The role of dipole moments on hole transport in triphenylamine-doped polymers

Abstract

Hole mobilities were measured in a series of triphenylamine (TPA) molecules with different dipole moments doped into apolar and highly polar poly(styrene)s. The results are described by a formalism based on disorder, due to Bässler and coworkers. The formalism is premised on the assumption 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, or DOS. For the apolar poly(styrene), the width of the DOS increases with increasing dipole moment of the TPA molecule, whereas for the highly polar poly(styrene), the width is independent of the dipole moment. The results are explained by an argument based on dipolar disorder. The argument is premised on the assumption that the total width is determined by dipolar components due to the dopant molecule and the polymer repeat unit, and a van der Waals component. For the apolar poly(styrene), the width is determined by a TPA dipolar component that increases with increasing dipole moment of the TPA molecule and a van der Waals component of 0.077 eV. For the highly polar poly(styrene), the total dipolar component is 0.090 eV, independent of TPA dipole moment, and the van der Waals component 0.090 eV. © 1996 John Wiley & Sons, Inc.