Synergistic optimization of the thermoelectric properties of the 2D MgI2/Bi2S3 heterostructure via biaxial strain

Abstract

The thermoelectric properties of 2D materials can be effectively modulated due to their high sensitivity to strain. Therefore, the thermoelectric properties of the MgI₂/Bi₂S₃ heterojunction under biaxial tensile–compressive strain (−4% to 4%) are systematically investigated using first-principles calculations combined with Boltzmann transport theory. It is found that the thermoelectric properties are synergistically modulated by tuning phonon spectra, group velocities, scattering phase space, and electronic band structures. The calculated results demonstrate that tensile strain can induce phonon softening and enhance phonon scattering anharmonicity, and a minimum thermal conductivity of 0.23 W m⁻¹ K⁻¹ is achieved at 4% tensile strain and 300 K. Concurrently, tensile strain can narrow the band gap and induce a direct-to-indirect band gap transition. A comprehensive comparison reveals that a 2% tensile strain can optimally balance a high power factor with a low thermal conductivity, leading to a peak ZT of 1.62 at 600 K, which surpasses those under other strains. The findings provide insights into the design of high-performance thermoelectric materials through strain engineering.