According to scientists, red onion dyes may be a lacking ingredient necessary to enhance ultraviolet (UV) protection in solar cells.
Solar cells are usually coated with petroleum-based films to protect against UV-induced decomposition. These films include oil-based materials such as vinyl fluoride (PVF) and polyethylene terephthalate (PET).
Nanocellulose has emerged as the forefront in its quest to promote the adoption of films made from more sustainable biologically based materials. Nanocellulose comes from plant-based materials and is produced by decomposition of cellulose into nanoscale fibers.
Researchers behind the new study found that combining nanocellulose with dyes made from skin extracts of red onion provides “very effective UV protection.” The team released their findings at ACS Applied Optical Materials on February 24th.
This study pointed out that the protective film made from this material eliminated 99.9% of UV radiation and eliminated a maximum wavelength of 400 nanometers. In particular, this filter outperformed the commercial pet-based UV filters currently available on the market.
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This represents “a promising option for applications where protective materials should be bio-based,” said Rustem Nizamov, a doctoral researcher at the University of Turk in Finland, in a statement.
Important tradeoffs
In this study, researchers compared the durability of four protective films made from cellulose nanofibers. These were treated in a variety of ways with edoonion extracts, lignin (a polymer found in the walls of several plant cells), and iron ions.
All of these provided adequate protection against UV rays, but the red onion dye option emerged as the most effective.
Solar cells face serious trade-offs, with UV radiation proven to be harmful at below 400 nm, the study states. However, visible light transmission – wavelengths between 700 and 1,200 nm – is important to allow cells to convert radiation into electricity.
With this in mind, it is important to develop materials that protect solar cells and promote energy absorption. For example, lignin is dark brown and, according to the statement, “restricts use in clear films.”
“The transmittance of these lignin-containing films is typically 50% between 400 and 600 nm, up to 85% above 600 nm,” the researchers added.
In comparison, nanocellulose membranes treated with red onion dye exceeded 80% light transmission at long wavelengths (650-1,100 nm) and maintained performance throughout the extended test period.
During this test period, we evaluated the durability and performance of the filter by placing the filter under artificial light for 1,000 hours. This corresponds to approximately one year of sunlight in the Central European climate. Nizamov said that this test period underscored the importance of long-term testing of UV filters. “For example, films treated with iron ions had good initial permeability that was reduced after aging.”
Nizamov said the study would have a major impact on a variety of solar cells, particularly perovskite and organic solar power generation, as well as other industries that require the use of bio-based filters.
This includes, for example, food packaging that allows biodegradable solar cells to be used as a source of sensors in sterile environments.
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