Self-Cleaning Microcavity Array for Photovoltaic Modules

Development of self-cleaning coatings is of great interest for photovoltaic (PV) industry, as soiling of the modules can significantly reduce their electrical output and increase operational costs. We fabricated flexible polymeric films with novel disordered microcavity array (MCA) topography from fluorinated ethylene propylene (FEP) by hot embossing. Due to their superhydrophobicity with water contact angles above 150° and roll-off angles below 5°, the films posses self-cleaning properties over a wide range of tilt angles, starting at 10°, and contaminant sizes (30µm - 900µm). Droplets which impact the FEP MCA surface with velocities of the same order of magnitude as rain, bounce off the surface without impairing its wetting properties. Additionally, the disordered MCA topography of the films enhances the performance of PV devices by improving light incoupling. Optical coupling of the FEP MCA films to a glass-encapsulated multicrystalline silicon solar cell results in 4.6% enhancement of the electrical output compared to an uncoated device.