• Energy Research

Reflection from the front glass of solar modules causes over 4% optical loss leading to a significant decrease in module efficiency. Single layer solution gelation (sol-gel) anti-reflective (AR) coatings are effective over a narrow range of wavelengths, whereas reflection losses can be reduced over a broader wavelength when multilayer broadband AR coatings are applied. In this work, three different multilayer AR coatings including 4-layer SiO2/ZrO2, 4-layer SiO2/ITO, and 6-layer SiO2/ZrO2 were deposited using magnetron sputtering. The abrasion resistance is important because the coatings will be subject to regular cleaning cycles. A variety of abraders including Felt pad, CS-10 and CS-8 under different loads are used. The optical performance and durability of these coatings were analyzed using a spectrophotometer, optical microscope, scanning electron microscope, and scanning white light interferometer. No damage was observed after abrasion of the coatings with a felt pad under 1 and 2 N loads. However, there was a slight increase in Weighted Average Reflection. When coatings were tested with CS-10 and CS-8 abraders, coatings with ZrO2 resulted in higher scratch resistance in comparison to coating with ITO. However, all-dielectric broadband AR coatings are more durable and have better optical performance compared to single layer sol-gel coatings.

Abstract Natural soiling and the subsequent requisite cleaning of photovoltaic (PV) modules result in abrasion damage to the cover glass. The durability of the front glass has important economic consequences, including determining the use of anti-reflective and/or anti-soiling coatings as well as the method and frequency of operational maintenance (cleaning). Artificial linear brush abrasion using Nylon 6/12 bristles was therefore examined to explore the durability of representative PV first-surfaces, i.e., the surface of a module incident to direct solar radiation. Specimens examined include silane surface functionalized-, roughened (etched)-, porous silica-coated-, fluoropolymer-coated-, and ceramic (TiO2 or ZrO2/SiO2/ZrO2/SiO2)-coated-glass, which are compared to monolithic-poly(methyl methacrylate) and -glass coupons. Characterization methods used in this study include: optical microscopy, ultraviolet–visible–near-infrared (UV-VIS-NIR) spectroscopy, sessile drop goniometry, white-light interferometry, atomic force microscopy (AFM), and depth-profiling X-ray photoelectron spectroscopy (XPS). The corresponding characteristics examined include: surface morphology, transmittance (i.e., optical performance), surface energy (water contact angle), surface roughness, scratch width and depth, and chemical composition, respectively. The study here was performed to determine coating failure modes; identify characterization methods that can detect nascent failures; compare the durability of popular contemporary coating materials; identify their corresponding damage characteristics; and compare slurry and dry-dust abrasion. This study will also aid in developing an abrasion standard for the PV industry.