Investigating the Influence of Grain Boundaries on Thermal and Electrical Conductivity in Two-Dimensional Molybdenum Disulfide

Transition metal dichalcogenides (TMDCs) have emerged as key semiconductors with tremendous potential for future semiconductor devices. Understanding the impact of defects, such as grain boundaries (GBs), on the thermal and electrical transport properties of two-dimensional (2D) TMDC materials is crucial for their application in energy-harvesting devices based on the thermoelectric effect. In this study, we employed nonequilibrium molecular dynamics simulations and first-principles quantum-mechanical calculations to investigate the thermal and electrical transport properties across and along GBs in a monolayer of the prototypical TMDC material, MoS₂. The results reveal the presence of an interfacial phase (or interphase) located within ~3.5 nm around a GB, exhibiting distinct anisotropic transport properties compared to the perfect crystal. Specifically, the interphase exhibits an 80% reduction in thermal conductivity across the GB, while 17% enhancement along the GB, relative to the perfect crystal. On the other hand, the electrical conductivity appears to be enhanced in both directions. These unique thermal and electrical transport properties exhibited by GB interphases hold key to thermoelectric applications of 2D TMDCs. By manipulating the arrangement of GBs, it is possible to achieve reduced thermal conductivity and enhanced electrical conductivity in these materials. Consequently, atomically thin van der Waals materials, such as MoS₂, show great promise as candidates for thermoelectric devices.