Molecular engineering of Y-series acceptors with oligo(ethylene glycol) side chains enables high efficiency in nonhalogenated solvent-processed organic solar cells

Most high-performance organic solar cells (OSCs) based on Y6-type acceptors are fabricated using chloroform, which hinders their commercialization due to issues with film uniformity and solvent toxicity. Although high-boiling-point non-halogenated solvents are promising alternatives, they typically suffer from low solubility and slow evaporation rates, complicating the crystallization process. Herein, we introduce Y-TEG, a Y-shaped acceptor functionalized with two oligo(ethylene glycol) (OEG) side chains on the pyrrole unit of Y6, which significantly enhances its solubility in non-halogenated solvents. OSCs based on PM6:Y-TEG processed from o-xylene achieved a power conversion efficiency (PCE) of 14.22%. The incorporation of Y6 as a third component further increased the PCE to 15.77%. This improvement is attributed to the role of Y6 in modulating intermolecular compatibility, optimizing crystallinity, and enhancing the phase separation morphology of the active layer. Consequently, the exciton dissociation and charge collection efficiency are improved, while charge recombination and energy losses are reduced. Notably, the PCE of 15.77% ranks among the highest reported for devices incorporating a host acceptor modified with OEG side chain and processed using non-halogenated solvents. These results demonstrate that side-chain engineering with OEG groups is a promising strategy for developing high-efficiency photovoltaic materials compatible with environmentally friendly processing solvents, providing confidence for future large-scale device fabrication.