Correlated Cs-Octahedra Motion Governs Structural Stability and Nonradiative Charge Recombination in CsPbBr ₃ Perovskites

Correlated motion between Cs ions and the inorganic octahedral framework plays a key role in the structural stability and nonradiative carrier dynamics of CsPbBr₃. By combining normal and frozen molecular dynamics with nonadiabatic molecular dynamics for the orthorhombic and tetragonal phases, we show that suppressing this correlated motion induces lattice distortions in both phases. The resulting structural perturbations reduce band-edge-state localization, increase electron-hole spatial overlap, enhance nonadiabatic coupling, and thereby accelerate nonradiative electron-hole recombination. Importantly, the magnitude of this effect is phase dependent. The orthorhombic phase exhibits larger atomic displacements and more pronounced octahedral distortions upon mode freezing, leading to a greater reduction in carrier lifetime than in the tetragonal phase. These results reveal a microscopic link between phase-dependent cation-framework dynamics, structural stability, and nonradiative recombination in all-inorganic halide perovskites, and provide mechanistic guidance for improving the performance of perovskite optoelectronic devices.