Enhanced thermoelectric performance of PEDOT:PSS films by solvent thermal treatment

Flexible free-standing PEDOT:PSS films were thermally treated by various of high polar organic solvents such as N-methyl-2-pyrrolidone (NMP), ethylene glycol (EG), dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF), and a comparative thermoelectric (TE) study was conducted in the present work. Due to the synergistic effect of high polar solvent and thermal treatment, the maximum electrical conductivity of PEDOT:PSS films was up to 520 S cm−1 by EG post-treatment at its boiling point (197 °C), resulting in a power factor of 14.9 μW m−1 K−2, which was four orders of magnitude higher than pure PEDOT:PSS film (~0.005 μW m−1 K−2). The improvement of TE performance is primarily caused by the increased electrical conductivity and the steady Seebeck coefficient. As observed from atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) characterization, the enhancement of electrical conductivity is attributed to the removal of excess insulating PSS from the PEDOT:PSS film surface and the separation of the rest PSS chains in the polymer matrix from the PEDOT phase.