2, National Institute of Advanced Industrial Science and Technology, Tsukuba, , Japan
Thermoelectric generators (TEGs) are used to generate electricity directly from waste heat. They are promising energy harvesters for independent, small circuits in sensor networks and wearable electronics since heat flux always accompanies human activity. Toward such an energy-harvesting use, there has been an effort in recent years to fabricate flexible, wearable TEGs from organic or organic/inorganic hybrid materials. Their thermoelectric figure of merit (ZT) is increasing year by year. However, in practical operating conditions where ambient air is the only medium for heat dissipation, the efficiency is restricted not only by the ZT value but also by the thickness and thermal conductivity of the device, which influence the temperature difference used for power generation. A total design of materials, device structure and fabrication process for these devices are therefore important to satisfy difficult requirements; thickness must be more than a few millimeters, but the device must be flexible.
Here, we propose a promising design for thickness-controllable, flexible, stretchable, and thermally insulating TEGs, or “thermoelectric fabrics.”  Carbon nanotubes (CNT) are spun into thread with binding polymers and p/n-doped to form striped patterns. By sewing the CNT thread into a felt fabric, operation of a prototype thermoelectric fabric by a finger touch is demonstrated, which indicates its potential as an easy-to-use power source for wearable electronics.
 M. Ito, T. Koizumi, H. Kojima, T. Saito, and M. Nakamura, J. Mater. Chem. A 5, 12068 (2017).