Optimizing Sublattice Correlation to Enhance Stability and Charge Carrier Lifetime in Mixed Halide Perovskites

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.