Comparative ab initio study of the electronic structure and thermoelectric properties of tin selenide with electron and hole conductivity

Ab initio calculations of the electronic structure and thermoelectric characteristics of low- and high-temperature phases of tin selenide, SnSe, with electronic and hole conductivity have been performed. It is shown that the calculations of thermoelectric properties on the basis of the Boltzmann-Onzager theory with consideration of carrier scattering on optical phonons lead to results in good agreement with experimental data. At temperatures below 600 K the modeling correctly reproduces the increased values of the figure-of-merit of electron-doped SnSe in comparison with almost stoichiometric or hole-doped selenide calculations. We explain anomalously high figure-of-merit values of the non-doped selenide at T > 600 K by the hole concentration increase due to oxidation of SnSe or the appearance of vacancies in the tin sublattice. For all the considered variants, i.e. for electron-doped low-temperature and high-temperature phases and low-temperature hole-doped phase, the modeling predicts the absence of figure-of-merit increase at exceeding some limiting concentration of current carriers.