Fibrillar Morphology Realized by Regulating Self‐Aggregation and Crystallization Kinetics from Non‐Volatile Solid Additives for Efficient Polymer Solar Cells

Abstract The bicontinuous double‐fibril interpenetrating network morphology is crucial for achieving high‐performance polymer solar cells (PSCs), which is closely related to complex crystallization kinetics. Constrained by the intrinsic properties of photovoltaic materials, polymer donors (PDs) are difficult to form well‐developed and highly ordered fibrillar structures, while non‐fullerene small‐molecule acceptors (NF‐SMAs) also struggle to spontaneously form fiber structures. To address this, two 3D non‐volatile solid additives, 1,3,5‐triphenylbenzene (TBB), and 1,3,5‐tri(2‐thienyl)benzene (TTB), are innovatively developed to modulate the self‐aggregation and crystallization behaviors of PDs and NF‐SMAs. Both solid additives significantly prolong the crystallization time of PM6 and L8‐BO. This extended crystallization process not only enhances the fibrillization of PM6, but also promotes the formation of L8‐BO fibers, ultimately successfully inducing the formation of a bicontinuous double‐fibril interpenetrating network morphology, which facilitates exciton dissociation and charge transport. Consequently, the TBB and TTB treated devices achieve power conversion efficiencies (PCEs) of 19.20% and 18.60%, respectively, significantly higher than the control device of 17.49%. Furthermore, applying TBB to the PM6:L8‐BO:BTP‐Cy‐4F ternary devices yield an excellent PCE of 20.30%. This work provides an effective strategy for achieving high‐performance PSCs through the construction of a bicontinuous double‐fibril interpenetrating network morphology.