Suppression of halide migration and improved stability in double-coated cesium lead halide perovskite nanocrystals for application in down conversion white-light-emitting diodes

In the past few years' cesium lead halide (C_sPbX₃: X= I, Br, Cl) perovskite nanocrystals (NCs) have shown tremendous progress in the field of white and color-tuning lighting technologies for their favorable color tunability, superior emission intensity, narrow emission spectra, and better color purity. However, the perovskite NCs degrade very easily in presence of water and are prone to the ion migration process. It's also very challenging to synthesize stable red-emitting perovskite NCs which is a major component for generating white light-emitting diodes (WLEDs). Here we report the synthesis of highly luminescent green-emitting Zn-doped CsPbX₃ NCs via the ligand-assisted reprecipitation (LARP) synthesis method at high humid conditions (RH > 60%). The red-emitting Zn-doped CsPbBrxI_3-x NCs were synthesized from pre-synthesized Zn-doped CsPbBr₃ NCs via the halide exchange process. We also grew polymer shells around the silica-coated NCs to further improve the stability. These double shelling around the NCs facilitates improved structural stability and demonstrates higher resistance to the halide exchange process among different NCs. Finally, we fabricated WLEDs by mixing double-coated green and red NCs and deposited them on a blue LED chip. The optimized WLED device exhibited a luminous efficiency of 28.08 Lm/W, a color gamut of 106.67%, and CIE chromaticity coordinates of (0.334, 0.326). Our research work provides very insightful ideas for synthesizing stable color-tunable NCs and also the fabrication of single-layer WLEDs, which will boost the development of high-performance lighting technologies. (author)