CN115117265A - Light emitting device and display panel - Google Patents

Abstract

The present disclosure provides a light emitting device and a display panel. The light emitting device can prevent metal ions in the first N-type charge generation layer from diffusing into the first P-type charge generation layer by providing the second P-type charge generation layer and the second N-type charge generation layer between the first P-type charge generation layer and the first N-type charge generation layer, and a PN junction formed at an interface between the second P-type charge generation layer and the second N-type charge generation layer. Meanwhile, the PN junction formed by the second P-type charge generation layer and the second N-type charge generation layer can also ensure that charges are efficiently distributed to the light emitting stack, and the current efficiency of the light emitting device is not affected while the P-type charge generation layer and the N-type charge generation layer play a role in blocking.

Description

Light emitting device and display panel

Technical Field

The present disclosure relates to the field of display, and in particular, to a light emitting device and a display panel using the same for display.

Background

A stacked Organic Light-Emitting Diode (TOLED), also called a Tandem Organic electroluminescent device, is developed based on an Organic Light-Emitting Diode (OLED), and has the advantages of Light weight, ultra-thinness, low energy consumption, flexibility, low working voltage (3V-5V), transparency, environmental protection, high brightness, and high efficiency.

However, the current TOLED is limited to the design of its own structure, and is prone to material degradation or deterioration during operation, thereby resulting in a decrease in the performance and lifetime of the TOLED. Therefore, it is necessary to provide a new light emitting device to extend the lifetime of the light emitting device of the TOLED structure.

Disclosure of Invention

The present disclosure provides a light emitting device in which metal ions in a first N-type charge generation layer are prevented from diffusing into a first P-type charge generation layer by providing the charge generation layer between the first P-type charge generation layer and the first N-type charge generation layer, thereby being capable of extending the lifetime of the light emitting device of a TOLED structure, and a display panel.

A first aspect of the present disclosure provides a light emitting device including a cathode, a first light emitting stack, a first P-type charge generation layer, a first N-type charge generation layer, and an anode, which are sequentially arranged. The first N-type charge generation layer is doped with a metal. The charge generation layer is positioned between the first P-type charge generation layer and the first N-type charge generation layer, and includes a second P-type charge generation layer and a second N-type charge generation layer, the second P-type charge generation layer being positioned between the first P-type charge generation layer and the second N-type charge generation layer.

In the present implementation, the charge generation layer is provided in the first P-type charge generation layer and the first N-type charge generation layer, and the charge generation layer can extend a path of diffusion of metal ions in the first N-type charge generation layer into the first P-type charge generation layer, so that it is possible to solve a problem of a lifetime reduction of the TOLED due to possible diffusion of metal into the first P-type charge generation layer. The second P-type charge generation layer and the second N-type charge generation layer form a PN junction which can further prevent metal ions in the first N-type charge generation layer from diffusing, and at the same time, the PN junction can ensure that charges are efficiently distributed to the light emitting stack, thereby functioning as a blocking layer without affecting the current efficiency of the light emitting device.

In one specific implementation of the first aspect of the present disclosure, the HOMO level of the second P-type charge generation layer increases in a direction from the first P-type charge generation layer to the first N-type charge generation layer.

The HOMO energy level of the second P-type charge generation layer is gradually increased from the first P-type charge generation layer to the first N-type charge generation layer, so that better energy band bending transition can be formed, potential barriers in the charge generation process are reduced, and effective charge separation is realized.

In one specific implementation of the first aspect of the present disclosure, the LUMO level of the second N-type charge generation layer decreases in a direction from the first N-type charge generation layer to the first P-type charge generation layer.

The LUMO energy level of the second N-type charge generation layer is gradually reduced from the first P-type charge generation layer to the first N-type charge generation layer, so that better energy band bending transition can be formed, the potential barrier in the charge generation process is reduced, and effective charge separation is realized.

In a specific embodiment of the first aspect of the present disclosure, the HOMO level of the second P-type charge generation layer is greater than-5.5 eV, and the LUMO level of the second N-type charge generation layer is less than-4.5 eV.

The energy difference between the second P-type charge generation layer and the second N-type charge generation layer is less than ± 1eV, which can solve the problem of electron injection degradation in the first N-type charge generation layer due to a large energy level difference between the first N-type charge generation layer and the first P-type charge generation layer, and improve the stability of the light emitting device.

In a specific implementation of the first aspect of the present disclosure, the second P-type charge generation layer has a thickness of 5 angstroms to 100 angstroms, and the second N-type charge generation layer has a thickness of 5 angstroms to 100 angstroms.

Setting the thicknesses of the second P-type charge generation layer 171 and the second N-type charge generation layer 172 to be between 5 angstroms and 100 angstroms, respectively, can block diffusion of metal ions without affecting the efficiency of electron transport.

In a specific implementation of the first aspect of the present disclosure, the first light emitting stack 130 includes a hole transport layer connected to a first P-type charge generation layer, and the HOMO level of the first P-type charge generation layer is between the hole transport layer and the second P-type charge generation layer.

For example, further, the HOMO level of the first P-type charge generation layer increases in the direction from the first hole transport layer to the second P-type charge generation layer.

In the above embodiments, since the HOMO level of the first P-type charge generation layer gradually increases in the direction from the first hole transport layer to the second P-type charge generation layer, it is possible to form a better band bending transition, reduce the potential barrier in the charge generation process, and achieve effective charge separation.

In a specific implementation of the first aspect of the present disclosure, the second light emitting stacked layer includes an electron transport layer connected to the first N-type charge generation layer, and the LUMO level of the first N-type charge generation layer is between the second electron transport layer and the second N-type charge generation layer.

For example, further, the LUMO level of the first N-type charge generation layer decreases in the direction from the second electron transport layer to the second N-type charge generation layer.

The LUMO level of the first N-type charge generation layer gradually decreases in the direction from the second electron transport layer to the second N-type charge generation layer, which can form better band bending transition, and reduce the potential barrier in the charge generation process, achieving effective charge separation.

In a specific implementation manner of the first aspect of the present disclosure, the material of the first P-type charge generation layer is a strong oxidizing material doped with an organic hole transport material.

For example, further, the doping concentration of the strong oxidizing material is 3% to 15%.

For example, the strongly oxidizing material may include at least one of molybdenum oxide, tungsten oxide, vanadium oxide, and an organic compound having a cyano group and/or a fluorine group, and the organic hole transporting material may include at least one of a polyparaphenylene group, a polythiophene group, a polysiloxane group, a triphenylmethane group, a triarylamine group, a hydrazone group, a pyrazoline group, a carbazole group, and a butadiene group.

In a specific implementation form of the first aspect of the present disclosure, the material of the first N-type charge generation layer is a metal-doped organic electron transport material.

For example, further, the metal includes at least one of an alkali metal, an alkaline earth metal, and a transition metal, and the organic electron transport material includes at least one of a phenanthroline derivative and a triazine derivative.

For example, further, the doping concentration of the metal is 1% -10%.

Too high doping concentration of the metal may decrease the transmission efficiency but may cause the diffusion of metal ions to be more severe, and thus, the doping concentration of the metal is set to 1% -10%. The diffusion of metal ions is reduced while the transmission efficiency is guaranteed.

A second aspect of the present disclosure provides a display panel including a display region in which a plurality of the light emitting devices of the first aspect described above are disposed.

The present disclosure can prevent metal ions in the first N-type charge generation layer from diffusing into the P-type charge generation layer by providing the second P-type charge generation layer and the second N-type charge generation layer between the first P-type charge generation layer and the first N-type charge generation layer, and a PN junction formed at an interface of the second P-type charge generation layer and the second N-type charge generation layer. Meanwhile, the PN junction formed by the second P-type charge generation layer and the second N-type charge generation layer can also ensure that charges are efficiently distributed to the light emitting stack, and the current efficiency of the light emitting device is not affected while the P-type charge generation layer and the N-type charge generation layer play a role in blocking.

Drawings

Fig. 1 is a schematic cross-sectional view of a light emitting device according to an embodiment of the present disclosure.

Fig. 2 is a schematic cross-sectional view of a light emitting device according to an embodiment of the present disclosure.

Fig. 3 is a schematic energy level diagram of a portion of a film layer of a light emitting device according to an embodiment of the present disclosure.

Fig. 4 is a schematic diagram of a display panel according to an embodiment of the disclosure.

Fig. 5 is a partial cross-sectional view of the display panel shown in fig. 4.

Detailed Description

The technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure, and it is obvious that the described embodiments are only a part of the embodiments of the present disclosure, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.

It should be noted that, in the embodiments of the present disclosure, the HOMO level and the LUMO level refer to a Highest Occupied Molecular Orbital (Highest Occupied Molecular Orbital) and a Lowest Unoccupied Molecular Orbital (low Unoccupied Molecular Orbital), respectively. Electrons can only move on specific and discrete orbitals outside the atomic nucleus, and electrons on each orbit have discrete energy, and the energy values are energy levels. According to the front-line orbital theory, the energy difference between the HOMO and LUMO is called the "energy bandgap," and this energy difference, called the HOMO-LUMO level, can sometimes be used to determine whether a molecule is easily excited, the smaller the bandgap, the easier it is to excite the molecule.

OLEDs are widely used in lighting and display devices, and the operating principle of OLEDs is: under the action of an electric field, holes and electrons are respectively injected from the anode and the cathode and meet after the holes and the electrons migrate to the light-emitting layer to generate energy excitons, so that light-emitting molecules in the light-emitting layer are excited to generate visible light.

The TOLED includes an anode, a cathode, at least two light emitting stacks positioned between the anode and the cathode, and a charge generation layer positioned between the light emitting stacks. That is, a plurality of light emitting stacks sequentially connected in series through the charge generation layer are provided between the anode and the cathode. The operating principle of the TOLED is as follows: two or more independent light-emitting stacks are connected by an intermediate Charge Generation Layer, and holes and electrons are generated by the Charge Generation Layer (CGL) under the action of an applied electric field, and are injected into a Hole Transport Layer (HTL) and an Electron Transport Layer (ETL) of an adjacent light-emitting stack, respectively, and are combined with electrons from a cathode and holes from an anode in a light-emitting Layer of the light-emitting stack, respectively, to emit light.

The charge generation layer in the TOLED may employ a heterojunction structure, for example, the charge generation layer includes a P-type charge generation layer and an N-type charge generation layer stacked between two light emitting stacks. The N-type charge generation layer serves to inject electrons into the light emitting stacks connected thereto, and the P-type charge generation layer serves to inject holes into the light emitting stacks connected thereto, whereby it is possible to improve current efficiency of the light emitting layers in the respective light emitting stacks while ensuring efficient distribution of charges to the light emitting stacks.

However, long-term operation of the TOLED results in degradation or deterioration of the material used for the charge generation layer. On one hand, when the N-type charge generation layer is doped with metal, metal ions may diffuse into the P-type charge generation layer, resulting in a reduction in the lifetime of the TOLED. On the other hand, due to the energy level difference between the N-type charge generation Layer and the P-type charge generation Layer, after long-term use, charges are generated at the interface between the P-type charge generation Layer and an adjacent Hole Injection Layer (HIL) or Hole Transport Layer (HTL). Accordingly, charges accumulated at the interface between the P-type charge generation layer and the adjacent hole injection layer or hole transport layer may cause holes to be not injected into the connected light emitting stack, thereby causing the charge generation layer to be not able to effectively separate holes and electrons, resulting in degradation of electron injection in the N-type charge generation layer, such that electron injection efficiency from the interface between the P-type charge generation layer and the adjacent hole injection layer or hole transport layer to the N-type charge generation layer is significantly reduced, and finally, electron injection efficiency from the N-type charge generation layer to the adjacent electron transport layer is also significantly reduced, resulting in reduction of performance and lifetime of the TOLED.

In view of this, the present disclosure provides a light emitting device capable of solving the problem of degradation or deterioration of a material for a charge generation layer due to long-term operation of a TOLED, thereby being capable of extending the lifespan of the TOLED.

Fig. 1 is a cross-sectional view of a light emitting device according to an embodiment of the present disclosure. As shown in fig. 1, a light emitting device 10 provided by an embodiment of the present disclosure includes a cathode 110, an anode 120, a first light emitting stack 130, a first P-type charge generation layer 150, a charge generation layer 170, a first N-type charge generation layer 160, and a second light emitting stack 140 sequentially arranged from the cathode 110 to the anode 120. That is, the light emitting device 10 includes the cathode 110, the first light emitting stack 130, the first P-type charge generation layer 150, the charge generation layer 170, the first N-type charge generation layer 160, the second light emitting stack 140, and the anode 120, which are sequentially arranged from top to bottom.

In one implementation of the disclosed embodiment, the first N-type charge generation layer 160 is doped with a metal and the first P-type charge generation layer 150 is doped with a strong oxide material. The charge generation layer 170 serves to prevent metal ions in the first N-type charge generation layer 160 from diffusing into the first P-type charge generation layer 150. Specifically, the charge generation layer 170 is a material that is not doped with a metal or a strong oxide material.

In the present implementation, the charge generation layer 170 is disposed between the first P-type charge generation layer 150 and the first N-type charge generation layer 160, and the charge generation layer 170 can extend a path of diffusion of metal ions in the first N-type charge generation layer 160 into the first P-type charge generation layer 150, so that a time required for the metal ions in the first N-type charge generation layer 160 to diffuse into the first P-type charge generation layer 150 is extended, thereby being able to solve a problem of a lifetime reduction of the TOLED due to a possibility of diffusion of metal into the first P-type charge generation layer 150.

To avoid the effect of the charge generation layer 170 on the current efficiency of the light emitting device, the present disclosure provides yet another implementation. For example, the charge generation layer 170 includes a second P-type charge generation layer 171 and a second N-type charge generation layer 172, and the second P-type charge generation layer 171 is positioned between the first P-type charge generation layer 150 and the second N-type charge generation layer. The material of the second P-type charge generation layer 171 is an undoped P-type organic semiconductor material, and the material of the second N-type charge generation layer 172 is an undoped N-type organic semiconductor material.

Specifically, the material of the second P-type charge generation layer 171 may include a triphenylamine-based compound, such as at least one of N, N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine (abbreviated as NPB), 4',4' -tris (carbazol-9-yl) triphenylamine (abbreviated as TCTA), N '-diphenyl-N, N' -bis (3-methylphenyl) -1,1 '-biphenyl-4, 4' -diamine (abbreviated as TPD), pentacene (pentacene), and 4,4',4' -tris (N-3-methylphenyl-N-phenylamino) triphenylamine (abbreviated as MTDATA).

Specifically, the material of the second N-type charge generation layer 172 may include at least one of 4,7-diphenyl-1,10-phenanthroline (4,7-diphenyl-1,10-phenanthroline), 8-Hydroxyquinoline aluminum (8-Hydroxyquinoline aluminum salt), 4,6-Bis (3, 5-Bis (4-pyridine) methylphenyl) -2-MethylpyriMidine (4,6-Bis (3,5-di (pyridine-4-yl) phenyl) -2-MethylpyriMidine), 1,3,5-Tris (1-phenyl-1H-benzimidazol-2-yl) benzene (1,3,5-Tris (1-phenyl-1H-benzimidazol-2-yl) benzene), and the like.

In the present embodiment, the charge generation layer 170 includes a second P-type charge generation layer 171 and a second N-type charge generation layer 172, the second P-type charge generation layer 171 and the second N-type charge generation layer 172 form a PN junction, that is, a space charge region (i.e., depletion layer) is formed at an interface between the second P-type charge generation layer 171 and the second N-type charge generation layer 172, that is, a self-established electric field directed from the second N-type charge generation layer 720 to the second P-type charge generation layer 171 is formed, and the positively charged metal ions are acted by a force directed from the second P-type charge generation layer 171 to the second N-type charge generation layer 172 in the self-established electric field, so that the space charge region can further prevent the metal ions in the first N-type charge generation layer 160 from diffusing into the first P-type charge generation layer 150. Meanwhile, the second P-type charge generation layer 171 and the second N-type charge generation layer 172 can ensure that holes and electrons are efficiently distributed to the first light emitting stack and the second light emitting stack, respectively, preventing the holes and electrons from moving in opposite directions. The current efficiency of the light-emitting device is not influenced while the blocking effect is achieved.

In order to provide better electrical performance of the light emitting device 10, and to avoid electron injection degradation caused by charge formation at the interface of the first P-type charge generation layer 150 and the hole transport layer adjacent thereto, the present disclosure provides yet another implementation manner. For example, the HOMO level of the second P type charge generation layer 171 increases in a direction from the first P type charge generation layer 150 to the first N type charge generation layer 160. Specifically, the HOMO level of the second P-type charge generation layer 171 is increased stepwise in the direction from the first P-type charge generation layer 150 to the first N-type charge generation layer 160.

In this implementation, the HOMO level of the second P type charge generation layer 171 gradually increases in the direction from the first P type charge generation layer 150 to the first N type charge generation layer 160, which enables formation of a better band bending transition, reducing the potential barrier during charge generation.

In order to improve the stability of the light emitting device 10, the present disclosure provides yet another implementation. For example, the LUMO level of the second N-type charge generation layer 172 decreases in a direction from the first N-type charge generation layer 160 to the first P-type charge generation layer 150. Specifically, the LUMO level of the second N-type charge generation layer 172 is decreased stepwise in the direction from the first N-type charge generation layer 160 to the first P-type charge generation layer 150.

In this implementation, the LUMO level of the second N-type charge generation layer 172 gradually decreases in the direction from the first N-type charge generation layer 160 to the first P-type charge generation layer 150, which can further form a better band bending transition, reducing the potential barrier during charge generation.

In order to prevent the second P-type charge generation layer 171 and the second N-type charge generation layer 172 from affecting the charge separation efficiency while blocking the diffusion of the metal ions, the present disclosure provides yet another implementation.

In one implementation of the embodiment of the present disclosure, the HOMO level of the second P-type charge generation layer 171 is greater than-5.5 eV, and the LUMO level of the second N-type charge generation layer 172 is less than-4.5 eV. And, the absolute value of the energy level difference of the second P-type charge generation layer 171 and the second N-type charge generation layer 172 is less than 1 eV.

In the present implementation, the absolute value of the energy level difference of the second P-type charge generation layer 171 and the second N-type charge generation layer 172 is less than ± 1 eV. Further, the absolute value of the energy level difference of the second P-type charge generation layer 171 and the second N-type charge generation layer 172 is less than ± 0.5 eV. Setting the energy level difference between the second P-type charge generation layer 171 and the second N-type charge generation layer 172 to be small enables formation of a better band bending transition, reduces a potential barrier in the charge generation process, and realizes effective charge separation. Accordingly, while the problem of diffusion of metal ions in the first N-type charge generation layer 160 into the first P-type charge generation layer 150 is solved, it is possible to solve the problem of electron injection degradation in the first N-type charge generation layer 160 due to a large energy level difference between the first N-type charge generation layer 160 and the first P-type charge generation layer 150, and to improve the stability of the light emitting device.

In one implementation of the embodiment of the present disclosure, the larger the thicknesses of the second P-type charge generation layer 171 and the second N-type charge generation layer 172, the better the blocking effect for the metal ions may be, but the excessive thicknesses of the second P-type charge generation layer 171 and the second N-type charge generation layer 172 may affect the efficiency of electron transfer, and thus setting the thicknesses of the second P-type charge generation layer 171 and the second N-type charge generation layer 172 to be between 5 angstroms and 100 angstroms, respectively, may enable blocking of diffusion of the metal ions without affecting the efficiency of electron transfer. For example, the second P-type charge generation layer 171 may have a thickness of 10 angstroms, 20 angstroms, 50 angstroms, or 80 angstroms, etc. For another example, the second N-type charge generation layer 172 may have a thickness of 10 angstroms, 20 angstroms, 50 angstroms, or 80 angstroms, etc.

In one implementation of the disclosed embodiment, the material of the first N-type charge generation layer 160 is a metal-doped organic electron transport material. Specifically, the doping concentration of the metal is 1% -10%. For example, the doping concentration of the metal is further 1%, 3%, 5%, 8%, and the like. More specifically, the metal includes at least one of an alkali metal, an alkaline earth metal, and a transition metal. For example, the metal may be lithium, sodium, potassium, rubidium, cesium, francium, chromium, manganese, iron, cobalt, nickel, copper, zinc, a lanthanide metal, an actinide metal, or the like. The organic electron transport material includes at least one of a phenanthroline derivative and a triazine derivative. It is to be understood that the organic electron transport material is not limited to the above materials. The first N-type charge generation layer 160 is set to a thickness of between 50 angstroms and 100 angstroms.

Too high doping concentration of the metal may decrease the transmission efficiency but may cause the diffusion of metal ions to be more severe, and thus, the doping concentration of the metal is set to 1% to 10%. The diffusion of metal ions is reduced while the transmission efficiency is guaranteed.

In one implementation of the disclosed embodiment, the material of the first P-type charge generation layer 150 is a strong oxidizing material doped with an organic hole transport material. Specifically, the doping concentration of the strong oxidizing material is 3% -15%. For example, the doping concentration of the strong oxidizing material is further 1%, 3%, 5%, 8%, or the like. The strong oxidizing material includes at least one of molybdenum oxide, tungsten oxide, vanadium oxide, and an organic compound containing a cyano group and/or a fluorine group. The organic hole transport material includes at least one of materials such as poly (p-phenylene vinylenes), polythiophenes, polysilanes, triphenylmethanes, triarylamines, hydrazones, pyrazolines, carbazoles, and butadienes. It is to be understood that the organic hole transport material is not limited to the above materials. The first P-type charge generation layer 150 is disposed between 50 angstroms and 100 angstroms thick.

Fig. 2 is a schematic cross-sectional view of a light emitting device according to an embodiment of the present disclosure. As shown in fig. 2, in an alternative implementation of the embodiment of the present disclosure, the light emitting device 10 includes a cathode 110, a first light emitting stack 130, a first P-type charge generation layer 150, a charge generation layer 170, a first N-type charge generation layer 160, a second light emitting stack 140, and an anode 120, which are sequentially arranged from top to bottom.

For example, in an alternative implementation, the cathode 110 may be composed of a conductive material, such as a conductive metal oxide. Conductive metal oxides such as zinc oxide, indium oxide, tin oxide, Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), fluorine-doped tin oxide, or the like).

Specifically, the material of the anode 120 may be a conductive material such as a metal, a conductive metal oxide, a conductive polymer, or a combination thereof. Specifically, the material of the anode 120 may be a metal or an alloy thereof, such as aluminum, magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, silver, gold, platinum, tin, lead, cesium, or barium. The material of the anode 120 may also be a material of a multi-layer structure, but is not limited thereto. It should be noted that when the thickness of the metal film is relatively small (e.g., as small as several hundred angstroms or less), the film may be transparent.

The first light emitting stack 130 includes a first hole transport layer 133 connected to the first P-type charge generation layer 150, and the second light emitting stack 140 includes a second electron transport layer 143 connected to the first N-type charge generation layer 160. Further, the first light emitting stack 130 includes a first electron transport layer 131, a first light emitting layer 132, and a first hole transport layer 133 sequentially stacked between the cathode 110 and the first P-type charge generation layer 150, and the second light emitting stack 140 includes a second hole transport layer 141, a light emitting layer 142, and a second electron transport layer 143 sequentially stacked between the anode 120 and the first N-type charge generation layer 160.

It is to be understood that the light emission color of the first and second light emitting stacks may be adapted as desired.

The light emitting device in this embodiment is illustrated by taking fig. 1 and fig. 2 as an example, in other implementation manners of this embodiment, other light emitting stacked layers may be further included, and the first light emitting stacked layer and the second light emitting stacked layer may further include film layers such as an electron blocking layer, an electron injection layer, a hole blocking layer, and a hole injection layer, respectively.

Fig. 3 is a schematic diagram of energy levels in a light emitting device according to an embodiment of the present disclosure. As shown in fig. 3, the HOMO level of the first P-type charge generation layer 150 is between the HOMO level of the first hole transport layer 133 and the HOMO level of the second P-type charge generation layer 171. In an alternative implementation, the HOMO level of the first P-type charge generation layer 150 increases in a direction from the first hole transport layer 133 to the second P-type charge generation layer 171.

The LUMO energy level of the first N-type charge generation layer 160 is interposed between the second electron transport layer 143 and the second N-type charge generation layer 172. In an alternative implementation, the LUMO energy level of the first N-type charge generation layer 160 decreases in a direction from the second electron transport layer 143 to the second N-type charge generation layer 172.

In this embodiment, by providing the HOMO level of the first P-type charge generation layer 150 to increase in the direction from the hole transport layer to the second P-type charge generation layer 171 and providing the LUMO level of the first N-type charge generation layer 160 to decrease in the direction from the second electron transport layer 143 to the second N-type charge generation layer 172, it is possible to further form a better band bending transition and reduce the potential barrier during charge generation.

At least one embodiment of the present disclosure provides a display panel including a display region in which a plurality of light emitting devices of the above-described embodiments are disposed. For example, the display panel may further include an array substrate on which the light emitting device array is arranged to constitute the sub-pixels of the display panel. For example, the sub-pixels of the display panel may be R (red), G (green), and B (blue) sub-pixels.

Fig. 4 is a schematic diagram of a display panel according to an embodiment of the disclosure. As shown in fig. 4, in one implementation, the display panel 20 is a display screen of a smart phone.

In other alternative implementations, the display panel may be any device having a display function, for example, a display screen of an electronic product such as a tablet computer, a computer monitor, a notebook computer, a palm computer, a vehicle-mounted electronic device, a game machine, a smart wearable device, and a television.

Fig. 5 is a partial cross-sectional view of the display panel shown in fig. 4. The cross-sectional structure shown in fig. 5 is a cross-sectional view of the region 201 shown in fig. 4, and as shown in fig. 4 and fig. 5, the display panel 20 may include an array substrate 210, and Thin Film Transistors (TFTs) disposed on the array substrate 210, where the TFTs include control units 230 for respectively controlling different sub-pixels. And an anode 120 disposed on the thin film transistor. A Pixel Definition Layer (PDL) 220 is formed on the anode 120, a plurality of openings are provided in the Pixel Definition Layer 210, and film layers such as a first light emitting stack (not shown), a charge generation Layer (not shown), and a second light emitting stack (not shown) of the light emitting device 10 in the above-described embodiment of the present disclosure are provided in the openings. The cathode 110 of the display panel 20 is formed in the opening of the light emitting device 10, and is electrically connected to the light emitting stack. The cathode 110 may be a light-transmissive metal, and the light-emitting side of the light-emitting device is the side where the cathode is located. In order to improve the processing efficiency, the cathode layer covers the upper surface of the light emitting stack and the upper surface of the pixel defining layer 210 in the form of a common layer. The display panel 20 further includes an encapsulation layer (not shown) disposed over the cathode 110, and a material of the encapsulation layer may be transparent plastic or glass, etc. In addition, the display panel 20 further includes conductive connection lines (not shown) for respectively connecting the control unit 230, the cathode 110, the anode 120, and the like to form a control circuit.

The light-emitting device provided according to any one of the embodiments of the present disclosure and the display panel provided by the embodiments of the present disclosure belong to the same inventive concept, and have corresponding film layer structures and beneficial effects. Details that are not described in detail in the embodiment of the display panel may be referred to in the embodiment section of the light emitting device, and are not described herein again.

The disclosure is to be considered as illustrative and not restrictive in character, and that all changes which come within the spirit and scope of the disclosure are desired to be protected.

Claims (10)

1. A light emitting device, comprising:

a cathode and an anode;

a first light emitting stack, a first P-type charge generation layer, a first N-type charge generation layer, and a second light emitting stack sequentially arranged from the cathode to the anode, wherein the first N-type charge generation layer is doped with a metal; and

and a charge generation layer between the first P-type charge generation layer and the first N-type charge generation layer, and including a second P-type charge generation layer between the first P-type charge generation layer and the second N-type charge generation layer and a second N-type charge generation layer.

2. The light-emitting device according to claim 1, wherein a HOMO level of the second P-type charge generation layer increases in a direction from the first P-type charge generation layer to the first N-type charge generation layer.

3. The light-emitting device according to claim 1, wherein a LUMO level of the second N-type charge generation layer decreases in a direction from the first N-type charge generation layer to the first P-type charge generation layer.

4. The light-emitting device according to claim 1,

the HOMO level of the second P-type charge generation layer is greater than-5.5 eV, and the LUMO level of the second N-type charge generation layer is less than-4.5 eV;

preferably, an absolute value of an energy level difference of the second P-type charge generation layer and the second N-type charge generation layer is less than 1 eV;

preferably, the absolute value of the difference in energy levels of the second P-type charge generation layer and the second N-type charge generation layer is less than ± 0.5 eV.

5. The light-emitting device according to claim 1, wherein the second P-type charge generation layer has a thickness of 5 to 100 angstroms, and wherein the second N-type charge generation layer has a thickness of 5 to 100 angstroms.

6. The light-emitting device according to any one of claims 1 to 5,

the first light emitting stack includes a first hole transport layer connected to the first P-type charge generation layer, the HOMO level of the first P-type charge generation layer being between the first hole transport layer and the second P-type charge generation layer;

preferably, the HOMO level of the first P-type charge generation layer increases in a direction from the first hole transport layer to the second P-type charge generation layer.

7. The light-emitting device according to any one of claims 1 to 5,

the second light emitting stacked layer includes a second electron transport layer connected to the first N-type charge generation layer, the LUMO level of the first N-type charge generation layer being interposed between the second electron transport layer and the second N-type charge generation layer;

preferably, the LUMO level of the first N-type charge generation layer decreases in a direction from the second electron transport layer to the second N-type charge generation layer.

8. The light-emitting device according to any one of claims 1 to 5,

the material of the first P-type charge generation layer comprises a strong oxidizing material doped in an organic hole transport material;

preferably, the doping concentration of the strong oxidizing material is 3% -15%;

preferably, the strong oxidizing material includes at least one of molybdenum oxide, tungsten oxide, vanadium oxide, and organic compounds containing cyano groups and/or fluorine groups, and the organic hole transport material includes at least one of materials such as polyparaphenylenes, polythiophenes, polysilanes, triphenylmethanes, triarylamines, hydrazones, pyrazolines, carbazoles, and butadienes.

9. The light-emitting device according to any one of claims 1 to 5,

the material of the first N-type charge generation layer includes doping a metal in an organic electron transport material;

preferably, the doping concentration of the metal is 1% -10%;

preferably, the metal includes at least one of an alkali metal, an alkaline earth metal, a lanthanide metal, an actinide metal, and a transition metal, and the organic electron transport material includes at least one of a phenanthroline derivative and a triazine derivative.

10. A display panel comprising a display region in which a plurality of the light-emitting devices according to any one of claims 1 to 9 are disposed.

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