Organic Photovoltaics Utilizing Small‐Molecule Donors and Y‐Series Nonfullerene Acceptors

Abstract The emerging Y‐series nonfullerene acceptors (Y‐NFA) has prompted the rapid progress of power conversion efficiency (PCE) of all‐small‐molecule organic solar cells (ASM‐OSCs) from around 12% to 17%. The excellent PCE improvement benefits from not only the outstanding properties of Y‐series acceptors but also the successful development of small‐molecule donors. The short‐circuit current density, fill factor, and nonradiative recombination are all optimized to the unprecedented values, providing a scenery that is obviously different from the ITIC‐series based ASM‐OSCs. In this review, OSCs utilizing small‐molecule donors and Y‐NFA are summarized and classified in order to provide an up‐to‐date development overview and give an insight on structure–property correlation. Then, the characteristics of bulk‐heterojunction (BHJ) formation of ASM‐OSCs are discussed and compared with that of polymer‐based OSCs. Finally, the challenges and outlook on designing ground‐breaking small‐molecule donor and forming an ideal BHJ morphology are discussed.