Structure-regulated fluorine-containing additives to improve the performance of perovskite solar cells

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.