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., CsPbBr 3 ) and red-emitting iodide (e.g., CsPbI 3 ) 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 (RNH 3 ) 2 PbI 4 (R = C 18 H 35 –, C 12 H 25 –, and C 8 H 17 –) and uniting these with red-emitting CsPbI 3 perovskite quantum dots (QDs). It relies on self-assembly from ligand-capped CsPbI 3 nanocrystals to form single-layer sheets of (C 18 H 35 NH 3 ) 2 PbI 4 : via judicious selection of alkylamines and alkyl acids, (RNH 3 ) 2 PbI 4 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.