Electrostatic regulation of high-dipole dithienophthalimide-based wide-bandgap polymer for efficient ternary all-polymer solar cells
All-polymer solar cells (all-PSCs) are promising for flexible and wearable electronics due to their excellent stability and mechanical stretchability. However, achieving high performance remains challenging due to difficulties in controlling the morphology of polymer blend films. In this study, a novel polymer donor, PBDTF-DTP, incorporating a weak electron-withdrawing yet large-dipole-moment dithienylphthalimide (DTP-2T) unit, was rationally designed and synthesized for ternary all-PSCs. Introducing PBDTF-DTP as a guest donor enables complementary light absorption and deepens the highest occupied molecular orbital level, simultaneously improving short-circuit current density (J_SC) and open-circuit voltage (V_OC). The large dipole moment of DTP-2T increases the dielectric constant, suppressing non-radiative energy loss and further boosting V_OC. Notably, PBDTF-DTP exhibits a relatively higher molecular electrostatic potential than the host donor, effectively tuning compatibility with both polymer donor and acceptor, regulating blend morphology, and promoting formation of a nanoscale fibrillar network. This optimized morphology facilitates efficient charge generation and transport while suppressing charge recombination. Consequently, ternary all-PSCs based on PM6:PBDTF-DTP:PYIT achieve a synergistic enhancement in J_SC, V_OC, and fill factor, yielding a remarkable power conversion efficiency of 18.01%, significantly higher than that of binary PM6:PYIT devices (15.51%). This study demonstrates that combining electrostatic potential optimization with a ternary strategy provides an effective approach to regulate morphology and achieve high-efficiency all-PSCs.