Efficient and durable Ga2O3 hybrid coating with spectral selectivity for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) has demonstrated significant potential in reducing energy consumption in building air-conditioning systems, particularly in hot and humid subtropical climates. PDRC materials incorporating disordered reflective fillers not only exhibit remarkable cooling performance but also allow for scalable fabrication. However, existing reflective fillers fail to achieve sufficient reflectivity in the ultraviolet and mid-wave infrared band, thereby restricting the practical application of PDRC materials. Herein, we introduce a durable hybrid coating (GC) comprising randomly distributed inorganic dielectric gallium oxide (Ga 2 O 3 ) particles, which realizes a high spectral selectivity ( η ε = 1.28). Despite the absence of a metal backing, GC achieves a high solar reflectance of 94.6%, an atmospheric window emittance of 93.5%, and a mid-wave infrared reflectance of 52.4%. Outdoor cooling tests reveal that GC achieved a maximum average sub-ambient cooling of 4.8 °C under solar irradiance exceeding 800 W m −2 , while maintaining superior cooling performance in both high-humidity environments and simulated outdoor urban scenarios. Furthermore, GC exhibits hydrophobicity, self-cleaning capability, and good weathering stability, while simulations demonstrate its substantial potential for reducing cooling-energy consumption. This work not only presents a novel strategy for designing spectrally selective PDRC materials but also paves the way for the practical implementation of such materials in subtropical regions.