Effect of spatial irregularities on the temperature and field dependence of the mobility in liquid-crystalline conjugated polymer films

We have performed simulations of time-of-flight measurements via the Monte Carlo approach for films made of conjugated polymers in the liquid-crystalline phase. In spatially regular films with a distribution of on-site energies the mobility is affected by the interplay between electrostatic and thermal energy. When the width of the on-site energy distribution is comparable to the thermal energy, the mobility increases with temperature at low fields, but shows the opposite behaviour at larger fields. However, when spatial irregularities in the arrangement of the film are introduced, the mobility is enhanced at all temperatures, as the electrostatic energy plays less of a role in charge transport than thermal activation over energy barriers.