Organic‐Inorganic Hybrid Cuprous‐Based Metal Halides with Unique Two‐Dimensional Crystal Structure for White Light‐Emitting Diodes

Abstract Ternary cuprous (Cu + )‐based metal halides, represented by cesium copper iodide (e.g., CsCu 2 I 3 and Cs 3 Cu 2 I 5 ), 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)CuX 2 (DFPD + =4,4‐difluoropiperidinium), which exhibits unique 2D layered crystal structure. Theoretical calculations reveal a highly dispersive conduction band of (DFPD)CuBr 2 , which is beneficial for charge carrier injection. It is also of particular significance to find that the 2D (DFPD)CuBr 2 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.