In Situ Observation of Light Illumination-Induced Degradation in Organometal Mixed-Halide Perovskite Films

Organometal mixed-halide perovskite materials hold great promise for next-generation solar cells, light-emitting diodes, lasers, and photodetectors. Except for the rapid progress in the efficiency of perovskite-based devices, the stability issue over prolonged light illumination has severely hindered their practical application. The deterioration mechanism of organometal halide perovskite materials under light illumination has seldom been conducted to date, which is indispensable to the understanding and optimization of photon-harvesting process inside perovskite-based optoelectronic devices. Here, explicit degradation pathways and comprehensive microscopic understandings of white-light-induced degradation have been put forward for two organometal mixed-halide perovskite materials (e.g., MAPbI_3-xCl_x and MAPbBr_3-xCl_x) under high vacuum conditions. In situ compositional analysis and real-time film characterizations reveal that the decomposition of both mixed-halide perovskites starts at the grain boundaries, leading to the formation of hydrocarbons and ammonia gas with the residuals of PbI₂(Cl), Pb, or PbCl_xBr_2-x in the films. The degradation has been correlated to the localized trap states that induce strong coupling between photoexcited carriers and the crystal lattice.