Marcus Theory of Thermoelectricity in Molecular Junctions

TL;DR

This paper develops a Marcus theory-based model for thermoelectricity in molecular junctions, highlighting the importance of vibrational effects, and identifies optimal conditions for high thermoelectric efficiency, exemplified by C60 molecules.

Contribution

It introduces a vibrationally coupled Marcus theory framework for molecular thermoelectricity, emphasizing the role of lifetime broadening and providing guidelines for high-performance materials.

Findings

Seebeck coefficient and power factor decrease with reorganization energy.

Optimal thermoelectric performance occurs at specific reorganization energies.

C60 molecules are promising candidates for thermoelectric applications.

Abstract

Thermoelectric energy conversion is perhaps the most promising of the potential applications of molecular electronics. Ultimately, it is desirable for this technology to operate at around room temperature, and it is therefore important to consider the role of dissipative effects in these conditions. Here, we develop a theory of thermoelectricity which accounts for the vibrational coupling within the framework of Marcus theory. We demonstrate that the inclusion of lifetime broadening is necessary in the theoretical description of this phenomenon. We further show that the Seebeck coefficient and the power factor decrease with increasing reorganisation energy, and identify the optimal operating conditions in the case of non-zero reorganisation energy. Finally, with the aid of DFT calculations, we consider a prototypical fullerene-based molecular junction. We estimate the maximum power factor that can be obtained in this system, and confirm that C$_{60}$ is an excellent candidate for thermoelectric heat-to-energy conversion. This work provides general guidance that should be followed in order to achieve high-efficiency molecular thermoelectric materials.