Unlocking Triple Interfacial Synergy in All-Inorganic Carbon-Based CsPbI2Br Perovskite Solar Cells via Molecular Interface Engineering.

All-inorganic CsPbI2Br perovskite solar cells suffer from efficiency and stability losses caused by defect-mediated recombination, unfavorable interfacial energetics, and environmental degradation in carbon-based architectures. Here, we report a molecular interface engineering strategy using N-methyl-4-bromobenzylammonium chloride (4-Br-NMBACl) that enables a triple interfacial synergy addressing these limitations simultaneously. The molecular post-treatment effectively passivates undercoordinated Pb2+ defects and halide vacancies through the coordination interactions of -NH- groups and the defect-compensating effect of Cl- ions, respectively, while simultaneously optimizing interfacial energy-level alignment and enhancing moisture resistance. These synergistic effects suppress non-radiative recombination, improve charge extraction, and enhance environmental resistance. As a result, the devices deliver a power conversion efficiency (PCE) of 14.22%, compared with 12.17% for control devices, together with significantly improved operational and ambient stability. This work demonstrates a simple and effective molecular strategy for simultaneously regulating defect chemistry, interfacial energetics, and moisture resistance in all-inorganic perovskite solar cells.