Hole transport in triarylamine doped polymers

Abstract

Hole mobilities have been measured in N,N′,N″,N‴-tetrakis(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine(TTB) and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) doped poly(styrene) (PS). 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 parameters are σ, the energy width of the hopping site manifold, and Σ, the degree of positional disorder. For 20% TTB and TPD doped PS, σ = 0.102 eV. The positional disorder parameter is Σ = 3.9 for TTB and Σ = 3.8 for TPD doped PS. The width of the hopping site manifold is described by a model based on dipolar disorder. The model is based on the assumption that the width is comprised of a dipolar component due to the dopant molecule and a van der Waals component. The results show that transport in both TTB and TPD can be described by disorder-controlled hopping without invoking polaronic contributions. Deviations from ideal disordercontrolled behavior have been observed for both compounds at low fields.