Transport Properties of Polymer Semiconductor Controlled by Ionic Liquid as a Gate Dielectric and a Pressure Medium

An effective way of using ionic liquid as a gate dielectric as well as a pressure medium to tune the transport of an exemplary polymer semiconductor, poly(2,5-bis(3-tetradecyl-thiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT-C14) is presented. Working as gate dielectrics, the ionic liquids exhibit the well-known ability to induce dense carriers (>10(20) cm(-3)) in the polymer film contributing to the high conductivity (approximate to 10(2) S cm(-1)). In addition, it is found that the ionic liquid works as a pressure medium at the highly charged state, leading to significant enhancement of conductivity. By combining both gating and pressuring, a crossover of transport properties is observed from one-dimensional to three-dimensional hopping, as the clear indication that the polymer film has accessed the regime adjacent to the transition region between insulator and metal. These results show an effective way of utilizing pressure effect of ionic liquid as a new degree of freedom in controlling transport of polymers, a method having strong potential to be generalized for even broader range of materials.