Polar quantum dots and methods of making and using the same

Abstract

The application belongs to the technical field of quantum dots, and provides a polar quantum dot and a preparation method and application thereof.The preparation method comprises the following steps: preparing a quantum dot core, then preparing an inorganic transition layer and an inorganic outer shell layer on the surface of the quantum dot core in sequence to obtain a stock solution containing composite quantum dots; under blue light irradiation, mixing the stock solution containing composite quantum dots and a polar ligand, performing a polar shell layer coating reaction, then performing post-processing to obtain the polar quantum dot; wherein the polar ligand has a chain structure and contains a first group and a second group, the first group is a mercapto group, and the second group is selected from any one or a combination of at least two of an ester group, a carboxyl group or an amino group.The preparation method can directly use a specific polar ligand to prepare a polar shell layer after the preparation of the inorganic outer shell layer, and combines with blue light assisted synthesis, so that high-brightness quantum dots which can be directly dissolved in a polar solvent can be obtained, and the quantum yield of the quantum dots is close to 100%.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot technology, and relates to a polar quantum dot, its preparation method and application. Background Technology

[0002] Quantum dots (QDs), as novel semiconductor nanomaterials, possess unique photoluminescence and electroluminescence properties due to quantum size and dielectric confinement effects. Furthermore, compared to traditional organic fluorescent dyes, quantum dots exhibit superior optical properties such as high quantum yield, high photochemical stability, high color purity, broad excitation range, and narrow emission range, making them promising candidates for applications in the display technology field.

[0003] Currently, quantum dots used for photoresists are synthesized and dissolved in nonpolar solvents such as heptane and octane. However, when making photoresists, quantum dots generally require ligand exchange, necessitating their dissolution in polar solvents (such as PGMEA or ethanol). Therefore, ligand exchange is an essential step in the preparation of quantum dot photoresists or inks.

[0004] However, ligand exchange requires the use of a polar ligand to strip the original ligands from the quantum dot before associating them with surface groups. This process increases surface defects in the quantum dot, thereby reducing its quantum yield.

[0005] Based on the above research, there is a need to provide a method for preparing polar quantum dots that can achieve high quantum dot yield and can be directly dissolved in polar solvents. Summary of the Invention

[0006] The purpose of this invention is to provide a polar quantum dot, its preparation method and application. The preparation method involves directly using a specific polar ligand to prepare the polar shell after the inorganic outer shell is prepared, and combining it with blue light-assisted synthesis to obtain high-brightness quantum dots that can be directly dissolved in a polar solvent, and the quantum yield of the quantum dots is close to 100%.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing polar quantum dots, the method comprising the following steps:

[0009] (1) Prepare a quantum dot core, and then prepare an inorganic transition layer and an inorganic outer shell layer on the surface of the quantum dot core to obtain a stock solution containing composite quantum dots;

[0010] (2) Under blue light irradiation, the original solution containing composite quantum dots and the polar ligands in step (1) are mixed to carry out a polar shell coating reaction. After the polar shell coating reaction is completed, post-processing is carried out to obtain the polar quantum dots.

[0011] The polar ligand has a chain structure and contains a first group and a second group. The first group is a thiol group, and the second group is selected from any one or a combination of at least two of ester, carboxyl, or amino groups.

[0012] To avoid ligand detachment from the quantum dot surface during ligand exchange and the influence of water and oxygen on ligand exchange, this invention addresses the following: First, after coating the quantum dot core with an inorganic transition layer and an inorganic outer shell, the original solution containing composite quantum dots and polar ligands undergo a polar shell coating reaction. The polar ligands contain thiol groups, which act as S-source anchors and polarly bind to metal ions to form the outermost polar shell. The polar ligands also contain ester, carboxyl, or amino groups, which can improve the dispersibility of the quantum dots. Furthermore, the polar ligands have a chain-like structure, which further enhances their shell protection. Moreover, since this invention completes the ligand exchange step within the reaction system, contact with external water and oxygen is eliminated, thus reducing the influence of water and oxygen on ligand exchange. Because the absence of water and oxygen causes defects on the quantum dot surface, the quantum dot yield is improved. On the other hand, the present invention coats a polar shell under blue light irradiation. Since blue light irradiation can continuously excite quantum dots, the radiative recombination part becomes more active and the non-radiative recombination is reduced. Therefore, blue light irradiation can improve the quantum yield of quantum dots.

[0013] It is understood that the composite quantum dot of the present invention includes a quantum dot core and an inorganic transition layer and an inorganic outer shell layer sequentially covering the surface of the quantum dot core; the polar quantum dot of the present invention includes a quantum dot core and an inorganic transition layer, an inorganic outer shell layer and a polar shell layer sequentially covering the surface of the quantum dot core.

[0014] Preferably, the polar ligand in step (2) includes any one or a combination of at least two of ethyl mercaptopropionate, mercaptopropionic acid, mercaptoacetic acid, 11-mercaptoundecylamine or 3-mercaptopropylamine.

[0015] The polar ligand in step (2) of this invention is preferably a mercapto ester material. Compared with other materials, mercapto ester materials are easily dissolved by solvents such as ethanol, PGMEA (propylene glycol methyl ether acetate) and other similar polar solvents. Mercapto ester materials can achieve a solubility of 800-1000 mg / mL in solvents, thus enabling quantum dots to be dispersed very well.

[0016] Preferably, the molar ratio of composite quantum dots to polar ligands in the stock solution containing composite quantum dots in step (1) is 1:(3-8), for example, it can be 1:3, 1:4, 1:5, 1:6, 1:7 or 1:8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the wavelength of the blue light in step (2) is 425nm-475nm, for example, it can be 425nm, 430nm, 440nm, 450nm, 460nm, 470nm or 475nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] This invention uses blue light of a specific wavelength for irradiation. If the wavelength of the blue light used is too large or too small, it will affect the excitation effect of the quantum dots, thereby affecting the quantum yield of the quantum dots.

[0019] Preferably, the power of the blue light in step (2) is 400 mW / cm². 2 -600mW / cm 2 For example, it could be 400mW / cm 2 450mW / cm 2 500mW / cm 2 550mW / cm 2 Or 600mW / cm 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0020] Preferably, the temperature of the polar shell coating reaction in step (2) is 160℃-200℃, for example, 160℃, 170℃, 180℃, 190℃ or 200℃, and the time is 1.5h-2.5h, for example, 1.5h, 2.0h or 2.5h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the polar shell coating reaction in step (2) is carried out in a nitrogen atmosphere and / or an inert gas.

[0022] Preferably, the post-processing in step (2) includes the following steps: after the polar shell coating reaction is completed, the temperature is lowered, then a polar solvent is added to the system, the supernatant is taken after centrifugation, and a non-polar solvent is added to the supernatant to precipitate quantum dots to obtain the polar quantum dots.

[0023] Preferably, the temperature is reduced to 70℃-90℃, for example, 70℃, 75℃, 80℃, 85℃ or 90℃, and the volume ratio of the supernatant to the nonpolar solvent is 2:(1-1.5), for example, 2:1.5, 2:1 or 2:1.25, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the preparation of the inorganic transition layer and the inorganic outer shell layer in step (1) is also carried out under blue light irradiation.

[0025] This invention prepares an inorganic transition layer and an inorganic outer shell layer under blue light irradiation, which can further improve the quantum yield of quantum dots.

[0026] Preferably, the method for preparing quantum dot nuclei in step (1) includes the following steps: mixing a first Cd source, a Zn source, an organic ligand and a solvent, and then adding a first Se source to carry out a nucleation reaction to obtain a solution containing quantum dot nuclei.

[0027] Preferably, the molar ratio of the first Cd source, Zn source, and first Se source is 1:(35-45):(2-4), for example, it can be 1:35:3, 1:45:4, or 1:30:2. The ratio of the molar amount of the first Cd source, the volume of the organic ligand, and the volume of the solvent is 1 mmol:(25-35) mL:(55-65) mL, for example, it can be 1 mmol:25 mL:65 mL, 1 mmol:30 mL:60 mL, or 1 mmol:35 mL:55 mL, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the temperature of the mixing reaction is 110℃-130℃, for example, 110℃, 115℃, 120℃, 125℃ or 130℃, and the time is 20min-40min, for example, 20min, 25min, 30min, 35min or 40min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the nucleation reaction temperature is 280℃-320℃, for example, 280℃, 300℃ or 320℃, and the time is 30min-40min, for example, 30min, 35min or 40min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the method for sequentially preparing the inorganic transition layer and the inorganic outer shell layer in step (1) includes the following steps: under blue light irradiation, a second Se source is added to a solution containing quantum dot nuclei to grow an inorganic transition layer, and then a second Cd source and S source are added to grow an inorganic outer shell layer to obtain a stock solution containing composite quantum dots.

[0031] Preferably, the molar ratio of the first Cd source, the second Se source, the second Cd source, and the S source is 1:(5-15):(4-8):(4-8), for example, it can be 1:5:5:4, 1:10:4:8 or 1:15:8:6, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the temperature for growing the inorganic transition layer is 280℃-320℃, for example, 280℃, 300℃ or 320℃, and the time is 25min-35min, for example, 25min, 30min or 35min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the temperature for growing the inorganic outer shell layer is 280℃-320℃, for example, 280℃, 300℃ or 320℃, and the time is 25min-35min, for example, 25min, 30min or 35min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] For example, the polar solvent of the present invention may be PGMEA or ethanol, and the nonpolar solvent may be heptane; the first Cd source includes CdO (cadmium oxide), the Zn source includes ZnAc (zinc acetate), the organic ligand includes OA (oleic acid), the solvent includes ODE (octadecene), the first Se source includes Se-TOP (selenium-tri-n-octylphosphine), the second Se source includes Se-TOP (selenium-tri-n-octylphosphine), the second Cd source includes Cd(OA)2 (cadmium oleate), and the S source includes S-TOP (sulfur-tri-n-octylphosphine).

[0035] In a second aspect, the present invention provides a polar quantum dot, which is prepared by the preparation method described in the first aspect.

[0036] Thirdly, the present invention provides an application of polar quantum dots as described in the second aspect, the application comprising dissolving polar quantum dots in a polar solvent to prepare photoresist.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] This invention involves coating the surface of a quantum dot core with an inorganic transition layer and an inorganic outer shell layer, then directly subjecting the original solution containing composite quantum dots and a polar ligand to a polar shell coating reaction. The polar ligand contains thiol groups, which act as S source anchors and polarly bind with metal ions to form the outermost polar shell layer. Simultaneously, the polar shell layer is coated under blue light irradiation. Since blue light irradiation can continuously excite the quantum dots, the radiative recombination portion becomes more active, while the non-radiative recombination portion decreases. Therefore, the quantum yield of the quantum dots can be improved, resulting in high-brightness quantum dots that are directly dissolved in a polar solvent. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0040] Example 1

[0041] This embodiment provides a method for preparing polar quantum dots, the method comprising the following steps:

[0042] Take 1 mmol of CdO, 40 mmol of ZnAc, 30 mL of OA and 60 mL of ODE and put them into a 250 mL three-necked flask. Keep it at 120 °C and N2 circulation for 30 min. Then raise the temperature to 300 °C and inject 3 mmol of Se-TOP to carry out the nucleation reaction for 35 min.

[0043] After nucleation, the blue light panel is turned on, with a wavelength of 450nm and a power of 500mW / cm. 2 Under blue light irradiation, 10 mmol of Se-TOP was injected and reacted at 300℃ for 30 min to generate a ZnSe layer. Then, 6 mmol each of Cd(OA)2 and S-TOP were injected and reacted at 300℃ for 30 min to form an inorganic shell. Finally, 5 mmol of ethyl mercaptopropionate was added and stirred at 180℃ for 2 h to generate a polar shell. The temperature was then lowered to 80℃, and ethanol (volume ratio of stock solution to ethanol was 1:1) was added to the original solution. The solution was then centrifuged and the supernatant was collected. Heptane (volume ratio of supernatant to heptane was 2:1) was added to the supernatant to precipitate quantum dots, thus obtaining the polar quantum dots. The polar quantum dots can be directly dissolved in a polar solvent such as ethanol for use.

[0044] Example 2

[0045] This embodiment provides a method for preparing polar quantum dots, the method comprising the following steps:

[0046] Take 1 mmol of CdO, 35 mmol of ZnAc, 25 mL of OA and 55 mL of ODE and put them into a 250 mL three-necked flask. Keep it at 110 °C and N2 circulation for 40 min. Then raise the temperature to 320 °C and inject 2 mmol of Se-TOP to carry out the nucleation reaction for 30 min.

[0047] After nucleation, the blue light panel was turned on, with a wavelength of 425nm and a power of 4600mW / cm². 2 Under blue light irradiation, 5 mmol of Se-TOP was injected and reacted at 280℃ for 35 min to generate a ZnSe layer. Then, 4 mmol each of Cd(OA)2 and S-TOP were injected and reacted at 320℃ for 25 min to generate a shell. Finally, 3 mmol of ethyl mercaptopropionate was added and stirred at 160℃ for 2.5 h to generate a polar shell. The temperature was then lowered to 70℃, and ethanol was added to the original solution (the volume ratio of original solution to ethanol was 1:1). The solution was then centrifuged and the supernatant was collected. Heptane was added to the supernatant (the volume ratio of supernatant to heptane was 2:1.5) to precipitate quantum dots, thus obtaining the polar quantum dots. The polar quantum dots can be directly dissolved in a polar solvent such as ethanol for use.

[0048] Example 3

[0049] This embodiment provides a method for preparing polar quantum dots, the method comprising the following steps:

[0050] Take 1 mmol of CdO, 45 mmol of ZnAc, 35 mL of OA and 65 mL of ODE and put them into a 250 mL three-necked flask. Keep it at 130 °C and N2 circulation for 20 min. Then raise the temperature to 280 °C and inject 4 mmol of Se-TOP to carry out the nucleation reaction for 40 min.

[0051] After nucleation, the blue light panel is turned on, with a wavelength of 475nm and a power of 400mW / cm. 2 Under blue light irradiation, 15 mmol of Se-TOP was injected and reacted at 320℃ for 25 min to generate a ZnSe layer. Then, 8 mmol each of Cd(OA)2 and S-TOP were injected and reacted at 280℃ for 35 min to generate a shell. Finally, 8 mmol of ethyl mercaptopropionate was added and stirred at 200℃ for 1.5 h to generate a polar shell. The temperature was then lowered to 90℃, and ethanol (volume ratio of stock solution to ethanol was 1:1) was added to the original solution. The solution was then centrifuged and the supernatant was collected. Heptane (volume ratio of supernatant to heptane was 2:1) was added to the supernatant to precipitate quantum dots, thus obtaining the polar quantum dots. The polar quantum dots can be directly dissolved in a polar solvent such as ethanol for use.

[0052] Example 4

[0053] This embodiment provides a method for preparing polar quantum dots. The preparation method is the same as in Example 1, except that ethyl mercaptopropionate is replaced with mercaptopropionic acid in equal molar amounts.

[0054] Example 5

[0055] This embodiment provides a method for preparing polar quantum dots. The preparation method is the same as in Example 1, except that ethyl mercaptopropionate is replaced with 11-mercaptoundecylamine in equal molar amounts.

[0056] Example 6

[0057] This embodiment provides a method for preparing polar quantum dots. The preparation method is the same as in Embodiment 1, except that the wavelength of the blue light is 400 nm.

[0058] Example 7

[0059] This embodiment provides a method for preparing polar quantum dots. The preparation method is the same as in Embodiment 1, except that the wavelength of the blue light is 500 nm.

[0060] Example 8

[0061] This embodiment provides a method for preparing polar quantum dots. The method differs in that the blue light panel is not turned on after nucleation, but rather when 5 mmol of ethyl mercaptopropionate is added, thus allowing the polar shell to be illuminated at a wavelength of 450 nm and a power of 500 mW / cm². 2 Except for being generated under blue light irradiation, it is the same as in Example 1.

[0062] Comparative Example 1

[0063] This comparative example provides a method for preparing quantum dots, which is the same as in Example 1 except that ethyl mercaptopropionate is replaced with OA.

[0064] Comparative Example 2

[0065] This comparative example provides a method for preparing quantum dots, which is the same as in Example 1 except that ethyl mercaptopropionate is replaced with p-toluenethiophenol.

[0066] Comparative Example 3

[0067] This comparative example provides a method for preparing quantum dots. Except for not turning on the blue light panel and not irradiating with blue light, the preparation method is the same as in Example 1.

[0068] The quantum dot yields of the above embodiments and comparative examples are shown in Table 1:

[0069] Table 1

[0070]

[0071] As can be seen from Table 1 above:

[0072] As shown in Examples 1-3 and Comparative Examples 1-2, when the specific polar ligands of this invention are not used, the surface defects of quantum dots increase, reducing the quantum yield of quantum dots. As shown in Examples 1 and Comparative Example 3, the preparation of the shell layer in this invention is carried out under blue light irradiation, which makes the radiative recombination part more active, thereby further improving the quantum yield. As shown in Examples 1 and 4-5, the polar ligands of this invention are preferably thiol ester materials, which can further improve the quantum yield of quantum dots. As shown in Examples 1 and 6-7, the wavelength of the blue light in this invention affects the excitation effect of quantum dots, thereby affecting the quantum yield of quantum dots. As shown in Examples 1 and 8, this invention preferably uses blue light irradiation during the preparation of the inorganic transition layer and the inorganic shell layer, which is beneficial to further improve the quantum yield of quantum dots.

[0073] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing polar quantum dots, characterized in that, The preparation method includes the following steps: (1) Prepare a quantum dot core, and then prepare an inorganic transition layer and an inorganic outer shell layer on the surface of the quantum dot core to obtain a stock solution containing composite quantum dots; (2) Under blue light irradiation, the original solution containing composite quantum dots and the polar ligands in step (1) are mixed to carry out a polar shell coating reaction. After the polar shell coating reaction is completed, post-processing is carried out to obtain the polar quantum dots. The polar ligand has a chain structure and contains a first group and a second group. The first group is a thiol group, and the second group is selected from any one or a combination of at least two of ester, carboxyl, or amino groups.

2. The preparation method according to claim 1, characterized in that, The polar ligand in step (2) includes any one or a combination of at least two of ethyl mercaptopropionate, mercaptopropionic acid, mercaptoacetic acid, 11-mercaptoundecylamine or 3-mercaptopropylamine; And / or, the molar ratio of composite quantum dots to polar ligands in the stock solution containing composite quantum dots in step (1) is 1:(1-3).

3. The preparation method according to claim 1 or 2, characterized in that, The wavelength of the blue light mentioned in step (2) is 425nm-475nm; And / or, the power of the blue light in step (2) is 400 mW / cm². 2 -600mW / cm 2 .

4. The preparation method according to claim 1 or 2, characterized in that, The polar shell coating reaction in step (2) is carried out at a temperature of 160℃-200℃ for 1.5h-2.5h. And / or, the polar shell coating reaction in step (2) is carried out in a nitrogen atmosphere and / or an inert gas.

5. The preparation method according to claim 1 or 2, characterized in that, The post-processing in step (2) includes the following steps: after the polar shell coating reaction is completed, the temperature is lowered, then a polar solvent is added to the system, the supernatant is taken after centrifugation, and a non-polar solvent is added to the supernatant to precipitate quantum dots to obtain the polar quantum dots; The temperature is lowered to 70℃-90℃, and the volume ratio of the supernatant to the nonpolar solvent is 2:(1-1.5).

6. The preparation method according to claim 1 or 2, characterized in that, The preparation of the inorganic transition layer and the inorganic outer shell layer in step (1) is also carried out under blue light irradiation.

7. The preparation method according to claim 1 or 2, characterized in that, The method for preparing quantum dot nuclei in step (1) includes the following steps: mixing a first Cd source, a Zn source, an organic ligand and a solvent, and then adding a first Se source to carry out a nucleation reaction to obtain a solution containing quantum dot nuclei; The molar ratio of the first Cd source, Zn source and the first Se source is 1:(35-45):(2-4), and the molar amount of the first Cd source, the volume of the organic ligand and the volume of the solvent are 1 mmol:(25-35) mL:(55-65) mL. The mixing reaction was carried out at a temperature of 110℃-130℃ for 20min-40min. The nucleation reaction is carried out at a temperature of 280℃-320℃ for a time of 30min-40min.

8. The preparation method according to claim 7, characterized in that, The method for sequentially preparing the inorganic transition layer and the inorganic outer shell layer in step (1) includes the following steps: under blue light irradiation, a second Se source is added to a solution containing quantum dot nuclei to grow an inorganic transition layer, and then a second Cd source and S source are added to grow an inorganic outer shell layer to obtain a stock solution containing composite quantum dots; The molar ratio of the first Cd source, the second Se source, the second Cd source, and the S source is 1:(5-15):(4-8):(4-8); The temperature for growing the inorganic transition layer is 280℃-320℃, and the time is 25min-35min; The temperature for growing the inorganic outer shell is 280℃-320℃, and the time is 25min-35min.

9. A polar quantum dot, characterized in that, The polar quantum dots are prepared by the preparation method according to any one of claims 1-8.

10. An application of the polar quantum dot as described in claim 9, characterized in that, The applications include preparing photoresists by dissolving polar quantum dots in polar solvents.

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