Stability of SnSe-Based Thermoelectric Compounds

SnSe compounds are studied as promising candidates for thermoelectric (TE) applications, primarily due to their remarkable achievement of a high <i>ZT</i> value and the relative abundance of their constituent elements. In former studies, a significant disparity in the performance of polycrystalline SnSe compounds has been observed, and the reasons for the non-reproducibility have been investigated. This study focuses on the impact of sintering temperature on the thermoelectric properties of both Br-doped and undoped SnSe materials. Through a targeted synthesis approach, we achieved a <i>ZT</i> value of 1.04 at <i>T</i> = 873 K. The results reveal a critical challenge in controlling the mobility of ions and defects for long-term application of SnSe-based thermoelectric materials. The peak <i>ZT</i> values observed in the initial measurements are not sustainable, as the thermoelectric performance experiences a decline during multiple heating-cooling cycles. This issue is further underscored by extended annealing experiments, which resulted in a substantial <i>ZT</i> decrease of approximately 50%. These outcomes emphasise the need for a comprehensive understanding of the long-term stability of SnSe materials in thermoelectric applications. Additionally, they emphasise the importance of conducting heating-cooling measurements in thermoelectric systems, particularly when aiming to achieve and maintain high <i>ZT</i> values for longer periods.