Fluid flow engineering in slot channel and shearing meniscus enables balanced crystallinity and efficient air-processed organic solar cells

Low-cost and scalable slot-die coating is highly desirable for the continuous manufacturing of high-efficiency organic solar cells (OSCs). However, precise morphology control during printing remains challenging because of the mismatched aggregation behaviors of donor and acceptor materials and the complex meniscus fluid dynamics. Here, we develop a micro-structured slot-die (ms-SD) coating strategy that enables synergistic regulation of donor and acceptor assembly during film formation. The ms-SD induces shear and extensional flows within the slot channel to promote polymer-chain alignment and donor ordering, while coating-speed-dependent meniscus convergence modulates acceptor assembly and suppresses excessive crystallization. This dual-region flow control framework yields films with more balanced donor/acceptor crystallinity, smaller phase domains, and reduced energetic disorder, thereby improving charge separation and transport. As a result, ms-SD-processed devices fabricated under ambient conditions achieve a champion power conversion efficiency exceeding 18.2%, among the highest reported for slot-die coated OSCs without post-treatment. Moreover, the approach is further applicable to multiple donor:acceptor systems, demonstrating its broader applicability. This work establishes fluid flow engineering as a practical strategy for controlling active-layer formation during solution processing, providing a post-treatment-free route toward high-performance and scalable printed OSCs.