Assessment of optical transmittance of oil impregnated and non-wetted surfaces in outdoor environment towards solar energy harvesting

Self-cleaning of optically transmitting surfaces is important to improve the performance of solar harvesting devices in harsh environments such as dust and humid ambient. Non-wetting characteristics of surfaces can create self-cleaning effects while lowering efforts required to remove dust from surfaces. Non-wetting, in which the texture has been filled with some lubricant, have robust self-cleaning characteristics than surfaces with air pockets trapped between the textures. Consequently, non-wetting surface in which the textures are impregnated with silicone oil is examined in relation to solar energy harvesting applications. In this case, a hierarchal texture is generated first onto the transparent glasses by the convective assembly of silica particles. The resulting textures are characterized incorporating scanning electron and atomic force microscopes. The textures are then impregnated with silicone oil after functionalization with OTS (Octadecyltrichlorosilane). Non-wetting behavior, film thickness and transmittance of the resulting surface are assessed using contact angle goniometer, ellipsometer, and UV-Visible spectrophotometer. The resulting surfaces are tested in outdoor environments and transmittance reduction of UV-visible spectrum is assessed. It is found that silicon oil impregnation improves water droplet mobility at the surface; however, optical transmittance reduces significantly over the time due to dust particles settlement at the silicon oil film interface.