SnSe2 monolayer with square lattice structure: a promising p-type thermoelectric material with an indirect bandgap and low lattice thermal conductivity

Inspired by the superior thermoelectric performance of two-dimensional (2D) materials, the thermoelectric properties of a novel SnSe2 monolayer with a square lattice structure were theoretically investigated by using first principles calculations and semiclassical Boltzmann transport theory. The novel SnSe2 monolayer is a thermodynamically and mechanically stable semiconductor with an indirect bandgap of 1.942 eV within the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional in combination with the spin-orbital coupling (SOC) effect. Further phonon and electronic transport property calculations show that the SnSe2 monolayer with a square lattice structure has small phonon group velocity, short phonon relaxation time and large Gruneisen parameter, which could suppress the thermal transport properties and lead to a low lattice thermal conductivity of similar to 1.82 W m K-1 at 900 K. Combined with its high Seebeck coefficient, high electrical conductivity and outstanding power factor, an optimal ZT similar to 2.64 at 900 K and average ZT similar to 1.76 in the temperature range of 300-900 K are obtained for the p-type SnSe2 monolayer, which indicates the great advantages of the SnSe2 monolayer as a promising p-type thermoelectric material. Our present work would not only clarify the fundamental understanding of the intrinsic geometrical structure and thermoelectric properties of the novel SnSe2 monolayer with a square lattice structure, but also provide theoretical insight for the experimental observations of the SnSe2 monolayer material with high thermoelectric performance.