Impact of the Density of States on the Electronic Mobility in Disordered Organic Materials

From the numerical solution of the master equation for hopping transport in disordered materials, we determine the effect of the density of states (DOS) on the dependence of the charge carrier mobility on the carrier concentration, on the electric field, and on the temperature. We consider the three principal DOS: Gaussian, exponential, and constant. These DOS lead to the same dependence over a large range of the concentration, temperature, or applied electric field. We find that there is no single DOS shape which can capture the full physical picture. Moreover we find that the phenomenon of negative differential resistance observed in disordered organic materials and amorphous semiconductors, seems to be an inherent signature of a constant DOS. Furthermore, we show that the Poole-Frenkel behavior is a common feature for the three densities of states, i.e., a common feature for all disordered systems.