Electron transport layer material and organic electroluminescent device

Abstract

The invention belongs to the technical field of organic electroluminescent devices, and discloses an electron transport layer material and an organic electroluminescent device.In the electron transport layer material, the compound structure is mainly composed of 9-alkyl-9-benzofluorene and two triazine groups, wherein the 9-alkyl-9-phenylfluorene is used as a bridging group, and the two triazine groups are respectively connected to phenyl in fluorene below the 9-alkyl-9-phenylfluorene group and phenyl on the 9-site. Through collaborative design of a fluorene bridging group and two triazine acceptor units, high electron mobility, adjustable energy level and excellent thin film form are realized, the material has a good electron transport function, and as an electron transport layer material, an organic electroluminescent device prepared from the material has the advantages of low driving voltage, high luminous efficiency and long service life, and can be widely applied to the field of organic electroluminescent devices. And meanwhile, the efficiency roll-off is small.

Description

Technical Field

[0001] This invention belongs to the field of organic electroluminescence technology, and more specifically, relates to an electron transport layer material and an organic electroluminescence device. Background Technology

[0002] Organic light-emitting diodes (OLEDs) possess a range of advantages, including self-illumination, low-voltage driving, all-solid-state operation, wide viewing angle, and simple composition and manufacturing processes. Compared to liquid crystal displays (LCDs), OLEDs do not require a backlight. Therefore, OLEDs have broad application prospects.

[0003] Organic light-emitting diodes (OLEDs) generally consist of an anode, a metal cathode, and an organic layer between them. The organic layer mainly includes a hole injection layer, a hole transport layer, an electron blocking layer, and a light-emitting layer. Among these, the electron transport layer plays a crucial role, providing an efficient path for electrons to travel quickly and effectively from the cathode to the light-emitting layer. This helps reduce electron loss during transport and improves the overall efficiency of the device.

[0004] Currently, there are many problems with the materials used in electron transport layers: 1) Electron mobility is usually lower than hole mobility in the hole transport layer, which leads to carrier imbalance. Moreover, low electron mobility may reduce current efficiency because electrons cannot be effectively transported to the light-emitting layer, thus affecting light generation.

[0005] 2) Poor energy level matching between the electron transport layer and the cathode leads to difficulties in electron injection or low injection efficiency, thereby increasing the interface resistance, reducing the driving voltage of the device, and thus affecting the efficiency and lifespan of the device.

[0006] 3) Some electron transport materials degrade after prolonged operation, especially at high current densities. This degradation may be caused by thermal effects, chemical reactions, or charge accumulation, leading to a decrease in device performance, such as brightness decay and shortened lifespan.

[0007] Currently, research on organic electroluminescent materials has been widely carried out in academia and industry, and a large number of high-performance organic electroluminescent materials have been developed. Overall, the future direction of organic electroluminescent devices is to develop devices with high efficiency, long lifespan, and low cost.

[0008] Therefore, designing and finding a stable and efficient compound to serve as the electron transport layer material for organic electroluminescent devices to overcome their shortcomings in practical applications is a key focus and future research trend in organic electroluminescent device materials research. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides an electron transport layer material and an organic electroluminescent device. In this electron transport layer material, the compound employs a synergistic design of a fluorene bridging group and two triazine acceptor units, achieving high electron mobility, tunable energy levels, and excellent thin film morphology. As an electron transport layer material, it can significantly improve the luminous efficiency and lifespan of organic electroluminescent devices.

[0010] To achieve the above objectives, the first objective of this invention is to provide an electron transport layer material. Compounds with the structure shown in Formula I: ; in, R is independently selected from substituted or unsubstituted C1-C8 alkyl groups; R1, R2, and R3 are independently selected from hydrogen and cyano groups, respectively; n1 is independently selected from 0, 1, 2, and 3; n2 and n3 are independently selected from 0, 1, 2, 3, and 4; Ar1, Ar2, Ar3, and Ar4 are each independently selected from substituted or unsubstituted C6-C30 aryl groups and substituted or unsubstituted C3-C30 heteroaryl groups, wherein the heteroatom contains at least one of O, S, N, Si, and Se.

[0011] In one embodiment of the invention, R is independently selected from substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted isopropyl, and substituted or unsubstituted tert-butyl.

[0012] In one embodiment of the present invention, Ar1, Ar2, Ar3, and Ar4 are each independently selected from substituted or unsubstituted C6-C20 aryl groups and substituted or unsubstituted C5-C18 heteroaryl groups, wherein the heteroatom contains at least one of O, S, N, Si, and Se.

[0013] In one embodiment of the present invention, Ar1, Ar2, Ar3, and Ar4 are each independently selected from the following structures: ; * indicates the linking site of a functional group.

[0014] In one embodiment of the present invention, the term "substituted or unsubstituted" as mentioned above means substituted by one, two or more of the following substituents: cyano, halogen, methyl, ethyl, propyl, butyl, tert-butyl, cyclopentane, cyclohexane, phenyl, biphenyl, naphthyl, fluorenyl, dimethylfluorenyl, phenanthrene, triphenylene, carbazolyl, furanyl, thiophene, pyrrole, pyridyl, benzofuranyl, benzothiophene, isobenzofuranyl, dibenzofuranyl, dibenzothiophene, or substituted by two or more substituents linked together from the substituents shown above, or without substituents.

[0015] In one embodiment of the present invention, chemical formula I has any one of the structures of compounds 1-548:

[0016] A second objective of this invention is to provide a method for preparing the material as described above.

[0017] It should be noted that the material with electron transport function in this invention can be prepared by methods known to those skilled in the art. Alternatively, the following reaction process is preferred for preparation, and the specific synthetic route is as follows:

[0018] Among them, R, R1-R3, n1-n3, Ar1-Ar4 are as defined in chemical formula I, and Hal1-Hal3 are selected from Cl, Br, and I.

[0019] The specific steps are as follows: Step 1 specifically includes the following processes: Add raw material A (1.0 eq), pinacol diborate (1.0-1.5 eq), and potassium acetate (2.0-4.0 eq) to a reaction flask, then add 1,4-dioxane, purge with nitrogen, and add tris(dibenzylacetone)dipalladium (0.02-0.10 eq) and X-Phos (0.1-0.2 eq) under nitrogen protection. Then raise the temperature to 110-120℃ and reflux for 2-30 h. Detect the reaction using thin-layer chromatography. After the reaction is complete, lower the temperature slightly, filter with diatomaceous earth to remove salts and catalysts, then add water and dichloromethane to the filtrate for separation and extraction. Concentrate the organic phase, and purify the intermediate 1 using a mixed solution of dichloromethane and petroleum ether (V:V=1:3-1:10) by column chromatography.

[0020] Step 2 specifically includes the following processes: Intermediate 1 (1.0 eq) and raw material B (1.0-1.3 eq) were added to a reaction flask, followed by a mixed solution of toluene, ethanol, and water (V:V:V = 3:1:1). Nitrogen gas was introduced, and tetrakis(triphenylphosphine)palladium (0.01-0.05 eq) and potassium carbonate (2.0-4.0 eq) were added under nitrogen protection. The mixture was then heated to 80℃-100℃ and refluxed for 2-30 h. The mixture was filtered with diatomaceous earth to remove salts and catalysts. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. Intermediate 2 was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:3-1:10).

[0021] Step 3 specifically includes the following processes: Cool to -78℃, add THF to the reaction flask, then add raw material C (1.1-1.5 eq) dissolved in it, replace with nitrogen three times, stir for 10-30 min, slowly add n-butyllithium (1.1-1.5 eq) to the reaction flask, react for 1-4 h, dissolve intermediate 2 (1.0 eq) in tetrahydrofuran, then slowly add the solution of intermediate 2 dropwise to the reaction flask, stir evenly, stop cooling, heat to room temperature and continue the reaction for 2-18 h; detect the reaction by thin-layer chromatography, wash three times with water after the reaction is complete, retain the organic phase, then extract the aqueous phase with dichloromethane, combine the organic phases and concentrate, and purify intermediate 3 by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:2-1:6).

[0022] Step 4 specifically includes the following processes: Dichloromethane was added to the reaction flask, followed by intermediate 3 (1.0 eq) dissolved therein. Triethylsilane (1.1-2.0 eq) was added while stirring at -10℃. After stirring for 15-60 min, methanesulfonic acid (2.0-4.0 eq) was added and stirring was continued for 10-30 min. The mixture was then transferred to room temperature and reacted for 1-4 h. The reaction was detected by thin-layer chromatography. After the reaction was completed, water was added to the reaction solution and stirred. The mixture was extracted and separated, retaining the organic phase. The aqueous phase was then extracted with dichloromethane. The organic phases were combined and concentrated. Intermediate 4 was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:4-1:12) or pure petroleum ether.

[0023] Step 5 specifically includes the following processes: THF was added to the reaction flask, followed by intermediate 4 (1.0 eq) dissolved in it. The mixture was stirred at room temperature until dissolved. Then, t-BuOK (2.0-10.0 eq) was slowly added to the reaction flask. After stirring for 1 h, starting material D (3.0-8.0 eq) was slowly added dropwise. The temperature was raised to 70-90℃, and the reaction was carried out for 6-20 h. The reaction was detected by thin-layer chromatography. After the reaction was completed, the temperature was lowered slightly, and the mixture was filtered with diatomaceous earth to remove salts. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. Intermediate 5 was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:4-1:12).

[0024] Step 6 specifically includes the following processes: Intermediate 5 (1.0 eq), pinacol diborate (1.0-1.5 eq), and potassium acetate (2.0-4.0 eq) were added to a reaction flask, followed by 1,4-dioxane. Nitrogen gas was introduced, and under nitrogen protection, tris(dibenzylacetone)dipalladium (0.02-0.10 eq) and X-Phos (0.1-0.2 eq) were added. The mixture was then heated to 110-120 °C and refluxed for 2-30 h. The reaction was detected by thin-layer chromatography. After the reaction was completed, the temperature was slightly lowered, and the mixture was filtered with diatomaceous earth to remove salts and catalysts. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. Intermediate 6 was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:3-1:10).

[0025] Step 7 specifically includes the following processes: Intermediate 6 (1.0 eq) and raw material E (1.0-1.3 eq) were added to a reaction flask, followed by a mixed solution of toluene, ethanol, and water (V:V:V = 3:1:1). Nitrogen gas was introduced, and tetrakis(triphenylphosphine)palladium (0.01-0.05 eq) and potassium carbonate (2.0-4.0 eq) were added under nitrogen protection. The mixture was then heated to 80-100℃ and refluxed for 2-30 hours. The mixture was filtered with diatomaceous earth to remove salts and catalysts. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. The solution of dichloromethane and petroleum ether (V:V = 1:3-1:10) was purified by column chromatography to obtain chemical formula I.

[0026] A third objective of the present invention is to provide an organic electroluminescent device comprising an anode, a cathode, and an organic layer disposed between the anode and the cathode, the organic layer containing the aforementioned material having electron transport function.

[0027] Preferably, the organic material layer of the organic electroluminescent device in this invention can be formed as a single-layer structure or as a multilayer structure with two or more organic material layers.

[0028] For example, the organic electroluminescent device may have a structure comprising organic material layers such as a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting auxiliary layer, a light-emitting layer, a hole blocking layer, an electron transport layer, and an electron injection layer. However, the structure of the organic electroluminescent device is not limited to this, and may include fewer or more organic material layers.

[0029] The fourth objective of this invention is to provide an application of a material with electron transport function, as described above, in an organic electroluminescent device.

[0030] Furthermore, the organic electroluminescent device can be used in organic electroluminescent apparatuses, including but not limited to flat panel displays, computer monitors, a medical monitor, a television set, billboards, a lamp for internal or external lighting and / or signaling, head-up displays, fully transparent or partially transparent displays, flexible displays, a laser printer, a telephone, a mobile phone, tablets, a photo album, a personal digital assistant (PDA), a wearable device, a laptop computer, a digital camera, a camcorder, a viewfinder, a microdisplay, a 3D display, a virtual reality or augmented reality display, vehicles, video walls comprising multiple displays tiled together, theater or stadium screens, phototherapy devices, and signs.

[0031] The beneficial effects of this invention are: In the electron transport layer material of this invention, the compound structure mainly consists of 9-alkyl-9-phenylfluorene and two triazine groups. The 9-alkyl-9-phenylfluorene acts as a bridging group, and the two triazine groups are respectively attached to the phenyl group at the 9-position of the fluorene group below the 9-alkyl-9-phenylfluorene group. This invention achieves high electron mobility, tunable energy levels, and excellent thin film morphology through the synergistic design of the fluorene bridging group and the two triazine acceptor units, exhibiting excellent electron transport function. As an electron transport layer material, organic electroluminescent devices prepared with it exhibit low driving voltage, high luminous efficiency, and long lifespan, while also showing minimal efficiency roll-off. Detailed analysis follows: 1) In the 9-alkyl-9-phenylfluorene group, the rigid planar structure of fluorene facilitates the formation of ordered molecular stacking, promoting π-π stacking and electron delocalization, thereby forming efficient electron transport channels and improving carrier mobility. The 9-position substituted phenyl and alkyl chains introduce appropriate steric hindrance, which can suppress excessive molecular aggregation, improve the uniformity of film morphology, and obtain a more uniform, defect-free film, ensuring film morphological stability and thus enabling the fabricated device to have good performance. Furthermore, the further substitution of a cyano group on the phenyl group below the 9-alkyl-9-phenylfluorene group or on the phenyl group at the 9-position alters the energy level, adjusting device performance. While the device lifespan decreases, the driving voltage decreases, and the luminous efficiency increases.

[0032] 2) Triazine groups are strongly electron-deficient units. Introducing two triazine groups at different sites (phenyl and fluorenyl) synergistically lowers the LUMO energy level of the material, enhancing electron affinity and thus more effectively promoting electron injection from the cathode. Furthermore, this structure allows for finer tuning of the HOMO / LUMO energy levels, making them more compatible with the energy levels of adjacent layers (such as the emissive layer or cathode), reducing the electron injection barrier and lowering the device driving voltage. The two triazine groups expand the conjugated system of the molecule and provide more electron transport paths, enhancing intramolecular and intermolecular electronic coupling, thereby improving electron mobility. Efficient electron injection and transport help balance electron-hole recombination, concentrating the exciton formation region within the emissive layer, reducing exciton quenching, and improving luminescence efficiency. The bistriazine groups increase molecular rigidity, improving the material's thermal stability and preventing thin-film crystallization or phase separation caused by heat during device operation, which leads to performance degradation and extends the device's lifespan. Attached Figure Description

[0033] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of compound 1 prepared in Example 1 of the present invention. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Additionally, it should be noted that the values ​​given in the following embodiments are as accurate as possible. However, those skilled in the art will understand that due to unavoidable measurement errors and experimental issues, each number should be understood as an approximation rather than an absolutely accurate value.

[0036] Example 1

[0037] Step 1 specifically includes the following processes: In a reaction flask, raw material A-1 (1.0 eq, CAS No.: 4269-13-0), pinacol diborate (1.3 eq), and potassium acetate (3.0 eq) were added, followed by 1,4-dioxane. Nitrogen gas was purged, and under nitrogen protection, tris(dibenzylacetone)dipalladium (0.03 eq) and X-Phos (0.1 eq) were added. The mixture was then heated to 120 °C and refluxed for 15 h. The reaction was detected by thin-layer chromatography. After the reaction was completed, the temperature was slightly lowered, and the mixture was filtered with diatomaceous earth to remove salts and catalysts. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. Intermediate 1-1 (yield: 77.5%) was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:4).

[0038] Step 2 specifically includes the following processes: Intermediate 1-1 (1.0 eq) and starting material B-1 (1.0 eq, CAS No.: 3842-55-5) were added to a reaction flask, followed by a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Nitrogen gas was introduced, and tetrakis(triphenylphosphine)palladium (0.02 eq) and potassium carbonate (3.0 eq) were added under nitrogen protection. The mixture was then heated to 95 °C and refluxed for 18 h. The mixture was filtered with diatomaceous earth to remove salt and catalyst. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. Intermediate 2-1 (yield: 84.9%) was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:4).

[0039] Step 3 specifically includes the following processes: The temperature was lowered to -78℃, THF was added to the reaction flask, and then raw material C-1 (1.3 eq, CAS No.: 108-37-2) was added and dissolved in it. Nitrogen gas was replaced three times, and the mixture was stirred for 30 min. Then, n-butyllithium (1.5 eq) was slowly added to the reaction flask, and the reaction was allowed to proceed for 2 h. Intermediate 2-1 (1.0 eq) was dissolved in tetrahydrofuran, and then the solution of intermediate 2-1 was slowly added dropwise to the reaction flask. The mixture was stirred until homogeneous, the refrigeration was stopped, and the temperature was raised to room temperature to continue the reaction for 12 h. The reaction was detected by thin-layer chromatography. After the reaction was completed, the mixture was washed three times with water, and the organic phase was retained. The aqueous phase was then extracted with dichloromethane. The organic phases were combined and concentrated. Intermediate 3-1 (yield: 65.8%) was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:2).

[0040] Step 4 specifically includes the following processes: Dichloromethane was added to the reaction flask, followed by intermediate 3-1 (1.0 eq) dissolved therein. Triethylsilane (2.0 eq) was added under stirring at -10°C. After stirring for 30 min, methanesulfonic acid (3.0 eq) was added, and stirring was continued for 20 min. The mixture was then transferred to room temperature and reacted for 2 h. The reaction was detected by thin-layer chromatography. After the reaction was completed, water was added to the reaction solution and stirred. The mixture was extracted and separated, retaining the organic phase. The aqueous phase was then extracted with dichloromethane. The organic phases were combined and concentrated. The intermediate 4-1 was purified by column chromatography using petroleum ether (yield: 73.8%).

[0041] Step 5 specifically includes the following processes: THF was added to the reaction flask, followed by intermediate 4-1 (1.0 eq) dissolved in it. The mixture was stirred at room temperature until dissolved. Then, t-BuOK (5.0 eq) was slowly added to the reaction flask, and the mixture was stirred for 1 h. Iodomethane (5.0 eq) was then slowly added dropwise, and the mixture was heated to 80 °C and reacted for 12 h. The reaction was detected by thin-layer chromatography. After the reaction was completed, the temperature was lowered slightly, and the mixture was filtered with diatomaceous earth to remove the salt. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. Intermediate 5-1 (yield: 67.1%) was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:4).

[0042] Step 6 specifically includes the following processes: Intermediate 5-1 (1.0 eq), pinacol diborate (1.3 eq), and potassium acetate (3.0 eq) were added to a reaction flask, followed by 1,4-dioxane. Nitrogen gas was purged, and tris(dibenzylacetone)dipalladium (0.03 eq) and X-Phos (0.1 eq) were added under nitrogen protection. The mixture was then heated to 120 °C and refluxed for 16 h. The reaction was detected by thin-layer chromatography. After the reaction was completed, the temperature was slightly lowered, and the mixture was filtered with diatomaceous earth to remove salts and catalysts. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. Intermediate 6-1 (yield: 78.3%) was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:4).

[0043] Step 7 specifically includes the following processes: Intermediate 6-1 (1.0 eq) and starting material E-1 (1.0 eq, CAS No.: 3842-55-5) were added to a reaction flask, followed by a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Nitrogen gas was introduced, and tetrakis(triphenylphosphine)palladium (0.04 eq) and potassium carbonate (4.0 eq) were added under nitrogen protection. The mixture was then heated to 95 °C and refluxed for 20 h. The mixture was filtered with diatomaceous earth to remove salts and catalysts. Water and dichloromethane were added to the filtrate for separation and extraction. The organic phase was retained and concentrated. Compound 1 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:5) (yield: 86.4%).

[0044] The obtained compound 1 was analyzed, and the results are as follows: HPLC purity: >99.8%.

[0045] Mass spectrometry test: Waters XEVO TQD mass spectrometer with ESI source.

[0046] Test value MS(ESI, m / Z): [M+H] + =719.37.

[0047] Elemental analysis: The test values ​​are: C, 83.29; H, 4.92; N, 11.83.

[0048] Nuclear magnetic resonance hydrogen spectrum: as shown Figure 1 As shown in (Compound 1).

[0049] In addition, it should be noted that other compounds of the present invention can be obtained by referring to the preparation methods of the examples listed above, so they will not be listed one by one here.

[0050] Device Application Example 1: Fabrication of organic electroluminescent devices (1) Anode (ITO): The ITO (Indium Tin Oxide)-Ag-ITO (Indium Tin Oxide) glass substrate with a coating thickness of 1500 angstroms was cleaned 3 times in distilled water, ultrasonically cleaned for 30 min, then cleaned repeatedly with distilled water 3 times, ultrasonically cleaned for 10 min. After cleaning, it was ultrasonically cleaned with methanol, acetone and isopropanol in sequence (5 min each time), dried, and then transferred to a plasma cleaner for 5 min. Then it was sent to a vapor deposition machine, using the substrate as the anode, and other functional layers were deposited on it in sequence.

[0051] (2) Hole injection layer (HIL): HT and P-dopant are vacuum-deposited as hole injection layers at a deposition rate of 1 Å / s, with a deposition rate ratio of 97:3 for HT and P-dopant and a thickness of 10 nm.

[0052] (3) Hole transport layer (HTL): HT is vacuum-deposited on the hole injection layer as a hole transport layer at a deposition rate of 1.5 Å / s, with a thickness of 125 nm.

[0053] (4) Prime: Prime is vacuum-deposited on the hole transport layer at a deposition rate of 0.5 Å / s as a prime as a light-emitting auxiliary layer with a thickness of 5 nm.

[0054] (5) Emitting layer (EML): The host material and the dopant material are vacuum deposited on the emitting auxiliary layer at a evaporation rate of 1 Å / s as the emitting layer, wherein the evaporation rate ratio of the host to the dopant is 98:2 and the thickness is 30 nm.

[0055] (6) Hole blocking layer (HBL): HB is vacuum-deposited on the light-emitting layer as a hole blocking layer at a deposition rate of 0.5 Å / s, with a thickness of 5 nm.

[0056] (7) Electron transport layer (ETL): Compound 1 and Liq are vacuum-deposited on the hole blocking layer at a deposition rate of 1 Å / s as an electron transport layer, wherein the deposition rate ratio of compound 1 and Liq is 50:50 and the thickness is 30 nm.

[0057] (8) Electron injection layer (EIL): A Yb film layer with a thickness of 1 nm is vacuum-deposited on the electron transport layer at a deposition rate of 0.5 Å / s.

[0058] (9) Cathode: Mg and Ag are vacuum-deposited on the electron injection layer at a deposition rate of 1 Å / s as cathodes. The deposition rate ratio of Mg to Ag is 1:9 and the thickness is 13 nm.

[0059] (10) Light extraction layer: CPL is vacuum-deposited on the cathode as a light extraction layer at a deposition rate of 1 Å / s, with a thickness of 65 nm.

[0060] (11) Encapsulate the substrate after vapor deposition: First, use a coating equipment to coat the cleaned cover plate with UV adhesive. Then, move the coated cover plate to the pressing section, place the vapor-deposited substrate on the top of the cover plate, and finally bond the substrate and cover plate together under the action of the bonding equipment, while simultaneously completing the UV adhesive photocuring.

[0061] The required material structure is shown below: .

[0062] Device Application Example 2-153 refers to the method provided in Device Application Example 1 above, and selects the corresponding compounds in Table 1 below to replace compound 1, performs electron transport layer evaporation, and prepares the corresponding organic electroluminescent devices, which are respectively referred to as Device Application Example 2-153.

[0063] Device Comparison Example 1-11 The device comparative example was prepared according to the method provided in Device Application Example 1 above, except that the electron transport layer (compound 1) in Device Application Example 1 was replaced with the existing comparative compound a-compound k, wherein the structural formula of compound a-compound k is as follows: .

[0064] The driving voltage, BI value, and lifetime of the organic electroluminescent devices prepared by Application Examples 1 to 153 and Comparative Examples 1 to 11 were characterized at a brightness of 1000 nits. The test results are shown in Table 1.

[0065] Table 1 Device Test Results

[0066]

[0067]

[0068]

[0069] Those skilled in the art will know that in blue top-emitting devices, luminous efficiency is greatly affected by chromaticity. Therefore, taking into account the influence of chromaticity on efficiency, the ratio of luminous efficiency to CIEy is defined as the BI value, i.e., BI = (cd / A) / CIEy. In the test, the CIEy value is adjusted to be between 0.044 and 0.046.

[0070] As can be seen from the comparison of the examples and comparative examples in Table 1, the organic electroluminescent devices prepared using the compound materials provided by the present invention exhibit superior device performance compared with the light-emitting devices prepared using the comparative compounds, such as lower driving voltage, higher luminous efficiency, and longer lifespan.

[0071] Among them, comparative compounds a, b, c, and d are parallel comparative examples to compounds 52, 278, 282, and 283 of the present invention. The difference lies in the structure of the compounds of the present invention: 9-alkyl-9-phenylfluorene group serves as the bridging group, with two triazine groups respectively attached to the phenyl group at the fluorene position below the 9-alkyl-9-phenylfluorene group and the phenyl group at the 9-position. In contrast, the corresponding bridging groups in comparative compounds a, b, c, and d are spirodifluorene group or 9,9-diphenylfluorene group. The increased molecular weight leads to a higher evaporation temperature. Excessive evaporation temperature increases the tendency for thermal decomposition of the material during device fabrication, affecting the device's lifespan and shortening its lifespan. Furthermore, the greater structural symmetry and more regular structural arrangement make the film more prone to recrystallization, generating grain boundaries and defects that become exciton quenching centers and charge traps, leading to accelerated device efficiency degradation.

[0072] Comparative compound e and compound 285 of this invention are parallel comparative examples. The difference lies in the structure of the compound: in this invention, the 9-alkyl-9-phenylfluorene group acts as a bridging group, with two triazine groups directly connected to the phenyl group at the 9-position and the phenyl group at the 9-position of the fluorene below the 9-alkyl-9-phenylfluorene group. In contrast, in comparative compound e, the triazine group connected to the phenyl group at the fluorene below the 9-alkyl-9-phenylfluorene group is not directly chemically bonded, but is separated by an alkyl group. This alkyl separation breaks the conjugation, thus severing the conjugation between the triazine and the fluorene core. Therefore, the overall conjugated system of the molecule is reduced, electron mobility decreases, electron-hole balance is disrupted, recombination region shifts, and luminescence efficiency and external quantum efficiency are reduced. Furthermore, the alkyl separation affects structural stability, leading to a shorter device lifespan.

[0073] The comparative compounds fk and compounds 2, 497, 468, 287, 1, and 222 of this invention are parallel comparative examples. The difference lies in the fact that the comparative compounds have only one triazine group connected to a 9-alkyl-9-phenylfluorene group, while the compounds of this invention have two triazine groups connected to a 9-alkyl-9-phenylfluorene group, respectively attached to the phenyl group in the fluorene group below the 9-alkyl-9-phenylfluorene group and the phenyl group at the 9-position. Introducing two triazine groups allows for more precise tuning of the HOMO / LUMO energy levels, making them more matched to the energy levels of adjacent layers (such as the light-emitting layer or cathode), reducing the electron injection barrier, and lowering the device driving voltage. It can also expand the conjugated system of the molecule and provide more electron transport paths. Efficient electron injection and transport help balance electron-hole recombination, making the exciton formation region more concentrated in the light-emitting layer, reducing exciton quenching, and improving luminescence efficiency. In addition, the bistriazine groups increase molecular rigidity, improve the thermal stability of the material, avoid thin film crystallization or phase separation caused by heat during device operation, and extend device life.

[0074] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those 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 invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electron transport layer material, characterized in that, A compound having a structure of Formula I: ； wherein, R is independently selected from substituted or unsubstituted C1-C8 alkyl; R1, R2, R3 are each independently selected from hydrogen, cyano; n1 is independently selected from 0, 1, 2, 3; n2, n3 are independently selected from 0, 1, 2, 3, 4; Ar1, Ar2, Ar3, Ar4 are each independently selected from substituted or unsubstituted C6-C30 aryl, substituted or unsubstituted C3-C30 heteroaryl, wherein the heteroatom contains at least one of O, S, N, Si, Se.

2. The electron transport layer material according to claim 1, characterized in that, R is independently selected from substituted or unsubstituted C1-C8 alkyl; 3. The electron transport layer material according to claim 1, wherein Ar1, Ar2, Ar3, Ar4 are each independently selected from substituted or unsubstituted C6-C20 aryl, substituted or unsubstituted C5-C18 heteroaryl, wherein the heteroatom contains at least one of O, S, N, Si, Se.

4. The electron transport layer material according to claim 1, characterized in that, Ar1, Ar2, Ar3, Ar4 are each independently selected from the following structures: ； * indicates the point of attachment of the group.

5. The electron transport layer material of claim 1, wherein, the "substituted or unsubstituted" means substituted with one, two or more of the following substituents: cyano, halogen, methyl, ethyl, propyl, butyl, t-butyl, cyclopentane, cyclohexane, phenyl, biphenyl, naphthyl, fluorenyl, dimethylfluorenyl, phenanthryl, triphenylenyl, carbazolyl, furanyl, thienyl, pyrrolyl, pyridyl, benzofuranyl, benzothienyl, isobenzofuranyl, dibenzofuranyl, dibenzothienyl, or a substituent connected with two or more of the substituents shown above, or no substituent.

6. The electron transport layer material according to claim 1, wherein the chemical formula I has any one of the following compounds 1-548: 。 7. An organic electroluminescent device, characterized by The organic electroluminescent device comprises an anode, a cathode, and an organic layer disposed between the anode and the cathode; the organic layer contains the electron transport layer material of any one of claims 1 to 6.

8. The organic electroluminescent device according to claim 7, characterized in that The organic layer in the organic electroluminescent device is a single-layer structure or a multi-layer structure of two or more organic layers.

9. The organic electroluminescent device according to claim 7, characterized in that, The organic electroluminescent device comprises a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting auxiliary layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer; the electron transport layer contains the electron transport layer material of any one of claims 1 to 6.

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