The role of biaxial strain and pressure on the thermoelectric performance of SnSe2: a first principles study

Controlled variation of the electronic properties of materials by applying strain and pressure has developed as a promising approach for designing materials for tailored applications. The electronic structure and thermoelectric (TE) properties of SnSe2 are analysed using first principles calculations and semi classical Boltzmann theory at 300 K and 800 K under biaxial tensile (BT) strain of 1% and 2%, biaxial compressive strain of 1% and 2% and hydrostatic pressure of 10 GPa and 20 GPa. The electronic structure suggests that there is a reduction in band gap under all strains and applied pressures. The band structure exhibits a change which is evident from the change in the effective mass in different symmetry directions. The thermopower shows a decrease under all strain and pressure conditions for both the temperatures studied. The electrical conductivity is enhanced under all conditions of strain and pressure at both temperatures. The maximum value of power factor (PF) shows a minor increase for 1% BT strain at 800 K and decreases for all other strains and temperatures. Under hydrostatic pressure of 10 GPa, PF decreases by 13% and 1% at 300 K and 800 K respectively. At 20 GPa an enhancement of 8% and 16% is exhibited at 300 K and 800 K respectively. The figure of merit is increased in out of plane direction at both temperatures. An appreciable enhancement of TE performance in out of plane direction is observed at both temperatures under the influence of BT strain and pressure.