Perovskite solar cells (PSCs) have seen remarkable progress in recent years, largely attributed to various additives that enhance both efficiency and stability. Among these, fluorine-containing additives have garnered significant interest because of their unique hydrophobic properties, effective defect passivation, and regulation capability on the crystallization process. However, a targeted structural approach to design such additives is necessary to further enhance the performance of PSCs. Here, fluoroalkyl ethylene with different fluoroalkyl chain lengths (CH₂CH(CF₂)_nCF₃, n = 3, 5, and 7) as liquid additives is used to investigate influences of fluoroalkyl chain lengths on crystallization regulation and defect passivation. The findings indicate that optimizing the quantity of F groups plays a crucial role in regulating the electron cloud distribution within the additive molecules. This optimization fosters strong hydrogen bonds and coordination effects with FA⁺ and uncoordinated Pb²⁺, ultimately enhancing crystal quality and device performance. Notably, 1H,1H,2H-perfluoro-1-hexene (PF₃) with the optimal number of F presents the most effective modulation effect. A PSC utilizing PF₃ achieves an efficiency of 24.05%, and exhibits exceptional stability against humidity and thermal fluctuations. This work sheds light on the importance of tailored structure designs in additives for achieving high-performance PSCs.