Molecular Origin of the Asymmetric Photoluminescence Spectra of CsPbBr3 at Low Temperature

CsPbBr 3 has received wide attention due to its superior emission yield and better thermal stability compared to other organic-inorganic lead halide perovskites. In this study, through an interplay of theory and experiments, we investigate the molecular origin of the asymmetric low-temperature photoluminescence spectra of CsPbBr 3 . We conclude that the origin of this phenomenon lies in a local dipole moment (and the induced Stark effect) due to the preferential localization of Cs + in either of two off-center positions of the empty space between the surrounding PbBr 6 octahedra. With increasing temperature, Cs + ions are gradually occupying positions closer and closer to the center of the cavities. The gradual loss of ordering in the Cs + position with increasing temperature is the driving force for the formation of tetragonal-like arrangements within the orthorhombic lattice.