Effects of different electrolytes and film thicknesses on structural and thermoelectric properties of electropolymerized poly(3,4-ethylenedioxythiophene) films

Abstract

The effects of the type of electrolyte and film thickness on the structural and thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films on indium-tin-oxide (ITO) substrates prepared using electropolymerization were investigated. Two electrolytes were prepared using two different solvents: a water/methanol solvent (protic solvent) and acetonitrile (aprotic solvent) with 3,4-ethylenedioxythiophene (EDOT) and LiCF₃SO₃, typically included in electrolytes as dopants. The electrochemical properties of the two electrolytes were analyzed; it was found that the polymerization process for EDOT on an ITO substrate varied based on the electrolyte used. When the electropolymerization time was increased, the surface morphology of the PEDOT films prepared using the water/methanol solvent appeared to contain grains approximately 100 nm in size whereas the PEDOT films prepared using acetonitrile appeared to contain aggregated grains connected by polymeric networks. Even though there were differences in the surface morphology and chemical bonds determined using Fourier-transform infrared spectroscopy/attenuated total reflectance analysis, the thermoelectric properties were strongly dependent on the film thickness and were only weakly dependent on the type of electrolyte used. The highest power factor was 41.3 μW (m⁻¹ K⁻²) for a PEDOT film with a thickness of 0.5 μm prepared using the water/methanol solvent electrolyte.