Chemical sensing using nanostructured polythiophene transistors.

We show that the chemical sensing responses of organic field-effect transistors based on nanostructured regioregular polythiophene are strongly dependent upon the gate biasing field. With different applied gate voltages, the source-drain current response can be different both in sign and magnitude for the same analyte. This implies that multiple competing sensing mechanisms exist at the same time. We propose that the sensing mechanisms for polycrystalline semiconducting polymer thin films are mainly an intragrain effect, which yields a positive response, and a grain boundary effect, which yields a negative response.