Nanoimprinted sol-gel materials for antireflective structures on silicon solar cells

Silicon solar cells are typically textured by means of wet chemical etching in order to enhance absorption. Within this work, we apply an optically functional layer onto a planar silicon surface. This layer is made of a high refractive index sol-gel material and can be patterned by nanoimprint lithography (NIL). In first experiments, we investigated various sol-gel based TiO2 precursors and evaluated their refractive index as well as the possibility to apply them in NIL. The refractive index was determined to be up to 2.25 using ellipsometry. This result was achieved with a solution composed of amorphous TiO2 precursors mixed with ethanol and 1,5-pentanediol. The topography of the patterned TiO2 layers were investigated using an atomic force microscope (AFM) and a scanning electron microscope (SEM) revealing a period of 1 mm and a pattern depth of 60 nm after sintering. Furthermore, optical modeling was used to optimize the structure parameters in order to minimize the weighted reflectance of an encapsulated silicon solar cell.