Abstract
In strongly disordered solids the complex conductivity has a remarkably uniform dependence on the number of carriers, temperature and frequency. Still, as we illustrate for randomly packed molecular cluster compounds, it is possible to derive the relevant hopping parameters. In particular the analysis of the transition from phonon- to photon-assisted hopping in the pair limit, when combined with the low-frequency data, yields precise information. In polymer blends and conjugated polymers the charge mobility behaves in a qualitatively similar way, but its temperature and frequency dependences deviate from the almost universal behaviour in the fully random systems. We show how these differences relate to the mesoscopic structure.