Most of the solar cells that convert sun light into electricity are based on crystalline silicon, en expensive material, whereas the remainder uses polycrystalline thin film cells, mostly cadmium telluride/cadmium sulfide. These thin film cells are cheaper to produce yet are based on rare and rather toxic elements. Therefore, “the demonstration of high efficiency in thin film solar cells based on abundantly available and cheap materials like as used in these perovskite based solar cells, allows for an increasing share of solar energy in the mix of renewable resources