From Band to Hopping Diffusion of Excitons and Charge Carriers in Molecular Crystals: I. Principles

The diffusion coefficient is deduced for an exciton or charge carrier interacting with phonons in a perfect molecular crystal. The method derived is based on the generalized master equation description of the exciton or carrier kinetics. Correct results are obtained in both the band and the hopping limits, namely a Boltzmann‐like expression with a transport relaxation time where appropriate, and a polaron hopping formula, respectively. An interpolation between these two limits is also obtained.