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

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 modifies the Na-doped SnS crystal structure by reinforcing lattice dynamical anisotropy and enhancing in-plane transport properties. Concurrently, the reconstructed valence-band structure evolves 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 the room-temperature power factor of ~101 µW cm−1K−2 in Sn0.96Na0.01Ag0.03S single crystals. Coupled with the intrinsically low thermal conductivity of SnS, the optimized crystal achieves 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 crystal structure modification and multiband engineering in SnS and establish it as a highly promising low-cost thermoelectric material for near-room-temperature energy conversion. This study shows that reshaping the crystal and electronic structures of SnS overcomes competing charge transport properties, enabling high thermoelectric performance and efficient energy conversion near room temperature.