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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.