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

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.