Flexible thermoelectric generator with radiative cooling for body-heat-driven self-powered Bluetooth low energy sensing system

Wearable electronics and wireless IoT sensors are increasingly expected to operate in a self-powered manner. However, their practical deployment remains limited due to the lack of compact, flexible, and sustainable energy sources. Thermoelectric generators (TEGs), which convert body heat into electricity, present a promising solution but are typically hindered by small temperature gradients and the requirement of bulky heat sinks that compromise flexibility. To address these challenges, we developed an ultra-thin flexible thermoelectric generator (FTEG) integrated with a radiative cooling (RC) layer that passively enhances heat dissipation under natural convection. The device, fabricated using high-performance thermoelectric materials on a soft silicone substrate, maintained a total thickness of just 2.26 mm. Finite element modeling and experimental validation confirmed that the RC layer effectively increased the temperature gradient across thermoelectric legs, significantly improving the output power compared to conventional graphite-based or no-cooling designs. The FTEG achieved a maximum normalized power density of 3.51 μW/cm 2 under temperature conditions representative of wearable use (T skin of 32 °C and T ambient of 26 °C). The harvested energy was then stored using a power management circuit and capacitor. This stored energy was successfully used to power a Bluetooth Low Energy (BLE) sensing module, enabling stable wireless transmission driven entirely by body heat. These results highlight the practical potential of integrating passive radiative cooling into flexible thermoelectric systems, paving the way for high-performance, battery-free wearable electronics and autonomous IoT applications.