Functional Radiative Cooling: Basic Concepts, Materials, and Best Practices in Measurements

Radiative cooling (RC) has garnered growing interest because of increasing energy demand for cooling, which is partially associated with global warming. While various strategies to improve the performance of RC have been reviewed, there have been limited reviews on functional RC, whose functionalities render traditional radiative coolers aesthetically appealing, transparent, and adaptive. In this review, we briefly introduce the fundamental concepts governing the overall process of RC. We then outline a wide range of strategies to couple diverse functionalities within RC devices as a means to produce distinct color and/or optical transparency while preserving the performance of RC. We also discuss approaches to achieve switchable optical contrast to effectively regulate cooling power in response to changes in the external environment. Moreover, based on the factors affecting the measurements, we offer our perspectives on the best measurement practices that are essential for accurate performance evaluation of functional RC. Finally, we conclude by outlining challenges associated with the commercialization of functional RC platforms.