Hole transport in vapor deposited enamines and enamine doped polymers

Abstract

Hole mobilities have been measured of a series of vapor deposited enamine glasses and enamine doped polymers. The enamines are weakly polar donor molecules with dipole moments between 0.38 and 0.66 debye. For the vapor deposited glasses, the room temperature mobilities approach 10 −2 cm 2/V s at high fields. For the doped polymers, the mobilities are in excess of 10 −3 cm 2/V s. The results are described by a formalism based on disorder. According to the formalism, charge transport occurs by hopping through a manifold of localized states that are distributed in energy and distance. The key parameters of the formalism are σ, the energy width of the hopping site distribution, Σ the degree of positional disorder, and μ 0 a prefactor mobility. The width of the hopping site manifold is described by a model of dipolar disorder. The model is premised on the assumption than the total width is comprised of a dipolar component and a van der Waals component. For weakly polar molecules, the dipolar component vanishes and the total width gives the van der Waals component directly. For the vapor deposited glasses, the van der Waals components are 0.075 eV. Values for the doped polymers are 0.082 eV. The prefactor mobilities for the vapor deposited glasses are approximately 0.20 cm 2/V s while values for the doped polymers are between 2 and 4 × 10 −2 cm 2/V s. Values of the positional disorder parameter are approximately 1.0 for the vapor deposited glasses and 1.7 to 2.0 for the doped polymers. The high mobilities in these materials are due to the low values of the van der Waals components and the high prefactor mobilities.