ZnOS / ZnO nanocrystal and preparation method thereof, and light-emitting device

Abstract

The present invention discloses ZnOS / ZnO nanocrystals, their preparation methods, and light-emitting devices. The ZnOS / ZnO nanocrystals comprise a ZnOS core and a ZnO shell coating the surface of the ZnOS core. By subjecting the ZnO nanocrystals to a certain degree of sulfurization and then coating the ZnOS core with a ZnO shell, the resulting ZnOS / ZnO nanocrystals are relatively large in size and exhibit excellent stability, resisting aggregation and aging. Furthermore, since the sulfur in the ZnOS core can regulate the energy band, wide-bandgap nanocrystals are more readily obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of ZnOS / ZnO nanocrystals and preparation method thereof, and the luminescent device of application of the ZnOS / ZnO nanocrystals. BACKGROUND

[0002] ZnO is a common II-VI semiconductor compound, and the band gap of its material can reach 3.34 eV, which is a typical direct band gap wide band gap semiconductor material. The solution ZnO nanocrystals synthesized by sol-gel method have the characteristics of low temperature, environmental protection, economy and suitable for solution film forming. However, due to its small particle size, it has a large specific surface area, which leads to unstable zinc oxide solution, solution aggregation and growth. Generally, ZnO nanocrystals of 5 nm will be unstable and prone to ripening and growth. SUMMARY

[0003] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a kind of ZnOS / ZnO nanocrystals and preparation method thereof, solve the problem of unstable small size ZnO nanocrystals in the prior art, easy to ripen and grow.

[0004] According to one aspect of the present application, a kind of ZnOS / ZnO nanocrystals is provided, including ZnOS core and ZnO shell layer coated on the surface of the above-mentioned ZnOS core.

[0005] Further, the size of the above-mentioned ZnOS / ZnO nanocrystals is 2-10 nm.

[0006] According to another aspect of the present application, a kind of ZnOS / ZnO nanocrystal preparation method is provided, comprising the following steps:

[0007] S1, providing ZnO nanocrystals;

[0008] S2, dispersing the above-mentioned ZnO nanocrystals in solvent, then adding sulfur source, and obtaining ZnOS core solution by reaction;

[0009] S3, adding zinc source to the above-mentioned ZnOS core solution, adding alkaline material after a period of time, and obtaining ZnOS / ZnO nanocrystals after reaction.

[0010] Further, the above-mentioned sulfur source in the above-mentioned step S2 is selected from one or more of the following: sulfide, thiol with carbon chain length of 2-6, mercapto carboxylic acid with carbon chain length of 2-6.

[0011] Further, the above-mentioned zinc source in the above-mentioned step S3 is selected from one or more of the following: zinc carboxylate, zinc nitrate, zinc chloride.

[0012] Further, the basic substance in the step S3 is a basic compound or a basic mixture including hydroxyl in chemical composition, preferably, the basic substance is selected from one or more of tetramethylammonium hydroxide, sodium hydroxide, potassium hydroxide, lithium hydroxide.

[0013] Further, the molar ratio of the ZnO nanocrystal to the sulfur source in the step S2 is (10 -6 :(0.05-1).

[0014] Further, the molar ratio of the sulfur source in the step S2 to the zinc source in the step S3 is (0.1-0.8):1.

[0015] According to still another aspect of the present application, there is further provided a ZnOS / ZnO nanocrystal prepared by the above nanocrystal preparation method of the present application.

[0016] According to another aspect of the present application, there is further provided a light emitting device comprising the above ZnOS / ZnO nanocrystal of the present application.

[0017] Compared with the prior art, the present application has the beneficial effects that: the present application obtains the ZnOS / ZnO nanocrystal with larger size by sulfidizing the ZnO nanocrystal to a certain extent and then including the ZnO shell layer outside the ZnOS core, which has good stability and is not easy to aggregate and mature, and in addition, the S in the ZnOS core can play a role in adjusting the energy band, so that the nanocrystal with wide band gap is more easily obtained. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 UV absorption curves of the ZnOS / ZnO nanocrystal of Example 1 and the ZnO nanocrystal of Comparative Example 1 at different time periods;

[0019] Figure 2 An electron microscope photo of the ZnO nanocrystal of Comparative Example 1.

[0020] Figure 3 An electron microscope photo of the ZnOS / ZnO nanocrystal of Example 1. DETAILED DESCRIPTION

[0021] Hereinafter, the present application will be further described in conjunction with specific embodiments, and it should be noted that the following described embodiments or technical features can be combined in any manner to form new embodiments without conflict.

[0022] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0023] The present application provides a ZnOS / ZnO nanocrystal, which comprises a ZnOS core and a ZnO shell layer coated on the surface of the ZnOS core.

[0024] The present application first obtains a ZnO nanocrystal with a small size, and then sulfurizes the ZnO nanocrystal to a certain extent to adjust the energy band, so as to obtain a ZnOS core after sulfurization, and then continue to grow a ZnO shell layer on the surface of the ZnOS core to obtain a suitable energy band structure. Since a ZnO shell layer is continued to grow outside the ZnOS core, the size of the ZnOS / ZnO nanocrystal will not be too small, and the problem of instability and easy Ostwald ripening of the small-size ZnO nanocrystal can be avoided.

[0025] In some embodiments, the size of the ZnOS / ZnO nanocrystal of the present application is 2-10 nm.

[0026] The present application also provides a preparation method of a ZnOS / ZnO nanocrystal, comprising the following steps:

[0027] S1, providing a ZnO nanocrystal;

[0028] S2, dispersing the above ZnO nanocrystal in a solvent, then adding a sulfur source, and reacting to obtain a ZnOS core solution;

[0029] S3, adding a zinc source to the above ZnOS core solution, then adding a basic substance after a period of time, and reacting to obtain a ZnOS / ZnO nanocrystal.

[0030] Step S1 provides a ZnO nanocrystal, step S2 sulfurizes the ZnO nanocrystal to obtain a ZnOS core, and then in step S3, a zinc source is first added, so that the zinc source is adsorbed on the surface of the ZnOS core and reacts with S, and then a basic substance is added, and a ZnO shell layer is grown outside the ZnOS core.

[0031] The application obtains the ZnOS / ZnO nanocrystals with larger size by sulfidizing the ZnO nanocrystals to a certain extent, then coating a ZnO shell outside the ZnOS core, which has good stability and is not easy to aggregate and mature, and the S in the ZnOS core can adjust the energy band, so that the nanocrystals with wide band gap are more easily obtained.

[0032] In some embodiments, the size of the ZnO nanocrystals in step S1 is 1-9 nm, and the size of the ZnOS / ZnO nanocrystals in step S3 is 2-10 nm.

[0033] In some embodiments, the ZnO nanocrystals in step S1 are prepared by sol-gel method. The ZnO nanocrystals can be prepared by dissolving a zinc source in a solvent, adding an alkaline substance after heating for a period of time, and obtaining the ZnO nanocrystals after reaction. The detailed preparation method of the ZnO nanocrystals is a prior art, and the application will not be described in detail. It should be noted that the ZnO nanocrystals in step S1 can be prepared by other methods, as long as the size of the obtained ZnO nanocrystals is appropriate.

[0034] In some embodiments, the sulfur source in step S2 is selected from one or more of sulfides, mercaptans with carbon chain length of 2-6, and mercapto carboxylic acids with carbon chain length of 2-6.

[0035] In some embodiments, the solvent in step S2 is selected from, but not limited to, one or more of dimethyl sulfoxide, methanol, ethanol, and N,N-dimethylformamide. The selected solvent can better disperse the ZnO nanocrystals.

[0036] In some embodiments, the zinc source in step S3 is selected from one or more of zinc carboxylate, zinc nitrate, and zinc chloride.

[0037] In some embodiments, the alkaline substance in step S3 is an alkaline compound or an alkaline mixture that includes hydroxide in chemical composition. Further, the alkaline substance is selected from one or more of tetramethylammonium hydroxide, sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0038] In some embodiments, a ligand is further added to the ZnOS core solution in step S3, and the ligand is selected from one or more of carboxylic acids, mercaptans, and alcohol amines.

[0039] In some embodiments, the molar ratio of the ZnO nanocrystals to the sulfur source in step S2 is 10 -6 :0.05-1.

[0040] In some embodiments, the molar ratio of the sulfur source in step S2 to the zinc source in step S3 is 0.1-0.8:1.

[0041] The application further provides a light-emitting device comprising the ZnOS / ZnO nanocrystal. It can be understood that the light-emitting device includes but is not limited to an LED, a quantum dot light-emitting diode (QLED), and an organic light-emitting diode (OLED) display panel.

[0042] Example 1

[0043] Preparation of ZnO nanocrystal: 1 mmol of zinc acetate dihydrate was dissolved in 30 mL of dimethyl sulfoxide, stirred at 100 ℃ for 1 h, then cooled to 60 ℃, and 2 mmol of 25% tetramethylammonium hydroxide alcohol solution was added dropwise, and the stirring was continued for 1 h to obtain ZnO nanocrystal. Then, 90 mL of ethyl acetate was added to the solution to precipitate and purify the ZnO nanocrystal.

[0044] Preparation of ZnOS / ZnO nanocrystal: the purified ZnO nanocrystal was dispersed in 30 mL of dimethyl sulfoxide, 0.1 mL of 20% ammonium sulfide aqueous solution was added, and the stirring was continued at room temperature for 20 min to obtain a ZnOS core solution. Then, 0.5 mmol of ethanolamine and 1 mmol of zinc acetate were added, and the stirring was continued at 30 ℃ for 20 min. Then, 1.5 mmol of 25% tetramethylammonium hydroxide alcohol solution was added dropwise, and the reaction was continued for 1 h to obtain ZnOS / ZnO nanocrystal.

[0045] Preparation of quantum dot light-emitting device:

[0046] (1) Cleaning of ITO glass: the ITO glass sheet with numbers engraved on the back was placed in a glass dish containing an ethanol solution, and the ITO surface was scrubbed clean with a cotton swab. The glass was sequentially ultrasonically cleaned with acetone, deionized water, and ethanol for 10 min each, and then dried with a nitrogen gun. Finally, the cleaned ITO glass sheet was placed in an oxygen plasma for 10 min of additional cleaning.

[0047] (2) Hole injection layer: the cleaned ITO glass sheet was spin-coated with Pedot:PSS in air at a speed of 3000 r / min for 45 s. After spin-coating, the sheet was annealed in air at a temperature of 150 ℃ for 30 min. After annealing, the sheet was quickly transferred to a nitrogen atmosphere glove box.

[0048] (3) Hole transport layer: the hole transport layer of 8-10 mg / mL TFB was spin-coated on the hole injection layer at a speed of 2000 r / min for 45 s. After spin-coating, the sheet was annealed in the glove box at a temperature of 150 ℃ for 30 min.

[0049] (4) Quantum dot light-emitting layer: green quantum dots (CdZnSeS / ZnS core-shell quantum dots, optical concentration of 30-40 at 350 nm) are dissolved in octane solvent, and the quantum dot solution is continuously spin-coated on the hole transport layer at a spin-coating speed of 2000 r / min and a spin-coating time of 45 seconds. After spin-coating, the next layer can be spin-coated without annealing;

[0050] (5) Electron transport layer: the solution of ZnOS / ZnO nanocrystals prepared in the foregoing is spin-coated on the quantum dot light-emitting layer at a speed of 2000 r / min for 45 seconds;

[0051] (6) Ag electrode: the prepared sample piece is placed in a vacuum cavity, and a top electrode is evaporated. The evaporation rate is controlled in the range of 0.1-0.2 nm / s in the first 10 nm, and the evaporation rate is increased to about 0.5-0.6 nm / s after 10 nm. The thickness of the silver electrode is 100 nm.

[0052]

Example 2

[0053] Preparation of ZnO nanocrystals: 1 mmol of zinc acetate dihydrate is dissolved in 30 mL of dimethyl sulfoxide, stirred at 100°C for 1 h, then cooled to 60°C, and 2 mmol of 25% tetramethylammonium hydroxide alcohol solution is added dropwise. Continue to stir for 1 h to prepare ZnO nanocrystals. Then 90 mL of ethyl acetate is added to the solution for precipitation, and the purified ZnO nanocrystals are obtained.

[0054] Preparation of ZnOS / ZnO nanocrystals: the purified ZnO nanocrystals are dispersed in 30 mL of dimethyl sulfoxide, 0.1 mL of ethanethiol is added, and stirred at room temperature for 20 min to obtain a ZnOS core solution. Then 0.5 mmol of ethanolamine and 1 mmol of zinc chloride are added, and stirred at 30°C for 20 min. Then 1.5 mmol of 25% tetramethylammonium hydroxide alcohol solution is added dropwise, and reacted for 1 h to obtain ZnOS / ZnO nanocrystals.

[0055]

Example 3

[0056] Preparation of ZnO nanocrystals: 1 mmol of zinc acetate dihydrate is dissolved in 30 mL of dimethyl sulfoxide, stirred at 100°C for 1 h, then cooled to 60°C, and 2 mmol of 25% tetramethylammonium hydroxide alcohol solution is added dropwise. Continue to stir for 1 h to prepare ZnO nanocrystals. Then 90 mL of ethyl acetate is added to the solution for precipitation, and the purified ZnO nanocrystals are obtained.

[0057] ​​Preparation of ZnOS / ZnO nanocrystals: The purified ZnO nanocrystals were dispersed in 30 mL of dimethyl sulfoxide, 0.1 mL of mercaptopropionic acid was added, and stirring was performed at room temperature for 20 min to obtain a ZnOS core solution. Then, 0.5 mmol of ethanolamine and 1 mmol of zinc nitrate were added, and stirring was performed at 30°C for 20 min. Subsequently, 1.5 mmol of a 25% potassium hydroxide solution was added dropwise, and reaction was performed for 1 h to obtain ZnOS / ZnO nanocrystals.

[0058] Example 4

[0059] Preparation of ZnO nanocrystals: 1 mmol of zinc acetate dihydrate was dissolved in 30 mL of dimethyl sulfoxide, and stirring was performed at 100°C for 1 h. Then, the solution was cooled to 60°C, 2 mmol of a 25% tetramethylammonium hydroxide alcohol solution was added dropwise, and stirring was performed for 1 h to obtain ZnO nanocrystals. Subsequently, 90 mL of ethyl acetate was added to the solution to precipitate the product, and the purified ZnO nanocrystals were obtained.

[0060] Preparation of ZnOS / ZnO nanocrystals: The purified ZnO nanocrystals were dispersed in 30 mL of dimethyl sulfoxide, 0.1 mL of a 20% sodium sulfide aqueous solution was added, and stirring was performed at room temperature for 20 min to obtain a ZnOS core solution. Then, 0.5 mmol of ethanolamine and 1 mmol of zinc acetate were added, and stirring was performed at 30°C for 20 min. Subsequently, 1.5 mmol of a 25% sodium hydroxide solution was added dropwise, and reaction was performed for 1 h to obtain ZnOS / ZnO nanocrystals.

[0061] Comparative Example 1

[0062] Preparation of ZnO nanocrystals: 1 mmol of zinc acetate dihydrate was dissolved in 30 mL of dimethyl sulfoxide, and stirring was performed at 100°C for 1 h. Then, the solution was cooled to 60°C, 2 mmol of a 25% tetramethylammonium hydroxide alcohol solution was added dropwise, and stirring was performed for 1 h to obtain ZnO nanocrystals. Subsequently, 90 mL of ethyl acetate was added to the solution to precipitate the product, and the purified ZnO nanocrystals were obtained.

[0063] The ZnOS / ZnO nanocrystals prepared in Example 1 were purified, and an ethanol solution having a concentration of 30 mg / mL was prepared. The solution was stored in air, and the change in UV absorption was measured at different time intervals. The results are shown in FIG. 1. Figure 1 The ZnO nanocrystals prepared according to the method of Comparative Example 1 were purified, and an ethanol solution having a concentration of 30 mg / mL was prepared. The solution was stored in air, and the change in UV absorption was measured at different time intervals. The results are shown in FIG. 2. Figure 1 . Figure 2 FIG. 1 is an electron microscope photograph of the ZnOS / ZnO nanocrystals of Example 1. Figure 3 FIG. 2 is an electron microscope photograph of the ZnO nanocrystals of Comparative Example 1. FIG. 3 is an electron microscope photograph of the ZnOS / ZnO nanocrystals of Example 2.

[0064] From Figure 1 It can be seen that the absorption peak of the ZnO nanocrystal is at 330 nm, and the absorption peak of the ZnOS / ZnO nanocrystal is at 308 nm, and the band gap of the ZnOS / ZnO nanocrystal is wider than that of the ZnO nanocrystal. In addition, compared with Figure 2 and Figure 3 It can be seen that the average size of the ZnOS / ZnO nanocrystal prepared in Embodiment 1 of the present application is larger, and therefore the ZnOS / ZnO nanocrystal is more stable and is not prone to ripening and growing.

[0065] The above embodiments are only preferred embodiments of the present application, and cannot be used to limit the scope of protection of the present application, and any non-essential changes and substitutions made by those skilled in the art on the basis of the present application are within the scope of protection of the present application.

Claims

1. A method for preparing ZnOS / ZnO nanocrystals, characterized in that: The following steps are involved: S1, providing ZnO nanocrystals; S2, dispersing the ZnO nanocrystals in a solvent, then adding a sulfur source to react to obtain a ZnOS core solution, wherein the solvent is selected from one or more of the following: dimethyl sulfoxide, methanol, ethanol, N,N-dimethylformamide; the molar ratio of the ZnO nanocrystals to the sulfur source in step S2 is 10 -6 :(0.05-1); the molar ratio of the sulfur source in step S2 to the zinc source in step S3 is (0.1-0.8):1; the sulfur source in step S2 is selected from one or more of the following: ammonium sulfide, sodium sulfide, a mercaptan with a carbon chain length of 2-6, and a mercaptocarboxylic acid with a carbon chain length of 2-6; S3, adding a zinc source to the ZnOS core solution, allowing the zinc source to be adsorbed on the surface of the ZnOS core and react with S for a period of time, and then adding an alkaline substance to obtain ZnOS / ZnO nanocrystals after the reaction.

2. The method for preparing nanocrystals according to claim 1, wherein: The zinc source in step S3 is selected from one or more of the following: zinc carboxylate, zinc nitrate, and zinc chloride.

3. The method for preparing nanocrystals according to claim 1, wherein: The alkaline substance in step S3 is an alkaline compound or alkaline mixture containing hydroxide in chemical composition.

4. The method for preparing nanocrystals according to claim 3, wherein: The alkaline substance is selected from one or more of the following: tetramethylammonium hydroxide, sodium hydroxide, potassium hydroxide, and lithium hydroxide.

5. A ZnOS / ZnO nanocrystal, characterized in that: The nanocrystal is prepared by the nanocrystal preparation method according to any one of claims 1 to 4.

6. The nanocrystal according to claim 5, characterized in that The size of the ZnOS / ZnO nanocrystals is 2-10 nm.

7. A light emitting device, characterized in that: Comprising the ZnOS / ZnO nanocrystals according to claim 5 or 6.

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