Dopant-induced crossover from 1D to 3D charge transport in conjugated polymers

The interplay between inter- and intrachain charge transport in bulk polythiophene in the hopping regime has been clarified by studying the conductivity $\ensuremath{\sigma}$ as a function of frequency $\ensuremath{\omega}/2\ensuremath{\pi}$ (up to 3 THz), temperature $T$, and doping level $c$. We present a model which quantitatively explains the observed crossover from quasi-one-dimensional transport to three-dimensional hopping conduction with increasing doping level. At high frequencies the conductivity is dominated by charge transport on one-dimensional conducting chains.