Scientists find red onion dye can shield solar cells from UV damage, outperforming conventional plastic filters

A new study has revealed that dye extracted from red onion skins could significantly improve ultraviolet (UV) protection for solar cells. The research published on February 24 in ACS Applied Optical Materials indicates that combining the natural dye with plant-based nanocellulose provides superior UV protection compared to current petroleum-based films.

Solar cells are usually coated with a petroleum-based film to protect against UV-induced degradation. These films include oil-based materials such as polyvinyl fluoride (PVF) and polyethylene terephthalate (PET). The findings may open the door to replacing these oil-based materials with a sustainable alternative drawn from agricultural waste.

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What the study found

The research team demonstrated that a protective film made from nanocellulose infused with red onion skin extract was able to eliminate 99.9 per cent of UV radiation up to 400 nanometers. Remarkably, the filter outperformed a commercial PET-based UV filter currently on the market.

“Nanocellulose films treated with red onion dye are a promising option in applications where the protective material should be bio-based,” says Doctoral Researcher Rustem Nizamov from the University of Turku, in a press release on March 19.

How onion dye could work in solar cells

Researchers compared four types of nanocellulose-based protective films, each treated with different natural additives known for UV-blocking ability: red onion extract, lignin, and iron ions. Among them, the film infused with red onion dye proved the most effective at shielding solar cells from ultraviolet (UV) damage.

Unlike lignin, which absorbs UV but gives films a dark brown tint that limits transparency, the onion-dye filter offered strong UV protection while still allowing more than 80 per cent of visible and near-infrared light (650–1,100 nanometers) to pass through, wavelengths crucial for generating electricity in solar cells.

Importantly, it maintained this performance during 1,000 hours of artificial light testing, equivalent to about a year of outdoor exposure in central Europe.

“The study emphasised 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,” said researcher Nizamov.

Possible use in the future

Looking ahead, the researchers envision solar cell components made from biodegradable materials that could serve as temporary, sustainable power sources, for instance, in food packaging sensors or other short-term electronics. “The forest industry is interested in developing new high-grade products. In the field of electronics, these may also be components for solar cells,” added Professor Kati Miettunen of the University of Turku’s SEMS group, which led the project.