Kinetics Manipulation Enables High‐Performance Thick Ternary Organic Solar Cells via R2R‐Compatible Slot‐Die Coating

Abstract Power conversion efficiency (PCE) of organic solar cells (OSCs) has crossed the 18% mark for OSCs, which are largely fabricated by spin‐coating, and the optimal photoactive thickness is limited to 100 nm. To increase reproducibility of results with industrial roll‐to‐roll (R2R) processing, slot‐die coating coupled with a ternary strategy for optimal performance of large‐area, thick OSCs is used. Based on miscibility differences, a highly crystalline molecule, BTR‐Cl, is incorporated, and the phase‐separation kinetics of the D18:Y6 film is regulated. BTR‐Cl provides an early liquid–liquid phase separation and early aggregation of Y6, which slightly improves the molecular crystallinity and vertical phase separation of the ternary blends, resulting in high PCEs of 17.2% and 15.5% for photoactive films with thicknesses of 110 and 300 nm, respectively. The ternary design strategy for large‐area and thick films is further used to fabricate high‐efficiency flexible devices, which promises reproducibility of the lab results from slot‐die coating to industrial R2R manufacturing.