Guest Donor With High Electrostatic Potential Enables Low‐Energy‐Loss Ternary All‐Polymer Solar Cells

ABSTRACT In ternary all‐polymer organic solar cells (all‐PSCs), while the short‐circuit current density ( J SC ) and fill factor (FF) are enhanced, further device efficiency improvement is constrained by the large energy loss. Here, a wide‐bandgap guest donor PTO2 with deeper energy level is introduced into the PM6:PYIT system to resolve this issue. Theoretical calculations indicate that PTO2 exhibits a more negative electrostatic potential (ESP), enabling the formation of a strong intermolecular electric field when paired with the acceptor that displays a positive surface ESP, thereby facilitating efficient exciton dissociation. Experimentally, PTO2 endows complementary light absorption, optimizes the vertical composition distribution, balances the crystallization kinetics, and promotes tighter π – π stacking. Meanwhile, PTO2 can effectively enhance the built‐in electric field and reduce charge generation/recombination associated energy loss. Consequently, the ternary device achieves an optimal efficiency of 19.12% with an enhanced open circuit voltage ( V OC ) of 0.963 V without sacrificing J SC and FF compared to PM6:PYIT. This work highlights the crucial role of ESP modulation and provides a novel matching approach for high‐performance ternary all‐PSCs.