Non‐Volatile Perfluorophenyl‐Based Additive for Enhanced Efficiency and Thermal Stability of Nonfullerene Organic Solar Cells Via Supramolecular Fluorinated Interactions

A novel non-volatile additive, fluorinated bis(perfluorophenyl)pimelate (BF7), is demonstrated to effectively improve both the efficiency and thermal stability of a highly efficient organic solar cell (OSC), comprising fluorinated Y6 as the small-molecule acceptor and PM6 as the polymer donor. Processed with optimized 0.5 wt% BF7 in solution, the PM6:Y6:BF7 device achieves an elevated power conversion efficiency (PCE) of 17.01%, compared to 15.16% of that processed without BF7. Moreover, the BF7-elevated PCE can sustain 95% of the best PCE over 100 degrees C annealing for 72 h. Grazing incidence X-ray scattering and differential scanning calorimetry results consistently indicate that BF7 in the PM6:Y6:BF7 device interacts preferentially with Y6, resulting in improved fractal-like network structures of the active layer with optimized size and orientation of Y6 nano-crystallites and elevated thermal stability. Molecular simulation also supports that the observed structure and thermal stability is associated with the F-pi noncovalent supramolecular interactions between the perfluorophenyl moieties of BF7 and difluorophenyl-based FIC-end-groups of Y6. Similar bifunctional BF7 effects are also observed in the well-known PM6:IT-4F system, suggesting that adding BF7 for concomitantly improved PCE and thermal stability might extend generally to OSCs that feature small molecule acceptors of difluorophenyl end-groups.