Copper indium gallium di-selenide (CIGS) is a semiconductor material composed of copper, indium, gallium, and selenium. It has a chemical formula of CuInxGa(1-x)Se2. CIGS is tetrahedrally bonded, with the chalcopyrite crystal structure, and a bandgap varying continuously with x  from about 1.0 eV (for copper indium selenide) to about 1.7 eV (for copper gallium selenide). It is used as light absorber for thin-film solar cells.