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

Summary

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 CsPbI_xBr_3-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.