The roles of side chains in Y6 ‐series non‐fullerene acceptors for high‐performance organic solar cells

Recent advancements in organic solar cells (OSCs) achieve power conversion efficiencies (PCEs) surpassing 20%, primarily driven by Y6‐series non‐fullerene acceptors (Y6‐NFAs). These NFAs are modified through three main structural approaches: core, end group, and side chain modifications. Among these, side chain modification emerges as a particularly effective strategy for enhancing PCEs by controlling solubility and molecular packing. Additionally, appropriate side chain selection fine‐tunes the energy levels and light absorption properties of Y6‐NFAs, enabling OSC efficiencies to increase from 15.7% to over 20%. Despite these advancements, substantial potential remains for further performance enhancement through continued side chain modifications. Previous studies provide a key understanding for designing new Y6‐NFAs. This review explores the progress in Y6‐NFA‐based OSCs driven by side chain modifications, emphasizing their impact on solubility, molecular packing, crystallinity, and device performance. Finally, future directions for advancing the OSC field are proposed, offering guidance for the development of innovative Y6‐NFAs for next‐generation OSC applications.