Temperature and p-doping dependence of the power factor in SnS: The role of crystalline symmetry

Temperature and doping dependence of the power factor of p-type SnS, and their dependence on space-group symmetry (Pnma(62)-SnS and C2mb(39)-SnS), were investigated by density functional theory calculation combined with the Boltzmann transport theory. Our results show that the anisotropy in electrical conductivity of C2mb-SnS (Pnma-SnS) in its in-plane value is six orders (one order) of magnitude greater than its corresponding out-of-plane value. The thermopower in C2mb-SnS is about eight times as large as that of in Pnma-SnS at high temperatures, and the maximum Power Factor for C2mb-SnS is two times as large as that of Pnma-SnS, being this difference considerably greater at high temperatures. Our findings indicate that the role of effective masses and bandgap characteristics are critical in reducing the impact of the bipolar transport effect at high temperatures, contributing to our predicted better performance of the C2mb-SnS as a thermoelectric device compared to Pnma-SnS.