Increased Lattice Stiffness Suppresses Nonradiative Charge Recombination in MAPbI₃ Doped with Larger Cations: Time-Domain Ab Initio Analysis

Hybrid organic–inorganic perovskites have attracted great attention as promising photovoltaic materials due to their excellent electronic and optical properties and facile synthesis. Experiments report that halide perovskites containing several organic cations exhibit much longer charge carrier lifetimes than pristine CH3NH3PbI3 (MAPbI3). Using time-domain density functional theory combined with nonadiabatic (NA) molecular dynamics, we demonstrate that partial replacement of MA with formamidinium (FA) or guanidinium (GA) significantly reduces the NA electron–vibrational coupling. The effect arises due to stiffening of the inorganic Pb–I lattice, which exhibits strongly decreased fluctuations while maintaining its original structure and electronic band gap. In addition to extending charge carrier lifetimes, reduced lattice motions, and particularly those of iodides, are indicative of decreased ion diffusion that is responsible for formation of defects, such as iodine interstitials and vacancies, and current–voltage hysteresis. The obtained excited-state lifetimes show good agreement with experiments. The mechanistic insights into the effect of organic cation mixing on charge carrier lifetimes, provided by our simulations, contributes to the fundamental understanding of the halide perovskite properties and generates important principles for design of high-performance perovskite solar cells.