Polyaniline-Enabled Dual Passivation of SnO_x Oxygen Vacancies and Perovskite Surface Defects

Oxygen-vacancy defects in SnO_x electron transport layers are a major source of interfacial recombination and instability in perovskite solar cells. Here, we introduce a bioderived dual interfacial strategy that regulates both defect states and interfacial energetics. Polyaniline-grafted chitin whiskers (CTW-g-PANI) coordinate with under-coordinated Sn sites, compensating oxygen-deficient states and inducing an upward shift of the SnO_x Fermi level. The resulting interfacial dipole improves band alignment with the perovskite and facilitates electron extraction. In parallel, a thin polyaniline (PANI) overlayer modulates the perovskite surface electronic structure through coordination with under-coordinated Pb²⁺ species, reducing trap-associated tail states and contributing to suppressed interfacial recombination. As a result, the dual-modified devices exhibit enhanced charge extraction and reduced trap density, delivering a power conversion efficiency of 17.73% compared to 14.46% for the untreated control. Nonencapsulated devices retain 93% of their initial efficiency after 30 days at 35% relative humidity, whereas the control retains only 80%. These findings demonstrate that the coordinated modulation of interfacial defect energetics and dipole formation enabled by the bioderived molecules plays a decisive role in stabilizing device operation and mitigating defect-mediated losses in perovskite photovoltaics.