Thermoelectricity in B₈₀-based single-molecule junctions: First-principles investigation

Abstract

Thermoelectricity is a thermorelated property that is of great importance in single-molecule junctions. The electrical conductance (σ), electron-derived thermal conductance (κ_el) and Seebeck coefficient (S) of B₈₀-based single-molecule junctions are investigated by using density functional theory in combination with non-equilibrium Green’s function. When the distance between the left/right electrodes is 11.4 Å, the relationship between σ and κ_el obeys the Wiedemann–Franz law very well because of the strong hybridization between B₈₀ molecular orbitals and the surface states of Au electrodes. Furthermore, the calculated Lorenz number is close to the famous value in metal or degenerate semiconductors. In addition, S is only –19.09 μV/K at 300 K, thus leading to the smaller electron’s thermoelectric figure of merit (Z_elT = S²σT/κ_el). Interestingly, the strain and chemical potential can modulate B₈₀-based single-molecule junctions from n-type to p-type when the compressive strain reaches –0.6 Å or the chemical potential shifts to –0.16 eV. This might be attributed that S reflects the asymmetry in the electrical conductance with respect to the chemical potential and is proportional to the slopes of the transmission spectrum.

Keywords

thermoelectricity / single-molecule junction / non-equilibrium Green function

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