Charge transport in oligothiophene single crystals

The charge transport in alpha -quaterthiophene and alpha -hexathiophene single crystals was studied by space charge limited current spectroscopy. Record high mobilities of up to 10 cm(2)/V s were observed at low temperatures. The strongly anisotropic charge transport in these materials is explained by the molecular packing giving rise to a strong pi-pi* overlap in the molecular planes due to short sulphur-carbon contacts, but almost no molecular overlap along the ends of the molecules. Therefore, the charge carrier can be described as a two-dimensionally extended polaron. The transport mechanism is governed by two-dimensional, band-like motion within the planes and a phonon-assisted, thermally activated hopping process perpendicular to them. To determine the influence of molecular packing on the charge transport two different single crystalline modifications have been investigated. (C) 2000 Elsevier Science S.A. All rights reserved.