Publisher Summary Among the different thin film technologies, the family of chalcopyrites has so far demonstrated the highest efficiency for solar cells in the laboratory as well as in production. A large number of chalcopyrites exhibit direct bandgaps and relatively narrow luminescent bands (sometimes at low temperatures only) made them an interesting candidate to obtain stimulated emission/ laser action. It could be demonstrated that stimulated emission could be achieved in six of the ternary compounds by brute force pumping with either a high-voltage electron beam or laser pumping. Thin film copper indium gallium selenide (CIGS) solar cells have exceeded 20% efficiency in 2010 and are almost at the same level as polycrystalline solar cells now. The ability to combine the Cu(In,Ga)(S,Se)2 materials family internally as well as with other materials to form multijunctions leaves the pathway open to further efficiency increases, especially for concentrator concept. However, to continue this road, further fundamental research to understand the basic material properties of the respective components as well as the interface behaviors is of great importance.