Carrier Recombination in Passivated Polycrystalline Perovskite Thin Films

有机-无机卤化物钙钛矿（ohp）是光伏和光电子研究的新星[1-3]。在过去的8年里，随着能量转换效率从3.8%飙升至22.7% [4,5]，OHP太阳能电池将在未来几年开始与硅基技术竞争。然而，钙钛矿材料中的高缺陷密度导致电荷载流子通过非辐射重组（NRR）寄生损失，限制了最先进设备的效率。钝化处理可以使这些缺陷变成惰性的。这类处理包括加工前钙钛矿溶液的化学掺杂和薄膜制作后的常压后处理[6-9]。我的博士项目的目的是有助于更好地理解驱动多晶钙钛矿薄膜中NRR的机制，并揭示用于消除缺陷的钝化处理背后的物理原理。利用快速光谱技术（时间分辨光致发光光谱，瞬态吸收光谱，时间分辨光发射电子显微镜…）的组合，我的目标是表征在各种钝化方法影响下载流子的行为，揭示更优化处理和增强设备性能的途径。我打算利用现有的表面复合速度模型[12]，以及构建三阳离子钙钛矿中空穴捕获的综合模型，重点了解表面缺陷的作用——表面缺陷被证明是OHP薄膜效率的最主要限制因素[10,11]。参考文献：[1]Stranks， S. D. & Snaith， H. J.光伏和发光器件用金属卤化物钙钛矿。自然纳米技术10,391-402（2015）。bbb10 Bhatt， M. D. & Lee， J. S.有机-无机卤化铅钙钛矿太阳能电池的最新进展和科学挑战。化学学报，41,10508-10527（2017）。[10]唐辉，何生，彭昌。高效钙钛矿太阳能电池的研究进展。纳米尺度研究快报12，Article 410（2017）。[10] Kojima， A., Teshima， K., Shirai， Y.和Miyasaka， T. .有机金属卤化物钙钛矿作为光伏电池的可见光敏化剂。j。化学。社会科学学报，2009,6050-6051。[5] Green, m.a.等。太阳能电池效率表（版本51）。光伏研究进展：研究与应用，26,3-12 (2018).[j] .[j]Abdi-Jalebi， M.等。利用钾钝化使卤化物钙钛矿的发光最大化和稳定。《自然》（英文版），2018年第4期。[10]唐志，等。无迟滞钙钛矿太阳能称为掺钾有机金属卤化物钙钛矿。科学通报7,12183（2017）。郑鑫，等。利用季铵盐阴离子和阳离子对杂化钙钛矿太阳能电池进行缺陷钝化。自然能源，17102 (2017)[j]。氧化石墨烯中间层表面钝化提高钙钛矿太阳能电池效率。ACS达成。板牙。接口9,38967-38976 (2017).[10]Yang， Y.等。顶部和底部表面限制了碘化铅钙钛矿薄膜中的载流子寿命。自然能源学报，2016,36 (6):444 - 444等。从阻抗分析看钙钛矿太阳能电池的表面复合和收集效率。期刊。化学。科学通报，2016,36 (2):481 - 481Yablonovitch， E., Allara， D. L., Chang， C. C., Gmitter， T.和Bright， T. B.硅和锗表面的异常低表面复合速度。理论物理。Rev. Lett. 57, 249-252（1986）。

Organic-inorganic halide perovskites (OHPs) are the rising stars of photovoltaic and optoelectronic research [1-3]. With power conversion efficiencies surging from 3.8% to 22.7% [4,5] in the last 8 years, OHP solar cells will begin to compete with silicon-based technology in the coming years. However, high defect densities within perovskite materials lead to the parasitic loss of charge carriers via non-radiative recombination (NRR), limiting the efficiencies of state-of-the-art devices. Passivation treatments can be employed to render these defects inert. Such treatments include the chemical doping of perovskite solutions before processing, and the atmospheric post-treatment of films after fabrication [6-9]. The aim of my PhD project is to contribute to a better understanding of the mechanisms that drive NRR in polycrystalline perovskite films, and to uncover the physics behind the passivation treatments which are employed to eliminate defects. Utilising a combination of fast spectroscopy techniques (time-resolved photoluminescence spectroscopy, transient absorption spectroscopy, time-resolved photoemission electron microscopy...) my goal is to characterise the behaviour of carriers under the influence of various passivation methods, to reveal pathways towards more optimal treatments and enhanced device performance. I intend to focus on understanding the role of surface defects - shown to be the most dominant limit on efficiency in OHP thin films [10,11] - using existing surface recombination velocity models [12], as well as through the construction of a comprehensive model of hole-trapping in triple-cation perovskite.References: [1] Stranks, S. D. & Snaith, H. J. Metal-halide perovskites for photovoltaic and light-emitting devices. Nature Nanotechnology 10, 391-402 (2015). [2] Bhatt, M. D. & Lee, J. S. Current progress and scientific challenges in the advancement of organic-inorganic lead halide perovskite solar cells. New Journal of Chemistry 41, 10508-10527 (2017). [3] Tang, H., He, S. & Peng, C. A Short Progress Report on High-Efficiency Perovskite Solar Cells. Nanoscale Research Letters 12, Article 410 (2017). [4] Kojima, A., Teshima, K., Shirai, Y. and Miyasaka, T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 131, 6050-6051 (2009). [5] Green, M. A. et al. Solar cell efficiency tables (version 51). Progress in Photovoltaics: Research and Applications 26, 3-12 (2018).[6] Abdi-Jalebi, M. et al. Maximising and stabilizing luminescence from halide perovskites with potassium passivation. Nature 555, 497-501 (2018). [7] Tang, Z. et al. Hysterisis-free perovskite solar calls made of potassium-doped organometal halide perovskite. Scientific Reports 7, 12183 (2017). [8] Zheng, X. et al. Defect passivation in hybrid perovskite solar cells using quaternary ammonium halide anions and cations. Nature Energy 2, 17102 (2017) [9] Li, H. et al. Enhancing Efficiency of Perovskite Solar Cells via Surface Passivation with Graphene Oxide Interlayer. ACS Appl. Mater. Interfaces 9, 38967-38976 (2017).[10] Yang, Y. et al. Top and bottom surfaces limit carrier lifetime in lead iodide perovskite films. Nature Energy 2, Article 16207 (2017).[11] Zarazua, I. et al. Surface Recombination and Collection Efficiency in Perovskite Solar Cells from Impedance Analysis. J. Phys. Chem. Lett. 7, 5105-5113 (2016).[12] Yablonovitch, E., Allara, D. L., Chang, C. C., Gmitter, T. & Bright, T. B. Unusually Low Surface-Recombination Velocity on Silicon and Germanium Surfaces. Phys. Rev. Lett. 57, 249-252 (1986).