Researchers have developed a PFAS-free double-layer sol-gel and hydrophobic silica coating that repels water, dust and dirt while maintaining high light transmission for solar panels. The transparent, self-cleaning coating improved photovoltaic efficiency from 13.90% to 14.56%, demonstrating strong durability and potential for future commercial applications.
An international research team has double-layer sol-gel and hydrophobic silica coating which can significantly improve the performance of solar cells by protecting the surface against dust accumulation, light reflection, bird droppings and water films.
“The double-layer coating repels water, dust and dirt without reducing the amount of light reaching the photovoltaic cells,” said the study’s corresponding author Shanhu Liu. pv magazine. “Unlike many other solutions on the market, it is made without forever chemicals, or per- and polyfluoroalkyl substances (PFAS).”
“Dust, dirt and bird droppings all affect the performance of solar panels. Maintenance can damage the panels, is expensive and sometimes a logistical challenge,” says co-author Sudhagar Pitchaimuthu. “Our clear, highly water-repellent coating works by combining a thin, self-adhesive base layer with hydrophobic silica nanoparticles that stay in place as the material cures. The microscopic roughness created by these particles traps air on the surface, causing water to pool and roll away, taking with it dirt. The result is a durable, transparent coating with strong self-cleaning properties.”
In the newspaper “Sol-gel preparation of transparent and superhydrophobic silica coatings for self-cleaning solar panels”, published in Colloids and surfaces A: physicochemical and technical aspectsthe scientists described the protective film as a double-layer transparent superhydrophobic coating that combines sol-gel-processed hydrophilic silica sol with hydrophobic silica nanoparticles.
The sol-gel process is a wet chemical method used to produce thin films, coatings or solid materials from a liquid precursor. Liquid precursors react by hydrolysis and condensation to form a colloidal solution (sol). As the reactions proceed, the particles connect into a three-dimensional network, turning the sol into a gel. The gel is then deposited on a surface and heat treated to form a thin, solid coating, such as an anti-reflective coating used in solar panels.
For the new coating, the research group used glass slides as substrates and chemicals such as tetraethyl orthosilicate (TEOS), ethanol, ammonia solution and hydrophobic silica nanoparticles. The glass substrates were first ultrasonically cleaned with detergent and ethanol, rinsed with deionized water, and dried to remove contaminants. Then, a silica sol was prepared using TEOS, ethanol, water, and ammonia as catalysts to promote hydrolysis and condensation reactions.
After aging, the sol formed a transparent solution that was used to coat the glass via a dip coating process, followed by drying to obtain a hydrophilic silica layer. To create a superhydrophobic surface, hydrophobic silica nanoparticles were dispersed in ethanol and deposited on the coated glass through repeated dip coating cycles. The number of coating cycles and nanoparticle concentrations were varied to optimize optical transmission and surface wettability. The samples were then sintered at different temperatures to improve the stability and performance of the coating.
The quality, composition and performance of the coating were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy.
The analysis showed that the coating exhibits excellent superhydrophobicity with a water contact angle of approximately 154° and a sliding angle of 1.5°. High optical transparency was also achieved, with transmission reaching 96.2% thanks to the refractive index gradient created by the silica layers. Mechanical testing also showed strong durability against abrasion, sand impact and water droplet impact, the scientists said, noting that the coating also showed good chemical stability in neutral and acidic environments and maintained performance during outdoor exposure.
Finally, the coating, applied as a cover glass for photovoltaic cells, increased light transmission and improved the efficiency of the solar cells from 13.90% to 14.56%.
“Improving the performance of solar cells and panels could have an incredible cumulative effect,” says co-author Sanjay S. Latthe.
“A range of coatings have been introduced to the market over the last twenty years, but they all have their limitations. Our next focus is to test the coating in panels in extreme weather conditions, from Scottish winters with low temperatures and rainfall to desert conditions in Dubai. We should have our product on the market within five years, if not sooner.”
The research team included scientists from China’s Research Institute of Petroleum Exploration and Development and Henan University, as well as India’s Vivekanand College and Heriot-Watt University in the United Kingdom.
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