Passivating Defects via Retarding the Reaction Rate of FAI and PbI₂ Enables Stable Perovskite Solar Cells

The two-step sequential deposition strategy has garnered widespread usage in the fabrication of high-performance perovskite solar cells based on FAPbI 3 . However, the rapid reaction between FAI and PbI 2 during preparation often leads to incomplete reactions, reducing the device efficiency and stability. Herein, we introduced a multifunctional additive, 2-thiophenyl trifluoroacetone (TTA), into the FAI precursor. The incorporation of TTA has proven to be highly effective in slowing the reaction rate between FAI and PbI 2, resulting in increased perovskite formation and improved efficiency and stability of the devices. TTA’s CF 3 groups interact with FAI via hydrogen bonding, effectively suppressing FA + defects. The S and C═O groups share lone pair electrons with uncoordinated Pb 2+, leading to a reduction in perovskite film defects and suppressing nonradiative recombination. Additionally, the CF 3 groups impart hydrophobicity, protecting the perovskite film from moisture-induced erosion. As a result, the TTA-modified perovskite film achieves a Champion efficiency of 23.42% compared to the control’s 21.52, with 20.58% efficiency for a 25 cm 2 solar module. Remarkably, the unencapsulated Champion device retains 86% of its initial PCE after 1080 h under dark conditions (60 ± 5 °C, 35 ± 5% RH), indicating enhanced long-term stability. These findings offer a promising and cost-effective tactic for high-quality perovskite film fabrication.