Hole Transport in Di-p-Tolyl-p-Nitrophenylamine Doped Poly(styrene)

Di-p-tolyl-p-nitrophenylamine (DTNA) is a highly polar donor molecule with a dipole moment of 5.78 D. Hole mobilities have been measured in DTNA doped poly(styrene) over a range of fields, temperatures, and DTNA concentrations. The results are described within the framework of a formalism based on disorder, due to Bassler and coworkers. In the disorder formalism, it is assumed that charge propagation occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. A key parameter of the formalism is the energy width of the hopping site manifold. For DTNA doped poly(styrene), the width is approximately 0.15 eV and independent of the intersite distance, or DTNA concentration. The width is described by a model based on dipolar disorder. The model is premised on the assumption that the width is determined by a dipolar component due to the DTNA molecule and a van der Waals component. The interpretation of the experimental results leads to the conclusion that the van der Waals component increases with increasing intersite distance.