Superhydrophobic surfaces with antireflection properties for solar applications: A critical review

Antireflective surfaces with superhydrophobic characteristics are of considerable current interest owing to their potential utility in solving key technological problems. Superhydrophobic surfaces possess self-cleaning characteristics due to their unique surface texture and chemistry, which control wettability. The surface micro/nano texturing combined with low surface energy of materials lead to enhance anti-wetting properties. Self-cleaning surfaces exhibit special anti-wetting properties owing to the water contact angle greater than 150° leading to the ready rolling-off of water droplets. The surfaces can be made hydrophobic using two key pathways: i) making a rough surface from a low surface energy material, and ii) making a rough surface and modifying it with material of low surface energy. Similarly, transparent surface coatings with suitable optical path differences can suppress reflection from surfaces. High transparency is crucial in improving the performance of optical equipment and devices, such as windows, lenses, solar panels, etc. A normal solar panel absorbs only about 25% of the incident solar radiation, the remainder being reflected. Design and implementation of transparent super hydrophobic surfaces that repel atmospheric dust from solar panels, and thus reduce reflectivity of the surfaces are thus highly desirable. In this review, recent developments in antireflective, transparent, and superhydrophobic surfaces, with particular emphasis on glass and polymer materials, are highlighted. The review contains four sections as follows: (i) brief description of the basic concepts and principles of antireflection and self-cleaning; (ii) detailed fabrication pathways and their mechanisms; (iii) challenges faced in practical applications; and (iv) trends of future developments. Overall, a comprehensive overview of antireflective surfaces with superhydrophobic characteristics is provided in light of the current challenges.