An organic electron transport material, a preparation method therefor and use thereof

Abstract

The present application relates to a kind of organic electron transport material and its preparation method and application, which is with triazine group as center core, pyridine is the conjugated organic small molecule material of outer ring substitution, the synthetic route of the organic small molecule material is simple, low in cost, higher yield, less environmental pollution;With the organic small molecule as electron transport layer, the problem of charge injection imbalance is well solved, especially in quantum dot light emitting diode (QLEDs), greatly improves the QLEDs device performance and stability, which has extremely great significance to the application field of QLEDs.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic electroluminescence, in particular to an organic electron transport material and a preparation method and application thereof. BACKGROUND

[0002] Quantum dot materials (QDs) are beneficial to realize the next generation of color gamut, high contrast, large area and flexible display, and thus are more attractive. However, QD-based display applications still have challenges in device performance, Cd-based QD material toxicity and QD pixel patterning, which greatly limit the development and application of QLEDs, and new materials and device optimization strategies are urgently needed in the commercial field to solve these problems. At present, the improvement of the performance of quantum dot light emitting diodes (QLEDs) is mainly based on the device structure of an organic hole transport layer / QDs / inorganic material, and inorganic nanomaterials such as ZnO, ZnMg x O and the like are used as electron transport layers (ETLs) to realize high performance of the device. However, such inorganic electron transport layers have many disadvantages, such as more surface defect states, too high electron mobility, easy aggregation, and difficulty in preservation, etc. This easily leads to quantum dot luminescence quenching, unbalanced electron and hole injection, and non-radiative Auger recombination. However, the research on organic electron transport layers in QLEDs is still relatively less at present, mainly because the LUMO energy level of the previous organic electron transport layer is too low, the conduction band energy level of the quantum dot is quite different, the electron injection barrier is large, and the mobility is often lower than the hole mobility, so the performance of the device based on the organic electron transport layer is often not ideal.

[0003] In order to overcome the above problems and further improve the electroluminescent performance of quantum dot light emitting diodes, it is necessary to develop and design an electron transport layer material with appropriate energy level and matching electron mobility and hole mobility. SUMMARY

[0004] In view of the technical problems existing in the prior art, the primary object of the present application is to provide an organic electron transport material and a preparation method and application thereof. The organic electron transport material is an organic small molecule material, the organic small molecule material takes triazine as a core and pyridine as a peripheral substituent, has good thermal stability, a deeper LUMO energy level, and can realize high efficiency and high stability of QLEDs devices as an electron transport layer material.

[0005] Another object of the present application is to provide a synthesis method of the organic electron transport material.

[0006] Another object of the present application is to provide an organic electroluminescent device, in particular a quantum dot light emitting diode, which has high brightness and luminous efficiency and exhibits excellent luminescent stability.

[0007] Another object of the present application is to provide the application of the organic electron transport material in organic photovoltaic devices, organic thin film transistors, organic photodetectors, organic field effect transistors.

[0008] In order to achieve the above object, the present application at least provides the following technical solutions:

[0009] The present application provides an organic electron transport material, which is an organic small molecule material with the following structural formula (I):

[0010]

[0011] The present application provides an organic electroluminescent device, which comprises an anode, a cathode and an organic layer, the organic layer at least comprising a hole injection layer, a hole transport layer, an electron injection layer and an electron transport layer, the electron transport layer at least comprising the above-mentioned organic electron transport material.

[0012] Further, the organic layer is sequentially stacked by the hole injection layer, the hole transport layer, the light-emitting layer, the electron transport layer and the electron injection layer.

[0013] Further, the organic electroluminescent device is a quantum dot light-emitting diode, and the light-emitting layer is a quantum dot light-emitting layer.

[0014] Further, the electron transport layer is the above-mentioned organic electron transport material.

[0015] The present application provides a preparation method of the organic electron transport material, comprising the following steps:

[0016] 2,4,6-tris(4-bromophenyl)-1,3,5-triazine, 4-pyridine boronic acid pinacol ester or 4-pyridine boronic acid, a catalyst, a basic solution and a polar solvent are mixed with water, and after replacing the inert gas, the mixture is reacted at 80-110℃ for 4-12 hours. After the reaction is completed, the solution is cooled to room temperature, and after extraction, the organic phase is collected, dried and separated to obtain white solid. Finally, the organic electron transport material is dried in a vacuum environment.

[0017] Further, the catalyst comprises at least one of Pd(pph3)4 and PdCl2(dppf); the basic solution comprises at least one of K2CO3, Na2CO3 and Cs2CO3 solution; and the polar solvent comprises at least one of toluene, dioxane and dichloromethane.

[0018] Further, the step of drying and separating is specifically drying by anhydrous sodium sulfate, solvent rotary evaporation, and separation by a chloroform:methanol silica gel chromatography column to obtain white solid.

[0019] Further, the molar ratio of the 2,4,6-tris(4-bromophenyl)-1,3,5-triazine to the catalyst is 1:(0.03-0.09); the molar ratio of the 2,4,6-tris(4-bromophenyl)-1,3,5-triazine to the 4-pyridine boronic acid pinacol ester or 4-pyridine boronic acid is 1:(3-4).

[0020] Compared with the prior art, the present application has at least the following beneficial effects:

[0021] (1) The synthesis process of the organic electron transport material preparation method provided by the present application is simple, easy to purify, has low raw material cost, high yield, and small environmental pollution, and is conducive to industrialized production.

[0022] (2) The organic small-molecule electron transport material has good thermal stability.

[0023] (3) The organic electron transport material provided by the present application introduces an electron-deficient pyridine group on the periphery of the triazine nucleus, and the pyridine group and the triazine have good electron transport capacity, which further enhances the electron transport capacity and stability of the electron transport material.

[0024] (4) The electron transport material has a deep LUMO energy level, which is conducive to the injection of electrons from the cathode into the quantum dot light-emitting layer when applied to a quantum dot light-emitting diode device.

[0025] (5) The organic electron transport material provided by the present application, as an electron transport layer, is applied in a green light and a red light quantum dot light-emitting diode device, which is conducive to the injection of electrons from the cathode into the quantum dot light-emitting layer, enhances the recombination of electrons and holes, helps to achieve the balance of electron-hole injection, greatly improves the brightness and light-emitting efficiency of the device. At the same time, the light-emitting stability of the device in a large current range is realized. This is very important for the commercialization of quantum dot light-emitting diodes in display. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The nuclear magnetic resonance hydrogen spectrum of the Py-T2T material prepared in Example 1 is shown in the figure.

[0027] Figure 2 The nuclear magnetic resonance carbon spectrum of the Py-T2T material prepared in Example 1 is shown in the figure.

[0028] Figure 3 The thermogravimetric curve of the Py-T2T material prepared in Example 1 is shown in the figure.

[0029] Figure 4 The structure diagram of the green light InP QELDs device prepared in Example 2 is shown in the figure.

[0030] Figure 5Current density-voltage-brightness curve graph of InP green quantum dot light emitting diode prepared for Example 2 and Comparative Example 1.

[0031] Figure 6 Brightness-current efficiency curve graph of InP green quantum dot light emitting diode prepared for Example 2 and Comparative Example 1.

[0032] Figure 7 Electroluminescence spectrum graph of InP green quantum dot light emitting diode prepared for Example 2.

[0033] Figure 8 Electroluminescence spectrum graph of InP green quantum dot light emitting diode prepared for Comparative Example 1.

[0034] Figure 9 Current density-voltage-brightness curve graph of InP red quantum dot light emitting diode prepared for Example 3 and Comparative Example 2.

[0035] Figure 10 Brightness-current efficiency spectrum graph of InP red quantum dot light emitting diode prepared for Example 3 and Comparative Example 2. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings of the present application. The described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application. In the following examples, the experimental methods are conventional methods unless otherwise specified, and the reagents and materials are commercially available unless otherwise specified.

[0037] The terms "have", "contain", "include", "comprise" and the like used in the present specification are open terms, indicating the presence of the stated features, but not excluding additional features. Unless the context clearly indicates otherwise.

[0038] One core aspect of the present application is to provide an organic small molecule material with the following structural formula (I) for use as an organic electron transport material.

[0039]

[0040] Another aspect of the present application is to provide the use of the organic electron transport material in an organic electroluminescent device, especially in a quantum dot light emitting diode.

[0041] In an embodiment, the organic electroluminescent device comprises at least an anode, a cathode and an organic layer, and the organic layer comprises at least a hole injection layer, a hole transport layer, an electron injection layer and an electron transport layer; in a preferred embodiment, the organic layer is stacked by the hole injection layer, the hole transport layer, the electron transport layer and the electron injection layer; in another preferred embodiment, the organic layer is stacked by the hole injection layer, the hole transport layer, the light-emitting layer, the electron transport layer and the electron injection layer; in another preferred embodiment, the organic layer is stacked by the hole injection layer, the hole transport layer, the hole blocking layer, the electron transport layer and the electron injection layer; in another preferred embodiment, the organic layer is stacked by the hole injection layer, the hole transport layer, the hole blocking layer, the light-emitting layer, the electron transport layer and the electron injection layer; preferably, the light-emitting layer is a quantum dot light-emitting layer.

[0042] In an embodiment, the electron transport layer material of the present application comprises at least the organic small molecule material; in another embodiment, the electron transport layer material of the present application is the organic small molecule material.

[0043] Another aspect of the present application is to provide a preparation method of the organic electron transport material, which has a high yield, the obtained organic electron transport material has a high purity, the method is beneficial to industrial production, and the operation is simple.

[0044] The preparation method involves that 2,4,6-tris(4-bromophenyl)-1,3,5-triazine and 4-pyridine boronic acid pinacol ester or 4-pyridine boronic acid are mixed with a catalyst, a basic solution, a polar solvent and water, in another alternative embodiment, 2,4,6-tris(4-bromophenyl)-1,3,5-triazine and 4-pyridine boronic acid are mixed with a catalyst, a basic solution, a polar solvent and water in a molar ratio of (1:3-4), and then the mixture is subjected to displacement of inert gas, and then reacted at 80-110°C for 4-12 hours, after the reaction is completed, the solution is cooled to room temperature, and then extracted, and the organic phase is collected, dried and separated to obtain a white solid, and finally dried in a vacuum environment to obtain the organic electron transport material.

[0045] Example 1

[0046] The preparation reaction equation of Py-T2T (i.e. the organic electron transport material of the present application) is as follows:

[0047]

[0048] 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (3.28 g, 6.0 mmol), pinacol 4-pyridineboronic acid (4.43 g, 21.6 mmol), tetrakis(triphenylphosphine)palladium (0.37 g, 0.32 mmol), 2M sodium carbonate solution (50 mL), toluene solvent (250 mL), and water (50 mL) were mixed, purged with nitrogen three times, and reacted at 85 °C for 5 hours. The reaction was monitored by LC-MS. After the reaction was complete, the solution was cooled to room temperature, and an appropriate amount of deionized water was added. The mixture was extracted with chloroform, and the organic phase was collected. The solution was dried over anhydrous sodium sulfate and evaporated to dryness with solvent. The product was then separated by chloroform:methanol (30:1) silica gel chromatography to obtain 2.06 g of white solid (63.5% yield). Finally, the product was dried under vacuum for 24 hours.

[0049] according to Figure 1 The 1H NMR spectrum of Py-T2T shows that... 1 H NMR (600MHz, CDCl3) δ8.90–8.85(m,6H),8.75–8.71(m,6H),7.87–7.82(m,6H),7.62–7.58(m,6H).

[0050] according to Figure 2 The carbon NMR spectrum of Py-T2T shows that... 13 C NMR (101MHz, CDCl3) δ171.13,150.51,147.32,142.13,136.57,129.73,127.28,121.63.

[0051] HPLC purity: >99.8%.

[0052] Examples 2 and 3 are quantum dot light-emitting diode devices fabricated using the organic electron transport layer material from Example 1. The electron transport layer used in Comparative Examples 1 and 2 is commercially available ZnO nanoparticles (purchased from Pujiafu Optoelectronics Technology Co., Ltd.).

[0053] Example 2: Fabrication of Green Quantum Dot Light Emitting Diode

[0054] The ITO substrate was ultrasonically cleaned sequentially with deionized water, acetone, and isopropanol, and then dried before undergoing O2 plasma cleaning for 10 min. PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid) was then spin-coated onto the cleaned ITO substrate at a spin speed of 3000 r / min for 30 s. Afterward, it was annealed at 150 °C for 20 min and cooled before being transferred to a glove box to obtain a hole injection layer (HIL) on the ITO substrate.

[0055] Next, a PVK chlorobenzene solution with a concentration of 4 mg / mL was spin-coated on the HIL layer by a spin-coating process at a rotation speed of 2000 r / min for 30 s, and then annealed at 120 degrees for 20 minutes to obtain a hole transport layer (HTL) on the HIL layer.

[0056] Next, a green InP quantum dot n-octane solution with a concentration of 10 mg / mL was spin-coated on the HTL layer by a spin-coating process at a rotation speed of 2000 r / min for 30 s, and then annealed at 100 degrees for 20 minutes to obtain a quantum dot light-emitting layer (EML) on the HTL layer.

[0057] Next, a Py-T2T electron transport layer (ETL) with a film thickness of 20-40 nm was vacuum deposited on the EML layer at a deposition rate of 0.1 A / s, and the thickness of the Py-T2T layer in this preferred embodiment was 40 nm.

[0058] Next, a LiF electron injection layer (EIL) with a film thickness of 1 nm was vacuum deposited on the ETL layer at a deposition rate of 0.1 A / s.

[0059] Next, an Al cathode with a film thickness of 100 nm was vacuum deposited on the EIL layer at a deposition rate of 0.1 A / s. A green quantum dot light-emitting diode device with a structure of ITO / PEDOT:PSS / PVK / green InP QDs / Py-T2T / LiF / Al was formed. The structure diagram thereof is shown in FIG. 2. Figure 4

[0060] Example 3 Red Quantum Dot Light-Emitting Diode

[0061] In this example, a red quantum dot light-emitting diode device with a structure of ITO / PEDOT:PSS / PVK / red InP QDs / Py-T2T / LiF / Al was formed, and the preparation process was the same as that of Example 2.

[0062] The difference from Example 2 is only that the quantum dot light-emitting layer is replaced by red InP quantum dots instead of green InP quantum dots.

[0063] Comparative Example 1 Green Quantum Dot Light-Emitting Diode

[0064] In this comparative example, a green quantum dot light-emitting diode device with a structure of ITO / PEDOT:PSS / PVK / green InP QDs / ZnO nanoparticles / Al was formed, and ZnO nanoparticles were used as an electron transport layer material, and LiF was not used as an electron injection layer. The corresponding preparation process was the same as that of Example 2.

[0065] Comparative Example 2 Red Quantum Dot Light-Emitting Diode​​​​

[0066] The red quantum dot light emitting diode device of ITO / PEDOT:PSS / PVK / red light InP QDs / ZnO nanoparticles / Al was formed in the comparative example. The corresponding preparation process was the same as that of comparative example 1.

[0067] Figure 3 The thermal gravimetric curve of the organic small molecule electron transport material Py-T2T prepared in example 1 is shown in the figure, and it can be known from the figure that the thermal decomposition temperature of the organic small molecule material Py-T2T is 477 DEG C. The thermal decomposition temperature indicates that the small molecule material has good thermal stability, and as an electron transport layer material, it fully meets the subsequent device heating process requirements and has good thermal stability.

[0068] Table 1

[0069]

[0070] In combination with Figure 5 to Figure 6 , Figure 9 to Figure 10 and Table 1, it can be seen that the quantum dot light emitting diode prepared by using the organic electron transport material Py-T2T of the application has excellent light emitting performance. For green light InP QLEDs, compared with comparative example 1, the turn-on voltage is reduced from 2.6V to 2.1V, the luminous brightness is increased from 3846 cd / m 2 to 14393 cd / m 2 , and the current efficiency is increased from 9.7 cd / A to 74.1 cd / A. At the same time, from the comparison of the EL spectrum of Figure 7 and Figure 8 , it can be seen that under the excitation current in the range of 1-100mA, compared with comparative example 1, the light emitting peak position and waveform of the quantum dot light emitting diode device with Py-T2T as the electron transport layer have almost no change, showing excellent light emitting stability. At the same time, the performance of the red light device has also been greatly improved, the current efficiency is increased from 3.7 cd / A to 43.0 cd / A. The brightness is increased from 2777 cd / m 2 to 4187 cd / m 2 .

[0071] The quantum dot light emitting diode prepared by using Py-T2T as the electron transport layer material of the application shows excellent brightness and light emitting efficiency. Compared with the traditional ZnO electron transport material device, the quantum dot light emitting diode of the application shows excellent light emitting stability under a large current condition.

[0072] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A quantum dot light-emitting diode, characterized in that, It includes an anode, a cathode, and an organic layer. The organic layer is composed of a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and an electron injection layer stacked sequentially. The electron transport layer is an organic small molecule material with the following structural formula (Ⅰ): Equation (Ⅰ).

2. The quantum dot light-emitting diode according to claim 1, characterized in that, The quantum dot emitting layer is a red quantum dot.

3. The quantum dot light-emitting diode according to claim 1, characterized in that, The quantum dot emitting layer is made of green quantum dots.

4. The quantum dot light-emitting diode according to claim 2, characterized in that, The red quantum dot is a red InP quantum dot.

5. The quantum dot light-emitting diode according to claim 3, characterized in that, The green quantum dot is a green InP quantum dot.

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