Shear Force Field‐Tailored Fibrillar Active Layer Morphology for High‐Efficiency Organic Solar Cells

Abstract This study introduces an off‐center spin‐coating strategy that strengthens the shear force field to induce a high degree of polymer chain orientation, facilitating the fabrication of high‐efficiency organic solar cells (OSCs). Under this approach, high‐molecular‐weight D18 (HW‐D18) solution demonstrates a marked shear‐thinning effect, yielding polymer films with improved crystallinity and a more pronounced face‐on molecular orientation. These enhancements significantly optimize the morphology of the D18:L8‐BO active layer, effectively boosting carrier mobility, exciton dissociation efficiency, and charge collection efficiency while suppressing bimolecular recombination. Using this method, an OSC with a 100 nm thick active layer achieves a fill factor (FF) of 81% and a power conversion efficiency (PCE) of 20.1%. Even for active layers with thicknesses of 200, 300, and 500 nm, the PCEs reach 19.1%, 18.5%, and 16.9%, respectively, showing excellent thickness tolerance. Furthermore, this device fabrication strategy is highly applicable to other material systems, such as PM6:BTP‐eC9‐4F and D18‐Cl:L8‐BO. Notably, the ternary system D18:L8‐BO:BTP‐eC9‐4Cl attains a PCE of 20.5%. This research offers a new insight into regulating active‐layer morphology via shear force fields and provides valuable guidance for fabricating high‐performance OSCs.