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

Abstract

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 Grüneisen parameter, which could suppress the thermal transport properties and lead to a low lattice thermal conductivity of ∼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 ∼ 2.64 at 900 K and average ZT ∼ 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.