Enhanced Performance\nand Stability of PEDOT:PSS Thin-Film\nThermoelectrics by De-doping with Nitrogen-Doped Graphene Quantum\nDots

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