Ionic transport and vacancy organization in MAPbI3 under electric fields: a kinetic Monte Carlo study

Ionic migration in methylammonium lead iodide ( MAPbI 3 ) is widely regarded as one of the principal factors limiting the long-term stability of halide perovskite devices. While the microscopic origin of iodide vacancy motion has been characterized through density functional theory and molecular dynamics, these approaches remain computationally prohibitive for capturing the collective dynamics of large defect populations over experimentally relevant timescales. In this work, we develop and apply a kinetic Monte Carlo ( KMC ) framework based on the Bortz–Kalos–Lebowitz residence-time algorithm to simulate vacancy-mediated ionic transport in MAPbI 3 across wide ranges of temperature, vacancy concentration, and electric field amplitude. Our simulations reproduce thermally activated vacancy transport with an Arrhenius activation energy of approximately 0.276 eV, within the broad range of migration barriers reported for iodide-related defects in MAPbI 3 . The calculated diffusion coefficient increases monotonically with vacancy concentration over the investigated range, while the largest connected-cluster fraction decreases, indicating a concentration-dependent evolution of vacancy organization. Under applied electric fields, the mean-square displacement develops an increasingly pronounced field-directed contribution, leading to a nonlinear enhancement of the MSD-derived effective transport coefficient. The corresponding event-resolved current-like response exhibits pronounced stochastic fluctuations associated with individual vacancy-hopping events. Field–concentration maps further summarize the coupled dependence of vacancy transport and organization on defect concentration and field-assisted hopping.