The Effects of Light Irradiation on CsPbIBr2 Films

In the present, we investigate the light-induced phase instability and the recovery in light-free for CsPbIBr2 film. Both 585 nm and 695 nm photoluminescence (PL) peaks are detected by illuminating films. Results show that the appearance and the intensity of 585 nm and 695 nm PL peaks are affected by the wavelength, remaining time, and intensity of the illuminating light. Under short time illumination, the 695 nm PL peak may disappear after staying light-free, with light-dark reversible behavior. Under long time illumination, the 695 nm PL peak still exist in light-free and become irreversible behavior, which is caused by the formation of I-rich and Br-rich small grains, destroyed the homogeneous phase structure, and formed new steady states. X-ray diffraction analysis and the first principle calculations proved the mechanism of light-induced phase separation. We argue that CsPbIBr2- based solar cells are difficult to be applied before inhibiting the phase separation of CsPbIBr2.