Solar cells convert the energy of sunlight to electricity. Most cells consist mainly of silicon, but additions of other metals and minerals are being developed and tested to improve efficiency and reduce costs. Thin film cells made from other materials are being developed to reduce the costs of solar cells by reducing the amount of material required. For instance cadmium tellurium photovoltaics are cheaper and have lower water use and a smaller carbon footprint. However tellurium is a very rare element and could limit the production of these cells. The highest efficiency of a thin film solar cell so far has been achieved by a copper indium gallium selenide solar cell. Beside the elements mentioned in the name of this cell, it also contains many others like molybdenum, zinc, cadmium, sulphur and aluminium.