The fill factor is a key parameter in perovskite solar cells and is strongly influenced by interfacial charge transfer processes and subsequently impacts the power conversion efficiency. Herein, to improve the fill factor, three fluorine substituted materials were designed, synthesized and characterized. By inserting them as thin interfacial layers at the perovskite/spiro-OMeTAD interface, the electron blocking properties and the hole extraction and transfer efficiency were simultaneously enhanced, resulting in an enhancement of the fill factor from 75% up to ∼80% while keeping the short-circuit current and the open-circuit voltage unchanged. Furthermore, the introduction of fluorine atoms increases the hydrophobicity, leading to an enhanced device stability.