Selective spectral absorption of nanofibers for color-preserving daytime radiative cooling.

Passive radiative cooling is a promising solution for cooling objects without consuming energy. However, chemical colors absorb visible light and generate heat, posing a challenge in the design of a colored sub-ambient daytime radiative cooler (CSDRC) in a simple and scalable way. Herein, we used nanofibers (NF) to achieve selective spectral absorption of the daytime radiative cooler through a dope-dyeing electrospinning technique. This approach allows for the selective absorption of desired colors in the visible spectrum, while the nanofiber structure provides strong visible and near-infrared light scattering to minimize solar heating. We selected cellulose acetate (CA) with mid-infrared emittance characteristics for efficient sky cooling. Our design enabled the CA NF CSDRC to exhibit an ultra-high NIR reflectance of 99%, a high MIR emittance of 95%, and vibrant colors. These unique optical properties resulted in a reduction of the maximum ambient temperature by 3.2 °C and a cooling power of ≈40 W m at a solar intensity of 700 W m. Additionally, the flexibility and deformability of the colored nanofiber cooler make it suitable for thermal management in various practical applications. Our work provides a simple and scalable solution for designing colored passive radiative cooling materials.