Olefin–Ag d – π Coupling Enables Organic Solar Cells With >83% Fill Factor

ABSTRACT In this study, we have discovered a previously neglected interface modification mechanism. Specifically, isolated olefin moieties are capable of donating π‐electrons to metal surfaces, which in turn generates an interfacial dipole and leads to a substantial reduction in the electrode work function. This strategy demonstrates broad applicability across a range of olefin‐containing molecules. Through comparative studies on various metals, it has been determined that silver (Ag) exhibits the most pronounced π→metal donation interaction. When olefin‐functionalized materials are employed as the cathode interlayer (CIL) in organic solar cells (OSCs), they can enhance the built‐in electric field, promote the formation of ohmic contact, improve charge extraction efficiency, and suppress trap‐assisted recombination, resulting in a power conversion efficiency (PCE) of 20.88% with a high fill factor over 83% in D18:L8‐BO system. Further analysis by depth‐profile x‐ray photoelectron spectroscopy (XPS) reveals a significant suppression of Ag migration, highlighting the ability of olefin CILs to enhance device stability. Our research indicates that olefins represent a novel class of electrode‐modifying groups with stable chemical properties and electron‐donating characteristics, offering promising prospects for the development of high‐performance, long‐lifetime organic photovoltaic cell technologies.