Molecular design and control of fullerene-based bi-thermoelectric materials

TL;DR

This study demonstrates that the thermoelectric properties of fullerene-based molecular junctions can be tuned by molecular orientation and pressure, highlighting the role of transport resonances in molecular thermoelectricity.

Contribution

It provides the first experimental evidence linking transport resonances to thermopower in fullerene molecular junctions and shows how pressure can modulate thermoelectric behavior.

Findings

Thermopower sign and magnitude depend on molecular orientation and pressure.

Pressure shifts the resonance near the Fermi level, tuning thermopower.

Sc3N@C80 exhibits both positive and negative thermopower, acting as a bi-thermoelectric material.

Abstract

Molecular junctions are a versatile test bed for investigating thermoelectricity on the nanoscale1-10 and contribute to the design of new cost-effective environmentally-friendly organic thermoelectric materials11. It has been suggested that transport resonances associated with the discrete molecular levels would play a key role in the thermoelectric performance12,13, but no direct experimental evidence has been reported. Here we study single-molecule junctions of the endohedral fullerene Sc3N@C80 connected to gold electrodes using a scanning tunnelling microscope (STM). We find that the magnitude and sign of the thermopower depend strongly on the orientation of the molecule and on applied pressure. Our theoretical calculations show that the Sc3N inside the fullerene cage creates a sharp resonance near the Fermi level, whose energetic location and hence the thermopower can be tuned by applying pressure. These results reveal that Sc3N@C80 is a bi-thermoelectric material, exhibiting both positive and negative thermopower, and provide an unambiguous demonstration of the importance of transport resonances in molecular junctions.