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

ABSTRACT Under light and oxygen operational conditions, perovskite solar cells suffer severe degradation from superoxide radicals (•). 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 Pb ²⁺ to passivate deep defects and regulate energy alignment, optimizing charge transport and device efficiency. It suppresses electron transfer to adsorbed oxygen and reduces • generation. Second, Equol acts as a hydrogen donor to scavenge • and restrain •‐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 N ₂ 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 •‐driven degradation, offering a bio‐inspired route to enhanced perovskite stability.