Stability in Photoinduced Instability in Mixed-Halide Perovskite Materials and Solar Cells

Abstract

Bandgap variation due to photoinduced instability in mixed-halide perovskites presents a major obstruction for their future commercial application. Here, the photoinduced process including ever-present halide-ion migration and consequent halide phase segregation is disclosed. We demonstrate that photoinduced halide-ion migration serves as a self-healing behavior, enabling an efficient yield of photoluminescence (PL) without peak shift. Photoinduced halide phase segregation is not reversible, exhibiting an obvious red-shifted PL spectrum due to the formed smaller-bandgap I-rich phase perovskite. The Br content in mixed-halide perovskite systems determines the transformation from halide-ion migration to halide phase segregation under illumination. By investigation of the relationships between the I-rich phase perovskite and the red-shifted PL spectra, the stable perovskite composition with a critical Br/I ratio is identified regardless of the high Br content in mixed-halide perovskite systems. Halide-ion migration could be a universal origin of photoinduced phase segregation in mixed-halide perovskites and instability of mixed-halide perovskite solar cells. Our result provides a reference for the adjustment of halogen composition of ternary cationic perovskites with excellent photostability.