As an emerging luminescent material, organic-inorganic hybrid metal halides have some advantages such as simple preparation methods, good solution processability, and tunable structures. They exhibit excellent optoelectronic properties and show a promising potential in cutting-edge applications such as solid-state lighting, anti-counterfeiting, scintillators, and detectors. Conventional high-efficiency organic-inorganic hybrid metal halides are mainly lead-based, but they have limited performance in terms of humidity and thermal stability, and the high toxicity of lead seriously restricts practical applications, necessitating a search for alternative metals. Metals that can replace Pb include those with a ns² configuration (i.e., mainly Ge²⁺, Sn²⁺, Sb³⁺, Bi³⁺, and Te⁴⁺, etc.) transition metals (i.e., Cu⁺, Zn²⁺, Ag⁺, etc.) and rare-earth metals. Among them, organic-inorganic hybrid Cu-based halides have some advantages such as low cost, simple synthesis methods, rich structures and luminescent properties, and high stability, making them effective materials to replace conventional high-efficiency organic-inorganic Pb-based halides, gradually attracting much attention.

This review summarizes the different synthesis methods, structures, optical properties, and practical applications of organic-inorganic hybrid copper-based halides in fields such as white LED lighting, X-ray imaging, near-infrared night vision imaging, and anti-counterfeiting. Organic-inorganic hybrid Cu-based halides are simple to be synthesized by some methods such as solvent evaporation, hydrothermal synthesis, cooling crystallization, anti-solvent diffusion, as well as more convenient methods like grinding and ultrasonication. Different structures can be obtained via simply changing the reaction conditions during synthesis, giving organic-inorganic hybrid Cu-based halides a significant advantage in synthesis. Organic-inorganic hybrid Cu-based halides are composed of independent organic cations and metal halide anions, with Cu exhibiting multiple coordination configurations and capable of forming various anionic structures with halide ions (i.e., Cl^-, Br^-, and I^-). Common low-dimensional (0D, 1D, and 2D) organic-inorganic hybrid Cu-based halides feature Cu in the inorganic part coordinated with halide ions in two-, three-, or four-coordination numbers. After halide coordination, various units are formed, such as linear (CuX₂)^-, triangular (CuX₃)^2-, and tetrahedral (CuX₄)^3- units. These units are further connected via sharing vertices, edges, or faces, and are periodically embedded into the organic matrix. They can combine with different types of organic cations to form diverse structures, resulting in richer and more tunable luminescent properties.

Organic-inorganic hybrid Cu-based halides possess a variety of luminescence mechanisms, such as self-trapped state emission, cluster emission, metal or halogen to organic ligand charge transfer, halogen to metal charge transfer, and d⁹s¹→d¹⁰ transitions of the metal center (MC). The complex luminescence mechanisms endow organic-inorganic hybrid Cu-based halides with fascinating optical properties, characterized by broad-band emission, large Stokes shifts, long lifetimes, and emission colors ranging from blue light to near-infrared. This review discusses the characteristics of different luminescence mechanisms and provides a detailed analysis of the effects of dimensional structures, types and sizes of organic cations, types of inorganic anions, types of halogens, crystal orientations, and solvent responses on the luminescent properties of organic-inorganic hybrid Cu-based halide single crystals. Subsequently, the applications of organic-inorganic hybrid Cu-based halides are studied. Organic-inorganic hybrid Cu-based halides can be applied in numerous fields like WLEDs, X-ray imaging, near-infrared night vision imaging, and anti-counterfeiting due to their low-cost synthesis, processability via solution methods, diverse structures, and tunable optical properties.