Correlating Halide Segregation with Photolysis in Mixed-Halide Perovskites via In situ Opto-gravimetric Analysis.

Halide oxidation plays a fundamental role in halide segregation and the degradation of halide perovskites, yet quantitative measurement of halide oxidation in solid-state perovskite samples remains challenging. Herein, we demonstrate that in situ opto-gravimetric measurements based on a quartz crystal microbalance can quantify the photolysis kinetics of solid-state perovskites. By investigating a series of mixed bromide/iodide perovskites with varying halide ratios, we demonstrate identical compositional thresholds ( ∼ 0.4 in the CsPb(BrI) system) for iodide oxidation, light-induced halide segregation, and photolysis. Our findings reveal the correlation between these light-induced instabilities and unambiguously explain the photolysis mechanism of mixed-halide perovskites. We also show that photolysis renders the perovskite film more -type without involving lead reduction. This study introduces a powerful methodology for quantitatively analyzing the mass loss kinetics of halide perovskites under both practical operational and accelerated aging conditions, offering deeper insights into the mechanisms of perovskite degradation.