An organic electroluminescence device, a preparation method thereof, and a display device

Abstract

The application belongs to the technical field of organic optoelectronic materials and devices, and discloses an organic electroluminescent device, a preparation method thereof and a display device. The device comprises, in sequence, an anode layer, a hole transport layer, a light-emitting layer, a second electron transport layer, a first electron transport layer composed of an n-type dopant and a first electron transport material, and a cathode layer. The electron transport structure has a small electron injection barrier between the second electron transport layer and the first electron transport layer and between the second electron transport layer and the host material. The organic electroluminescent device prepared by the electron transport structure has good voltage stability during the aging process, thereby reducing the power consumption rise of the organic electroluminescent device during the aging process. The small electron injection barrier can reduce the driving voltage of the device, and the organic electroluminescent device has low driving voltage, long service life and stable voltage.

Description

Technical Field

[0001] This invention belongs to the field of organic optoelectronic materials and devices technology, specifically relating to an organic electroluminescent device and its preparation method, as well as a display device. Background Technology

[0002] Organic light-emitting diode (OLED) technology is a technology that uses organic semiconductor thin films to emit light under an applied voltage. It boasts numerous advantages such as flexibility, self-illumination, thinness, and low power consumption, and has been widely applied in smartphones, wearable devices, and automotive displays. Furthermore, OLED technology can also be used in indoor and outdoor lighting, medical lighting, and automotive lighting. For the OLED technology industry chain, organic light-emitting materials are a crucial component and a significant technological barrier; therefore, exploring OLED light-emitting materials that meet the requirements of display panels is of great importance.

[0003] With the continuous development and iteration of OLED technology, OLED devices are required to possess properties such as low driving voltage, high luminous efficiency, long operating life, and high color purity. Besides the luminous efficiency and spectral full width at half maximum (FWHM) of OLED materials, which have received considerable attention in recent years, achieving low driving voltage and long lifespan is also crucial for realizing high-performance OLED devices. Since hole mobility is generally higher than electron mobility, it is necessary to address the voltage drop across the electron transport layer to reduce the device's driving voltage. On the other hand, ensuring the stability of the electron transport layer's lifespan is also very important, as it determines the overall operating life of the device. To achieve these electron transport layer design goals, the following material and device structure design strategies are typically adopted: 1) Using n-doped electron transport materials to replace traditional nitrogen-doped heterocyclic electron transport materials. Due to the charge transfer effect between the n-dopant and the electron transport material, electron mobility is significantly improved, reducing the voltage drop across the electron transport layer; 2) Using an energy level-matched electron injection layer structure to achieve barrier-free electron injection between the cathode and the electron transport layer, reducing the voltage drop at the cathode and simultaneously improving the device's operating life. However, most current patents and research focus on the electron injection barrier between the electron transport material and the cathode, or the electron mobility of the electron transport material itself, with little attention paid to the electron injection barriers between the electron transport layer and the hole blocking layer, or between the hole blocking layer and the emissive layer. Furthermore, during the constant-current aging process of OLED devices, not only does brightness decay occur, but the device driving voltage also increases, leading to increased power consumption. There is almost no coverage of the device voltage stability issues caused by device aging in relevant patents and papers, indicating that further research is needed in this area. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an organic electroluminescent device including an electron transport structure. This electron transport structure can reduce the driving voltage of the OLED device and solve the problem of driving voltage stability during device aging, thereby achieving OLED device performance with low driving voltage, high efficiency, and stable lifetime. Based on this, a first aspect of this invention provides an organic electroluminescent device, comprising, from bottom to top, an anode layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode layer.

[0005] The light-emitting layer comprises a binary blend composition or a ternary blend composition, wherein the binary blend composition comprises a host material and a light-emitting guest material, and the ternary blend composition comprises a host material, a light-emitting guest material, and a sensitizer;

[0006] The electron transport layer comprises, from bottom to top, a second electron transport layer and a first electron transport layer; the first electron transport layer is composed of an n-type dopant and a first electron transport material; the second electron transport layer is composed of a second electron transport material; the difference between the LUMO energy level of the second electron transport layer and the LUMO energy level of the first electron transport layer is less than or equal to 0.10 eV, and the difference between the LUMO energy level of the host material or the sensitizer and the LUMO energy level of the second electron transport layer is less than or equal to 0.15 eV.

[0007] The electron transport structure requires that there be a small difference in the lowest occupied molecular orbital energy level between the electron transport material and the hole blocking layer, as well as between the hole blocking layer and the light-emitting layer. This enables the organic electroluminescent device to have low driving voltage characteristics and reduces the voltage rise during the device aging process, so that the device power consumption remains stable during the aging process, resulting in an organic electroluminescent device with high efficiency, low driving voltage, and high lifetime stability.

[0008] In some implementations, to further enhance the hole blocking effect of the hole blocking layer, the HOMO level of the second electron transport material is at least 0.4 eV deeper than the HOMO level of the host material.

[0009] In some implementations, the structure of the second electron transport material is as shown in equation (1):

[0010]

[0011] Wherein, X and Y are independently selected from carbon or nitrogen atoms, and at least one of X and Y is a nitrogen atom; R1 and R2 are independently selected from weakly electron-withdrawing groups, including phenylcyano and its derivatives, fluorophenyl and its derivatives, benzothiophene and its derivatives, benzofuran and its derivatives, fluorenyl and its derivatives.

[0012] Preferably, the structure of the second electron transport material is as shown in formula (2), formula (3), or formula (4):

[0013]

[0014] Wherein, X and Y are independently selected from carbon or nitrogen atoms, and at least one of X and Y is a nitrogen atom; R2 and R3 are independently selected from weakly electron-withdrawing groups, including phenylcyano and its derivatives, fluorophenyl and its derivatives, benzothiophene and its derivatives, benzofuran and its derivatives, fluorenyl and its derivatives.

[0015] More preferably, the structure of the second electron transport material is any one of compounds 4-1 to 4-64:

[0016]

[0017]

[0018]

[0019]

[0020] In some implementations, since the LUMO level matching between the first and second electron transport layers is particularly important for achieving low driving voltage and high voltage stability, and the first electron transport layer is also required to have high electron mobility to achieve good electron transport performance, the n-type dopant is preferably Li, Na, K, Rb, Cs, Yb, Ag, Mg, Zn, Au, Cs₂CO₃, or Li₂CO₃; the structure of the first electron transport material is preferably any one of compounds 5-1 to 5-44.

[0021]

[0022]

[0023]

[0024] Meanwhile, in order to obtain the first electron transport layer with high electron mobility and to avoid the n-type dopant causing luminescence quenching of the light-emitting layer, the doping concentration of the n-type dopant is preferably 0.5%-20% by mass.

[0025] In some implementations, the LUMO level matching between the second electron transport layer and the light-emitting layer is particularly important for achieving the goals of low driving voltage and high voltage stability. Therefore, the structure of the host material is preferably any one of compounds 7-1 to 7-76.

[0026]

[0027]

[0028]

[0029]

[0030] Meanwhile, the structure of the sensitizer is preferably any one of compounds 6-1 to 6-50:

[0031]

[0032]

[0033]

[0034]

[0035] In the aforementioned organic electroluminescent device, the anode layer primarily functions 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 is greater than 80%. Furthermore, the sheet resistance of the anode layer is preferably 500 Ω / cm. -1 The preferred film thickness is 10nm-200nm.

[0036] In the aforementioned organic electroluminescent devices, the cathode layer primarily functions to inject electrons into the electron injection layer, electron transport layer, or light-emitting layer, and is preferably made of a material with a low work function. The cathode material is not particularly limited, but is preferably made of aluminum, magnesium, silver, magnesium-silver alloys, magnesium-aluminum alloys, or aluminum-lithium alloys. Similar to the anode layer, the cathode layer can be formed into a thin film using methods such as thermal evaporation or sputtering, with a preferred film thickness of 10 nm to 200 nm. Additionally, light emission can be extracted from the cathode side as needed.

[0037] The hole transport layer in the aforementioned organic light-emitting device is an organic layer formed between the emissive layer and the anode layer (or hole injection layer), whose main function is to transport holes from the anode to the emissive layer. The hole transport layer may consist of two organic layers, with the side closer to the anode defined as the hole injection layer and the side closer to the emissive layer defined as the first hole transport layer; or it may consist of three organic layers, with the hole injection layer, the first hole transport layer, and the second hole transport layer sequentially from the side closer to the anode layer to the emissive layer. The thickness of the hole transport layer is not particularly limited, but is preferably 20nm-200nm. Specifically, when the hole transport layer of the organic light-emitting device consists of a first hole transport layer, the thickness of the first hole transport layer is preferably 20nm-200nm; when the hole transport layer of the organic light-emitting device consists of a first hole transport layer and a second hole transport layer, the thickness of the first hole transport layer is preferably 19nm-150nm, and the thickness of the second hole transport layer is preferably 1nm-50nm. As the hole transport material for the hole transport layer, aromatic amine compounds, such as aromatic amine derivatives as shown in formula (70) below, are preferred.

[0038]

[0039] In the above formula (70), 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, or fused aromatic hydrocarbon groups with 6-50 (preferably 6-30, more preferably 6-20, and even more preferably 6-12) substituted or unsubstituted cyclic carbon groups, or fused 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, or groups formed by bonding these aromatic hydrocarbon groups or fused aromatic hydrocarbon groups with aromatic heterocyclic groups or fused aromatic heterocyclic groups.

[0040] Rings can be formed between Ar1 and Ar2, and between Ar3 and Ar4. In addition, in the above formula (70), 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.

[0041] Alternatively, an aromatic amine compound as shown in formula (71) can be used:

[0042]

[0043] In the above equation (71), the definitions of Ar1-Ar3 are the same as those of Ar1-Ar4 in equation (70).

[0044] According to equations (70) and (71) above, the hole transport material can preferably be selected from any of the following structures:

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051] The organic electroluminescent device of the present invention preferably has a hole injection layer 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 layer is composed of a p-type dopant material (deep LUMO level), or a blend of a p-type dopant material and a hole transport material. As a specific example, the hole transport material is preferably a compound of HT-1-HT-63, and the p-type dopant material is preferably HATCN, F4TCNQ, HI-3, etc. The doping concentration of the p-type dopant is preferably 0.1% by mass to 50.0% by mass. The film thickness of the hole injection layer is not particularly limited, but is preferably selected in the range of 1 nm to 50 nm.

[0052] The structural formulas of p-type doped materials HATCN, F3-TCNQ, and HI-3 are as follows:

[0053]

[0054] The organic electroluminescent device of the present invention preferably has an electron injection layer composed of an n-type dopant disposed between the electron transport layer and the cathode layer. Here, specific examples of the n-type dopant include Li, Cs, Ba, Yb, CsF, BaO, Liq, Naq, Libpp, Bepq2, Bepp2, LiF, CsCO3, ZnO, etc., and the doping concentration of the n-type dopant is preferably 1.0%-90.0% by mass. The structural formulas of the n-type dopant materials Liq, Naq, Libpp, Bepq2, and Bepp2 are as follows:

[0055]

[0056]

[0057] A second aspect of the present invention provides a method for fabricating the above-mentioned organic electroluminescent device, comprising the following steps: sequentially depositing the hole transport layer, the light-emitting layer, the electron transport layer and the cathode layer on the anode layer.

[0058] A third aspect of the present invention provides an organic electroluminescent display device comprising the above-described organic electroluminescent device.

[0059] The beneficial effects of this invention are as follows: 1) Thanks to the smaller electron injection barrier between the n-doped electron transport layer and the hole blocking layer, and between the hole blocking layer and the light-emitting layer, the voltage rise problem during the aging process of organic electroluminescent devices is effectively solved, achieving a smaller change in driving voltage, thereby reducing the power consumption increase problem of organic electroluminescent devices during the aging process. Furthermore, the smaller electron injection barrier can reduce the driving voltage of the device, resulting in an organic electroluminescent device with long lifespan, high voltage stability, and low driving voltage; 2) By preferentially using triazine or pyrimidine compounds as the hole blocking layer, and further introducing weakly withdrawn units onto these compounds, the electron injection barrier between the electron transport layer and the light-emitting layer is adjusted, thereby achieving a smaller electron injection barrier, reducing the device driving voltage, and significantly improving power efficiency performance. Moreover, triazine derivatives have good chemical stability, extending the device's operating life; 3) Using an n-doped electron transport layer instead of traditional nitrogen heterocyclic electron transport materials, due to the significant charge transfer effect between the n-dopant and the electron transport material, the electron mobility of the electron transport layer is greatly improved, resulting in a significant reduction in the voltage drop of the electron transport layer. This results in low-driving-voltage, high-efficiency device light-emitting performance. Attached Figure Description

[0060] Figure 1The diagram shows the structure of an organic electroluminescent device. In the diagram, 10 is the anode layer; 11 is the hole injection layer; 12 is the first hole transport layer; 13 is the second hole transport layer; 14 is the light-emitting layer; 15 is the second electron transport layer; 16 is the first electron transport layer; 17 is the electron injection layer; and 18 is the cathode layer. Detailed Implementation

[0061] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0062] The structures of compounds HATCN, HT-48, HT-65, host material 7-60, sensitizer 6-27, host material 7-66, sensitizer 6-15, and sensitizer 6-18 are shown below:

[0063]

[0064] The structures of compounds 4-1 to 4-64 are shown below:

[0065]

[0066]

[0067]

[0068]

[0069] The structures of compounds 5-1 to 5-44 are shown below:

[0070]

[0071]

[0072]

[0073] A schematic diagram of an organic electroluminescent device is shown below. Figure 1 As shown, its preparation method includes the following steps:

[0074] A 30mm×30mm×0.7mm thick glass substrate with an ITO / Ag / ITO reflective anode (anode layer 10, ITO film thickness 10nm, Ag thickness 150nm) was ultrasonically cleaned in isopropanol. The cleaned ITO glass substrate was then placed in an oven at 100℃ and baked for 3 hours. The baked ITO glass substrate was then subjected to ozone cleaning treatment by ultraviolet lamp irradiation for 3 minutes.

[0075] The glass substrate treated with ultraviolet light is mounted on the substrate holder of a vacuum evaporation apparatus. First, HATCN compound is deposited on the side where transparent electrode lines are formed in a manner that covers the transparent electrode, forming a hole injection layer 11 with a film thickness of 10 nm.

[0076] Compound HT-48 is deposited on the hole injection layer 11 to form a first hole transport layer 12 with a thickness of 135 nm.

[0077] Subsequently, compound HT-65 is deposited on the first hole transport layer to form a second hole transport layer 13 with a film thickness of 10 nm.

[0078] Subsequently, a ternary blend composition consisting of host material 7-60, sensitizer 6-27 and luminescent guest material 1 is co-deposited on the second hole transport layer, wherein the doping concentration of sensitizer 6-27 is 30% by mass and the doping concentration of luminescent guest material 1 is 0.5% by mass, forming a luminescent layer 14 with a film thickness of 30 nm.

[0079] The chemical structural formula of luminescent guest material 1 is as follows:

[0080]

[0081] Subsequently, a second electron transport layer 15 with a thickness of 15 nm is deposited on the light-emitting layer 14.

[0082] Subsequently, a first electron transport layer 16 with a thickness of 25 nm is deposited on the second electron transport layer 15.

[0083] In addition, Yb is deposited on the first electron transport layer 16 to form an electron injection layer 17 with a thickness of 1 nm.

[0084] Then, metallic Ag is deposited on the electron injection layer to form a cathode layer 18 with a film thickness of 20 nm.

[0085] Examples 1-6 are formed by adjusting the material combination of the second electron transport layer 15 and the first electron transport layer, as shown in Table 1.

[0086] Table 1

[0087]

[0088] While keeping everything else unchanged in Example 2, the main material and sensitizer in the light-emitting layer were adjusted to form Examples 7-9, as shown in Table 2.

[0089] Table 2

[0090] Example Main materials Sensitizer Object materials 7 7-60 6-15 Luminescent object material 1 8 7-60 6-18 Luminescent object material 1 9 7-66 6-27 Luminescent object material 1

[0091] Thin films of 1% Ag:5-6, 1% Yb:5-6, Comparative Compound 1, and Comparative Compound 2 were deposited on the above-mentioned conductive substrates, respectively, and were designated as Examples 10-13. The time-of-flight measurements of the thin films prepared in Examples 10-13 were performed at 300 (V / cm) using the time-of-flight method. 1 / 2 Electron mobility under electric field strength. To compare the electron transport capability when using an n-doped electron transport material as the first electron transport layer, the electron mobility results measured in Examples 10-13 are shown in Table 3.

[0092] Table 3

[0093]

[0094] The comparative compounds 1 and 2 have the following structural formulas:

[0095]

[0096] The combination of the second electron transport layer 15 and the first electron transport layer 16 of the organic electroluminescent devices prepared in Comparative Examples 20-27 is changed as shown in Table 4 below.

[0097] Table 4

[0098]

[0099] The comparative compound 3 has the following structural formula:

[0100]

[0101] Performance evaluation of organic electroluminescent devices

[0102] The performance of the organic electroluminescent devices prepared in Examples 1-6, 7-9, and Comparative Examples 20-27 of this application was measured using a spectroradiometer CS-2000 (Konica Minolta) and a digital source meter 2420 (Keithley) at 1000 cd / m². 2 Current efficiency at brightness, measured at 10 mA / cm² 2 Driving voltage at current density. Using an OLED device lifetime testing system at 10 mA / cm². 2 The lifetime of the constant current driven measurement device at current density when it decays to 95% of its initial brightness, and the change in driving voltage when the device decays to 90% of its initial brightness. E 第二电-第一电 E is defined as the difference between the LUMO energy level of the second electron transport layer and the LUMO energy level of the first electron transport layer. 敏-第二电 It is defined as the difference between the sensitizer LUMO energy level and the second electron transport layer LUMO energy level.

[0103] The device performance results for Examples 1-6, Examples 7-9 and Comparative Examples 20-27 are shown in Table 5.

[0104] Table 5

[0105]

[0106] Comparing the device performance results of Examples 1-6 and Comparative Examples 20-22 and 26 in Table 5, it can be seen that, under the condition that other materials in the organic electroluminescent device structure are the same, the electron transport structure described in this application, when the LUMO energy level difference between the second electron transport layer and the first electron transport layer and the LUMO energy level difference between the second electron transport layer and the host material or sensitizer material of the light-emitting layer are relatively small, the driving voltage rise during device aging is significantly smaller, and the driving voltage of the device decreases, thereby suppressing the problem of power consumption rise during the aging process of the light-emitting device, and obtaining an organic electroluminescent device with long life, high voltage stability and low driving voltage. The electron mobility results measured in Examples 10-13 show that the electron mobility of the n-doped electron transport layer is significantly superior to that of the conventional nitrogen heterocyclic electron transport material. Furthermore, the injection barrier for electrons from the cathode to the electron transport layer is small, which significantly reduces the driving voltage of the device. Therefore, by comparing the device performance results of Example 2 and Comparative Examples 24 and 25 in Table 5, it can be seen that the driving voltage of Example 2, which uses an n-doped electron transport layer to replace the conventional nitrogen heterocyclic electron transport material, is significantly lower than that of Comparative Examples 24 and 25.

[0107] The experimental data above show that the novel organic material of this application, as the light-emitting object of organic electroluminescent devices, is a high-performance organic light-emitting functional material and is expected to be promoted for commercial application.

[0108] The above description is merely a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. Any embodiment that achieves the technical effects of the present invention using the same means should fall within the protection scope of the present invention. Within the protection scope of the present invention, various modifications and variations can be made to the technical solutions and / or implementation methods.

Claims

1. An organic electroluminescent device, characterized by comprising: from bottom to top comprising an anode layer, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode layer; the light-emitting layer comprises a binary blend composition or a ternary blend composition, the binary blend composition being a host material and a light-emitting guest material, the ternary blend composition being a host material, a light-emitting guest material and a sensitizer; the electron transport layer comprises from bottom to top a second electron transport layer and a first electron transport layer; the first electron transport layer is composed of an n-type dopant and a first electron transport material; the second electron transport layer is composed of a second electron transport material; a difference between a LUMO energy level of the second electron transport layer and a LUMO energy level of the first electron transport layer is less than or equal to 0.10 eV, and a difference between a LUMO energy level of the host material or the sensitizer and a LUMO energy level of the second electron transport layer is less than or equal to 0.15 eV; the second electron transport material has a structure as shown in formula (2), formula (3) or formula (4): wherein X and Y are independently selected from carbon or nitrogen atom, and at least one of X and Y is nitrogen atom; R2 and R3 are independently selected from weakly electron-accepting groups, the weakly electron-accepting groups comprising benzonitrile group and derivatives thereof, fluorophenyl group and derivatives thereof, benzothiophene and derivatives thereof, benzofuran and derivatives thereof, fluorene group and derivatives thereof.

2. The organic electroluminescent device according to claim 1, wherein the HOMO energy level of the second electron transport material is at least 0.4 eV deeper than the HOMO energy level of the host material.

3. The organic electroluminescent device according to claim 1, wherein the second electron transport material has a structure as any one of compound 4-1 to compound 4-64:

4. The organic electroluminescent device according to claim 1, wherein the n-type dopant is Li, Na, K, Rb, Cs, Yb, Ag, Mg, Zn, Au, Cs2CO3, Li2CO3; and / or, a doping concentration of the n-type dopant is 0.5 mass% - 20 mass%; and / or, the first electron transport material has a structure as any one of compound 5-1 to compound 5-44:

5. The organic electroluminescent device according to claim 1, wherein the host material has a structure as any one of compound 7-1 to compound 7-76:

6. The organic electroluminescent device according to claim 1, wherein the sensitizer has a structure as any one of compound 6-1 to compound 6-50:

7. A method of producing an organic electroluminescent device according to any one of claims 1 to 6, characterized by, comprising the following steps: forming the hole transport layer, the light-emitting layer, the electron transport layer and the cathode layer on the anode layer by evaporation in sequence.

8. An organic electroluminescent display device, characterized by comprising: the organic electroluminescence device of any one of claims 1 to 6.

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