Charge transport in disordered organic host-guest systems: Effects of carrier density and electric field

We investigate charge transport in disordered organic host-guest systems with a bimodal Gaussian density of states. The energy difference between the peaks of the two Gaussians defines the trap depth. By solving the Pauli master equation for the hopping of charge carriers on a regular lattice we obtain the dependence of the charge-carrier mobility on the relative guest concentration, the trap depth, the energetic disorder, the charge-carrier density, and the electric field. Our results for the zero-field mobility are generally in a good agreement with recent semi-analytical model results. However, in the regime where the mobility attains a minimum our results can be almost one order of magnitude larger than as predicted semi-analytically. Furthermore, it is shown that field-induced detrapping can contribute strongly to the electric-field dependence of the mobility. (C) 2009 Elsevier B.V. All rights reserved.