Testing the abrasion resistance of porous SiO₂ anti-reflection coatings for solar cover glass

The cover glass sheet on solar modules can cause reflection losses as well as soiling build-up. Reflection losses can be addressed with anti-reflection (AR) coatings, whilst soiling is removed by mechanical cleaning processes that are effective but can have adverse effects on surface coatings. In this work, multilayer broadband and commercial porous SiO₂ AR coatings have been subject to abrasion testing that simulates the regular cleaning of solar modules in the field, using Felt Pad and CS-10 abradant materials. The Felt Pad abrasion has no impact on the multilayer coating, but caused visible damage to the porous SiO₂, increasing WAR from 5.97% to 6.75% after 100 cycles. After 50 and 100 abrasion cycles of CS-10, significant scratches are visible on the porous SiO₂ coating, and the weighted average reflectance (WAR) of the coating increases from 5.97% to 7.08% after 100 cycles. The coating is fully removed in some abraded areas. The multilayer AR coating also experiences some damage after CS-10 abrasion, increasing WAR from 5.84% to 6.68%. Optical microscopy and Scanning Electron Microscopy (SEM) show the nature of the abrasion damage caused. Overall, the multilayer AR coating shows significantly higher abrasion resistance than the porous SiO₂. Significant abrasion damage to porous SiO₂ AR coatings is a major problem for solar asset managers resulting in long-term power losses.