Reviewed by Lexie CornerMar 20 2025
Researchers from the University of Turku in Finland investigated the production of efficient UV protection films for solar cells using bio-based materials. The study is the first to compare the long-term changes in the properties of various bio-based UV filters.
Doctoral Researcher Rustem Nizamov observes dye-sensitized solar cells in a laboratory. Image Credit: Väinö Anttalainen
Petroleum-based films, such as polyvinyl fluoride (PVF) and polyethylene terephthalate (PET), are commonly used to protect solar cells from UV-induced degradation.
Materials engineering research is focused on finding bio-based alternatives, including nanocellulose, to replace oil-based polymers. Nanocellulose is created by breaking cellulose into small fibers, which can then be treated in various ways to provide UV protection.
A recent study by Wageningen University in the Netherlands, and the University of Turku and Aalto University in Finland, found that nanocellulose colored with red onion skin extract provides excellent UV protection. The nanocellulose film blocked 99.9 % of UV radiation up to 400 nm, outperforming the commercial PET-based UV filter used as the industry standard in the study.
Nanocellulose films treated with red onion dye are a promising option in applications where the protective material should be bio-based.
Rustem Nizamov, Doctoral Researcher, University of Turku
The study examined the properties and durability of four different cellulose nanofiber-based protective films. The nanocellulose films were coated with red onion extract, lignin, and iron ions, all of which have demonstrated effective UV-blocking properties in previous studies. The film coated with red onion extract was found to be the most effective at blocking UV rays.
Preserving Transmission of Visible Light
UV light (below 400 nm) can damage solar cells, but transmission of visible and partial infrared light, particularly between 700 and 1,200 nm, is essential as this light is used by solar cells to generate power.
When developing bio-based materials, there is often a trade-off between UV protection and visible light transmission. For example, lignin, a natural polymer with UV-absorbing properties, has a dark brown color, which limits its use in clear films.
The film coated with red onion dye demonstrated more than 80 % light transmission at longer wavelengths (650–1,100 nm), making it a promising option. The film also continued to perform effectively during the extended testing period.
The performance and durability of the filters were tested for 1,000 hours under artificial light, which is equivalent to about one year of outdoor sunlight in central Europe’s climate. Visual changes in the solar cells and filter materials were tracked using digital photography.
The study emphasized the importance of long-term testing for UV filters, as the UV protection and light transmittance of the other bio-based filters changed significantly over time. For example, the films treated with iron ions had good initial transmittance, which reduced after aging.
Rustem Nizamov, Doctoral Researcher, University of Turku
Dye-sensitized solar cells were used to test the UV filter films, as they are particularly vulnerable to UV-induced damage.
“These 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,” said Nizamov.
The research aims to develop biodegradable solar cell types that could be used as power sources for applications such as sensors in food packaging.
The forest industry is interested in developing new high-grade products. In the field of electronics, these may also be components for solar cells.
Kati Miettunen, Professor, Materials Engineering, University of Turku
The University of Turku's Solar Energy Materials and Systems (SEMS) research group is investigating the integration of solar energy and systems into the broader energy network. The study was part of the BioEST project, supported by the Finnish Research Council.
Journal Reference:
Nizamov, R., et al. (2025) Sustainable Nanocellulose UV Filters for Photovoltaic Applications: Comparison of Red Onion (Allium cepa) Extract, Iron Ions, and Colloidal Lignin. ACS Applied Optical Materials. doi/10.1021/acsaom.4c00484?goto=supporting-info