Thermoelectric Properties of Pristine Graphyne and the BN-Doped Graphyne Family

Abstract

In this paper, we have investigated the thermoelectric properties of BN-doped graphynes and compared them with respect to their pristine counterpart using first-principles calculations. The effect of temperature on the thermoelectric properties has also been explored. Pristine γ-graphyne is an intrinsic band gap semiconductor and the band gap significantly increases due to the incorporation of boron and nitrogen atoms into the system, which simultaneously results in high electrical conductivity, a large Seebeck coefficient, and low thermal conductivity. The Seebeck coefficient for all these systems is significantly higher than that of conventional thermoelectric materials, suggesting their potential in thermoelectric applications. Among all the considered systems, the "graphyne-like BN sheet" has the highest electrical conductance and lowest thermal conductance, ensuring its superiority in thermoelectric properties over the other studied systems. We find that a maximum full ZT of ∼6 at room temperature is accessible in the "graphyne-like BN sheet".

Figure 1

Representative device model showing two electrodes and the SR (a) for pristine γ-graphyne nanojunction; (b) for γ-graphyne nanojunction with BN at the linear chain; (c) for the γ-graphyne nanojunction with BN at the hexagonal ring (d) for γ-graphyne-like BN sheet nanojunction. LE and RE represent the left electrode and right electrode, respectively.

Figure 2

Variation of zero-bias transmission spectra with energy for (a) pristine γ-graphyne; (b) γ-graphyne with BN at linear chain; (c) γ-graphyne with BN at hexagonal ring; and (d) γ-graphyne-like BN sheet. T(E) describes the transmission probability of electrons with energy E traversing from one side of the device to the other side. This is combined with eq 5 to calculate temperature-dependent quantities such as the conductance and the Seebeck coefficient (see the Computational Methodology section).

Figure 3

Variation of the Seebeck coefficient with Fermi energy for (a) pristine γ-graphyne; (b) γ-graphyne with BN at the linear chain; (c) γ-graphyne with BN at the hexagonal ring; and (d) γ-graphyne-like BN sheet at different temperatures.

Figure 4

Variation of electrical conductance with Fermi energy for (a) pristine γ-graphyne; (b) γ-graphyne with BN at the linear chain; (c) γ-graphyne with BN at the hexagonal ring; and (d) γ-graphyne-like BN sheet at different temperatures.

Figure 5

Variation of the electronic part of thermal conductance with Fermi energy for (a) pristine γ-graphyne; (b) γ-graphyne with BN at the linear chain; (c) γ-graphyne with BN at the hexagonal ring; and (d) γ-graphyne-like BN sheet at different temperatures.

Figure 6

Variation of the figure of merit with Fermi energy for (a) pristine γ-graphyne; (b) γ-graphyne with BN at the linear chain; (c) γ-graphyne with BN at the hexagonal ring; and (d) γ-graphyne-like BN sheet at different temperatures.