Optimizing thermoelectric performances of low-temperature SnSe compounds by electronic structure design

TL;DR

This study uses electronic structure calculations and transport theory to optimize the thermoelectric performance of SnSe compounds at low temperatures, achieving high ZT values through carrier concentration tuning.

Contribution

It introduces a method to enhance SnSe thermoelectric efficiency by electronic structure design and carrier optimization, providing insights into bonding and band structure effects.

Findings

ZT along the b-axis can reach 2.57 with carrier optimization

Calculated ZT values agree with experimental data below 675 K

Heavy-light band overlap and mixed bonding enhance thermoelectric performance

Abstract

Recently SnSe compound was reported to have a peak thermoelectric figure-5 of-merit (ZT) of 2.62 at 923 K, but the ZT values at temperatures below 750 K are relatively low. In this work, the electronic structures of SnSe are calculated using the density functional theory, and the electro- and thermo-transport properties upon varying chemical potential (or carrier density) are evaluated by the semi-classic Boltzmann transport theory, showing that the calculated ZT values along the a10 and c-axes below 675 K are in agreement with reported values, but that along the b-axis can be as high as 2.57 by optimizing the carrier concentration to ~3.6*1019 cm-3. It is revealed that a mixed ionic-covalent bonding and heavy-light band overlapping near the valence band are the reasons for the higher thermoelectric performance