Bioinspired Colored Films with Humidity-Induced Dynamic Reflectivity and Emissivity for Self-Adaptive, Efficient Radiative Cooling

Passive daytime radiative cooling (PDRC) has been considered an effective zero-power cooling method, and colored PDRC films can efficiently avoid glare effects as well as expand aesthetic and functional demands. However, the spectral designs of most colored radiative coolers are complex, and they have shortcomings in adaptability to weather changes due to static optical properties. It remains a great challenge to develop self-adaptive colored radiative coolers for all-humidity efficient radiative cooling and to expand moisture-responsive applications. Herein, based on the bionic concept derived from the color-changing characteristic of chameleons in response to environmental conditions, an insight into humidity-driven dynamically reversible dual-band spectral regulation is proposed. Humidity-sensitive colored film (HSCF) possessing spectral self-regulation abilities across both solar and mid-infrared wavelength ranges is developed, which shows dynamically enhanced solar reflection and mid-infrared emissivity as ambient humidity increases. Outdoor tests demonstrate that the obtained colored film can achieve self-adaptive efficient PDRC over a wide ambient humidity range (25-90%) throughout the whole day. More importantly, the dynamic dual-band regulation process is autonomous, energy-free, and reversible. This work provides a route to develop self-adaptive colored radiative coolers for application in all humidity conditions.