Colored Polymeric Films with a Bilayer Porous Design for Efficient Subambient Radiative Cooling

Passive radiative cooling has emerged as an efficient and environmentally friendly thermal regulation technology characterized by zero-energy consumption and negligible greenhouse gas emissions. However, a majority of investigated radiative cooling materials rely on a white appearance to optimize their cooling performance. The quest for an approach that simultaneously achieves esthetic perception and efficient subambient cooling in a straightforward and cost-effective manner is highly desirable. In this study, we present the development of colored porous films by incorporating functional nanoparticles into waterproof poly(vinyl chloride) (PVC), employing a bilayer structure that combines spin-coating and phase separation techniques. The bilayer film comprises a white porous main layer and a customizable colored top layer, incorporating three narrowband organic pigments─including quinacridone, iron oxide green, and Prussian blue, to achieve the desired appearance. The resulting red, green, and blue coolers exhibit high sunlight reflectivity values of 0.89, 0.90, and 0.85, respectively. The inclusion of BN nanoplates, possessing a high refractive index, contributes to the improved reflectivity. Furthermore, the incorporation of TiO2 nanoparticles and pigments enhances the mid-infrared thermal emittance, yielding emissivity of 0.90, 0.92, and 0.93, respectively. Consequently, the colored films achieve an average temperature reduction of 6.5–7.5 °C below ambient temperature under a maximum solar intensity of 628 W m–2 and exhibit a maximum average temperature drop of 3.5 °C during nighttime. Additionally, we develop a three-dimensional (3D) printing method utilizing additive manufacturing techniques to fabricate intricately structured colored radiative coolers, which exhibit notable antifouling properties and outdoor durability. The proposed design of the colored bilayer cooler offers a practical and effective solution to achieve both esthetic appeal and superior cooling capabilities, thus opening up possibilities for various real-world applications.