CN117529138A

CN117529138A - Organic electroluminescent device and display panel

Info

Publication number: CN117529138A
Application number: CN202311152773.7A
Authority: CN
Inventors: 杨伟恒; 廖志超; 蔡莉
Original assignee: Suzhou China Star Optoelectronics Technology Co Ltd
Current assignee: Suzhou China Star Optoelectronics Technology Co Ltd
Priority date: 2023-09-07
Filing date: 2023-09-07
Publication date: 2024-02-06

Abstract

The application provides an organic electroluminescent device and display panel, the organic electroluminescent device includes: a substrate; a light extraction layer on the substrate; an anode on the light extraction layer; a light-emitting functional layer located on the anode; a cathode located on the light-emitting functional layer; wherein the refractive index of the light extraction layer gradually decreases in a direction from a side near the anode to a side near the substrate, and the refractive index of the light extraction layer is greater than the refractive index of the substrate and less than the refractive index of the anode. According to the organic electroluminescent device and the display panel, the light extraction layer with the gradually reduced refractive index is arranged between the anode and the substrate, so that the problem of abrupt change of the refractive index from the anode to the substrate in the OLED device is solved, the total reflection angle of emergent light between the anode and the substrate is reduced, the light extraction rate is improved, and the external quantum efficiency of the OLED device is improved.

Description

Organic electroluminescent device and display panel

Technical Field

The application relates to the technical field of display, in particular to an organic electroluminescent device and a display panel.

Background

Organic electroluminescent devices (Organic Light Emitting Diode, OLED) are widely used in the display field. However, a significant difficulty currently faced by OLED devices is how to effectively increase the luminous efficiency of the device. The external quantum efficiency is an important parameter for evaluating the performance of the OLED device, the size of the external quantum efficiency is mainly determined by the internal quantum efficiency and the optical coupling-out efficiency of the device, and the external quantum efficiency of the OLED device can only reach 20-30% at present due to the influences of a substrate mode, a waveguide mode and a surface plasmon effect.

The main reason for the light loss of the OLED device is that the refractive indexes of the functional layers of the device are not matched, and photons emitted by the light emitting layer at the interface of the functional layers with different refractive indexes are mostly limited in the device due to total reflection, so that the photons cannot escape from the device.

For conventional bottom-emitting OLED devices, since the total thickness of the anode is about several hundred nanometers, the refractive index (typically 1.7-1.8) is significantly higher than that of the substrate (typically 1.5), and thus the stacked structure of the OLED device forms a planar waveguide, resulting in about 20% of light being localized in the anode/light-emitting functional layer (i.e., waveguide mode), resulting in light loss, reduced light extraction, and thus reduced external quantum efficiency of the OLED device.

Disclosure of Invention

The application provides an organic electroluminescent device and a display panel, which can improve the problem of abrupt change of refractive index from an anode to a substrate in an OLED device, improve the light emitting rate of the OLED device and further improve the external quantum efficiency.

The application provides an organic electroluminescent device, comprising:

a substrate;

a light extraction layer on the substrate;

an anode on the light extraction layer;

a light emitting functional layer on the anode;

a cathode located on the light-emitting functional layer;

wherein the refractive index of the light extraction layer gradually decreases in a direction from a side near the anode to a side near the substrate, and the refractive index of the light extraction layer is greater than the refractive index of the substrate and less than the refractive index of the anode.

In an alternative embodiment of the present application, the light extraction layer includes a first region and a second region stacked, the first region being adjacent to the anode, the second region being adjacent to the substrate, and the refractive index of the first region being greater than the refractive index of the second region.

In an alternative embodiment of the present application, the light extraction layer further includes a transition region, the transition region being located between the first region and the second region, the transition region having a refractive index greater than the refractive index of the second region and less than the refractive index of the first region.

In an alternative embodiment of the present application, the light extraction layer comprises a substrate and particles distributed in the substrate, wherein the first region comprises first particles, the second region comprises second particles, and the transition region comprises the first particles and the second particles.

In an alternative embodiment of the present application, the refractive index of the first particles is greater than the refractive index of the second particles.

In an alternative embodiment of the present application, the first particles have a particle size ranging from 60nm to 70nm, and the second particles have a particle size ranging from 40nm to 60nm.

In an alternative embodiment of the present application, both the first particles and the second particles are transparent particles.

In an alternative embodiment of the present application, the particles are non-periodically distributed in the substrate.

In an alternative embodiment of the present application, the material of the substrate is a resin.

In an alternative embodiment of the present application, the refractive index of the first region ranges from 1.60 to 1.65, and the refractive index of the second region ranges from 1.50 to 1.60.

The application also provides a display panel comprising the organic electroluminescent device according to any of the embodiments above.

The application provides an organic electroluminescent device and display panel, this application is through setting up the light extraction layer between positive pole and base, the refracting index of light extraction layer reduces gradually in the direction from positive pole to base, and the refracting index of light extraction layer is greater than the refracting index of base and is less than the refracting index of positive pole for from positive pole to the refracting index between the base reduce gradually, thereby improve the refractive index mutation problem from positive pole to the base in the OLED device, reduce the total reflection angle of emergent light between positive pole and base, thereby improve the light-emitting rate, promote the external quantum efficiency of OLED device.

Drawings

In order to more clearly illustrate the embodiments or the technical solutions in the prior art, the following description will briefly introduce the drawings that are needed in the embodiments or the description of the prior art, it is obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of an organic electroluminescent device in the prior art;

fig. 2 is a schematic structural diagram of an organic electroluminescent device according to an embodiment of the present application;

fig. 3 is a schematic view of a light extraction layer structure of an organic electroluminescent device according to an embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.

In the description of the present application, it should be understood that the azimuth or positional relationship indicated by the terms "upper", "lower", etc. are based on the azimuth or positional relationship shown in the drawings, and are merely for convenience of description of the present application and to simplify the description, and do not indicate or imply that the apparatus or element referred to must have a specific azimuth, be configured and operated in a specific azimuth, and thus should not be construed as limiting the present application. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more of the described features. In the description of the present application, the meaning of "a plurality" is two or more, unless specifically defined otherwise.

The present application may repeat reference numerals and/or letters in the various examples, and such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

As shown in fig. 1, a schematic structural diagram of an organic electroluminescent device in the prior art is shown, where the organic electroluminescent device (Organic Light Emitting Diode, OLED) includes a substrate 100, an anode 300, a light-emitting functional layer 400, and a cathode 500, which are sequentially stacked; the light emitting functional layer 400 includes at least one light emitting unit including a hole injection layer 410, a hole transport layer 420, a light emitting layer 430, an electron transport layer 440, and an electron injection layer 450 stacked in this order, wherein the hole injection layer 410 is adjacent to the anode 300, and the electron injection layer 450 is adjacent to the cathode 500.

The basic principle of the light emission of the OLED device is that after a certain voltage is applied between the two electrodes, holes are transferred from the anode 300 into the hole injection layer 410, pass through the hole transport layer 420 and reach the light emitting layer 430, electrons are transferred from the cathode 500 into the electron injection layer 450, pass through the electron transport layer 440 and reach the light emitting layer 430, and the holes and the electrons meet in the light emitting layer 430 to form excitons, so that the light emitting molecules are excited to finally generate visible light.

For a bottom-emitting OLED device, the light exiting from the light-emitting layer 430 exits from the anode 300 side. In an OLED device, the refractive index of the substrate 100 is generally about 1.5, the refractive index of the anode 300 is generally between 1.7 and 1.8, the refractive index of the anode 300 is significantly higher than that of the substrate 100, and when light emitted from the light emitting layer 430 is incident into the substrate 100 through the anode 300, a planar waveguide is formed between the anode 300 and the light emitting layer 430 due to abrupt change of the refractive index of the film layer, so that about 20% of the light is confined in the anode 300/the light emitting functional layer 400, resulting in light loss, decreasing the light yield of the OLED device, and further decreasing the external quantum efficiency of the OLED device.

In order to solve the above problems, the application provides an organic electroluminescent device and a display panel, which can improve the light extraction rate of an OLED device, thereby improving the external quantum efficiency.

The organic electroluminescent device and the display panel provided by the present application will be described in detail below with reference to specific embodiments and drawings.

As shown in fig. 2, an organic electroluminescent device provided in the present application includes:

a substrate 100;

a light extraction layer 200 on the substrate 100;

an anode 300 on the light extraction layer 200;

a light emitting functional layer 400 on the anode 300;

a cathode 500 on the light emitting functional layer 400;

wherein the refractive index of the light extraction layer 200 gradually decreases in a direction from a side near the anode 300 to a side near the substrate 100, and the refractive index of the light extraction layer 200 is greater than the refractive index of the substrate 100 and less than the refractive index of the anode 300.

The substrate 100 may be glass or a flexible material, and the substrate 100 is formed of a transparent material so that the outgoing light of the light emitting function layer 400 can be emitted through the substrate 100. The substrate 100 further includes a driving unit, such as a thin film transistor, wherein the thin film transistor includes an active layer, a gate electrode, and source and drain electrodes, the anode 300 is electrically connected to the source or drain electrodes, the cathode 500 is electrically connected to the anode 300, so that the thin film transistor drives the anode 300 and the cathode 500 to generate a voltage, and the light emitting functional layer 400 emits light under the action of the driving voltage.

The light extraction layer 200 is positioned at one side of the substrate 100, the light extraction layer 200 is a single-layer film, the refractive index of the light extraction layer 200 gradually decreases in a direction from one side of the light extraction layer 200 near the anode 300 to one side of the light extraction layer 200 near the substrate 100, and the refractive index of the light extraction layer 200 near the anode 300 is smaller than that of the anode 300, and the refractive index of the light extraction layer 200 near the substrate 100 is greater than that of the substrate 100, thereby gradually decreasing the refractive index from the anode 300 to the substrate 100, so that a problem of low light extraction caused by abrupt change of refractive index from anode to substrate in an OLED device is avoided.

The anode 300 is located at a side of the light extraction layer 200 away from the substrate 100, and the anode 300 is a transparent electrode, so that the emitted light of the light emitting functional layer 400 can pass through the anode 300, and the light extraction rate is improved. The material of the anode 300 may be conductive oxide, metal, transparent conductive polymer, graphene, or the like. The conductive Oxide may be indium tin Oxide (Indium Tin Oxides, ITO), indium tin Oxide (Indium Zinc Oxide, IZO), aluminum-Doped Zinc Oxide (AZO); the metal may be copper (Au); the transparent conductive polymer may be poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonic acid) (PEDOT: PSS), but is not limited thereto.

The light emitting functional layer 400 is located at a side of the anode 300 remote from the light extracting layer 200, and the light emitting functional layer 400 includes at least one light emitting unit including a hole injecting layer 410, a hole transporting layer 420, a light emitting layer 430, an electron transporting layer 440, and an electron injecting layer 450 stacked in this order, the hole injecting layer 410 being adjacent to the anode 300, and the electron injecting layer 450 being adjacent to the cathode 500. Wherein the material of the hole injection layer 410 may be, but is not limited to, moO ₃ At least one of HAT-CN, PEDOT: PSS, etc.; the material of the hole transport layer 420 may be, but is not limited to, at least one of NPB, TAPC, etc.; the light emitting color of the OLED device depends on the material of the light emitting layer 430, and the material of the light emitting layer 430 may be, but is not limited to, phosphorescent materials based on triplet transition excitons, such as red phosphorescent material Ir (MDQ) 2acac, green phosphorescent material Ir (ppy) 3, blue phosphorescent material FIrpic, etc.; the material of the electron transport layer 440 may be, but is not limited to, at least one of Alq3, TPBi, P0-T2T, bephen, etc.; the material of the electron injection layer 450 may be, but is not limited to, li F.

It should be noted that the light emitting functional layer 400 may include one light emitting unit, and the light emitting functional layer 400 may also include a plurality of light emitting units. When the light emitting functional layer 400 includes a plurality of light emitting units, the plurality of light emitting units are stacked in a direction perpendicular to the substrate 100, two adjacent light emitting units are connected by a connection layer (e.g., a charge generating layer), and the plurality of light emitting units are stacked to form an OLED device having a tandem structure. The light emitting layers 430 of the light emitting units may have the same or different light emitting colors, and the OLED device may be a single color (e.g., red, green, or blue) OLED device, or may be a white OLED device formed by combining multiple colors of light, which is not particularly limited herein.

The cathode 500 is located at a side of the light emitting function layer 400 remote from the anode 300. The material of the cathode 500 may be, but is not limited to, elemental metal or alloy. The elemental metal may be Li, mg, al, ag, etc., and the alloy may be magnesium silver alloy (10:1), lithium aluminum alloy (0.6% Li), etc., but is not limited thereto.

In an alternative embodiment of the present application, as shown in fig. 3, the light extraction layer 200 includes a first region 210 and a second region 220 stacked, the first region 210 is adjacent to the anode 300, the second region 220 is adjacent to the substrate 100, and the refractive index of the first region 210 is greater than the refractive index of the second region 220. By disposing the light extraction layer 200 as two stacked portions, the first region 210 of high refractive index and the second region 220 of low refractive index, the light extraction layer 200 is formed as a film layer having a gradual refractive index in a direction along the anode 300 to the substrate 100 such that the refractive index gradually decreases from the anode 300 to the substrate 100.

In an alternative embodiment of the present application, as shown in fig. 3, the light extraction layer 200 further includes a transition region 230, where the transition region 230 is located between the first region 210 and the second region 220, and the refractive index of the transition region 230 is greater than the refractive index of the second region 220 and less than the refractive index of the first region 210. In order to avoid abrupt change of refractive index between the interfaces of the first region 210 and the second region 220, the refractive index of the first region 210 and the refractive index of the second region 220 of the light extraction layer 200 are gradually transited, so as to further improve the light extraction efficiency of the OLED device, a transition region 230 is formed between the first region 210 and the second region 220, and the refractive index of the transition region 230 is between the refractive index of the first region 210 and the refractive index of the second region 220, so that the refractive index of the light extraction layer 200 is gradually reduced from the first region 210 to the transition region 230 to the second region 220, and abrupt change of refractive index between the regions is avoided.

In an alternative embodiment of the present application, the light extraction layer 200 includes a substrate and particles distributed in the substrate, wherein the first region 210 includes first particles 211, the second region 220 includes second particles 221, and the transition region 230 includes the first particles 211 and the second particles 221.

By adding particles in the light extraction layer 200 to change the refractive index of the substrate and adding the first particles 211 in the substrate of the first region 210 and the second particles 221 in the substrate of the second region 220, the refractive indices of the first region 210 and the second region 220 are made different. By adjusting the particle concentration, particle distribution, particle diameter, particle material, and the like of the first particles 211 and the second particles 221 in the first region 210 and the second region 220, the first region 210 having a high refractive index and the second region 220 having a low refractive index are formed inside the light extraction layer 200, and the refractive index of the first region 210 is smaller than the refractive index of the anode 300, and the refractive index of the second region 220 is larger than the refractive index of the substrate 100, i.e., the light extraction layer 200 forms a film layer having a gradually decreasing refractive index in a direction from the anode 300 to the substrate 100, such that the refractive index from the anode 300 to the substrate 100 gradually decreases.

The transition region 230 includes the first particles 211 and the second particles 221 mixed so that the refractive index of the transition region 230 is between the refractive index of the first region 210 and the refractive index of the second region 220, thereby gradually reducing the refractive index of the light extraction layer 200 from the first region 210 to the transition region 230 to the second region 220 and avoiding abrupt refractive index changes between the regions.

In this embodiment, particles are added to the light extraction layer 200 to gradually decrease the refractive indexes of the first region 210, the transition region 230, and the second region 220, so that the refractive index of the film layer from the anode 300 to the substrate 100 is gradually decreased even if the light extraction layer 200 forms a film layer structure with gradually changed refractive indexes in the direction from the anode 300 to the substrate 100, thereby improving the problem of abrupt change of refractive index from the anode 300 to the substrate 100 in the OLED device, reducing the total reflection angle of the emergent light between the anode 300 and the substrate 100, and further improving the light extraction rate. Meanwhile, the particles in the light extraction layer 200 can scatter light, change the emergent direction of the light, extract the light limited in the anode 300/the light-emitting functional layer 400, and improve the external quantum efficiency of the OLED device.

In some embodiments, there may be no distinct boundary between the transition region 230 and the first region 210 and the second region 220, and between the first region 210 and the second region 220, a portion of the first particles 211 may permeate into the second region 220, and a portion of the second particles 221 may permeate into the first region 210, thereby forming a transition region 230 between the first region 210 and the second region 220, in which the first particles 211 and the second particles 221 are mixed, such that the refractive index of the light extraction layer 200 gradually decreases in a direction from the anode 300 to the substrate 100.

In an alternative embodiment of the present application, the particles are non-periodically distributed in the substrate. Specifically, as shown in fig. 3, the first particles 211 are non-periodically (i.e., irregularly) distributed in the first region 210 of the light extraction layer 200, the second particles 221 are non-periodically (i.e., irregularly) distributed in the second region 220 of the light extraction layer 200, and the first particles 211 and the second particles 221 are also non-periodically distributed in the transition region 230. In the embodiment, the aperiodic structure has strong plasticity, so that the problem of poor brightness uniformity and spectrum stability caused by the periodic structure can be solved, and the brightness uniformity and stability of the OLED device are further improved.

In an alternative embodiment of the present application, the particle concentration of the first region 210, the particle concentration of the transition region 230, and the particle concentration of the second region 220 are gradually decreased. Since the refractive index of the light extraction layer 200 is related to the particle concentration of the particles contained therein, the larger the particle concentration in the film layer, the larger the overall refractive index of the film layer, since the refractive index of the anode 300 is larger than that of the substrate 100, in order to gradually decrease the refractive index from the anode 300 to the substrate 100, even if the refractive index of the light extraction layer 200 gradually decreases in the direction from the anode 300 to the substrate 100, the refractive index of the light extraction layer 200 can be changed by adjusting the particle concentration within the light extraction layer 200. In order to provide the light extraction layer 200 with a graded refractive index structure, the light extraction layer is divided into the first region 210, the transition region 230, and the second region 220, and the particle concentration in the first region 210 is made larger than that in the transition region 230, and the particle concentration in the transition region 230 is made larger than that in the second region 220, so that the refractive index of the first region 210 is made larger than that of the transition region 230, and the refractive index of the transition region 230 is made larger than that of the second region 220, forming a structure in which the refractive index of the inside of the light extraction layer 200 is gradually reduced.

In this embodiment, the materials or particle diameters of the first particles 211 and the second particles 221 may be equal or unequal, and the refractive index of each region of the light extraction layer may be set.

In an alternative embodiment of the present application, the refractive index of the first particles 211 is greater than the refractive index of the second particles 221. The refractive index of the light extraction layer 200 is related to the refractive index of the first particles 211 and the second particles 221, and the refractive index of the first region 210 of the light extraction layer 200 is greater than the refractive index of the second region 220 by adding the first particles 211 with a high refractive index in the first region 210 and the second particles 221 with a low refractive index in the second region 220. The transition region 230 includes both the first particles 211 having a high refractive index and the second particles 221 having a low refractive index, and thus the refractive index of the transition region is between the refractive index of the first region 210 and the refractive index of the second region 220, thereby realizing a structure in which the refractive index of the inside of the light extraction layer 200 is gradually reduced.

In an alternative embodiment of the present application, the particle size of the first particles 211 ranges from 60nm to 70nm, and the particle size of the second particles 221 ranges from 40nm to 60nm. The refractive index of the light extraction layer 200 is related to the particle sizes of the first particles 211 and the second particles 221, and the larger the particle size is, the higher the refractive index is. By adding first particles 211 having a large particle size in the first region 210 and second particles 221 having a small particle size in the second region 220, the refractive index of the first region 210 of the light extraction layer 200 is larger than that of the second region 220. The transition region 230 includes both the first particles 211 having a large particle size and the second particles 221 having a small particle size, and thus the refractive index of the transition region is between the refractive index of the first region 210 and the refractive index of the second region 220, thereby realizing a structure in which the refractive index of the inside of the light extraction layer 200 gradually decreases. In addition, the first particles 211 and the second particles 221 are nano-sized particles, the particle sizes of the first particles 211 and the second particles 221 are smaller, the non-periodic distribution in the light extraction layer 200 is large in distribution density, and light rays entering at various angles can be scattered when passing through the first particles 211 and the second particles 221, so that the emergent direction of the light rays is changed, the light rays limited in the anode 300/the light-emitting functional layer 400 are extracted, the light extraction rate is improved, and the external quantum efficiency of the OLED device is further effectively improved.

In an alternative embodiment of the present application, the first particles 211 and the second particles 221 are transparent particles. The materials of the first particles 211 and the second particles 221 are transparent materials so as not to affect the transmittance of the light extraction layer 200. Further, the materials of the first particles 211 and the second particles 221 are inorganic materials, such as oxides, etc. In particular, the first particles 211 may be transparent oxide particles having a high refractive index, such as titanium dioxide, etc., and the second particles 221 may be transparent oxide particles having a low refractive index, such as silicon dioxide, etc., but are not limited thereto.

In an alternative embodiment of the present application, the material of the substrate may be a resin, such as an epoxy acrylate oligomer, but is not limited thereto.

In an alternative embodiment of the present application, the refractive index of the first region 210 ranges from 1.60 to 1.65, and the refractive index of the second region 220 ranges from 1.50 to 1.60. Since the refractive index range of the anode 300 is generally between 1.7 and 1.8, the refractive index range of the substrate 100 is generally about 1.5, by setting the refractive index range of the first region 210 to be close to and lower than the refractive index of the anode 300, the refractive index range of the second region 220 to be close to and higher than the refractive index of the substrate 100, and the refractive index of the first region 210, the refractive index of the transition region 230 and the refractive index of the second region 220 are sequentially reduced, so as to gradually reduce the refractive index from the anode 300 to the light extraction layer 200 and then to the substrate 100, the problem of abrupt change of refractive index from the anode 300 to the substrate 100 in the OLED device is improved, the total reflection angle of emergent light between the anode 300 and the substrate 100 is reduced, and the light extraction rate is further improved.

In an alternative embodiment of the present application, the thickness of the light extraction layer 200 in the direction perpendicular to the substrate 100 ranges from 90nm to 110nm. Further, the thickness of the light extraction layer 200 may be set to 100nm. By disposing a film layer (i.e., the light extraction layer 200) between the anode 300 and the substrate 100, and forming a graded refractive index structure inside the light extraction layer 200, that is, a graded refractive index process from the anode 300 to the substrate 100 can be achieved through one film layer, compared with a stacked structure of a plurality of film layers with different refractive indexes, the structure of the present application has a simple process and low cost.

Further, the display panel comprises the organic electroluminescent device and an encapsulation layer positioned on the organic electroluminescent device, wherein the encapsulation layer is used for protecting the organic electroluminescent device. The organic electroluminescent device may be a single-layer OLED device (including one light emitting unit), a double-layer OLED device (including two light emitting units stacked), and a multi-layer OLED device (including a plurality of light emitting units stacked). The organic electroluminescent device may be a monochromatic (e.g., red, green, or blue) OLED device or a white OLED device, and is not particularly limited herein.

In summary, the present application provides an organic electroluminescent device and a display panel, where a light extraction layer is disposed between an anode and a substrate, the refractive index of the light extraction layer gradually decreases in a direction from the anode to the substrate, and the refractive index of the light extraction layer is greater than that of the substrate and less than that of the anode, so that the refractive index between the anode and the substrate gradually decreases, thereby improving the problem of abrupt change of refractive index from the anode to the substrate in the OLED device, reducing the total reflection angle of emergent light between the anode and the substrate, thereby improving the light yield, and improving the external quantum efficiency of the OLED device.

In summary, although the present application has been described with reference to the preferred embodiments, the preferred embodiments are not intended to limit the application, and those skilled in the art can make various modifications and adaptations without departing from the spirit and scope of the application, and the scope of the application is therefore defined by the claims.

Claims

1. An organic electroluminescent device, comprising:

a substrate;

a light extraction layer on the substrate;

an anode on the light extraction layer;

a light emitting functional layer on the anode;

a cathode located on the light-emitting functional layer;

2. The organic electroluminescent device of claim 1, wherein the light extraction layer comprises laminated first and second regions, the first region being adjacent to the anode, the second region being adjacent to the substrate, and the first region having a refractive index greater than a refractive index of the second region.

3. The organic electroluminescent device of claim 2, wherein the light extraction layer further comprises a transition region between the first region and the second region, the transition region having a refractive index greater than a refractive index of the second region and less than a refractive index of the first region.

4. The organic electroluminescent device of claim 3, wherein the light extraction layer comprises a substrate and particles distributed in the substrate, wherein the first region comprises first particles, the second region comprises second particles, and the transition region comprises the first particles and the second particles.

5. The organic electroluminescent device of claim 4, wherein the refractive index of the first particles is greater than the refractive index of the second particles.

6. The organic electroluminescent device of claim 4, wherein the first particles have a particle size ranging from 60nm to 70nm and the second particles have a particle size ranging from 40nm to 60nm.

7. The organic electroluminescent device of claim 4, wherein the first particles and the second particles are transparent particles.

8. An organic electroluminescent device as claimed in any one of claims 4 to 7, wherein the particles are non-periodically distributed in the substrate.

9. The organic electroluminescent device according to any one of claims 4 to 7, wherein the material of the substrate is a resin.

10. The organic electroluminescent device of any one of claims 2-7, wherein the first region has a refractive index in the range of 1.60 to 1.65 and the second region has a refractive index in the range of 1.50 to 1.60.

11. A display panel comprising an organic electroluminescent device as claimed in any one of claims 1 to 10.