Polyaniline‐Enabled Defect Passivation for Stable and Efficient MAPbI 3 ‐Based Perovskite Solar Cells

ABSTRACT Defect‐induced nonradiative recombination and poor operational stability remain major challenges for methylammonium lead iodide (MAPI) perovskite solar cells. Here, we demonstrate polyaniline (PANI) in its emeraldine base form as a multifunctional additive to simultaneously improve film quality, charge‐carrier dynamics, device performance, and stability of MAPI perovskites. PANI incorporation enhances crystallinity and grain size without altering the intrinsic bandgap (∼1.6 eV). X‐ray photoelectron spectroscopy reveals strong Lewis acid–base coordination between the amine/imine groups of PANI and undercoordinated Pb 2+ defect sites, leading to effective defect passivation. Consequently, PANI‐modified films exhibit enhanced optical absorption, increased photoluminescence intensity, and prolonged charge‐carrier lifetimes. The optimized MAPI_30 film shows an increase in average carrier lifetime from 813.4 to 971.6 ns, indicating suppressed nonradiative recombination. Interfacial PL/TRPL studies further confirm efficient electron extraction at the perovskite/TiO 2 interface. These improvements translate into enhanced device performance in HTL‐free perovskite solar cells, achieving a power conversion efficiency of 11.55% and an open‐circuit voltage of 1.04 V, compared to 9.41% for pristine MAPI. Moreover, PANI‐modified films exhibit excellent thermal stability at 85°C for 48 h and strong photostability under continuous illumination. This work establishes polyaniline as a simple and scalable strategy for developing efficient and durable perovskite solar cells.