Preparation method of high-conversion-efficiency quantum dot color conversion layer and full-color display application thereof

Abstract

This invention discloses a method for preparing a high-efficiency quantum dot color conversion layer. The method involves patterning the surface of a rigid transparent substrate to obtain a discrete array of raised structures, and depositing quantum dot units on the patterned surface to obtain a quantum dot color conversion layer. The patterned surface can help photons propagate longitudinally inside the device, thereby improving light extraction efficiency. It is suitable for Micro-LED full-color displays, with good display effect, simple manufacturing process, avoidance of mass transfer, low cost, and can be used as a packaging layer for displays, making it easier to mass-produce.

Description

Technical Field

[0001] This invention relates to the field of quantum dot displays, and in particular to a method for designing and fabricating a quantum dot color conversion layer with high light conversion efficiency and its application in Micro-LED full-color displays. Background Technology

[0002] With the increasing demand for high-quality information exchange, Micro-LED is attracting more and more attention. Due to its advantages such as long lifespan, high brightness, and low power consumption, its market share is getting higher and higher. Micro-LED is also known as the "next-generation display technology", showing huge market potential and attracting extensive research in academia and industry.

[0003] There are many methods to achieve full-color Micro-LEDs, such as the three-color RGB method. However, when applied to large-size light-emitting devices, the difficulty and cost of mass transfer are very high, resulting in high prices for Micro-LED equipment. Other methods include adding quantum dot fluorescent materials, photolithography, and microfluidic processes to the surface of ultraviolet / blue light Micro-LEDs.

[0004] Quantum dots (QDs) are semiconductor nanostructures in which excitons are bound in three directions. They possess advantages such as high luminescence efficiency, tunable emission wavelength, and low fabrication cost, making them widely favored by academia and the market. The luminescence principle of quantum dots originates from the recombination of internal electron-hole pairs. Quantum dots absorb high-energy photons, causing electrons to transition to the conduction band and holes to form excitons. Utilizing this property, quantum dot materials can be used as color conversion layer devices, thus avoiding the massive transfer difficulties associated with the three-color RGB method, and the implementation method is relatively simple.

[0005] Existing technologies directly fabricate quantum dot solutions into different patterns, achieving color conversion, but inevitably suffer from drawbacks such as low light extraction efficiency and poor morphology. To address the issues of low absorption and conversion efficiency, traditional solutions mostly involve altering ink ratios and solvents, placing high demands on the quantum dot solution and making implementation difficult. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a method for preparing a quantum dot color conversion layer with high light conversion efficiency and its application in Micro-LED full-color displays. By patterning the glass surface, the patterned structure helps photons propagate longitudinally inside the device, thereby improving light extraction efficiency.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for preparing a high-conversion-efficiency quantum dot color conversion layer includes the following steps:

[0009] 1) Provide a hard transparent substrate with a thickness of 0.4 to 0.6 mm, and use photolithography and etching technology to pattern the surface of the hard transparent substrate to obtain a discrete array of protrusion structures, wherein the height of the protrusion structure is ≤2 μm, the size is 1 to 5 μm, and the spacing is 1 to 5 μm;

[0010] 2) Plan a sub-pixel forming region matrix and an isolation region separating the sub-pixel forming regions on the patterned surface, and perform hydrophobic treatment on the surface of the isolation region; wherein each sub-pixel forming region includes several protrusion structures, and the protrusion structures are evenly distributed in the sub-pixel forming region;

[0011] 3) Quantum dot units are formed in the sub-pixel formation area using inkjet printing technology, wherein the thickness of the quantum dot units is greater than the height of the protrusion structure.

[0012] Optionally, the sub-pixel forming region matrix has mutually perpendicular row and column directions, wherein adjacent rows of the protrusion structure array are staggered in the row direction and adjacent columns of the protrusion structure array are staggered in the column direction.

[0013] Optionally, the rigid transparent substrate is a glass substrate, and step 1) specifically includes:

[0014] 1.1) A chromium layer and a photoresist layer are sequentially formed on the surface of a glass substrate;

[0015] 1.2) Pattern the photoresist layer, and after exposure and development, leave several discretely spaced masking areas;

[0016] 1.3) Using a patterned photoresist layer as a mask, etch away the chromium layer in the unmasked areas;

[0017] 1.4) Etch the surface of the glass substrate in the unshielded area, with the etching depth being the height of the protrusion structure;

[0018] 1.5) Sequentially peel off the patterned photoresist layer and the chromium layer to form the raised structure array on the surface of the glass substrate.

[0019] Optionally, in 1.3) and 1.5), the chromium layer is wet-etched using an aqueous solution of cerium ammonium nitrate / glacial acetic acid.

[0020] Optionally, in step 1), the etching technology includes ICP etching, RIE etching, and wet etching.

[0021] Optionally, in 1.4), the glass substrate is wet-etched using a BOE solution, wherein the composition of the BOE aqueous solution includes HF, HNO3 and NH4F.

[0022] Optionally, the glass substrate is thinned to the specified thickness using a waterfall-style or vertical spray method, and its surface is treated with grinding and polishing.

[0023] Optionally, the protruding structure is a column or platform perpendicular to the surface of the rigid transparent substrate, and the cross-section of the column or platform is circular, polygonal, or irregular.

[0024] Optionally, in step 2), a hard mask is used to cover the sub-pixel formation area, exposing the isolation area, and the area is placed in a hydrophobic material atmosphere at 50-70°C for 2-4 hours; the hydrophobic material includes PFS, OTS and APTES.

[0025] A high-conversion-efficiency quantum dot color conversion layer prepared by the above-mentioned preparation method includes a rigid transparent substrate. The rigid transparent substrate has a patterned surface formed by an array of protruding structures. Red quantum dot units and green quantum dot units are disposed on the patterned surface. The patterned surface also has a blue light-transmitting region. The red quantum dot units, green quantum dot units and blue light-transmitting region are arranged in a matrix as sub-pixel units.

[0026] A Micro-LED full-color display device includes the aforementioned high-efficiency quantum dot color conversion layer and a blue LED chip array. The blue LED chip array is disposed on the side of the rigid transparent substrate away from the patterned surface, and the blue LED chips correspond one-to-one with the sub-pixel units.

[0027] The dimensions referred to here are the characteristic dimensions projected onto the substrate surface. For example, for a circle, it is the diameter; for a square, it is the side length; and for an irregular shape, it is the diameter of the circumcircle.

[0028] The beneficial effects of this invention are as follows:

[0029] By depositing quantum dot units on a discretely spaced array of protrusions on a patterned hard transparent substrate surface, it is possible to help photons propagate longitudinally inside the device, thereby improving light extraction efficiency.

[0030] It is used for Micro-LED full-color displays, with good display effect and simple manufacturing process. It avoids mass transfer, has low cost, and can be used as a packaging layer for displays, making it easier to mass-produce. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the waterfall-style thinned glass in Example 1;

[0032] Figure 2 This is a schematic diagram of the glass substrate surface patterning process in Example 1;

[0033] Figure 3 This is a top view of the photoresist-masked area in Example 1;

[0034] Figure 4 This is a top view schematic diagram of the patterned surface of the glass substrate in Example 1;

[0035] Figure 5 This is a front view schematic diagram of the patterned surface of the glass substrate in Example 1;

[0036] Figure 6 This is a schematic diagram of the combination of patterned glass and rigid mask in Example 1;

[0037] Figure 7 This is a schematic diagram of the structure of quantum dot units formed on a patterned surface in Example 1;

[0038] Figure 8 This is a schematic diagram of the structure of the Micro-LED full-color display device in Example 1;

[0039] Figure 9 A schematic diagram illustrating the light extraction efficiency of a patterned surface on a blue micro-LED as simulated by FDTD.

[0040] Figure 10 This is a schematic diagram of the light extraction efficiency in FDTD simulation example 1. Detailed Implementation

[0041] 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.

[0042] The embodiment employs photolithography, wet etching, and super inkjet printer (SIJ) to fabricate a color conversion layer, which includes a patterned hard transparent material, a quantum dot color conversion layer, and an encapsulation layer, to achieve a color conversion layer that enhances light extraction efficiency and enables color conversion function.

[0043] 1. Patterned rigid transparent material substrate

[0044] Rigid transparent materials include, but are not limited to, glass and quartz. Patterns with controllable arrangement, size, and height are created on the surface of a rigid transparent material substrate using methods such as photolithography and etching. The patterns can be designed to enhance light extraction efficiency and facilitate quantum dot deposition; this example uses a cylindrical array. Etching techniques include, but are not limited to, ICP etching, RIE etching, and wet etching. The patterns are distributed on the light-emitting side of the Micro-LED to change the light emission angle and avoid total internal reflection. The pattern spacing can be adjusted, but cannot be less than the precision of the photolithography machine. The pattern height can be determined by the etching time using chemical methods; the longer the time, the more tapered the pattern, but the time cannot exceed the time required to completely etch the pattern. The unpatterned side is in direct contact with the backlight blue micro-LED.

[0045] 2. Quantum dot color conversion layer

[0046] Quantum dots are printed in the sub-pixel formation area using inkjet printing. The thickness of the sprayed quantum dots can be controlled by adjusting the inkjet printing power and tip speed. The printing trajectory is adjusted to print a quantum dot matrix, which must match the underlying LED array. Red and green quantum dots are printed, while no quantum dots are printed in the blue light-transmitting area. The quantum dot volume percentage concentration is greater than or equal to 5V% and less than or equal to 80V%. Finally, the quantum dots are UV cured.

[0047] The basic principle of inkjet printing technology is to spray dissolved red, green, and blue quantum dots onto a specific substrate, and to achieve pixelation of the quantum dots by controlling the ink material, ink droplet size, droplet dimensions, etc. It has advantages such as low cost, no mask required, and ease of industrial production.

[0048] 3. Bonding

[0049] The patterned glass substrate is directly contacted with the back blue micro-LED. The sub-pixel formation area is aligned and bonded to the chip under microscopic observation. Red and green quantum dots emit red and green light when excited by blue light, and blue light is directly transmitted through the blue light transmission area, forming an RGB unit array to achieve full-color display.

[0050] Example 1

[0051] The rigid transparent material substrate uses a glass substrate, which is then thinned. Glass thinning methods include, but are not limited to, waterfall flow and vertical spraying. Figure 1 The process involves a waterfall-style thinning of a glass substrate, including pre-cleaning, etching, cleaning, and drying. The glass is etched using a buffered oxide etchant (BOE solution) that reacts with SiO2. After grinding and cleaning, the surface is polished. The resulting glass substrate is 0.4mm-0.6mm in height, designed to prevent reduced light transmission caused by an excessively thick substrate.

[0052] Rinse the thinned glass substrate with deionized water for 5-10 minutes, then dry it with nitrogen. The purpose is to remove surface impurities.

[0053] Figure 2 The diagram illustrates the specific steps of pattern fabrication. First, a 120nm thick chromium layer 2 and a photoresist layer 3 are sequentially homogenized onto a glass substrate 1. The desired pattern is then fabricated using photolithography. Preferably, a positive photoresist is used as the photoresist 3 for photolithography. The glass substrate with the photoresist is exposed to ultraviolet light; the exposure time depends on the parameters and power of the photolithography machine. After photolithography, development is performed using a developer specifically for either positive or negative photoresist; the solution concentration and development time are related. The image is observed under a microscope. If the development effect is insufficient, the above steps are repeated. The patterned photoresist layer formed after development is shown below. Figure 3 As shown, it has discretely spaced masking regions 31, which are circular in this embodiment. Furthermore, negative photoresist can also be used, and the corresponding mask is selected based on a pattern complementary to the desired pattern. Then, using the patterned photoresist layer as a mask, the exposed chromium layer 2 is etched away. The chromium layer is removed by reacting a solution of cerium ammonium nitrate (100g): glacial acetic acid (17.5ml): water (500ml). The masked areas do not react with the solution due to the protection of the photoresist. Then, the surface of the unmasked glass substrate 1 is etched using an aqueous BOE solution (HF:HNO3:NH4F) to a depth equal to the height of the desired raised structure. Due to the isotropic nature of wet etching, the remaining raised structure 11 is a frustum structure. Finally, the photoresist is removed by ultrasonic removal with an ethanol solution, and the chromium layer is removed with a cerium ammonium nitrate solution, resulting in a patterned surface with an array of raised structures.

[0054] The purpose of using a chromium layer is to increase the acid resistance of the photoresist. Using the chromium layer as a mask improves the etching effect on glass devices.

[0055] refer to Figure 4 and Figure 5 The images show a top view and a front view of the patterned glass, respectively. The resulting patterned surface has an array of discretely spaced protrusions 11, which are frustum-shaped structures with a bottom diameter of approximately 3 μm and a bottom spacing of approximately 3 μm. The protrusions 11 are uniformly distributed in the array.

[0056] Next, a sub-pixel formation region matrix and isolation regions separating the sub-pixel formation regions are planned on the patterned surface. A hard mask 4 is used, preferably made of glass. Partially hollowed-out areas of the mask material are aligned with the isolation regions, while non-hollowed-out areas are aligned with the sub-pixel formation regions, such as... Figure 6As shown. After a tight bond, the glass is placed in a hydrophobic material atmosphere at 60°C for approximately 3 hours. The hydrophobic material includes, but is not limited to, PFS, OTS, and APTES. The hydrophobic material diffuses into the isolation area of ​​the patterned glass and the non-perforated area of ​​the hard mask. The purpose of this step is surface modification to make the isolation area of ​​the patterned glass hydrophobic. The patterned glass is removed after 3 hours.

[0057] refer to Figure 7 The sub-pixel formation areas are arranged in a matrix to plan the quantum dot deposition area. A quantum dot solution is sprayed using a super inkjet printer (SIJ) to form red quantum dot units R and green quantum dot units G. The precision of the quantum dot solution spraying is related to the power of the SIJ and the tip movement speed. The size of the quantum dot unit corresponds to the size of the back Micro-LED (10×10μm in this embodiment). Repeated spraying is used to form a uniform quantum dot film, with a thickness slightly higher than the raised structure, i.e., covering the upper surface of the raised structure 11 to form an integral layer. Since the isolation area at the edge is hydrophobic, the quantum dots will not escape from the edge. Thus, each quantum dot unit is covered with several raised structures 11. The raised structures change the photon emission angle, avoid total internal reflection, and increase light extraction efficiency.

[0058] The red quantum dot deposition area is formed by depositing red quantum dots with wavelengths of 615-680 nm under blue light excitation, while the green quantum dot deposition area is formed by depositing green quantum dots with wavelengths of 518-580 nm under blue light excitation. Additionally, the sub-pixel formation matrix includes a blue light transmission region B, which is not coated with quantum dots. The red quantum dot unit R and the green quantum dot unit G achieve color conversion between red and green light, while the blue light region B enhances blue light transmission; all three serve as sub-pixel units. After quantum dot deposition, the layers are cured under ultraviolet light at a low temperature for 2 hours. This results in a quantum dot color conversion layer with high light conversion efficiency.

[0059] Specifically, the sub-pixel forming region matrix has mutually perpendicular row directions (x-direction) and column directions (y-direction). In the x-direction, adjacent rows of the protrusion structure array are staggered; in the column direction, adjacent columns of the protrusion structure array are staggered. Thus, within the sub-pixel forming region, several protrusion structures 11 are evenly distributed, achieving better light emission uniformity, better color conversion light emission effect, and eliminating the need for special alignment during spraying and printing.

[0060] refer to Figure 8A quantum dot color conversion layer is assembled onto a blue micro-LED chip array 200 to form a Micro-LED full-color display device. The blue micro-LED chip array 200 is located on the side of the glass substrate 1 away from the patterned surface, and the blue LED chips 201 correspond one-to-one with the sub-pixel units. A flip-chip structure of blue micro-LEDs can be used. Taking a 10×10μm blue micro-LED array as an example, the RGB pixel units are aligned with the blue micro-LEDs.

[0061] Using FDTD software simulation, a patterned surface was formed on the surface of a blue micro-LED by referring to the process of Example 1.

[0062] The rear-mounted chips employ both single-chip and array combinations of five chips, with the array structure designed to reduce errors. The results are as follows: Figure 9 As shown, the light extraction efficiency of the unpatterned chip is compared to that of the unpatterned chip. Surface patterning can eliminate total internal reflection and lateral propagation of the optical waveguide mode on the chip surface. It can be seen that the light extraction efficiency of a single chip is improved under different conditions, with a maximum improvement of 29.86%. The light extraction efficiency of the array structure chip is 69.28% with a patterned protrusion structure length of 3μm, a period of 6μm, and a height of 1μm, which is 24.99% higher than that of the unpatterned chip. Simulation results demonstrate that surface patterning can improve the light extraction efficiency of the chip.

[0063] According to the method of Example 1, 0.4 mm thick glass was used, and a pattern was formed on the glass surface. With a pattern length of 3 μm and a period of 6 μm, the height of the raised pattern was varied; however, due to the conical structure, the pattern height could not be increased indefinitely. (Reference) Figure 10 As can be seen, the light extraction efficiency increases with the pattern height, stabilizes at a height of 1.1 μm, and reaches its maximum at 1.4 μm, at 61.232%, representing a 10.47% improvement in LEE compared to unpatterned chips. This is because SiO2 has a lower refractive index than GaN, allowing more light to escape into it. When light propagates through the patterned structure, encountering the sidewalls alters the initial incident conditions, causing more light to escape into the air. Therefore, the higher the pattern height, the greater the probability of light escape, and the higher the light extraction efficiency. Finally, this is combined with a quantum dot layer to form a high-efficiency color conversion layer device.

[0064] The above embodiments are only used to further illustrate the preparation method of a high conversion efficiency quantum dot color conversion layer of the present invention and its full-color display application. 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 a high-conversion-efficiency quantum dot color conversion layer, characterized in that, Includes the following steps: 1) Provide a glass substrate with a thickness of 0.4~0.6mm, and sequentially form a chromium layer and a photoresist layer on the surface of the glass substrate; pattern the photoresist layer, and after exposure and development, leave a number of discretely spaced masking areas; using the patterned photoresist layer as a mask, etch away the chromium layer in the unmasked areas; etch the surface of the glass substrate in the unmasked areas, with the etching depth being the height of the raised structure. The patterned photoresist layer and the chromium layer are sequentially peeled off to form a discrete array of raised structures on the surface of the glass substrate, wherein the height of the raised structures is ≤2μm, the size is 1~5μm, and the spacing is 1~5μm; 2) Plan a sub-pixel forming region matrix and an isolation region separating the sub-pixel forming regions on the patterned surface, and perform hydrophobic treatment on the surface of the isolation region; wherein each sub-pixel forming region includes several protrusion structures, and the protrusion structures are evenly distributed in the sub-pixel forming region; 3) Quantum dot units are formed in the sub-pixel formation area using inkjet printing technology, wherein the thickness of the quantum dot units is greater than the height of the protrusion structure.

2. The method of claim 1, wherein the method further comprises: The sub-pixel forming region matrix has mutually perpendicular row and column directions. In the row direction, adjacent rows of the protrusion structure array are staggered; in the column direction, adjacent columns of the protrusion structure array are staggered.

3. The method for preparing a high-conversion-efficiency quantum dot color conversion layer according to claim 1, characterized in that: In step 1), the chromium layer is wet-etched using an aqueous solution of cerium ammonium nitrate / glacial acetic acid.

4. The method of claim 1, wherein the method further comprises: In step 1), the glass substrate is wet-etched using a BOE solution, the composition of which includes HF, HNO3 and NH4F.

5. The method for preparing a high-conversion-efficiency quantum dot color conversion layer according to claim 1, characterized in that: The glass substrate is thinned to the specified thickness using either a waterfall-style or vertical spray method, and its surface is treated with grinding and polishing.

6. The method for preparing a high-conversion-efficiency quantum dot color conversion layer according to claim 1, characterized in that: The protruding structure is a column or platform perpendicular to the surface of a rigid transparent substrate, and the cross-section of the column or platform is circular, polygonal, or irregular.

7. The method for preparing a high-conversion-efficiency quantum dot color conversion layer according to claim 1, characterized in that: In step 2), a hard mask is used to cover the sub-pixel formation area, exposing the isolation area, and the area is placed in a hydrophobic material atmosphere at 50~70℃ for 2~4 hours; the hydrophobic material includes PFS, OTS and APTES.

8. A high-conversion-efficiency quantum dot color conversion layer prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The invention includes a rigid transparent substrate having a patterned surface formed by an array of protruding structures, red quantum dot units and green quantum dot units disposed on the patterned surface, and a blue light-transmitting region arranged on the patterned surface. The red quantum dot units, green quantum dot units and blue light-transmitting region are arranged in a matrix as sub-pixel units.

9. A Micro-LED full-color display device, characterized in that: It includes the high conversion efficiency quantum dot color conversion layer as described in claim 8 and a blue LED chip array, wherein the blue LED chip array is disposed on the side of the rigid transparent substrate away from the patterned surface, and the blue LED chip corresponds one-to-one with the sub-pixel unit.

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