Excellent thermoelectric performances of the SiSe2 monolayer and layered bulk

The excellent thermoelectric performance of the SiSe2 monolayer and layered bulk is identified by employing the density functional theory and the semi-classical Boltzmann transport theory. The geometrical structures of the SiSe2 monolayer and bulk are fully relaxed, and the dynamic and thermal stabilities have been confirmed through phonon dispersions and ab initio molecular dynamics simulations. By introducing a method to avoid the vacuum space of the supercell influence on the volume of the monolayer, we have obtained the lattice thermal conductivity, the Seebeck coefficient, electrical conductivity, power factor, and electron thermal conductivity for both the monolayer and the bulk. The ZT relative to temperature and carrier concentration are obtained to evaluate the thermoelectric performance. For the SiSe2 monolayer, the maximum ZT can reach 4.84 at 700 K with the p-type carrier concentration of 9.60 × 1019 cm−3, while for the SiSe2 bulk, the maximum ZT can also attain 4.11 at 700 K with the n-type carrier concentration of 2.38 × 1019 cm−3 . Therefore, both the SiSe2 monolayer and bulk are favorable candidates for thermoelectric applications. The mechanism for the superior thermoelectric properties is also examined.