Dispersive and nondispersive charge transport in a molecularly doped polymer with superimposed energetic and positional disorder

Time-of-flight photocurrent measurements of 1,1-bis(di-4-tolylaminophenyl)cyclohexane doped bisphenol-A-polycarbonate show dispersive features at low temperatures. Within the nondispersive regime, transients show anomalously broad tails of universal shape. Their relative width is in quantitative accord with Monte Carlo simulations of a material characterized by degrees of energetic and positional disorder that have previously been determined from the temperature and field dependencies of the mobility. The transition to dispersive transport, delineated by a change of the temperature dependence of the carrier mean transit time, occurs at a critical energetic disorder parameter as predicted by simulation. The effect of positional disorder is to decrease the slope of the trailing edge of the photocurrent transient.