CN113097402A - Organic electroluminescent device, preparation method thereof and display panel - Google Patents
Organic electroluminescent device, preparation method thereof and display panel Download PDFInfo
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
- H10K30/80—Constructional details
- H10K30/865—Intermediate layers comprising a mixture of materials of the adjoining active layers
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K2101/00—Properties of the organic materials covered by group H10K85/00
- H10K2101/40—Interrelation of parameters between multiple constituent active layers or sublayers, e.g. HOMO values in adjacent layers
Abstract
The present disclosure provides an organic electroluminescent device, a method of manufacturing the same, and a display panel. The organic electroluminescent device comprises an anode layer, a first buffer layer, a first light-emitting layer, a second buffer layer, a second light-emitting layer and a cathode layer which are sequentially stacked on a substrate, wherein the first buffer layer and the second buffer layer both comprise materials with hole mobility larger than electron mobility.
Description
Technical Field
The disclosure relates to the technical field of display, in particular to an organic electroluminescent device, a preparation method thereof and a display panel.
Background
Organic electroluminescent devices (OLEDs) have received great attention in the field of flat panel displays and lighting due to their advantages of high brightness, color saturation, thinness, and flexibility. Through the regulation effect of each functional layer, not only can better voltage, efficiency and service life characteristics be obtained, but also the luminous recombination center can be regulated to the interface of the buffer layer and the luminous layer, so that higher exciton concentration is obtained, and higher current efficiency can be obtained under low current density.
Disclosure of Invention
In one aspect, the present disclosure provides an organic electroluminescent device, including an anode layer, a first buffer layer, a first light emitting layer, a second buffer layer, a second light emitting layer, and a cathode layer, which are sequentially stacked on a substrate, wherein the first buffer layer and the second buffer layer each include a material having a hole mobility greater than an electron mobility.
In one embodiment of the present disclosure, the first light emitting layer includes a P-type light emitting material having a hole mobility greater than an electron mobility, and the second light emitting layer includes an N-type light emitting material having an electron mobility greater than a hole mobility.
In one embodiment of the present disclosure, a thickness of the first buffer layer is greater than a thickness of the second buffer layer.
In one embodiment of the present disclosure, the second buffer layer has a thickness ranging from 1 to 5 nm.
In one embodiment of the present disclosure, the organic electroluminescent device further includes a hole injection layer and a hole transport layer stacked between the first buffer layer and the anode layer.
In one embodiment of the present disclosure, the organic electroluminescent device further includes a reflective layer and a driving circuit which are stacked between the substrate and the anode layer.
In one embodiment of the present disclosure, the organic electroluminescent device further includes a hole blocking layer, an electron transport layer, and an electron injection layer, which are stacked between the second light emitting layer and the cathode layer.
In one embodiment of the present disclosure, a difference between a highest occupied orbital level of the first buffer layer and the hole transport layer level is less than 0.2eV, and a lowest unoccupied orbital level of the first buffer layer is higher than the first light emitting layer by more than 0.2 eV.
In one embodiment of the present disclosure, the organic electroluminescent device further comprises a light extraction layer on a side of the cathode layer remote from the substrate.
In another aspect, the present disclosure provides a display panel including: a plurality of pixel units, each pixel unit comprising a plurality of sub-pixels, at least one of the sub-pixels comprising an organic electroluminescent device according to the present disclosure or prepared by the preparation method of the present disclosure.
In another aspect, the present disclosure provides a method of making an organic electroluminescent device, comprising: sequentially forming on a substrate: the light-emitting diode comprises an anode layer, a first buffer layer, a first light-emitting layer, a second buffer layer, a second light-emitting layer and a cathode layer, wherein the first buffer layer and the second buffer layer are both made of materials with hole mobility larger than electron mobility.
In one embodiment of the present disclosure, the first light emitting layer is made of a P-type light emitting material having a hole mobility greater than an electron mobility, and the second light emitting layer is made of an N-type light emitting material having an electron mobility greater than a hole mobility.
In one embodiment of the present disclosure, a thickness of the first buffer layer is greater than a thickness of the second buffer layer, and the thickness of the second buffer layer ranges from 1 to 5 nm.
In one embodiment of the present disclosure, the method further comprises: forming a driving circuit, a reflecting layer, a hole injection layer, a hole transport layer, a hole blocking layer, an electron transport layer and an electron injection layer, wherein the driving circuit is positioned between the substrate and the anode layer; the reflecting layer is positioned on one side of the driving circuit far away from the substrate; the hole injection layer is positioned on one side of the anode layer far away from the substrate; the hole transport layer is positioned on one side of the hole injection layer, which is far away from the substrate; the hole blocking layer is positioned on one side of the second light-emitting layer far away from the substrate; the electron transport layer is positioned on one side of the hole blocking layer far away from the substrate; and the electron injection layer is positioned on one side of the electron transport layer far away from the substrate, and the hole injection layer is formed by doping 1-50% of a hole injection material with the hole transport material, and the hole transport layer is formed by the hole transport material.
In one embodiment of the present disclosure, a difference between a highest occupied orbital level of the first buffer layer and the hole transport layer level is less than 0.2eV, and a lowest unoccupied orbital level of the first buffer layer is higher than the first light emitting layer by more than 0.2 eV.
Drawings
In accordance with various disclosed embodiments, the following drawings are merely examples for illustrative purposes and are not intended to limit the scope of the invention.
Fig. 1 shows a graph of current efficiency versus current density for a prior art OLED structure.
Fig. 2 shows a schematic structural diagram of an organic electroluminescent device according to an embodiment of the present disclosure.
Fig. 3 shows a schematic diagram of a recombination center for a prior art OLED structure.
Fig. 4 shows a schematic diagram of a recombination center of an OLED structure according to an embodiment of the disclosure.
Fig. 5 shows a flow chart of a method of fabricating an organic electroluminescent device according to an embodiment of the present disclosure.
Reference numerals
A substrate 1; a drive circuit 2; a reflective layer 3; an anode layer 4; a hole injection layer 5; a hole transport layer 6; a first buffer layer 7; a first light-emitting layer 8; a second buffer layer 9; a second light-emitting layer 10; a hole blocking layer 11; an electron transport layer 12; an electron injection layer 13; a cathode layer 14; a light extraction layer 15.
Detailed Description
Other objects, advantages and effects of the present disclosure will be understood by the following description of specific embodiments with reference to the accompanying drawings. In the drawings, like parts are provided with the same reference numerals.
To more clearly illustrate the objects, aspects and advantages of the present disclosure, embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It is to be understood that the following description of the embodiments is intended to illustrate and explain the general concepts of the disclosure and should not be taken as limiting the disclosure. In the specification, the same or similar reference numerals refer to the same or similar parts or components.
Additionally, the drawings are not necessarily drawn to scale in order to clearly illustrate the present disclosure.
The existing OLED device structure includes an anode, a hole injection layer, a hole transport layer, a buffer layer (electron blocking layer), a light emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, a cathode, and the like. However, such a structure has a problem of efficiency roll-off.
Fig. 1 shows a graph of current efficiency versus current density for a prior art OLED structure. As shown in FIG. 1, the current density (J (mA/cm) was varied2) Due to the increase of the carrier recombination rate, a large number of excitons are generated, and due to the fact that the exciton service life is long, the exciton concentration is too high, exciton quenching is aggravated, and finally the efficiency roll-off phenomenon occurs. That is, as the current density increases, the current efficiency rapidly decreases.
The present disclosure provides an organic electroluminescent device, a method for manufacturing the same, and a display panel, in which the structure of the organic electroluminescent device is optimized, and the injection balance of carriers is adjusted, so that the recombination center position of the carriers is affected, thereby alleviating the efficiency roll-off phenomenon.
The present disclosure provides an organic electroluminescent device, including on a substrate, in order stacked: the light-emitting diode comprises an anode layer, a first buffer layer, a first light-emitting layer, a second buffer layer, a second light-emitting layer and a cathode layer, wherein the first buffer layer and the second buffer layer are both made of materials with hole mobility larger than electron mobility.
Fig. 2 shows a schematic structural diagram of an organic electroluminescent device according to an embodiment of the present disclosure. As shown in fig. 2, an embodiment of the present disclosure provides an organic electroluminescent device, which may include a hole injection layer 5, a hole transport layer 6, a first buffer layer 7, a first light emitting layer 8, a second buffer layer 9, a second light emitting layer 10, a hole blocking layer 11, an electron transport layer 12, an electron injection layer 13, and a cathode layer 14, which are sequentially stacked on a substrate 1. The organic electroluminescent device further includes: an anode layer 4 on the side of the hole injection layer 5 remote from the hole transport layer 6, and a reflective layer 3 on the side of the anode layer 4 remote from the hole transport layer 6. In addition, in one embodiment, the organic electroluminescent device may further include: a light extraction layer 15 on the side of the cathode layer 14 remote from the substrate 1. In the embodiment of the present disclosure, a driving circuit 2 is further provided between the reflective layer 3 and the substrate 1. In an embodiment of the present disclosure, a voltage is applied between the anode layer 4 and the cathode layer 14. In an embodiment of the present disclosure, the substrate 1 may be a glass substrate. The four layers are marked in fig. 2 with brackets in order to clearly show the first buffer layer 7, the first light-emitting layer 8, the second buffer layer 9, and the second light-emitting layer 10.
In the embodiment of the present disclosure, the first buffer layer 7 and the second buffer layer 9 are each made of a material having a hole mobility greater than an electron mobility. Further, the thickness of the first buffer layer 7 is greater than that of the second buffer layer 9, and the thickness of the second buffer layer 9 ranges from 1nm to 5 nm.
In the embodiment of the present disclosure, the first light emitting layer 8 is a P-type light emitting material and has a hole mobility greater than an electron mobility, and the second light emitting layer 10 is an N-type light emitting material and has an electron mobility greater than a hole mobility.
In the embodiment of the present disclosure, the first buffer layer 7 mainly plays an optical adjustment role. In the light emitting device structure of the embodiment of the present disclosure, an optical resonant cavity is formed between the reflective layer 3 and the cathode layer 14, so as to improve the light extraction efficiency, and the second buffer layer 9 is interposed between the reflective layer 3 and the cathode layer 14, so that the thickness of the second buffer layer 9 cannot be too thick, so as to avoid completely blocking electrons from passing through, so that the first light emitting layer 8 plays a role in optical adjustment, and simultaneously, the efficiency roll-off is reduced.
In the embodiment of the present disclosure, the difference between the energy level of the Highest Occupied Molecular Orbital (HOMO) of the first buffer layer 7 and the energy level of the hole transport layer 6 may be less than 0.2eV, and the energy level of the Lowest Unoccupied Molecular Orbital (LUMO) of the first buffer layer 7 may be higher than the energy level of the first light emitting layer 8 by more than 0.2 eV.
Fig. 3 shows a schematic diagram of a recombination center for a prior art OLED structure. Fig. 4 shows a schematic diagram of a recombination center of an OLED structure according to an embodiment of the disclosure. Fig. 3 and 4 show the formation positions of the carrier recombination centers in both cases, respectively.
The formation of carrier recombination centers is related to the energy level matching and carrier mobility of the material. The first buffer layer and the second buffer layer are made of a material having an electron mobility much lower than a hole mobility, and have a higher LUMO level, thereby blocking electrons. In the embodiment of the present disclosure, it is difficult for electrons to pass through the second buffer layer 9 after the second buffer layer 9 is provided, and even if a part of the electrons pass through the second buffer layer 9, a large number of holes are recombined at the interface of the first light emitting layer 8 and the second buffer layer 9.
Through the above-described OLED structure according to the embodiment of the present disclosure, the carrier recombination center position can be adjusted, and two carrier recombination centers are present on both the left and right sides of the second buffer layer 9. Compared with a single carrier recombination center (fig. 3) in an OLED structure of an existing device, the double carrier recombination center (fig. 4) in the OLED structure according to the embodiment of the present disclosure can adjust carrier injection balance, and further affect the position of the carrier recombination center, so that an efficiency roll-off phenomenon is alleviated.
In another aspect, the present disclosure provides a display panel. In some embodiments, a display panel includes a plurality of pixel units, each pixel unit including a plurality of sub-pixels, at least one of the plurality of sub-pixels including an organic electroluminescent device described herein or manufactured by a method described herein.
Since the display panel of the embodiment of the present disclosure includes the organic electroluminescent device described herein or manufactured by the method described herein, the display panel may adjust carrier injection balance, thereby affecting a carrier recombination center position, and thus alleviating an efficiency roll-off phenomenon.
In another aspect, the present disclosure provides a method of fabricating an organic electroluminescent device, including sequentially forming on a substrate: the organic electroluminescent device comprises an anode layer, a hole injection layer, a hole transport layer, a first buffer layer, a first light emitting layer, a second buffer layer, a second light emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer and a cathode layer. The method further comprises the following steps: a reflective layer is formed on the anode layer on the side remote from the hole transport layer. In addition, a driving circuit is formed between the reflective layer and the substrate. Wherein the first buffer layer and the second buffer layer are both made of a material having a hole mobility greater than an electron mobility.
Fig. 5 shows a flow chart of a method of fabricating an organic electroluminescent device according to an embodiment of the present disclosure.
Specifically, as shown in fig. 5, the method for manufacturing an organic electroluminescent device provided by the present disclosure includes the following steps:
1. a driving circuit is fabricated on the substrate for lighting a pixel region of the organic electroluminescent device.
2. And forming a reflecting layer on the side of the driving circuit far away from the substrate, and forming an anode layer on the side of the reflecting layer far away from the substrate.
3. And forming a hole injection layer and a hole transport layer on one side of the anode layer, which is far away from the substrate, by adopting a vacuum evaporation process.
The hole injection layer is formed by doping 1% to 50% of a hole injection material with a hole transport material, and has a thickness ranging from 1nm to 10 nm. The hole transport layer is formed by direct evaporation of a hole transport material.
Wherein the hole injection material comprises: NDP series P type doping materials (NDP-2, NDP-9 and the like), 2,3,5, 6-tetrafluoro-7, 7',8,8' -tetracyanodimethyl-P-benzene (F4-TCNQ), tris (4-bromophenyl) ammonium hexachloroantimonate (TBAHA) and the like;
the hole transport material includes: n, N '-di (1-naphthyl) -N, N' -diphenyl-1, 1 '-biphenyl-4-4' -diamine (NPB), triphenyldiamine derivative (TPD), TPTE, 1,3, 5-tris (N-3-methylphenyl-N-phenylamino) benzene (TDAB), and the like.
4. And forming a first buffer layer and a first light-emitting layer on the sides, far away from the substrate, of the hole injection layer and the hole transport layer in sequence by adopting a vacuum evaporation process.
The first buffer layer is made of a material having a HOMO level less than the hole transport layer level by 0.2eV and a LUMO level higher than the first light emitting layer level by 0.2eV or more, and includes: 2- (4-tert-butylphenyl) -5- (4-biphenyl) 1,3, 4-diazole, 3 (biphenyl) -4-benzene-5- (4-tert-butylphenyl) -4H-1,2, 4-triazole; the thickness of the first buffer layer is 5nm to 100 nm; the hole mobility of the first buffer layer is greater than the electron mobility;
the first light emitting layer has a hole mobility greater than an electron mobility. The first light-emitting layer has a T1 energy level in the range of 2.5eV to 2.7eV and a HOMO energy level less than-5.5 eV. The materials of the first light-emitting layer include: carbazole aromatic amine-based materials, 9-ethyl-3, 6-bis (4',4 ″ -dimethyltriphenylamine), 4,4',4 ″ -tris (carbazol-9-yl) triphenylamine, tris (4-carbazol-9-ylphenyl) amine, N-bis [4- (9H-9-carbazolyl) phenyl ] -3, 5-dibromoaniline, N '-diphenyl-, N' -bis (3-methylphenyl-1, 1 '-biphenyl-, 4,4' -diamine, N '-diphenyl-, N' -dipentyl-1, 1 '-biphenyl-4, 4' -diamine, and the like.
5. And forming a second buffer layer and a second light-emitting layer on one side of the first light-emitting layer, which is far away from the substrate, in sequence by adopting a vacuum evaporation process.
The material of the second buffer layer is the same as that of the first buffer layer, and the thickness of the second buffer layer is 1nm to 5 nm;
the electron mobility of the second light emitting layer is greater than the hole mobility. The second light-emitting layer has a T1 energy level ranging from 2.7eV to 2.9eV, and a HOMO energy level greater than-5.5 eV. The material of the second light emitting layer includes: azines, triphenyl-1, 3, 5-s-triazine, 2- (5-fluoro- [ [1,1 '-biphenyl ] -2-yl) -4, 6-diphenyl-1, 3, 5-triazine, 6-phenyl-1, 3, 4-triazine-2, 4-diamine, 2-chloro-4- (4- (2-naphthyl) benzene) -6-phenyl-1, 3, 5-triazine 2,4, 6-tris (3-bromophenyl) -1,3, 5-triazine, 2- (4-bromophenyl) -4, 6-dimethyl-1, 3, 5-triazine, N', N "-tris (3-toluylamino) -1,3, 5-s-triazine, 4, 6-bis (biphenyl-4-yl) -2- [3- (3-piperidinylidene) -5- (4,4,5, 5-tetramethyl-1, 3, 2-dioxaborolan-2-yl) phenyl ] -1,3, 5-treble, 2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-triazine, N- (3-chlorophenyl) -1,3, 5-triazine-2, 4-diamine, 2, 4-dimethyl-6-phenyl-1, 3, 5-triazine, 2-chloro-4- (benzonitrile-3-yl) -6-phenyl-1, 3, 5-triazine, and the like.
6. And sequentially forming a Hole Blocking Layer (HBL), an Electron Transport Layer (ETL), an Electron Injection Layer (EIL) and a cathode layer on one side of the second light-emitting layer, which is far away from the substrate, by adopting a vacuum evaporation process.
The hole blocking layer includes: 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene. The thickness of the hole blocking layer is 1nm to 10 nm;
the materials of the electron transport layer include: 2- (4-biphenyl) -5-phenyl oxadiazole (PBD), 2, 5-bis (1-naphthyl) -1,3, 5-oxadiazole (BND), 2,4, 6-triphenoxy-1, 3, 5-Triazine (TRZ), and the like. The thickness of the electron transport layer is 10nm to 40 nm.
The materials of the electron injection layer include: alkali metal fluoride MF (M can be Li, Na, K, Rb, Cs, etc.), Li2O、LiBO2. The thickness of the electron injection layer is 5nm to 10 nm.
The cathode layer can be one of metal materials such as Mg, Ag, Al, Li, K, Ca and the like, or alloys of the metal materials such as MgxAg (1-x), LixAl (1-x), LixCa (1-x) and LixAg (1-x). The thickness of the cathode layer is 10nm to 20 nm.
7. And forming a light extraction layer on the side of the cathode layer far away from the substrate by adopting a method such as vacuum evaporation or ink-jet printing.
In embodiments of the present disclosure, other processes may be used to form the layers in steps 3-6, such as a solution process.
Through the organic electroluminescent device prepared by the method according to the embodiment of the disclosure, the position of the carrier recombination center can be adjusted, and two carrier recombination centers are respectively arranged on the left side and the right side of the second buffer layer. Compared with a single-carrier recombination center in an OLED structure of an existing device, the double-carrier recombination center in the OLED structure prepared by the method disclosed by the embodiment of the disclosure can adjust carrier injection balance, so that the position of the carrier recombination center is influenced, and the efficiency roll-off phenomenon is relieved.
It is to be understood that the above embodiments are merely exemplary embodiments that have been employed to illustrate the principles of the present disclosure, and that the present disclosure is not limited thereto. It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the disclosure, and these changes and modifications are to be considered within the scope of the invention as defined in the following claims.
The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or exemplary embodiments disclosed. The foregoing description is, therefore, to be considered illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to explain the principles of the invention and its best mode practical application to enable one skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents, in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Thus, the terms "present invention" and the like do not necessarily limit the scope of the claims to particular embodiments, and references to exemplary embodiments of the invention are not meant to limit the invention, and no such limitation is to be inferred. The invention is to be limited only by the spirit and scope of the appended claims. Furthermore, these claims may refer to the use of "first," "second," etc., followed by a noun or element. These terms should be understood as nomenclature and should not be construed as limiting the number of elements modified by these nomenclature, unless a specific number has been given. Any advantages and benefits described may not apply to all embodiments of the invention. It will be appreciated that variations to the described embodiments may be made by those skilled in the art without departing from the scope of the invention, as defined by the appended claims. Furthermore, no element or component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the appended claims.
Claims (15)
1. An organic electroluminescent device comprises an anode layer, a first buffer layer, a first light-emitting layer, a second buffer layer, a second light-emitting layer and a cathode layer which are sequentially stacked on a substrate, wherein the first buffer layer and the second buffer layer both comprise materials with hole mobility larger than electron mobility.
2. The organic electroluminescent device according to claim 1, wherein the first light emitting layer comprises a P-type light emitting material having a hole mobility greater than an electron mobility, and the second light emitting layer comprises an N-type light emitting material having an electron mobility greater than a hole mobility.
3. The organic electroluminescent device according to claim 1, wherein a thickness of the first buffer layer is greater than a thickness of the second buffer layer.
4. The organic electroluminescent device according to claim 3, wherein the second buffer layer has a thickness ranging from 1 to 5 nm.
5. The organic electroluminescent device according to any one of claims 1 to 4, further comprising a hole injection layer and a hole transport layer which are stacked between the first buffer layer and the anode layer.
6. The organic electroluminescent device according to any one of claims 1 to 4, further comprising a reflective layer and a driving circuit which are stacked between the substrate and the anode layer.
7. The organic electroluminescent device according to any one of claims 1 to 4, further comprising a hole blocking layer, an electron transport layer, and an electron injection layer, which are stacked between the second light-emitting layer and the cathode layer.
8. The organic electroluminescent device according to claim 5, wherein the difference between the highest occupied orbital level of the first buffer layer and the hole transport layer level is less than 0.2eV, and the lowest unoccupied orbital level of the first buffer layer is higher than the first light emitting layer by 0.2eV or more.
9. An organic electroluminescent device according to any one of claims 1 to 4, further comprising a light extraction layer on the side of the cathode layer remote from the substrate.
10. A display panel, comprising: a plurality of pixel units, each pixel unit comprising a plurality of sub-pixels, at least one of the sub-pixels comprising an organic electroluminescent device according to any one of claims 1 to 9.
11. A method of making an organic electroluminescent device comprising:
sequentially forming on a substrate: an anode layer, a first buffer layer, a first light-emitting layer, a second buffer layer, a second light-emitting layer, and a cathode layer,
wherein the first buffer layer and the second buffer layer are both made of a material having a hole mobility greater than an electron mobility.
12. The method of claim 11, wherein the first light emitting layer is made of a P-type light emitting material having a hole mobility greater than an electron mobility, and the second light emitting layer is made of an N-type light emitting material having an electron mobility greater than a hole mobility.
13. The method of claim 11, wherein the first buffer layer has a thickness greater than a thickness of the second buffer layer, and the second buffer layer has a thickness in a range of 1 to 5 nm.
14. The method of any of claims 11 to 13, further comprising: forming a driving circuit, a reflective layer, a hole injection layer, a hole transport layer, a hole blocking layer, an electron transport layer, and an electron injection layer,
wherein the driving circuit is located between the substrate and the anode layer;
the reflecting layer is positioned on one side of the driving circuit far away from the substrate;
the hole injection layer is positioned on one side of the anode layer far away from the substrate;
the hole transport layer is positioned on one side of the hole injection layer, which is far away from the substrate;
the hole blocking layer is positioned on one side of the second light-emitting layer far away from the substrate;
the electron transport layer is positioned on one side of the hole blocking layer far away from the substrate; and
the electron injection layer is positioned on one side of the electron transport layer away from the substrate, an
Wherein the hole injection layer is formed by doping a hole transport material with 1% to 50% of the hole injection material, and the hole transport layer is formed of the hole transport material.
15. The method of claim 14, wherein the difference between the highest occupied orbital level of the first buffer layer and the hole-transporting layer level is less than 0.2eV, and the lowest unoccupied orbital level of the first buffer layer is greater than the first light-emitting layer by more than 0.2 eV.
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