Abstract
For the inorganic perovskite CsPbI(3), 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 CsPbI(3). Specifically, 3-(aminomethyl)piperidinium iodide (3AMPI(2)), an organic salt insoluble in the CsPbI(3) 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 CsPbI(3), 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.