Enhanced Performance and Stability of PEDOT:PSS Thin-Film Thermoelectrics by De-doping with Nitrogen-Doped Graphene Quantum Dots

Conducting polymers have recently garnered attention owing to their high flexibility, low-cost fabrication, and environmental friendliness, along with a tunable doping level suitable for various prospective electronic devices. When it comes to thermoelectric (TE) devices that can convert low-grade heat to electricity, achieving optimal carrier concentration (n) through post-treatment is significant because electrical conductivity (σ) and the Seebeck coefficient (S) have an interdependent relationship in terms of n. It is thus crucial to continuously explore doping strategies that can boost the TE properties while maintaining polymer morphology to minimize the sacrifice of σ upon de-doping. In this work, we propose a de-doping method for poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) by incorporating nitrogen-doped graphene quantum dots (GQDs) in a post-treatment process. We discovered that GQDs can modulate the doping level of PEDOT:PSS while preserving the linear quinoid structure of the PEDOT chains. Based on various analyses, we found that the minimally deteriorated microstructure primarily originated from the intrinsically hydrophilic nature of GQDs, allowing strong π–π interactions with PEDOT chains, and electron-donation-based de-doping by GQDs. Consequently, S could be enhanced from 18.0 μV K–1 to 33.4 μV K–1 with less than a 30% decrease in σ to achieve a high thermoelectric power factor of 84.3 μW m–1 K–2. Furthermore, the TE properties were well-maintained under ambient and humid conditions, owing to the robust PEDOT network by GQDs. We believe that our de-doping technique using nitrogen-doped GQDs can lead to a direction for stable and high-performance TE devices.