Hole-trapping in molecularly doped polymers

Hole mobilities have been measured in tri-p-tolylamine (TTA) doped poly(styrene) containing different concentrations of di- p-tolyl-p-anisylamine (DTA) or tri-p-anisylamine (TAA). DTA and TAA are traps with depths of 0.08 and 0.22 eV, respectively. For low concentrations of DTA or TAA, the transport processes are trap controlled and the mobilities decrease with increasing trap concentration. For high TAA concentrations, however, the transport processes are dominated by trap-to-trap hopping and the mobilities increase with increasing trap concentrations. The threshold concentration for the transition from trap controlled to trap-to-trap transport is approximately 10-1. A transition to trap- to-trap hopping is not observed for TTA containing DTA. The results are discussed within the framework of the Hoesterey- Letson formalism and the recent simulations of Wolf et al. and Borsenberger et al.