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TMDCs are pivotal semiconductor materials with immense potential for future devices. Understanding the impact of defects, especially GBs, on thermal and electrical transport in 2D TMDCs is crucial for thermoelectric applications. In this research, we have harnessed nonequilibrium molecular dynamics simulations and first-principles quantum-mechanical calculations to study the thermal and electrical transport properties across and along GBs within a monolayer of the quintessential TMDC material, MoS₂.

We found the presence of an interfacial phase (or interphase) within 4 nm from GBs, exhibiting distinctly anisotropic transport characteristics when compared to the pristine crystal lattice. Specifically, the interphase exhibits an astonishing 80% reduction in thermal conductivity across GBs, in stark contrast with negligible effects on heat conduction parallel to GBs. More remarkable is enhanced electrical conductivity in both directions, which can be attributed to unique mid-gap states at GBs that bridge electronic states within the discrete density of states of the pristine material, effectively smoothing them and thereby amplifying electrical conductivity.

The distinct properties of GB interphases unlock the thermoelectric potential of 2D TMDCs. Strategically arranging GBs achieves the balance needed for MoS₂'s thermoelectric promise.