Hole transport in tri-p-tolylamine doped polymers: the role of the polymer dipole moment Original Research Article

Hole mobilities have been measured in tri-p-tolylamine (TTA) doped polymers with polymer dipole moments that range from near-zero to 1.7 debye. The results are described within the framework of a formalism based on disorder, due to Bässler and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameter of the formalism is σ, the variance of the hopping site energies. The principal observations of this work are: (1) σ increases with increasing intersite distance for all polymers studied, and (2) σ increases with increasing dipole moment of the polymer. The interpretation of the results leads to the conclusion that for weakly polar dopant molecules, a major contribution to the width of the distribution of hopping site energies is the component due to van der Waals forces. For TTA doped poly(styrene)s, the van der Waals component is estimated as between 0.074 and 0.116 eV, increasing with incresing intersite distance or decreasing TTA concentration.