Room-temperature preparation method of ultra-small perovskite quantum dots

Abstract

The invention discloses a room-temperature preparation method of ultra-small-size perovskite quantum dots, and belongs to the technical field of ultra-small-size perovskite quantum dots, and the method comprises the following steps: S1, placing CsBr, PbBr2 and aromatic acid powder in a container, adding a polar solvent, and stirring and mixing to obtain a transparent precursor solution; s2, adding an amine solution into the precursor solution to obtain a mixed solution, and adding the mixed solution into an anti-solvent to obtain a quantum dot coarse solution; s3, adding a metal salt solution into the quantum dot coarse solution, stirring, centrifuging, adding an organic solvent into supernate obtained by centrifuging, and centrifuging again to obtain quantum dot precipitates; and 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 quantum dot interface is reconstructed through cooperation of FeBr3 and aromatic acid, so that the quantum dot obtains PLQY close to 100% and shows long-term stability.

Description

Technical Field

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

[0002] Metal halide perovskite light-emitting diodes (PeLEDs) with pure blue light emission have serious problems of insufficient brightness and efficiency, which severely restrict their applications in the display field. The preparation of blue perovskites usually adopts methods of Br / Cl component regulation and quantum confinement effect regulation. The Br / Cl component regulation has stability problems caused by phase separation, while all-bromine-based two-dimensional perovskites and quantum dots based on the quantum confinement effect show greater potential. The exciton Bohr radius of the CsPbBr 3 bulk material is 3.5 nm. Therefore, quantum dots with a size less than 7 nm achieve blue light emission through strong quantum confinement effects. Among them, ultra-small-sized CsPbBr with a particle size of about 4 nm 3 quantum dots exhibit pure blue light (<470 nm) emission.

[0003] Ultra-small-sized perovskite quantum dots have problems such as difficult synthesis, poor long-term stability, and surface defects. In addition, in the prior art, the ligand-assisted reprecipitation method (LARP) is used to synthesize ultra-small-sized perovskite quantum dots at room temperature, but only CsPbBr3 quantum dots with a size of ~8 nm to ~15 nm can be obtained, and the poor crystallization quality of the quantum dots leads to a broad emission PL spectrum and a very low PLQY. In addition, in some technologies, liquid nitrogen is added to the toluene antisolvent, and the ultralow reaction temperature is used to inhibit the ultra-fast nucleation and growth of perovskite, and thus quantum dots (3 nm) with a PLQY as high as 98% are obtained by the LARP method. This method requires low-temperature control, has poor operability, and the high cost of liquid nitrogen is not suitable for large-scale preparation. The patent with the publication number CN112125332A discloses a perovskite blue light quantum dot based on recrystallization and its preparation method, but its controllability is not strong.

[0004] Based on this, a room-temperature preparation method for ultra-small-sized perovskite quantum dots is proposed, which enables the PLQY of the quantum dots to be 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-sized perovskite quantum dots to solve the problems in the background art.

[0006] To achieve the above purpose, the present invention provides a room-temperature preparation method for ultra-small-sized perovskite quantum dots, including the following steps: S1. Mix CsBr and PbBr2 Place CsBr and aromatic acid powder in a container, add a polar solvent and stir to mix. After complete dissolution, a transparent precursor solution is obtained. S2. Add an amine solution to the precursor solution to obtain a mixed solution, and add the mixed solution to an anti-solvent to obtain a crude quantum dot solution. S3. Add a metal salt solution to the crude quantum dot solution, stir and then centrifuge. Add an organic solvent to the supernatant obtained by centrifugation, and centrifuge again to obtain a quantum dot precipitate. 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.

[0007] Preferably, in S1, the ratio of CsBr to PbBr 2 is 0 to 1; the concentration of the aromatic acid is 0.01 to 2 M, the stirring time is 25 to 40 min, and the ratio of the aromatic acid to PbBr 2 is 0.6 to 1.4.

[0008] 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.

[0009] Preferably, in S2, the volume ratio of the precursor solution to the amine solution is 1 to 200, and the volume ratio of the mixed solution to the anti-solvent is 1 to 100.

[0010] Preferably, in S2, the amine solution is one of oleylamine, n-propylamine, n-butylamine, n-pentylamine, n-hexylamine, n-octylamine, phenethylamine, and phenylbutylamine; the anti-solvent is one of toluene, chlorobenzene, n-hexane, and cyclohexane.

[0011] Preferably, in S3, the volume ratio of the crude quantum dot solution to the metal salt solution is 1 to 200, the concentration of the metal salt solution is 0.01 to 2 M, the stirring time is 1 to 20 min; the volume ratio of the supernatant to the organic solvent is 0.2 to 5.

[0012] Preferably, in S3, the metal salt solution is one of sodium bromide, potassium bromide, rubidium bromide, tin bromide, iron bromide, and indium bromide, and the organic solvent is one of ethyl acetate, methyl acetate, methyl formate, ethyl formate, and acetone.

[0013] Preferably, in S4, the volume ratio of toluene to DMF is 100:2.5.

[0014] Preferably, in S3 and S4, the centrifugation speed is 5000 to 14000 rpm / min, and the centrifugation time is 1 to 8 min.

[0015] Therefore, a room-temperature preparation method of ultra-small-sized perovskite quantum dots according to the present invention has the following beneficial effects: (1) In the method of the present invention, based on aromatic acids, the LARP method can obtain ultra-small-sized quantum dots emitting blue light under room-temperature conditions. Aromatic acids, especially picolinic acid, have the effect of slowly releasing ions, can well control the crystallization rate, thereby realizing the preparation of ultra-small-sized perovskite quantum dots, and picolinic acid has the effect of in-situ passivating defects and can well improve the luminescence efficiency of quantum dots.

[0016] (2) In the post-treatment of the present invention, ion interface reconstruction is carried out. By using metal salt solutions for post-treatment, the stability of ultra-small-sized perovskite quantum dots can be well maintained, realizing long-term wavelength stability and non-decaying efficiency.

[0017] (3) After the quantum dots prepared in the present invention are treated with metal salts, the surface components of the ultra-small-sized quantum dots are reconstructed, effectively passivating the vacancy defects on the surface of the quantum dots, thereby obtaining a PLQY close to 100%. The treated quantum dots have the same TEM morphology and PL spectrum as the initial quantum dots. Their PLQY is still higher than 95% after storage for 7 days, and the PL spectrum of the quantum dots is consistent with the initial state after 55 days, showing long-term stability.

[0018] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the PL spectrum diagram of Example 1 of the present invention; Figure 2 It is the PL spectrum diagram of Comparative Example 1 of the present invention; Figure 3 It is the change diagram of the PLQY and PL spectrum of Example 1 of the present invention with the storage time, where (a) is the PLQY diagram and (b) is the PL spectrum diagram; Figure 4 It is the change diagram of the PL spectrum of Comparative Example 1 of the present invention with the storage time; Figure 5 It is the TEM diagrams of the quantum dots in Example 1 of the present invention in the initial state and after being stored for 10 days. Among them, (a) is the initial state and (b) is the state after 10 days; Figure 6 It is the PL spectrum change diagram within 55 days of Example 1 of the present invention; Figure 7 It is the TEM diagram of Example 1 of the present invention, and the inset is the HRTEM diagram; Figure 8 It is the TEM diagram of Comparative Example 2 of the present invention; Figure 9PL spectra comparison chart of Example 1, Comparative Example 3, and Comparative Example 4 of the present invention; Figure 10 In FeBr of Example 1 of the present invention 3 Schematic diagram of the process of synergistically reconstructing the quantum dot surface with 2PA. Detailed implementation manners

[0020] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] To make the objectives, 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 with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention.

[0022] Example 1 Prepare CsPbBr 3 Quantum dots, the steps are as follows: S1. Place 0.1 mmol CsBr, 0.5 mmol PbBr 2 and 0.5 mmol 2PA (2-pyridinecarboxylic acid) in a container, add 10 mL DMF and stir to mix. After complete dissolution, a transparent precursor solution is obtained; S2. Take 1 mL of the precursor solution and add 50 μL of oleylamine solution to obtain a mixed solution; add 50 μL of the mixed solution to 2 mL of toluene and stir for 10 min to obtain a crude quantum dot solution; S3. Dissolve 0.2 mmol FeBr 3 in 1 mL of DMF to obtain a FeBr 3 solution. Inject 10 μL of the FeBr 3 solution into the crude quantum dot solution under stirring. After continuing to stir for 2 min, centrifuge at 5000 rpm for 2 min to remove the unreacted FeBr 3 insoluble matter. Then add an EA solution with a volume ratio of 2:1 to the supernatant obtained by centrifugation and centrifuge at 10000 rpm for 5 min to remove the supernatant to obtain a precipitate; S4. Dissolve the obtained quantum dot precipitate in a mixed solution of toluene and DMF with a volume ratio of 100:2.5. After dissolution, centrifuge again at 10000 rpm for 1 min to remove the quantum dots that cannot be completely dissolved to obtain a clear and transparent quantum dot solution.

[0023] Comparative Example 1 Prepare CsPbBr 3 Quantum dots, the steps are as follows: S1. Place 0.1 mmol CsBr, 0.5 mmol PbBr2 0.5 mmol of 2PA (2-pyridinecarboxylic acid) was placed in a container, and 10 mL of DMF was added for stirring and mixing. After complete dissolution, a transparent precursor solution was obtained; S2. 50 μL of oleylamine solution was added to 1 mL of the precursor solution to obtain a mixed solution; 50 μL of the mixed solution was added to 2 mL of toluene and stirred for 10 min to obtain a quantum dot solution; S3. An ethyl acetate solution with a volume ratio of 2:1 was added to the crude quantum dot solution, and centrifuged at 10000 rpm for 5 min. The supernatant was removed to obtain a precipitate, and the precipitate was dissolved in toluene solution again to obtain a clear and transparent quantum dot solution.

[0024] The products in Example 1 and Comparative Example 1 were detected. The PL spectra of the quantum dot solution before and after being treated with FeBr 3 in Example 1 are as Figure 1 shown. The PL spectra of Comparative Example 1 after being washed, purified and treated with ethyl acetate and centrifugal redispersion are as Figure 2 shown. It can be seen that for both Example 1 and Comparative Example 1, the main peak wavelengths of the solutions before and after different treatment and purification are 465 nm. This is because the strong binding ability of 2PA on the surface of the quantum dots prevents the ripening growth of the quantum dots. Therefore, the initial PL properties can be better retained.

[0025] The quantum dot solutions in Example 1 and Comparative Example 1 were detected. The graphs of the change of PLQY and PL spectra of Example 1 with storage time are as Figure 3 shown. The graph of the change of the PL spectrum of Comparative Example 1 with storage time is as Figure 4 shown. By comparison, it can be seen that although there is no obvious change in the quantum dots in Comparative Example 1 within 5 min, after 1 h, its emission wavelength redshifts from 465 nm to 486 nm, and a significant broadening of the emission peak appears, indicating that the stability decreases after being treated with ethyl acetate. And Figure 3 in Example 1, after being treated with FeBr 3 , its PLQY reaches 97%, indicating that FeBr 3 treatment can effectively passivate the defects on the surface of the quantum dots and improve their luminescence efficiency. The quantum dots after being treated with FeBr 3 show long-term stability. Its PLQY hardly decreases significantly within 7 d and can still maintain more than 95% of the PLQY. From the comparison of the PL spectra, it can be seen that the PL of the 2PA quantum dot solution after being stored for 7 d is basically the same as the initial PL spectrum, with only a slight decrease in the PL intensity. This indicates that FeBr 3 treatment can achieve the long-term stability of 2PA quantum dots.

[0026] Figure 5It is FeBr 3 TEM images of the 2PA quantum dots before and after being stored for 10 days after FeBr treatment were processed. It can be observed from the figures that the quantum dots always maintain a monodisperse morphology and the particle size does not increase significantly, further verifying that FeBr 3 The post-treatment significantly improves the long-term stability of the 2PA quantum dots; Figure 6 In [reference], the PL spectral changes of the 2PA quantum dots after FeBr 3 treatment within 55 days were compared. The shape of the PL spectrum basically remained the same, further verifying its long-term stability.

[0027] Comparative Example 2 CsPbBr 3 quantum dots were prepared as follows: S1. 0.1 mmol CsBr, 0.5 mmol PbBr 2 and 0.5 mmol 2PA (2-pyridinecarboxylic acid) were placed in a container, and 10 mL of DMF was added for stirring and mixing. After complete dissolution, a transparent precursor solution was obtained; S2. 50 μL of oleylamine solution was added to 1 mL of the precursor solution to obtain a mixed solution; 50 μL of the mixed solution was added to 2 mL of toluene and stirred for 10 min to obtain a quantum dot solution.

[0028] 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 are shown in Figure 7 and Figure 8 respectively. The post-treatment operation of FeBr 3 did not change the morphology and size of the ultra-small quantum dots. The lattice fringe spacing of 0.184 nm was measured in the HRTEM image of the 2PA quantum dots, which is consistent with the (310) lattice fringe spacing of CsPbBr 3 .

[0029] Comparative Example 3 This Comparative Example 3 was the same as the steps of Example 1, except that the dosage ratio of the aromatic acid to PbBr 2 was changed to 1.8.

[0030] Comparative Example 4 This Comparative Example 4 was the same as the steps of Example 1, except that the dosage ratio of the aromatic acid to PbBr 2 was changed to 0.2.

[0031] The products of Example 1, Comparative Example 3, and Comparative Example 4 were detected. The comparative PL spectra of the quantum dots are shown in Figure 9As shown, it can be seen that the PL spectrum shows a broad peak emission from 440nm to 500nm when 2PA / Pb=0.2, and 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 size of quantum dots. 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 this embodiment 1 can effectively passivate the non-radiative composite defects on the surface of the quantum dots.

[0032] In this embodiment 1, FeBr 3 Schematic diagram of the process of coordinating 2PA to reconstruct the surface of quantum dots Figure 10 As shown in the figure, the surface of the initially synthesized 2PA quantum dots contains ligands of oleylamine and 2PA, among 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 FeBr 3 The treatment can effectively passivate the vacancy defects on the surface of quantum dots, thereby obtaining a PLQY close to 100%. After washing with EA (ethyl acetate) and centrifugation, the oleylamine ligands on the surface of the quantum dots are basically removed, while the 2PA and Fe 3+ And Br - Ions reconstruct the surface of quantum dots. Fe 3+ ions can form a multi-coordinated network structure with 2PA molecules, so FeBr 3 A dense coordination polymer protective layer is formed on the surface of quantum dots with 2PA molecules. This in-situ formed interface layer has strong binding ability, inhibiting the ripening growth between quantum dots, thus achieving long-term stability.

[0033] Therefore, in the room temperature preparation method of ultra-small perovskite quantum dots of the present invention, the aromatic acid in the raw material has the function of slow-release ions, which can well control the crystallization rate, thereby realizing the preparation of ultra-small perovskite quantum dots, and has the function of in-situ passivation of defects, which can well improve the luminescence efficiency of the quantum dots; and then post-treatment with a metal salt solution can well maintain the stability of the ultra-small perovskite quantum dots, and achieve long-term wavelength stability and no efficiency attenuation.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent replacements, and these modifications or equivalent replacements cannot make the modified technical solutions 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 powder in a container, add a polar solvent and stir to mix, and obtain a transparent precursor solution after all of them are dissolved; S2, adding an amine solution to the precursor solution to obtain a mixed solution, and adding the mixed solution to an anti-solvent to obtain a crude quantum dot solution; S3, adding a metal salt solution to the crude solution of quantum dots, stirring and centrifuging, adding an organic solvent to the supernatant obtained by centrifugation, and centrifuging again to obtain a quantum dot precipitate; 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 preparation method of ultra-small size perovskite quantum dots according to claim 1, characterized in that: In the 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.

3. The room temperature preparation method of ultra-small perovskite quantum dots according to claim 1, characterized in that: In the S1, the aromatic acid is 2-pyridinecarboxylic acid, and the polar solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

4. The room temperature preparation method of ultra-small perovskite quantum dots according to claim 1, characterized in that: 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.

5. The room temperature preparation method of 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, phenethylamine, and phenbutylamine; and the antisolvent is one of toluene, chlorobenzene, n-hexane, and cyclohexane.

6. The room temperature preparation method of ultra-small perovskite quantum dots according to claim 1, characterized in that: 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 0.01-2M, and the stirring time is 1-20 min; the volume ratio of the supernatant to the organic solvent is 0.2-5.

7. The room temperature preparation method of ultra-small perovskite quantum dots according to claim 1, characterized in that: 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.

8. The room temperature preparation method of 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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