This lecture discusses the importance of photovoltaics in transitioning to a sustainable society due to finite fossil fuel reserves and global warming. It explores the economical impact of photovoltaic power plants and the potential for ultra-high efficiency using tandem solar cells. The synergy approach combines high-efficiency technologies with low-cost ones, addressing technological challenges and achieving scientific impact. The lecture also covers the performance and reliability of GaAs nanowire cells, perovskite cells, and their up-scaling to mini-modules, as well as the development of near-infrared transparent cells and 4-terminal tandem cells. An energy harvesting demonstrator showcasing tandem cells controlled by low-power boards is presented.