Concentration dependence of the hopping mobility in disordered organic solids

Traditionally the dependance of the drift mobility, μ, on the concentration of localized states, N, in disordered organic solids is plotted in the form μ ∝ exp[−C(Nα3)−p] with p = 1/3 and constant C. This representation cannot be correct, because transport in disordered organic solids is essentially a variablerange‐hopping process with a weaker dependence μ(N). We study this dependence theoretically and show that both parameters p and C strongly depend on temperature and hence they are not universal. Only at very high temperatures the formula with p = 1/3 is valid. The result is significant in particular for a correct diagnostics of the localization length α from the measured dependence μ(N). (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)