Interfacial Dipole Engineering Suppresses Charge Recombination for Achieving High‐Performance Binary Organic Solar Cells With 20.26% Efficiency

ABSTRACT Rational molecular engineering of cathode interlayers (CILs) is critical for boosting photovoltaic performance in organic solar cells (OSCs). Herein, a perylene diimide (PDI)‐based CIL (PDINB‐BP) is synthesized via quaternization strategy. The quaternary ammonium groups in PDINB‐BP endow it with a strong molecular dipole moment, excellent alcohol solubility, and facile synthesis, while suppressing excessive aggregation when depositing CIL. As a result, PDINB‐BP efficiently modulates the work function ( WF ) of silver (Ag) electrode from 4.68 to 3.98 eV. Furthermore, it also enhances the interfacial CIL‐cathode adhesion, reduces defects, and induces a strong oriented interfacial dipole at cathode interface to accelerate electron transport and suppress charge carrier recombination. Through using PDINB‐BP as CIL, the binary OSC achieves a champion power conversion efficiency (PCE) of 20.26% and an excellent fill factor (FF) of 81.26%. To the best of our knowledge, this PCE is one of the highest reported data by using a very simple‐structured PDI‐based CIL in a binary OSC. Moreover, PDINB‐BP integrates a broad universality within various active layers including non‐fullerene and all‐polymer systems, excellent thermal stability, and remarkable thickness tolerance. This practical quaternization engineering in CIL design offers a feasible strategy for developing high‐efficiency and stable OSCs.