Recent progress towards high performance of tin chalcogenide thermoelectric materials

Thermoelectric materials have been extensively studied for decades to help resolve the global energy shortage and environmental problems. Many efforts have been focused on the improvement of the figure of merit (ZT) for highly efficient power generation. Lead telluride is one of the materials with high ZT, but lead toxicity is always a concern, which has inspired research on lead-free tin chalcogenides. ZT values as high as ∼2.6 at 923 K for SnSe single crystals and ∼1.6 at 923 K for Sn_0.86Mn_0.14Te(Cu₂Te)_0.05-5 atm% Sn were recently reported, attracting extensive attention for potential applications. In this review, we present the progress in SnTe, SnSe, and SnS, mainly discussing the effective tuning of the electron and phonon transport based on the intrinsic properties, along with the challenges for further optimization and applications. For SnTe, successful strategies, including resonant doping, band convergence, defect engineering, etc., are discussed. For SnSe, we focus on the analysis of the intrinsic low thermal conductivity due to strong anharmonicity and a high Seebeck coefficient because of the multi-valley bands. For SnS, high performance is expected considering its similar band structure and crystal structure to SnSe.