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 ΔTcooling = 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 (Pmax) 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 Pmax 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.

Bioinspired Design of a Binary Synergistic Photonic Structure for Daytime Radiative Cooling

“…The cooling system as a necessity for humans accounts for 10% of global electricity consumption. , This will exacerbate the energy crisis as well as accelerate global warming . Passive daytime radiative cooling (PDRC) as a novel cooling technology has aroused widespread interest among researchers for its electricity-free and environment-friendly cooling mode. − PDRC with zero energy input can reflect the incident sunlight (0.3–2.5 μm) to minimize the solar heat gain and radiate heat to the universe (∼3 K) through the atmospheric window (8–13 μm). − Over the past years, this technology has emerged as a frontier and a variety of PDRC designs have been reported, such as photonic structures, − porous polymer films, , particle-embedded coatings, , and fibers. , Among these, photonic structures exhibit tailored spectrum via tuning the subwavelength structural features, realizing distinctive radiative cooling performance. , Strategies for constructing photonic structures like multilayer stacks, periodic structures, random structures, and bioinspired structures thrive in achieving highly efficient passive radiative cooler . Raman et al first reported a multilayer photonic structure used for radiative cooling with a solar reflectance of 97% and selective emissivity across the atmospheric transparency window.…”

“…7−10 Over the past years, this technology has emerged as a frontier and a variety of PDRC designs have been reported, such as photonic structures, 11−13 porous polymer films, 14,15 particleembedded coatings, 16,17 and fibers. 18,19 Among these, photonic structures exhibit tailored spectrum via tuning the subwavelength structural features, realizing distinctive radiative cooling performance. 20,21 Strategies for constructing photonic structures like multilayer stacks, 22 periodic structures, 23 random structures, 24 and bioinspired structures 25 thrive in achieving highly efficient passive radiative cooler.…”

Maximizing electrical power through the synergistic utilization of solar and space energy sources

“…Concerning materials, researchers are dedicated to developing novel RC materials with high emissivity in the atmospheric window and low absorption of the solar spectrum. This involves the incorporation of various strategies, including the utilization of porous structures, 24 nanomaterials, 25 , 26 , 27 and infrared radiation materials, 28 , 29 , 30 , 31 aimed at maximizing the absorption of energy from the cosmic cold source. Additionally, the optimization of heat transfer materials is considered a key means to enhance power generation efficiency, as efficient heat transfer materials can reduce the heat exchange between the system and the surrounding environment, thus minimizing thermal losses and enhancing energy utilization efficiency.…”

“… 34 Moreover, some have proposed the integration of the TEG’s hot side with human body heat sources. 25 , 26 , 27 , 31 Therefore, it is possible to flexibly adjust system parameters and manage heat flow direction based on the specific system structure and application context.…”

“…Nevertheless, even though some RC-TE systems have achieved electricity generation from solar energy and space cold source energy, achieving high power generation efficiency remains challenging due to the constraints imposed by thermoelectric materials and the temperature difference between the hot and cold sides. Currently, the highest value stands at only 185.9 mW/m 2 , 27 which can supply tiny mW and μW sensors or LEDs, making large-scale practical applications infeasible. While photovoltaic cells exhibit higher power density, their average cost remains relatively high due to the limitations imposed by the day-night cycle.…”