Tensile Strain Induced Enhancement in the Thermoelectric Performance of monolayer MoS$_{2}$

First-principles calculations based on density functional theory, coupled with the semi-classical Boltzmann transport theory, have been performed to investigate the strain- and temperature-induced tunability of the thermoelectric properties of monolayer (ML) MoS$_2$. The electronic band gap reduces with increasing tensile strain, and a semiconductor to metal transition occurs for $10\%$ biaxial strain. Tensile strains, in most of the cases, are seen to have a diminishing effect on the thermopower and power factor of monolayer MoS$_2$, with larger impact on the p-type carriers. Performing anharmonic phonon calculations, it is seen that tensile strain, in general and uniaxial tensile strain along the zig-zag direction, in particular, significantly reduces the thermal conductivity of ML-MoS$_2$. The combined effect of reduced phonon relaxation time, ZA-optical phonon frequency gap and the Debye temperature is found to be the driving force behind the lowering of the thermal conductivity. The large reduction in thermal conductivity and increase in power factor under the action of tensile strains along the zigzag direction act in concert to result in an enhanced efficiency and hence, improved thermoelectric performance. The thermoelectric efficiency of ML-MoS$_2$ is seen to increase with increasing temperature, suggesting its use as a high-temperature thermoelectric material. Nearly 75\% enhancement in the thermoelectric efficiency can be achieved with optimal doping concentration. We, therefore, highlight the significance of in-plane tensile strains in improving the thermoelectric performance of ML-MoS$_2$, which could open avenues for its application in emerging areas in 2D-thermoelectrics.