Nonperturbative lattice effects on electron-hole recombination in lead halide perovskites

Hybrid lead halide perovskites are a class of materials that have unique photophysical properties due to their anharmonic lattices and predominately ionic bonding. Since both electrons and holes are diffusive and strongly couple to an anharmonic lattice, elucidating the nature of how photogenerated electrons and holes bind, dissociate and recombine is theoretically difficult. Subsequently, little is known about the mechanism underpinning observations of low recombination rates and small exciton binding energies. In this work, we develop a Gaussian field theory to describe the effective interactions between electrons and holes as mediated by the perovskite lattice. We find that the inclusion of a spatially dependent screening produces a repulsive exciton interaction at intermediate distances which can be responsible for the decrease in exciton binding energy and the increase in free carrier lifetimes. We validate this theory using quasiparticle-based path integral molecular dynamics and evaluate the recombination rate and binding energies from free energy calculations. The quasiparticle-based path integral molecular dynamics framework uses an effective mass model of the charge carriers and an atomistic model for perovskite lattice, allowing us to capture all orders of anharmonicity, reducing the computational complexity associated with studying this system, which would be intractable from standard solid state methods.