A method for supercritical carbon dioxide assisted preparation of perovskite quantum dots

Abstract

The embodiment of the application relates to a method for preparing perovskite quantum dots assisted by supercritical carbon dioxide, and belongs to the technical field of perovskite quantum dots. The method solves the problems of complex process of hot injection method, large amount of anti-solvent required by ligand assisted precipitation method and difficult size control. The specific steps include: 1) dissolving lead halide and ligand 1 in polar solvent 1 to form precursor solution A; 2) dissolving cesium halide and ligand 2 in polar solvent 2 to form solution B; 3) premixing solution A and supercritical carbon dioxide to be homogeneous; 4) adding anti-solvent 3 into the reaction kettle and introducing the homogeneous phase of solution A and supercritical carbon dioxide; 5) rapidly injecting solution B for reaction, and releasing pressure after crystal nucleation and growth; 6) collecting and purifying the product. The method is green and efficient, and the prepared perovskite quantum dots are suitable for the fields of optoelectronic devices, display and lighting, etc.

Description

Technical Field

[0001] This invention relates to the preparation technology of nanomaterials and optoelectronic materials, and in particular to a method for preparing highly efficient and stable CsPbX3 (X=Br,I) perovskite quantum dots in a supercritical carbon dioxide (scCO2) medium. Background Technology

[0002] Perovskite quantum dots possess unique semiconductor properties and achieve controllable exciton dynamics through quantum confinement effects. Their excellent photoelectric properties and low-cost solution preparation technology make perovskite materials widely used in optoelectronic fields. Due to their high photoluminescence quantum yield (PLQY), narrow full width at half maximum (FWHM), and high carrier mobility, they have become promising materials for optoelectronic devices. Furthermore, the size and composition of perovskite quantum dots can be tunable, enabling bandgap tuning across the entire visible light spectrum and efficient color emission. These properties make them outstanding in LEDs, solar cells, and bioimaging. However, perovskite quantum dots are susceptible to the effects of moisture and oxygen in air, and their performance is significantly affected by surface defects (such as halogen vacancies). These defects can lead to decreased luminescence performance, broadband emission, and charge transport imbalances, resulting in a rapid decline in their photoelectric properties. Therefore, how to prepare perovskite quantum dots with good environmental stability under mild conditions has become a pressing technical challenge.

[0003] Currently, the main methods for synthesizing perovskite quantum dots include hot injection and room-temperature ligand-assisted reprecipitation. Hot injection is a common method for synthesizing perovskite quantum dots, suitable for preparing quantum dots with uniform size and few defects. This method involves rapidly injecting a precursor solution at high temperature and stopping crystal growth by rapid cooling. This method allows control over the size and shape of the quantum dots, and the resulting perovskite quantum dots exhibit high photoluminescence quantum yield. In contrast, ligand-assisted reprecipitation is performed at room temperature and is suitable for large-scale preparation. This method involves rapidly mixing the precursor solution with an antisolvent, leading to supersaturation and crystal formation. Publication number CN116410747A discloses "a method for preparing ultra-small CsPbBr3 perovskite quantum dots with high luminescence performance". Using a cesium source, DBSA ligand and ODE, a Cs-DBSA precursor is prepared. Then, the Cs-DBSA precursor solution is injected into a PbBr2 solution by a hot injection method to prepare controllable and efficient ultra-small CsPbBr3 perovskite quantum dots, resulting in extremely high PLQY (up to 100%) and stability. Publication No. CN116004230A discloses "A controllable crystallization growth method for CsPbI3 perovskite quantum dots and its preparation method," employing a hot-injection reaction at a temperature of 160–180 °C. One or more sterically hindered nucleating agents are introduced, including a copolymer of styrene-N-phenylmaleimide-maleic anhydride and N,N'-m-phenylenebismaleimide. By adding these sterically hindered nucleating agents, lead ions can be effectively complexed, acting as ligands to regulate the critical radius and NCs growth rate. Simultaneously, the steric hindrance suppresses the Oswald ripening effect, limiting growth. This extends the reaction time from 5 seconds to over 3 minutes, enabling successful industrialization. This not only improves the stability of the quantum dots but also ensures a high fluorescence quantum efficiency approaching 90%. CN112877064A discloses "A method for preparing pure Cs4PbBr6 perovskite quantum dots and the product thereof." The preparation method of this invention introduces a small amount of water during the preparation process, which greatly improves the luminescence performance and stability. The prepared Cs4PbBr6 perovskite quantum dots can emit green light under near-ultraviolet and blue light excitation, and the quantum lifetime reaches the microsecond level. The Cs4PbBr6 perovskite quantum dots prepared by this invention using the ligand-assisted reprecipitation method have advantages such as effective near-ultraviolet excitation, high emission intensity, uniform phase, good thermal stability, and high quantum lifetime. Although the hot-injection method and the ligand-assisted precipitation method have made some progress, the hot-injection method requires operation at high temperature and inert atmosphere, making the process complex and difficult to carry out on a large scale. The ligand-assisted precipitation method, due to its fast reaction rate, makes it difficult to separate the nucleation and growth stages, making it difficult to precisely control the size and shape of the quantum dots, resulting in more crystal defects. At the same time, the possible generation of by-products during the reaction process leads to poor purity and uniformity of the final product, affecting the performance of the quantum dots.These factors limit their widespread application in industrial settings, necessitating the search for simpler, more controllable, and environmentally friendly preparation methods. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a novel method for the preparation of perovskite quantum dots using supercritical carbon dioxide (scCO2). By rapidly crystallizing the perovskite precursor in a scCO2 environment, the size and morphology of the quantum dots can be effectively controlled, improving their environmental stability and photoelectric properties. Furthermore, the method eliminates the need for rapid cooling from high temperatures and the consumption of large amounts of antisolvents. This method is simple, efficient, and highly scalable, making it suitable for large-scale production of high-quality perovskite quantum dots.

[0005] To achieve the above objectives, this application provides a method for preparing perovskite quantum dots with supercritical carbon dioxide assistance, comprising the following steps:

[0006] Step 1: Dissolve lead halide (such as PbBr2 or PbI2) and ligand 1 in polar solvent 1 to form precursor solution A;

[0007] Step 2: Dissolve cesium halide (such as CsBr or CsI) and ligand 2 in polar solvent 2 to form precursor solution B;

[0008] Step 3: Add solution A into supercritical carbon dioxide and premix for several minutes to make solution A and supercritical carbon dioxide homogeneous.

[0009] Step 4: After adding antisolvent 3 into the reactor, homogeneous solution A and supercritical carbon dioxide are introduced into the reactor and stirred for several minutes.

[0010] Step 5: Quickly pump solution B into the reactor using a plunger pump, stir vigorously for several seconds, and after the crystals have grown uniformly through nucleation, open the pressure relief valve to quickly release pressure for several seconds.

[0011] Step 6: After collecting the antisolvent 3 containing the perovskite quantum dot product, centrifuge and purify it, then redisperse it in n-hexane for storage.

[0012] The specific parameter range of the method is as follows:

[0013] The reaction temperature in steps one and two is 30-60℃;

[0014] The supercritical carbon dioxide conditions in step three are: temperature 30-80℃, pressure 10-25MPa;

[0015] The reaction conditions in steps four and five are: temperature 50-90℃, pressure 15-30MPa;

[0016] The pressure relief time should be controlled within 3-30 seconds, and the pressure relief rate should be 0.5-2 MPa / s. Specific implementation plan:

[0017] In some embodiments that may include the above embodiments, in step one, the polar solvent 1 is one of N,N-dimethylformamide (DMF), 2-methoxyethanol (2ME), acetonitrile (ACN), and 2-pyrrolidone (2P).

[0018] In some embodiments that may include the above embodiments, in step one, the ligand 1 is one of oleic acid (OA), oleylamine (OAm), sulfobetaine, dodecylbenzenesulfonic acid (DBSA), tri-n-octylphosphine (TOP), and tri-n-octylphosphine oxide (TOPO).

[0019] In some embodiments that may include the above embodiments, in step two, the polar solvent 2 is one of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), γ-valerolactone (GVL), and N,N-dimethylformamide (DMF).

[0020] In some embodiments that may include the above embodiments, in step two, the ligand 2 is one of oleic acid (OA), oleylamine (OAm), bis(2,4,4-trimethylpentyl)phosphonic acid (DOPA), lecithin, and triphenylphosphine oxide.

[0021] In some embodiments that may include the above embodiments, in step four, the antisolvent 3 is one of toluene, n-hexane, chlorobenzene, chloroform, and mesitylene.

[0022] In some embodiments that may include the above embodiments, the volume of solvent 1 added to the lead halide salt is one of 5 to 200 mL; the volume of solvent 2 added to the cesium halide salt is one of 5 to 200 mL.

[0023] This invention also provides a quantum dot synthesis system, such as Figure 1 As shown, the system includes a perovskite precursor solution container, a CO2 cylinder assembly, a high-pressure isochoric dual-plunger pump, a high-pressure high-flow pump, a high-pressure reactor and its heating jacket, a stirrer, a recovery tank, a ceramic filter, and corresponding control valve systems. Among these:

[0024] The perovskite precursor solution containers are used to store and transport precursor solutions A and B; the CO2 cylinder group is used to provide the supercritical CO2 reaction medium; the high-pressure isochoric dual-plunger pump and the high-pressure high-flow pump are used to transport and pressurize the reactants. The high-pressure reactor is equipped with: a heating jacket for temperature control; a stirring device to ensure uniform mixing of the reaction; an electric heating device for precise temperature control; and a rapid injection valve for precise addition of the precursor solution. The control valve system includes: a back pressure valve for system pressure control; a vent valve for system venting; a rapid pressure relief valve for reaction termination control; a flushing valve for system cleaning; and a recovery valve for product collection.

[0025] The quantum dot synthesis system also includes an online characterization and real-time monitoring system, comprising a visualization observation system, a dynamic light scattering (DLS) online monitoring system, and a real-time monitoring system combining ultraviolet-visible spectroscopy (UV-vis) and photoluminescence (PL), for real-time monitoring of the generation and performance of perovskite quantum dots.

[0026] The working principle of the perovskite quantum dot synthesis-monitoring system described above is as follows:

[0027] Precursor solution preparation stage: Precursor solutions A and B are prepared separately in perovskite precursor solution containers; the solutions are delivered to the system using a high-pressure isochoric dual-plunger pump; the composition and homogeneity of the precursor solutions are monitored in real time.

[0028] Supercritical CO2 premixing stage: CO2 is supplied by CO2 cylinders and pressurized by a high-pressure, high-flow pump; it is premixed with precursor solution A in a high-pressure reactor to form a homogeneous phase; the phase behavior changes are observed in real time through a viewing window; and the system state is recorded using a pressure density monitoring system.

[0029] Reaction process control: The reaction temperature is controlled by a heating jacket and an electric heating device; a stirring device is used to ensure uniform mixing of the reaction; the addition time of precursor solution B is precisely controlled by a rapid injection valve; the formation process of quantum dots is monitored in real time by UV-vis spectroscopy; the changes in the luminescence properties of quantum dots are tracked by PL spectroscopy; the particle size distribution of quantum dots is measured by dynamic light scattering; and the reaction parameters are adjusted in real time based on the monitoring results.

[0030] Product collection and purification: The optimal reaction endpoint is determined based on optical performance indicators; the reaction is terminated by a rapid pressure relief valve after completion; the product enters the recovery tank, is filtered by a ceramic filter, and then separated from supercritical CO2; the system can be cleaned and maintained via a flushing valve. The obtained perovskite quantum dots can be collected directly as dry powder; alternatively, solvents such as toluene, chloroform, and n-hexane can be added to the recovery tank beforehand to disperse the quantum dots; the dispersed perovskite quantum dot solution can be collected by opening the recovery valve.

[0031] Compared with existing synthesis methods, the embodiments of this application have the following advantages:

[0032] The method described in this application is a method for preparing perovskite quantum dots via a crystal supersaturation reaction in a supercritical carbon dioxide environment. Using supercritical CO2 as the reaction medium, it enables quantum dot preparation under mild conditions, avoiding the high-temperature operation required in traditional methods. By controlling the pressure and temperature of supercritical CO2, the size distribution of the quantum dots can be precisely controlled. Utilizing the characteristics of supercritical CO2, rapid separation and purification of quantum dots are achieved. A non-invasive measurement method is used to avoid interference from the sampling process, and real-time data analysis and feedback enable intelligent optimization of process parameters. The process is environmentally friendly, uses less solvent, and is easily scaled up for continuous industrial production. Attached Figure Description

[0033] Figure 1 This is a simplified diagram of a device for preparing perovskite quantum dots using supercritical CO2.

[0034] Figure 2 These are transmission electron microscopy (TEM) images and particle size distribution diagrams of the perovskite quantum dots prepared in Example 1.

[0035] Figure 3 The images show transmission electron microscopy (TEM) images and particle size distributions of the perovskite quantum dots prepared in Comparative Example 2. Detailed Implementation

[0037] Various exemplary implementations of the embodiments of this application are now described in detail. This detailed description should not be regarded as a limitation on the embodiments of this application, but should be understood as a more detailed description of certain aspects, features and implementations of the embodiments of this application.

[0038] It should be understood that the terminology used in the embodiments of this application is merely for describing particular implementations and is not intended to limit the embodiments of this application. Furthermore, for numerical ranges in the embodiments of this application, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in the embodiments of this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art described in the embodiments of this application. While only preferred methods and materials are described in the embodiments of this application, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of the embodiments of this application. All references to this specification are incorporated by way of citation to disclose and describe the methods and materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0040] Various improvements and variations can be made to the specific implementation methods of the embodiments described in this application without departing from the scope or spirit of the embodiments, which will be obvious to those skilled in the art. Other implementation methods derived from the description of the embodiments of this application will be obvious to those skilled in the art. The description and embodiments of the embodiments of this application are merely exemplary.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] Example 1

[0043] (1) Preparation of PbBr2 precursor:

[0044] At 30°C, 3 mmol of lead bromide was mixed with 100 mL of LDM, 10.7 mL of oleylamine was added, and the mixture was stirred vigorously until PbBr2 was completely dissolved. The mixture was then cooled to room temperature.

[0045] (2) Preparation of CsBr precursor:

[0046] At 30°C, 3 mmol of cesium bromide was mixed with 100 mL of DMSO, and 20 mL of oleic acid was added. The mixture was stirred vigorously until the cesium bromide was completely dissolved, and then cooled to room temperature. 10 mL of the solution was injected into the premixing vessel of the apparatus using a syringe, and supercritical carbon dioxide was introduced to 10 MPa and stirred until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure that the solution was clear and transparent.

[0047] (3) Preparation and process detection of CsPbBr3 quantum dots:

[0048] At 50°C, 20 mL of toluene was injected into the reactor. The homogeneous supercritical carbon dioxide and CsBr precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 20 MPa while stirring. The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0049] The PbBr2 precursor from step (1) was pumped into 10 mL at a rate of 100 mL / min using a plunger pump. The reaction was carried out under vigorous stirring for 5 seconds, and the redshift evolution of the UV-vis absorption peak was monitored in real time. The increasing intensity trend of the PL emission spectrum was also monitored simultaneously. After stirring was stopped for 5 seconds, the real-time particle size distribution was obtained by rapid DLS analysis.

[0050] After the crystals have grown uniformly through nucleation, the pressure relief valve is opened to rapidly release pressure for 3 seconds. Spectral changes during the pressure relief process are monitored to ensure product stability. The collection vessel is then opened to obtain CsPbBr3 perovskite quantum dots.

[0051] Example 2

[0052] (1) Preparation of PbBr2 precursor:

[0053] At 40°C, 3 mmol of lead bromide was mixed with 100 mL of 2-methoxyethanol, and 10.7 mL of oleylamine was added. The mixture was stirred vigorously until PbBr2 was completely dissolved, and then cooled to room temperature.

[0054] (2) Preparation of CsBr precursor:

[0055] At 40°C, 3 mmol of cesium bromide was mixed with 100 mL of NMP, and 20 mL of oleic acid was added. The mixture was stirred vigorously until the cesium bromide was completely dissolved, and then cooled to room temperature. 12 mL of the solution was injected into the premixing vessel of the apparatus using a syringe, and supercritical carbon dioxide was introduced to 15 MPa and stirred until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure that the solution was clear and transparent.

[0056] (3) Preparation of CsPbBr3 quantum dots:

[0057] At 60°C, 25 mL of toluene was injected into the reactor. The homogeneous supercritical carbon dioxide and CsBr precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 20 MPa while stirring. The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0058] The PbBr2 precursor from step (1) was pumped into 12 mL at a rate of 120 mL / min using a plunger pump. The mixture was stirred vigorously for 10 seconds, and the redshift evolution of the UV-vis absorption peak was monitored in real time. Simultaneously, the intensification trend of the PL emission spectrum was monitored. Stirring was stopped for 5 seconds, and the real-time particle size distribution was obtained by rapid DLS analysis.

[0059] After uniform nucleation and growth of the crystals, the pressure relief valve was opened to rapidly release pressure for 5 seconds. Spectral changes during the pressure relief process were monitored to ensure product stability. The collection vessel was then opened to obtain CsPbBr3 perovskite quantum dots.

[0060] Example 3

[0061] (1) Preparation of PbBr2 precursor:

[0062] At 50°C, 5 mmol of lead bromide was mixed with 200 mL of acetonitrile, and 10 mmol of sulfobetaine was added. The mixture was stirred vigorously until PbBr2 was completely dissolved, and then cooled to room temperature.

[0063] (2) Preparation of CsBr precursor:

[0064] At 50°C, 3 mmol of cesium bromide was mixed with 100 mL of DMSO, and 6 mmol of bis(2,4,4-trimethylpentyl)phosphonic acid was added. The mixture was stirred vigorously until the cesium bromide was completely dissolved, and then cooled to room temperature. 15 mL of the solution was injected into the premixing vessel of the apparatus using a syringe, and supercritical carbon dioxide was introduced to 15 MPa and stirred until homogeneous.

[0065] (3) Preparation of CsPbBr3 quantum dots:

[0066] At 60℃, 30 mL of toluene was injected into the reactor. The homogeneous supercritical carbon dioxide and CsBr precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 20 MPa while stirring. 15 mL of the PbBr2 precursor from step (1) was pumped in at a rate of 150 mL / min using a plunger pump. The reaction was carried out for 20 seconds with vigorous stirring. After uniform nucleation and growth of the crystals, the pressure relief valve was opened to rapidly release the pressure for 10 seconds. The collection vessel was then opened to obtain CsPbBr3 perovskite quantum dots.

[0067] Example 4

[0068] (1) Preparation of PbBr2 precursor:

[0069] At 50°C, 5 mmol of lead bromide was mixed with 200 mL of LDM, and 10 mmol of sulfobetaine was added. The mixture was stirred vigorously until PbBr2 was completely dissolved, and then cooled to room temperature.

[0070] (2) Preparation of CsBr precursor:

[0071] At 70°C, 5 mmol of cesium bromide was mixed with 100 mL of DMSO, and 10 mmol of lecithin was added. The mixture was stirred vigorously until the cesium bromide was completely dissolved, and then cooled to room temperature. 10 mL of the solution was accurately measured using a syringe and injected into the premixing vessel of the apparatus. Supercritical carbon dioxide was introduced to 15 MPa, and the mixture was stirred at 600 rpm until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure the solution was clear and transparent.

[0072] (3) Preparation and process detection of CsPbBr3 quantum dots:

[0073] At 90°C, 20 mL of toluene was injected into the reactor. The homogeneous supercritical carbon dioxide and CsBr precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 20 MPa while stirring (750 rpm). The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0074] The PbBr2 precursor from step (1) was pumped into 15 mL at a rate of 150 mL / min using a plunger pump. The reaction was carried out under vigorous stirring for 120 seconds, and the redshift evolution of the UV-vis absorption peak was monitored in real time. The increasing intensity trend of the PL emission spectrum was also monitored simultaneously. Stirring was stopped for 5 seconds, and the real-time particle size distribution was obtained by rapid DLS analysis.

[0075] After the crystals have grown uniformly through nucleation, the pressure relief valve is opened to rapidly release pressure for 30 seconds. Spectral changes during the pressure relief process are monitored to ensure product stability. The collection vessel is then opened to obtain CsPbBr3 perovskite quantum dots.

[0076] Example 5

[0077] (1) Preparation of PbBr2 precursor:

[0078] At 50°C, 5 mmol of lead bromide was mixed with 200 mL of 2-pyrrolidone, and 10 mmol of dodecylbenzenesulfonic acid was added. The mixture was stirred vigorously until PbBr2 was completely dissolved, and then cooled to room temperature.

[0079] (2) Preparation of CsBr precursor:

[0080] At 50°C, 5 mmol of cesium bromide was mixed with 200 mL of GBL, and 10 mmol of lecithin was added. The mixture was stirred vigorously until the cesium bromide was completely dissolved, and then cooled to room temperature. 20 mL of the solution was accurately measured using a syringe and injected into the premixing vessel of the apparatus. Supercritical carbon dioxide was introduced to 20 MPa, and the mixture was stirred at 650 rpm until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure the solution was clear and transparent.

[0081] (3) Preparation and process detection of CsPbBr3 quantum dots:

[0082] At 70°C, 30 mL of toluene was injected into the reactor. The homogeneous supercritical carbon dioxide and CsBr precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 25 MPa while stirring (800 rpm). The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0083] The PbBr2 precursor from step (1) was pumped into 20 mL at a rate of 150 mL / min using a plunger pump. The reaction was carried out under vigorous stirring for 150 seconds, and the redshift evolution of the UV-vis absorption peak was monitored in real time. The increasing intensity trend of the PL emission spectrum was also monitored simultaneously. After stirring was stopped for 5 seconds, the real-time particle size distribution was obtained by rapid DLS analysis.

[0084] After the crystals have grown uniformly through nucleation, the pressure relief valve is opened to rapidly release pressure for 5 seconds. Spectral changes during the pressure relief process are monitored to ensure product stability. The collection vessel is then opened to obtain CsPbBr3 perovskite quantum dots.

[0085] Example 6

[0086] (1) Preparation of PbI2 precursor:

[0087] At 60°C, 5 mmol of lead iodide was mixed with 200 mL of acetonitrile, 10 mmol of DBSA was added, and the mixture was stirred vigorously until PbI2 was completely dissolved. The mixture was then cooled to room temperature.

[0088] (2) Preparation of CsI precursor:

[0089] At 60°C, 3 mmol of cesium iodide was mixed with 100 mL of GBL, and 6 mmol of DOPA was added. The mixture was stirred vigorously until the cesium iodide was completely dissolved, and then cooled to room temperature. 15 mL of the solution was accurately measured using a syringe and injected into the premixing vessel of the apparatus. Supercritical carbon dioxide was introduced to 15 MPa, and the mixture was stirred at 550 rpm until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure the solution was clear and transparent.

[0090] (3) Preparation and process detection of CsPbI3 quantum dots:

[0091] At 80°C, 30 mL of chlorobenzene was injected into the reactor. The homogeneous supercritical carbon dioxide and CsI precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 23 MPa while stirring (800 rpm). The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0092] The PbI2 precursor from step (1) was pumped into 15 mL at a rate of 150 mL / min using a plunger pump. The reaction was carried out under vigorous stirring for 20 seconds, and the redshift evolution of the UV-vis absorption peak was monitored in real time. The increasing intensity trend of the PL emission spectrum was also monitored simultaneously. Stirring was stopped for 5 seconds, and the real-time particle size distribution was obtained by rapid DLS analysis.

[0093] After the crystals have grown uniformly through nucleation, the pressure relief valve is opened to rapidly release pressure for 10 seconds. Spectral changes during the pressure relief process are monitored to ensure product stability. The collection vessel is then opened to obtain CsPbI3 perovskite quantum dots.

[0094] Example 7

[0095] (1) Preparation of PbBr2 precursor:

[0096] At 60°C, 5 mmol of lead bromide was mixed with 150 mL of DMF, and 10 mmol of tri-n-octylphosphine was added. The mixture was stirred vigorously until PbBr2 was completely dissolved, and then cooled to room temperature.

[0097] (2) Preparation of FA precursors:

[0098] At 60°C, 3 mmol of formamidin salt was mixed with 200 mL of DMF, and 9 mmol of lecithin was added. The mixture was stirred vigorously for 30 minutes until the formamidin salt was completely dissolved, and then cooled to room temperature. 20 mL of the solution was accurately measured using a syringe and injected into the premixing vessel of the apparatus. Supercritical carbon dioxide was introduced to 20 MPa, and the mixture was stirred at 550 rpm for 15 minutes until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure the solution was clear and transparent.

[0099] (3) Preparation and process detection of FAPbBr3 quantum dots:

[0100] At 90°C, 50 mL of toluene was injected into the reactor. The homogeneous supercritical carbon dioxide and FA precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 30 MPa while stirring (750 rpm). The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0101] The PbBr2 precursor from step (1) was pumped into 10 mL at a rate of 150 mL / min using a plunger pump. The reaction was carried out under vigorous stirring for 100 seconds, and the redshift evolution of the UV-vis absorption peak was monitored in real time. The increasing intensity trend of the PL emission spectrum was also monitored simultaneously. After stopping stirring for 5 seconds, the real-time particle size distribution was obtained by rapid DLS analysis.

[0102] After the crystals have grown uniformly through nucleation, the pressure relief valve is opened to rapidly release pressure for 30 seconds. Spectral changes during the pressure relief process are monitored to ensure product stability. The collection vessel is then opened to obtain FAPbBr3 perovskite quantum dots.

[0103] Example 8

[0104] (1) Preparation of PbBr2 precursor:

[0105] At 75°C, 4 mmol of lead bromide was mixed with 180 mL of 2-methoxyethanol, and 8 mmol of dodecylbenzenesulfonic acid was added. The mixture was stirred vigorously until PbBr2 was completely dissolved, and then cooled to room temperature.

[0106] (2) Preparation of MA precursors:

[0107] At 65°C, 4 mmol of methylamine salt was mixed with 150 mL of GBL, and 12 mmol of oleic acid was added. The mixture was stirred vigorously for 35 minutes until the methylamine salt was completely dissolved, and then cooled to room temperature. 15 mL of the solution was accurately measured using a syringe and injected into the premixing vessel of the apparatus. Supercritical carbon dioxide was introduced to 18 MPa, and the mixture was stirred at 600 rpm for 20 minutes until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure the solution was clear and transparent.

[0108] (3) Preparation and process detection of MAPbBr3 quantum dots:

[0109] At 85°C, 40 mL of chlorobenzene was injected into the reactor. The homogeneous supercritical carbon dioxide and MA precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 28 MPa while stirring (800 rpm). The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0110] The PbBr2 precursor from step (1) was pumped into 15 mL at a rate of 130 mL / min using a plunger pump. The reaction was carried out under vigorous stirring for 80 seconds, and the redshift evolution of the UV-vis absorption peak was monitored in real time. The increasing intensity trend of the PL emission spectrum was also monitored simultaneously. After stirring was stopped for 5 seconds, the real-time particle size distribution was obtained by rapid DLS analysis.

[0111] After the crystals have grown uniformly through nucleation, the pressure relief valve is opened to rapidly release pressure for 25 seconds. Spectral changes during the pressure relief process are monitored to ensure product stability. The collection vessel is then opened to obtain MAPbBr3 perovskite quantum dots.

[0112] Example 9

[0113] (1) Preparation of PbI2 precursor:

[0114] At 70°C, 6 mmol of lead iodide was mixed with 160 mL of acetonitrile, 12 mmol of oleylamine was added, and the mixture was stirred vigorously for 50 minutes until PbI2 was completely dissolved. The mixture was then cooled to room temperature.

[0115] (2) Preparation of FA precursors:

[0116] At 55°C, 6 mmol of formamidinium salt was mixed with 120 mL of NMP, and 15 mmol of tri-n-octylphosphine oxide was added. The mixture was stirred vigorously for 25 minutes until the formamidinium salt was completely dissolved, and then cooled to room temperature. 25 mL of the solution was accurately measured using a syringe and injected into the premixing vessel of the apparatus. Supercritical carbon dioxide was introduced to 22 MPa, and the mixture was stirred at 650 rpm for 25 minutes until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure the solution was clear and transparent.

[0117] (3) Preparation and process detection of FAPbI3 quantum dots:

[0118] At 75°C, 45 mL of chlorobenzene was injected into the reactor. The supercritical carbon dioxide and FA precursor from step (2) were homogeneously introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 24 MPa while stirring (700 rpm). The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0119] The PbI2 precursor from step (1) was pumped into 18 mL at a rate of 140 mL / min using a plunger pump. The reaction was carried out under vigorous stirring for 90 seconds, and the redshift evolution of the UV-vis absorption peak was monitored in real time. The increasing intensity trend of the PL emission spectrum was also monitored simultaneously. Stirring was stopped for 5 seconds, and the real-time particle size distribution was obtained by rapid DLS analysis.

[0120] After the crystals have grown uniformly through nucleation, the pressure relief valve is opened to rapidly release pressure for 15 seconds. Spectral changes during the pressure relief process are monitored to ensure product stability. The collection vessel is then opened to obtain FAPbI3 perovskite quantum dots.

[0121] Example 10

[0122] (1) Preparation of PbBr2 / PbCl2 mixed precursor:

[0123] At 65°C, 3.75 mmol lead bromide and 1.25 mmol lead chloride were mixed with 150 mL DMF, 10 mmol tri-n-octylphosphine was added, and the mixture was stirred vigorously for 45 minutes until the lead salt was completely dissolved. The mixture was then cooled to room temperature.

[0124] (2) Preparation of CsBr / CsCl mixed precursor:

[0125] At 60°C, 3.75 mmol of cesium bromide and 1.25 mmol of cesium chloride were mixed with 150 mL of DMSO, and 15 mmol of oleic acid was added. The mixture was stirred vigorously for 35 minutes until the cesium salts were completely dissolved, and then cooled to room temperature. 20 mL of the solution was accurately measured using a syringe and injected into the premixing vessel of the apparatus. Supercritical carbon dioxide was introduced to 18 MPa, and the mixture was stirred at 600 rpm for 20 minutes until homogeneous. The dissolution process was monitored in real time using a visual observation system to ensure the solution was clear and transparent.

[0126] (3) Preparation and process detection of CsPb(Br / Cl)3 quantum dots:

[0127] At 80°C, 40 mL of toluene was injected into the reactor. The homogeneous supercritical carbon dioxide and mixed cesium salt precursor from step (2) were introduced into the reactor from the premixing vessel, and the pressure was slowly increased to 25 MPa while stirring (750 rpm). The initial absorption baseline of the system was monitored by UV-vis spectroscopy.

[0128] The mixed lead salt precursor from step (1) was pumped into 15 mL at a rate of 130 mL / min using a plunger pump. The mixture was reacted for 70 seconds with vigorous stirring. The redshift evolution of the UV-vis absorption peak was monitored in real time, and the intensification trend of the PL emission spectrum was monitored simultaneously. Stirring was stopped for 5 seconds, and the real-time particle size distribution was obtained by rapid DLS analysis.

[0129] After the crystals have grown uniformly through nucleation, the pressure relief valve is opened to rapidly release pressure for 20 seconds. Spectral changes during the pressure relief process are monitored to ensure product stability. The collection vessel is then opened to obtain CsPb(Br / Cl)3 mixed halide perovskite quantum dots.

[0130] To further illustrate the beneficial effects of the embodiments of this application, the following comparative examples are constructed.

[0131] Comparative Example 1

[0132] This comparative example provides a method for preparing perovskite quantum dots. The difference from Example 1 is that it uses the traditional hot-injection method as the synthesis method. The specific preparation process is as follows:

[0133] (1) Preparation of Cs precursor:

[0134] 1.8 mmol PbBr2, 10 mL oleylamine, and 12 mL oleic acid were dissolved in 45 mL of the high-boiling-point solvent ODE. The solution was treated under vacuum at 120 °C for 25 minutes to remove moisture and oxygen. Subsequently, the temperature was raised to 160 °C under nitrogen protection until the solution became clear and colorless.

[0135] (2) Preparation of PbBr2 precursor:

[0136] Mix 20 mmol Cs₂CO₃ and 15 mL oleic acid in 300 mL ODE. Stir and dry under vacuum at 120 °C for 1 hour, then heat to 160 °C under nitrogen protection until completely dissolved to form a Cs-oleate solution. Preheat to 90 °C before injection.

[0137] (3) Preparation of CsPbBr3 quantum dots:

[0138] The reaction system was maintained at 170°C, and 4 mL of preheated cesium precursor solution was rapidly injected. After reacting for 3 seconds, the mixture was transferred to an ice bath for rapid cooling. The mixture was centrifuged, the supernatant was discarded, and the resulting precipitate was redispersed in hexane.

[0139] Comparative Example 2

[0140] This comparative example provides a method for preparing perovskite quantum dots. The difference from Example 1 is that it uses the traditional ligand-assisted precipitation method as the synthesis method. The specific preparation process is as follows:

[0141] (1) Preparation of CsPbBr3 precursor:

[0142] At room temperature, 3.5 mmol CsBr and 3.5 mmol PbBr2 were dissolved in 80 mL LDM. 8 mL oleic acid and 4 mL oleylamine were added as ligands, and the mixture was stirred at room temperature for 30 minutes until the solution was clear and transparent.

[0143] (2) Preparation of CsPbBr3 quantum dots:

[0144] Take 10 mL of the precursor solution obtained in step (1) and inject it rapidly into 150 mL of toluene under vigorous stirring to obtain perovskite quantum dots.

[0145] 1. Perovskite quantum dot photoluminescence quantum yield (PLQY) detection

[0146] The photoluminescence quantum yield of the perovskite quantum dots prepared in Examples 1-10 and Comparative Examples 1-2 was tested, and the results are shown in Table 1.

[0147] Table 1

[0148]

[0149]

[0150] As shown in Table 1, Quantum Dots were successfully prepared in Examples 1-10 and Comparative Examples 1-2 of this application by changing different ligands and solvents. Compared with the traditional LARP method (Comparative Example 2), the PLQY of the examples in this application is significantly improved. Among them, the PLQY of the all-inorganic CsPbBr3 system (Examples 1-5) can reach 88-95%, the PLQY of the mixed halogen CsPb(Br / Cl)3 system (Example 10) reaches 90%, and the PLQYs of the organic-inorganic hybrid systems FAPbBr3 and MAPbBr3 (Examples 7-8) are 82% and 78%, respectively. Compared with the hot injection method (Comparative Example 1, PLQY of 85%), the examples in this application, through supercritical CO2-assisted synthesis under mild conditions, still obtained higher photoluminescence quantum yields, with the highest PLQY of Example 4 reaching 95%.

[0151] 2. Perovskite quantum dot transmission electron microscopy (TEM) and full width at half maximum (FWHM) measurement

[0152] Transmission electron microscopy (TEM) was used to calculate the particle size distribution and measure the full width at half maximum (FWHM) of the perovskite quantum dots prepared in Examples 1-10 and Comparative Examples 1-2. The results are shown in the figure. Figure 2 (Example 1) Figure 3 (Comparative Example 2) and Table 2.

[0153] Table 2

[0154]

[0155]

[0156] As shown in Table 2, the quantum dots obtained in Examples 1-10 and Comparative Examples 1-2 of this application exhibit significant differences in size and luminescence properties due to variations in ligands and solvents. Compared to the traditional LARP method, the quantum dots prepared in the examples of this application have a more uniform size distribution and a narrower full width at half maximum (FWHM). In particular, the CsPbBr3 system (Examples 1-5) has a particle size controlled within the range of 8.5-9.2 nm, with a FWHM of only 14-17 nm. In contrast, the quantum dots prepared in Comparative Example 2 have a larger particle size (13.21 nm) and a wider FWHM (32 nm). Compared to the hot-injection method (Comparative Example 1), the perovskite quantum dots synthesized in the examples of this application show significant improvements in both size uniformity and luminescence purity. Furthermore, the preparation process is gentler, requiring no rapid cooling from high temperatures, demonstrating significant process advantages and industrialization potential.

[0157] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing perovskite quantum dots with supercritical carbon dioxide assistance, characterized in that, Includes the following steps: Step 1: Dissolve lead halide and ligand 1 in polar solvent 1 to form precursor solution A; Step 2: Dissolve cesium halide and ligand 2 in polar solvent 2 to form precursor solution B; Step 3: Premix solution A in supercritical carbon dioxide until homogeneous; Step 4: Add antisolvent 3 to the reactor and introduce the homogeneous mixture of solution A and supercritical carbon dioxide into the reactor for stirring; Step 5: Quickly add solution B to the reactor for reaction, and after uniform nucleation and growth of crystals, quickly depressurize; Step 6: Collect the product containing perovskite quantum dots and purify it.

2. The method for preparing perovskite quantum dots according to claim 1, characterized in that, The specific process parameters are as follows: the reaction temperature in steps one and two is 30-60℃; the supercritical carbon dioxide conditions in step three are: temperature 30-80℃, pressure 10-25MPa; the reaction system conditions in steps four and five are: temperature 50-90℃, pressure 15-30MPa; the depressurization time is controlled within 3-30 seconds, and the depressurization rate is 0.5-2MPa / s.

3. The method for preparing perovskite quantum dots according to claim 1, characterized in that, In step one, the polar solvent 1 is one of N,N-dimethylformamide (DMF), 2-methoxyethanol (2ME), acetonitrile (ACN), and 2-pyrrolidone (2P).

4. The method for preparing perovskite quantum dots according to claim 1, characterized in that, In step one, the ligand 1 is one of oleic acid (OA), oleylamine (OAm), sulfobetaine, dodecylbenzenesulfonic acid (DBSA), tri-n-octylphosphine (TOP), and tri-n-octylphosphine oxide (TOPO).

5. The method for preparing perovskite quantum dots according to claim 1, characterized in that, In step two, the polar solvent 2 is one of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), γ-valerolactone (GVL), and N,N-dimethylformamide (DMF).

6. The method for preparing perovskite quantum dots according to claim 1, characterized in that, In step two, the ligand 2 is one of oleic acid (OA), oleylamine (OAm), bis(2,4,4-trimethylpentyl)phosphonic acid (DOPA), lecithin, and triphenylphosphine oxide.

7. The method for preparing perovskite quantum dots according to claim 1, characterized in that, In step four, the antisolvent 3 is one of toluene, n-hexane, chlorobenzene, chloroform, and mesitylene.

8. The method for preparing perovskite quantum dots according to claim 1, characterized in that, The volume of solvent 1 added to the lead halide salt is one of 5 to 200 mL; the volume of solvent 2 added to the cesium halide salt is one of 5 to 200 mL.

Images