Enhanced Thermopower in Single-Fullerene Junctions via Interface Engineering

Fullerenes are promising thermoelectric candidates due to their unique electronic structure with small and multiple energy levels, and their single-molecule thermoelectric devices demonstrated significantly higher thermopowers than those of conventional organic systems. However, the interface engineering of the fullerene-electrode remains unexplored due to the experimental challenges in controlling the interfacial coupling at the single-molecule scale. Here, we investigate the thermopower properties of three fullerene derivatives Sc 2 C 2 @ C s (10528)-C 72, Sc 2 C 2 @ C 3 v -C 82, and C 2 (3)-C 82 in single-molecule junctions with different electrode configurations, including gold–fullerene–gold (Au–Au), asymmetric gold–fullerene–graphene (Au–Gr), and graphene–fullerene–graphene (Gr–Gr), using scanning tunneling microscope break-junction (STM-BJ) techniques. We find that the Seebeck coefficient increases consistently from Au–Au to Au–Gr to Gr–Gr junctions for all three fullerene molecules, in agreement with theoretical predictions. Notably, a Seebeck coefficient of −61.34 μV/K is achieved in graphene-Sc 2 C 2 @C 82 -graphene single-molecule junctions, the highest value reported to date for single-fullerene junctions. Our findings establish interface engineering as an effective pathway for improving the thermoelectric performance of single-molecule devices.