Fluorinated Perylene‐Diimides: Cathode Interlayers Facilitating Carrier Collection for High‐Performance Organic Solar Cells

Abstract Organic solar cells (OSCs) have experienced rapid progress with the innovation of near‐infrared (NIR)‐absorbing small‐molecular acceptors (SMAs), while the unique electronic properties of the SMAs raise new challenges in relation to cathode engineering for effective electron collection. To address this issue, two fluorinated perylene‐diimides (PDIs), PDINN‐F and PDINN‐2F, are synthesized by a simple fluorination method, for application as cathode interlayer (CIL) materials. The two bay‐fluorinated PDI‐based CILs possess a lower lowest unoccupied molecular orbital (LUMO) energy level of ≈−4.0 eV, which improves the energy level alignment at the NIR‐SMAs (such as BTP‐eC9)/CIL for a favorable electron extraction efficiency. The monofluorinated PDINN‐F shows higher electron mobility and better improved interfacial compatibility. The PDINN‐F‐based OSCs with PM6:BTP‐eC9 as active layer exhibit an enhanced fill factor and larger short‐circuit current density, leading to a high power conversion efficiency (PCE) exceeding 18%. The devices with PDINN‐F CIL retain more than 80% of their initial PCE after operating at the maximum power point under continuous illumination for 750 h. This work prescribes a facile, cost‐effective, and scalable method for the preparation of stable, high‐performance fluorinated CILs, and instilling promise for the NIR‐SMAs‐based OSCs moving forward.