Preparation method and application of a micron-scale quantum dot light-emitting diode array device

Abstract

The application discloses a preparation method and application of a micron quantum dot light emitting diode array device, which comprises the following steps: sequentially forming a hole injection layer, a hole transport layer, a patterned insulating layer, a quantum dot light emitting layer, an electron transport layer and a top electrode on an indium tin oxide substrate, using photoresist to prepare the patterned insulating layer, and spin-coating quantum dots to form an array light emitting layer, wherein the photoresist is used to inhibit the generation of electron leakage at pixel gaps, high resolution is realized, and record-breaking Micro-QLED array device performance is realized; and a new cross-linking hole transport layer PF8Cz-X is used to verify and solve the problem that a strong oxidizing photoacid is generated by a photoacid generator component in the photoresist, the problem of damaging the triphenylamine structure hole transport layer in the QLED device is solved through a free radical coordination combination mode, and a thermal cross-linking group is designed to avoid physical dissolution of a developing solution in a micro-nano processing process, a compatible solution processing technology is constructed, and a non-destructive photoetching system for the Micro-QLED array device is constructed.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano device fabrication technology, and specifically relates to a method for fabricating and applying a micron-scale quantum dot light-emitting diode array device. Background Technology

[0002] In advanced display technologies, photolithography is a process with high processing precision that can efficiently produce large-area display panels. It also has advantages such as mature process technology and simple operation, thus becoming a research hotspot for the production of high-resolution, large-area quantum dot light-emitting diodes.

[0003] In common photolithography techniques, insulating photoresist is typically used as a patterned interlayer to realize micron-scale quantum dot light-emitting diodes (Micro-QLEDs). Photoresists such as ARP 5350, AZ 5214, and MicroChem SU8 are incompatible with the solution fabrication process of QLED devices. Their electron and hole transport layers are easily dissolved by the developer, thus damaging the device structure. In addition, the potential interface inversion of the photoactive components in commercial photoresists on the functional layer materials in the QLED device structure is still unknown. Therefore, the current mainstream research focus is on realizing quantum dot patterning through photosensitive additives or quantum dot surface ligand engineering.

[0004] Patent document CN114839835A discloses a technical route for preparing patterned quantum dot films by using a photosensitive crosslinking agent containing a diacrylidine group mixed with a quantum dot solution. When diacrylidine is exposed to ultraviolet light, an intermediate singlet carbene is generated. The carbene undergoes an insertion reaction with the carbon-hydrogen bonds in the adjacent quantum dot ligands, thereby bridging the two adjacent quantum dots and changing the solubility, thus enabling the patterning of quantum dot films.

[0005] However, processes such as adding additional photosensitive additives to the quantum dot solution to achieve regional exposure patterning or changing the ligands of the quantum dots themselves significantly damage the photoelectric properties of the quantum dots and cannot prevent electron leakage between pixels, making it difficult to fabricate high-performance electroluminescent Micro-QLED array devices. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for fabricating and applying a micron-scale quantum dot light-emitting diode array device. This fabrication method is simple and easy to operate, and can realize the fabrication of large-area, high-resolution Micro-QLED arrays.

[0007] The first aspect of the present invention provides a method for fabricating a micron-scale quantum dot light-emitting diode array device, comprising the following steps: sequentially depositing a hole injection layer, a hole transport layer, a patterned insulating layer, a quantum dot light-emitting layer, an electron transport layer, and a metal electrode on a transparent conductive substrate, namely an indium tin oxide (ITO) glass substrate; wherein the thickness of the patterned insulating layer is 20 nm to 100 nm, and an arrayed light-emitting layer is formed by spin-coating quantum dots on the patterned insulating layer.

[0008] Furthermore, the formation of the arrayed light-emitting layer is accomplished through the following steps:

[0009] (2.1) An insulating photoresist layer with a thickness of less than 100 nm is formed on the hole transport layer;

[0010] (2.2) The insulating photoresist layer is patterned to micro-nano dimensions using photolithography, electron beam direct writing or laser direct writing methods;

[0011] (2.3) A micro-nano-scale quantum dot light-emitting array is deposited in the insulating photoresist layer after micro-nano-scale patterning by spin coating or inkjet printing.

[0012] Specifically, the material of the insulating photoresist layer is any one or a combination of photoresists of type ARP 5350, AZ 5214, and MicroChem SU8.

[0013] Specifically, the quantum dot is any one or a combination of CdSe quantum dots, InP quantum dots, halide perovskite quantum dots, or organic fluorescent quantum dots.

[0014] Furthermore, the hole transport layer is a novel cross-linked poly((9,9-dioctylfluorenyl-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl)) that can avoid the free radical reaction of the photoresist during photolithography and the physical dissolution during the development step.

[0015] Specifically, the electron transport layer material is any one or more of the following: a mixture of zinc oxide nanoparticles and polymers, zinc oxide nanoparticles, or zinc oxide nanoparticles doped with metal cations.

[0016] Furthermore, the hole injection layer material is one or more combinations of polymer PEDOT:PSS, molybdenum oxide, or nickel oxide.

[0017] The second aspect of the present invention is the application of the method for fabricating the micron-scale quantum dot light-emitting diode array device in the fabrication of micro- and nano-light-emitting diodes.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] (1) This invention proposes a method for fabricating and applying a micron-scale quantum dot light-emitting diode array device. It is a process route for fabricating a patterned insulating layer using photoresist. By suppressing electron leakage at the pixel gaps through photoresist, high resolution is achieved while simultaneously recording the external quantum efficiency of the patterned quantum dot light-emitting diode array device fabricated by photolithography, which greatly improves the performance of the Micro-QLED array device.

[0020] (2) The novel cross-linked hole transport layer PF8Cz-X was used to verify and solve the problem of photoacid generator (PAG) components in commercial negative chemical amplification photoresists (such as SU-8) generating strong oxidizing photoacids represented by fluoroantimony acid, which damage the triphenylamine structure hole transport layer (HTL) (such as TFB, Ploy-TPD, CBP, TCTA) commonly used in QLED devices through free radical coordination. Furthermore, by designing thermal cross-linking groups, the physical dissolution of the developer in the micro-nano fabrication process was avoided, and a solution-compatible processing technology was constructed, which is a photolithography system that is non-destructive to Micro-QLED array devices.

[0021] (3) The present invention uses a carbazole-based crosslinked hole transport layer with strong solvent resistance, which can avoid damage from free radical reaction with commercial photoresist and physical dissolution during the development process. A patterned insulating photoresist layer made of ultrathin insulating photoresist is provided between the electron transport layer and the hole transport layer to form pattern intervals and block electron transport between adjacent patterns. The pit wall of each pixel pit is a charge blocking layer, and any two adjacent pixel pits are separated by an insulating photoresist charge blocking layer. Light-emitting points are provided in the blank area inside each pixel pit. The upper and lower parts of the light-emitting layer are in contact with the electron transport layer and the hole transport layer, respectively, so as to excite the light-emitting layer. Several light-emitting pixels form a light-emitting array. Attached Figure Description

[0022] Figure 1 This is a structural diagram of the micro / nano light-emitting diode device prepared in the embodiments of the present invention;

[0023] Figure 2 This is a flowchart illustrating the patterned light-emitting layer prepared in an embodiment of the present invention;

[0024] Figure 3The absorption spectra of two HTLs, poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)] (TFB) and poly((9,9-dioctylfluorene-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl))(PF8Cz), before and after reaction with PAC are shown in the figures. The structural formulas of the corresponding HTL materials are shown in the figures. Figure (a) shows the change in absorption spectrum of TFB before and after reaction with PAC; Figure (b) shows the change in absorption spectrum of PF8Cz before and after reaction with PAC.

[0025] Figure 4 The figures show the absorption spectra of commonly used triphenylamine structures HTL before and after reaction with PAC, with the corresponding structural formulas of the HTL materials shown in the figures. Figure (a) shows the absorption spectrum changes of 4,4',4”-tris(carbazole-9-yl)triphenylamine (TCTA) before and after reaction with PAG; Figure (b) shows the absorption spectrum changes of poly[bis(4-phenyl)(4-butylphenyl)amine] (Poly-TPD) before and after reaction with PAG.

[0026] Figure 5 This is a graph showing the change in film thickness during the development process of non-crosslinked PF8Cz after dissolution.

[0027] Figure 6 This is a curve showing the stability of the film thickness during the dissolution of cross-linked PF8Cz-X in the development process;

[0028] Figure 7 Microscopic image of a patterned insulating layer with a pixel diameter of approximately 3μm obtained after micro-nano fabrication;

[0029] Figure 8 Electroluminescence microscope image of the final fabricated Micro-QLED array device with a pixel diameter of approximately 2 μm;

[0030] Figure 9 This is a record of the efficiency of the 2μm pixel diameter Micro-QLED array device obtained by the present invention. Specific Implementation

[0031] This invention provides a micrometer-scale quantum dot light-emitting diode array device and its fabrication method. The fabrication method is simple and easy to operate, enabling the fabrication of large-area, high-resolution Micro-QLED arrays. It is important to emphasize that this invention employs a carbazole-based crosslinked hole transport layer with strong solvent resistance, avoiding damage from free radical reactions with commercial photoresist and physical dissolution during development. A patterned insulating photoresist layer made of ultrathin (film thickness greater than 20 nm and less than 100 nm) insulating photoresist is disposed between the electron transport layer and the hole transport layer to form pattern intervals and block electron transport between adjacent patterns. The pit wall of each pixel pit is a charge-blocking layer, and any two adjacent pixel pits are separated by an insulating photoresist charge-blocking layer. A light-emitting layer is disposed in the blank area within each pixel pit, with the upper and lower parts of the light-emitting layer in contact with the electron transport layer and the hole transport layer, respectively, to facilitate excitation of the light-emitting layer. Several light-emitting pixels form a light-emitting array.

[0032] A classic photolithography fabrication system for Micro-QLED arrays includes an electron transport layer and a hole transport layer. A patterned insulating photoresist layer is disposed between the electron transport layer and the hole transport layer to block electron movement. The photoresist layer forms a mesh pixel pit array after undergoing micro-nano processing such as exposure and development.

[0033] The walls of each pixel pit are made of insulating photoresist, and any two adjacent pixel pits are separated by a charge-blocking layer of photoresist. The empty areas within each pixel pit are filled with quantum dot solution to form a light-emitting layer. The upper and lower sides of the light-emitting layer are in contact with the electron transport layer and hole transport layer, respectively, to facilitate excitation of the light-emitting layer, thereby forming a light-emitting array. The structure of the light-emitting diode in this application is referenced. Figure 1 As shown.

[0034] By adopting the above technical solution: the hole transport layer of this application needs to be a cross-linked PF8Cz-X. Compared with the general-purpose hole transport layer TFB, the carbazole structural group in PF8Cz is chemically more stable than the triphenylamine structural group in TFB, which can avoid the damage to the hole transport layer caused by the photoacid generator (PAG) in the photoresist. This confirms that commonly used triphenylamine-based HTLs all suffer from free radical reaction damage problems, such as... Figure 3 As shown, the structural changes of PF8Cz-X and TFB, and the damage of PAG to TFB are as follows: Figure 4 As shown (TFB and PF8Cz-X structural formulas, such as...) Figure 4 (a) As shown in the figure, the main absorption peak disappears after the reaction of TFB and PAG, while Figure 4 (b) The main absorption peaks of PF8Cz-X remained almost unchanged after the reaction with PAG, confirming the chemical stability of PF8Cz-X.

[0035] Furthermore, cross-linked PF8Cz-X exhibits stronger solvent resistance compared to non-cross-linked hole transport layers, and is well-compatible with solution processing techniques in classic Micro-QLED lithography fabrication. This contrasts with the physical dissolution of the hole transport layer during surface development, where the thickness of the non-cross-linked hole transport layer (TFB) changes significantly before and after development. Figure 5 As shown, the cross-linked PF8Cz-X exhibits stable film thickness before and after development. Figure 6 The image shown is a microscopic photograph of a patterned insulating layer with a pixel diameter of approximately 3 μm obtained after micro-nano fabrication.

[0036] Preferably, the photoresist used is MicroChem SU8 2000.5 diluted with cyclopentanone.

[0037] Preferably, it further includes a transparent conductive substrate, wherein the electron transport layer is disposed on the ITO layer of the transparent conductive substrate as a substrate.

[0038] Preferably, the thermal crosslinking temperature of the crosslinked PF8Cz-X is 230°C.

[0039] Preferably, the required exposure dose of the photoresist on the cross-linked PF8Cz-X substrate is 50–60 mJ / cm. -2 .

[0040] The light-emitting layer includes: CdSe quantum dots, InP quantum dots, or halide perovskite quantum dots.

[0041] This invention uses insulating photoresist as a patterned charge blocking layer, which cleverly avoids excessive electron transport and improves the performance of light-emitting diode devices. It also uses cross-linked PF8Cz-X to avoid the physical dissolution of the hole transport layer by the developer during photolithography and the damage to the hole transport layer by the interfacial reaction of the photoactive components contained in the photoresist.

[0042] Preferably, the pixel pit array includes polygonal arrays, circular arrays, elliptical arrays, and star arrays; wherein, the polygonal array includes square arrays, rectangular arrays, rhombus arrays, and hexagonal arrays; and the star array includes pentagonal star arrays and polygonal star arrays.

[0043] The fabrication sequence includes sequentially depositing a hole injection layer, a hole transport layer, a patterned light-emitting layer, an electron transport layer, and a metal anode on an ITO layer on a transparent conductive substrate. The fabrication steps for the patterned light-emitting layer are as follows:

[0044] A hole injection layer and a crosslinked PF8Cz-X hole transport layer were spin-coated onto an ITO substrate, followed by annealing at 230°C to obtain the PF8Cz-X substrate.

[0045] (2) Provide an insulating photoresist layer with charge blocking effect, and fabricate a patterned thin film with pixel array through micro-nano processing technology;

[0046] (3) Fill the pixel pit array with luminescent material to obtain a patterned luminescent layer.

[0047] Methods for filling the pixel pit array with luminescent material include inkjet printing or spin coating.

[0048] The electron transport layer material is: a mixture of zinc oxide nanoparticles and polymers, zinc oxide nanoparticles, or zinc oxide nanoparticles doped with metal cations.

[0049] The hole injection layer material is one of the following: polymer PEDOT:PSS, molybdenum oxide, or nickel oxide.

[0050] Metal anode materials include gold, silver, or aluminum.

[0051] Example

[0052] The application of the method of this invention in the fabrication of micro / nano-scale light-emitting quantum dot array devices provides a method for fabricating micro / nano-scale light-emitting diodes. This method involves sequentially forming a first electrode, a first functional material layer, a patterned quantum dot light-emitting layer, a second functional material layer, and a second electrode on a substrate. The first electrode serves as the anode, the first functional material layer as the hole transport layer, and the second electrode as the cathode, with the second functional material layer serving as the electron transport layer; or the first electrode is the cathode, the first functional material layer as the electron transport layer, the second electrode as the anode, and the second functional material layer as the hole transport layer, resulting in... Figure 1 The light-emitting diode device shown includes the following steps in its fabrication method for the patterned light-emitting layer: Figure 2 As shown:

[0053] (1) A hole injection layer and a crosslinked PF8Cz-X hole transport layer were spin-coated onto an ITO substrate and then annealed at 230°C to obtain a PF8Cz-X substrate.

[0054] (2) Provide an insulating photoresist layer with charge blocking effect, and fabricate a patterned thin film with a pixel array by ultraviolet lithography process;

[0055] (3) Fill the pixel pit array with luminescent material to obtain the patterned luminescent layer.

[0056] The process flow of the present invention will be described in more detail below through examples.

[0057] Example 1:

[0058] (1) The transparent conductive substrate (i.e., “substrate”) was cleaned in water, acetone, water and ethanol in sequence, and then dried with nitrogen gas flow.

[0059] (2) Place the transparent conductive substrate in an O2 plasma cleaner for 10 minutes to perform surface hydrophilic treatment on the substrate;

[0060] (3) PEDOT:PDD hole transport layer and cross-linked PF8Cz-X hole transport layer were deposited on the substrate by spin coating and annealed at 230°C for 30 minutes.

[0061] (4) MicroChem SU8 2000.5 was diluted with cyclopentanone at a 1:1 volume ratio to obtain an ultrathin SU8 photoresist. It was then exposed to 365nm ultraviolet light at an exposure dose of 60mJ / cm² in an ultraviolet lithography machine. Following this, it was developed in propylene glycol methyl ether acetate (PGMEA) developer for 3 seconds to obtain a patterned insulating photoresist layer, such as... Figure 5 As shown in the figure, the film thickness of cross-linked PF8Cz-X remains stable during the development process. As shown in the figure, the film thickness height step hardly changes, which shows the strong solvent resistance of cross-linked PF8Cz-X during the development process.

[0062] (5) A patterned light-emitting layer is prepared by spin-coating a blue quantum dot solution with an absorbance (OD value) of 30 onto the patterned insulating photoresist layer obtained in step (4) at 2000 rpm for 30 s. Subsequently, a ZnMgO electron transport layer is spin-coated at 2000 rpm for 30 s, and a 100 nm aluminum electrode is deposited using a vacuum deposition machine to prepare a Micro-QLED array device. Figure 7 The image shown is an electroluminescence microscope image of a Micro-QLED array device; 3μm pixel diameter.

[0063] (6) Applying voltage to the device obtained in step (5) using a portable power supply yields an electroluminescent diode device with a unit light-emitting pixel size of approximately 2 μm, such as Figure 8 As shown.

[0064] In this embodiment, a Micro-QLED array device with a pixel density of approximately 6000 ppi and external quantum efficiencies of 16.5%, 20.1%, and 12.7% for red, green, and blue light, respectively, was fabricated by introducing a novel cross-linked PF8Cz-X hole transport layer and an ultrathin SU8 photoresist diluted with cyclopentanone. This represents the highest value for photolithography-based electroluminescent Micro-QLED fabrication. Figure 9 As shown.

[0065] In summary, the method of this invention is simple and easy to implement, and compared with technologies such as ligand engineering and photosensitive additives, it has greater feasibility for fabricating large-area, high-resolution light-emitting diodes. Furthermore, the failure mechanism of Micro-QLED devices fabricated by classical photolithography was analyzed in detail, and the problem was solved by using a cross-linked PF8Cz-X hole transport layer, resulting in a high-performance, high-resolution Micro-QLED device array.

[0066] The above embodiments are merely illustrative of the technical concept and features of the present invention, enabling those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes made based on the substance of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for fabricating a micrometer-scale quantum dot light-emitting diode array device, characterized in that, Includes the following steps: A hole injection layer, a hole transport layer, a patterned insulating layer, a quantum dot light-emitting layer, an electron transport layer, and a metal electrode are sequentially deposited on a transparent conductive substrate, namely an indium tin oxide (ITO) glass substrate. The patterned insulating layer has a thickness of 20 nm to 100 nm, and an arrayed light-emitting layer is formed by spin-coating quantum dots on the patterned insulating layer. The hole transport layer is a novel cross-linked poly((9,9-dioctylfluorenyl-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl)) that can avoid the free radical reaction of photoresist during photolithography and physical dissolution during the development step. The formation of the arrayed light-emitting layer is accomplished through the following steps: (2.1) An insulating photoresist layer with a thickness of less than 100 nm is formed on the hole transport layer; (2.2) The insulating photoresist layer is patterned to micro-nano dimensions using photolithography, electron beam direct writing or laser direct writing methods; (2.3) A micro-nano-scale quantum dot light-emitting array is deposited in the insulating photoresist layer after micro-nano-scale patterning by spin coating or inkjet printing.

2. The method according to claim 1, characterized in that, The insulating photoresist layer is made of any one or a combination of photoresists of type ARP5350, AZ 5214, and MicroChem SU8.

3. The method according to claim 1, characterized in that, The quantum dot is any one or a combination of CdSe quantum dots, InP quantum dots, halide perovskite quantum dots, or organic fluorescent quantum dots.

4. The method according to claim 1, characterized in that, The electron transport layer material is any one or more of the following: a mixture of zinc oxide nanoparticles and polymers, zinc oxide nanoparticles, or zinc oxide nanoparticles doped with metal cations.

5. The method according to claim 1, characterized in that, The hole injection layer material is one or more combinations of polymer PEDOT:PSS, molybdenum oxide, or nickel oxide.

6. The application of the fabrication method of the micron-scale quantum dot light-emitting diode array device as described in any one of claims 1-5 in the fabrication of micro / nano light-emitting diodes.

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