The role of dipole moments on hole transport in triphenylamine doped poly(styrene) Original Research Article

Hole mobilities have been measured in a series of triphenylamine (TPA) molecules with different dipole moments doped into poly(styrene)(PS). The results are described within the framework of a formalism based on disorder. The formalism is premised on the assumption that charge propagation occurs by hopping through a manifold of localized states with superimposed energetic disorder. The key parameter of the formalism is the energy width of the hopping site manifold, or DOS. For TPA doped PS, the width of the DOS increases with decreasing TPA concentration for weakly polar TPA molecules and is independent of the TPA concentration for highly polar molecules. The width is described by a model based on dipolar disorder and leads to the conclusion that the width is determined by a dipolar component due to the TPA molecules and a van der Waals component that increases with decreasing TPA concentration.