Enhanced thermoelectric properties of electropolymerized poly (3,4-ethylenedioxythiophene) thin films by optimizing electrolyte temperature and thermal annealing temperature

Effects of electrolyte temperature and annealing temperature on ClO4-doped poly (3,4-ethylenedioxythiophene) (PEDOT) thin films were investigated. Prior to the electropolymerization of the thin films, we performed cyclic voltammetry (CV) analysis while changing the electrolyte temperature between 0 °C and 60 °C. The current density increased with increasing electrolyte temperature, and the onset oxidation potential was mostly constant at approximately 1.3 V. From the CV analysis, we determined the electropolymerization condition of electrolyte temperature 50 °C and applied potential 1.52 V. Following the electropolymerization of the PEDOT thin films, thermal annealing was implemented in the range 80 °C to 140 °C with a mixture of argon (95%) and hydrogen (5%) gases at atmospheric pressure. ESR analysis showed that the intensity of the ESR spectra decreased with increased annealing temperature because of the decrease of charge-trapping related defects. In the annealed samples, the electrical conductivity of PEDOT thin films increased and the Seebeck coefficient decreased with increased annealing temperature; this was supported by the ESR analysis results. As a result, PEDOT thin films annealed at 80 °C and 100 °C exhibited a maximum power factor of 0.8 μW/(m·K2). Therefore, we conclude that the moderate annealing treatment enabled the thermoelectric performance to improve.