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

Abstract

The invention discloses a preparation method and application of a micron-sized quantum dot light-emitting diode array device, and the method comprises the steps: sequentially forming a hole injection layer, a hole transmission layer, a patterned insulating layer, a quantum dot light-emitting layer, an electron transmission layer and a top electrode on an indium tin oxide substrate, and preparing the patterned insulating layer through photoresist; quantum dots are spin-coated to form a process route of an array light-emitting layer, electron leakage generated at pixel gaps is inhibited through photoresist, high resolution is achieved, and meanwhile the performance of a recorded Micro-QLED array device is achieved; a novel cross-linked hole transport layer PF8Cz-X is adopted to verify and solve the problem that a photoacid generator component in the photoresist generates strong oxidizing photoacid, and a triphenylamine structure hole transport layer in the QLED device is damaged by a reaction in a free radical coordination binding mode; and physical dissolution of a developing solution in a micro-nano processing technology is avoided by designing a thermal crosslinking group, and a photoetching system which is compatible with a solution processing technology and lossless to the Micro-QLED array device is constructed.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano device preparation, and in particular relates to a preparation method and application of a micron-level quantum dot light-emitting diode array device. Background Art

[0002] In advanced display technology, photolithography is a process with high processing precision and can efficiently realize the production of large-area display panels. It also has the advantages of mature process technology and easy operation. Therefore, it has become a research hotspot for the production of high-resolution, large-area quantum dot light-emitting diodes.

[0003] In common photolithography technology, insulating photoresist is usually used as a patterned interlayer to realize micron-scale quantum dot light-emitting diodes (Micro-QLED). Photoresists represented by ARP 5350, AZ 5214, and MicroChem SU8 are not compatible with the solution preparation process of QLED devices. Their electron and hole transport layers are easily dissolved by the developer and thus destroy the device structure. In addition, the potential interface inversion of the functional layer materials in the QLED device structure by the photoactive components in commercial photoresists is still unknown. Therefore, the current mainstream research hotspot is to achieve quantum dot patterning through photosensitive additives or quantum dot surface ligand engineering.

[0004] Patent document with publication number CN114839835A discloses a technical route for preparing patterned quantum dot films by means of a mixed quantum dot solution with a photosensitive cross-linker containing a diazirine group. When the diazirine is exposed to ultraviolet light, an intermediate singlet carbene is generated. The carbene undergoes an insertion reaction with the carbon-hydrogen bond in the adjacent quantum dot ligand, thereby achieving bridging between two adjacent quantum dots, thereby changing the solubility and realizing patterning of the quantum dot film.

[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 have greatly damaged the photoelectric properties of the quantum dots themselves, and cannot prevent the electron leakage in the pixel gaps, making it difficult to produce high-performance electroluminescent Micro-QLED array devices. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a preparation method and application of a micron-scale quantum dot light-emitting diode array device. The preparation method is simple and easy to operate, and can realize the preparation of large-area, high-resolution Micro-QLED arrays.

[0007] The first aspect of the present invention provides a method for preparing a micron-scale quantum dot light-emitting diode array device, comprising the following steps: 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 in sequence on a transparent conductive substrate, i.e., 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.

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

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

[0010] (2.2) performing micro-nano-scale patterning on the insulating photoresist layer by photolithography, electron beam direct writing or laser direct writing;

[0011] (2.3) Using spin coating or inkjet printing to form a deposited micro-nanoscale quantum dot light-emitting array in the insulating photoresist layer after micro-nanoscale patterning.

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

[0013] Specifically, the quantum dots are any one or more combinations of CdSe quantum dots, InP quantum dots, halogen 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 free radical reaction of photoresist during photolithography and physical dissolution in the development step.

[0015] Specifically, 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, or any one or more combinations thereof.

[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: application of the method for preparing the micron-scale quantum dot light-emitting diode array device in the preparation of micro-nano light-emitting diodes.

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

[0019] (1) The present invention proposes a method for preparing a micron-scale quantum dot light-emitting diode array device and its application, which is a process route for preparing a patterned insulating layer using photoresist. The photoresist suppresses the electron leakage generated at the pixel gap, achieves high resolution, and realizes the external quantum efficiency record of the patterned quantum dot light-emitting diode array device prepared by photolithography, which greatly improves the performance of the Micro-QLED array device.

[0020] (2) The new cross-linked hole transport layer PF8Cz-X was used to verify and solve the problem that the photoacid generator (PAG) component present in commercial negative chemically amplified photoresists (such as SU-8) generates strong oxidizing photoacids represented by fluoroantimonic acid, which reacts and damages 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 processing technology was avoided, and a solution processing-compatible lithography system was constructed that is non-destructive to the Micro-QLED array device.

[0021] (3) The present invention adopts a carbazole-based cross-linked hole transport layer with strong solvent resistance, which can avoid damage from free radical reactions generated by commercial photoresists and physical dissolution during the development process. A patterned insulating photoresist layer made of ultra-thin insulating photoresist is arranged between the electron transport layer and the hole transport layer to form a pattern interval and block electron transmission in the gap 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 as a charge blocking layer; a light-emitting point is arranged in the blank area in the pit of each pixel pit, and the upper and lower parts of the light-emitting layer are respectively in contact with the electron transport layer and the hole transport layer to facilitate the excitation of the light-emitting layer, and a plurality of light-emitting pixels form a light-emitting array. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0024] Figure 3The absorption spectrum data of two HTLs: poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)] (TFB) and poly((9,9-dioctylfluorenyl-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl))(PF8Cz) before and after the reaction with PAC, and the structural formula of the corresponding HTL materials is shown in the figure; Figure (a) is a curve diagram of the absorption spectrum change before and after the reaction of TFB with PAG; Figure (b) is a curve diagram of the absorption spectrum change before and after the reaction of PF8Cz with PAG;

[0025] Figure 4 The absorption spectrum data of the commonly used triphenylamine structure HTL before and after the reaction with PAC, and the structure of the corresponding HTL material is shown in the figure; Figure (a) is a curve diagram of the absorption spectrum change before and after the reaction of 4,4',4"-tri(carbazole-9-yl)triphenylamine (TCTA) with PAG; Figure (b) is a curve diagram of the absorption spectrum change before and after the reaction of poly[bis(4-phenyl)(4-butylphenyl)amine] (Poly-TPD) with PAG;

[0026] Figure 5 It is the dissolution film thickness variation curve of non-cross-linked PF8Cz during the development process;

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

[0028] Figure 7 This is a microscope photo of a patterned insulating layer with a pixel diameter of about 3 μm obtained after micro-nano processing;

[0029] Figure 8 The electroluminescence microscope image of the Micro-QLED array device with a pixel diameter of about 2μm was finally prepared;

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

[0031] The present invention provides a micron-scale quantum dot light-emitting diode array device and a preparation method thereof. The preparation method is simple and easy to operate, and can realize the preparation of a large-area, high-resolution Micro-QLED array. It should be emphasized that: the present invention adopts a carbazole-based cross-linked hole transport layer with strong solvent resistance, which can avoid free radical reaction damage with commercial photoresist and physical dissolution during the development process. A patterned insulating photoresist layer made of ultra-thin (film thickness greater than 20nm and less than 100nm) insulating photoresist is arranged between the electron transport layer and the hole transport layer to form a pattern interval and block electron transmission in the gap 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 as a charge blocking layer; a light-emitting layer is arranged in the blank area in the pit of each pixel pit, and the upper and lower parts of the light-emitting layer are respectively in contact with the electron transport layer and the hole transport layer to facilitate the excitation of the light-emitting layer, and a plurality of light-emitting pixels form a light-emitting array.

[0032] A classical photolithography preparation system for a Micro-QLED array, comprising an electron transport layer and a hole transport layer, wherein a patterned insulating photoresist layer for blocking electron movement is disposed between the electron transport layer and the hole transport layer, and the photoresist layer forms a mesh pixel pit array after undergoing micro-nano processing such as exposure and development;

[0033] The wall of each pixel pit is an insulating photoresist, and any two adjacent pixel pits are separated by a photoresist as a charge blocking layer; the blank area in each pixel pit is used to fill the quantum dot solution to form a light-emitting layer, and the upper and lower sides of the light-emitting layer are respectively in contact with the electron transport layer and the hole transport layer to facilitate the excitation of the light-emitting layer, thereby forming a light-emitting array. Figure 1 shown.

[0034] By adopting the above technical solution: the hole transport layer of the present application needs to be a cross-linked PF8Cz-X. Compared with the general hole transport layer TFB, the carbazole structural group in PF8Cz is chemically stable compared with the triphenylamine structural group in TFB, which can avoid the damage of the hole transport layer to the hole transport layer by the free radical generated by the photoacid generator (PAG) in the photoresist. It is confirmed that the commonly used triphenylamine-based HTL has the problem of free radical reaction damage, such as Figure 3 As shown in Figure 2, the structural changes of PF8Cz-X and TFB and the damage of PAG to TFB are shown in Figure 2. Figure 4 As shown (TFB and PF8Cz-X structure, such as Figure 4 (a) It can be seen that the main absorption peak disappears after the reaction of TFB and PAG. Figure 4 (b) The main absorption peak of PF8Cz-X remains almost unchanged after the reaction with PAG, confirming the chemical stability of PF8Cz-X).

[0035] In addition, the cross-linked PF8Cz-X has stronger solvent resistance than the non-cross-linked hole transport layer, and is well compatible with the solution processing technology in the classic photolithography preparation of Micro-QLED. The physical dissolution of the hole transport layer during the surface development process, the thickness change of the non-cross-linked hole transport layer (TFB) before and after development is as follows Figure 5 As shown, the film thickness of cross-linked PF8Cz-X is stable before and after development. Figure 6 The microscopic photograph of the patterned insulating layer with a pixel diameter of about 3 μm obtained after micro-nano processing is shown.

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

[0037] Preferably, a transparent conductive substrate is further included, and the electron transport layer is arranged on the ITO layer of the transparent conductive substrate as a base.

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

[0039] Preferably, the exposure dose required for 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 halogen perovskite quantum dots.

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

[0042] Preferably, the pixel pit array includes a polygonal array, a circular array, an elliptical array, and a star array; wherein the polygonal row array includes a square array, a rectangular array, a diamond array, and a hexagonal array; and the star array includes a pentagram array and a polygonal star array.

[0043] The preparation 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 the ITO layer of the transparent conductive substrate. The preparation steps of the patterned light-emitting layer are as follows:

[0044] A hole injection layer and a cross-linked PF8Cz-X hole transport layer are spin-coated on an ITO substrate, followed by annealing at 230° C. to obtain a PF8Cz-X substrate;

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

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

[0047] Methods for filling the pixel pit array with light-emitting 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 polymer PEDOT:PSS, molybdenum oxide or nickel oxide.

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

[0051] Example

[0052] A method for preparing a micro-nano light-emitting diode is prepared by using the method of the present invention in preparing a micro-nano light-emitting quantum dot array device. The method is to sequentially form 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, wherein the first electrode is an anode, the first functional material layer is a hole transport layer, the second electrode is a cathode, and the second functional material layer is an electron transport layer; or the first electrode is a cathode, the first functional material layer is an electron transport layer, the second electrode is an anode, and the second functional material layer is a hole transport layer, to obtain a first electrode, a first functional material layer, a first functional material layer, a second functional material layer, and a second electrode. Figure 1 The light emitting diode device shown in the figure, wherein the method for preparing the patterned light emitting layer comprises the following steps: Figure 2 As shown:

[0053] (1) spin coating and depositing a hole injection layer and a cross-linked PF8Cz-X hole transport layer on an ITO substrate, followed by annealing at 230° C. to obtain a PF8Cz-X substrate;

[0054] (2) providing an insulating photoresist layer having a charge blocking effect, and forming a patterned film having a pixel array by ultraviolet photolithography;

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

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

[0057] Embodiment 1:

[0058] (1) washing the transparent conductive substrate (i.e., the "substrate") in water, acetone, water, and ethanol in sequence, and then drying it with a nitrogen gas flow;

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

[0060] (3) Spin coating of a PEDOT:PDD hole transport layer and a cross-linked PF8Cz-X hole transport layer on the substrate and annealing at 230 °C for 30 min

[0061] (4) MicroChem SU8 2000.5 was diluted with cyclopentanone at a volume ratio of 1:1 to obtain an ultrathin SU8 photoresist, which was then exposed to ultraviolet light at a wavelength of 365 nm and an exposure dose of 60 mJ / cm2 in an ultraviolet photolithography machine, and then developed in a propylene glycol methyl ether acetate (PGMEA) developer for 3 seconds to obtain a patterned insulating photoresist layer, such as Figure 5 As shown (the film thickness of the cross-linked PF8Cz-X remains stable during the development process. As shown in the figure, the height step of the film thickness has almost no change, which shows the strong solvent resistance of the cross-linked PF8Cz-X during the development process).

[0062] (5) Spin coating a blue light quantum dot solution with an absorbance (OD value) of 30 on the patterned insulating photoresist layer obtained in step (4) at 2000 rpm for 30 s to prepare a patterned light-emitting layer, then spin coating a ZnMgO electron transport layer at 2000 rpm for 30 s and depositing a 100 nm aluminum electrode by a vacuum coating machine to prepare a Micro-QLED array device; Figure 7 Shown (electroluminescence microscope photograph of Micro-QLED array device; 3μm pixel diameter).

[0063] (6) applying voltage to the device obtained in step (5) through a portable power source to obtain an electroluminescent diode device with a unit light-emitting pixel of about 2 μm, such as Figure 8 shown.

[0064] In this embodiment, by introducing a novel cross-linked PF8Cz-X hole transport layer and an ultra-thin SU8 photoresist obtained by diluting cyclopentanone, a Micro-QLED array device with a pixel density of about 6000ppi and external quantum efficiencies of 16.5%, 20.1%, and 12.7% for red, green, and blue, respectively, is prepared, which is the highest value for preparing electroluminescent Micro-QLEDs by photolithography process. Fig. 9 shown.

[0065] In summary, the method of the present invention is simple and easy to implement. Compared with ligand engineering, photosensitive additives and other technologies, it is more feasible for the preparation of large-area, high-resolution light-emitting diodes. It also analyzes in detail the failure mechanism of previous classical photolithography-prepared Micro-QLED devices, and solves the problem through a cross-linked PF8Cz-X hole transport layer to obtain a high-performance, high-resolution Micro-QLED device array.

[0066] The above embodiments are only for illustrating the technical concept and features of the present invention, so that ordinary technicians in the field can understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a micron-scale quantum dot light-emitting diode array device, characterized in that: The following steps are involved: 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, i.e., an indium tin oxide (ITO) glass substrate; 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.

2. The method according to claim 1, characterized in that The formation of the arrayed light-emitting layer is completed by the following steps: (2.1) forming an insulating photoresist layer with a thickness of less than 100 nm on the hole transport layer; (2.2) performing micro-nano-scale patterning on the insulating photoresist layer by photolithography, electron beam direct writing or laser direct writing; (2.3) Using spin coating or inkjet printing to form a deposited micro-nanoscale quantum dot light-emitting array in the insulating photoresist layer after micro-nanoscale patterning.

3. The method according to claim 2, characterized in that The material of the insulating photoresist layer is any one or more combinations of photoresists of model ARP5350, AZ 5214, and MicroChem SU8.

4. The method according to claim 1, characterized in that: The quantum dots are any one or more combinations of CdSe quantum dots, InP quantum dots, halogen perovskite quantum dots or organic fluorescent quantum dots.

5. The method according to claim 1, characterized in that: 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 free radical reaction of photoresist during photolithography and physical dissolution in the development step.

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

7. 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.

8. Application of the method for preparing a micron-scale quantum dot light-emitting array device according to any one of claims 1 to 7 in preparing micro-nano light-emitting diodes.

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