Side‐Chain Fluorination Tunes Nucleation and Domain Formation for High‐Performance Non‐Fused Electron Acceptor Solar Cells

Controlling nucleation behavior represents a critical yet underexplored avenue for improving non‐fused acceptor–based organic solar cells (OSCs), where sluggish nucleation and uncontrolled phase separation often limit optimal morphology formation. Here, we propose an effective strategy to modulate nucleation dynamics through side‐chain fluorination. Two non‐fused acceptors, 3TT‐0F and 3TT‐9F, were designed to probe how side‐chain fluorination modulates thermodynamics and intermolecular organization. Differential scanning calorimetry reveals that 3TT‐9F exhibits a larger Gibbs free energy difference between liquid and crystalline phases, indicating a reduced nucleation barrier. Complementary density functional theory and molecular dynamics simulations demonstrate that side‐chain fluorination enhances molecular dipole moment and strengthens intermolecular interactions, fostering tighter packing and improved donor–acceptor interaction. Consequently, 3TT‐9F forms smaller domain sizes and purer phase domains with enhanced molecular ordering in blend films, which is confirmed by grazing‐incidence wide‐angle x‐ray scattering and Resonant soft x‐ray scattering analysis. These synergistic effects facilitate more balanced charge transport and suppressed recombination. Devices incorporating 3TT‐9F achieve outstanding efficiencies of 17.2% in binary and 20.0% in ternary devices. This work establishes fluorination as an effective strategy to regulate nucleation behavior and morphological evolution in high‐performance non‐fused acceptor systems.