Vaporization-Guided Morphology Evolution Enables Precision Control in Blade-Coated Organic Solar Cells

Controlling the morphology evolution of blade-coated bulk-heterojunction active layers is crucial for achieving high-efficiency organic solar cells (OSCs), yet remains challenging because rapid solvent evaporation and unbalanced donor–acceptor aggregation often lead to poorly regulated phase separation and disordered molecular packing. Herein, a vaporization-guided morphology regulation strategy is developed by introducing 1,4-diiodobenzene (DIB) as a volatile solid additive into a blade-coated PM6:L8-BO device. Optical analysis reveals that an appropriate amount of DIB mainly regulates the acceptor-related aggregation state, as evidenced by the red-shifted L8-BO absorption, enhanced vibronic intensity ratios, and narrowed spectral width. In situ UV–vis absorption and photoluminescence (PL) measurements further demonstrate that DIB delays premature acceptor crystallization and prolongs the kinetic window for donor–acceptor phase evolution, thereby enabling more synchronized aggregation during blade coating. Morphology characterization confirms that 50 wt % DIB promotes better-defined nanoscale phase separation, enhanced lamellar ordering, and balanced π–π stacking, whereas excessive DIB induces over-aggregation. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations reveal that DIB preferentially interacts with L8-BO and transiently participates in molecular self-assembly, guiding the acceptor toward more compact and favorable packing motifs after additive removal. Consequently, the optimized device exhibits an increased power conversion efficiency (PCE) from 17.27 to 18.75%, accompanied by enhanced exciton dissociation, suppressed recombination, and more balanced charge transport. This work provides a molecular-level understanding of volatile solid additive-mediated morphology evolution and offers an effective strategy for precision morphology control in scalable blade-coated OSCs.