Thermoelectric Properties of Benzothieno-Benzothiophene Self-Assembled Monolayers in Molecular Junctions

TL;DR

This study combines experimental and theoretical methods to investigate the thermoelectric properties of benzothieno-benzothiophene monolayers in molecular junctions, revealing notably low thermal conductance and measurable Seebeck coefficients.

Contribution

It provides new experimental measurements and theoretical insights into the thermoelectric behavior of specific molecular junctions with exceptionally low thermal conductance.

Findings

Thermal conductance per molecule is 15 pW/K and 8.8 pW/K, among the lowest reported.

Seebeck coefficients are 36 μV/K and 245 μV/K for different derivatives.

Thermoelectric figure of merit ZT reaches approximately 1E-4 at 300K.

Abstract

We report a combined experimental (C-AFM and SThM) and theoretical (DFT) study of the thermoelectric properties of molecular junctions made of self-assembled monolayers on Au of thiolated benzothieno-benzothiophene (BTBT) and alkylated BTBT derivatives (C8-BTBT-C8). We measure the thermal conductance per molecule at 15 pW/K and 8.8 pW/K, respectively, among the lowest values for molecular junctions so far reported (10-50 pW/K). The lower thermal conductance for C8-BTBT-C8 is consistent with two interfacial thermal resistances introduced by the alkyl chains, which reduce the phononic thermal transport in the molecular junction. The Seebeck coefficients are 36 {\mu}V/K and 245 {\mu}V/K, respectively, the latter due to the weak coupling of the core BTBT with the electrodes. We deduce a thermoelectric figure of merit ZT up to ca. 1E-4 for the BTBT molecular junctions at 300K, on a par with the values reported for archetype molecular junctions (olygo(phenylene ethynylene) derivatives).