High-efficiency and super-stability lead-free perovskite cesium zinc chloride / silicon oxide nano composite material and preparation method thereof

Abstract

The invention discloses a lead-free Cs2ZnCl4 / SiO2 nano composite material with high photoluminescence quantum yield and super stability and a preparation method of the lead-free Cs2ZnCl4 / SiO2 nano composite material. By adopting a loading method, the problems of low luminous efficiency and poor stability of Cs2ZnCl4 colloidal quantum dots synthesized by a ligand-assisted reprecipitation method are solved. Mesoporous nano SiO2 is used as a carrier, Cs2ZnCl4 quantum dots are loaded on the nano SiO2, Si-O-Si is formed on the outer layer of the nano SiO2 to further rivet the Cs2ZnCl4 quantum dots, the Cs2ZnCl4 / SiO2 nanocrystal is obtained, the photoluminescence intensity is enhanced by 10 times, the high photoluminescence quantum yield is up to 74.28%, and the ultrafast photoluminescence service life is 2.4 ns. The Cs2ZnCl4 / SiO2 nano composite material obtained by the invention has high photoluminescence quantum yield and super stability, and can adapt to the application of light display and light storage. The preparation method has the advantages of simple preparation process, good stability, short period, environmental protection and the like.

Description

Technical Field

[0001] This invention relates to a synthetic lead-free Cs2ZnCl4 / SiO2 nanocomposite material with high photoluminescence quantum yield and ultra-stable properties and its preparation method, belonging to the field of optoelectronic functional materials. Background Technology

[0002] All-inorganic metal halide perovskite quantum dots have shown great application potential in optoelectronic devices due to their outstanding properties—tunable bandgap, high photoluminescence quantum yield (PLQY), and excellent monochromaticity. These properties enable their application in light-emitting diodes (LEDs), solar cells, lasers, photodetectors, and X-ray scintillators. Among them, chloride-based metal halide nanocrystals (Cs₂ZnCl₄, Cs₂CuCl₄, Cs₂SnCl₆) have significant advantages over bromide (Br) and iodide (I) systems: non-toxicity, enhanced stability, wider bandgap, efficient bandgap tunability, and excellent process compatibility. However, these materials still suffer from insufficient stability under ambient temperature and harsh conditions (such as high humidity and polar solvents).

[0003] Therefore, a large amount of research has focused on improving the optical properties and stability of perovskite quantum dots through various methods, including matrix passivation, metal ion doping, encapsulation, and the use of mesoporous metal-organic frameworks. For example, Qin et al. introduced a SiO2 shell through surface modification to form CsPb. 0.7 Zn 0.3 Br3@SiO2 core-shell nanocrystals. The resulting CsPb 0.7 Zn 0.3 Br3@SiO2 core-shell nanocrystals retained 43% of their original photoluminescence intensity after immersion in water for 36 hours, and 39% after ethanol treatment for 210 minutes. Meng et al. reported that CsPbBr3 encapsulated in a SiO2 shell maintained a stable photoluminescence yield (PL) at 515 nm after heating at 60 °C for 84 hours, and retained 90% of its original PL intensity after storage in a high humidity environment for 6 hours. Ren et al. embedded perovskite quantum dots CsPbBrCl2 into a MOF cage structure to form CsPbBrCl2@MOF composites. The resulting composites retained 46.2% of their original luminescence intensity under level 4 UV irradiation. Zhang et al. used MOF-74 as a template to confine the growth of Cs3Cu2I5 quantum dots (4.33 nm). The resulting Cs3Cu2I5@MOF-74 film retained 89% of its original photoluminescence quantum yield (15.64%) after storage in an environment with a relative humidity exceeding 70% for 1440 hours.

[0004] Therefore, this invention develops a lead-free Cs2ZnCl4 / SiO2 nanocomposite material with high photoluminescence quantum yield and ultra-stable properties, along with its preparation method, using a loading method. This material is a lead-free perovskite with high quantum efficiency. The method involves loading lead-free Cs2ZnCl4 quantum dots onto mesoporous nano-SiO2, creating a spatial confinement effect to prevent the aggregation and quenching of Cs2ZnCl4 quantum dots, passivating surface defects, and reducing non-radiative recombination pathways, thus achieving a Cs2ZnCl4 / SiO2 nanocomposite material with high photoluminescence quantum yield and ultra-stable properties. The sample preparation process involves first preparing Cs2ZnCl4 colloidal quantum dots using a ligand-assisted precipitation method. Then, mesoporous nano-SiO2 is used as a carrier to load the Cs2ZnCl4 quantum dots onto the nano-SiO2, and a Si-O-Si layer is formed on the outer layer to further anchor the Cs2ZnCl4 quantum dots, resulting in the Cs2ZnCl4 / SiO2 nanocomposite material, effectively improving the luminescence efficiency and stability of the Cs2ZnCl4 quantum dots. Summary of the Invention

[0005] This invention provides a method for synthesizing a lead-free Cs₂ZnCl₄ / SiO₂ nanocomposite material with high photoluminescence quantum yield and ultrastability. The method involves first preparing Cs₂ZnCl₄ colloidal quantum dots using a ligand-assisted precipitation method. CZ₂ quantum dots dispersed in hexane are then added dropwise to ethanol, followed by the slow addition of mesoporous SiO₂ nanoparticles. The mixture is stirred for 60 minutes and then allowed to settle to precipitate. The resulting product is centrifuged and washed with an APTES / ethanol mixture. Finally, it is dried at 60°C for 12 h to obtain the Cs₂ZnCl₄ / SiO₂ nanocomposite material exhibiting high photoluminescence quantum yield and ultrastability.

[0006] The present invention exhibits significant technical advantages. By loading Cs₂ZnCl₄ quantum dots onto mesoporous nano-SiO₂, a spatial confinement effect is created, preventing the aggregation and quenching of Cs₂ZnCl₄ quantum dots, passivating surface defects, and reducing non-radiative recombination pathways. The mesoporous nano-SiO₂, with its strong adsorption properties, adsorbs Cs₂ZnCl₄ quantum dots into its pores and surface, creating a spatial confinement effect that prevents the quantum dots from being quenched due to aggregation. Its silanol groups (Si-OH) coordinate or electrostatically interact with uncoordinated ions (Zn²⁺ vacancies or Cl⁻ vacancies) on the exposed surface of the Cs₂ZnCl₄ quantum dots, stabilizing the quantum dot surface structure and reducing non-radiative recombination pathways. APTES adhere to the nano-silica surface and undergo hydrolysis-condensation reactions upon exposure to air, forming a Si-O-Si network. This Si-O-Si network not only passivates surface defects of the Cs₂ZnCl₄ quantum dots but also further anchors them within the mesoporous structure of the nano-silica. Compared to other direct conversion methods, this post-processing strategy ensures that Cs₂ZnCl₄ quantum dots are completely embedded in the nanopores of nano-silica without damaging the crystal structure of the material. Therefore, this invention has two advantages: First, the spatial confinement effect provided by mesoporous nano-SiO₂ prevents the aggregation and quenching of Cs₂ZnCl₄ quantum dots, passivates surface defects, and reduces non-radiative recombination pathways, ultimately ensuring the excellent high luminescence efficiency and environmental / chemical stability of the Cs₂ZnCl₄ / SiO₂ nanocomposite material. Second, the preparation process of this invention is simple, has good stability, a short cycle time, and a high yield, which can save production costs to a certain extent. Attached Figure Description

[0007] Figure 1 This is the XRD pattern of the Cs2ZnCl4 / SiO2 nanocomposite sample prepared in this invention.

[0008] Figure 2 This is a transmission electron microscope (TEM) image of the Cs2ZnCl4 / SiO2 nanocomposite sample prepared in this invention.

[0009] Figure 3 This is the photoluminescence emission pattern of the Cs2ZnCl4 / SiO2 nanocomposite sample prepared in this invention under 365 nm ultraviolet light excitation. Detailed Implementation

[0010] The method for preparing high ultraviolet-emitting Cs2ZnCl4 / SiO2 nanocomposite samples according to the present invention is described in detail below: Using CsCl and ZnCl2 as raw materials, cesium chloride, oleylamine and oleic acid are dissolved in N,N-dimethylformamide to form solution A; Solution B is prepared by dissolving a stoichiometric amount of zinc chloride in a minimum volume of concentrated hydrochloric acid; Subsequently, solution B was rapidly added to solution A under vigorous stirring to promote the rapid nucleation and growth of Cs2ZnCl4 quantum dots; Centrifuge the crude Cs2ZnCl4 quantum dot solution at 8000 rpm for 5 minutes to separate unreacted components as much as possible; The final product was purified using the following steps: 2 mL of n-hexane was added to the solution, and the mixture was centrifuged at 8000 rpm for 5 minutes to remove potential aggregates. Then, 2 mL of ethyl acetate was added to the supernatant to precipitate the nanocrystals, and the mixture was centrifuged again at 8000 rpm for 5 minutes. The final precipitate was dispersed in 1 mL of n-hexane and sealed in a glove box. CZC quantum dots dispersed in n-hexane (1 mL) were dropped into ethanol (20 mL) and ultrasonically dispersed. Then 0.2 g of nano silica was slowly added to the solution (6), and the mixture was stirred for 60 minutes and then allowed to stand to precipitate.

[0011] The product obtained in (7) was centrifuged and washed with an APTES / ethanol mixture. Finally, the product was dried at 60°C for 12 h.

[0012] Figure 1 The X-ray diffraction (XRD) pattern of the prepared Cs2ZnCl4 / SiO2 nanocomposite sample is shown. The horizontal axis represents the diffraction angle (2θ) in degrees (º), and the vertical axis represents the diffraction intensity. The XRD pattern shows the diffraction peak positions as 20.339°, 22.865°, 23.816°, 24.031°, 27.543°, 28.264°, 29.232°, 30.783°, 31.083°, 33.135°, 33.357°, 34.478°, and 36.871°, which correspond to the (121), (211), (031), (002), (230), (310), (122), (320), (212), (132), (222), (330), and (042) crystal planes, respectively. This confirms that the Cs2ZnCl4 / SiO2 nanocomposite material is in an orthorhombic (Pnma) phase consistent with Cs2ZnCl4 quantum dots (PDF#70-1965).

[0013] Figure 2 The transmission electron microscope (TEM) image of the prepared Cs2ZnCl4 / SiO2 nanocomposite sample shows uniformly dispersed Cs2ZnCl4 quantum dots with a size consistent with the original quantum dots (~10 nm). The lattice fringes of Cs2ZnCl4 are clearly visible within the nano-SiO2 matrix, which corresponds to the (002) crystal plane of the orthorhombic Cs2ZnCl4 structure.

[0014] Figure 3The photoluminescence emission spectrum of the prepared Cs₂ZnCl₄ / SiO₂ nanocomposite sample under 365 nm ultraviolet light excitation is shown. It exhibits strong ultraviolet emission under ultraviolet excitation, with a 10-fold increase in luminescence intensity compared to Cs₂ZnCl₄ colloidal quantum dots.

Claims

1. This invention discloses a lead-free Cs2ZnCl4 / SiO2 nanocomposite material with high photoluminescence quantum yield and ultra-stable properties. This material is obtained by loading lead-free Cs2ZnCl4 onto nano-SiO2 using a loading method. By using Si-O-Si rivets to attach Cs2ZnCl4 quantum dots, a 10-fold increase in photoluminescence intensity and ultra-high stability are achieved.

2. Based on claim 1, the preparation process of the composite material is as follows: First, Cs2ZnCl4 colloidal quantum dots are prepared by ligand-assisted precipitation. Cs2ZnCl4 quantum dots dispersed in n-hexane (1 mL) are dropped into ethanol (20 mL), and then 0.2 g of mesoporous nano-SiO2 is slowly added. The mixture is stirred for 60 minutes and then allowed to stand to precipitate. The obtained product is separated by centrifugation, washed with APTES / ethanol mixture, and finally dried at 60 °C for 12 h.

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