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 mu on the concentration of localized states N in the form muproportional toexp[-C(Nalpha(3))(-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 alpha from the plots ln(mu) versus N-1/3. We study the mu(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 alpha employing the dependence mu(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.