Photovoltaics (PV) is a viable alternate energy source, as it is clean, reliable and unlimited. High throughput manufacturing technologies for high efficiency thin-film and crystalline-silicon cells are required. Many universities and business firms are testing different materials and developing new ways of harvesting energy. Rugate filters are being developed for a super-high-efficiency solar-concentrator system in which the sunlight focuses on the entrance of the sphere. Thin film materials are good alternatives for making solar cells in which layers of different electricity producing materials are applied sequentially to glass, plastic or steel backing.