High hole-mobility of rrP3HT in organic field-effect transistors using low-polarity polyurethane gate dielectric

We report unusually high charge carrier mobilities for regioregular poly(3-hexyltiophene) (rrP3HT) in organic field-effect transistors (OFETs) using polyurethane (PU) as dielectric layer. Our devices display hole mobilities up to 1.37 cm(2)/V in the saturation regime and an ON/OFF current ratio higher than 10(3), operating at voltages as low as -10 V, with a high I-DS current of 1.5 mu A. We assign the measured high mobilities mainly to the low density of randomly-oriented electric dipoles at the semiconductor/dielectric interface, which leads to a narrow energy distribution of the electronic levels available for charge transport in rrP3HT. This is confirmed by experimental and theoretical techniques: (1) temperature-dependent transport measurements for extraction of disorder-induced distribution of electronic levels; (2) density functional theory (DFT) calculations of electric dipole moments of PU; and (3) liquid contact-angle measurements for the dipolar component of dielectric surface tension.