Electronegativity-Engineered Multidimensional Interactions Enable 20% Efficiency Organic Solar Cells

The innovation of Y-series acceptors with A-DAʹD-A architecture has significantly advanced the efficiency of organic solar cells (OSCs). However, the role of their central electron-deficient unit (Aʹ) in determining photovoltaic performance remains incompletely understood. Herein, Y6, AQx-2, and Y11, which feature BT, Qx, and BTz with varying electronegativities, respectively, are selected as the research subjects. These results reveal that as the electronegativity of the Aʹ unit decreases, the porosity and molecular stacking distance in single crystal structures are gradually reduced, leading to enhanced charge carrier diffusion. Additionally, the vertical phase distribution of blend films becomes more uniform, accompanied by strengthened multidimensional interactions. Furthermore, devices based on these acceptors exhibit progressively reduced energy loss, due to the strong coupling between the charge transfer and the localized excited state. Meanwhile, the short-circuit current initially increases and then decreases with the reduction in electronegativity. Through optimizing the electronegativity of the Aʹ unit via ternary strategy, a significantly improved efficiency of 19.0% for PM6:Y6:Y11 is achieved. Further extending this strategy to the D18:L8-BO:Y11 system yields an outstanding efficiency of 20.1%. These findings provide valuable insights into designing high-efficiency non-fullerene electron acceptors and establish a clear structure-property relationship for future OSC development.