Charge transport in oligothiophene single crystals

The charge transport in alpha -quaterthiophene and alpha -hexathiophene sin gle crystals was studied by space charge limited current spectroscopy. Reco rd 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 mole cular 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 mechani sm 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 t wo different single crystalline modifications have been investigated. (C) 2 000 Elsevier Science S.A. All rights reserved.