On the generation and fate of free carriers in non fullerene acceptor organic solar cells Organic solar cells offer an efficient and cost effective alternative for solar energy harvesting. This type of photovoltaic cell typically consists of a blend of two organic semiconductors an electron donating polymer and a low molecular weight electron acceptor to create what is known as a bulk heterojunction (BHJ) morphology. Traditionally fullerene based acceptors have been used for this purpose. In recent years the development of new acceptor molecules so called non fullerene acceptors (NFA) has breathed new life into organic solar cell research enabling record efficiencies close to 19%. Today NFA based solar cells are approaching their inorganic competitors in terms of photocurrent generation but lag in terms of open circuit voltage (V_OC). Interestingly the V_OC of these cells benefits from small offsets of orbital energies at the donor NFA interface although previous knowledge considered large energy offsets to be critical for efficient charge carrier generation. In addition there are several other electronic and ...