4-Iodobenzonitrile as Effective Solid Additive for High-Efficiency Polymer Solar Cells

Solid additive engineering is a well-established and effective strategy for enhancing active layer morphology in polymer solar cells (PSCs), thereby improving their power conversion efficiency (PCE). However, the availability of effective solid additive molecules remains limited, especially those combining simple structural units with a large dipole moment to promote strong interactions with active materials. In this study, we introduce 4-iodobenzonitrile (IBZN), a commercially available, low-cost, and structurally simple molecule with a high dipole moment (3.33 debye), as a solid additive for PSCs. Theoretical calculations, ultraviolet-visible (UV-Vis) spectroscopy experiments, and a morphology analysis demonstrate that IBZN forms strong interactions with L8-BO, subsequently enhancing the packing mode and crystallization. The incorporation of IBZN into PM6:L8-BO-based PSCs resulted in an increased fill factor (FF) of 79.54% and a boosted PCE from 17.49% to 18.77%. Furthermore, IBZN has also demonstrated outstanding regulatory effects in systems based on other Y-series acceptors, such as Y6 and BTP-ec9. This study not only introduces a structurally simple solid additive molecule characterized by a large dipole moment but also offers valuable insights for the subsequent development of novel solid additives aimed at enhancing the morphology and efficiency of PSCs.