Surface wettability effects on self-cleaning efficacy: Outdoor experimental study

Self-cleaning coatings of photovoltaic (PV) panel and building glass have received a great deal of attention over the last two decades, using both hydrophobic and hydrophilic treatments. Here, we present a comparison study of the outdoor self-cleaning performances of superhydrophilic, hydrophobic and superhydrophobic glass coatings, over 200 days, using different tilt angles. It was found that the average transmission of all the samples linearly decreased over time after rainfall. We have defined relative self-cleaning efficacy (RSCE), using the average transmission difference of coated and uncoated samples, at a given tilt angle. We have found that the RSCE depends on both surface wettability and tilt angle. The superhydrophobic coating was found to have the best RSCE, with the superhydrophilic coating next, although both superhydrophobic and superhydrophilic coating have similar RSCE when cleaned by rainfall. Surprisingly, the RSCE is higher at a lower tilt angle for all the samples, despite a higher transmission at a higher tilt angle, suggesting that the RSCE is higher at lower tilt angles due to weaker interaction between dust particles and the surfaces.