Organic-Inorganic Hybrid Cuprous-Based Metal Halides with Unique Two-Dimensional Crystal Structure for White...

Ternary cuprous (Cu⁺)-based metal halides, represented by cesium copper iodide (e.g., CsCu₂I₃ and Cs₃Cu₂I₅), are garnering increasing interest for light-emitting applications owing to their intrinsically high photoluminescence quantum yield and direct band gap. Toward electrically driven light-emitting diodes (LEDs), it is highly desirable for the light emitters to have a high structural dimensionality as it may favor efficient electrical injection. However, unlike lead-based halide perovskites whose light-emitting units can be facilely arranged in three-dimensional (3D) ways, to date, nearly all ternary Cu⁺-based metal halides crystallize into 0D or 1D networks of Cu-X (X=Cl, Br, I) polyhedra, whereas 3D and even 2D structures remain mostly uncharted. Here, by employing a fluorinated organic cation, we report a new kind of ternary Cu⁺-based metal halides, (DFPD)CuX₂ (DFPD⁺=4,4-difluoropiperidinium), which exhibits unique 2D layered crystal structure. Theoretical calculations reveal a highly dispersive conduction band of (DFPD)CuBr₂, which is beneficial for charge carrier injection. It is also of particular significance to find that the 2D (DFPD)CuBr₂ crystals show appealing properties, including improved ambient stability and an efficient warm white-light emission, making it a promising candidate for single-component lighting and display applications.