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 FcF by integrating two pentafluorophenyl (CF) groups into the cyclopentadienyl (CP) rings of ferrocene (Fc) through ester linkages. The FcF 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 CF rings in FcF and the CF rings in Y6. The FcF-incorporated (3.75 wt %) PM6:Y6-based solar cell device achieved a higher power conversion efficiency (PCE) of 17.00%, with a of 0.85 V, a of 27.35 mA cm, 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 FcF additive facilitates non-covalent interactions with Y6, such as F···F, F···π, and π···π interactions between the Cp and CF rings in FcF 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 -spacing, and increased coherence lengths of Y6. Furthermore, the PM6:Y6:FcF device demonstrates superior thermal stability, retaining 88% of its initial PCE after prolonged thermal annealing at 85 °C. Overall, the incorporation of FcF achieves an optimized and stable donor-acceptor morphology, offering a promising approach for high-performance and thermally stable organic photovoltaics.