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Organic-inorganic halide perovskites achieved tremendous success in solar cells, however, their commercialization has not yet been realized. The primary reason is the intrinsic property of perovskite film. The significant density of defects in the polycrystalline perovskite layers influenced not only the performance of the solar cell as well its long-term stability. Here, we employed a post-surface treatment of the perovskite layer by tetrabutylammonium tetrafluoroborate (TBATFB). TBATFB interacted through hydrogen bonding with the 3D perovskite and formed an in situ a 1D TBAPbI_1.66Br_0.34BF₄ on the surface of the 3D perovskite. This low-dimensional 1D perovskite (perovskitoid) capping layer represses the defects in perovskite by blocking the nonradiative recombination centers and minimizing the surface and grain boundary defects. Our experimental results verified both the electron and hole defects were …