As global energy and environmental challenges become increasingly severe, thermoelectric materials have garnered significant attention for their potential as eco-friendly energy conversion systems. These materials can efficiently convert heat into electrical energy, making them rather important for applications in key technology areas such as aerospace, industrial waste heat recovery, and active cooling. Despite notable advancements in the research of traditional thermoelectric materials, the development of environmentally friendly alternatives with high-ranged performance remains in its nascent stages. In this context, tin sulfide (SnS), a wide bandgap thermoelectric material, emerges as a promising candidate for achieving high-efficiency thermoelectric conversion over a broad temperature range. This review provides a detailed discussion of the fundamental properties of SnS materials, including their crystal, electronic, and phonon structures. A systematic review of the preparation methods for single-crystal growth and polycrystal synthesis is also presented. Building upon this foundation, we comprehensively analyze and summarize the optimization strategies and the latest research advancements related to SnS-based crystals and polycrystals, with a focus on the key representative findings. Additionally, we conduct an in-depth analysis of the current challenges faced by SnS-based thermoelectric materials and devices, as well as offer a perspective on future development directions. This paper begins with a detailed discussion of the crystal structure of the low-temperature Pnma phase of SnS. Emphasis is placed on its unique low-symmetry layered structure, which contributes to its strongly anisotropic properties. These characteristics are analyzed through the phonon structure perspective, revealing their critical role in the material's intrinsically low thermal conductivity. Furthermore, the electronic band structure of SnS is explored in depth to understand its multiple band transport characteristics. Significant improvements in electrical transport properties are achieved through the collaborative optimization of carrier mobility and effective mass. Subsequently, the paper systematically reviews the various technologies for SnS-based crystal growth and polycrystal synthesis, including the temperature gradient method, chemical vapor deposition, melting method, mechanical alloying, chemical methods, and spark plasma sintering. Based on this, strategies and recent advancements in optimizing the thermoelectric properties of SnS crystals and polycrystals are discussed in detail. These strategies include carrier concentration regulation, texture control, and band structure engineering, etc. Given the research results, it is expected that p-type SnS materials hold considerable potential for applications in thermoelectric power generation and electronic cooling, potentially serving as viable alternatives to the traditional and commercial bismuth telluride-based thermoelectrics. However, the practical application of p-type SnS is currently hindered by issues such as insufficient processability, the complexity of preparation methods, as well as the lack of research on ptype SnS-based thermoelectric devices. Therefore, realizing compromise between thermoelectric and mechanical properties might be of substantial importance for further development. Additionally, n-type SnS-based thermoelectric materials remain primarily at the theoretical level and have not yet been developed with promising performance, making the fabrication of all-SnS-based thermoelectric devices rather difficult. These challenges highlight the current limitations in SnS-based thermoelectric research while also providing clear directions for future investigation. This review not only enhances the theoretical understanding of p-type SnS-based thermoelectric materials, but also offers innovative perspectives and solutions for their practical applications in the near future.
