3-(Aminomethyl)piperidinium Spacer-Induced Dion-Jacobson 2D Perovskite Beneath CsPbI3 for Stable and Efficient Inorganic Perovskite Solar Cells.

For the inorganic perovskite CsPbI₃, while many strategies have focused on passivating the top surface, engineering the interface beneath the perovskite layer remains a critical yet underexplored avenue, primarily due to the high crystallization temperature and the dissolution of underlying layers during solution processing. Here, these longstanding challenges are addressed by introducing a strategic placement of a Dion-Jacobson quasi-2D perovskite layer beneath CsPbI₃. Specifically, 3-(aminomethyl)piperidinium iodide (3AMPI₂), an organic salt insoluble in the CsPbI₃ precursor solution, is employed to form a robust quasi-2D interlayer without degradation during perovskite deposition and annealing. This bottom-layer integration passivates interfacial defects, promotes favorable crystallization of CsPbI₃, and results in significantly enhanced device performance, achieving a power conversion efficiency of 20.98%, an open-circuit voltage (V_oc) of 1.21 V, a short-circuit current density (J_sc) of 20.59 mAcm^-2, and a fill factor of 84.21%, along with robust long-term operational stability. The findings demonstrate a targeted interfacial design approach that unlocks new opportunities for simultaneously optimizing efficiency and stability in inorganic perovskite photovoltaics.