Structured preparation method of charge generation layer of laminated quantum dot light emitting diode

Abstract

The invention provides a structured preparation method of a charge generation layer of a laminated quantum dot light-emitting diode. The structured preparation method comprises the following steps: preparing a first light-emitting unit comprising a first electron transport layer; forming a patterned electron transport layer on the first electron transport layer through a transfer printing process; preparing a second light-emitting unit comprising a second hole injection layer on the patterned electron transport layer; wherein the first electron transport layer, the patterned electron transport layer and the second hole injection layer jointly form a structured charge generation layer; the transfer printing process comprises the following steps: S1, preparing a PDMS seal with patterned bulges; s2, generating an electron transport material thin film through an LB film drawing process; s3, adhering a convex part of a PDMS (Polydimethylsiloxane) seal to the thin film to obtain a patterned electron transport material; and S4, attaching the PDMS seal adhered with the patterned electron transport material to the first electron transport layer, and performing press separation and transfer printing to form the patterned electron transport layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation methods and structural optimization of quantum dot light-emitting diodes (QLEDs), and specifically relates to a structured preparation method for a charge generation layer of a stacked quantum dot light-emitting diode. Background Art

[0002] In recent years, colloidal quantum dot light-emitting diodes (QLEDs) have attracted widespread attention from both academia and industry as a key candidate for next-generation display technology. Compared to traditional organic light-emitting diodes (OLEDs) and liquid crystal displays (LCDs), QLEDs offer significant advantages in display technology, including high color purity, a wide color gamut, tunable emission wavelengths, and the potential for low-cost solution-based fabrication. Although QLEDs excel across multiple performance metrics, their low efficiency and instability remain significant bottlenecks hindering their widespread adoption. To further enhance the overall performance of QLEDs, researchers have begun exploring various improvement strategies, with the use of stacked structures considered a promising solution. However, despite the significant potential for performance enhancement in stacked quantum dot (QD) LEDs, related research and reports remain relatively limited, particularly in the area of ​​fully solution-based stacked QD LEDs. The fabrication of stacked quantum dot light-emitting diodes faces numerous challenges, the most critical of which are insufficient charge generation capacity in the charge generation layer and poor device performance reproducibility due to solvent non-orthogonality between functional layers. Because the charge generation capacity of the charge generation layer directly depends on the contact area between its constituent materials, the interface of charge generation layers prepared by spin coating or thermal evaporation is a two-dimensional planar structure, making it difficult to further improve charge generation efficiency. Summary of the Invention

[0003] This paper proposes a structured fabrication method to address the issues of insufficient charge generation layer efficiency and solvent erosion in existing stacked quantum dot light-emitting diodes. Existing technologies are limited by the two-dimensional structure of the charge generation interface, resulting in a physical bottleneck in carrier separation efficiency. Furthermore, the lack of orthogonality in the solvent during the all-solution fabrication process can easily lead to deformation of the underlying functional film, severely impacting device performance reproducibility.

[0004] This solution innovatively designs a charge generation layer with a three-layer composite structure, consisting of a first electron transport layer, a patterned electron transport layer, and a second hole injection layer. By introducing a three-dimensional micro-nano interface, the material contact area is significantly expanded, fundamentally breaking through the charge generation efficiency limitations of planar structures. The realization of this structure relies on a precision transfer process: first, a PDMS stamp with specific patterned protrusions (such as a cylindrical array with a diameter of 500nm and a depth of 1.5μm) is prepared; then, a zinc oxide nanocrystal film is generated using the LB film drawing technique with n-octane as the solvent; the film is selectively adhered to the stamp protrusions to form a patterned material; finally, a pressing and separation operation is performed to accurately transfer the patterned electron transport layer to the surface of the first electron transport layer. During the process, the overlapping steps can be repeated according to the depth requirements to achieve active control of the interface structure.

[0005] To ensure process compatibility and stability, the solution simultaneously optimized the material system: the electron transport layer utilizes metal oxide nanoparticles such as ZnO and SnO2, while the hole injection layer uses low-corrosive materials such as PEDOT:PSS and MoO3. After transfer, a low-temperature annealing treatment at 80°C enhances film density while minimizing damage to the underlying quantum dot material. This innovative trinity of "structural design, transfer process, and material synergy" not only significantly improves charge generation efficiency but also fundamentally eliminates film deformation caused by solvent erosion.

[0006] This fabrication method successfully balances high-precision structure with full solution processing compatibility. The patterned electron transport layer acts as a physical barrier, effectively isolating the upper layer from the solvent's erosion of the lower layer. The three-dimensional interface structure significantly increases the charge generation area, surpassing the performance limits of existing multi-layer QLEDs in terms of brightness and lifetime.

[0007] And it is directly related to the device interface quality through the pressing and separating operation of the transfer process.

[0008] This solution provides a new technical paradigm for the mass production of high-stability stacked QLEDs, and has clear application prospects in cutting-edge fields such as AR / VR microdisplays and flexible screens.

[0009] The technical solution specifically adopted by the present invention to solve the technical problem is: A method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode comprises: preparing a first light-emitting unit comprising a first electron transport layer; forming a patterned electron transport layer on the first electron transport layer by a transfer process; preparing a second light-emitting unit including a second hole injection layer on the patterned electron transport layer; The first electron transport layer, the patterned electron transport layer and the second hole injection layer together constitute a structured charge generation layer; The transfer process includes: S1: Preparation of PDMS stamp with patterned protrusions; S2: Generate electron transport material thin film by LB film drawing process; S3: adhering the raised portion of the PDMS stamp to the film to obtain a patterned electron transport material; S4: The PDMS stamp with the patterned electron transport material adhered thereto is attached to the first electron transport layer, and after separation by pressing, the stamp is transferred to form a patterned electron transport layer.

[0010] Furthermore, the electron transport material in step S2 is a zinc oxide nanocrystal solution using n-octane as solvent.

[0011] Furthermore, steps S1 to S3 are repeatedly performed according to the structural depth requirement to achieve multi-layer thin film stacking.

[0012] Furthermore, after the transfer in step S4, the patterned electron transport layer is subjected to an annealing treatment at 80°C.

[0013] Furthermore, the patterned protrusion is a cylindrical structure.

[0014] Furthermore, the diameter of the cylindrical structure is 500 nm.

[0015] Furthermore, the depth of the cylindrical structure is 1.5 μm.

[0016] Furthermore, the materials of the first electron transport layer and the second electron transport layer are respectively selected from ZnO, SnO2, and TiO2 nanoparticles.

[0017] Furthermore, the materials of the first hole injection layer and the second hole injection layer are respectively selected from PEDOT:PSS, MoO3, NiOx, V2O5, and CuSCN.

[0018] Furthermore, the pressing and separating operation includes the steps of pressing and separating the PDMS stamp in sequence.

[0019] Compared with the prior art, the present invention and its preferred embodiments have at least the following beneficial effects: First, by innovatively designing the charge generation layer as a three-dimensional structured system (a coordinated structure of a first electron transport layer, a patterned electron transport layer, and a second hole injection layer), the physical limitations of traditional two-dimensional planar interfaces are effectively overcome. This configuration significantly increases the contact area between the carrier materials, thereby achieving substantial improvements in charge separation and injection efficiency at the device level, laying the structural foundation for the performance breakthroughs of stacked QLEDs.

[0020] Secondly, a transfer process combining PDMS stamps and LB film technology enables precise fabrication of micro- and nanostructures while avoiding solution erosion. This process, through a physical transfer method of pressure separation, protects the integrity of underlying functional layers (such as the quantum dot light-emitting layer) while ensuring a clear morphology of the patterned electron transport layer. This non-contact processing mechanism fundamentally addresses the interlayer miscibility issues encountered in all-solution fabrication, significantly improving device performance reproducibility and yield.

[0021] In terms of material systems, the preferred material for the transport layer is zinc oxide in n-octane solvent, coupled with a low-temperature annealing process at 80°C. This ensures film density while avoiding high-temperature damage to the quantum dot material. The targeted selection of materials for the electron transport layer and hole injection layer (such as ZnO / SnO2 nanoparticles and PEDOT:PSS) further optimizes energy level matching and interfacial compatibility, resulting in a synergistic enhancement effect.

[0022] Of particular note is the repetitive stacking process design, which provides an active means of controlling the depth of the structure. By configuring the PDMS stamp in a cylindrical array (e.g., 500nm diameter and 1.5μm depth in this example), the charge generation interface achieves three-dimensional scalability, enabling greater flexibility in controlling device performance.

[0023] Finally, the entire fabrication method maintains the cost advantages of a full solution method while also enabling high-precision patterning. This technical compatibility enables the mass production of stacked QLEDs, providing a new technological paradigm for high-resolution displays. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 is a schematic diagram of the device structure prepared in an embodiment of the present invention; Figure 2 It is a schematic diagram of the film-drawing transfer process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the features and advantages of the present invention more clearly understood, the following embodiments are given for detailed description: It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which this application belongs.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0027] The present invention aims to overcome the shortcomings of the prior art and provide a method for preparing a structured charge generation layer for a stacked quantum dot light-emitting diode. This method utilizes a film-drawing-transfer technique to prepare a patterned electron transport layer, thereby achieving a structured charge generation layer with controllable contact interface area, significantly improving charge generation efficiency.

[0028] The stacked quantum dot light-emitting diode based on the charge generation layer structure includes an anode, a first hole injection layer, a first hole transport layer, a first quantum dot light-emitting layer, a first electron transport layer, a patterned electron transport layer, a second hole injection layer, a second hole transport layer, a second quantum dot light-emitting layer, a second electron transport layer, and a metal cathode, which are arranged in sequence from bottom to top. Among them, the first electron transport layer, the patterned electron transport layer and the second hole injection layer together constitute a structured charge generation layer. The patterned electron transport layer is formed by self-assembly of electron transport materials and is prepared by a transfer process, such as Figure 2 The specific steps are as follows: 1) Pre-prepare a PDMS stamp with patterned protrusions; 2) Generate an LB film of electron transport material using an LB film drawing machine; 3) Adhere the LB film of electron transport material to the raised part of the PDMS stamp to obtain a patterned electron transport material; 4) Repeat the above steps according to the structure depth requirements; 5) A PDMS stamp with patterned protrusions and an electron transport material adhered thereto is attached to the light-emitting layer. The PDMS stamp is pressed and separated in sequence, so that the patterned electron transport material is successfully transferred to the first electron transport layer, forming a patterned electron transport layer. The present invention can not only effectively increase the charge generation area and significantly enhance the charge generation capacity of the charge generation layer, but also effectively avoid the problem of non-reproducibility of the film morphology caused by the impact of the solvent of the upper functional layer on the lower functional layer, thereby significantly improving the stability and reproducibility of the device performance.

[0029] In a preferred embodiment of the present invention, after the patterned electron transport material is transferred onto the first quantum dot light-emitting layer, it is annealed at 80°C.

[0030] In a preferred embodiment of the present invention, the material of the first and second hole injection layers is one of polymer poly (3,4-ethylenedioxythiophene) (PEDOT:PSS), molybdenum oxide, nickel oxide, vanadium oxide, and cuprous thiocyanate.

[0031] In a preferred embodiment of the present invention, the material of the first and second hole transport layers is one or a mixture of polymer 1,2,4,5-tetrakis(trifluoromethyl)benzene (TFB), polytriphenylamine (Poly:TPD), and polyvinylcarbazole (PVK).

[0032] In a preferred embodiment of the present invention, the first and second electron transport layers are n-type metal oxide nanoparticle films; the n-type metal oxide nanoparticles are ZnMgO, ZnO, SnO2, TiO2 nanoparticles, ZnO nanoparticles doped with metal cations, and a mixture of ZnO nanoparticles and polymers.

[0033] In a preferred embodiment of the present invention, the material of the quantum dots in the first and second quantum dot light-emitting layers is one of CdSe / ZnS, ZnSe / ZnS, InP, and halogen perovskite.

[0034] In a preferred embodiment of the present invention, the material of the metal cathode is gold, silver, aluminum, or copper.

[0035] In a preferred embodiment of the present invention, the material of the patterned electron transport layer is a zinc oxide solution with n-octane as solvent.

[0036] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: (1) The first electron transport layer, the patterned electron transport layer, and the second hole transport layer together constitute a structured charge generation layer with a controllable charge generation area; (2) The dense electron transport layer prepared by film transfer can effectively protect the first electron transport layer material and prevent it from being corroded by the solvent during the spin coating process of the second hole transport layer; (3) In the stacked quantum dot light-emitting device, due to the introduction of a patterned electron transport layer, its electron transport layer exhibits a higher charge generation efficiency, thereby significantly improving the electroluminescent performance of the device.

[0037] The following is a more specific application example to further illustrate and introduce the embodiment of the present invention. The preparation results are as follows: Figure 1 As shown, the specific steps include: 1) Preparation of a PDMS stamp with cylindrical structures: First, polydimethylsiloxane (PDMS) was coated on a silicon-based master template. The coated sample was then heated at 80°C for 50 minutes to cure. After curing, the PDMS was carefully separated from the template. The prepared PDMS stamp had an area of ​​1.2 cm² and a thickness of 0.5 mm. Each cylindrical structure had a diameter of 500 nm and a depth of 1.5 μm. The PDMS was prepared by mixing the liquid components with a curing agent in a 10:1 mass ratio. After mixing, the mixture was stirred for 10 minutes and placed in a vacuum drying oven for degassing. After standing for 1 hour, the sample was removed, completing the PDMS pretreatment.

[0038] 2) Preparation of a patterned electron transport layer: First, zinc oxide nanocrystals were prepared into a solution with a concentration of 5 mg / ml in n-octane. Subsequently, a continuous, complete zinc oxide LB film was produced using a Langmuir-Blodgett (LB) film drawing machine. Next, a pre-prepared PDMS stamp with a raised structure was used to adhere the zinc oxide LB film, enabling selective removal of the zinc oxide material. Finally, the PDMS stamp was attached to the surface of the quantum dot light-emitting layer. By pressing and separating, the patterned zinc oxide film was successfully transferred to the quantum dot light-emitting layer, completing the preparation of the patterned electron transport layer.

[0039] 3) The structure of the stacked quantum dot light-emitting diode device with a structured charge generation layer is, from bottom to top, an anode, a first hole injection layer, a first hole transport layer, a first quantum dot light-emitting layer, a first electron transport layer, a patterned electron transport layer, a second hole injection layer, a second hole transport layer, a second quantum dot light-emitting layer, a second electron transport layer, and a metal cathode.

[0040] The anode is an ITO conductive film prepared by magnetron sputtering and spin-coated using a spin coater. PEDOT:PSS is used as the first and second hole injection layers, annealed at 120°C, with a thickness of approximately 30 nm. TFB is used as the first and second hole transport layers, annealed at 120°C, with a thickness of approximately 40 nm. Quantum dots are used as the first and second quantum dot light-emitting layers, annealed at 80°C, with a thickness of approximately 30 nm. ZnO is used as the first and second electron transport layers, annealed at 80°C, with a thickness of approximately 50 nm. A 100 nm thick Ag electrode is deposited by vacuum evaporation as the cathode.

[0041] It should be noted that, unless otherwise defined, the technical or scientific terms used in the present invention should have the usual meanings understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

[0043] The present invention is not limited to the above-mentioned optimal embodiment. Anyone can derive various other forms of a structured preparation method for the charge generation layer of a stacked quantum dot light-emitting diode under the inspiration of the present invention. All equivalent changes and modifications made within the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode, characterized in that: include: preparing a first light-emitting unit comprising a first electron transport layer; forming a patterned electron transport layer on the first electron transport layer by a transfer process; preparing a second light-emitting unit including a second hole injection layer on the patterned electron transport layer; The first electron transport layer, the patterned electron transport layer and the second hole injection layer together constitute a structured charge generation layer; The transfer process includes: S1: Preparation of PDMS stamp with patterned protrusions; S2: Generate electron transport material thin film by LB film drawing process; S3: adhering the raised portion of the PDMS stamp to the film to obtain a patterned electron transport material; S4: The PDMS stamp with the patterned electron transport material adhered thereto is attached to the first electron transport layer, and after separation by pressing, the stamp is transferred to form a patterned electron transport layer.

2. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 1, characterized in that: The electron transport material in step S2 is a zinc oxide nanocrystal solution using n-octane as a solvent.

3. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 1, characterized in that: S1 to S3 are repeatedly executed according to the structural depth requirement to achieve multi-layer thin film stacking.

4. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 1, characterized in that: After the transfer in step S4, the patterned electron transport layer is further subjected to an annealing treatment at 80°C.

5. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 1, characterized in that: The patterned protrusion is a cylindrical structure.

6. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 5, characterized in that: The diameter of the cylindrical structure is 500 nm.

7. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 5, characterized in that: The depth of the cylindrical structure is 1.5 μm.

8. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 1, characterized in that: The materials of the first electron transport layer and the second electron transport layer are respectively selected from ZnO, SnO2, and TiO2 nanoparticles.

9. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 1, characterized in that: The materials of the first hole injection layer and the second hole injection layer are respectively selected from PEDOT:PSS, MoO3, NiOx, V2O5, and CuSCN.

10. The method for preparing a structured charge generation layer of a stacked quantum dot light-emitting diode according to claim 1, characterized in that: The pressing and separating operation includes the steps of pressing and separating the PDMS stamp in sequence.

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