Controlling Band Alignment in Molecular Junctions: Utilizing Two-Dimensional Transition-Metal Dichalcogenides as Electrodes for Thermoelectric Devices

摘要

Although chemical space is vast, there are many instances where chemical modifications make only insignificant changes in the current that passes through a molecule. This insensitivity comes, in part, from the energy mismatch between the molecular resonances and the Fermi level of the electrodes used. Here, we present a strategy to overcome this problem by employing two-dimensional transition-metal dichalcogenides as electrodes. The work function of the electrodes can be tuned across the entire molecular energy range (from the highest occupied molecular orbital to the lowest unoccupied molecular orbital) at a low bias with the appropriate choice of electrode material. We illustrate the effectiveness of this strategy by investigating the thermoelectric properties of the junctions with a model molecular system, as optimal thermoelectric performance requires a delicate balance between the electronic and the heat transport properties. By using van der Waals contacts between the binding groups and the electrodes, similar to the binding groups used in graphene junctions, we find that we can effectively suppress the phonon contribution to the heat transport while achieving high levels of electron transport and thermopower as the molecular level is tuned into near resonance.