# Temperature- and doping-dependent roles of valleys in thermoelectric performance of SnSe: a first-principles study

## TL;DR

This study uses first-principles calculations to analyze how different valleys and orbitals in SnSe influence its thermoelectric performance across various doping levels and temperatures, revealing multi-valley contributions and orbital-specific roles.

## Contribution

It provides a detailed first-principles analysis of valley and orbital contributions to SnSe's thermoelectric properties, highlighting temperature and doping effects on valley dominance.

## Key findings

- Valence band valleys near U-Z and along Γ-Y contribute to hole doping performance.
- The U-Z valley dominates at room temperature, while Γ-Y becomes significant at higher temperatures.
- Conduction band around Γ is key for electron doping, with a quasi-one-dimensional structure.

## Abstract

We theoretically investigate how each orbital and valley play a role for high thermoelectric performance of SnSe. In the hole-doped regime, two kinds of valence band valleys contribute to its transport properties: one is the valley near the U-Z line, mainly consisting of the Se-$p_z$ orbitals, and the other is the one along the $\Gamma$-Y line, mainly consisting of the Se-$p_y$ orbitals. Whereas the former valley plays a major role in determining the transport properties at room temperature, the latter one also offers comparable contribution and so the band structure exhibits multi-valley character by increasing the temperature. In the electron-doped regime, the conduction band valley around the $\Gamma$ point solely contributes to the thermoelectric performance, where the quasi-one-dimensional electronic structure along the $a$-axis is crucial. This study provides an important knowledge for the thermoelectric properties of SnSe, and will be useful for future search of high-performance thermoelectric materials.