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 Sc₂C₂@<i>C</i>_<i>s</i>(10528)-C₇₂, Sc₂C₂@<i>C</i>_3<i>v</i>-C₈₂, and <i>C</i>₂(3)-C₈₂ 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-Sc₂C₂@C₈₂-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.