Enhanced thermoelectric properties of sorbitol-mixed PEDOT:PSS thin films by chemical reduction

This study systematically examined the thermoelectric (TE) properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films by enhancing the electrical conductivity with D-sorbitol and by controlling the oxidation level with tetrakis (dimethylamino) ethylene (TDAE) vapor treatment. Mixing sorbitol into PEDOT:PSS changed the morphology of the films, increasing the electrical conductivity up to 722.06 S cm⁻¹, which is over two orders of magnitude higher than that of pristine PEDOT:PSS (1.53 S cm⁻¹). For even better TE properties, we subsequently exposed the films to TDAE vapor (which is a well-known reducing agent) for various treatment times to control their oxidation levels. The difference in the redox state as a function of the reduction time was easily identified by the naked eye owing to the electrochromic properties of PEDOT:PSS. As a result, we obtained a high power factor of 22.28 μW m⁻¹ K⁻² from the sorbitol-mixed PEDOT:PSS thin films that were treated via chemical reduction. This value is three times higher than that of devices without TDAE treatment (7.26 μW m⁻¹ K⁻²). The properties and changes in the films fabricated with sorbitol and TDAE treatments were characterized by atomic force microscopy and UV–Vis-NIR absorption.