Pd$_{2}$Se$_{3}$ Monolayer: A Promising Two Dimensional Thermoelectric Material with Ultralow Lattice Thermal Conductivity and High Power Factor

TL;DR

This study shows that Pd$_{2}$Se$_{3}$ monolayer has both ultralow thermal conductivity and high power factor, making it a promising 2D thermoelectric material with high efficiency at moderate doping levels.

Contribution

First-principles calculations reveal Pd$_{2}$Se$_{3}$ monolayer's exceptional thermoelectric properties due to its unique structure and phonon anharmonicity, highlighting its potential for applications.

Findings

Ultralow lattice thermal conductivity comparable to bulk thermoelectrics.

High power factor due to pudding-mold band structure.

Potential for high $zT$ at moderate doping levels.

Abstract

A high power factor and low lattice thermal conductivity are two essential ingredients of highly efficient thermoelectric materials. Although monolayers of transition metal dichalcogenides possess high power factors, high lattice thermal conductivities significantly impede their practical applications. Our first-principles calculations show that these two ingredients are well fulfilled in the recently synthesized Pd$_{2}$Se$_{3}$ monolayer, whose crystal structure is composed of [Se$_{2}$]$^{2-}$ dimers, Se$^{2-}$ anions, and Pd$^{2+}$ cations coordinated in a square planar manner. Our detailed analysis of third-order interatomic force constants reveals that the anharmonicity and soft phonon modes associated with [Se$_2$]$^{2-}$ dimers lead to ultra-low lattice thermal conductivities in Pd$_{2}$Se$_{3}$ monolayers (1.5 and 2.9 Wm$^{-1}$K$^{-1}$ along the $a$- and $b$-axes at 300\,K respectively), which are comparable to those of high-performance bulk thermoelectric materials such as PbTe. Moreover, the "pudding-mold" type band structure, caused by Pd$^{2+}$ ($d^{8}$) cations coordinated in a square planar crystal field, leads to high power factors in Pd$_{2}$Se$_{3}$ monolayers. Consequently, both electron and hole doped thermoelectric materials with a considerably high $zT$ can be achieved at moderate carrier concentrations, suggesting that Pd$_{2}$Se$_{3}$ is a promising two-dimensional thermoelectric material.