Organic solar cells (OSC), a part of the larger emerging field of organic electronics, have the potential to become a very cheap, large area and flexible photovoltaic technology that can in principle scale up fast to terawatt in installed capacity. However, to tap their potential, many questions on the scientific fundamentals need to better understood. The underlying theme of this project is advance the understanding of OSC and making OSC become a reality. To achieve this goal, the project will generate knowhow in three strands of research and bring together in stable OSC with high efficiencies: molecular p- and n-doping of organic semiconductors, structure-property relationships, and degradation mechanisms of OSC. To address these fundamental questions and carry out reliable experiments, this research will use highly purified small molecules, molecular doping technology, and the excellent control of vacuum processes for the deposition of thin organic films. These are the same technologies that made commercial organic light emitting diodes (OLEDs) a reality, and recent results for OSC point in a similar direction, showing that this unique approach not only allows for solid fundamental studies, but also world record OSC. This research will address key question of how molecular p- and n-doping works and how to improve it, how the chemical structure of molecules influences the optoelectronic properties of OSC made with them and how to derive better working molecules, how the degradation of OSC takes place and how it can be slowed down, and how to bring these results together to stable OSC with high efficiencies, and at the same time generating knowhow that is of benefit for the future of organic electronics in general.