Quantum dot and electroluminescent device

Abstract

The present disclosure relates to a quantum dot and an electroluminescent device. The quantum dot comprises an inner core, and at least one inner shell layer unit and an outer shell layer which successively coat the surface of the inner core; the material of the inner core is ZnxCd1-xS, x being 0-1, and the size of the inner core being not less than 3 nm; each inner shell layer unit comprises a first inner shell layer and a second inner shell layer in a direction away from the inner core; the material of the first inner shell layer is selected from among at least one of ZnyCd1-ySS and ZnSeS, y being x-1, and x＜y＜1; the material of the second inner shell layer is selected from among at least one of ZnZCd1-zS, ZnCdSe and ZnCdSeS, z＜y, and the band gap of the first inner shell layer being greater than the band gap of the inner core and the band gap of the second inner shell layer; the material of the outer shell layer is selected from among at least one of ZnCdS, ZnSeS and ZnS, the band gap of the outer shell layer being greater than or equal to the band gap of the first inner shell layer. The present disclosure designs the size and core-shell structure of quantum dots, so that the photoluminescent property of the quantum dots is more resistant to the damage effect of accumulated charges, thereby providing QLEDs with longer lifespans.

Description

Quantum dots and electroluminescent devices Technical Field

[0001] The present disclosure relates to the field of display technology, and in particular to a quantum dot and an electroluminescent device.

[0002] Background of the Invention

[0003] Active Matrix Quantum Light-Emitting Diode (AMQLED) display technology is widely regarded as the next generation display technology due to its wide color gamut, high color purity, high brightness, low power consumption, high response speed, and flexibility.

[0004] Currently, red, green, and blue QLEDs are approaching or reaching their theoretical efficiency limits. Their lifespans are also sufficient to meet commercialization requirements. The only bottleneck is the insufficient lifespan of blue QLEDs. Therefore, addressing the lifespan issue of blue QLEDs is crucial for promoting QLED commercialization.

[0005] Summary of the Invention

[0006] Based on this, it is necessary to provide a quantum dot and electroluminescent device to address the problem of how to improve the lifespan of blue light QLED.

[0007] A quantum dot comprising a core, at least one group of inner shell units and an outer shell layer sequentially coated on the surface of the core;

[0008] The material of the core is Zn x Cd 1-x S, wherein x is 0 to 1; the size of the core is not less than 3 nm;

[0009] Each group of inner shell units includes a first inner shell and a second inner shell in a direction away from the inner core, wherein the band gap of the first inner shell is larger than the band gap of the inner core and the band gap of the second inner shell;

[0010] The band gap of the outer shell layer is greater than or equal to the band gap of the first inner shell layer.

[0011] The quantum dots using the technical solution disclosed herein have a larger core size, which can reduce the destructive effect of accumulated charge on the quantum dot exciton transition when QLED charges accumulate, thereby maintaining a high photoluminescence quantum yield for a longer period of time and helping to improve the lifespan of the QLED. The first inner shell has a larger band gap than the core, which can effectively confine electrons or holes to the surface of the core, resulting in a high photoluminescence quantum yield for the quantum dots disclosed herein. The first inner shell has a larger band gap than the second inner shell, which can more efficiently allow charge carriers to enter the quantum dot through the tunneling process, thereby improving the charge balance level of the QLED and helping to achieve high device efficiency. The outer shell has the widest band gap, which can enable the quantum dot to have a high photoluminescence quantum yield and stability, further improving the lifespan of the QLED. Therefore, by designing the size of the quantum dot and the core-shell structure, the present disclosure achieves a quantum dot whose photoluminescence properties are more resistant to the destructive effects of accumulated charge, thereby extending the lifespan of the QLED.

[0012] Experimental verification shows that the electroluminescent device disclosed in the present invention has high efficiency and lifespan, and is suitable for wide application.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG1 is a schematic structural diagram of a quantum dot according to an embodiment of the present disclosure;

[0015] FIG2 is a schematic diagram of the band gap of quantum dots according to one embodiment of the present disclosure;

[0016] FIG3 is a schematic structural diagram of a quantum dot according to another embodiment of the present disclosure;

[0017] FIG4 is a schematic structural diagram of an electroluminescent device according to an embodiment of the present disclosure;

[0018] FIG5 is a CE-L curve diagram of the QLED of Example 8 and Comparative Example 2 of the present disclosure;

[0019] FIG6 is a graph showing the LT curves of the QLEDs of Example 8 and Comparative Example 2 of the present disclosure.

[0020] Modes for Carrying Out the Invention

[0021] According to relevant research, blue QLEDs have a significant charge accumulation problem. The accumulated charge may exist in the hole transport layer, the light-emitting layer, or the electron transport layer. This accumulated charge causes complex physical and chemical processes, which is a key factor in the short lifespan of blue QLEDs. To this end, this disclosure proposes a quantum dot and electroluminescent device that can prevent the photoluminescence quantum yield (PLQY) of quantum dots from decreasing too quickly, thereby improving the lifespan of blue QLEDs.

[0022] 1 and 2 , a quantum dot 100 according to an embodiment of the present disclosure includes a core 110, at least one group of inner shell units 120 and an outer shell 130 sequentially coated on the surface of the core 110. Specifically, in this embodiment, the number of groups of the inner shell units 120 is one.

[0023] The material of the core 110 is Zn x Cd 1-x S, where x is 0 to 1; the size of the core 110 is no less than 3 nm. Here, x is preferably greater than 0 and less than 1. "Size" in this disclosure generally refers to diameter. The larger size of the core 110 in the quantum dot 100 of this embodiment reduces the destructive effects of accumulated charge on quantum dot exciton transitions when QLED charge accumulates, thereby maintaining a high photoluminescence quantum yield for a longer period of time and helping to improve the QLED lifespan.

[0024] The inner shell unit 120 includes a first inner shell 121 and a second inner shell 122, extending away from the core 110. The band gap of the first inner shell 121 is larger than that of the core 110 and the second inner shell 122. The larger band gap of the first inner shell 121 than that of the core 110 effectively confines electrons or holes to the surface of the core 110, enabling the quantum dot 100 of this embodiment to have a high photoluminescence quantum yield, reaching over 80%. Furthermore, the larger band gap of the first inner shell 121 than that of the second inner shell 122 allows charge carriers to more efficiently enter the quantum dot 100 through tunneling, thereby improving the charge balance of the QLED and contributing to high device efficiency.

[0025] The band gap of the outer shell 130 is greater than or equal to the band gap of the first inner shell 121. In this embodiment, the band gap of the outer shell 130 is greater than or equal to the band gap of the first inner shell 121, which enables the quantum dots to have a high photoluminescence quantum yield and stability, further improving the lifespan of the QLED. Stability refers to both photostability and chemical stability.

[0026] Based on the aforementioned embodiment, the size of the core 110 is 3 nm to 15 nm. In this case, the core 110 size can be kept relatively large to reduce the destructive effects of accumulated charge on quantum dot exciton transitions when the QLED charges accumulate, thereby maintaining a high photoluminescence quantum yield for a longer period of time and helping to improve the QLED lifespan. This also prevents the core 110 size from being too large, which can affect wavelength requirements and the selection of the inner shell unit 120 and outer shell 130. Furthermore, the core 110 size can be, for example, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, or 15 nm.

[0027] Based on the aforementioned embodiment, the size of quantum dot 100 is 10 nm to 30 nm. The size of quantum dot 100 is the sum of the size of core 110, the thickness of at least one set of inner shell units 120, and the thickness of outer shell 130. In this case, quantum dot 100 can achieve more stable luminous efficiency and effective charge injection under charge accumulation conditions.

[0028] Based on the aforementioned embodiment, the thicknesses of the first inner shell layer 121, the second inner shell layer 122, and the outer shell layer 130 are all between 0.35 nm and 3.5 nm. The first inner shell layer 121, the second inner shell layer 122, and the outer shell layer 130 within these thickness ranges can repair defects on the surface of the core 110. Furthermore, the thicknesses of the first inner shell layer 121, the second inner shell layer 122, and the outer shell layer 130 can be, for example, 0.35 nm, 0.7 nm, 1.05 nm, 1.4 nm, 1.75 nm, 2.1 nm, 2.45 nm, 2.8 nm, 3.15 nm, or 3.5 nm.

[0029] Based on the aforementioned embodiment, the material of the core 110 is ZnxCd1-xS, where x is 0.2 to 0.7. In this case, the band gap of the core 110 can be reasonably matched with the band gaps of the inner shell unit 120 and the outer shell 130, which helps to achieve high device efficiency and device life. Furthermore, x in the material of the core 110 is 0.2, 0.3, 0.4, 0.5, 0.6, or 0.7.

[0030] Based on the above embodiment, the material of the core 110 is Zn x Cd 1-x S, where x is 0.4 to 0.6. In this case, the band gap of the core 110 is optimally matched with the band gaps of the inner shell unit 120 and the outer shell 130, which helps to obtain higher device efficiency and device life.

[0031] On the basis of the above embodiment, the material of the first inner shell layer 121 is selected from Zn y Cd 1-y At least one of S and ZnSeS, wherein y is x-1, and x<y<1; the material of the second inner shell layer 122 is selected from Zn z Cd 1-z At least one of S, ZnCdSe, and ZnCdSeS, where z < y; and the material of outer shell 130 is selected from at least one of ZnCdS, ZnSeS, and ZnS. In the quantum dot 100 of this embodiment, the lattice matching of the materials of core 110, first inner shell 121, second inner shell 122, and outer shell 130 can prevent collapse of quantum dot 100.

[0032] Based on the above embodiment, the material of the second inner shell layer 122 is Zn z Cd 1-z S, where z≥x. In this case, the band gap of the second inner shell layer 122 is larger than the band gap of the core 110, and the second inner shell layer 122 can still play a role in confining excitons in the core, which is conducive to obtaining high luminous efficiency.

[0033] Based on the aforementioned embodiment, the difference between the band gap of the first inner shell layer 121 and the band gap of the core 110 is 0.2 eV to 1 eV, the difference between the band gap of the first inner shell layer 121 and the band gap of the second inner shell layer 122 is 0.1 eV to 1 eV, and the difference between the band gap of the outer shell layer 130 and the band gap of the first inner shell layer 121 is 0.1 eV to 1 eV. In this case, the band gaps of the core 110, the first inner shell layer 121, the second inner shell layer 122, and the outer shell layer 130 are reasonably matched, which helps to achieve higher device efficiency and device life.

[0034] Based on the aforementioned embodiment, the surface of the quantum dot 100 has a ligand. The surface ligand of the quantum dot 100 can be an amino group, an organic phosphorus, a carboxylic acid or a thiol, etc. The surface ligand can make the quantum dot of the present disclosure have high PLQY and solubility.

[0035] On the basis of the above embodiment, the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.5 Cd 0.5 S, Zn 0.8 Cd 0.2 S, Zn 0.6 Cd 0.4 S and ZnS. Experimental verification shows that the quantum dot structure of this embodiment can enable the electroluminescent device to have high efficiency and lifespan.

[0036] On the basis of the above embodiment, the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.4 Cd 0.6 S, ZnSeS, ZnCdSe and ZnS. Experimental verification shows that the quantum dot structure of this embodiment can enable the electroluminescent device to have high efficiency and lifespan.

[0037] On the basis of the above embodiment, the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.2 Cd 0.8 S, ZnSeS, ZnCdSe and ZnS. Experimental verification shows that the quantum dot structure of this embodiment can enable the electroluminescent device to have high efficiency and lifespan.

[0038] On the basis of the above embodiment, the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.2 Cd 0.8 S, Zn 0.8 Cd 0.2 S, ZnCdSe and ZnS. Experimental verification shows that the quantum dot structure of this embodiment can enable the electroluminescent device to have high efficiency and lifespan.

[0039] On the basis of the above embodiment, the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.6 Cd 0.4 S, ZnSeS, ZnCdSe and ZnS. Experimental verification shows that the quantum dot structure of this embodiment can enable the electroluminescent device to have high efficiency and lifespan.

[0040] On the basis of the above embodiment, the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.7 Cd 0.3 S, ZnSeS, ZnCdSe and ZnS. Experimental verification shows that the quantum dot structure of this embodiment can enable the electroluminescent device to have high efficiency and lifespan.

[0041] In the above embodiment, the number of groups of inner shell units is one, but in the quantum dots disclosed herein, the number of groups of inner shell units is not limited thereto, and may also be two or more groups.

[0042] 3 , a quantum dot 200 according to another embodiment of the present disclosure includes a core 210, an inner shell unit 220 and an outer shell 230 sequentially covering the surface of the core 210. The inner shell unit 220 includes a first inner shell 221 and a second inner shell 222 in a direction away from the core 210.

[0043] Unlike the quantum dot 100 of the previous embodiment, the quantum dot 200 of this embodiment includes two groups of inner shell units 220. The materials for the first inner shell layer 221 and the second inner shell layer 222 of each group of inner shell units 220 remain the same as those previously described, but their thicknesses are reduced. For example, the total thickness of the two groups of inner shell units 220 is the same as the total thickness of one inner shell unit in the previous embodiment.

[0044] On the basis of the above embodiment, the materials of the core 210, the first inner shell 221, the second inner shell 222, the first inner shell 221, the second inner shell 222 and the outer shell 230 from the core 210 to the outer shell 230 are Zn, 0.5 Cd 0.5 S, Zn0.8 Cd 0.2 S, Zn 0.6 Cd 0.4 S, Zn 0.8 Cd 0.2 S, Zn 0.6 Cd 0.4 S and ZnS. Experimental verification shows that the quantum dot structure of this embodiment can enable the electroluminescent device to have high efficiency and lifespan.

[0045] In the quantum dot 200 of this embodiment, the core 210 can reduce the destructive effect of accumulated charge on the exciton transition of the quantum dot when the QLED charge accumulates, thereby maintaining a high photoluminescence quantum yield for a longer period of time, which helps to improve the life of the QLED; the band gap of the first inner shell layer 221 is greater than the band gap of the core 210, which can effectively confine electrons or holes to the surface of the core 210, so that the quantum dot 200 of this embodiment has a high photoluminescence quantum yield of up to 80% or more; the band gap of the first inner shell layer 221 is greater than the band gap of the second inner shell layer 222, and the combination of two sets of thinner inner shell layer units 220 can further enable charge carriers to enter the quantum dot 200 more efficiently through the tunneling process, thereby improving the charge balance level of the QLED and helping to obtain high device efficiency; the band gap of the outer shell layer 230 is greater than or equal to the band gap of the first inner shell layer 221, which can enable the quantum dot to have a high photoluminescence quantum yield and stability, further improving the life of the QLED.

[0046] The quantum dots using the technical solution disclosed herein have a larger core size, which can reduce the destructive effect of accumulated charge on the quantum dot exciton transition when QLED charges accumulate, thereby maintaining a high photoluminescence quantum yield for a longer period of time and helping to improve the lifespan of the QLED. The first inner shell has a larger band gap than the core, which can effectively confine electrons or holes to the surface of the core, resulting in a high photoluminescence quantum yield for the quantum dots disclosed herein. The first inner shell has a larger band gap than the second inner shell, which can more efficiently allow charge carriers to enter the quantum dot through the tunneling process, thereby improving the charge balance level of the QLED and helping to achieve high device efficiency. The outer shell has the widest band gap, which can enable the quantum dot to have a high photoluminescence quantum yield and stability, further improving the lifespan of the QLED. Therefore, by designing the size of the quantum dot and the core-shell structure, the present disclosure achieves a quantum dot whose photoluminescence properties are more resistant to the destructive effects of accumulated charge, thereby extending the lifespan of the QLED.

[0047] An electroluminescent device according to one embodiment includes a quantum dot light-emitting layer, wherein the quantum dot light-emitting layer includes any of the aforementioned quantum dots. The electroluminescent device may be a positive-type device or a reverse-type device, which is not limited in this disclosure.

[0048] 4 , an electroluminescent device 300 according to one embodiment includes a substrate 310, an anode 320, a hole injection layer (HIL) 330, a hole transport layer (HTL) 340, a quantum dot light-emitting layer 350, an electron transport layer (ETL) 360, and a cathode 370, which are sequentially arranged. The anode 320 may be made of, for example, ITO or IZO; the hole injection layer 330 may be made of, for example, PEDOT:PSS, phosphomolybdic acid, or phosphotungstic acid; the hole transport layer 340 may be made of, for example, TFB, PVK, Poly-TPD, NPB, CBP, TCTA, and NiO; the electron transport layer 360 may be made of, for example, ZnO, doped ZnO (doped with Al, Mg, Ga, Hf, N, P, or a combination thereof), or SnO2; and the cathode 370 may be made of, for example, Al or Ag.

[0049] Experimental verification shows that the electroluminescent device disclosed in the present invention has high efficiency and lifespan, and is suitable for wide application.

[0050] With reference to the above implementation contents, in order to make the technical solution of this application more specific, clear and easy to understand, the technical solution of this application is now given as an example. However, the content to be protected by this application is not limited to the following Examples 1 to 14.

[0051] Example 1

[0052] This embodiment provides a quantum dot and a preparation method thereof. The structure of the quantum dot 100 of this embodiment is shown in FIG1 , and includes a core 110, a group of inner shell units 120 and an outer shell 130 sequentially coated on the surface of the core 110, and the inner shell unit 120 includes a first inner shell 121 and a second inner shell 122. The materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn, Zn, Zn, Zn- ... 0.5 Cd 0.5 S / Zn 0.8 Cd 0.2 S / Zn 0.6 Cd 0.4 The diameter of the quantum dot 100 of this embodiment is 14.6 nm, the diameter of the core 110 is 5 nm, and the thicknesses of the first inner shell 121 , the second inner shell 122 , and the outer shell 130 are 2.1 nm, 1.5 nm, and 1.2 nm, respectively.

[0053] The steps for preparing the quantum dots in this embodiment are as follows:

[0054] 1) Add 4 mmol of zinc acetate, 0.6 mmol of cadmium acetate, and 10 ml of oleic acid to a 100 ml three-necked flask, introduce nitrogen, heat to 180°C, and stir until the solution becomes clear. Then, add 20 ml of octadecene and raise the temperature to 320°C.

[0055] 2) dissolving 1 mmol of sulfur powder in 1 ml of trioctylphosphine, and then rapidly injecting the solution in 1) and reacting for 25 minutes to obtain a quantum dot core solution;

[0056] 3) Dissolve 0.5 mmol of sulfur powder in 0.5 ml of trioctylphosphine and 0.15 mmol of cadmium acetate in 1.5 ml of oleic acid, then mix the two and slowly (0.07 ml / min) inject them into the quantum dot core solution in 2) to grow the first inner shell layer, and react for 30 minutes;

[0057] 4) Dissolve 0.25 mmol of sulfur powder in 0.25 ml of trioctylphosphine and 0.1 mmol of cadmium acetate in 1 ml of oleic acid, then mix the two and slowly (0.05 ml / min) inject them into the solution in 3) to grow the second inner shell layer. React for 20 minutes.

[0058] 5) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0059] 6) Cooling the solution in 5) to room temperature, adding excess acetone to precipitate quantum dots, then removing the acetone and adding n-octane to dissolve to obtain a quantum dot solution. This process is repeated three times to obtain a pure quantum dot solution.

[0060] Example 2

[0061] This embodiment provides a quantum dot and a preparation method thereof. The difference between the quantum dot 100 of this embodiment and the quantum dot 100 of embodiment 1 is that the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.4 Cd 0.6 S / ZnSeS / ZnCdSe / ZnS. The diameter of the quantum dot 100 of this embodiment is 14.1 nm, the diameter of the core 110 is 4.5 nm, and the thicknesses of the first inner shell 121, the second inner shell 122, and the outer shell 130 are 2.1 nm, 1.5 nm, and 1.2 nm, respectively.

[0062] The steps for preparing the quantum dots in this embodiment are as follows:

[0063] 1) Add 3 mmol of zinc acetate, 0.7 mmol of cadmium acetate, and 10 ml of oleic acid to a 100 ml three-necked flask, introduce nitrogen, heat to 180°C, and stir until the solution becomes clear. Then, add 20 ml of octadecene and raise the temperature to 320°C.

[0064] 2) dissolving 1 mmol of sulfur powder in 1 ml of trioctylphosphine, and then rapidly injecting the solution in 1) and reacting for 20 minutes to obtain a quantum dot core solution;

[0065] 3) Dissolving 0.25 mmol of sulfur powder and 0.25 mmol of selenium powder in 0.5 ml of trioctylphosphine, and then slowly injecting (0.03 ml / min) into the quantum dot core solution in 2) to grow the first inner shell layer, and reacting for 20 minutes;

[0066] 4) Dissolve 0.25 mmol of selenium powder in 0.25 ml of trioctylphosphine and 0.1 mmol of cadmium acetate in 1 ml of oleic acid, then mix the two and slowly (0.05 ml / min) inject them into the solution in 3) to grow the second inner shell layer. React for 20 minutes.

[0067] 5) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0068] 6) Cooling the solution in 5) to room temperature, adding excess acetone to precipitate quantum dots, then removing the acetone and adding n-octane to dissolve to obtain a quantum dot solution. This process is repeated three times to obtain a pure quantum dot solution.

[0069] Example 3

[0070] This embodiment provides a quantum dot and a preparation method thereof. The difference between the quantum dot 100 of this embodiment and the quantum dot 100 of embodiment 1 is that the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.2 Cd 0.8 S / ZnSeS / ZnCdSe / ZnS. The diameter of the quantum dot 100 of this embodiment is 12.7 nm, the diameter of the core 110 is 3.1 nm, and the thicknesses of the first inner shell 121, the second inner shell 122, and the outer shell 130 are 2.1 nm, 1.5 nm, and 1.2 nm, respectively.

[0071] The steps for preparing the quantum dots in this embodiment are as follows:

[0072] 1) Add 3 mmol of zinc acetate, 0.9 mmol of cadmium acetate, and 10 ml of oleic acid to a 100 ml three-necked flask, introduce nitrogen, heat to 180°C, and stir until the solution becomes clear. Then, add 20 ml of octadecene and raise the temperature to 320°C.

[0073] 2) dissolving 1 mmol of sulfur powder in 1 ml of trioctylphosphine, and then rapidly injecting the solution in 1) and reacting for 15 minutes to obtain a quantum dot core solution;

[0074] 3) Dissolving 0.25 mmol of sulfur powder and 0.25 mmol of selenium powder in 0.5 ml of trioctylphosphine, and then slowly injecting (0.03 ml / min) into the quantum dot core solution in 2) to grow the first inner shell layer, and reacting for 20 minutes;

[0075] 4) Dissolve 0.25 mmol of selenium powder in 0.25 ml of trioctylphosphine and 0.1 mmol of cadmium acetate in 1 ml of oleic acid, then mix the two and slowly (0.05 ml / min) inject them into the solution in 3) to grow the second inner shell layer. React for 20 minutes.

[0076] 5) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0077] 6) Cooling the solution in 5) to room temperature, adding excess acetone to precipitate quantum dots, then removing the acetone and adding n-octane to dissolve to obtain a quantum dot solution. This process is repeated three times to obtain a pure quantum dot solution.

[0078] Example 4

[0079] This embodiment provides a quantum dot and a preparation method thereof. The difference between the quantum dot 100 of this embodiment and the quantum dot 100 of embodiment 1 is that the materials of the core 110, the first inner shell 121, the second inner shell 122 and the outer shell 130 are Zn 0.2 Cd 0.8 S / Zn 0.8 Cd 0.2 S / ZnCdSe / ZnS. The diameter of the quantum dot 100 of this embodiment is 12.7 nm, the diameter of the core 110 is 3.1 nm, and the thicknesses of the first inner shell 121, the second inner shell 122, and the outer shell 130 are 2.1 nm, 1.5 nm, and 1.2 nm, respectively.

[0080] The steps for preparing the quantum dots in this embodiment are as follows:

[0081] 1) Add 3 mmol of zinc acetate, 0.9 mmol of cadmium acetate, and 10 ml of oleic acid to a 100 ml three-necked flask, introduce nitrogen, heat to 180°C, and stir until the solution becomes clear. Then, add 20 ml of octadecene and raise the temperature to 320°C.

[0082] 2) dissolving 1 mmol of sulfur powder in 1 ml of trioctylphosphine, and then rapidly injecting the solution in 1) and reacting for 25 minutes to obtain a quantum dot core solution;

[0083] 3) Dissolve 0.5 mmol of sulfur powder in 0.5 ml of trioctylphosphine and 0.15 mmol of cadmium acetate in 1.5 ml of oleic acid, then mix the two and slowly (0.07 ml / min) inject them into the quantum dot core solution in 2) to grow the first inner shell layer, and react for 30 minutes;

[0084] 4) Dissolve 0.25 mmol of selenium powder in 0.25 ml of trioctylphosphine and 0.1 mmol of cadmium acetate in 1 ml of oleic acid, then mix the two and slowly (0.05 ml / min) inject them into the solution in 3) to grow the second inner shell layer. React for 20 minutes.

[0085] 5) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0086] 6) Cooling the solution in 5) to room temperature, adding excess acetone to precipitate quantum dots, then removing the acetone and adding n-octane to dissolve to obtain a quantum dot solution. This process is repeated three times to obtain a pure quantum dot solution.

[0087] Example 5

[0088] This embodiment provides a quantum dot and a method for preparing the same. The quantum dot 100 of this embodiment differs from the quantum dot of Example 2 in that x is 0.6. The diameter of the quantum dot 100 of this embodiment is 15.3 nm, the diameter of the core 110 is 5.7 nm, and the thicknesses of the first inner shell 121, the second inner shell 122, and the outer shell 130 are 2.1 nm, 1.5 nm, and 1.2 nm, respectively.

[0089] The steps for preparing the quantum dots in this embodiment are as follows:

[0090] 1) Add 3 mmol of zinc acetate, 0.5 mmol of cadmium acetate, and 10 ml of oleic acid to a 100 ml three-necked flask, introduce nitrogen, heat to 180°C, and stir until the solution becomes clear. Then, add 20 ml of octadecene and raise the temperature to 320°C.

[0091] 2) dissolving 1 mmol of sulfur powder in 1 ml of trioctylphosphine, and then rapidly injecting the solution in 1) and reacting for 20 minutes to obtain a quantum dot core solution;

[0092] 3) Dissolving 0.25 mmol of sulfur powder and 0.25 mmol of selenium powder in 0.5 ml of trioctylphosphine, and then slowly injecting (0.03 ml / min) into the quantum dot core solution in 2) to grow the first inner shell layer, and reacting for 20 minutes;

[0093] 4) Dissolve 0.25 mmol of selenium powder in 0.25 ml of trioctylphosphine and 0.1 mmol of cadmium acetate in 1 ml of oleic acid, then mix the two and slowly (0.05 ml / min) inject them into the solution in 3) to grow the second inner shell layer. React for 20 minutes.

[0094] 5) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0095] 6) Cooling the solution in 5) to room temperature, adding excess acetone to precipitate quantum dots, then removing the acetone and adding n-octane to dissolve to obtain a quantum dot solution. This process is repeated three times to obtain a pure quantum dot solution.

[0096] Example 6

[0097] This embodiment provides a quantum dot and a method for preparing the same. Quantum dot 100 of this embodiment differs from the quantum dot of Example 2 in that x is 0.7. Quantum dot 100 of this embodiment has a diameter of 16.1 nm, core 110 has a diameter of 6.5 nm, and the thicknesses of first inner shell 121, second inner shell 122, and outer shell 130 are 2.1 nm, 1.5 nm, and 1.2 nm, respectively.

[0098] The steps for preparing the quantum dots in this embodiment are as follows:

[0099] 1) Add 3.5 mmol of zinc acetate, 0.4 mmol of cadmium acetate, and 10 ml of oleic acid to a 100 ml three-necked flask, introduce nitrogen, heat to 180°C, and stir until the solution becomes clear. Then, add 20 ml of octadecene and raise the temperature to 320°C.

[0100] 2) dissolving 1 mmol of sulfur powder in 1 ml of trioctylphosphine, and then rapidly injecting the solution in 1) and reacting for 20 minutes to obtain a quantum dot core solution;

[0101] 3) Dissolving 0.25 mmol of sulfur powder and 0.25 mmol of selenium powder in 0.5 ml of trioctylphosphine, and then slowly injecting (0.03 ml / min) into the quantum dot core solution in 2) to grow the first inner shell layer, and reacting for 20 minutes;

[0102] 4) Dissolve 0.25 mmol of selenium powder in 0.25 ml of trioctylphosphine and 0.1 mmol of cadmium acetate in 1 ml of oleic acid, then mix the two and slowly (0.05 ml / min) inject them into the solution in 3) to grow the second inner shell layer. React for 20 minutes.

[0103] 5) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0104] 6) Cooling the solution in 5) to room temperature, adding excess acetone to precipitate quantum dots, then removing the acetone and adding n-octane to dissolve to obtain a quantum dot solution. This process is repeated three times to obtain a pure quantum dot solution.

[0105] Example 7

[0106] The structure of the quantum dot 200 of this embodiment is shown in FIG2 , and includes a core 210, two groups of inner shell units 220 and an outer shell 230 sequentially coated on the surface of the core 210, and each group of inner shell units 220 includes a first inner shell 221 and a second inner shell 222. The materials of the core 210, the first inner shell 221, the second inner shell 222, the first inner shell 221, the second inner shell 222 and the outer shell 230 in the direction from the core 210 to the outer shell 230 are Zn, ... 0.5 Cd 0.5 S / Zn 0.8 Cd 0.2 S / Zn 0.6 Cd 0.4 S / Zn 0.8 Cd 0.2 S / Zn 0.6 Cd 0.4 S / ZnS, the diameter of the quantum dot 200 in this embodiment is 14.6nm, the diameter of the core 210 is 5nm, the thickness of the first inner shell 221 is 1.05nm, the thickness of the second inner shell is 0.75nm, the thickness of the first inner shell 221 is 1.05nm, the thickness of the second inner shell 222 is 0.75nm, and the thickness of the outer shell 230 is 1.2nm.

[0107] The steps for preparing the quantum dots in this embodiment are as follows:

[0108] 1) Add 6 mmol of zinc acetate, 0.6 mmol of cadmium acetate, and 10 ml of oleic acid to a 100 ml three-necked flask, introduce nitrogen, heat to 180°C, and stir until the solution becomes clear. Then, add 20 ml of octadecene and raise the temperature to 320°C.

[0109] 2) dissolving 1 mmol of sulfur powder in 1 ml of trioctylphosphine, and then rapidly injecting the solution in 1) and reacting for 25 minutes to obtain a quantum dot core solution;

[0110] 3) Dissolve 0.25 mmol of sulfur powder in 0.25 ml of trioctylphosphine and 0.07 mmol of cadmium acetate in 0.7 ml of oleic acid, then mix the two and slowly (0.04 ml / min) inject them into the quantum dot core solution in 2) to grow the first inner shell layer, and react for 15 minutes;

[0111] 4) Dissolve 0.12 mmol of sulfur powder in 0.15 ml of trioctylphosphine and 0.05 mmol of cadmium acetate in 0.5 ml of oleic acid, then mix the two and slowly (0.04 ml / min) inject them into the solution in 3) to grow a second inner shell layer. React for 10 minutes.

[0112] 5) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0113] 6) Dissolve 0.12 mmol of sulfur powder in 0.15 ml of trioctylphosphine and 0.05 mmol of cadmium acetate in 0.5 ml of oleic acid, then mix the two and slowly (0.04 ml / min) inject them into the solution in 3) to grow the second inner shell layer. React for 10 minutes.

[0114] 7) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0115] 8) Cooling the solution in 7) to room temperature, adding excess acetone to precipitate quantum dots, then removing the acetone and adding n-octane to dissolve to obtain a quantum dot solution. Repeat this process three times to obtain a pure quantum dot solution.

[0116] Example 8 to Example 14

[0117] The quantum dots of Examples 1 to 7 were respectively fabricated to obtain QLEDs of Examples 8 to 14, in the following steps:

[0118] 1) Cleaning the patterned ITO glass substrate, drying it and performing UVO treatment;

[0119] 2) PEDOT:PSS was deposited as HIL on an ITO substrate using a solution method with a thickness of 40 nm;

[0120] 3) Depositing TFB as HTL on the HIL using a solution method with a thickness of 30 nm;

[0121] 4) Depositing the quantum dot solutions of Examples 1 to 7 as EML on the HTL using a solution method to a thickness of 40 nm;

[0122] 5) Mg-doped ZnO nanoparticles were deposited on the EML using a solution method as an ETL with a thickness of 50 nm;

[0123] 6) Ag was deposited on the ETL as a cathode using an evaporation method with a thickness of 100 nm.

[0124] Comparative Example 1

[0125] This comparative example is a comparative example of Example 1, and provides a quantum dot and a preparation method thereof. The difference between this comparative example and the quantum dot of Example 1 is that the core material is Zn0.2Cd0.8S, the core diameter is 2.5nm, and the quantum dot diameter is 12.1nm.

[0126] The preparation steps of the quantum dots of this comparative example are as follows:

[0127] 1) Add 3 mmol of zinc acetate, 0.9 mmol of cadmium acetate, and 10 ml of oleic acid to a 100 ml three-necked flask, introduce nitrogen, heat to 180°C, and stir until the solution becomes clear. Then, add 20 ml of octadecene and raise the temperature to 320°C.

[0128] 2) dissolving 1 mmol of sulfur powder in 1 ml of trioctylphosphine, and then rapidly injecting the solution in 1) and reacting for 15 minutes to obtain a quantum dot core solution;

[0129] 3) Dissolve 0.5 mmol of sulfur powder in 0.5 ml of trioctylphosphine and 0.15 mmol of cadmium acetate in 1.5 ml of oleic acid, then mix the two and slowly (0.07 ml / min) inject them into the quantum dot core solution in 2) to grow the first inner shell layer, and react for 30 minutes;

[0130] 4) Dissolve 0.25 mmol of sulfur powder in 0.25 ml of trioctylphosphine and 0.1 mmol of cadmium acetate in 1 ml of oleic acid, then mix the two and slowly (0.05 ml / min) inject them into the solution in 3) to grow the second inner shell layer. React for 20 minutes.

[0131] 5) Dissolve 0.2 mmol of sulfur powder in 0.2 ml of trioctylphosphine, and then slowly (0.02 ml / min) inject it into the solution in 4) to grow the outer shell layer. React for 10 minutes.

[0132] 6) Cooling the solution in 5) to room temperature, adding excess acetone to precipitate quantum dots, then removing the acetone and adding n-octane to dissolve to obtain a quantum dot solution. This process is repeated three times to obtain a pure quantum dot solution.

[0133] Comparative Example 2

[0134] The quantum dots of Comparative Example 1 were used to produce the QLED of Comparative Example 2, in the following steps:

[0135] 1) Cleaning the patterned ITO glass substrate, drying it and performing UVO treatment;

[0136] 2) PEDOT:PSS was deposited as a HIL on an ITO substrate using a solution method with a thickness of 40 nm;

[0137] 3) Depositing TFB as HTL on the HIL using a solution method with a thickness of 30 nm;

[0138] 4) Depositing the quantum dots of Comparative Example 1 as EML on the HTL using a solution method with a thickness of 40 nm;

[0139] 5) Mg-doped ZnO nanoparticles were deposited on the EML using a solution method as an ETL with a thickness of 50 nm;

[0140] 6) Ag was deposited on the ETL as a cathode using an evaporation method with a thickness of 100 nm.

[0141] Performance testing:

[0142] The QLEDs of Examples 8 to 14 and Comparative Example 2 were subjected to performance tests using the following methods. The test results are shown in Table 1, Figures 5 and 6.

[0143] CE-L curve: obtained by performing IVL (current-voltage-luminance) testing on QLEDs; CE is current efficiency, in cd / A; L is luminance, in cd / m2;

[0144] LT curve: obtained by testing the lifespan of QLEDs; L is brightness, T is time; generally, a constant current source is used to input current to the QLED, and the curve of its brightness changing over time is recorded. A commonly used lifetime parameter is T95, which represents the time it takes for the QLED's brightness to decay from its initial value to 95% of its initial value.

[0145] Table 1 Performance test results of QLEDs of Examples 8 to 14 and Comparative Example 2

[0146] As can be seen from Table 1, the efficiency and lifespan of the QLEDs of Examples 8 to 14 are relatively high, indicating that the quantum dot structure disclosed herein can enable the electroluminescent device to have high efficiency and lifespan.

[0147] As can be seen from FIG5 , the efficiency of the QLEDs of Example 8 and Comparative Example 2 is comparable; as can be seen from FIG6 , the lifespan of the QLED of Example 8 is significantly increased compared with the QLED of Comparative Example 2, indicating that the quantum dot structure disclosed herein can effectively improve the device lifespan.

[0148] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0149] The above-described embodiments merely represent several implementation methods of the present disclosure. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the scope of the present disclosure, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the disclosed patent shall be determined by the appended claims.

Claims

1. A quantum dot, comprising a core, at least one group of inner shell units and an outer shell layer sequentially coated on the surface of the core; The material of the core is Zn x Cd 1-x S, wherein x is 0 to 1; the size of the core is not less than 3 nm; Each group of the inner shell units comprises a first inner shell and a second inner shell in a direction away from the inner core, wherein the band gap of the first inner shell is larger than the band gap of the inner core and the band gap of the second inner shell; The band gap of the outer shell layer is greater than or equal to the band gap of the first inner shell layer.

2. The quantum dot according to claim 1, wherein The size of the core is 3nm to 15nm; and / or The size of the quantum dots is 10 nm to 30 nm; and / or The thickness of the first inner shell layer, the second inner shell layer and the outer shell layer are all 0.35 nm to 3.5 nm.

3. The quantum dot according to claim 1 or 2, wherein The material of the core is Zn x Cd 1-x S, where x is 0.2 to 0.

7.

4. The quantum dot according to claim 1 or 3, wherein The material of the core is Zn x Cd 1-x S, where x is 0.4 to 0.

6.

5. The quantum dot according to any one of claims 1 to 4, wherein The material of the first inner shell layer is selected from Zn y Cd 1-y At least one of S and ZnSeS, wherein y is x-1, and x<y<1; The material of the second inner shell layer is selected from Zn z Cd 1-z At least one of S, ZnCdSe and ZnCdSeS, wherein z<y; The material of the outer shell layer is selected from at least one of ZnCdS, ZnSeS and ZnS.

6. The quantum dot according to claim 5, wherein The material of the second inner shell layer is Zn z Cd 1-z S, where z ≥ x.

7. The quantum dot according to any one of claims 1 to 6, wherein The difference between the band gap of the first inner shell layer and the band gap of the core is 0.2eV~1eV, the difference between the band gap of the first inner shell layer and the band gap of the second inner shell layer is 0.1eV~1eV, and the difference between the band gap of the outer shell layer and the band gap of the first inner shell layer is 0.1eV~1eV.

8. The quantum dot according to any one of claims 1 to 7, characterized in that The number of groups of the inner shell units is one group; The materials of the core, the first inner shell layer, the second inner shell layer and the outer shell layer are Zn 0.5 Cd 0.5 S, Zn 0.8 Cd 0.2 S, Zn 0.6 Cd 0.4 S and ZnS; or The materials of the core, the first inner shell layer, the second inner shell layer and the outer shell layer are Zn 0.4 Cd 0.6 S, ZnSeS, ZnCdSe and ZnS; or The materials of the core, the first inner shell layer, the second inner shell layer and the outer shell layer are Zn 0.2 Cd 0.8 S, ZnSeS, ZnCdSe and ZnS; or The materials of the core, the first inner shell layer, the second inner shell layer and the outer shell layer are Zn 0.2 Cd 0.8 S, Zn 0.8 Cd 0.2 S, ZnCdSe and ZnS; or The materials of the core, the first inner shell layer, the second inner shell layer and the outer shell layer are Zn 0.6 Cd 0.4 S, ZnSeS, ZnCdSe and ZnS; or The materials of the core, the first inner shell layer, the second inner shell layer and the outer shell layer are Zn 0.7 Cd 0.3 S, ZnSeS, ZnCdSe and ZnS.

9. The quantum dot according to claim 1, wherein The number of groups of the inner shell units is two, and each group of the inner shell units includes a first inner shell layer and a second inner shell layer.

10. The quantum dot according to claim 9, wherein The materials of the inner core, the first inner shell layer, the second inner shell layer, the first inner shell layer, the second inner shell layer and the outer shell layer from the inner core to the outer shell layer are Zn 0.5 Cd 0.5 S, Zn 0.8 Cd 0.2 S, Zn 0.6 Cd 0.4 S, Zn 0.8 Cd 0.2 S, Zn 0.6 Cd 0.4 S and ZnS.

11. An electroluminescent device comprising a quantum dot light-emitting layer, wherein the quantum dot light-emitting layer comprises the quantum dots according to any one of claims 1 to 10.

12. The electroluminescent device according to claim 11, wherein Also includes: A substrate, an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer and a cathode are arranged in sequence.

13. The electroluminescent device according to claim 12, wherein: The material of the anode is ITO or IZO.

14. The electroluminescent device according to claim 12 or 13, wherein: The material of the hole injection layer is any one of PEDOT:PSS, phosphomolybdic acid and phosphotungstic acid.

15. The electroluminescent device according to any one of claims 12 to 14, wherein: The material of the hole transport layer is at least one of TFB, PVK, Poly-TPD, NPB, CBP, TCTA and NiO.

16. An electroluminescent device according to any one of claims 12 to 15, wherein: The material of the electron transport layer is any one of ZnO, SnO2 and doped ZnO, wherein the dopant in the doped ZnO includes any one or more combinations of Al, Mg, Ga, Hf, N and P.

17. An electroluminescent device according to any one of claims 12 to 16, wherein: The cathode is made of Al or Ag.

Images