Exciplex-Facilitated Charge Extraction and Defect Chelation to Improve Inorganic Perovskite Solar Cells

Rational molecular engineering of the perovskite/hole transport layer interface offers a promising route to simultaneously address inefficient charge extraction, defect-mediated recombination, and lead leakage in CsPbI3–xBrx perovskite solar cells. Herein, we introduce 2,2′-dinitro-9,9′-spirobifluorene (DN-SBF) as an interfacial molecular bridge to tackle these challenges. DN-SBF optimizes energy level alignment, establishes π–π interactions, and forms exciplexes with Spiro-OMeTAD, thereby facilitating interfacial charge transport. Meanwhile, DN-SBF passivates undercoordinated Pb2+ through multiple coordination modes, including robust bidentate chelation formed by adjacent nitro groups, effectively passivating defects and suppressing non-radiative recombination. Importantly, multipoint coordination immobilizes leachable Pb2+, substantially mitigating lead leakage and improving film biocompatibility. As a result, DN-SBF-engineered CsPbI3–xBrx devices achieve a champion power conversion efficiency of 22.40% along with significantly enhanced operational and environmental stability. This work highlights the potential of versatile molecular bridges to concurrently enhance performance, stability, and eco-friendliness, which may contribute to the development of more sustainable perovskite photovoltaics.