Inherent Photoluminescence-Enhanced Daytime Radiative Cooling by Highly Crystalline Cellulose Films

Frequent high-temperature weather imposes high demands on the performance of passive daytime radiative cooling (PDRC) materials. Natural cellulose is a sustainable raw material with promising PDRC performance based on its unique macromolecular structure and hierarchical aggregation structure. However, it is still a great challenge to improve the PDRC performance of regenerated cellulose materials. In this work, it is found that the high crystal structure of the regenerated cellulose film can enhance its photoluminescence (PL) capacity. This intrinsic PL behavior will enhance its PDRC performance through the photon conversion mechanism. By converting the absorbed ultraviolet band photons into visible light for emission effectively, the regenerated cellulose film presents a higher reflectivity in the visible light band and a higher cooling power. The regenerated cellulose film with a crystallinity of 73.71% can achieve an average reflectivity of 93.48% in the 0.3-2.5 μm waveband, which is 4.79% higher than that of the regenerated cellulose film without PL enhancement, thereby increasing the cooling power by 115.9%. This kind of highly crystalline cellulose film with high PDRC performance is expected to make contributions to energy conservation in cities under diverse climatic conditions.