The Internet Era is accompanied by an increasing demand for alternative power source in mW-to-mW range to drive distributed, wearable and implantable microelectronics. It is hard for traditional electrochemical battery to keep up with the fast-paced progress of microelectronics in miniaturization, packing density, mechanical flexibility, bio-safety and reliability. Nonetheless, thermoelectric battery excels where electrochemical battery falls short. 

Thermoelectrics is the simplest technique to directly convert heat, ubiquitous in environment, into electricity, a versatile form of energy. Thermoelectric devices are all solid-state, free of greenhouse emissions or moving parts, friendly for miniaturization, and low-maintain in the long term. However, they generally lack in mechanical flexibility, a key ingredient for wearable electronics.  

Based upon the early discovery of the flexible inorganic semiconductor Ag₂S, the research team led by Prof. SHI Xun and Prof. CHEN Lidong from Shanghai Institute of Ceramics of the Chinese Academy of Sciences, in collaboration with Prof. HE Jian from Clemson University, fabricated the world’s first flexible full-inorganic thermoelectric power generation module based on silver calcogenides. The study was published in Energy and Environmental Science. 

Since Ag₂S has poor thermoelectric performance despite its flexibility, Ag₂Se and Ag₂Te exhibit the opposite. It took serious materials research efforts via doping Se and Te on the S-site and controlling native defects to attain a delicate balance between the material’s thermoelectric performance (state-of-the-art figures of merit zTs up to 0.44 at 300 K and 0.63 at 450K) and flexibility.  

The material’s mechanical, electrical and thermal properties survived bending tests, meeting the requirements of wearable electronics. 

Besides, the researchers solved several architecture design problems of the device. The as-fabricated 6-leg device exhibits a normalized maximum power density up to 0.08 W·m^-1 near room temperature under a temperature difference of 20 K, orders of magnitude higher than organic devices and organic-inorganic hybrid devices. 

These results constitute a key initial step towards the new paradigm of flexible thermoelectrics. The study shall inspire more follow-up research efforts, e.g., developing p-type legs in place of Pt/Rh wires.