Most of the energy of the human body is released in the form of heat. The average temperature difference between human body and outside circumstances is about 5-30 ℃, therefore human body heat can be a good energy source for thermoelectric generators. Compared with traditional generators, wearable thermoelectric generators can harvest and convert low-grade heat released by the human body into usable electrical energy, which may be sufficient for some wireless sensor nodes whose power demand is less than milliwatts. Wearable thermoelectric generators offer a new choice for the power supply of wearable devices, and seem superior to secondary rechargeable batteries owing to the merits of non-pollution, light weight, and continuity. Currently the global upsurge of research interest in this field mainly focuses on three types of generators which are fabricated based on different types of thermoelectric materials-bulk materials, thin films, and fabrics. The first type is generators based on bulk thermoelectric materials with high room-temperature thermoelectric properties (mainly bismuth telluride-based alloys and bismuth telluride-based alloys). This type of generators can output the power of generally tens of microwatts per square centimeter, and their output performance and flexibility are relatively poor and need to be improved through further investigations. The second type of generators (based on thermoelectric thin films) can output the power density ranging from nanowatts to microwatts per square centimeter, and can be divided further into horizontal type and vertical type according to the device structure. The horizontal type can produce relatively larger output voltage and is usually realized by different ways of arrangement of thermoelectric arms, such as stacking, rolling, or folding. In comparison, the vertical type devices have higher area-average numbers of thermoelectric arm pairs, and hence, larger power density. The third type of generators fabricated based on thermoelectric fabrics, notwithstanding low output power density, is adaptable to 3D deformation because of their high stretch, bending and in-plane shear properties, making them more suitable for collecting heat on the curved surface of human skin. The present review summarizes the research status of the above mentioned three types of potential wearable thermoelectric generators. It also analyzes the merits and demerits of each type of generators from the perspectives of design, structure and performance. © 2023 Cailiao Daobaoshe/ Materials Review. All rights reserved.
