DIM Additive-Induced Morphology Engineering for Efficient Nonfullerene Organic Solar Cells

The photovoltaic performance of organic solar cells (OSCs) is fundamentally governed by the bulk heterojunction morphology of the active layer for its critical influence on charge generation, transport, and carrier recombination. In this study, diiodomethane (DIM) was employed as a processing additive in the D18:L8-BO-based binary OSCs to optimize active layer morphology. The DIM molecular migration-driven morphology optimization improves the phase separation and crystallinity of the active layer simultaneously during the film formation process. This morphology engineering approach facilitates enhanced intermolecular interactions, particularly through halogen bonding, resulting in well-ordered molecule stacking with long-range uniformity. The optimized active layer morphology enhances charge transport and collection while suppressing charge recombination effectively, yielding an impressive power conversion efficiency (PCE) of 19.31%. This work not only establishes an effective morphology regulation strategy for high-performance OSCs but also provides fundamental insights into the relationship between processing additive, active layer nanostructure, and device performance, offering valuable guidance for future development of organic photovoltaics.