Morphological Homogeneity and Interface Modification as Determinant Factors of the Efficiency and Stability for Upscaling Organic Solar Cell

Abstract Morphological homogeneity and interfacial traps are essential issues to achieve high‐efficiency and stable large‐area organic solar cells (OSCs). Herein, by the investigation of three quinoxaline‐based acceptors, i.e., PM6:Qx‐1, PM6:Qx‐2, and PM6:Qx‐p‐4Cl, the performance degradation in up‐scaling OSCs is explored. The inhomogeneous morphology in PM6:Qx‐2 induces a nonuniform spatial distribution of charge generation, showing a rapid decline in efficiency and stability in large‐area OSCs. In comparison, the homogeneous morphology in PM6:Qx‐1 and PM6:Qx‐p‐4Cl alleviates the stability drop. When utilizing 2‐phenylethylmercaptan to fill the interfacial traps, the stability drop disappears for PM6:Qx‐1 and PM6:Qx‐p‐4Cl, while it persists for PM6:Qx‐2. The PM6:Qx‐1 large‐are device yields a high efficiency of 13.47% and superior thermal stability (T 80 = 2888 h). Consequently, the interface modification dominates the performance degradation of large‐area devices with homogeneous morphology, while it cannot eliminate the traps in inhomogeneous film. These results provide a clear understanding of degradation mechanisms in upscaling devices.