Perfluorophenyl-Incorporated Ferrocene: A Non-Volatile Solid Additive for Boosting Efficiency and Stability in Organic Solar Cells

In this study, we designed and synthesized a new non-volatile solid additive FcF₁₀ by integrating two pentafluorophenyl (C₆F₅) groups into the cyclopentadienyl (CP) rings of ferrocene (Fc) through ester linkages. The FcF₁₀ with a three-dimensional (3D) framework facilitated morphological optimization in the PM6:Y6 system through a combination of π···π, F···π, and F···F interactions between the CP and C₆F₅ rings in FcF₁₀ and the C₆F₂ rings in Y6. The FcF₁₀-incorporated (3.75 wt %) PM6:Y6-based solar cell device achieved a higher power conversion efficiency (PCE) of 17.00%, with a <i>V</i>_oc of 0.85 V, a <i>J</i>_sc of 27.35 mA cm^-2, and an FF of 73.29%, compared to the pristine PM6:Y6 device. These improvements are attributed to the formation of a favorable active layer morphology, which enhances exciton dissociation and charge transport while reducing bimolecular and trap-assisted recombination. The FcF₁₀ additive facilitates non-covalent interactions with Y6, such as F···F, F···π, and π···π interactions between the Cp and C₆F₅ rings in FcF₁₀ and the FIC end groups in Y6. These supramolecular interactions improve molecular stacking and crystallinity within the Y6 domain, as evidenced by red-shifted Y6 absorption, reduced π-π stacking <i>d</i>-spacing, and increased coherence lengths of Y6. Furthermore, the PM6:Y6:FcF₁₀ device demonstrates superior thermal stability, retaining 88% of its initial PCE after prolonged thermal annealing at 85 °C. Overall, the incorporation of FcF₁₀ achieves an optimized and stable donor-acceptor morphology, offering a promising approach for high-performance and thermally stable organic photovoltaics.