Thermoelectric behavior of poly(3,4-ethylenedioxythiophene)/graphene composites depending on benzenesulfonate derivatives doped in polymer chains

Abstract

Ferric benzenesulfonate (Fe(Bzs)(3)), ferric para-methylbenzenesulfonate (Fe(p-MeBzs)(3)), and ferric para-ethylbenzenesulfonate (Fe(p-EtBzs)(3)) were synthesized and used as oxidants. Thermoelectric composites were fabricated from synthesized benzenesulfonate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-Bzs), para-methylbenzenesulfonate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-p-MeBzs), and para-ethylbenzenesulfonate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-p-EtBzs) matrices with varied contents of conductive graphene filler. Dodecylbenzenesulfonic acid was used as both a surfactant to form graphene micelles and a doping agent to coat a PEDOT layer on the graphene surface. The PEDOT-Bzs produced the highest electrical conductivity among the PEDOT materials, exhibiting higher doping level of the polymer main chain than the PEDOT-p-MeBzs and PEDOT-p-EtBzs. The electrical conductivity and the Seebeck coefficient of the composite increased significantly with increasing graphene content through the extended chain conformation, which reduces the charge carrier hopping barrier to increase carrier mobility. The maximum figure of merit (ZT) value of the PEDOT-Bzs composites with 75 wt% graphene filler content was estimated at 0.015 at room temperature, higher than that of PEDOT-p-MeBzs (0.013) and PEDOT-p-EtBzs (0.01).