TE properties of CNT yarns

The pristine CNT yarns are favorable P-type TE elements, which demonstrate a Seebeck coefficient of ~66 μV/K, an electrical conductivity of ~16246 S/m, and an average power factor of 70.77 μW/(m·K²). The physical adsorption of PEI onto pristine CNTs converts them from P-type to N-type ascribed to the amine-rich polymer-donating electrons to the nanotubes. The influences of PEI adsorption on the Fermi energy shifting of pristine CNTs were evaluated according to the UV photoelectron spectroscopy (UPS) and the absorption spectra (fig. S33). The PEIs acting as donors shift the Fermi energy upward compared to its initial energy state, contributing to N-type behavior (49), which demonstrate a Seebeck coefficient of ~−65 μV/K, an electrical conductivity of ~18011 S/m, and an average power factor of 76.10 μW/(m·K²). It demonstrates a successful doping method to prepare N-type TE elements. The electrical conductivity ρ was measured using the formula: the cross section of the fiber is considered circular, ρ = L/(πr²R), where L, R, and r are the gauge length (10 cm), electric resistance, and mean radius of the tested gauge, respectively.