A method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings

Abstract

The present 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. The preparation method comprises the following steps: dissolving a carbon source, a nitrogen source and polyethyleneimine in deionized water, ultrasonically dispersing, obtaining a quantum dot mother liquor by hydrothermal reaction, and then subjecting the quantum dot mother liquor to ultrasonic extraction and purification to obtain a spherical quantum dot solution. The spherical quantum dot solution prepared by the preparation method of the present invention has strong bluish-violet fluorescence, a maximum emission peak of 420nm, a spherical particle size of 1-4nm, a quantum yield greater than 60%, is water-soluble, has a constant fluorescence intensity after being placed for 6 months, and has good stability; the preparation method is simple and low in cost; the spherical quantum dot solution prepared by the present invention is sprayed on the surface of a photovoltaic panel after dilution, which can increase the photoelectric conversion efficiency.

Description

Technical Field

[0001] The present 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] Silicon photovoltaic cells absorb sunlight in the wavelength range of 350-950nm. When exposed to ultraviolet or visible light, electrons in the valence band can be excited to the conduction band, converting light energy into electrical energy. To further increase the generation of photoexcited free electrons, a UV-excited quantum dot coating can be applied to the photovoltaic panel surface to improve photoelectric conversion efficiency. In recent years, graphene quantum dots have been developed as the latest member of the graphene family. They are highly sought after for their excellent water solubility, biocompatibility, low toxicity, and stable fluorescence. Furthermore, because they inherit the excellent properties of graphene while also exhibiting quantum confinement and boundary effects, they have greatly expanded the application prospects of graphene quantum dots in energy, environmental, and other fields.

[0003] Chinese patent CN201710215428.1 discloses nitrogen-doped fluorescent graphene quantum dots and their preparation method. Glycine is added to ultrapure water, stirred, and then a sodium citrate solution is added. The mixture is then transferred to a polytetrafluoroethylene-lined autoclave for reaction. High-speed centrifugation is performed to obtain a nitrogen-doped fluorescent graphene quantum dot solution. This solution is then subjected to rotary evaporation and vacuum freeze-drying to obtain a white solid powder of nitrogen-doped fluorescent graphene quantum dots. The nitrogen-doped fluorescent graphene quantum dots have a particle size of 3 to 10 nm, a spherical shape, and contain nitrogen. The solution exhibits strong blue-violet fluorescence, with a maximum emission peak at 440 to 460 nm and a maximum excitation wavelength of 360 to 380 nm. The solid powder emits 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 as follows:

[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] Based on 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 this invention, the two hydrogen groups of the terminal amino group of ethylenediamine are polymerized with ternary citric acid under the induction of polyethyleneimine to form spherical quantum dots containing pyridinic nitrogen structures. The abundant pyridinic nitrogen structures significantly increase the quantum dot yield and maintain long-lasting fluorescence stability. Specifically, the large number of pyridinic nitrogen structures effectively passivates defects on the quantum dot surface, reduces non-radiative recombination, and improves 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 pyridinic nitrogen structures not only improve the quantum yield but also effectively passivate the quantum dot surface, reducing oxidation and photodegradation. This passivation protects the quantum dots over the long term, maintaining 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, 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 solution, 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 supernatant 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 from the reaction system, while the water-soluble quantum dots remain in the aqueous phase. The ultrasonic oscillation process increases the contact area between the two phases, improving the extraction efficiency, while the long-term static state ensures the completeness of the 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 through extraction avoids damage to the quantum dot structure, preserving its high quantum yield and good optical properties.

[0016] In a second aspect, the present invention provides spherical quantum dots with ultra-high quantum yield 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 420 nm.

[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 coatings 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 unchanged fluorescence intensity after 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any 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 the 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 the N1s high-resolution XPS graph of the quantum dot solution before extraction in Example 3 of the present invention;

[0028] Figure 5 This is the N1s high-resolution XPS graph 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 the fluorescence excitation-emission spectrum 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 embodiments described 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 making creative efforts 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 120°C for 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. The volume ratio of quantum dot solution to chloroform was 1:1. The ultrasonic treatment was carried out 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.

[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 at 200°C for 4 hours. The reaction was then cooled to prepare a quantum dot solution.

[0039] (2) The quantum dot mother liquor was subjected to ultrasonic extraction and purification. The volume ratio of quantum dot solution to chloroform was 1:1. The ultrasonic treatment was carried out 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.

[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 at 180°C for 8 hours. The reaction was then 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) Ethylenediamine and citric acid were weighed in a molar ratio of 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 120°C for 4 hours, and cooled to prepare a quantum dot mother solution.

[0047] (2) The quantum dot mother liquor was subjected to ultrasonic extraction and purification. The volume ratio of quantum dot solution to chloroform was 1:1. The ultrasonic treatment was carried out 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.

[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 120°C for 4 hours, and cooled to prepare a quantum dot mother solution.

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

[0052] Application Examples

[0053] The quantum yields of the examples and comparative examples were measured using quinine sulfate as a standard reference. The quantum dot solutions prepared in the examples and comparative examples were diluted 100-fold and sprayed onto the surface of a photovoltaic panel, and the photocurrent was measured. 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. As can be seen from the figure, the quantum dots are spherical, evenly dispersed, and have a narrow particle size distribution. The particle size is 1-4 nm and the average particle size is 2.5 nm.

[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 N1s high-resolution XPS graph of the quantum dot solution before extraction in Example 3 of the present invention is shown. Figure 5 The N1s high-resolution XPS pattern of the quantum dot solution after extraction in Example 3 of the present invention is shown. The figure shows that the N1s high-resolution XPS pattern of the quantum dot solution before extraction contains a high proportion of graphitic nitrogen. However, the N1s high-resolution pattern 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. As can be seen from the figure, 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. As can be seen from the figure, when the excitation light wavelength is 350nm, the quantum dot solution has the maximum fluorescence intensity, and as the excitation light wavelength changes, the emission wavelength remains stable at 442nm, indicating that the quantum dots have size uniformity and a stable surface state.

[0061] As shown in Table 1, the quantum dots prepared in the present invention are spherical nanodots with a 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 scope of protection of the present invention.

Claims

1. A method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings, characterized by: The method comprises the following steps: dissolving a carbon source, a nitrogen source and polyethyleneimine 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; The molar ratio of the nitrogen source, polyethyleneimine and carbon source is 1:0.1-0.5:2-4; The carbon source is citric acid, and the nitrogen source is ethylenediamine.

2. The method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings 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.

3. 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 includes: mixing the quantum dot mother liquor and the extractant, ultrasonicating for 15-25 minutes, standing for 22-26 hours, and taking the supernatant after the extraction is completed to obtain a spherical quantum dot solution.

4. The method for preparing ultra-high quantum yield spherical quantum dots for photovoltaic panel coatings according to claim 3, characterized in that: The volume ratio of the quantum dot mother liquor to the extractant is 1:0.8-1.2, and the extractant is carbon tetrachloride.

5. An ultra-high quantum yield spherical quantum dot prepared by the preparation method according to any one of claims 1 to 4.

6. The ultra-high quantum yield spherical quantum dot according to claim 5, characterized in that: The ultra-high quantum yield spherical quantum dots have strong blue-violet fluorescence, and the maximum emission peak is 420nm.

7. The ultra-high quantum yield spherical quantum dot according to claim 5, characterized in that: The spherical particle size of the ultra-high quantum yield spherical quantum dots is 1-4 nm.

8. Use of an ultra-high quantum yield spherical quantum dot prepared by the preparation method according to any one of claims 1 to 4, 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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