Surface and bulk mobilities of oligothiophene single crystals

High-quality single crystals of α-quaterthiophene (α-4T) and α-hexathiophene (α-6T) were investigated to compare intrinsic bulk and surface electrical properties. The bulk properties of these organic p-type semiconductors are derived from extended current–voltage characteristics and the surface properties from single crystal field-effect transistor measurements. Most significantly, charge carrier mobilities as high as 0.5 cm2/V s are observed in α-6T both in the bulk and at the surface. The high quality and purity of the crystals are evident from the low trap densities(<1015 cm−3) and the even lower dopant concentrations (2×1013 for α-4T and 7×1010 cm−3 for α-6T). These intrinsically high performance figures, together with the ease of processing, make these oligothiophenes attractive materials for “plastic electronic” devices.