Abstract

A-site cations in ABX3 metal halide perovskites do not contribute to the frontier electronic states. They influence optoelectronic properties indirectly through interaction with the BX3 sublattice. By systematically investigating correlated motions of Cs cations and the PbX3 lattice (X = Cl, Br, I), we demonstrate that the interaction between the two subsystems depends on electronegativity and size of the X-site anion. The most electronegative Cl halide minimizes thermal atomic fluctuations, favoring optoelectronic performance. CsPbI3 is improved by Cl-doping. Nonadiabatic molecular dynamics simulations demonstrate that charge carrier lifetime is extended by nearly an order of magnitude when atomic fluctuations are minimized, due to reduced electron–vibrational interactions, in agreement with experiments. The detailed atomistic examination of the significant impact of correlated motion of the A-site and BX3 sublattices and its influence on perovskite stability and exciton lifetime offers theoretical guidelines for optimizing perovskite optoelectronic devices.