Dual-Function Equol Molecule Suppresses Superoxide-Mediated Degradation in Perovskite Solar Cells

Under light and oxygen operational conditions, perovskite solar cells suffer severe degradation from superoxide radicals ( $O_2^{-}$ •). These radicals are generated when photogenerated electrons reduce adsorbed oxygen, and they rapidly decompose the perovskite by oxidizing iodide ions and deprotonating organic cations. Here, we introduce Equol, a phenolic natural isoflavonoid, into the perovskite precursor solution for two critical functions. First, phenolic oxygen coordinates with undercoordinated Pb²⁺ to passivate deep defects and regulate energy alignment, optimizing charge transport and device efficiency. It suppresses electron transfer to adsorbed oxygen and reduces $O_2^{-}$ • generation. Second, Equol acts as a hydrogen donor to scavenge $O_2^{-}$ • and restrain $O_2^{-}$ •-induced degradation. Its phenoxyl radical possesses resonance stabilization and low reactivity, avoiding further oxidative chain reactions. Additionally, Equol improves perovskite hydrophobicity and long-term environmental stability. As a result, the target device achieves a power conversion efficiency of 24.08% and shows excellent stability, retaining 80.18% of its initial efficiency after 2000 h under N₂ and 64.51% after 1000 h under ambient conditions (25°C, 40%-60% relative humidity), far exceeding the performance of control devices. This work establishes Equol as a multifunctional stabilizer against $O_2^{-}$ •-driven degradation, offering a bio-inspired route to enhanced perovskite stability.