High Power Factor of p- and n-Type Single-walled Carbon Nanotubes by Solution Processing

Organic thermoelectric materials are not only used in low-grade waste heat recovery but also have frontier applications in sensors, wearable self-powered devices, biomaterials, and smart materials with the development of flexible electronics. However, investigation on the thermoelectric performance of single-walled carbon nanotubes (SWCNTs) comparable to that of conducting polymers and their composites with SWCNTs has been rarely attempted, and there were few reports on SWCNTs alone as organic thermoelectric materials. Certainly, SWCNTs possess high Young’s modulus, high thermal stability, flexibility, lightweight, easily controllable doping level, and facile p–n transition, while the mechanism of molecular doping of SWCNTs remains to be well understood. Here, facile solution processing achieved the enhancement of p-type and n-type thermoelectric performance of SWCNTs. Small-molecular-weight polyethylene glycol treatment improved electrical conductivity and the Seebeck coefficient of SWCNTs (p-SWCNTs) simultaneously, with the power factor of 303.17 ± 46.25 μW·m⁻¹·K⁻². Small amount of polyethylenimine doping made the Seebeck coefficient of SWCNTs (n-SWCNTs) turn negative and rendered great air stability of n-SWCNTs. The electrical conductivity and power factor of n-SWCNTs reached 1,702.56 ± 164.13 S·cm⁻¹ and 418.49 ± 46.30 μW·m⁻¹·K⁻² at 298 K, respectively. The power factor of n-SWCNTs got even higher at 319.5 K in vacuo, reaching a high value of 643.35 μW·m⁻¹·K⁻². Finally, mechanism study in this work provided inspiration and guidance for the application of these types of dopants in the performance improvement of SWCNTs.