Variable-Range Hopping Conduction in Ion-Gel-Gated Electrochemical Transistors of Regioregular Poly(3-hexylthiophene)

Ion-gel-gated transistors enable controlled carrier doping into conjugated polymers in identical devices measurable at low temperatures. Using this technique, the carrier transport of regioregular poly(3-hexylthiophene) was investigated in a wide temperature range down to 15 K. At room temperature, carrier mobility exhibited an electrochemical behavior with a minimum at a doping level of approximately 0.4% and a subsequent sharp increase up to 0.5 cm(2) V-1 s(-1). At doping levels above similar to 3%, the ohmic conductivity of the transistor channel deviated from thermal activation and showed a quasi-one-dimensional variable-range hopping behavior. This result indicates the enhanced carrier transport through the overlap of carrier wavefunctions developing toward a doping level of similar to 10% under electrochemical doping in a transistor channel.