New multifunctional additive of 4-fluorophthalic anhydride for efficient and stable perovskite solar cells

Perovskite solar cells (PSCs) are promising photovoltaic candidates owing to their high efficiency and low-cost fabrication. However, their performance is significantly limited by defects at grain boundaries and surfaces, which induce non-radiative recombination and accelerate degradation. In this study, 4-fluorophthalic anhydride (4-FA) additive was applied to selectively anchor and passivate defects in PSCs for the first time. The result showed that the uncoordinated Pb²⁺ was coordinated by a lone pair of electrons in the carbonyl group through Lewis acid-base interaction. Additionally, the hydrogen bonds were formed between F atoms in 4-FA and -NH₂ in FAI, improving the crystal quality. Moreover, the hydrophobic nature of F atoms enhanced the environmental stability of PSCs. As a result, the 4-FA-modified perovskite film exhibited a reduced defect density and a longer carrier lifetime. In addition, the power conversion efficiency of the film increased from 21.37 % to 24.10 %, retaining 87 % of its initial value after 60 days in unencapsulated ambient air.