A charge generation layer and a stacked quantum dot electroluminescent device

Abstract

This invention discloses a charge generation layer and a stacked quantum dot electroluminescent device, belonging to the field of optoelectronic technology. The charge generation layer is composed of modified ZnO nanocrystals and p-type materials; the modified ZnO nanocrystals involve modifying the surface of ZnO nanoparticles with organic compounds possessing strong dipolarizing groups to form an organic oxide film. This invention, by modifying ZnO with organic compounds to form an organic film on the surface of ZnO particles, can passivate surface defects, effectively prevent exciton quenching at the QD / ZnO interface, and the organically modified ZnO is less prone to aggregation, exhibiting greater stability. Furthermore, it can prevent leakage current problems associated with the all-solution method for fabricating stacked QLED devices, achieving efficient carrier injection balance.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology, specifically relating to a charge generation layer and its preparation method, and a stacked quantum dot electroluminescent device. Background Technology

[0002] QLED, as an emerging display technology, has attracted significant attention from academia and industry due to its superior color performance, high brightness, and low energy consumption. Its core advantages stem from the quantum confinement effect and size-dependent luminescence characteristics of quantum dots. By precisely controlling the quantum dot particle size (2-10nm), it can achieve pure color light emission with a narrow half-width (FWHM < 30nm). Traditional QLED devices are single-layer structures, simple to fabricate, but have limitations in device efficiency and lifetime. To overcome these limitations, stacked QLED devices have emerged, which vertically stack multiple light-emitting units through a charge generation layer (CGL). The charge generation layer (CGL) is a key functional layer in stacked devices, such as stacked organic solar cells and stacked quantum dot light-emitting diodes (QLEDs). It connects multiple sub-cells, enabling charge generation, separation, and transport while maintaining the overall electrical neutrality of the device. It is typically composed of a pair of p-type and n-type materials.

[0003] The charge generation layer (CGL), a crucial component of stacked devices, is typically a bilayer structure composed of n-type and p-type semiconductor materials. When a forward bias is applied to the device, electrons and holes are injected from the cathode and anode, respectively, into adjacent light-emitting units. Simultaneously, electrons and holes are generated and separated at the n / p-type material interface of the CGL, recombine with the injected holes and electrons in the light-emitting layer to emit light. Injecting a single electron-hole pair into a stacked device with two light-emitting units results in the emission of two photons, achieving an internal quantum efficiency of 200% and twice the EQE. Clearly, at the same current density, compared to single-layer devices, stacked devices exhibit greater brightness, higher efficiency, and longer lifetime. Furthermore, by controlling the free combination of different light-emitting units within the stacked device, different colors can be emitted, thus achieving a wider color gamut.

[0004] In addition, stacked devices can effectively improve the carrier utilization of the device. Generally speaking, devices prepared by solution method tend to generate large leakage current. However, the leakage current generated in stacked devices has a probability of being captured by the light-emitting layer of the upper light-emitting unit after passing through the charge generation layer, and recombine with the injected electrons / holes, thereby suppressing the leakage current of the device and improving the charge utilization.

[0005] In the prior art, ZnMgO / PEDOT:PSS is usually used (J.Mater.Chem.C, 2024, 12, 10053-10060) to suppress the PL quenching effect of ZnO on QD by doping with Mg; or by inserting an ultrathin metal Al layer between ZnO and p-type material PMA to form an inorganic semiconductor-metal-dielectric CGL:PMA / Al:AlOx, which helps to generate and separate electrons at CGL (Adv.Mat, 2022, 34(4)); or by introducing a PMA intermediate layer between PVK and PEDOT:PSS to construct PVK / PMA / PEDOT:PSS / ZnO CGL, which enhances charge generation and promotes carrier balance (Adv.Mater.Interfaces, 2024, 2400098). However, the above solutions also bring other technical drawbacks. ZnO / PEDOT:PSS is the most common solution-based CGL, but ZnO faces many problems and challenges in device fabrication, mainly including: ZnO has poor charge generation ability, and the nanoparticles are highly chemically active and have poor stability. They are easily corroded by water and oxygen in the air and are prone to agglomeration, which will adversely affect the efficiency and lifespan of the device. Secondly, ZnO nanoparticles have many surface defects, which can cause exciton quenching at the QD / ZnO interface. At the same time, the batch stability problem in the ZnO synthesis process cannot be ignored.

[0006] In view of the above limitations, the present invention provides a highly efficient charge generation layer. By modifying the surface of ZnO and then constructing a charge generation layer with a p-type material, the energy band bending at the ZnO / p-type material is promoted, making it easier for charges to separate at the interface, thereby improving the charge generation capability of CGL. Summary of the Invention

[0007] The purpose of this invention is to provide a modified ZnO nanocrystal, a charge generation layer, and its application to overcome the shortcomings of the prior art.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution.

[0009] As a first aspect of the invention, the present invention provides a modified ZnO nanocrystal, comprising modifying the surface of ZnO nanoparticles with an organic compound having a strong dipolarizing group to form a dipolar interface layer.

[0010] In a preferred embodiment, the strong dipolarizing group is -NH2.

[0011] In a preferred embodiment, the organic compound has the general formula X-(CH2CH2). n-NH2, wherein X includes, but is not limited to, at least one of -Si(OMe)3, -SH, -COOH, and -NH2.

[0012] Preferably, the organic compound is any one of 3-aminopropyltrimethoxysilane, 3-aminopropanethiol, 1,3-propanediamine, and 4-aminobutyric acid.

[0013] As one of the objectives of this invention, the present invention also provides a method for preparing the above-mentioned charge generation layer, the specific steps of which include:

[0014] (1) Provide zinc oxide precursor solution;

[0015] An organic zinc salt solution is mixed with tetramethoxyammonium hydroxide to form a zinc oxide precursor solution;

[0016] (2) Preparation of modified zinc oxide nanocrystals

[0017] The zinc oxide precursor solution is added and heated, and then an organic compound solution containing strong dipolarization groups is added and stirred evenly. The strong dipolarization groups are then modified on the surface of the generated zinc oxide particles. After post-treatment, modified zinc oxide nanocrystals are obtained.

[0018] In a preferred embodiment, the mixing of the organic zinc salt solution and tetramethoxyammonium hydroxide in step (1) is carried out in an MCR reactor, with the ratio of the two flow rates entering the MCR reactor being 3:2.

[0019] In a preferred embodiment, in step (1), the molar ratio of the organic zinc salt solution to tetramethoxyammonium hydroxide is 1:2 to 5, preferably 3:10.

[0020] In a preferred embodiment, the molar ratio of the organozinc to the organic compound containing a strong dipolarizing group is 1:3.

[0021] In a preferred embodiment, the post-processing includes centrifuging the generated zinc oxide particles after sedimentation with ethyl acetate.

[0022] As another aspect of the invention, the present invention provides a charge generation layer, which is formed by spin-coating a p-type material onto the surface of the modified ZnO nanocrystals and then annealing the ZnO nanocrystals. This charge generation layer can be used to prepare stacked quantum dot electroluminescent devices.

[0023] As a preferred embodiment, the p-type material includes, but is not limited to, any one of PEDOT:PSS, PMA, WO3, NiO, V2O5, Cu(SCN)2, CuPc, HATCN, etc.

[0024] As one of the objectives of the invention, the present invention also provides a quantum dot electroluminescent device, which includes at least the charge generation layer as described above.

[0025] In a preferred embodiment, the quantum dot electroluminescent device is a stacked electroluminescent device, comprising an anode / hole injection layer / first hole transport layer / first light-emitting layer / charge generation layer / second hole transport layer / second light-emitting layer / electron transport layer / cathode stacked sequentially.

[0026] In a preferred embodiment, the anode is indium tin oxide glass (ITO), aluminum zinc oxide glass (AZO), or indium zinc oxide glass (IZO).

[0027] Preferably, the anode is ITO.

[0028] In a preferred embodiment, the hole injection layer is formed on the anode surface, and the material of the hole injection layer is PEDOT:PSS.

[0029] In a preferred embodiment, the first hole transport layer and the second hole transport layer are formed on the surface of the anode and the surface of the second hole injection layer, respectively, and the first hole transport layer and the second hole transport layer are TFB (poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)]) thin film layers.

[0030] Preferably, the thickness of both the first hole transport layer and the second hole transport layer is 20nm to 60nm; more preferably 20 to 40nm; and even more preferably 30nm.

[0031] In a preferred embodiment, the first light-emitting layer and the second light-emitting layer are quantum dot thin film layers.

[0032] Preferably, quantum dots include, but are not limited to, any one of CdSe, CdS, CdZnSe, ZnSe, InP, perovskite, etc.

[0033] Preferably, the thickness of the first light-emitting layer and the second light-emitting layer is 5 nm to 40 nm, and more preferably 20 nm.

[0034] The first charge generation layer and the second charge generation layer are formed on the surfaces of the first light-emitting layer and the second light-emitting layer, respectively. Due to the modification of the charge generation layer with organic compounds, it is equivalent to forming an organic molecular film on the surface of ZnO nanoparticles, which passivates the defects on the surface of ZnO nanoparticles and can effectively improve exciton quenching at the QD / ZnO: interface, thereby solving the problem of severe efficiency roll-off of the device at high current density. At the same time, the ZnO surface modification also enhances charge generation and promotes carrier balance, further avoiding the generation of leakage current.

[0035] The first charge generation layer and / or the second charge generation layer include a ZnO layer and a p-type material layer (or a hole injection material layer), wherein the p-type material layer is spin-coated onto the surface of the ZnO layer to form the charge generation layer.

[0036] Preferably, the thickness of the ZnO layer in the first charge generation layer is 20–80 nm; more preferably, it is 50 nm.

[0037] Preferably, the thickness of the p-type material layer is 20–60 nm; more preferably, it is 40 nm.

[0038] In a preferred embodiment, the cathode is formed on the surface of the second charge-generating layer. The material is selected from at least one of silver (Ag), aluminum (Al), platinum (Pt), and gold (Au); preferably Al.

[0039] More preferably, the thickness of the cathode is 60 nm to 300 nm, and more preferably 100 nm.

[0040] Compared with the prior art, the present invention has at least the following beneficial effects:

[0041] 1. This invention prepares multilayer QLED devices using a full solution method. Modifying ZnO particles with -NH2, which has strong dipoleization, can promote band bending at the CGL interface, enhance the charge generation capability of the CGL, and make it easier for charges to be generated and separated at the CGL interface, thus effectively improving the performance of the multilayer device. The prepared multilayer device has the characteristics of high external quantum efficiency and low turn-on voltage.

[0042] 2. This invention modifies ZnO with organic materials to form an organic film on the surface of ZnO particles, which can passivate surface defects, effectively prevent exciton quenching at the QD / ZnO interface, and the organic-modified ZnO is less prone to agglomeration and has more stable properties. It can also prevent leakage current problems caused by the whole solution method for preparing stacked QLED devices and achieve efficient carrier injection balance. Attached Figure Description

[0043] Figure 1This is a comparison diagram showing the charge generation capabilities of different charge generation layers (CGL) prepared in the embodiments of the present invention and the charge generation layer prepared in the comparative example.

[0044] Figure 2 This is a schematic diagram of the energy levels of the stacked QLED device prepared according to the embodiments of the present invention.

[0045] Figure 3 This is a comparative analysis of the external quantum efficiency (EQE) of different stacked QLED devices prepared according to the embodiments of the present invention.

[0046] Figure 4 This is a particle size distribution diagram of the ZnO nanocrystals prepared in Example 1 of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0048] The technical solution of the present invention will be explained in more detail below with reference to several embodiments.

[0049] Example 1

[0050] This embodiment provides a method for preparing modified ZnO nanocrystals for preparing charge-generating layers (CGLs). This embodiment uses ZnO modified with 3-aminopropyltrimethoxysilane, and the specific steps include:

[0051] 0.6585 g of Zn(Ac)₂·2H₂O was dissolved in 30 mL of DMSO to prepare a 0.1 mol / L solution. Next, 0.9062 g of TMAH (tetramethylammonium hydroxide pentahydrate) was dissolved in 10 mL of ethanol to prepare a 0.5 mol / L solution. Then, 0.1792 g of 3-aminopropyltrimethoxysilane was dissolved in 10 mL of ethanol to prepare a 0.1 mol / L solution. The Zn(Ac)₂·2H₂O (DMSO) solution and the TMAH (ethanol) solution were passed through an MCR reactor at flow rates of 3 mL / min and 2 mL / min, respectively, to prepare precursor solutions. The mixture was collected in a flask, and 0.3 mL of 3-aminopropyltrimethoxysilane solution was slowly added dropwise to an oil bath at 85 °C. After stirring for 15 min, the mixture was cooled to room temperature. The mixture was precipitated with excess ethyl acetate for 2 hours, followed by centrifugation at 3000 rpm for 5 min. After centrifugation, the supernatant was removed, and this process was repeated three times. Finally, the 3-aminopropyltrimethoxysilane-modified ZnO nanocrystals (ZnO NC) were... sThe ZnO nanocrystals were uniformly dispersed in ethanol to prepare a 30 mg / mL solution, sealed, and stored in the freezer for later use. The prepared ZnO nanocrystals were designated as ZnO1.

[0052] See Figure 4 The figure shows the particle size distribution of the prepared ZnO nanocrystals. As can be seen from the figure, the particle size is mainly distributed in the range of 2-5 nm.

[0053] Example 2

[0054] This embodiment provides a method for preparing modified ZnO nanocrystals for preparing charge-generating layers (CGLs). The ZnO modified with 3-aminopropanethiol in this embodiment includes the following steps:

[0055] Zn(Ac)₂·2H₂O was dissolved in DMSO to prepare a 0.1 mol / L solution. Next, TMAH (tetramethoxyammonium hydroxide) was dissolved in ethanol to prepare a 0.5 mol / L solution. Then, 0.0912 g of 3-aminopropanethiol was dissolved in 10 mL of ethanol to prepare a 0.1 mol / L solution. The Zn(Ac)₂·2H₂O (DMSO) solution and the TMAH (ethanol) solution were passed through an MCR reactor at flow rates of 3 mL / min and 2 mL / min, respectively, to prepare precursor solutions. The mixture was collected in a flask, and 0.3 mL of the 3-aminopropanethiol solution was slowly added dropwise to an oil bath at 85 °C. After stirring for 15 min, the mixture was cooled to room temperature. Excess ethyl acetate was added to precipitate the mixture for 2 hours, followed by centrifugation at 3000 rpm for 5 min. After centrifugation, the supernatant was removed, and the process was repeated three times. Finally, the 3-aminopropanethiol-modified ZnO NCs were uniformly dispersed in ethanol to prepare a 30 mg / mL solution, which was then sealed and stored in the freezer for later use. The prepared ZnO nanocrystals were classified as ZnO2.

[0056] Example 3

[0057] This embodiment provides a method for preparing modified ZnO nanocrystals for preparing charge-generating layers (CGLs). This embodiment uses 1,3-propanediamine-modified ZnO, and the specific steps include:

[0058] Zn(Ac)₂·2H₂O was dissolved in DMSO to prepare a 0.1 mol / L solution. Next, TMAH (tetramethoxyammonium hydroxide) was dissolved in ethanol to prepare a 0.5 mol / L solution. Then, 0.0741 g of 1,3-propanediamine was dissolved in 10 mL of ethanol to prepare a 0.1 mol / L solution. The Zn(Ac)₂·2H₂O (DMSO) solution and the TMAH (ethanol) solution were passed through an MCR reactor at flow rates of 3 mL / min and 2 mL / min, respectively, to prepare precursor solutions. The mixture was collected in a flask, and 0.3 mL of 1,3-propanediamine solution was slowly added dropwise to an oil bath at 85 °C. After stirring for 15 min, the mixture was cooled to room temperature. Excess ethyl acetate was added for precipitation for 2 hours, followed by centrifugation at 3000 rpm for 5 min. After centrifugation, the supernatant was removed, and the process was repeated three times. Finally, the 1,3-propanediamine-modified ZnO NCs were uniformly dispersed in ethanol to prepare a 30 mg / mL solution, which was then sealed and stored in the freezer for later use. The prepared ZnO nanocrystals were classified as ZnO3.

[0059] Example 4

[0060] This embodiment provides a method for preparing modified ZnO nanocrystals for preparing charge-generating layers (CGLs). This embodiment uses 4-aminobutyric acid-modified ZnO, and the specific steps include:

[0061] Zn(Ac)₂·2H₂O was dissolved in DMSO to prepare a 0.1 mol / L solution. Next, TMAH (tetramethoxyammonium hydroxide) was dissolved in ethanol to prepare a 0.5 mol / L solution. Then, 0.0103 g of 4-aminobutyric acid was dissolved in 10 mL of ethanol to prepare a 0.1 mol / L solution. The Zn(Ac)₂·2H₂O (DMSO) solution and the TMAH (ethanol) solution were passed through an MCR reactor at flow rates of 3 mL / min and 2 mL / min, respectively, to prepare precursor solutions. The mixture was collected in a flask, and 0.3 mL of 4-aminobutyric acid solution was slowly added dropwise to an oil bath at 85 °C. After stirring for 15 min, the mixture was cooled to room temperature. Excess ethyl acetate was added for precipitation for 2 hours, followed by centrifugation at 3000 rpm for 5 min. After centrifugation, the supernatant was removed, and the process was repeated three times. Finally, the 4-aminobutyric acid-modified ZnO NCs were uniformly dispersed in ethanol to prepare a 30 mg / mL solution, which was then sealed and stored in the freezer for later use. The prepared ZnO nanocrystals were classified as ZnO4.

[0062] The modified ZnO nanocrystals and unmodified ZnO nanoparticles (particle size 2-5 nm) prepared in Examples 1-4 were used to prepare ITO / CGL / Al devices. The charge generation capability of the charge generation layer CGL was analyzed. Specifically, the following steps were taken: a dispersion of ZnO nanocrystals or ZnO nanoparticles was spin-coated onto the treated ITO surface at 3000 rpm for 30 seconds, baked at 90°C for 15 min, and cooled for 5 min to a thickness of 50 nm; then, a PEDOT:PSS solution was spin-coated onto the ZnO layer (3000 rpm, 30 s), and annealed at 100°C for 15 min in an atmospheric atmosphere, followed by transfer to a nitrogen glove box (O2 < 1 ppm, H2O < 1 ppm).

[0063] When forward (charge generation process) and reverse (charge quenching process) bias voltages are applied to the device, the current density of the device also increases as the applied voltage increases.

[0064] See results Figure 1 The figure illustrates the charge generation process of ZnO, organically modified ZnO, and CGLs prepared by PEDOT:PSS. Due to the numerous defect states and high surface energy on the ZnO NC surface, its charge quenching ability is far greater than its charge generation ability. APTMS can passivate defects on the ZnO surface, effectively reducing charge quenching. Furthermore, the strong dipole interaction of -NH2 gives it a strong charge generation ability. Therefore, the ZnO@APTMS-based CGLs exhibit higher JV curve symmetry and more balanced carrier injection, making them more suitable for fabricating multilayer devices.

[0065] Furthermore, the modified ZnO nanocrystals prepared in Examples 1-5 were used to prepare stacked quantum dot electroluminescent devices. The specific steps included:

[0066] (1) Cleaning: Clean the surface of the ITO glass substrate with glass cleaner, ultrasonically clean it 3 times with deionized water, and then ultrasonically clean it for 20 minutes with anhydrous ethanol. After drying with nitrogen, treat it with oxygen plasma (O-plasma) for 5 minutes to obtain a cleaned ITO glass substrate.

[0067] (2) Preparation of PEDOT:PSS HIL layer: On the ITO glass substrate cleaned in step (1), PEDOT:PSS solution is spin-coated onto the treated ITO glass substrate (4000 rpm, 40 s), and annealed at 130°C for 15 min in an atmospheric atmosphere, and then transferred to a nitrogen glove box (O2<1ppm, H2O<1ppm).

[0068] (3) Preparation of TFB-HTL layer: spin-coat TFB chlorobenzene solution (8mg / mL) on the HIL layer obtained in step (2) at 3000 rpm for 30 seconds, anneal at 130℃ for 15 min, and let cool for 5 min.

[0069] (4) Preparation of quantum dot light-emitting layer: spin-coat the HTL layer obtained in step (3) with red quantum dot solution dispersed in octane (15 mg / mL), and then anneal at 100 °C for 2 minutes.

[0070] (5) Preparation of CGL-ZnO layer: The modified ZnO nanocrystals (dispersed in ethanol, 30 mg / mL) obtained in step (4) were spin-coated on the QD at a speed of 3000 rpm for 30 seconds, baked at 90℃ for 15 min, and cooled for 5 min.

[0071] (6) Preparation of CGL-PEDOT:PSS layer: ITO glass substrate was transferred to atmospheric atmosphere, PEDOT:PSS solution was spin-coated onto ZnO obtained in step (5) (3000 rpm, 30 s), and annealed at 100 °C for 15 min in atmospheric atmosphere, and then transferred to nitrogen glove box (O2<1ppm, H2O<1ppm).

[0072] (7) Preparation of TFB-HTL layer: spin-coat TFB chlorobenzene solution (8mg / mL) onto the PEDOT:PSS layer obtained in step (6) at 3000 rpm for 30 seconds, anneal at 100℃ for 15 min, and let cool for 5 min.

[0073] (8) Preparation of quantum dot light-emitting layer: spin-coat the HTL layer obtained in step (7) with an octane-dispersed red quantum dot solution (15 mg / mL) and then anneal at 100 °C for 2 minutes.

[0074] (9) Preparation of ETL-ZnO layer: The modified nanocrystals (dispersed in ethanol, 30 mg / mL) obtained in step (8) were spin-coated on the QD at 3000 rpm for 30 seconds, baked at 90℃ for 15 min, and cooled for 5 min.

[0075] (10) The wafer is placed in a vacuum evaporation chamber and a 100 nm aluminum electrode (Al, 3 Å / s) is vacuum evaporated to obtain a quantum dot electroluminescent device.

[0076] The structure of the QLED stacked device is as follows: ITO (~110nm) / PEDOT: PSS (~28nm) / TFB (10nm) / QDs (~20nm) / Modified ZnO (~50nm) / PEDOT: PSS (~40nm) / TFB (10nm) / QDs (~20nm) / Modified ZnO (~50nm) / Al (~100nm)

[0077] See Figure 2 This diagram illustrates the energy levels of the stacked quantum dot electroluminescent device (CGL) fabricated using the aforementioned method and the charge generation mechanism of CGL. When a bias voltage is applied, the strong dipole effect of the -NH2 groups on the ZnO@APTMS surface generates an interfacial dipole at the interface, causing the vacuum level towards the PEDOT:PSS side to shift upwards. This promotes the generation and separation of holes and electrons at the interface, which then recombine with electrons and holes injected from the cathode and anode, respectively, to emit light.

[0078] As a comparison, the present invention also uses the zinc oxide nanocrystals prepared in Examples 1-4 to prepare monolayer QLED devices, the preparation steps of which include:

[0079] (1) Cleaning: Clean the surface of the ITO glass substrate with glass cleaner, ultrasonically clean it 3 times with deionized water, and then ultrasonically clean it for 20 minutes with anhydrous ethanol. After drying with nitrogen, treat it with oxygen plasma (O-plasma) for 5 minutes to obtain a cleaned ITO glass substrate.

[0080] (2) Preparation of PEDOT:PSS HIL layer: On the ITO glass substrate cleaned in step (1), PEDOT:PSS solution is spin-coated onto the treated ITO glass substrate (4000 rpm, 40 s), and annealed at 130°C for 15 min in an atmospheric atmosphere, and then transferred to a nitrogen glove box (O2<1ppm, H2O<1ppm).

[0081] (3) Preparation of TFB-HTL layer: spin-coat TFB chlorobenzene solution (8mg / mL) on the HIL layer obtained in step (2) at 3000 rpm for 30 seconds, anneal at 130℃ for 15 min, and let cool for 5 min.

[0082] (4) Preparation of quantum dot light-emitting layer: spin-coat the HTL layer obtained in step (3) with red quantum dot solution dispersed in octane (15 mg / mL), and then anneal at 100 °C for 2 minutes.

[0083] (5) Preparation of ETL-ZnO layer: The modified ZnO nanocrystals (dispersed in ethanol, 30 mg / mL) obtained in step (4) were spin-coated on the QD at a speed of 3000 rpm for 30 seconds, baked at 90℃ for 15 min, and cooled for 5 min.

[0084] (6) The wafer is placed in a vacuum evaporation chamber and a 100 nm layer of aluminum electrode (Al, 3 Å / s) is vacuum evaporated to obtain a single-layer quantum dot electroluminescent device.

[0085] The structure of a single-layer QLED device is ITO (~110nm) / PEDOT:PSS (~28nm) / TFB (10nm) / QDs (~20nm) / modified ZnO (~50nm) / Al (100nm).

[0086] The quantum dots used in the aforementioned stacked QLED devices and single-layer QLED devices are CdSe red quantum dots. Performance test data for these devices are shown in Table 1 and... Figure 3 .

[0087] In this context, monolayer 1 and stack 1 represent those prepared using ZnO1 prepared in Example 1, and so on from monolayer 2 and stack 2 to monolayer 4 and stack 4. Monolayer 5 and stack 5 are QLED devices prepared using unmodified zinc oxide particles.

[0088] Table 1 Summary of performance of red QLED devices with different modified ZnO single-layer and multilayer structures

[0089]

[0090]

[0091] From Table 1 and Figure 3 It is evident that ZnO has poor charge generation capabilities, resulting in low efficiency and high turn-on voltage in both single-layer and multilayer devices. Modified ZnO / PEDOT:PSS, as a multilayer device in a CGL, achieves a maximum external quantum efficiency of 26.39%, more than twice that of the corresponding single-layer device, exhibiting high efficiency and low turn-on voltage. This demonstrates that this CGL possesses highly efficient charge generation capabilities, indicating that the CGL according to the exemplary embodiments of the present invention can effectively improve the performance of multilayer QLED devices.

[0092] Furthermore, the display screen assembled using the stacked QLED devices provided by this invention has the advantages of lower energy consumption and stronger stability.

[0093] On the other hand, the quantum dots in this invention are not limited to the blue quantum dots mentioned above. Other quantum dots such as red quantum dots, indium quantum dots, perovskites, etc., or any one of CdSe, CdS, CdZnSe, ZnSe, etc. can also be selected.

[0094] It should be noted that the above description is only a preferred embodiment of the present invention and the foregoing embodiments have been used to describe the present invention in detail. The embodiments are not intended to limit the present application. Although those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included within the protection scope of the present invention.

Claims

1. A charge-generating layer, characterized in that, Composed of modified ZnO nanocrystals and p Composition of type materials; The modified ZnO nanocrystals include modifying the surface of ZnO nanoparticles with an organic compound having a strong dipolarization group to form a dipolar interface layer.

2. The charge generation layer according to claim 1, characterized in that, The strong dipolarizing group is -NH2; The general formula of the organic compound is X-(CH2). n -NH2, wherein X includes at least one of -Si(OMe)3, -SH, -COOH, and -NH2; wherein n = 2-6; And / or, the p-type material is spin-coated onto the surface of a thin film layer formed by modified ZnO nanocrystals, and then annealed to form the charge-generating layer.

3. The charge generation layer according to claim 1, characterized in that, The organic compound is any one of 3-aminopropyltrimethoxysilane, 3-aminopropanethiol, 1,3-propanediamine, and 4-aminobutyric acid. The p-type material includes any one of PEDOT: PSS, PMA, WO3, NiO, V2O5, Cu(SCN)2, CuPc, and HATCN.

4. The charge-generating layer according to any one of claims 1-3, characterized in that, The preparation method of the modified ZnO nanocrystals includes the following specific steps: (1) Provide zinc oxide precursor solution; An organic zinc salt solution is mixed with tetramethoxyammonium hydroxide to form a zinc oxide precursor solution; (2) Preparation of modified zinc oxide nanocrystals; The zinc oxide precursor solution is added and heated, and then an organic compound solution containing strong dipolarization groups is added and stirred evenly. The strong dipolarization groups are then modified on the surface of the generated zinc oxide particles. After post-treatment, modified zinc oxide nanocrystals are obtained.

5. The charge generation layer according to claim 4, characterized in that, The mixing of the organic zinc salt solution and tetramethoxyammonium hydroxide in step (1) is carried out in an MCR reactor, with the ratio of the two flow rates entering the MCR reactor being 3:2; And / or, the molar ratio of the organic zinc salt solution to tetramethoxyammonium hydroxide is 1:2 to 5; preferably 3:10; And / or, the molar ratio of the organozinc to the organic compound containing a strong dipolarizing group is 1:3; And / or, the post-processing includes centrifuging the generated zinc oxide particles after precipitation with ethyl acetate.

6. A stacked quantum dot electroluminescent device, characterized in that, It includes at least the charge generation layer as described in any one of claims 1-5.

7. The stacked quantum dot electroluminescent device according to claim 6, characterized in that, The quantum dot electroluminescent device is a stacked electroluminescent device, comprising an anode / hole injection layer / first hole transport layer / first light-emitting layer / charge generation layer / second hole transport layer / second light-emitting layer / electron transport layer / cathode stacked sequentially.

8. The stacked quantum dot electroluminescent device according to claim 6, characterized in that, The anode is indium tin oxide glass (ITO), aluminum zinc oxide glass (AZO), or indium zinc oxide glass (IZO); preferably, it is ITO. And / or, the hole injection layer is formed on the anode surface, and the material of the hole injection layer is PEDOT:PSS; And / or, the first hole transport layer and the second hole transport layer are respectively formed on the surface of the anode and the surface of the second hole injection layer, and the first hole transport layer and the second hole transport layer are TFB (poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)]) thin film layers; And / or, the thickness of both the first hole transport layer and the second hole transport layer is 20nm to 60nm; preferably 20 to 40nm; more preferably 30nm. And / or, the charge generation layer includes a ZnO layer and a p-type material layer (or a hole injection material layer), wherein the p-type material layer is spin-coated onto the surface of the ZnO layer to form the charge generation layer; Preferably, the thickness of the ZnO layer in the charge generation layer and / or the electron transport layer is 20–80 nm; more preferably 50 nm. Preferably, the thickness of the p-type material layer is 20–60 nm; more preferably, it is 40 nm. And / or, the cathode is formed on the surface of the electron transport layer; And / or, the cathode is formed on the surface of the electron transport layer by vacuum evaporation; The cathode material is selected from at least one of silver, aluminum, platinum, and gold; preferably aluminum. More preferably, the thickness of the cathode is 60 nm to 300 nm, and more preferably 100 nm.

9. The stacked quantum dot electroluminescent device according to claim 6, characterized in that, The first light-emitting layer and the second light-emitting layer are quantum dot thin film layers; And / or, the quantum dots include any one of CdSe, CdS, CdZnSe, ZnSe, InP, perovskite, etc. The thickness of the first light-emitting layer and the second light-emitting layer is 5nm to 40nm, preferably 20nm.

10. A display screen comprising at least the stacked quantum dot electroluminescent device as described in any one of claims 6-9.

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