The art of texturing glass for Photovoltaics

Abstract

Thin-film silicon technology creates electricity out of micrometer thick silicon absorber layers, which makes this technology less material heavy compared to classic crystalline technology. This advantage can be further exploited with the transition towards flexible thin-film technology, where the non-modular cost can be further reduced compared to traditional crystalline solar parks ect. However, thin films have limited absorption coefficients at higher wavelengths which means the optical pathlength must be maximised to overcome this limitation. In literature, the highest efficiencies are obtained with the creation of periodic textures resulting in 10.2%, 12.7% or 14% for nanocrystalline, micromorph and triple junction silicon technology. All these cells are made on silicon substrates which means the back of the cell is textured but if the front side of the solar cell is textured, efficiencies can outperform the current holding records. A methodology is designed to create periodic micro-textures on Corning glass to improve the total absorption of lower energetic wavelengths. However, the creation of random micro-textures (Aluminum Zinc oxideand Indium Tin Oxide sacrificial texturing)(AZO-/ ITO textures) is also researched because different methodologies exist and limited knowledge exists on which methodology results in the highest amount of scattering. Second, a comparison between random and periodic textures must be made. Both types of textures undergo optical- and physical parametrisation after which both aspects are correlated to each other to gain a deeper understanding of light management. For random textures, Haze-values between 93-86% are obtained. These high values are obtained because the created craters are characterised by an increased depth for identical crater widths. Second, each methodology has its characteristic depth-width ratio which explains the optical superiority of one (ITO textures). For periodic textures, Haze-values lie between 50-3% with a maximum obtained aspect ratio of 0.18 but the optical response is not comparable to random textures because diffraction is the dominant light management technique. Therefore Angular Intensity Distribution measurements must be performed, which resulted in the conclusion that the created ITO textures stay superior (also compared to literature) while the AZO textures have a similar performance compared to the periodic texture. This translates itself in a superior external quantum efficiency (EQE) of ITO from 800nm on. Between 600-800nm, the periodic textures are superior.