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.