A Unified microscopic picture of cation and anion migration in MAPbI₃

Original · EN

Passivating defects and restricting defect mobilities in halide perovskites to increase device lifetimes has become a main field of research. Modeling structure and mobility of point defects is an essential contribution to this endeavor. We employ molecular dynamics, based on neural network potentials trained on density functional theory data, to model ion migration in MAPbI₃ triggered by I and MA vacancies or interstitials. Most of these species diffuse rapidly at room temperature, with migration barriers between 0.15 and 0.20 eV. MA interstitials are highly mobile despite their molecular nature, owing to a concerted migration mechanism involving multiple MA ions. No evidence of MA vacancy migration is obtained. Whereas diffusion of I-related defects appreciably depends on their charge state, diffusion of MA defects does not. These results revise the conventional picture of ion transport in hybrid perovskites and highlight the role of collective molecular motion in enabling fast ionic migration.