Theoretical insight into the thermoelectric behavior of tri-nuclear metal-string complexes laced with gold nanoelectrodes: A first-principles study

TL;DR

This study uses first-principles calculations to explore the thermoelectric properties of tri-nuclear metal-string complexes bridged with gold nanowires, revealing potential for high-efficiency molecular thermoelectric devices.

Contribution

It provides a detailed theoretical analysis of the thermoelectric behavior of specific metal-string complexes, highlighting how metal composition influences transport properties and device efficiency.

Findings

High thermopower of up to 172 μV/K at 300 K.

Potential figure of merit ZT ~ 2 at room temperature.

Alteration of inter-dot interactions enhances thermoelectric efficiency.

Abstract

Metal-string complexes in the quasi-1D framework may play an important role in molecular electronics by serving not only as nanoscale interconnects but also as active functional elements for nanoelectronic devices. However, because of the potential volumetric heat generation across such nanojunctions, the circuit stability becomes often a major concern, which necessitates to study the heat transport properties at the molecular-scale. Here we report the thermoelectric behavior of various tr-nuclear metal-string complexes, $[M-M-M](dpa)_4(NCS)_2$ for $M \in \{Cr,Ru\}$, bridging Au(111) nanowires as nanoelectrodes. Based on our charge transport analysis from \textit{first-principles}, we find that the dominant transmission peaks tend to move away from the Fermi level upon systematic rutheniation in chromium-based metal-string complexes due mainly to the coupling of $\pi^{*}$ orbitals from Ru and $\sigma_{nb}$ orbitals from Cr. Such type of a metal-string junction can also exhibit strong Coulomb interaction so that its thermoelectric behavior begins to deviate from the Wiedemann-Franz law. Our results further suggest that metal-string complexes can render better thermoelectric devices especially at the molecular-scale with the thermopower as high as 172 $\mu V/K$ at 300 K. Considering the contributions from both electrons and phonons, even a high \textit{figure of merit} of $ZT \sim 2$ may be attained for Cr-Cr-Cr based metal-string molecular junctions at room temperature. Resonant enhancement in the thermoelectric efficiency appears to occur in such systems through alteration of inter-dot electrostatic interactions, which can be controlled by incorporating Cr and Ru atoms in such tri-nuclear metal-string complexes.