The negative effect of photoinduced halide segregation (PIHS) on the properties of hybrid halide perovskites poses a major obstacle for its future commercial application. Therefore, the in-depth understanding of halide-ion segregation and its causes is an urgent and intractable problem. When PIHS reaches a certain threshold, it will aggravate the deterioration of the film surface morphology and form nanoscale cracks. Herein, the formation mechanism and types of cracks are revealed by exploring the stress distribution in the film. Using the femtosecond time-resolved transient absorption spectroscopy, the ultrafast formation of the iodine rich phase is observed, which appears earlier than the bromine rich phase. In addition, the introduction of organic ligand didodecyldimethylammonium bromide can significantly inhibit PIHS and improve the surface morphology of the film, which can promote the device efficiency from 9.63 to 11.20%. This work provides a novel perspective for the exploration of the PIHS.
Keywords: halide perovskites; organic ligand; photoinduced halide segregation; photoinduced stress distribution; surface crack.