Wearable thermoelectric silver sulfides: From materials to applications

In the developing world population, there is an increasing need for wearable electronics in the field of wearable multi-functional sensors (i.e., medical sector), watches, and other electronic devices (earplugs). Still, the power supply system is deficient in capacity and short life span (batteries). Silver Sulfide (Ag2S) is the first inorganic ductile, flexible (sustainable) semiconducting material with excellent thermoelectric performance. Compared with conventional organic, inorganic, and hybrid flexible thermoelectric materials, it is best suited for the human body heat harvesting process to wearable self-powered devices (i.e., unlimited power supply). This review discusses the crystal structure (polymorphism), the contribution of mechanical properties, and synthesis methods in the thermoelectric performance of silver sulfides. Detailed the different strategies like doping, substitution, composite formation, and nano-inclusion for the improvement of thermoelectric behaviors and device fabrication for real-time applications. Finally, concludes with the demerits and the solutions to rectify the shortcomings of Ag2S thermoelectric material. Further, elaborated the strategies to optimize the material performance for the next-generation wearable thermoelectric applications.