Solar cells with the highest efficiencies deliver electricity cost-effectively, demanding less space and materials. High efficiencies also enable new products, such as energy-independent buildings or electric cars, which can be recharged via solar cells. However, the efficiency of silicon solar cells can no longer be arbitrarily increased. The physical limits responsible for this can be overcome using tandem solar cells. With them, efficiencies above 35% are possible. Tandem solar cells are therefore in the focus of current solar cell research. At the same time, the photovoltaic capacity added annually will increase to more than 1 TWP worldwide within the next 5–10 years. These quantities also mean that critical materials (e.g. lead) are to be consistently avoided in the production of solar modules. Consequently, in the Fraunhofer MaNiTU project, six Fraunhofer institutes are joining forces in developing sustainable, highly efficient and cost-effective tandem solar cells based on new absorber materials.