Investigations on the Strong Light-Changed Photoluminescence Performance and the Crystalline Structure of MAPbBr₁Cl₂ Mixed Halide Perovskites

As excellent optoelectronic materials, MAPbBr1Cl2 mixed halide perovskites are inevitably exposed to external illumination during their operation. Therefore, gaining a deep understanding of how the working performances of these materials are affected by such illumination is crucial. Herein, we synthesized a MAPbBr1Cl2 single crystal using a low-temperature-gradient crystallization method. The X-ray diffraction pattern of the MAPbBr1Cl2 single crystal confirmed its high crystallinity. Moreover, the MAPbBr1Cl2 single crystal exhibited excellent photoluminescence (PL) emission. Most interestingly, the PL peak of MAPbBr1Cl2 underwent a redshift from 504 to 517 nm with increasing excitation intensity. To explain this phenomenon, the power-dependent Raman spectrum was analyzed. As the laser intensity increased from 1 to 100%, the Raman mode softened from 324.27 to 320.82 cm–1. This indicated that laser irradiation weakens the bonding interactions and expands the MAPbBr1Cl2 single crystal, resulting in a redshift of the Raman peak, known as the photostriction effect. Furthermore, density functional theory calculations were conducted to simulate the MAPbBr1Cl2 supercells under normal and photostrictive conditions. The calculated band structures confirmed that light-induced lattice expansion reduces the band gap, contributing to the observed redshift of the PL peaks. Thus, when MAPbBr1Cl2 is irradiated by light under the working conditions, it exhibits a pronounced photostriction effect. This effect subsequently influences the electronic and luminescence properties of the material. This is a critical issue that needs to be addressed to develop reliable and sustainable perovskite optoelectronic devices