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, are 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 interaction, 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 (VOC) and short‐circuit current density (JSC), due to the reduced energy loss and efficient exciton dissociation. Inspired by its high VOC×JSC, 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 non‐fully conjugated Y‐GMAs. Our developed hybrid linking‐site engineering for constructing high‐performance Y‐GMAs offers an approach to boost device efficiency.