  Charge transport is crucial to the performance of hybrid halide perovskite
solar cells. A theoretical model based on large polarons is proposed to
elucidate charge transport properties in the perovskites. Critical new physical
insights are incorporated into the model, including the recognitions that
acoustic phonons as opposed to optical phonons are responsible for the
scattering of the polarons; these acoustic phonons are fully excited due to the
"softness" of the perovskites, and the temperature-dependent dielectric
function underlies the temperature dependence of charge carrier mobility. This
work resolves key controversies in literature and forms a starting point for
more rigorous first-principles predictions of charge transport.
