Facile charge carrier adjustment for improving thermopower of doped polyaniline

We report a facile method of improving thermopower of doped polyaniline (PANI). It is believed that the electrical properties were altered by controlling the concentration of charge carriers with camphor sulfonic acid (CSA) and ammonium hydroxide. With CSA doping followed by drying and annealing at temperatures below ∼100 °C, the electrical conductivity was increased up to ∼5700 S/m with a thermopower value, ∼14 μV/K at room temperature. The power factor reached ∼1 μW/m-K² after optimizing the drying and annealing temperature, which is 5-1000 times larger than those of other doped PANI without stretching. This thermopower of PANI-CSA films was monotonically improved in proportion to the time period of the ammonium hydroxide reaction, resulting in ∼115 μV/K at room temperature, which is 1.2-10 times higher than those of other doped PANI. The intensity changes of Fourier transform infrared spectra before and after the de-doping process with ammonium hydroxide indicates the thermopower increase is likely to be from the reduction in the charge carrier concentration. This method is a facile and convenient way of adjusting carrier concentrations, which are crucial to find the optimum doping level for high performance thermoelectrics. We believe further studies to improve crystallinity of doped PANI may dramatically raise the electrical conductivity in addition to the large thermopower, so as to obtain a high performance PANI-containing polymer composite for thermoelectric applications.