Charge transfer complex-doped single-walled carbon nanotubes with reduced correlations between electrical conductivity and Seebeck coefficient for flexible thermoelectric generators

Abstract

Carbon-based materials have ascended as promising candidates for thermoelectric energy conversion. This study demonstrated charge transfer complexes (CTCs) as novel p-dopants for single-walled carbon nanotubes (SWCNTs), which established reduced correlations between electrical conductivity and Seebeck coefficient compared with those of traditional p-dopants. The SWCNT films doped with 0.07 wt% CTCs of tetrathiafulvalene-7,7,8,8-tetracyanoquinodimethane (TTF-TCNQ) exhibited a maximum power factor of 248 μW m⁻¹ K⁻² at room temperature, which was 51% higher than that of the undoped SWCNTs and 20% higher than that of the TCNQ-doped SWCNT films. Flexible thermoelectric generators solely from TTF-TCNQ-doped SWCNT films exhibited a maximum output power of 17.4 nW under a temperature bias of ΔT = 22.8 K from a device with 12 active modules, while the device composed of TCNQ-doped SWCNT films did not produce recordable output power. The more efficient thermoelectric conversion capability for the CTC-doped SWCNT could be explained by its lower amount of structural defects, higher carrier mobility and reduced charge transfer process between SWCNT and dopant molecules. This work demonstrated that charge transfer complexes were more superior p-dopants, which were generally applicable for SWCNT-based thermoelectric materials and generators.