Molecular engineering of Y‐series acceptors for nonfullerene organic solar cells

The power conversion efficiencies (PCEs) of single-junction organic solar cells (OSCs) have surpassed 19%, owing to the emerging Y-series nonfullerene acceptors (NFAs). Undoubtedly, the power and flexibility of chemical design has been a strong driver for this rapid efficiency improvement in the OSC field. Over the course of the past 3 years, a variety of modifications have been made to the structure of the Y6 acceptor, and a large number of Y-series NFAs have been reported to further improve performance. Herein, we present our insights into the rationale behind the Y6 acceptor and discuss the design principles toward high-performance Y-series NFAs. It is clear that structural modifications through choice of heteroatom, soluble chains, pi spacers, central cores, and end groups alter the material characteristics and properties, contributing to distinctive photovoltaic performance. Subsequently, we analyze various design strategies of Y-series-containing materials, including polymerized small-molecule acceptors (PSMA), non-fused-ring acceptors (NFRA), and all-fused-ring acceptors (AFRA). This review is expected to be of value in providing effective molecular design strategies for high-performance NFAs in future innovations.