Interfacial modification is crucial to fully develop the potential of semiconductor devices, including the revolutionary halide perovskite-based optoelectronics, such as photovoltaics, light-emitting diodes, and photodetectors. The all-inorganic halide perovskites, which are potential long-term stable photovoltaic materials, are suffering from poor interfacial contact with metal oxide charge-selective layer, severely limiting the power conversion efficiency and stability of inorganic perovskite solar cells. Here, we propose an intermediate-phase engineering strategy to improve the inorganic perovskite/metal oxide interface by utilizing volatile salts. The introduction of organic cations (such as methylammonium and formamidinium), which can be doped into the perovskite lattice, leads to the formation of an organic-inorganic hybrid perovskite intermediate phase, promoting a robust interfacial contact through hydrogen bonding. A champion CsPb(I0.75Br0.25)(3)-based device with a power conversion efficiency of 17.0% and an open-circuit voltage of 1.34 V was realized, implying that a record of over 65% of the Shockley-Queisser efficiency limit is achieved.