Simultaneous enhancements in the Seebeck coefficient and conductivity of PEDOT:PSS by blending ferroelectric BaTiO3 nanoparticles

Abstract

Thermoelectric polymers have attracted great attention because of their unique merits including low thermal conductivity, low cost, non- or low toxicity and high mechanical flexibility. However, their thermoelectric properties particularly the Seebeck coefficient should be greatly increased for practical applications. Although dedoping and energy filtering can increase the Seebeck coefficient, they lower the conductivity because the Seebeck coefficient and conductivity are interdependent. Here, we report simultaneous enhancements in the Seebeck coefficient and conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) that is the most popular thermoelectric polymer by adding ferroelectric barium titanate (BaTiO₃) nanoparticles. The BaTiO₃ nanoparticles can enhance the Seebeck coefficient from 23.8 to 40.7 μV K⁻¹ and the power factor from 34.4 to 117.0 μW m⁻¹ K⁻², and the insulating BaTiO₃ nanoparticles do not decrease but increase the conductivity of PEDOT:PSS. The conductivity of the continuous PEDOT:PSS phase in the composite films can be enhanced from 587 to 1552 S cm⁻¹. The enhancement in the Seebeck coefficient is ascribed to the energy filtering of low-energy charge carriers in PEDOT:PSS due to the spontaneous electric polarization of BaTiO₃, and the increase in the conductivity is attributed to the secondary doping of PEDOT:PSS related to the high dielectric constant of the BaTiO₃ nanoparticles.