Solution processed intrinsically conductive polymer films with high thermoelectric properties and good air stability

Abstract

It is important to study thermoelectric (TE) materials because they can directly convert heat into electricity. Although intrinsically conducting polymers have the advantages of nontoxicity, low cost, high mechanical flexibility and low thermal conductivity, their thermoelectric properties must be significantly improved for practical application. Here, we report a solution-processed conducting polymer, poly(3,4-ethylenedioxythiophene):trifluoromethanesulfonate (PEDOT:OTf), with very high TE properties. As-prepared PEDOT:OTf films from their precursor solution can exhibit a power factor of 346 ± 39 μW m⁻¹ K⁻². The power factor can be further enhanced by a post treatment with NaOH or a reducing agent like glucose or ascorbic acid. The NaOH treatment can give rise to a power factor of 568 ± 64 μW m⁻¹ K⁻² with a Seebeck coefficient of 49.2 ± 1.4 μV K⁻¹ and an electrical conductivity of 2342 ± 98 S cm⁻¹. This power factor is higher than those obtained by treatment with the reducing agents. The different power factors by NaOH and reducing agent treatments are attributed to their different effects on the doping. The NaOH treatment can remove the protonic doping while the reducing agents can lower the normal oxidation level of PEDOT. The charge carriers due to protonic acid doping have lower energy, and thus the removal of protonic acid doping can significantly enhance the Seebeck coefficient while not lowering the electrical conductivity too much.