## 1 Introduction  
As the Paris Agreement was signed in 2015 to limit the global temperature increase and to reduce carbon emissions, 195 countries agreed that they would set and implement their own greenhouse gas reduction targets until the launch of the post-2020 climate regime in 2020. Among the renewable energy sources, solar power generation is the most eco-friendly power generation method that does not generate pollution and use fossil fuels. Such solar power generation requires large installation areas to produce a large amount of power and must be installed outdoors to receive sunlight. This causes different performances depending on the installation environment [1; 2; 3; 4]. Photovoltaic (PV) modules installed outdoors are exposed to various pollutants, such as yellow dust, bird excrement, and rainfall sediment. Such pollutants reduce the sunlight that enters PV modules and thereby lower power generation efficiency. Therefore, various studies have been underway recently to effectively prevent the surface pollution of PV modules [5; 6].  
The PV module surface coating materials being researched must have anti-pollution functions and endure severe external temperature differences, as well as external shocks, and they must also endure chemical factors, such as bird's excrement and acid rain. In addition, they must have a light transmittance of 95% or higher [7; 8]. Existing solar power plants have been installed in large areas to produce a large amount of power and, thus, a massive amount of time and cost is required for maintenance, including surface cleaning. Therefore, if pollutants can be easily removed using natural rainfall, the economic efficiency of solar power generation systems will be significantly improved. For the development of a coating material capable of enduring physical and chemical environments, the development of innovative source materials and coating processes are required. Currently, surface self-cleaning coating technology using photocatalysts is available, but this technology has low durability due to its low adhesion and hardness. It also requires energy sources that cause catalysis, and the facility investment cost is low as is demand [9]. In addition, studies have been conducted for decades to prevent fogging on transparent surfaces. One representative method among the methods to address such problems is to modify these surfaces into hydrophilic or hydrophobic surfaces or to apply a coating [10].  
As hydrophobic coatings form water droplets in a nearly perfect spherical shape, water droplets remove dust particles from the surface as they roll off. In this case, however, an appropriately rough surface is required and this rough surface may reduce the transmittance by increasing light scattering [11]. On the other hand, a hydrophilic coating removes dust by spreading water on the surface instead of forming water droplets on the surface. This method allows water droplets to spread between pollutants and the substrate surface, thereby removing the pollutants to be attached to the substrate and letting them flow with water droplets [12; 13; 14; 15; 16]. The water-soluble polymer materials TiO\({}_{2}\) and silica are known to have excellent hydrophilicity [17]. In this study, we used silica-based material with high light transmittance and durability as a functional material for the anti-pollution function of cover glass for PV modules.  
As such, this study aims to propose a new coating process technology that can improve the anti-pollution characteristics of PV modules. First, a hydrophilic silica-based coating material was coated on the surface of cover glass for PV modules and annealed, and then the anti-pollution characteristics were analyzed. In this instance, gas was injected when annealing was performed. The annealing ambient conditions were H\({}_{2}\), N\({}_{2}\), Ar, O\({}_{2}\), and vacuum. For the fabricated functional coating films, the contact angle, anti-pollution characteristics, transmittance, hardness, surface adhesion, and morphological properties were measured.