Nonlocal Screening Dictates the Radiative Lifetimes of Excitations in Lead Halide Perovskites

We use path integral molecular dynamics simulations and theory to elucidate\nthe interactions between charge carriers, as mediated by a lead halide\nperovskite lattice. We find that the charge-lattice coupling of MAPbI$_3$\nresults in a repulsive interaction between electrons and holes at intermediate\ndistances. The effective interaction is understood using a Gaussian field\ntheory, whereby the underlying soft, polar lattice contributes a nonlocal\nscreening between quasiparticles. Path integral calculations of this nonlocal\nscreening model are used to rationalize the small exciton binding energy and\nlow radiative recombination rate observed experimentally and are compared to\ntraditional Wannier-Mott and Fr\\"ohlich models, which fail to do so. These\nresults clarify the origin of the high power conversion efficiencies in lead\nhalide perovskites. Emergent repulsive electron-hole interactions provide a\ndesign principle for optimizing soft, polar semiconductors.\n