With the growing global demand for clean energy and efficient energy conversion technologies, thermoelectric technology has attracted significant attention due to its ability to directly convert waste heat into electricity. The conversion efficiency of thermoelectric materials is determined by their dimensionless figure of merit (ZT), with higher ZT values indicating superior performance. Among various thermoelectric materials, tin selenide (SnSe) has become a research hotspot due to its outstanding performance in single-crystal form. However, polycrystalline SnSe, which offers lower cost and better mechanical strength, has long lagged behind p-type materials or single-crystal SnSe in terms of performance, particularly n-type polycrystalline SnSe, limiting its practical applications. This is mainly attributed to its high lattice thermal conductivity and the adverse effects of tin vacancies (V_Sn) on carrier transport, which have become bottlenecks hindering its real-world use.

Professor Li Jing-Feng’s team from Tsinghua University has reported an innovative study on optimizing the thermoelectric performance of SnSe via liquid phase sintering. The research team introduced excess metallic tin (Sn) during the preparation process. During high-temperature sintering, the excess tin melted to form a liquid phase. Part of this liquid phase was extruded under pressure, while the remainder infiltrated the SnSe matrix. The infiltrated tin atoms effectively filled the intrinsic tin vacancies, reducing electron trapping and scattering, thereby significantly increasing carrier concentration and electrical conductivity while maintaining a high Seebeck coefficient. The liquid phase sintering process introduced an extremely high density of dislocations and dislocation networks within the material. These defects efficiently scatter phonons (particularly mid-frequency phonons), resulting in a lattice thermal conductivity as low as 0.21 W·m⁻¹·K⁻¹ at 793 K, approaching the theoretical minimum for this material.
Through this synergistic optimization of electron and phonon transport, the research team achieved an exceptional ZT value of approximately 1.9 at 793 K in n-type polycrystalline SnSe, along with a high average ZT value of 0.72 across a broad temperature range of 300–873 K. This performance ranks among the best reported for n-type SnSe-based thermoelectric materials.

This work not only presents a novel approach for enhancing the thermoelectric performance of n-type SnSe, but also demonstrates the considerable potential and universality of liquid-phase sintering technology in the design and fabrication of high-performance thermoelectric materials. In the future, high-performance, environmentally friendly thermoelectric materials are expected to find widespread applications in mid-temperature range (300–900 K) waste heat power generation and solid-state cooling devices. This research provides strong material support and innovative ideas for promoting the industrial development of thermoelectric technology and achieving the "dual carbon" goals.

The complete study is accessible via DOI:10.34133/research.0962