Solution-phase p-type doping of highly enriched semiconducting single-walled carbon nanotubes for thermoelectric thin films

Single-walled carbon nanotubes (SWCNTs) are attractive materials for next-generation energy-harvesting technologies, including thermoelectric generators, due to their tunable opto-electronic properties and high charge carrier mobilities. Controlling the Fermi level within these unique 1D nanomaterials is often afforded by charge transfer interactions between SWCNTs and electron or hole accepting species. Conventional methods to dope SWCNT networks typically involve the diffusion of molecular redox dopant species into solid-state thin films, but solution-phase doping could potentially provide routes and/or benefits for charge carrier transport, scalability, and stability. Here, we develop a methodology for solution-phase doping of polymer-wrapped, highly enriched semiconducting SWCNTs using a p-type charge transfer dopant, F(4)TCNQ. This allows doped SWCNT inks to be cast into thin films without the need for additional post-deposition doping treatments. We demonstrate that the introduction of the dopant at varying stages of the SWCNT dispersion process impacts the ultimate thermoelectric performance and observe that the dopant alters the polymer selectivity for semiconducting vs metallic SWCNTs. In contrast to dense semiconducting polymer films, where solution-phase doping typically leads to disrupted morphologies and poorer TE performance than solid-state doping, thin films of solution-doped s-SWCNTs perform similarly to their solid-state doped counterparts. Interestingly, our results also suggest that solution-phase F(4)TCNQ doping leads to fully ionized and dimerized F(4)TCNQ anions in solid-state films that are not observed in films doped with F(4)TCNQ after deposition. Our results provide a framework for the application of solution-phase doping to a broad array of high-performance SWCNT-based thermoelectric materials and devices that may require high-throughput deposition techniques. Published under an exclusive license by AIP Publishing.

Automated summary

Single-walled carbon nanotubes (SWCNTs) are promising materials for next-generation energy-harvesting technologies, such as thermoelectric generators, due to their customizable opto-electronic properties and high charge carrier mobilities. This study develops a method for solution-phase doping of highly enriched semiconducting SWCNTs wrapped in polymers using a p-type charge transfer dopant, F(4)TCNQ. Introduction of the dopant at different stages of the SWCNT dispersion process impacts the thermoelectric performance and alters polymer selectivity for semiconducting vs metallic SWCNTs. Solution-doped thin films of semiconducting SWCNTs perform similarly to solid-state doped films, suggesting potential benefits for high-throughput deposition techniques in SWCNT-based thermoelectric materials and devices.