High Conductivity in PEDOT:PSS Thin-Films by Secondary Doping with Superacid Vapor: Mechanisms and Application to Thermoelectrics

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a conductive polymer, have attracted attention as promising materials for future electronic applications, owing to its tunable doping level for high electrical conductivity (σ) through simple post-treatments. A novel post-treatment method for conventionally doped PEDOT:PSS thin-films (immersed in methanol) is presented to further enhance σ via doping with the superacid, trifluoromethanesulfonic acid (TFSA). The origin of the improved σ in PEDOT:PSS thin-films treated with this dual approach is investigated. The study reveals that the superacid vapor treatment uniquely enhances the lamellar stacking of PEDOT chains and induces vertical phase separation between PEDOT and PSS, leading to improved carrier mobility by a factor of three. This behavior differs from conventional post-treatments, making the combined methanol immersion and TFSA vapor treatment an effective strategy for achieving a high σ of ≈2053 S cm⁻¹, making these films ideal candidates for various polymer-based electronics. Furthermore, the findings demonstrate that the thermoelectric power factor of PEDOT:PSS subjected to secondary doping with superacid vapor exhibits a threefold enhancement (104.2 µW m⁻¹ K⁻²) compared to samples treated solely with methanol (29.7 µW m⁻¹ K⁻²). This post-treatment method and the resulting insights will advance the understanding of doping mechanisms and charge transport in conductive polymers.