Metal halide perovskite nanocrystals and methods of making the same

Abstract

The application discloses a kind of metal halide perovskite nanocrystals and preparation method thereof, belong to nanometer material preparation and application technical field.The method is prepared Cs source precursor solution under inert atmosphere, after dehydration and deoxidation, inject preheated solution containing PbBr2, oleylamine and trifunctional dynamic ligand system, at 150-170 °C reaction 5-15 minutes.The ligand system includes oleyl phosphoric acid, poly (vinyl alcohol-graft-urea) and octadecenyl acrylamide, respectively as strong interface anchoring, dynamic growth control and potential crosslinking unit.After reaction, by ultralow temperature cooling, centrifugal purification and light-induced crosslinking treatment, obtain the nanocrystal with crosslinking protective shell on surface.The nanocrystal size distribution is narrow (half-width 12-18 nm), and the luminescent efficiency is high (quantum yield ≥90%), and the luminescent intensity retention rate is ≥85% after 1500 hours storage under 85 °C / 85%RH condition, effectively solve the problem of nanocrystal size distribution wide, low luminescent efficiency and poor stability in prior art.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation and application technology, specifically, it relates to a metal halide perovskite nanocrystal and its preparation method. Background Technology

[0002] Metal halide perovskite nanocrystals have shown great potential for application in next-generation quantum dot display technology, lighting, and optoelectronic devices due to their excellent optoelectronic properties, such as tunable emission wavelength, high color purity, and high photoluminescence quantum yield. However, their practical application still faces three interrelated core technical challenges: uneven size distribution, insufficient luminous efficiency, and poor environmental stability.

[0003] First, the nucleation and growth of nanocrystals are difficult to control precisely during the synthesis process. While traditional hot-injection methods can produce nanocrystals in batches, the temperature and concentration gradients of the reaction system are difficult to maintain uniformity, resulting in poor consistency in the nucleation and growth processes. This often leads to products with a wide size distribution (half-width at half maximum often greater than 25 nm), which cannot meet the stringent requirements of narrow emission linewidths for high-color-purity display applications. Although Ostwald ripening can be used for later adjustment, this method is passive and cannot suppress size differentiation in the early stages of growth.

[0004] Secondly, the presence of numerous dangling bonds and defects (such as halogen vacancies) on the surface of nanocrystals creates nonradiative recombination centers, significantly reducing luminescence efficiency. Commonly used ligands (such as oleic acid and oleylamine) have weak binding forces to the crystal planes and are easily detached during purification, storage, or device fabrication, leading to the re-exposure of defects. This not only exacerbates nonradiative recombination and reduces luminescence efficiency but also makes the material more susceptible to corrosion from environmental factors such as water, oxygen, light, and heat, severely impacting device lifespan.

[0005] Furthermore, perovskite nanocrystals are highly sensitive to environmental factors such as moisture, oxygen, light, and heat, and their insufficient stability is the most critical bottleneck restricting their industrialization. The easy shedding of the aforementioned ligands further exacerbates this problem, causing the nanocrystals to rapidly degrade under service conditions. Existing improvement strategies, such as introducing excessive passivating agents or trying novel single ligands, may improve a certain performance (efficiency or stability) to some extent, but they often come at the expense of other aspects, making it difficult to achieve a simultaneous improvement in overall performance. For example, strengthening defect passivation may neglect the regulation of growth kinetics, leading to a wider size distribution; while focusing on size uniformity may not provide sufficient surface protection and passivation effects.

[0006] At its root, existing technologies mostly follow a "divide and conquer" approach, addressing single issues such as size control, defect passivation, or stability improvement in isolation. They lack an effective strategy for integrated, phased, and synergistic control throughout the entire process of nanocrystal formation, growth, surface terminalization, and final stabilization. In particular, there is a lack of a universal method that can simultaneously achieve dynamic and precise control of the growth process, efficient and durable passivation of surface defects, and ultimate stabilization of the ligand layer through in-situ methods.

[0007] Furthermore, metal halide perovskite nanocrystals have shown great potential in fluorescence sensing and detection, particularly in the high-sensitivity identification of rare earth elements. However, they face severe challenges in practical applications: rare earth element detection often involves aqueous or polar environments, and the inherent instability of perovskite nanocrystals makes them prone to degradation in such media, leading to fluorescence quenching and signal failure, which severely limits their feasibility as reliable fluorescent probes.

[0008] Therefore, developing a perovskite nanocrystal that combines high fluorescence efficiency, excellent stability, and surface tunability will not only help promote its application in displays and optoelectronic devices, but also extend to high-value-added detection fields such as environmental monitoring, rare earth resource recycling, and bioimaging, which has important scientific value and industrialization prospects. Summary of the Invention

[0009] This invention addresses the problems of wide size distribution, low luminescence efficiency, and poor environmental stability in existing metal halide perovskite nanocrystal preparation techniques. It provides a method that simultaneously optimizes size uniformity, high luminescence efficiency, and high stability during the preparation stage, resulting in perovskite nanocrystals with superior performance. This method introduces a ligand system with three functional characteristics: strong interface anchoring, dynamic growth control, and in-situ crosslinking protection. First, it achieves refined and adaptive control during nanocrystal nucleation and growth, simultaneously completing efficient and durable surface defect passivation. Then, a gentle post-processing step completes crosslinking protection, ultimately achieving synergistic optimization of the overall performance of the nanocrystals.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0011] This invention provides a metal halide perovskite nanocrystal, the surface of which is anchored by a cross-linked network protective shell through chemical bonding. The photoluminescence spectrum of the nanocrystal has a full width at half maximum (FWHM) of 12 nm to 18 nm, a photoluminescence quantum yield of not less than 85%, and after being stored in an 85°C / 85% RH environment for 1500 hours, its photoluminescence intensity retention rate is not less than 85% of the initial value.

[0012] The present invention also provides a method for preparing the aforementioned metal halide perovskite nanocrystals, comprising the following steps:

[0013] (a) A Cs source precursor solution was prepared by mixing Cs source, oleic acid and 1-octadecene under an inert atmosphere;

[0014] (b) The solution obtained in step (a) is heated and dehydrated and deoxygenated under vacuum, and then heated to 150°C to 170°C under an inert atmosphere;

[0015] (c) Inject a preheated mixed solution into the solution obtained in step (b) to form a reaction system, wherein the mixed solution contains a binary metal halide PbBr2, oleylamine and a trifunctional dynamic ligand system, wherein the trifunctional dynamic ligand system includes oleyl phosphate as a strong interface anchoring group, poly(vinyl alcohol-grafted-urea) as a dynamic growth regulating unit and octadecenyl acrylamide as a potential crosslinking unit;

[0016] (d) After injection, react at 150°C to 170°C for 5 to 15 minutes;

[0017] (e) After the reaction is complete, the reaction system of step (c) is subjected to ultra-low temperature cooling to terminate the reaction and obtain the product after the reaction;

[0018] (f) The cooled product from step (e) is centrifuged, washed, and redispersed to obtain a primary nanocrystalline dispersion;

[0019] (g) The primary nanocrystal dispersion obtained in step (f) is post-treated to activate the octadecenylacrylamide as a potential crosslinking unit, initiating an intermolecular crosslinking reaction to form a crosslinking protective shell on the surface of the nanocrystals. After centrifugation, washing and redispersing, the metal halide perovskite nanocrystals are obtained.

[0020] Further, in step (b), the temperature of the dehydration and deoxygenation treatment is 100°C to 160°C, the vacuum pressure is maintained below 20 Pa, and the treatment time is 30 to 60 minutes.

[0021] Further, in step (c), the molar ratio of the oil-based phosphoric acid to the binary metal halide PbBr2 is 0.05:1 to 0.2:1.

[0022] Further, in step (c), the molar ratio of the poly(vinyl alcohol-grafted-urea) to the binary metal halide PbBr2, based on its repeating units, is 0.01:1 to 0.05:1.

[0023] Further, in step (c), the molar ratio of the octadecenylacrylamide to the binary metal halide PbBr2 is 0.05:1 to 0.15:1.

[0024] Further, in step (e), the cryogenic cooling process involves cooling the reaction system to -196°C or below using liquid nitrogen or liquid helium.

[0025] Further, in steps (f) and (g), the centrifugation is performed at a speed of 7000 rpm to 9000 rpm to separate the precipitate; the solvent used for redispersion is anhydrous toluene.

[0026] Further, the post-treatment in step (g) is a photo-induced crosslinking reaction, in which the photoinitiator α,α-dimethoxy-α-phenylacetophenone (DMPA) is added to the primary nanocrystal dispersion, and the crosslinking reaction is carried out under ultraviolet light irradiation; the wavelength of the ultraviolet light is 365 nm, and the intensity is 10-50 mW / cm. 2 The solution is irradiated for 1-5 minutes; wherein the amount of photoinitiator DMPA added is 1 wt% of the total weight of the solution.

[0027] The strong interfacial anchoring group (oil-based phosphoric acid), dynamic growth control unit (poly(vinyl alcohol-grafted-urea)), and potential crosslinking unit (octadecenylacrylamide) described in this invention exhibit a significant synergistic effect during nanocrystal formation. The poly(vinyl alcohol-grafted-urea) preferentially adsorbs onto specific crystal faces during the early stages of nanocrystal nucleation and growth through its dynamic and reversible hydrogen bonding interactions, effectively suppressing the Ostwald ripening process and providing a foundation for the formation of uniformly sized nanocrystals. Simultaneously, the oil-based phosphoric acid, with its strong coordination ability, rapidly and persistently anchors to surface defect sites on the newly formed nanocrystals, achieving immediate and efficient passivation. More importantly, the dynamic interfacial environment provided by the poly(vinyl alcohol-grafted-urea) promotes the uniform distribution and full coverage of the oil-based phosphoric acid, while the firm anchoring of the oil-based phosphoric acid stabilizes the regular morphology and size regulated by the poly(vinyl alcohol-grafted-urea). The potential crosslinking unit (octadecenylacrylamide) remains chemically inert during the synthesis and growth stages of the nanocrystals, stably existing on the nanocrystal surface. After the nanocrystal synthesis is completed, a mild post-processing step (light irradiation) activates octadecenylacrylamide, triggering an in-situ cross-linking polymerization reaction between molecules. This results in the formation of a highly interconnected, chemically bonded 'self-assembled protective shell' on the nanocrystal surface. This shell tightly connects all the ligand molecules on the nanocrystal surface into a robust three-dimensional network, greatly enhancing the stability and density of the ligand layer and more effectively blocking environmental corrosive agents such as water and oxygen. The aforementioned triple ligands—oil-based phosphoric acid, poly(vinyl alcohol-grafted-urea), and octadecenylacrylamide—work synergistically during the nanocrystal synthesis process, thereby achieving perovskite nanocrystals with narrow size distribution, high luminescence efficiency, and excellent environmental stability.

[0028] The beneficial effects of this invention are:

[0029] This invention provides a method for preparing metal halide perovskite nanocrystals and the resulting product. It introduces a trifunctional dynamic ligand system composed of oil-based phosphoric acid, poly(vinyl alcohol-grafted-urea), and octadecenylacrylamide, overcoming the technical bottleneck of prior art where nanocrystal size distribution, luminescence efficiency, and environmental stability are difficult to optimize synergistically. The oil-based phosphoric acid effectively passivates surface defects and provides durable protection through multi-point strong coordination. Poly(vinyl alcohol-grafted-urea) achieves precise control of growth kinetics through reversible hydrogen bonding. Octadecenylacrylamide forms a highly interconnected chemically bonded self-assembled protective shell through photoinduced polymerization and cross-linking reactions. The synergistic effect of these three components enables the nanocrystals to simultaneously possess narrow size distribution, high luminescence efficiency, and long lifetime. Even after storage in a harsh environment of 85°C / 85% RH for 1500 hours, the photoluminescence intensity retention rate remains above 85%, exhibiting a lifetime superior to existing technologies. This method has good process adaptability and provides an effective solution for the preparation of high-performance perovskite nanocrystals. Attached Figure Description

[0030] Figure 1 Transmission electron microscope image of the metal halide perovskite nanocrystals prepared according to the present invention; the scale bar in the image is 100 nm.

[0031] Figure 2 The comparison results of CsPbBr3 perovskite nanocrystals PLQY prepared in the embodiments and comparative examples of the present invention are shown.

[0032] Figure 3 The results show the comparison of storage stability of CsPbBr3 perovskite nanocrystals prepared in the embodiments and comparative examples of this invention. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions of this invention, the present application will be further described in detail below with reference to embodiments. Example 1

[0034] 1. Preparation of Cs-derived precursor solution:

[0035] In an argon-filled glove box, precisely add 0.1 mmol of Cs₂CO₃ (99.9% purity), 0.5 mL of oleic acid (OA, 90%), and 8 mL of 1-octadecene (ODE, 90%) to a 100 mL three-necked flask. Place a magnetic stir bar in the flask, seal it, and remove it from the glove box.

[0036] 2. Heating, dehydration, and deoxygenation treatment:

[0037] Place the three-necked flask on an oil bath and connect it to a vacuum system. Turn on the magnetic stirrer (500 rpm), heat to 100°C and begin evacuation, maintaining the system pressure at 10 Pa for 30 minutes. After completion, turn off the vacuum and purge with high-purity argon to atmospheric pressure. Then raise the oil bath temperature to 150°C and maintain it for 10 minutes.

[0038] 3. Synergistic injection reaction and nanocrystal formation:

[0039] (1) Synthesis of strong interfacial anchoring group - oleophosphate:

[0040] a. Phosphorylation reaction: Under nitrogen protection, 50 mmol of oleyl alcohol (purity ≥90%) was dissolved in 50 mL of anhydrous toluene and placed in a three-necked flask. Under ice-water bath cooling and continuous stirring, 25 mmol of P₂O₅ powder (purity ≥98%) was slowly and batch-wise added over 30 minutes, maintaining the reaction temperature below 40°C throughout. After the addition was complete, the ice bath was removed, the reaction system was heated to 80°C, and refluxed at this temperature for 5 hours.

[0041] b. Hydrolysis treatment: Cool the reaction mixture to room temperature (25°C). While continuously stirring, slowly add 10 mL of deionized water dropwise over 1 hour, keeping the temperature below 30°C. After the deionized water addition is complete, continue stirring for 2 hours to ensure complete hydrolysis.

[0042] c. Purification: Transfer the reaction mixture to a separatory funnel and wash the organic phase twice with 50 mL of saturated brine to remove residual phosphoric acid and water-soluble impurities. Dry the organic phase overnight with anhydrous sodium sulfate. After filtering to remove the drying agent, remove the toluene solvent by rotary evaporation under reduced pressure at a water bath temperature of 50°C to obtain a pale yellow viscous liquid product, which is the target compound, oleophosphate (mainly a mixture of monoesters and diesters). The product can be used in the next step without further purification.

[0043] (2) Synthesis of the dynamic growth control unit—poly(vinyl alcohol-grafted-urea):

[0044] a. PVA dissolution: Add 5 g of vinyl alcohol (PVA, Mw=89000–98000, degree of hydrolysis ≥99%) to 100 mL of deionized water and stir vigorously at 90°C for 2 hours until the PVA is completely dissolved to obtain a clear and homogeneous solution.

[0045] b. Grafting reaction: Cool the PVA solution to 60°C, add 2 g of urea (purity ≥99.5%) and 0.3 mL of 0.1 MHCl solution (adjust pH to 4-5). Raise the temperature to 110°C and stir the reaction at this temperature for 5 hours to allow the amino groups of urea to undergo a grafting condensation reaction with the hydroxyl groups of PVA.

[0046] c. Purification and Drying: After the reaction was complete, the solution was cooled to room temperature. Under vigorous stirring, 200 mL of anhydrous ethanol was slowly added to the solution, causing the polymer to precipitate. The precipitate was collected by suction filtration through a Buchner funnel. The precipitate was washed three times thoroughly with anhydrous ethanol to completely remove unreacted urea and catalyst. The resulting solid product was placed in a vacuum oven and dried at 50°C for 24 hours to constant weight, yielding a white solid poly(vinyl alcohol-grafted-urea). The product can be used in the next step without further purification.

[0047] (3) Synthesis of the potential crosslinking unit—octadecenylacrylamide:

[0048] In a dry round-bottom flask, 20 mmol of octadecenylamine (purity ≥70%) and 50 mL of anhydrous dichloromethane were added and stirred to dissolve, yielding a dichloromethane (DCM) solution. Under an ice-water bath (0–5°C) and nitrogen protection, 10 mL of a DCM solution containing 20 mmol of acrylic anhydride (purity ≥98%) and 10 mL of a DCM solution containing 20 mmol of triethylamine (purity ≥99%) were slowly added dropwise over approximately 1 hour. After the addition was complete, the ice bath was removed, and the reaction was allowed to proceed at room temperature for 5 hours. After the reaction was complete, the organic phase was washed with deionized water and saturated brine, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain a pale yellow liquid product, octadecenylacrylamide. The product can be used in the next step without further purification.

[0049] (4) Preparation of mother liquor of trifunctional dynamic ligand (DFDL) system: Weigh 0.01 mmol of synthesized oleo-based phosphoric acid, 0.002 mmol (based on repeating units) of synthesized poly(vinyl alcohol-grafted-urea) and 0.01 mmol of octadecenylacrylamide, dissolve them together in 0.3 mL of oleylamine (OLA, 70%), heat gently and vortex to mix them thoroughly.

[0050] (5) Preparation of injection mixture: In a glove box, 0.2 mmol PbBr2 (99.99%) was mixed with the above DFDL stock solution in a glass vial and then preheated to 150°C on a hot plate.

[0051] (6) Injection reaction: Using a preheated syringe, rapidly (within about 5 seconds) inject the mixture into the Cs source precursor solution at 150°C. After injection, maintain the temperature at 150°C and continue the reaction for 5 minutes.

[0052] 4. Ultra-low temperature cooling treatment:

[0053] After the reaction was completed, the three-necked flask was immediately immersed in liquid nitrogen (-196°C) for rapid cooling and quenching to extinguish the reaction.

[0054] 5. Product purification and dispersion:

[0055] The reaction mixture, after cooling to room temperature, was transferred to a centrifuge tube and centrifuged at 7000 rpm for 8 minutes, discarding the supernatant. The precipitate was washed twice with 5 mL of anhydrous ethyl acetate (centrifuged under the same conditions after each wash). Finally, the precipitate was dispersed in 4 mL of anhydrous toluene and sonicated for 5 minutes to obtain a primary nanocrystalline dispersion.

[0056] 6. Photoinduced in-situ crosslinking protection:

[0057] A small amount of photoinitiator DMPA (concentration of 1 wt% of the total weight of the solution) is added to the primary nanocrystal dispersion obtained in step (5). The mixed solution is then spin-coated onto a substrate to form a thin film.

[0058] The film was irradiated with ultraviolet light (wavelength 365 nm, intensity 10 mW / cm²) under inert gas (nitrogen) protection. 2 5 minutes. Ultraviolet light activates the photoinitiator, causing it to generate active free radicals, which in turn triggers the polymerization and cross-linking reaction of the acrylate groups in octadecenylacrylamide, forming a highly interconnected chemically bonded self-assembled protective shell on the surface of the nanocrystals.

[0059] 7. Separation and purification of the final product:

[0060] After crosslinking, the nanocrystals are centrifuged again (8000 rpm, 10 min), washed (2-3 times with anhydrous ethyl acetate or acetone), and then dispersed in anhydrous toluene to obtain CsPbBr3 perovskite nanocrystals with a highly interconnected, chemically bonded self-assembled protective shell on the surface. Example 2

[0061] 1. Preparation of Cs-derived precursor solution:

[0062] The procedure is the same as in Example 1, and the amount of reagents used is the same as in Example 1.

[0063] 2. Heating, dehydration, and deoxygenation treatment:

[0064] The procedure was the same as in Example 1, except that the dehydration and deoxygenation temperature was set to 120°C and maintained for 45 minutes. The reaction temperature was then raised to 160°C and held for 10 minutes.

[0065] 3. Synergistic injection reaction and nanocrystal formation:

[0066] Preparation of DFDL system mother liquor: Weigh 0.025 mmol of oleophosphate synthesized in Example 1, 0.006 mmol of poly(vinyl alcohol-grafted-urea) synthesized in Example 1, and 0.02 mmol of octadecenylacrylamide synthesized in Example 1, and dissolve them together in 0.3 mL of OLA.

[0067] Preparation of injection mixture: Mix 0.2 mmol PbBr2 with DFDL stock solution and preheat to 160°C.

[0068] Injection reaction: The mixture was rapidly injected into the Cs source solution at 160°C and reacted at 160°C for 10 minutes.

[0069] 4. Ultra-low temperature cooling treatment:

[0070] Same as Example 1.

[0071] 5. Product purification and dispersion:

[0072] The procedure was the same as in Example 1, except that the centrifugation conditions were adjusted to 8000 rpm for 10 minutes; the washing solvent was 8 mL of anhydrous acetone; and the mixture was redispersed in 5 mL of anhydrous toluene.

[0073] 6. Photoinduced in-situ crosslinking protection:

[0074] The procedure is the same as in Example 1, with ultraviolet light irradiation (wavelength unchanged, intensity adjusted to 30 mW / cm). 2 3 minutes.

[0075] 7. Separation and purification of the final product:

[0076] The procedure is the same as in Example 1, dispersing the sample in anhydrous toluene. Example 3

[0077] 1. Preparation of Cs-derived precursor solution:

[0078] The procedure is the same as in Example 1, and the amount of reagents used is the same as in Example 1.

[0079] 2. Heating, dehydration, and deoxygenation treatment:

[0080] The dehydration and deoxygenation temperature was set to 160°C and maintained for 60 minutes. The reaction temperature was then raised to 170°C and held for 10 minutes.

[0081] 3. Synergistic injection reaction and nanocrystal formation:

[0082] Preparation of DFDL system mother liquor: Weigh 0.04 mmol of oleophosphate synthesized in Example 1, 0.01 mmol of poly(vinyl alcohol-grafted-urea) synthesized in Example 1 and 0.03 mmol of octadecenylacrylamide synthesized in Example 1, and dissolve them together in 0.3 mL of OLA.

[0083] Preparation of injection mixture: Mix 0.2 mmol PbBr2 with DFDL stock solution and preheat to 170°C.

[0084] Injection reaction: The mixture was rapidly injected into the Cs source solution at 170°C and reacted at 170°C for 15 minutes.

[0085] 4. Ultra-low temperature cooling treatment: Same as in Example 1.

[0086] 5. Product purification and dispersion:

[0087] The procedure was the same as in Example 1, except that the centrifugation conditions were adjusted to 9000 rpm for 12 minutes; the washing solvent was 10 mL of anhydrous ethyl acetate; and the mixture was redispersed in 6 mL of anhydrous toluene.

[0088] 6. Photoinduced in-situ crosslinking protection:

[0089] The procedure is the same as in Example 1, with ultraviolet light irradiation (wavelength unchanged, intensity adjusted to 50 mW / cm). 2 1 minute.

[0090] 7. Final product separation and purification: Same as in Example 1.

[0091] Comparative Example 1: Traditional heat injection method, without DFDL system

[0092] Repeat all the steps of Example 2, but in step 3, ole-based phosphoric acid, poly(vinyl alcohol-grafted-urea), and octadecenylacrylamide are not added at all. The injection mixture consists only of 0.2 mmol PbBr2 dissolved in 0.8 mL OLA, and all other parameters are exactly the same as in Example 2.

[0093] Comparative Example 2: Contains only oleophosphate and octadecenylacrylamide, and does not contain poly(vinyl alcohol-grafted-urea).

[0094] The steps of Example 2 were repeated, but in the preparation of the DFDL mother liquor in step 3, only 0.025 mmol of oleophosphate and 0.02 mmol of octadecenylacrylamide were added, without adding poly(vinyl alcohol-grafted-urea). The injection mixture consisted of PbBr2, OLA, oleophosphate, and octadecenylacrylamide.

[0095] Comparative Example 3: Contains only poly(vinyl alcohol-grafted-urea) and octadecenylacrylamide, and does not contain oleophosphate.

[0096] The steps of Example 2 were repeated, but in the preparation of the DFDL mother liquor in step 3, only 0.006 mmol of poly(vinyl alcohol-grafted-urea) and 0.02 mmol of octadecenylacrylamide were added, without the addition of oleophosphate. The injection mixture consisted of PbBr2, OLA, poly(vinyl alcohol-grafted-urea), and octadecenylacrylamide.

[0097] Comparative Example 4: Contains only oleoyl phosphate and poly(vinyl alcohol-grafted-urea), and does not contain octadecenyl acrylamide.

[0098] Repeat all the steps of Example 2, but in the preparation of the DFDL mother liquor in step 3, only 0.025 mmol of oleophosphate and 0.006 mmol of poly(vinyl alcohol-grafted-urea) are added, without adding octadecenylacrylamide. The injection mixture consists of PbBr2, OLA, oleophosphate and poly(vinyl alcohol-grafted-urea).

[0099] Performance testing

[0100] To quantify the performance advantages of the metal halide perovskite nanocrystals prepared by the method of this invention, the following key performance tests were performed on the metal halide perovskite nanocrystals prepared in Examples 1-3 and Comparative Examples 1-4. The data for each performance test are summarized in Table 1.

[0101] 1. Size and morphology analysis:

[0102] The morphology and size of the nanocrystals were observed using transmission electron microscopy. A diluted nanocrystal dispersion was dropped onto an ultrathin carbon film copper grid, dried, and then tested. The sizes of 200 nanoparticles were randomly selected using ImageJ software, and their mean size and standard deviation (σ) were calculated to evaluate the uniformity of size distribution.

[0103] 2. Optical performance testing:

[0104] Photoluminescence quantum efficiency (PLQY): Absolute quantum efficiency was measured using a fluorescence spectrometer equipped with an integrating sphere. A nanocrystalline dispersion was injected into a standard quartz cuvette, and a xenon lamp with a wavelength of 518 nm was used as the excitation source. The emission spectrum was measured, and the PLQY value was calculated.

[0105] Emission spectrum and half-width at half-maximum (FWHM): The photoluminescence (PL) spectrum of the nanocrystalline dispersion was measured using the same fluorescence spectrometer. The wavelength of its emission peak was read, and the width at half the height of the spectral peak, i.e., the half-width at half-maximum (FWHM), was calculated to evaluate the color purity of the emission.

[0106] 3. Environmental stability test:

[0107] The nanocrystalline dispersion was placed in a constant temperature and humidity test chamber and aged under conditions of 85°C and 85% relative humidity (85°C / 85% RH). Samples were periodically removed and their photoluminescence intensity was measured under the same test conditions. With the initial intensity as 100%, the retention rate of PL intensity at different time points was calculated to evaluate its long-term environmental stability.

[0108] Table 1

[0109] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Average size (nm) 9.8 10.5 11.2 12.5 / 10.3 10.5 Size distribution (σ, nm) ±0.9 ±0.7 ±1.0 ±2.5 ±1.8 ±0.8 ±0.7 Photoluminescence quantum yield (PLQY, %) 92 96 94 78 90 82 95 Full width at half maximum (FWHM, nm) 18 15 17 26 22 16 15 PL strength retention rate after 1000 hours (%, 85°C / 85% RH) 90 95 92 <50200 hours later 75 <50300 hours later 65 PL strength retention rate after 1500 hours (%, 85°C / 85% RH) 86 93 89 / / / 58

[0110] Note: Size distribution (σ): represents the standard deviation; a smaller value indicates a more uniform size distribution. Average size of Comparative Example 2: Due to severe Ostwald curing, the size is uneven, and no single average size is given. PL strength retention rate at 1000 hours: Comparative Example 1 had a PL strength retention rate of <50% after 200 hours, Comparative Example 3 had a retention rate of <50% after 300 hours, and Comparative Example 2 had a retention rate of 75% at 1000 hours, but did not reach the 1500-hour test threshold. The 1500-hour retention rate was only tested for Examples 1-3 and Comparative Example 4.

[0111] As shown in Table 1, the nanocrystals prepared in Examples 1-3 using the trifunctional dynamic ligand system of the present invention exhibit the following characteristics:

[0112] (1) Improved size uniformity: The standard deviation of size distribution (σ) is in the range of ±0.7~±1.0 nm. Figure 1 This represents an improvement over Comparative Example 1 (±2.5 nm) and Comparative Example 2 (±1.8 nm).

[0113] (2) Higher luminous efficiency: The photoluminescent quantum yield (PLQY) is in the range of 92% to 96%, which is higher than the results of Comparative Example 1 (78%) and Comparative Example 3 (82%). Figure 2 ).

[0114] (3) Improved environmental stability: After aging for 1500 hours at 85°C / 85% RH, the photoluminescence intensity retention rate remained in the range of 86%~93%, showing better stability compared to comparative examples 1-4. Figure 3 ).

[0115] Comparative Example 2 (containing only oleoyl phosphate and octadecenyl acrylamide, without poly(vinyl alcohol-grafted-urea)) showed better size distribution (σ=±1.8 nm) than the traditional method (Comparative Example 1, σ=±2.5 nm) despite the suppression of Ostwald ripening through crosslinking, but lacking dynamic growth control of poly(vinyl alcohol-grafted-urea) during the synthesis stage. This resulted in size differentiation of the nanocrystals in the early stages of growth, leading to a still relatively wide final size distribution and poor luminescence purity (FWHM=22 nm). This indicates that while crosslinking can improve particle dispersion, it cannot reverse the size inhomogeneity formed during the growth stage, further demonstrating the indispensability of fine control of poly(vinyl alcohol-grafted-urea) during nucleation and the early stages of growth.

[0116] Comparative Example 3 (containing only poly(vinyl alcohol-grafted-urea) and octadecenylacrylamide, without oleophosphate) was also crosslinked, but due to the lack of strong passivation by oleophosphate, there were many defects on the nanocrystal surface, resulting in a much lower luminescence efficiency (PLQY=82%) than the examples, and poor stability. This proves that oleophosphate is indispensable for obtaining high luminescence efficiency.

[0117] Comparative Example 4 (containing only oleoyl phosphate and poly(vinyl alcohol-grafted-urea), without octadecenylacrylamide) could not undergo an effective crosslinking reaction (due to the lack of octadecenylacrylamide with polymerizable groups). Therefore, its product was equivalent to nanocrystals prepared and purified using only oleoyl phosphate and poly(vinyl alcohol-grafted-urea). Although its initial optical properties (PLQY=95%, FWHM=15 nm) were comparable to Example 2, its long-term stability (58%) was inferior to that of Examples 1-3 (86%-93%). These results demonstrate that octadecenylacrylamide and the in-situ crosslinking reaction it initiates are the main reasons for the stability.

[0118] Furthermore, Examples 1-3 all maintained good overall performance under different DFDL dosage conditions (PLQY > 90%, σ < ±1.0 nm, and retention rate > 80% after 1000 hours), indicating that the scheme has good process adaptability and avoids the sensitivity dependence of traditional methods on process parameters.

[0119] In summary, the trifunctional ligand system described in this invention forms an organic whole. The oil-based phosphoric acid effectively passivates surface defects and provides durable protection through multi-point strong coordination; poly(vinyl alcohol-grafted-urea) achieves precise control of growth kinetics through reversible hydrogen bonding; and octadecenylacrylamide forms a highly interconnected chemically bonded self-assembled protective shell through photoinduced polymerization and cross-linking reactions. These three components are complementary and indispensable. Ultimately, perovskite nanocrystals with narrow size distribution, high luminescence efficiency (photoluminescence quantum yield), and excellent environmental stability were successfully prepared, providing a feasible technical solution for addressing related technical problems.

Claims

1. A metal halide perovskite nanocrystal, characterized in that, Its surface is anchored with a cross-linked network protective shell by chemical bonding, and the photoluminescence spectrum of the nanocrystal has a full width at half maximum (FWHM) of 12 nm to 18 nm, a photoluminescence quantum yield of not less than 85%, and after being stored in an 85°C / 85% RH environment for 1500 hours, its photoluminescence intensity retention rate is not less than 85% of the initial value. The method for preparing the metal halide perovskite nanocrystals includes the following steps: (a) A Cs source precursor solution was prepared by mixing Cs source, oleic acid and 1-octadecene under an inert atmosphere; (b) The solution obtained in step (a) is heated and dehydrated and deoxygenated under vacuum, and then heated to 150°C to 170°C under an inert atmosphere; (c) Inject a preheated mixed solution into the solution obtained in step (b) to form a reaction system, wherein the mixed solution contains a binary metal halide PbBr2, oleylamine and a trifunctional dynamic ligand system, wherein the trifunctional dynamic ligand system includes oleyl phosphate as a strong interface anchoring group, polyvinyl alcohol-grafted-urea as a dynamic growth regulating unit and octadecenyl acrylamide as a potential crosslinking unit. (d) After injection, react at 150°C to 170°C for 5 to 15 minutes; (e) After the reaction is complete, the reaction system of step (c) is subjected to ultra-low temperature cooling to terminate the reaction and obtain the product after the reaction; (f) The cooled product from step (e) is centrifuged, washed, and redispersed to obtain a primary nanocrystalline dispersion; (g) The primary nanocrystal dispersion obtained in step (f) is post-treated to activate the octadecenylacrylamide as a potential crosslinking unit, which initiates an intermolecular crosslinking reaction to form a crosslinking protective shell on the surface of the nanocrystals. After centrifugation, washing and redispersing, the metal halide perovskite nanocrystals are obtained.

2. The metal halide perovskite nanocrystals according to claim 1, characterized in that, In step (b), the temperature of the dehydration and deoxygenation treatment is 100°C to 160°C, the vacuum pressure is maintained below 20 Pa, and the treatment time is 30 to 60 minutes.

3. The metal halide perovskite nanocrystals according to claim 1, characterized in that, In step (c), the molar ratio of the oil-based phosphoric acid to the binary metal halide PbBr2 is 0.05:1 to 0.2:

1.

4. The metal halide perovskite nanocrystals according to claim 1, characterized in that, In step (c), the molar ratio of the polyvinyl alcohol-grafted-urea to the binary metal halide PbBr2, based on its repeating unit, is 0.01:1 to 0.05:

1.

5. The metal halide perovskite nanocrystals according to claim 1, characterized in that, In step (c), the molar ratio of the octadecenylacrylamide to the binary metal halide PbBr2 is 0.05:1 to 0.15:

1.

6. The metal halide perovskite nanocrystals according to claim 1, characterized in that, In step (e), the cryogenic cooling process involves cooling the reaction system to -196°C or below using liquid nitrogen or liquid helium.

7. The metal halide perovskite nanocrystals according to claim 1, characterized in that, In steps (f) and (g), the centrifugation process involves centrifuging at a speed of 7000 rpm to 9000 rpm to separate the precipitate; the solvent used for redispersion is anhydrous toluene.

8. The metal halide perovskite nanocrystals according to claim 1, characterized in that, The post-treatment described in step (g) is a photo-induced crosslinking reaction, in which the photoinitiator α,α-dimethoxy-α-phenylacetophenone is added to the primary nanocrystal dispersion, and the crosslinking reaction is carried out under ultraviolet light irradiation; the wavelength of the ultraviolet light is 365 nm, and the intensity is 10-50 mW / cm. 2 The photoinitiator is added and irradiated for 1-5 minutes; wherein the amount of photoinitiator added is 1 wt% of the total weight of the solution.

Images