Charge Localization, Stabilization, and Hopping in Lead Halide Perovskites: Competition between Polaron Stabilization and Cation Disorder

Metal halide perovskites, of general formula ABX3, show a complex interplay of the inorganic BX3 sublattice and the organic/inorganic A-site cations, which likely determines some of their peculiar optoelectronic properties. Comprehension of the physics underlying this interaction may reveal further means of fine-tuning their optoelectronic response. Here, we investigate in depth charge–lattice interactions associated with the formation of polarons in different models of the prototypical CH3NH3PbI3 perovskite through advanced electronic structure calculations. We demonstrate that charge localization, while induced by the disordered dipolar field of the organic cations, is stabilized by distortions in the inorganic sublattice. Polaron hopping between neighboring minima is related to the random reorientation of the organic cations and occurs via a delocalized transition state. Our simulations highlight a struggle between thermally induced disorder, driven by the motion of A-site cations, and polaron stabilization within the BX3 sublattice, which explains the simultaneous low mobility and high diffusion length of charge carriers in lead halide perovskites.