Chlorine Positional Isomerization Enables Quadrupole Moment Engineering with Low Voltage Loss for High‐Efficiency Organic Solar Cells

ABSTRACT Amplifying the quadrupole moment of non‐fullerene acceptors (NFAs) is key to facilitating exciton dissociation and suppressing recombination in organic solar cells (OSCs), yet current molecular design strategies predominantly enhance quadrupole moments by strengthening the electron‐withdrawing character of acceptor end groups, inevitably deepening frontier energy levels, and penalizing open‐circuit voltage ( V OC ). Here, we introduce chlorine positional isomerization to amplify the molecular quadrupole moment without altering frontier orbital energies. By relocating a chlorine atom between asymmetric end groups, we improve the quadrupole moment from 154.5 to 176.0 Debye·Å, without altering the frontier energy level. This electrostatic reconfiguration accelerates exciton dissociation under minimal energetic offsets, as evidenced by ultrafast transient absorption spectroscopy. As a result, the optimized binary device achieves a power conversion efficiency of 19.0%, combining enhanced short‐circuit current and fill factor with low voltage loss. When incorporated as a guest acceptor in a ternary blend, this strategy further enables a promising efficiency of 20.3%, together with exceptional thickness tolerance (410 nm) and a scalable module (20.25 cm 2 ), with maximum efficiencies exceeding 16.5%. This work establishes positional isomerization as a general electrostatic design handle to decouple quadrupole‐moment enhancement from energy‐level deepening, offering a transferable pathway to overcome exciton dissociation limits in OSCs.