Photothermal cycle-induced reversal of phase segregation in mixed-halide perovskites

The degradation of optoelectronic properties due to light-induced phase segregation in mixed-halide perovskites presents a major challenge for their future commercial applications. However, the mechanism behind their phase separation behavior under continuous illumination or high temperature is still under debate. Here, we systematically measure the phase separation reversal behavior of CsPbI_1.2Br_1.8 polycrystalline films under photo-thermal cycling. The distribution of halide ions on the film surface corresponded to the phase separation caused by the number of cycles by confocal laser microscope. It was observed that the uniform dots formed at the grain boundary under photothermal cycling were attributed to the oxides generated by light. Finally, according to the optical thermal cycle phenomenon, a low-cost, contactless read-write and erase optical memory is developed, which provides an opportunity for the use of mixed halide perovskite in optical memory applications.