Hybrid Linking Sites Constructed Non-Fully Conjugated Asymmetric Dimerized Giant Molecule Acceptors for Organic Solar Cells with an Efficiency of ≈20%

Linking-site engineering, used to graft two or more monomers, is crucial for achieving high-performance Y-series giant molecule acceptors (Y-GMAs). However, the reported Y-GMAs all use a single-typed linking site, making it difficult to finely-tune their optoelectronic properties. Herein, we develop a non-fully conjugated Y-GMA (named 2Y-we), with hybrid linking sites at the wing and end-group of monomers, to combine the respective advantages of the wing and end-group site linked counterparts. Compared to its parental monomer, 2Y-we shows different intermolecular interactions, crystallinity, packing, and glass transition temperature, allowing optimized active layer morphology (including appropriate phase separation and ordered molecular packing) and stability. Consequently, the D18/2Y-we-based organic solar cells (OSCs) obtain an improved power-conversion-efficiency (PCE) of 17.4% with both higher open-circuit voltage (V_OC) and short-circuit current density (J_SC), due to the reduced energy loss and efficient exciton dissociation. Inspired by its high V_OC× J_SC, 2Y-we is introduced into D18:L8-BO to fabricate ternary devices. Thanks to the further optimized morphology and improved charge transport, the ternary OSCs achieve a superior PCE of 19.9%, which is the highest value among the reported nonfully conjugated Y-GMAs. Our developed hybrid linking-site engineering for constructing high-performance Y-GMAs offers an approach to boost device efficiency.