Colored Transparent Radiative Cooling Glass Based on a Cellulose Nanocrystal Sandwich Structure

Advances enable passive thermal management in transparent radiative cooling, yet colorless designs limit aesthetic diversity. Colored glass poorly regulates near-infrared solar heat gain, motivating materials that integrate vivid color, high transparency, and efficient radiative cooling. Here, a colored transparent radiative cooling glass based on a cellulose nanocrystal (CNC) sandwich architecture is proposed. The design incorporates a half-wave plate (HWP) between two CNC layers, overcoming polarization-selective reflection inherent to single-layer CNC films and enabling efficient reflection of both circular polarizations. This structural enhancement boosts visible reflectivity, while an indium tin oxide (ITO) reflector elevates near-infrared reflectivity above 45% to suppress solar heating, and a hydrophobic coating enhances durability. The resulting CNC/HWP/CNC/ITO multilayer glass maintains high visible transparency (32.08-59.02%) with vibrant structural colors, and exhibits excellent thermal emissivity (> 91%) within the atmospheric transparent window, enabling passive radiative cooling. Outdoor field tests demonstrate a maximum average temperature reduction of 12.06°C relative to a black reference, with cooling performance largely color-insensitive. Sunroom validation confirms a 4.20°C average indoor temperature reduction over ordinary glass during daytime. By reconciling aesthetic coloration with efficient passive cooling and durability, this work provides a practical, scalable approach for energy-efficient glazing, especially for applications in lower-attitude regions.