Researchers from the University of Turku have developed a biodegradable film using nanocellulose and red onion skin extract to protect solar cells from ultraviolet damage. The study, published in ACS Applied Optical Materials on February 24, showed the film blocked 99.9% of UV radiation up to 400 nanometers. Tests compared four nanocellulose-based films with different natural additives, and the onion dye proved most effective. Unlike lignin, which darkened films and reduced transparency, onion extract-maintained clarity. The film allowed over 80% of visible and near-infrared light to pass, crucial for electricity generation. It retained performance during 1,000 hours of artificial light exposure, equal to one year outdoors in central Europe. Researchers suggested such biodegradable filters could replace petroleum-based coatings in solar cells and temporary electronic devices.