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Solar power is one of the best tools in humanity\u2019s decarbonization toolbox, but even these green energy<\/a> technologies aren\u2019t 100 percent sustainable. For example, solar cells only convert light in the visible and near-infrared part of the spectrum, and actually require UV filters (light below the 400 nanometers) to protect critical components like passivation layers and the underlying silicon. <\/p>\n\n\n\n Typically, commercial solar panels rely on petroleum-based filters made from polyvinyl fluoride (PVF) and polyethylene terephthalate (PET) to do this job. While bio-based replacements would be a preferable material, these oil-based filters get the job done in large commercial solar farms where panels can be responsibly recycled<\/a>. However, some solar applications could benefit immensely from having a system that was safely biodegradable, particularly in microsensors. In a recent study – carried out by scientists at University of Turku and Aalto University in Finland and Wageningen University in the Netherlands – found that an unlikely ally could aid us in our quest for a more biodegradable solar sensor. In fact, it might even be in your fridge. <\/p>\n\n\n\n In the study, published in the journal\u00a0ACS Applied Optical Materials<\/a><\/em>, scientists developed UV protection film using nanocellulose – a natural material typically harvested from bacteria or plants that just so happens to be\u00a0the most abundant organic polymer<\/u><\/a>\u00a0on Earth. Then, the team coated the film with other bio-based material to provide\u00a0UV<\/a> protection, including lignin, iron ions, and red onion extract. While these options provided varying levels of protection, red onion extract out performed them all, providing 99.9 percent UV protection. It even outperformed commercial PET filters.<\/p>\n\n\n\n \u201cNanocellulose films treated with red onion dye are a promising option in applications where the protective material should be bio-based,\u201d Rustem Nizamov, the lead author of the study from the University of Turku, said in a press statement<\/a>. \u201cThese results are also relevant for the UV protection of other types of solar cells, including perovskite and organic photovoltaics, as well as any application where the use of a bio-based UV filter is paramount.\u201d<\/p>\n\n\n\n Developing an effective solar cell filter isn\u2019t easy. While the filter<\/a> needs to provide robust UV protection, it also<\/em> needs to allow a significant amount of light transmission in the 700 to 1200 nanometer range\u2014the energy-producing sweet spot for solar cells. The scientists discerned that red onion extract provided 80 percent light transmission between 650 to 1,100 nanometers while maintaining performance over the 1,000-hour testing period (equivalent to roughly one year of sunlight). <\/p>\n\n\n\n This performance-over-time aspect proved especially important because filters treated with iron ions<\/a> performed admirably at first, but degraded rapidly over the testing period. <\/p>\n\n\n\n \u201cThe study emphasized the importance of long-term testing for UV filters, as the UV protection and light<\/a> transmittance of the other bio-based filters changed significantly over time,\u201d Nizamov said in a press statement. <\/p>\n\n\n\n