A white light organic electroluminescent device and its application

Abstract

The present invention discloses an organic light-emitting device, which relates to a white organic electroluminescent device (WOLED) with a three-band structure. Among them, all three light-emitting layers use thermally activated delayed fluorescence (TADF) materials to emit red, green, and blue light respectively to form white light. And an interlayer is provided between two of the light-emitting layers, and the interlayer contains the TADF materials of the adjacent two light-emitting layers. It can simultaneously reduce the energy level barrier of carrier transfer and improve the energy utilization efficiency of triplet excitons, realizing a high-efficiency and low-power-consumption white OLED.

Description

Technical Field

[0001] The present invention relates to the technical field of organic electroluminescence, and particularly to a white organic electroluminescent device and its application. Background Art

[0002] As a new generation of display technology, organic electroluminescent materials (OLEDs) have the advantages of being ultra-thin, self-luminous, wide viewing angle, fast response, high luminous efficiency, good temperature adaptability, simple production process, low driving voltage, and low energy consumption. They have been widely used in industries such as flat panel displays, flexible displays, solid state lighting, and in-vehicle displays.

[0003] Among them, white organic light-emitting devices have gradually attracted market attention because they can be used for lighting, as backlights for liquid crystal displays, and for full-color OLED displays. According to the different device structures, white organic light-emitting devices can be divided into three categories: three-layer light-emitting devices, double light-emitting layer devices, and single light-emitting layer devices, that is, three or two different colors of light are emitted from three, two different light-emitting organic layers and the same organic layer, respectively, and then synthesized into white light. Among them, multi-layer structures can obtain white light devices with better performance, and it is easy to commercialize under fixed voltage and current, so they are adopted by many researchers. However, due to the change of the carrier recombination region caused by voltage variation, the emission color of the device is often not satisfactory.

[0004] According to the luminescence mechanism, the materials that can be used in the OLED light-emitting layer mainly include fluorescent materials, phosphorescent materials, triplet-triplet annihilation (TTA) materials, and thermally activated delayed fluorescence (TADF) materials. Among them, thermally activated delayed fluorescence (TADF) materials are a new type of low-cost and high-efficiency organic light-emitting materials, known as the third generation of organic light-emitting materials. Through ingenious molecular design, the molecule has a small lowest singlet-triplet energy level difference (ΔE ST ), and can convert triplet excitons into singlet excitons through thermally activated reverse intersystem crossing for radiative emission, thus breaking through the theoretical limit of 25% exciton utilization efficiency of traditional fluorescent materials and achieving 100% luminescence quantum efficiency. Due to the process of exciton reverse intersystem crossing from the triplet state to the singlet state, TADF materials usually exhibit a long-lived fluorescence phenomenon of photochemistry (delayed fluorescence), and the delayed fluorescence lifetime can reach the order of microseconds to milliseconds, which is significantly different from traditional fluorescent materials. TADF materials combine the advantages of good stability of organic fluorescent materials and high luminous efficiency of transition metal complex phosphorescent materials, and have broad application prospects, which is one of the current research hotspots. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide an organic electroluminescent device based on TADF materials with high efficiency and low power consumption and its application.

[0006] The present invention provides an organic light-emitting device, comprising:

[0007] a first electrode and a second electrode, the first electrode and the second electrode being disposed opposite to each other;

[0008] a first light-emitting layer, a second light-emitting layer, and a third light-emitting layer which are stacked between the first electrode and the second electrode, and the first light-emitting layer, the second light-emitting layer, and the third light-emitting layer have different emission colors;

[0009] The first light-emitting layer comprises a first thermally activated delayed fluorescence material and a first fluorescent dye;

[0010] The second light-emitting layer comprises a second thermally activated delayed fluorescence material and a second fluorescent dye;

[0011] The third light-emitting layer comprises a third thermally activated delayed fluorescence material and a third fluorescent dye;

[0012] a first spacer layer located between the first light-emitting layer and the second light-emitting layer, and the first spacer layer comprises a first thermally activated delayed fluorescence material and a second thermally activated delayed fluorescence material.

[0013] Compared with the prior art, the present invention uses a spacer layer to prepare a three-band TADF organic light-emitting device, and an exciton spacer layer is added between two adjacent light-emitting layers, and the exciton spacer layer contains the TADF materials of the adjacent light-emitting layers; First, the TADF material molecules have a small lowest singlet-triplet energy difference (ΔE ST ), and can convert triplet excitons into singlet excitons through thermally activated reverse intersystem crossing for radiative emission, thereby breaking through the theoretical limit of 25% of the exciton utilization rate of traditional fluorescent materials, realizing 100% luminous quantum efficiency, using TADF materials doped as the spacer layer between the light-emitting layers, reducing the energy level barrier for carrier transfer between the two light-emitting layers, reducing power consumption, and improving the energy utilization efficiency of triplet excitons; Second, the three-band light-emitting layers use TADF emission at the same time, which can greatly improve the efficiency of triplet exciton energy, avoid non-radiative transitions, improve the luminous efficiency of the device, and realize an organic light-emitting device with high efficiency and low power consumption; Moreover, the three-band organic light-emitting device does not require a fine metal mask, greatly simplifies the manufacturing process, and reduces the manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic structural diagram of the organic light-emitting device provided by the present invention;

[0015] Figure 2 is a schematic energy level relationship diagram of the organic light-emitting device provided by the present invention;

[0016] Figure 3 is a schematic energy level relationship diagram of the organic light-emitting device provided by the present invention;

[0017] Figure 4 Schematic diagram of the energy level relationship of the organic light-emitting device provided by the present invention;

[0018] Figure 5 Schematic diagram of the energy level relationship of the organic light-emitting device provided by the present invention. Detailed implementation manners

[0019] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] The present invention provides an organic electroluminescent device, including:

[0021] A first electrode and a second electrode, the first electrode and the second electrode are oppositely arranged;

[0022] A first light-emitting layer, a second light-emitting layer, and a third light-emitting layer that are stacked between the first electrode and the second electrode, and the emission colors of the first light-emitting layer, the second light-emitting layer, and the third light-emitting layer are different from each other;

[0023] The first light-emitting layer includes a first thermally activated delayed fluorescence material and a first fluorescent dye;

[0024] The second light-emitting layer includes a second thermally activated delayed fluorescence material and a second fluorescent dye;

[0025] The third light-emitting layer includes a third thermally activated delayed fluorescence material and a third fluorescent dye;

[0026] A first spacer layer located between the first light-emitting layer and the second light-emitting layer, and the first spacer layer includes the first thermally activated delayed fluorescence material and the second thermally activated delayed fluorescence material.

[0027] The organic electroluminescent device provided by the present invention uses three-band light-emitting layers and simultaneously uses TADF emission, which can greatly improve the efficiency of triplet exciton energy, avoid non-radiative transitions, improve the light-emitting efficiency of the device, and realize an organic electroluminescent device with high efficiency and low power consumption.

[0028] See Figure 1 , Figure 1 Schematic diagram of the structure of the organic electroluminescent device provided by the present invention.

[0029] The organic electroluminescent device provided by the present invention includes a first electrode and a second electrode that are oppositely arranged, and the first electrode and the second electrode are an anode and a cathode respectively.

[0030] Among them, in the present invention, the anode material for forming the anode can be selected from metals such as copper, gold, silver, iron, chromium, nickel, manganese, palladium, platinum, etc. and their alloys; it can also be selected from metal oxides such as indium oxide, zinc oxide, indium tin oxide (ITO), indium zinc oxide (IZO), etc.; the anode material can also be selected from conductive polymers such as polyaniline, polypyrrole, poly(3-methylthiophene), etc. In addition, the anode material can also be selected from materials and their combinations that contribute to hole injection other than the anode materials listed above, including known materials suitable for making anodes.

[0031] In the organic light-emitting device provided by the present invention, the cathode material can be selected from metals such as aluminum, magnesium, silver, indium, tin, titanium, etc. and their alloys. The cathode material can also be selected from multi-layer metal materials such as LiF / Al, LiO2 / Al, BaF2 / Al, etc. In addition to the cathode materials listed above, the cathode material can also be materials and their combinations that contribute to electron injection, including known materials suitable for making cathodes.

[0032] A first light-emitting layer, a second light-emitting layer, and a third light-emitting layer are stacked between the first electrode and the second electrolyte; the light-emitting colors of the first light-emitting layer, the second light-emitting layer, and the third light-emitting layer are different. In the present invention, optionally, the first light-emitting layer, the second light-emitting layer, and the third light-emitting layer are respectively one of a red light-emitting layer, a green light-emitting layer, and a blue light-emitting layer; a high-efficiency and low-power white OLED can be formed through an R / G / B three-band structure; further optionally, the first light-emitting layer is a blue light-emitting layer, and the first light-emitting layer is located on the side of the second light-emitting layer close to the first electrode, which is more conducive to energy transfer; more preferably, the first electrode is an anode, that is, the first light-emitting layer is located on the side close to the anode, which is more conducive to the transport of carriers.

[0033] The first light-emitting layer includes a first thermally activated delayed fluorescence material; optionally, the first thermally activated delayed fluorescence material is a hole-transporting material or an electron-transporting layer material; more preferably, the first thermally activated delayed fluorescence material is a hole-transporting material; in the present invention, the energy level difference between the singlet state and the triplet state of the first thermally activated delayed fluorescence material is not greater than 0.5 eV; optionally, the first thermally activated delayed fluorescence material is a triazine compound and / or a cyanocarbazole compound; in the present invention, specifically, the first thermally activated delayed fluorescence material is selected from one or more of those shown in Formulas (I) to (VI):

[0034]

[0035]

[0036] The first light-emitting layer further includes a first fluorescent dye; optionally, the difference between the peak wavelength of the photoluminescence spectrum of the first thermally activated delayed fluorescence material in the first light-emitting layer and the peak wavelength of the ultraviolet absorption spectrum of the first fluorescent dye does not exceed 20 nm; optionally, the highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material is deeper than the highest occupied molecular orbital energy level of the first fluorescent dye; the lowest unoccupied molecular orbital energy level of the first thermally activated delayed fluorescence material is shallower than the lowest unoccupied molecular orbital energy level of the first fluorescent dye; optionally, the doping concentration of the first fluorescent dye is 0.05 to 10 wt%; further optionally, the doping concentration of the first fluorescent dye is 1 to 3 wt%; in the embodiments provided by the present invention, the first fluorescent dye is specifically DSA-PH.

[0037] The second light-emitting layer includes a second thermally activated delayed fluorescence material; in the present invention, it is only necessary that the second thermally activated delayed fluorescence material and the first thermally activated delayed fluorescence material are different types of transport materials, that is, the first thermally activated delayed fluorescence material is a hole transport type material and the second thermally activated delayed fluorescence material is an electron transport type material; or the first thermally activated delayed fluorescence material is an electron transport type material and the second thermally activated delayed fluorescence material is a hole transport type material; further optionally, the second thermally activated delayed fluorescence material is an electron transport type material; in the present invention, specifically, the energy level difference between the singlet state and the triplet state of the second thermally activated delayed fluorescence material is not greater than 0.5 eV; optional types, the second thermally activated delayed fluorescence material is a triazine compound and / or a cyanocarbazole compound; in the present invention, specifically, the second thermally activated delayed fluorescence material is selected from one or more of those shown in Formula (I) to Formula (VI).

[0038] The second light-emitting layer further includes a second fluorescent dye; the difference between the peak wavelength (i.e., the wavelength corresponding to the peak) of the photoluminescence spectrum of the second thermally activated delayed fluorescence material in the second light-emitting layer and the peak wavelength of the ultraviolet absorption spectrum of the second fluorescent dye does not exceed 20 nm; optionally, the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is deeper than the highest occupied molecular orbital energy level of the second fluorescent dye; the lowest unoccupied molecular orbital energy level of the second thermally activated delayed fluorescence material is shallower than the lowest unoccupied molecular orbital energy level of the second fluorescent dye; optionally, the doping concentration of the second fluorescent dye is 0.05 to 10 wt%; further optionally, the doping concentration of the second fluorescent dye is 1 to 3 wt%; in the embodiments provided by the present invention, the second fluorescent dye is specifically DPT.

[0039] In the present invention, a first spacer layer is disposed between the first light-emitting layer and the second light-emitting layer; the first spacer layer includes the first thermally activated delayed fluorescence material and the second thermally activated delayed fluorescence material; in certain embodiments provided by the present invention, specifically, the difference between the highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material and the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than or equal to 0.4 eV, and the difference between the lowest occupied molecular orbital energy of the first thermally activated delayed fluorescence material and the lowest unoccupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than or equal to 0.4 eV; optionally, the molar ratio of the first thermally activated delayed fluorescence material to the second thermally activated delayed fluorescence material in the first spacer layer is (1:99) to (99:1), further optionally, the molar ratio of the first thermally activated delayed fluorescence material to the second thermally activated delayed fluorescence material in the first spacer layer is (30:70) to (70:30), and more preferably, the molar ratio of the first thermally activated delayed fluorescence material to the second thermally activated delayed fluorescence material in the first spacer layer is (40:60) to (60:40). The organic electroluminescent device provided by the present invention uses a TADF material doped as a spacer layer between the light-emitting layers, and the two TADF materials can form an exciplex, thereby reducing the carrier transport energy level barrier and reducing power consumption.

[0040] There are no special restrictions on the thicknesses of the first light-emitting layer, the first spacer layer, and the second light-emitting layer in the organic electroluminescent device provided by the present invention, and the thicknesses can be those conventional in the art; in a specific embodiment provided by the present invention, the thickness ratio of the first light-emitting layer to the second light-emitting layer is specifically 1:0.5 to 1:2, and can also be specifically 1:0.6 to 1:1; the thickness ratio of the first light-emitting layer to the first spacer layer is specifically 1:1 to 5:1, and can also be specifically 2:1 to 4:1, and can also be specifically 3:1.

[0041] In the organic electroluminescent device provided by the present invention, the third light-emitting layer includes a third thermally activated delayed fluorescence material; in the present invention, the third thermally activated delayed fluorescence material and the first thermally activated delayed fluorescence material can be of the same type of transport material; further optionally, the third thermally activated delayed fluorescence material is a hole-transporting material; in the present invention, specifically, the energy level difference between the singlet state and the triplet state of the third thermally activated delayed fluorescence material is not greater than 0.5 eV; optional types, the third thermally activated delayed fluorescence material is a triazine compound and / or a cyanocarbazole compound; in the present invention, specifically, the third thermally activated delayed fluorescence material is selected from one or more of those shown in Formulas (I) to (VI).

[0042] The third light-emitting layer further includes a third fluorescent dye; the difference between the peak wavelength of the photoluminescence spectrum of the third thermally activated delayed fluorescence material in the third light-emitting layer and the peak wavelength of the ultraviolet absorption spectrum of the third fluorescent dye does not exceed 20 nm; optionally, the highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is deeper than the highest occupied molecular orbital energy level of the third fluorescent dye; the lowest unoccupied molecular orbital energy level of the third thermally activated delayed fluorescence material is shallower than the lowest unoccupied molecular orbital energy level of the third fluorescent dye; optionally, the doping concentration of the third fluorescent dye is 0.05 to 10 wt%; further optionally, the doping concentration of the third fluorescent dye is 1 to 3 wt%; in the embodiment provided by the present invention, the third fluorescent dye is specifically DPP.

[0043] In the present invention, optionally, a second spacer layer is further provided between the second light-emitting layer and the third light-emitting layer; the second spacer layer includes a second thermally activated delayed fluorescence material and a third thermally activated delayed fluorescence material; in some specific embodiments provided by the present invention, specifically, the difference between the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material and the highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than or equal to 0.4 eV, and the difference between the lowest occupied molecular orbital energy of the second thermally activated delayed fluorescence material and the lowest unoccupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than or equal to 0.4 eV; optionally, the molar ratio of the second thermally activated delayed fluorescence material to the third thermally activated delayed fluorescence material in the second spacer layer is (1:99) to (99:1), further optionally, the molar ratio of the second thermally activated delayed fluorescence material to the third thermally activated delayed fluorescence material in the second spacer layer is (30:70) to (70:30), and more preferably, the molar ratio of the second thermally activated delayed fluorescence material to the third thermally activated delayed fluorescence material in the second spacer layer is (40:60) to (60:40).

[0044] The organic electroluminescent device provided by the present invention has no special limitation on the thickness of the second spacer layer and the third light-emitting layer, and the conventional thickness in the art can be adopted; in a specific embodiment provided by the present invention, the thickness ratio of the first light-emitting layer to the third light-emitting layer is specifically 1:0.5 to 1:2, and can also be specifically 1:0.6 to 1:1; the thickness ratio of the first light-emitting layer to the second spacer layer is specifically 1:1 to 5:1, and can also be specifically 2:1 to 4:1, and can also be specifically 3:1.

[0045] To further reduce the energy level barrier for carrier transport and lower the power, according to an embodiment of the organic electroluminescent device of the present invention, the organic electroluminescent device includes a first light-emitting layer, a first spacer layer, a second light-emitting layer, a second spacer layer, and a third light-emitting layer stacked between the first electrode and the second electrode. The difference between the highest occupied molecular orbital energy of the first thermally activated delayed fluorescence material and the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than or equal to 0.4 eV, and the difference between the highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material and the lowest unoccupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than or equal to 0.4 eV. At the same time, the difference between the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material and the highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than or equal to 0.4 eV, and the difference between the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material and the lowest unoccupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than or equal to 0.4 eV. There is no special limitation on the energy level magnitudes among the first thermally activated delayed fluorescence material, the second thermally activated delayed fluorescence material, and the third thermally activated delayed fluorescence material, as long as the energy level difference between adjacent thermally activated delayed fluorescence materials is greater than or equal to 0.4 eV. See Figures 2 to 5 , Figures 2 to 5 which is a schematic diagram of the energy level relationship of the organic electroluminescent device provided by the present invention.

[0046] According to an embodiment of the organic electroluminescent device of the present invention, in the organic electroluminescent device, the highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than the highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material, and the lowest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than the lowest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material. And the highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material is greater than the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material, and the lowest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material is greater than the lowest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material.

[0047] According to an embodiment of the organic electroluminescent device of the present invention, in the organic electroluminescent device, the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than the highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material, and the lowest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than the lowest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material. And the highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than the highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material, and the lowest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than the lowest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material.

[0048] According to an embodiment of the organic electroluminescent device of the present invention, in the organic electroluminescent device, the highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material is greater than that of the second thermally activated delayed fluorescence material, the lowest unoccupied molecular orbital energy level of the first thermally activated delayed fluorescence material is greater than that of the second thermally activated delayed fluorescence material, and the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than that of the third thermally activated delayed fluorescence material, and the lowest unoccupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than that of the third thermally activated delayed fluorescence material.

[0049] According to an embodiment of the organic electroluminescent device of the present invention, in the organic electroluminescent device, the highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than that of the second thermally activated delayed fluorescence material, the lowest unoccupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than that of the second thermally activated delayed fluorescence material, and the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than that of the first thermally activated delayed fluorescence material, and the lowest unoccupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than that of the first thermally activated delayed fluorescence material.

[0050] According to an embodiment of the organic electroluminescent device of the present invention, the organic light-emitting device preferably further includes one or more of a hole injection layer, a hole transport layer, an electron blocking layer, a hole blocking layer, an electron transport layer, and an electron injection layer.

[0051] According to an embodiment of the organic electroluminescent device of the present invention, the organic electroluminescent device includes a first electrode, a hole injection layer, a hole transport layer, a first light-emitting layer, a first spacer layer, a second light-emitting layer, a second spacer layer, a third light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode which are sequentially arranged.

[0052] The organic electroluminescent device can be fabricated by methods well known in the art and will not be elaborated herein. In the present invention, the organic electroluminescent device can be fabricated as follows: an anode is formed on a transparent or opaque smooth substrate, an organic thin layer is formed on the anode, and a cathode is formed on the organic thin layer. The organic thin layer can be formed by known film-forming methods such as evaporation, sputtering, spin coating, dipping, ion plating, etc.

[0053] The present invention also provides a display device including the above-mentioned display panel. In the present invention, the display device can be a mobile phone display screen, a computer display screen, a television display screen, a smart watch display screen, a smart car display screen, a VR or AR helmet display screen, a display screen of various smart devices, etc.

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] The present invention uses the measured performance of an OLED device to illustrate the effects of the present invention. The structure of the OLED device is as follows, with the film thickness unit being nm. HIL is the English abbreviation for the hole injection layer. HTL is the English abbreviation for the hole transport layer. EBL is the English abbreviation for the electron blocking layer. EML is the English abbreviation for the emitting layer. HBL is the English abbreviation for the hole blocking layer. ETL is the English abbreviation for the electron transport layer. LiF and Al are the abbreviations for lithium fluoride and aluminum respectively.

[0056] The present invention uses the measured performance of an OLED device to illustrate the effects of the present invention. The structure of the OLED device sequentially includes: a glass substrate, an indium tin oxide (ITO) anode of 15 nm, a hole injection layer of 10 nm, a hole transport layer of 110 nm, an emitting layer (including a spacer layer) of 45 nm, an electron transport layer of 35 nm, an electron injection layer of 1.5 nm, a cathode of 13 nm (magnesium-silver electrode, with a magnesium-silver mass ratio of 1:9), and a capping layer (CPL) of 65 nm.

[0057] The general preparation steps of the OLED device are as follows:

[0058] (1) Mount the glass substrate with the ITO anode on a vacuum deposition device;

[0059] (2) Under a vacuum of 2×10 -6 Pa, simultaneously vacuum deposit the compounds F4-TCNQ and NPB on the ITO anode layer with a mass ratio of 1:99 and a thickness of 10 nm as the hole injection layer;

[0060] (3) Vacuum deposit the compound NPB on the hole injection layer as the hole transport layer with a thickness of 110 nm;

[0061] (4) Vacuum deposit the emitting layer on the hole transport layer, and sequentially vacuum deposit TADF1 and DSA-PH (mass ratio of 98:2, thickness of 15 nm), TADF1 and TADF2 (mass ratio of 6:4, thickness of 5 nm), TADF2 and DPT (mass ratio of 99:1, thickness of 10 nm), TADF2 and TADF3 (mass ratio of 5:5, thickness of 5 nm), TADF3 and DPP (mass ratio of 99:1, thickness of 10 nm);

[0062] (5) Vacuum-deposit TPBi as an electron transport layer on the light-emitting layer with a thickness of 35 nm;

[0063] (6) Vacuum evaporation of metal Yb on the electron transport layer as an electron injection layer with a thickness of 1.5 nm;

[0064] (7) A magnesium-silver electrode was vacuum-deposited on the electron injection layer as a cathode, with a mass ratio of Mg to Ag of 1:9 and a thickness of 13 nm;

[0065] (8) A high refractive index compound CBP was vacuum-deposited on the cathode with a thickness of 65 nm to serve as the cathode covering layer (cap layer, CPL).

[0066] The structures of the compounds used in the preparation of OLED devices are as follows:

[0067]

[0068]

[0069] Device Comparison

[0070] The only difference between the comparative example of the present device and the embodiment of the device is that, in step (4), the light-emitting layer is vacuum-deposited in sequence by TADF1 and DSA-PH (mass ratio of 98:2, thickness of 15 nm), TADF2 and DPT (mass ratio of 99:1, thickness of 15 nm), and TADF3 and DPP (mass ratio of 99:1, thickness of 15 nm); the other steps are the same.

[0071] Performance evaluation of OLED devices:

[0072] The current of the OLED device at different voltages was measured using a Keithley 2365A digital nanovoltmeter, and the current was divided by the luminous area to obtain the current density of the OLED device at different voltages. The brightness and radiant energy flux density of the OLED device at different voltages were measured using a Konicaminolta CS-2000 spectroradiometer. Based on the current density and brightness of the OLED device at different voltages, the current density (10 mA / cm 2 )’s driving voltage, current efficiency and color coordinates CIE (x, y), the specific data are shown in Table 1.

[0073] Table 1 Performance evaluation results of OLED devices

[0074] CIE(x, y) Voltage (v) Current efficiency Example 0.34，0.35 4.7 115％ Comparative example 0.35，0.36 5.2 100％

[0075] From the data in the above table, it can be seen that compared with the devices in the comparative examples, the electroluminescent device using the structure of the present invention has a lower driving voltage, so the power consumption of the device can be effectively reduced, and the device using the structure of the present invention has a higher current efficiency.

[0076] The OLED device structure provided by the present invention has excellent carrier transport performance and higher exciton utilization rate, which can significantly improve the light-emitting efficiency of the device and reduce energy consumption.

[0077] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be pointed out that for those of ordinary skill in the art of the present technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An organic electroluminescent device, characterized in that, Comprising: A first electrode and a second electrode, the first electrode and the second electrode being disposed opposite to each other; A first light-emitting layer, a second light-emitting layer, and a third light-emitting layer stacked between the first electrode and the second electrode, the first light-emitting layer, the second light-emitting layer, and the third light-emitting layer having different light-emitting colors; The first light-emitting layer includes a first thermally activated delayed fluorescence material and a first fluorescent dye; The second light-emitting layer includes a second thermally activated delayed fluorescence material and a second fluorescent dye; The third light-emitting layer includes a third thermally activated delayed fluorescence material and a third fluorescent dye; A first spacer layer between the first light-emitting layer and the second light-emitting layer, the first spacer layer including the first thermally activated delayed fluorescence material and the second thermally activated delayed fluorescence material; The first thermally activated delayed fluorescence material is a hole-transporting material, and the second thermally activated delayed fluorescence material is an electron-transporting material; Or the first thermally activated delayed fluorescence material is an electron-transporting material, and the second thermally activated delayed fluorescence material is a hole-transporting material.

2. The organic electroluminescent device according to claim 1, wherein The first light-emitting layer, the second light-emitting layer, and the third light-emitting layer are selected from one of a red light-emitting layer, a green light-emitting layer, and a blue light-emitting layer.

3. The organic electroluminescent device according to claim 1, wherein The first light-emitting layer is a blue light-emitting layer, and the first light-emitting layer is located on the side of the second light-emitting layer close to the first electrode.

4. The organic electroluminescent device according to claim 1, wherein The energy level difference between the singlet state and the triplet state of the first thermally activated delayed fluorescence material is not greater than 0.5 eV; The energy level difference between the singlet state and the triplet state of the second thermally activated delayed fluorescence material is not greater than 0.5 eV.

5. The organic electroluminescent device according to claim 1, wherein, The energy level difference between the highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material and the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than or equal to 0.4 eV, and the energy level difference between the lowest unoccupied molecular orbital energy level of the first thermally activated delayed fluorescence material and the lowest unoccupied molecular orbital energy level of the second thermally activated delayed fluorescence material is greater than or equal to 0.4 eV.

6. The organic electroluminescent device according to claim 1, characterized in that, The molar ratio of the first thermally activated delayed fluorescence material to the second thermally activated delayed fluorescence material in the first spacer layer is (1:99) to (99:1).

7. The organic electroluminescent device according to claim 1, characterized in that, The difference between the peak wavelength of the photoluminescence spectrum of the first thermally activated delayed fluorescence material and the peak wavelength of the ultraviolet absorption spectrum of the first fluorescent dye does not exceed 20 nm; The difference between the peak wavelength of the photoluminescence spectrum of the second thermally activated delayed fluorescence material and the peak wavelength of the ultraviolet absorption spectrum of the second fluorescent dye does not exceed 20 nm; The difference between the peak wavelength of the photoluminescence spectrum of the third thermally activated delayed fluorescence material and the peak wavelength of the ultraviolet absorption spectrum of the third fluorescent dye does not exceed 20 nm.

8. The organic electroluminescent device according to claim 1, wherein, The doping concentration of the first fluorescent dye is 0.05 to 10 wt%; The doping concentration of the second fluorescent dye is 0.05 to 10 wt%; The doping concentration of the third fluorescent dye is 0.0� to 10 wt%.

9. The organic electroluminescent device according to claim 1, wherein The highest occupied molecular orbital energy level of the first thermally activated delayed fluorescence material is deeper than the highest occupied molecular orbital energy level of the first fluorescent dye; the lowest unoccupied molecular orbital energy level of the first thermally activated delayed fluorescence material is shallower than the lowest unoccupied molecular orbital energy level of the first fluorescent dye; The highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material is deeper than that of the second fluorescent dye; The lowest unoccupied molecular orbital energy level of the second thermally activated delayed fluorescence material is shallower than that of the second fluorescent dye; The highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is deeper than that of the third fluorescent dye; The lowest unoccupied molecular orbital energy level of the third thermally activated delayed fluorescence material is shallower than that of the third fluorescent dye.

10. The organic electroluminescent device according to claim 1, characterized in that, It further includes a second spacer layer located between the second light-emitting layer and the third light-emitting layer; the second spacer layer includes the second thermally activated delayed fluorescence material and the third thermally activated delayed fluorescence material.

11. The organic electroluminescent device according to claim 10, wherein, The third thermally activated delayed fluorescence material and the first thermally activated delayed fluorescence material are of the same type of transport materials.

12. The organic electroluminescent device according to claim 10, wherein, The energy difference between the singlet state and the triplet state of the second thermally activated delayed fluorescence material is not greater than 0.5 eV.

13. The organic electroluminescent device according to claim 10, characterized in that, The energy level difference between the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material and the highest occupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than or equal to 0.4 eV, and the energy level difference between the highest occupied molecular orbital energy level of the second thermally activated delayed fluorescence material and the lowest unoccupied molecular orbital energy level of the third thermally activated delayed fluorescence material is greater than or equal to 0.4 eV.

14. The organic electroluminescent device according to claim 10, wherein The molar ratio of the second thermally activated delayed fluorescence material to the third thermally activated delayed fluorescence material in the second spacer layer is (1:99) to (99:1).

15. A display device, characterized in that, An organic electroluminescent device according to any one of claims 1 to 14 is included.

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