Over 13% Efficient Organic Solar Cells Based on Low‐Cost Pentacyclic A‐DA′D‐A‐Type Nonfullerene Acceptor

Recent studies have almost focused on finding active layer materials with extended π‐conjugation structures for high‐performance organic solar cells (OSCs). However, with the extension of conjugate length, the synthesis difficulty and cost of materials will increase. Achieving high efficiency while reducing material costs is a prerequisite for the commercialization of OSCs. Herein, two low‐cost A‐DA′D‐A‐type (where A and D represent an electron‐withdrawing unit and an electron‐donating unit, respectively) nonfullerene acceptors (Y25,Y26) are synthesized with pentacyclic fused backbone as the DA′D electron‐deficient core and 5,6‐difluoro‐3‐(dicyandiamethyl) indigo as the end groups. Compared with classical Y series acceptors with heptacyclic backbone, although Y25 and Y26 own the reduced conjugated length, they still show moderate performance (11.65% and 13.34%), and the cost of synthesis is significantly reduced. Therefore, we provide a new molecular design idea for commercially efficient nonfullerene OSCs acceptors. We also find that adding alkyl chains to the β site of thiophenes is beneficial to obtaining the reduced energetic disorder, dominant molecular stacking, and desirable morphology, which can facilitate charge carrier transport and prompt higher short‐circuit current density ( J sc ) as well as fill factor.