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

Abstract

In this study, we systematically investigate the thermal and electronic transport properties of a two-dimensional (2D) 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 antibonding 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 · m⁻¹ · K⁻¹, 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 $$ {\kappa_{{\rm{L}}}} $$ in this heterostructure due to their larger group velocities than the acoustic phonons. 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 2D layered thermoelectric materials.

Keywords

Thermoelectric material / lattice thermal conductivity / four-phonon scattering / first-principles calculations