Compressive strain induced enhancement in thermoelectric-power-factor in monolayer MoS₂ nanosheet

Strain and temperature induced tunability in the thermoelectric properties in monolayer MoS₂ (ML-MoS₂) has been demonstrated using density functional theory coupled to semi-classical Boltzmann transport theory. Compressive strain, in general and uniaxial compressive strain (along the zig-zag direction), in particular, is found to be most effective in enhancing the thermoelectric power factor, owing to the higher electronic mobility and its sensitivity to lattice compression along this direction. Variation in the Seebeck coefficient and electronic band gap with strain is found to follow the Goldsmid-Sharp relation. n-type doping is found to raise the relaxation time-scaled thermoelectric power factor higher than p-type doping and this divide widens with increasing temperature. The relaxation time-scaled thermoelectric power factor in optimally n-doped ML-MoS₂ is found to undergo maximal enhancement under the application of 3% uniaxial compressive strain along the zig-zag direction, when both the (direct) electronic band gap and the Seebeck coefficient reach their maximum, while the electron mobility drops down drastically from 73.08 to 44.15 cm² V^-1 s^-1. Such strain sensitive thermoelectric responses in ML-MoS₂ could open doorways for a variety of applications in emerging areas in 2D-thermoelectrics, such as on-chip thermoelectric power generation and waste thermal energy harvesting.