A recent Slovakian study improved the combined anti-reflective and hydrophobic properties in a durable, long-lasting coating suitable for PV modules and other optical systems requiring high transparency and self-cleaning surfaces.
Study Highlights
- Development of a double-layer antireflective (AR) hydrophobic coating on glass using the sol-gel dip coating method.
- Achieved a 7% increase in transmittance at 550 nm compared to uncoated glass.
- The top layer of OTES-modified SiO2 significantly enhanced hydrophobicity.
- The double-layer AR coating maintained adhesion and high transmittance after two years of ambient exposure.
- This highly transparent and hydrophobic coating is suitable for a wide range of practical applications.
Abstract
A double-layer coating was created on glass using sol-gel technology, with a silica-titania (SiO2–TiO2) bottom layer and an OTES-modified SiO2 upper layer. The sols for SiO2 and TiO2 were prepared using TEOS and TIP precursors. The refractive indices of the layers were 1.79 and 1.45, with thicknesses of 76.8 nm and 94.2 nm, respectively. The coating increased transmittance by 7% and improved hydrophobicity, raising the water contact angle from 56° to 102°.
Introduction
AR coatings are used in various optical systems, including photovoltaic (PV) modules, to suppress light reflection and increase transmission. PV cells, which convert solar energy to electricity, benefit from highly transparent glass with AR coatings to maximize efficiency. However, AR coatings must balance refractive indices and thickness to minimize reflection losses. Multilayer coatings, particularly those combining SiO2 and TiO2, are effective but need enhancements in adhesion and mechanical properties. Adding hydrophobic layers can provide self-cleaning properties, crucial for PV applications.
Experiment details
- Preparation of SiO2 Sol: TEOS, IPA, and HNO3 were mixed and aged overnight.
- Preparation of TiO2 Sol: Ti(iPr)4, IPA, HNO3, and AcAc were mixed and aged overnight.
- Preparation of SiO2–TiO2 Sol: Mixed sols at various ratios, aged for a day.
- OTES-Modified SiO2 Sol: TEOS and OTES were combined with IPA and HNO3, then refluxed.
- Deposition: The SiO2–TiO2 and OTES-modified SiO2 coatings were deposited on glass using dip-coating and heat-treated.
Results
- Optimization: The refractive index and thickness of each layer were controlled for optimal AR properties. The SiO2–TiO2 coating’s refractive index was 1.79, and the OTES-modified SiO2 layer was 1.45, with thicknesses of 77.0 nm and 95.9 nm, respectively.
- Optical Properties: The double-layer AR coating achieved 99% transmittance at 550 nm, significantly reducing reflection compared to uncoated glass.
- Wetting Properties: The SiO2–TiO2 layer was more wettable, while the OTES-modified SiO2 and double-layer coatings exhibited high water contact angles and low surface free energy, indicating hydrophobicity.
- Durability and Adhesion: The double-layer AR coating showed excellent adhesion and stability in transmittance after two years of exposure.
Conclusions
The study successfully developed a double-layer AR hydrophobic coating combining SiO2–TiO2 and OTES-modified SiO2 layers. This coating improved light transmission, hydrophobicity, adhesion, and durability, making it suitable for applications like PV modules. The combination of AR and self-cleaning properties in a single coating provides significant advantages for practical use.
Source
High performance double layer hydrophobic antireflective coatings on glass prepared by sol–gel method, Nature, 2024-05-016
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