Optimising 1T-NiS2 monolayer thermoelectric performance via valley engineering

The thermoelectric figure of merit i.e., ZT indicates the materials thermoelectric performance and its value is limited by the interplay of transport parameters. In the present work, the biaxial strain is applied to tune the band valleys, which effectively alters the electronic and thermoelectric properties of monolayer 1 T-NiS2 by using Boltzmann transport theory combined with density functional theory. The band valley alteration sufficiently changed the values of Seebeck coefficient, effective mass and relaxation time. The thermal conductivity is decreased with tensile strain due to phonon softening. It is predicted that biaxial tensile strain of 3% improved the ZT value for p-type doping upto 68% and biaxial compressive strain of 2% enhanced the ZT upto 11% for n-type doping at 300 K. The ZT value of p-type doping is 0.89 whereas for n-type doping, it is 0.82. Our findings support that biaxial strain is used for enhancing the thermoelectric performance of the CdI2-type 1 T-NiS2 monolayer.