Characterization of reliability of anti-soiling coatings using tapping mode-AFM phase imaging

Power loss due to dust deposition on photovoltaic (PV) modules (also referred to as soiling) is a severe challenge to the economic viability of PV deployment in sunbelt countries like India and the Middle East. Anti-soiling coatings are nano/micrometer thick transparent coatings, which mitigate dust deposition on PV module. In this study, Tapping Mode Atomic Force Microscopy (TM-AFM) phase imaging was used to characterize the surface changes of four different commercial hydrophobic anti-soiling coatings as they were subjected to outdoor field exposure tests and three different indoor accelerated stress tests. The anti-soiling coatings were applied via manual spray coating method on solar glass substrates. The phase angle for not-coated glass shows a tight distribution around zero. The phase angle distribution of coated surface showed a larger spread. When the coatings were subjected to different environmental stressors, the phase angle distributions became tighter and, in some cases, collapsed to tight distributions around zero, indicating that the coatings were partly or completely removed from the glass surface. We demonstrate a correlation of the changes in surface coverage identified from phase angle distributions to contact angle and surface roughness, thus establishing TM-AFM phase imaging as a promising approach to characterize anti-soiling coatings subjected to environmental stress. While the analysis of the phase angle distribution is able to resolve the removal of the coating, contact angle and surface roughness cannot do so unambiguously.