Interference enhanced thermoelectricity in quinoid type structures

TL;DR

This study demonstrates that quinoid molecular structures exhibit quantum interference effects that can be chemically tuned to significantly enhance thermoelectric performance, making them promising for efficient energy conversion devices.

Contribution

It reveals how destructive quantum interference features in quinoid molecules can be controlled to optimize thermoelectric properties, a novel approach in molecular thermoelectrics.

Findings

Two destructive QI features cause transmission dips near frontier orbitals.

Chemical modifications shift transmission dips and molecular levels.

High thermoelectric power factor and figure of merit achieved in quinoid molecules.

Abstract

Quantum interference (QI) effects in molecular junctions may be used to obtain large thermoelectric responses. We study the electrical conductance G and the thermoelec- tric response of a series of molecules featuring a quinoid core using density functional theory (DFT), as well as a semi-empirical interacting model Hamiltonian describing the {\pi}-system of the molecule which we treat in the GW approximation. Molecules with a quinoid type structure are shown to have two distinct destructive QI features close to the frontier orbital energies. These manifest themselves as two dips in the transmission, that remain separated, even when either electron donating or withdraw- ing side groups are added. We find that the position of the dips in the transmission and the frontier molecular levels can be chemically controlled by varying the electron donating or withdrawing character of the side groups as well as the conjugation length inside the molecule. This feature results in a very high thermoelectric power factor S^2G and figure of merit ZT, where S is the Seebeck coefficient, making quinoid type molecules potential candidates for efficient thermoelectric devices.