Anti-reflective coatings (ARCs) have evolved into highly effective reflectance and glare reducing components for various optical and opto-electrical equipments. Extensive research in optical and biological reflectance minimization as well as the emergence of nanotechnology over the years has contributed to the enhancement of ARCs in a major way. In this study the prime objective is to give a comprehensive idea of the ARCs right from their inception, as they were originally conceptualized by the pioneers and lay down the basic concepts and strategies adopted to minimize reflectance. The different types of ARCs are also described in greater detail and the state-of-the-art fabrication techniques have been fully illustrated. The inspiration that ARCs derive from nature ('biomimetics') has been an area of major research and is discussed at length. The various materials that have been reportedly used in fabricating the ARCs have also been brought into sharp focus. An account of application of ARCs on solar cells and modules, contemporary research and associated challenges are presented in the end to facilitate a universal understanding of the ARCs and encourage future research.

This review article summarizes the key areas of self-cleaning coatings, primarily focusing on various materials that are widely used in recent research and also in commercial applications. The scope of this article orbits around hydrophobic and hydrophilic coatings, their working mechanism, fabrication techniques that enable the development of such coatings, various functions like Anti-icing, Electrowetting, Surface switchability and the areas where selfcleaning technology can be implemented. Moreover, different characterization techniques and material testing feasibilities are also analyzed and discussed. Though several companies have commercialized a few products based on self-cleaning coating technology, much potential still remains in this field.

This review article exemplifies the importance of self-cleaning materials and coatings. Selfcleaning coatings are becoming an integral part of our daily life because of their utility in various applications such as windows, solar panels, cements, paints, etc. In this review, various categories of materials for the fabrication of hydrophilic, hydrophobic, oleophobic, amphiphobic and multifunctional coatings and their synthesis routes have been discussed. Furthermore, different natural organisms exhibiting superhydrophobic behaviour have been analysed. This review also covers the fundamentals of self-cleaning attributes such as water contact angle, surface energy, contact angle hysteresis, etc. Fig. 1 Pictures of water droplets on Lotus (left) and Ramee (right) leaf indicating the self-cleaning property inherent in nature. 1 Inset of a: pictures of water droplet on Lotus (left) and Ramee leaf (right) indicating their inherent selfcleaning nature.

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