Beyond the metal-insulator transition in polymer electrolyte gated polymer field-effect transistors

We have studied the carrier transport in poly(2,5-bis(3-tetradecyl- thiophen-2-yl)thieno[3,2-b]thiophene) field-effect transistors (FETs) at very high field-induced carrier densities (10(15) cm(-2)) using a polymer electrolyte as gate and gate dielectric. At room temperature, we find high current densities, 2 x 10(6) A/cm(2), and high metallic conductivities, 10(4) S/cm, in the FET channel; at 4.2 K, the current density is sustained at 10(7) A/cm(2). Thus, metallic conductivity persists to low temperatures. The carrier mobility in these devices is approximate to 3.5 cm(2.)V(-1.)s(-1) at 297 K, comparable with that found in fully crystalline organic devices.