Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Investigation of the effective operational parameters of self-cleaning glass surface coating to improve methylene blue removal efficiency; application in solar cells Maryam Sadat Hosseini a , Masoud Ebratkhahan b, ⁎ , Zahra Shayegan c , Aligholi Niaei a , Dariush Salari b , Ali Rostami d , Javad Raeisipour b a Catalyst & Reactor Research Group, Department of Chemical & Petroleum Engineering, University of Tabriz, P.O. Box 5166616471, Tabriz, Iran b Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, P.O. Box 5166616471, Tabriz, Iran c Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, Quebec H3G 1M8, Canada d Photonics and Nano-Crystals Research Lab., Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran ARTICLE INFO Keywords: Dip-coating Light transmittance Methylene blue Self-cleaning Solar cell TiO 2 ABSTRACT Among renewable energies, using photovoltaic systems to convert solar energy into electricity without noise, toxin production and release of greenhouse gases has become increasingly important. These panels are diversely used on building roofs in urban areas, which exposes them to problems such as rapid deposition of dust and pollution that reduces light transmittance and cell efficiency. The present study aimed to enhance the self- cleaning ability of the glass surface of the solar cells. Therefore, titanium dioxide (TiO 2 ) coating was applied for ultraviolet light section. TiO 2 doped with nitrogen (N-TiO 2 ) and four metals including copper (Cu-TiO 2 ), cobalt (Co-TiO 2 ), iron (Fe-TiO 2 ) and silver (Ag-TiO 2 ) coating were applied for visible light section. The surfaces were prepared by nanosol/dip-coating method. Using an ultraviolet–visible (UV–Vis) spectrometer, self-cleaning of glass surface, removal of methylene blue (MB) and light transmittance was investigated. Moreover, the prepared samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) analysis. 1. Introduction Environmental pollutions such as air, water and soil pollution are one of the major problems that are encountered in both developed and developing societies in recent decades, which are mostly due to the use of fossil fuels (Beeldens, 2006). Considering the growing global demand for energy and the reduction of fossil fuels and other non-renewable energies, the use of renewable energy sources such as sunlight, wind, tide and geothermal energy has become increasingly important in re- cent years. In the meantime, solar panels have become more prominent with the direct conversion of light energy to electrical energy without sound, toxic and greenhouse gas emissions, as well as relatively low main- tenance costs. To improve the efficiency of solar cells and reduce pro- duction costs, this technology was developed in three generations: si- licon solar cells, thin film solar cells and the third generation solar cells (Zhou et al., 2010). One of the issues that occurs in silicon solar cells is the loss of light, which is mostly due to the reflection of its front surface. To solve this problem, two methods including texturing of the silicon surface and using anti-reflective coatings are employed (Deubener et al., 2009). The other main issue is accumulation of dust on a glass cover of solar cells, which will cause gradual reduction of transmission coeffi- cient. Dust deposition is observed in countries with a dry climate in the Middle East (Gholami et al., 2018, 2017b). Dust accumulation amount depends on the weather, but normally PV surfaces cleaned every 20 days. Mechanical methods, such as blowing, brushing, vibration and ultrasonic excitement are some of the applied methods for dust removal of solar cells. These methods have disadvantages like high-power con- sumption and expenses relating to the machinery maintenance. Com- paring the above mentioned methods, titanium dioxide (TiO 2 ) nano- coatings have better efficiency (Gholami et al., 2017a). In the design of a solar cell, glass is used to trap the light and to reflect more light in the joint zone of the silicon and glass, as well as to protect the cell from air pollutants such as dust and various con- taminants (Deubener et al., 2009). There are three self-cleaning https://doi.org/10.1016/j.solener.2020.06.109 Received 25 March 2020; Received in revised form 11 June 2020; Accepted 29 June 2020 ⁎ Corresponding authors. E-mail addresses: masoudebratkhahan@yahoo.com (M. Ebratkhahan), aniaei@tabrizu.ac.ir, niaei@yahoo.com (A. Niaei). Solar Energy 207 (2020) 398–408 0038-092X/ © 2020 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved. T