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Fluorine side chain functionalization of non-fullerene acceptors (NFAs) represents an effective strategy for enhancing the performance of organic solar cells (OSCs). However, a knowledge gap persists regarding the relationship between structural changes induced by fluorine functionalization and the resultant impact on device performance. In this work, varying amounts of fluorine atoms were introduced into the outer side chains of Y-series NFAs to construct two acceptors named BTP-F0 and BTP-F5. Theoretical and experimental investigations reveal that side-chain fluorination significantly increase the overall average electrostatic potential (ESP) and charge balance factor, thereby effectively improving the ESP-induced intermolecular electrostatic interaction, and thus precisely tuning the molecular packing and bulk-heterojunction morphology. Therefore, the BTP-F5-based OSC exhibited enhanced crystallinity, domain purity, reduced domain spacing, and optimized phase distribution in the vertical direction. This facilitates exciton diffusion, suppresses charge recombination, and improves charge extraction. Consequently, the promising power conversion efficiency (PCE) of 17.3 % and 19.2 % were achieved in BTP-F5-based binary and ternary devices, respectively, surpassing the PCE of 16.1 % for BTP-F0-based OSCs. This work establishes a structure-performance relationship and demonstrates that fluorine functionalization of the outer side chains of Y-series NFAs is a compelling strategy for achieving ideal phase separation for highly efficient OSCs. © 2024 Wiley-VCH GmbH.

Laboratory-scale all-polymer solar cells (all-PSCs) have exhibited remarkable power conversion efficiencies (PCEs) exceeding 19%. However, the utilization of hazardous solvents and nonvolatile liquid additives poses challenges for eco-friendly commercialization, resulting in the trade-off between device efficiency and operation stability. Herein, an innovative approach based on isomerized solid additive engineering is proposed, employing volatile dithienothiophene (DTT) isomers to modulate intermolecular interactions and facilitate molecular stacking within the photoactive layers. Through elucidating the underlying principles of the DTT-induced polymer assembly on molecular level, a PCE of 18.72% is achieved for devices processed with environmentally benign solvents, ranking it among the highest record values for eco-friendly all-PSCs. Significantly, such superiorities of the DTT-isomerized strategy afford excellent compatibility with large-area blade-coating techniques, offering a promising pathway for industrial-scale manufacturing of all-PSCs. Moreover, these devices demonstrate enhanced thermal stability with a promising extrapolated T80 lifetime of 14 000 h, further bolstering their potential for sustainable technological advancement. The isomerized solid additive engineering based on volatile dithienothiophene (DTT) isomers is empolyed to achieve a remarkable PCE of 18.72% for all-PSCs processed with green solvent. More importantly, the all-PSCs fabricated with this approach offer excellent compatibility with large-area blade-coating techniques, and demonstrate exceptional thermal stability with extrapolated T80 lifetime of 14 000 h.image