Crystallinity‐Engineered Schiff‐Base Nickel Cathode Interlayers for Thermally Stable and High‐Efficiency Organic Solar Cells

ABSTRACT Stable and efficient cathode interlayers (CILs) materials pivotal to achieving efficient and stable organic solar cells (OSCs). Here, we report a library of ten Schiff‐base nickel complexes engineered as CILs and investigate their device performance and stability. Given their exceptional charge‐transport and interfacial properties, three structurally distinct representatives (Ni‐Nap, Ni‐Ph, and Ni‐CH ₃ ) were strategically selected for mechanistic investigation. When incorporated into PM6:L8‐BO OSCs, devices with Ni‐CH ₃ achieved a power conversion efficiency (PCE) of 19.31%, surpassing Ni‐Ph (18.40%) and Ni‐Nap (15.11%). Notably, an even higher PCE of 20.01% was achieved in D18:L8‐BO OSCs. Ni‐CH ₃ possessed the lowest crystallinity, and its morphologically stable, crack‐free nature was conclusively demonstrated by comprehensive structural characterization techniques. Therefore, Ni‐CH ₃ ‐employed device exhibited outstanding storage stability, with a T80 lifetime exceeding 816 h, significantly surpassing those employing of Ni‐Nap and Ni‐Ph (<24 h). This work overcomes the stability challenge of Schiff‐base nickel complexes when employed as CILs in OSCs, establishing them as outstanding candidate CILs for high performance OSCs.