Abstract Electroactive ionenes combining caged‐shaped diazabicyclic cations and aromatic diimides were developed as interlayers in organic solar cells (OSCs). These ionenes reduce the work‐function of air‐stable metal electrodes (e.g., Ag, Cu and Au) by generating strong interfacial dipoles, and their optoelectronic and morphological characters can be modulated by aromatic diimides, leading to high conductivity and good compatibility with active layers. The optimal ionene exhibits superior charge‐transport, desirable crystallinity, and weak visible‐absorption, boosting the efficiency of benchmark PM6 : Y6‐based OSCs up to 17.44 . The corresponding normal devices show excellent stability at maximum power point test under one sun illumination for 1000 h. Replacing Y6 with L8‐BO promotes the efficiency to 18.43 , one of the highest in binary OSCs. Notably, high efficiencies >16 are maintained as the interlayer thickness increasing to 105 nm, the best result with interlayer‐thickness over 100 nm.
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