The Influence of Donor/Acceptor Interfaces on Organic Solar Cells Efficiency and Stability Revealed through Theoretical Calculations and Morphology Characterizations

End‐groups halogenation strategies, generally refers to fluorination and chlorination, have been confirmed as simple and efficient methods to regulate the photoelectric performance of non‐fullerene acceptors (NFAs), but a controversy over which one is better has existed for a long time. Here, two novel NFAs, C9N3‐4F and C9N3‐4Cl, featured with different end‐groups were successfully synthesized and blended with two renowned donors, D18 and PM6, featured with different electron‐withdrawing units. Detailed theoretical calculations and morphology characterizations of the interface structures indicate NFAs based on different end‐groups possess different binding energy and miscibility with donors, which shows an obvious influence on phase‐separation morphology, charge transport behavior and device performance. After verified by other three pairs of reported NFAs, a universal conclusion obtained as the devices based on D18 with fluorination‐end‐groups‐based NFAs and PM6 with chlorination‐end‐groups‐based NFAs generally show excellent efficiencies, high fill factors and stability. Finally, the devices based on D18: C9N3‐4F and PM6: C9N3‐4Cl yield outstanding efficiency of 18.53 % and 18.00 %, respectively. Suitably selecting donor and regulating donor/acceptor interface can accurately present the photoelectric conversion ability of a novel NFAs, which points out the way for further molecular design and selection for high‐performance and stable organic solar cells. The donor/acceptor interface structures and features show an obvious influence on blending phase‐separation morphology and charge transport behavior. It is not reasonable to simply judge the quality of fluorinated and chlorinated acceptors without suitable selection of donors, and regulating donor/acceptor interfaces can accurately present the photoelectric conversion ability of a novel acceptors.