Concentration dependence of the hopping mobility in disordered organic solids

It has already become a tradition in the field of disordered organic solids to plot the dependence of the carrier mobility μ on the concentration of localized states N in the form μ∝exp[-C(Nα3)-p] with p=1/3 and constant C. Moreover, it is this concentration dependence that is usually employed in order to determine experimentally the localization length of charge carriers α from the plots ln(μ) versus N-1/3. We study the μ(N) dependence theoretically and show that both parameters p and C are not universal and that they essentially depend on temperature. This result is general and it shows that the estimate of the wave function decay α employing the dependence μ(N) should be based on the appropriate theory which takes into account the temperature dependences of the parameters p and C. Results are compared with those of computer simulations and with experimental data.