Optimal Thermoelectric Power Factor of Narrow-Gap Semiconducting Carbon Nanotubes with Randomly Substituted Impurities

TL;DR

This paper theoretically analyzes the thermoelectric properties of narrow-gap nitrogen-doped carbon nanotubes, identifying optimal impurity concentrations for maximum power factor and estimating the figure of merit at room temperature.

Contribution

It introduces a self-consistent model for N-impurity bands in narrow-gap SWCNTs and determines optimal doping levels for enhanced thermoelectric performance.

Findings

Maximum power factor of 0.30 W/K^2m at 300K.

Optimal N concentration of 3.1×10^{-5} per unit cell.

Estimated figure of merit ZT ≈ 0.1 at room temperature.

Abstract

We have theoretically investigated thermoelectric (TE) effects of narrow-gap single-walled carbon nanotubes (SWCNTs) with randomly substituted nitrogen (N) impurities, i.e., N-substituted (20,0) SWCNTs with a band gap of 0.497 eV. For such a narrow-gap system, the thermal excitation from the valence band to the conduction band contributes to its TE properties even at the room temperature. In this study, the N-impurity bands are treated with both conduction and valence bands taken into account self-consistently. We found the optimal N concentration per unit cell, $c_{\rm opt}$, which gives the maximum power factor ($PF$) for various temperatures, e.g., $PF=$0.30$\rm{W/K^2m}$ with $c_{\rm opt}=3.1\times 10^{-5}$ at 300K. In addition, the electronic thermal conductivity has been estimated, which turn out to be much smaller than the phonon thermal conductivity, leading to the figure of merit as $ZT\sim 0.1$ for N-substituted (20,0) SWCNTs with $c_{\rm opt}=3.1\times 10^{-5}$ at 300K.