Colored Radiative Cooling: from Photonic Approaches to Fluorescent Colors and Beyond

Abstract

Radiative cooling technology is gaining prominence as a sustainable solution for improving thermal comfort and reducing energy consumption associated with cooling demands. To meet diverse functional requirements such as aesthetics, switchable cooling, camouflage, and colored smart windows, color is often preferred over a white opaque appearance in the design of radiative cooling materials. Colored radiative cooling (CRC) has emerged as a prevailing technology not only for achieving a colorful appearance but also for increasing the effective solar reflectance to enhance cooling performance (through the incorporation of fluorescent materials). This paper reviews recent advancements in CRC and its profound impact on energy savings and real-world applications. After introducing the fundamentals of CRC and color characterization, various photonic approaches are explored that leverage resonant structures to achieve coloration in radiative cooling, comparing them with conventional coloration methods based on optical materials like fluorescent pigments that can convert absorbed ultraviolet light into visible-light emission. Furthermore, the review delves into self-adaptive CRC materials featuring dynamic optical modulation that responds to temperature fluctuations. Lastly, the potential application of CRC materials is assessed, a comprehensive outlook on their future development is offered, and the critical challenges in practical applications are discussed.