Self-cleaning performance of superhydrophobic hot-embossed fluoropolymer films for photovoltaic modules

Abstract

The soiling of photovoltaic (PV) modules can significantly reduce their energy yield unless a mitigation strategy is employed. One solution investigated in this work involves the implementation of a passive self-cleaning superhydrophobic top cover. To this end, superhydrophobicity was induced by hot-embossing random microtextures on a highly transmissive and photostable fluorinated ethylene propylene (FEP) film. The impact of fabrication parameters (hot-embossing force and temperature) on achieving high contact angles (> 150°) and low roll-off angles (< 10°), which characterizes a surface as superhydrophobic, were investigated. It was found that a minimum threshold force of at least 15 kN and 5 kN must be used to achieve superhydrophobicity for processing temperatures of 270 °C and 280 °C respectively. Meanwhile at the highest investigated temperature of 290 °C, any force within the investigated range of 500 N to 50 kN suffices. The best fabrication parameters were identified (5 kN at 280 °C), resulting in a contact angle of 156 ± 1° and a roll-off angle of 8 ± 3°. When incorporated into a silicon PV mini-module, the addition of the textured FEP film enhances the short circuit current density (JSC) by 1.1%. Moreover, the self-cleaning properties of the textured FEP films result in a recovery ratio of 93.6% (in terms of JSC), which is significantly greater than that of the reference glass encapsulated PV mini-module (61.1%).