Annealing Temperature Tuning of Thermoelectric Properties in Conductive Polymers: Transition from Ionic to Electronic Thermoelectrics

Thermoelectric materials (TEMs) have attracted considerable interest for applications in low-grade energy harvesting, refrigeration, and sensing. Conductive polymers (CPs) represent an important class of TEMs, as they have garnered considerable attention for their dual functionality in facilitating ion transport through channel formation, while simultaneously enabling hole–electron conduction via conjugated networks. However, researchers have overlooked the connection between CP-based ionic thermoelectrics and electronic thermoelectrics. Here, we demonstrate tunable thermoelectric properties achieved exclusively through polymer annealing without any additional substance incorporation. For the PEDOT:PSS/EMIM:DCA composites, a distinct transition from ionic to electronic TEMs was observed for the first time upon annealing above 140 °C. Through comprehensive characterization techniques, we demonstrated that this transition originates from the construction of conductive networks induced by phase separation. Furthermore, by utilizing materials annealed at different temperatures, we constructed a hybrid ionic-electronic thermoelectric converter achieving energy density of 13.99 J m–2, more than 17-fold enhancement compared to a pure ionic thermoelectric converter. This work not only provides fundamental insights into charge transport in CPs but also provides insights into the design of high-performance TEMs.