Modelling the effect of dipole ordering on charge-carrier mobility in organic semiconductors

Abstract

The hopping mobility in organic semiconductors is strongly influenced by the correlated on-site noise — i.e. the dipole–dipole interaction between neighbouring molecules. In this paper, we use Kinetic Monte Carlo (KMC) to study the effect of dipole moment and structural order on the hole mobility of organic molecular semiconductors. While the effect on the charge mobility of the dipole–dipole interactions can be approximately reproduced by a global Gaussian disorder model, our present results show that there are non-trivial local effects that are not incorporated into such an approach. The dipole–dipole interactions give rise to large energy barriers that restrict charged particles to smaller and smaller regions as the dipole magnitude increases. While this effect can only reduce the mobility in any given system, we note that if the dipoles self-organize, potentially driven by the dipole moment itself or by an increase in packing density, the negative effect on the mobility can be reduced.