Color Design for Daytime Radiative Cooling: Fundamentals and Approaches

The escalating global energy crisis and the worsening global warming have intensified the heat threats posed by high temperatures. Traditional cooling methods like air conditioning are not only energy-intensive but also contribute to environmental degradation. In response, there is a pressing demand for novel, eco-friendly cooling technologies, particularly amid the growing global push for carbon neutrality. As a passive cooling method that does not require any extra power input, radiative cooling offers a promising solution, utilizing thermal radiation to cool the Earth by transferring heat directly to outer space. However, current radiative cooling materials generally have a monotonous white appearance due to their high reflectivity to solar radiation, which, considering their prospects for outdoor applications, has prompted the need for color design. Recent advancements have led to the development of colored passive radiative cooling (CPRC) materials, offering passive cooling without additional energy input, colorful aesthetic appearance, and facile preparation methods. In this review, the latest progress in CPRC materials are summarized, covering fundamental principles, various color design solutions, and potential applications. Besides, the coloration strategy including chemical, structural, and luminescent approaches for CPRC are comprehensively analyzed, providing insights into the future development and deployment of CPRC materials for outdoor energy efficient systems and thermal regulation.