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Abstract Morphologically noticeable mixed‐dimensional perovskite films induced by ionic liquids (ILs) engineering have been rarely reported. This work (DOI: 10.1002/inf2.12459) innovatively introduced IL 1‐(3‐cyanopropyl) ‐3‐methylimidazolium chloride (CPMIMCl) into the 3D perovskite precursor system to form 1D‐3D mixed perovskite via two‐step method. The generated 1D CPMIMPbI₃ with in‐plane orientation resides at the grain boundaries of 3D perovskite can be appreciably observed from the morphology level, leading to creation of high‐quality films with enlarged grain size. image