Defect contributions to conductivity in poly(3-hexylthiophene)?

We find evidence for a gradual change in the electronic properties of spin coated poly(3-hexylthiophene) thin films with temperature. The conduction properties appears to be mediated by hopping conduction dominated by a low density of defects states within the highest occupied molecular orbital to lowest unoccupied molecular orbital gap, not by a change in band gap. The photoemission and transport measurements indicate a loss of charge mobility or carrier concentration occurs with decreasing temperature, while the molecular configuration (through chain conjugation) also changes with temperature. The defects states identified by photoemission (-1.7 eV) as well as others contributing to the transport properties are believed to be very heterogeneous along the polymer backbone. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.