Hole transport in pentacene single crystals

Hole transport in high-quality pentacene single crystals is investigated using space-charge-limited current spectroscopy in a temperature range from 2 to 500 K. The temperature and electric-field dependence of the charge-carrier mobility below room temperature indicates a bandlike charge transport. The effective electronic bandwidth at low temperatures is estimated to be on the order of 400 meV. However, due to electron-phonon interaction the bandwidth narrows significantly, leading to a localization of the charge carriers and the formation of a lattice polaron above approximately 400 K. As a result, the transport mechanism crosses over from coherent bandlike motion to incoherent hopping.