Optimization of Wet-Spun PEDOT:PSS Fibers for Thermoelectric Applications Through Innovative Triple Post-treatments

Owing to the high flexibility, low thermal conductivity, and tunable electrical transport property, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) exhibits promising potential for designing flexible thermoelectric devices in the form of films or fibers. However, the low Seebeck coefficient and power factor of PEDOT:PSS have restricted its practical applications. Here, we sequentially employ triple post-treatments with concentrated sulfuric acid (H₂SO₄), sodium borohydride (NaBH₄), and 1-ethyl-3-methylimidazolium dichloroacetate (EMIM:DCA) to enhance the thermoelectric performance of flexible PEDOT:PSS fibers with a high power factor of (55.4 ± 1.8) μW m⁻¹ K⁻² at 25 °C. Comprehensive characterizations confirm that excess insulating PSS can be selectively removed after H₂SO₄ and EMIM:DCA treatments, which induces conformational changes to increase charge carrier mobility, leading to enhanced electrical conductivity. Simultaneously, NaBH₄ treatment is employed to adjust the oxidation level, further optimizing the Seebeck coefficient. Additionally, the assembled flexible fiber thermoelectric devices show an output power density of (60.18 ± 2.79) nW cm⁻² at a temperature difference of 10 K, proving the superior performance and usability of the optimized fibers. This work provides insights into developing high-performance organic thermoelectric materials by modulating polymer chains. Graphical Abstract: (Figure presented.)