Kinetics and mechanism of light-induced phase separation in a mixed-halide perovskite

Abstract

•Utilized in situ cryoelectron-microscopy-cathodoluminescence spectroscopy •Observed the morphological and band-gap evolution of iodide-rich clusters in situ •Performed quantitative studies of the characteristic length scale of phase separation •Phase field modeling prediction is consistent with spinodal decomposition Halide ion phase separation is a barrier to the application of mixed-halide perovskites whereby the presence of large populations of photogenerated or injected carriers causes undesirable changes in the local band gap. We investigate the mechanism of phase separation in CsPbIxBr3-x perovskite single crystals driven by light. The phase separation process and its dynamics are visualized at the nanometer scale at cryogenic temperatures using in situ scanning transmission electron microscopy and cathodoluminescence. Combined with phase field modeling, which accounts for the coupling between electronic and chemical driving forces, our observations point to a spinodal decomposition mechanism in which both the amplitude of composition fluctuation and the characteristic length scale grow non-linearly with time. Our findings provide microscopic insights that can assist in further engineering mixed-halide perovskites either for stability or for intentional programming of the local halide ion composition, opening pathways to a wide range of applications. Halide ion phase separation is a barrier to the application of mixed-halide perovskites whereby the presence of large populations of photogenerated or injected carriers causes undesirable changes in the local band gap. We investigate the mechanism of phase separation in CsPbIxBr3-x perovskite single crystals driven by light. The phase separation process and its dynamics are visualized at the nanometer scale at cryogenic temperatures using in situ scanning transmission electron microscopy and cathodoluminescence. Combined with phase field modeling, which accounts for the coupling between electronic and chemical driving forces, our observations point to a spinodal decomposition mechanism in which both the amplitude of composition fluctuation and the characteristic length scale grow non-linearly with time. Our findings provide microscopic insights that can assist in further engineering mixed-halide perovskites either for stability or for intentional programming of the local halide ion composition, opening pathways to a wide range of applications.