Vacancy-Mediated Anion Photosegregation Kinetics in Mixed Halide Hybrid Perovskites: Coupled Kinetic Monte Carlo and Optical Measurements

Solution-processed mixed halide perovskites are excellent materials for multijunction solar cells. Unfortunately, light-induced halide phase segregation has prevented their effective integration into working devices. In this study, we rationalize and quantify anion photosegregation in stoichiometric and halide-deficient MAPb(I1-xBrx)(3) thin films through kinetic Monte Carlo simulations and complementary optical measurements. Our study reveals that segregation rates are dictated by halide vacancy hopping barriers and are modulated by vacancy concentrations. The simulations further suggest that near-ubiquitous emission energies, which converge on that for MAPb(I0.8Br0.2)(3) (i.e., x approximate to 0.2) following photosegregation, arise from the existence of kinetically trapped Br- within nucleated I-rich domains. An established photosegregation excitation intensity threshold is independent of the number of vacancies and instead depends critically on parameters such as carrier diffusion length, lifetime, and bandgap tunability. The study thus sheds new light on important parameters that define halide photosegregation and presents opportunities for controlling the phenomenon.