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 photo-physical 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(I1-xBrx)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. © 2022 Cailiao Daobaoshe/ Materials Review. All rights reserved.
