Stable N-Type Single-Walled Carbon Nanotube/Mesh Sheets by Cationic Surfactant Doping and Fluoropolymer Coating for Flexible Thermoelectric Generators

Single-walled carbon nanotubes (SWCNTs) offer promise as materials for thermoelectric generators (TEGs) due to their flexibility, durability, and non-toxic nature. However, a key barrier to their application lies in their high thermal conductivity, which hampers the generation of temperature differences in TEGs. To address this challenge, we explored a method of enhancing the heat dissipation of SWCNT-based TEGs by coating SWCNT layers onto polymer mesh sheets. During TEG fabrication, achieving stable n-type SWCNT/mesh sheets proved considerably more challenging than their p-type counterparts. This difficulty stemmed from the inferior dispersibility of the n-type SWCNT ink compared to the p-type SWCNT ink. To produce n-type SWCNT/mesh sheets, we initially prepared p-type SWCNT/mesh sheets using p-type SWCNT ink, subsequently doping them with a cationic surfactant solution to induce n-type characteristics. To stabilize the n-type thermoelectric properties in SWCNT/mesh sheets, we applied a fluoropolymer coating to the SWCNT surfaces, mitigating the adsorption of oxygen molecules. This approach yielded n-type SWCNT/mesh sheets capable of long-term maintenance. Furthermore, flexible TEGs fabricated using both p- and n-type SWCNT/mesh sheets demonstrated an output voltage of 15 mV, which can operate IoT sensors using the latest booster circuits, and a maximum power of 100 nW at a temperature difference of 71 K.