Combined anti-soiling and anti-reflection coatings for solar modules

The cover glass on solar modules provides protection for the underlying solar cells but also leads to two forms of power loss: reflection losses and soiling losses. In this work we explore the addition of a thin hydrophobic layer of refractive index n=1.35 to the outer surface of a broadband multilayer anti-reflection (MAR) coating, comparing modelling with the actual performance of the coating. Systems with hydrophobic layers from 5nm to 300nm in thickness deposited on the surface of a broadband AR coating have been modelled, with reflectance curves and weighted average reflection (WAR) calculations showing that the total reflection stays below that of uncoated glass at all thicknesses. However, the optimal coating is determined to be ∼5nm in thickness. Addition of the hydrophobic layer increases the water contact angle of the MAR coating from 7° to 114°, with a significant increase in anti-soiling properties. This provides proof of principle of the benefits of combining a high performance AR coating with a hydrophobic anti-soiling coating on module cover glass.