That energetic disorder is the key behind the Poole-Frenkel mobility of photoinjected charges in molecularly doped polymers has always been suspected. In recent years, considerable experimental evidence for the importance of group dipoles has led to the realization that the charge-dipole interaction provides an important contribution to the Gaussian density of states. Here we discuss how the peculiarities of dipolar-disorder, in particular, the manner with which the dipolar disorder is spatially correlated, lead directly to the facts that (i) the mobility in these systems is strongly field-dependent at relatively low fields, (ii) the mobility increases exponentially with √E , and (iii) the field-dependence of the mobility is relatively insensitive to the nature of the underlying hopping rates.
D. H. Dunlap, V. M. Kenkre, P. E. Parris, "What is Behind the √E?" in Journal of Imaging Science and Technology, 1999, pp 437 - 443, https://doi.org/10.2352/J.ImagingSci.Technol.1999.43.5.art00007