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

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.