Hole transport in enamine-doped polymers

Abstract

Hole mobilities of a series of enamine (ENA) derivatives doped into poly(styrene) (PS) have been measured over a wide concentration range. At high fields and high ENA concentrations, the room temperature mobilities are in excess of 10 -3 cm 2 /Vs. These are the highest of any doped polymers described in the literature. The results are described by a model based on disorder. According to the model, charge transport occurs by hopping through a manifold of localized states that are distributed in energy and distance. The key parameters of the model are σ, the energy width of the hopping site distribution, Σ the degree of positional disorder, and μ 0 , a prefactor mobility. The width of the hopping site manifold is described by a model of dipolar disorder. The model is premised on the assumption that the total width is comprised of a dipolar component and a van der Waals component. For weakly polar molecules, the dipolar component vanishes and the total width is determined only by the van der Waals component. The values for ENA doped PS are betweeen 0.077 and 0.103 eV, increasing with increasing dilution. The prefactor mobilities are between 10 -6 and 10 -1 cm 2 /Vs, increasing with increasing concentration. Values of the positional disorder parameter are between 1.6 and 4.8. The high mobilities in these materials are due to the low values of the van der Waals components and the high prefactor mobilities.