Sustainable Preparation of a Superhydrophobic and Low-Reflective Polymer Film with Hierarchical Microstructure for Solar Cells

The actual photoelectric conversion efficiency of solar cells that work outdoors for a long time is easily affected by adverse environmental factors, including dust, rain, ice, and snow accumulation. At present, most of them adopt manual maintenance methods to cope with the impact of adverse environmental factors. In recent years, some researchers have prepared a superhydrophobic surface by constructing rough microstructures, utilizing their self-cleaning and anti-icing functions to improve this situation. However, constructing rough microstructures also increases surface reflectivity, which is not conducive to the absorption of light energy by the solar cell. In response to this issue, this study proposes a preparation method for superhydrophobic and low-reflective polymer film with hierarchical microstructure based on wire electrical discharge machining (WEDM) and a template method. The hierarchical microstructure includes surface discharge morphology (micrometer) and surface texture (submillimeter). First, the simulation models for solid-liquid contact angle and reflectivity on the surface with hierarchical microstructures are established. To obtain a large contact angle and low reflectivity, the influence of discharge process parameters and the design parameters of surface texture (submillimeter) on the solid-liquid contact angle and reflectivity on the surface discharge morphology (micrometer) is analyzed. Subsequently, WEDM is used to prepare the metal template. The hierarchical microstructure characterization, wettability, and reflectivity tests on the metal template are completed to verify the rationality of discharge process parameters and surface texture design parameters. Finally, based on the prepared metal template, the template method is used to prepare the polymer film. The hierarchical microstructure characterization, wettability, reflectivity, anti-icing, self-cleaning, and photoelectric conversion efficiency of the polymer film are systematically studied. The experimental results show that, on the metal template, the surface discharge morphology (micrometer) can reduce the average reflectivity from 48.31% to 25.13% and increase the contact angle from 58.15° to 133.23°. Besides, the hierarchical microstructure can further reduce the average reflectivity to 4.79% and increase the contact angle to 163.4°. In addition, on the polymer film, the forming rate of surface texture is higher than 95%, and the micrometer discharge pits and protrusions on the metal template can be successfully replicated into the polymer film. Compared with smooth PDMS films, the prepared hierarchical microstructure PDMS films can increase the actual photoelectric conversion efficiency from 12.60% to 13.20%. More importantly, the prepared polymer film also has good anti-icing and self-cleaning properties. This enables it to effectively reduce the impact of adverse environmental factors, such as snow and dust in nature, on the efficiency of solar cells. This breaks the contradictory situation of sacrificing reflectivity in the preparation of superhydrophobic surfaces. Hence, the preparation method of superhydrophobic and low-reflective polymer film with hierarchical microstructure and provide some basic theory and enabling technology for improving solar energy utilization efficiency.