A quantum dot film with a dot-wall structure, a QLED device, and its fabrication method

Abstract

This invention belongs to the field of quantum dot display technology, specifically relating to a quantum dot film with a dot-wall structure, a QLED device, and its fabrication method. The quantum dot film of the QLED device comprises ordered pixels composed of a single layer of quantum dots and a charge isolation layer composed of a double layer of quantum dots located between the pixels. The quantum dot film is fabricated simultaneously via a PDMS stamp: a single-layer film is formed by the self-assembly of quantum dots on a liquid surface, which is then picked up and transferred onto a hole transport layer using a PDMS stamp with a specific microstructure, thus obtaining the "dot" and "wall" structure in one step. This method is simple and efficient, requiring no additional isolation materials or processes, avoiding the performance degradation caused by such processes, and achieving simple and efficient fabrication of the charge isolation layer, showing promising application prospects in the field of quantum dot displays.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot display technology, specifically relating to a quantum dot film with a dot-wall structure, a QLED device, and its fabrication method. Background Technology

[0002] With the development of next-generation display technologies centered on near-eye display technology, higher demands are being placed on pixel resolution in next-generation displays. Colloidal quantum dots (QDs) have been extensively studied due to their excellent optoelectronic properties, such as high luminous quantum efficiency, narrow emission bandwidth, wide range of tunable emission wavelengths, and high stability. Over the past few decades, research on quantum dot light-emitting diodes (QLEDs) using QDs as the emitting layer has achieved technological breakthroughs. QLEDs possess advantages such as high color purity, high brightness, and wide color gamut, demonstrating broad application prospects in next-generation displays.

[0003] Methods for achieving high-resolution patterning of QDs mainly include inkjet printing, photolithography, and transfer printing. Inkjet printing directly sprays ink from nozzles to pattern QDs, but due to nozzle size limitations, it is difficult to manufacture high-resolution QD pixels (<500 PPI). Photolithography for QD pixel fabrication cannot avoid problems such as photoresist residue and solvent damage, leading to performance degradation; furthermore, due to limitations in photolithography technology, QD pixel sizes are typically larger than a few micrometers. Transfer printing technology offers advantages such as low cost, no pollution, and high resolution in achieving high-resolution QD patterning. However, QLEDs manufactured by transfer printing have a lower external quantum efficiency (EQE) compared to their spin-coated counterparts. This performance degradation is attributed to the large leakage current caused by the direct contact between the electron transport layer (ETL) and hole transport layer (HTL) in pixel-free areas in transfer-printed QLEDs. To address this issue, polymethyl methacrylate (PMMA) is typically spin-coated between the ETL and HTL as a charge isolation layer; however, this method, as an additional step in the QLED device manufacturing process, increases the difficulty and cost of device fabrication.

[0004] Therefore, developing a simple and efficient method for fabricating a charge isolation layer that does not introduce additional materials and process steps is of great significance for manufacturing high-performance QLED devices. Summary of the Invention

[0005] To address the shortcomings of existing technologies, one objective of this invention is to provide a quantum dot film with a dot-wall structure. This quantum dot film uses a PDMS stamp to simultaneously prepare quantum dot pixels and a charge isolation layer in a single transfer process, avoiding the additional materials and process steps introduced by preparing a PMMA charge isolation layer. This achieves simple and efficient preparation of the charge isolation layer, and thus constructs QLED devices.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a quantum dot film with a dot-wall structure, the quantum dot film comprising quantum dot pixels arranged in an ordered dot matrix and a charge isolation layer distributed between the pixels, the quantum dot pixels being composed of a single layer of quantum dots and the charge isolation layer being composed of a double layer of quantum dots, the quantum dot pixels and the charge isolation layer being prepared simultaneously by using a PDMS stamp for one-time transfer.

[0007] A second objective of this invention is to provide a method for preparing the above-mentioned quantum dot film with a dot-wall structure, comprising the following steps:

[0008] S11. Add quantum dot solution to the surface of deionized water to allow the quantum dots to self-assemble at the gas-liquid interface to form a monolayer quantum dot film.

[0009] S12. Use a pre-made PDMS stamp to pick up a single-layer quantum dot film on the surface of deionized water; the PDMS stamp has a hexagonal array of cones, the distance between the centers of adjacent cones is 800-1200 nm, the bottom diameter of the cones is 740-750 nm, the aspect ratio is 0.5-0.55, and the tip curvature radius is 30-40 nm.

[0010] S13. The PDMS stamp with the single-layer quantum dot film is attached to the surface of the hole transport layer, and after pressing, separation and annealing, quantum dot pixels and charge isolation layer are obtained on the hole transport layer at the same time.

[0011] Further improvements were made to the preparation method of quantum dot films with dot-wall structures:

[0012] Preferably, in step S11, the quantum dot material in the quantum dot solution is a core-shell structured CdSe / ZnS, with CdSe as the core and ZnS as the outer shell, and the solvent is n-octane.

[0013] Preferably, in step S11, the concentration C of the quantum dot material in the quantum dot solution is 5-10 mg / ml, the volume V of the added quantum dot solution is 10-45 μL, the radius R of the container holding the deionized water is 3-4.5 cm, and the numerical relationship between C×V and R is C×V = (10~12)R. 2 .

[0014] Preferably, the PDMS stamp is prepared by the following method:

[0015] S21. Mix the PDMS prepolymer and curing agent at a mass ratio of 10:1 and stir until homogeneous to form a PDMS mixture;

[0016] S22. Take a patterned substrate with a non-penetrating, ordered lattice arrangement of microstructures on its surface, pour the PDMS mixture onto the surface of the microstructures in the patterned substrate, let it stand in vacuum, and then heat it at 40-100℃ to solidify the PDMS mixture.

[0017] S23. Separate the cured PDMS from the patterned substrate to obtain the PDMS stamp. The shape of the cone on the PDMS stamp corresponds to the shape of the microstructure on the patterned substrate.

[0018] The third objective of this invention is to provide a QLED device, the QLED device structure comprising, from bottom to top, an ITO substrate, a hole injection layer, a hole transport layer, a quantum dot film with a dot-wall structure, an electron transport layer, and a metal cathode.

[0019] A third objective of this invention is to provide a method for fabricating the aforementioned QLED device, comprising the following steps:

[0020] S1. Spin-coat a hole injection layer material onto a clean, hydrophilic ITO substrate and anneal it to form a hole injection layer.

[0021] S2. Spin-coat hole transport layer material onto hole injection layer and anneal it to form hole transport layer.

[0022] S3. Using a PDMS stamp, quantum dot pixels and a charge isolation layer are simultaneously prepared by transferring them onto the hole transport layer once. The quantum dot film is obtained by annealing at 60-100 °C.

[0023] S4. Spin-coat an electron transport layer material onto a quantum dot film and anneal it to form an electron transport layer.

[0024] S5. A metal electrode is deposited on the electron transport layer as a metal cathode, and then packaged to obtain a QLED device.

[0025] As a further improvement to the fabrication method of the above-mentioned QLED devices:

[0026] Preferably, the rotation speed of the spin coating material in steps S1, S2 and S4 is 2000-4000 rpm and the time is 40-60 s.

[0027] Preferably, the annealing temperature in steps S1, S2 and S4 is 80-130 ℃ and the time is 10-30 min.

[0028] Preferably, in step S5, the thickness of the metal cathode is 80-130 nm.

[0029] The advantages of this invention compared to the prior art are as follows:

[0030] (1) This invention discloses a quantum dot film with a dot-wall structure, comprising quantum dot pixels arranged in an ordered lattice and a charge isolation layer distributed between the pixels. The pixels are composed of a single layer of quantum dots arranged in an ordered lattice, emitting light when the QLED device is working, and are referred to as "dots". The charge isolation layer is composed of a double layer of quantum dots distributed between the pixels, acting as an isolation layer between the hole transport layer and the electron transport layer, and does not emit light when the QLED device is working, and is referred to as "walls". The "dots" and "walls" are simultaneously fabricated in a single transfer process using a PDMS stamp to transfer quantum dots, and are collectively referred to as a quantum dot film with a dot-wall structure. This method simultaneously prepares quantum dot pixels and a charge isolation layer in a single transfer process, and the pixels and the charge isolation layer are made of the same quantum dot material, avoiding the increased process difficulty and decreased device performance caused by introducing additional materials and process steps in the preparation of the charge isolation layer, thus achieving simple and efficient preparation of the charge isolation layer.

[0031] (2) This invention provides a QLED device composed of a quantum dot film with a dot-wall structure. The device, from bottom to top, comprises an ITO substrate, a hole injection layer, a hole transport layer, a quantum dot film, an electron transport layer, and a metal cathode. The QLED device fabrication process is simple, eliminating the need for complex photolithography or inkjet printing processes, thus reducing device fabrication costs. The patterned substrate, used as a template for fabricating PDMS stamps, can be reused. No additional charge isolation layer materials or processing steps are required, avoiding the increased processing difficulty and performance degradation caused by introducing additional materials. This allows for wide application in displays and optoelectronics. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the process of preparing a cone-shaped PDMS stamp in Example 1 and transferring quantum dots using the cone-shaped PDMS stamp.

[0033] Figure 2 (a) is a scanning electron microscope image of the patterned substrate with cone-shaped pits used in Example 1, and (b) is a scanning electron microscope image of the obtained cone-shaped PDMS stamp.

[0034] Figure 3 In the figures (a), (b), and (c), the contact angles between the cone-shaped PDMS stamps prepared in Examples 1-3 and water are shown, respectively.

[0035] Figure 4 This is a schematic diagram illustrating the process of preparing a hemispherical PDMS stamp in Example 4 and transferring quantum dots using the hemispherical PDMS stamp.

[0036] Figure 5(a) is a scanning electron microscope image of the patterned substrate with hemispherical pits used in Example 4, and (b) is a scanning electron microscope image of the hemispherical PDMS stamp.

[0037] Figure 6 This is a schematic diagram illustrating the principle of using a cone-shaped PDMS stamp to pick up a single-layer quantum dot film on the water surface in Example 1.

[0038] Figure 7 (a) is a scanning electron microscope image of the quantum dot pixels and charge isolation layer prepared using the PDMS stamp of Preparation Example 1, the inset in the upper right corner is a schematic diagram of the quantum dot pixels and charge isolation layer, and (b) is a fluorescence microscope image of it. Figure 7 (c) shows the thickness characterization of the quantum dot pixel and charge isolation layer prepared in Example 1.

[0039] Figure 8 In the middle (a) and (b), respectively, are scanning electron microscope and fluorescence microscope images of the complete quantum dot film prepared by the cone-shaped hydrophilic PDMS stamp of Preparation Example 2; Figure 8 In the middle (c) and (d), respectively, are scanning electron microscope images and fluorescence microscope images of quantum dot pixels prepared using the cone-shaped hydrophobic PDMS stamp of Preparation Example 3; Figure 8 In the middle (e) and (f), respectively, are scanning electron microscope and fluorescence microscope images of quantum dot pixels obtained using a hemispherical PDMS stamp.

[0040] Figure 9 In Figures (a) and (b), respectively, a schematic diagram of the structure of the QLED device prepared in Example 1 and an electroluminescent photograph.

[0041] Figure 10 Tables (a)-(f) show the performance test results of the QLED devices prepared in Examples 1-3 and Comparative Examples 1-3, respectively. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0043] Preparation Example 1

[0044] This preparation example provides a method for preparing a cone-shaped PDMS stamp, the process of which is as follows: Figure 1 (a)-(b) specifically includes the following steps:

[0045] S21. Mix PDMS prepolymer and PDMS curing agent at a mass ratio of 10:1 and stir until homogeneous to form PDMS mixture;

[0046] S22, Subsequently, a patterned substrate with a non-penetrating, ordered lattice arrangement of microstructures on its surface is taken (its scanning electron microscope image is shown in Figure 1). Figure 2 As shown in (a), the microstructure is cone-shaped and the adjacent cones are arranged in a hexagonal pattern. The distance between the centers of the adjacent cones, i.e. the period, is 1000 nm. The opening diameter of the cone is 740 nm, the depth-to-width ratio is 0.55, and the radius of curvature of the tip is 35 nm.

[0047] The PDMS mixture was poured onto the surface of the microstructure in the patterned substrate, left to stand in vacuum for 2 hours, and then heated at 60°C to cure the PDMS mixture.

[0048] S23. Separate the cured PDMS from the patterned substrate to obtain the PDMS stamp.

[0049] Scanning electron microscope images of the PDMS stamps prepared above are shown below. Figure 2 As shown in (b), its surface has an ordered array of cones arranged in a lattice. The distance between the centers of adjacent cones is 1000 nm, the diameter of the base of the cone is 740 nm, the aspect ratio is 0.55, and the radius of curvature of the tip is 35 nm. Testing shows that... Figure 3 As shown in (a), its contact angle with water is 116.6°.

[0050] Preparation Example 2

[0051] This preparation example provides a method for preparing a cone-shaped hydrophilic PDMS stamp. The specific steps are the same as in Example 1, except that the PDMS stamp obtained in step S23 undergoes surface oxygen plasma treatment to make the stamp surface hydrophilic. Testing showed that... Figure 3 As shown in (b), the contact angle between the hydrophilic PDMS stamp and water is 75.0°.

[0052] Preparation Example 3

[0053] This preparation example provides a method for preparing a cone-shaped hydrophobic PDMS stamp. The specific steps are the same as in Example 1, except that the cone-shaped PDMS stamp obtained in step S23 undergoes a surface hydrophobic treatment: it is immersed in a hexane solution of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) for 30 min, then the PDMS stamp is removed and the residual FDTS solution on its surface is washed off, and then it is placed in a 60 ℃ oven to dry completely. Testing shows that... Figure 3 As shown in (c), the contact angle between the hydrophobic PDMS stamp and water is 134.7°.

[0054] Preparation Example 4

[0055] This preparation example provides a method for preparing a hemispherical PDMS stamp, the process of which is as follows: Figure 4 (a)-(b) specifically includes the following steps:

[0056] S21. Mix PDMS prepolymer and PDMS curing agent in a 10:1 ratio and stir to form a PDMS mixture;

[0057] S22, Subsequently, a patterned substrate with a non-penetrating, ordered lattice arrangement of microstructures on its surface is taken (its scanning electron microscope image is shown in Figure 1). Figure 5 As shown in (a), the microstructure is a hemispherical pit with adjacent pits arranged in a hexagonal pattern. The distance between the centers of adjacent pits, i.e. the period, is 1000 nm. The opening diameter of the pit is 860 nm, the depth-to-width ratio is 0.55, and the radius of curvature of the tip is 500 nm.

[0058] The PDMS mixture was poured onto the surface of the microstructure in the patterned substrate, left to stand in vacuum for 2 hours, and then heated at 60°C to cure the PDMS mixture.

[0059] S23. Separate the cured PDMS from the patterned substrate to obtain the PDMS stamp.

[0060] Scanning electron microscope images of the PDMS stamps prepared above are shown below. Figure 5 As shown in (b), its surface has an ordered array of hemispherical dots, the distance between the centers of adjacent hemispheres is 1000 nm, the bottom diameter of the hemisphere is 860 nm, the aspect ratio is 0.55, and the radius of curvature of the tip of the hemispherical structure is 500 nm.

[0061] Example 1

[0062] This embodiment provides a method for fabricating a QLED device with a quantum dot film having a dot-wall structure, comprising the following steps:

[0063] S1. First, the ITO substrate with a size of 3 cm × 3 cm is ultrasonically cleaned in acetone, ethanol and deionized water for 10 min in sequence to make its surface clean. Then, it is cleaned with O2 in a plasma cleaner for 10 min to ensure that the substrate surface is hydrophilic.

[0064] Hole injection layer material PEDOT:PSS was spin-coated onto a clean, hydrophilic ITO substrate. The PEDOT:PSS solution concentration was 1.5 wt%, the spin-coating speed was 4000 rpm, and the spin-coating time was 40 s. Then, the substrate was annealed at 120 ℃ for 20 min to form a hole injection layer.

[0065] S2. Spin-coat the hole transport layer material TFB onto the hole injection layer. The TFB solution concentration is 7 mg / ml, the spin-coating speed is 4000 rpm, the spin-coating time is 40 s, and the layer is annealed at 120 ℃ for 30 min to form the hole transport layer.

[0066] S3. Add deionized water to a culture dish with a radius of 3 cm, and then add 10 μL of red CdSe / ZnS quantum dot solution with a concentration of 10 mg / ml to the culture dish. The solvent of the solution is n-octane. The quantum dots self-assemble at the liquid-gas interface to form a monolayer quantum dot film.

[0067] The PDMS stamp prepared in Preparation Example 1 was used to pick up the monolayer quantum dot film on the water surface. Then, the PDMS stamp with the picked-up quantum dot film was attached to the hole transport layer prepared in step S2. By pressing and separating the PDMS stamp in sequence, quantum dot pixels and a charge isolation layer can be formed on the hole transport layer. After annealing at 80 °C for 10 min, the quantum dot film was obtained. The transfer process is as follows. Figure 1 (c)-(d);

[0068] S4. Spin-coat ZnO nanoparticles, an electron transport layer material, onto a quantum dot film. The ZnO solution concentration is 30 mg / ml, the spin-coating speed is 2000 rpm, the spin-coating time is 60 s, and the film is annealed at 80 ℃ for 10 min to form an electron transport layer.

[0069] S5. A 100 nm thick Ag electrode is deposited on the electron transport layer and then encapsulated to obtain a QLED device.

[0070] The process for transferring and preparing quantum dot films using the cone-shaped PDMS stamp from Preparation Example 1 is as follows: Figure 1 As shown in (c)-(d) of Example 1, in step S3, when a 10 μL quantum dot solution with a concentration of 10 mg / ml is dropped onto the water surface in a petri dish with a radius of 3 cm, these appropriate amounts of quantum dots undergo gas-liquid interface self-assembly at the water surface under the influence of water surface tension, forming a dense monolayer quantum dot film. Subsequently, a cone-shaped PDMS stamp is used to pick up the monolayer quantum dot film on the water surface. A schematic diagram of the picking process is shown below. Figure 6As shown, during the pickup process, the top of the cone-shaped PDMS stamp first contacts the monolayer quantum dot film on the water surface, at which point the top of the stamp picks up the monolayer quantum dots. At this point, due to the low surface energy of the cone-shaped PDMS stamp, the integrity of the water surface is not disrupted; instead, a curved liquid surface forms between the cone-shaped microstructures of the stamp. As the pickup process continues, the stamp gradually immerses in the water. At this point, due to the sharpness of the cone-shaped microstructures of the PDMS stamp (its tip curvature radius is approximately 35 nm), the integrity of the water surface is disrupted, and the surface tension causes it to contract towards the center. The monolayer quantum dot film on the water surface then converges towards the center and deposits in the bottom gaps between the cone-shaped microstructures of the PDMS stamp, forming a double layer of quantum dots. Finally, the quantum dots picked up on the PDMS stamp are transferred to the hole transport layer, thus simultaneously preparing quantum dot pixels and a charge isolation layer.

[0071] Figure 7 (a) is a scanning electron microscope image of the quantum dot pixels and charge isolation layer prepared using the PDMS stamp of Preparation Example 1, and (b) is a fluorescence microscope image of the same. The thickness of the quantum dot pixels and charge isolation layer is as follows: Figure 7 As shown in (c), the pixels are composed of a single layer of quantum dots, and the charge isolation layer is composed of a double layer of quantum dots.

[0072] Referring to steps S1-S3 in Example 1, the cone-shaped hydrophilic PDMS stamp prepared in Preparation Example 2, the cone-shaped hydrophobic PDMS stamp prepared in Preparation Example 3, and the hemispherical PDMS stamp prepared in Preparation Example 4 were used to transfer and prepare quantum dot films on the hole transport layer.

[0073] Figure 8 In the middle (a) and (b), respectively, are scanning electron microscope and fluorescence microscope images of the complete quantum dot film prepared by using a cone-shaped hydrophilic PDMS stamp. Figure 8 In the middle (c) and (d), respectively, are scanning electron microscope and fluorescence microscope images of quantum dot pixels obtained by using a cone-shaped hydrophobic PDMS stamp. Figure 8 Images (e) and (f) are scanning electron microscope (SEM) and fluorescence microscope (FMS) images of quantum dot pixels obtained using a hemispherical PDMS stamp, respectively. Figure 8 It is evident that the microstructure morphology and surface energy (represented by the contact angle between the stamp and water) of the PDMS stamp directly determine the morphology of the quantum dot structure obtained by transfer printing. When the microstructure morphology of the PDMS stamp is the cone-shaped protrusion structure described in Preparation Example 1, and the contact angle between the stamp and water is 116.6°, a point-wall structure quantum dot film can be obtained; when the contact angle between the stamp and water increases or decreases, only complete quantum dot films or quantum dot pixels can be obtained; when the radius of curvature of the tip of the stamp microstructure increases, only quantum dot pixels can be obtained.

[0074] The structural schematic diagram of the QLED device fabricated using a cone-shaped PDMS stamp in Example 1 is shown in Figure 9(a), and the electroluminescence photograph is shown in Figure 9(a). Figure 9 As shown in (b). From Figure 9 It can be seen that the QLED device prepared by the method described in Example 1 has a complete light-emitting area, demonstrating the feasibility of this method in preparing large-area QLED devices with quantum dot films having a dot-wall structure.

[0075] Example 2

[0076] This embodiment provides a method for preparing a QLED device with a quantum dot film having a dot-wall structure. The specific steps are the same as in Embodiment 1, except that in step S3, deionized water is added to a culture dish with a radius of 3 cm, and then 20 μL of a red CdSe / ZnS quantum dot solution with a concentration of 5 mg / ml is added dropwise to the culture dish. The solvent of the solution is n-octane, and the quantum dots self-assemble on the water surface to form a monolayer quantum dot film.

[0077] Using the PDMS stamp prepared in Preparation Example 1, a monolayer quantum dot film was picked up from the water surface. The PDMS stamp containing the picked-up quantum dot film was then attached to the hole transport layer from step S1. By pressing and separating the PDMS stamp sequentially, quantum dot pixels and a charge isolation layer were fabricated on the hole transport layer. Annealing at 80 °C for 10 min yielded the quantum dot film. Finally, a QLED device was fabricated.

[0078] Example 3

[0079] This embodiment provides a method for preparing a QLED device with a quantum dot film having a dot-wall structure. The specific steps are the same as in Embodiment 1, except that in step S3, deionized water is added to a culture dish with a radius of 4.5 cm, and then 45 μL of a red CdSe / ZnS quantum dot solution with a concentration of 5 mg / ml is added to the culture dish. The solvent of the solution is n-octane, and the quantum dots self-assemble on the water surface to form a monolayer quantum dot film.

[0080] Using the PDMS stamp prepared in Preparation Example 1, a monolayer quantum dot film was picked up from the water surface. The PDMS stamp containing the picked-up quantum dot film was then attached to the hole transport layer from step S1. By pressing and separating the PDMS stamp sequentially, quantum dot pixels and a charge isolation layer were fabricated on the hole transport layer. Annealing at 80 °C for 10 min yielded the quantum dot film. Finally, a QLED device was fabricated.

[0081] Comparative Example 1

[0082] This comparative example provides a method for fabricating a QLED device. The specific steps are the same as in Example 1, except that in step S3, the PDMS stamp from Example 4 is used to prepare a quantum dot film via a transfer method. The transfer process is as follows: Figure 4 (c)-(d). The QLED device is finally obtained.

[0083] The process for transferring and preparing quantum dot films using the hemispherical PDMS stamp from Preparation Example 4 is as follows: Figure 4 As shown in (c)-(d), during the picking process, the top of the hemispherical PDMS stamp first contacts the monolayer quantum dot film on the water surface, at which point the top of the stamp picks up the monolayer quantum dots. As the picking process continues, the stamp gradually immerses in the water. Because the hemispherical PDMS stamp has a low surface energy and a relatively gentle hemispherical microstructure (its tip curvature radius is approximately 500 nm), the stamp cannot disrupt the integrity of the water surface, thus only picking up quantum dots at the top of the stamp. Therefore, the quantum dot film transferred using the hemispherical PDMS stamp only has quantum dot pixels composed of a single layer of quantum dots, without a charge isolation layer. It is impossible to simultaneously prepare quantum dot pixels and a charge isolation layer through a single transfer using this stamp.

[0084] Comparative Example 2

[0085] This comparative example provides a method for fabricating a QLED device. The specific steps are the same as in Example 1, except that in step S3, a quantum dot film is prepared by transfer using the PDMS stamp from Example 4. This quantum dot film has quantum dot pixels composed of a single layer of quantum dots, but does not have a charge isolation layer. The transfer process is as described above. Figure 4 (c)-(d); then, PMMA, a charge isolation layer material, was spin-coated onto the quantum dot film. The PMMA solution concentration was 1 mg / ml, the spin-coating speed was 3000 rpm, the spin-coating time was 40 s, and the film was annealed at 100 ℃ for 20 min to form the charge isolation layer. Finally, the QLED device was fabricated.

[0086] Comparative Example 3

[0087] This comparative example provides a method for fabricating a QLED device. The specific steps are the same as in Example 1, except that in step S3, a complete quantum dot film is prepared by spin coating: a quantum dot film is spin-coated onto the hole transport layer at a spin speed of 2000 rpm for 30 s, and then annealed at 80 °C for 20 min to form a complete quantum dot film. The QLED device is then finally obtained.

[0088] The QLED devices prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests and compared. The electroluminescence performance was tested using the Xipu Optoelectronics XP-EQE-Adv electroluminescence efficiency measurement system, and the test results are as follows. Figure 10 As shown. Figure 10Figures (a)-(f) show the performance test results of the QLED devices prepared in Examples 1-3 and Comparative Examples 1-3, respectively. As shown in the figures, the maximum brightness of the QLED devices prepared in Examples 1-3 is 105056 cd·m. -2 The maximum current density is 1067 mA·cm. -2 The average maximum external quantum efficiency was 16.10%; the maximum luminance of the QLED device prepared in Comparative Example 1 was 67289 cd·m². -2 The maximum current density is 1560 mA·cm. -2 The maximum external quantum efficiency was 5.82%; the maximum luminance of the QLED device prepared in Comparative Example 2 was 93183 cd·m². -2 The maximum current density is 1143 mA·cm. -2 The maximum external quantum efficiency was 15.95%; the maximum luminance of the QLED device prepared in Comparative Example 3 was 100117 cd·m². -2 The maximum current density is 947 mA·cm. -2 The maximum external quantum efficiency is 16.78%. Comparative test results show that the QLED device without a charge isolation layer in Comparative Example 1 exhibits a larger leakage current (i.e., current density) (1560 mA·cm⁻¹) due to the direct contact of the charge transport layer. -2 Therefore, it has a low external quantum efficiency (5.82%); Comparative Example 2 prepared a PMMA charge isolation layer based on Comparative Example 1, thus its leakage current was significantly reduced (1143 mA·cm). -2 The external quantum efficiency increased accordingly (15.95%). In the QLED devices prepared in Examples 1-3, the wall structure in the dot-wall quantum dot film served as a charge isolation layer, achieving an effect comparable to PMMA, which significantly reduced the leakage current of the device (1114 mA·cm). -2 The external quantum efficiency increased significantly (15.90%). Comparing Examples 1-3 with Comparative Example 3, it can be seen that the QLED devices manufactured by the transfer method described in Examples 1-3 do not show a significant decrease in performance compared with the QLED devices manufactured by spin coating, and remain at a high level.

[0089] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A quantum dot film with a dot-wall structure, characterized in that, The quantum dot film includes quantum dot pixels arranged in an ordered lattice and a charge isolation layer distributed between the pixels. The quantum dot pixels are composed of a single layer of quantum dots, and the charge isolation layer is composed of a double layer of quantum dots. The quantum dot pixels and the charge isolation layer are prepared simultaneously by using a PDMS stamp for one-time transfer.

2. A method for preparing a quantum dot film with a dot-wall structure as described in claim 1, characterized in that, Includes the following steps: S11. Add quantum dot solution to the surface of deionized water to allow the quantum dots to self-assemble at the gas-liquid interface to form a monolayer quantum dot film. S12. Use a pre-made PDMS stamp to pick up a single-layer quantum dot film on the surface of deionized water; the PDMS stamp has a hexagonal array of cones, the distance between the centers of adjacent cones is 800-1200 nm, the diameter of the bottom surface of the cone is 740-750 nm, the aspect ratio is 0.5-0.55, and the radius of curvature of the tip is 30-40 nm. S13. The PDMS stamp with the single-layer quantum dot film is attached to the surface of the hole transport layer, and after pressing, separation and annealing, quantum dot pixels and charge isolation layer are obtained on the hole transport layer at the same time.

3. The method for preparing a quantum dot film with a dot-wall structure according to claim 2, characterized in that, In step S11, the quantum dot material in the quantum dot solution is a core-shell structured CdSe / ZnS, with CdSe as the core and ZnS as the outer shell, and the solvent is n-octane.

4. The method for preparing a quantum dot film with a dot-wall structure according to claim 3, characterized in that, In step S11, the concentration C of the quantum dot material in the quantum dot solution is 5-10 mg / ml, the volume V of the added quantum dot solution is 10-45 μL, and the radius R of the container holding the deionized water is 3-4.5 cm. The numerical relationship between C×V and R is C×V = (10~12)R. 2 .

5. The method for preparing a quantum dot film with a dot-wall structure according to claim 3, characterized in that, The PDMS stamp is prepared by the following method: S21. Mix the PDMS prepolymer and curing agent at a mass ratio of 10:1 and stir until homogeneous to form a PDMS mixture; S22. Take a patterned substrate with a non-penetrating, ordered lattice arrangement of microstructures on its surface, pour the PDMS mixture onto the surface of the microstructures in the patterned substrate, let it stand in vacuum, and then heat it at 40-100℃ to solidify the PDMS mixture. S23. Separate the cured PDMS from the patterned substrate to obtain the PDMS stamp. The shape of the cone on the PDMS stamp corresponds to the shape of the microstructure on the patterned substrate.

6. A QLED device, the QLED device structure comprising, from bottom to top, an ITO substrate, a hole injection layer, a hole transport layer, a quantum dot film with a dot-wall structure as described in claim 1, an electron transport layer, and a metal cathode.

7. A method for fabricating the QLED device according to claim 6, characterized in that, Includes the following steps: S1. Spin-coat a hole injection layer material onto a clean, hydrophilic ITO substrate and anneal it to form a hole injection layer. S2. Spin-coat hole transport layer material onto hole injection layer and anneal it to form hole transport layer. S3. Using a PDMS stamp, quantum dot pixels and a charge isolation layer are simultaneously prepared by transferring them onto the hole transport layer once. The quantum dot film is obtained by annealing at 60-100 °C. S4. Spin-coat an electron transport layer material onto a quantum dot film and anneal it to form an electron transport layer. S5. A metal electrode is deposited on the electron transport layer as a metal cathode, and then packaged to obtain a QLED device.

8. The method for fabricating a QLED device according to claim 7, characterized in that, In steps S1, S2 and S4, the rotation speed of the spin-coating material is 2000-4000 rpm and the time is 40-60 s.

9. The method for fabricating the QLED device according to claim 7 or 8, characterized in that, The annealing temperature in steps S1, S2 and S4 is 80-130 ℃ and the time is 10-30 min.

10. The method for fabricating a QLED device according to claim 7, characterized in that, In step S5, the thickness of the metal cathode is 80-130 nm.

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