Scaling behavior of nondispersive charge transport in disordered molecular solids

The results of Monte Carlo simulations are presented, which delineate the spatial spreading of a packet of charge carriers drifting within an energetically and (possibly) geometrically disordered hopping-site manifold under the influence of an applied field. At large values of the energetic disorder parameter (σ/kT>4) the tail width of an otherwise nondispersive photocurrent transient is independent of sample length L, while at lower values of σ/kT the dispersion follows a ${\mathit{L}}^{\mathrm{-}1/2}$ relationship above a critical sample length. Experimental results on vapor-deposited 1,1-bis(di-4-tolylaminophenyl)cyclohexane bear out the predicted transition between the two regimes upon varying temperature. This confirms that the scaling behavior of nondispersive photocurrent transients with respect to sample length and/or field is a consequence of energetic disorder. Geometrical disorder alone is unable to produce the scaling properties.