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

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Abstract
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.

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