Optical–Acoustic Phonon Hybridization Enhanced Thermoelectric Performance in a 1T′ Phase OsTe2 Monolayer

A comprehensive study for thermoelectric (TE) properties of the OsTe2 monolayer with a 1T′ phase structure is presented, which is a two-dimensional transition metal dichalcogenide (2D-TMD). We find that, at 300 K, the Seebeck coefficient of the OsTe2 monolayer is very high and can reach 739 μV K–1 at a hole concentration of 1 × 1011 cm–2. The ultrahigh Seebeck coefficient results from the high degeneracy of the electronic band structure. At the same time, the n-type OsTe2 monolayer along the y-axis has a larger electrical conductivity than the other cases. This is because the electron along the y-axis has the longest relaxation time. An excellent power factor (PF) of 27.44 m W m–1 K–2 along the y-axis for n-type doping is found, which is better than many well-known TE materials. Our calculation shows that lattice thermal conductivity of the 1T′ OsTe2 monolayer is much lower than typical 2D-TMDs. The calculation of phonon dispersion and phonon density of states (DOS) reveals that, different from typical TMD monolayers, the optical–acoustic phonon was strongly hybridized. The hybridization of the optical–acoustic phonon significantly reduces the lifetime of the phonon and then the lattice thermal conductivity. Combined with satisfactory thermal conductivity and Seebeck coefficient, the optimal ZT value of the OsTe2 monolayer is 1.83, which is several times higher than typical TMD monolayers. Our study suggests that the 1T′ phase OsTe2 monolayer is an excellent TE material in the TMD family.