  We explore polaronic quantum transport in three-dimensional models of
disordered organic crystals with strong coupling between electronic and
vibrational degrees of freedom. By studying the polaron dynamics in a static
disorder environment, temperature dependent mobilities are extracted and found
to exhibit different fingerprints depending on the strength of the disorder
potential. At low temperatures and for strong enough disorder, coherence
effects induce weak localization of polarons. These effects are reduced with
increasing temperature (thermal disorder) resulting in mobility increase.
However at a transition temperature, phonon-assisted contributions driven by
polaron-phonon scattering prevail, provoking a downturn of the mobility. The
results provide an alternative scenario to discuss controversial experimental
features in molecular crystals.
