High Efficiency Breathable Thermoelectric Skin Using Multimode Radiative Cooling/Solar Heating Assisted Large Thermal Gradient

Abstract This study proposes a Janus structure‐based stretchable and breathable thermoelectric skin with radiative cooling (RC) and solar heating (SH) functionalities for sustainable energy harvesting. The challenge of the wearable thermoelectric generator arises from the small temperature difference. Thus, this dual‐sided structure maximizes the thermal gradient between the body and the surrounding environment, unlike the previous works that rather concentrate on the efficiency of the thermoelectric generator itself. The Janus structure allows the device to switch to the other mode, optimizing electricity generation from a given weather condition. For these functionalities, for the first time, boron nitride‐polydimethylsiloxane (BP) and graphene nanoplatelet‐polydimethylsiloxane (GP) nanofiber (NF) are developed as substrates. The BP NF generates the RC capability of Δ T cooling = 4 °C, and the high solar absorbance of the GP NF enables it to be photothermally heated. The flip‐overable thermoelectric skin (FoTES) achieves a maximum power output ( P max ) of 5.73 µW cm −2 in RC mode, surpassing SH mode by 5.55 µW cm −2 in the morning. In the afternoon, it generates a P max of 18.59 µW cm −2 in SH mode, outperforming RC mode by 15.56 µW cm −2 . This work contributes to the advancement of wearable electronics, offering a sustainable power source in a wearable form.