Realizing Promising Thermoelectric Efficiency in N-type SnS Polycrystals via Structural Regulation

The environmentally benign and low-cost tin sulfide (SnS) is a promising thermoelectric (TE) material, owing to its intrinsically low thermal conductivity and favorable electronic structure. SnS crystals have exhibited excellent performance, while the time-consuming preparation process and poor mechanical properties still severely restrict their applications. In contrast, SnS polycrystals that can be rapidly fabricated by powder metallurgy with promising mechanical reliability have long suffered from inferior electrical transport. Herein, we demonstrate that structural regulation can substantially stimulate the TE potential of n-type SnS polycrystals. Pb alloying in Br-doped SnS_0.55Se_0.45 polycrystals narrows the bandgap and enhances lattice symmetry, leading to increased carrier concentration and mobility. Simultaneously, the suppressed optical branches lead to strong phonon scattering and ultralow thermal conductivity. Moreover, trace Cu intercalation activates interlayer charge transport at elevated temperatures, yielding a substantial enhancement in the electrical power factor. Consequently, a record-high maximum ZT exceeding 1.6 is achieved at 873 K in an n-type Sn_0.6Pb_0.4S_0.55Se_0.45-0.4%Cu polycrystal, corresponding to a maximum theoretical conversion efficiency of approximately 8.5%, being the superior candidate among layered polycrystalline TE sulfides. This work highlights the critical role of structural regulation in decoupling electrical and thermal transports, establishing that n-type SnS polycrystals are efficient for mid-temperature TE power generation.