Enhanced thermoelectric properties of SWCNT by new nitrogen chains doping

Abstract

Single walled carbon nanotubes (SWCNT) are attractive materials for thermoelectric (TE) devices because of their unique one-dimensional structure and provide us for developing a flexible TE devices due to their mechanical properties. In this paper, the TE properties of pristine small SWCNT (3,3) and three new nitrogen (N) doping models namely CN, C2N2 (doping by two N-chains) and C4N2 (doping by three N-chains) are calculated using the density functional theory (DFT) combined with Boltzmann's semi-classical transport theory. Dynamical and energetic stability of the compounds are confirmed from the phonon density of states curve and formation energy calculations. The values of Seebeck coefficient (S), electrical conductivity (σ), thermal conductivity (κ), power factor (PF) and figure of merit (ZT) are reported at different temperature and discussed in detail. The results show that N-doping significantly improves the TE properties of the pristine nanotube and show a reasonable agreement with previous experiments and ab-initio calculations. It was found that the C2N2 configuration presents the largest Seebeck coefficient of 70.53 μV/K and the figure of merit ZT of 0.25 compared to other doping models. N-chains doping is therefore a new suitable way to improve the TE properties of small SWCNT in order to making them a good candidate for flexible TE devices.