OLED device containing polydopamine modified carbon nanotubes and preparation method thereof

Abstract

The invention belongs to the technical field of photoelectric materials, and relates to an OLED device containing a polydopamine modified carbon nanotube and a preparation method of the OLED device. The anode electrode layer is formed on the substrate; the organic light-emitting unit is formed on the anode electrode layer, the organic light-emitting unit sequentially comprises a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer and an electron injection layer from bottom to top, and the light-emitting layer is made of a composite material containing polydopamine modified carbon nanotubes; and the cathode electrode layer is formed on the organic light-emitting unit. The polydopamine modification is functional modification, and solves the problems of poor dispersibility and interface cohesiveness of the traditional carbon nanotubes in the OLED device, thereby improving the photoelectric properties of the OLED device.

Description

Technical Field

[0001] The invention belongs to the technical field of optoelectronic materials, and in particular relates to an OLED device containing polydopamine-modified carbon nanotubes and a preparation method thereof. Background Art

[0002] Organic electroluminescent (OLED) devices are regarded as a new generation of display technology with broad application prospects due to their advantages such as self-luminescence, high contrast, fast response, ultra-thin and lightweight, and flexible display. However, OLED devices are inevitably affected by a variety of complex factors, and their luminous efficiency and mechanical stability still have room for improvement. In particular, material properties and preparation processes will limit their performance. Currently, improving the performance of OLED devices by modifying organic light-emitting materials is one of the key research directions.

[0003] The Chinese patent application with publication number CN 106831448 A discloses a new type of aromatic amine luminescent material and its application in OLED devices, and specifically discloses a high-efficiency OLED device with benzo 9,9-dimethylfluorene compounds as luminescent materials. The material has the characteristics of excellent carrier mobility, high glass transition temperature, low driving voltage and long service life. After the new aromatic amine compound material is applied to the device, its luminous efficiency, power efficiency and external quantum efficiency are significantly improved, and the device life is also significantly extended. After 500 hours of accelerated aging test, the brightness can still maintain more than 80% of the initial value, and the color coordinate change is less than 0.02. The Chinese patent application with publication number CN 109887959 B discloses an OLED device with high stability and its preparation method, and specifically discloses a method for improving the stability of the device by optimizing the isolation column and electrode structure. The method effectively increases the pixel aperture ratio and improves the stability of the screen by not setting an insulating material layer under the isolation column. However, although this structural design improves the stability and luminous efficiency of the device, it may pose challenges to the long-term stability of the device.

[0004] Carbon nanotubes (CNTs) have attracted much attention due to their unique electrical and mechanical properties. However, their poor dispersibility and interfacial adhesion in organic solvents have greatly restricted their effective application in OLED devices. Polydopamine (PDA), as an excellent functional material, can improve the dispersibility and interfacial adhesion of CNTs by virtue of its own adhesion and reactivity, thereby improving the performance of OLED devices. Therefore, it is of great significance to study the application of polydopamine-modified carbon nanotubes in improving the optoelectronic performance of OLED devices, and it is also one of the current research hotspots. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides an OLED device containing polydopamine-modified carbon nanotubes and a preparation method thereof. The polydopamine modification is a functional modification that solves the problem of poor dispersion and interface adhesion of traditional carbon nanotubes in OLED devices, thereby improving the photoelectric performance of OLED devices.

[0006] The technical solution provided by the present invention is as follows:

[0007] The present invention provides an OLED device containing polydopamine-modified carbon nanotubes, comprising: substrate; an anode electrode layer formed on the substrate; An organic light-emitting unit formed on the anode electrode layer, the organic light-emitting unit comprising, from bottom to top, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer and an electron injection layer, wherein the light-emitting layer is a composite material containing polydopamine-modified carbon nanotubes; A cathode electrode layer is formed on the organic light emitting unit.

[0008] The present invention also provides a method for preparing the above-mentioned OLED device containing polydopamine-modified carbon nanotubes, wherein the polydopamine-modified carbon nanotubes and the light-emitting layer material are dispersed by resonant acoustic dispersion to obtain a composite material containing polydopamine-modified carbon nanotubes, and a hole injection layer, a hole transport layer, a light-emitting layer containing polydopamine-modified carbon nanotubes, an electron transport layer, an electron injection layer and a cathode electrode layer are sequentially deposited on an OLED device substrate having an anode electrode layer by vacuum evaporation technology.

[0009] Furthermore, the mass ratio of the polydopamine-modified carbon nanotubes to the light-emitting layer material is 1-10:100.

[0010] Furthermore, the light-emitting layer material is a mixture of mCP and Ir(ppy)_3, and the mass ratio of mCP to Ir(ppy)_3 is 1:(1~3).

[0011] Furthermore, the frequency of the resonant sound dispersion is 20-40 kHz, the time is 20-60 min, and the temperature is 20-40° C.; the vacuum degree of the vacuum evaporation is 1×10 -4 ~5×10 -4 Pa, the temperature is 100~200℃, and the evaporation rate is controlled at 0.1Å / s ~ 1Å / s.

[0012] Furthermore, the preparation method of polydopamine-modified carbon nanotubes comprises the following steps: The carbon nanotubes are added into a mixed solution consisting of deionized water and anhydrous ethanol and dispersed by magnetic stirring; Tris buffer was added to the solution in the above step to adjust the pH to 5-10, and then dopamine hydrochloride was added. After electromagnetic stirring, the supernatant was poured out to collect the solid precipitate, which was washed and dried to obtain polydopamine-modified carbon nanotubes.

[0013] Furthermore, the mass ratio of dopamine hydrochloride to carbon nanotubes is (1-3):1.

[0014] Furthermore, the carbon nanotube is a hollow tubular structure formed by curling one or more layers of graphene sheets, with a tube diameter of 1-50 nm and a tube length of 1-10 μm.

[0015] Furthermore, the mass ratio of the deionized water to the anhydrous ethanol is 5:1-1:5, and the carbon nanotubes account for 10%-30% of the total volume of the deionized water and the anhydrous ethanol.

[0016] Furthermore, the magnetic stirring dispersion time is 20 min to 2 h; the rotation speed of the electromagnetic stirring is 100 to 300 rpm, and the reaction time is 6 to 12 h.

[0017] Beneficial Effects

[0018] The present invention provides a polydopamine-modified carbon nanotube, which utilizes the unique electrical and mechanical properties of carbon nanotubes and improves the dispersibility and interfacial bonding of carbon nanotubes through the adhesion and reactivity of polydopamine to form a composite material with excellent performance; the luminous efficiency of OLED devices is improved by modifying carbon nanotubes with polydopamine; the compatibility of polydopamine with other materials in OLED devices is utilized to enhance the interfacial bonding force between carbon nanotubes and various layers of the device, thereby forming an OLED device with good mechanical stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a structural diagram of the OLED device prepared by the present invention, from the lower layer to the upper layer, there are transparent substrate layer 1, ITO 2, hole injection layer 3, hole transport layer 4, light-emitting layer 5, electron transport layer 6, electron injection layer 7, cathode electrode layer 8, wherein the light-emitting layer involves the polydopamine-modified carbon nanotube material of the present invention. DETAILED DESCRIPTION

[0020] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0021] The experimental methods used in the embodiments of the present invention are conventional methods unless otherwise specified.

[0022] The manufacturers and models of some raw materials in the present invention are as follows:

[0023] Carbon nanotubes, product number: 914533, Beijing Bailingwei Technology Co., Ltd., outer diameter: 30-60 nm, inner diameter: 20-50 nm, length: 1-10 um; anhydrous ethanol, Sigma-Aldrich, 100% purity; tris (hydroxymethyl) aminomethane Tris buffer, product number: PCL-2023HC002-500ml, Beijing Bailingwei Technology Co., Ltd., pH = 7.5; dopamine hydrochloride, CAS: 62-31-7, Beijing Bailingwei Technology Co., Ltd., 98% purity; NPB (N, N'-diphenyl-N, N'-(1-naphthyl)-1, 1'-biphenyl-4, 4'-diamine), CAS: 123847-85-8, Beijing Bailingwei Technology Co., Ltd., 99% purity; TCTA (4, 4', 4"-tris (carbazole-9-yl) triphenylamine), CAS: 139092-78-7, Beijing Bailingwei Technology Co., Ltd., 99% purity; mCP (1,3-dicarbazole-9-ylbenzene) CAS: 550378-78-4 Beijing Bailingwei Technology Co., Ltd., 99% purity Ir(ppy)_3 (tris(2-phenylpyridine)iridium), CAS: 94928-86-6, Beijing Bailingwei Technology Co., Ltd., 99% purity; Alq3 (8-hydroxyquinoline aluminum), product number: 252565, Sigma-Aldrich, 98.5% purity; lithium fluoride (LiF), product number: L104230, Shanghai Aladdin Biochemical Technology Co., Ltd., 99.9% purity.

[0024] Synthesis example 1

[0025] First, a mixture of carbon nanotubes (3 g), deionized water (10 g) and anhydrous ethanol (50 g) was added to a reaction container and dispersed under magnetic stirring at room temperature for 20 min; then the pH of the reaction system was adjusted to 5 by using Tris buffer; dopamine hydrochloride (1 g) was added to the reaction container, and after electromagnetic stirring for 6 h, the supernatant was poured out to collect the solid precipitate, wherein the speed of electromagnetic stirring was 100-300 rpm; finally, the polydopamine-modified carbon nanotubes PDA-CNT-1 were obtained by washing with deionized water and drying.

[0026] Synthesis example 2

[0027] First, carbon nanotubes (3 g) and a mixture of solvent deionized water (20 g) and anhydrous ethanol (40 g) are added to a reaction container and dispersed under magnetic stirring at room temperature for 40 minutes; then the pH of the reaction system is adjusted to 7 by using tris (hydroxymethyl) aminomethane Tris buffer; dopamine hydrochloride (2 g) is added to the reaction container, and after electromagnetic stirring for 8 hours, the supernatant is poured out to collect the solid precipitate, wherein the speed of electromagnetic stirring is 100~300 rpm; finally, the polydopamine-modified carbon nanotubes PDA-CNT-2 are obtained by washing with deionized water and drying.

[0028] Synthesis example 3

[0029] First, carbon nanotubes (3 g) and a mixture of solvent deionized water (30 g) and anhydrous ethanol (30 g) are added to a reaction container and dispersed under magnetic stirring at room temperature for 80 minutes; then the pH of the reaction system is adjusted to 8 by using tris (hydroxymethyl) aminomethane Tris buffer; dopamine hydrochloride (3 g) is then added to the reaction container, and after electromagnetic stirring for 10 hours, the supernatant is poured out to collect the solid precipitate, wherein the speed of electromagnetic stirring is 100-300 rpm; finally, the polydopamine-modified carbon nanotubes PDA-CNT-3 are obtained by washing with deionized water and drying.

[0030] Synthesis example 4

[0031] First, carbon nanotubes (3 g) and a mixture of solvent deionized water (40 g) and anhydrous ethanol (20 g) are added to a reaction container and dispersed under magnetic stirring at room temperature for 120 minutes; then the pH of the reaction system is adjusted to 10 by using tris (hydroxymethyl) aminomethane Tris buffer; dopamine hydrochloride (3 g) is added to the reaction container, and after electromagnetic stirring for 12 hours, the supernatant is poured out to collect the solid precipitate, wherein the speed of electromagnetic stirring is 100~300 rpm; finally, the polydopamine-modified carbon nanotubes PDA-CNT-4 are obtained by washing with deionized water and drying.

[0032] Example 1-1

[0033] like Figure 1 As shown, this embodiment provides an OLED device containing polydopamine-modified carbon nanotubes and a preparation method thereof, comprising: substrate; an anode electrode layer formed on the substrate; An organic light-emitting unit formed on the anode electrode layer, the organic light-emitting unit comprising, from bottom to top, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer and an electron injection layer, wherein the light-emitting layer is a composite material containing polydopamine-modified carbon nanotubes; A cathode electrode layer is formed on the organic light emitting unit.

[0034] Specifically, the preparation method comprises the following steps:

[0035] The ITO anode electrode layer (film thickness of 150 nm) was washed, that is, alkaline washing, pure water washing, drying and then ultraviolet-ozone washing were performed in sequence to remove organic residues on the ITO surface.

[0036] The ITO anode electrode layer 2 after the above washing is formed on the transparent substrate layer 1, and NPB (N, N'-diphenyl-N, N'-(1-naphthyl)-1, 1'-biphenyl-4, 4'-diamine) is evaporated using a vacuum evaporation device with a film thickness of 10nm. This layer is used as the hole injection layer 3. Then, TCTA (4, 4', 4"-tri(carbazole-9-yl) triphenylamine) is evaporated with a thickness of 20nm as the hole transport layer 4.

[0037] After the above-mentioned hole transport material evaporation is completed, the vacuum evaporation of the light-emitting layer 5 of the OLED light-emitting device is continued, and the OLED light-emitting layer 5 includes the light-emitting material, namely a mixture of mCP and Ir(ppy)_3 and PDA-CNT-1. The specific preparation method includes: polydopamine-modified carbon nanotubes and the light-emitting layer material are dispersed by resonant acoustic dispersion to obtain a composite material containing polydopamine-modified carbon nanotubes, wherein the mass ratio of mCP and Ir(ppy)_3 is 1:2, the doping ratio of PDA-CNT-1 is 1% by weight of the light-emitting material, the thickness of the light-emitting layer is 25nm, the frequency of the resonant acoustic dispersion is 20~40 kHz, the time is 20~60min, and the temperature is 20~40℃.

[0038] After the above-mentioned light-emitting layer, the electron transport layer material is vacuum-evaporated and Alq3 (8-hydroxyquinoline aluminum) is formed. The vacuum-evaporated film thickness of the material is 20 nm. This layer is the electron transport layer 6.

[0039] On the electron transport layer 6 , a lithium fluoride (LiF) layer with a thickness of 1 nm was formed by a vacuum evaporation device. This layer was the electron injection layer 7 .

[0040] On the electron injection layer 7 , an aluminum (Al) layer with a film thickness of 80 nm was formed by a vacuum evaporation device. This layer was used as the cathode electrode layer 8 .

[0041] The vacuum degree of the above vacuum evaporation is 1×10 -4 ~5×10 -4 Pa, the temperature is 100~200℃, the evaporation rate is controlled at 0.1Å / s ~ 1Å / s, and preferably, the temperature of the vacuum evaporation substrate is controlled at 80°C ~ 150°C, and the pressure in the evaporation chamber is less than 4×10 -4Pa, the evaporation rate is controlled at 0.1Å / s ~ 1Å / s.

[0042] Example 1-2

[0043] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-1 is 3% by weight.

[0044] Examples 1-3

[0045] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-1 is 5% by weight.

[0046] Example 2-1

[0047] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-2 is 1% by weight.

[0048] Example 2-2

[0049] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-2 is 3% by weight.

[0050] Example 2-3

[0051] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-2 is 5% by weight.

[0052] Example 3-1

[0053] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-3 is 1% by weight.

[0054] Example 3-2

[0055] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-3 is 3% by weight.

[0056] Example 3-3

[0057] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-3 is 5% by weight.

[0058] Example 4-1

[0059] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-4 is 1% by weight.

[0060] Example 4-2

[0061] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-4 is 3% by weight.

[0062] Example 4-3

[0063] The difference between this embodiment and embodiment 1 is that in the light-emitting layer of the OLED device, the doping ratio of PDA-CNT-4 is 5% by weight.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that in the light-emitting layer of the OLED device, the CNT doping ratio is 3% by weight, and the PDA-CNT-1 doping ratio is 0.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that in the light-emitting layer of the OLED device, the CNT doping ratio is 0 and the PDA-CNT-1 doping ratio is 0.

[0068] After the OLED light emitting device is completed as described above, the anode and cathode are connected with a known driving circuit, and the luminous efficiency, luminous spectrum and current-voltage characteristics of the device are measured. The results are shown in Table 1.

[0069] Photoelectric performance test: The prepared OLED device was subjected to current density-voltage-brightness test and current efficiency-brightness-power efficiency test. The test conditions are: at an ambient temperature of 25°C, the device was uniformly illuminated with a standard light source, and the current density, brightness, and corresponding current efficiency and power efficiency at different voltages were recorded; by placing the OLED device in an integrating sphere and connecting it to a spectrometer, the voltage provided by the source meter was adjusted until the device brightness reached 1000 cd / m², and the spectral distribution of the light emitted by the device was recorded and analyzed. The test conditions are: ambient temperature of 25°C, the spectrometer resolution was set to 1nm, and the scanning range covered the visible light region.

[0070] Mechanical stability test: The test method of the tensile test is IEC 62666-2:200, and the number of stretching times required for the brightness to drop from the initial value to half is recorded; the test method of the bending test is JESD22-B111 - JEDEC, and the number of bending times required for the brightness to drop from the initial value to half is recorded; the test method of the friction test is: use 300-grit sandpaper as the friction surface, and record the number of friction times required for the brightness to drop from the initial value to half; the friction rate is set to 1Hz, and the friction force is 100g weight load.

[0071] Table 1 Results of the fabricated OLED light-emitting devices

[0072]

[0073] It can be seen from the results in Table 1 that the present invention uses polydopamine-modified carbon nanotubes for the light-emitting layer of the OLED device, and the brightness of the device remains almost unchanged, but the luminous efficiency, bending times, stretching times and friction times are greatly improved, which significantly improves the device life.

Claims

1. An OLED device containing polydopamine-modified carbon nanotubes, characterized in that: include: substrate; an anode electrode layer formed on the substrate; An organic light-emitting unit formed on the anode electrode layer, the organic light-emitting unit comprising, from bottom to top, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer and an electron injection layer, wherein the light-emitting layer is a composite material containing polydopamine-modified carbon nanotubes; A cathode electrode layer is formed on the organic light emitting unit.

2. A method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 1, characterized in that: A composite material containing polydopamine-modified carbon nanotubes is obtained by resonant acoustic dispersion of polydopamine-modified carbon nanotubes and a light-emitting layer material. A hole injection layer, a hole transport layer, a light-emitting layer containing polydopamine-modified carbon nanotubes, an electron transport layer, an electron injection layer and a cathode electrode layer are sequentially deposited on an OLED device substrate having an anode electrode layer by vacuum evaporation technology.

3. The method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 2, characterized in that: The mass ratio of the polydopamine modified carbon nanotubes to the light-emitting layer material is 1-10:

100.

4. The method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 2, characterized in that: The light-emitting layer material is a mixture of mCP and Ir(ppy)_3, and the mass ratio of mCP to Ir(ppy)_3 is 1:(1~3).

5. The method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 2, characterized in that: The frequency of the resonant sound dispersion is 20-40 kHz, the time is 20-60 min, and the temperature is 20-40°C; the vacuum degree of the vacuum evaporation is 1×10 -4 ~5×10 -4 Pa, the temperature is 100~200℃, and the evaporation rate is controlled at 0.1Å / s ~ 1Å / s.

6. The method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 2, characterized in that: The method for preparing polydopamine-modified carbon nanotubes comprises the following steps: The carbon nanotubes are added into a mixed solution consisting of deionized water and anhydrous ethanol and dispersed by magnetic stirring; Tris buffer was added to the solution in the above step to adjust the pH to 5-10, and then dopamine hydrochloride was added. After electromagnetic stirring, the supernatant was poured out to collect the solid precipitate, which was washed and dried to obtain polydopamine-modified carbon nanotubes.

7. The method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 3, characterized in that: The mass ratio of dopamine hydrochloride to carbon nanotubes is (1-3):

1.

8. The method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 3, characterized in that: The carbon nanotube is a hollow tubular structure, formed by curling one or more layers of graphene sheets, with a tube diameter of 1-50 nm and a tube length of 1-10 μm.

9. The method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 3, characterized in that: The mass ratio of the deionized water to the anhydrous ethanol is 5:1-1:5, and the carbon nanotubes account for 10%-30% of the total volume of the deionized water and the anhydrous ethanol.

10. The method for preparing an OLED device containing polydopamine-modified carbon nanotubes according to claim 3, characterized in that: The magnetic stirring dispersion time is 20min~2h; the rotation speed of the electromagnetic stirring is 100~300rmp, and the reaction time is 6~12h.

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