Enhanced thermoelectric performance by alcoholic solvents effects in highly conductive benzenesulfonate-doped poly(3,4-ethylenedioxythiophene)/graphene composites

Benzenesulfonate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-Bzs)/graphene thermoelectric (TE) composites with various graphene filler contents were synthesized in five different kinds of solvents. Dodecylbenzenesulfonic acid (DBSA) was used to achieve good dispersion of graphene into the PEDOT matrix. Among the synthesized PEDOT materials, the one synthesized in methanol (PEDOT-MeOH) had the highest electrical conductivity. X-ray photoelectron spectroscopy (XPS) analysis showed almost the same charge carrier concentration for all PEDOT materials. However, the X-ray diffraction (XRD) analysis highlighted the enhancement of PEDOT chain stacking by shorter-chain alcoholic solvents, as a result of which the carrier mobility and electrical conductivity were increased. The electrical conductivity and the Seebeck coefficient of the PEDOT/graphene composites were significantly improved with increasing the graphene content, which strongly depended on increased carrier mobility. The thermal conductivity of the composites exhibited relatively small changes, attributed to phonon scattering effects. The maximum TE efficiency of the PEDOT-MeOH/graphene composite with 75 wt % graphene showed a substantially improved value of 1.9 × 10^-2, higher than that of the other PEDOT/graphene composites.