A facile chemical reduction approach for effectively tuning thermoelectric properties of PEDOT films

Poly(3,4-ethylenedioxythiophene)–tosylate–polyethylene glycol–polypropylene glycol–polyethylene glycol (PEDOT–Tos–PPP) films were prepared via a vapor phase polymerization (VPP) method. The films possess good electrical conductivity (1550 S cm^?1), low Seebeck coefficient (14.9 μV K^?1) and thermal conductivity (0.501 W m^?1 K^?1), and ZT ～ 0.02 at room temperature (RT, 295 K). Then, the films were treated with NaBH₄/DMSO solutions of different NaBH₄ concentrations to adjust the redox level. After the NaBH₄/DMSO treatment (dedoping), the electrical conductivity of the films continuously decreased from 1550 to 5.7 S cm^?1, whereas the Seebeck coefficient steeply increased from 14.9 to 143.5 μV K^?1. A maximum power factor of 98.1 μW m^?1 K^?2 has been achieved at an optimum redox level. In addition, the thermal conductivity of the PEDOT–Tos–PPP films decrease from 0.501 to 0.451 W m^?1 K^?1 after treated with 0.04% NaBH₄/DMSO solution. A maximum ZT value of 0.064 has been achieved at RT. The electrical conductivity and thermal conductivity (Seebeck coefficient) of the untreated and 0.04% NaBH₄/DMSO treated PEDOT–Tos–PPP films decrease (increases) with increasing temperature from 295 to 385 K. And the power factor of the films monotonically increases with temperature. The ZT at 385 K of the 0.04% NaBH₄/DMSO treated film is 0.155.