Organic electroluminescent device and use thereof

Abstract

This invention discloses an organic electroluminescent device and its application. The organic electroluminescent device includes, from bottom to top, an anode layer, a light-emitting layer, an electronic functional layer, and a cathode layer. The electronic functional layer includes an electron injection layer, which is composed of m first electron injection layers and m second electron injection layers arranged alternately, where m = 2–8. The first electron injection layer material is an undoped inert metal or alkaline earth metal, and the second electron injection layer material is an undoped metal oxide compound. The work function of the first electron injection layer material is greater than that of the second electron injection layer material. By introducing an electron injection layer formed by alternating m first electron injection layers and m second electron injection layers, this invention can reduce the electron injection barrier from the cathode metal, preventing electron accumulation, and simultaneously improve the electron transport capability of the electron injection layer, thereby improving the efficiency roll-off phenomenon and extending the device's lifespan.

Description

Technical Field

[0001] This invention relates to the field of electroluminescence technology, and more particularly to an organic electroluminescent device and its applications. Background Technology

[0002] Organic light-emitting diodes (OLEDs) have high brightness and low power consumption, and have a very broad technological prospect compared with traditional liquid crystal and inorganic light-emitting diode display technologies. Specifically, they can achieve: 1. ultra-high resolution (above 400ppi); 2. flexible display; 3. high contrast; 4. wide color gamut.

[0003] Currently, there are two bottlenecks limiting the development of OLED display technology: 1. Lifespan is typically only 5,000 hours, lower than the at least 10,000 hours of LCD; 2. Luminous efficiency is not high enough. The highest internal quantum efficiency of traditional fluorescent materials is only 25%, and although phosphorescent materials can reach 100% internal quantum efficiency, their efficiency is reduced due to the obstruction of light extraction. Therefore, developing high-performance, long-lifespan organic electroluminescent devices is the key to OLED display technology and is of great significance in promoting its industrialization.

[0004] It is generally believed that the thermal stability of OLED devices is mainly related to the electrode-organic interface and the glass transition temperature of the material. Therefore, there are two main ways to improve the thermal stability of OLED devices: 1. Introduce n-type or p-type dopants in the transport layer to reduce the carrier injection barrier and avoid carrier accumulation, thereby improving the thermal stability of the device; 2. Use materials with rigid structures and high triplet energy levels as transport materials, such as phenanthroline, anthracene, fluorene and other derivatives, to avoid the material structure from being damaged during use and thus degrading the device performance.

[0005] Therefore, how to reduce the carrier injection barrier in the electron injection layer is a major issue in improving the lifetime of OLED devices. Commonly used electron injection layer materials include LiF, CsF, and NaF. Although these materials can match the work function of the cathode metal as electron injection layers, the cathode metal can migrate to the organic layer or even the light-emitting layer through metal migration during the aging process. This affects the migration of carriers in the organic layer or their recombination in the light-emitting layer, leading to efficiency decay during the electro-aging process.

[0006] Therefore, preventing the migration of cathode metal into the organic layer is crucial for improving the aging lifespan of OLED devices. Current technologies require further improvement and development. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide an organic electroluminescent device and its application, aiming to solve the problems of large efficiency roll-off and short service life of existing organic electroluminescent devices.

[0008] The technical solution of the present invention is as follows:

[0009] An organic electroluminescent device includes, from bottom to top, an anode layer, a light-emitting layer, an electronic functional layer, and a cathode layer; the electronic functional layer includes an electron injection layer, which is composed of m first electron injection layers and m second electron injection layers arranged alternately, where m = 2-8, and the first electron injection layer is directly connected to the cathode layer; the material of the first electron injection layer is an undoped inert metal or alkaline earth metal, and the material of the second electron injection layer is an undoped metal oxide compound, wherein the work function of the first electron injection layer material is greater than the work function of the second electron injection layer material.

[0010] In the organic electroluminescent device, the first electron injection layer material is one of Yb and its alloys, Ba and its alloys, and Mg and its alloys.

[0011] In the organic electroluminescent device, the second electron injection layer material is one of Yb2O3, Li3N, Cs2CO3, CsN3, and Al2O3.

[0012] In the organic electroluminescent device, the work function of the first electron injection layer material is less than the work function of the cathode layer material.

[0013] The organic electroluminescent device further includes an electron transport layer disposed between the electron injection layer and the light-emitting layer, wherein the work function of the second electron injection layer material differs from the LUMO energy level of the electron transport layer by less than 0.5 eV.

[0014] In the organic electroluminescent device, the thickness of the first electron injection layer is 0.5-1 nm, and the thickness of the second electron injection layer is 0.5-1 nm.

[0015] The organic electroluminescent device, wherein the total thickness of the electron injection layer is 2-16 nm.

[0016] In the organic electroluminescent device, the transmittance of the first electron injection layer and the second electron injection layer is higher than 90%.

[0017] In the organic electroluminescent device, a hole functional layer is further disposed between the anode layer and the light-emitting layer, wherein the hole functional layer includes one or more of a hole injection layer, a hole transport layer, and an electron blocking layer.

[0018] An application of an organic electroluminescent device, wherein the organic electroluminescent device is used to fabricate an organic electroluminescent display or an organic electroluminescent lighting device.

[0019] Beneficial effects: The electron injection layer of the organic electroluminescent device provided by the present invention is composed of m first electron injection layers and m second electron injection layers arranged alternately, which has the following advantages compared with conventional OLED devices in the prior art:

[0020] Inserting a second electron injection layer with a relatively low work function between the first electron injection layer, which has a relatively high work function, can reduce the injection barrier between the cathode metal and the electron transport layer, thereby reducing the turn-on voltage of the OLED device. Moreover, electrons tend to migrate to materials with high work functions, and the interface between the second and first electron injection layers can accelerate electron transfer, which is beneficial to promoting the electron transport characteristics of the device's electronic structure, thereby improving the balance between electron and hole carriers in the light-emitting layer. On the other hand, since the electron transfer is accelerated and the interface barrier between the cathode interface and the electron transport layer is reduced, the accumulation of carriers or excitons at the cathode interface can be effectively reduced, thereby avoiding the induced interface quenching and organic layer aging problems, which affect the luminous efficiency and lifetime stability of the device.

[0021] In this invention, the first electron injection layer (undoped inert metal or alkaline earth metal) and the second electron injection layer (undoped metal oxide compound) arranged at intervals have stable material properties and do not undergo severe metal migration like active metals (which would damage the organic layer or even the light-emitting layer structure if the metal migrates into the organic layer). In other words, the first and second electron injection layers arranged at intervals in this invention can form a barrier layer between the cathode layer metal and the organic layer, thus more effectively blocking the metal migration from the cathode layer metal to the organic layer. This protects the normal recombination of carriers in the light-emitting layer during the use of the OLED device, especially in high-temperature environments, thereby improving the efficiency roll-off phenomenon of the electroluminescent device and increasing the device's lifespan.

[0022] Compared to existing technologies that use a single metal as the electron injection layer, the introduction of spaced metal oxides and other high-valence metal compounds in this invention can avoid device performance degradation due to defects caused by metal oxidation reactions during use.

[0023] For materials with poor electron transport capabilities, the electron transport capability can be optimized multiple times through the spaced electron injection layer structure of this invention to achieve carrier recombination balance, thus broadening the selection range of electron transport materials. Furthermore, the electron injection layer structure of this invention does not require doping, which can also ensure that the device has a low start-up voltage and high luminous efficiency. The simplified manufacturing process is conducive to commercial production. Attached Figure Description

[0024] Figure 1 A schematic diagram of the structure of the organic electroluminescent device of the present invention is shown;

[0025] In the figure: 11 is the cathode layer, 12 is the electron injection layer described in this patent (where A and B in 12-1A, 12-1B...12-mA, 12-mB represent the materials of the first and second electron injection layers), 13 is the second electron transport layer, 14 is the first electron transport layer, 15 is the light-emitting layer, 16 is the second hole transport layer, 17 is the first hole transport layer, 18 is the hole injection layer, and 19 is the anode layer. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this invention.

[0027] It should be understood that, without conflict, any and all embodiments of the present invention can be combined with technical features of any other embodiment or multiple other embodiments to obtain other embodiments. The present invention includes such combinations to obtain other embodiments.

[0028] In this specification, groups and their substituents may be selected by those skilled in the art to provide stable structural moieties and compounds. When a substituent is described by a conventional chemical formula written from left to right, the substituent also includes chemically equivalent substituents obtained when the structural formula is written from right to left.

[0029] The chapter headings used in this specification are for organizational purposes only and should not be construed as limiting the subject matter. All references or portions thereof cited in this invention, including but not limited to patents, patent applications, articles, books, user manuals, and papers, are incorporated herein by reference in their entirety.

[0030] Unless otherwise specified, all technical and scientific terms used herein have the standard meaning in the field to which the claimed subject matter pertains. Where multiple definitions exist for a term, the definition herein shall prevail.

[0031] It should be understood that the singular forms used in this invention, such as "a," include plural references unless otherwise specified. Furthermore, the term "comprising" is an open-ended limitation, not a closed one; that is, it includes the contents specified in this invention but does not exclude other aspects.

[0032] This invention provides an organic electroluminescent device, which, from bottom to top, consists of an anode layer, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode layer.

[0033] Next, the composition of the organic electroluminescent device of this application will be further described.

[0034] The anode layer and / or cathode layer are transparent. Specifically, the organic electroluminescent device needs to emit light from at least one side of the anode layer and cathode layer, which requires that the substrate of the light-emitting side to be transparent. Generally, only one side needs to emit light, so the anode layer or cathode layer is made transparent.

[0035] The primary function of the anode layer is to inject holes into the hole transport layer or the light-emitting layer. Anode layer materials with a work function of 4.5 eV or higher are preferred. Specific examples of anode layer materials include indium tin oxide (ITO), tin oxide (NESA), indium gallium zinc oxide (IGZO), and silver. The anode layer can be formed into a thin film using methods such as thermal evaporation or sputtering. Preferably, the light transmittance of the visible area of ​​the anode layer is greater than 80%. Furthermore, the sheet resistance of the anode layer is preferably 500 Ω / cm. -1 The film thickness is preferably selected in the range of 10-200 nm.

[0036] The primary function of the cathode layer is to inject electrons into the electron injection layer, electron transport layer, or light-emitting layer. Materials with a low work function are preferred. The cathode layer material is not particularly limited, but aluminum, magnesium, silver, magnesium-silver alloys, magnesium-aluminum alloys, and aluminum-lithium alloys are preferred. The cathode layer can also be formed into a thin film using methods such as thermal evaporation or sputtering. The cathode layer thickness is preferably selected within the range of 10-200 nm. Additionally, light emission can be extracted from the cathode layer side as needed.

[0037] In the aforementioned organic electroluminescent device, the luminescence of the luminescent layer is mainly achieved through the recombination of holes from the hole transport layer and electrons from the electron transport layer to form excitons. These excitons then convert electrical energy into light energy through radiative transitions. The luminescent layer structure generally includes host and guest materials. Guest materials are mainly divided into fluorescent and phosphorescent materials. The requirements for guest materials are that they possess high quantum efficiency fluorescence or phosphorescence properties, with emission spectra mainly distributed in the 400-700 nm range (within the visible light range), and simultaneously exhibit good conductivity, film-forming properties, thermal stability, and photostability.

[0038] For example, red fluorescent materials include DCM1, DCM2, DCJTB, (PPA)(PSA)Pe, BZTA2, TPP, ACY, BAM, etc.

[0039] Green fluorescent materials include Alq3, Courmarin6, C-545T, C-545MT, QA, QD5, etc.

[0040] Blue fluorescent materials mainly include aromatic hydrocarbons, aromatic amines, organoboron compounds, silicon compounds, and carbazole derivatives containing only carbon and hydrogen elements, such as Perylene, TBPe, AND, TF, DPYFL01, DSA, DSA-amine, CzOxa, and DPVBi.

[0041] Phosphorescent materials are mainly composed of noble metal complexes such as iridium, platinum, ruthenium and rhenium. Common red phosphorescent materials include (btfmp)2Ir(dbm), (btfmp)2Ir(pic), (btmp)2Ir(acac), (btp)2Ir(acac) and (btfmp)2Ir(acac).

[0042] Green phosphorescent materials mainly include Ir(ppy)3, Ir(mppy)3, Ir(chpy)3 and Ir(mchpy)3, etc.

[0043] Blue phosphorescent materials mainly include Firpic, Fir6, Ir(F4ppy)3, FirN4, fac-Ir(mpptz)3, Firtaz, (dfpmp)3Ir(ptz), Ir(ppz)3 and Pt-4, etc.

[0044] It also includes a novel TADF material that can generate sufficient reverse intersystem crossing from triplet excited state to singlet excited state through thermal excitation, transforming triplet excitons into singlet excitons, including 4CzIPN, PPZDPO, PPZ-3TPT, PPZ-DPS, etc.

[0045] The doping concentration of the guest is generally classified according to the type of luminescent guest. The doping concentration of fluorescent guests is 1%-10%, and the doping concentration of phosphorescent guests is 5%-15%.

[0046] The host material primarily transfers the energy of excitons formed by the recombination of holes and electrons to the guest material, thereby enabling the guest material to emit light and preventing the concentration quenching of the guest material. Therefore, to effectively prevent energy from being transferred back from the shell material to the host material, the E of the host material... g and E T Both must be higher than the host material. The host material is typically a high-E content material containing carbazole, fluorine, arylsilane, dibenzofuran, and dibenzothiophene, etc. T Materials with functional groups, such as CBP, DmCBP, mCP, DCB, TRZ2, PPO1, BCPDB, CPBDC, TPCz, BSB, BST, mDPFB, TFTPA, etc.

[0047] In the organic electroluminescent device described above, the preferred thickness of the electron transport layer is 10nm-50nm.

[0048] The electron transport layer is an organic layer formed between the light-emitting layer and the cathode layer, and its main function is to transport electrons from the cathode layer to the light-emitting layer. As the electron transport material for the electron transport layer, aromatic heterocyclic compounds containing one or more heteroatoms within the molecule are preferred, and nitrogen-containing ring derivatives are particularly preferred. Furthermore, as nitrogen-containing ring derivatives, aromatic rings having a nitrogen-containing six-membered or five-membered ring skeleton, or fused aromatic ring compounds having a nitrogen-containing six-membered or five-membered ring skeleton, are preferred.

[0049] The electron transport layer of the organic electroluminescent device of the present invention is preferably derived from, but is not limited to, the following compounds:

[0050]

[0051]

[0052] The hole transport layer of the organic light-emitting device of this application is an organic layer formed between the light-emitting layer and the anode layer (or hole injection layer), and its main function is to transport holes from the anode layer to the light-emitting layer. The hole transport layer may consist of one organic layer material, defined as the first hole transport layer; or it may consist of two organic layer materials, with the organic layer closer to the anode layer defined as the first hole transport layer and the organic layer closer to the light-emitting layer defined as the second hole transport layer. As the hole transport material for the hole transport layer, an aromatic amine compound is preferably used, wherein the aromatic amine compound is at least one of a first aromatic amine derivative and a second aromatic amine derivative. The general structural formula of the first aromatic amine derivative is shown in formula (I), and the general structural formula of the second aromatic amine derivative is shown in formula (II). Wherein, Ar1-Ar4 represent an aromatic hydrocarbon group with 6-50 (preferably 6-30, more preferably 6-20, and even more preferably 6-12) substituted or unsubstituted cyclic carbon groups with 6-50 (preferably 6-30, more preferably 6-20, and even more preferably 6-12) substituted aromatic heterocyclic groups with 5-50 (preferably 5-30, more preferably 5-20, and even more preferably 5-12) substituted or unsubstituted cyclic carbon groups with 5-50 (preferably 5-30, more preferably 5-20, and even more preferably 5-12) substituted or unsubstituted cyclic carbon groups with 5-50 (preferably 5-30, more preferably 5-20, and even more preferably 5-12) substituted or unsubstituted cyclic carbon groups, or groups formed by bonding these aromatic hydrocarbon groups or fused aromatic hydrocarbon groups with aromatic heterocyclic groups or fused aromatic heterocyclic groups. A ring can be formed between Ar1 and Ar2, or between Ar3 and Ar4; L represents an aromatic hydrocarbon group with 6-50 (preferably 6-30, more preferably 6-20, and even more preferably 6-12) substituted or unsubstituted cyclic carbon groups, or a fused aromatic hydrocarbon group with 6-50 (preferably 6-30, more preferably 6-20, and even more preferably 6-12) cyclic carbon groups that may have substituents, or an aromatic heterocyclic group with 5-50 (preferably 5-30, more preferably 5-20, and even more preferably 5-12) substituted or unsubstituted cyclic carbon groups, or a fused aromatic heterocyclic group with 5-50 (preferably 5-30, more preferably 5-20, and even more preferably 5-12) substituted or unsubstituted cyclic carbon groups.

[0053] In the organic electroluminescent device of this application, the hole transport layer material is preferably selected from, but not limited to, the following compounds:

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062] Furthermore, the thickness of the hole transport layer is not particularly limited, but is preferably 20-200 nm. Specifically, when the hole transport layer of the organic electroluminescent device is composed of a first hole transport layer, the thickness of the first hole transport layer is preferably 20-200 nm; when the hole transport layer of the organic electroluminescent device is composed of a first hole transport layer and a second hole transport layer, the thickness of the first hole transport layer is preferably 19-150 nm, and the thickness of the second hole transport layer is preferably 1-50 nm.

[0063] Furthermore, it is preferable to dope the electron transport layer with an n-type dopant and the hole transport layer with a p-type dopant. The main functions of the n-type and p-type dopants are to improve the transport properties of the electron transport layer and the hole transport layer, respectively, and to reduce the driving voltage of the organic electroluminescent device. In one or more embodiments, the n-type dopant is preferably one of Li, Cs, Ba, Yb, CsF, BaO, Liq, Naq, Libpp, Bepq2, Bepp2, LiF, CsCO3, ZnO, etc.; in one or more embodiments, the p-type dopant is preferably one of HATCN, F4TCNQ, HI-3, etc. When the hole transport layer contains a p-type dopant and a hole transport material, the doping concentration of the p-type dopant is preferably 0.1% by mass to 50.0% by mass; when the electron transport layer contains the aforementioned n-type dopant and electron transport material, the doping concentration of the n-type dopant is preferably 1.0% by mass to 90.0% by mass. The structural formulas of the n-type doped materials Liq, Naq, Libpp, Bepq2, and Bepp2 are shown below:

[0064]

[0065] In the organic electroluminescent device of this application, an electron injection layer is preferably disposed at the interface region between the cathode layer and the electron transport layer or the light-emitting layer. The main function of the electron injection layer is to promote the injection of electrons from the cathode layer to the electron transport layer or the light-emitting layer, thereby improving the luminous brightness and device lifetime of the organic electroluminescent device. In this application, the electron injection layer is composed of m first electron injection layers and m second electron injection layers arranged alternately, where m = 2-8. The first electron injection layer is directly connected to the cathode layer. The material of the first electron injection layer is an undoped inert metal or alkaline earth metal, and the material of the second electron injection layer is an undoped metal oxide compound. The work function of the first electron injection layer material is greater than that of the second electron injection layer material, and the work function of the first electron injection layer material is less than that of the cathode layer material. Further, the difference between the work function of the second electron injection layer material and the LUMO energy level of the electron transport layer is less than 0.5 eV.

[0066] This application inserts a second electron injection layer with a relatively low work function between a first electron injection layer with a relatively high work function. This reduces the injection barrier between the cathode metal and the electron transport layer, thereby lowering the turn-on voltage of the OLED device. Furthermore, electrons tend to migrate to materials with high work functions, and the interface between the second and first electron injection layers can accelerate electron transfer, which is beneficial for promoting electron transport characteristics in the electronic structure of the device, thus improving the balance between electron and hole carriers in the emitting layer. On the other hand, since the electron transfer is accelerated and the interface barrier between the cathode interface and the electron transport layer is reduced, the accumulation of carriers or excitons at the cathode interface can be effectively reduced, thereby avoiding the induced interface quenching and organic layer aging problems, which affect the luminous efficiency and lifetime stability of the device.

[0067] In this application, the first electron injection layer material is one of Yb and its alloys, Ba and its alloys, Mg and its alloys, but not limited thereto; the second electron injection layer material is one of Yb2O3, Li3N, Cs2CO3, CsN3, and Al2O3, but not limited thereto. The first electron injection layer (undoped inert metal or alkaline earth metal) and the second electron injection layer (undoped metal oxide compound) arranged alternately in this application have stable material properties and do not undergo severe metal migration like active metals. Once metal migrates into the organic layer, it will damage the organic layer and even the structure of the light-emitting layer. That is to say, the first and second electron injection layers arranged alternately in this invention can form a barrier layer between the cathode layer metal and the organic layer, thus more effectively blocking the metal migration phenomenon from the cathode layer metal to the organic layer. This protects the normal recombination of carriers in the light-emitting layer during the use of the OLED device, especially in high-temperature environments, thereby improving the efficiency roll-off phenomenon of the electroluminescent device and increasing the device's lifespan. Compared to existing technologies that use a single metal as the electron injection layer, the introduction of spaced-alternating metal oxides and other high-valence metal compounds in this application can avoid device performance degradation due to defects caused by metal oxidation reactions during use. For materials with poor electron transport capabilities, the electron transport capability can be optimized multiple times through the spaced-alternating electron injection layer structure of this invention to achieve carrier recombination balance, thus broadening the selection of electron transport materials. Furthermore, the electron injection layer structure of this invention does not require doping, ensuring that the device has a low start-up voltage and high luminous efficiency. The simplified manufacturing process is beneficial for commercial production.

[0068] In this application, the electron injection layer can be formed into a thin film by thermal evaporation, and the evaporation rate is preferably... The total thickness of the electron injection layer is 2–8 nm, of which the thickness of the first electron injection layer is 0.5–1 nm and the thickness of the second electron injection layer is 0.5–1 nm.

[0069] In the organic electroluminescent device of this application, a hole injection layer is preferably present at the interface region between the anode layer and the hole transport layer (or the light-emitting layer). The main function of the hole injection layer is to promote the injection of holes from the anode layer to the hole transport layer or the light-emitting layer, thereby reducing the driving voltage of the organic electroluminescent device and improving the luminous brightness and device lifetime. Here, the hole injection material refers to an acceptor-type organic material containing a deep LUMO energy level. As a specific example, it is preferably selected from HATCN, F4-TCNQ, HI-3, etc., wherein the structural formulas of the hole injection layer materials HATCN, F4-TCNQ, and HI-3 are shown below:

[0070]

[0071] Furthermore, the thickness of the hole injection layer is not particularly limited, but is preferably 5-100 nm.

[0072] In some embodiments, an application of the organic electroluminescent device is also provided, in which the organic electroluminescent device of the present invention is used to prepare organic electroluminescent displays or organic electroluminescent lighting devices.

[0073] Furthermore, the present invention also provides a specific method for fabricating a multilayer organic electroluminescent device, and the fabrication method of the present invention will be further described below through specific embodiments.

[0074] The present invention does not impose any particular restrictions on the source of the raw materials used in the following embodiments, which can be commercially available products or prepared by methods known to those skilled in the art.

[0075] Examples 1-8

[0076] 1. For example Figure 1 As shown, a 30mm × 30mm × 0.7mm thick glass substrate with an anode layer 19 (the anode layer being a 95nm ITO transparent electrode) was sequentially ultrasonically cleaned in acetone (1 time), cleaning solution (1 time), ultrapure water (3 times), and isopropanol (1 time), with each ultrasonic cleaning step lasting 10 minutes. The cleaned glass substrate with the anode layer 18 was then placed in an oven at 80℃ and baked for 3 hours. The cleaning solution is a cleaning solution for cleaning ITO glass, formulated with solid salts, polyoxyethylene ethers, and other nonionic surfactants. It is used to clean dirt and oil adhering to the surface of the glass substrate with the ITO transparent electrode. This is a commercially available product and will not be described in detail here.

[0077] 2. The baked ITO glass substrate with anode layer 19 is subjected to vacuum plasma cleaning treatment for 10 minutes. The plasma-treated glass substrate with anode layer 19 is mounted on the substrate holder of the vacuum evaporation apparatus. First, HATCN compound is deposited on the side with transparent electrode lines to cover the transparent electrode, forming a hole injection layer 18 with a film thickness of 10 nm.

[0078] 3. HT-10 compound is vapor-deposited on the hole injection layer 18 to form a first hole transport layer 17 with a film thickness of 60 nm;

[0079] 4. Deposit compound HT-45 on the first hole transport layer 17 to form a second hole transport layer 16 with a film thickness of 10 nm;

[0080] 5. A host material GH-1 and a guest material Ir(mppy)3 are co-deposited on the second hole transport layer 16 to form a light-emitting layer 15 with a thickness of 30 nm. The structural formulas of GH-1 and Ir(mppy)3 are shown below:

[0081]

[0082] 6. On the light-emitting layer 15, compound ET-15 is deposited by vapor deposition to form a first electron transport layer 14 with a film thickness of 10 nm;

[0083] 7. Then, Liq and ET-4 are co-deposited on the first electron transport layer 14, with the mass concentration of Liq set to 30% and the balance being ET-4, to form a second electron transport layer 13 with a film thickness of 20 nm.

[0084] 8. A first material and a second material are deposited at intervals on the second electron transport layer 13 to form an electron injection layer 12 with a total film thickness of 2 nm, consisting of a first electron injection layer and a second electron injection layer, wherein the first electron injection layer is 0.5 nm and the second electron injection layer is 0.5 nm. In Examples 1-8, the total film thickness, number of intervals, and film thickness of the first and second electron injection layers in each example are shown in Table 1 below:

[0085] Table 1. Composition parameters of the electron injection layer in Examples 1-8

[0086]

[0087]

[0088] 8. Metallic Al is deposited on the electron injection layer 12 (the spaced arrangement structure in the electron injection layer ensures that the first material is in contact with Al) to form a cathode layer 11 with a film thickness of 100 nm, thus obtaining an organic electroluminescent device.

[0089] Comparative Examples 1-5

[0090] The organic electroluminescent devices prepared in Comparative Examples 1-5 have variations in the composition of the first and second electron injection layers, as shown in Table 2. Comparative Example 2 has an electron injection layer without an interleaved structure; Comparative Example 3 uses LiF, which has a higher work function than Yb₂O₃ and a larger energy level difference with Yb; Comparative Examples 4 and 5 consist of only the first and second materials as electron injection layers. Otherwise, the organic electroluminescent devices were prepared using the same procedures as in Examples 1-8.

[0091] Table 2. Composition parameters of the electron-injected layers in Comparative Examples 1-5

[0092]

[0093]

[0094] Performance evaluation of organic electroluminescent devices

[0095] The organic electroluminescent devices prepared in Examples 1-8 and Comparative Examples 1-5 of this application were subjected to performance tests. The CIE 1931 chromaticity coordinates (x, y), the highest external quantum efficiency of the devices, and the performance at 3000 cd / m² were measured using a CS-2000 spectroradiometer (Konica Minolta) and a 2420 digital source meter (Keithley). 2 External quantum efficiency and full width at half maximum (FWHM) of electroluminescence spectrum at brightness (unit: nm).

[0096] In addition, the T95 (time taken for brightness to decay to 95% of initial brightness) lifetime test of organic electroluminescent devices was performed using OLED lifetime testing equipment at a constant current density of 25 mA / cm². 2 The T95 lifetime (in hours) is shown below. The device performance evaluation results for Examples 1-8 and Comparative Examples 1-5 are as follows:

[0097] As shown in Table 3.

[0098]

[0099]

[0100]

[0101] Comparing the device performance results of Examples 1-8 and Comparative Examples 1-3 in Table 3, it can be seen that, with other materials being the same in the organic electroluminescent device structure, the OLED devices with the spaced arrangement structure used in Examples 1-8 of this application have higher device efficiency and device lifetime compared to the devices without spaced arrangement in Comparative Examples 4-5. This indicates that inserting Yb2O3 with a relatively low work function into the relatively high work function Yb can reduce the injection barrier between the cathode metal and the electron transport layer, improve the uniformity of hole and electron distribution in the light-emitting layer, and reduce the accumulation of charge carriers or excitons at the interface, thereby improving the luminous efficiency and lifetime stability of the OLED device.

[0102] Compared with Comparative Example 2, Examples 1-3 all contain Yb2O3 and Yb. The devices in Examples 1-3, which contain a multilayer Yb spaced arrangement structure, have better lifetime. This is because the structure can more effectively block the metal migration of cathode metal to organic layer, thereby protecting the normal recombination of carriers in the light-emitting layer during the use of OLED devices, thus improving the efficiency roll-off phenomenon of electroluminescent devices and increasing the lifespan of devices.

[0103] Compared to Comparative Example 3, Comparative Example 1 has a larger electron injection barrier due to the difference between the energy levels of LiF (work function 2.9 eV) and Yb (work function 2.6 eV). Compared to the smaller energy level difference between Yb2O3 and Yb, this affects electron injection, resulting in uneven distribution of holes and electrons. This induces interface quenching and organic layer aging, affecting the luminous efficiency and lifetime stability of the device.

[0104] The experimental data above show that the novel organic electroluminescent device of this application has a significant performance improvement compared with conventional organic light-emitting devices, and is expected to be promoted for commercial application.

[0105] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. An organic electroluminescent device, characterized by comprising: The organic electroluminescent device comprises, from bottom to top, an anode layer, a light-emitting layer, an electronic functional layer, and a cathode layer. The electronic functional layer includes an electron injection layer, which is composed of m first electron injection layers and m second electron injection layers arranged alternately, where m = 2-8. The first electron injection layer is directly connected to the cathode layer. The material of the first electron injection layer is one of Yb and its alloys, Ba and its alloys, and Mg and its alloys. The material of the second electron injection layer is one of Yb₂O₃, Li₃N, Cs₂CO₃, CsN₃, and Al₂O₃. In one embodiment, the work function of the first electron injection layer material is greater than that of the second electron injection layer material; the electronic functional layer further includes an electron transport layer disposed between the electron injection layer and the light-emitting layer, wherein the difference between the work function of the second electron injection layer material and the LUMO energy level of the electron transport layer is less than 0.5 eV; the single-layer thickness of the first electron injection layer is 0.5-1 nm, the single-layer thickness of the second electron injection layer is 0.5-1 nm, the total thickness of the electron injection layer is 2-16 nm, and the transmittance of the first and second electron injection layers is higher than 90%.

2. The organic electroluminescent device according to claim 1, characterized in that, The work function of the first electron injection layer material is less than the work function of the cathode layer material.

3. The organic electroluminescent device according to claim 1, characterized in that, A hole functional layer is further disposed between the anode layer and the light-emitting layer, the hole functional layer including one or more of a hole injection layer, a hole transport layer and an electron blocking layer.

4. An application of the organic electroluminescent device as described in any one of claims 1-3, characterized in that, The organic electroluminescent device is used to prepare organic electroluminescent displays or organic electroluminescent lighting devices.

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