Bioinspired metafilms for all-weather energy harvesting: Adaptive thermal regulation and raindrop electricity generation

Tremendous efforts have been dedicated to facilitating heat dissipation into cold universe through radiative cooling. Nevertheless, its applications remain limited by overcooling in cold conditions and reduced effectiveness under nonclear skies. We present a robust metafilm inspired by the adaptive capabilities of horned lizards ( Phrynosoma ) to overcome these challenges. This design extends energy harvesting to rainy conditions while maintaining thermal regulation on clear days. The metafilm features a sandwich structure with fluorinated ethylene propylene/indium tin oxide outer layers for raindrop-induced electricity generation and thermochromic core layers for self-regulated heating and cooling. It achieves an optical contrast exceeding 63% in the visible spectrum, enabling sub-ambient cooling in hot conditions and above-ambient heating when cold. In addition, it demonstrates efficient droplet-induced electricity generation, delivering a high-voltage output of 208 volts with exceptional long-term stability. This multifunctional metafilm overcomes key limitations of traditional radiative coolers, offering a versatile approach for all-weather energy harvesting.