**Acknowledgements**

of conventional wearable TEGs, they present a wearable solar TEG possessing a high △T value of ~20.9°C by introducing a local solar absorber and thermoelectric legs on a polyimide

The structure and thickness of each layer was carefully designed to absorb sunlight at maximum extent. A dispenser printing technique was employed to prepare thermoelectric legs on the substrate. The n- and p-type ink were made by alloyed BiTe-based powders and Sb<sup>2</sup>

based sintering additive dispersed in glycerol. A wearable TEG prototype consisting of 10 pairs of thermoelectric legs exhibits an open circuit voltage of 55.15 mV and an output power of 4.44 μW when exposed to sunlight. The generated high △T of ~20.9°C between the hot solar absorber and cold edges is also the highest △T value of all wearable TEGs reported to date. In 2016, Melissa Hyland et al. also reported a wearable TEG device with optimized heat spreaders to increase the △T of wearable TEG [27]. The integration of heat spreader would improve the dissipation of heat and cooling throughout the wearable TEG. In their design, a three-layered device structure were used. Two flat heat spreaders were equipped on the top and bottom of TEG respectively. The sandwich structure was chosen as the final design due

With the rapid growth in wearable and flexible electronics, the demand in flexible self-power technologies are also increased. Thermoelectric energy conversion technology shows great potential in make use of our human body heat to generate power, which would be an ideal power source candidate for wearable electronic systems. In most of the developed flexible thermoelectric materials and generators, textile-based thermoelectric materials and TEG have unique advantage in body heat energy conversion due to their excellent air permeability, flexibility, and wearing comfort, especially for natural materials such as silk and cotton, which shows good biocompatibility. Therefore, a fabric-based thermoelectric generator with great wearability would overcome the wearable difficulty of existing organic film generators, which shows promising application in flexible and wearable self-powered electronic systems by harvesting body heat to generate electricity. In the past years of study, many textile thermoelectric materials were prepared in forms of fibers and fabrics including some traditional inorganic semiconductors and the newly developed organic polymers and composites. Compared with 2D fabrics, fiber-based thermoelectric legs would give more design flexibility for the flexible TEGs. Besides, some pioneering researches also designed and fabricated several novel textile TEGs with excellent flexibility and thermoelectric performance. Various TEG structures such as 2D generator making use of in-plane temperature difference and 3D generators generating temperature difference along fabric thickness directions are included. These textile-based TEGs with multiple structures are more practical and suitable for wearing than the previous widely studied film TEG, which shows promising application in future self-powered wearable system driven by body heat. The study of flexible and wearable thermoelectric materials and generators is just beginning. The efficiency of textile thermoelectric materials and generator need to be further improved for real application. These creative works bring many inspira-

superlattice.

Te3 -

substrate [26]. The prepared solar absorber is composed of a five-period Ti/MgF<sup>2</sup>

to its high efficiency and low form factor.

tions for the future explorations in thermoelectric field.

**4. Conclusion**

34 Bringing Thermoelectricity into Reality

This work was supported by University Research Grants Council, PolyU 5162/12E, Shen Zhen Government Key Incubation Fund, JC201104210132A, National Key Technology R & D Program Project, The Ministry of Science and Technology of P.R.C, 2012BAI17B06, and National Natural Science Foundation of China, 51673162.
