for the first time in order to absorb the light having wide range of wavelength. In addition, three-dimensional W electrodes were fabricated on the thick TiO2 layer in order to collect electrons in the TiO2 layer effectively. Solid type DSCs are reported. High performance quasi-solid DSCs were fabricated by preparing ionic paths in the quasi-solid electrolyte layers. The ionic path was fabricated by the surface modification of the straight nano-pore walls in a porous Al2O3 membrane, where, I-/I-3(-) ion species were concentrated and were expected to diffuse by Grotthuss mechanism.
International conference proceedings, English

Differences in characteristics of dye-sensitized solar cells containing acetonitrile and ionic liquid-based electrolytes studied using a novel model
Toshihiro Oda; Shigenori Tanaka; Shuzi Hayase
SOLAR ENERGY MATERIALS AND SOLAR CELLS, ELSEVIER SCIENCE BV, 90, 16, 2696-2709, Oct. 2006, Peer-reviwed, A performance simulation model of dye-sensitized solar cells including a "bulk" electrolyte layer separated from a TiO2, layer has been presented. The calculation results with this novel model agree well with experimental results, which indicates the importance of considering the bulk electrolyte layer in theoretical models. The model allows us to specify the diffusion coefficients of ionic species in nano-pores of the TiO2 layer and in the bulk electrolyte layer separately, and the importance of ionic diffusions in each layer is discussed. We further clarify the difference between ionic liquid-type cells and acetonitrile type cells, and discuss the important issues for increasing the efficiencies in cells containing ionic liquid-based electrolytes. (c) 2006 Elsevier B.V. All rights reserved.
Scientific journal, English

Dye-sensitized Solar Cells Consisting of CuI-containing Gels
KADO Takashi; SOEDA Kuniko; NEGORO Kenji; HAYASE Shuzi
Chemistry Letters, The Chemical Society of Japan, 35, 4, 444-445, 05 Apr. 2006, CuI-containing gels for dye-sensitized solar cells are reported. CuI-containing gels consist of CuI, methylpropylimidazolium iodide, iodine, and gelators consisting of polyvinylpyridine and tetra(iodomethyl)benzene. The efficiency increases with an increase in the amount of iodine molecules in the presence of methylpropylimidazolium iodide, which is different from the previous reports in the absence of methylpropylimidazolium iodide. Solidification of the sticky CuI layers is carried out by cross-linking reaction of gelators without decreasing the photovoltaic performances.
English

Latent gel electrolyte precursors for quasi-solid dye sensitized solar cells - The comparison of nano-particle cross-linkers with polymer cross-linkers
T Kato; A Okazaki; S Hayase
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 179, 1-2, 42-48, Apr. 2006, Peer-reviwed, New latent gel electrolyte precursors (Precursor 1) consisting of ionic liquids and latent gelators are reported. The gelators are composed of poly(vinylpyridine) (PVP) and di-carboxylic acids. Gelation is caused by the reaction between PVP and di-carboxylic acid. Precursor I is liquid and is injected into cells and porous TiO2 electrodes. Because of the latent properties, the viscosity of Precursor 1 does not increase at room temperature. After the Precursor 1 is injected into cells and into porous TiO2 layers, the cell is heated at 90 degrees C. Solidification occurs swiftly. The latent mechanism is discussed. The trend of photo-voltaic performance for the cell filled with Precursor 1 before and after gelation was compared with that for the cell filled with previously reported latent gel electrolyte Precursor 2 composed of nano-particles and di-carboxylic acids. Photo-voltaic performance for the former decreased after quasi-solidification, but the latter did not. This is explained by insufficient phase-separations of gelator backbone from ionic liquid electrolytes after solidification. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English

Analysis of dominant factors for increasing the efficiencies of dye-sensitized solar cells: Comparison between acetonitrile and ionic liquid based electrolytes
Toshihiro Oda; Shigenori Tanaka; Shuzi Hayase
Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 45, 4 A, 2780-2787, Apr. 2006, Factors determining the photovoltaic performance of cells containing ionic liquid based electrolytes are compared with those of cells containing acetonitrile based electrolytes. The difference is made clear by using a simulation model having a bulk electrolyte layer. In the former case, ionic diffusions in bulk electrolytes determine photocurrents. In contrast, in the latter case, electron diffusion in nano-porous TiO2 layers determines the photovoltaic performances. The increase in photocurrents for the former cells would be made most effectively by increasing ionic diffusions in electrolytes. © 2006 The Japan Society of Applied Physics.
Scientific journal

Fabrication of ion-paths for ionic liquid type quasi-solid dye sensitized solar cell
Takashi Kado; Takehito Kato; Takeshi Kogo; Fumi Inakazu; Yusuke Noma; Yuhei Ogomi; Yoshihiro Yamaguchi; Mitsuru Kohno; Shuzi Hayase
Materials Research Society Symposium Proceedings, Materials Research Society, 965, 392-397, 2006, A direction to increasing photovoltaic performances of dye sensitized solar cells (DSC) is proposed. An interface between TiO2/dye and an electrolyte layer is focused on. It is proved that better coverage of TiO 2 layers with dye molecules increases photovoltaic performances, where dye staining is carried out in pressurized CO2 atmosphere. This is explained by decreases in the amount of surface traps on TiO2 nano-particles, which is discussed by thermally stimulated current (TSC). The decrease in the surface trap density increases electron diffusion coefficient and improves electron lifetime in TiO2 layers. In addition, the TiO2-staining with dye molecules having the larger dipole moment seems to leave less amount of electron trap. Another crucial research item is solidification. Quasi-solidification is carried out by using surface modified anodically-oxidized Al2O3 films filled with ionic liquids, where ion paths are fabricated on the surface-modified Al2O 3 walls by concentrating iodine and iodide molecules on the walls. Because of the fabrication of the ion path, photovoltaic performances increased even after solidification. Grötthuss type mechanism is introduced to explain the increase in the photovoltaic performances after the solidification. © 2007 Materials Research Society.
International conference proceedings, English

Quasi-solid dye sensitized solar cells equipped with hybrid electrolytes consisting of linear conduction paths
Shuzi Hayase; Takehito Kato; Fumi Inakazu; Keisuke Okada
Polymer Preprints, Japan, 55, 2, 4647-4648, 2006, Quasi-solid dye sensitized solar cells are fabricated by use of surface modified porous alumina filled with ionic liquid type electrolytes. This realizes straight ion or electron diffusions from the TiO2 layer to the counter electrode. The porous alumina surface is modified with self-organized imidazolium iodides bearing long alkyl chains directly bonded to the alumina nano-pore walls or PEDOT-PSS. Filling the nano-pores with ionic liquids gives a flexible electrolyte sheet. DSC equipped with the sheet shows high photovoltaic performance, which is the same as or better than that before solidification. Hybrid electrolytes consisting of low iodine concentration for high penetration depth in TiO2 layers and high iodine concentrations for high conduction are proposed.
International conference proceedings, Japanese

Quasi-solid dye sensitized solar cells bearing straight ion-paths
Shuzi Hayase; Takehito Kato; Shuhei Tanaka
Polymer Preprints, Japan, 55, 2, 4144-4145, 2006, Quasi-solid dye sensitized solar cells consisting of porous alumina/ionic liquid electrolyte composites (AL-IL) are reported. The straight nano-pores of the porous alumina film are surface-modified with self-organized imidazolium iodide moieties bearing long alkyl groups. By filling the pores with ionic liquids, straight ion paths are fabricated along the aligned the imidazolium moieties, where, iodine molecules are highly concentrated. The swift ion diffusion is explained by Grotthuss mechanism. A new hybrid quasi-solid electrolyte consisting of low I2 concentration for high light penetration layer and high I2 concentration for a carrier layer is proposed.
International conference proceedings, Japanese

Ru dye uptake under pressurized CO 2 improvement of photovoltaic performances for dye-sensitized solar cells
Yuhei Ogomi; Shohei Sakaguchi; Takashi Kado; Mitsuru Kono; Yoshihiro Yamaguchi; Shuzi Hayase
Journal of the Electrochemical Society, 153, 12, A2294-A2297, 2006, Swift uptake of Ru dyes and improvement of photovoltaic performances for dye-sensitized solar cells (DSC) are reported. Ru dyes such as black dye [ (C4 H9) 4 N]3 [Ru (Htcterpy) (NCS)3] (tcterpy=4, 4′, 4″ -tricarboxy- 2, 2′: 6′, 2″ -terpyridine) and N3 dye [cis-di(thiocyanato)- N, N′ -bis (2, 2′ -bipyridyl- 4, 4′ -dicarboxylato) ruthenium (II)] are adsorbed on nano-porous Ti O2 layers under a pressurized C O2 atmosphere to bond Ru dyes on inner surfaces of Ti O2 in nano-porous layers effectively. The time needed for N3 dye adsorption under a pressurized C O2 condition is drastically shortened to 30 min from 300 min needed for a dipping process. The amount of N3 dye molecules increases from 15 to 20 nmol cm2 μm when N3 dye is adsorbed under a pressurized C O2 atmosphere. The pressurized C O2 process increases short circuit current, fill factor, and open circuit voltage which are associated with better coverage of Ti O2 surfaces with dye molecules. They decrease surface traps of porous Ti O2 layers. This retards back electron transfers from Ti O2 layers to iodine in electrolytes and facilitates electron diffusion in Ti O2 layer. Measurement of the electron lifetime and electron diffusion coefficient in the cells supports the mechanism.The Electrochemical Society © 2006 The Electrochemical Society.
Scientific journal, English

Quasi-solid dye sensitized solar cells with ionic liquid type gel electrolytes
T. Kato; A. Okazaki; Y. Ogomi; T. Kado; S. Tanaka; T. Beppu; S. Hayase
ECS Transactions, 1, 32, 23-30, 2006, Solidification of dye sensitized solar cells (DSC) is carried out in two methods. One is a method to use soft gels containing less than 10 % of chemically crosslinkable gelators. The soft gel is characterized with the latent property. The other is a method to use hard gels containing 100 % of surface modified TiO2 nanoparticles as gelators. In both cases, electrolytes are solidified without decreasing photovoltaic performances even after solidification by fabricating ion-paths in the solidified electrolytes associated with self-organization of long alkyl groups. copyright The Electrochemical Society.
International conference proceedings

Quasi-solid dye-sensitized solar cells containing nanoparticles modified with ionic liquid-type molecules
T Kato; T Kado; S Tanaka; A Okazaki; S Hayase
JOURNAL OF THE ELECTROCHEMICAL SOCIETY, ELECTROCHEMICAL SOC INC, 153, 3, A626-A630, 2006, Peer-reviwed, Gel electrolytes for quasi-solid dye-sensitized solar cells (QDSC) are reported. The gel electrolyte consists of ionic liquids and nanoparticles modified with imidazolium cations. Ionic liquid-type gel electrolytes containing nanoparticles are well-known. The difference between previous reports and this report is that imidazolium cations are bonded to nanoparticles through Ti-O-CO bonds and long alkyl chains. The role of the long alkyl chains turns out to be critical for high performances. When unmodified nanoparticles are added into ionic liquids until the gel becomes of clay-like hardness, the photovoltaic performances decrease with an increase in the bare nanoparticle content. However, the decreases in photovoltaic performances are retarded when surface-modified nanoparticles are added. Photovoltaic performances increase with an increase in the chain lengths connecting nanoparticles and imidazolium cations. When the chain length becomes 12 and counter anion is I-, solidification occurs without losing the performance of DSCs having the parent liquid electrolytes. The photocurrents of QDSCs do not decrease even when the ratio (nanoparticles/ionic liquids) increases to 0.9 and the feature looks like hard clay. Ionic paths between nanoparticles are discussed. (c) 2006 The Electrochemical Society.
Scientific journal, English

Dye sensitized solar cells consisting of ionic liquid and solidification
Yuhei Ogomi; Takehito Kato; Shuzi Hayase
JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY, TECHNICAL ASSOC PHOTOPOLYMERS,JAPAN, 19, 3, 403-408, 2006, Peer-reviwed, Two crucial research items on dye sensitized solar cells (DSC), increasing photovoltaic performances and solidification of liquid electrolytes, are reported. A direction to increasing photo-voltaic performances of DSCs is proposed. An interface between TiO2/dye and an electrolyte layer is focused on. It is proved that better coverage of TiO2 layers with dye molecules increases photovoltaic performances. The results are discussed by using electron diffusion coefficient and electron life time in TiO2 layers. Another crucial research item is solidification. Liquid electrolytes are quasi-solidified without decreasing the parent liquid type DSCs, where Grotthuss type mechanism are introduced to the solidified electrolytes. Because of this, charge carrier can move swiftly even in the hard clay like electrolytes.
Scientific journal, English

Dye Sensitized Solar Cells : The Research Trend and the Future
HAYASE Shuzi
Kobunshi, The Society of Polymer Science, Japan, 54, 12, 878-881, 01 Dec. 2005, 色素増感太陽電池の研究開発動向をまとめた。要素研究では性能向上と固体化に関する研究に焦点。プラスチック化で軽量化,タンデム型で性能向上を狙う。大型モジュールの試作で耐久性を含めた総合試験が始まった。今後,実用に近い環境での試験が加速する。
Japanese

Low-temperature Fabrication of Nano-porous TiO_2 Layers for Dye-sensitized Solar Cells. Fabrication of Ion-diffusion Paths
KADO Takashi; KUBOTA Yukihumi; HAYASE Shuzi
Chemistry Letters, The Chemical Society of Japan, 34, 7, 1006-1007, 05 Jul. 2005, In dye-sensitized solar cells, it is required to build up both of ion paths and electron paths in TiO₂ layers for low-temperature fabrication process. In this report, ion paths are focused on. Semiconductive layers are composed of TiO₂ nanocrystals (P25) and needle-shape TiO₂ crystals (FTL 100). By adding 20% of the needles into P25, photocurrent increased from 5.3 to 7.7 mA/cm². Pore distributions, surface areas, Cole–Cole plot and currents passing through TiO₂ layers were measured. These results suggest that the increase in the photocurrent is associated with the formation of ion paths in TiO₂ layers.
English

Photooxidized Polysilane Binders for Low Temperature Fabrication of Dye-sensitized Solar Cells
SOEDA Kuniko; KOSUGI Daishi; KADO Takashi; HAYASE Shuzi
Chemistry Letters, The Chemical Society of Japan, 34, 5, 650-651, 05 May 2005, Photooxidized polysilanes were evaluated as binders connecting nano-TiO₂ particles for low temperature baking process. Both of Jsc and Voc increased after TiO₂ nanoparticles (P25) were connected with photooxidized polysilanes. The amount of dyes adsorbed on TiO₂ layers, TiO₂ flat band potentials, electron diffusion co-efficient, electron life time were measured. The increases in the Jsc and Voc were associated with increases in electron diffusion coefficients and electron life time in TiO₂ layers.
English

Latent gel electrolyte precursors for quasi-solid dye sensitized solar cells
Takehito Kato; Akio Okazaki; Shuzi Hayase
Chemical Communications, Royal Society of Chemistry, 3, 363-365, 21 Jan. 2005, New latent chemically-cross-linked gel electrolyte precursors for quasi-solid dye sensitized solar cells (QDSC) are reported. The gel electrolyte precursors consist of nano-particles and dicarboxylic acids as the latent gelators. The viscosity of the precursor is low at first and does not increase during storage at room temperature. However, when the precursor is baked at 80 °C, it solidifies immediately. Photo-voltaic performance is maintained after solidification.
Scientific journal, English

Quasi-solid-state dye sensitized solar cells by use of ionic liquid type latent gel electrolyte precursors
Takehito Kato; Akio Okazaki; Yuhei Ogomi; Wataru Takashima; Keichi Kaneto; Shuzi Hayase; Koichi Yamashita
Polymer Preprints, Japan, 54, 1, 1445, 2005, We propose latent gel electrolyte precursors for quasi-solid-state dye sensitized solar cells. New latent gel precursors have long self-life at room temperature and solidification abilities at 80°C within 30 sec. The precursors consist of dicarboxylic acids and nano particles. 7% of photo-energy conversion efficiency was achieved. Because of the long self life and the swift gelation, the latent gel precursors are effective for fabrication of large area cells.
International conference proceedings, Japanese

Fabrication of quasi-solidified dye sensitized solar cells - Relationship between crosslinker structure and PV performance
Shuzi Hayase; Takehito Kato; Akio Okazaki; Shuhei Tanaka; Takashi Kado
Polymer Preprints, Japan, 54, 2, 4591-4592, 2005, Three kinds of quasi-solid dye sensitized solar cell are reported. One is latent gel electrolytes consisting of nano-particles and Hexadecanedioic acid in ionic liquid type electrolytes. Solidification occurs by the reaction of the nano-particles with di-carboxylic acids. The longer alkyl moieties are favorable, because the chains cause phase-separation during solidification, which retards decrease in I3- diffusion coefficient. The second one is the nano-particle-rich gel electrolytes. These surfaces are modified with ionic liquid type molecules, which retards the decrease in Jsc after solidification. The third one is solid rich electrolyte consisting of Cul and small amount of ionic liquid and iodine (additives) The additives increase Jsc. The mechanisms are discussed.
International conference proceedings, Japanese

Increase in electrochemiluminescence intensities by use of nanoporous TiO2 electrodes
S Okamoto; K Soeda; T Iyoda; T Kato; T Kado; S Hayase
JOURNAL OF THE ELECTROCHEMICAL SOCIETY, ELECTROCHEMICAL SOC INC, 152, 8, A1677-A1681, 2005, Peer-reviwed, Intense electrochemiluminescence (ECL) was observed from sandwich cells. The cell structure is as follows: F-doped SnO2/nanoporous TiO2/tris (2,2'-bipyridyl) ruthenium (II) complex [Ru(bpy)(3)(PF6)(2)] in acetonitrile/ F-doped SnO2. Intense ECL was observed only when negative cell voltage was applied to nanoporous TiO2 electrodes. The ECL increased with an increase in the surface area of porous TiO2 layers. ECL increase was observed for porous ZnO electrodes, but not for porous SnO2 electrodes. It was concluded that increases in ECL are associated with the formation of Ru+ in porous TiO2 electrodes and the process taking place after reduction of Ru2+ which occurs in the porous electrodes. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1946587] All rights reserved.
Scientific journal, English

Additives for increased photoenergy conversion efficiencies of quasi-solid, dye-sensitized solar cells
T Kato; M Fujimoto; T Kado; S Sakaguchi; D Kosugi; R Shiratuchi; W Takashima; K Kaneto; S Hayase
JOURNAL OF THE ELECTROCHEMICAL SOCIETY, ELECTROCHEMICAL SOC INC, 152, 6, A1105-A1108, 2005, Peer-reviwed, Dye-sensitized solar cells (DSCs) are solidified with gelators containing polyvinylpyridine and 1,2,4,5-tetra(bromomethyl) benzene. The photoconversion efficiencies are improved by new additives. LiI and t-butylpyridine are commonly added in electrolytes for increasing short-circuit current (Jsc) and open-circuit voltage (Voc). These additives inhibit our gel electrolyte precursors from solidifying. We found that new additives, combinations of acetic acid, and methylpyrimidine or methylbenzimidazole, do not inhibit the solidification and are effective for increasing both Jsc and Voc. These mechanisms are discussed in terms of electron diffusion coefficients, I-3(-) ion diffusion coefficients, and charge-transfer resistances between counter electrodes and gel electrolytes. © 2005 The Electrochemical Society. All rights reserved.
Scientific journal, English

Quasi-solid dye sensitized solar cells solidified with chemically cross-linked gelators - Control of TiO2/gel electrolytes and counter Pt/gel electrolytes interfaces
S Sakaguchi; H Ueki; T Kato; T Kado; R Shiratuchi; W Takashima; K Kaneto; S Hayase
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 164, 1-3, 117-122, Jun. 2004, Peer-reviwed, Dye sensitised solar cells (DSSCs) were solidified with chemically cross-linked gelators without losing the performance of DSSCs before gelation. The electrolytes contain ionic liquids (1-methyl-3-propylimidazolium iodide) solidified with polyvinylpyridine and 1,2,4,5-tetra(bromomethyl)benzene. The solidification was carried out by baking the cells after the gel electrolyte precursors were injected in the cells. This brought about sufficient physical contacts between gel electrolytes and TiO2 nano-crystals in nano-porous TiO2 electrolytes. Small amount of water was added in order to decrease initial viscosities for ionic liquid type gel precursors, which makes it possible for the gel precursors to impregnate into nano-pores in TiO2 layers. The addition of water also has an advantage for decreasing charge transfer resistances between electrolytes and counter Pt. It was found that short circuit current (J(sc)) and open crcuit voltage (V-oc) increased much, when TiO2 layers with N3 dye were dipped in dilute carboxylic acid solutions and dried. Decreases in resistant of TiO2 layers were observed after the carboxylic acid treatments were carried out. This method is useful for increase in performance DSSC containing ionic liquid type electrolytes. (C) 2004 Published by Elsevier B.V.
Scientific journal, English

Quasi-solid-dye-sensitized solar cells control of TiO2-gel electrolyte interfaces
S Hayase; T Kato; T Kado; S Sakaguchi; H Ueki; W Takashima; K Kaneto; R Shiratuchi; H Sumino; S Murai; S Mikoshiba
ORGANIC PHOTOVOLTAICS IV, SPIE-INT SOC OPTICAL ENGINEERING, 5215, 16-23, 2004, Peer-reviwed, Quasi-solid dye sensitized solar cells(Q-DSSC) were fabricated by employing gel electrolytes containing ionic liquids and gelators. Sufficient physical contacts between nano-crystalline TiO2 particles and gel electrolytes in nano-porous TiO2 layers were achieved by solidifying gel electrolyte precursors after the cells are filled with the electrolytes. Photocurrents increased largely by embedding carboxylic acids among dye molecules on TiO2 crystals. The nano-porous TiO2 electrolytes were fabricated by dipping the dye anchored TiO2 substrates in dilute solutions of carboxylic acids. It was found that resistances in the TiO2 layers decreased by these treatments.
International conference proceedings, English

Quasi-solid dye sensitised solar cells filled with ionic liquid - increase in efficiencies by specific interaction between conductive polymers and gelators
Y Shibata; T Kato; T Kado; R Shiratuchi; W Takashima; K Kaneto; S Hayase
CHEMICAL COMMUNICATIONS, ROYAL SOC CHEMISTRY, 21, 21, 2730-2731, Nov. 2003, Peer-reviwed, Photo-energy conversions for quasi-solid dye sensitised solar cells increased when gel electrolytes were combined with conductive polymers as counter electrodes and the conversion surpassed that for DSSCs equipped with conventional Pt counter electrodes.
Scientific journal, English

Composite Catalysts Consisting of Aluminum Complexes and Silanol Derivatives for Addition Reaction of Epoxy Resins with Active Hydrogen Compounds.
SUZUKI Shuichi; HAYASE Shuzi
Kobunshi Kagaku, The Society of Polymer Science, Japan, 51, 5, 315-321, 1994, The composite catalysts (AS catalysts) consisting of aluminum complexes and silanol derivatives have been found to acceralate the addition reactions of epoxy resins and active hydrogen compounds. Catalytic activity was not observed when one of the two components is absent, as in the case of the ring opening polymerization of epoxy resins. The catalytic activity was affected by the structures of aluminum complexes and silanol derivatives. Triphenyl silanol was more active than diphenyldiethoxysilane which was decomposed thermally to form a silanol. The acceleration effects were observed even with a small amount of the catalyst, i. e., 0.1wt% of catalyst. The DSC curve of the product from an epoxy resin and an aromatic amine with the AS catalyst showed an exothermic peak 30°C lower than that of the non-catalyst resin systems. The epoxy resins cured with the AS catalysts exhibit excellent electrical, mechanical, physical, and thermal properties which meet the requirements of electrical and space/aeronautical applications.
Japanese

色素増感太陽電池からハロゲン化ペロブスカイト太陽電池へ : 最近の研究動向と今後の展望—Transition from Dye Sensitized Solar Cells to Halide Perovskite Solar Cells : Recent Progress and Future Perspective—特集 第17回光機能性材料セミナー
早瀬 修二
Feb. 2022, 日本写真学会誌 = Journal of the Society of Photography and Imaging of Japan, 85, 1, 45-52, Japanese, 0369-5662, AN00191766

Tin lead perovskite solar cells with narrow band gap working as bottom cell of tandem solar cell
Hayase Shuzi
The Japan Photovoltaic Society, 12 Oct. 2021, Proceedings of the Annual Meeting of the Japan Photovoltaic Society, 1, 12-13, Japanese, 2436-6498

スズ系ペロブスカイト太陽電池の高電圧、高効率化
早瀬 修二
光機能材料研究会, Aug. 2021, 会報光触媒 = Photocatalysis, 66, 4-9, Japanese, 1345-5818, 40022679070

Research trend of Pb free perovskite solar cells
早瀬 修二
電気学会, 01 Mar. 2021, 電気学会研究会資料. DEI, 2021, 33, 1-3, Japanese, 40022544133

ペロブスカイト/シリコンタンデム太陽電池の開発—Development of Perovskite/Silicon Tandem Solar Cells—タンデム太陽電池の最近の動向
五反田 武志; 早瀬 修二; 松井 卓矢; 齋 均
2021, 応用電子物性分科会誌 = Bulletin of solid state physics and applications / 応用物理学会応用電子物性分科会 編, 27, 2, 51-56, Japanese, 1341-5123

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

Development of Perovskite/Silicon Tandem Solar Cells
五反田武志; 五反田武志; 西村滉平; CHEN Mengmeng; 廣谷太佑; 廣谷太佑; 早瀬修二; 齋均; 松井卓矢; 箕輪直子; 戸張智博; 齊田穣
2021, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 68th, 202102268787138678

Large-Scale Flexible Perovskite Solar Cells with p-i-n Structure
菊池創太; 早瀬修二
2021, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 68th, 202102285806584166

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

Modularization of p-i-n structure perovskite solar cells using solvents
菊池創太; 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, 202202236521769351

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

High Efficiency Lead-free Wide Bandgap Perovskite Solar Cells via Guanidinium Bromide Incorporation
カマルディン ムハマドアクマル; 沈 青; 早瀬 修二
2021, ACS Applied Energy Materials, 未定, Peer-reviwed, with international co-author(s)

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
The Japan Society of Applied Physics, 26 Aug. 2020, JSAP Annual Meetings Extended Abstracts, 2020.2, 1937-1937, Japanese, 2436-7613

Research Trend on Pb Free Sn Perovskite Solar Cell
Hayase Shuzi
The Japan Society of Applied Physics, 26 Aug. 2020, JSAP Annual Meetings Extended Abstracts, 2020.2, 167-167, Japanese, 2436-7613

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
The Japan Society of Applied Physics, 26 Aug. 2020, JSAP Annual Meetings Extended Abstracts, 2020.2, 1650-1650, Japanese, 2436-7613

Effect of A site cations on Sn vacancy in Sn perovskite
Iikubo Satoshi; Okumura Taichi; Okumura Ryo; Hayase Shuzi
The Japan Society of Applied Physics, 26 Aug. 2020, JSAP Annual Meetings Extended Abstracts, 2020.2, 1654-1654, Japanese, 2436-7613

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
The Japan Society of Applied Physics, 26 Aug. 2020, JSAP Annual Meetings Extended Abstracts, 2020.2, 1653-1653, Japanese, 2436-7613

Enhancement of Stability and efficiency of perovskite solar battery by using sulfur atom
早瀬 修二
硫酸協会, Aug. 2020, 硫酸と工業, 73, 8, 88-94, Japanese, 0370-8047, 40022335090, AN00251176

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
The Japan Society of Applied Physics, 28 Feb. 2020, JSAP Annual Meetings Extended Abstracts, 2020.1, 2403-2403, Japanese, 2436-7613

Research trend for Pb-free perovskite solar cells
Hayase Shuzi
The Japan Society of Applied Physics, 28 Feb. 2020, JSAP Annual Meetings Extended Abstracts, 2020.1, 218-218, Japanese, 2436-7613

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
The Japan Society of Applied Physics, 28 Feb. 2020, JSAP Annual Meetings Extended Abstracts, 2020.1, 2400-2400, Japanese, 2436-7613

Photoexcited carrier dynamics of PbS/CdS core-shell quantum dots
Oguri Naoki; Ding Chao; Yoshida Koji; Zhang Yaohong; Hayase Shuzi; Toyoda Taro; Shen Qing
The Japan Society of Applied Physics, 28 Feb. 2020, JSAP Annual Meetings Extended Abstracts, 2020.1, 2879-2879, Japanese, 2436-7613

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

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

研究総括の役割（さきがけ）
早瀬 修二
公益社団法人 応用物理学会, 10 Aug. 2019, 応用物理, 88, 8, 543-545, Japanese, 0369-8009, 2188-2290, 130007709597, AN00026679

The Info-powered Energy System that Supports the Social Quality of a Super Smart Society
横川 慎二; 市川 晴久; 曽我部 東馬; 澤田 賢治; 早瀬 修二; 大川 富雄
日本品質管理学会, Jul. 2019, 品質, 49, 3, 228-231, Japanese, 0386-8230, 40021976970, AN00354769

高エネルギー変換効率が期待される太陽電池の作製技術の開発 : 中間バンド型太陽電池の液相プロセス作製
細川 浩司; 澤田 拓也; 小此木 明徳; 佐藤 治之; 矢野 聡宏; 玉置 亮; 岡田 至崇; 尾込 裕平; 早瀬 修二
日本工業出版, May 2019, クリーンエネルギー, 28, 5, 22-28, Japanese, 0918-7510, 40021903309, AN10502148

Perovskite solar cells with narrow bandgap : Approach for Pb-free perovskite solar cells
早瀬 修二
電気学会, 22 Jan. 2019, 電気学会研究会資料. DEI, 2019, 1, 41-43, Japanese, 0913-5685, 40021797599, AN10013334

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

液相法で作製したPbS量子ドット/ペロブスカイト中間バンド型太陽電池-(1)設計と作製
細川浩司; 玉置亮; 澤田拓也; 小此木明徳; 佐藤治之; 尾込裕平; 尾込裕平; 早瀬修二; 岡田至崇; 矢野聡宏
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902224694841483

液相法で作製したPbS量子ドット/ペロブスカイト中間バンド型太陽電池-(2)特性評価
玉置亮; 細川浩司; 澤田拓也; 小此木明徳; 佐藤治之; 尾込裕平; 尾込裕平; 早瀬修二; 岡田至崇; 矢野聡宏
2019, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 66th, 201902237900384358

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

塗布型ハロゲン化ペロブスカイト薄膜の熱伝導率
西尾僚馬; 與那嶺亮; 佐脇卓弥; 廣谷太佑; SAINI Shrikant; 早瀬修二; 矢吹智英; 宮崎康次
2019, 日本伝熱シンポジウム講演論文集(CD-ROM), 56th, 1346-1532, 201902230664269053

様々な状態におけるペロブスカイト太陽電池の発電挙動について
斎藤英純; 青木大輔; 馬飼野信一; 高木克彦; 早瀬修二
2019, 電気化学会大会講演要旨集(CD-ROM), 86th, 201902247570309456

狭バンドギャップを有するペロブスカイト太陽電池の研究開発動向
早瀬修二
2019, 日本化学会春季年会講演予稿集(CD-ROM), 99th, 201902270358512012

PbS量子ドット/ペロブスカイトからなる中間バンド型太陽電池の液相プロセス作製
細川浩司; 玉置亮; 澤田拓也; 小此木明徳; 佐藤治之; 尾込裕平; 早瀬修二; 岡田至崇; 矢野聡宏
2019, 日本化学会春季年会講演予稿集(CD-ROM), 99th, 201902291605017941

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

鉛フリー有機無機ペロブスカイトの電子状態計算
井手敦子; 山本久美子; 奥村崚; 飯久保智; 飯久保智; 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, 201902238764797803

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

Thermal Conductivity of a Halide Perovskite Thin Film
NISHIO Ryoma; SAINI Shrikant; BARANWAL Ajay Kumar; HAYASE Shuzi; YABUKI Tomohide; MIYAZAKI Koji
In order to improve thermoelectric performance of printed halide perovskite, CsSnI3 thin films were fabricated under different conditions. The cross-plane thermal conductivities of thin films were measured by 3ω method. The surface morphology was observed using Scanning Electron Microscopy. Thin films annealed at 100oC and 130oC had uneven and smaller crystal grains than the one at 70oC. Thin films which have finer crystal grains on the surface tend to have lower thermal conductivity. Influence of phonon grain boundary scattering is considered as one of the factors for lower thermal conductivity. For further development, we will observe cross-sectional crystal grains since the thermal conductivity was measured along the film thickness direction., The Japan Society of Mechanical Engineers, 2019, The Proceedings of the Symposium on Micro-Nano Science and Technology, 2019.10, 21pm1PN304, Japanese, 2432-9495, 130007846953

Thermoelectric Properties of Perovskite Thin Film
Miyazaki Koji; Saini Shirikant; Yabuki Tomohide; Branwal Ajay; Yonamine Akira; Hayase Shuzi
The Japan Society of Mechanical Engineers, 2019, The Proceedings of the Thermal Engineering Conference, 2019, 0108, Japanese, 2424-290X, 130007836119

Review Article, Perovskite solar cells with narrow band gap
Shuzi Hayase
2019, Current Opinion in Electrochemistry, 2018, 11, 146-150., Current Opinion in Electrochem, 146-150, English, Peer-reviwed, Invited, Introduction commerce magazine

シリコンを使わない新しい太陽電池 : 塗布で作製できる高効率ペロブスカイト太陽電池
HAYASE Shuzi
太陽の光を直接電気に変換できる太陽電池は近年急速に普及しているが，ほとんどはシリコン（Si）を原料にしており，作製に1500度以上の高温が必要であった。太陽電池を作るためのエネルギーを回収できる年限（エネルギーペイバックタイム：EPT）は，シリコン系太陽電池は1～2.5年程度とされているが，低温で作製できる塗布型の太陽電池は1年以内といわれている。これまで低温で作製する太陽電池は半導体特性が結晶性シリコンほど良くなく，太陽光変換効率は結晶性シリコンの半分程度であった。最近，低温塗布で作製しても結晶性シリコンに迫る効率を有するペロブスカイト型太陽電池が発明され，世界中で多くの研究者が基礎研究，応用研究，実用化研究に取り組んでいる。本講座では，ペロブスカイト太陽電池の基礎，仕組み，研究動向について解説する。, The Chemical Society of Japan, 20 Jul. 2018, CHEMISTRY & EDUCATION, 66, 7, 346-349, Japanese, 0386-2151, 2424-1830, 130007670978, AN10033386

Facile fabrication of large area oriented conjugated polymer films by ribbon-shaped FTM and its implication on anisotropic charge transport
Atul SM Tripathi; Nikita Kumari; Shuichi Nagamatsu; Shuzi Hayase; Shyam S Pandey
2018, Organic Electronics, 65, 1-7

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

Thermoelectric Properties of a Coated Perovskite Thin Film
Yonamine Akira; Hirotani Daisuke; Sawaki Takuya; Saini Shrikant; Yabuki Tomohide; Hayase Shuzi; Miyazaki Koji
The discovery of hybrid perovskite can lead to the net-generation energy conversion platforms due to ultra-low thermal conductivity and large Seebeck coefficient. However, optimization of enhanced electrical conductivity is still challenging. In this work, we study growth parameters and thermoelectric properties of a coated CsSnI₃ perovskite thin film. We investigated the effects of mixing time, heating temperature and heating time on the properties of a perovskite film. We measured thermoelectric properties near room temperature and found that growth parameters influence the crystal grain size further the value of figure of merit. Our results shows that the best ZT about 0.086 at room temperature for sample with solvent mixing time about 5 h, heating temperature about 100°C and heating time is 10 min. These result and analysis are preliminary. In future, our plan is to optimize the growth parameters such as spin coating conditions, heating temperature and time to enhance the value of ZT., The Japan Society of Mechanical Engineers, 2018, The Proceedings of the Thermal Engineering Conference, 2018, 0124, Japanese, 2424-290X, 130007637672

Recent progress on Pb free and Sn perovskite solar cells
早瀬 修二
日本太陽エネルギー学会, 2017, 太陽エネルギー = Journal of Japan Solar Energy Society, 43, 2, 29-34, Japanese, 0388-9564, 40021177222, AN00352129

ペロブスカイト太陽電池の現状と将来展望
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, 229-242, Japanese, 2423-8805, 40021070507, AN10464559

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
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

蒸着法によりインターカレートを制御した単純積層型CsPbI₃ペロブスカイト太陽電池の作製
米澤 叶祐; 山本 晃平; SHAHIDUZZAMAN Md; 古本 嘉和; 浜田 啓太郎; RIPOLLES Teresa S.; 桑原 貴之; 高橋 光信; 早瀬 修二; 當摩 哲也
電子情報通信学会, 14 Jul. 2016, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 116, 134, 23-26, Japanese, 0913-5685, 40020907144, AA1123312X

Sn系ペロブスカイト太陽電池と界面制御
尾込 祐平; 早瀬 修二
光機能材料研究会, Jun. 2016, 会報光触媒, 49, 54-61, Japanese, 1345-5818, 40020897143

Pb Free Perovskite Solar Cells : Present and Future
早瀬 修二
大阪工研協会, May 2016, 科学と工業 = Science and industry, 90, 5, 143-149, Japanese, 0368-5918, 40020851295, AN00354430

交互積層法によりインターカレートを制御した蒸着型CsPbI₃ペロブスカイト太陽電池の高効率化
米澤叶祐; 山本晃平; SHAHIDUZZAMAN Md; 古本嘉和; RIPOLLES Teresa S.; 辛川誠; 辛川誠; 桑原貴之; 桑原貴之; 高橋光信; 高橋光信; 早瀬修二; 當摩哲也; 當摩哲也
2016, フロンティア太陽電池セミナー, 1st, 201902279320015925

ヘテロ界面構造がSn系ペロブスカイト太陽電池効率に及ぼす影響
早瀬修二
2016, フロンティア太陽電池セミナー, 1st, 201902299224950307

非Pb系ペロブスカイト型太陽電池の研究開発動向
OGOMI Yuhei; HAYASE Shuji
The Electrochemical Society of Japan, 2016, Electrochemistry, 84, 6, 449-453, English, 1344-3542, 2186-2451, 130005154342, AN00151637

Facile synthesis and characterization of sulfur doped low bandgap bismuth based perovskites by soluble precursor route
Vigneshwaran M; Ohta T; Iikubo S; Kapil G; Ripolles T; Ogomi Y; Ma T; Pandey S; Shen Q; Toyoda T; Yoshino K; Minemoto T; Hayase S
2016, Chemistry of Materials, 28, 18, 6436-6440

Perovskite solar cell covering Infrared regions and trial to Pb-free perovskite solar cells
早瀬 修二
オプトロニクス社, Jul. 2015, オプトロニクス, 34, 7, 82-86, Japanese, 0286-9659, 40020532392, AN00360965

Printable Solar Cells with Self-organized Structure
早瀬 修二
小峰工業出版, Jul. 2015, 化學工業, 66, 7, 553-558, Japanese, 0451-2014, 40020515087, AN00037245

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

Perovskite Solar Cells : Present and Future
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, 6-13, Japanese, 0913-6150, 40021171702, AN00015672

ペロブスカイト型太陽電池の光活性層界面に生成する光電荷分離状態の時間分解EPR
宮崎晃侑; 長谷川将司; 尾込裕平; 立川貴士; 早瀬修二; 小堀康博
2015, 電子スピンサイエンス学会年会講演要旨集, 54th, 201502215097118287

Coverage up to the infrared region: cocktail perovskite solar cells
HAYASE Shuzi
Printable Pb perovskite solar cells have attracted interest because of a high power conversion efficiency that can reach 17%. However, the light harvesting region has been limited in the visible region to 800 nm. In order to increase the power conversion efficiency further, device structures harvesting energy from the near infrared area are desired. We have succeeded in harvesting light up to 1000 nm by using Sn/Pb cocktail perovskite materials. HOMO-LUMO energy levels were tunable and the stability in air was improved by changing the Sn/Pb ratio. When this was compared to a Pb perovskite solar cell with 14.3% efficiency, the decrease in shunt resistance was remarkable. In order to increase the efficiency further, a design for the charge separation interface that avoids charge recombination is needed., The Japan Society of Applied Physics, 10 Aug. 2014, Oyo Buturi, 83, 8, 660-664, Japanese, 0369-8009, 2188-2290, 130007718603, AN00026679

Non-vacuum Process of CuInS_2 Thin Films From Metal Xanthate Precursors
Mochihara Akiko; Yoshino Kenji; Kawano Minobu; Ogomi Yuhei; Pandey Shyam S.; Shen Qing; Toyoda Taro; Hayase Shuzi
Cu–III–VI_2 compounds have attracted considerable interest because of their possible photovoltaic applications. The ternary semiconductor copper indium sulfide (CuInS_2) is one of the promising materials for thin film solar cells because its bandgap energy of 1.5 eV and the absorption coefficient of 10^5 cm^<-1>. CuInS_2 thin film on glass substrate is grown by dipping-coat from Cu- and In-xanthate solution as precursor materials. X-ray diffraction pattern indicated that peaks of CuInS_2 (112) are observed at 150℃. This temperature is lowest in non-vacuum process of CuInS_2 film. The all CuInS_2 films are p-type conductivity by thermo prove analysis because Cu atom in In site defects are dominant in the samples from EPMA results., Miyazaki University, 31 Jul. 2014, Memoirs of the Faculty of Engineering, Miyazaki University, 43, 81-84, Japanese, 0540-4924, 120007122054, AA00732558

Sn based perovskite solar cells covering infrared region
早瀬 修二
日本太陽エネルギー学会, 2014, 太陽エネルギー = Journal of Japan Solar Energy Society, 40, 4, 17-24, Japanese, 0388-9564, 40020179390, AN00352129

完全封止型円筒型色素増感太陽電池の作製と特徴
早瀬 修二; 馬 廷麗; .藤澤 繁樹
オーム社, Jan. 2014, 101, 1, 54-56, Japanese, 0386-5576, 40019945499, AN10400363

植物由来溶媒による有機半導体薄膜の作製
永松秀一; 高嶋授; PANDEY Shyam S.; 早瀬修二
2013, 応用物理学会秋季学術講演会講演予稿集(CD-ROM), 74th, 201302287699045529

Transparent conductive oxide-less dye-sensitized solar cells (TCO-less DSC) with back contact structure
早瀬 修二
日本太陽エネルギー学会, 30 Nov. 2012, 太陽エネルギー = Solar energy, 38, 6, 31-38, Japanese, 0388-9564, 10031128559, AN00352129

One-Step Deposition of Self-Oriented β-Phase Polyfluorene Thin Films for Polarized Polymer Light-Emitting Diodes
DAUENDORFFER Arnaud; MIYAJIMA Shougo; NAGAMATSU Shuichi; TAKASHIMA Wataru; HAYASE Shuzi; KANETO Keiichi
25 Sep. 2012, Applied physics express, 5, 9, "092101-1"-"092101-3", English, 1882-0778, 10031005197, AA12295133

Proposal of high efficiency Quasi-solid dye sensitized solar cell with Amylose-iodine
幸後健; 早瀬修二; 海宝龍夫; 田口充
2012, 鈴鹿工業高等専門学校紀要(Web), 45, 0286-5483, 202002253973241274

豊胸術後の乳がん検診症例の検討
多田豊治; 牧野愛; 早瀬洋子; 高川真唯; 宮本有佳; 浅井葉子; 立松志歩子; 坂本修二; 松本好市
2012, 総合健診, 39, 1, 1347-0086, 201202276233720502

豊胸術後の乳がん検診症例の検討
早瀬洋子; 立松志歩子; 松岡詠巳; 高川真唯; 牧野愛; 浅井葉子; 宮本有佳; 坂本修二; 多田豊治; 松本好市
2011, 人間ドック, 26, 2, 1880-1021, 201102281699311820

Robust Hole Transport in a Thienothiophene Derivative toward Low-cost Electronics
Shinya Oku; Kazuhiro Takamiya; Daisuke Adachi; Shuhei Ishikawa; Shuichi Nagamatsu; Wataru Takashima; Shuzi Hayase; Keiichi Kaneto
A new p-type organic semiconductor, bis(hexylthiophenyl)thienothiophene, was synthesized and evaluated for its transport characteristics A robust hole transport was observed even on bare SiO2/Si and on flexible substrates under dark-air conditions The discovered characteristics reduce the surface preparation necessary for device fabrication for low cost electronics, CHEMICAL SOC JAPAN, Dec. 2010, CHEMISTRY LETTERS, 39, 12, 1315-1316, English, 0366-7022, 1348-0715, 10027468710, WOS:000285814100033

TCO-less dye-sensitized solar cells consisting of all metal electrodes
早瀬 修二
化学工業社, Apr. 2009, 化学工業, 60, 4, 249-255, Japanese, 0451-2014, 40016570609, AN00037245

Solidification of dye sensitized solar cells with self organization
INAKAZU Fumi; KOGO Ken; HAYASE Shuzi
Solidification of dye sensitized solar cells is one of crucial problems to be solved in order to improve the durability. In this report, the solidification of ionic liquid type dye sensitized solar cells is reported. The bottom line is that the solar cell performance is maintained by fabrication of ionic path in the solid media after the solidification. The ionic path is built by use of self organization of ionic liquids. Two layer charge carrier medium consisting of high carrier concentration in the bulk layer and low carrier concentration in the TiO_2 layer is proposed. The former keeps the high conductivity in the solid media and the latter inhibits the back electron transfer from the TiO_2 layer to the electrolyte. The validity of the two layer structure is proved by using several cell structures., The Institute of Electronics, Information and Communication Engineers, 19 Oct. 2007, IEICE technical report, 107, 292, 13-17, Japanese, 0913-5685, 110006452560, AN10013334

Effect of Nanoparticle Addition into Anode Electrodes for Direct Ethanol Fuel Cells
PARK Namsin; SHIRAISHI Takeyuki; KAMISUGI Kazuyoshi; HAYASE Shuzi
05 Jul. 2007, Chemistry letters, 36, 7, 922-923, English, 0366-7022, 10019745720, AA00603318

Dye-sensitized solar cells consisting of ionic liquids
早瀬 修二
電気化学会溶融塩委員会, 2007, Molten salts, 50, 3, 103-108, Japanese, 0916-1589, 40015692503, AN10179993

アミロースヨウ素錯体を用いたイオンパス構築の試み
幸後健; 早瀬修二; 海宝龍夫; 田口充; 細谷佳代
2007, 化学関連支部合同九州大会・外国人研究者交流国際シンポジウム講演予稿集, 44th, 200902241190893668

Dye adsorption, Blocking molecule adsorption and Characteristic of dye sensitized solar cells by Supercritical fluid : Performance improvement of dye sensitized solar cells
SAKAGUCHI Shohhei; HAYASE Syuzi
In order to increase photo voltaic performances, it is necessary to increase the amount dye molecules on TiO2 surfaces and to block the bare TiO2 surfaces with blocking molecules. It has been reported that molecules can diffuse well in super critical liquids. We applied this super critical liquids to dye sensitized solar cells. When adsorptions of dyes and blocking molecules are carried out in super critical CO2 liquids, Jsc and Voc increased, compared with those made in conventional adsorption methods., The Institute of Electronics, Information and Communication Engineers, 01 Sep. 2006, IEICE technical report, 106, 228, 33-36, Japanese, 0913-5685, 110004823598, AN10013334

Fabrication of ion-paths for ionic liquid type quasi-solid dye sensitized solar cell
KATO Takehito; HAYASE Shuzi
Quasi-solid dye sensitized solar cells consisting of porous alumina/ionic liquid electrolyte composites are reported. The straight nano-pores of the porous alumina film are surface-modified with self-organized imidazolium iodide moieties bearing long alkyl groups. By filling the pores with ionic liquids, straight ion paths are fabricated along the aligned the imidazolium moieties, where, iodine molecules are highly concentrated. The swift ion diffusion is explained by Grotthuss mechanism. A new hybrid quasi-solid electrolyte consisting of low I_2 concentration for high light penetration layer and high I_2 concentration for a carrier layer is proposed., The Institute of Electronics, Information and Communication Engineers, 01 Sep. 2006, IEICE technical report, 106, 228, 23-27, Japanese, 0913-5685, 110004823596, AN10013334

Dye Sensitized Solar Cells Consisting of Thermally Stable Nb-doped-Titanium Dioxide Nanowire
BEPPU Takayuki; HAYASE Shuzi
Recently, dye sensitized solar cells using titanium dioxide nanowire and nanotube were reported. Typically, 450℃ anneal process were required for electrode formation. Used by high baking process broke their shapes. In this article, we reported Nb doped titanium dioxide nanowire. The nanowire held shapes and improved photovoltaic performance, The Institute of Electronics, Information and Communication Engineers, 01 Sep. 2006, IEICE technical report, 106, 228, 29-32, Japanese, 0913-5685, 110004823597, AN10013334

ナノ界面制御による擬固体色素増感太陽電池の高性能化
早瀬 修二
Jun. 2006, Molecular electronics and bioelectronics, 17, 2, 121-128, Japanese, 10019161180, AN10464559

Electrodes/Gel Electrolytes interfaces and Quasi-solid Dye Sensitized Solar Cell Efficiencies
HAYASE Shuji
日本太陽エネルギ-学会, 31 Jul. 2003, Journal of Japan Solar Energy Society, 29, 4, 12-17, Japanese, 0388-9564, 10011753731, AN00352129

Yesterday, Today, and Tomorrow of Silicon Chemistry. Application Research of Silicon Compounds to Most Advanced Semiconductor Materials.
早瀬修二
2002, ケイ素化学協会誌, 17, 200902124093627094

色素増感太陽電池の実用化を目指して
早瀬 修二; 角野 裕康; 村井 伸二; 御子 柴智
日本太陽エネルギ-学会, 31 Jul. 2001, 太陽エネルギー = Solar energy, 27, 4, 28-31, Japanese, 0388-9564, 10007498637, AN00352129

Quasi-solid dye sensitized solar cells using gel electrolytes
Hayase Shuzi; Sumino Yasuhiro; Murai Shinji; Mikoshiba Satoshi
We invectigate quasi-solid dye sensitized solar cells(DSC)using chemically crosslinked gels. Ge1-electrolyte-precursors containing room-temperature molten salts and gelators are liquid at first. After they are injected in the cell, gels form in the cell by heating it at 80℃. The gelator was designed to make gels even in the presence of iodine which is an inhibitor for conventional gelators. The gelator is also designed so that gelation occurs by the addition of only 5wt% gelators by controlling the interaction between the gelators and the electrolytes. The quasi-solid DSCs exhibit high performances corresponding to those containing liquid electrolytes., The Institute of Electronics, Information and Communication Engineers, 26 Jul. 2001, Technical report of IEICE. OME, 101, 226, 27-32, Japanese, 0913-5685, 110003301356, AN10013334

Recent progress on narrow band gap perovskite solar cells
Shuzi Hayase
Keynote oral presentation, English, IEEE ICASI, 2019 IEEE International Conference on Applied System Innovation, Invited, IEEE, 北九州市, International conference
12 Apr. 2019

狭バンドギャップペロブスカイト太陽電池の研究開発動向
早瀬修二
Oral presentation, Japanese, 日本化学会, 日本化学会, 甲南大学, Domestic conference
16 Mar. 2019

狭バンドギャップを有するペロブスカイト太陽電池
早瀬修二
Public discourse, Japanese, NICE研究会講演会, NICE研究会, 北九州, Domestic conference
22 Feb. 2019

Recent research progress on narrow band gap perovskite solar cells and Pb free perovskite solar cells
Shuzi Hayase
Keynote oral presentation, English, International Symposium on Solar Energy Materials, Invited, 甲南大学, 甲南大学, International conference
25 Jan. 2019

狭バンドギャップペロブスカイト太陽電池ー鉛を用いないペロブスカイト太陽電池へのアプローチー
早瀬修二
Invited oral presentation, Japanese, 有機エレクトロニクス研究会, Invited, Domestic conference
23 Jan. 2019

Progress of perovskite solar cells with Sn
Shuzi Hayase
Invited oral presentation, English, 12 th Aseanian Conference on Nano-hybrid Solar Cells (NHSC), 12 th Aseanian Conference on Nano-hybrid Solar Cells (NHSC), China, International conference
18 Dec. 2018

Snを含むペロブスカイト太陽電池の現状と今後
早瀬修二
Invited oral presentation, Japanese, 第3回フロンティア太陽電池セミナー, Invited, 宮崎大学, 宮崎, Domestic conference
13 Dec. 2018

SnPb and Pb-Free SnGe Perovskite Solar Cells -Narrow band gap perovskite solar cell
Shuzi Hayase
Invited oral presentation, English, IIJWBME(India-Japan workshop on biomolecular electronics & organic nanotechnologyfor environment preservation-2018), Invited, IIJWBME organizer, India, International conference
06 Dec. 2018

SnPb and Pb-Free SnGe Perovskite Solar Cells -Narrow band gap perovskite solar cell
Shuzi Hayase
Invited oral presentation, English, MRS, MRS, Boston, International conference
29 Nov. 2018

有 機 系 お よ び ペ ロ ブ ス カ イ ト 太 陽 電 池 の 現 状 と 将 来 展 望
早瀬修二
Public discourse, Japanese, 有機エレクトロニクス材料研究会チュートリアル, Invited, 有機エレクトロニクス材料研究会, 九州大学, Domestic conference
20 Nov. 2018

Narrow band gap perovskite solar cell
Shuzi Hayase
Invited oral presentation, English, 7th Korea-Japan Joint Seminar on PV 2018, Invited, 7th Korea-Japan Joint Seminar, Korea, International conference
08 Nov. 2018

ペロブスカイト太陽電池の現状と課題
早瀬修二
Invited oral presentation, Japanese, 半導体パッケージロードマップ講演会, Invited, 半導体パッケージロードマップ員会, 東京, Domestic conference
19 Oct. 2018

Halogenated perovskite solar cells with Sn
Shuzi Hayase
Invited oral presentation, English, IPS22(22nd International Conference on Photochemical Conversion and Storage of Solar Energy), Invited, IPS, China, International conference
31 Jul. 2018

Toward less Pb and Pb-free perovskite solar cells, -Photoelectric conversion in near IR region
Shuzi Hayase
Invited oral presentation, English, The 8th Sungkyun International Solar Forum 2019, Invited, Sungkyunkwan University (SKKU), Seoul, Korea, International conference
26 Jun. 2018

Design guideline to mixed metal SnPb-perovskite solar cells with 17.42% and Pb free Sn-perovskite solar cells with 5.52%
Shuzi Hayase
Invited oral presentation, English, MRS spring meeting, MRS, International conference
04 Apr. 2018

高分子学会

日本化学会

電気化学会

American Chemical Society

Electrochemisal Society

応用物理学会

MRS

小規模創電・蓄電の統合運用を可能にするインターネット型電力プラットフォーム
横川 慎二; 川喜田 佑介; 早瀬 修二; 澤田 賢治; 曽我部 東馬; 中山 舜民; 戸辺 義人
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), 23H01636
01 Apr. 2023 - 31 Mar. 2027

無鉛型高次元ハライドペロブスカイト材料による太陽電池の高効率・高耐久化
宮坂力
2019 - 2024

Control of the nano-interface of heterojunction quantum dot solar cells and improvement of the charge separation efficiency for multiple excitons
沈 青; 豊田 太郎; 早瀬 修二
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), ホットインジェクション法を用いて、ペロブスカイトAPbX3（X = Cl-、Br-、およびI-）量子ドット（PQD）を作製し、量子ドット太陽電池へ適用した。今年では、PQD のAサイトはそれぞれセシウム（Cs）、メチルアンモニウム（MA ）、またはホルムアミジニウム（FA）とそれらの混晶を用いた。主にAサイトの違いによるPQD結晶構造、光物性と光励起キャリアダイナミクスおよび量子ドット太陽電池の光電変換特性の変化について検討した。透過型電子顕微鏡（TEM）およびエネルギー分散型X線分光（EDS）測定の結果から、混晶したPQDでは、混晶されたＡサイトの成分はPQD全体でランダムに分布していることが判明した。さらに、Ａサイトの混晶化によりPQDのフォトルミネッセンス量子収率が向上したことを見つけた。大変興味深いことは、Ａサイトの混晶化により、ペロブスカイト量子ドット太陽電池の光電変換効率は12％ぐらいから約15％までに向上したことに成功した。さらに、ＡサイトはPQDの光励起キャリアダイナミクス、特にホットキャリアの緩和プロセスに大きな影響を与えることを見出した。さらに、カルボキシル基を持つ一連の半導体配位子を使用することにより、PQDからCoolキャリアとホットキャリア両方を効率的に抽出することが可能であることを発見した。光励起ホットキャリアダイナミクスを解析した結果、PQDのホットキャリアの冷却が大幅に延長され、ホットキャリアの抽出が容易になることが分かった。半導体リガンドとCsPbI3QDの間の化学結合、電子結合、およびキャリア移動は、ドナー-アクセプターシステムでは互いに共生していることが示唆された。これらの結果は、Coolとホットキャリアの抽出と太陽電池への利用を実現する要因に光を当て、多重励起子型とホットキャリア型太陽電池を設計するための戦略を提供できる。, 20H02565
01 Apr. 2020 - 31 Mar. 2023

鉛を含まないSn-ペロブスカイト太陽電池の高効率化指針提案
早瀬修二
2019 - 2021

錫ペロブスカイト光電変換素子の発電阻害機構解明とナノへテロ界面構築による高効率化
早瀬修二
Principal investigator
01 Apr. 2017 - 31 Mar. 2020

Direct observation of spin formation and charge accmulation in perovskite solar cells and the performance improvement
MARUMOTO Kazuhiro; HAYASE Shuji
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, University of Tsukuba, Grant-in-Aid for Challenging Exploratory Research, Perovskite solar cells have attracted much attention as a next-generation solar cell because they show high efficiency and can be fabricated at a low-cost fabrication process. In this study, we have directly observed spin and charge states in perovskite solar cells under device operation using electron spin resonance spectroscopy from a microscopic viewpoint in order to elucidate the degradation mechanism of the cells. As a result, we have found the correlation between the spin-charge states and the degradation of the device performance, and have clarified the origin of the degradation mechanism of the cells. Such elucidation of the correlation between the spin-charge states and the performance degradation at the molecular level would give deep insight into the operation mechanism of the cells and would be useful for further improvement of the device performance., 15K13329
01 Apr. 2015 - 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

In-situ measurement of perovskite crystal growth and the solar cell efficiency.
HAYASE SHUZI
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kyushu Institute of Technology, Grant-in-Aid for Challenging Exploratory Research, This report deals with the relationship between perovskite(Pb-PVK) solar cell efficiency and the crystal structure affected by nano-pore walls. Crystal structures of perovskite (Pb-PVK) created in the TiO2 nano-pore was smaller than that of the bulk Pb-PVK and were affected by the wall structures passivated with thin Al2O3, Y2O3 and ZrO2 layer. Crystal defect density was also affected by the surface structure. The presence of chloride anion increased the crystal size as well as the grain size. In addition, density of Ti-O-Pb linkages which present at the hetero-interface between the Pb-PVK layer and nano-pore wall of TiO2 and work for decreasing charge recombination centers, was enhanced by the presence of the chloride anion. The above results explain the efficiency enhancement of the solar cell in the presence of chloride anion. It was found that nano-pore wall structure is one of the factors for determining the efficiency., 15K13774
01 Apr. 2015 - 31 Mar. 2017

Carrier diffusions and their electronic states at interfaces in perovskite solar cells
Kobori Yasuhiro; HAYASE SHUJI; OGOMI YUHEI
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kobe University, Grant-in-Aid for Challenging Exploratory Research, In recent years, great attentions have been attracted on the perovskite solar cells as the next generation thin-film photovoltaics that can be low-cost, flexible and light. In this study, we observed photoinduced separated charges in the photoactive layers in the perovskite (CH3NH3PbI3) solar cells by using the time-resolved electron paramagnetic resonance spectroscopy for the three layer thin films (Spiro-OMeTAD/CH3NH3PbI3/TiO2 on a glass substrate) composed of the organic hole transport layer (Spiro-OMeTAD), the CH3NH3PbI3 layer and the mesoporous TiO2 fabricated by spin coating method on the mesoporous TiO2 films. We have characterized the spin density distributions of the trapped holes of the CH3NH3PbI3 layer at 110 K. Furthermore, from the ESP generated in the trapped hole, we have estimated the J coupling in the primary electron-hole pairs which will give us an insight on the electronic coupling of the Wannier excitons., 26620065
01 Apr. 2014 - 31 Mar. 2017

Investigation of suitable dye molecular framework focusing small driving force for electron injection and dye regeneration in NIR dyes for efficient photoconversion
PANDEY SHYAM S.
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kyushu Institute of Technology, Grant-in-Aid for Scientific Research (C), Combined theoretical and experimental approaches have been applied for the design and development of novel sensitizing dyes aiming towards the NIR photon harvesting. Utilizing a model far-red sensitive squaraine dye, TD-DFT theoretical calculations were performed to optimize the best calculation parameters giving minimum possible error between the calculated and experimental values of the energetics and electronic absorption spectrum. Optimization of calculation parameters gave only an error of 0.1 eV for the energy of HOMO and 40-60 nm in the absorption maximum tested for a series of squaraine dyes. It has also been found that it is possible to have facile electron injection and dye regeneration with the minimum energy barrier of 0.15 eV and 0.12 eV, respectively. This led to conclude that it is possible to design novel sensitizers having photon harvesting up to 1060 nm., 26410206
01 Apr. 2014 - 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

Proposal of photoelectric conversion device structures fabricated by merging molecular diffusion engineering in continuous nanopores and photoelectron conversion interface engineering
HAYASE Shuzi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kyushu Institute of Technology, Grant-in-Aid for Scientific Research (B), Our objective is to propose items which are necessary to increase efficiency of dye-sensitized solar cells from the view point of diffusion of redox species in TiO2 nanopores whose wall is stained by dye molecules. When wall of nano pores was stained by dyes having similar size of substituents, diffusion of redox species in nanopores stained with dyes bearing polar substituents became low and open circuit voltage was low. This was explained by facile charge recombination between slowly diffused redox speciesand TiO2 electrons in nanopores. Dyes with hydrophobic long alkyl groups are proposed to be preferable for dye-sensitized solar cells with high open circuit voltage from the view point of redox diffusion in nanopores stained by dyes., 21350079
2009 - 2012

酸化物半導体ナノホールアレイからの電気化学発光と波長制御
早瀬 修二
日本学術振興会, 科学研究費助成事業, 九州工業大学, 萌芽研究, 本テーマの目的はナノスペースからの発光を利用し、電気化学発光の高効率化を図ることおよびその波長をナノ構造によって制御可能かどうかを検証することである。電気化学発光種にはRu錯体を用いた。Ru錯体の酸化体と還元体が衝突することにより励起Ru錯体が生成し、これが基底状態に戻るときに発光が観察される。昨年はチタニアのナノホールアレイを用い、ナノホールでの限られた空間でRu錯体酸化体と還元体の衝突頻度を増大することによって、発光強度を増大させることに成功した。今年は、チタニアナノホールアレイより作製が容易で大面積作製が可能なZnOナノロッドアレイを電極に用いた。ZnOナノロッドアレイ間のナノ空間からの電気化学発光を観察し、ナノ空間を使った発光強度増大を検討した。素子は、透明導電膜基板/酸化亜鉛ナノドットアレイ/Ru錯体溶液/透明導電膜基板からなる。素子に交流を印加したところ、平板の電極に比べ10倍以上の大きな発光の増大が見られた。さらに特徴的なことは、発光開始電圧が平板電極型素子の2.5-3Vに比較し酸化亜鉛ナノロッドを使ったセルでは1.5Vと大きく低電圧化できたことである。ZnOナノロッドの長さを4.0ミクロンから8.1ミクロン、11.5ミクロンと長くすると、さらに発光強度の増大が見られた。発光の時間分解特性を詳細に検討することにより反応のメカニズムを検討した。負の電位から正の電位に変化したときにミリ秒の時間スケールで大きな発光が持続することがわかった。これはZnOナノロッドから電子が注入されてナノスペースに生成した多量のRu錯体還元体(負極)が、電極の極性が変わった後で(正極)、酸化亜鉛ナノロッド底部の透明導電膜基板で生成したRu錯体酸化体がナノスペース中を煙突として移動し、効率よくナノスペース中でRu酸化体と還元体が衝突するためと考えられた。このようにナノスペースを用いた発光現象を利用することによって、電気化学発光の低電圧発光、発光の高効率化が可能になることを実証できた。, 19655070
2007 - 2008

Low temperature fabrication of electron-nano-path and the performance of the solar cell consisting of the bi-continuous nano-path.
HAYASE Shuzi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kyushu Institute of Technology, Grant-in-Aid for Scientific Research (B), The improvement of the photovoltaic performance for dye sensitized solar cells prepared at low temperatures was discussed from the view point of the fabrication of nano-paths for electrons and ions in the TiO_2 electrodes. The effect of ionic diffusions in the TiO_2 nano-porous electrodes on the solar cell performance was simulated by using a new model. It was concluded that the retardation of the ionic diffusions in the TiO_2 electrode causes the deterioration of the solar cell performance. The results suggested that the nano-pores have to be designed well. In order to improve the ionic diffusions in the TiO_2 nano-porous electrode, TiO_2 electrodes consisting of fractal like structures were fabricated by the electro-spray deposition of TiO_2 nano-particles on the conductive substrate. The short circuit current (Jsc) increased due to the increase in ionic diffusion coefficients in the nano-pores, which was consistent with the simulation results. In addition, we found that the addition of needle like TiO_2 help increase the ionic diffusions in the TiO_2 nano-porous electrodes. The addition of the needle increased the Jsc. Another approach for the improvement is to make electron paths at low temperature. We focused on TiO_2 grain boundary. Low V acceleration electron beam exposure (LVEB) which does not damage the substrate because of the low voltage was tried at room temperature. After the LVEB exposure, the increases in the electron diffusion coefficient and Jsc were observed, suggesting that the LVEB is useful for linking the boundary at low temperatures. The dye-staining of TiO2 surface under CO_2 super critical conditions increased Jsc because of the increase in the surface coverage of the nano-porous TiO_2 electrode. However, the surface trap passivation with dye molecules did not increase the electron diffusion coefficient because on the traps remaining at the interface of the grain boundary. This contrasted the results of DSCs prepared at 450℃., 15350112
2003 - 2006

Highly Efficiency Solar Energy Conversion Using Photointerface System
FUJISHIMA Akira; MURAKAMI Taketoshi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research on Priority Areas, Toward important technical developments in the effective use of solar energy, many devices by the application of photofunctional interface based on TiO2 have been investigated. In this research, we had investigated the followings that were particularly considered as playing the major roles in such devices. -Development of Fabrication Process of Dye-Sensitized Solar Cell: With regard to wet-type dye-sensitized solar cells, there have been practical problems in terms of stability and durability due to the use of an electrolyte. To solve the problems, we fabricated a complete-solid-type dye-sensitized solar cell by using CuI as a p-type semiconductor in place of an electrolyte. Triethylamine hydro-thiocyanate was used as a grain refiner of CuI crystal. With this complete-solid-type dye-sensitized solar cell made by using a CuI automatic application device, photovoltaic conversion efficiency with reproducibility was achieved. -Research on Low Reflectance Self-Cleaning Glass: The utilization of self-cleaning properties of photocatalyst for preventing stains on glass is disadvantageous in that the light transmittance of glass is reduced due to a high refractive-index and light reflectivity of TiO2. In order to solve this problem, we developed a low-reflectance self-cleaning glass using SiO2 particles and TiO2 nanoparticles. As a result, we succeeded in coating a glass substrate with a TiO2-SiO2 double layer, which showed a high self-cleaning function as well as a maximum light transmittance of 97% or higher. -Research on Water Purification Reactor using Photocatalyst: A photocatalyst water purification reactor can treat 10 liters of water at a time. It can also be used in continuous water flow. With this reactor, the degradation of thionine solution having reproducibility was confirmed. -Research on TiO2 Nano-Fiber: TiO2-SiO2 nano composite fiber is an excellent material that is expected to have high photocatalyst property, heat stability, and low thermal expansion. In this research, TiO2-SiO2 nano composite fiber was researched and developed on the basis of a new adjustment method that used P-25 (Nippon Aerosil) as Ti source and TEOS (Tetraethoxy-silane)-PDMS (Polydimethylsiloxane) sol composite as Si cource. By implanting TiO2 nanoparticles into a SiO2 fiber based on this method, we succeeded in developing a TiO2-SiO2 nano composite fiber having a diameter of 500-700nm and consisting of a TiO2-SiO2 linear complex chain with high mechanical strength., 14050023
2002 - 2006

High efficiency quasi-solid dye sensitized solar cells consisting of organic-inorganic hybrid ionic paths
HAYASE Shuzi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kyushu Institute of Technology, Grant-in-Aid for Scientific Research on Priority Areas, Solidification of dye sensitized solar cells (DSC) is one of the most crucial research items. Solidification generally decreases ionic diffusion and lower the solar cell efficiency. Because of this, quasi-solidification is one of the most promising candidates for the solidification. However, quasi-solidified DSCs reported so far are soft gel and the solidification ratio (solid part/all carrier layer) was less than 10-20% because the high solidification ratio lowers the efficiency. Our purpose is to propose high efficiency quasi-solid DSCs with high solid content more than 50% (so-call high solid type quasi-solid DSCs). In this research program, we proposes hybrid quasi-solid DSCs consisting of a high carrier density layer and a low carrier density layer. The former fills the bulk layer between a TiO_2 layer and a counter electrode and the latter fills the nano-pores in TiO_2 layers. The former brings about high conductivities in the solid state layer (bulk layer) and the latter prevents back electron transfer from the TiO_2 to carrier layer. The proposal was realized by three cell structures, namely, surface modified porous Al_2O_3/ionic liquid type electrolyte, surface modified nano-oxide materials/ionic liquid type electrolyte, and a composite carrier transport layer consisting of porous Al_2O_3 membrane/conductive polymer/ionic liquid type electrolyte. In all cases, carriers were concentrated in the surface-modified nano-structured materials, resulting in making high carrier concentration areas. The photovoltaic properties of the high solid type solar cells (solidification ratio/more than 50%) were almost the same as or higher than those of the cells before the solidification. It was proved that the hybrid solar cells consisting of two carrier concentration layers are effective structure having high photovoltaic properties and the idea has generality for fabricating high efficiency solid solar cells., 17029051
2001 - 2006

擬固体電解質とナノチタニア層との界面最適化による擬固体色素増感太陽電池の高性能化
早瀬 修二
日本学術振興会, 科学研究費助成事業, 九州工業大学, 特定領域研究, 色素増感太陽電池(DSSC)は揮発性有機溶剤を含んだ電解液を使用しており、耐久性を確保するには十分な封止技術が必要である。我々は不揮発性の室温溶融塩をゲル化することにより電解質を固体化する技術が耐久性向上に有効であることを実証してきた。しかし室温溶融塩は有機溶剤タイプの電解液に比較し粘度が高くイオンの拡散定数が低いという欠点があった。限界電流を大きくするため電荷輸送体であるヨウ素の濃度を有機溶剤系電解液より10倍程度高くする必要があった。このため暗電流が大きくなり太陽電池性能の低下がしばしば見られた。チタニア界面を修飾して逆電子移動を抑制する試みが従来の溶剤系電解液で試みられてきた。しかしSnO_2を半導体電極に使った場合には大きな性能向上効果が報告されているがチタニアを使った場合には効果は小さいと報告されている。我々は溶融塩を電解液とするDSSCのチタニアナノ界面を修飾しその効果を調べた。チタニアナノ界面は色素分子で覆われているが、その隙間から逆電子移動が起こる。色素の間を埋めるblocking materialとして、(1)チタニア表面と反応しやすい、(2)色素の間を埋めることができるように分子が小さいなどの理由から、カルボン酸を選んだ。チタニア界面を酢酸でブロックしたチタニア電極を用いたDSSCは、未処理のDSSCに比較し短絡電流が8mA/cm2から13mA/cm2と大きく向上した。界面修飾は室温溶融塩を使ったDSSCの効率向上に非常に有効である。, 14050077
2002 - 2002