The commercialization of perovskite solar cells is mainly limited by their operational stability. Interlayer modification by thin interface materials between the perovskite and the charge transport layers is one of the most effective methods to promote the efficiency and stability of perovskite devices. However, the commonly used interlayer materials do not meet all the demands, including good film quality, excellent stability, and passivation capability without interfering with the charge transport. In this work, we propose a new material, water stable haloplumbate [TBA]PbI3 for interfacial modification, which is formed on the perovskite surface in-situ by tetra-butylammonium iodide (TBAI) treatment. Benefiting from its passivation effect and robustness, the modified devices result in a power conversion efficiency of 22.90% with excellent environmental and operational stability.