Method for preparing quantum dot color conversion layer based on microchannel and electrophoretic deposition and application thereof

Abstract

The application discloses a method for preparing a quantum dot color conversion layer based on a microchannel and electrophoretic deposition, which comprises the following steps: setting a metal ring electrode and a connecting electrode on the periphery of an array-arranged transparent electrode, depositing an insulating layer, opening a to-be-deposited area, using a micro-channel technology, bonding with a micro-channel cover plate, and then feeding a charged quantum dot solution into a micro-channel passage, combining with an electrophoretic deposition technology, so that the quantum dot solution is deposited on the transparent electrode of the to-be-deposited area to form a quantum dot unit. The prepared quantum dot color conversion layer is bonded with a Micro-LED chip array to realize full-color display. The application combines the micro-channel technology and the electrophoretic deposition technology through the design of the metal electrode surrounding the transparent electrode, realizes the quantum dot color conversion layer with the advantages of small pixel size, high PPI, high light emission uniformity, fast deposition speed, high raw material utilization rate and being conducive to large-area preparation, and thus promotes the industrialization of the full-color Micro-LED.

Description

Technical Field

[0001] This invention belongs to the field of display technology, specifically a method for preparing a quantum dot color conversion layer based on microchannel technology and electrophoretic deposition technology to achieve full-color micro-LED display. Background Technology

[0002] Micro-LEDs, with their excellent photoelectric performance, high energy efficiency, fast response time, and high reliability, are considered an ideal choice for next-generation display technology. With the continued growth in demand for larger and higher-resolution displays, Micro-LEDs are poised to become the industry's next breakthrough technology. However, achieving full-color displays by integrating a single-chip red-green-blue main chip based on mass transfer technology suffers from serious problems such as high cost and poor yield during large-scale production. Therefore, quantum dot color conversion layer technology has emerged, achieving full-color Micro-LED displays by exciting the quantum dot color conversion layer with ultraviolet or blue light. When using photoexcitation of quantum dots to achieve full-color displays, issues such as color purity, brightness, insufficient quantum dot thickness leading to blue light leakage, and the uniformity of quantum dot film thickness significantly impact the overall performance of Micro-LED full-color displays.

[0003] When quantum dot materials are used as color conversion layers, the brightness of the Micro-LED excitation light source determines the color conversion efficiency and the quality of red, green, and blue light. Traditional microfluidic technology for preparing quantum dot color conversion layers suffers from several drawbacks. After the solvent in the quantum dot solution evaporates, less solute is deposited, requiring multiple depositions to achieve the desired thickness. This process is cumbersome, time-consuming, and labor-intensive, hindering large-scale industrial production. Furthermore, when purging the quantum dot solution outside the deposition area in the microfluidic channel, already deposited quantum dots are easily carried out, resulting in less quantum dot deposition and blue light leakage after color conversion. Additionally, after solvent evaporation, the quantum dots are randomly distributed within the deposition area, leading to uneven quantum dot film deposition and poor photoluminescence color uniformity. Traditional electrophoretic deposition technology involves contact between the two quantum dot solutions, which easily causes contamination and color mixing after color conversion. Therefore, there is an urgent need for a method that can achieve the required thickness with a single quantum dot deposition, while preventing the two quantum dot solutions from contacting each other to avoid color mixing, and simultaneously improving the uniformity of photoluminescence color. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method and application for preparing quantum dot color conversion layers based on microchannels and electrophoretic deposition.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing quantum dot color conversion layers based on microchannels and electrophoretic deposition includes the following steps:

[0007] 1) Forming an array of spaced transparent electrodes on a transparent substrate;

[0008] 2) Deposit metal to form a metal electrode, which includes a surrounding electrode, a longitudinal connecting electrode and a transverse connecting electrode. The surrounding electrode surrounds the outer periphery of each transparent electrode and is electrically connected to the transparent electrode. The longitudinal connecting electrode is connected to the surrounding electrode in the same row and is connected to the transverse connecting electrode.

[0009] 3) Deposit an insulating layer, etch the insulating layer to form openings for each transparent electrode, and form electrical contact areas by openings on the lateral connecting electrodes;

[0010] 4) Bond the patterned substrate obtained in step 3) to the microchannel cover plate, wherein the microchannel cover plate has microchannels, and the microchannels and the columns of transparent electrodes form microchannel pathways.

[0011] 5) Inject charged quantum dot solution into the microchannel pathway;

[0012] 6) Connect the electrical contact area to the power supply, and use electrophoretic deposition process to conduct the circuit so that quantum dots are deposited on the transparent electrode to form quantum dot units, wherein the surface electrical properties of the quantum dots are opposite to the conductivity of the electrical contact area;

[0013] 7) Remove excess quantum dot solution, rinse with cleaning solution, peel off the microchannel cover, dry, and form a quantum dot color conversion layer.

[0014] Optionally, the edge of the surrounding electrode covers the peripheral surface of the transparent electrode to achieve electrical connection.

[0015] Optionally, between steps 1) and 3), a step of etching the transparent electrode to form an uneven microstructure surface is also included.

[0016] Optionally, the microstructure surface is formed by etching several spaced grooves, the depth of which is 10% to 50% of the thickness of the transparent electrode.

[0017] Optionally, the thickness of the transparent electrode is 100-500 nm, and the thickness of the surrounding electrode is 500 nm-3 μm.

[0018] Optionally, the lateral connecting electrode includes a first lateral connecting electrode and a second lateral connecting electrode disposed on opposite sides of the transparent electrode array, and is connected to the first lateral connecting electrode, the second lateral connecting electrode and the transparent electrode column that does not participate in the connection, arranged alternately in sequence.

[0019] Optionally, the microchannel cover plate includes a first microchannel and a second microchannel, which are interdigitated and correspond to the transparent electrode array connected to the first lateral connecting electrode and the transparent electrode array connected to the second lateral connecting electrode, respectively.

[0020] Optionally, a red quantum dot solution is introduced into the first microchannel, and a green quantum dot solution is introduced into the second microchannel, wherein the red quantum dot solution and the green quantum dot solution have opposite charges.

[0021] Optionally, the electrophoretic deposition voltage is 3-15V, the current is 10-30A, and the time is 20-30min.

[0022] A method for fabricating a micro-LED full-color display device involves preparing a quantum dot color conversion layer using the aforementioned method based on microchannels and electrophoretic deposition; and then bonding the quantum dot color conversion layer to a Micro-LED chip array.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. Employing a surround electrode design, the metal electrodes encircle the ITO transparent electrode, resulting in more uniform electrical expansion across the entire ITO transparent electrode. This allows for more even deposition of charged quantum dots on the transparent electrode surface during electrophoretic deposition, thereby improving the overall light emission uniformity after color conversion. The opaque metal electrodes surrounding the entire ITO transparent electrode area connect the electrical properties of the same-color quantum dot deposition areas. Simultaneously, they act as a reflective layer to limit light crosstalk between sub-pixels, improving the color quality of full-color displays and reducing the occurrence of light crosstalk.

[0025] 2. Combining microchannel technology with electrophoretic deposition enables the fabrication of large-area quantum dot patterned color conversion layers with small pixel size, high PPI, high luminous uniformity, fast deposition speed, high raw material utilization, and facilitates the preparation of such layers, thereby promoting the industrialization of full-color Micro-LEDs. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the patterned array of ITO transparent electrodes during the color conversion layer fabrication process in Example 1.

[0027] Figure 2 This is a schematic diagram of the patterned array of metal electrodes surrounding ITO electrodes during the color conversion layer fabrication process in Example 1.

[0028] Figure 3 The diagram shows a top view (a) and a cross-section (b) of the microstructure of a single ITO transparent electrode during the fabrication process of the color conversion layer in Example 1.

[0029] Figure 4This is a schematic diagram of the insulating layer deposition and pore structure during the color conversion layer preparation process in Example 1;

[0030] Figure 5 This is a top view schematic diagram of the PDMS microchannel cover plate during the color conversion layer preparation process in Example 1;

[0031] Figure 6 This is a top view schematic diagram of the bonding between the PDMS microchannel cover plate and the patterned electrode substrate during the color conversion layer preparation process in Example 1.

[0032] Figure 7 This is a schematic cross-sectional view of the bonding between the PDMS microchannel cover plate and the patterned electrode substrate during the color conversion layer preparation process in Example 1.

[0033] Figure 8 A top view schematic diagram of the quantum dot solution being injected into and filling the microfluidic channels during the color conversion layer preparation process in Example 1;

[0034] Figure 9 A schematic diagram of the cross-section of the quantum dot solution injected into and filling the microchannel during the color conversion layer preparation process in Example 1;

[0035] Figure 10 This is a schematic diagram of quantum dot solution electrodeposition during the color conversion layer preparation process in Example 1;

[0036] Figure 11 This is a schematic diagram of the peeling cross section of the PDMS microchannel cover plate during the color conversion layer preparation process in Example 1;

[0037] Figure 12 This is a top view of the quantum dot color conversion layer in Example 1;

[0038] Figure 13 This is a schematic diagram of the cross-sectional structure of the quantum dot color conversion layer in Example 1;

[0039] Figure 14 A schematic diagram illustrating the combination of a quantum dot color conversion layer and a Micro-LED chip array to achieve full-color display; Detailed Implementation

[0040] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. The accompanying drawings are merely illustrative to facilitate understanding of the invention, and their specific proportions can be adjusted according to design requirements. The vertical relationships of relative elements and the definitions of front / back in the graphics described herein should be understood by those skilled in the art to refer to the relative positions of the components; therefore, they can all be flipped to present the same component, and all of this should fall within the scope disclosed in this specification.

[0041] The technical solution of the embodiment includes the following three parts:

[0042] 1. ITO Microstructure Electrode Design. A trapezoidal microstructured ITO electrode is designed on a single pixel area using a two-step photolithography, one-step deposition, and one-step etching process. This increases the adsorption of oppositely charged quantum dots without affecting conductivity. Simultaneously, light is refracted and scattered on the microstructure surface, increasing the light transmission path, improving color conversion efficiency, and enhancing brightness. (The transparent conductive electrode material can be ITO thin film, transparent conductive glass, or zinc oxide; the example described uses an ITO transparent conductive thin film electrode.)

[0043] 2. Metal electrode surrounding ITO design. As an indium tin oxide with current spreading properties, the adsorption effect of ITO on quantum dots on its surface determines the uniformity of overall light emission after color conversion. Therefore, the electrical distribution on its surface plays a crucial role. By surrounding the entire sub-pixel ITO electrode with metal electrodes, the electrical spreading of the ITO electrode in the entire sub-pixel area is made more uniform, thereby enabling more uniform adsorption of quantum dots and better color uniformity after photoluminescence conversion.

[0044] 3. Electrophoresis combined with microchannel technology design. By configuring two quantum dot solutions with opposite charges and combining them with microfluidic technology, the charged quantum dot solutions are injected into the microchannels and confined to the pre-deposited vertical sub-pixel region. Quantum dot deposition is achieved by adsorbing the oppositely charged quantum dot solutes through the bottom transparent electrode. Since the red and green quantum dot solutions are in two separate microchannels, direct contact between the two quantum dots is avoided in traditional electrophoretic deposition, preventing color mixing and improving color purity. The adsorption and deposition of charged quantum dots in the microchannel by the bottom ITO transparent electrode overcomes the uneven quantum dot deposition and easy sweeping of quantum dots from the deposition area in traditional microfluidic combined with hydrophilic and hydrophobic modification methods, which result in thin quantum dot films and blue light leakage after solvent evaporation. By controlling the voltage and current of the bottom ITO electrode, the thickness of the quantum dot deposition can be controlled. The required thickness can be achieved in a single deposition, eliminating the need for multiple depositions, simplifying the preparation process, and increasing the deposition rate.

[0045] Example 1

[0046] Fabrication of a patterned array of ITO transparent electrodes. Using photoresist as a mask, a patterned array of transparent electrodes 2 is first deposited on the surface of a transparent insulating glass substrate 1, such as... Figure 1 As shown. This technical solution mainly adopts magnetron sputtering, in which the sputtering system has an RF power of 70W, an argon flow rate of 110 / 70sccm, a gas pressure of 5 Pa, a pre-sputtering time of 30s, a formal sputtering time of 1500s, and deposits an ITO transparent electrode structure with a thickness of 300nm to form a patterned ITO transparent electrode array.

[0047] Surrounding metal electrode deposition. For example... Figure 2 As shown, an Au metal electrode 3 is deposited using an electron beam thin-film deposition evaporation system. Specifically, the deposition rate is set to 10 A / s, the gas pressure is 5 Pa, and the metal deposition thickness is 2 μm. The metal electrode 3 includes a surrounding electrode 31, a longitudinal connecting electrode 32, and transverse connecting electrodes 33a and 33b. The surrounding electrode 31 surrounds the outer periphery of each ITO transparent electrode 2, with half of its width covering the peripheral surface of the transparent electrode 2 for electrical connection. The longitudinal connecting electrode 32 connects to the surrounding electrode 31 in the same column and is connected to the transverse connecting electrode. The transverse connecting electrodes 33a and 33b are located on opposite outer sides of the electrode area. Three columns of transparent electrodes form a unit, with one column connected to the transverse connecting electrode 33a, one column connected to the transverse connecting electrode 33b, and one column unconnected, arranged alternately. The metal electrode surrounds the ITO transparent electrode, resulting in a more uniform current spread across the entire ITO transparent electrode. This allows for more uniform deposition of charged quantum points on the transparent electrode surface during electrophoretic deposition, thereby improving the overall light emission uniformity after color conversion. The opaque metal electrode surrounds the entire ITO transparent electrode area, which serves to electrically connect the quantum dot deposition areas of the same color. At the same time, it acts as a reflective layer to limit light crosstalk between sub-pixels, improve the color quality of full-color display, and reduce the occurrence of light crosstalk.

[0048] ITO microstructure fabrication. Using photoresist as a mask, ITO transparent electrodes 2 were etched via inductively coupled plasma etching (ICP). The ICP etching power was 400W, the etching gases were SF6 and CF4, the gas flow rates were 40 sccm and 10 sccm respectively, the etching time was 75 s, and the etching depth was 100 nm. This resulted in the formation of several inverted trapezoidal microstructure grooves 21 on each ITO transparent electrode 2. In this embodiment, the array of microstructure grooves formed on each ITO transparent electrode 2 is a 3*3 microstructure region. Figure 3 As shown, the design of the ITO microstructure increases the contact area of ​​the quantum dot solution, improving the adsorption of charged quantum dot solutes. Blue light is refracted on the surface of the ITO microstructure, and the refracted light enters the quantum dot film layer. The light undergoes multiple scattering and refractions within the quantum dot solute and microstructure, increasing the light transmission path between quantum dot solute particles, improving the light conversion of the quantum dot solute to the excitation source, enhancing photoluminescence, and improving color conversion efficiency.

[0049] Insulating layer deposition and aperture opening. An insulating silicon dioxide or silicon nitride insulating layer 4 with a thickness of 200 nm is deposited on the surface using plasma-enhanced chemical vapor deposition (PECVD) or atomic deposition. After photolithography and development, dry etching (ICP) or wet etching (BOE solution, ITO etching solution) is performed to form exposed electrical contact regions 33a-1, 33b-1 and the ITO transparent electrode 2. (Example...) Figure 4 As shown, a patterned electrode substrate is obtained.

[0050] Fabrication of microchannel PDMS devices. A photoresist mold resembling interdigitated electrodes is fabricated on a silicon wafer using photolithography. The microchannel cover plate is then fabricated using methods such as hot pressing, molding, and injection molding. This technical solution uses a transparent PDMS microchannel cover plate 5 as an example for illustration. Figure 5 As shown, the microchannel cover plate includes two independent microchannels 5a and 5b. The microchannels 5a and 5b are distributed in an interdigitated shape and are respectively provided with liquid inlets 51 and 52 and liquid suction ports 53 and 54. The interdigitated shape matches the longitudinal column of the ITO transparent electrode 2 which is connected to the transverse connecting electrodes 33a and 33b respectively. The main purpose is to allow quantum dot solutions of the same color to flow into the designated deposition area through the microchannels.

[0051] PDMS microchannels are bonded to a patterned electrode substrate. Using a dedicated laminator, the PDMS microchannel cover plate 5 is bonded to the patterned electrode substrate. Microchannel 5a, in conjunction with the lateral connecting electrode 33a and the connected longitudinal electrode column, forms a conductive channel. Microchannel 5b, in conjunction with the lateral connecting electrode 33b and the connected longitudinal electrode column, also forms a conductive channel. These two microchannels are independent of each other and are used for the introduction of quantum dot solutions of different colors. For example... Figure 6 As shown, after bonding, the edges of each microchannel are tightly bonded to the electrode edges. A pressure controller is used to press them together to prevent swelling. The cross-section is shown in the figure. Figure 7 As shown.

[0052] Quantum dot solution injection. A pressure injector was used to inject red quantum dot solution R and green quantum dot solution G into two independent interdigitated microchannels 5a and 5b, ensuring uniform filling of the channels with quantum dot solution. Figure 8 As shown, after the quantum dots fill the entire microchannel, the pressure at inlets 51 and 52 remains constant, and the quantum dot solution inside the microchannel remains full. The cross-sectional view is shown below. Figure 9 As shown. The quantum dots used in this embodiment are negatively charged red quantum dot solution R and positively charged green quantum dot solution G. The negatively charged red quantum dot solution R consists of colloidal CdSe / ZnS core / shell quantum dots capped with polyethylene glycol (PEG)-COOH in propylene glycol methyl ether acetate (PGMEA), with a solubility of 50 mg / mL; the positively charged green quantum dot solution G consists of colloidal CdSe / ZnS core / shell quantum dots capped with PEG-NH2 in ethanol solution, with a solubility of 60 mg / mL.

[0053] Quantum dot electrodeposition. Electrical contact regions 33a-1 and 33b-1 are connected to source surfaces S1 and S2 respectively using wires. Source surface S1 controls the deposition of red quantum dots R, and electrical contact region 33a-1 is connected to the positive electrode of the source surface. Source surface S2 controls the deposition of green quantum dots G, and electrical contact region 33b-1 is connected to the negative electrode of the source surface. Figure 10 The voltage of source meter S1 is 3-10V and the current is 10-30A, while the voltage of source meter S2 is 5-10V and the current is 20-25A. The quantum dot deposition time is 20-30 minutes. Quantum dots are deposited on the ITO transparent electrode 2 to form quantum dot units. The quantum dots flow into the pre-deposited electrophoretic deposition substrate through microchannels. Due to the adsorption of the ITO electrode, single particles will form oligomers, thereby increasing the gap between each quantum dot and increasing the effective optical path of the excitation light, achieving higher efficiency light conversion.

[0054] Quantum dot recovery and cleaning. After deposition, while maintaining the electrical connection between source surfaces S1 and S2, excess quantum dot solution is removed and recovered using a pressure injector through suction ports 53 and 54, improving the utilization rate of quantum dot materials and reducing costs. After removing excess quantum dots through suction ports 53 and 54, while maintaining the electrical connection between source surfaces S1 and S2, a pure propylene glycol methyl ether acetate (PGMEA) solution is injected into inlet 51, while suction port 53 continuously absorbs the removed cleaning solution; similarly, a pure ethanol solution is injected into inlet 52, while suction port 54 continuously absorbs the removed cleaning solution. The cleaning time is 10-20 minutes.

[0055] Microchannel peeling and quantum dot drying. The microchannel cover plate 5 is peeled off from the deposition substrate 1, as follows: Figure 11 As shown. The substrate 1 with deposited quantum dots was then placed in a drying oven and dried at 80°C for 20 minutes to form a solidified quantum dot pattern. A top view is shown below. Figure 12 As shown, the side view is as follows Figure 13 As shown, an array of sub-pixel units, including red quantum dot units R, green quantum dot units G, and blue light-transmitting regions B, forms a quantum dot color conversion structure.

[0056] A full-color display is achieved by combining a quantum dot color conversion structure with a Micro-LED chip array. The flip-chip LED array is fabricated using typical LED processes such as cleaning, photolithography, thin film deposition, etching, evaporation, polishing, and substrate lift-off. It is then bonded to a driving substrate to achieve controlled light emission. A conventional GaN-based blue Micro-LED chip array 6 can be used in this embodiment. A high-precision bonding machine is used to bond the flip-chip blue Micro-LED chip array 6 to the sub-pixels R\G\B in the quantum dot color conversion structure deposited with quantum dots, achieving a one-to-one full-color display. Figure 14 As shown.

[0057] The above embodiments are only used to further illustrate the method and application of preparing quantum dot color conversion layers based on microchannels and electrophoretic deposition according to the present invention. However, the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing quantum dot color conversion layers based on microchannels and electrophoretic deposition, characterized in that, Includes the following steps: 1) Forming an array of spaced transparent electrodes on a transparent substrate; 2) Deposit metal to form a metal electrode, which includes a surrounding electrode, a longitudinal connecting electrode, and a transverse connecting electrode. The surrounding electrode surrounds the outer periphery of each transparent electrode and is electrically connected to the transparent electrode. The longitudinal connecting electrode is connected to the surrounding electrode in the same column and is connected to the transverse connecting electrode. The transverse connecting electrode includes a first transverse connecting electrode and a second transverse connecting electrode disposed on opposite sides of the transparent electrode array. The first transverse connecting electrode, the second transverse connecting electrode, and the transparent electrode column that does not participate in the connection are arranged alternately in sequence. 3) Deposit an insulating layer, etch the insulating layer to form openings for each transparent electrode, and form electrical contact areas by openings on the lateral connecting electrodes; 4) Bond the patterned substrate obtained in step 3) to the microchannel cover plate. The microchannel cover plate includes a first microchannel and a second microchannel. The first microchannel and the second microchannel are interdigitated and correspond to the transparent electrode array connected to the first lateral connecting electrode and the transparent electrode array connected to the second lateral connecting electrode to form a microchannel pathway. 5) Inject charged quantum dot solution into the microchannel pathway; 6) Connect the electrical contact area to the power supply, and use electrophoretic deposition process to conduct the circuit so that quantum dots are deposited on the transparent electrode to form quantum dot units, wherein the surface electrical properties of the quantum dots are opposite to the conductivity of the electrical contact area; 7) Remove excess quantum dot solution, rinse with cleaning solution, peel off the microchannel cover, dry, and form a quantum dot color conversion layer.

2. The method for preparing a quantum dot color conversion layer based on microchannels and electrophoretic deposition according to claim 1, characterized in that: The edge of the surrounding electrode covers the peripheral surface of the transparent electrode to achieve electrical connection.

3. The method for preparing a quantum dot color conversion layer based on microchannels and electrophoretic deposition according to claim 1, characterized in that: Between steps 2) and 3), there is also a step of etching the transparent electrode to form an uneven microstructure surface.

4. The method for preparing a quantum dot color conversion layer based on microchannels and electrophoretic deposition according to claim 3, characterized in that: The surface of the microstructure is formed by etching several spaced grooves, the depth of which is 10% to 50% of the thickness of the transparent electrode.

5. The method for preparing a quantum dot color conversion layer based on microchannels and electrophoretic deposition according to claim 1, characterized in that: The thickness of the transparent electrode is 100~500 nm, and the thickness of the surrounding electrode is 500 nm~3 μm.

6. The method for preparing a quantum dot color conversion layer based on microchannels and electrophoretic deposition according to claim 1, characterized in that: A red quantum dot solution is introduced into the first microchannel, and a green quantum dot solution is introduced into the second microchannel. The red quantum dot solution and the green quantum dot solution have opposite electrical properties.

7. The method for preparing a quantum dot color conversion layer based on microchannels and electrophoretic deposition according to claim 1, characterized in that: The electrophoretic deposition is performed at a voltage of 3-15V, a current of 10-30A, and a time of 20-30min.

8. A method for manufacturing a micro-LED full-color display device, characterized in that: A quantum dot color conversion layer is prepared using the method for preparing a quantum dot color conversion layer based on microchannels and electrophoretic deposition as described in any one of claims 1 to 7; the quantum dot color conversion layer is then bonded to a Micro-LED chip array.

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