Polyaniline-Enabled Defect Passivation for Stable and Efficient MAPbI₃-Based Perovskite Solar Cells

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 Pb²⁺ 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/TiO₂ 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.