Field-Effect Control of Graphene-Fullerene Thermoelectric Nanodevices

TL;DR

This study demonstrates electrostatic control of molecular energy levels in graphene-fullerene thermoelectric devices, enabling tuning of their power factor close to theoretical limits and advancing understanding of molecular charge transport.

Contribution

It introduces a graphene nanogap platform with reduced screening for precise control of molecular orbitals, revealing how level alignment affects thermoelectric performance.

Findings

Power factor can be tuned over several orders of magnitude.

Level position is controllable by hundreds of meV.

Power factor approaches the theoretical limit of an isolated resonance.

Abstract

Although it was demonstrated that discrete molecular levels determine the sign and magnitude of the thermoelectric effect in single-molecule junctions, full electrostatic control of these levels has not been achieved to date. Here, we show that graphene nanogaps combined with gold microheaters serve as a testbed for studying single-molecule thermoelectricity. Reduced screening of the gate electric field compared to conventional metal electrodes allows control of the position of the dominant transport orbital by hundreds of meV. We find that the power factor of graphene-fullerene junctions can be tuned over several orders of magnitude to a value close to the theoretical limit of an isolated Breit-Wigner resonance. Furthermore, our data suggest that the power factor of an isolated level is only given by the tunnel coupling to the leads and temperature. These results open up new avenues for exploring thermoelectricity and charge transport in individual molecules and highlight the importance of level alignment and coupling to the electrodes for optimum energy conversion in organic thermoelectric materials.