Compositions for making hole buffer structures for flexible organic optoelectronic devices and uses thereof

Abstract

This invention provides a composition for preparing a hole buffer structure for flexible organic optoelectronic devices and its application. The composition comprises the following components by mass percentage: 0.1wt%~0.4wt% single-walled carbon nanotubes, 0.3wt%~0.5wt% polystyrene sulfonate, 0.1wt%~5wt% p-type dopant, 0.1wt%~0.3wt% anionic surfactant, 0.1wt%~0.3wt% stabilizer, and the balance being a solvent, including water. The single-walled carbon nanotubes have hydrophilic groups on their surface, and the polystyrene sulfonate is adsorbed onto the surface of the single-walled carbon nanotubes through π-π conjugation and electrostatic adsorption, forming polystyrene sulfonate-modified single-walled carbon nanotubes. The hole buffer structure formed based on this composition has a tunable work function, thereby achieving efficient hole injection and electron blocking, significantly reducing device driving voltage, improving luminous efficiency and lifespan, while maintaining excellent mechanical flexibility and low resistance characteristics.

Description

Technical Field

[0001] This invention belongs to the field of flexible organic optoelectronic device technology, specifically relating to a composition for preparing a hole buffer structure for flexible organic optoelectronic devices and its application. Background Technology

[0002] Flexible organic light-emitting diodes (OLEDs), as a third-generation display and solid-state lighting technology, have attracted much attention in consumer electronics and new lighting fields due to their self-emissive, high-brightness, high-contrast, and flexible bending characteristics. The overall performance of OLED devices is highly dependent on the energy level matching and carrier transport characteristics of the internal functional layers. Among them, the hole buffer layer (HBL), located between the anode and the light-emitting layer, plays a dual role in interface modification and charge balance. The material of this layer directly affects the device's performance, such as turn-on voltage and lifetime, by reducing the hole injection barrier and optimizing the carrier migration path.

[0003] Traditional hole buffer layer materials, such as poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS), while exhibiting acceptable conductivity and improving hole injection efficiency to some extent, suffer from acidic properties that can degrade organic layer materials and are prone to cracking after repeated mechanical bending, thus limiting their application in flexible devices. Other inorganic metal oxide hole buffer layers, such as V₂O₅ and MoO₃, offer good work function matching, but their high-temperature annealing or vacuum high-temperature evaporation requirements are unfavorable for flexible fabrication processes, and the brittle films are prone to cracking during repeated bending. In recent years, novel nanomaterials, represented by carbon nanotubes (CNTs), have regained attention. These materials, with their unique quasi-one-dimensional conductive network structure and intrinsic flexibility, possess excellent conductivity, high specific surface area, and good flexibility, providing new ideas for constructing high-performance flexible optoelectronic devices. In particular, single-walled carbon nanotubes (SWCNTs) have a single-atom-layer tube wall structure that gives them higher carrier mobility (>104 cm² / V·s) and more flexible structural deformation capabilities, and their high light transmittance is more suitable for the fabrication of OLED devices.

[0004] Existing technologies have attempted to introduce SWCNTs into OLED hole transport systems, for example, by dispersing SWCNTs into a PEDOT:PSS matrix through physical blending to enhance conductivity. However, this method struggles to address the interfacial contact loss problem caused by SWCNT aggregation. Furthermore, unmodified SWCNTs, due to their uneven surface energy level distribution, are prone to forming carrier transport barriers at the anode interface, affecting hole injection efficiency, leading to increased device drive voltage and accelerated efficiency roll-off.

[0005] Furthermore, traditional flexible OLED devices suffer from poor energy level matching between hole buffer layer materials such as PEDOT:PSS and the emissive layer materials, leading to low interface hole injection efficiency. Additionally, when PEDOT:PSS is used as a hole buffer layer material, its acidity and hygroscopicity make it prone to corroding ITO, resulting in device performance degradation after damp-heat aging. Summary of the Invention

[0006] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions:

[0007] A first aspect of the present invention provides a composition for preparing a hole buffer layer for a flexible organic optoelectronic device, the composition comprising the following components by mass percentage: 0.1wt%~0.4wt% single-walled carbon nanotubes, 0.3wt%~0.5wt% polystyrene sulfonate, 0.1wt%~5wt% p-type dopant, 0.1wt%~0.3wt% anionic surfactant, 0.1wt%~0.3wt% stabilizer, and the balance being a solvent, wherein the solvent comprises water;

[0008] The single-walled carbon nanotubes have hydrophilic groups on their surface, and the polystyrene sulfonate is adsorbed onto the surface of the single-walled carbon nanotubes through π-π conjugation and electrostatic adsorption to form polystyrene sulfonate modified single-walled carbon nanotubes.

[0009] In the composition provided by the present invention, the surface of the single-walled carbon nanotubes (SWCNTs) has hydrophilic groups (such as one or more of carboxyl, hydroxyl, and amino groups), which can improve the water dispersibility and reactivity of the single-walled carbon nanotubes; and the stable dispersibility of the single-walled carbon nanotubes is further improved by utilizing the π-π conjugation and electrostatic adsorption between polystyrene sulfonate (PSS) and the single-walled carbon nanotubes.

[0010] Meanwhile, the functionalization of SWCNTs by PSS provides a carrier basis for P-type doping. Utilizing the strong electron acceptor properties of PSS and P-type dopants, SWCNTs are directionally doped. Specifically, PSS, as a functionalized substrate, provides negative charge sites with its sulfonate groups, which can directionally fix the P-type dopants onto the SWCNT surface through electrostatic interactions and π–π interactions, thereby forming a stable P-type doped structure. This effectively increases the work function of the SWCNT, achieving energy level matching with ITO anodes or other high work function materials, thus improving hole injection efficiency and device stability. In some embodiments, the work function of the SWCNT can be increased from the original 4.3 eV to 4.8 eV~5.4 eV, significantly reducing the barrier energy level between the hole buffer layer formed by this composition and the anode (e.g., 5.1 eV for ITO anodes), thereby improving hole injection efficiency. In this invention, P-type doping of SWCNTs is achieved synergistically by PSS and P-type dopant. Without PSS, SWCNTs tend to agglomerate and settle in aqueous systems, making it difficult for the dopant to disperse uniformly and make sufficient contact with the SWCNTs. This results in a significant decrease in doping efficiency, incomplete charge transfer, and an inability to achieve effective work function regulation, thereby affecting the device's luminous efficiency and lifetime. Therefore, PSS is both a key component for achieving stable dispersion and an important medium for synergistic doping and energy level regulation in this invention. Its absence will lead to a double decrease in the composition's structural stability and energy level regulation capability.

[0011] Furthermore, the composition provided by this invention can be spin-coated or spray-coated to form a film at temperatures below 100°C, which greatly adapts to the requirements of flexible substrates, simplifies the process flow, and reduces manufacturing costs. It also solves the problem in existing technologies where metal oxides (such as MoO3 and V2O5) require high-temperature vapor deposition and have poor mechanical flexibility. Moreover, this composition can use water as a solvent to form an aqueous slurry, reducing the use of organic solvents, aligning with environmental policies, and facilitating large-scale green production.

[0012] In some embodiments, the P-type dopant includes one or more of conductive polymers, metal nanoparticles, or small molecule organic materials (such as organic compounds).

[0013] In some embodiments, the P-type dopant includes one or more combinations of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS), polyaniline (PANI), and polythiophene derivatives (such as PTAA).

[0014] In some embodiments, the metal nanoparticles include gold nanoparticles (Au NPs) and NiO. x Nanoparticles, one or more of MoO3 nanoparticles.

[0015] In some embodiments, the small molecule organic material includes one or more combinations of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinoxaline (F4-TCNQ) and organic acidic dopants (such as fluorobenzoic acid, trifluoroacetic acid, etc.).

[0016] In some embodiments, the anionic surfactant includes, but is not limited to, sodium dodecyl sulfate, sodium lignin sulfonate, sodium maleic acid-acrylic acid copolymer, sodium dodecylbenzene sulfonate, sodium α-olefin sulfonate, sodium lauroyl sarcosinate, sodium decyl sulfate, sodium nonylphenol polyoxyethylene ether sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium alkyl sulfosuccinate, sodium dialkyl succinate, sodium naphthalene sulfonate formaldehyde condensate, or polycarboxylate dispersant.

[0017] In some embodiments, the stabilizer is a polymer stabilizer, including, but not limited to, one or more of the following: polyvinylpyrrolidone, copovidone-polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl ether, polyethylene oxide, polyacrylic acid, sodium polyacrylate, polyvinyl ether-maleic anhydride copolymer, copovidone, polyvinyl butyral, hydroxypropyl methylcellulose, polyethyleneimine, and copolymers thereof.

[0018] A second aspect of the present invention provides a method for preparing the composition for preparing a hole buffer layer of a flexible organic optoelectronic device, comprising:

[0019] Hydrophilic groups are introduced onto the surface of the single-walled carbon nanotubes;

[0020] Single-walled carbon nanotubes with hydrophilic groups were dispersed in an aqueous solution of polystyrene sulfonate to obtain a PSS / SWCNT composite dispersion.

[0021] The PSS / SWCNT composite dispersion was mixed with anionic surfactant and stabilizer, and then emulsified and homogenized sequentially to form an aqueous slurry.

[0022] The P-type dopant is added to the aqueous slurry and uniformly dispersed to obtain a composition for preparing a hole buffer structure for a flexible organic optoelectronic device.

[0023] In some embodiments, introducing hydrophilic groups on the surface of the single-walled carbon nanotubes specifically includes: mixing the single-walled carbon nanotubes with a mixed acid and subjecting them to ultrasonic treatment, wherein the mixed acid includes nitric acid and sulfuric acid in a volume ratio of 1:2 to 1:4, thereby forming hydroxyl and carboxyl groups on the surface of the single-walled carbon nanotubes.

[0024] In some embodiments, the emulsification includes high-shear emulsification at a rotational speed of 5000 rpm to 10000 rpm.

[0025] In some embodiments, the homogenization process includes: high-pressure homogenization under pressure conditions of 500 bar to 900 bar, and cyclically repeated 3 to 5 times.

[0026] After emulsification and high-pressure homogenization under the above conditions, a stable aqueous slurry with a particle size distribution of less than 200 nm can be obtained.

[0027] A third aspect of the present invention provides a hole buffer layer for a flexible organic optoelectronic device, which is formed from the composition described in any of the technical solutions.

[0028] In some embodiments, the work function of the hole buffer layer of the flexible organic optoelectronic device is 4.8 eV to 5.4 eV.

[0029] The work function of the hole buffer layer can be adjusted at least by controlling the concentration of P-type dopant and / or PSS in the composition. Specifically, the hole buffer layer with an appropriate work function can be selected according to the energy levels of the anode and other organic functional layers of the flexible organic optoelectronic device to be prepared.

[0030] A fourth aspect of the present invention provides a flexible organic optoelectronic device, comprising an anode, a hole buffer structure, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode arranged sequentially, wherein the hole buffer structure includes the hole buffer layer of the flexible organic optoelectronic device.

[0031] Based on the synergistic effect of PSS functionalization and P-type doping, the hole buffer layer in the flexible organic optoelectronic device provided by this invention has a suitable energy level system, which can achieve efficient hole injection and electron blocking, significantly reduce the device driving voltage, improve luminous efficiency and lifespan; and also has excellent conductivity, which can effectively reduce the overall series resistance of the flexible organic optoelectronic device, improve current injection efficiency and reduce the turn-on voltage.

[0032] In some embodiments, the concentration of either polystyrene sulfonate or the p-type dopant in the hole buffer structure increases gradually away from the anode, or both concentrations increase simultaneously away from the anode. This creates a gradual work function distribution, allowing for more precise control of the energy levels of the hole buffer layer, reducing the interface barrier, effectively optimizing the hole injection interface, and improving the overall device efficiency and stability.

[0033] For example, the fabrication method of the flexible organic optoelectronic device may include: providing a flexible substrate, and sequentially forming an anode, a hole buffer structure, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode on the flexible substrate; wherein, the fabrication method of the hole buffer structure includes: coating the composition onto the anode and removing the solvent to form the hole buffer structure. For example, after coating, a low-temperature heat treatment is performed at a temperature not exceeding 100°C to remove moisture and form a dense film, thereby forming a hole buffer layer with a thickness of 10 nm to 50 nm. Furthermore, by adjusting one or more of the following: the concentration of the P-type dopant and / or polystyrene sulfonate in the composition, the rotation speed during coating, or the number of coatings, the concentration of the P-type dopant and / or polystyrene sulfonate in the formed hole buffer structure is gradually increased in a direction away from the anode.

[0034] In some embodiments, the hole buffer structure includes multiple hole buffer layers stacked in the thickness direction. Each of the multiple hole buffer layers is formed from the composition containing different concentrations of P-type dopant and / or polystyrene sulfonate. Furthermore, in any two adjacent hole buffer layers, the total concentration of P-type dopant and / or polystyrene sulfonate in the hole buffer layer closer to the light-emitting layer is greater than the total concentration of P-type dopant and / or polystyrene sulfonate in the hole buffer layer closer to the anode. For example, a series of compositions with progressively increasing concentrations of P-type dopant and / or polystyrene sulfonate can be prepared and coated onto the anode in ascending order of P-type dopant and / or polystyrene sulfonate concentration.

[0035] In some embodiments, the hole buffer layer has a thickness of 10 nm to 50 nm, and the concentration of the P-type dopant and / or polystyrene sulfonate varies along the thickness direction within it.

[0036] In some embodiments, the thickness of the anode is 80 nm to 200 nm, and / or the thickness of the hole transport layer is 5 nm to 50 nm, and / or the thickness of the light-emitting layer is 20 nm to 100 nm, and / or the thickness of the electron transport layer is 20 nm to 80 nm, and the thickness of the cathode is 50 nm to 200 nm.

[0037] The materials of the anode, hole transport layer, light-emitting layer, electron transport layer, and cathode can be any materials known in the art, and the present invention does not impose any particular limitation on them.

[0038] In some embodiments, the work function of the hole buffer layer of the flexible organic optoelectronic device is 4.8 eV to 5.4 eV. From the perspective of energy level matching, the anode material can be, for example, a high work function transparent conductive material such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO2), or molybdenum oxide (MoO3), but is not limited to these; the hole transport layer material can be, for example, an organic hole transport material such as tris(4-trimethylaminophenyl)amine (TCTA), N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (NPB), or polytriphenylamine (PTAA) to achieve effective matching with the energy level of the hole buffer layer and promote hole injection and transport.

[0039] In some embodiments, the flexible organic optoelectronic device is a flexible OLED device.

[0040] Compared with the prior art, the present invention has at least the following beneficial effects:

[0041] (1) This invention utilizes the synergistic effect of PSS functionalization and P-type dopant to regulate the energy level of the hole buffer layer based on single-walled carbon nanotubes, so that it matches the energy level of the anode and organic layer in the flexible organic optoelectronic device, thereby achieving efficient hole injection and electron blocking, significantly reducing the device driving voltage, improving luminous efficiency and lifespan.

[0042] (2) The present invention forms a gradual work function distribution by changing the concentration gradient of P-type dopant and / or PSS in the hole buffer structure, thereby further precisely controlling the energy level of the hole buffer structure, reducing the interface barrier, effectively optimizing the hole injection interface, and improving the overall device efficiency and stability.

[0043] (3) The hole buffer layer provided by the present invention has excellent conductivity, which can effectively reduce the overall series resistance of the device, improve the current injection efficiency, and reduce the start-up voltage.

[0044] (4) The hole buffer layer provided by the present invention has excellent mechanical flexibility and can maintain excellent electrical and optical performance under repeated bending conditions, thus extending the device life and solving the problem that the hole buffer layer material of the existing flexible organic optoelectronic device has insufficient mechanical flexibility and is prone to cracking when bent, leading to device failure.

[0045] (5) The hole buffer layer provided by the present invention has good transmittance of visible light and will not affect the light output of the device, which helps to improve the luminous efficiency and display quality of flexible organic optoelectronic devices.

[0046] (6) The cavity buffer layer provided by the present invention also has good stability and weather resistance. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a photograph of the uniform and stable PSS-functionalized P-type doped SWCNT aqueous slurry prepared in Example 1 of this invention.

[0049] Figure 2 This is a scanning electron microscope image of the hole buffer layer prepared in Embodiment 1 of the present invention;

[0050] Figure 3 This is a partial structural schematic diagram of the flexible OLED device obtained in Embodiment 1 of the present invention;

[0051] Figure 4 This is a schematic diagram of the energy levels of the devices in Example 2 and Comparative Example 1;

[0052] Figure 5 This is a comparison chart of the JVL curves of the devices in Example 2 and Comparative Example 1;

[0053] Figure 6 This is a comparison chart of the EQE-brightness curves of the devices in Example 2 and Comparative Example 1;

[0054] Figure 7 This is a comparison chart of the JVL curves of the device in Example 2 before and after 500 bends;

[0055] Figure 8 This is a comparison chart of the EQE-brightness curves of the device in Example 2 before and after 500 bends;

[0056] Figure 9 This is a comparison chart of the JVL curves of the device in Comparative Example 1 before and after 500 bends.

[0057] Figure 10 This is a comparison chart of the EQE-brightness curves of the device in Comparative Example 1 before and after 500 bends. Detailed Implementation

[0058] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention. The specific functional details disclosed herein should not be construed as limiting, but are merely intended to form the basis of the claims and to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0059] In addition, unless otherwise specified, all raw materials used in the following embodiments can be purchased from the market or other sources, and all production and testing equipment used are known in the art, as are the testing methods used.

[0060] Example 1

[0061] This embodiment provides a PSS-functionalized P-type doped SWCNT aqueous slurry and its preparation method, specifically including the following steps:

[0062] (1) 0.6 g of high-purity single-walled carbon nanotubes (diameter between 0.4-10 nm, length between 0.5-500 μm, purity above 80%) were placed in a mixed acid (nitric acid and sulfuric acid volume ratio 1:3) and ultrasonically treated for 2 hours to introduce carboxyl functional groups on the single-walled carbon nanotubes. Then, the nanotubes were repeatedly filtered with deionized water until neutral to obtain acidified SWCNTs.

[0063] (2) Disperse acidified SWCNTs in 200 mL of deionized water, add 10 mL of 0.6 wt% sodium polystyrene sulfonate (PSS) aqueous solution, and sonicate for 1 h at room temperature to form a PSS / SWCNT composite dispersion, in which PSS is fully adsorbed on the surface of single-walled carbon nanotubes to achieve functionalization.

[0064] (3) Add 0.4 g of sodium dodecyl sulfate and 0.4 g of copovidone to the above PSS / SWCNT composite dispersion, emulsify at high speed at 8000 rpm, and then continue to perform high pressure homogenization treatment at 800 bar pressure and cycle 5 times to obtain a stable aqueous slurry with a particle size distribution of less than 200 nm.

[0065] (4) Using PEDOT:PSS as a P-type dopant, add 0.2 g of PEDOT:PSS to the aqueous slurry obtained above and sonicate for 1 hour to obtain PSS-functionalized P-type doped SWCNT aqueous slurry, which is the composition for preparing hole buffer layer of flexible organic optoelectronic device described in this invention.

[0066] Figure 1 This is a photograph of the uniform and stable PSS-functionalized P-type doped SWCNT aqueous slurry prepared in this embodiment.

[0067] This embodiment also provides a hole buffer layer for flexible OLED devices prepared using the above-mentioned PSS-functionalized P-type doped SWCNT aqueous slurry, the preparation method of which specifically includes the following steps:

[0068] A flexible substrate (PET film) with an ITO conductive thin film anode (100 μm thick) is provided, which is then cleaned, surface-treated, and dried.

[0069] Using a syringe with a filter, draw 5 mL of the PSS-functionalized P-type doped SWCNT aqueous slurry from Example 1, and gently drop approximately 4-5 drops onto the center of the ITO conductive film, ensuring that the aqueous slurry does not exceed the edge of the ITO conductive film. Using a spin coater, first spin at 600 rpm for 6 seconds to spread it evenly on the surface of the ITO conductive film, then adjust the speed to 3000 rpm and spin for 30 seconds to spread it evenly on the ITO conductive film to form a uniform film. Then place it in a 90 °C oven and bake for 5 minutes to form a uniform and dense film, i.e., a hole buffer layer.

[0070] The surface morphology of the prepared thin film was observed using a scanning electron microscope. Figure 2 This is a scanning electron microscope image of the hole buffer layer prepared in this embodiment, as shown. Figure 2 As shown, the single-walled tube-based thin film was found to be uniformly laid on the flexible substrate, and its thickness was measured to be approximately 40 nm using a film thickness gauge, with a surface roughness of less than 2 nm.

[0071] This embodiment also provides a flexible OLED device. Figure 3 This is a partial structural schematic diagram of the flexible OLED device in this embodiment, which includes a flexible substrate PET film ( Figure 3 (not shown in the image), and an ITO conductive thin film anode sequentially formed on a flexible substrate (…). Figure 3 (Not shown in the image), a hole buffer structure, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode. The fabrication method of this flexible OLED device specifically includes the following steps:

[0072] On the structure prepared above (flexible substrate-ITO conductive thin film anode-hole buffer layer), organic functional layers are further prepared by sequentially depositing a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode using vacuum evaporation under room temperature conditions.

[0073] N,N'-bis(naphthyl-1-yl)-N,N'-diphenylbenzidine (NPB) was selected as the hole transport layer (HTL), with a wavelength of 1-2 Å s. -1 The deposition rate was approximately 40 nm; tris(8-hydroxyquinoline)aluminum (Alq3) was selected as the emissive layer (EML), with a deposition rate of 1-2 Å s. -1The deposition rate was approximately 20 nm; 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) was selected as the electron transport layer (ETL), with a deposition rate of 1-2 Å s. -1 The electron transport layer was then deposited at a rate of 40 nm; finally, 5 nm lithium fluoride (LiF) and 150 nm aluminum (Al) electrodes were deposited on the electron transport layer by vacuum evaporation at rates of approximately 5 Å min. -1 and 10-15 Å s -1 .

[0074] The obtained devices were subjected to current density-voltage-luminance (JVL) and lifetime tests.

[0075] Example 2

[0076] Example 2 provides a hole buffer structure with gradient doped p-type dopant and its preparation method, specifically including the following steps:

[0077] (1) Three PSS-functionalized P-type doped SWCNT aqueous slurries with P-type dopant concentrations of 1 wt%, 2 wt%, and 3 wt% are provided. The preparation method of the slurry used in this embodiment is basically the same as that in Example 1, except that different concentrations of PEDOT:PSS are added to make their concentrations 1 wt%, 2 wt%, and 3 wt% respectively.

[0078] (2) Provide a flexible substrate (PET film) with an ITO conductive thin film anode (100 μm thick), clean and surface treat it, and then dry it;

[0079] (3) Using a syringe with a filter tip, draw 5 mL of water-based slurry with a PEDOT:PSS concentration of 1 wt%, and lightly drop an appropriate amount onto the center of the ITO conductive film, ensuring that the water-based slurry does not exceed the edge of the ITO conductive film; use a spin coater to first rotate at 600 rpm for 6 seconds to spread it evenly on the surface of the ITO conductive film, and then adjust the speed to 4000 rpm and rotate for 30 seconds to spread it evenly on the ITO conductive film to form a uniform film. Then place it in a 90 °C oven and bake for 5 minutes to form a first hole buffer layer with a thickness of about 10 nm.

[0080] Next, following a similar method, an aqueous slurry with PEDOT:PSS concentrations of 2 wt% and 3 wt% was spin-coated sequentially to form a second hole buffer layer with a thickness of approximately 15 nm and a third hole buffer layer with a thickness of approximately 15 nm. The first, second, and third hole buffer layers constitute the hole buffer structure of this embodiment.

[0081] In the hole buffer structure formed in this embodiment, the concentration of P-type dopant (PEDOT:PSS) varies gradient along the thickness direction and increases away from the anode, forming a gradual work function distribution. This helps to further improve energy level matching and reduce interface injection barriers. Kelvin probe force microscopy (KPFM) testing of this hole buffer structure showed that, due to the sequentially increasing PEDOT:PSS doping concentration in the three thin films, the work function also exhibited a gradient increasing trend: approximately 4.8 eV for the first layer, approximately 5.1 eV for the second layer, and approximately 5.4 eV for the third layer.

[0082] This embodiment also provides a flexible OLED device in which the PEDOT:PSS concentration in the hole buffer structure varies with a gradient along the thickness direction. The specific fabrication method is as follows:

[0083] On the structure (flexible substrate-ITO conductive thin film anode-hole buffer structure) prepared above, an organic functional layer is further prepared by sequentially depositing a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode under room temperature conditions using a vacuum evaporation method.

[0084] N,N'-bis(naphthyl-1-yl)-N,N'-diphenylbenzidine (NPB) was selected as the hole transport layer (HTL) with a wavelength of 1-2 Å s. -1 The deposition rate was approximately 40 nm; tris(8-hydroxyquinoline)aluminum (Alq3) was selected as the emissive layer (EML), with a deposition rate of 1-2 Å s. -1 The deposition rate was approximately 20 nm; 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) was selected as the electron transport layer (ETL), with a deposition rate of 1-2 Å s. -1 The electron transport layer was then deposited at a rate of 40 nm; finally, 5 nm lithium fluoride (LiF) and 150 nm aluminum (Al) electrodes were deposited on the electron transport layer by vacuum evaporation at rates of approximately 5 Å min. -1 and 10-15 Å s -1 .

[0085] The obtained devices were subjected to current density-voltage-luminance (JVL) and lifetime tests.

[0086] Example 3

[0087] This embodiment provides a PSS-functionalized P-type doped SWCNT aqueous slurry, the composition of which is as follows:

[0088] Single-walled carbon nanotubes: 0.3 wt%

[0089] Polystyrene sulfonate: 0.45 wt%;

[0090] Au nanoparticles: 0.1 wt%

[0091] Sodium dodecyl sulfate: 0.2 wt%

[0092] Polyvinylpyrrolidone: 0.2 wt%;

[0093] The remainder is water.

[0094] The preparation method of the PSS functionalized P-type doped SWCNT aqueous slurry in this embodiment is the same as that in Example 1, except that the raw materials in Example 1 are replaced with the above-mentioned raw materials.

[0095] Flexible OLED devices were fabricated using the PSS-functionalized P-type doped SWCNT aqueous slurry of this embodiment, following the same method as in Example 2, and the results were comparable to those in Example 2.

[0096] Example 4

[0097] This embodiment provides a PSS-functionalized P-type doped SWCNT aqueous slurry, the composition of which is as follows:

[0098] Single-walled carbon nanotubes: 0.3 wt%

[0099] Polystyrene sulfonate: 0.5 wt%;

[0100] 2,3,5,6-Tetrafluoro-7,7,8,8-Tetracyanoquinoxaline (F4-TCNQ): 0.2wt%

[0101] Sodium dodecyl sulfate: 0.3 wt%

[0102] Polyvinylpyrrolidone: 0.2 wt%;

[0103] The remainder is water.

[0104] The preparation method of the PSS functionalized P-type doped SWCNT aqueous slurry in this embodiment is the same as that in Example 1, except that the raw materials in Example 1 are replaced with the above-mentioned raw materials.

[0105] Flexible OLED devices were fabricated using the PSS-functionalized P-type doped SWCNT aqueous slurry of this embodiment, following the same method as in Example 2, and the results were comparable to those in Example 2.

[0106] Example 5

[0107] This embodiment provides a PSS-functionalized P-type doped SWCNT aqueous slurry, the composition of which is as follows:

[0108] Single-walled carbon nanotubes: 0.1 wt%

[0109] Polystyrene sulfonate: 0.3 wt%;

[0110] Polyaniline: 0.1 wt%

[0111] Sodium lignosulfonate: 0.2 wt%

[0112] Polyvinyl alcohol: 0.15 wt%;

[0113] The remainder is water.

[0114] The preparation method of the PSS functionalized P-type doped SWCNT aqueous slurry in this embodiment is the same as that in Example 1, except that the raw materials in Example 1 are replaced with the above-mentioned raw materials.

[0115] Flexible OLED devices were fabricated using the PSS-functionalized P-type doped SWCNT aqueous slurry of this embodiment, following the same method as in Example 2, and the results were comparable to those in Example 2.

[0116] Example 6

[0117] This embodiment provides a PSS-functionalized P-type doped SWCNT aqueous slurry, the composition of which is as follows:

[0118] Single-walled carbon nanotubes: 0.4 wt%

[0119] Polystyrene sulfonate: 0.5 wt%;

[0120] Fluorobenzoic acid: 5wt%

[0121] Sodium maleic acid-acrylic acid copolymer: 0.3 wt%;

[0122] Hydroxypropyl methylcellulose: 0.1 wt%

[0123] The remainder is water.

[0124] The preparation method of the PSS functionalized P-type doped SWCNT aqueous slurry in this embodiment is the same as that in Example 1, except that the raw materials in Example 1 are replaced with the above-mentioned raw materials.

[0125] Flexible OLED devices were fabricated using the PSS-functionalized P-type doped SWCNT aqueous slurry of this embodiment, following the same method as in Example 2, and the results were comparable to those in Example 2.

[0126] Comparative Example 1

[0127] Comparative Example 1 provides a flexible OLED device with PEDOT:PSS material as the hole buffer layer. The only difference between Comparative Example 1 and Example 2 is that the hole buffer layer of Comparative Example 1 is made of PEDOT:PSS and the PEDOT:PSS concentration is constant at 1.3~1.7 wt%. The rest is the same as Example 2 and will not be described again here.

[0128] The present invention performs current density-voltage-luminance (JVL) and lifetime tests on the devices of Example 2 and Comparative Example 1. Figure 4 This is a schematic diagram of the energy levels of the devices in Example 2 and Comparative Example 1. Figure 5 This is a comparison chart of the JVL curves of the devices in Example 2 and Comparative Example 1. Figure 6 This is a comparison chart of the EQE-brightness curves of the devices in Example 2 and Comparative Example 1.

[0129] exist Figure 4 In the energy level comparisons shown, to avoid ambiguity, the work function and molecular orbital energy levels described in this specification are characterized as absolute values ​​(unit: eV) relative to the vacuum energy level. Taking the hole transport layer material NPB used in this invention as an example, its HOMO energy level is typically located around 5.3~5.4 eV. Therefore, from the perspective of static energy level matching, when the work function of the hole buffer layer is close to or equal to this HOMO energy level, the hole injection barrier between the anode and the hole transport layer is lower, and the hole injection process is more favorable. The results show that the PSS functionalized and P-type doped hole buffer structure can effectively improve the energy level matching with the anode and organic layer due to the tunable energy levels, and the hole injection efficiency can be improved. Furthermore, due to the high conductivity brought by the single-walled transistor, the series resistance of the overall device is reduced, the device driving voltage and turn-on voltage are reduced, resulting in a more efficient carrier injection efficiency. This can promote the recombination efficiency of electrons and holes in the light-emitting layer and improve the luminous efficiency and brightness of the device. The device’s turn-on voltage dropped significantly from 2.9 V to 2.6 V, and the external quantum efficiency increased from about 14.3% to about 19.6%.

[0130] Comparative Example 2

[0131] The composition provided in Comparative Example 2 is basically the same as that in Example 1, except that the composition in Comparative Example 2 does not contain PSS. The rest is the same as in Example 1, and will not be repeated here.

[0132] Flexible OLED devices were prepared using this composition in accordance with the same method as in Examples 2 and 5.

[0133] Comparative Example 3

[0134] The composition provided in Comparative Example 3 is basically the same as that in Example 1, except that the composition in Comparative Example 3 does not contain the P-type dopant PEDOT:PSS. The rest is the same as in Example 1, and will not be repeated here.

[0135] Flexible OLED devices were prepared using this composition in accordance with the same method as in Examples 2 and 5.

[0136] Table 1 lists the lifetime test data of the devices prepared in the embodiments and comparative examples of the present invention to evaluate the effect of the proposed single-walled carbon nanotube-based hole buffer layer in improving the stability of flexible OLED devices. All devices were tested under constant current driving conditions at room temperature (25±2°C) and relative humidity below approximately 45%, and their initial brightness decay to 50% (T0) was recorded. 50 ) and the time to decay to 90% (T 90 ( ) as a lifespan indicator.

[0137] Table 1. Comparison of lifetime data for the devices in the examples and comparative examples.

[0138]

[0139] Test results show that the OLED device of Example 2 has a T 50 and T 90 The lifespan is more than double that of Comparative Example 1, fully demonstrating the effectiveness and application potential of this material system in improving the lifespan of flexible OLED devices.

[0140] Comparative Example 1 uses conventional PEDOT:PSS as a hole buffer layer. Since PEDOT:PSS itself has certain acidity and hygroscopicity, it is easy to react with ITO or absorb water, which leads to the degradation of the internal interface of the device, thereby accelerating the decline of organic layer performance and carrier injection imbalance, resulting in poor working lifetime.

[0141] For Comparative Example 2, since the composition of Comparative Example 2 does not contain sodium polystyrene sulfonate (PSS), single-walled carbon nanotubes are difficult to form a stable dispersion in an aqueous system, resulting in a significant increase in the surface roughness of the film and discontinuity of local conductive channels. This leads to more serious leakage points and non-uniform hole injection behavior at the interface, which significantly reduces the device lifetime, with a half-life (T50) of only 65 h.

[0142] Although Comparative Example 3 contains PSS, which can provide some surface functionalization and improve the dispersion of single-walled carbon nanotubes compared to Comparative Example 2, the overall work function is low due to the lack of synergistic P-type doping of PEDOT in the system. The hole injection resistance is still large, resulting in a device lifetime that is better than Comparative Example 2, but still significantly lower than the embodiment of the present invention.

[0143] Compared to Comparative Examples 1-3 above, Example 1 of this invention, through the synergistic regulation of interface energy levels and film density by single-walled carbon nanotubes and PSS, increases the device lifetime (T50) to 295 h, significantly improving the brightness decay rate. In Example 2, a vertically oriented gradient doped structure is further constructed, which further reduces the interface hole injection barrier and enhances the continuity of the conductive network, ultimately increasing the device lifetime to 425 h and exhibiting the lowest start-up voltage rise. In Example 3, the introduction of trace amounts of gold nanoparticles further improves device stability, due to gold's chemical inertness and excellent resistance to damp heat. In Example 4, the dopant F4-TCNQ is a strong acceptor, significantly improving initial hole injection efficiency, but subsequent migration or interface reactions may occur, resulting in slightly inferior long-term stability compared to gold nanoparticles or the gradient doped structure.

[0144] Furthermore, in the hole buffer layer formed by PSS-functionalized p-type doped SWCNTs, the flexible carbon nanotube framework structure maintains a good conductive path during repeated thermal cycling and current carrying processes, which helps maintain the long-term operating state of the device. In other words, due to the excellent flexibility and mechanical stability of SWCNTs, the hole buffer layer formed by them can maintain good structural integrity and electrical performance under repeated mechanical stress. Therefore, applying SWCNT-based hole buffer layers to flexible OLED devices helps improve the device's adaptability to mechanical deformation and overall reliability.

[0145] To verify its flexibility advantage, the devices in Example 2 and Comparative Example 1 were subjected to 500 repeated bending cycles (bending radius of 5 mm, speed of 1 Hz) and their luminescence performance stability was tested. Figure 7 This is a comparison chart of the JVL curves of the device in Example 2 before and after 500 bends. Figure 8 This is a comparison chart of the EQE-brightness curves of the device in Example 2 before and after 500 bends. Figure 9 This is a comparison chart of the JVL curves of the device in Comparative Example 1 before and after 500 bends. Figure 10 This is a comparison of the EQE-brightness curves of the device in Comparative Example 1 before and after 500 bends. It can be clearly observed that the device in Example 2 shows almost no significant decrease in brightness-current performance before and after bending, with peak brightness and efficiency remaining at 85%-90% of their original levels, demonstrating excellent photoelectric stability. In contrast, the device in Comparative Example 1 shows a significant decrease in luminous efficiency, with peak brightness and efficiency decreasing to approximately 60% of their original levels. These results indicate that the hole buffer layer formed by PSS-functionalized P-type doped SWCNTs can effectively alleviate problems such as interface cracking and charge injection mismatch in flexible OLED devices during bending, thereby maintaining stable charge transport channels and device structure, which is beneficial for achieving highly reliable flexible display or lighting applications.

[0146] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0147] All aspects, embodiments, features, and examples of this invention should be considered illustrative and used to explain and illustrate the invention, but not to limit the invention. The scope of the invention is defined only by the claims.

[0148] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements in the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed, but rather to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A composition for preparing a hole buffer layer for flexible organic optoelectronic devices, characterized in that, The hole buffer layer is located between the anode and the hole transport layer of the flexible organic optoelectronic device; The composition comprises the following components by mass percentage: 0.1wt% to 0.4wt% single-walled carbon nanotubes, 0.3wt% to 0.5wt% polystyrene sulfonate, 0.1wt% to 5wt% p-type dopant, 0.1wt% to 0.3wt% anionic surfactant, 0.1wt% to 0.3wt% stabilizer, and the balance being a solvent, wherein the solvent includes water; wherein the surface of the single-walled carbon nanotubes has hydrophilic groups, and the polystyrene sulfonate is adsorbed onto the surface of the single-walled carbon nanotubes through π-π conjugation and electrostatic adsorption to form polystyrene sulfonate modified single-walled carbon nanotubes; The p-type dopants include poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate, polyaniline, polythiophene derivatives, gold nanoparticles, and NiO. x The nanoparticles are selected from one or more combinations of MoO3 nanoparticles, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinoxaline, and organic acidic dopants; the hydrophilic groups include one or more of carboxyl and hydroxyl groups. The method for preparing the composition includes: introducing hydrophilic groups onto the surface of the single-walled carbon nanotubes; Single-walled carbon nanotubes with hydrophilic groups were dispersed in an aqueous solution of polystyrene sulfonate to obtain a PSS / SWCNT composite dispersion. The PSS / SWCNT composite dispersion was mixed with an anionic surfactant and a stabilizer, and then subjected to emulsification and homogenization treatments to form an aqueous slurry. The P-type dopant was added to the aqueous slurry and uniformly dispersed to obtain a composition for preparing hole buffer structures for flexible organic optoelectronic devices.

2. The composition according to claim 1, characterized in that, The anionic surfactant includes one or more of the following: sodium dodecyl sulfate, sodium lignosulfonate, sodium maleic acid-acrylic acid copolymer, sodium dodecylbenzenesulfonate, sodium α-olefin sulfonate, sodium lauroyl sarcosinate, sodium decyl sulfate, sodium nonylphenol polyoxyethylene ether sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium alkyl sulfosuccinate, sodium dialkyl succinate, sodium naphthalene sulfonate, formaldehyde condensate, or polycarboxylate dispersant.

3. The composition according to claim 1, characterized in that, The stabilizer is a polymer stabilizer, including one or more of the following: polyvinylpyrrolidone, copovidone-polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl ether, polyethylene oxide, polyacrylic acid, sodium polyacrylate, polyvinyl ether-maleic anhydride copolymer, copovidone, polyvinyl butyral, hydroxypropyl methylcellulose, polyethyleneimine, and copolymers thereof.

4. The composition according to claim 1, characterized in that, The specific steps of introducing hydrophilic groups on the surface of the single-walled carbon nanotubes include: mixing the single-walled carbon nanotubes with a mixed acid and subjecting them to ultrasonic treatment, wherein the mixed acid includes nitric acid and sulfuric acid in a volume ratio of 1:2 to 1:4, so as to introduce carboxyl and hydroxyl groups on the surface of the single-walled carbon nanotubes.

5. The composition according to claim 1, characterized in that, The emulsification includes high-shear emulsification at a rotation speed of 5000 rpm to 10000 rpm.

6. The composition according to claim 1, characterized in that, The homogenization process includes high-pressure homogenization under pressure conditions of 500 bar to 900 bar, and repeated 3 to 5 times.

7. A hole buffer layer for a flexible organic optoelectronic device, characterized in that, Formed from the composition according to any one of claims 1-6.

8. The hole buffer layer of the flexible organic optoelectronic device according to claim 7, characterized in that, The work function of the hole buffer layer of the flexible organic optoelectronic device is 4.8 eV to 5.4 eV.

9. A flexible organic optoelectronic device, characterized in that, It includes an anode, a hole buffer structure, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode arranged in sequence, wherein the hole buffer structure includes the hole buffer layer of the flexible organic optoelectronic device as described in claim 7 or 8.

10. The flexible organic optoelectronic device according to claim 9, characterized in that, In the hole buffer structure, the concentration of either polystyrene sulfonate or P-type dopant increases in a gradient away from the anode, or the concentrations of both increase simultaneously away from the anode.

11. The flexible organic optoelectronic device according to claim 9 or 10, characterized in that, The hole buffer structure includes multiple hole buffer layers stacked in the thickness direction. The multiple hole buffer layers are formed by the composition containing different concentrations of P-type dopant and / or polystyrene sulfonate. In any two adjacent hole buffer layers, the total concentration of P-type dopant and / or polystyrene sulfonate in the hole buffer layer closer to the light-emitting layer is greater than the total concentration of P-type dopant and / or polystyrene sulfonate in the hole buffer layer closer to the anode.

12. The flexible organic optoelectronic device according to claim 9, characterized in that, The hole buffer layer has a thickness of 10 nm to 50 nm, and the concentration of P-type dopant and / or polystyrene sulfonate varies along the thickness direction within it.

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