Charge Carrier Transport in Nonpolar Disordered Organic Materials: What is the Reason for Poole-Frenkel Behavior?

Recently it was found that the mobility field dependence in disordered organic materials is closely connected with the spatial decay of the energy correlation function. For example, a dipolar glass produces a correlation function decaying as inverse distance, thus leading to a well-known Poole-Frenkel (PF) field dependence. From this point of view a frequent experimental observation of the PF dependence in nonpolar organic materials cannot be explained. We show that the model of quadrupolar glass which is suitable to describe transport properties of nonpolar materials produces a field dependence that is very close to the PF one if measured in not very wide field range. Dispersive effects bring this dependence even more close to the PF one.