CN102437290B - A kind of display of organic electroluminescence blue-light device and preparation method thereof - Google Patents

Abstract

The present invention provides a blue light device for an organic electroluminescent display, which comprises an anode, a hole transport layer, a blue light emitting layer, an electron transport layer and a cathode stacked in sequence, and the blue light emitting layer includes a host material and a dye for the light emitting layer, wherein the The HOMO energy level of the host material is not greater than -5.7eV, the HOMO energy level of the light-emitting layer dye is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between the HOMO energy levels of the host material and the light-emitting layer dye And the difference with the energy level of the HOMO of the dye in the light-emitting layer is >0.3eV. The invention also provides a method for preparing the blue light device for the organic electroluminescent display, an organic electroluminescent display with the blue light device and a preparation method for the organic electroluminescent display. Compared with the prior art, the blue light device of the invention has higher luminous efficiency and better chromaticity.

Description

A kind of blue light device for organic electroluminescence display and preparation method thereof

technical field

The invention relates to a blue light device for an organic electroluminescence display, an organic electroluminescence display with the blue light device, and a method for preparing the blue light device for an organic electroluminescence display and the organic electroluminescence display.

Background technique

An organic electroluminescence display (OLED) becomes a color display by means of light-emitting devices of three colors: red, green, and blue. Since blue light with better chromaticity can significantly reduce the power consumption of displays, blue light devices have been one of the main directions of OLED research.

To improve the chromaticity of blue light, materials for the light-emitting layer with a wide bandgap are usually required. For example, Idemitsu Kosan disclosed in the patent application CN1643105A a material with a bandgap >2.8eV, which can obtain blue light with a chromaticity between (0.12, 0.11) and (0.16, 0.19). However, the use of such wide-bandgap luminescent materials can easily cause charges to enter the transport layer, thereby affecting the luminous efficiency and lifetime of the device.

In order to avoid the above-mentioned problems, a charge blocking layer is usually added in the light-emitting layer and the charge-transporting layer to confine the charges in the light-emitting layer. However, the use of a charge blocking layer increases the turn-on voltage of the device. At the same time, adding a functional layer makes the fabrication process of the device more complicated.

Contents of the invention

In order to solve the above problems, the present invention provides a blue light device for an organic electroluminescence display, which can obtain better chromaticity without using a charge blocking layer, and at the same time improve the luminous efficiency of the device. The device includes an anode, a hole transport layer, a blue light-emitting layer, an electron transport layer and a cathode stacked in sequence. The blue light-emitting layer contains a host material and a dye in the light-emitting layer, wherein the HOMO energy level of the host material is not greater than -5.7eV, and emits light. The HOMO energy level of the layer dye is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between the HOMO energy level of the host material and the light-emitting layer dye and the difference between the energy level of the HOMO of the light-emitting layer dye >0.3eV.

The present invention also provides a method for preparing a blue light device for an organic electroluminescent display, comprising sequentially depositing an anode, a hole transport layer, a blue light emitting layer, an electron transport layer and a cathode on a substrate, wherein the blue light emitting layer comprises A host material and an emitting layer dye, wherein the HOMO energy level of the host material is not greater than -5.7eV, the HOMO energy level of the emitting layer dye is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between the host material and The difference between and between the HOMO energy levels of the light-emitting layer dyes and the HOMO energy levels of the light-emitting layer dyes is >0.3eV.

The present invention also provides an organic electroluminescence display, which includes a blue light device, a red light device and a green light device, wherein the blue light device is the blue light device of the present invention.

The present invention also provides a method for preparing the organic electroluminescent display, comprising sequentially depositing a laminated anode and a hole transport layer on a substrate, and depositing a parallel blue light emitting layer and a green light emitting layer on the hole transport layer , a red light-emitting layer, and then sequentially deposit a laminated electron transport layer and a cathode, and then package, the blue light-emitting layer includes a host material and a light-emitting layer dye, wherein the HOMO energy level of the host material is not greater than -5.7eV, and the light-emitting layer The HOMO energy level of the dye is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between the HOMO energy level of the host material and the luminescent layer dye and the difference between the HOMO energy level of the luminescent layer dye > 0.3eV.

The present inventors have found that when the HOMO energy levels of the host material, the luminescent layer dye, and the hole transport layer material satisfy the above-mentioned relationship, holes are more easily injected into the deeper energy level of the HOMO energy band of the luminescent layer dye, and then are related to the LUMO energy level. Level electrons form excitons with higher energy, so as to obtain blue light with better chromaticity. Moreover, the probability of charge entering the transport layer is greatly reduced, thereby improving the luminous efficiency of the device. Therefore, the blue light device of the present invention has higher luminous efficiency and better chromaticity, and the lifetime is also improved.

Description of drawings

FIG. 1 is a schematic diagram of a single pixel of an organic light emitting display of the present invention.

in,

1 is the substrate;

2 is the anode

3 is the hole injection layer

4 is the hole transport layer

5R is the red light emitting layer

5G is the green light-emitting layer

5B is the blue light emitting layer

6 is the electron transport layer

7 is the electron injection layer

8 is the cathode.

detailed description

The blue light device for an organic electroluminescence display of the present invention comprises an anode, a hole transport layer, a blue light emitting layer, an electron transport layer and a cathode stacked in sequence, and the blue light emitting layer comprises a host material and a dye of the light emitting layer, wherein the HOMO of the host material The energy level is not greater than -5.7eV, the HOMO energy level of the light-emitting layer dye is not less than -5.2eV, and the HOMO energy level of the hole-transporting layer material is between the HOMO energy level of the host material and the light-emitting layer dye and is comparable to that of the light-emitting layer dye The difference between the energy levels of the HOMO is >0.3eV.

The difference between the HOMO energy level of the preferred luminescent layer dye and the HOMO energy level of the hole transport layer material>0.4eV, at this time, the excitons formed on the luminescent layer dye can be more effectively confined in the luminescent layer, thereby increasing the Exciton transition probability, thereby improving the luminous efficiency of blue light devices.

Preferably, the band gap of the hole transport material is greater than that of the dye in the light-emitting layer; further, it is preferred that the band gap of the hole transport material is also greater than that of the host material of the light-emitting layer.

Preferably, the hole-transporting material has a triplet energy level greater than 2.45eV, thus, in an organic electroluminescent display, besides the blue-light organic light-emitting device, it also includes a red-light organic light-emitting device and a green-light organic light-emitting device and red, When the green light and blue light organic light emitting devices use the same hole transport material, the luminous efficiency of the red light and green light organic light emitting devices is improved, so that the organic electroluminescent display can obtain higher brightness.

Preferably, the material of the hole transport layer has a lower conjugation property, which is beneficial to obtain a wider band gap and a lower HOMO energy level, thereby improving the chromaticity and luminous efficiency of the device. Preferred hole transport layer materials are compounds having the following general formula:

Among them, R ₁ -R ₄ , R ₅ -R ₈ , R _5' -R ₈ ' are selected from hydrogen elements, halogen elements, CN, NO ₂ , amino, fused aryl, fused heteroaryl, An alkyl group and an alcohol group, the condensed ring aryl group is preferably a condensed ring aryl group with 6 to 30 carbon atoms, and the condensed heterocyclic aryl group is preferably a condensed hetero ring group with 6 to 30 carbon atoms Cycloaryl group, the alkyl group is preferably an alkyl group with 6 to 20 carbon atoms, and the alcohol group is preferably an alcohol group with 6 to 30 carbon atoms. A and B are respectively selected from phenyl, naphthyl and anilino. R ₉ , R ₁₀ , R ₉ ′ and R ₁₀ ′ are each an aryl group, preferably an aryl group having 6 to 30 carbon atoms.

Also preferred as material for the hole transport layer are indenofluorene derivatives, more preferably indenofluorene derivatives having the following structure:

Wherein, A and B are respectively selected from phenyl, naphthyl and anilino. R ₁ and R ₂ , R ₁ ' and R ₂ ' are respectively selected from aryl groups, preferably aryl groups with 6 to 30 carbon atoms. _R3 is an alkyl group having 1-6 carbon atoms, especially methyl, ethyl, propyl, isopropyl, butyl, isobutyl, n-pentyl or n-hexyl.

Also preferred as hole-transport layer materials are compounds of the general formula:

Wherein, A and B are respectively selected from phenyl, naphthyl and anilino. R ₁ and R ₂ , R ₁ ' and R ₂ ' are respectively aryl groups, preferably aryl groups having 6 to 30 carbon atoms.

Also preferred as hole-transport layer materials are compounds of the general formula:

Wherein, A and B are respectively selected from phenyl, naphthyl and anilino. R ₁ and R ₂ , R ₁ ' and R ₂ ' are respectively aryl groups, preferably aryl groups having 6 to 30 carbon atoms.

A particularly preferred class of hole transport layer materials are the following compounds HTL-1 to HTL-5:

Another class of particularly preferred hole transport layer materials are the following compounds HTL-6 to HTL-10:

Another class of particularly preferred hole transport layer materials are the following compounds HTL-11 to HTL-15:

Another class of particularly preferred hole transport layer materials are the following compounds HTL-16 to HTL-20:

The host material is preferably an anthracene derivative, especially an asymmetric anthracene derivative or a phenylanthracene derivative, or a compound of the general formula (Cz)nMm, wherein Cz represents a substituted or unsubstituted carbazolyl group, M represents a substituted or unsubstituted heteroaromatic ring group having 2-40 carbon atoms and nitrogen atoms, n represents an integer of 2 to 3, and m represents an integer of 1 to 3.

As the host material, the following anthracene derivative compounds are preferred:

As the host material, compound BH-1, compound BH-2 which are phenylanthracene derivatives, compound BH-3, compound BH-4 which are asymmetric anthracene derivatives, and compound BH-5 are particularly preferable.

The dye for the light-emitting layer is preferably indenobenzofluorene derivatives, among which the following compounds BD-1 to BD-11 are preferred:

The following compounds BD-12 to BD-22 are also preferred:

The ratio of the host material to the dye in the light-emitting layer is preferably 2 wt %-8 wt % based on the host material.

The electron transport layer can adopt the materials commonly used as the electron transport layer in organic electroluminescent devices in the prior art, such as metal-organic complexes, aromatic fused rings or o-phenanthrolines, etc. can be used.

In addition, there may be a hole injection layer between the anode and the hole transport layer, and an electron injection layer between the cathode and the electron transport layer. Both the hole injection layer and the electron injection layer can use materials commonly used in the hole injection layer or electron injection layer in the prior art.

The cathode can be made of metal or metal mixture, such as Ag-doped Mg, Ag-doped Ca, etc. The electron injection layer can also be combined with the cathode to form an electron injection layer/metal layer structure, such as LiF/Al, Li ₂ O/Al and other common structures.

The anode can be an anode commonly used in organic electroluminescent devices in the prior art, such as an ITO anode.

There is also preferably a second hole-transport layer between the hole-transport layer and the hole-injection layer, which has a higher hole mobility than the hole-transport layer. Higher brightness can be obtained by adding a second hole transport layer. As the material of the second hole transport layer, it is preferred to use arylamine derivatives such as N,N'-diphenyl-N,N'-bis(1,1'-biphenyl)-4,4'- Diamine (NPB).

The thickness of each layer may be conventional for layers of these materials used in the prior art. Wherein, the hole transport layer preferably has a thickness of 5 nm-50 nm, more preferably 5 nm-15 nm.

The present invention also provides a method for preparing a blue light device for an organic electroluminescent display, comprising sequentially depositing an anode, a hole transport layer, a blue light emitting layer, an electron transport layer and a cathode on a substrate, wherein the blue light emitting layer comprises The host material and the luminescent layer dye, wherein the HOMO energy level of the host material is not greater than -5.7eV, the HOMO energy level of the luminescent layer dye is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between that of the luminescent layer host The difference between the energy level of the HOMO of the dye of the light-emitting layer and the energy level of the HOMO of the dye of the light-emitting layer is >0.3eV.

The deposition can be achieved by conventional deposition methods used in the prior art to form layers of these materials, such as physical vapor deposition, chemical vapor deposition, and the like.

Preferably a hole-injection layer is also deposited between the anode and the hole-transport layer, and/or an electron-injection layer is deposited between the cathode and the electron-transport layer. If a hole-injection layer is deposited, preferably a second hole-transport layer is also deposited between the hole-transport layer and the hole-injection layer, said second hole-transport layer being defined above.

The present invention also provides an organic electroluminescence display, which includes a blue light device, a red light device and a green light device, wherein the blue light device is the blue light device of the present invention. Preferably, at least one of the red and green organic light-emitting devices is an organic phosphorescent light-emitting device.

The present invention also provides a method for preparing the organic electroluminescence display, which includes sequentially depositing a laminated anode and a hole transport layer on a substrate, and depositing a parallel blue light-emitting layer, a green light-emitting layer, a red light-emitting layer on the hole transport layer. The light-emitting layer, followed by sequentially depositing a laminated electron transport layer and cathode, and then packaging, the blue light-emitting layer includes a host material and a light-emitting layer dye, wherein the HOMO energy level of the host material is not greater than -5.7eV, and the light-emitting layer dye The HOMO energy level is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between the HOMO energy level of the host material and the luminescent layer dye and the difference between the HOMO energy level of the luminescent layer dye>0.3eV .

The encapsulation can be performed by a encapsulation method commonly used in organic electroluminescent devices in the prior art.

The present invention is further illustrated by the following examples, but the present invention is not limited to these specific examples.

In the following examples, the HOMO energy level of the material was determined by cyclic voltammetry.

Example 1:

Deposit ITO on the glass substrate as the anode of the OLED blue light device, and etch out the desired pattern, and treat it with _O2 plasma for 3 minutes. The resulting substrate was placed in a vacuum, and 50 nm of a mixture of MTDATA and F4TCNQ was deposited by co-evaporation as a hole injection layer, wherein F4TCNQ was 4% by weight relative to MTDATA. Next, 20 nm of HTL-1 was deposited as a hole transport layer. A 40 nm mixture of BH-3 and BD-1 was then co-evaporated as an emitting layer, wherein BD-1 was 5% by weight relative to BH-3. Then 20nm of Bphen was deposited as electron transport layer. Keeping the vacuum constant, deposit 0.5nm LiF as electron injection layer. Finally, 150 nm of Al is deposited as the cathode. Pass the substrate into a pure _N environment for encapsulation. Thus, an OLED blue light device is fabricated.

The structural formulas of MTDATA, F4TCNQ, and BPhen are as follows:

The HOMO levels and band gaps of the selected materials HTL-1, BH-3, and BD-1 are shown in Table 1 below.

Table 1

Material HTL-1 BH-3 BD-1 HOMO -5.52eV -5.8eV -5.1eV Bandgap width 3.2eV 3.0eV 2.8eV

Example 2

The OLED blue light device was prepared according to the method described in Example 1. The difference is that HTL-1 is replaced by HTL-2, BH-3 is replaced by BH-1, and BD-1 is replaced by BD-2.

The HOMO levels and band gaps of the selected HTL-2, BH-1, and BD-2 are shown in Table 2 below.

Table 2

Material HTL-2 BH-1 BD-2 HOMO -5.45eV -5.75eV -5.1eV

Bandgap width 3.2eV 3eV 2.8eV

Example 3

The OLED blue light device was prepared according to the method described in Example 1. The difference is that the material of the hole transport layer is HTL-3 with a thickness of 10nm, and a second hole transport layer with a thickness of 10nm is added between the hole injection layer and the hole transport layer and the material is NPB.

table 3

Material HTL-3 BH-3 BD-1 NPB HOMO -5.51eV -5.8eV -5.1eV -5.4eV Bandgap width 3.2eV 3eV 2.8eV 3.0eV

Example 4

The OLED blue light device was prepared according to the method described in Example 1. The difference is that BH-4 is used instead of BH-3.

The HOMO levels and bandgap widths of the selected HTL-1, BH-4, and BD-1 are shown in Table 4 below.

Table 4

Material HTL-1 BH-4 BD-1 HOMO -5.52eV -5.8eV -5.1eV Bandgap width 3.2eV 3.1eV 2.8eV

Example 5

The OLED blue light device was prepared according to the method described in Example 1. The difference is that BH-5 is used instead of BH-3.

The HOMO levels and bandgap widths of the selected HTL-1, BH-5, and BD-1 are shown in Table 5 below.

table 5

Material HTL-1 BH-5 BD-1 HOMO -5.52eV -5.75eV -5.1eV Bandgap width 3.2eV 3.0eV 2.8eV

Comparative example 1:

OLED devices were fabricated according to the method described in Example 1 except that NPB was used instead of HTL-1.

Comparative example 2:

OLED devices were fabricated according to the method described in Example 2, except that NPB was used instead of HTL-1.

The performance comparison of the OLED blue light devices prepared in Examples 1-5 and Comparative Examples 1-2 is shown in the following table. Among them, the brightness and chromaticity are measured by the photometric colorimeter PR655, the luminous efficiency is obtained by the ratio of the brightness and the current density measured by the current and voltage meter Keithley, and the life is the half-life time of the brightness, which is continuously observed by the brightness meter.

Table 6

It can be seen from Table 6 that compared with Comparative Examples 1-2, the devices of Examples 1-5 can obtain better chromaticity, higher luminous efficiency and/or longer lifetime.

Claims (26)

1. A blue light device for an organic electroluminescence display, the device comprises a stacked anode, a hole transport layer, a blue light emitting layer, an electron transport layer and a negative electrode in sequence, and the blue light emitting layer comprises a host material and a light emitting layer dye, wherein the The HOMO energy level of the host material is not greater than -5.7eV, the HOMO energy level of the light-emitting layer dye is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between the HOMO energy levels of the host material and the light-emitting layer dye and The difference from the energy level of the HOMO of the emissive layer dye is >0.3eV. 2. The blue light device for organic electroluminescence display according to claim 1, characterized in that the difference between the HOMO energy level of the dye in the light-emitting layer and the HOMO energy level of the hole transport layer material is >0.4eV. 3. The blue light device for organic electroluminescence display according to claim 1, characterized in that the forbidden band width of the hole transport layer material is larger than the forbidden band width of the light emitting layer dye. 4. The blue light device for organic electroluminescence display according to claim 3, characterized in that the band gap of the material of the hole transport layer is also larger than the band gap of the host material of the light emitting layer. 5. The blue light device for organic electroluminescence display according to claim 1, characterized in that, the material of the hole transport layer has a triplet energy level greater than 2.45eV. 6. The blue light device for organic electroluminescence display according to claim 1, characterized in that the hole transport layer material is a compound with the following general formula: Among them, R ₁ -R ₄ , R ₅ -R ₈ , R _5' -R ₈ ' are selected from hydrogen elements, halogen elements, CN, NO ₂ , amino, fused aryl, fused heteroaryl, Alkyl and alcohol; A and B are respectively selected from phenyl, naphthyl and anilino; R ₉ , R ₁₀ , R ₉ 'and R ₁₀ ' are aryl; or indenofluorene derivatives; or a compound of the following general formula: Wherein, A and B are respectively selected from phenyl, naphthyl and anilino; R ₁ and R ₂ , R ₁ ' and R ₂ ' are respectively aryl; or a compound of the following general formula: Wherein, A and B are respectively selected from phenyl, naphthyl and anilino; R ₁ and R ₂ , R ₁ ' and R ₂ ' are respectively aryl. 7. The blue light device for organic electroluminescent display according to claim 6, characterized in that, in the definition of the groups R ₁ -R ₄ , R ₅ -R ₈ , R ₅ '-R ₈ ' in the following general formula The fused ring aryl group is a fused ring aryl group with 6 to 30 carbon atoms, the fused heterocyclic aryl group is a fused heterocyclic aryl group with 6 to 30 carbon atoms, and the alkyl is an alkyl group with 6 to 20 carbon atoms, and the alcohol group is an alcohol group with 6 to 30 carbon atoms. 8. The blue light device for organic electroluminescence display according to claim 6, characterized in that R ₉ , R ₁₀ , R ₉ ′ and R ₁₀ ′ are respectively aryl groups with 6 to 30 carbon atoms. 9. The blue light device for organic electroluminescent display according to claim 6, characterized in that, the indenofluorene derivative has the following structure: Wherein, A and B are respectively selected from phenyl, naphthyl and anilino; R ₁ and R ₂ , R ₁ ' and R ₂ ' are respectively selected from aryl; R ₃ is an alkyl group with 1-6 carbon atoms. 10. The blue light device for organic electroluminescence display according to claim 9, characterized in that, R ₁ and R ₂ , R ₁ ' and R ₂ ' in the indenofluorene derivatives are respectively selected from those with carbon atoms ranging from 6 to 30 aryl. 11. the blue light device for organic electroluminescence display of claim 9, is characterized in that, R in the described indenofluorene derivative ₃ is methyl, ethyl, propyl, isopropyl, butyl, isobutyl , n-pentyl or n-hexyl. 12. The blue light device for organic electroluminescence display according to claim 6, characterized in that, in the compound of the following general formula R ₁ and R ₂ , and R ₁ ′ and R ₂ ′ are each an aryl group having 6 to 30 carbon atoms. 13. The blue light device for organic electroluminescence display according to claim 6, characterized in that, in the compound of the following general formula R ₁ and R ₂ , and R ₁ ′ and R ₂ ′ are each an aryl group having 6 to 30 carbon atoms. 14. The blue light device for organic electroluminescence display according to claim 6, characterized in that the thickness of the hole transport layer is 5nm-50nm. 15. The blue light device for organic electroluminescence display according to claim 6, characterized in that the thickness of the hole transport layer is 5nm-15nm. 16. The blue light device for organic electroluminescence display according to claim 6, characterized in that the hole transport layer material is selected from the following compounds HTL-1～HTL-5: Or selected from the following compounds HTL-6～HTL-10: Or selected from the following compounds HTL-11～HTL-15: Or be selected from following compound HTL-16～HTL-20: 17. The blue light device for organic electroluminescent display according to claim 1, characterized in that, the host material is an anthracene derivative, or a compound of the general formula (Cz)nMm, wherein Cz represents a substituted or unsubstituted carba Azolyl, M represents a substituted or unsubstituted heteroaromatic ring group with 2-40 carbon atoms and nitrogen atoms, n represents an integer from 2 to 3, and m represents an integer from 1 to 3. 18. The blue light device for an organic electroluminescent display according to claim 17, characterized in that the host material is an asymmetric anthracene derivative or a phenylanthracene derivative. 19. The blue light device for organic electroluminescence display according to claim 17, characterized in that, the host material is selected from the following anthracene derivative compounds: 20. The blue light device for organic electroluminescence display according to claim 19, characterized in that, the host material is selected from the group consisting of compound BH-1, compound BH-2 as phenylanthracene derivatives, compounds as asymmetric anthracene derivatives BH-3, Compound BH-4, and Compound BH-5. 21. The blue light device for organic electroluminescence display according to claim 1, characterized in that, the dye in the light-emitting layer is an indenobenzofluorene derivative. 22. The blue light device for organic electroluminescence display according to claim 21, characterized in that, the dyes in the light-emitting layer are selected from the following compounds BD-1 to BD-11: And the following compounds BD-12～BD-22: 23. The blue light device for organic electroluminescence display according to claim 1, characterized in that, the ratio of the host material to the dye in the light-emitting layer is that the dye in the light-emitting layer is 2 wt %-8 wt % relative to the host material. 24. A method for preparing a blue light device for an organic electroluminescent display, comprising sequentially depositing an anode, a hole transport layer, a blue light emitting layer, an electron transport layer and a cathode on a substrate, wherein the blue light emitting layer comprises a host material and an emitting layer dye, wherein the HOMO energy level of the host material is not greater than -5.7eV, the HOMO energy level of the emitting layer dye is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between the host material and the emitting layer The difference between the HOMO energy levels of the dyes and between the energy levels of the HOMO of the dyes of the light-emitting layer is >0.3eV. 25. An organic electroluminescence display, comprising a blue light device, a red light device and a green light device, wherein the blue light device is the blue light device according to any one of claims 1-23. 26. A method for preparing an organic electroluminescent display, comprising sequentially depositing a laminated anode and a hole transport layer on a substrate, and depositing a parallel blue light emitting layer, a green light emitting layer, and a red light emitting layer on the hole transport layer layer, and then sequentially deposit the stacked electron transport layer and cathode, and then package. The blue light-emitting layer includes a host material and a light-emitting layer dye, wherein the HOMO energy level of the host material is not greater than -5.7eV, and the HOMO energy level of the light-emitting layer dye The level is not less than -5.2eV, and the HOMO energy level of the hole transport layer material is between the HOMO energy level of the host material and the light-emitting layer dye, and the difference between the energy level of the HOMO of the light-emitting layer dye is >0.3eV.