It has been recently shown that the Poole-Frenkel field dependence of the mobility of injected charges in molecuarly doped polymers arises as a natural consequence of the spatially correlated energetic disorder associated with the charge-dipole interaction. Small polaron hopping is compatible with this mechanism for disorder, provided that the polaron binding energy is in a range which is neither too large nor too small; If the binding energy is large, the size of the hopping matrix element which is required to account for the magnitude of the mobility must also be large, and may be unacceptable for an organic solid. If the binding energy is too small, on the other hand, the small polaron rates tend to become “inverted” by the energetic disorder. In this regime there is an increase in the Poole-Frenkel slope with decreasing temperature which may be described by Gill's compensation temperature.
David H. Dunlap, "Small Polaron Hopping in the Inverted Regime and the Compensation Temperature" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP15), 1999, pp 646 - 650, https://doi.org/10.2352/ISSN.2169-4451.1999.15.1.art00069_2