Strain Driven Anomalous Anisotropic Enhancement in the Thermoelectric Performance of Monolayer MoS₂

The anisotropic tuning of the transport and thermoelectric properties of monolayer MoS₂ with the application of in-plane tensile strains along the armchair (AC) and the zigzag (ZZ) direction have been explored based on first-principles calculations. Tensile strain, in general, is found to have a diminishing effect on the thermopower and power factor of monolayer MoS₂, with greater impact on the p-type carriers. However, considering the intrinsic carrier-phonon scattering, we found that the charge carrier mobility (µ) and relaxation time (τ) increases remarkably for strains along the ZZ direction. Concomitantly, strain along the ZZ direction significantly reduces the lattice thermal conductivity (κ_L) of ML-MoS₂. The combined effect of shortened phonon relaxation time and group velocity, and the reduced Debye temperature is found to be the driving force behind the lowering of κ_L. The large reduction in κ_L and increase in τ, associated with the strains along the ZZ direction, acts in unison to result in an enhanced efficiency and hence, improved thermoelectric performance throughout the temperature range of 200K to 900K. Nearly 150% enhancement in the thermoelectric efficiency can be achieved with the optimal doping concentration. We, therefore, highlight the significance of in-plane tensile strains, in general and strains along the ZZ direction, in particular, in improving the thermoelectric performance of ML-MoS₂, which could open avenues for its application in emerging areas of 2D-thermoelectrics.