A room-temperature preparation method for ultra-small perovskite quantum dots

Abstract

The present invention discloses a room-temperature preparation method for ultra-small perovskite quantum dots, belonging to the technical field of ultra-small perovskite quantum dots. The method comprises the following steps: S1, placing CsBr, PbBr2, and aromatic acid powders in a container, adding a polar solvent and stirring and mixing to obtain a transparent precursor solution; S2, adding an amine solution to the precursor solution to obtain a mixed solution, which is then added to an antisolvent to obtain a crude quantum dot solution; S3, adding a metal salt solution to the crude quantum dot solution, stirring and centrifuging, adding an organic solvent to the supernatant obtained by centrifugation, and centrifuging again to obtain a quantum dot precipitate; S4, dissolving the quantum dot precipitate in a mixed solution of toluene and DMF, and centrifuging again to obtain a clear and transparent quantum dot solution. The present invention uses FeBr3 to coordinate with the aromatic acid to reconstruct the quantum dot interface, so that the quantum dots obtain a PLQY close to 100% and exhibit long-term stability.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-small-sized perovskite quantum dots, and in particular to a room-temperature preparation method of ultra-small-sized perovskite quantum dots. Background Art

[0002] Purely blue-emitting metal halide perovskite light-emitting diodes (PeLEDs) suffer from severe brightness and efficiency deficiencies, severely restricting their application in displays. Blue-emitting perovskites are typically prepared using Br / Cl compositional manipulation and quantum confinement effects. Br / Cl compositional manipulation presents stability issues due to phase separation, while all-bromine-based two-dimensional perovskites and quantum dots (QDs) based on the QD effect demonstrate greater potential. The exciton Bohr radius of bulk CsPbBr3 is 3.5 nm, enabling quantum dots (QDs) smaller than 7 nm to achieve blue emission through strong QD effects. Ultra-small CsPbBr3 QDs with a particle size of approximately 4 nm exhibit pure blue emission (<470 nm).

[0003] Ultra-small perovskite quantum dots (QDs) face challenges such as difficulty in synthesis, poor long-term stability, and surface defects. Existing techniques employ ligand-assisted reprecipitation (LARP) to synthesize QDs at room temperature, but only yield CsPbBr3 QDs ranging from ~8nm to ~15nm in size. These QDs also exhibit poor crystalline quality, resulting in broad PL spectra and extremely low PLQY. Furthermore, some techniques employ the addition of liquid nitrogen to a toluene antisolvent, utilizing extremely low reaction temperatures to inhibit the ultrafast nucleation and growth of the perovskite. This approach, using LARP, yields QDs (3nm) with a PLQY as high as 98%. However, this method requires low-temperature control, is not practical, and the high cost of liquid nitrogen makes it unsuitable for large-scale production. Patent publication number CN112125332A discloses a recrystallized all-bromine perovskite blue QD and its preparation method, but its controllability is limited.

[0004] Based on this, a room-temperature preparation method for ultra-small perovskite quantum dots is proposed, which makes the PLQY of quantum dots close to 100%, and the PL spectrum of the purified solution does not change under long-term storage conditions, showing very good stability. Summary of the Invention

[0005] The purpose of the present invention is to provide a room temperature preparation method for ultra-small perovskite quantum dots to solve the problems in the background technology.

[0006] To achieve the above object, the present invention provides a room temperature method for preparing ultra-small perovskite quantum dots, comprising the following steps:

[0007] S1. Place CsBr, PbBr2 and aromatic acid powder in a container, add a polar solvent and stir to mix until all are dissolved to obtain a transparent precursor solution;

[0008] S2. adding an amine solution to the precursor solution to obtain a mixed solution, and adding the mixed solution to an antisolvent to obtain a crude quantum dot solution;

[0009] S3, adding a metal salt solution to the crude quantum dot solution, stirring and then centrifuging, adding an organic solvent to the supernatant obtained by centrifugation, and centrifuging again to obtain a quantum dot precipitate;

[0010] S4. Dissolve the quantum dot precipitate in a mixed solution of toluene and DMF, and centrifuge again to obtain a clear and transparent quantum dot solution.

[0011] Preferably, in S1, the ratio of CsBr to PbBr2 is 0-1; the concentration of aromatic acid is 0.01-2M, the stirring time is 25-40 min, and the ratio of aromatic acid to PbBr2 is 0.6-1.4.

[0012] Preferably, in S1, the aromatic acid is 2-pyridinecarboxylic acid, and the polar solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0013] Preferably, in S2, the volume ratio of the precursor solution to the amine solution is 1-200, and the volume ratio of the mixed solution to the anti-solvent is 1-100.

[0014] Preferably, in S2, the amine solution is one of oleylamine, n-propylamine, n-butylamine, n-pentylamine, n-hexylamine, n-octylamine, phenylethylamine, and phenylbutylamine; and the antisolvent is one of toluene, chlorobenzene, n-hexane, and cyclohexane.

[0015] Preferably, in S3, the volume ratio of the crude quantum dot solution to the metal salt solution is 1-200, the concentration of the metal salt solution is 0.01-2 M, and the stirring time is 1-20 min; the volume ratio of the supernatant to the organic solvent is 0.2-5.

[0016] Preferably, in S3, the metal salt solution is one of sodium bromide, potassium bromide, rubidium bromide, tin bromide, ferric bromide, and indium bromide, and the organic solvent is one of ethyl acetate, methyl acetate, methyl formate, ethyl formate, and acetone.

[0017] Preferably, in S4, the volume ratio of toluene to DMF is 100:2.5.

[0018] Preferably, in S3 and S4, the centrifugal speed is 5000-14000 rpm / min, and the centrifugal time is 1-8 min.

[0019] Therefore, the room temperature preparation method of ultra-small perovskite quantum dots of the present invention has the following beneficial effects:

[0020] (1) The method of the present invention is based on aromatic acids and adopts the LARP method to obtain ultra-small quantum dots that emit blue light at room temperature. Aromatic acids, especially pyridinic acid, have the function of slow-releasing ions and can well control the crystallization rate, thereby realizing the preparation of ultra-small perovskite quantum dots. In addition, pyridinic acid has the function of in-situ passivation of defects, which can well improve the luminescence efficiency of quantum dots.

[0021] (2) The present invention performs ion interface reconstruction in post-processing and uses a metal salt solution for post-processing, which can well maintain the stability of ultra-small perovskite quantum dots and achieve long-term wavelength stability and efficiency without attenuation.

[0022] (3) After the quantum dots prepared in the present invention are treated with metal salts, the surface components of the ultra-small quantum dots are reconstructed, and the vacancy defects on the surface of the quantum dots are effectively passivated, thereby obtaining a PLQY close to 100%. The treated quantum dots have the same TEM morphology and PL spectrum as the initial quantum dots, and their PLQY is still higher than 95% after storage for 7 days. After 55 days, the PL spectrum of the quantum dots is consistent with the initial state, showing long-term stability.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 PL spectrum of Example 1 of the present invention;

[0025] Figure 2 PL spectrum of Comparative Example 1 of the present invention;

[0026] Figure 3 Graphs showing changes in PLQY and PL spectrum over storage time of Example 1 of the present invention, wherein (a) is a PLQY graph and (b) is a PL spectrum graph;

[0027] Figure 4 PL spectrum of Comparative Example 1 of the present invention changes with storage time;

[0028] Figure 5 TEM images of the quantum dots in Example 1 of the present invention in the initial state and after 10 days of storage, wherein (a) is the initial state and (b) is the state after 10 days;

[0029] Figure 6 This is a graph showing the PL spectrum change within 55 days of Example 1 of the present invention;

[0030] Figure 7TEM image of Example 1 of the present invention, and the inset is HRTEM image;

[0031] Figure 8 TEM image of Comparative Example 2 of the present invention;

[0032] Figure 9 PL spectra comparison diagram of Example 1, Comparative Example 3, and Comparative Example 4 of the present invention;

[0033] Figure 10 Schematic diagram of the process of FeBr3 cooperating with 2PA to reconstruct the quantum dot surface in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0036] Example 1

[0037] The steps for preparing CsPbBr3 quantum dots are as follows:

[0038] S1. Place 0.1 mmol CsBr, 0.5 mmol PbBr2, and 0.5 mmol 2PA (2-picolinic acid) in a container, add 10 mL DMF, stir and mix, and obtain a transparent precursor solution after all the substances are dissolved.

[0039] S2. Add 50 μL of oleylamine solution to 1 mL of the precursor solution to obtain a mixed solution; add 50 μL of the mixed solution to 2 mL of toluene and stir for 10 minutes to obtain a crude quantum dot solution;

[0040] S3. Dissolve 0.2 mmol FeBr3 in 1 mL DMF to obtain a FeBr3 solution. Inject 10 μL of the FeBr3 solution into the crude quantum dot solution under stirring. Continue stirring for 2 minutes, then centrifuge at 5000 rpm for 2 minutes to remove unreacted FeBr3 insoluble matter. Then, add EA solution at a volume ratio of 2:1 to the supernatant obtained by centrifugation, centrifuge at 10000 rpm for 5 minutes, and remove the supernatant to obtain a precipitate.

[0041] S4. The obtained quantum dot precipitate was dissolved in a mixed solution of toluene and DMF with a volume ratio of 100:2.5. After dissolution, the solution was centrifuged again at 10,000 rpm for 1 minute to remove the quantum dots that could not be completely dissolved, thereby obtaining a clear and transparent quantum dot solution.

[0042] Comparative Example 1

[0043] The steps for preparing CsPbBr3 quantum dots are as follows:

[0044] S1. Place 0.1 mmol CsBr, 0.5 mmol PbBr2, and 0.5 mmol 2PA (2-picolinic acid) in a container, add 10 mL DMF, stir and mix, and obtain a transparent precursor solution after all the substances are dissolved.

[0045] S2. Add 50 μL of oleylamine solution to 1 mL of the precursor solution to obtain a mixed solution; add 50 μL of the mixed solution to 2 mL of toluene and stir for 10 minutes to obtain a quantum dot solution;

[0046] S3. Add ethyl acetate solution with a volume ratio of 2:1 to the crude quantum dot solution, centrifuge at 10,000 rpm for 5 minutes, remove the supernatant to obtain a precipitate, and dissolve the precipitate in toluene solution to obtain a clear and transparent quantum dot solution.

[0047] The products in Example 1 and Comparative Example 1 were tested. The PL spectra of the quantum dot solution before and after FeBr3 treatment in Example 1 are shown in FIG. Figure 1 As shown, the PL spectrum of Comparative Example 1 after washing and purification with ethyl acetate and centrifugal redispersion is as follows Figure 2 As shown, it can be seen that no matter Example 1 or Comparative Example 1, the main peak wavelength of the solution before and after different treatments and purifications is 465 nm. This is because the strong binding ability of 2PA on the surface of quantum dots prevents the ripening growth of quantum dots, so the initial PL properties can be better preserved.

[0048] The quantum dot solutions in Example 1 and Comparative Example 1 were tested. The changes of PLQY and PL spectrum of Example 1 with storage time are shown in the figure below. Figure 3 As shown in FIG. 1 , the PL spectrum of Comparative Example 1 changes with storage time. Figure 4 As shown, by comparison, it can be seen that although the quantum dots in Comparative Example 1 did not undergo significant changes within 5 minutes, their emission wavelength red-shifted from 465nm to 486nm after 1 hour, and a significant luminescence peak broadening occurred, indicating that the stability decreased after treatment with ethyl acetate. Figure 3In Example 1, the PLQY reached 97% after FeBr3 treatment, demonstrating that FeBr3 treatment effectively passivates surface defects on the quantum dots and improves their luminescence efficiency. FeBr3-treated quantum dots exhibit long-term stability, with their PLQY showing little noticeable decrease within 7 days, remaining above 95%. Comparison of PL spectra reveals that the PL of the 2PA quantum dot solution after 7 days of storage is essentially consistent with the initial PL spectrum, with only a slight decrease in PL intensity. This demonstrates that FeBr3 treatment can achieve long-term stability for the 2PA quantum dots.

[0049] Figure 5 The following are TEM images of 2PA quantum dots treated with FeBr3 in their initial state and after 10 days of storage. It can be observed from the figure that the quantum dots always maintain a monodisperse morphology and the particle size does not increase significantly, further verifying that the FeBr3 post-treatment significantly improves the long-term stability of 2PA quantum dots. Figure 6 The PL spectrum changes of 2PA quantum dots treated with FeBr3 within 55 days were compared, and the PL spectrum shape remained basically consistent, further verifying its long-term stability.

[0050] Comparative Example 2

[0051] The steps for preparing CsPbBr3 quantum dots are as follows:

[0052] S1. Place 0.1 mmol CsBr, 0.5 mmol PbBr2, and 0.5 mmol 2PA (2-picolinic acid) in a container, add 10 mL DMF, stir and mix, and obtain a transparent precursor solution after all the substances are dissolved.

[0053] S2. Add 50 μL of oleylamine solution to 1 mL of the precursor solution to obtain a mixed solution; add 50 μL of the mixed solution to 2 mL of toluene and stir for 10 minutes to obtain a quantum dot solution.

[0054] The quantum dot morphology of the products of Example 1 and Comparative Example 2 was detected. The TEM images of the products of Example 1 and Comparative Example 2 were as follows: Figure 7 、 Figure 8 As shown, the FeBr3 post-treatment operation did not change the morphology and size of its ultra-small quantum dots. A 0.184 nm interplanar spacing was measured in the HRTEM image of 2PA quantum dots, which is consistent with the (310) interplanar spacing of CsPbBr3.

[0055] Comparative Example 3

[0056] The steps of Comparative Example 3 are the same as those of Example 1, except that the ratio of aromatic acid to PbBr2 is changed to 1.8.

[0057] Comparative Example 4

[0058] The steps of Comparative Example 4 are the same as those of Example 1, except that the ratio of aromatic acid to PbBr2 is changed to 0.2.

[0059] The products of Example 1, Comparative Example 3 and Comparative Example 4 were tested, and the PL spectra of the quantum dots were compared as shown in the figure below. Figure 9 As shown, it can be seen that the PL spectrum shows a broad peak emission from 440nm to 500nm when 2PA / Pb=0.2, while when 2PA / Pb=1, the PL spectrum shows a narrow single peak emission and the luminescence peak is 465nm. When 2PA / Pb=1.8, no fluorescence phenomenon was observed. Therefore, 2PA has a significant effect on the uniformity of the quantum dot size. When the 2PA content is insufficient, the quantum dots cannot achieve a concentrated size distribution, resulting in a wide luminescence peak. Only when 2PA is sufficient can the quantum dots achieve a uniform particle size. This shows that the protection method in Example 1 can effectively passivate the non-radiative recombination defects on the surface of the quantum dots.

[0060] The schematic diagram of the process of FeBr3 cooperating with 2PA to reconstruct the surface of quantum dots in this embodiment 1 is as follows Figure 10 As shown in the figure, the surface of the initially synthesized 2PA quantum dots contains ligands of oleylamine and 2PA, of which the oleylamine ligand plays a dominant role. Although the 2PA molecule has a passivating effect, its large steric hindrance cannot completely passivate the surface defects. There are a large number of Pb vacancies and Br vacancies on the surface of the quantum dots. Further introduction of FeBr3 treatment can effectively passivate the vacancy defects on the surface of the quantum dots, thereby obtaining a PLQY close to 100%. After washing with EA (ethyl acetate) and centrifugation, the oleylamine ligand on the surface of the quantum dots is basically removed, while the 2PA and Fe that can be tightly bound to the surface of the quantum dots are removed. 3+ and Br - Ions reconstruct the surface of quantum dots. Fe 3+ Ions can form a multi-coordinated network structure with 2PA molecules. Therefore, FeBr3 and 2PA molecules form a dense coordination polymer protective layer on the surface of quantum dots. This in situ formed interface layer has a strong binding ability, inhibiting the ripening growth between quantum dots, thus achieving long-term stability.

[0061] Therefore, the room-temperature preparation method of ultra-small-sized perovskite quantum dots of the present invention has the function of slow-release ions, which can well control the crystallization rate, thereby realizing the preparation of ultra-small-sized perovskite quantum dots, and has the function of in-situ passivation of defects, which can well improve the luminous efficiency of the quantum dots; and then using a metal salt solution for post-treatment can well maintain the stability of the ultra-small-sized perovskite quantum dots, thereby achieving long-term wavelength stability and no efficiency attenuation.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A room temperature method for preparing ultra-small perovskite quantum dots, characterized in that: The following steps are involved: S1. Place CsBr, PbBr2, and aromatic acid powders in a container, add a polar solvent, stir and mix, and obtain a transparent precursor solution after all are dissolved; the ratio of CsBr to PbBr2 is 0.2:1, the concentration of the aromatic acid is 0.01~2M, the stirring time is 25~40min, and the aromatic acid is 2-pyridinecarboxylic acid; the ratio of aromatic acid to PbBr2 is 1; S2. adding an amine solution to the precursor solution to obtain a mixed solution, and adding the mixed solution to an antisolvent to obtain a crude quantum dot solution; S3, adding a metal salt solution to the crude quantum dot solution, wherein the volume ratio of the crude quantum dot solution to the metal salt solution is 205:1, stirring and centrifuging, adding an organic solvent to the supernatant obtained by centrifugation, and centrifuging again to obtain a quantum dot precipitate; the metal salt solution is ferric bromide; and the concentration of the metal salt solution is 0.01~2M; S4. Dissolve the quantum dot precipitate in a mixed solution of toluene and DMF, and centrifuge again to obtain a clear and transparent quantum dot solution.

2. The room temperature method for preparing ultra-small perovskite quantum dots according to claim 1, characterized in that: In the above-mentioned S1, the polar solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

3. The room temperature method for preparing ultra-small perovskite quantum dots according to claim 1, characterized in that: In the above-mentioned S2, the volume ratio of the precursor solution to the amine solution is 1-200, and the volume ratio of the mixed solution to the anti-solvent is 1-100.

4. The room temperature method for preparing ultra-small perovskite quantum dots according to claim 1, characterized in that: In S2, the amine solution is one of oleylamine, n-propylamine, n-butylamine, n-pentylamine, n-hexylamine, n-octylamine, phenylethylamine, and phenylbutylamine; and the antisolvent is one of toluene, chlorobenzene, n-hexane, and cyclohexane.

5. The room temperature method for preparing ultra-small perovskite quantum dots according to claim 1, characterized in that: In the step S3, the stirring time is 1 to 20 minutes; and the volume ratio of the supernatant to the organic solvent is 0.2 to 5.

6. The room temperature method for preparing ultra-small perovskite quantum dots according to claim 1, characterized in that: In the step S3, the organic solvent is one of ethyl acetate, methyl acetate, methyl formate, ethyl formate, and acetone.

7. The room temperature method for preparing ultra-small perovskite quantum dots according to claim 1, characterized in that: In S3 and S4, the centrifugal speed is 5000-14000 rpm / min, and the centrifugal time is 1-8 min.

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