Special Anti-Fog Coatings to Boost Efficiency in Solar Panels

Polymeric materials are increasingly becoming part of our daily lives. Despite being discovered in the early 20th century, within just a century nearly countless polymer varieties and applications have emerged. Among these applications, polymeric coatings are now visible in many sectors, from the paints industry to aerospace, construction and automotive sectors. Special coatings beyond paints have been developed over time.

Over time, polymeric coatings have evolved from being merely corrosion-preventive coatings to become one of the "Functional Materials" that exhibit very special effects and can significantly alter the surface they coat. Within functional materials, anti-fogging coatings are critical for many different applications across diverse sectors. [caption id="attachment_103491" align="aligncenter"] Figure 1[/caption] Solar cells are growing rapidly in our country and worldwide and emerging as a very important energy sector for the world. The effective operation of solar cells depends on many factors. One of these, contrary to what is thought, is not the intense and hot arrival of sunlight. It is known that at lower temperatures and when sunlight radiates through clouds, solar cells are more effective [1]. The location photographed in Figure 1 is the United Kingdom, and solar cells are actively used in rainy Britain. Another issue is the cleaning of solar cells and the fogging that forms on them. Fog formation occurs when sunlight does not arrive clearly and in cloudy environments. The need to prevent fog formation emerges. Coatings that prevent fog formation form the basis of our work. In the studies conducted, it was determined that fog formation prevents light from effectively reaching the solar cells. Below is detailed work by 3M company on how light will be effective on the surface with the anti-fogging coating it applies. High-efficiency solar cells require high absorption rates of incoming solar radiation. In commercial monocrystalline and polycrystalline Si cells based on solar cell plates, absorption is routinely improved through surface texturing with pyramid shapes of a few micrometers. This texture increases light scattering in the cell through a non-reflective silicon nitride coating. This approach is not practical for thin-film silicon solar cells where the absorbing layer thickness is on the order of 1-3 µm and can even be less. In these cells, the surface of the material used as a substrate or solar glass is engineered to increase absorption. The cover glass comprises approximately 25% of silicon thin-film (Si) modules and approximately 10-15% of crystalline Si modules. For this reason, improving the cover glass becomes necessary to reduce costs. In this context, there are two ways to be effective on glass to reduce costs. The first would be to reduce costs in glass manufacturing and the second would be to increase solar light transmission through the glass; because a 5% increase in solar transmittance can result in up to a 10% improvement in efficiency. Normal coatings are typically porous SiO2, Si2 N3 or MgF2 films, generally do not have self-cleaning capability and therefore do not have high hydrophobicity that would require maintenance. Self-cleaning primers are one way to achieve less maintenance. There are two low-cost and scalable techniques related to self-cleaning surface technology; spray coating and dip coating. By modifying the roughness of the surface at the nano scale, it is possible to create hydrophilic surfaces that prevent fogging or create hydrophobic surfaces with self-cleaning effects [2,3]. For high-performance solid state dye-sensitized solar cells (ssDSSCs), a simple method is provided to produce anti-fogging (AF) and anti-reflection (AR) coating functionalized photoanodes through single-step SiO2 nanoparticle coating. In this method, AF and AR coating functionalized photoanodes are prepared by spin coating a partially assembled SiO2 colloidal solution. Poly ((1- (4-ethenylphenyl) methyl) -3-butyl-imidazolium iodide) (PEBII), prepared by free radical polymerization, is used as a solid electrolyte in I2-free ssDSSCs. Under fogging conditions, UV-visible spectroscopy and incident photon-electron conversion efficiency (IPCE) curves are systematically investigated for the improved light harvesting properties of ssDSSCs based on AF and AR coating functionalized photoanodes. Compared to conventional photoanode-based ssDSSCs, AF and AR coating functionalized photoanodes significantly suppress fogging and reduce reflection, particularly leading to significantly improved light harvesting under fogging conditions. ssDSSCs made from AF and AR coating functionalized photoanodes exhibit improved photovoltaic efficiency of 6% and 5.9% under fogging and fogging conditions, respectively, and maintain device efficiency for at least 20 days; this contrasts with conventional photoanodes for ssDSSCs (4.7% and 1.9% under fogging and fogging conditions, respectively). AF and AR functionalization through single-step SiO2 colloidal coating is a promising method to improve light harvesting characteristics in various solar energy conversion applications [3] In another study on anti-fogging coatings, a polymer-silica coating with superhydrophilicity, high transparency and anti-fogging properties was produced through a low-cost single-step cap sol-gel method without any additional chemical modification. Figure 2 shows the effect of the antifog coating [4]. Composite solutions were prepared using two different production methods: one-step-one pot and two-step-two pot, both involving free radical and sol-gel reactions. The wettability of these surfaces and their anti-fogging performance were investigated depending on the content of silica particles. At the same time, the effects of changes in production technique on the wettability and anti-fogging properties of these surfaces with 20% silica particle content by weight were also examined. [caption id="attachment_103492" align="aligncenter"] Figure 2[/caption] In another study on anti-fogging coatings, a polymer-silica coating with superhydrophilicity, high transparency and anti-fogging properties was produced through a low-cost single-step cap sol-gel method without any additional chemical modification. Figure 2 shows the effect of the antifog coating [4]. Composite solutions were prepared using two different production methods: one-step-one pot and two-step-two pot, both involving free radical and sol-gel reactions. The wettability of these surfaces and their anti-fogging performance were investigated depending on the content of silica particles. At the same time, the effects of changes in production technique on the wettability and anti-fogging properties of these surfaces with 20% silica particle content by weight were also examined. It has been shown that superhydrophilic, transparent, anti-fogging surfaces can be prepared using an environmentally friendly coating technique. The mechanism of the coating developed by 3M company is also indicated in Figure 3. This is suitable for industrial applications such as self-cleaning car windows, eyeglasses, bathroom mirrors and especially outdoor solar cells [5]. Our research group, which conducts research on polymeric materials, is working on anti-fogging coating studies and various formulation experiments due to sector needs in this area. In particular, a new venture is being launched in Teknopark for these coatings that could increase solar cell efficiency by 5%. References 1. Hamdi, R.T.A., Hafad, S.A., Kazem, H.A., Chaichan, M.T., 2018. "Humidity impact on photovoltaic cells performance: A review", International Journal of Recent Engineering Research and Development, Volume3-Issue11, 27-37. 2. Baquedo, E., Torne, L., Cano, P., Postigo, P.A., 2017. "Increased efficiency of solar cells protected by hydrophobic and hydrophilic anti-reflecting nanostructured glasses", Nanomaterials, Volume7-Issue12, 437-448. 3. Park, J.T., Kim, J.H., Lee, D., 2014. "Excellent anti-fogging dye-sensitized solar cells based on superhydrophilic nanoparticle coatings", Nanoscale, 6, 7362-7368. 4. Duran, I. R., Laroche G., 2019, "Water drop-surface interactions as the basis for the design of anti-fogging surfaces: Theory, practice, and applications trends", Advances in Colloid and Interface Science, 263, 68-94. 5. Topçu Kaya, A.S., Cengiz, U., 2019. "Fabrication and application of superhydrophilic antifog surface by sol-gel method", Progress in Organic Coatings, 126, 75-82. Dr. M. Özgür Seydibeyoğlu İzmir Kâtip Çelebi University Faculty of Engineering Materials Science and Engineering Nihan Özveren İzmir Kâtip Çelebi University Faculty of Engineering Materials Science and Engineering