混合卤化物钙钛矿中的光致相分离效应

Review of Light-induced Phase Segregation in Mixed Halide Perovskites

卤化物钙钛矿材料由于具有良好的光电特性和低廉的制造成本引起了人们的普遍关注。卤化物钙钛矿太阳能电池被认为有望成为下一代主流的光伏技术,其最高光电转化效率在短短的数年间提升至25.2%。特别地,混合卤化物钙钛矿的带隙能够通过改变卤素比例进行调整,因此其是制备串联太阳能电池顶部吸收层和发光二极管活性层的理想材料。然而,混合卤化物钙钛矿在光照下呈现出可逆的卤素分离现象。这种不稳定效应显著影响材料的光物理特性,严重限制了混合卤化物钙钛矿的应用。因此,近五年来学者们对其进行了大量的研究,旨在揭示光致卤素分离的基本机制,以及从化学计量和制备工艺等方面多角度探讨抑制这种不稳定效应的方法。目前,通过光谱表征与物相分析等技术,研究者们逐渐认识到混合卤化物钙钛矿中的光致相分离效应是一种内在的不稳定性,并受到热力学和动力学的共同影响。研究表明,选择合适的组分以及调控光照、温度等条件可以减轻卤素分离的程度;此外,钝化表面缺陷或控制结晶度也能够在一定程度上提高薄膜的光稳定性。然而,人们对光致相分离效应的认识仍不全面,提高混合卤化物钙钛矿光稳定性的策略也没有得到充分的研究。本文以当前典型的混合卤化物钙钛矿材料MAPb(I 1-x Br x)3为主要研究对象,回顾并分析目前对光致相分离效应的相关实验认识,结合理论分析对其发生机理进行分类阐述,最后对抑制光致相分离效应的研究进展进行了总结,以期为开发出具有光稳定性的混合卤化物钙钛矿材料提供参考。

Halide perovskite materials have attracted much attention due to their excellent photoelectronic properties and low manufacturing cost.Halide perovskite solar cells are expected to become the next generation of photovoltaic technology,because their best power conversion efficiency has increased to 25.2%in just a few years.In particular,the band gap of mixed halide perovskites can be tuned by altering the composition of halides,making them ideal materials for preparing the top absorption layer of tandem solar cells and the active layer of light-emitting diodes.Unfortunately,mixed halide perovskites exhibit reversible halide segregation under illumination.This instability significantly affects the photophysical properties of the materials and severely limits the application prospect of mixed halide perovskites.Therefore,a large amount of research has been performed in the past five years,aiming to reveal the basic mechanism of the photoinduced halide segregation;the methods to restrain this instability were also discussed from the aspects of stoichiometry and preparation process.Recently,it has been gradually realized that light-induced phase segregation represents an intrinsic instability by means of optical and structural measurements in mixed halide perovskites,and is affected by both thermodynamics and kinetics.Phase segregation can be mitigated by selecting suitable components and controlling illumination and temperature.In addition,the surface defects passivation and crystallinity control can also improve photostability of mixed halide perovskites.However,the understanding of the light-induced phase segregation is still incomplete,and the strategies to improve the photostability of mixed halide perovskites also have not been fully explored.Here,we review and analyze experimental observations of light-induced phase segregation in mixed halide perovskite,especially for the typical material MAPb(I 1-x Br x)3.We also classify the mechanism of halide segregation combined with theoretical analysis,and finally summarize ongoing research to suppress the phenomenon.We hope this review will provide a reference for the development of photostable mixed-halide perovskite materials.