Hole transport in triarylamine doped polymers

Hole mobilities have been measured in a series of triarylamine molecules doped into a poly(styrene) host. The results are described by a formalism based on disorder, due to Bassler and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameter of the formalism is the energy width of the hopping site manifold. The width is described by a model based on dipolar disorder. According to the model, the width is comprised of a dipolar component and a van der Waals component. The dipolar component is in good agreement with the recent analysis of Young. The results show that the van der Waals component increases with decreasing dopant concentration. This effect, which is not predicted from first order treatment arguments, is attributed to increasing structural randomness with dilution.