A method for fabricating a self-assembled bilayer light extraction micro-nano structure quantum dot light emitting device

Abstract

The application relates to a method for preparing a self-assembled double-layer light extraction micro-nano structure quantum dot light-emitting device. A hole injection layer, a hole transport layer and a quantum dot film, an electron transport layer, a metal cathode and an ITO layer back of a conductive substrate are sequentially deposited on an ITO layer of a transparent conductive substrate to prepare a light extraction micro-nano structure in a self-assembled manner; the light extraction micro-nano structure prepared in the self-assembled manner is operated as follows: (1) a dense and ordered micro-nano structure is formed through a polystyrene microsphere (PS ball) self-assembled technology; (2) the PS ball after self-assembly is transferred to a polyvinyl butyral (PVB) film on the back of the substrate through a fishing method; (3) a flat silicon wafer is placed on the PS ball micro-nano structure to exert a certain pressure, so that the PS ball can be embedded in the PVB film. The application forms a dense and ordered PS ball array through a self-assembled process, and the PS array and the PVB form a closely adhered double-layer micro-nano structure through pressure exertion, so that the light extraction efficiency of the quantum dot light-emitting device is strengthened.

Description

Technical Field

[0001] This invention belongs to the technical field of quantum dot light-emitting diodes and other light-emitting devices, specifically relating to a method for self-assembling a double-layer light extraction micro / nano structure quantum dot light-emitting device. It successfully eliminates the need for a template, directly forming a double-layer micro / nano structure, effectively improving light loss in substrate mode, enhancing light extraction efficiency, and optimizing QLED device performance. Background Technology

[0002] Among various light-emitting materials for next-generation displays, quantum dots stand out for their unique optoelectronic properties, such as high brightness and narrow emission spectrum, wide color tunability, high quantum yield, and good stability. While quantum dots have achieved nearly 100% photoluminescence quantum yield (PLQY), the low external quantum efficiency due to light loss remains a major obstacle to the commercialization of QLEDs. To improve light extraction efficiency and device performance, thin-film micro / nanostructures have been introduced into light-emitting devices. These structures range in size and period from nanometers to micrometers. Commonly used microstructure morphologies are categorized into internal and external optical coupling structures based on their placement. Light extraction efficiency is improved by suppressing light loss in waveguide mode, surface plasmons mode, and substrate mode. However, the complex manufacturing process, poor stability, and high cost of current light extraction micro / nanostructures hinder their rapid development. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing quantum dot light-emitting diodes (LEDs) such as high light loss and low efficiency. It provides a method for fabricating a self-assembled bilayer light extraction micro / nano structure quantum dot LED. Utilizing microsphere self-assembly technology, the method effectively controls the formation of a self-assembled array of PS microspheres at the deionized water / air interface. After retrieval, pressure is applied to embed the PS microspheres into a PVB film, forming a bilayer micro / nano light extraction structure. This method optimizes and improves the parameters for fabricating other functional layers of the quantum dot LED. The fabrication method of this invention features high process repeatability, simple operation, and high yield, making it suitable for large-scale industrial production.

[0004] To achieve the above objectives, the technical solution of the present invention is: a method for self-assembling a double-layer light extraction micro / nano structure quantum dot light-emitting device, which constructs a light extraction micro / nano structure combining a concave mirror and a lens.

[0005] In one embodiment of the present invention, the concave mirror is a concave mirror structure made of PVB film.

[0006] In one embodiment of the present invention, the lens is a PS microsphere lens array structure embedded in a concave mirror.

[0007] In one embodiment of the present invention, the PS microsphere lens array structure is realized by PS microsphere self-assembly technology.

[0008] In one embodiment of the present invention, the PS microsphere self-assembly technology involves mixing a PS microsphere solution and an ethanol solution at a 1:1 volume ratio, and slowly and uniformly adding the mixture onto the surface of a deionized water solution using a syringe, thereby forming a stable PS microsphere lens array structure through a self-assembly process.

[0009] In one embodiment of the present invention, the concave mirror structure made of PVB film is formed by applying pressure to a flat silicon wafer placed on a PS microsphere lens array structure under a heated state, so that the PS microspheres of the PS microsphere lens array structure are embedded in the PVB film to form a concave mirror structure.

[0010] In one embodiment of the present invention, the PVB film is spin-coated onto the back of the ITO layer of a transparent conductive substrate.

[0011] In one embodiment of the present invention, a hole injection layer, a hole transport layer, a quantum dot film, an electron transport layer, a metal cathode, and a light extraction micro / nano structure on the back side of the ITO layer of the transparent conductive substrate are sequentially deposited on the ITO layer of the transparent conductive substrate.

[0012] In one embodiment of the present invention, the fabrication steps of the light-extracting micro / nano structure are as follows:

[0013] (1) A dense and ordered micro-nano structure, namely a PS microsphere lens array structure, is formed by self-assembly technology of polystyrene microspheres, i.e., PS microspheres;

[0014] (2) The self-assembled PS microspheres were transferred onto the polyvinyl butyral (PVB) film on the back of the ITO layer of a transparent conductive substrate by a retrieval method.

[0015] (3) A predetermined pressure is applied by placing a flat silicon wafer on the PS microsphere lens array structure, so that the PS microspheres are embedded in the PVB film.

[0016] In one embodiment of the present invention, the specific implementation steps of the method are as follows:

[0017] S1. Prepare the substrate: ITO glass is selected as the substrate and ultrasonically cleaned in ethanol, acetone and deionized water in sequence. After drying, before depositing the functional layer, the surface of ITO glass is treated with plasma to change the hydrophilicity and hydrophobicity of ITO.

[0018] S2, Spin-coated hole injection layer (HIL): The hole injection layer material is spin-coated onto the pretreated substrate at a spin speed of 4000 rpm and then annealed at 140°C for 20 min on a heating stage; the thickness is 30 nm.

[0019] S3, Spin-coated hole transport layer HTL: The hole transport layer is deposited on the hole injection layer HIL using spin coating technology to generate an organic semiconductor thin film. The spin coating speed is 3000 rpm, and the film is annealed at 120°C for 20 min on a heating stage; the thickness is 30 nm.

[0020] S4. Spin-coated light-emitting layer, i.e. quantum dot film: The light-emitting material, i.e. quantum dot material, is deposited on the hole transport layer HTL using spin-coating technology. The spin-coating speed is 2000 rpm, and the film is annealed at 80°C for 10 min on a heating stage.

[0021] S5, Spin-coated electron transport layer (ETL): Spin-coat electron transport layer material onto the annealed substrate at a spin speed of 2000 rpm, and then anneal at 80°C for 10 minutes on a heating stage.

[0022] S6. Evaporated silver electrode, i.e., metal cathode: Ag electrode is vapor-deposited on an evaporation machine, and a film thickness of 100nm is deposited by controlling the evaporation time.

[0023] S7. Packaging: The device is packaged using transparent materials.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The first proposed double-layer light extraction micro-nano structure enhances light extraction efficiency and solves the problem of severe light loss in traditional quantum dot light-emitting devices.

[0026] (2) It is simple, low-consumption, fast, easy to operate and has a high yield. The design of the double-layer micro-nano structure does not require the assistance of additional templates, which greatly reduces the complexity of the process and is suitable for large-scale industrial production.

[0027] (3) It avoids damage to other functional layers of quantum dot light-emitting devices, protects their electrical properties and stability, and effectively extends the device life. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the quantum dot light-emitting device in an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram of the self-assembled PS microsphere array retrieval method in an embodiment of the present invention.

[0030] Figure 3 This is an image observed under an optical microscope of PS microspheres transferred onto a PVB film in an embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram of the optical extraction dual structure in an embodiment of the present invention.

[0032] Figure 5 A dual-structure flowchart is constructed for embodiments of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0034] This invention provides a method for self-assembling a bilayer light extraction micro / nano structure quantum dot light-emitting device. The method involves sequentially depositing a hole injection layer, a hole transport layer, a quantum dot film, an electron transport layer, a metal cathode, and an external light extraction structure on an ITO layer of a transparent conductive substrate. Figure 1 The quantum dot light-emitting device is shown. Specific operation: (1) A dense and ordered micro-nano structure is formed by self-assembly of polystyrene microspheres (PS spheres). (2) The self-assembled PS spheres are transferred onto a polyvinyl butyral (PVB) film on the back of a substrate by a retrieval method. (3) A flat silicon wafer is placed on the PS sphere micro-nano structure and a certain pressure is applied so that the PS spheres can be embedded in the PVB film.

[0035] Example 1 (see Figure 5 ):

[0036] 1. Substrate Preparation: Select a suitable substrate (such as ITO glass) and ultrasonically clean it sequentially in ethanol, acetone, and deionized water. After drying, before depositing the functional layer, treat the ITO glass surface with plasma to alter the hydrophilicity and hydrophobicity of ITO.

[0037] 2. Spin-coating Hole Injection Layer (HIL): A hole injection layer material such as PEDOT:PSS is spin-coated onto the pretreated substrate at a spin speed of 4000 rpm, followed by annealing at 140°C for 20 minutes on a heated stage. The thickness is approximately 30 nm.

[0038] 3. Spin-coated hole transport layer (HTL): A hole transport layer, such as TFB, is deposited on the PEDOT:PSS layer using spin-coating technology to form an organic semiconductor thin film. The spin-coating speed is 3000 rpm, and the film is annealed at 120°C for 20 min on a heating stage. The thickness of this layer is about 30 nm.

[0039] 4. Spin-coating the luminescent layer: Luminescent materials, such as quantum dots, are deposited onto the hole transport layer using spin-coating technology. The spin-coating speed is 2000 rpm, and the layer is then annealed at 80°C for 10 minutes on a heated stage.

[0040] 5. Spin-coating electron transport layer (ETL): Spin-coating electron transport layer material such as ZnO or ZnMgO solution onto the annealed substrate at a spin speed of 2000 rpm, and then annealing it at 80°C for 10 min on a heating stage. The thickness of this layer is about 60 nm.

[0041] 6. Evaporation of silver electrode: Ag electrode is deposited on an evaporation machine, and a film thickness of 100nm is deposited by controlling the evaporation time.

[0042] 7. Encapsulation: Use polymers (UV-curable optical adhesive materials), glass, or other transparent materials to encapsulate the device to protect and fix the circuit and provide moisture protection and environmental isolation.

[0043] In this example, the PS microsphere self-assembly technology involves mixing a PS microsphere solution and an ethanol solution at a 1:1 volume ratio and slowly and uniformly adding the mixture dropwise onto the surface of deionized water using a syringe. Due to the Marangoni effect, the surface tension gradient causes the liquid surface to be pushed away from the low surface tension region. Since the PS suspension contains the dispersant ethanol, its addition to the water surface immediately alters the surface tension in that region, making it lower than the surface tension in the far-field region, generating a surface tension gradient and forming Marangoni convection along the outer diameter direction. The diffusion and evaporation of ethanol along the concentration gradient also enhance convection in the solvent. The PS microspheres rapidly diffuse on the water surface along with the dispersant, eventually covering the entire water surface and forming a dense hexagonal close-packed structure as the amount of PS microsphere solution injected increases. The PS microspheres on the water surface are balanced by the interaction of various factors, including their own gravity, electrostatic repulsion and capillary forces between particles, and the movement of the solvent.

[0044] In this example, the PVB film is spin-coated: the PVB film is spin-coated onto the back of the quantum dot display device substrate in a static spin-coating manner with a concentration of 100 mg / ml, a solvent of n-butanol, and a spin-coating parameter of 3000 rpm.

[0045] In this example, the transfer of the PS microsphere array involves slowly lifting the quantum dot device, which has already undergone PVB film fabrication, from beneath the PS microsphere array, along with the neatly arranged PS microsphere array, as shown below. Figure 2 As shown. Then, annealing is performed on a 40°C heating stage to evaporate any residual deionized water solution on the device. (See figure) Figure 3 As shown, a 2µm self-assembled array of PS microspheres was observed under an optical fiber microscope.

[0046] In this example, the fabrication of the bilayer micro / nano structure involves placing a smooth, flat silicon wafer that completely covers the light-emitting points onto a PS microsphere array. A clip is used to hold the silicon wafer and the quantum dot light-emitting device together, applying constant pressure to the PS microsphere array. The array is then placed on a heating stage at 120°C. Due to the strong thermoplasticity of PVB films at high temperatures, the PS microspheres can be successfully embedded into the PVB film at 120°C for 10 minutes, with an embedding depth of 500 nm. At this point, the PVB film forms a concave mirror structure, and the PS microsphere array forms a convex mirror structure. Figure 4 As shown.

[0047] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for self-assembling a double-layer light extraction micro / nano structure quantum dot light-emitting device, characterized in that, A light extraction micro / nano structure combining a concave mirror and a lens is constructed. The concave mirror is a structure made of PVB film. The lens is a PS microsphere lens array structure embedded in the concave mirror. The PS microsphere lens array structure is realized through PS microsphere self-assembly technology. The PS microsphere self-assembly technology involves mixing a PS microsphere solution and an ethanol solution at a 1:1 volume ratio, and slowly and uniformly dripping the mixture onto the surface of deionized water using a syringe to form a stable PS microsphere lens array structure through self-assembly. The concave mirror structure made of PVB film is constructed by applying pressure to a flat silicon wafer placed on the PS microsphere lens array structure under heating, causing the PS microspheres of the PS microsphere lens array structure to embed into the PVB film, thus forming the concave mirror structure. The PVB film is spin-coated onto the back of the ITO layer of a transparent conductive substrate. A hole injection layer, a hole transport layer, a quantum dot film, an electron transport layer, a metal cathode, and the light extraction micro / nano structure on the back of the ITO layer of the transparent conductive substrate are sequentially deposited on the ITO layer of the transparent conductive substrate.

2. The method for self-assembling a double-layer light extraction micro / nano structure quantum dot light-emitting device according to claim 1, characterized in that, The fabrication steps of the optically extracted micro / nano structure are as follows: (1) A dense and ordered micro-nano structure, namely a PS microsphere lens array structure, is formed by the self-assembly technology of polystyrene microspheres, i.e. PS microspheres; (2) The self-assembled PS microspheres were transferred onto the polyvinyl butyral (PVB) film on the back of the ITO layer of a transparent conductive substrate by a retrieval method. (3) A flat silicon wafer is placed on the PS microsphere lens array structure and a predetermined pressure is applied to embed the PS microspheres into the PVB film.

3. The method for self-assembling a double-layer light extraction micro / nano structure quantum dot light-emitting device according to claim 1, characterized in that, The specific implementation steps of this method are as follows: S1. Substrate preparation: ITO glass is selected as the substrate and ultrasonically cleaned in ethanol, acetone and deionized water in sequence. After drying, before depositing the functional layer, the surface of ITO glass is treated with plasma to change the hydrophilicity and hydrophobicity of ITO. S2, Spin-coated hole injection layer (HIL): The hole injection layer material is spin-coated onto the pretreated substrate at a spin speed of 4000 rpm and then annealed at 140°C for 20 min on a heating stage; the thickness is 30 nm. S3, Spin-coated hole transport layer HTL: The hole transport layer is deposited on the hole injection layer HIL using spin coating technology to generate an organic semiconductor thin film. The spin coating speed is 3000 rpm, and the film is annealed at 120°C for 20 min on a heating stage; the thickness is 30 nm. S4. Spin-coated light-emitting layer, i.e. quantum dot film: The light-emitting material, i.e. quantum dot material, is deposited on the hole transport layer HTL using spin-coating technology. The spin-coating speed is 2000 rpm, and the film is annealed at 80°C for 10 min on a heating stage. S5, Spin-coated electron transport layer (ETL): Spin-coat electron transport layer material onto the annealed substrate at a spin speed of 2000 rpm, and then anneal at 80°C for 10 minutes on a heating stage. S6. Evaporated silver electrode, i.e., metal cathode: Ag electrode is vapor-deposited on an evaporation machine, and a film thickness of 100nm is deposited by controlling the evaporation time. S7. Packaging: The device is packaged using transparent materials.

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