Direct photoetching quantum dot patterning method and QLED device manufactured by same

Abstract

The invention discloses a direct photoetching quantum dot patterning method and a QLED device prepared by the same, and belongs to the field of quantum dot (QD) nanotechnology, a hole transport material poly ((9, 9-dioctylfluorenyl-2, 7-diyl)-alt-(9-(2-ethynyl)-carbazole-3, 6-diyl)) (PF8Cz) and a photoinitiator benzophenone (BP) or bis-benzophenone (BPBP) are added into a toluene QD solution, so that the QD mixed solution has a photosensitive characteristic, selective exposure is realized, and the quantum dot is prepared by the method. According to the method, the solubility of the QD in an original solution is changed, and development is carried out, so that direct photoetching patterning of the QD is realized, a high-resolution and high-precision QD pattern is obtained, and a patterned QLED device with good performance is prepared. The main reaction mechanism is that after BP or BPBP is subjected to ultraviolet exposure, C = O in molecules is converted into active free radicals, and the active free radicals and alkyl branched chains in PF8Cz are subjected to cross-linking reaction to form a cross-linked network, so that QD in an exposure area is fixed, and a QD pattern is formed. The patterning mode does not need participation of quantum dot ligands, the risk that the quantum dot ligands fall off is reduced, and damage to the light emitting performance of the QD in the photoetching process can be reduced.

Description

Technical Field

[0001] The present invention belongs to the field of quantum dot (QD) nanotechnology, and particularly relates to a direct lithography quantum dot patterning method and a QLED device prepared thereby. Background Art

[0002] Semiconductor quantum dots have unique optical and electronic properties that traditional semiconductor materials do not have. Their band gaps can be precisely modified according to their size and shape, and depending on the material selection, they can cover the range from ultraviolet to the entire visible light spectrum. In addition, they have a high absorption coefficient and a high photoluminescence quantum yield, with extremely high color purity and narrow emission and absorption spectra. Because of these advantages, they have been intensively studied and are considered to be very promising luminescent materials for next-generation displays.

[0003] With the progress of the times, in today's society, the demand for advanced displays has increased exponentially, especially for head-mounted and near-eye displays used in augmented reality (AR) and virtual reality (VR) applications, which not only provide an unparalleled visual experience but also meet the growing expectations of consumers in various industries. Therefore, improving image quality and developing high-resolution displays with vivid and accurate colors have become crucial. However, making small displays such as AR / VR head-mounted displays and smart glasses requires a high pixel density to present vivid and clear images. To better apply quantum dots to such small displays as AR / VR, using lithography technology to obtain a high-resolution QD pattern is a method with high feasibility, strong practicability, and simple operation.

[0004] The lithography processes for quantum dot patterning are mainly divided into three types: conventional lithography, lift-off process, and direct lithography. Both conventional lithography and lift-off process require the introduction of a separate photoresist layer as an auxiliary, and the processes are complicated and will inevitably damage the quantum dot pattern during the introduction and stripping of the photoresist. In contrast, the direct lithography process, that is, directly forming a quantum dot pattern only after spin-coating, ultraviolet exposure, and development, does not require the introduction and stripping of the photoresist during the process, greatly simplifies the pattern fabrication process, and can avoid the damage of the material by chemical reagents in multiple procedures. The key to realizing direct lithography is that the quantum dot solution needs to have a certain photosensitivity, and the irradiated quantum dot film can change its own solubility to leave a precise quantum dot pattern.

[0005] Currently, there are mainly three types of formulations for photosensitive quantum dot solutions: The first type is to add a photoacid generator to the original quantum dot solution, such as 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (MBT). The acid generated by these molecules after ultraviolet light irradiation can strip the ligands on the surface of the quantum dots, thereby changing the solubility of the quantum dots in the original solvent (Cho H, Pan J A, Wu H, et al. Direct Optical Patterning of Quantum Dot Light-Emitting Diodes via In Situ Ligand Exchange[J]. Adv. Mater. 2020, 32, 2003805); The second type is to use a ligand exchange strategy to replace the original ligands of the quantum dots with ligands carrying photosensitive groups. After ultraviolet exposure, cross-linking reactions will occur between the ligands, forming a fixed cross-linked network, and then realizing quantum dot patterning (Hahm D, Lim J , Kim H, et al. Direct patterning of colloidal quantum dots with adaptable dual-ligand surface[J]. Nature Nanotechnology 2022, 17, 952-958.). The third type is to add a photosensitive material to the quantum dot solution, such as an organic molecule with an azide group, and fix the quantum dots by cross-linking between the photosensitive material and the quantum dot ligands (Yang J, Hahm D, Kim K, et al. High-resolution patterning of colloidal quantum dots via non-destructive, light-driven ligand crosslinking[J]. Nature Communications, 2020, 11, 2874.). A common feature of these types is that the participation of quantum dot ligands (ligand stripping or ligand cross-linking) is required during the photolithography process. Therefore, some ligands will detach from the surface of the quantum dots, causing surface defects of the quantum dots and affecting the luminescence performance of the patterned quantum dots.

[0006] To reduce the risk of ligand detachment from the quantum dot surface, ligand participation in the cross-linking reaction should be inhibited. Li et al. (Qie Y, Hu H, Yu K, et al. Ligand-nondestructive direct photolithography assisted by semiconductor polymer cross-linking for high-resolution quantum dot light-emitting diodes[J]. Nano Letters, 2024, 24(4): 1254-1260.) added the hole-transporting material poly[9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine] (TFB) and the photosensitive material 2,2-dimethoxy-2-phenylacetophenone (DMPA) to the octane quantum dot solution. After ultraviolet exposure, TFB and DMPA cross-linked to form a "network framework" that confined the QDs, thus fabricating a QD-patterned device. However, this strategy has two problems. One is that the hole-transporting material TFB is poorly soluble in n-octane quantum dots. Therefore, heating and stirring are required after mixing, and TFB precipitation is likely to occur during the spin-coating process, which is difficult to operate and hinders large-scale production. Moreover, excessive heating will cause loss of quantum dot performance. Also, for hole-transporting layer materials that are insoluble in n-octane, such as PF8Cz, it is difficult to form a uniform and flat thin film by this method, so this method cannot be extended to a larger application scope. The other is that the pattern quality formed by cross-linking DMPA with the polymer is limited. This may be due to the limited number of cross-linking sites on the DMPA molecule, resulting in limited cross-linking effect. At the same time, the molecular weight of DMPA is small, and the formed active free radicals are prone to diffuse into the unexposed area, which also causes a decrease in pattern quality.

[0007] Therefore, there is still a lack of a general, easy-to-implement, suitable for large-scale promotion, and ligand-function-unaffected direct quantum dot patterning method. The key to overcoming this problem lies in designing a better formulation of the photosensitive quantum dot solution, and the relationships among the quantum dot solvent, cross-linking polymer, and photosensitive material need to be carefully considered. Here, the present invention provides a simple formulation of the photosensitive quantum dot solution, which can be obtained at normal temperature and pressure, and high-resolution quantum dot patterns and QLED pixel arrays can be formed using direct photolithography. At the same time, by selecting a photosensitive material with multiple cross-linking sites and a larger molecular weight as the cross-linking medium, the pixel pattern quality of the QLED array is effectively improved. Summary of the Invention

[0008] The focus of the present invention is to provide a direct lithography quantum dot patterning method and a QLED device prepared thereby. By using the direct lithography method, a hole semiconductor transport material poly((9,9-dioctylfluorenyl-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl)) (PF8Cz) and a photoinitiator benzophenone (BP) or bisbenzophenone (BPBP) are added to a toluene QD solution, so that the QD mixed solution has photosensitive properties. Selective exposure is carried out to change the solubility of QDs in the original solution, and then development is carried out, thereby realizing direct lithography patterning of QDs, obtaining a QD pattern with high resolution and high precision, and preparing a patterned QLED device with good performance. The main reaction mechanism is that after BP or BPBP is exposed to ultraviolet light, the C=O in the molecule is converted into active free radicals, and cross-linking reaction occurs with the alkyl side chains in PF8Cz to form a cross-linked network, and then the QDs in the exposed area are fixed to form a QD pattern. This patterning method does not require the participation of quantum dot ligands, reduces the risk of quantum dot ligand shedding, and can reduce the damage to the luminescence performance of QDs during the lithography process; and our results show that compared with BP, the patterning strategy based on the BPBP molecule can obtain a clearer QLED pixel array, which may be attributed to a more effective cross-linking method and less free radical diffusion.

[0009] Based on the above object, the present invention adopts the following technical solutions: A direct lithography quantum dot patterning method, the main steps are as follows: Step 1, preparation of photosensitive QD mixed solution In the QD solution, add a hole transport material (PF8Cz) solution and a photoinitiator benzophenone (BP) solution or a photoinitiator bisbenzophenone (BPBP) solution, mix and stir evenly; obtain a QD mixed solution with photosensitive properties; Step 2, preparation of patterned QD film Spin-coat the photosensitive QD mixed solution obtained in Step 1 evenly on the surface of the substrate to obtain a transparent film with uniform thickness. Using the photomask technology, selectively expose the QD film to ultraviolet light through the photomask and a portable ultraviolet lamp, so as to change the solubility of QDs in the original solvent, and develop by washing with the original solvent to obtain the required QD pattern, as Figure 1 shown.

[0010] Furthermore, the mass ratio of the quantum dots, PF8Cz and benzophenone or bisbenzophenone is 10:(0.5~1):(1~1.5).

[0011] Further, the quantum dots are CdZnSe quantum dots, and the quantum dot solution is prepared by dissolving CdZnSe quantum dots in toluene. The concentration of CdZnSe quantum dots in toluene is 20 mg / mL to 30 mg / mL.

[0012] Further, the PF8Cz solution is prepared by dissolving PF8Cz in chlorobenzene. The concentration of PF8Cz in chlorobenzene is 5 to 10 mg / mL.

[0013] Further, the benzophenone or bis-benzophenone solution is prepared by dissolving benzophenone or bis-benzophenone in chlorobenzene. The concentration of benzophenone or bis-benzophenone in chlorobenzene is 10 to 30 mg / mL.

[0014] Further, the wavelength of the UV is 365 nm, and the power density ranges from 25 mW / cm 2 to 400 mW / cm 2 , and the exposure time is 1 s to 100 h.

[0015] A quantum dot patterned QLED device includes, from bottom to top, an ITO substrate, a PEDOT:PSS hole injection layer, a PF8Cz hole transport layer, a patterned QD light-emitting layer, a PMMA electron blocking layer, a ZnMgO electron transport layer, and a cathode electrode. It is characterized in that the patterned QD light-emitting layer is prepared by the above direct photolithography quantum dot patterning method.

[0016] The preparation method of the above quantum dot patterned QLED device is as follows: The structure of this patterned QLED device is similar to that of a traditional QLED device. First, a hole injection layer and a hole transport layer are spin-coated on an ITO glass substrate. Then, the photosensitive QD mixed solution obtained in step 1 is used to spin-coat the light-emitting layer, and the method of step 2 is used to obtain the required QD pattern. Finally, an electron blocking layer, an electron transport layer, and aluminum plating are spin-coated to prepare a patterned QLED device.

[0017] Preferably, the patterned QD light-emitting layer is single-layer or double-layer.

[0018] Preferably, the thickness of the PEDOT:PSS hole injection layer is 30 to 60 nm, the thickness of the PF8Cz hole transport layer is 20 to 50 nm, the thickness of the patterned QD light-emitting layer is 15 to 40 nm, the thickness of the PMMA electron blocking layer is 5 to 10 nm, the thickness of the ZnMgO electron transport layer is 20 to 50 nm, and the cathode electrode is aluminum with a thickness of 100 nm.

[0019] By adding a hole transport material and a photoinitiator to the QD solution, the present invention endows the QD solution with photosensitive properties. According to the ultraviolet exposure crosslinking of the hole transport material and the photoinitiator, a "network framework" structure is formed to confine the QDs therein, thereby changing their solubility in the original solution. A method for directly lithographing QD patterning has been successfully developed. Through this method, patterned QLED devices are further prepared, providing high-resolution and high-precision patterned QD films and patterned QLED devices for small-screen displays such as Micro-LED and VR / AR glasses, which has significant innovation and practical value. In addition, the hole transport material PF8Cz can be well dissolved in chlorobenzene. Adding the PF8Cz chlorobenzene solution to the QD toluene solution will not cause the precipitation of PF8Cz, which is beneficial to the subsequent simple preparation of QD patterns.

[0020] The present invention provides a method for preparing quantum dot patterns and patterned QLED devices by direct lithography. Similar to the preparation methods of traditional QLED devices, the processing technology is compatible, the implementation method is simple, convenient for actual operation, and can efficiently and quickly fabricate patterned QLED devices.

[0021] Secondly, the direct lithography method adopted by the present invention does not involve ligand exchange and ligand stripping, which can reduce the damage to the QD performance. And by adding an electron blocking layer, the leakage current is reduced, further protecting the performance of the patterned QLED device. Brief Description of the Drawings

[0022] Figure 1 It is a specific lithography flow chart of the photosensitive QD solution prepared in Example 1 of the present invention and the preparation of QD patterns; Figure 2 It is a comparison chart of the pattern results of CdZnSe quantum dots dispersed in (a) toluene solvent and (b) octane solvent (pixel size is 50 μm); Figure 3 It is a strip-shaped QD pattern of different sizes prepared in Example 1 of the present invention using 5 μm and 10 μm masks; Figure 4 It is a comparison of the PL intensities of QDs crosslinked with the hole transport materials TFB, PVK, PF8Cz and BP; Figure 5 It is a photo of the patterned QLED device and QLED pixel array prepared in Example 1 of the present invention; Figure 6 It is the current density-voltage-luminance (J-V-L) curve of the patterned QLED device prepared in Example 1 of the present invention; Figure 7It is the EQE-luminance-current efficiency (CE) curve of the patterned QLED device prepared in Example 1 of the present invention; Figure 8 It is the EQE-current density curve of the patterned QLED device prepared in Example 1 of the present invention; Figure 9 It is the EL emission spectrum of the patterned QLED device prepared in Example 1 of the present invention; Figure 10 It is the cross-linking schematic diagram of BPBP and PF8Cz in Example 2 of the present invention; Figure 11 It is the cross-linking principle diagram of PF8Cz and BPBP in Example 2 of the present invention; Figure 12 It is the strip-shaped QD patterns with different sizes prepared by using 5 μm and 10 μm photomasks in Example 2 of the present invention; Figure 13 It is the structure diagram of the double-layer patterned QLED device prepared in Example 2 of the present invention; Figure 14 It is the J-V-L curve of the patterned device prepared in Example 2 of the present invention; Figure 15 It is the EQE-L curve of the patterned device prepared in Example 2 of the present invention (the inserted figure is the EL emission photo of the pixelated device, and the minimum size is 50 μm); Figure 16 Comparison of patterned QLED devices based on two cross-linking methods (a) BPBP-PF8Cz and (b) BP-PF8Cz (50μm pattern). Specific Embodiments

[0023] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate and explain the present invention by way of example, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection of the present invention.

[0024] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by known methods.

[0025] Example 1 A method for preparing a QLED device by directly lithographing quantum dot patterning, as Figure 1 shown, the process is as follows: (1) The specific preparation method of the photosensitive QD mixed solution is as follows: First, dissolve 150 mg of green CdZnSe quantum dots in 5 mL of toluene or octane. Take 20 mg of TFB, 20 mg of PVK, and 20 mg of PF8Cz and dissolve them in 2.5 mL of chlorobenzene respectively. Dissolve 150 mg of BP in 5 mL of toluene, and ultrasonically stir to make the original QD solution, PF8Cz solution, and BP solution evenly. Then, take 1 mL of the QD solution, add 240 μL of the PF8Cz solution and 100 μL of the BP solution in sequence, and mix and stir evenly. Finally, the required photosensitive QD mixed solution is obtained.

[0026] (2) Fabricate the patterned QD film Spin-coat the photosensitive QD mixed solution prepared in step (1) evenly on the surface of the glass substrate to form a transparent film with a uniform thickness. Then, closely attach the mask plate to the glass substrate, and use a portable ultraviolet lamp with a wavelength of 365 nm. Under the conditions of a power density of 25 mW / cm 2 , and an exposure time of 25 s, perform UV exposure. Finally, use n-octane as the developer to develop the exposed glass substrate to obtain the required patterned QD film.

[0027] Figure 2 Comparison diagram of the pattern results of CdZnSe quantum dots dispersed in (a) toluene solvent and (b) octane solvent (pixel size is 50 μm). It can be seen from Figure 2 that for the quantum dots in the octane solvent, PF8Cz precipitation and poor patterning quality will occur after patterning, while the quantum dots using the toluene solvent can well avoid these problems. Note that when using octane as the quantum dot solvent, the solvents of PF8Cz and BP need to be changed to anisole, otherwise a radial film will appear, that is, a complete film cannot be formed.

[0028] Figure 3 This is the strip QD pattern with different sizes prepared by using 5 μm and 10 μm mask plates in Example 1 of the present invention.

[0029] Figure 4 Comparison of the PL intensities of QD after cross-linking of the hole transport materials TFB, PVK, PF8Cz and BP; It can be seen from Figure 4 that the cross-linking combination of BP and PF8Cz-QD shows the maximum fluorescence intensity.

[0030] (3) Fabricate the patterned QLED device First, the ITO glass substrate with a size of 2 cm × 2 cm was ultrasonically washed with washing solution, ultrapure water, acetone, and isopropanol for 15 minutes each to make its surface clean without impurities. Then, after ozone treatment of the washed ITO glass substrate for 15 minutes, PEDOT:PSS with a thickness of 40 nm was spin-coated and annealed at 130 °C for 15 minutes; after cooling, PF8Cz with a thickness of 30 nm was spin-coated and annealed at 150 °C for 30 minutes; after cooling, the photosensitive QD mixed solution prepared in step (1) (CdZnSe quantum dots using toluene as a solvent, PF8Cz crosslinked with BP) was spin-coated. Using the direct photolithography method in step (2), selective exposure was carried out through a mask plate and a portable ultraviolet lamp. After exposure, development was carried out with n-octane to obtain the desired patterned QD light-emitting layer, and annealing was carried out at 80 °C for 10 minutes, and the thickness of the patterned QD film was 15 nm; then, 6 nm of PMMA was spin-coated as an electron blocking layer and annealed at 80 °C for 10 minutes to reduce the leakage current generated by the patterned device; then 30 nm of ZnMgO was spin-coated and annealed at 60 °C for 30 minutes. Finally, aluminum plating (100 nm) and encapsulation were carried out to obtain a patterned QLED device, as Figure 5 shown. After preparing the patterned QLED device, various performance parameters (external quantum efficiency, brightness, current density, current efficiency, etc.) of the patterned QLED device and its EL emission spectrum were obtained using an Ocean Optics spectrometer (USB2000, relative irradiance mode) and a Keithley 2400 source meter. Among them, the maximum EQE was 0.56%, and the maximum brightness could reach 32099 cd / m 2 .

[0031] The current density-voltage-brightness (J-V-L) curve of the prepared patterned QLED device is shown in detail in Figure 6 , and from Figure 6 it can be seen that the J-V-L characteristic curve shows typical diode characteristics, starts to light up at 2.6 V, and reaches the maximum brightness of 32099 cd / m at 6.6 V 2 .

[0032] The EQE-brightness-current efficiency (CE) curve of the prepared patterned QLED device is shown in detail in Figure 7 , and from Figure 7 it can be seen that when the brightness is 12867 cd / m 2 , the device reaches the maximum EQE and CE, which are 0.56% and 1.68 cd / A respectively.

[0033] The EQE-current density curve of the prepared patterned QLED device is shown in detail in Figure 8 , and from Figure 8 it can be seen that when the current density is 766.2 mA / cm 2When the EQE of the device is the largest, it is 0.56%.

[0034] The EL emission spectrum of the prepared patterned QLED device is shown in detail in Figure 9 , from Figure 9 it can be seen that the peak wavelength is 519.89 nm, the full width at half maximum is about 23.4 nm, and when the applied voltage increases from 4 V to 7 V, the shape and peak position of the EL spectrum of the device do not change.

[0035] Example 2 A method for preparing a QLED device by directly lithographic patterning of quantum dots is as follows: (1) The specific preparation method of the photosensitive QD mixed solution is as follows: First, prepare a green QD solution by dissolving 200 mg of green CdZnSe quantum dots in 10 mL of toluene solution and stirring evenly by ultrasonic oscillation. Then prepare a PF8Cz solution by dissolving 16 mg of PF8Cz in 2 mL of chlorobenzene solution and stirring evenly by ultrasonic oscillation. At the same time, prepare a BPBP solution by dissolving 10 mg of BPBP in 1 mL of toluene solution and stirring evenly by ultrasonic oscillation. Next, take 500 μL of the QD solution, add 80 μL of the PF8Cz solution and 40 μL of the BPBP solution successively, mix ultrasonically, and stir evenly. Finally, the required photosensitive QD mixed solution is prepared.

[0036] (2) Fabricate a patterned QD thin film Coat the photosensitive QD mixed solution prepared in step (1) on the surface of a glass substrate by spin coating in a glove box to form a transparent thin film with a uniform thickness. Then, closely attach the self-made mask to the glass substrate and perform UV exposure using a portable ultraviolet lamp with a wavelength of 365 nm under the conditions of a power density of 25 mW / cm 2 and an exposure time of 60 s. Next, use n-octane as the developer to wash and develop the exposed glass substrate. Finally, the required patterned QD thin film is prepared, and the film thickness is 10 nm. As Figure 10 and 11 shown, dibenzophenone BPBP is activated under light to form active free radicals, which can carry out C-H insertion reaction with the carbon chain on PF8Cz, and then form a crosslinked network. The quantum dots are trapped in the crosslinked network. Thus, the quantum dots can resist the cleaning of the developer, and thus leave a quantum dot pattern in the exposed area. Figure 12 This is the bar-shaped QD pattern with different sizes prepared using 5 μm and 10 μm masks in Example 2 of the present invention.

[0037] (3) Fabricate a double-layer patterned QLED device Similar to the preparation method of traditional QLED devices, first, the ITO glass substrate is ultrasonically cleaned in a washing solution, ultrapure water, acetone, and isopropanol for 15 minutes each. Subsequently, the washed ITO glass substrate is dried with a nitrogen gun and treated with ozone for 15 minutes. Then, PEDOT:PSS is spin-coated as a hole injection layer (with a thickness of 40 nm) in an air environment and annealed at 130 °C for 15 minutes; after cooling, PF8Cz is spin-coated as a hole transport layer (with a thickness of 30 nm) in a glove box and annealed at 150 °C for 30 minutes; after cooling, two layers of the photosensitive QD mixed solution prepared in step (1) are spin-coated on the hole transport layer (first spin-coat the first layer with a thickness of 10 nm, and after natural drying, spin-coat the second layer to reach a total thickness of 20 nm). Using the direct photolithography method in Example 2, selective exposure is carried out through a mask and a 365 nm portable ultraviolet lamp. After exposure, washing and developing are carried out with n-octane developer to obtain the required double-layer patterned QD light-emitting layer (with a thickness of 20 nm), and it is annealed at 80 °C for 10 minutes; then, PMMA is spin-coated as an electron blocking layer (with a thickness of 6 nm) in a glove box and annealed at 80 °C for 10 minutes to reduce leakage current; subsequently, ZnMgO is spin-coated as an electron transport layer (with a thickness of 30 nm) in a glove box and annealed at 60 °C for 30 minutes. Finally, an aluminum electrode (100 nm) is deposited and encapsulated to obtain a patterned QLED device, and the structure is as Figure 13 shown. From bottom to top, it includes an ITO substrate, a PEDOT:PSS hole injection layer, a PF8Cz hole transport layer, a double-layer patterned QD light-emitting layer, a PMMA electron blocking layer, a ZnMgO electron transport layer, and an aluminum cathode electrode. The device structure of the present invention adopts a double-layer quantum dot structure, which can effectively increase the luminous efficiency and reduce leakage current. After preparing the patterned QLED device, performance parameters such as the external quantum efficiency (EQE), brightness, and current density of the patterned QLED device are obtained using an Ocean Optics spectrometer (USB2000, relative irradiance mode) and a Keithley 2400 source meter.

[0038] The J-V-L curve of the patterned device prepared in Example 2 is shown in detail in Figure 14 ; as can be seen from Figure 14 , the J-V-L characteristic curve shows typical diode characteristics, starts to light up at 2.4 V, and reaches the maximum brightness of 23544 cd / m 2 .

[0039] The EQE-L curve of the patterned device prepared in Example 2 (the inset is the EL emission photo of the pixelated device, with a minimum size of 50 μm) is shown in detail in Figure 15 , as can be seen from Figure 15 , at a brightness of 8896 cd / m 2When the device reaches the maximum EQE, which is 0.34%.

[0040] Figure 16 This is a comparison of the patterned QLED devices prepared in Example 1 and Example 2 (50 μm pattern); as can be seen from Figure 16 this, compared with single benzophenone BP, the patterning strategy based on bis-benzophenone BPBP can obtain a clearer and higher-quality patterned QLED array, which may be attributed to two aspects. One is that the probability of cross-linking of BPBP molecules with two benzophenone groups and PF8Cz is higher and a more effective cross-linking method can be formed. The other is that the molecular weight of BPBP is relatively large, which to a certain extent limits the diffusion of the formed free radicals.

[0041] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A direct photolithography quantum dot patterning method, characterized in that: Add hole transport material PF8Cz solution and photoinitiator benzophenone or dibenzophenone solution to the quantum dot solution, stir evenly, spin-coat on the substrate, selectively expose through a mask and UV, and then develop to obtain the desired QD pattern.

2. The direct photolithography quantum dot patterning method according to claim 1, characterized in that: The mass ratio of the quantum dots, PF8Cz and benzophenone or dibenzophenone is 10:(0.5-1):(1-1.5).

3. The direct photolithography quantum dot patterning method according to claim 1, characterized in that: The quantum dots are CdZnSe quantum dots, and the quantum dot solution is prepared by dissolving CdZnSe quantum dots in toluene. The concentration of the CdZnSe quantum dots in toluene is 20 mg / mL to 30 mg / mL.

4. The direct photolithography quantum dot patterning method according to claim 1, characterized in that: The PF8Cz solution is prepared by dissolving PF8Cz in chlorobenzene, and the concentration of PF8Cz in chlorobenzene is 5-10 mg / mL.

5. The direct photolithography quantum dot patterning method according to claim 1, characterized in that: The benzophenone or bisbenzophenone solution is prepared by dissolving benzophenone or bisbenzophenone in chlorobenzene, and the concentration of benzophenone or bisbenzophenone in chlorobenzene is 10-30 mg / mL.

6. The direct photolithography quantum dot patterning method according to claim 1, characterized in that: The wavelength of UV is 365nm and the power density range is 25 mW / cm 2 ~400 mW / cm 2 , exposure time is 1 s~100 h.

7. A quantum dot patterned QLED device, comprising from bottom to top an ITO substrate, a PEDOT:PSS hole injection layer, a PF8Cz hole transport layer, a patterned QD light-emitting layer, a PMMA electron blocking layer, a ZnMgO electron transport layer and a cathode electrode, characterized in that: The patterned QD light-emitting layer is prepared by the direct photolithography quantum dot patterning method described in any one of claims 1 to 6.

8. The quantum dot patterned QLED device according to claim 7, characterized in that: The patterned QD light-emitting layer is a single layer or a double layer.

9. The quantum dot patterned QLED device according to claim 8, characterized in that: The thickness of the PEDOT:PSS hole injection layer is 30~60nm, the thickness of the PF8Cz hole transport layer is 20~50nm, the thickness of the patterned QD light-emitting layer is 15~40nm, the thickness of the PMMA electron blocking layer is 5~10nm, the thickness of the ZnMgO electron transport layer is 20~50nm, and the cathode electrode is aluminum with a thickness of 100 nm.

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