NONDISPERSIVE AND DISPERSIVE TRANSPORT IN RANDOM ORGANIC PHOTOCONDUCTORS

A previously developed hopping concept for rationalizing charge transport in random organic photoconductors is further elaborated. It rests on the premise that random molecular packing gives rise to energetic disorder that can be accounted for in terms of a Gaussian-shaped density of hopping states (DOS). Computer simulations confirm that an array of randomly positioned dipoles generates a Gaussian DOS whose width is in excellent agreement with experiment. The existence of energetic disorder can explain in a quantitative manner the scaling behavior of the shape of time of flight signals with respect to sample length and electric field as well as the transition to dispersive transport at low temperatures.