Interaction of light with nanocellulose for sustainable energy-efficient applications

With its intrinsic optical anisotropy, minimal light absorption, renewable origin, scalable processability, and tunable fibril orientation, nanocellulose provides a versatile platform for precise control of light-matter interactions, offering promising potential to advance low-carbon, sustainable optical technologies. This review outlines recent progress in nanocellulose thin films with engineered fibril orientation and elucidates how processing-structure-property relationships determine light-regulating performance across disordered to highly ordered structures. We first discuss scalable production routes for cellulose nanomaterials, followed by key correlations linking processing, structure, and optical response. Particular emphasis is placed on forward scattering, birefringence-driven interference colors, and the coupling of intrinsic spectral emission with cholesteric self-assembly. Fabrication strategies, from laboratory-scale casting to roll-to-roll manufacturing, are then evaluated in terms of scalability and industrial relevance. Furthermore, emerging applications in energy-efficient buildings are highlighted, including haze-tunable films for enhanced daylight harvesting, birefringent systems for spectrally selective polychromatic lighting, and structural coloration for passive radiative cooling. Key challenges related to structure-optics coupling, process optimization, large-area device integration, durability and scalability, and artificial intelligence-assisted predictive design are also discussed. This review establishes a design framework for nanocellulose thin films as next-generation sustainable materials toward advanced light-management technologies.