Pressure induced bands convergence and strength enhancement in thermoelectric semiconductor β-InSe

The semiconductor InSe possesses an exceptional ductility at room temperature, but its weak electronic transport properties leads to the low thermoelectric properties, limiting its applications in flexible thermoelectric devices. In this work, we applied first principles to find that the hydrostatic pressure can remarkably improve the thermoelectric and mechanical properties of β-InSe. The multiple conduction bands convergence is observed at the hydrostatic pressure of 5 GPa, resulting in a maximum zT value of 0.235 at 300 K, which is 170 % higher than the intrinsic zT value of 0.087. The point defect calculations suggest that In0.96Pb0.04Se or InSe0.96Cl0.04 could obtain the optimal carrier concentration of 7.65 × 1019 cm−3 with the highest zT value. In addition, we find that the (001)/<110>slip system of InSe exhibits the lowest ideal shear strength of 0.68 GPa, due to the weak interlayered van der Waals SeSe bonds. While the hydrostatic pressure can reduce the bond lengths and strengthen the van der Waals SeSe bonds. At 5 GPa, a maximum stretching force constant of van der Waals SeSe bond is obtained, giving rise to a maximum shear ideal strength of 1.45 GPa, which is 113 % higher than that without pressure. This hydrostatic pressure induced strain engineering strategy provides a theoretical guidance to synthesize high-performance thermoelectric β-InSe with robust mechanical properties.