## 1 Introduction  
A typical photovoltaic (PV) module can be classified as a conventional or light weight module. In a conventional module, glass is used as a top cover and accounts for approximately 70% of the module weight. On the contrary, in lightweight c-Si PV modules, glass is replaced by acrylic (poly methyl methacrylate: PMMA) or other polymers [1; 2; 3] to enable such modules to be used in applications where the light weight of the PV module must be limited. Reflection losses are one of the major issues that decrease the effective efficiency of PV modules. A reflection loss of approximately 8% occurs at the front surface of the glass and PMMA because their higher refractive indexes are higher than that of air [4]. This issue can be resolved by using an anti-reflection coating (ARC) material with an ultra-low refractive index (much lower than that of glass) on the front surface of glass. The use of ARC has already been recognized as crucial for various optical and PV panel applications [5; 6]. A simple and cost-effective ARC comprises a single layer coating of a material with a refractive index suitable for the desired wavelength spectrum [7]. In this context, optical coatings of fluoride and oxide materials have been investigated widely owing to their higher band gap. Optical coatings have been widely used in the areas of optoelectronics [8], optics [9], and PV modules [10].  
Recently, magnesium fluoride (MgF\({}_{2}\)) has gained much attention as an ARC suitable for application on the front cover of PV modules, owing to its low refractive index (\(n\) = 1.37 at 600 nm); however, it was proven to be less durable in outdoor environments [11]. CaF\({}_{2}\) belongs to a similar category of materials and has been widely investigated by the optics community [12], owing to its lower refractive index (1.43 at 600 nm), when compared to that of glass substrates. It also has a broad transmittance spectrum from 130 to 10,000 nm [13]. Furthermore, it exhibits less solubility in water when compared to MgF\({}_{2}\)[14], which can be a significant factor in view of the chemical resistance towards environmental conditions. Furthermore, it is also used as an ARC in outdoor conditions, optical applications, IR imaging system, and photolithography systems [15]. Therefore, the application of CaF\({}_{2}\) as an ARC for PV modules has been explored in this work. It is important to note that the excellent surface uniformity of ARC is highly dependent on the deposition technique. Numerous techniques have been introduced for depositing CaF\({}_{2}\) thin films on substrates for various purposes such as electron beam evaporation [16; 17; 18; 19], radio frequency magnetron sputtering [20], molecular beam epitaxial [21], pulsed laser deposition [22; 23] and thermionic vacuum arc [24]. Of these techniques, thermal evaporation has been found to be the most suitable because of its advantages of large-area deposition, low-temperature, and simple process, and it has been proven to be a cheap fabrication process [25].  
In this work, a CaF\({}_{2}\) coating was deposited by vacuum thermal evaporation on borosilicate glass (BSG). In this process, the substrates were tilted and rotated at constant speed, resulting in the uniform deposition of the material. The thickness of the ARC was first optimized using the Essential Macleod simulation tool. The optical properties of the thermally evaporated CaF\({}_{2}\) on the glass substrate were investigated using ultraviolet-visible spectroscopy. The electrical performance of the solar cell (SC) was compared by replacing the uncoated glass (Un CG), with CaF\({}_{2}\)-coated glass (CG) in a conventional PV module and placing a thin CaF\({}_{2}\)-CG between the PMMA and SC in the light weight PV module.