Effect of thermal disorder on the electronic structure and the charge mobility of acenes

The effect of thermal disorder on the electronic structure and transport properties of two prototypical organic semiconductors, naphthalene and pentacene, has been studied by combining molecular dynamics simulations with ab initio electronic structure calculations. Our approach explicitly account for the influence of thermal disorder on the site energy and on the intermolecular interactions. It is shown that thermal disorder shifts the polaronic energy levels with respect to the perfectly ordered crystal and stabilize charge localization, even in the case of pentacene, with a significant contribution provided by local rearrangement of the first neighbours. Evaluation of charge mobilities, carried out by kinetic Monte Carlo simulations, shows that site energy fluctuations play the most significant role in slowing down charge diffusion, leading to computed mobilities which are in very good agreement with the experimental ones.