Preparation method of red light perovskite quantum dots

Abstract

The invention provides a preparation method of red light perovskite quantum dots, and belongs to the technical field of luminescent materials. The method specifically comprises the following steps: preparing a precursor solution A containing monovalent cesium cations; a precursor solution B containing a monovalent iodine source, a divalent lead source, acid and amine is prepared, and the molar ratio of iodine to lead in the precursor solution B is larger than 3: 1; injecting the preheated A into the B for reaction to form quantum dots; cooling a reaction product, and adding acyl bromide in a specific temperature interval for surface modification; and carrying out ice-water bath again, cleaning and centrifuging to obtain the quantum dots with adjustable luminescence peaks of 620-700nm. The addition amount of the acyl bromide is 1-30% of the volume of the amine in the reaction system. The acyl bromide is introduced in the cooling stage, accurate wavelength regulation and control are achieved, meanwhile, lattice integrity is kept, water oxygen and ultraviolet stability is improved, and the requirement for high-definition display of high-color-purity red light is met.

Description

Technical Field

[0001] This invention belongs to the field of light-emitting quantum dot preparation technology, and particularly relates to a method for preparing red perovskite quantum dots with a light emission band of 620-700nm, which is especially suitable for high color purity red light emission that is continuously tunable in the range of 620nm-700nm. Background Technology

[0002] Perovskite quantum dot luminescent materials are considered a candidate material for next-generation high-definition displays due to their wide color gamut, high luminous efficiency, and high color purity. However, the bulk CsPbI3 material has a band gap of approximately 1.75 eV, corresponding to an emission wavelength of approximately 710 nm, which falls within the deep red and even near-infrared emission region. The human eye has very low sensitivity to this spectral region, therefore perovskite luminescent devices based on this material are not suitable for high-definition displays and would struggle to meet the Rec.2020 requirements. As one of the three primary colors in displays, researchers define red light with an emission wavelength between 620-650 nm as "pure red light," and light within this wavelength range can meet the Rec.2020 requirements.

[0003] However, existing hot-injection methods only control the crystal nucleus size through temperature-time coupling parameters, resulting in batch-to-batch wavelength fluctuations of up to ±8nm, and emission peaks mostly occurring after 680nm, which is insufficient to meet the precision requirements of high-definition displays. Furthermore, CsPbI3 is prone to H2O / O2-induced phase transitions (cubic to orthorhombic) and ion migration, leading to luminescence quenching. While surface passivation can improve stability, conventional alkyl silicon halides and alkylphosphine ligands require prolonged reflow at 80-120℃, which easily triggers Ostwald ripening, causing lattice distortion and broadening of the full width at half maximum (FWHM). Currently, there are two strategies for preparing pure red perovskite quantum dots. One is the strong quantum confinement effect. Based on the quantum confinement effect, to further achieve a blue shift in the emission peak of quantum dots, their size can be further reduced to enhance the influence of the quantum confinement effect on the spectrum. However, small-sized quantum dots have large surface energies and are prone to further growth to form a non-luminescent phase. The other is mixed halide ion engineering. Since the photoluminescence (PL) spectrum of lead halide perovskites can be easily tuned in the visible light range through halide anion exchange reactions, mixed halide composition engineering is still the main strategy for realizing pure red perovskite quantum dot LEDs. However, due to the impure phase composition, phase separation easily occurs under external voltage and high temperature, resulting in extremely poor stability.

[0004] Therefore, there is an urgent need to develop a suitable, efficient and stable method for preparing pure red perovskite quantum dots to promote the application of perovskite quantum dots in the field of high-definition displays. Summary of the Invention

[0005] To address the issues of existing red-light perovskite quantum dots exhibiting a bias towards deep red light and the instability caused by commonly used halide perovskites to adjust the emission peak wavelength, this invention provides a method for preparing red-light perovskite quantum dots. First, an excess of iodine source is controlled in precursor solution B, i.e., I:Pb > 3:1. Then, during the cooling process (60-120℃), ≤30% of the volume of oleylamine acyl bromide is introduced, followed by further cooling. By varying the content and type of acyl bromide introduced, precise control of the emission wavelength of the red-light perovskite quantum dots can be achieved, meeting the requirement for high-purity red light emission.

[0006] To achieve the above objectives, this invention employs a method for preparing red-light perovskite quantum dots, the method specifically comprising the following steps:

[0007] First, a precursor solution A containing monovalent cesium cations and a precursor solution B containing monovalent iodine source, divalent lead source, acid and amine are prepared respectively, wherein the molar ratio of iodine to lead in the precursor solution B is greater than 3:1.

[0008] Next, at an injection reaction temperature of 150-190°C, the precursor solution A is injected into the precursor solution B to react and generate perovskite quantum dots.

[0009] The key is to cool the reaction system after the reaction is complete, and then add acyl bromide to the system to modify the surface when the temperature is cooled to 60-120℃.

[0010] Finally, after cooling and purification, red perovskite quantum dots with emission wavelengths between 620-700 nm were obtained.

[0011] The method employs a hot injection approach, with the mixing reaction temperature of precursor solution A and precursor solution B at 150-190℃. In precursor solution B, the molar ratio of iodine to lead is greater than 3:1. During the cooling process of the reaction, the addition of acyl bromide can alter the surface properties of the quantum dots, further restricting their size. Through quantum confinement effects and surface state modification, the emission spectrum undergoes a blue shift, achieving a transition from deep red light (>680nm) to pure red light (620-650nm). Multi-stage cooling can improve the crystallinity of the quantum dots.

[0012] Furthermore, the Cs element in the precursor solution A is derived from one or more of cesium oleate (Cs-OA), cesium carbonate (Cs2CO3), and cesium acetate (CsCH3COO).

[0013] Furthermore, the iodine element in the precursor solution B is derived from one or more of zinc iodide (ZnI2), hydrogen iodide (HI), lead iodide (PbI2), and potassium iodide (KI).

[0014] Furthermore, the lead element in the precursor solution B originates from lead acetate (Pb(AC)2), lead iodide (PbI2), and lead oleate (Pb).

[0015] One or more of (OA)2 and lead oxide (PbO).

[0016] Furthermore, organic amines and organic acids need to be added to the precursor solution B, with the volume ratio of acid to amine being 1:1-1.5.

[0017] Furthermore, the structure of the acyl bromide is as follows:

[0018] Where R is an organic group, the timing of the addition of the acyl bromide is very important and must be...

[0019] To add the acyl bromide during the cooling process after the hot injection reaction, rapid cooling methods such as ice-water baths or metal heat sinks can be used to maintain the solution temperature between 60-120°C before adding the acyl bromide. The role of the acyl bromide is to first react with residual organic acids and amines on the quantum dot surface and in the solution, altering the ligand equilibrium state on the original quantum dot surface. This causes some surface ligands to detach and further react with the acyl bromide, attaching functional groups and bromine atoms to the quantum dot surface. Because the introduced bromine atoms react during the quantum dot formation process, the structural instability caused by the introduction of new atoms is greatly reduced, maintaining structural stability while achieving the desired luminescent performance.

[0020] Furthermore, the amount of acyl bromide added should be less than 30% of the volume of oleic acid and oleylamine added, preferably within the range of 3%-20% of the oleylamine volume. Excessive addition will severely erode the surface ligands of the quantum dots. Since surface ligands play a major role in maintaining the stability of quantum dots, this will lead to a significant decrease in quantum dot stability. In addition, acyl bromides are volatile and react with water in the air. This reaction requires segmented cooling during the cooling process; rapid cooling first ensures the basic formation of quantum dots without excessive stability. If acyl bromide is added only after complete cooling, the reaction of the quantum dots will not achieve the expected results.

[0021] In addition, when adding acyl bromide, it can be dissolved in a preferred solvent such as toluene to reduce volatilization during the addition process or reduce the direct concentration of acyl bromide in the reaction zone.

[0022] Furthermore, the pure red perovskite quantum dots require purification for further use. The purification process primarily involves adding an antisolvent to the quantum dot stock solution. Common antisolvents include methyl acetate, ethyl acetate, isopropanol, and acetone. The solution is then centrifuged in centrifuge tubes. The supernatant is removed, and the precipitate is retained. The precipitate must be dispersed in benzene or alkane solvents for storage. Additionally, some experiments require repeated dissolution and purification steps.

[0023] The pure red light quantum dot method proposed in this application can be used to adjust the wavelength of red perovskite quantum dots in the range of 620-700nm.

[0024] This invention modifies the surface of quantum dots by adding acyl bromide during the cooling stage (60-120℃) after the hot-injection reaction. This further confines the quantum dot size and enhances the quantum confinement effect through surface ligand exchange and etching. Simultaneously, surface state passivation and other synergistic effects shift the quantum dot emission spectrum from the deep red region to the pure red region (620-650nm), solving the problem of unsuitable emission wavelengths for conventional CsPbI3 quantum dots. Furthermore, the quantum dots prepared by this method exhibit a photoluminescence quantum yield of over 80%, excellent optical properties, and are suitable for Rec.2020 standard pure red perovskite luminescent materials. Attached Figure Description

[0025] Figure 1 The normalized fluorescence emission spectra of CsPbI3 quantum dots obtained in Examples 1-5 and Comparative Example 1 of this invention are shown below.

[0026] Table 1 compares the peak wavelength and fluorescence quantum yield before and after treatment in Examples 1-5 and Comparative Example 1 of the present invention.

[0027] Figure 2 The light emission attenuation of quantum dots under ultraviolet light in Example 1 (with surface modification) and Comparative Example 1 (without surface modification) of the present invention.

[0028] Figure 3 Comparison of TEM images of Example 1 and Comparative Example 1 of the present invention

[0029] Figure 4 The XRD patterns of Example 1 and Comparative Example 1 are shown for comparison, where T-CsPbI3 represents the sample treated according to the present invention (Example 1), and P-CsPbI3 represents the untreated original (Pristine) sample (Comparative Example 1). Detailed implementation method:

[0030] This invention provides a method for preparing red-light perovskite quantum dots. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the raw materials used in this invention are all purchased directly from the market and require no special processing; they can be prepared directly by those skilled in the art using familiar methods.

[0031] Example 1

[0032] This embodiment provides a method for preparing red-light perovskite quantum dots, mainly including the following steps:

[0033] S1: Take 100 mg of cesium carbonate (Cs2CO3), add 10 mL of ODE and 0.7 mL of oleic acid to a three-necked flask, heat and stir at 120 °C until the solution is clear, and continue stirring for half an hour to obtain precursor solution A;

[0034] S2: Take 220 mg lead iodide, 450 mg zinc iodide, and 12.6 mL octadecene and place them in a three-necked flask. Heat and stir to 120 °C for 1 hour. Then add 3 mL oleylamine and 3 mL oleic acid, continue the reaction and heat to 170 °C to obtain precursor solution B.

[0035] S3: Injection reaction: Inject 2 mL of preheated precursor solution A into precursor solution B at 170°C, maintain the reaction at 170°C for 10 seconds to obtain quantum dot stock solution;

[0036] S4: Cooling and surface modification: Quickly place the reaction flask in an ice-water bath to cool. When the solution temperature drops to about 100°C, add 300 μL of benzoyl bromide and continue stirring for 1 minute.

[0037] S5: After cooling the quantum dots obtained in S4, take 4 mL of the quantum dots and place them in a 10 mL centrifuge tube. Add 6 mL of methyl acetate and centrifuge at 8000 r / min for 5 min. Discard the supernatant and disperse the precipitate with 3 mL of toluene. Continue to centrifuge at 5000 r / min for 2 min. The resulting supernatant is the final perovskite quantum dots.

[0038] The purified quantum dots dispersed in toluene were subjected to optical performance testing. The fluorescence emission peak was measured at 631 nm, and the photoluminescence quantum yield (PLQY) was 93%. The normalized fluorescence emission spectrum is shown below. Figure 1 The curve corresponds to 300 μL.

[0039] Example 2

[0040] This embodiment provides a method for preparing red light perovskite quantum dots. The preparation process is the same as that in Example 1, except that the amount of benzoyl bromide used in step S4 is adjusted to 100 μL. All other steps are the same as in Example 1.

[0041] The purified quantum dots dispersed in toluene were subjected to optical performance testing. The fluorescence emission peak was measured at 645 nm, and the photoluminescence quantum yield (PLQY) was 88%. The normalized fluorescence emission spectrum is shown below. Figure 1 The curve corresponds to 100 μL.

[0042] Example 3

[0043] This embodiment provides a method for preparing red light perovskite quantum dots. The preparation process is the same as that in Example 1, except that the amount of benzoyl bromide used in step S4 is adjusted to 200 μL. All other steps are the same as in Example 1.

[0044] The purified quantum dots dispersed in toluene were subjected to optical performance testing. The fluorescence emission peak was measured at 635 nm, and the photoluminescence quantum yield (PLQY) was 81%. The normalized fluorescence emission spectrum is shown below. Figure 1 The curve corresponds to 200 μL.

[0045] Example 4

[0046] This embodiment provides a method for preparing red light perovskite quantum dots. The preparation process is different from that in Example 1, except that the amount of benzoyl bromide used in step S2 is adjusted to 400 μL, while the other steps are the same as in Example 1.

[0047] The purified quantum dots dispersed in toluene were subjected to optical performance testing. The fluorescence emission peak was measured at 627 nm, and the photoluminescence quantum yield (PLQY) was 68%. The normalized fluorescence emission spectrum is shown below. Figure 1 The curve corresponds to 400 μL.

[0048] Example 5

[0049] This embodiment provides a method for preparing red light perovskite quantum dots. The preparation process is the same as that in Example 1, except that the amount of benzoyl bromide used in step S4 is adjusted to 500 μL. All other steps are the same as in Example 1.

[0050] The purified quantum dots dispersed in toluene were subjected to optical performance testing. The fluorescence emission peak was measured at 617 nm, and the photoluminescence quantum yield (PLQY) was 30%. The normalized fluorescence emission spectrum is shown below. Figure 1 The midline corresponds to 500 μL.

[0051] Comparative Example 1

[0052] This comparative example provides a method for preparing red-light perovskite quantum dots, the specific steps of which are as follows:

[0053] S1: Take 100 mg of cesium carbonate (Cs2CO3), add 10 mL of ODE and 0.7 mL of oleic acid to a three-necked flask, heat and stir at 120 °C until the solution is clear, and continue stirring for half an hour to obtain precursor solution A;

[0054] S2: Take 220 mg lead iodide, 450 mg zinc iodide, and 12.6 mL octadecene and place them in a three-necked flask. Heat and stir to 120 °C for 1 hour. Then add 3 mL oleylamine and 3 mL oleic acid, continue the reaction and heat to 170 °C to obtain precursor solution B.

[0055] S3: Take 2 mL of precursor solution A and inject it into precursor solution B to obtain quantum dot stock solution;

[0056] The quantum dot stock solution obtained in S3 was placed in an ice-water bath and cooled until it solidified. After it naturally warmed to room temperature, 4 mL of the stock solution was placed in a 10 mL centrifuge tube, and 6 mL of methyl acetate was added. The mixture was centrifuged at 8000 r / min for 5 min, and the supernatant was discarded. The precipitate was dispersed with 3 mL of toluene and centrifuged at 5000 r / min for 2 min. The resulting supernatant was the final perovskite quantum dots that had not been treated with acyl bromide.

[0057] The quantum dots, purified and dispersed in toluene, were subjected to optical performance testing. The fluorescence emission peak was measured to be at 661 nm, and the photoluminescence quantum yield (PLQY) was 71.67%.

[0058] The following characterization tests were performed on Examples 1-5 and Comparative Example 1.

[0059] Figure 1 The normalized fluorescence emission spectra of the CsPbI3 quantum dots prepared in Examples 1-5 and Comparative Example 1 show that the emission peak undergoes a significant blue shift with different amounts of benzoyl bromide added.

[0060] Table 1 compares the emission peak and fluorescence quantum yield of Examples 1-5 and Comparative Example 1 with the introduction of benzoyl bromide. It can be seen that the emission peak can be precisely adjusted between 660nm and 617nm depending on the amount introduced. The CsPbI3 quantum dots synthesized in Example 1 better meet the emission requirements for red light in high-definition displays, and also have a higher fluorescence quantum yield. However, we also found that when too much acyl bromide is added, the fluorescence quantum yield of the sample decreases, even falling below that of the comparative example, indicating that the amount of acyl bromide added should be reasonably controlled.

[0061] Table 1

[0062]

[0063]

[0064] Figure 2To investigate the luminescence decay of quantum dots in Example 1 and Comparative Example 1 under ultraviolet light, Example 1 and Comparative Example 1 were irradiated under ultraviolet lamps with fixed power and wavelength. The irradiation time was extended, and it was found that the luminescence intensity of both decreased significantly with the increase of irradiation time. However, the decrease in Example 1 was less than that in the Comparative Example. In the same time period, the luminescence decay intensity of Example 1 was about 20% slower than that of the Comparative Example 1.

[0065] Figure 3 The TEM and particle size distribution comparison of Example 1 and Comparative Example 1 shows that the average size of the quantum dots is smaller after the addition of benzoyl bromide, decreasing from 7.87 nm in the comparative example to 6.06 nm. This indicates an enhanced quantum confinement effect, and the size uniformity is also increased.

[0066] Figure 4 A comparison of the XRD patterns of Example 1 (T-CsPbI3) and Comparative Example 1 (P-CsPbI3) shows that PDF#97-016-1481 is the cubic phase CsPbI3, which is a perovskite quantum dot capable of luminescence, while PDF#97-016-1480 is the orthorhombic phase, which is a non-luminescent phase. During the XRD test, Comparative Example 1 showed two phases, and the disorder increased as the test progressed, indicating that it is not resistant to the impact of high-energy particles and is more unstable.

[0067] This invention uses specific examples to illustrate the principles and implementation methods of the invention. The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the invention, including the best mode, so that any person skilled in the art can understand and practice the invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, several improvements and modifications can be made to the invention without departing from the principles of the invention, and these improvements and modifications also fall within the protection scope of the claims of the invention. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the wording of the claims, or if they include equivalent structural elements that are not substantially different from the wording of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing red-light perovskite quantum dots, characterized in that, The method includes the following steps: S1: Prepare a precursor solution A containing monovalent cesium cations; S2: Prepare a precursor solution B containing a monovalent iodine source, a divalent lead source, an acid, and an amine, wherein the molar ratio of iodine to lead in the precursor solution B is greater than 3:

1. S3: At an injection reaction temperature of 150°C to 190°C, the precursor liquid A is injected into the precursor liquid B to carry out the reaction; S4: Cool the reaction product of S3, and when it is cooled to 60°C to 120°C, add an acyl bromide to modify the surface; S5: Obtain the pure red perovskite quantum dots.

2. The method for preparing red-light perovskite quantum dots according to claim 1, characterized in that, The cesium-containing precursor solution A includes at least one of cesium oleate (Cs-OA), cesium carbonate (Cs2CO3), and cesium acetate (CsCH3COO).

3. The method for preparing red-light perovskite quantum dots according to claim 1, characterized in that, The monovalent iodine source is at least one of zinc iodide (ZnI2), lead iodide (PbI2), potassium iodide (KI), and hydrogen iodide (HI).

4. The method for preparing red-light perovskite quantum dots according to claim 1, characterized in that, The lead source in the precursor solution B is at least one of lead oxide (PbO), lead iodide (PbI2), and lead oleate (Pb(OA)2).

5. The method for preparing red-light perovskite quantum dots according to claim 1, characterized in that, The ratio of acid to amine in the precursor solution B is 1:1 to 1:1.

5.

6. The method for preparing red-light perovskite quantum dots according to claim 1, characterized in that... The acyl bromide refers to an organic compound with the following structure: Where R is an organic group.

7. The method for preparing red-light perovskite quantum dots according to claim 1, characterized in that, The volume content of the acyl bromide is 1%-30% of the volume of the added amine.

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