Mobility variation with field in conducting polymer films

Poole–Frenkel (P–F) behavior, i.e. the exponential dependence of the mobility on the square root of the electric field intensity, has been found for many conducting polymer films. It has been suggested that, as in molecularly doped polymers, this dependence is due to the interaction between the charge carriers and randomly distributed permanent dipoles. However, the dipole concentration in the polymers is much too small. We show by Monte Carlo simulations that introduction of short range correlation between the energies of the hopping sites, on the scale of the coherence length measured by X-rays, can account for the measured field- and temperature-dependence of MEH-PPV films. We show also that inhomogeneity, while still permitting P–F behavior, has important effects on the size, field-dependence and temperature-dependence of the mobility.