Light-emitting device and display device

Abstract

The invention relates to a light-emitting device and a display device. The light-emitting device comprises a light-emitting layer, a first functional layer and an electron capture layer located between the light-emitting layer and the first functional layer. The electron capture layer is used for capturing electrons, generating blue light excitons and transferring exciton energy to the light-emitting layer in a fluorescence resonance energy transfer mode; the first functional layer is used for forming a stepped barrier with the electron capture layer, wherein the stepped barrier is beneficial to hole injection and transmission. According to the light-emitting device adopting the technical scheme, the electron capture layer can capture electrons and generate blue light excitons, and exciton energy is transferred to the light-emitting layer in a fluorescence resonance energy transfer mode; the first functional layer and the electron capture layer can form a step barrier facilitating hole injection and transmission, and hole injection and transmission are facilitated. The efficiency of the light-emitting device can be improved, and wide application is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of display technologies, and particularly to a light-emitting device and a display device. Background Art

[0002] Light-emitting devices such as quantum dot light-emitting diodes (QLEDs) have gradually gained favor in the commercial world in the field of new display technologies, because quantum dots have relatively excellent properties such as good color purity and stability of light emission. Conventional QLED light-emitting devices include a first electrode, a first functional layer, a quantum dot light-emitting layer (QD), a second functional layer, and a second electrode that are sequentially stacked. However, in conventional QLED light-emitting devices, there is excessive electron accumulation or leakage, which seriously affects the efficiency of QLED light-emitting devices. Summary of the Invention

[0003] Based on this, it is necessary to provide a light-emitting device and a display device for the problem of how to improve the device efficiency.

[0004] A light-emitting device includes:

[0005] a light-emitting layer, a first functional layer, and an electron trapping layer located between the light-emitting layer and the first functional layer;

[0006] The electron trapping layer is configured to trap electrons and generate blue light excitons, and transfer the exciton energy to the light-emitting layer by means of fluorescence resonance energy transfer;

[0007] The first functional layer is configured to form a step potential barrier that is conducive to hole injection and transport with the electron trapping layer.

[0008] In the light-emitting device applying the technical solution of the present invention, the electron trapping layer can trap electrons and generate blue light excitons, and transfer the exciton energy to the light-emitting layer by means of fluorescence resonance energy transfer; the first functional layer can form a step potential barrier that is conducive to hole injection and transport with the electron trapping layer, which is beneficial to hole injection and transport. The above overall can improve the efficiency of the light-emitting device of the present invention and is conducive to wide application.

[0009] In a feasible implementation manner, the electron trapping layer includes an electron trapping material, the HOMO energy level of the electron trapping material ≥ 5.5 eV, and the LUMO energy level of the electron trapping material ≤ 2.5 eV;

[0010] The first functional layer includes a host material and a guest material doped in the host material. The host material has the same energy level and mobility as the electron trapping material. The absolute value of the difference between the HOMO energy level of the guest material and the HOMO energy level of the electron trapping material is < 0.3 eV. The LUMO energy level of the guest material is lower than the LUMO energy level of the electron trapping material, and the absolute value of the difference between the LUMO energy level of the guest material and the LUMO energy level of the electron trapping material is > 0.5 eV;

[0011] Preferably, the host material is the same as the electron trapping material;

[0012] Preferably, the first functional layer is a hole transport layer;

[0013] Preferably, the light-emitting layer is a quantum dot light-emitting layer.

[0014] In a feasible implementation, the HOMO energy level of the electron trapping material is 5.5 eV to 7.5 eV, and the LUMO energy level of the electron trapping material is 1.0 eV to 2.5 eV.

[0015] In a feasible implementation, the HOMO energy level of the guest material is the same as the HOMO energy level of the electron trapping material.

[0016] In a feasible implementation, the absolute value of the difference between the LUMO energy level of the guest material and the LUMO energy level of the electron trapping material is 0.5 eV to 3 eV.

[0017] In a feasible implementation, in the first functional layer, the doping concentration of the guest material is 1% to 10%.

[0018] In a feasible implementation, both the electron trapping material and the host material of the first functional layer are selected from at least one of (9,9’,9”,9”’-((6-phenyl-1,3,5-triazine-2,4-diyl)bis(benzene-5,3,1-triyl))tetra-carbazole and tris(4-carbazol-9-ylphenyl)amine).

[0019] In a feasible implementation, the guest material of the first functional layer is selected from at least one of poly(N-vinylcarbazole), poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] and poly[bis(4-phenyl)(4-butylphenyl)amine].

[0020] In a feasible implementation, the thickness of the electron trapping layer is 5 nm to 10 nm.

[0021] A display device includes the light-emitting device described in any one of the above.

[0022] In the display device of the technical solution of the present invention, the electron capture layer of the light-emitting device can capture electrons and generate blue light excitons, and transfer the exciton energy to the light-emitting layer in a fluorescence resonance energy transfer manner; the first functional layer can form a step potential barrier that is conducive to hole injection and transport with the electron capture layer, which is beneficial to hole injection and transport. The above overall can improve the efficiency of the light-emitting device and the display device of the present invention, which is conducive to wide application. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of a light-emitting device according to an embodiment of the present invention;

[0024] Figure 2 It is a step potential barrier diagram of a light-emitting device according to an embodiment of the present invention;

[0025] Figure 3 It is a schematic diagram of a light-emitting device according to another embodiment of the present invention;

[0026] Figure 4 It is a light emission principle diagram of a light-emitting device according to another embodiment of the present invention. Detailed Embodiments

[0027] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the detailed embodiments of the present invention with reference to the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0029] Please refer to Figure 1 and Figure 2 , a light-emitting device 100 according to an embodiment of the present invention includes a light-emitting layer 110, a first functional layer 120, and an electron capture layer 130 located between the light-emitting layer 110 and the first functional layer 120. Among them, the electron capture layer 130 is used to capture electrons and generate blue light excitons, and transfer the exciton energy to the light-emitting layer 110 in a fluorescence resonance energy transfer (FRET) manner. Among them, the first functional layer 120 is used to form a step potential barrier that is conducive to hole injection and transport with the electron capture layer 130, which is beneficial to hole injection and transport.

[0030] When the light-emitting device 100 of the present embodiment is applied, the electron trapping layer 130 can trap electrons and generate blue light excitons, and transfer the exciton energy to the light-emitting layer 110 in a manner of fluorescence resonance energy transfer; the first functional layer 120 can form a step potential barrier that is conducive to hole injection and transport with the electron trapping layer 130, which is beneficial to the injection and transport of holes. The above overall can improve the efficiency of the light-emitting device 100 of the present embodiment and is conducive to wide application.

[0031] On the basis of the foregoing embodiment, the electron trapping layer 130 includes an electron trapping material, the HOMO energy level of the electron trapping material ≥ 5.5 eV, and the LUMO energy level of the electron trapping material ≤ 2.5 eV. The above numerical ranges of the HOMO energy level and the LUMO energy level of the electron trapping material can effectively trap electrons and generate blue light excitons, and transfer the exciton energy to the quantum dots in a FRET (fluorescence resonance energy transfer) manner.

[0032] On the basis of the foregoing embodiment, the first functional layer 120 includes a host material and a guest material doped in the host material. The energy level and mobility of the host material are the same as those of the electron trapping material. The absolute value of the difference between the HOMO energy level of the guest material and the HOMO energy level of the electron trapping material < 0.3 eV, the LUMO energy level of the guest material is lower than the LUMO energy level of the electron trapping material, and the absolute value of the difference between the LUMO energy level of the guest material and the LUMO energy level of the electron trapping material > 0.5 eV.

[0033] The above numerical ranges of the host material and the guest material of the first functional layer 120 and the electron trapping material can form a step potential barrier. As Figure 2 shown, the potential barrier for hole injection and transport is small, so it helps the effective injection and transport of holes. Specifically, as Figure 2 shown, the HOMO energy level of the guest material can be greater than, equal to, or less than the HOMO energy level of the electron trapping material. When the HOMO energy level of the guest material is equal to the HOMO energy level of the electron trapping material, the bottom of the first functional layer 120 is flush with the bottom of the electron trapping layer 130; when the HOMO energy level of the guest material is greater than the HOMO energy level of the electron trapping material, the bottom of the first functional layer 120 is higher than the bottom of the electron trapping layer 130, and the difference between the HOMO energy level of the guest material and the HOMO energy level of the electron trapping material < 0.3 eV; when the HOMO energy level of the guest material is less than the HOMO energy level of the electron trapping material, the bottom of the first functional layer 120 is lower than the bottom of the electron trapping layer 130, and the difference between the HOMO energy level of the electron trapping material and the HOMO energy level of the guest material < 0.3 eV.

[0034] In the above embodiments, the same energy levels of the host material and the electron-trapping material mean that the HOMO energy level of the host material is the same as that of the electron-trapping material, and the LUMO energy level of the host material is the same as that of the electron-trapping material; the same mobility of the host material and the electron-trapping material means that the mobility of the carriers in the host material and the electron-trapping material is the same.

[0035] Based on the foregoing embodiments, the host material is the same as the electron-trapping material. At this time, the HOMO energy level of the host material is the same as that of the electron-trapping material, and the LUMO energy level of the host material is the same as that of the electron-trapping material. The effect is that there is no hole injection barrier, which promotes hole injection and transport.

[0036] Based on the foregoing embodiments, the first functional layer 120 is a hole transport layer, and the light-emitting layer 110 is a quantum dot light-emitting layer.

[0037] Based on the foregoing embodiments, the HOMO energy level of the electron-trapping material is 5.5 eV to 7.5 eV, and the LUMO energy level of the electron-trapping material is 1 eV to 2.5 eV.

[0038] Based on the foregoing embodiments, the HOMO energy level of the guest material is the same as that of the electron-trapping material. The effect is that there is no hole injection barrier, which promotes hole injection and transport.

[0039] Based on the foregoing embodiments, the LUMO energy level of the guest material is 0.5 eV to 3 eV lower than that of the electron-trapping material. Further, the LUMO energy level of the guest material is 0.5 eV, 0.6 eV, 0.7 eV, 0.8 eV, 0.9 eV, 1.0 eV, 1.1 eV, 1.2 eV, 1.3 eV, 1.4 eV, 1.5 eV, 1.6 eV, 1.7 eV, 1.8 eV, 1.9 eV, 2.0 eV, 2.1 eV, 2.2 eV, 2.3 eV, 2.4 eV, 2.5 eV, 2.6 eV, 2.7 eV, 2.8 eV, 2.9 eV or 3 eV lower than that of the electron-trapping material.

[0040] Based on the foregoing embodiments, in the first functional layer 120, the doping concentration of the guest material is 1% to 10%. The doping concentration of the guest material can be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0041] Based on the foregoing embodiments, both the electron-capturing material and the host material of the first functional layer 120 are selected from at least one of (9,9’,9”,9”’-((6-phenyl-1,3,5-triazine-2,4-diyl)bis(benzene-5,3,1-triyl))tetra-carbazole (DDCzTRz) and tris(4-carbazol-9-ylphenyl)amine (TCTA).

[0042] Based on the foregoing embodiments, the guest material of the first functional layer 120 is selected from at least one of poly(N-vinylcarbazole) (PVK), poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB), and poly[bis(4-phenyl)(4-butylphenyl)amine] (p-TPD).

[0043] Based on the foregoing embodiments, the thickness of the electron-capturing layer 130 is 5 nm to 10 nm. When the thickness of the electron-capturing layer 130 is 5 nm to 10 nm, it is possible to avoid reducing the hole transport rate and promote carrier balance. Further, the thickness of the electron-capturing layer 130 can be, for example, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm.

[0044] Please refer to Figure 3 and Figure 4 Based on the foregoing embodiments, the light-emitting device 100 further includes a cathode 140 and an electron transport layer 150 located below the light-emitting layer 110, and a hole injection layer 160 and an anode 170 located above the first functional layer 120. Among them, the electron transport layer 150 is located between the cathode 140 and the light-emitting layer 110, the first functional layer 120 is a hole transport layer, and the hole injection layer 160 is located between the first functional layer 120 and the anode 170. Among them, the present invention does not limit the materials and thicknesses of the cathode 140, the electron transport layer 150, the light-emitting layer 110, the hole injection layer 160, and the anode 170, and they can be the functional layer materials and thicknesses commonly used in the art.

[0045] As Figure 4 shown, in the present embodiment, the HOMO energy level of the guest material in the first functional layer 120 is preferably equal to the HOMO energy level of the electron-capturing material, so the first functional layer 120 is flush with the bottom of the electron-capturing layer 130. It should be noted that the HOMO energy level of the guest material can also be greater than or less than the HOMO energy level of the electron-capturing material.

[0046] For the light-emitting device applying the technical solution of the present invention, the above numerical ranges of the HOMO energy level and the LUMO energy level of the electron trapping material can effectively trap electrons and generate blue light excitons, and transfer the exciton energy to the quantum dots in the form of FRET; the host material and the guest material of the first functional layer and the above numerical ranges of the electron trapping material can form a stepped potential barrier conducive to hole injection and transport, which helps the effective injection and transport of holes. The above overall can improve the efficiency of the light-emitting device of the present invention and is conducive to wide application.

[0047] A method for preparing a light-emitting device according to an embodiment of the present invention includes the following steps:

[0048] S10. Form an electron transport layer on the cathode by a wet film-forming process.

[0049] S20. Form a light-emitting layer on the electron transport layer by a wet film-forming process.

[0050] S30. Form an electron trapping layer on the light-emitting layer by an evaporation process. The electron trapping layer includes an electron trapping material, and the HOMO energy level of the electron trapping material ≥ 5.5 eV, and the LUMO energy level of the electron trapping material ≤ 2.5 eV.

[0051] S40. Form a hole transport layer on the electron trapping layer by an evaporation process. The hole transport layer includes a host material and a guest material doped in the host material. The energy level and mobility of the host material are the same as those of the electron trapping material. The absolute value of the difference between the HOMO energy level of the guest material and the HOMO energy level of the electron trapping material < 0.3 eV. The LUMO energy level of the guest material is lower than the LUMO energy level of the electron trapping material, and the absolute value of the difference between the LUMO energy level of the guest material and the LUMO energy level of the electron trapping material > 0.5 eV.

[0052] S50. Form a hole injection layer on the hole transport layer by an evaporation process.

[0053] S60. Form an anode on the hole injection layer by an evaporation process.

[0054] The method for preparing a light-emitting device according to the technical solution of the present invention has a simple process. The light-emitting device prepared by the above preparation method has a high efficiency and is conducive to wide application.

[0055] A display device according to an embodiment includes any one of the above light-emitting devices.

[0056] In the display device of the technical solution of the present invention, the electron capture layer of the light-emitting device can capture electrons and generate blue light excitons, and transfer the exciton energy to the light-emitting layer in a fluorescence resonance energy transfer manner; the first functional layer can form a step potential barrier that is beneficial to hole injection and transport with the electron capture layer, which is conducive to the injection and transport of holes. The above overall can improve the efficiency of the light-emitting device and the display device of the present invention, which is conducive to wide application.

[0057] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, the technical solution of the present invention is now exemplified. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0058] Example 1

[0059] Step 1: Cleaning of ITO cathode conductive glass: Use deionized water, acetone, and isopropanol for ultrasonic cleaning for 10 minutes respectively. After drying with nitrogen, place it in a petri dish.

[0060] Step 2: Preparation of electron transport layer: Take 100 microliters of ZnO ethanol solution and spin-coat it on the anode at 3000 revolutions per minute for 30 seconds. Then anneal it under a 100 °C flat heating table for 5 minutes to obtain an electron transport layer with a thickness of 50 nm.

[0061] Step 3: Preparation of quantum dot light-emitting layer: Take 50 microliters of the prepared QD (ZnCdSe / ZnS) dissolved in n-octane solution and spin-coat it on the electron transport layer at 3000 revolutions per minute for 30 seconds. Then anneal it under a 100 °C flat heating table for 5 minutes to obtain a quantum dot light-emitting layer with a thickness of 5 nm.

[0062] Step 4: Preparation of electron capture layer: Transfer the substrate to a vacuum chamber and evaporate an electron capture layer with a thickness of 5 nm at 4 × 10 -4 Pa; the electron capture layer includes an electron capture material, and the electron capture material is (9,9’,9”,9”’-((6-phenyl-1,3,5-triazine-2,4-diyl)bis(benzene-5,3,1-triyl))tetra-carbazole;

[0063] Step 5: Preparation of hole transport layer: In a vacuum chamber, evaporate the hole transport layer at 4 × 10 -4 Pa; the hole transport layer includes a host material and a guest material doped in the host material. The host material is (9,9’,9”,9”’-((6-phenyl-1,3,5-triazine-2,4-diyl)bis(benzene-5,3,1-triyl))tetra-carbazole, and the guest material is poly(N-vinylcarbazole). The doping concentration of the guest material is 5%;

[0064] Step 6: Preparation of hole injection layer: In a vacuum chamber, 4 × 10 -4Deposit a hole injection layer with a thickness of 30 nm under a pressure of [[Pa]], and the hole injection material is 2,3,6,7,10,11 - hexacyano - 1,4,5,8,9,12 - hexaazatriphenylene;

[0065] Step 7: Cathode preparation: Deposit a 100 - nm silver electrode under a pressure of 4×10 -4 Pa.

[0066] Example 2

[0067] This example provides a light - emitting device and its preparation method. The difference from Example 1 is only that the thickness of the electron - trapping layer is 10 nm.

[0068] Example 3

[0069] This example provides a light - emitting device and its preparation method. The difference from Example 1 is only that the thickness of the electron - trapping layer is 3 nm.

[0070] Example 4

[0071] This example provides a light - emitting device and its preparation method. The difference from Example 1 is only that the thickness of the electron - trapping layer is 15 nm.

[0072] Example 5

[0073] This example provides a light - emitting device and its preparation method. The difference from Example 1 is only that the doping concentration of the guest material is 10%.

[0074] Comparative Example 1

[0075] This comparative example is a comparative example of Example 1. It provides a light - emitting device and its preparation method. The difference from the preparation method of Example 1 is only that there is no electron - trapping layer.

[0076] Comparative Example 2

[0077] This comparative example is a comparative example of Example 5. It provides a light - emitting device and its preparation method. The difference from the preparation method of Example 5 is only that there is no electron - trapping layer.

[0078] Performance test:

[0079] Perform performance tests on the light - emitting devices of Examples 1 - 5 and Comparative Examples 1 - 2. Specifically, use the EQE test method, and in the test method, use a PR - 655 spectrometer. The test results are shown in Table 1.

[0080] Table 1 Test results of the light - emitting devices of Examples 1 - 5 and Comparative Examples 1 - 2

[0081]

[0082] As can be seen from Table 1, when comparing the inverted QLEDs of Example 1 and Comparative Example 1, there is no electron capture layer in the light-emitting device of Comparative Example 1, and the device efficiency is only 20; the thickness of the electron capture layer in the light-emitting device of Example 1 is 5 nm, and the device efficiency can reach 25; thus, it can be seen that with the presence of the electron capture layer from none to some, the device efficiency can be increased from 20 to 25, which indicates that setting an electron capture layer in the light-emitting device is beneficial to improving the device efficiency;

[0083] When comparing the inverted QLEDs of Example 5 and Comparative Example 2, there is no electron capture layer in the light-emitting device of Comparative Example 2, and the device efficiency is only 18; the thickness of the electron capture layer in the light-emitting device of Example 5 is 5 nm, and the device efficiency can reach 20; thus, it can be seen that with the presence of the electron capture layer from none to some, the device efficiency can be increased from 18 to 20, which indicates that setting an electron capture layer in the light-emitting device is beneficial to improving the device efficiency;

[0084] When comparing the inverted QLEDs of Example 1 to Example 4, an electron capture layer is provided in each of the inverted QLEDs of Example 1 to Example 4, and the thickness of the electron capture layer gradually increases in Example 3, Example 1, Example 2, and Example 4, while the device efficiency of the inverted QLEDs of Example 3, Example 1, Example 2, and Example 4 first increases and then decreases. This indicates that as the thickness of the electron capture layer increases, the effect on improving the device efficiency becomes greater; and it is speculated that the subsequent decrease is due to the fact that the greater the thickness of the electron capture layer, the more electrons are captured, thus resulting in a decrease in device efficiency.

[0085] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0086] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A light-emitting device, characterized in that, comprising: a light-emitting layer, a first functional layer, and an electron-trapping layer located between the light-emitting layer and the first functional layer; the electron-trapping layer is used to trap electrons and generate blue-light excitons, and transfer the exciton energy to the light-emitting layer in a fluorescence resonance energy transfer manner; the first functional layer is used to form a step potential barrier conducive to hole injection and transport with the electron-trapping layer.

2. The light-emitting device according to claim 1, characterized in that, the electron-trapping layer comprises an electron-trapping material, the HOMO energy level of the electron-trapping material ≥ 5.5 eV, and the LUMO energy level of the electron-trapping material ≤ 2.5 eV; the first functional layer comprises a host material and a guest material doped in the host material, the energy levels and mobilities of the host material and the electron-trapping material are the same, the absolute value of the difference between the HOMO energy level of the guest material and the HOMO energy level of the electron-trapping material < 0.3 eV, the LUMO energy level of the guest material is lower than the LUMO energy level of the electron-trapping material, and the absolute value of the difference between the LUMO energy level of the guest material and the LUMO energy level of the electron-trapping material > 0.5 eV; preferably, the host material is the same as the electron-trapping material; preferably, the first functional layer is a hole-transporting layer; preferably, the light-emitting layer is a quantum dot light-emitting layer.

3. The light-emitting device according to claim 2, characterized in that, the HOMO energy level of the electron-trapping material is 5.5 eV to 7.5 eV, and the LUMO energy level of the electron-trapping material is 1.0 eV to 2.5 eV.

4. The light-emitting device according to claim 2, characterized in that, the HOMO energy level of the guest material is the same as the HOMO energy level of the electron-trapping material.

5. The light-emitting device according to claim 2, characterized in that, the absolute value of the difference between the LUMO energy level of the guest material and the LUMO energy level of the electron-trapping material is 0.5 eV to 3 eV.

6. The light-emitting device according to claim 2, characterized in that, in the first functional layer, the doping concentration of the guest material is 1% to 10%.

7. The light-emitting device according to claim 2, characterized in that, both the electron-trapping material and the host material of the first functional layer are selected from at least one of (9,9’,9”,9”’-((6-phenyl-1,3,5-triazine-2,4-diyl)bis(benzene-5,3,1-triyl))tetra-carbazole) and tris(4-carbazol-9-ylphenyl)amine.

8. The light-emitting device according to claim 2, characterized in that, the guest material of the first functional layer is selected from at least one of poly(N-vinylcarbazole), poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine], and poly[bis(4-phenyl)(4-butylphenyl)amine].

9. The light-emitting device according to claim 1, characterized in that, the thickness of the electron-trapping layer is 5 nm to 10 nm.

10. A display device, characterized in that, The light-emitting device according to any one of claims 1 to 9.

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