Phase-Dependent Photoinduced Lattice Deformation in Lead Halide Perovskites

Lead halide perovskites (LHPs) display rich carrier–lattice coupling phenomena─including photostriction and large-polaron formation─that underpin their unique optoelectronic properties. However, experimentally observed photoinduced structural responses vary considerably across studies, and the microscopic mechanism remains poorly understood. Here, we employ occupation-constrained density functional theory to investigate photoinduced structural distortions in CsPbBr3 and MAPbBr3. We find that the structural deformations are significant in the tetragonal phase but negligible in the orthorhombic and cubic phases. This phase selectivity arises from symmetry-induced level splitting at the band edges. These findings highlight the critical role of structural phase in governing photostriction and carrier–lattice responses in LHPs.