Delocalized Charge Transport in Thermoelectric Composites of Semiconducting Carbon Nanotubes Wrapped with a P-Type Polymer

In this work, thermoelectric composites comprised of semiconducting single-walled carbon nanotubes (sc-SWCNTs) and a p-type polymer, poly(3-dodecylthiophene-2,5-diyl) (P3DDT), are produced by selectively dispersing the sc-SWCNTs through P3DDT wrapping, followed by solution-based deposition. Through comprehensive electrical and spectroscopic characterizations, coupled with a semi-localized transport model, It is confirmed that, the sc-SWCNT/P3DDT composites, when adequately doped with FeCl₃, can exhibit highly delocalized charge carrier transport. This leads to thermoelectric power factors up to 98.2 µW mK⁻². The efficient charge delocalization is enabled by the reduced coulombic binding energy at high carrier concentration, as well as the small transport barrier between the polymers and the SWCNTs. It is also shown that polymer wrapping of sc-SWCNTs enhances phonon scattering, and sc-SWCNT/P3DDT composites show lower thermal conductivity relative to unsorted SWCNTs mixed with P3DD. This study provides insight into the thermoelectric behavior of hybrid materials and also demonstrates the possibility of using sc-SWCNTs as inclusions in composites for thermoelectrics.