Light emitting device, method of manufacturing the same and use thereof

Abstract

The application discloses a light-emitting device and a preparation method and application thereof. The preparation method forms an electron transport layer in a mixed atmosphere of inert gas and oxygen, wherein the electron transport layer comprises ZnO, and the oxygen content in the mixed atmosphere is 5-10 v%. The preparation method can significantly improve the stability of the electron transport layer by only changing the atmosphere environment when forming the electron transport layer, and is simple in process, can effectively solve the problem that the light-emitting area of the light-emitting device is reduced or uneven with the increase of the placing time in air, and can improve the initial efficiency of the light-emitting device and keep the light-emitting device stable for a long time.

Description

Technical Field

[0001] This invention belongs to the field of electronics, and more specifically, relates to light-emitting devices, their preparation methods, and applications. Background Technology

[0002] Currently, most electroluminescent QD-LEDs use metal oxide nanoparticles as the electron transport layer material. These nanoparticles are typically dispersed in polar organic solvents, such as lower alcohols with carbon chain lengths of 1-4 (one or more combinations of methanol, ethanol, propanol, isopropanol, and butanol). A commonly used electron transport layer is ZnO nanoparticles spin-coated into a film. However, ZnO, as an n-type semiconductor gas-sensitive material, readily adsorbs gases such as oxygen from the air, causing the light-emitting area of ​​the QLED device to shrink or become uneven as the device is exposed to air for an extended period. Summary of the Invention

[0003] This invention aims to at least partially solve the technical problems in related technologies. Therefore, one object of this invention is to provide a light-emitting device, its fabrication method, and its application. This fabrication method can significantly improve the stability of the electron transport layer simply by changing the atmospheric environment during the formation of the electron transport layer. It is not only simple in process but also effectively solves the problem of the light-emitting area of ​​the device shrinking or becoming uneven as the exposure time in air increases. Simultaneously, it improves the initial efficiency of the light-emitting device and maintains its stability over a long period.

[0004] This application is based primarily on the following questions and findings:

[0005] Current research has confirmed that ZnO surfaces can adsorb oxygen. Oxygen ions take electrons from the ZnO interior, forming oxygen ions. The electron concentration difference between the surface and interior creates a grain boundary barrier, restricting the movement of free electrons and reducing the material's conductivity. When a fabricated QLED device is placed in air for a period of time, due to the UV adhesive encapsulation on the quantum dot emitting area, insufficient hermeticity will allow oxygen to diffuse from the surrounding areas into the emitting area. This leads to increased ZnO resistance in the surrounding regions and reduced luminous brightness, while the central region of the quantum dot can still maintain high brightness. This results in a reduced luminous area or uneven luminous emission (e.g., ...). Figure 1As shown, the QLED device has a large luminous area before being placed in air. However, after being placed in air for a period of time, oxygen permeates from the UV resin around the device and combines with the metal oxide nanoparticles in the electron transport layer, resulting in a decrease in the luminous area. However, the inventors of this application discovered that due to energy level mismatch, hole injection efficiency is generally lower than electron injection efficiency, leading to an imbalance in charge injection in the quantum dot. This makes the quantum dot non-electrically neutral, significantly reducing its luminous efficiency. When the quantum dot device is placed in air for a period of time, the overall resistance of the electron transport layer increases due to oxygen adsorption by ZnO, appropriately reducing the electron transport layer injection efficiency. This, in turn, causes the hole and electron injection efficiencies to tend towards equilibrium, improving the efficiency of the quantum dot device.

[0006] Therefore, according to a first aspect of the present invention, a method for preparing a light-emitting device is provided. According to an embodiment of the present invention, in this preparation method, an electron transport layer is formed in a mixed atmosphere of an inert gas and oxygen, wherein the electron transport layer comprises ZnO, and the oxygen content in the mixed atmosphere is 5-10 v%.

[0007] According to the method for preparing a light-emitting device according to the above embodiments of the present invention, an electron transport layer is formed by mixing 5-10 vol% oxygen into an inert gas as the ambient atmosphere. On the one hand, the inert gas protects the stability of ZnO; on the other hand, the oxygen in the mixed atmosphere is directly and uniformly adsorbed onto the surface of the electron transport layer, including ZnO, ensuring that even if the light-emitting device is placed in air for a long time, the oxygen concentration around and in the center of the electron transport layer will not change significantly, the resistance around and in the center of the electron transport layer will not show significant differences or changes, and the electron injection will not change significantly, thus improving the stability of the light-emitting area. Simultaneously, the slightly increased overall resistance of the electron transport layer in the micro-oxygen atmosphere can promote an increase in the initial efficiency of the light-emitting device and maintain its stability over a long period. In summary, this preparation method can significantly improve the stability of the electron transport layer simply by changing the atmospheric environment during the formation of the electron transport layer. It is not only simple in process but also effectively solves the problem of the light-emitting area shrinking or becoming uneven as the light-emitting area of ​​the light-emitting device increases with prolonged exposure to air, while simultaneously improving the initial efficiency of the light-emitting device and maintaining its stability over a long period.

[0008] In addition, the method for preparing a light-emitting device according to the above embodiments of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, at least one of the following conditions is met: the electron transport layer is formed of ZnO nanoparticles, or is formed of ZnO nanoparticles and nanoparticles selected from at least one of NiO, W2O3, Mo2O3, TiO2, SnO, ZrO2, and Ta2O3; and the oxygen content in the mixed atmosphere is 6-8%.

[0010] In some embodiments of the present invention, the light-emitting device is a QLED device.

[0011] In some embodiments of the present invention, the method for preparing the light-emitting device includes: (1) sequentially depositing a hole injection layer, a hole transport layer, and a quantum dot light-emitting layer on a transparent anode substrate; (2) depositing an electron transport layer including ZnO on the quantum dot light-emitting layer in a mixed atmosphere of an inert gas and oxygen with an oxygen content of 5-10 v%; (3) depositing a metal cathode on the electron transport layer; and (4) encapsulating the device using UV resin.

[0012] In some embodiments of the present invention, step (3) includes: (3-1) depositing metal oxide nanoparticles on the electron transport layer to form an electron injection layer; and (3-2) depositing a metal cathode on the electron injection layer.

[0013] In some embodiments of the present invention, in step (3-1), the metal oxide nanoparticles are different from the metal oxide nanoparticles that form the electron transport layer.

[0014] In some embodiments of the present invention, at least one of the following conditions is met: the thickness of the hole injection layer is 30-40 nm; the thickness of the hole transport layer is 25-35 nm; the thickness of the quantum dot light-emitting layer is 20-35 nm; the thickness of the electron transport layer is 35-45 nm; the thickness of the metal cathode is 80-160 nm; and the metal cathode reflects visible light at a rate of not less than 98%.

[0015] According to a second aspect of the present invention, a light-emitting device is provided. According to an embodiment of the present invention, the light-emitting device is obtained using the above-described preparation method. Compared with existing light-emitting devices, this light-emitting device has good electron transport layer stability and high initial efficiency, and even when placed in air for a long time, it is not prone to problems such as shrinkage or unevenness of the light-emitting area.

[0016] According to a third aspect of the present invention, a display substrate is provided. According to an embodiment of the present invention, the display substrate has the above-described light-emitting device or a light-emitting device obtained by the above-described preparation method. Compared with the prior art, this display substrate has high luminous efficiency and good luminous uniformity and stability.

[0017] According to a fourth aspect of the present invention, a display device is provided. According to an embodiment of the present invention, the display device includes the aforementioned display substrate. Compared with the prior art, this display device has high luminous efficiency, good luminous uniformity and stability, better display effect, and a longer service life.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0020] Figure 1 This is a comparison chart showing the changes in the light-emitting area of ​​an existing QLED light-emitting device before and after it is placed in the air. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] According to a first aspect of the present invention, a method for fabricating a light-emitting device is provided. According to an embodiment of the present invention, in this fabrication method, an electron transport layer is formed in a mixed atmosphere of an inert gas and oxygen, wherein the electron transport layer comprises ZnO, and the oxygen content in the mixed atmosphere is 5-10 v%. This fabrication method can significantly improve the stability of the electron transport layer simply by changing the atmospheric environment during the formation of the electron transport layer. It is not only simple in process but also effectively solves the problem of the light-emitting area of ​​the light-emitting device decreasing or becoming uneven as the exposure time in air increases. Simultaneously, it improves the initial efficiency of the light-emitting device and keeps it stable over a long period.

[0023] The method for preparing the light-emitting device according to the above embodiments of the present invention will be described in detail below.

[0024] According to embodiments of the present invention, the inventors have discovered that a moderate increase in the overall resistance of the electron transport layer can bring hole injection and electron injection efficiencies towards equilibrium, thereby improving the efficiency of the light-emitting device. This increase in the overall resistance of the electron transport layer can be achieved by controlling the oxygen content of the ambient atmosphere during its fabrication. However, excessive oxygen content can significantly reduce the conductivity of the electron transport layer, including ZnO, and negatively impact other light-emitting device materials, such as causing oxidation of the hole transport layer and affecting hole transport. Furthermore, uneven oxygen content distribution can lead to a reduced or non-uniform light-emitting area. Conversely, excessively low oxygen content has little effect on improving the efficiency of the light-emitting device. Therefore, controlling the oxygen content of the ambient atmosphere is crucial. To this end, the inventors envision thoroughly mixing an inert gas with oxygen and strictly controlling the oxygen content in the mixed gas to simultaneously improve the uniformity, stability, and luminous efficiency of the light-emitting device. Based on this, the inventors conducted in-depth research and discovered that by mixing 5-10% oxygen into an inert gas as an ambient atmosphere to form an electron transport layer, the inert gas can be used to protect the stability of ZnO. On the other hand, the oxygen in the mixed atmosphere can be directly and uniformly adsorbed onto the surface of the electron transport layer, including ZnO, ensuring that even if the light-emitting device is placed in air for a long time, the oxygen concentration around and in the center of the electron transport layer will not change significantly. The resistance around and in the center of the electron transport layer will not show significant differences or changes, and the electron injection will not change significantly, thus improving the stability of the light-emitting area. At the same time, the micro-oxygen atmosphere will slightly increase the overall resistance of the electron transport layer, which can promote the initial efficiency of the light-emitting device and maintain its stability for a long time.

[0025] According to a specific embodiment of the present invention, the electron transport layer of the light-emitting device can be any electron transport layer including ZnO. For example, the electron transport layer can be formed solely by ZnO nanoparticles, or it can be formed by ZnO nanoparticles and nanoparticles selected from at least one of NiO, W2O3, Mo2O3, TiO2, SnO, ZrO2 and Ta2O3. Specifically, metal oxide nanoparticles (such as ZnO) can be deposited as the electron transport layer in a glove box atmosphere with a high purity nitrogen-oxygen mixed atmosphere of 5-10v%.

[0026] According to another specific embodiment of the present invention, the oxygen content in the mixed atmosphere of inert gas and oxygen used in the present invention can be 5v%, 5.5v%, 6v%, 6.5v%, 7v%, 7.5v%, 8v%, 8.5v%, 9v%, 9.5v%, or 10v%, etc. Preferably, the oxygen content in the mixed atmosphere can be 6-8v%, which can further improve the efficiency of the light-emitting device and the uniformity and stability of the light-emitting area. Furthermore, it should be noted that the type of inert gas in the present invention is not particularly limited, and those skilled in the art can select it according to actual needs; for example, the inert gas can be high-purity nitrogen, etc.

[0027] According to another specific embodiment of the present invention, the light-emitting device in the present invention can be a QLED device, that is, a quantum dot light-emitting device. It should be noted that the quantum dot light-emitting layer of the QLED device in the present invention is not particularly limited, and those skilled in the art can select appropriate quantum dot materials to form the light-emitting layer according to actual needs.

[0028] According to another specific embodiment of the present invention, the method for preparing a light-emitting device may include: (1) sequentially depositing a hole injection layer, a hole transport layer, and a quantum dot light-emitting layer on a transparent anode substrate; (2) depositing an electron transport layer including ZnO on the quantum dot light-emitting layer in a mixed atmosphere of an inert gas and oxygen with an oxygen content of 5-10 vol%; (3) depositing a metal cathode on the electron transport layer; and (4) encapsulating with UV resin. Further, when electron injection is difficult, step (3) may further include: (3-1) depositing metal oxide nanoparticles on the electron transport layer to form an electron injection layer; and (3-2) depositing a metal cathode on the electron injection layer, thereby further improving the performance of the light-emitting device. It should also be noted that the metal oxide nanoparticles forming the electron injection layer and the metal oxide nanoparticles forming the electron transport layer may be the same or different.

[0029] According to another specific embodiment of the present invention, the method for fabricating a light-emitting device may include at least one of the following conditions: when depositing a hole injection layer on a transparent anode substrate, the thickness of the hole injection layer may be 30-40 nm, for example, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, or 40 nm, wherein the hole injection layer can be deposited by spin coating, and after spin coating, it can be annealed at 150-170°C for 10-20 min; the thickness of the hole transport layer may be 25-35 nm, for example, 25 nm, 27 nm, 29 nm, 31 nm, 33 nm, or 35 nm, wherein the hole transport layer can be deposited by spin coating, and after spin coating, it can be annealed at 140-160°C for 8-15 min; the thickness of the quantum dot light-emitting layer may be 20-35 nm, for example, 20 nm, 23 nm, 26 nm, 28 nm, or 40 nm, etc. The thickness of the quantum dot light-emitting layer can be 35-45 nm, for example, 35 nm, 37 nm, 39 nm, 41 nm, 43 nm, or 45 nm. The electron transport layer can also be deposited using spin coating, followed by annealing at 70-90 °C for 20-40 min. The metal cathode can have a thickness of 80-160 nm, for example, 80 nm, 84 nm, 88 nm, 92 nm, 96 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, or 160 nm, preferably 80-100 nm. Vacuum evaporation can be used to deposit the metal cathode, which should reflect at least 98% of visible light. This further improves the overall performance of the light-emitting device.

[0030] In summary, the method for preparing light-emitting devices according to the above embodiments of the present invention has at least the following advantages: 1. By controlling the preparation atmosphere of the electron transport layer to be a micro-oxygen inert atmosphere, on the one hand, the inert gas can be used to protect the stability of ZnO, and on the other hand, the oxygen in the mixed atmosphere can be directly and uniformly adsorbed on the surface of the electron transport layer including ZnO, ensuring that even if the light-emitting device is placed in the air for a long time, the oxygen concentration around the electron transport layer and the central region will not change significantly, the resistance around the electron transport layer and the central region will not have significant differences or changes, and the electron injection will not change significantly, thus improving the stability of the light-emitting region; 2. The micro-oxygen atmosphere will slightly increase the overall resistance of the electron transport layer, which can promote the improvement of the initial efficiency of the light-emitting device and maintain its stability for a long time; 3. This preparation method does not require changes to the existing preparation device, and can significantly improve the stability of the electron transport layer simply by changing the atmosphere environment when the electron transport layer is formed. It is not only simple in process, but also effectively solves the problem that the light-emitting area of ​​the light-emitting device decreases or becomes uneven as the time of placement in the air increases, while improving the initial efficiency of the light-emitting device and keeping it stable for a long time.

[0031] According to a second aspect of the present invention, a light-emitting device is provided. According to an embodiment of the present invention, the light-emitting device is obtained by the above-described preparation method. Compared with existing light-emitting devices, this light-emitting device has good electron transport layer stability and high initial efficiency, and even when placed in air for a long time, it is not prone to problems such as shrinkage or unevenness of the light-emitting area. It should be noted that the features and effects described in the above-described method for preparing the light-emitting device also apply to this light-emitting device, and will not be repeated here.

[0032] According to a third aspect of the present invention, a display substrate is provided. According to an embodiment of the present invention, the display substrate has the above-described light-emitting device or a light-emitting device obtained by the above-described preparation method. Compared with the prior art, the display substrate has high luminous efficiency and good luminous uniformity and stability. It should be noted that the features and effects described for the above-described light-emitting device and the method for preparing the light-emitting device also apply to this display substrate, and will not be repeated here.

[0033] According to a fourth aspect of the present invention, a display device is provided. According to an embodiment of the present invention, the display device includes the aforementioned display substrate. Compared with the prior art, the display device has high luminous efficiency, good luminous uniformity and stability, better display effect, and longer service life. It should be noted that the type of display device in the present invention is not particularly limited, and those skilled in the art can select it according to actual needs. Furthermore, it should be noted that the features and effects described for the aforementioned display substrate also apply to this display device, and will not be repeated here.

[0034] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0035] Example 1

[0036] 1) A hole injection layer was spin-coated onto a transparent anode substrate ITO, with a thickness controlled at 35 nm. After spin-coating, the layer was annealed at 160 °C for 15 min.

[0037] 2) A hole transport layer was spin-coated onto the hole injection layer, with a thickness of 30 nm. After spin-coating, the layer was annealed at 150 °C for 10 min.

[0038] 3) Spin-coat a quantum dot light-emitting layer onto the hole transport layer, controlling the thickness to 25 nm. After spin-coating, anneal at 250 °C for 60 min.

[0039] 4) In a glove box atmosphere of high-purity nitrogen / oxygen mixed gas with an oxygen content of 5v%, metal oxide nanoparticles ZnO were spin-coated onto the quantum dot luminescent layer as an electron transport layer, with a thickness of 40nm. After spin-coating, the layer was annealed at 80℃ for 30min.

[0040] 5) Deposit a metal cathode on the electron transport layer, controlling the thickness to 150 nm, and ensure that the cathode (silver) reflects at least 98% of visible light;

[0041] 6) UV resin encapsulation yields quantum dot light-emitting devices.

[0042] Example 2

[0043] The difference from Example 1 is that, in step 4), the oxygen content in the high-purity nitrogen / oxygen mixture is 8% (v).

[0044] Example 3

[0045] The difference from Example 1 is that in step 4), the oxygen content in the high-purity nitrogen / oxygen mixture is 10% (v).

[0046] Comparative Example 1

[0047] The difference from Example 1 is that in step 4), the oxygen content in the high-purity nitrogen / oxygen mixed gas is 0.

[0048] Comparative Example 2

[0049] The difference from Example 1 is that, in step 4), the oxygen content in the high-purity nitrogen / oxygen mixture is 3% (v).

[0050] Comparative Example 3

[0051] The difference from Example 1 is that, in step 4), the oxygen content in the high-purity nitrogen / oxygen mixture is 15% (v).

[0052] evaluate:

[0053] The maximum external quantum efficiency and luminescence uniformity of the quantum dot light-emitting devices prepared in Examples 1-3 and Comparative Examples 1-3 were tested under the same conditions. The test results are shown in Table 1. Among them, luminescence uniformity is the percentage of the luminescent area of ​​the quantum dot light-emitting devices after being placed in air for the same period of time (30 days) after different atmospheric treatments, compared with the luminescent area before being placed in air.

[0054] Table 1 Test Results

[0055]

[0056]

[0057] Results and conclusions: Based on the examples, comparative examples and Table 1, it can be seen that when preparing quantum dot light-emitting devices, controlling the oxygen content to a high-purity nitrogen / oxygen mixed gas atmosphere of 5v% can result in a light-emitting device with greater device efficiency and better luminescence uniformity.

[0058] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0059] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for fabricating a light-emitting device, characterized in that, include: (1) A hole injection layer, a hole transport layer, and a quantum dot light-emitting layer are sequentially deposited on a transparent anode substrate; (2) An electron transport layer comprising ZnO is deposited on the quantum dot light-emitting layer in a mixed atmosphere of inert gas and oxygen with an oxygen content of 5~10v%. (3) Deposit a metal cathode on the electron transport layer; (4) Encapsulation using UV resin; The light-emitting device is a QLED device.

2. The method according to claim 1, characterized in that, At least one of the following conditions must be met: The electron transport layer is formed of ZnO nanoparticles, or of ZnO nanoparticles and nanoparticles selected from at least one of NiO, W2O3, Mo2O3, TiO2, SnO, ZrO2 and Ta2O3. The oxygen content in the mixed atmosphere is 6-8%.

3. The method according to claim 1, characterized in that, Step (3) includes: (3-1) Deposit metal oxide nanoparticles on the electron transport layer to form an electron injection layer; (3-2) Deposit a metal cathode on the electron injection layer.

4. The method according to claim 3, characterized in that, In step (3-1), the metal oxide nanoparticles are different from the metal oxide nanoparticles that form the electron transport layer.

5. The method according to claim 1 or 4, characterized in that, At least one of the following conditions must be met: The thickness of the hole injection layer is 30~40nm; The thickness of the hole transport layer is 25~35nm; The thickness of the quantum dot luminescent layer is 20~35nm; The thickness of the electron transport layer is 35~45nm; The thickness of the metal cathode is 80~160nm, and the metal cathode reflects at least 98% of visible light.

6. A light-emitting device obtained by the preparation method according to any one of claims 1 to 5.

7. A display substrate, characterized in that, Includes the light-emitting device according to claim 6 or the light-emitting device obtained by the preparation method according to any one of claims 1 to 5.

8. A display device, characterized in that, Includes the display substrate as described in claim 7.

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