An organic electroluminescent device

Abstract

The application relates to the technical field of organic electroluminescence, and discloses an organic electroluminescence device, which comprises, from bottom to top, an anode layer, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer and a metal cathode layer; the light-emitting layer comprises a host material, a sensitizer and a blue fluorescent dye; the sensitizer is doped in the host material in a gradient doping concentration mode, the doping concentration of the sensitizer is gradiently reduced from the electron blocking layer to the hole blocking layer, and the blue fluorescent dye is doped in the host material in a fixed doping concentration mode. The organic electroluminescence device can improve the efficiency roll-off and service life by optimizing the device structure and material collocation system.

Description

Technical Field

[0001] This application relates to the field of organic electroluminescence technology, and mainly to an organic electroluminescent device. Background Technology

[0002] In recent years, organic light-emitting diodes (OLEDs) have captured a significant market share in the current full-color flat panel display field and have also shown broad application prospects in the future energy-saving and environmentally friendly solid-state lighting field, attracting increasing attention from academic and commercial enterprises and experiencing rapid development. Materials are a key factor determining device performance, and researching and exploring organic electroluminescent materials that meet market requirements is of great significance.

[0003] In recent decades, OLED luminescent materials have undergone a seamless transition from fluorescent and phosphorescent materials to thermally activated delayed fluorescence (TADF), significantly increasing the choices available in the OLED material market. Currently, through innovation in material molecular structures and continuous optimization of device processes, the efficiency and lifespan of OLED devices based on blue, green, and red light-emitting materials have been continuously improved and extended, with significant breakthroughs achieved in color purity, some already meeting commercialization requirements. However, current OLED devices based on blue light-emitting materials often suffer from one or more drawbacks, such as large efficiency roll-off, insufficient lifespan, and poor color purity. For blue light-emitting materials, device structure design and material system matching will significantly impact their efficiency, lifespan, and color purity. On the one hand, phosphorescent and TADF materials have relatively long exciton lifetimes (microseconds to milliseconds), which can easily lead to the annihilation of excitons and polarons inside the device under high brightness, resulting in non-radiative energy loss and aging degradation of organic materials. This causes severe efficiency roll-off and a significantly shortened lifespan, which seriously restricts the development of the blue OLED device market. On the other hand, in order to improve the efficiency and lifespan of the device, multiple functional layers are usually used to achieve high-efficiency light emission. However, the energy level matching problem of the multifunctional layers can lead to the imbalance of carrier transport in the light-emitting layer and the narrowing of the recombination region in the light-emitting layer. This results in exciton accumulation at the interface between the light-emitting layer and the transport layer, further inducing exciton quenching and aging of the organic layer, affecting the luminous efficiency and lifespan stability of the device, and preventing the efficiency and lifespan of OLED devices from meeting industrialization requirements.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this application is to provide an organic electroluminescent device that aims to solve the problems of low efficiency and short lifespan of existing blue OLED devices.

[0006] The technical solution of this application is as follows:

[0007] An organic electroluminescent device, comprising, from bottom to top, an anode layer, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a metal cathode layer;

[0008] The light-emitting layer comprises a host material, a sensitizer, and a blue fluorescent dye;

[0009] The sensitizer is doped into the host material using a gradient doping concentration method. The doping concentration of the sensitizer is between 5-50 wt%, and the doping concentration of the sensitizer decreases gradually from the electron blocking layer to the hole blocking layer.

[0010] The blue fluorescent dye is doped into the host material at a fixed doping concentration, which ranges from 0.1 to 10 wt%.

[0011] In the organic electroluminescent device, the sensitizer is a phosphorescent sensitizer or a thermally activated delayed fluorescence sensitizer.

[0012] The organic electroluminescent device of this application can improve efficiency roll-off and service life by optimizing the device structure and material combination system.

[0013] When the sensitizer is a phosphorescent sensitizer, the material composition of the emissive layer is host material + phosphorescent sensitizer (P) + blue fluorescent dye (F) = PSF system. When the sensitizer is a thermally activated delayed fluorescence sensitizer (TADF), the material composition of the emissive layer is host material + thermally activated delayed fluorescence sensitizer (TADF) + blue fluorescent dye (F) = TASF system. Using these material compositions can improve the device's lifetime and external quantum efficiency.

[0014] In the organic electroluminescent device, the phosphorus photosensitizer is one of an iridium complex or a platinum complex;

[0015] The thermally activated delayed fluorescence sensitizer is one of donor-acceptor type TADF material or multiple resonance type TADF material.

[0016] The organic electroluminescent device, wherein the hole injection layer has a thickness of 5-20 nm, the hole transport layer has a thickness of 20-100 nm, the electron blocking layer has a thickness of 5-10 nm, the light-emitting layer has a thickness of 20-40 nm, the hole blocking layer has a thickness of 5-10 nm, the electron transport layer has a thickness of 30-100 nm, and the electron injection layer has a thickness of 0.5-10 nm.

[0017] In the organic electroluminescent device, the thickness of the anode layer is 60–120 nm, and the thickness of the metal cathode layer is 200–300 nm.

[0018] In the organic electroluminescent device, the triplet energy level of the host material is greater than or equal to the triplet energy levels of the sensitizer and the blue fluorescent dye.

[0019] In the organic electroluminescent device, the triplet energy level of the sensitizer is greater than or equal to the triplet energy level of the blue fluorescent dye.

[0020] In the organic electroluminescent device, the HOMO energy level of the host material is greater than or equal to the HOMO energy level of the sensitizer and the blue fluorescent dye; the LUMO energy level of the host material is greater than or equal to the LUMO energy level of the sensitizer and the blue fluorescent dye.

[0021] In the organic electroluminescent device, the HOMO energy level of the sensitizer is greater than or equal to the HOMO energy level of the blue fluorescent dye; the LUMO energy level of the sensitizer is greater than or equal to the LUMO energy level of the blue fluorescent dye.

[0022] In the organic electroluminescent device, the sensitizer is the organic phosphorescent material Ir(cb)3;

[0023] The blue fluorescent dye is DABNA;

[0024] The main material is a material with electron transport properties or hole transport properties; the material with electron transport properties is DPEPO; the material with hole transport properties is mCBP.

[0025] The hole injection layer is composed of HATCN;

[0026] The hole transport layer is composed of TAPC;

[0027] The electron blocking layer is composed of mCP;

[0028] The hole-blocking layer is composed of TSPO1;

[0029] The electron transport layer is composed of TmPyPB;

[0030] The electron injection layer is composed of alkali metals;

[0031] The anode layer is composed of ITO or indium gallium zinc oxide;

[0032] The metal cathode layer is composed of aluminum or a magnesium-aluminum alloy.

[0033] Beneficial effects: The organic electroluminescent device of this application can improve efficiency roll-off and service life by optimizing the device structure and material matching system. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the organic electroluminescent device of this application.

[0035] Figure 2 This is a schematic diagram of the charge transport mechanism of the light-emitting layer (sensitizer gradient doping concentration) of the organic electroluminescent device of this application (from the boundary of the electron blocking layer to the boundary of the hole blocking layer).

[0036] Figure 3 This is a schematic diagram of the charge transport mechanism in the light-emitting layer (with uniform concentration of sensitizer doping) of an existing organic electroluminescent device (from the boundary of the electron blocking layer to the boundary of the hole blocking layer).

[0037] Labeling Explanation: 1. Anode layer; 2. Hole injection layer; 3. Hole transport layer; 4. Electron blocking layer; 5. Light emitting layer; 6. Hole blocking layer; 7. Electron transport layer; 8. Electron injection layer; 9. Metal cathode layer; 51. Main material; 52. Sensitizer; 53. Blue fluorescent dye; 54. Exciton; 41. Hole; 61. Electron. Detailed Implementation

[0038] This application provides an organic electroluminescent device. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0039] To address the issues of low efficiency and short lifespan in existing blue OLED devices, this application provides an organic electroluminescent device that, by optimizing the device structure and material combination system, can improve efficiency roll-off and lifespan.

[0040] Specifically, such as Figure 1 As shown, the organic electroluminescent device of this application includes, from bottom to top, an anode layer 1, a hole injection layer 2, a hole transport layer 3, an electron blocking layer 4, a light-emitting layer 5, a hole blocking layer 6, an electron transport layer 7, an electron injection layer 8, and a metal cathode layer 9.

[0041] The light-emitting layer 5 includes a host material, a sensitizer, and a blue fluorescent dye, with the sensitizer and blue fluorescent dye being doped into the host material.

[0042] The sensitizer is doped into the host material in a gradient doping concentration manner. The doping concentration of the sensitizer is between 5-50 wt%, and the doping concentration of the sensitizer decreases in a gradient from the electron blocking layer 4 to the hole blocking layer 6.

[0043] The blue fluorescent dye is doped into the host material at a fixed concentration, ranging from 0.1 to 10 wt%.

[0044] The doping concentration range of the blue fluorescent dye is 0.1-10 wt%, meaning that the blue fluorescent dye accounts for 0.1-10 wt% of the main material. The doping concentration range of the sensitizer is 5-50 wt%, meaning that the mass ratio of the sensitizer to the main material is 5-50 wt%. The highest doping concentration of the sensitizer on the side of the light-emitting layer 5 closest to the electron blocking layer 4 can be 50 wt%, and the lowest doping concentration of the sensitizer on the side of the light-emitting layer 5 closest to the hole blocking layer 6 can be 5 wt%. For example, in the embodiment of this application, the doping concentration range of the sensitizer is 30-50 wt%, that is, the doping concentration of the sensitizer on the side of the light-emitting layer 5 closest to the electron blocking layer 4 is 50 wt%, and the doping concentration of the sensitizer decreases gradually from the electron blocking layer 4 to the hole blocking layer 6, with the doping concentration of the sensitizer on the side of the light-emitting layer 5 closest to the hole blocking layer 6 being 30 wt%. The sensitizer is doped into the host material using a gradient doping concentration, ranging from 5 to 50 wt%. This helps balance the transport rates of holes and electrons, bringing the hole-electron recombination region closer to the center of the light-emitting layer 5, widening the exciton formation region, and effectively reducing concentration quenching between excitons and polarons. The gradient doping concentration of the sensitizer can be achieved by changing the evaporation rate, specifically by setting the evaporation source of the sensitizer to a uniformly decreasing evaporation temperature or rate.

[0045] In this application, a gradient doping concentration method is used to prepare the light-emitting layer, thereby controlling the balance of charge carriers in the light-emitting layer, widening the exciton recombination region of the light-emitting layer, avoiding non-radiative energy loss and exciton quenching caused by excessive exciton accumulation, avoiding the annihilation of excitons and polarons and the formation of high-energy thermal excitons, and improving the efficiency roll-off and device lifespan of organic electroluminescent devices at high brightness.

[0046] Furthermore, the sensitizer can be a phosphorescent sensitizer or a thermally activated delayed fluorescence sensitizer (TADF).

[0047] When the sensitizer is a phosphorescent sensitizer, the material combination system of the emitting layer is host material + phosphorescent sensitizer (P) + blue fluorescent dye (F) = PSF system. This material combination system can effectively utilize the intersystem crossing process (ISC process) of the phosphorescent sensitizer, maximizing exciton utilization and ultimately improving the device lifetime and external quantum efficiency.

[0048] When the sensitizer is a thermally activated delayed fluorescence sensitizer, the material combination system of the emitting layer is host material + thermally activated delayed fluorescence sensitizer (TADF) + blue fluorescent dye (F) = TASF system. This material combination system can effectively utilize the reverse gap crossing process (RISC process) of the thermally activated delayed fluorescence sensitizer, maximizing exciton utilization and ultimately improving the device lifetime and external quantum efficiency.

[0049] The phosphorus sensitizer can be one of iridium complexes, platinum complexes, etc. In the embodiments of this application, the phosphorus sensitizer is the organic phosphorescent material Ir(cb)3.

[0050] Thermally activated delayed fluorescence sensitizers can be one of donor-acceptor type TADF materials, multiple resonance type TADF materials, etc.

[0051] Blue fluorescent dyes are composed of fluorescent small molecule materials. In the embodiments of this application, the blue fluorescent dye used is DABNA.

[0052] Furthermore, the triplet energy level of the host material is greater than or equal to the triplet energy level of the sensitizer and the blue fluorescent dye. Even further, the triplet energy level of the sensitizer is greater than or equal to the triplet energy level of the blue fluorescent dye. Only by using this material combination system can energy transfer be effectively achieved.

[0053] Furthermore, the HOMO (Highest Occupied Molecular Orbits) energy level of the host material is greater than or equal to the HOMO energy level of the sensitizer and the blue fluorescent dye; the LUMO (Lowest Occupied Molecular Orbits) energy level of the host material is greater than or equal to the LUMO energy level of the sensitizer and the blue fluorescent dye. Even further, the HOMO energy level of the sensitizer is greater than or equal to the HOMO energy level of the blue fluorescent dye; the LUMO energy level of the sensitizer is greater than or equal to the LUMO energy level of the blue fluorescent dye. Using this energy level-matched material combination system is beneficial for achieving efficient energy transfer, reducing non-radiative energy loss, lowering the device's turn-on voltage, and improving device efficiency and lifetime.

[0054] In this application, the host material of the light-emitting layer can be a material with electron transport properties or hole transport properties. The host material itself must be able to effectively transport holes or electrons to ensure that the device works effectively. The host material can have electron transport properties or hole transport properties, or it can be a bipolar transport material that can effectively transport both electrons and holes.

[0055] Materials with electron transport properties can be DPEPO (bis[2-((oxo)diphenylphosphino)phenyl] ether), TSPO1 (bisphenyl[4-(triphenylsilyl)phenyl]oxophosphine), or TPBi (1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene). In the embodiments of this application, the material with electron transport properties is DPEPO (bis[2-((oxo)diphenylphosphino)phenyl] ether). Materials with hole transport properties can be mCBP (3,3-bis(carbazole)biphenyl), CBP (4,4'-bis(9-carbazole)biphenyl), or TCTA (4,4',4''-tris(carbazole-9-yl)triphenylamine). In the embodiments of this application, the material with hole transport properties is mCBP (3,3-bis(carbazole)biphenyl).

[0056] In this application, the hole injection layer 2 has a thickness of 5-20 nm, the hole transport layer 3 has a thickness of 20-100 nm, the electron blocking layer 4 has a thickness of 5-10 nm, the light-emitting layer 5 has a thickness of 20-40 nm, the hole blocking layer 6 has a thickness of 5-10 nm, the electron transport layer 7 has a thickness of 30-100 nm, and the electron injection layer 8 has a thickness of 0.5-10 nm.

[0057] Among them, the hole injection layer 2 is composed of organic small molecule materials with hole transport properties, such as HATCN (2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene).

[0058] Hole transport layer 3 is composed of small organic molecule materials with hole transport properties, such as TAPC (4,4'-cyclohexylbis[N,N-di(4-methylphenyl)aniline]).

[0059] The electron blocking layer 4 is composed of organic electron blocking materials, such as mCP (N,N-dicarbazolyl-3,5-benzene).

[0060] Hole blocking layer 6 is composed of organic hole blocking materials, such as TSPO1 (diphenyl[4-(triphenylsilyl)phenyl]oxyphosphine).

[0061] Electron transport layer 7 is composed of small organic molecule materials with electron transport properties, such as TmPyPB (3,3'-[5'-[3-(3-pyridyl)phenyl][1,1':3',1''-terphenyl]-3,3''-diyl]dipyridine).

[0062] The electron injection layer 8 is composed of materials with electron injection capability, including alkali metals, alkali metal compounds, etc., such as LiF (lithium fluoride).

[0063] In this application, the anode layer 1 can be composed of ITO (Indium Tin Oxide) or Indium Gallium Zinc Oxide (IGZO), with a thickness of 60–120 nm. The metal cathode layer 9 can be composed of a low work function metal material, such as aluminum or magnesium-aluminum alloy, with a thickness of 200–300 nm.

[0064] This application also provides a method for fabricating an organic electroluminescent device, including the fabrication of a light-emitting layer, specifically comprising the following steps:

[0065] Fabrication of the luminescent layer: The luminescent layer is prepared by vacuum evaporation. The host material, sensitizer, and blue fluorescent dye are placed in different evaporation sources. A gradient doping concentration of the sensitizer is achieved by changing the evaporation temperature or rate of the sensitizer evaporation source. A fixed doping concentration of the blue fluorescent dye is achieved by stabilizing the evaporation temperature or rate of the blue fluorescent dye evaporation source. Stable evaporation of the host material is achieved by stabilizing the evaporation temperature or rate of the host material evaporation source. The desired luminescent layer thickness is achieved by controlling the evaporation time, forming a luminescent layer with a gradient in sensitizer doping concentration. Figure 2 As shown.

[0066] Furthermore, the method for fabricating the organic electroluminescent device of this application further includes the following steps:

[0067] A hole injection layer, a hole transport layer, and an electron blocking layer are sequentially formed on the anode layer by vacuum evaporation. The thickness of the hole injection layer, the hole transport layer, and the electron blocking layer is controlled by the thermal evaporation time.

[0068] The aforementioned light-emitting layer is formed on the electron blocking layer;

[0069] A hole blocking layer, an electron transport layer, and an electron injection layer are sequentially formed on the aforementioned light-emitting layer by vacuum evaporation. The thickness of the hole blocking layer, electron transport layer, and electron injection layer is controlled by the thermal evaporation time.

[0070] A metal cathode layer is formed on the electron injection layer by high-temperature metal evaporation, and the thickness of the metal cathode layer is controlled by the evaporation time.

[0071] In the embodiments of this application, the vacuum degree during vacuum evaporation of each organic layer is 10. -4 ~10 -5 Within the Pa range, during vacuum evaporation, the evaporation rates are as follows: hole injection layer: 0.01-0.05 nm / s; hole transport layer: 0.01-0.5 nm / s; electron blocking layer: 0.01-0.1 nm / s; hole blocking layer: 0.01-0.5 nm / s; evaporation rates for the host material, sensitizer, and blue fluorescent dye in the luminescent layer: 0.01-0.3 nm / s; electron transport layer: 0.01-0.5 nm / s; electron injection layer: 0.01-0.05 nm / s; metal cathode layer: 0.1-1 nm / s. The evaporation rates for different layers depend on the layer thickness; relatively thinner layers have relatively lower evaporation rates. Appropriate rates are beneficial for forming dense and uniform films.

[0072] Compared to conventional OLED device structures in existing technologies, this application presents an optimized device structure and material combination system, which improves the efficiency roll-off and lifespan of organic electroluminescent devices. The specific advantages are reflected in the following two aspects:

[0073] (1) such as Figures 2-3 As shown, Figure 2 This is a schematic diagram of the charge transport mechanism of the light-emitting layer prepared by gradient doping concentration in this application. The concentration of sensitizer 52 in the host material 51 gradually decreases from left to right. The concentration of blue fluorescent dye 53 is uniformly doped in the host material 51. The left side is the electron blocking layer EBL with holes 41, and the right side is the hole blocking layer HBL with electrons 61. Figure 3 This diagram illustrates the charge transport mechanism of the luminescent layer prepared using a conventional fixed doping concentration method. The sensitizer 52 and blue fluorescent dye 53 have uniform concentrations in the host material 51. The left side represents the electron blocking layer EBL with holes 41, and the right side represents the hole blocking layer HBL with electrons 61. Unlike the conventional fixed doping concentration method, this application uses a gradient doping concentration method to prepare the luminescent layer. This method controls the balance of charge carriers in the luminescent layer, broadens the exciton recombination region of the luminescent layer, avoids nonradiative energy loss and exciton quenching caused by excessive exciton 54 accumulation, avoids the annihilation of exciton 54 and polarons, and avoids the formation of high-energy thermal excitons. This improves the efficiency roll-off and device lifetime of organic electroluminescent devices at high brightness.

[0074] (2) For blue light devices, the most mature light-emitting layer material combination system is "TTA (triple-triplet annihilation material abbreviation: TTA) host + fluorescent dye". However, although its color and lifetime are excellent, its efficiency still needs to be improved. This application adopts a new material combination system (PSF system or TASF system), which can greatly improve the light-emitting efficiency of the device while maintaining good device lifetime and color purity.

[0075] The present application will be further described below through specific embodiments.

[0076] Example 1

[0077] like Figure 1 As shown, the blue organic electroluminescent device provided in this embodiment comprises, from bottom to top, the following structures:

[0078] Anode layer 1, with a thickness of 100 nm, is composed of ITO (Indium Tin Oxide);

[0079] Hole injection layer 2, with a thickness of 5 nm, is composed of HATCN (2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene);

[0080] Hole transport layer 3, with a thickness of 40 nm, is composed of TAPC (4,4'-cyclohexylbis[N,N-di(4-methylphenyl)aniline]);

[0081] Electron blocking layer 4, with a thickness of 5 nm, is composed of mCP (N,N-dicarbazo-3,5-benzene);

[0082] The light-emitting layer 5, with a thickness of 30 nm, is composed of a host material, a sensitizer, and a blue fluorescent dye. The host material is DPEPO (di[2-((oxo)diphenylphosphino)phenyl] ether), the sensitizer is the organic phosphorescent material Ir(cb)3, and the blue fluorescent dye is DABNA.

[0083] Hole blocking layer 6, with a thickness of 5 nm, is composed of TSPO1 (diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide);

[0084] Electron transport layer 7, with a thickness of 30 nm, is composed of TmPyPB (3,3'-[5'-[3-(3-pyridyl)phenyl][1,1':3',1''-terphenyl]-3,3''-diyl]dipyridine);

[0085] The electron injection layer 8 has a thickness of 1 nm and is composed of LiF (lithium fluoride);

[0086] The metal cathode layer 9 has a thickness of 250 nm and is composed of aluminum.

[0087] The method for fabricating the blue organic electroluminescent device in this embodiment includes the following steps:

[0088] A hole injection layer, a hole transport layer, and an electron blocking layer are sequentially formed on the anode layer by vacuum evaporation. The thicknesses of the hole injection layer, hole transport layer, and electron blocking layer are controlled by the thermal evaporation time. In this step, the vacuum degree of vacuum evaporation is 10. -5 Pa, the evaporation rate of the hole injection layer is 0.05 nm / s, the evaporation rate of the hole transport layer is 0.5 nm / s, and the evaporation rate of the electron blocking layer is 0.1 nm / s;

[0089] A light-emitting layer is formed on an electron blocking layer by vacuum evaporation. The evaporation process is described as follows: The host material, sensitizer, and blue fluorescent dye are placed in different evaporation sources. The gradient doping concentration of the sensitizer is achieved by changing the evaporation rate of the sensitizer evaporation source. The initial doping concentration is 30 wt% (i.e., the doping concentration on the side closer to the electron blocking layer is 30 wt%), and the final doping concentration is 50 wt% (i.e., the doping concentration on the side closer to the hole blocking layer is 50 wt%). A fixed doping concentration of the blue fluorescent dye is achieved by stabilizing the evaporation rate of the blue fluorescent dye evaporation source, with a doping concentration of 5 wt%. Stable evaporation of the host material is achieved by stabilizing the evaporation rate of the host material evaporation source. The desired light-emitting layer thickness is achieved by controlling the evaporation time, forming a light-emitting layer with a gradient of doping concentration. In this step, the vacuum degree of vacuum evaporation is 10... -5 Pa, the evaporation rate of the main material is 0.3 nm / s, the initial evaporation rate of the sensitizer is 0.05 nm / s, the final evaporation rate is 0.25 nm / s, and the evaporation rate of the blue fluorescent dye is 0.02 nm / s;

[0090] A hole blocking layer, an electron transport layer, and an electron injection layer are sequentially formed on the light-emitting layer by vacuum evaporation. The thicknesses of the hole blocking layer, electron transport layer, and electron injection layer are controlled by the thermal evaporation time. In this step, the vacuum degree of vacuum evaporation is 10. -5 Pa, the evaporation rate of the hole blocking layer is 0.05 nm / s, the evaporation rate of the electron transport layer is 0.5 nm / s, and the evaporation rate of the electron injection layer is 0.01 nm / s;

[0091] A metal cathode layer is formed on the electron injection layer by high-temperature metal evaporation, and the thickness of the metal cathode layer is controlled by the evaporation time; in this step, the evaporation rate of the metal cathode layer is 1 nm / s.

[0092] Comparative Example 1

[0093] Comparative Example 1 is identical to the device structure in Example 1 in all aspects except that the sensitizer in the light-emitting layer is doped with a fixed doping concentration.

[0094] The light-emitting layer of Comparative Example 1 was prepared as follows:

[0095] A light-emitting layer is formed on the electron blocking layer by vacuum evaporation: the host material, sensitizer and blue fluorescent dye are placed in different evaporation sources respectively, and the evaporation rate of different evaporation sources is stabilized by a pre-set doping concentration ratio (the doping concentration of the sensitizer is fixed at 30wt% and the doping concentration of the blue fluorescent dye is fixed at 5wt%). The expected thickness of the light-emitting layer is controlled by the evaporation time, so as to form a light-emitting layer with uniform sensitizer doping concentration.

[0096] The performance of the organic electroluminescent device prepared in Example 1 was compared with that of the organic electroluminescent device prepared in Comparative Example 1. The results are shown in Table 1.

[0097] Table 1

[0098]

[0099] As shown in Table 1, the organic electroluminescent device provided in Example 1, by employing gradient doping with sensitizers, can effectively broaden the exciton recombination region of the light-emitting layer and improve the carrier balance of the light-emitting layer, thereby reducing exciton quenching and the formation of high-energy thermal excitons (especially under high brightness). This effectively reduces the efficiency roll-off of the device under high brightness and improves the device's operating lifetime. The half-life of the device is 1.54 times that of the device in Example 1.

[0100] Example 2

[0101] like Figure 1 As shown, the blue organic electroluminescent device provided in this embodiment comprises, from bottom to top, the following structures:

[0102] Anode layer 1, with a thickness of 100 nm, is composed of ITO (Indium Tin Oxide);

[0103] Hole injection layer 2, with a thickness of 5 nm, is composed of HATCN (2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene);

[0104] Hole transport layer 3, with a thickness of 40 nm, is composed of TAPC (4,4'-cyclohexylbis[N,N-di(4-methylphenyl)aniline]);

[0105] Electron blocking layer 4, with a thickness of 5 nm, is composed of mCP (N,N-dicarbazolyl-3,5-benzene);

[0106] The light-emitting layer 5, with a thickness of 30 nm, is composed of a host material, a sensitizer, and a blue fluorescent dye. The host material is mCBP (3,3-bis(carbazoyl)biphenyl), the sensitizer is the organic phosphorescent material Ir(cb)3, and the blue fluorescent dye is DABNA.

[0107] Hole blocking layer 6, with a thickness of 5 nm, is composed of TSPO1 (diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide);

[0108] Electron transport layer 7, with a thickness of 30 nm, is composed of TmPyPB (3,3'-[5'-[3-(3-pyridyl)phenyl][1,1':3',1''-terphenyl]-3,3''-diyl]dipyridine);

[0109] The electron injection layer 8 has a thickness of 1 nm and is composed of LiF (lithium fluoride);

[0110] The metal cathode layer 9 has a thickness of 250 nm and is composed of aluminum.

[0111] The method for fabricating the blue organic electroluminescent device in this embodiment includes the following steps:

[0112] A hole injection layer, a hole transport layer, and an electron blocking layer are sequentially formed on the anode layer by vacuum evaporation. The thicknesses of the hole injection layer, hole transport layer, and electron blocking layer are controlled by the thermal evaporation time. In this step, the vacuum degree of vacuum evaporation is 10. -5 Pa, the evaporation rate of the hole injection layer is 0.05 nm / s, the evaporation rate of the hole transport layer is 0.5 nm / s, and the evaporation rate of the electron blocking layer is 0.01 nm / s;

[0113] A light-emitting layer is formed on an electron blocking layer by vacuum evaporation. The evaporation process is described as follows: The host material, sensitizer, and blue fluorescent dye are placed in different evaporation sources. The gradient doping concentration of the sensitizer is achieved by changing the evaporation rate of the sensitizer evaporation source. The initial doping concentration is 30 wt% (i.e., the doping concentration on the side closer to the electron blocking layer is 30 wt%), and the final doping concentration is 50 wt% (i.e., the doping concentration on the side closer to the hole blocking layer is 50 wt%). A fixed doping concentration of the blue fluorescent dye is achieved by stabilizing the evaporation rate of the blue fluorescent dye evaporation source, with a doping concentration of 5 wt%. Stable evaporation of the host material is achieved by stabilizing the evaporation rate of the host material evaporation source. The desired light-emitting layer thickness is achieved by controlling the evaporation time, forming a light-emitting layer with a gradient of doping concentration. In this step, the vacuum degree of vacuum evaporation is 10...-5 Pa, the evaporation rate of the main material is 0.3 nm / s, the initial evaporation rate of the sensitizer is 0.05 nm / s, the final evaporation rate is 0.25 nm / s, and the evaporation rate of the blue fluorescent dye is 0.02 nm / s;

[0114] A hole blocking layer, an electron transport layer, and an electron injection layer are sequentially formed on the light-emitting layer by vacuum evaporation. The thicknesses of the hole blocking layer, electron transport layer, and electron injection layer are controlled by the thermal evaporation time. In this step, the vacuum degree of vacuum evaporation is 10. -5 Pa, the evaporation rate of the hole blocking layer is 0.05 nm / s, the evaporation rate of the electron transport layer is 0.5 nm / s, and the evaporation rate of the electron injection layer is 0.01 nm / s;

[0115] A metal cathode layer is formed on the electron injection layer by high-temperature metal evaporation, and the thickness of the metal cathode layer is controlled by the evaporation time; in this step, the evaporation rate of the metal cathode layer is 1 nm / s.

[0116] Comparative Example 2

[0117] Comparative Example 2 is identical to the device structure in Example 2 in all aspects except that the sensitizer in the light-emitting layer is doped with a fixed doping concentration.

[0118] The light-emitting layer of Comparative Example 2 was prepared as follows:

[0119] A light-emitting layer is formed on the electron blocking layer by vacuum evaporation: the host material, sensitizer and blue fluorescent dye are placed in different evaporation sources respectively, and the evaporation rate of different evaporation sources is stabilized by a pre-set doping concentration ratio (the doping concentration of the sensitizer is fixed at 30wt% and the doping concentration of the blue fluorescent dye is fixed at 5wt%). The expected thickness of the light-emitting layer is controlled by the evaporation time, so as to form a light-emitting layer with uniform sensitizer doping concentration.

[0120] The performance of the organic electroluminescent device prepared in Example 2 was compared with that of the organic electroluminescent device prepared in Comparative Example 2. The results are shown in Table 2.

[0121] Table 2

[0122]

[0123] As shown in Table 2, the organic electroluminescent device provided in Example 2, by employing gradient doping with sensitizers, effectively broadens the exciton recombination region of the light-emitting layer and improves the carrier balance of the light-emitting layer, reducing exciton quenching and the formation of high-energy thermal excitons (especially under high brightness). This effectively reduces the efficiency roll-off of the device under high brightness and improves the device's operating lifetime. The half-life of the device is 1.61 times that of the device in Example 2.

[0124] It should be understood that the application of this application 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 this application.

Claims

1. An organic electroluminescent device, characterized in that, From bottom to top, it includes an anode layer, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a metal cathode layer. The light-emitting layer comprises a host material, a sensitizer, and a blue fluorescent dye; The sensitizer is doped into the host material using a gradient doping concentration method. The doping concentration of the sensitizer is between 5-50 wt%, and the doping concentration of the sensitizer decreases gradually from the electron blocking layer to the hole blocking layer. The blue fluorescent dye is doped into the host material at a fixed doping concentration, which ranges from 0.1% to 10% wt%. The sensitizer is a phosphorescent sensitizer or a thermally activated delayed fluorescence sensitizer; The main material is a material with electron transport properties or hole transport properties; The phosphorus photosensitizer is one of an iridium complex or a platinum complex; The thermally activated delayed fluorescence sensitizer is one of donor-acceptor type TADF material and multiple resonance type TADF material; The triplet energy level of the host material is greater than or equal to the triplet energy level of the sensitizer and the blue fluorescent dye; The triplet energy level of the sensitizer is greater than or equal to the triplet energy level of the blue fluorescent dye.

2. The organic electroluminescent device according to claim 1, characterized in that, The hole injection layer has a thickness of 5-20 nm, the hole transport layer has a thickness of 20-100 nm, the electron blocking layer has a thickness of 5-10 nm, the light-emitting layer has a thickness of 20-40 nm, the hole blocking layer has a thickness of 5-10 nm, the electron transport layer has a thickness of 30-100 nm, and the electron injection layer has a thickness of 0.5-10 nm.

3. The organic electroluminescent device according to claim 1, characterized in that, The thickness of the anode layer is 60–120 nm, and the thickness of the metal cathode layer is 200–300 nm.

4. The organic electroluminescent device according to claim 1, characterized in that, The HOMO energy level of the host material is greater than or equal to the HOMO energy level of the sensitizer and the blue fluorescent dye; the LUMO energy level of the host material is greater than or equal to the LUMO energy level of the sensitizer and the blue fluorescent dye.

5. The organic electroluminescent device according to claim 4, characterized in that, The HOMO energy level of the sensitizer is greater than or equal to the HOMO energy level of the blue fluorescent dye; the LUMO energy level of the sensitizer is greater than or equal to the LUMO energy level of the blue fluorescent dye.

6. The organic electroluminescent device according to claim 1, characterized in that, The sensitizer is an organic phosphorescent material Ir(cb)3; The blue fluorescent dye is DABNA; The material with electron transport properties is DPEPO; the material with hole transport properties is mCBP. The hole injection layer is composed of HATCN; The hole transport layer is composed of TAPC; The electron blocking layer is composed of mCP; The hole-blocking layer is composed of TSPO1; The electron transport layer is composed of TmPyPB; The electron injection layer is composed of alkali metals; The anode layer is composed of ITO or indium gallium zinc oxide; The metal cathode layer is composed of aluminum or a magnesium-aluminum alloy.

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