Unlocking The Potential of Solution-Processed PEDOT:PSS Thin Films for Efficient Thermoelectric Energy Conversion

Thermoelectric (TE) generation using solution-processable conjugated polymers holds great promise for low-temperature energy harvesting due to their versatility in materials, processes and form-factors. Among these polymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is considered a promising candidate owing to its high electrical conductivity, flexibility, and air stability. However, a lack of understanding on the relationship between microstructure and TE charge transport properties has been a significant obstacle, impeding further enhancements in performance of solution-processable PEDOT:PSS. Here, we present a solution-processed, high-performance TE device based on a PEDOT:PSS thin film and thoroughly investigate their microstructure–thermoelectric performance–charge transport property relationships. We first fabricated a highly conductive PEDOT:PSS films using a super acid, where the <i>σ</i> values increased up to ~3600 S cm⁻¹ primarily due to the highly ordered microstructure with PSS removal. Through a successive reduction process, we achieved the highest power factor of 534.5 μW m⁻¹ K⁻² with delocalized charge transport properties. Additionally, high electronic tunability of the reducer allowed us to investigate the Seebeck–conductivity relation over a wide range of <i>σ</i>, suggesting that the maximum <i>PF </i>value may surpass the experimentally obtained values. To identify the origin of the discrepancy, we analyzed the macro- and micro-scale charge transport properties using the temperature-dependent <i>σ</i>, Hall effects, and magnetoconductance of the films, together with the morphology, and found out that the connectivity between crystalline domains and the resulting high degree of percolation for transport are important factors toward the theoretically ideal <i>PF</i>.