Unraveling carrier lifetime variations in MAPbI3 perovskite from octahedral distortions and spin–orbit coupling effects

Abstract

Designing efficient halide perovskites (HPs) is critical for advancing optoelectronic device performance. Herein, we systematically investigate the excited-state dynamics of three crystalline systems with distinct symmetries using time-domain nonadiabatic dynamics simulations. Compared to the tetragonal phase P4 mm with higher symmetry, the orthorhombic phase Fmmm significantly alters the spin polarization at the conduction band minimum, leading to the classification of two exciton types: charge-transfer excitons and Frenkel excitons. The two exciton types exhibit distinct temporal responses under photoexcitation. To ensure the generality of our findings, we employed a comprehensive set of crystalline models for MAPbI3, including Fmmm, Im3, Pm  3¯ m, Pnma, I4/mcm, P4 mm, and P4/mbm symmetries, which were optimized and subjected to ab initio nonadiabatic molecular dynamics (NAMD) simulations. Incorporating spin–orbit coupling effects to approximate realistic scenarios, the NAMD simulations reveal that the electron–hole recombination in the tetragonal P4 mm phase with a narrow bandgap occurs within approximately 78.63 fs, whereas the orthorhombic Fmmm phase exhibits an extended carrier lifetime of ∼93 fs due to the spatial separation of charge density between electrons and holes. Our findings highlight an effective strategy to modulate the excited-state dynamics in metal HPs through tailored structural ordering, offering critical insights for designing high-performance perovskite materials tailored for optoelectronic applications.