Asymmetric‐Isomerization Dimer Acceptors via Modular Molecular Design Enable Highly Efficient Binary Organic Solar Cells

ABSTRACT Dimer acceptors are attractive for organic solar cells (OSCs) owing to their combination of stability and high efficiency, yet the efficiency of dimer‐based binary devices has long stagnated below 20%. The limitation stems from weak intramolecular charge transfer (ICT) and poor locally excited/charge‐transfer (LE/CT) state hybridization, which are direct consequences of the canceled dipole moments in symmetric dimer architectures. In this work, we adopt an asymmetric‐isomerization strategy to design two novel dual‐asymmetric isomeric dimer acceptors QCl‐YF and QF‐YCl. Compared with QCl‐YF, QF‐YCl exhibits an enhanced ICT effect as evidenced by a larger electron‐hole spatial separation, which promotes LE/CT hybridization and enables more efficient carrier dynamics. Moreover, the stronger electrostatic potential and dipole moment of QF‐YCl enhances the intermolecular interactions to improve donor/acceptor compatibility and film‐forming process in blend film, consequently leading to more ordered film morphology. Consequently, the QF‐YCl‐based device achieves a record PCE of 20.23% (vs. 19.60% for QCl‐YF), achieving the highest efficiency for dimer‐based binary OSCs. This work demonstrates that asymmetric‐isomerization is a precise and effective design strategy for high‐performance dimer acceptors.