Boosting Efficiency and Stabilizing the Precursor Ink via Aggregation Regulation in Non‐Halogenated Solvent‐Processed Organic Solar Cells

ABSTRACT The instability of precursor inks poses a major bottleneck for the scalable manufacturing of organic solar cells (OSCs) processed from eco‐friendly, non‐halogenated solvents, severely limiting processing windows and batch reproducibility. Herein, we address this challenge using the halogen‐free solid additive dithieno[3,2‐b:2′,3′‐d]thiophene (DTT) in o‐xylene‐processed OSCs through a dual‐functional strategy. DTT acts as a crystallization template in the solid state, selectively interacting with the acceptor to optimize molecular packing and morphology, yielding high power conversion efficiencies of 18.50% and 20.01% for binary and ternary devices, respectively. More critically, DTT functions as a kinetic stabilizer in the solution state. Mechanistic investigations uncover that the instability of the ink is primarily driven by the gradual aggregation of the acceptor molecules. DTT effectively retards this time‐dependent coarsening process, thereby extending the shelf‐life of the precursor ink from 5 to 10 days while maintaining 90% of the initial device efficiency. This work not only identifies a key origin of ink degradation but also establishes a practical paradigm in which a single halogen‐free additive concurrently delivers high device performance, exceptional ink stability, and scalable green processing, offering a viable pathway toward the industrial fabrication of OSCs.