Enhancing Charge Separation in Y-Series Acceptors via π-End Group Substitutions for Organic Solar Cells

Y-series non-fullerene acceptors (NFAs) have been widely used to enhance the power conversion efficiencies (PCEs) of organic solar cells (OSCs). To rationally explore an effective approach to improve PCE, we employ density functional theory (DFT) and molecular dynamics (MD) simulations to analyze four Y-series NFAs: BTP-C9-ICB, BTP-C9-ICN, BTP-C9-ICT, and BTP-eC9. DFT calculations reveal that thiophene extension in BTP-C9-ICT enhances light absorption and intramolecular charge transfer but has a limited effect on the overall performance. MD simulations further investigate molecular stacking in acceptor−donor blends, identifying efficient π–π interactions (DD, AA, and AD) via K-means clustering. While DD and AA stackings influence charge transport asymmetry, they are not the sole determinants of PCE. Instead, BTP-eC9 achieves superior performance due to an increased number of AD stackings, driven by chlorine-induced intermolecular interactions and enhanced long-range electronic couplings. This study underscores the critical role of charge separation in OSCs, suggesting that optimizing charge separation may be more impactful than simply improving charge mobility in high-performance organic semiconductors.