Due to the precisely tunable energy levels, structural versatility, and broad absorption spectra extending into the near-infrared region, the Y-series of nonfullerene acceptors (NFAs) have attracted a lot of attention from researchers in recent years. Among the various methods for optimizing material structure, side-chain modification is a simple and efficient way to improve the corresponding device performance of the material. Because of the large steric hindrance, the introduction of aromatic groups into the side chain is an effective method to adjust the planarity of the molecular skeleton and the morphology of the active layer. Despite the numerous reviews on the acceptor materials, there are scarcely any comprehensive summaries focusing on aromatic side chains optimized Y6 acceptors. Therefore, this paper mainly focuses on the aromatic side chain modification strategy on Y6 materials, which include the synthetic methods and research status for introducing aromatic side chains into the inner and the outer side chains of Y6-series materials. The structure-performance relationship is also comprehensively discussed, and the future design directions and challenges of Y-series NFAs are proposed.

Compared with perovskite solar cells and silicon solar cells, the excessive voltage loss (V_loss) becomes a stubborn stone that seriously hinders the further improvement of organic photovoltaic (OPV). Thus, many researchers focus on finding an effective material system to achieve high-performance OPVs with low V_loss. In recent 5 years, acceptor-donor-acceptor’-donor-acceptor (A-DA’D-A) type non-fullerene acceptors (NFAs) have attracted great attention because of their promising photovoltaic performance. Among them, A-DA’D-A type NFAs containing non-halogenated end group (NHEG) exhibit the large potential to achieve high open-circuit voltage (V_OC) for the state-of-the-art OPVs, because of high-lying molecular energy levels and decreasing V_loss. In this review, we systematically summarize the recent development of A-DA’D-A type NHEG-NFAs and the impact of different NHEGs on the optoelectronic properties as well as the photovoltaic performance. In addition, we especially analyze the V_loss of NHEG-NFAs in the binary and ternary OPV devices. At last, we provide perspectives on the further molecular design and future challenges for this kind of materials as well as suggested solutions.