Simulation of charge carrier transport in disordered molecular solids

摘要

We study the effect of energetic and spatial disorder, anisotropy and sample orientation on the field-dependent mobility of charge carriers using a dynamic Monte Carlo simulation. Our transfer rate is based on a polaronic model of phonon-assisted hopping in an effective diabatic potential (Marcus-theory). We find that our simulations, in contrast to the Gaussian Disorder Model or the Correlated Disorder Model, neither require unphysical model parameters nor correlated disorder to explain experimental data for the field and temperature dependence of mobilities. Our simulations show, that no energetic disorder is necessary to fit experiments. A clear transition from a 3-D diffusion and drift limited mobility to a quasi 1-D drift limited process with increasing external fields in the presence of spatial disorder can be observed. A well-controlled degree of disorder can under certain conditions increase carrier mobility. Simulation of mobilities on a regular lattice are found to strongly depend on the direction of the external field with respect to the lattice in a non-trivial and field-dependent manner. This usually neglected effect is highly sensitive to the choice of the hopping rate and the underlying lattice and can easily modify mobilities by 25% or more.