An asymmetrical fused-ring electron acceptor designed by a cross-conceptual strategy achieving 15.6% efficiency

Due to their unique merits, asymmetrical fused-ring electron acceptors (FREAs) have received increasing attention in the field of organic photovoltaics (OPVs). Herein, we designed and synthesized an asymmetrical FREA, namelyAY6, by employing a cross-conceptual strategy which combines the structural features of asymmetricalIT6-4Fwith high-performanceY6. Compared to Y-shapeY6, X-shapeAY6shows poor crystallization properties and thus a significantly blue-shifted absorption. However, it is precisely because of this unfavorable self-stacking effect thatAY6has an opportunity to pack withPM6and form a new intermixed phase. As a result, thePM6:AY6blend film exhibits a perfect face-on orientation with stronger pi-pi stacking than thePM6:Y6blend film, which facilitates efficient exciton dissociation and balanced carrier transport, and therefore higher FF. In general, such a cross-conceptual design strategy is an effective method which not only boosts the efficiency of asymmetrical FREA-based OSCs but also increases the fill factors of OSCs based onY6-like FREAs.