Preparation method of ultrahigh-quantum-yield spherical quantum dots for photovoltaic panel coating

Abstract

The invention relates to the technical field of luminescent materials, in particular to a preparation method of ultrahigh-quantum-yield spherical quantum dots for a photovoltaic panel coating. The preparation method comprises the following steps: mixing and dissolving a carbon source, a nitrogen source and polyethyleneimine in deionized water, carrying out ultrasonic dispersion, carrying out a hydrothermal reaction to obtain a quantum dot mother solution, and then carrying out ultrasonic extraction and purification on the quantum dot mother solution to obtain a spherical quantum dot solution. The spherical quantum dot solution prepared by the preparation method has strong bluish violet fluorescence, the maximum emission peak value is 420 nm, the particle size of spherical particles is 1-4 nm, the quantum yield is higher than 60%, the spherical quantum dot solution has water solubility, the fluorescence intensity is not changed after the spherical quantum dot solution is placed for 6 months, and the stability is good; meanwhile, the preparation method is simple and low in cost; the prepared spherical quantum dot solution is diluted and then sprayed on the surface of a photovoltaic panel, and the photoelectric conversion efficiency can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of luminescent materials, and in particular to a method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings. Background Art

[0002] The absorption spectrum of silicon photovoltaic cells for sunlight is between 350-950nm. Under the irradiation of ultraviolet and visible light sources, the electrons in the valence band can be excited to the conduction band, that is, light energy is converted into electrical energy. In order to further increase the generation of light-excited free electrons, a UV-excited quantum dot coating can be applied on the surface of the photovoltaic panel to improve the photoelectric conversion efficiency. In recent years, graphene quantum dots have been developed as the latest member of the graphene family. It is highly favored due to its good water solubility, biocompatibility, low toxicity, stable fluorescence and other characteristics. Moreover, because it inherits the excellent properties of graphene while also having quantum confinement effects and boundary effects, it has greatly opened up the application prospects of graphene quantum dots in the fields of energy and environment.

[0003] Chinese patent CN201710215428.1 discloses a nitrogen-doped fluorescent graphene quantum dot and its preparation method. Glycine is added to ultrapure water, and sodium citrate solution is added after stirring, and then transferred to a high-pressure reactor lined with polytetrafluoroethylene for reaction, and high-speed centrifugation is performed to obtain a nitrogen-doped fluorescent graphene quantum dot solution. After rotary evaporation and vacuum freeze drying, a nitrogen-doped fluorescent graphene quantum dot white solid powder is obtained. The nitrogen-doped fluorescent graphene quantum dot has a particle size of 3 to 10 nm, a spherical morphology, and contains N elements. Its solution has strong blue-purple fluorescence, with a maximum emission peak at 440 to 460 nm and a maximum excitation wavelength of 360 to 380 nm; its solid powder can emit strong blue fluorescence, with a maximum emission peak at 420 to 450 nm and a maximum excitation wavelength of 360 to 380 nm. However, the quantum yield of graphene quantum dots prepared by the above preparation method is only 22-31%, and the liquid storage time is more than 1 month, and the solid storage time is more than 3 months. It can be seen that the existing graphene quantum dot preparation method still has problems such as low fluorescence quantum yield and unstable luminescence. Summary of the invention

[0004] In view of this, the present invention proposes a method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings to solve the problems of low fluorescence quantum yield and unstable luminescence in existing graphene quantum dot preparation methods.

[0005] The technical solution of the present invention is achieved in this way:

[0006] In the first aspect, the present invention provides a method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings, comprising the following steps: mixing a carbon source, a nitrogen source and polyethyleneimine and dissolving them in deionized water, ultrasonically dispersing them, obtaining a quantum dot mother liquor through a hydrothermal reaction, and then ultrasonically extracting and purifying the quantum dot mother liquor to obtain a spherical quantum dot solution.

[0007] Based on the above technical solution, preferably, the molar ratio of the nitrogen source, polyethyleneimine and carbon source is 1:0.1-0.5:2-4.

[0008] On the basis of the above technical solution, preferably, the carbon source is citric acid and the nitrogen source is ethylenediamine.

[0009] The synthesis principle of the present invention is as follows:

[0010]

[0011] In the present invention, two hydrogen groups of the terminal amino group of ethylenediamine are used to polymerize with ternary citric acid under the induction of polyethyleneimine to form spherical quantum dots containing pyridine nitrogen structures, wherein a large number of pyridine nitrogen structures lead to a significant increase in the quantum dot yield and long-lasting fluorescence stability. Specifically, a large number of pyridine nitrogen structures can effectively passivate defects on the surface of quantum dots, reduce non-radiative recombination, and improve the efficiency of radiative transitions; the spherical structure provides a larger specific surface area and uniformity, increases the number of luminescent centers and reduces surface defects. The pyridine nitrogen structure not only improves the quantum yield, but also effectively passivates the surface of quantum dots, reduces oxidation and photodegradation, and this passivation can protect the quantum dots for a long time and maintain their fluorescence properties.

[0012] On the basis of the above technical solution, preferably, the hydrothermal reaction is carried out in a high-pressure reactor lined with polytetrafluoroethylene, and the temperature of the hydrothermal reaction is 120-200° C. and the time is 4-12 hours.

[0013] On the basis of the above technical scheme, preferably, the ultrasonic extraction and purification specifically includes: mixing the quantum dot mother liquor and the extractant, ultrasonically shaking for 15-25 minutes, standing for 22-26 hours, and taking the upper clear liquid after the extraction is completed to obtain a spherical quantum dot solution.

[0014] On the basis of the above technical solution, preferably, the volume ratio of the quantum dot mother liquor to the extractant is 1:0.8-1.2, and the extractant is carbon tetrachloride.

[0015] Specifically, carbon tetrachloride, as a non-polar solvent, can effectively remove excess organic matter and unstable intermediates in the reaction system, while water-soluble quantum dots remain in the aqueous phase. The ultrasonic oscillation process increases the contact area between the two phases and improves the extraction efficiency, while long-term standing ensures the completeness of phase separation. This step not only improves the purity of the quantum dots, but also may enhance the stability of the quantum dots by removing unstable surface groups. At the same time, purification by extraction can avoid damage to the quantum dot structure and retain its high quantum yield and good optical properties.

[0016] In a second aspect, the present invention provides ultra-high quantum yield spherical quantum dots prepared by any of the above preparation methods.

[0017] On the basis of the above technical solutions, preferably, the ultra-high quantum yield spherical quantum dots have strong blue-violet fluorescence, and the maximum emission peak is 420nm.

[0018] On the basis of the above technical solution, preferably, the spherical particle size of the ultra-high quantum yield spherical quantum dots is 1-4 nm.

[0019] In a third aspect, the present invention provides an application of ultra-high quantum yield spherical quantum dots, wherein the ultra-high quantum yield spherical quantum dots are made into a solution and sprayed on the surface of a photovoltaic panel.

[0020] The method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coating of the present invention has the following beneficial effects compared with the prior art:

[0021] (1) The spherical quantum dot solution prepared by the preparation method of the present invention has strong blue-violet fluorescence, a maximum emission peak of 420nm, a spherical particle size of 1-4nm, a quantum yield of more than 60%, is water-soluble, has a constant fluorescence intensity after being placed for 6 months, and has good stability; at the same time, the preparation method is simple and low-cost.

[0022] (2) The spherical quantum dot solution prepared by the present invention is diluted and sprayed on the surface of the photovoltaic panel to increase the photoelectric conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 This is a TEM image of the quantum dots prepared in Example 1 of the present invention;

[0025] Figure 2 This is a particle size distribution diagram of quantum dots prepared in Example 1 of the present invention;

[0026] Figure 3 The AFM image and height distribution diagram of the quantum dots prepared in Example 2 of the present invention;

[0027] Figure 4 This is a high-resolution XPS image of N1s of the quantum dot solution before extraction in Example 3 of the present invention;

[0028] Figure 5 This is a high-resolution XPS graph of N1s of the quantum dot solution after extraction in Example 3 of the present invention;

[0029] Figure 6 This is the UV-visible absorption spectrum of the quantum dots prepared in Example 3 of the present invention;

[0030] Figure 7 This is a fluorescence excitation-emission spectrum diagram of the quantum dots prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] This embodiment provides a method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings, which specifically includes the following steps:

[0034] (1) Ethylenediamine, polyethyleneimine, and citric acid were weighed in a molar ratio of 1:0.1:2, dissolved in deionized water, and stirred to obtain a mixed solution. The mixed solution was ultrasonically dispersed for 30 minutes, transferred to a hydrothermal reactor for hydrothermal reaction at a reaction temperature of 120°C for a reaction time of 4 hours, and cooled to prepare a quantum dot mother solution.

[0035] (2) The quantum dot mother liquor was subjected to ultrasonic extraction and purification, with the volume ratio of quantum dot solution to chloroform being 1:1, and the ultrasonic treatment was performed for 20 min, followed by standing for 24 h to further remove other excess organic matter. After the extraction was completed, the supernatant was the spherical quantum dots.

[0036] Example 2

[0037] This embodiment provides a method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings, which specifically includes the following steps:

[0038] (1) Ethylenediamine, polyethyleneimine, and citric acid were weighed in a molar ratio of 1:0.5:4, dissolved in deionized water, and stirred to obtain a mixed solution; the mixed solution was ultrasonically dispersed for 30 minutes, and transferred to a hydrothermal reactor for hydrothermal reaction. The reaction temperature was 200°C, the reaction time was 4 hours, and the solution was cooled to prepare a quantum dot solution.

[0039] (2) The quantum dot mother liquor was subjected to ultrasonic extraction and purification, with the volume ratio of quantum dot solution to chloroform being 1:1, and the ultrasonic treatment was performed for 20 min, followed by standing for 24 h to further remove other excess organic matter. After the extraction was completed, the supernatant was the spherical quantum dots.

[0040] Example 3

[0041] This embodiment provides a method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings, which specifically includes the following steps:

[0042] (1) Ethylenediamine, polyethyleneimine, and citric acid were weighed in a molar ratio of 1:0.2:3, dissolved in deionized water, and stirred to obtain a mixed solution; the mixed solution was ultrasonically dispersed for 30 minutes, and transferred to a hydrothermal reactor for hydrothermal reaction. The reaction temperature was 180°C, the reaction time was 8 hours, and the solution was cooled to prepare a quantum dot solution.

[0043] (2) The synthesized quantum dot solution was subjected to ultrasonic extraction and purification. The volume ratio of the quantum dot solution to chloroform was 1:1. The solution was ultrasonically treated for 20 minutes and then allowed to stand for 24 hours to further remove other excess organic matter. After the extraction was completed, the supernatant was the spherical quantum dots.

[0044] Comparative Example 1

[0045] This comparative example provides a method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings, which specifically includes the following steps:

[0046] (1) Weigh ethylenediamine and citric acid in a molar ratio of 1:2, dissolve in deionized water, and stir to obtain a mixed solution. Ultrasonic disperse the mixed solution for 30 minutes, transfer it to a hydrothermal reactor for hydrothermal reaction at a reaction temperature of 120°C for 4 hours, and cool it to prepare a quantum dot mother solution.

[0047] (2) The quantum dot mother liquor was subjected to ultrasonic extraction and purification, with the volume ratio of quantum dot solution to chloroform being 1:1, and the ultrasonic treatment was performed for 20 min, followed by standing for 24 h to further remove other excess organic matter. After the extraction was completed, the supernatant was the spherical quantum dots.

[0048] Comparative Example 2

[0049] This comparative example provides a method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings, which specifically includes the following steps:

[0050] (1) Ethylenediamine, polyethyleneimine, and citric acid were weighed in a molar ratio of 1:0.1:2, dissolved in deionized water, and stirred to obtain a mixed solution. The mixed solution was ultrasonically dispersed for 30 minutes, transferred to a hydrothermal reactor for hydrothermal reaction at a reaction temperature of 120°C for a reaction time of 4 hours, and cooled to prepare a quantum dot mother solution.

[0051] (2) Purify the quantum dot mother liquor by using a dialysis bag to purify the quantum dot mother liquor for 24 hours to obtain spherical quantum dots.

[0052] Application Examples

[0053] The quantum yields of the examples and comparative examples were tested using quinine sulfate as a standard reference. The quantum dot solutions prepared in the examples and comparative examples were diluted 100 times and then sprayed on the surface of the photovoltaic panel to test the photocurrent. The test results are shown in Table 1.

[0054] Table 1 Quantum yield and photocurrent

[0055] Quantum yield Photocurrent increase Example 1 64％ 0.51％ Example 2 81％ 0.59％ Example 3 88％ 0.89％ Comparative Example 1 42％ 0.27％ Comparative Example 2 50％ 0.36％

[0056] Figure 1 The TEM image of the quantum dots prepared in Example 1 of the present invention is shown. Figure 2 The particle size distribution diagram of the quantum dots prepared in Example 1 of the present invention is shown. It can be seen from the figure that the quantum dots are spherical, evenly dispersed, and have a narrow particle size distribution. The particle size is 1-4nm and the average particle size is 2.5nm.

[0057] Figure 3 The AFM image and height distribution diagram of the quantum dots prepared in Example 2 of the present invention are shown. According to the AFM test results, the thickness of the quantum dots is 1.89-2.09 nm.

[0058] Figure 4 The high-resolution XPS graph of N1s of the quantum dot solution before extraction in Example 3 of the present invention is shown. Figure 5 The N1s high-resolution XPS graph of the quantum dot solution after extraction in Example 3 of the present invention is shown. It can be seen from the figure that the N1s high-resolution graph of the quantum dot solution before extraction contains a high proportion of graphitic nitrogen. However, the N1s high-resolution graph of the quantum dot solution after extraction contains a high proportion of pyridinic nitrogen, indicating that the extraction has purified the quantum dots.

[0059] Figure 6 The UV-visible absorption spectrum of the quantum dots prepared in Example 3 of the present invention is shown. It can be seen from the figure that the high proportion of pyridinic nitrogen greatly improves its quantum yield due to n-π* transition.

[0060] Figure 7 The fluorescence excitation-emission spectrum of the quantum dots prepared in Example 3 of the present invention is shown. It can be seen from the figure that when the wavelength of the excitation light is 350nm, the quantum dot solution has the maximum fluorescence intensity, and as the wavelength of the excitation light changes, the emission wavelength remains stable at 442nm, indicating that the quantum dots have uniform size and a stable surface state.

[0061] As can be seen from Table 1, the quantum dots prepared in the present invention are spherical nanodots with a relatively high quantum yield of more than 60%. The photocurrent can be increased by diluting the quantum dot solution and spraying it on the surface of the photovoltaic panel.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings, characterized in that: The method comprises the following steps: mixing a carbon source, a nitrogen source and polyethyleneimine and dissolving them in deionized water, performing ultrasonic dispersion, obtaining a quantum dot mother liquor through hydrothermal reaction, and then performing ultrasonic extraction and purification on the quantum dot mother liquor to obtain a spherical quantum dot solution.

2. The method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coating according to claim 1, characterized in that: The molar ratio of the nitrogen source, polyethyleneimine and carbon source is 1:0.1-0.5:2-4.

3. The method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coating according to claim 1, characterized in that: The carbon source is citric acid, and the nitrogen source is ethylenediamine.

4. The method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coating according to claim 1, characterized in that: The hydrothermal reaction is carried out in a high-pressure reactor lined with polytetrafluoroethylene, the temperature of the hydrothermal reaction is 120-200° C., and the time is 4-12 hours.

5. The method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coating according to claim 1, characterized in that: The ultrasonic extraction and purification specifically comprises: mixing the quantum dot mother liquor and the extractant, ultrasonicating for 15-25 minutes, standing for 22-26 hours, and taking the upper clear liquid after the extraction is completed to obtain the spherical quantum dot solution.

6. The method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coating according to claim 1, characterized in that: The volume ratio of the quantum dot mother solution to the extractant is 1:0.8-1.2, and the extractant is carbon tetrachloride.

7. An ultra-high quantum yield spherical quantum dot prepared by the preparation method according to any one of claims 1 to 6.

8. The ultra-high quantum yield spherical quantum dot according to claim 7, characterized in that: The ultra-high quantum yield spherical quantum dots have strong blue-violet fluorescence, and the maximum emission peak is 420nm.

9. The ultra-high quantum yield spherical quantum dot according to claim 7, characterized in that: The spherical particle size of the ultra-high quantum yield spherical quantum dots is 1-4 nm.

10. The use of an ultra-high quantum yield spherical quantum dot according to any one of claims 1 to 6, characterized in that: The ultra-high quantum yield spherical quantum dots are made into a solution and sprayed on the surface of the photovoltaic panel.

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