A comparative investigation into the thermoelectric properties of doped graphene nanoribbons in different doping manners

By using first-principles density functional theory and nonequilibrium Green's function, we systematically study the thermoelectric (TE) properties of graphene nanoribbons (GNRs) doped by different atoms including B, N, Si, and Be. Correspondingly, the doped GNRs can be categorized into three kinds: p-type, n-type, and same-group-element doped GNRs. First, we find the Seebeck coefficients S of the doped GNRs are dependent on the kinds of doping atoms, the doping position, and the doping concentration. However, no sharp increase of S can be induced by all dopings in the GNRs. Then we find for all three doping manners the doped GNRs will show strongly enhanced figures of merit ZTs in comparison with the undoped pure GNRs. In addition, the ZTs are always dependent on the doping positions, and will increase with the increasing of the doping concentration. However, different dopings can induce sharply different variations of the ZT peaks, and different sensitivities of the dependence of ZT and Seebeck coefficients on the doping position and concentration. The p-type B (n-type N) doping will move the ZT peaks and the S peak upwards (downwards) to the high-energy (low-energy) direction, while the same-group-element Si doping does not change the positions of the ZT peaks. Also, the p-type Be (n-type N) doping leads to the highest (lowest) ZT peak maximums, while both the B and Si dopings show the similar intermediate ZT peak maximums. Especially, the ZTs of the GNRs with the same-group-element Si doping behave more like those of the p-type B doped GNRs. This work will greatly deepen the understanding of the TE properties of the doped GNRs, and should be an important reference in utilizing the different doping manners to manipulate the TE performance of the GNRs.