Single‐Layer Sheets of Alkylammonium Lead Iodide Perovskites with Tunable and Stable Green Emission for White Light‐Emitting Devices

Recently, metal halide perovskites have attracted considerable interest as highly emissive phosphors for use in white light-emitting diodes (WLEDs). In perovskites, the migration of halide anions between green-emitting bromide (e.g., CsPbBr3) and red-emitting iodide (e.g., CsPbI3) materials is one obstacle to application. Here perovskite WLEDs that do not suffer from the anion exchange problem are reported: this is done by developing green-emitting single-layer sheets of (RNH3)(2)PbI4 (R = C18H35-, C12H25-, and C8H17-) and uniting these with red-emitting CsPbI3 perovskite quantum dots (QDs). It relies on self-assembly from ligand-capped CsPbI3 nanocrystals to form single-layer sheets of (C18H35NH3)(2)PbI4: via judicious selection of alkylamines and alkyl acids, (RNH3)(2)PbI4 single-layer sheets that exhibit bright and stable green emission with well-defined single-layer thickness are produced. Emission from 505, 512 to 536 nm is tuned and a narrow (<20 nm) linewidth is retained. Perovskite LEDs that produce white light with chromaticity coordinates (0.32, 0.33) and color gamut that reaches 117% National Television System Committee (NTSC) in the International Commission on Illumination (CIE) 1931 color space are demonstrated.