Efficient power generation near room temperature in earth-abundant thermoelectric tin sulfide

The inefficient carrier transport of earth-abundant tin sulfide (SnS), arising from its intrinsically low crystal symmetry, limits its thermoelectric performance at low temperatures. Here, the substitutional Ag ⁺ doping modified the Na-doped SnS crystal structure by reinforcing lattice dynamical anisotropy and enhancing in-plane transport properties. Concurrently, the reconstructed valence-band structure evolved into a modulated multiband configuration, increasing the density-of-states effective mass while preserving high carrier mobility. The resulting highly metallic conductivity combined with high thermopower yields an ultrahigh room-temperature power factor of ~ 101 µW cm ^-1 K ^-2 in Sn _0.96 Na _0.01 Ag _0.03 S single crystals. Coupled with the intrinsically low thermal conductivity of SnS, the optimized crystal achieved the figure of merit ( zT ) of ~ 1.06 at 300 K and ~ 2.0 at 573 K, delivering a conversion efficiency of ~ 3.3% and an output power density of ~ 0.31 W cm ^-2 in a single-leg module under a 243 K temperature gradient. These results demonstrate the effectiveness of multiband engineering in SnS and establish it as a highly promising low-cost thermoelectric material for near-room-temperature energy conversion.