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Efficient and Stable CsPbBr3 Quantum-Dot Powders Passivated and Encapsulated with a Mixed Silicon Nitride and Silicon Oxide Inorganic Polymer Matrix
- Yoon, Hee Chang, Lee, Soyoung, Song, Jae Kyu, Yang, Heesun, Do, Young Rag
- ACS applied materials & interfaces 2018 v.10 no.14 pp. 11756-11767
- air, cesium, coatings, color, diodes, filters, humidity, hydrolysis, lead, ligands, liquid crystal display, mixing, photoluminescence, polymethylmethacrylate, powders, quantum dots, silica, silicon nitride, temperature
- Despite the excellent optical features of fully inorganic cesium lead halide (CsPbX₃) perovskite quantum dots (PeQDs), their unstable nature has limited their use in various optoelectronic devices. To mitigate the instability issues of PeQDs, we demonstrate the roles of dual-silicon nitride and silicon oxide ligands of the polysilazane (PSZ) inorganic polymer to passivate the surface defects and form a barrier layer coated onto green CsPbBr₃ QDs to maintain the high photoluminescence quantum yield (PLQY) and improve the environmental stability. The mixed SiNₓ/SiNₓOy/SiOy passivated and encapsulated CsPbBr₃/PSZ core/shell composite can be prepared by a simple hydrolysis reaction involving the addition of adding PSZ as a precursor and a slight amount of water into a colloidal CsPbBr₃ QD solution. The degree of the moisture-induced hydrolysis reaction of PSZ can affect the compositional ratio of SiNₓ, SiNₓOy, and SiOy liganded to the surfaces of the CsPbBr₃ QDs to optimize the PLQY and the stability of CsPbBr₃/PSZ core/shell composite, which shows a high PLQY (∼81.7%) with improved thermal, photo, air, and humidity stability as well under coarse conditions where the performance of CsPbBr₃ QDs typically deteriorate. To evaluate the suitability of the application of the CsPbBr₃/PSZ powder to down-converted white-light-emitting diodes (DC-WLEDs) as the backlight of a liquid crystal display (LCD), we fabricated an on-package type of tricolor-WLED by mixing the as-synthesized green CsPbBr₃/PSZ composite powder with red K₂SiF₆:Mn⁴⁺ phosphor powder and a poly(methyl methacrylate)-encapsulating binder and coating this mixed paste onto a cup-type blue LED. The fabricated WLED show high luminous efficacy of 138.6 lm/W (EQE = 51.4%) and a wide color gamut of 128% and 111% without and with color filters, respectively, at a correlated color temperature of 6762 K.