Remarkable electron and phonon band structures lead to a high thermoelectric performance: ZT > 1 in earth-abundant and eco-friendly SnS crystals

Tin selenide (SnSe), a simple binary compound with low-cost, earth-abundant and eco-friendly elements, has aroused extensive interest in the thermoelectric community on account of its promising power generation. Herein, we report a much more advantageous SnS crystal with promising thermoelectric performance, as an alternative to SnSe. We found that the maximum ZT > 1.0 at 873 K and high device ZT (ZT_dev) > 0.57 from 300 to 873 K can be achieved in hole-doped SnS crystals, projecting a conversion efficiency of ∼10.4%. We attribute the excellent performance of SnS to its remarkable electron and phonon band structures. SnS possesses multiple valence bands, which can be activated by hole doping through pushing the Fermi level deep into the valence band structure, and activating several Fermi pockets to produce enhanced Seebeck coefficients and high power factors ∼30 μW cm^-1 K^-2 at 300 K. Meanwhile, the anharmonic and anisotropic bonding of SnS leads to a low thermal conductivity, which ranges from 0.65 to 0.85 W m^-1 K^-1 at 873 K. Our results indicate that SnS is a promising thermoelectric material for energy conversion applications in low and moderate temperature ranges.