Enhanced Power Factor of PEDOT:PSS Films Post-treated Using a Combination of Ethylene Glycol and Metal Chlorides and Temperature Dependence of Electronic Transport (325–450 K)

We report temperature dependence of electrical conductivity and thermopower for poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films post-treated using a combination of an organic polar solvent of ethylene glycol (EG) and transition metal chlorides. The pristine and post-treated PEDOT:PSS films are characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM), Raman spectroscopy techniques, and Hall effect measurements. Structural changes are confirmed by crystallinity improvement and Raman shift of the PEDOT:PSS, which correlate with a significant enhancement in thermoelectric power factor. The large variation of electronic transport in these films post-treated with three different metal chlorides can be attributed to the complex contribution of different conduction pathways. Among post-treated films, the highest electrical conductivity and power factor are attained for the EG/1 M ZnCl2 post-treated PEDOT:PSS film with 1979 S/cm and 132 μW/m K2 at 375 K. In general, organic conductive polymers have very low thermal conductivity; a zT = 0.24 at 375 K could be attained by assuming a thermal conductivity of 0.2 W/m-K. These results indicate that a combination of polar organic solvent EG and metal chlorides to post-treat a PEDOT:PSS film is a promising approach to enhance the thermoelectric properties of the conductive polymers of PEDOT:PSS.