Charge transport in vapor deposited molecular glasses

Hole mobilities have been measured in a series of vapor deposited molecular glasses over a wide range of fields and temperatures. The results are described by a theory based on disorder, due to Bassler and coworkers. The theory is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed tie and positional disorder. A key parameter of the theory is sigma, the energy width of the hopping site manifold. Values of sigma are in agreement with a model based on dipolar disorder, due to Young. The model assumes that the total width is comprised of a dipolar component and a van der Waals component. These results, in conjunction with literature results for a wide range of donor and acceptor glasses, suggest that the van der Waals component is largely of positional or geometrical origin.