SnSe Alloying Enables High Thermoelectric Efficiency in Out-of-Plane PbSnS₂ Crystals

Layered thermoelectrics inherently possess low thermal conductivity along the out-of-plane direction. However, the sluggish interlayer electron transport arising from the distorted rock-salt structure and Pb/Sn cation disorder severely restricts the further enhancement of overall thermoelectric performance in PbSnS₂. Herein, this study proposes an effective strategy to synergistically optimize the out-of-plane performance of n-type PbSnS₂ via SnSe alloying. The incorporation of SnSe elevates carrier concentration and markedly boosts out-of-plane charge mobility, which can be primarily attributed to the improved lattice symmetry and optimized electronic bands. Additionally, alloying-induced point defects intensify phonon scattering, enabling effective decoupling of electron and phonon transports in n-type PbSnS₂ crystals. Experimental results reveal that the optimized n-type (PbSnS₂)_0.7(SnSe)_0.3 achieves a maximum out-of-plane ZT of ∼1.9 at 750 K. Subjected to a temperature gradient of 529 K, the assembled single-leg device exhibits a power generation efficiency of ∼7.9%. Both material and device-level performance stand at the forefront among all reported n-type PbSnS₂-based thermoelectrics. This work elucidates a novel pathway for optimizing interlayer charge transport through structural manipulation and underscores the promising prospect of earth-abundant PbSnS₂ for medium-temperature power generation.