High power density of radiative-cooled compact thermoelectric generator based on body heat harvesting

Advancements in flexible and wearable electronics have led to the development of self-powered, wearable systems. Thermoelectric generators (TEGs) offer promising solutions toward self-powered energy harvesting from body heat. However, previously developed TEGs are large-sized owing to their heat sinks. Hence, high-quality heat sinks are required for flexible TEGs with a small size and high power for wearable devices. Herein, a TEG integrated with a flexible, micron-thin poly(vinylidene fluoride-co-hexafluoropropylene) radiative-cooled heat sink, with an emissivity of 97.47%, is proposed. The TEG with the radiative heat sink (TEG_rad) generates power by depositing heat into a cold space (temperature of 3 K) through passive radiative cooling. Thus, TEG_rad achieved a power density of 12.48 µW/cm² with a temperature difference (ΔT) of 1.9 °C, higher than those of flexible TEGs that were previously reported, based on body heat harvesting under natural convection. Further, TEG_rad is not only more than two times compact, but also delivers high power output compared with a TEG with a bulky finned heat sink. Moreover, a flexible lithium–sulfur (Li-S) battery was coupled with TEG_rad to store the generated power for uninterrupted power supply to a self-powered wearable system.