Abstract

Traditionally, much attention has been given to the dependence of the charge-carrier mobility in disordered semiconducting polymers on the electric field. However, it has recently become clear that the dependence of the mobility on the charge-carrier density cannot be neglected, not even in polymer light-emitting diodes, where this density is very low. From a numerical study of hopping transport on lattices with a Gaussian on-site energy disorder we have come to a unified description of the dependence of the mobility on density, electric field, and temperature. With this description, experimental current-voltage characteristics of hole-only devices with PPV derivatives as semiconductor can be fitted excellently. We come to the conclusion that the traditionally supposed electric field dependence of the mobility is actually, for a large part, a density dependence. Only at high voltages and low temperatures the dependence on electric field becomes important and this dependence can also be excellently modeled with our description.