Charge carrier diffusion in energy landscape created by static charges: Poole-Frenkel model revised

Effect of static charges on charge carrier transport in disordered organic materials is considered. We show that the mobility dependence on temperature and concentration of charged traps differs drastically from the prediction of the model of isolated charged trap (Poole-Frenkel model), yet, by accident, the mobility field dependence remains the same with the logarithm of the mobility being proportional to the square root of the electric field. The ultimate reason for the difference is a long range nature of the Coulomb interaction of a carrier with charged traps. This interaction produces huge fluctuations of carrier energy in the medium overcoming carrier interaction with the isolated static charge. A possibility to observe this quasi-Poole-Frenkel transport regime in experiments is discussed. We argue that the model of isolated charged trap may be applied only to the case of charge transport in extremely thin transport layers.