Hole trapping in tri- p-tolylamine-doped poly(styrene)

Abstract

Hole mobilities have been measured in tri- p-tolylamine-doped poly(styrene) containing different concentrations of di- p-tolyl- p-anisylamine (DTA), di- p-anisyl- p-tolylamine (DAT), and tri- p-anisylamine (TAA). DTA, DAT and TAA are traps with depths of 0.08, 0.15 and 0.22 eV. The mobilities decrease with increasing trap concentration and trap depth while the field and temperature dependencies remain unchanged. The prefactor mobilities are independent of trap concentrations and depths. The results are discussed within the framework of the recent simulations of Wolf et al. The results are in good agreement and confirm the argument that for shallow trapping the basic phenomenology of transport, as revealed by the field and temperature dependencies of the mobility, remain unchanged. Quantitatively, the effects of traps can be accounted for by the replacement of the energy width of the hopping site manifold by an effective width whose square increases linearly with trap depth and the logarithm of the trap concentration.