Porous SiO 2 anti-reﬂective coatings on large-area substrates by electrospinning and their application to solar modules Hemant Kumar Raut a,b,c,d , A. Sreekumaran Nair e , Saman Safari Dinachali a,c , V. Anand Ganesh a,b,c,d , Timothy Michael Walsh d , Seeram Ramakrishna a,b,n a Department of Mechanical Engineering, National University of Singapore, Singapore 117574, Republic of Singapore b Centre for Nanoﬁbres and Nanotechnology, National University of Singapore, Nanoscience and Nanotechnology Initiative, 2 Engineering Drive 3, Singapore 117576, Singapore c Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602, Republic of Singapore d Solar Energy Research Institute of Singapore, National University of Singapore, Singapore 117574, Singapore e Amrita Centre for Nanosciences and Molecular Medicine, Amrita Institute of Medical Sciences and Research Centre, Amrita Vishwa Vidyapeetham University, Kerala 682 041, India article info Article history: Received 15 May 2012 Received in revised form 22 October 2012 Accepted 12 December 2012 Available online 17 January 2013 Keywords: Anti-reﬂective coatings Electrospinning Porous SiO 2 Solar modules abstract Fabrication of large-area anti-reﬂective coatings (ARCs) on glass substrates by using a cost-efﬁcient and simple approach, especially for applications in photovoltaics, remains a challenge. This study proposes electrospinning as a technique to fabricate porous SiO 2 ARCs on large-area glass substrates (20  20 cm 2 ). The existing electrospinning setup is modiﬁed to enable large-area glass coatings and electrospinning process parameters are optimized to achieve sub-wavelength ARCs. The post-sintered SiO 2 ARC is thoroughly characterized for the ﬁlm morphology and optical properties. The transmittance for one-side and both-sides coated glass is found to be 94.3% and 96% respectively. The anti-reﬂective glass is incorporated in solar modules to determine the increase in short circuit current. The increase in short-circuit current is found to be 3%. Electrospinning as a fabrication technique has potential in offering a cost effective solution for synthesizing ARCs on large-area substrates for photovoltaic applications. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Anti-reﬂective coatings (ARCs) have played an important role in boosting the amount of sunlight coupled to solar cells, thus enhancing the efﬁciency of the solar cells [1–3]. ARC made from PE-CVD-deposited SiN x have been used on Si wafer solar cells for many years [4,5]. More recently, there has been interest in applying ARCs to the front side of the cover glass of photovoltaic (PV) modules to further reduce reﬂectance and increase PV performance [6]. In addition, ARCs have been used to reduce reﬂectance in several other applications such as surface-emitting lasers [7], optical data storage [8], camera lenses [9] and eye- glasses [10]. The glare reduction property of ARCs have been used in sensors for aeronautical applications [11], automotive glass [12] and ﬂat panel displays [13]. The anti-reﬂective property can be achieved by using mono- layer coatings of sub-wavelength thickness (l/4) with refractive index matched to the geometric mean of the refractive indices of the media above and below [1]. Destructive interference of the reﬂected light rays at the interfaces is the key here. This idea is extended in multi-layer coatings [1,14] that exhibit broadband anti-reﬂection properties. Porous SiO 2 layers of sub-wavelength thickness have proved quite effective in exhibiting anti-reﬂective properties on glass substrates. [15,16] ARCs have been fabricated by conventional nanofabrication techniques such as plasma-enhanced chemical vapor deposition (PE-CVD) [17,18], glancing angle deposition (GLAD) [19], magne- tron sputtering [20] as well as simple inexpensive techniques such as spin coating [21] and hydro thermal growth [22]. Emer- ging new techniques such as nano-imprint lithography (NIL) have also been used to fabricate highly efﬁcient moth eye nanostruc- ture arrays [23]. However, in all these techniques, there is a trade- off between the cost of coating and the size of the substrate. Industrial coating techniques such as CVD, PVD, sputtering, etc. are also highly cost intensive, and the cost increases as the size of the substrate increases. Dip-coating and spin-coating on the other hand are simple and inexpensive techniques. However, in case of dip coating the coating is produced on both sides, which may not be desired in many cases, especially when the glass has materials of different refractive index on either side, e.g., in a solar module. One-side dip coating techniques have also been devised, but they Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.solmat.2012.12.023 n Corresponding author at: National University of Singapore, Centre for Nano- ﬁbres and Nanotechnology, Nanoscience and Nanotechnology Initiative, 2 Engi- neering Drive 3, Singapore, Singapore 117576. E-mail address: seeram@nus.edu.sg (S. Ramakrishna). Solar Energy Materials & Solar Cells 111 (2013) 9–15