# Sample, Scalable Route to Produce Transparent Superhydrophobic/Hydrophilic Film Surfaces
## 1 Introduction  
Solar energy is one of the most reliable and environmentally friendly sources of backup power. The recent rise in photovoltaics (PVs) alongside wind turbines [1, 2] has accelerated the employment of renewable energy sources and helped reduce carbon emissions from the production of electricity via conventional methods. However, the initial cost and ongoing maintenance expenses are the main disadvantages PVs face. Additionally, the PV panel's exposed surface, which absorbs solar energy, significantly impacts the panel's efficiency [1]. Therefore, efficiency will be considerably reduced if this exposed surface becomes covered with dust or water droplets [3, 4]. Typically, manual cleaning is costly and hostile to the environment because it requires a lot of water and detergents. Researchers have demonstrated several active and passive self-cleaning techniques for maintaining the conversion efficiency of PV panels [4, 5, 6, 7, 8, 9, 10, 11]. Active methods mainly consist of two approaches: electrostatic and mechanical. Power sources must generate triboelectric charging and dielectric forces to apply the electrostatic approach to remove dust [12, 13]. NASA first developed the electrostatic dust-repellent kit [14]. It consists of a parallel electrode coupled to a single-phase AC voltage source that creates standing waves and pushes Mars dust particles away. Three years later, The University of Tokyo's Aoyama Japan group substantially improved the initial dust-repellent kit by developing the multiple-phase voltage [15]. The standing and traveling waves produced by the multiple-phase voltage carry the dust particles together with the electric field. As a result, a strong electric field must overcome the cohesive force and gravitational force of dust particles. Since more electric sources are needed to create a potent electric field strong enough to drive dust particles away, this electrostatic approach cannot be used with a PV system. In addition, the dust-repellent kit does not work as efficiently on days when it rains or the weather changes. On the other hand, the mechanical cleaning approach needs power to move the cleaning robots [16; 17], spray nozzles [2], and mechanical PV panel wipers. The main drawbacks of mechanical cleaning are the use of large electric power sources and the development of micro-scratches on the PV panel surfaces. Due to considerable problems with the active cleaning technique, advancements in coating application technologies in recent years, and the possibility of using sophisticated materials, passive self-cleaning is gaining more attention. Both superhydrophobic and superhydrophobic coatings fall within the category of the passive approach. The key benefit of this approach is that it does not need electricity to generate any movement when the PV panel is cleaning itself. Furthermore, natural raindrops can easily wash off the organic pollutants and small particles on the glass panel. For PV panel applications, transparent self-cleaning coatings have been demonstrated by researchers worldwide to increase conversion efficiency. Utilizing spin-coating and reactive ion etching, [PERSON] et al. created the self-cleaning coating on solar-cell glass [18]. The produced superhydrophobic self-cleaning coating has an optical transmission coating of 88% in the wavelength range of 300-800 nm, and a WCA of about 154\({}^{\circ}\). After being cleaned by wind or water, its self-cleaning ability can restore the solar cells' efficiency up to 99% and 100%, respectively [19]. Using hydrophobic dual-sized silica nanoparticles and an acid-catalyzed silica precursor, a substrate-flexible method for the fabrication of strong antireflective and superhydrophobic coatings with excellent self-cleaning properties in a range of environments was developed by [PERSON] et al. [20]. Another group developed a transparent superhydrophobic alumina-based coating utilizing spin-coating technology and a thermal-heating process at 400 \({}^{\circ}\)C, substantially simplifying the fabrication process [21].