Thermoelectric transport properties in graphene connected molecular junctions

TL;DR

This study investigates thermoelectric properties of a graphene-based molecular junction, revealing how different graphene gaps influence efficiency and violate classical laws, with potential for optimized thermoelectric performance.

Contribution

It introduces a detailed numerical analysis of thermoelectric transport in graphene-molecular junctions considering various graphene gap scenarios, highlighting the impact on the figure of merit.

Findings

Fano effect causes violation of Wiedemann-Franz law.

Significant increase in figure of merit due to thermal coefficient reduction.

Optimal energy gap enhances thermoelectric efficiency.

Abstract

We study the electronic contribution to the main thermoelectric properties of a molecular junction consisting of a single quantum dot coupled to graphene external leads. The system electrical conductivity (G), Seebeck coefficient ($S$), and the thermal conductivity ($\kappa$), are numerically calculated based on a Green's function formalism that includes contributions up to the Hartree-Fock level. We consider the system leads to be made either of pure or gapped-graphene. To describe the free electrons in the gapped-graphene electrodes we used two possible scenarios, the massive gap scenario, and the massless gap scenario, respectively. In all cases, the Fano effect is responsible for a strong violation of the Wiedemann-Franz law and we found a substantial increase of the system figure of merit $ZT$ due to a drastic reduction of the system thermal coefficient. In the case of gapped-graphene electrodes, the system figure of merit presents a maximum at an optimal value of the energy gap of the order of $\Delta/D\sim$ 0.002 (massive gap scenario) and $\Delta/D\sim$ 0.0026 (massless gap scenario). Additionally, for all cases, the system figure of merit is temperature dependent.