Thermodynamic model of photoexcitation-induced intensity dependent halide segregation in mixed-halide perovskite thin films

Light-induced halide segregation is an undesirable phenomenon in lead-based mixed-halide perovskites, impeding their potential applications like tandem solar cells. Past experiments have revealed that this segregation is reversible and leads to the formation of impure domains. Our recent experiments on photosegregation in formamidinium-cesium mixed halide perovskites show that the terminal stoichiometry of segregated domains depends on excitation intensity. Exisiting thermodynamic models, based on stoichiometry-dependent band gaps, cannot explain this observation. In this talk, I will present a modified thermodynamic model, accounting for segregated domain subpopulations and photocarrier funneling efficiency, which leads to good agreement between theoretically predicted and measured terminal stoichiometries. The model suggests methods for mitigating photo-induced segregation, which is required for the applications of this promising material.