Controlling Thermoelectric Properties through Molecular Orientation in Asymmetric Anthracene Junctions

In this study, we conduct a comprehensive theoretical investigation of single-molecule junctions using asymmetric anthracene derivatives with different terminal groups. We explore the electronic and thermoelectric properties of these molecular junctions using density functional theory (DFT) alongside quantum transport calculations. Specifically, three asymmetric anthracene-based molecules have been examined, each featuring different anchoring groups: pyridyl (Py), thioacetate (SAc), and SnMe3. Our findings indicate that the Seebeck coefficient (S) is highly sensitive to the molecular orientation. Altering the orientation of the asymmetric molecule within the junction can result in a change in the sign of the Seebeck coefficient, shifting from positive to negative or vice versa. Two of the molecular systems we studied display bi-thermoelectric behavior, attributed to the presence of a pyridyl terminal group on one end and either a SnMe3 or thioacetate group on the other. This behavior stems from orientation-dependent changes in the alignment of molecular energy levels with respect to the electrode Fermi level, causing a switch between HOMO- and LUMO-dominated transport. These results highlight the potential of asymmetric single-molecule junctions in bi-thermoelectric applications and provide a promising strategy for controlling thermovoltage generation in molecular-scale thermoelectric energy harvesting devices.