A comprehensive review on the output voltage/power of wearable thermoelectric generators concerning their geometry and thermoelectric materials

Highlights: • Fully coating the thermoelectric legs with a stretchable elastomer reduces the output power. • Varying the boundary condition along the legs was considered to solve this problem. • The covering region of the substrate and its thermal conductivity were manipulated. • A nonhomogeneous boundary condition along the legs showed superior output power than a homogeneous one. • The results provide a clear insight into the importance of the boundary condition along the thermoelectric legs. Wearable thermoelectric generators (TEGs) are considered as a promising power supply for low power wearable electronics. To obtain high thermoelectric (TE) generation, the focus should be on two main factors, including TE materials and the configurations of TE legs. Concerning these two factors, this paper provides a comprehensive review of recent studies on wearable TEGs. In general, TE materials can be classified into three categories, including inorganic, organic, and hybrid (inorganic-organic). In addition, the TE legs can be prepared in three different configurations, including ingot-shaped, film-shaped, and yarn-shaped. Based on the reviewed literatures, the superior output powers of all the three configurations were achieved by the inorganic, hybrid, and organic TE materials, respectively. It should be noted that the ingot- and the yarn-shaped legs were mostly composed of the inorganic and the organic TE materials, respectively. Whereas, all the three types of TE materials were almost equally used to prepare the film-shaped legs. Regarding power density, the ingot-shaped legs stood first followed by the film- and the yarn-shaped legs, respectively. Precisely, the output powers of the ingot- and the film-shaped legs were at µW/cm² level, dropping to nW/cm² for the yarn-shaped legs.