Long-Distance Ionic Diffusion in Cesium Lead Mixed Halide Perovskite Induced by Focused Illumination

Understanding the nature of mobile ions is crucial for revealing their energy landscape in halide perovskites. Here we visualize the diffusion of light-activated mobile ions in mixed halide perovskite polycrystals by monitoring phase segregation in both the illuminated “bright” spot and the nonilluminated “dark” region. Upon light activation, a long distance of mobile ion diffusion and substitution of halide ions, up to 12 μm, is observed without any stimulation of wide-field illumination or biased electric field. Specifically designed fluorescence lifetime imaging microscopy experiments show mobile ions, once photoactivated, can diffuse for a long distance in the dark and induce phase segregation in a mixed halide perovskite. This investigation provides an understanding of mobile ions and the photophysics of hybrid halide perovskite, aids the design of perovskite solar cells, and provides a new pathway for the development of ionic applications of perovskites for compacted energy harvesting and storage.