Defining Solid Additive's Pivotal Role on Morphology Regulation in Organic Solar Cells Produced by Layer‐by‐layer Deposition

Abstract Herein, two emerging device optimization methods, solid additive and layer‐by‐layer (LBL) process, for organic solar cells (OSCs) are simultaneously studied. Through traditional blend cast and recently proposed identical solvent LBL cast, BDCB (2‐monobromo‐1,3‐dichloro‐bezene), a benzene derivative, is used to improve the device performance based on celebrity combination PM6:L8‐BO. The results reveal that finely optimized BDCB concentration in PM6 solution can push the efficiency of LBL to 19.03% compared to blend cast with only 18.12% while the power conversion efficiency (PCE) changing trend is determined by BDCB's ratio in L8‐BO's precursor. The morphology characterizations confirm there exists no significant stratification for LBL‐processed devices, supported by a previously reported swelling‐intercalation‐phase separation (SIPS) model. Thereby, the solid additive's 2D optimization is considered a smart strategy for finely tuning the SIPS process, which results in various final morphology states. This work not only reports a cutting‐edge efficiency for binary OSCs, but also new insight and deep understanding for LBL method‐based morphology optimization strategy development.