Multiterminal single-molecule--graphene-nanoribbon thermoelectric devices with gate-voltage tunable figure of merit ZT

TL;DR

This paper investigates a graphene-nanoribbon based thermoelectric device with a single molecule, demonstrating tunable efficiency via gate voltage and achieving ZT values up to 2.5 at low temperatures.

Contribution

It introduces a multiterminal device design with gate-tunable thermoelectric performance using advanced quantum transport modeling.

Findings

Achieves ZT ~ 0.5 at room temperature

Tunable ZT between 0.5 and 2.5 with gate voltage

Suppresses phonon transport for improved thermoelectric efficiency

Abstract

We study thermoelectric devices where a single 18-annulene molecule is connected to metallic zigzag graphene nanoribbons (ZGNR) via highly transparent contacts that allow for injection of evanescent wave functions from ZGNRs into the molecular ring. Their overlap generates a peak in the electronic transmission, while ZGNRs additionally suppress hole-like contributions to the thermopower. Thus optimized thermopower, together with suppression of phonon transport through ZGNR-molecule-ZGNR structure, yield the thermoelectric figure of merit ZT ~ 0.5 at room temperature and 0.5 < ZT < 2.5 below liquid nitrogen temperature. Using the nonequilibrium Green function formalism combined with density functional theory, recently extended to multiterminal devices, we show how the transmission resonance can also be manipulated by the voltage applied to a third ZGNR electrode, acting as the top gate covering molecular ring, to tune the value of ZT.