Comparative study of hole transport in poly(<i>p</i>-phenylene vinylene) derivatives

The dc mobility of holes in four poly(p-phenylene vinylene) (PPV) derivatives (three fully conjugated polymers with different side chains and one partially conjugated PPV) is examined as a function of temperature T and applied electrical field E. In all cases the mobility $\ensuremath{\mu}$ follows the empirical $\ensuremath{\mu}\ensuremath{\propto}\mathrm{exp}\ensuremath{\gamma}\sqrt{E}$ law. The specific temperature and electrical field dependence of the mobility is fitted within a (correlated) Gaussian disorder model. From the fits the energetic disorder, localization length, and average transport-site separation are determined. In the case of the fully conjugated polymers the different T and E dependencies of $\ensuremath{\mu}$ are completely determined by the energetic disorder. The relation between the obtained microscopic transport parameters and the specific chemical composition of the polymer material is discussed.