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2. Identifying dominant recombination mechanisms in perovskite solar cells by measuring the transient ideality factor

Author

Calado, Phil, Burkitt, Dan, Yao, Jizhong, Troughton, Joel, Watson, Trystan M., Carnie, Matt J., Telford, Andrew M., O'Regan, Brian C., Nelson, Jenny, and Barnes, Piers R. F.

Subjects
Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

The ideality factor determined by measuring the open circuit voltage (VOC) as function of light intensity is often used as a means to identify the dominant recombination mechanism in solar cells. However, applying this Suns-VOC technique to perovskite cells is problematic since the VOC evolves with time in a way which depends on the previously applied bias (Vpre), the light intensity, and the device architecture/processing. Here we show that the dominant recombination mechanism in two structurally similar CH3NH3PbI3 devices containing either mesoporous Al2O3 or TiO2 layers can be identified from the signature of the transient ideality factor following application of a forward bias, Vpre, to the device in the dark. The transient ideality factor, is measured by monitoring the temporal evolution of VOC at different light intensities. The initial values of the transient ideality were consistent with corresponding photoluminescence vs intensity as well as electroluminescence vs current density measurements. Time-dependent simulations of the measurement on modelled devices, which include the effects of mobile ionic charge, show that Shockley Read Hall (SRH) recombination through deep traps at the charge collection interfaces is dominant in both devices. Using transient photovoltage measurements superimposed on the evolving VOC of bifacial devices we further show that the charge collection interface extends throughout the mesoporous TiO2 layer, consistent with a transient ideality signature corresponding to SRH recombination in the bulk of the film. This information could not be inferred from an ideality factor determined from only steady-state VOC values. The method we have developed will be useful for identifying performance bottlenecks in new variants of perovskite devices by comparison with the transient ideality signatures we have predicted for a range of possible recombination schemes., Comment: Main manuscript and supporting information

Published
2018
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3. The issues on the commercialization of perovskite solar cells

Author

zhang, lixiu, primary, Wang, Yousheng, additional, Meng, Xiangchuan, additional, Zhang, Jia, additional, Wu, Pengfei, additional, Wang, Min, additional, Cao, Fengren, additional, Chen, Chunhao, additional, Wang, Zhaokui, additional, Yang, Fu, additional, Li, Xiaodong, additional, Zou, Yu, additional, Jin, Xi, additional, Jiang, Yan, additional, Li, Hengyue, additional, Liu, Yucheng, additional, Bu, Tongle, additional, Yan, Buyi, additional, Li, Yaowen, additional, Fang, Junfeng, additional, Xiao, Lixin, additional, Yang, Junliang, additional, Huang, Fuzhi, additional, Liu, Shengzhong, additional, Yao, Jizhong, additional, Liao, Liangsheng, additional, Li, Liang, additional, Zhang, Fei, additional, Zhan, Yiqiang, additional, Chen, Yiwang, additional, Mai, Yaohua, additional, and Ding, Liming, additional

Published
2024
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5. Studies of recombination in organic and hybrid solar cells using electroluminescence

Author

Yao, Jizhong and Nelson, Jenny

Subjects
621.31
Abstract

The performance of solution processed solar cells such as organic bulk heterojunction (OPV) devices is limited by strong recombination. However, the mechanisms are still unclear. In this thesis, I develop a toolbox using steady-state spectroscopy measurements to explore the recombination mechanisms in a range of solution-processed solar cells. In the first results chapter, I use the reciprocity relation between light absorption and light emission to explore theoretical and practical performance limits for solar cells based on organic semiconductors and perovskites and compare the results with data for state-of-the-art photovoltaic cells made from GaAs, c-Si, and CIGS. In OPV systems, I show that the energetic losses due to the mismatch of the bandgap have been significantly reduced through optimisation of the donor polymer, but the non-radiative recombination losses remain the same and become the major barrier to higher performance. In the next two chapters, I use light intensity dependence of open-circuit voltage measurement (suns-VOC) and electroluminescence – injection current measurement (EL-J) to disentangle recombination mechanisms in OPV and perovskite cells, respectively. First, I identify the present of Shockley-Read-Hall recombination and surface recombination in OPV devices. I intentionally control the sample geometry to modulate the amount of surface recombination and demonstrate that surface recombination can significantly affect the device performance. In the following chapter, I analyse time dependent suns-VOC and EL-J measurements on perovskite cells with different architectures and pre-conditioning regimes used. I identify the changes in recombination mechanisms with delay time and pre-conditions. The effects of ion migration are used to interpret the results. In the final chapter, I apply luminescence spectroscopy techniques to investigate the degree of fullerene crystallinity in polymer:fullerene blends. Charge-transfer state emission is used to probe the onset of the crystallisation of fullerenes in an amorphous polymer. I relate the CT peak shift directly to the change in microstructure of a blend film.

Published
2017
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11. Seed‐Assisted Growth of Methylammonium‐Free Perovskite for Efficient Inverted Perovskite Solar Cells

Author

Wang, Pengjiu, primary, Chen, Xu, additional, Liu, Tianyu, additional, Hou, Cheng‐Hung, additional, Tian, Yue, additional, Xu, Xuehui, additional, Chen, Zeng, additional, Ran, Peng, additional, Jiang, Tingming, additional, Kuan, Chun‐Hsiao, additional, Yan, Buyi, additional, Yao, Jizhong, additional, Shyue, Jing‐Jong, additional, Qiu, Jianbei, additional, and Yang, Yang (Michael), additional

Published
2022
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13. High-performance see-through power windows

Author

Wang, Di, primary, Li, Yuhao, additional, Zhou, Guanqing, additional, Gu, Emely, additional, Xia, Ruoxi, additional, Yan, Buyi, additional, Yao, Jizhong, additional, Zhu, Haiming, additional, Lu, Xinhui, additional, Yip, Hin-Lap, additional, Chen, Hongzheng, additional, and Li, Chang-Zhi, additional

Published
2022
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17. Identifying dominant recombination mechanisms in perovskite solar cells by measuring the transient ideality factor

Author

Calado, Phil, Burkitt, Dan, Yao, Jizhong, Troughton, Joel, Watson, Trystan M., Carnie, Matt J., Telford, Andrew M., O'Regan, Brian C., Nelson, Jenny, Barnes, Piers R. F., Engineering and Physical Sciences Research Council, Engineering & Physical Science Research Council (EPSRC), Engineering & Physical Science Research Council (E, and EPSRC

Subjects
Condensed Matter - Materials Science, Science & Technology, METHYLAMMONIUM LEAD IODIDE, MIGRATION, Physics, Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences, Applied Physics (physics.app-ph), Physics - Applied Physics, DEFECTS, PERFORMANCE, EVOLUTION, TRANSPORT, cond-mat.mtrl-sci, Physics, Applied, OPEN-CIRCUIT VOLTAGE, DENSITY, Physical Sciences, physics.app-ph, HYSTERESIS, LOSSES
Abstract

The ideality factor determined by measuring the open circuit voltage (VOC) as function of light intensity is often used as a means to identify the dominant recombination mechanism in solar cells. However, applying this Suns-VOC technique to perovskite cells is problematic since the VOC evolves with time in a way which depends on the previously applied bias (Vpre), the light intensity, and the device architecture/processing. Here we show that the dominant recombination mechanism in two structurally similar CH3NH3PbI3 devices containing either mesoporous Al2O3 or TiO2 layers can be identified from the signature of the transient ideality factor following application of a forward bias, Vpre, to the device in the dark. The transient ideality factor, is measured by monitoring the temporal evolution of VOC at different light intensities. The initial values of the transient ideality were consistent with corresponding photoluminescence vs intensity as well as electroluminescence vs current density measurements. Time-dependent simulations of the measurement on modelled devices, which include the effects of mobile ionic charge, show that Shockley Read Hall (SRH) recombination through deep traps at the charge collection interfaces is dominant in both devices. Using transient photovoltage measurements superimposed on the evolving VOC of bifacial devices we further show that the charge collection interface extends throughout the mesoporous TiO2 layer, consistent with a transient ideality signature corresponding to SRH recombination in the bulk of the film. This information could not be inferred from an ideality factor determined from only steady-state VOC values. The method we have developed will be useful for identifying performance bottlenecks in new variants of perovskite devices by comparison with the transient ideality signatures we have predicted for a range of possible recombination schemes., Main manuscript and supporting information

Published
2019

18. 19.34 cm2 large-area quaternary organic photovoltaic module with 12.36% certified efficiency

Author

Sheng Rui, Yang Yang, Yan Buyi, Xu Chen, Yao Jizhong, Haiming Zhu, Ziyan Jia, and Zeng Chen

Subjects
Physics, Fabrication, Organic solar cell, Absorption spectroscopy, business.industry, Photovoltaic system, 02 engineering and technology, 021001 nanoscience & nanotechnology, 01 natural sciences, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Indium tin oxide, 010309 optics, 0103 physical sciences, Optoelectronics, 0210 nano-technology, business
Abstract

In this study, a quaternary blending strategy was applied in the fabrication of organic photovoltaic devices and large-area modules. As a result, the ultimate quaternary organic solar cells (OSCs) deliver 16.71% efficiency for small-area devices and 13.25% for large-area ( 19.34 cm 2 ) modules (certified as 12.36%), which is one of the highest efficiencies for organic solar modules to date. Our results have proved the synergistic effects of multiple components in OSCs, providing an effective strategy for achieving high-performance organic photovoltaic devices and modules.

Published
2021

21. The Effect of Stoichiometry on the Stability of Inorganic Cesium Lead Mixed-Halide Perovskites Solar Cells

Author

Ma, Qingshan, Huang, Shujuan, Chen, Sheng, Zhang, Meng, Lau, Cho Fai Jonathan, Lockrey, Mark N., Mulmudi, Hemant K., Shan, Yuchao, Yao, Jizhong, Zheng, Jianghui, Deng, Xiaofan, Catchpole, Kylie, Green, Martin A., and Ho-Baillie, Anita W. Y.

Abstract

Metal halide perovskite solar cells that use the inorganic cation Cs have been shown to have better thermal stability than the organic cation containing counterparts, and CsPbI2Br has a more suitable (lower) band gap than CsPbIBr2as a photovoltaic energy harvesting material. However, increase in iodine content reduces structural stability due to the preference toward the non-perovskite orthorhombic phase when the film is exposed to air. In this work, the effect of varying stoichiometry of CsPbI2Br perovskite on film quality such as the grain size, presence of impurities and nature of impurity grains, photoluminescence, morphology, and elemental distribution are studied. Details on how to vary the stoichiometry during the dual source thermal evaporation process are reported. It is found that the air stability of CsPbI2Br film correlates with the CsBr-to-PbI2deposition rate ratio, in which the CsBr-rich CsPbI2Br is the most stable upon air exposure, while the stoichiometrically balanced CsPbI2Br perovskite film gives the best photovoltaic performance. The encapsulated device maintains 90% of the initial performance after 240 h damp and heat test at 85 °C and 85% relative humidity.

Published
2024
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24. Studies of recombination in organic and hybrid solar cells using electroluminescence

Author

Yao, Jizhong, Nelson, Jenny, and Imperial College London

Abstract

The performance of solution processed solar cells such as organic bulk heterojunction (OPV) devices is limited by strong recombination. However, the mechanisms are still unclear. In this thesis, I develop a toolbox using steady-state spectroscopy measurements to explore the recombination mechanisms in a range of solution-processed solar cells. In the first results chapter, I use the reciprocity relation between light absorption and light emission to explore theoretical and practical performance limits for solar cells based on organic semiconductors and perovskites and compare the results with data for state-of-the-art photovoltaic cells made from GaAs, c-Si, and CIGS. In OPV systems, I show that the energetic losses due to the mismatch of the bandgap have been significantly reduced through optimisation of the donor polymer, but the non-radiative recombination losses remain the same and become the major barrier to higher performance. In the next two chapters, I use light intensity dependence of open-circuit voltage measurement (suns-VOC) and electroluminescence – injection current measurement (EL-J) to disentangle recombination mechanisms in OPV and perovskite cells, respectively. First, I identify the present of Shockley-Read-Hall recombination and surface recombination in OPV devices. I intentionally control the sample geometry to modulate the amount of surface recombination and demonstrate that surface recombination can significantly affect the device performance. In the following chapter, I analyse time dependent suns-VOC and EL-J measurements on perovskite cells with different architectures and pre-conditioning regimes used. I identify the changes in recombination mechanisms with delay time and pre-conditions. The effects of ion migration are used to interpret the results. In the final chapter, I apply luminescence spectroscopy techniques to investigate the degree of fullerene crystallinity in polymer:fullerene blends. Charge-transfer state emission is used to probe the onset of the crystallisation of fullerenes in an amorphous polymer. I relate the CT peak shift directly to the change in microstructure of a blend film. Open Access

Published
2016
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25. The Effect of Stoichiometry on the Stability of Inorganic Cesium Lead Mixed-Halide Perovskites Solar Cells

Author

Ma, Qingshan, primary, Huang, Shujuan, additional, Chen, Sheng, additional, Zhang, Meng, additional, Lau, Cho Fai Jonathan, additional, Lockrey, Mark N., additional, Mulmudi, Hemant K., additional, Shan, Yuchao, additional, Yao, Jizhong, additional, Zheng, Jianghui, additional, Deng, Xiaofan, additional, Catchpole, Kylie, additional, Green, Martin A., additional, and Ho-Baillie, Anita W. Y., additional

Published
2017
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28. Experimental and theoretical optical properties of methylammonium lead halide perovskites

Author

Leguy, Aurélien M. A., primary, Azarhoosh, Pooya, additional, Alonso, M. Isabel, additional, Campoy-Quiles, Mariano, additional, Weber, Oliver J., additional, Yao, Jizhong, additional, Bryant, Daniel, additional, Weller, Mark T., additional, Nelson, Jenny, additional, Walsh, Aron, additional, van Schilfgaarde, Mark, additional, and Barnes, Piers R. F., additional

Published
2016
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29. Role of Polymer Fractionation in Energetic Losses and Charge Carrier Lifetimes of Polymer: Fullerene Solar Cells

Author

Baran, Derya, primary, Vezie, Michelle S., additional, Gasparini, Nicola, additional, Deledalle, Florent, additional, Yao, Jizhong, additional, Schroeder, Bob C., additional, Bronstein, Hugo, additional, Ameri, Tayebeh, additional, Kirchartz, Thomas, additional, McCulloch, Iain, additional, Nelson, Jenny, additional, and Brabec, Christoph J., additional

Published
2015
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31. Polaron pair mediated triplet generation in polymer/fullerene blends

Author

Dimitrov, Stoichko D., primary, Wheeler, Scot, additional, Niedzialek, Dorota, additional, Schroeder, Bob C., additional, Utzat, Hendrik, additional, Frost, Jarvist M., additional, Yao, Jizhong, additional, Gillett, Alexander, additional, Tuladhar, Pabitra S., additional, McCulloch, Iain, additional, Nelson, Jenny, additional, and Durrant, James R., additional

Published
2015
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32. Vertical stratification and its impact on device performance in a polycarbazole based copolymer solar cells

Author

Wang, Tao, primary, Scarratt, Nicholas W., additional, Yi, Hunan, additional, Coleman, Iain F., additional, Zhang, Yiwei, additional, Grant, Richard T., additional, Yao, Jizhong, additional, Skoda, Maximilian W. A., additional, Dunbar, Alan D. F., additional, Jones, Richard A. L., additional, Iraqi, Ahmed, additional, and Lidzey, David G., additional

Published
2015
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33. Spectroscopic Evaluation of Mixing and Crystallinity of Fullerenes in Bulk Heterojunctions

Author

Guilbert, Anne A. Y., primary, Schmidt, Malte, additional, Bruno, Annalisa, additional, Yao, Jizhong, additional, King, Simon, additional, Tuladhar, Sachetan M., additional, Kirchartz, Thomas, additional, Alonso, M. Isabel, additional, Goñi, Alejandro R., additional, Stingelin, Natalie, additional, Haque, Saif A., additional, Campoy-Quiles, Mariano, additional, and Nelson, Jenny, additional

Published
2014
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36. The Progress in Hard Ferrite Industrial Manufacture

Author

Xu Youyi, Yao Jizhong, and Lu Baoshun

Subjects
Materials science, Metallurgy, Ferrite (magnet), Electrical and Electronic Engineering, Condensed Matter Physics, Instrumentation, Electronic, Optical and Magnetic Materials
Published
1998

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