Effective transport energy versus the energy of most probable jumps in disordered hopping systems

An analytic expression for the effective transport energy in a positionally random and energetically disordered hopping system is obtained. It is shown that multiple carrier jumps within pairs of occasionally close localized states strongly affect the position of the effective transport level on the energy scale and lead to a noticeable difference between the effective transport energy and the energy of most probable jumps. In a hopping system with a Gaussian density-of-states energy distribution, the equilibrium carrier mobility is found to be an almost factorized function of temperature and concentration of localized states.