Asymmetrical Elongation of Branched Alkyl Chains in Non-Fullerene Acceptors for Large-Area Organic Solar Modules

Abstract

With the drive toward the development of large-area organic solar cells (OSCs), there is a critical need for advanced fabrication techniques that ensure both their efficiency and scalability. In particular, a shift from toxic halogenated solvents to safer non-halogenated alternatives such as o-xylene, which have lower environmental and health impacts, is required. However, transitioning to non-halogenated solvents can lead to serious problems, including aggregation within the active layer, which compromises film morphology and the resulting efficiency of OSCs. To address this aggregation, in the present study, the 2-ethylhexyl (EH) groups in L8-BO(EH-EH) are replaced with longer chains (2-heptylundecyl [HU], 2-decyltetradecyl [DT], and 2-dodecylhexadecyl [DH] groups) to synthesize the non-fullerene acceptors (NFAs) of L8-BO(HU-HU), L8-BO(HU-DT), and L8-BO(HU-DH). The NFAs with the longer alkyl chains are highly soluble in o-xylene and produce highly uniform films, making them more suitable for use in large-area OSCs. Using the NFAs, slot-die-coated organic solar modules with an active area of 200 cm2 are fabricated; the L8-BO(HU-DT)-based module exhibits an impressive power conversion efficiency of 11.44%. This work thus underscores the asymmetrical elongation of alkyl chains in the NFAs to mitigate severe NFA phase separation and improve film printability in the practical production of organic solar modules. Asymmetrically elongated non-fullerene acceptors (NFAs) are designed with high solubility in o-xylene and miscibility with a PM6 donor. In particular, L8-BO(HU-DT) leads to the formation of homogeneous and uniform PM6:NFA:PC70BM films via slot-die coating, which in turn are used to fabricate 200 cm2 eco-solvent-processed modules with an APCE of 11.44%. This work highlights the significance of alkyl chain fine-tuning for high-performance organic solar modules. image