Monte Carlo simulations of charge transport in molecular solids: a modified Miller Abrahams type jump rate approach

Charge transport properties in disordered organic materials show some unive rsal characteristics which are related to the "intrinsic" degree of disorde r both energetically and spatially rather than to the dominance of impurity effects. This behaviour is usually explained in terms of charge transport via elementary hopping processes between localised "sites" in terms of Gaus sian Disorder Model. Quantum mechanical models for the charge transfer in donor-acceptor complex es in the diabatic approximation suggest electronic transfer rates which ar e dependent on the energy difference between initial and final state as wel l as some reorganisation energy in both directions of the electron transfer , i.e., independent of the sign of the energy difference. This contrasts a ubiquitous factor 1 for jumps downward in energy and gives rise to what we believe is a more accurate description of the dynamic properties of charge transport. In order to clarify the influence of such a modification on the macroscopic charge transport, we set up dynamic MC calculations. The temper ature and field dependence of the mobility for both jump rate expressions a re compared. We study the effect of spatial and energetic Gaussian disorder and discuss implications for the interpretation of experimental data. (C) 2000 Elsevier Science S.A. All rights reserved.