Fabrication and characterization of transparent, self-cleaning glass covers for solar photovoltaic cells Arkadeep Datta a , Vikash K. Singh a , Chayan Das a , Arijit Halder b , Debajyoti Ghoshal b , Ranjan Ganguly a,⇑ a Department of Power Engineering, Jadavpur University, Kolkata 700106, India b Department of Chemistry, Jadavpur University, Kolkata 700032, India article info Article history: Received 21 May 2020 Received in revised form 12 July 2020 Accepted 13 July 2020 Available online 16 July 2020 Keywords: Solar photovoltaic cells Self-cleaning glass cover Superhydrophobic surfaces Sol-gel preparation Nanocomposites Wettability abstract Solar photovoltaic (SPV) cells have become ubiquitous in meeting the increasing global energy demand, but they face major challenge of performance degradation due to dust on the SPV panels. The traditional mechanical methods of cleaning are costly and time consuming. To ameliorate this problem, a ‘‘self- cleaning” superhydrophobic coating is laid on the upper glass cover of SPV array that repels water. This promotes droplet roll-off, enabling a very small amount of water to clean the surface. Herein, such a coating on glass has been developed by depositing 10–20 nm silica nanoparticles via a facile sol–gel method on glass surface and grafting a layer of fluoroalkylsilane above it. Surface roughness, wettability and durability of the fabricated coating are characterized through surface profiling, contact angle mea- surements and droplet impact test, respectively. The treated surface shows an attenuation of 6 ± 1.24% of the incident radiation, while the SPV voltage output is only slightly affected. Moreover, the treated sur- faces show significantly better recovery in the SPV-cell performance upon cleansing with a measured quantity of water than that observed with the untreated surface. Ó 2020 Elsevier B.V. All rights reserved. 1. Introduction Solar photovoltaic (SPV) cells have emerged as key player in global renewable energy sector. Despite its ubiquity, a major unre- solved problem in SPV-based technology is the accumulation of dust on SPV panels, which degrades the conversion efficiency over time. Periodic cleaning of the SPV panels are often restricted by water budget and manpower restrictions. Development of novel surfaces through micro- and nano-engineering has opened a new approach towards fabrication of ‘‘self-cleaning” covers for SPV pan- els to resolve this problem. The idea is to lay, on the upper glass cover of the SPV panels, a superhydrophobic coating of extremely low contact angle hysteresis [1]. A water droplet, sprinkled on such an inclined surface, would roll-off (Fig. 1(a)), picking up the depos- ited dust, thus performing self-cleaning with minimal water usage and without any physical intervention. Such attribute is typically obtained on a low-energy surface with micro- and nano-scale roughness features. However, the surface roughness on the glass surface increases scattering, thus posing a limitation on its trans- missivity. The challenge in developing self-cleaning glass cover for SPV cells can be met by striking a balance between the reduced transmissivity at the relevant wavelengths and the enhanced self- cleaning behaviour [2]. The above-mentioned tasks have been attempted by several groups using different approaches. Chen et al. [3] fabricated a transparent, stable, and superhydrophobic surface by dip-coating silica colloid particles and diethoxydimethylsilane cross-linked sil- ica nano-particles on glass. Zuo et al. developed a transparent superhydrophobic surface by grafting ZnO nanorods through mag- netron sputtering [4]. Zhou et al. [5] developed a self-cleaning paint by containing amino silicon oil-modified palygorskite and aminopropyl-triethoxysilane, but it was opaque. Verma et al. [6] proposed a non-lithographic nanostructuring of glass surface through SF 6 plasma etching and found that 200 nm size structures gave the best optical transmissivity. Ming et al. [7] prepared a superhydrophobic film with hierarchical roughness via Stöber method, which was later adopted by Deng et al. [8] for fabricating a transparent superhydrophobic surface. While all these studies have successfully demonstrated achieving a certain combination of transparency and superhydrophobicity, they have not extended the studies to verify the SPV cell performance improvement upon cleansing the dust with a specified water budget. Herein, we address this issue in a single study through develop- ing a durable, self-cleaning, superhydrophobic coating on a glass cover, and quantifying the improvement it renders to the perfor- mance of an underlying SPV cell under different dust loads. Exper- https://doi.org/10.1016/j.matlet.2020.128350 0167-577X/Ó 2020 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: ranjan.ganguly@jadavpuruniversity.in (R. Ganguly). Materials Letters 277 (2020) 128350 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue