Abstract:The power conversion efficiencies of organic solar cells (OSCs) have now reached high values approaching 20%. These recent advances in OSCs based on non-fullerene acceptors (NFAs) come with reduced non-radiative voltage losses. In contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the non-radiative voltage losses in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining dynamic vibronic simulations with temperature-dependent electroluminescence experiments, we provide a unified description of non-radiative voltage losses for both fullerene- and NFA-based devices. We highlight that the photoluminescence yield of the pristine materials defines the lower limit of non-radiative voltage losses. We also demonstrate that the reduction in non-radiative voltage losses (for example, <0.2 V) can be obtained without sacrificing charge generation efficiency. We further extend our understanding to ternary OSCs, providing rational materials design rules for the third component in efficient ternary devices.