Solar cell development has been a key research topic at Fraunhofer ISE since its founding forty years ago with the aim of increasing efficiencies, reducing costs and saving valuable material resources. Our competence in the tandem technology is based on decades of research on the development of multi-junction solar cells. In the concentrator technology we have achieved efficiences up to 47.6 %. This is presently the highest efficiency reached to date by any solar cell worldwide. Largely promising are the newest approaches of tandem cell architectures where we focus on the development of both III-V-silicon and perovskite-silicon tandem solar cells.