Optimization of the Thermoelectric Properties of SnSe2 Using First-Principles Calculations

We present a first-principles framework to study the electronic properties of SnSe2, a potentially good layered thermoelectric material. We use density functional theory and solutions of the Boltzmann transport equation under relaxation time approximation including electron-phonon and ionized impurity interactions to calculate the thermoelectric power factor where electron-phonon scattering is computed using the PERTUBO package, and the modified Brooks-Herring approach is used to model the ionized impurity scattering. We study the temperature-dependent transport properties at different carrier concentrations with and without the inclusion of van der Waals interactions. The inclusion of van der Waals interactions increases the electron-phonon scattering, but the total relaxation time is mostly dominated by ionized impurity scattering at high concentration levels. We first validate our theory by comparing the results to available experimental data and then optimize the thermoelectric performance of SnSe2 as a function of temperature and carrier concentration. The optimized power factor times temperature happens at a carrier concentration of 4 x 10(19) cm(-3) and reaches the maximum value of 0.49 W m(-1) K-1 at 523 K in the in-plane direction and 0.185 W m(-1) K-1 at 700 K in the cross-plane direction. Finally, the lattice thermal conductivity is evaluated using Callaway's model. Our optimized model shows the highest ZT value of 1.1 at 950 K originating in the ultralow thermal conductivity across the SnSe2 layers.

Automated summary

We propose a first-principles framework to study the electronic properties of SnSe2 and optimize its thermoelectric performance. By using density functional theory and the Boltzmann transport equation, we calculate the thermoelectric power factor considering electron-phonon and ionized impurity interactions. Furthermore, we evaluate the lattice thermal conductivity and find that the SnSe2 layers exhibit ultra-low thermal conductivity, resulting in a high ZT value of 1.1 at 950 K.