Preparation method of sandwich structure quantum dots

Abstract

The invention discloses a preparation method of sandwich structure quantum dots, and belongs to the field of photoelectric materials and devices. A special reaction container is adopted to prepare a precursor solution, and sandwich structure quantum dots are obtained after a reaction system is formed; the quantum dot has a core-shell-shell structure of a metal oxide core, a perovskite CsPbX3 central layer and a metal oxide shell. A metal oxide is introduced into a precursor to serve as a structure-directing agent, epitaxial growth is induced, and surface defects are passivated; the photoluminescence quantum yield of the obtained quantum dots reaches up to 95%, and the emission wavelength is continuously adjusted to 690 nm (dark red light) from 518 nm (green light). In severe environments such as high temperature, water immersion and ultraviolet radiation, the luminous intensity retention rate exceeds 70%, and the stability is excellent. The full-perovskite white light LED device prepared from the material has the color gamut coverage of 134.34% NTSC and 100.47% Rec. 2020, and has huge application potential in the fields of wide color gamut display and efficient illumination. The method is simple and convenient in process, good in repeatability and good in environmental stability, and provides an effective path for improving the performance of the perovskite quantum dots.

Description

Technical Field

[0001] This invention relates to the field of quantum dot synthesis technology, and in particular to a method for preparing sandwich-structured quantum dots applicable to the perovskite field. Background Technology

[0002] Perovskite quantum dots, as a new type of semiconductor nanocrystal, have shown great potential in the field of optoelectronics due to their outstanding characteristics such as high photoluminescence quantum yield, narrow emission half-width at half-maximum, excellent color purity, and continuous tuning of emission wavelength in the visible light region through composition and size. Among them, all-inorganic CsPbX3 (X = Cl, Br, I) perovskite quantum dots are considered one of the ideal light-emitting materials for realizing next-generation wide color gamut displays and high-efficiency solid-state lighting due to their excellent thermal stability and optical properties more suitable for device integration. By controlling the proportion of halogen anions, their emission wavelength can cover the entire visible light spectrum, theoretically meeting the stringent requirements of the Rec. 2020 wide color gamut standard for red, green, and blue light points.

[0003] However, the industrial application of CsPbX3 quantum dots, especially CsPbI3 with iodine composition introduced to achieve red light emission and mixed halide perovskite quantum dots, faces a key bottleneck: insufficient intrinsic stability. The perovskite lattice is relatively "soft," and its ionic crystal properties make it susceptible to phase transitions, ion migration, and structural degradation under the influence of moisture, oxygen, light, and thermal stress, resulting in fluorescence quenching and color drift. Traditionally, constructing a core-shell structure is considered an effective strategy to improve the stability of quantum dots. By epitaxially growing a semiconductor material with a wider bandgap (such as ZnS, SiO2, etc.) around the core quantum dot, environmental erosion can be effectively isolated and surface defects passivated. However, for perovskite quantum dots, the traditional hot-injection method faces severe challenges in constructing such core-shell structures. High-temperature reaction environments (typically >150°C) easily lead to non-uniform epitaxial growth of the perovskite shell, causing lattice mismatch, interface defects, and even leakage and degradation of the core material. Furthermore, the inherent intermittent production mode, stringent process control requirements, and high-cost organic solvent consumption of the hot-injection method make it difficult to meet the demands of large-scale, continuous industrial production. Therefore, developing a novel structure and scalable fabrication technology that can achieve efficient and uniform encapsulation of perovskite quantum dots under mild conditions, while possessing excellent optical properties and superior environmental stability, has become a core issue that urgently needs to be addressed to propel perovskite quantum dots from the laboratory to practical applications. Summary of the Invention

[0004] Technical Problem: The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing sandwich-structured quantum dots. By using sandwich-structured metal oxide / perovskite composite quantum dots and their one-pot synthesis, the stability and synthesis process of perovskite quantum dots are solved.

[0005] Technical Solution: The present invention provides a method for preparing sandwich-structured quantum dots, comprising using a dedicated reaction vessel, which includes a three-necked round-bottom flask and a heating jacket disposed below the flask. The three necks of the three-necked round-bottom flask are respectively connected to a temperature sensor, a vacuum conduit, an inert gas input pipe, and a solvent injector. A vacuum gas control valve is installed at the inlet of the vacuum conduit, and an inert gas control valve is installed at the inlet of the inert gas input pipe. The preparation method includes the following steps:

[0006] (1) Preparation of precursor solution I

[0007] Cesium carbonate containing the A-site cation, organic acid, and organic solvent were injected into a three-necked round-bottom flask at a molar volume ratio of 1 mmol : 6 mmol : 10 mL using a solvent injector. After mixing, the vacuum gas control valve was turned on, and the vacuum tube connected to the vacuum source was used to evacuate the dedicated reaction vessel, creating a vacuum reaction environment inside the dedicated reaction vessel. The temperature inside the dedicated reaction vessel was raised to 110~130℃ using a temperature sensor and kept constant. After dehydration under vacuum and 110~130℃ conditions for 20~40 minutes, the vacuum was stopped, and the inert gas control valve was turned on. Inert gas was sent into the three-necked round-bottom flask through the inert gas input tube, switching the reaction atmosphere inside the dedicated reaction vessel to an inert environment. Under the condition of continuous heating at 110~130℃, the mixture in the dedicated reaction vessel became clear and transparent, thus obtaining the precursor solution I of the cesium-organic acid salt solution, which is used to provide the A-site cation constituting the central layer of CsPbX3 perovskite. This solution was then taken out for later use.

[0008] (2) Preparation of precursor solution II

[0009] Lead halide containing B-site cations, metal oxide nanocrystals, organic acid, and organic solvent were mixed in a three-necked round-bottom flask at a molar volume ratio of 1 mmol : 0.5 mmol : 8 mmol : 15 mL using a solvent injector. After dehydration under vacuum and at 110–130 °C for 20–40 minutes, the mixture was switched to an inert atmosphere and heated to 110–130 °C to fully dissolve the raw materials. Subsequently, the temperature was raised to 140–170 °C and held constant to obtain precursor solution II, which is used to provide B-site cations and halide anions that constitute the central layer of ABX3 perovskite.

[0010] (3) Formation of the reaction system

[0011] Using a glass syringe, 1–10 mL of precursor solution I was drawn and rapidly injected into precursor solution II, maintained at 140–170°C, within 0.5–5 seconds via a programmed injection pump or manual injection. The reaction was continued at a constant temperature of 140–170°C for 4–10 seconds. Utilizing the lattice matching and structure-directing effect of ZnO nanocrystals, the CsPbX3 perovskite phase rapidly epitaxially grew on its surface. Simultaneously, excess metal oxide nanocrystals reacted in situ with oleic acid to generate a ZnO outer shell layer encapsulating the CsPbX3 perovskite central layer. The construction of the metal oxide / CsPbX3 / metal oxide sandwich heterostructure was completed simultaneously within 4–10 seconds.

[0012] (4) Obtaining the product

[0013] After injecting precursor solution I, react for 4–10 seconds, immediately remove the reaction vessel from the heating mantle and quickly place it in an ice-water bath at 0–5°C, shaking or stirring vigorously for 10 seconds to rapidly lower the reaction system temperature to below 40°C within 1 minute, thus terminating further crystal growth. Add 3–10 times the volume of antisolvent to the cooled reaction system, shake thoroughly until a distinct flocculent precipitate appears, let stand for 5–10 minutes, and then centrifuge at 8000–12000 rpm for 10 minutes, discarding the supernatant. Wash the precipitate 2–3 times with a mixture of antisolvent / organic solvent at a volume ratio of 5:1–10:1, centrifuging at 10000 rpm for 10 minutes after each wash. Finally, redisperse the purified precipitate in 5–20 mL of organic solvent. The resulting dispersion is a sandwich-structured quantum dot with a metal oxide core-perovskite CsPbX3 central layer-metal oxide outer shell, where X represents a halogen.

[0014] In step (1), the functional component constituting the A-site cation of the CsPbX3 perovskite central layer is a cesium-oleate complex generated by the reaction of a cesium source with an organic acid, thereby providing cesium ions (Cs + ); where the A-site cation is selected from Cs + CH3NH3 + (MA + ), NH2CHNH2 + (FA + ), Rb + K + Na + At least one of the following, the corresponding A-site cation source includes at least one of: Cs2CO3, CsX, CH3NH3X(MAX), NH2CHNH2X(FAX), RbX, KX, NaX, cesium acetate, methylammonium acetate, and formamidine acetate, wherein X is a halogen.

[0015] The organic acid is selected from organic compounds with coordination ability, including one or more of the following: oleic acid (OA), oleylamine (OAm), octadecene (ODE), octanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, trioctylphosphine (TOP), trioctylphosphine oxide (TOPO), tributylphosphine (TBP), dodecyl mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, mercaptoethanol, mercaptoethylamine, cysteine, glutathione, bromine oleate, octyl bromide, tetrabutylammonium iodide, ammonium perfluorooctanoate, polyethylene glycol thiols, dihydrolipoic acid, and guanidine thiocyanate.

[0016] In step (1), the precursor solution I includes an oleate as the A-site cation precursor, which is one or more of cesium-oleate, methylamine-oleate, formamidinium-oleate, rubidium-oleate, and potassium-oleate; the A-site cation (Cs + Located at the center of the cubic octahedron of the perovskite ABX3 lattice, it mainly affects the structural stability of the crystal; the A-site cation precursor is prepared by reacting the corresponding carbonate or acetate with oleic acid in octadecene at 70-160℃.

[0017] In step (2), the functional components constituting the B-site cations and halide anions of the ABX3 perovskite central layer are lead ions (Pb) provided by the lead source. 2+ ) and halide anions (X) provided by lead sources and / or organic ligands. - The B-site cation (Pb) 2+ Located at the center of the BX6 octahedron, it interacts with the halide anion (X). - Together, they constitute [PbX6]. 4- The inorganic framework mainly determines the photoelectric properties of the prepared perovskite;

[0018] The B-site cation is selected from Pb. 2+ Sn 2+ 、Ge 2+ Mn 2+ Cd 2+ Zn 2+ Bi 3+ In 3+ At least one of the following, the corresponding B-site cation source includes, but is not limited to, at least one of: PbX2, SnX2, GeX2, MnX2, CdX2, ZnX2, BiX3, InX3, lead acetate, tin acetate, manganese acetate, lead acetylacetone, lead oleate, and lead stearate, wherein X is a halogen.

[0019] In step (2), the precursor solution II includes metal oxide nanocrystals as a structure directing agent. The metal oxide nanocrystals are selected from one or more of TiO2, Al2O3, ZrO2, SiO2, SnO2, In2O3, and Ga2O3. The metal oxide nanocrystals serve as a pre-synthesized core template in the reaction and guide the formation of sandwich-structured quantum dots through the surface properties of the metal oxide nanocrystals. The ZnO shell layer in the final product is a newly generated metal oxide during the reaction, and its chemical composition is the same as or different from that of the core. The metal oxide nanocrystals are added in the form of an aqueous phase, alcohol phase, or oil phase dispersion, with a concentration range of 10-60 wt%. The amount of metal oxide nanocrystals added is 5-200 mg / mmol, calculated based on the molar amount of the B-site cation.

[0020] In step (4), the centrifuge speed is 8000-12000 rpm and the time is 10 minutes.

[0021] The sandwich structure quantum dot is a core-shell-shell three-layer structure with metal oxide nanocrystals as the core, APbX3 perovskite as the central layer, and metal oxide as the outer shell. The central layer of the sandwich structure quantum dot is an APbX3 type perovskite crystal structure, where A represents a monovalent organic or inorganic cation located at the center of the lattice cube, and B represents a divalent metal cation located at the vertex of the cube.

[0022] The organic solvent is selected from one or more of octadecene, n-hexane, N,N-dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, N-methylpyrrolidone, and dimethylacetamide; the antisolvent is selected from one or more of ethyl acetate, methyl acetate, butyl acetate, acetone, butanone (methyl ethyl ketone), methanol, ethanol, isopropanol, n-propanol, methyl tert-butyl ether, diethyl ether, isopropyl ether, dichloromethane, chloroform, tetrahydrofuran, acetonitrile, n-hexane, n-heptane, and cyclohexane.

[0023] The emission wavelength of the sandwich-structured quantum dots can be continuously tuned within the range of 450 nm to 690 nm. When halogen X is pure Br, the center of the photoluminescence peak of the quantum dots is located at 518 nm. When halogen X is a mixture of Br and I (iodine), the center wavelength of the quantum dot emission peak continuously red-shifts from 518 nm to 690 nm as the I content increases. When halogen X is pure Cl, the center wavelength of the quantum dot emission peak is 450 nm. When halogen X is a mixture of Cl and Br, the center wavelength of the quantum dot emission peak continuously red-shifts from 450 nm to 518 nm as the Br content increases.

[0024] Beneficial Effects: By employing the above-mentioned technical solution, this invention introduces metal oxides as structure-directing agents into the precursor to induce epitaxial growth and passivate surface defects. The resulting quantum dots exhibit a photoluminescence quantum yield as high as 95%, and the emission wavelength can be continuously tuned from 518 nm (green light) to 690 nm (deep red light). Under harsh environments such as high temperature, water immersion, and ultraviolet irradiation, the luminous intensity retention exceeds 70%, demonstrating excellent stability. The all-perovskite white LED device prepared using this technology achieves a color gamut coverage of 134.34% NTSC and 100.47% Rec. 2020, showing great potential for application in wide color gamut displays and high-efficiency lighting. This invention achieves controllable preparation of sandwich-structured metal oxide / perovskite / metal oxide quantum dots through a one-pot hot-injection strategy. The synthesis method is simple, reproducible, and environmentally stable, providing an effective path to improve the performance of perovskite quantum dots. Its operation is simple and effective, and it has wide applicability in this technical field. The main advantages compared to existing technologies are:

[0025] (1) Heterogeneous nucleation and surface encapsulation can be completed simultaneously in a single reaction system, avoiding the interface contamination and structural damage problems in the traditional stepwise coating process. Through the structural guidance of metal oxide nanocrystals, the epitaxial growth of the perovskite phase is effectively guided, significantly increasing the photoluminescence quantum yield of quantum dots from about 52% of traditional CsPbX3 quantum dots to more than 95%, while extending the fluorescence lifetime from about 147 ns to 553 ns, confirming the effective suppression of defect state density;

[0026] (2) By precisely controlling the amount of metal oxide added (50 µL is optimal) and reaction parameters (reaction at 150℃ for 5 seconds), uniform control of the morphology and size of quantum dots was achieved. Compared with traditional coating techniques that require complex post-processing, this method can complete the construction of the core-shell-shell structure in a single reactor, significantly simplifying the process flow and providing good batch-to-batch repeatability, thus laying the foundation for large-scale production.

[0027] (3) The sandwich-structured quantum dots of the present invention exhibit excellent environmental stability. Under multiple stress conditions such as heating at 100°C, immersion in water for 15 days, and ultraviolet irradiation, their luminescence intensity retention rate exceeds 70%, which is far superior to unencapsulated quantum dots (typically <30%). This structure effectively blocks water and oxygen erosion and inhibits halogen migration through the synergistic protection of inner and outer metal oxide layers, providing a reliable guarantee for the long-term stable operation of perovskite quantum dots in harsh environments;

[0028] (4) By precisely controlling the halogen composition, continuously tunable emission from 518 nm to 690 nm was achieved, with the full width at half maximum (FWHM) maintained in a narrow range of 20-35 nm. The all-perovskite white LED device fabricated by integrating green and red light sandwich quantum dots achieved a color gamut coverage of 130% NTSC and 100% Rec. 2020 standard, demonstrating its application potential in the high-end display field. At the same time, the patterned thin film fabricated by it exhibits bright luminescence characteristics under ultraviolet light irradiation, expanding its application prospects in fields such as fluorescent anti-counterfeiting. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the hot injection apparatus used in the preparation of multi-system nanocrystalline materials according to the present invention.

[0030] In the diagram: 1. Three-necked round-bottom flask, 2. Heating mantle, 3. Temperature sensor, 4. Vacuum conduit, 5. Vacuum gas control valve, 6. Inert gas inlet pipe, 7. Inert gas control valve, 8. Solvent injector.

[0031] Figure 2 This is a structural diagram of the green ZnO / CsPbBr3 / ZnO perovskite quantum dot material prepared in Example 1 of the present invention.

[0032] The diagram shows: an outer shell of ZnO, a central layer of CsPbBr3, and a core of ZnO.

[0033] Figure 3 The fluorescence spectrum of the green ZnO / CsPbBr3 / ZnO perovskite quantum dot material prepared in Example 1 of this invention is shown under blue light excitation.

[0034] Figure 4 This is a transmission electron microscope image of the green ZnO / CsPbBr3 / ZnO perovskite quantum dot material prepared in Example 1 of this invention.

[0035] Figure 5 This is a graph showing the effect of the photoluminescence intensity of the light conversion thin film prepared by the green ZnO / CsPbBr3 / ZnO perovskite quantum dot material in Example 1 of the present invention decaying over time at high temperature. Detailed Implementation

[0036] The embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0037] The method for preparing sandwich-structured ZnO / CsPbX3 / ZnO quantum dots of the present invention employs a dedicated reaction vessel, which includes a three-necked round-bottom flask 1 and a heating jacket 2 located below the round-bottom flask 1. The three necks of the three-necked round-bottom flask 1 are respectively connected to a temperature sensor 3, a vacuum conduit 4, an inert gas input pipe 6, and a solvent injector 8. A vacuum gas control valve 5 is installed at the inlet of the vacuum conduit 4, and an inert gas control valve 7 is installed at the inlet of the inert gas input pipe 6. The preparation process uses a hot-injection synthesis technique, including the preparation of a cesium-oleate precursor, the preparation of a lead precursor solution containing metal oxide nanocrystals, and the construction of the sandwich structure through a rapid hot-injection reaction. Precursor solution I and precursor solution II have their flow rates controlled by precision injection pumps. Precursor solution I is a cesium-oleate solution, and precursor solution II includes a lead source, metal oxide nanocrystals, and ligands. Precursor solution I was rapidly injected into precursor solution II, which was kept constant at 140-170℃, using a solvent injector. After injection, the reaction system was continuously and vigorously stirred at a constant temperature for 4-10 seconds. Utilizing the structure-directing effect of ZnO nanocrystals, the CsPbX3 perovskite phase was guided to grow epitaxially on its surface, and the outer ZnO encapsulation was achieved simultaneously. After the reaction was completed, the system was immediately rapidly cooled to room temperature using an ice-water bath to terminate the reaction. The resulting product was precipitated, centrifuged, washed, and finally dispersed in n-hexane.

[0038] The specific preparation method steps are as follows:

[0039] (1) Preparation of precursor solution I

[0040] Cesium carbonate containing A-site cations, organic acid, and organic solvent are injected into a three-necked round-bottom flask 1 at a molar volume ratio of 1 mmol : 6 mmol : 10 mL using a solvent injector 8. After mixing, the vacuum gas control valve 5 is opened, and the vacuum conduit 4 connected to the vacuum source is used to evacuate the dedicated reaction vessel, creating a vacuum reaction environment inside the dedicated reaction vessel. The temperature inside the dedicated reaction vessel is raised to 110~130℃ using a temperature sensor 3 and kept constant. After dehydration under vacuum and 110~130℃ conditions for 20~40 minutes, the vacuuming is stopped, and the inert gas control valve 7 is opened. Inert gas is sent into the three-necked round-bottom flask 1 through the inert gas input pipe 6, switching the reaction atmosphere inside the dedicated reaction vessel to an inert environment. Under the condition of continuous heating at 110~130℃, the mixture inside the dedicated reaction vessel becomes clear and transparent, thus obtaining the precursor solution I of cesium-organic acid salt solution, which is used to provide A-site cations constituting the central layer of CsPbX3 perovskite. This solution is then taken out for later use.

[0041] The functional component constituting the A-site cation of the CsPbX3 perovskite central layer is a cesium-oleate complex generated by the reaction of a cesium source with an organic acid, thereby providing cesium ions (Cs... +); where the A-site cation is selected from Cs + CH3NH3 + (MA + ), NH2CHNH2 + (FA + ), Rb + K + Na + At least one of the following, the corresponding A-site cation source includes at least one of: Cs2CO3, CsX, CH3NH3X(MAX), NH2CHNH2X(FAX), RbX, KX, NaX, cesium acetate, methylammonium acetate, and formamidine acetate, wherein X is a halogen.

[0042] The precursor solution I comprises an oleate as an A-site cation precursor, which is one or more selected from cesium-oleate, methylamine-oleate, formamidinium-oleate, rubidium-oleate, and potassium-oleate; the A-site cation (Cs + Located at the center of the cubic octahedron of the perovskite ABX3 lattice, it mainly affects the structural stability of the crystal; the A-site cation precursor is prepared by reacting the corresponding carbonate or acetate with oleic acid in octadecene at 70-160℃.

[0043] (2) Preparation of precursor solution II

[0044] Lead halide containing B-site cations, metal oxide nanocrystals, organic acid and organic solvent were mixed in a three-necked round-bottom flask 1 at a molar volume ratio of 1 mmol : 0.5 mmol : 8 mmol : 15 mL using a solvent injector (8). After dehydration under vacuum and at 110~130℃ for 20~40 minutes, the mixture was switched to an inert atmosphere and heated to 110~130℃ to fully dissolve the raw materials. Then the temperature was raised to 140~170℃ and held constant to obtain precursor solution II, which was used to provide B-site cations and halide anions that constitute the central layer of ABX3 perovskite.

[0045] The functional components constituting the B-site cations and halide anions of the ABX3 perovskite central layer are lead ions (Pb) provided by the lead source. 2+ ) and halide anions (X) provided by lead sources and / or organic ligands. - The B-site cation (Pb) 2+ Located at the center of the BX6 octahedron, it interacts with the halide anion (X). - Together, they constitute [PbX6]. 4- The inorganic framework mainly determines the photoelectric properties of the prepared perovskite;

[0046] The B-site cation is selected from Pb. 2+ Sn 2+、Ge 2+ Mn 2+ Cd 2+ Zn 2+ Bi 3+ In 3+ At least one of the following, the corresponding B-site cation source includes, but is not limited to, at least one of: PbX2, SnX2, GeX2, MnX2, CdX2, ZnX2, BiX3, InX3, lead acetate, tin acetate, manganese acetate, lead acetylacetone, lead oleate, and lead stearate, wherein X is a halogen.

[0047] The precursor solution II includes metal oxide nanocrystals as a structure directing agent, which are selected from one or more of TiO2, Al2O3, ZrO2, SiO2, SnO2, In2O3, and Ga2O3. The metal oxide nanocrystals serve as pre-synthesized core templates in the reaction and guide the formation of sandwich-structured quantum dots through their surface properties. The ZnO shell layer in the final product is a newly generated metal oxide during the reaction, and its chemical composition may be the same as or different from that of the core. The metal oxide nanocrystals are added in the form of aqueous, alcoholic, or oily dispersions at a concentration range of 10-60 wt%. The amount of metal oxide nanocrystals added is 5-200 mg / mmol, calculated based on the molar amount of the B-site cation.

[0048] The organic acid is selected from organic compounds with coordination ability, including one or more of the following: oleic acid (OA), oleylamine (OAm), octadecene (ODE), octanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, trioctylphosphine (TOP), trioctylphosphine oxide (TOPO), tributylphosphine (TBP), dodecyl mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, mercaptoethanol, mercaptoethylamine, cysteine, glutathione, bromine oleate, octyl bromide, tetrabutylammonium iodide, ammonium perfluorooctanoate, polyethylene glycol thiols, dihydrolipoic acid, and guanidine thiocyanate.

[0049] (3) Formation of the reaction system

[0050] Using a glass syringe 8, 1–10 mL of precursor solution I was drawn. The entire precursor solution I was then rapidly injected into precursor solution II, which was maintained at 140–170°C, within 0.5–5 seconds using a programmed injection pump or manual injection. The reaction was continued at a constant temperature of 140–170°C for 4–10 seconds. Utilizing the lattice matching and structure-directing effect of ZnO nanocrystals, the CsPbX3 perovskite phase rapidly epitaxially grew on its surface. Simultaneously, excess metal oxide nanocrystals reacted in situ with oleic acid to generate a ZnO outer shell layer encapsulating the CsPbX3 perovskite central layer. The construction of the metal oxide / CsPbX3 / metal oxide sandwich heterostructure was completed simultaneously within 4–10 seconds.

[0051] (4) Obtaining the product

[0052] After injecting precursor solution I, react for 4–10 seconds, immediately remove the reaction vessel from heating jacket 2 and quickly place it in an ice-water bath at 0–5°C, shaking or stirring vigorously for 10 seconds to rapidly lower the reaction system temperature to below 40°C within 1 minute, thus terminating further crystal growth. Add 3–10 times the volume of antisolvent to the cooled reaction system, shake thoroughly until a distinct flocculent precipitate appears, let stand for 5–10 minutes, and then centrifuge at 8000–12000 rpm for 10 minutes, discarding the supernatant. Wash the precipitate 2–3 times with a mixed solvent of antisolvent / organic solvent at a volume ratio of 5:1–10:1, centrifuging at 10000 rpm for 10 minutes after each wash. Finally, redisperse the purified precipitate in 5–20 mL of organic solvent. The resulting dispersion is a sandwich-structured quantum dot with a metal oxide core-perovskite CsPbX3 central layer-metal oxide outer shell, where X represents halogen. The centrifuge has a centrifugation speed of 8000-12000 rpm and a centrifugation time of 10 minutes.

[0053] The sandwich-structured quantum dot has a core-shell-shell three-layer structure, with metal oxide nanocrystals as the core, APbX3 perovskite as the central layer, and metal oxide as the outer shell. The central layer of the sandwich-structured quantum dot is an APbX3 type perovskite crystal structure, where A represents a monovalent organic or inorganic cation located at the center of the lattice cube, and B represents a divalent metal cation located at the vertex of the cube.

[0054] The organic solvent is selected from one or more of octadecene, n-hexane, N,N-dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, N-methylpyrrolidone, and dimethylacetamide; the antisolvent is selected from one or more of ethyl acetate, methyl acetate, butyl acetate, acetone, butanone (methyl ethyl ketone), methanol, ethanol, isopropanol, n-propanol, methyl tert-butyl ether, diethyl ether, isopropyl ether, dichloromethane, chloroform, tetrahydrofuran, acetonitrile, n-hexane, n-heptane, and cyclohexane.

[0055] In the preparation of sandwich-structured quantum dots, the emission wavelength of the product can be effectively controlled by adjusting the halogen composition in the central layer of CsPbX3 perovskite. By adjusting the type and molar ratio of the halide anion X (X can be one or more of Cl, Br, and I), the photoluminescence emission wavelength of the quantum dots can be continuously varied within the range of 450 nm to 720 nm. The emission wavelength of the sandwich-structured quantum dots is continuously tunable within the range of 450 nm to 690 nm. This control is achieved by changing the composition and ratio of lead halide in the precursor solution II: when pure lead bromide is used, the quantum dot emission peak is located at 518 nm; if lead bromide and lead iodide are mixed at different molar ratios and the proportion of lead iodide is gradually increased, the emission wavelength can be continuously red-shifted from 518 nm to 690 nm; when pure lead chloride is used, the emission wavelength is 450 nm; and by adjusting the molar ratio of lead chloride to lead bromide and gradually increasing the proportion of lead bromide, the emission wavelength can be continuously red-shifted from 450 nm to 518 nm. Therefore, by precisely setting the lead halide feeding ratio during the precursor preparation stage, the control and preparation of quantum dot luminescence color can be achieved directly and repeatedly.

[0056] The halogen composition is controlled by changing the ratio of halogen sources in the precursor, including lead halide, organic ammonium halides, or ammonium halides, ultimately making the optical bandgap of the quantum dot precisely tunable in the range of 1.72 eV to 2.76 eV, thereby covering the visible light region from blue to red light.

[0057] Example 1: Preparation of sandwich-structured ZnO / CsPbBr3 / ZnO quantum dots:

[0058] like Figure 1As shown, Cs₂CO₃ (0.163 g), oleic acid OA (0.5 mL), and octadecene ODE (8 mL) were added to a 50 mL three-necked round-bottom flask and dehydrated at 120 °C for 1 hour under vacuum. The solution was then maintained at 120 °C under a nitrogen atmosphere until a clear cesium-oleate precursor solution was formed, which was designated as precursor solution II. PbBr₂ (0.144 g), oleic acid OA (1 mL), oleylamine OAM (1 mL), an aqueous dispersion of metal oxides (40 wt%, 50 μL), and octadecene ODE (10 mL) were added to another 50 mL three-necked round-bottom flask and dehydrated at 120 °C for 1 hour under vacuum. After the raw materials were completely dissolved, the solution was heated to 150 °C under nitrogen protection and maintained to form a mixed precursor solution, designated as precursor solution I. 0.8 g of Cs₂CO₃ (0.163 g), oleic acid OA (0.5 mL), and octadecene ODE (8 mL) were added to a 50 mL three-necked round-bottom flask and dehydrated at 120 °C for 1 hour under vacuum. After the raw materials were completely dissolved, the solution was heated to 150 °C and maintained under nitrogen protection to form a mixed precursor solution, designated as precursor solution I. A mL cesium-oleate precursor solution (precursor solution II) was rapidly injected into a mixed precursor solution (precursor solution I) at 150 °C. After reacting for 5 seconds, the reaction was immediately terminated by cooling to room temperature in an ice-water bath. The resulting product was precipitated with ethyl acetate, centrifuged at 5000 rpm for 5 minutes, and finally dispersed in n-hexane to obtain metal oxide / CsPbBr3 / metal oxide sandwich structure quantum dots. Characterization results showed that the quantum dots exhibited a regular cubic morphology with an average size of 8.5 ± 1.2 nm. The photoluminescence peak was located at 522 nm, with a full width at half maximum (FWHM) of 20 nm, and the photoluminescence quantum yield reached 97%. Time-resolved fluorescence spectroscopy showed an average fluorescence lifetime of 80.025 ns, which was significantly longer than that of CsPbBr3 quantum dots without added metal oxide (10.763 ns). XPS analysis confirmed the successful incorporation of Zn, and the O 1s peak intensity was significantly increased, indicating that the metal oxide was effectively coated.

[0059] Example 2: Fabrication and Flexible Device Application of Sandwich Structure Al2O3 / MAPbBr3 / Al2O3 Quantum Dots:

[0060] CH3NH3Br (0.12 g), oleic acid OA (0.5 mL) and N,N-dimethylformamide DMF (8 mL) were added to a 50 mL three-necked round-bottom flask and stirred and dissolved at 80 °C under argon protection to form a methylamine lead bromide precursor solution, which is used as precursor solution II.

[0061] PbBr2 (0.144 g), Al2O3 nanocrystals (30 wt% isopropanol dispersion, 80 μL), oleic acid OA (1 mL), oleylamine OAm (1 mL) and DMF (10 mL) were added to another reaction vessel and stirred at 80 °C to dissolve and form a mixed precursor solution, which is used as precursor solution I.

[0062] 1.0 mL of methylamine lead bromide precursor solution was rapidly injected into the mixed precursor solution at 100 °C, and the reaction was immediately cooled in an ice bath after 3 seconds. The product was precipitated with ethyl acetate, centrifuged at 6000 rpm for 8 minutes, and dispersed in butanol to obtain Al2O3 / MAPbBr3 / Al2O3 quantum dots.

[0063] Performance characterization showed that the average size of the quantum dots was 7.8±1.1 nm, the emission peak was located at 530 nm, the full width at half maximum (FWHM) was 25 nm, and the power spectral density (PLQY) reached 89%. The flexible light-emitting film prepared by combining the quantum dots with polyurethane elastomers exhibited a PL intensity retention rate of over 92% after 1000 bending cycles, demonstrating excellent mechanical stability and making it suitable for flexible display devices.

[0064] Example 3: Preparation of a cadmium-free system of sandwich-structured ZnO / InP / ZnO quantum dots

[0065] In(acac)3 (0.15 g), myristic acid (0.2 g), and 1-octadecene ODE (10 mL) were added to a reaction vessel and dehydrated at 120 °C under vacuum for 30 min. The mixture was then heated to 180 °C under nitrogen to form precursor solution I. Metal oxide nanocrystals (50 wt% toluene dispersion, 60 μL), (TMS)3P (0.5 mL), and ODE (5 mL) were mixed to form precursor solution II. In a continuous feed reactor, precursor solutions I and II were simultaneously injected into ODE solvent at a flow rate ratio of 3:1 at 280 °C. The reaction was carried out for 15 seconds followed by rapid cooling. The product was purified by ethanol precipitation to obtain metal oxide / InP / metal oxide quantum dots. The quantum dots exhibited an emission peak at 620 nm, a full width at half maximum (FWHM) of 40 nm, and a PLQY of 78%. It exhibits good biocompatibility in cytotoxicity tests, with an LD50 > 500 µg / mL, which is far superior to cadmium-containing quantum dots (LD50 < 50 μg / mL), and has potential applications in the field of bioimaging.

[0066] Example 4: Deep Red Light Emission System of Sandwich Structure MgO / CdSe / MgO Quantum Dots

[0067] CdO (0.05 g), oleic acid (OA) (2 mL), and octadecene ODE (15 mL) were added to a reaction flask and reacted at 150 °C under argon atmosphere to form a Cd-oleate solution. MgO nanocrystals (25 wt% cyclohexane dispersion, 100 μL) and selenium powder (0.02 g) were added, and the mixture was heated to 240 °C and reacted for 5 minutes to form precursor solution I. Sulfur powder (0.01 g) and ODE (5 mL) were dispersed uniformly under ultrasonication to form precursor solution II. Precursor solution II was rapidly injected into precursor solution I, and the mixture was reacted at 220 °C for 10 minutes. The product was precipitated with methanol and centrifuged at 5200 rpm for 6 minutes to obtain MgO / CdSe / MgO quantum dots. The quantum dots exhibited an emission peak at 680 nm, a full width at half maximum (FWHM) of 30 nm, and a PLQY of 85%. In near-infrared imaging experiments, the quantum dots maintained strong emission in the 700-800 nm wavelength range, making them suitable for deep tissue bioimaging and infrared detection devices. After incubation in physiological saline solution for 72 hours, the PL intensity retention rate exceeded 80%, demonstrating good stability in biological media.

Claims

1. A method for preparing sandwich-structured quantum dots, comprising using a dedicated reaction vessel, the dedicated reaction vessel comprising a three-necked round-bottom flask (1) and a heating mantle (2) disposed below the three-necked round-bottom flask (1), wherein the three necks of the three-necked round-bottom flask (1) are respectively connected to a temperature sensor (3), a vacuum conduit (4), an inert gas input pipe (6), and a solvent injector (8); a vacuum gas control valve (5) is provided at the inlet of the vacuum conduit (4), and an inert gas control valve (7) is provided at the inlet of the inert gas input pipe (6); characterized in that, The preparation method includes the following steps: (1) Preparation of precursor solution I Cesium carbonate containing the A-site cation, organic acid, and organic solvent were mixed using a solvent syringe (8) at a ratio of 1 mmol : 6 mmol : 10 mmol. After mixing the cesium-organic acid salt solution in a three-necked round-bottom flask (1) at a molar volume ratio of mL, the vacuum gas control valve (5) is opened, and the vacuum conduit (4) connected to the vacuum source is used to evacuate the special reaction container, forming a vacuum reaction environment inside the special reaction container. The temperature inside the special reaction container is raised to 110~130℃ and kept constant by the temperature sensor (3). After dehydration for 20~40 minutes under vacuum and 110~130℃ conditions, the vacuuming is stopped, and the inert gas control valve (7) is opened at the same time. The inert gas is sent into the three-necked round-bottom flask (1) through the inert gas input pipe (6), and the reaction atmosphere inside the special reaction container is switched to an inert environment. Under the condition of continuous heating at 110~130℃, the mixture inside the special reaction container is kept clear and transparent until it becomes clear and transparent. The precursor solution I of the cesium-organic acid salt solution is obtained and used to provide the A-site cation that constitutes the central layer of CsPbX3 perovskite. It is taken out for later use. (2) Preparation of precursor solution II Lead halide containing B-site cations, metal oxide nanocrystals, organic acid and organic solvent were mixed in a three-necked round-bottom flask (1) using a solvent injector (8) at a molar volume ratio of 1 mmol : 0.5 mmol : 8 mmol : 15 mL. After dehydration under vacuum and at 110~130℃ for 20~40 minutes, the mixture was switched to an inert atmosphere and heated to 110~130℃ to fully dissolve the raw materials. Then the temperature was raised to 140~170℃ and held constant to obtain precursor solution II, which was used to provide B-site cations and halide anions that constitute the central layer of ABX3 perovskite. (3) Formation of the reaction system Using a glass syringe (8), 1-10 mL of precursor solution I was drawn. The entire precursor solution I was rapidly injected into precursor solution II, which was maintained at 140-170°C, within 0.5-5 seconds by a programmed injection pump or manual injection. The reaction continued for 4-10 seconds at a constant temperature of 140-170°C. The lattice matching and structure guiding effect of ZnO nanocrystals enabled the rapid epitaxial growth of the CsPbX3 perovskite phase on its surface. At the same time, excess metal oxide nanocrystals reacted with oleic acid in situ to generate a ZnO shell layer that encapsulated the CsPbX3 perovskite core layer. The construction of the metal oxide / CsPbX3 / metal oxide sandwich heterostructure was completed simultaneously within 4-10 seconds. (4) Obtaining the product After the precursor solution I is injected, the reaction vessel is immediately removed from the heating jacket (2) after 4-10 seconds of reaction. It is then placed in an ice-water bath at 0-5℃ and shaken or stirred vigorously for 10 seconds to rapidly reduce the temperature of the reaction system to below 40℃ within 1 minute to terminate further growth of the crystal nuclei. 3-10 times the volume of antisolvent is added to the cooled reaction system. After thorough shaking until obvious flocculent precipitate appears, the system is allowed to stand for 5-10 minutes. Then, it is centrifuged at 8000-12000 rpm for 10 minutes and the supernatant is discarded. The precipitate is washed 2-3 times with a mixture of antisolvent and organic solvent at a volume ratio of 5:1-10:

1. After each wash, it is centrifuged at 10000 rpm for 10 minutes. Finally, the purified precipitate is redispersed in 5-20 mL of organic solvent. The resulting dispersion is a sandwich structure quantum dot with a core-shell-shell structure of metal oxide core-perovskite CsPbX3 central layer-metal oxide outer shell, where X represents halogen.

2. The method for preparing sandwich-structured quantum dots according to claim 1, characterized in that: In step (1), the functional component constituting the A-site cation of the CsPbX3 perovskite central layer is a cesium-oleate complex generated by the reaction of a cesium source with an organic acid, thereby providing cesium ions (Cs + ); The A-site cation is selected from Cs. + CH3NH3 + (MA + ), NH2CHNH2 + (FA + ), Rb + K + Na + At least one of the following, the corresponding A-site cation source includes at least one of: Cs2CO3, CsX, CH3NH3X(MAX), NH2CHNH2X(FAX), RbX, KX, NaX, cesium acetate, methylammonium acetate, and formamidine acetate, wherein X is a halogen.

3. The method for preparing sandwich-structured quantum dots according to claim 1 or 2, characterized in that: The organic acid is selected from organic compounds with coordination ability, including one or more of the following: oleic acid (OA), oleylamine (OAm), octadecene (ODE), octanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, trioctylphosphine (TOP), trioctylphosphine oxide (TOPO), tributylphosphine (TBP), dodecyl mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, mercaptoethanol, mercaptoethylamine, cysteine, glutathione, bromine oleate, octyl bromide, tetrabutylammonium iodide, ammonium perfluorooctanoate, polyethylene glycol thiols, dihydrolipoic acid, and guanidine thiocyanate.

4. The method for preparing sandwich-structured quantum dots according to claim 1, characterized in that: In step (1), the precursor solution I includes an oleate as the A-site cation precursor, which is one or more of cesium-oleate, methylamine-oleate, formamidinium-oleate, rubidium-oleate, and potassium-oleate; the A-site cation (Cs + Located at the center of the cubic octahedron of the perovskite ABX3 lattice, it mainly affects the structural stability of the crystal; the A-site cation precursor is prepared by reacting the corresponding carbonate or acetate with oleic acid in octadecene at 70-160℃.

5. The method for preparing sandwich-structured quantum dots according to claim 1, characterized in that: In step (2), the functional components constituting the B-site cations and halide anions of the ABX3 perovskite central layer are lead ions (Pb) provided by the lead source. 2+ ) and halide anions (X) provided by lead sources and / or organic ligands. - The B-site cation (Pb) 2+ Located at the center of the BX6 octahedron, it interacts with the halide anion (X). - Together, they constitute [PbX6]. 4- The inorganic framework mainly determines the photoelectric properties of the prepared perovskite; The B-site cation is selected from Pb. 2+ Sn 2+ 、Ge 2+ Mn 2+ Cd 2+ Zn 2+ Bi 3+ In 3+ At least one of the following, the corresponding B-site cation source includes, but is not limited to, at least one of: PbX2, SnX2, GeX2, MnX2, CdX2, ZnX2, BiX3, InX3, lead acetate, tin acetate, manganese acetate, lead acetylacetone, lead oleate, and lead stearate, wherein X is a halogen.

6. The method for preparing sandwich-structured quantum dots according to claim 1, characterized in that: In step (2), the precursor solution II includes metal oxide nanocrystals as a structure directing agent. The metal oxide nanocrystals are selected from one or more of TiO2, Al2O3, ZrO2, SiO2, SnO2, In2O3, and Ga2O3. The metal oxide nanocrystals serve as a pre-synthesized core template in the reaction and guide the formation of sandwich-structured quantum dots through the surface properties of the metal oxide nanocrystals. The ZnO shell layer in the final product is a newly generated metal oxide during the reaction, and its chemical composition is the same as or different from that of the core. The metal oxide nanocrystals are added in the form of an aqueous phase, alcohol phase, or oil phase dispersion, with a concentration range of 10-60 wt%. The amount of metal oxide nanocrystals added is 5-200 mg / mmol, calculated based on the molar amount of the B-site cation.

7. The method for preparing sandwich-structured quantum dots according to claim 1, characterized in that: In step (4), the centrifuge speed is 8000-12000 rpm and the time is 10 minutes.

8. The method for preparing sandwich-structured quantum dots according to claim 1, characterized in that: The sandwich structure quantum dot is a core-shell-shell three-layer structure with metal oxide nanocrystals as the core, APbX3 perovskite as the central layer, and metal oxide as the outer shell. The central layer of the sandwich structure quantum dot is an APbX3 type perovskite crystal structure, where A represents a monovalent organic or inorganic cation located at the center of the lattice cube, and B represents a divalent metal cation located at the vertex of the cube.

9. The method for preparing sandwich-structured quantum dots according to claim 1, characterized in that: The organic solvent is selected from one or more of octadecene, n-hexane, N,N-dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, N-methylpyrrolidone, and dimethylacetamide; the antisolvent is selected from one or more of ethyl acetate, methyl acetate, butyl acetate, acetone, butanone (methyl ethyl ketone), methanol, ethanol, isopropanol, n-propanol, methyl tert-butyl ether, diethyl ether, isopropyl ether, dichloromethane, chloroform, tetrahydrofuran, acetonitrile, n-hexane, n-heptane, and cyclohexane.

10. The method for preparing sandwich-structured quantum dots according to claim 1, 6, or 8, characterized in that: The emission wavelength of the sandwich-structured quantum dots can be continuously tuned within the range of 450 nm to 690 nm. When halogen X is pure Br, the center of the photoluminescence peak of the quantum dots is located at 518 nm. When halogen X is a mixture of Br and I (iodine), the center wavelength of the quantum dot emission peak continuously red-shifts from 518 nm to 690 nm as the I content increases. When halogen X is pure Cl, the center wavelength of the quantum dot emission peak is 450 nm. When halogen X is a mixture of Cl and Br, the center wavelength of the quantum dot emission peak continuously red-shifts from 450 nm to 518 nm as the Br content increases.

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