Large area, low cost anti-reflective coating for solar glasses

• A low-cost, large-area AR coating has been developed for c-Si and thin-film solar modules.
• An absolute transmission increase of up to 3.6 % is reported for single-side coated glass.
• The coating relies on wet-deposition of aqueous silicate solutions and atmospheric treatment.
• The process of coating deposition and consolidation is elucidated.

We present on line formation of a sol from wet-deposited aqueous potassium silicate solutions as a novel route for the generation of highly performing large-area anti-reflective (AR) surfaces on glasses for solar energy conversion. Compared to alternative technologies, the present approach enables processing at very low cost. The mechanism of coating formation and consolidation was evaluated. Following deposition, the aqueous potassium silicate solution dries into a gel of interconnected SiO2 colloids and dispersed potassium hydroxides and carbonates. A typical size of ~20–40 nm of the colloids is established already at this stage without significant growth in the later process. Potassium species are removed in a subsequent washing procedure, leaving only a minor amount of residual potassium at the interface between coating and substrate in an otherwise nanoporous silica layer. Physically and chemically bound water species are driven-out of the coating in a final annealing step. In this way, an AR layer of nanoporous silica with a thickness of ~100–150 nm is easily created. The AR effect is caused by two-beam interference at this layer, enabling an absolute transmission increase of 3.6% at a wavelength of 550 nm and a relative transmission increase of 3.1% over the spectral range of 400–1100 nm for a single-side coating on solar glass for c-Si as well as thin-film modules.