Polymer Films with High Stability Embedded Within CsPbBr3@ZnO Quantum Dots

Objective Perovskite quantum dots (PQDs) are widely employed in solar cells, LED displays, photodetectors, gas sensing, and other fields due to their high photoluminescence quantum yield, tunable wavelength, wide absorption range, and unique quantum limiting effect. However, their poor stability and easy degradation in environmental conditions limit the application. When PQDs are exposed to the air, the oxygen in the air will combine with the surface defects of perovskite, which is prone to form superoxygen electric pairs under light, causing cascade damage and rapid performance decay of perovskite. Furthermore, water and oxygen in the air easily result in degraded octahedral structure of PQDs, thus losing PQDs are emission performance and transforming into a non-emission state. Similarly, chemical degradation of PQDs occurs when PQDs are exposed to environmental conditions, and the surface organic amines absorb water, which can easily decrease their quantum yield. Since this limits the application of PQDs in the commercialization process, how to improve their stability has become an urgent problem to be solved. We synthesize ZnO-coated CsPbBr3 quantum dots (QDs) by a simple solution processing route and embed them in a polymethyl methacrylate polymer. ZnO coating and polymer packaging enhance the stability and degradability of CsPbBr3 QDs and they are applied to white light display devices. This co-passivation strategy of metal oxide coating and polymer encapsulation broadens the existing strategies to improve the QD stability and provides a new idea for practical applications of CsPbBr3 QDs. Methods Diethylzinc is in situ coated on the surface of CsPbBr3 QDs, and the polymer poly (methyl methacrylate, PMMA) is adopted for encapsulation. The QDs coordinated with diethylzinc on the surface are embedded into PMMA and then exposed to air to oxidize diethylzinc into ZnO, which brings a stable PMMA film with ZnO-coated CsPbBr3 QDs. Among them, we first characterize the structure of the synthesized CsPbBr3 QDs and the elemental characterization after ZnO coating to prove the QDs synthesis and the successful coating of ZnO. Then, we investigate the synthesis temperature of CsPbBr3 QDs and the ratio of bromine to determine the best effect. After that, we explore the effects of different Zn contents on the optical properties of CsPbBr3 QDs. After determining the optimal Zn content, water stability, thermal stability, and device operating stability of CsPbBr3/PMMA and CsPbBr3@ZnO/PMMA are tested and the results are analyzed. Finally, CsPbBr3@ZnO/PMMA thin film is applied to the white light display device for display effect testing. Results and Discussions The synthesized CsPbBr3@ZnO/PMMA QDs are monodisperse cubic in the solvent with an average size of 12. 22 nm, showing good homogeneity. The stable PMMA films coated with ZnO CsPbBr3 QDs have excellent water stability and optical properties, with an average carrier decay life of 33. 44 ns, and the photoluminescent quantum yield (PLQY) is up to 82. 2%. After seven days of immersion in water, the fluorescence intensity remains at 55. 4% of the initial value (Fig. 5). After heating at 90 degrees C for 40 min, the fluorescence intensity remains at 62. 2% of the initial value (Fig. 6). Subsequently, the prepared green QD film is combined with the red film prepared by K2SiF6 : Mn4+ (KSF) red powder and the blue LED to produce a white light-emitting device. The device displays white light coordinates of (0. 32, 0. 34), covering 127. 18% of the NTSC color gamut and 94. 96% of the Rec. 2020 color gamut (Fig. 7). Conclusions ZnO-coated CsPbBr3 QDs are synthesized by a simple solution processing route and embedded into PMMA films. The prepared green QD films have good optical properties and excellent stability, and the photoluminescence quantum yield is as high as 82. 2%. After seven days of water stability test and 40 min of high-temperature heating test, the fluorescence intensity remains at 55. 4% and 62. 2% of the initial value respectively. Finally, the CsPbBr3@ZnO/PMMA green QD film is combined with red phosphor and blue LED chip to make a white light-emitting device. The device displays white light coordinates of (0. 32, 0. 34), covering 127. 18% of the NTSC gamut and 94. 96% of the Rec. 2020 gamut. In summary, we propose a strategy for synergistically enhancing the stability of PQDs using metal oxides and polymers, which may promote practical applications of PQDs.