Additive‐Induced Fibrillation of Acceptor Enhances the Efficiency of Sequentially Deposited Organic Solar Cells Approaching 20%

Abstract In organic solar cells (OSCs), it is often desirable to have a fibril‐like morphology, which is considered an effective way to enhance exciton dissociation and diffusion due to its long‐range order and abundant interfaces. In this work, three selenium‐based morphological modifiers, DBrS, DPSE, and DPDSE are used to induce fibril formation of the acceptor. Introducing heavy atoms, these additives tune intermolecular interactions, enabling the acceptor to self‐assemble into nanofibrils with improved crystallinity. By employing the sequential deposition method, the well‐formed fibril‐like morphology is preserved, leading to a favorable match between the morphological characteristic parameters (crystallinity, drying dynamics, and vertical composition distribution) and the optoelectronic parameters (the increased exciton diffusion length, exciton dissociation, and charge transport). Ultimately, the Se‐based additives lead to 19.5% and 19.8% power conversion efficiencies for the halogenated‐solvent and the fully non‐halogenated‐solvent processed OSCs, offering an innovative strategy based on the additive design of high‐efficiency photovoltaics.