Fabrication of quasi-hexagonal Si nanostructures and its application for flexible crystalline ultrathin Si solar cells

Optimally designed Si nanostructures can serve as effective light trapping structures for flexible crystalline ultrathin Si solar cells. In this study, we develop a unique quasi-hexagonal inverted nano-pyramid in a hexagonal array, fabricated by a combined process of nanosphere lithography and wet etching. Self-assembled silica nanoparticles were deposited on Si wafers by spin coating, followed by deposition of triangular metal nanodisks in a hexagonal array. The metal nanodisks were used as a wet etch mask in an alkaline solution to create the quasi-hexagonal Si nanostructures. We investigated a temporal evolution of the Si nanostructures with increasing the etch time to optimize optical performances. The newly developed nanostructures take a quasi-hexagonal inverted pyramid, which provides geometrically high compatibility with the self-assembled monolayers in a hexagonal array. We incorporated these quasi-hexagonal nanostructures to the flexible crystalline ultrathin Si solar cells, and the novel nanostructures exhibited optical performances comparable to conventional micro-pyramid textures while showing the enhanced mechanical flexibility of the ultrathin Si-based solar cells.