Researchers in Spain developed a porous silica anti-reflective coating for solar panels that boosts optical transmission while balancing durability and mechanical stability through optimized sol–gel chemistry.
A research team led by Spain’s Center for Energy, Environmental and Technological Research (CIEMAT), has developed a novel anti-reflective (AR) coating for use in solar panels.
“By jointly tuning pore-forming agent concentration, thermal treatment, and silica precursor chemistry, we show that it is possible to tailor coatings that combine near-unity transmittance with mechanical and environmental stability suitable for real solar installations,” said corresponding author Gema San Vicente to pv magazine. “This balance is essential for solar systems, where even small optical gains are only meaningful if the coating survives years of outdoor exposure.”
“A particularly surprising finding was that prolonged thermal treatment does not necessarily improve durability,” she went on to say. “In highly porous coatings, longer calcination times significantly reduced mechanical resistance, despite maintaining excellent optical performance. This shows that processing conditions that seem beneficial from a materials perspective can have unintended negative effects when porosity is pushed to extreme levels.”
To balance optical performance and mechanical and environmental durability, the scientists tested different pore-forming agent concentrations, thermal treatment conditions, and silicon precursor ratios.
They prepared silica precursor solutions with varying ratios of methyltriethoxysilane (MTES) and tetraethyl orthosilicate (TEOS), specifically TEOS:MTES ratios of 50:50, 70:30, and 90:10. Ethanol and deionized water were then added in the presence of sulfuric acid as a catalyst to form the sol–gel solution. The mixture was stirred for 24 hours to promote hydrolysis and condensation reactions. Next, pore-forming agent Pluronic P-123 was added in concentrations between 0 and 3.3% v/v.
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Solar transmittance gain vs bare glass
Image: CIEMAT-PSA
The coatings were deposited on 3-mm-thickness borosilicate glass substrates and polished silicon wafers. When different TEOS:MTES ratios were tested, the Pluronic concentration was kept at 2.5% v/v. In contrast, when the different Pluronic concentrations were analyzed, the TEOS: MTES ratio was kept at 50:50. All samples underwent thermal treatment at 500 C for 15 minutes or 1 hour to evaluate the effect of thermal treatment on the final coating properties.
According to the research team, the addition of Pluronic effectively reduced the refractive index, thereby enhancing AR properties by increasing porosity. At the same time, the TEOS:MTES ratio played a key role in determining the coatings’ porosity and durability. Samples sintered at 500 C for 15 minutes maintained better abrasion resistance and structural integrity than those sintered for 1 hour.
Ultimately, optimal balanced performance was achieved with 2% v/v Pluronic and a TEOS:MTES ratio of 70:30. Moreover, an increase of up to 5.2% in optical transmission was achieved compared to bare glass, with transmittance reaching 99.8% at 600 nm.
“We have a follow-up research focused on further improving the balance between optical performance and durability under real operating conditions,” Gema San Vicente concluded. “In particular, we are investigating double configurations, combining an external surface more durable and with anti-soiling properties to reduce sensitivity to moisture and soiling, with an internal ultra-high optical transparent layer.”
The new AR coating was presented in “Tailored highly transparent porous silica coatings for enhanced optical and mechanical performance of solar covers,” published in Materials & Design. Scientists from Spain’s CIEMAT, the Autonomous University of Madrid, and Slovenia’s National Institute of Chemistry have contributed to the research.
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