Copper iodide (CuI) thin films were grown on Si(100) substrates using a copper film iodination reaction method. It was found that γ-CuI films have a uniform and dense microstructure with (111)-orientation. Transmission spectra indicated that CuI thin films have an average transmittance of about 60% in the visible range and the optical band gap is 3.01 eV. By checking the effect of the thickness of the Cu films and annealing condition on the photoluminescence (PL) character of CuI films, the luminescence mechanisms of CuI have been comprehensively analyzed, and the origin of different PL emissions are proposed with Cu vacancy and iodine vacancy as defect levels.

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All‐inorganic Cu‐based perovskite CsxCuyIx+y thin films are deposited with vacuum thermal evaporation using CuI and CsI mixed powder with different proportion as evaporation sources. With CuI film as buffer‐layer, the as grown CsxCuyIx+y perovskite films only have CsCu2I3 phase owing to the epitaxy on CuI layer. And the thin film quality and optoelectronic properties of CsCu2I3 are also improved. Then, metal–semiconductor–metal UV detectors based on CsCu2I3 films with Au interdigital electrodes are fabricated and the enhancement of photoresponse performance is investigated in detail. The peak responsivity and specific detectivity of the detector are 49.22 mA W−1 and 2.49 × 1012 cm Hz1/2 W−1, which are 74 and 138 times larger than that of the device without the CuI buffer‐layer, respectively.