High Color Rendering Index White-Light Emission from UV-Driven LEDs Based on Single Luminescent Materials: Two-Dimensional Perovskites (C₆H₅C₂H₄NH₃)₂PbBr<i>_x</i>Cl_4–<i>x</i>

Two-dimensional (2D) white-light-emitting hybrid perovskites (WHPs) are promising active materials for single-component white-light-emitting diodes (WLEDs) driven by UV. However, the reported WHPs exhibit low quantum yields (≤9%) and low color rendering index (CRI) values less than 85, which does not satisfy the demand of solid-state lighting applications. In this work, we report a series of mixed-halide 2D layered WHPs (C₆H₅C₂H₄NH₃)₂PbBr<i>_x</i>Cl_4–<i>x</i> (0 < <i>x</i> < 4) obtained from the phenethylammonium cation. Unlike the reported WHPs including (C₆H₅C₂H₄NH₃)₂PbCl₄, the mixed-halide perovskites display morphology-dependent white emission for the different extents of self-absorption. Additionally, the amount of Br has a huge influence on the photophysical properties of mixed-halide WHPs. With the increasing content of Br, the quantum yields of WHPs increase gradually from 0.2 to 16.9%, accompanied by tunable color temperatures ranging from 4000 K (“warm” white light) to 7000 K (“cold” white light). When applied to the WLEDs, the mixed-halide perovskite powders exhibit tunable white electroluminescent emission with very high CRI of 87–91