Ultralow thermal conductivity via weak interactions in PbSe/PbTe monolayer heterostructure for thermoelectric design

TL;DR

This paper demonstrates that PbSe/PbTe monolayer heterostructures have ultralow thermal conductivity and high thermoelectric efficiency due to weak interactions and optical phonon contributions, offering new design strategies for 2D thermoelectric materials.

Contribution

It reveals the dominant role of optical phonons in thermal transport and provides a theoretical framework for designing high-performance 2D thermoelectric heterostructures.

Findings

Thermal conductivity as low as 0.31 W/mK along y direction.

Achieves a ZT of 5.3 at 800 K.

Optical phonons contribute ~59% to thermal conductivity.

Abstract

In this study, we systematically investigate the thermal and electronic transport properties of two-dimensional PbSe/PbTe monolayer heterostructure by combining first-principles calculations, Boltzmann transport theory, and machine learning methods. The heterostructure exhibits a unique honeycomb-like corrugated and asymmetric configuration, which significantly enhances phonon scattering. Moreover, the relatively weak interatomic interactions in PbSe/PbTe lead to the formation of anti-bonding states, resulting in strong anharmonicity and ultimately yielding ultralow lattice thermal conductivity (${\kappa_{\rm L}}$). In the four-phonon scattering model, the ${\kappa_{\rm L}}$~values along the $x$ and $y$ directions are as low as 0.37 and 0.31 W/mK, respectively. Contrary to the conventional view that long mean free path acoustic phonons dominate heat transport, we find that optical phonons contribute approximately 59\% of the lattice thermal conductivity in this heterostructure. These optical phonons exhibit large Gr\"uneisen parameters, strong anharmonic scattering, and relatively high group velocities, thereby playing a crucial role in the low ${\kappa_{\rm L}}$ regime. Further analysis of thermoelectric performance shows that at a high temperature of 800 K, the heterostructure achieves an exceptional dimensionless figure of merit ($ZT$) of 5.3 along the $y$ direction, indicating outstanding thermoelectric conversion efficiency. These findings not only provide theoretical insights into the transport mechanisms of PbSe/PbTe monolayer heterostructure but also offer a practical design strategy for developing high-performance two-dimensional layered thermoelectric materials.