An organic electroluminescent device comprising a light-emitting layer and a hole transport region

Abstract

The invention discloses an organic electroluminescent device including a light-emitting layer and a hole transport region, comprising: a first electrode, a second electrode facing the first electrode, a light-emitting layer between the first electrode and the second electrode, and a hole transport region between the first electrode and the light-emitting layer; the hole transport region comprises a hole injection layer, a first hole transport layer, and a second hole transport layer; the HOMO energy level of the compound represented by formula I of the second hole transport layer disclosed by the invention is ‑5.45eV~‑5.40eV, and the HOMO energy level of the compound represented by formula II of the light-emitting layer is ‑5.85eV~‑5.65eV; in this scheme, the group modification of the compound represented by chemical formula I, especially the introduction of R'3, increases the steric hindrance of the material, limits the deformation ability of the material, reduces the energy level disorder of the material, increases the mobility, and ensures the high efficiency, long life and low driving voltage of the final device.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic materials, and more particularly to an organic electroluminescent device comprising a light-emitting layer and a hole transport region. Background Art

[0002] Organic electroluminescent device technology can be used to manufacture new display products and new lighting products, and is expected to replace existing liquid crystal displays and fluorescent lighting, with a wide range of applications. As a current device, when voltage is applied to the electrodes at both ends of the organic electroluminescent device and the electric field acts on the positive and negative charges in the organic functional material film layer, the positive and negative charges are further compounded in the organic light-emitting layer, generating organic electroluminescence.

[0003] Organic electroluminescent devices are generally multi-layer structures. In addition to the light-emitting layer, various auxiliary functional layers also play a vital role in the performance of the device. Reasonable device structure can effectively improve the performance of the device. The electron injection layer, electron transport layer, hole blocking layer, light-emitting layer, electron blocking layer, hole transport layer and hole injection layer are widely used to improve the performance of the device.

[0004] Conventional hole transport regions have limitations in improving the efficiency of the light-emitting layer. For fast hole mobility, the hole transport region requires a compound with a high HOMO energy level. If the compound has a high HOMO energy level, the driving voltage is reduced, but the efficiency of the light-emitting layer is also reduced. On the contrary, if the compound has a low HOMO energy level, the efficiency of the light-emitting layer is increased, but the driving voltage is also increased, which makes it difficult to achieve high luminous efficiency of the device.

[0005] In organic electroluminescent devices, not all materials have a good match in terms of energy levels, and the potential barriers between them seriously hinder the effective injection of holes. A reasonable energy level structure is conducive to the formation of step barriers in the energy levels of each layer of the device, which can reduce the barrier to hole injection and the driving voltage of the device, thereby improving the luminous efficiency and life of the device.

[0006] Therefore, there is a continuous need to develop organic electroluminescent devices with excellent luminous efficiency and lifespan. The present invention aims to provide a specific red light host material and a second hole transport material, ultimately obtaining an organic electroluminescent device with improved luminous efficiency, driving voltage and lifespan. Summary of the invention

[0007] The present invention can provide an organic electroluminescent device having low driving voltage, high luminous efficiency and / or long life characteristics by including a specific arylamine derivative represented by formula I of the present disclosure in the hole transport region and a specific combination of fused azulene derivatives represented by formula II of the present disclosure in the light-emitting layer.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] An organic electroluminescent device including a light-emitting layer and a hole transport region includes: a first electrode, a second electrode facing the first electrode, a light-emitting layer between the first electrode and the second electrode, and a hole transport region between the first electrode and the light-emitting layer.

[0010] Preferably, the hole transport region includes a hole injection layer, a first hole transport layer, and a second hole transport layer;

[0011] Wherein, the second hole transport layer comprises the structure of formula I, and the HOMO energy level is -5.45eV to -5.40eV;

[0012]

[0013] In the above formula, R'3 is selected from deuterium, methyl, ethyl, isopropyl, tert-butyl, phenyl or methoxy;

[0014] R'4 is selected from hydrogen, methyl, phenyl or naphthyl;

[0015] Ar1 and Ar2 are connected to N at any connectable position; and Ar1 and Ar2 are each independently selected from dimethylfluorenyl, biphenyl, naphthyl, phenyl, phenylnaphthyl, dibenzofuranyl, dibenzothiophenyl, benzofuranyl, benzothiophenyl, phenyldibenzofuran, phenyldibenzothiophene, phenylbenzothiophene or phenylbenzofuran.

[0016] Preferably, the light-emitting layer comprises the structure of formula II, and the HOMO energy level is -5.85 eV to -5.65 eV;

[0017]

[0018] In the above formula, L is selected from a linker, a biphenyl group, a phenyl group or a naphthyl group;

[0019] R1-R4 are each independently selected from hydrogen or phenyl;

[0020] R1-R4 are connected to adjacent rings by substitution or ring fusion;

[0021] Ar is selected from hydrogen, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, substituted or unsubstituted pyrimidinyl, substituted or unsubstituted triazinyl, substituted or unsubstituted pyridyl; or, substituted or unsubstituted following groups:

[0022]

[0023] Preferably, the formula I comprises the following structure:

[0024]

[0025]

[0026] Preferably, the formula II comprises the following structure:

[0027]

[0028]

[0029] Preferably, the compound of formula I is prepared by the following method:

[0030]

[0031] Under N2 protection, reactant A (1.0 eq), reactant B (1.1 eq), tetrakis(triphenylphosphine)palladium (0.01-0.02 eq) and potassium carbonate (2.0-3.0 eq) were added to a mixed solvent of toluene, ethanol and water (volume ratio 2-4:1:1) in a reaction vessel, heated to 100-110°C, reacted for 6-10 hours, cooled to room temperature after the reaction was completed, filtered after solid precipitation, and dried the filter cake. Recrystallized in 1,4-dioxane to obtain Formula I.

[0032] Preferably, the formula II is prepared by the following method:

[0033]

[0034] Under nitrogen protection, reactant a (1.0 eq) and reactant b (1.0-1.2 eq) are added to a reaction vessel and dissolved in toluene, and then tri(dibenzylideneacetone)dipalladium (0.01 eq), tri-tert-butylphosphine (0.05-0.1 eq) and sodium tert-butyl oxide (2.0-3.0 eq) are added, and then the temperature is raised to 100-110° C. and the reaction is carried out for 6-8 hours. Celite is used for hot filtration to remove salt and catalyst, and after the filtrate is cooled to room temperature, a rotary evaporator is used to remove the solvent, and the obtained solid is dried and passed through a silica gel funnel, and dichloromethane: petroleum ether volume ratio of 1: (1-4) is used as an eluent, and the filtrate is removed by a rotary evaporator, and the obtained solid is dried to obtain Formula II.

[0035] The present invention can provide an organic electroluminescent device having low driving voltage, high luminous efficiency and / or long life characteristics by including a compound represented by formula I in the second hole transport layer having a specific HOMO energy level: -5.45eV≤HOMO energy level≤-5.40eV, and a specific combination of a compound represented by formula II in the light-emitting layer having a HOMO energy level: -5.85eV≤HOMO energy level≤-5.65eV.

[0036] The organic electroluminescent device of the present invention can be a top-emitting type, a bottom-emitting type or a bidirectional-emitting type. The device of the present invention can be used in an organic light-emitting device, an organic solar cell, an electronic paper, an organic photoreceptor or an organic thin film transistor.

[0037] The organic electroluminescent device of the present invention includes a first electrode, a second electrode facing the first electrode, a light-emitting layer between the first electrode and the second electrode, a hole transport region between the first electrode and the light-emitting layer, and an electron transport region between the light-emitting layer and the second electrode. One of the first electrode and the second electrode is an anode, and the other is a cathode.

[0038] The organic light emitting element may have a structure including a hole injection layer, a hole transport layer, an electron blocking layer, a second hole transport layer, a light emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, etc. as organic layers. However, the structure of the organic light emitting element is not limited thereto, and may include fewer or more organic layers.

[0039] The organic light emitting element can be manufactured by sequentially stacking a first electrode, an organic layer, and a second electrode on a substrate, and can be manufactured by a physical vapor deposition (PVD) method such as sputtering or electron beam evaporation.

[0040] A first electrode is formed by vapor-depositing a metal or a conductive metal oxide or an alloy thereof on a substrate, an organic layer including a hole injection layer, a hole transport layer, a light-emitting layer and an electron transport layer is formed on the first electrode, and then a substance that can be used as a second electrode is vapor-deposited on the organic layer. In addition to this method, an organic light-emitting element can also be manufactured by vapor-depositing a second electrode substance, an organic layer, and a first electrode substance on a substrate in sequence.

[0041] In addition, when manufacturing an organic light-emitting element, the compounds represented by the chemical formula I and formula II can be formed into an organic layer by not only vacuum evaporation but also solution coating, wherein the so-called solution coating refers to spin coating, dip coating, blade coating, inkjet printing, screen printing, spraying, roller coating, etc., but is not limited thereto.

[0042] In the present invention, the first electrode is an anode, and the second electrode is a cathode.

[0043] As the anode material, in order to enable holes to be smoothly injected into the organic layer, a material with a large work function is preferably used. Specific examples of the anode material that can be used in the present invention include metals such as vanadium, chromium, copper, zinc, gold, or their alloys; metal oxides such as zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO); combinations of metals and oxides such as ZnO:Al or SnO2:Sb; conductive polymers such as polypyrrole and polyaniline, etc.

[0044] As the cathode material, in order to facilitate the injection of electrons into the organic layer, a material with a small work function is preferably used. Specific examples of cathode materials include metals such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin and lead, or alloys thereof: multilayer structures such as LiF / Al or LiO2 / Al, and Mg / Ag.

[0045] The hole transport region means a region in which holes are transported between the first electrode and the light-emitting layer. The hole transport region is a region that receives holes from the hole injection layer and transports the holes to the light-emitting layer. The hole transport region may be placed between the anode (or the hole injection layer) and the light-emitting layer. The hole transport region may be used to smoothly move holes transferred from the anode to the light-emitting layer and block electrons transferred from the cathode to remain in the light-emitting layer.

[0046] The hole transport region of the present invention includes a hole injection layer, a first hole transport layer, and a second hole transport layer. The second hole transport layer may also be referred to as a light-emitting auxiliary layer and an electron blocking layer in the present invention.

[0047] In the present invention, the hole injection layer is preferably a p-doped hole injection layer, which means a hole injection layer doped with a p-dopant. The p-dopant is a material that can impart p-type semiconductor characteristics. The p-type semiconductor characteristics mean the characteristics of injecting holes or transporting holes at the HOMO energy level, that is, the characteristics of a material with high hole conductivity.

[0048] The second hole transport layer can be placed between the anode and the light-emitting layer, or between the cathode and the light-emitting layer. When the second hole transport layer is placed between the anode and the light-emitting layer, it can be used to promote hole injection and / or hole transport, or to prevent electron overflow. When the second hole transport layer is placed between the cathode and the light-emitting layer, it can be used to promote electron injection and / or electron transport, or to prevent hole overflow. Moreover, the hole auxiliary layer can be placed between the hole transport layer (or hole injection layer) and the light-emitting layer, and the hole transport rate (or hole injection rate) can be effectively promoted or blocked, so that the charge balance can be controlled. In addition, the electron blocking layer can be placed between the hole transport layer (or hole injection layer) and the light-emitting layer, and the excitons can be confined in the light-emitting layer by blocking the electrons from overflowing from the light-emitting layer to prevent luminescence leakage. When the organic electroluminescent device includes two or more hole transport layers, the hole transport layer further included can be used as a hole auxiliary layer or an electron blocking layer. The second hole transport layer, the hole auxiliary layer and / or the electron blocking layer can have the effect of improving the efficiency and / or life of the organic electroluminescent device.

[0049] The light-emitting material of the light-emitting layer is a material that can receive holes and electrons from the hole transport layer and the electron transport layer, respectively, and combine them to emit light in the visible light region, and is preferably a material with high quantum efficiency for fluorescence or phosphorescence.

[0050] The light emitting layer may include a host material and a dopant material.

[0051] The electron transport region may include at least one of an electron buffer layer, a hole blocking layer, an electron transport layer, and an electron injection layer, and preferably at least one of an electron transport layer and an electron injection layer. The electron transport region is a layer that can improve the problem of degradation of luminous brightness due to changes in current characteristics in the device when the device is exposed to high temperature during the process of manufacturing the panel, and it can control charge flow characteristics.

[0052] Except for the specific combination of Formula I in the second hole transport layer and Formula II in the light-emitting layer disclosed herein, there is no particular limitation on the materials of other layers in the OLED device. Existing hole injection materials, hole transport materials, dopant materials, hole blocking layer materials, electron transport layer materials and electron injection materials can be used.

[0053] The hole injection layer materials include metal porphyrins, oligothiophenes, aromatic amine derivatives, hexanitrile hexaazatriphenylene organics, quinacridone organics, perylene organics, anthraquinone, polyaniline and polythiophene conductive polymers, etc. The p-doped P dopant can be illustrated by the following compounds, but is not limited to them.

[0054]

[0055] The first hole transport material can be selected from aromatic amine derivatives, conductive polymers, and block copolymers having both conjugated and non-conjugated parts. Specifically, the first hole transport layer material is selected from the following compounds, but is not limited thereto.

[0056]

[0057]

[0058] The second hole transport layer is a compound represented by general formula I of the present invention.

[0059] The main material is the compound represented by the general formula II of the present invention.

[0060] The dopant material of the present invention is selected as a red light doping material, including aromatic amine derivatives, styrylamine compounds, boron complexes, fluoranthene compounds, metal complexes, etc. Specifically, the red light doping material of the present invention is selected from the following compounds, but is not limited thereto.

[0061]

[0062] Materials for the electron transport layer (hole blocking layer) include derivatives of oxazole, imidazole, thiazole, triazine, etc., metal chelates, quinoline derivatives, oxaline derivatives, diazanthracene derivatives, diazine derivatives, silicon-containing heterocyclic compounds, perfluorinated oligomers, etc. Specifically, the electron transport layer material is selected from the following compounds, but is not limited thereto.

[0063]

[0064] The electron injection layer materials specifically include fluorenone, anthraquinone dimethane, diphenoquinone, thiopyran dioxide, oxazole, oxadiazole, triazole, imidazole, perylenetetracarboxylic acid, fluorenyl methane, anthrone, and their derivatives, metal complexes, and nitrogen-containing five-membered ring derivatives, but are not limited thereto.

[0065] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0066] Usually, the HOMO and LUMO energies of electroluminescent materials are fixed values. However, in reality, due to the different molecular orientations in the stacking process and the influence of intermolecular forces, the energy levels are not fixed values. It is generally believed that they are in the range of Gaussian distribution:

[0067]

[0068] Mechanical squeezing and group twisting will affect the molecular energy levels, and electrical factors (high polarity, polarization) will lead to exponential distribution of energy levels, making the energy level disorder greater.

[0069] In the Gaussian disordered mode, the mobility increases as the energy level disorder decreases:

[0070]

[0071] Different from the comparative example, the group modification in this scheme, especially the introduction of R'3, increases the steric hindrance of the material, limits the deformation ability of the material, reduces the energy level disorder of the material, increases the mobility, and ensures the high efficiency of the final device.

[0072] Macus charge jumping theory:

[0073]

[0074] The Dexter energy transfer / transfer rate based on Macus charge hopping theory is divided into three situations: ① normal region; ② region with no activation energy; ③ inversion region.

[0075] The electron transfer rate constant will increase with the increase of Gibbs free energy change in the normal region, and decrease with the increase of Gibbs free energy change in the inversion region. In short, the electron transfer rate between energy level interfaces is closely related to the energy difference between the two interfaces, and there is an optimal energy range.

[0076] Based on the above principles,

[0077] The HOMO of the compound represented by Formula I in the second hole transport layer provided by the present invention needs to meet the following conditions:

[0078] -5.45eV≤HOMO level≤-5.40eV;

[0079] The HOMO of the compound represented by the light-emitting layer formula II disclosed in the present invention needs to meet the following conditions:

[0080] -5.85eV≤HOMO level≤-5.65eV;

[0081] The driving voltage, luminous efficiency and life of the prepared organic electroluminescent device are significantly improved. DETAILED DESCRIPTION

[0082] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0083] Preparation of red organic electroluminescent device:

[0084] a. ITO anode: Wash the ITO (indium tin oxide)-Ag-ITO (indium tin oxide) glass substrate with a coating thickness of 150nm in distilled water twice, ultrasonically wash for 30 minutes, and then repeatedly wash it with distilled water twice, ultrasonically wash for 10 minutes. After washing, transfer it to a spin dryer for drying, and finally bake it in a vacuum oven at 220℃ for 2 hours. After baking, cool it down and it can be used. Use this substrate as the anode, use an evaporation machine to carry out the evaporation device process, and evaporate other functional layers on it in sequence;

[0085] b. HIL (hole injection layer): The hole injection layer materials HT-a and P-dopant are vacuum evaporated at a deposition rate of 97:3, and the thickness is 10 nm;

[0086] c. HTL (hole transport layer): At a deposition rate of 100%, 125 nm of HT-a was vacuum-deposited on the hole injection layer as a hole transport layer.

[0087] d. The second hole transport layer: At a deposition rate of , vacuum-deposit 90 nm of the compound represented by formula I provided by the present invention on the hole transport layer as a second hole transport layer;

[0088] e. EML (light-emitting layer): Then on the second hole transport layer, The host material (Host) and dopant material (Dopant-1) shown in formula II are vacuum-deposited at a thickness of 40 nm as the light-emitting layer. The chemical formulas of Host and Dopant are shown below. The evaporation rate ratio of Host to Dopant is 97:3;

[0089] f. HB (hole blocking layer): The hole blocking layer HB-1 with a thickness of 5.0 nm was vacuum-deposited at a deposition rate of 1.

[0090] g. ETL (Electron Transport Layer): The evaporation rate of ET-10 and Liq was vacuum evaporated to a thickness of 30nm as the electron transport layer. The evaporation rate ratio of ET-10 and Liq was 50:50;

[0091] h. EIL (electron injection layer): The evaporation rate is 1.0 nm, and a Yb film layer is evaporated to form an electron injection layer;

[0092] i. Cathode: 18 nm of magnesium and silver were evaporated at a deposition rate ratio of 1:9 to form a cathode;

[0093] j. Light extraction layer: At a deposition rate of , CPL-1 with a thickness of 70 nm was vacuum-deposited on the cathode as a light extraction layer;

[0094] k. Package the substrate after evaporation. First, use the glue coating equipment to coat the cleaned cover with UV glue, then move the coated cover to the pressing section, place the evaporation-deposited substrate on the upper end of the cover, and finally bond the substrate and cover with the bonding equipment, and complete the light curing of the UV glue.

[0095] Red light device structure:

[0096] ITO / Ag / ITO / HT-a:P-dopant (10nm) / HT-a (125nm) / Formula I (90nm) / Formula II: Dopant-R-1 (40nm) / HB-1 (5nm) / ET-10: Liq (30nm) / Yb (1nm) / Mg:Ag (18nm) / CPL (70nm).

[0097] The materials required for each layer are as follows:

[0098] Table 1:

[0099]

[0100]

[0101]

[0102] Embodiment 1-11

[0103] The organic electroluminescent devices of Examples 1 to 11 were prepared according to the above-mentioned method for preparing an organic electroluminescent device, using the compound RH-13 shown in Table 1 as the main material, and HT-4, HT-7, HT-8, HT-9, HT-12, HT-13, HT-15, HT-23, HT-29, HT-31, and HT-32 for the second hole transport layer.

[0104] Comparative Example 1-2

[0105] HT-a-1 and HT-a-2 fall into formula I, but the HOMO energy level is not between -5.45 eV≤HOMO energy level≤-5.40 eV.

[0106]

[0107] An organic electroluminescent device was prepared according to the above method for preparing an organic electroluminescent device, using the compound RH-13 shown in Table 1 as a host material, and HT-a-1 and HT-a-2 as a second hole transport layer.

[0108] Comparative Examples 3-5

[0109] HT-b-1, HT-b-2, and HT-b-3 do not fall into formula I, and their HOMO energy levels are between -5.45 eV≤HOMO energy level≤-5.40 eV.

[0110]

[0111] An organic electroluminescent device was prepared according to the above method for preparing an organic electroluminescent device, using compound RH-13 shown in Table 1 as a host material, and HT-b-1, HT-b-2, and HT-b-3 as a second hole transport layer.

[0112] Comparative Examples 6-8

[0113]

[0114] HT-c-1, HT-c-2, and HT-c-3 were used to prepare organic electroluminescent devices according to the above-mentioned method for preparing organic electroluminescent devices, using the compound RH-13 shown in Table 1 as the main material, and HT-c-1, HT-c-2, and HT-c-3 for the second hole transport layer.

[0115] The driving voltage, luminous efficiency, and life of the organic electroluminescent devices obtained from the device embodiments 1-11 and the device comparative examples 1-8 were characterized at a brightness of 6000 (nits). The test results are shown in Table 2 below:

[0116] Table 2 Luminous characteristics test results (brightness value is 6000nits)

[0117]

[0118] Examples 12-22

[0119] The organic electroluminescent devices of Examples 12-22 were prepared according to the above-mentioned method for preparing an organic electroluminescent device, using the compound RH-17 shown in Table 1 as the main material, and HT-4, HT-7, HT-8, HT-9, HT-12, HT-13, HT-15, HT-23, HT-29, HT-31, and HT-32 for the second hole transport layer.

[0120] Comparative Examples 9-10

[0121] HT-a-1 and HT-a-2 fall into formula I, but the HOMO energy level is not between -5.45 eV≤HOMO energy level≤-5.40 eV.

[0122] An organic electroluminescent device was prepared according to the above method for preparing an organic electroluminescent device, using the compound RH-17 shown in Table 1 as a host material, and HT-a-1 and HT-a-2 as a second hole transport layer.

[0123] Comparative Examples 11-13

[0124] HT-b-1, HT-b-2, and HT-b-3 do not fall into formula I, and their HOMO energy levels are between -5.45 eV≤HOMO energy level≤-5.40 eV.

[0125] An organic electroluminescent device was prepared according to the above-mentioned method for preparing an organic electroluminescent device, using the compound RH-17 shown in Table 1 as a host material, and HT-b-1, HT-b-2, and HT-b-3 as a second hole transport layer.

[0126] Comparative Examples 14-16

[0127] HT-c-1, HT-c-2, and HT-c-3 were used to prepare organic electroluminescent devices according to the above-mentioned method for preparing organic electroluminescent devices, using the compound RH-17 shown in Table 1 as the main material, and HT-c-1, HT-c-2, and HT-c-3 for the second hole transport layer.

[0128] The driving voltage, luminous efficiency, and life of the organic electroluminescent devices obtained from the device embodiments 12-22 and the device comparative examples 9-16 were characterized at a brightness of 6000 (nits). The test results are shown in Table 3 below:

[0129] Table 3 Luminous characteristics test results (brightness value is 6000nits)

[0130]

[0131]

[0132] Comparative Examples 17-38

[0133] RH-a-1 and RH-a-2 fall into formula II, but the HOMO energy level is not between -5.85 eV ≤ HOMO energy level ≤ -5.65 eV.

[0134]

[0135] An organic electroluminescent device was prepared according to the above-mentioned method for preparing an organic electroluminescent device, and the compounds HT-4, HT-7, HT-8, HT-9, HT-12, HT-13, HT-15, HT-23, HT-29, HT-31, and HT-32 shown in Table 1 were used for the second hole transport layer. RH-a-1 and RH-a-2 were used as the host materials.

[0136] The driving voltage, luminous efficiency, and lifespan of the organic electroluminescent devices obtained in the above device comparative examples 17 to 38 were characterized at a brightness of 6000 (nits). The test results are shown in Table 4 below:

[0137] Table 4 Luminous characteristics test results (brightness value is 6000nits)

[0138]

[0139]

[0140]

[0141] Comparative Examples 39-71

[0142] RH-b-1, RH-b-2, and RH-3-2 do not fall into Formula II, but their HOMO energy levels are between -5.85 eV ≤ HOMO energy level ≤ -5.65 eV.

[0143]

[0144] An organic electroluminescent device was prepared according to the above-mentioned method for preparing an organic electroluminescent device, and the compounds HT-4, HT-7, HT-8, HT-9, HT-12, HT-13, HT-15, HT-23, HT-29, HT-31, and HT-32 shown in Table 1 were used for the second hole transport layer. RH-b-1, RH-b-2, and RH-b-3 were used as host materials.

[0145] The driving voltage, luminous efficiency, and life of the organic electroluminescent devices obtained in the above device comparative examples 39 to 71 were characterized at a brightness of 6000 (nits). The test results are shown in Table 5 below:

[0146] Table 5 Luminous characteristics test results (brightness value is 6000nits)

[0147]

[0148]

[0149]

[0150] The materials used for the second hole transport layer are HT-4, HT-7, HT-8, HT-9, HT-12, HT-13, HT-15, HT-23, HT-29, HT-31, HT-32, HT-a-1, HT-a-2, HT-b-1, HT-b-2, HT-b-3, HT-c-1, HT-c-2, HT-c-3, and the HOMO energy levels are shown in Table 6.

[0151] Table 6 HOMO energy levels of compounds contained in the second hole transport layer

[0152]

[0153] The HOMO levels of the host compounds RH-13, RH-17, RH-a-1, RH-a-2, RH-b-1, RH-b-2, and RH-b-3 used in the light-emitting layer are shown in Table 7 below.

[0154] Table 7 HOMO of the main compound in the luminescent layer

[0155]

[0156] In Table 2,

[0157] Compared with Comparative Example 1-2 (HT-a-1, HT-a-2 falls within Formula I, but the HOMO energy level is not the second hole transport layer of -5.45 eV≤HOMO energy level≤-5.40 eV);

[0158] Comparative Example 3-5 (HT-b-1, HT-b-2, HT-b-3 do not fall into Formula I, and the second hole transport layer with HOMO energy level of -5.45 eV≤HOMO energy level≤-5.40 eV);

[0159] Comparative Examples 6-8 (the second hole transport layer of HT-c-1, HT-c-2, and HT-c-3);

[0160] The above light-emitting layers are all RH-13. Compared with the examples, the devices prepared in examples 1-11 are improved in driving voltage, high light-emitting efficiency and lifespan.

[0161] In Table 3,

[0162] Comparative Examples 9-10 (HT-a-1, HT-a-2 fall within Formula I, but the HOMO energy level is not the second hole transport layer of -5.45 eV≤HOMO energy level≤-5.40 eV);

[0163] Comparative Examples 11-13 (HT-b-1, HT-b-2, HT-b-3 do not fall into Formula I, and the second hole transport layer with HOMO energy level of -5.45 eV≤HOMO energy level≤-5.40 eV);

[0164] Comparative Examples 14-16 (the second hole transport layers of HT-c-1, HT-c-2, and HT-c-3);

[0165] The light-emitting layer is RH-17. Compared with the examples, the devices prepared in Examples 12 to 22 are improved in driving voltage, high luminous efficiency and lifespan.

[0166] In Table 4,

[0167] In comparative examples 17-38, the light-emitting layer is replaced so that RH-a-1 and RH-a-2 fall into formula II, but the HOMO energy level is not between -5.85eV≤HOMO energy level≤-5.65eV, resulting in a decrease in device performance in terms of driving voltage, high luminous efficiency and lifespan.

[0168] In Table 5,

[0169] In comparative examples 39-71, the light-emitting layer is replaced so that RH-b-1, RH-b-2, and RH-3-2 do not fall into formula II, but the HOMO energy level is between -5.85eV≤HOMO energy level≤-5.65eV, resulting in a decrease in device performance in terms of driving voltage, high luminous efficiency, and lifespan.

[0170] Based on the above device results, the second hole transport layer formula I satisfies: -5.45eV≤HOMO energy level≤-5.40eV; the HOMO of the compound shown in the light-emitting layer formula II needs to satisfy: -5.85eV≤HOMO energy level≤-5.65eV. The organic electroluminescent device prepared by the device meeting the above conditions is significantly improved in driving voltage, high luminous efficiency and life.

[0171] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An organic electroluminescent device comprising a light-emitting layer and a hole transport region, It is characterized in that include: A first electrode, a second electrode facing the first electrode, a light-emitting layer between the first electrode and the second electrode, and a hole transport region between the first electrode and the light-emitting layer; The hole transport region includes a hole injection layer, a first hole transport layer, and a second hole transport layer; Wherein, the HOMO energy level of the second hole transport layer is -5.45eV to -5.40eV, and is any one of the following structural compounds: The HOMO energy level of the light-emitting layer is -5.85eV to -5.65eV, and is any one of the following structural compounds:

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