Progressive Optimization of <i>ZT</i> Value in n‐Type PbSnS ₂ Polycrystals via Heterovalent Doping and Crystal Structure Modification

ABSTRACT PbSnS 2 has garnered increasing attention as a novel, cost‐effective, and high‐performance thermoelectric material. Herein, we have achieved an advanced performance in n ‐type PbSnS 2 polycrystals, demonstrating a peak ZT exceeding 1.0 at 873 K. This outstanding thermoelectric performance stems from the progressive optimization via Cl doping and Se alloying. Cl doping modulates the Fermi level of the intrinsically insulator‐like PbSnS 2 , while the resulting weakened bond strength further reduces its inherently low thermal conductivity, which can be corroborated by band structure calculations and crystal orbital Hamiltonian population analysis (COHP). Plus, Se alloying mitigates the degree of lattice distortion in PbSnS 2 and modifies its crystal structure, as validated by Rietveld refinement of XRD patterns. The beneficial effects achieved through heterovalent doping coupled with crystal structure engineering in n ‐type polycrystalline PbSnS 2 highlight the potential applicability of these strategies to other thermoelectric materials characterized by poor electrical transport properties and low‐symmetry crystal structures.