Soft-covered wearable thermoelectric device for body heat harvesting and on-skin cooling

The recent emergence of self-powered wearable electronics gives rise to a growing demand for flexible, sustainable, and portable power supply. Wearable thermoelectric devices (WTEDs) are promising power sources for wearable electronics through directly converting body heat into electricity. However, the output power of WTEDs is still low due to the extremely small effective temperature difference across thermoelectric pillars, which hinders their practical applications. Commonly used strategies to enlarge the effective temperature difference for WTEDs, such as introducing metallic heat sinks or increasing the length of thermoelectric pillars, usually lead to clunky devices that are not suitable for wearable electronics. Here, we report on a soft-covered WTED for body heat harvesting and on-skin cooling, which demonstrates the desirable performance and wearer comfort. Distinct from the previously reported flat soft heat spreaders, this work presents the design and fabrication of a pin-fin soft cover that can serve as a flexible heat sink for WTEDs. The pin-fin soft cover was fabricated by curing the liquid metal/elastomer composite in a meltable wax mold. Systematic theoretical and finite element analysis was conducted to optimize the output power and wearability of the soft-covered WTED. The optimized WTED achieves a power density of 6.63 mu W cm(-2) on a stationary human body under natural convection condition with an ambient temperature of 20 ?C, which is higher than the previously reported WTEDs with flat soft covers made of high-thermal-conductivity elastomers. Furthermore, our WTED can realize a 1.5 ?C temperature drop for the human skin through Peltier cooling. This work demonstrates a new route to develop soft-covered WTEDs for self-powered wearable electronics and personal thermoregulation.