Transport properties and high thermopower of SnSe₂: A full ab-initio investigation

Motivated by the observation that many known layered chalcogenides show promising thermoelectric properties, we investigate the similar properties of SnSe₂ by solving the Boltzmann transport equation for both lattice and electron. A selfconsistent single parabolic band model (SPB) is employed to compute the electron relaxation time rigorously. The obtained intrinsic lattice thermal conductivities in a and c directions are 6.78 and 0.79 W/m·K at 300 K. The results show that acoustic phonon branches play the dominant role in heat transport. Thermoelectric properties of n-type SnSe₂ are found to be significantly better than those of p-type doping for temperatures between 200 and 800 K and carrier concentrations between 10¹⁷ and 10²⁰ cm^-3. At n = 10²⁰ cm^-3 and 300 K, we find σ_a = 4.97 × 10⁵ Ω^-1·m^-1 and σ_c = 3.39 × 10⁴ Ω^-1·m^-1 and the ratio σ_a/σ_c = 14.67 for n-type SnSe₂. Both electrical and lattice thermal conductivities show a strong anisotropic feature. A high thermoelectric figure of merit is revealed in n-type SnSe₂ (ZT_a = 2.95 and ZT_c = 0.68 at n = 10²⁰ cm^-3 and 800 K). The large ZT value indicates that SnSe₂ is a promising candidate for thermoelectric applications.