Method for preparing and use of quantum dot inks for electrohydrodynamic inkjet printing

Abstract

The application discloses a preparation method of quantum dot ink for electrohydrodynamic inkjet printing, adopts two or more ligands to passivate perovskite quantum dots, mixes the passivated quantum dots in two or more solvents to obtain quantum dot ink. The multi-ligand system provides a multiple passivation mechanism, optimizes ligand coverage, and improves optical performance, enhances the stability and dispersibility of nanoparticles, the multi-solvent system can improve the solubility, optimize the viscosity and surface tension of the solution, and improve the stability, and the synergistic effect of the two can significantly improve the performance and application prospect of the ink for electrohydrodynamic inkjet printing, and high-quality full-color Micro-LED display is realized.

Description

Technical Field

[0001] This invention belongs to the field of display technology, specifically relating to a method for preparing quantum dot ink for electrohydrodynamic inkjet printing and its application. Background Technology

[0002] In the development of full-color display technology, quantum dot inks are gradually becoming a research focus in this field due to their superior performance and broad application prospects. As the forefront of next-generation display technology, micro-LEDs have attracted much attention for their low power consumption, high brightness, excellent durability, and fast response. However, efficiently mechanically transferring red, green, and blue (RGB) micro-LED chips onto the same substrate to achieve full-color display remains a significant technical challenge.

[0003] To overcome this challenge, researchers began exploring methods using quantum dot inks as color conversion layers. Quantum dot inks possess unique advantages, such as high brightness, high photoluminescence quantum yield, narrow peak linewidth, and tunable emission wavelength, offering new possibilities for the design of full-color Micro-LED chips. By depositing red, green, and blue quantum dot inks, these materials can be effectively excited by ultraviolet Micro-LED chips to emit the three primary colors of light, thus serving as sub-pixel units.

[0004] Methods for achieving precise patterning of quantum dot inks include stenciling, inkjet printing, photolithography, laser direct writing, microfluidics, and transfer printing. Among these methods, electrohydrodynamic inkjet printing (EHD) has attracted much attention due to its maskless operation, digital manipulation, high material utilization, and excellent patterning resolution.

[0005] However, the stability of quantum dot inks during EHD printing remains a key challenge for achieving high-quality full-color Micro-LED displays. The stability of quantum dot inks directly affects the performance of the color conversion layer, thus impacting the color accuracy and long-term stability of Micro-LED displays. In particular, halide ion migration becomes a critical issue during patterning in electrohydrodynamic inkjet printing. Halide ion migration not only affects the optical properties of quantum dots but can also lead to clogging and instability during the printing process. Furthermore, traditional electrohydrodynamic inkjet printing technologies typically rely on polar solvents to achieve efficient inkjet processes. While these polar solvents play a crucial role in the printing process, they also introduce limitations such as selectivity for printing materials, environmental impact, and cost-effectiveness. Therefore, developing a novel EHD full-color quantum dot ink is of great significance for advancing Micro-LED display technology. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by proposing a method for preparing and applying EHD full-color quantum dot inks. By employing a multi-ligand, multi-solvent system, the stability and printing quality of quantum dots are significantly improved, achieving high-resolution and wide-gamut full-color display effects.

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

[0008] A method for preparing quantum dot ink for electrohydrodynamic inkjet printing, comprising:

[0009] 1) Preparation of perovskite quantum dot solutions or dispersions;

[0010] 2) Prepare a surface ligand solution, wherein the surface ligand solution comprises two or more ligands, wherein the ligands are selected from thiols, esters, phospholipids, long-chain alkanes and aromatic hydrocarbons;

[0011] 3) Mix the surface ligand solution and the perovskite quantum dot solution or dispersion to bind the ligands to the quantum dots and obtain passivated quantum dots; the molar ratio of ligands to quantum dots in the mixture is 0.005 to 0.2:1;

[0012] 4) The passivated quantum dots are mixed in two or more solvents to obtain quantum dot ink; the solvents include at least one nonpolar solvent, and the concentration of quantum dots in the quantum dot ink is 5 mg / ml-60 mg / ml.

[0013] Optionally, the ligand has groups that form coordinate bonds with metal ions and / or halide ions on the surface of the quantum dot.

[0014] Optionally, the group includes at least two of the following: phosphate group, quaternary ammonium salt group, thiol group, carboxylic acid group, and sulfonic acid group.

[0015] Optionally, in step 4), the solvent is selected from alkane solvents, aromatic hydrocarbon solvents, ester solvents, and ketone solvents.

[0016] Optionally, the solvent includes at least two of 1,3,5-triethylbenzene, n-tetradecane, n-octane, hexane, heptane, xylene, and cyclohexane.

[0017] Optionally, the quantum dot is a red quantum dot, and step 1) includes:

[0018] Preparation of Cs-derived precursor solution;

[0019] ODE, PbBr2, PbI2, OA and OAm were mixed, evacuated and heated to 110℃~130℃, then nitrogen gas was introduced to raise the temperature to 160℃~180℃, Cs source precursor solution was added and reacted for 5~15s, then cooled to room temperature in an ice bath, centrifuged and the precipitate obtained by centrifugation was dispersed or dissolved in a solvent to obtain quantum dot solution or dispersion.

[0020] Optionally, the quantum dot is a green quantum dot, and step 1) includes:

[0021] Preparation of Cs-derived precursor solution;

[0022] ODE, PbBr2, OA and OAm were mixed, evacuated and heated to 110℃~130℃, then nitrogen gas was introduced to raise the temperature to 160℃~180℃. After adding Cs source precursor solution and reacting for 5~15s, the mixture was cooled to room temperature in an ice bath. After centrifugation, the precipitate obtained by centrifugation was dispersed or dissolved in a solvent to obtain quantum dot solution or dispersion.

[0023] The ligands can include, but are not limited to: thiols such as octetranol and n-dodecyl mercaptan; esters such as ethyl oleate; phospholipids such as lecithin; long-chain alkanes such as n-tetradecane; and aromatic hydrocarbons. These ligands are carefully selected to effectively bind to the surface of quantum dots, forming a stable protective layer that inhibits the migration of halide ions. For example, phosphate groups (PO4) - ) and quaternary ammonium salt groups (NR3) + These groups can form stable coordination bonds with metal ions and halide ions on the surface of quantum dots. This coordination helps reduce surface defects, thereby improving the stability of quantum dots.

[0024] An EHD inkjet printing technology is optimized for quantum dots using a multi-solvent system. The multi-solvent system is designed with the physical and chemical properties of quantum dots in mind. By carefully selecting solvents with different volatility, viscosity, and dielectric constants, an ink formulation that effectively disperses and stabilizes quantum dots is created. Solvents can include alkane solvents and aromatic hydrocarbon solvents. This multi-solvent system improves the uniformity of quantum dot dispersion in the ink and optimizes the interaction between the ink and the printing device, ensuring stability and controllability during the printing process.

[0025] An electrohydrodynamic inkjet printing process is disclosed, which uses the aforementioned quantum dot ink for electrohydrodynamic inkjet printing.

[0026] Optionally, the nozzle tip size for inkjet printing can be as small as 2 μm.

[0027] The application of the above-mentioned electrohydrodynamic inkjet printing process in full-color Micro-LED displays involves preparing quantum dot inks of different colors by printing them into an array using the electrohydrodynamic inkjet printing process to prepare a color conversion layer.

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

[0029] 1. Significantly improved stability of quantum dots: Multiple ligands are used to passivate the surface of quantum dots. They form strong coordination bonds with metals and halide ions on the surface of quantum dots, forming a stable protective layer, which enhances the chemical and photophysical stability of quantum dots and effectively inhibits the migration of halide ions.

[0030] 2. Optimized color performance of full-color Micro-LED displays: With the improvement of quantum dot stability, the performance of the color conversion layer has been significantly improved. Full-color Micro-LED displays now display more accurate and vibrant colors, meeting users' demands for high-quality displays.

[0031] 3. Improved production efficiency and material utilization: Optimization of electrohydrodynamic inkjet printing technology enables quantum dots to be deposited more stably on the substrate, forming a uniform color conversion layer. This not only improves production efficiency but also reduces material waste and lowers production costs.

[0032] 4. It has promoted the development of Micro-LED display technology: providing new ideas and methods for the development of full-color Micro-LED display technology. Its successful application will help promote the widespread use of Micro-LED display technology in the commercial field and promote the rapid development of related industries.

[0033] 5. Optimized solvent selection: Through multi-solvent optimization, quantum dots can be stably maintained in nonpolar or weakly polar solvents such as hexane, heptane, and cyclohexane, and can be effectively printed using electrohydrodynamic inkjet printing technology. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the red quantum dot in Example 1;

[0035] Figure 2 This is a schematic diagram of the printed pattern in Example 1;

[0036] Figure 3 This is a schematic diagram of the printed pattern for Example 2;

[0037] Figure 4 This is a schematic diagram of the printed pattern for Comparative Example 1;

[0038] Figure 5 This is a schematic diagram of the printed pattern for Comparative Example 2;

[0039] Figure 6 This is a schematic diagram of full-color display in Example 3. 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 embodiments achieve effective passivation of quantum dot inks by optimizing the selection and introduction of ligands, suppressing adverse factors, and improving their stability during the manufacturing process. Moreover, through precise patterning technology, they provide strong technical support for the development of full-color Micro-LED display technology, and promote the development of display technology towards higher resolution, wider color gamut and longer lifespan.

[0042] Example 1

[0043] Preparation of Cs source: Mix 0.407g Cs2CO3 (cesium carbonate), 1.25ml OA (oleic acid), and 20ml ODE (octadecene) in a 100ml three-necked flask; then heat under vacuum to 120℃ and keep warm for 1h to completely remove water and oxygen from the flask; then purge with nitrogen and heat to 150℃ and keep warm for 10min to completely dissolve Cs2CO3, obtaining a clear yellow Cs source precursor solution, which is then poured into a brown reagent bottle and stored in a refrigerator away from light. Before use, it should be heated to 130℃.

[0044] Preparation of red quantum dots: 40 ml ODE, 0.196 g PbBr2 (lead bromide), 0.492 g PbI2 (lead iodide), 4 ml OA, and 4 ml OAm were simultaneously added to a 100 ml three-necked flask. The mixture was evacuated and heated to 120 °C for 1 hour. Nitrogen gas was then introduced, and the temperature was raised to 170 °C. After 3 minutes, 3.2 ml of the prepared Cs precursor solution was injected into the three-necked flask, and the reaction was allowed to proceed for 10 seconds. The flask was then immediately placed in an ice bath to cool to room temperature. An equal volume of methyl acetate was then added, and the resulting solution was divided into four centrifuge tubes and centrifuged at 8000 rpm for 5 minutes. The resulting precipitate was dissolved in 400 μl of xylene.

[0045] Surface ligand preparation: A mixed solution of n-dodecyl mercaptan and lecithin was prepared by using xylene as a solvent to make the concentration of n-dodecyl mercaptan 0.08 mmol / ml and the concentration of lecithin 0.026 mmol / ml.

[0046] Quantum dot ink preparation: 40 μl of ligand solvent was added to the quantum dot solution and stirred at room temperature for 5 min. Then, it was centrifuged at 4000 rpm for 5 min. The supernatant was filtered through a 0.22 μm hydrophobic PTFE membrane. After filtration, it was mixed with a 0.05 g / ml polybutadiene n-octane solution at a volume ratio of 2:1 to obtain quantum dot ink.

[0047] The crystal structure of red perovskite quantum dots is as follows: Figure 1 As shown. In this embodiment, n-dodecyl mercaptan and lecithin are used as ligands. Their thiol and phosphate groups interact strongly with lead and cesium ions on the quantum dot surface, thereby achieving surface passivation of the quantum dots and enhancing their stability. The solvent for the quantum dot ink includes an octane solution of polybutadiene and xylene. This multi-solvent system can improve solubility, optimize the viscosity and surface tension of the solution, improve stability, and avoid problems such as poor solubility, viscosity and surface tension mismatch, and poor stability that may occur with a single solvent.

[0048] The aforementioned quantum dot ink was applied to electrohydrodynamic inkjet printing using an ultra-fine inkjet printer (SIJ-350) with an ultra-fine nozzle (SIJ-SFN) and a nozzle tip size of 2μm. A square wave voltage was used with an amplitude of 1000V, a bias of 1000V, and a frequency of 1000Hz. The printing speed was set to 2mm / s, and the printing acceleration was set to 5mm / s. 2 The printing temperature was 25℃ and the relative humidity was 50%. Parallel line patterns were printed with a line width of 4.5μm and a spacing of 10μm, resulting in the pattern shown below. Figure 2 As shown, by precisely controlling printing parameters and optimizing ink formulation, a red perovskite quantum dot pattern with high graphic accuracy, high luminescence uniformity, and good stability was successfully prepared, meeting the requirements of high-performance display technology.

[0049] Example 2

[0050] Preparation of Cs source: Mix 0.407g Cs2CO3 (cesium carbonate), 1.25ml OA (oleic acid), and 20ml ODE (octadecene) in a 100ml three-necked flask; then heat under vacuum to 120℃ and keep warm for 1h to completely remove water and oxygen from the flask; then purge with nitrogen and heat to 150℃ and keep warm for 10min to completely dissolve Cs2CO3, obtaining a clear yellow Cs source precursor solution, which is then poured into a brown reagent bottle and stored in a refrigerator away from light. Before use, it should be heated to 100℃.

[0051] Preparation of green quantum dots: 40 ml ODE, 0.552 g PbBr2 (lead bromide), 5.2 ml OA, and 5.2 ml OAm were added to a 100 ml three-necked flask. The mixture was heated to 120 °C and vacuum-treated to remove moisture and oxygen for 30 min. Nitrogen gas was introduced, and the mixture was heated to 180 °C and maintained for 10 min. Then, 3.2 ml of the prepared Cs precursor solution was injected, and the three-necked flask was immediately transferred to an ice bath after 5 seconds. After cooling to room temperature, the solution was centrifuged at 10000 rpm for 5 min, and the obtained precipitate was dispersed in 3 ml n-hexane. The dispersed solution was then centrifuged at 5000 rpm for 5 min, and the supernatant was collected and dispersed in 3 ml n-hexane.

[0052] Surface ligand preparation: 3.06 mg of bis(dodecyldimethylammonium bromide) (DDAB), 8 mg of tri-n-octylphosphine (TOP), 1 ml of toluene, and 12.2 mg of PbBr2 were added to a reagent bottle and heated to 40 °C. (The ligands are DDAB and TOP.)

[0053] Quantum dot ink preparation: 0.75 ml of surface ligand solution, 3 ml of toluene, and 3 ml of the supernatant dispersed in n-hexane were added to a new reagent bottle and stirred for 1 h. Then, 9 ml of methyl acetate was added. After centrifugation at 10000 rpm for 5 min, the precipitate was collected. 400 μl of 1,3,5-triethylbenzene and 400 μl of n-tetradecane solvent were added to the precipitate, and the mixture was centrifuged at 5000 rpm for 5 min, and the supernatant was collected. The quantum dot ink was obtained by filtration through a 0.22 μm hydrophobic PTFE membrane.

[0054] In this embodiment, the ligands used are bis(dodecyldimethylammonium bromide) and tri-n-octylphosphine. Their quaternary ammonium salt groups allow them to form strong electrostatic interactions with negatively charged sites on the quantum dot surface, and coordinate bonds are formed between the phosphine groups and metal ions on the quantum dot surface. These two interactions help repair defects on the quantum dot surface, thereby improving the surface stability of the quantum dots. The solvents used include 1,3,5-triethylbenzene and n-tetradecane, which can improve solubility, optimize solution viscosity and surface tension, and improve stability.

[0055] The aforementioned quantum dot ink was applied to electrohydrodynamic inkjet printing using an ultra-fine inkjet printer (SIJ-350) with an ultra-fine nozzle (SIJ-SFN) and a tip size of 2μm. A square wave voltage was used with an amplitude of 300V, a bias of 300V, and a frequency of 1000Hz. The printing speed was set to 3mm / s, and the printing acceleration was set to 5mm / s. 2 The printing temperature was 25℃ and the relative humidity was 50%. A dotted array pattern was obtained, with each dot having a diameter of 12μm and a dot spacing of 50μm, as shown in the image. Figure 3 As shown.

[0056] Comparative Example 1

[0057] The preparation of Cs sources and green quantum dots is the same as in Example 2.

[0058] Preparation of quantum dot ink:

[0059] Quantum dot ink preparation: 3 ml of toluene and 3 ml of the supernatant dispersed in n-hexane were added to a new reagent bottle and stirred for 1 h. Then, 9 ml of methyl acetate was added. After centrifugation at 10000 rpm for 5 min, the precipitate was collected. 400 μl of 1,3,5-triethylbenzene and 400 μl of n-tetradecane solvent were added to the precipitate, and the mixture was centrifuged at 5000 rpm for 5 min, and the supernatant was collected. The supernatant was obtained by filtration through a 0.22 μm hydrophobic PTFE membrane. The above quantum dot ink was applied to electrohydrodynamic inkjet printing with the same parameters as in Example 2, and the resulting pattern is shown below. Figure 4 As shown.

[0060] Comparative Example 2

[0061] The preparation of Cs sources and green quantum dots is the same as in Example 2.

[0062] Surface ligand preparation: 5 mg of bis(dodecyl)dimethylammonium bromide (DDAB), 1 ml of toluene, and 12.2 mg of PbBr2 were added to a reagent bottle and heated to 40 °C.

[0063] Quantum dot ink preparation: 0.75 ml of surface ligand solution, 3 ml of toluene, and 3 ml of the supernatant dispersed in n-hexane were added to a new reagent bottle and stirred for 1 h. Then, 9 ml of methyl acetate was added. After centrifugation at 10000 rpm for 5 min, the precipitate was collected. 400 μl of 1,3,5-triethylbenzene and 400 μl of n-tetradecane solvent were added to the precipitate, and the supernatant was collected after centrifugation at 5000 rpm for 5 min. The supernatant was filtered through a 0.22 μm hydrophobic PTFE membrane to obtain the quantum dot ink. The above quantum dot ink was applied to electrohydrodynamic inkjet printing with the same parameters as in Example 2, and the resulting pattern is shown below. Figure 5 As shown.

[0064] Depend on Figures 3 to 5 As can be seen, Comparative Example 1, without the addition of a ligand, produced coffee ring or conical structures during evaporation, resulting in uneven luminescence. Comparative Example 2, with the addition of a single ligand, exhibited a pronounced coffee ring phenomenon and uneven luminescence. Example 2, using a dual-ligand system, effectively suppressed the coffee ring effect, achieving high uniformity and good stability. It is evident that multi-ligand systems, by providing multiple passivation mechanisms, optimizing ligand coverage, and improving optical properties, enhance the stability and dispersibility of nanoparticles, avoiding the problems of poor passivation, uneven coverage, and insufficient optical performance that may occur with single-ligand systems.

[0065] In the above embodiments, by using the multi-ligand passivation method, quantum dots can be stably maintained in nonpolar or weakly polar solvents, and can be effectively printed using electrohydrodynamic inkjet printing technology by means of the polarity of the quantum dots themselves.

[0066] Example 3

[0067] refer to Figure 6 The red quantum dot ink of Example 1 and the green quantum dot ink of Example 2 are sequentially used and arranged in a matrix to form rows of red quantum dot patterns and rows of green quantum dot patterns on a substrate, respectively, while retaining rows of blue light-transmitting areas, forming sub-pixel units of RGB three primary colors, thus obtaining a color conversion layer. The color conversion layer is combined with a blue light Micro-LED light-emitting chip array so that the blue light Micro-LED light-emitting chip units correspond one-to-one with the sub-pixel units, thereby realizing full-color display.

[0068] The above embodiments are only used to further illustrate a method for preparing and applying EHD full-color quantum dot ink 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. The application of an electrohydrodynamic inkjet printing process in full-color Micro-LED displays, characterized in that: Red quantum dot ink and green quantum dot ink are used sequentially and arranged in a matrix to form rows of red quantum dot patterns and rows of green quantum dot patterns on a substrate, while retaining rows of blue light-transmitting areas, forming sub-pixel units of RGB three primary colors, thus obtaining a color conversion layer. The color conversion layer is then combined with a blue light Micro-LED light-emitting chip array so that the blue light Micro-LED light-emitting chip units correspond one-to-one with the sub-pixel units. in The preparation method of the green quantum dot ink includes: 1) Preparation of Cs source precursor solution: ODE, PbBr2, OA and OAm are mixed, vacuumed and heated to 110℃~130℃, then nitrogen gas is introduced to raise the temperature to 160℃~180℃, Cs source precursor solution is added and reacted for 5~15s, then cooled to room temperature in an ice bath, centrifuged, and the precipitate obtained by centrifugation is dispersed or dissolved in a solvent to obtain quantum dot solution or dispersion. 2) Prepare a surface ligand solution, wherein the surface ligand solution comprises dodecyldimethylammonium bromide and tri-n-octylphosphine; 3) Mix the surface ligand solution and the perovskite quantum dot solution or dispersion to bind the ligands to the quantum dots and obtain passivated quantum dots; the molar ratio of ligands to quantum dots in the mixture is 0.005~0.2:1; 4) The passivated quantum dots were mixed in 1,3,5-triethylbenzene and n-tetradecane solvent to obtain green quantum dot ink; the concentration of quantum dots in the green quantum dot ink was 5 mg / ml-60 mg / ml; The preparation method of the red quantum dot ink includes: 1) Preparation of Cs source precursor solution: ODE, PbBr2, PbI2, OA and OAm are mixed, vacuumed and heated to 110℃~130℃, then nitrogen gas is introduced to raise the temperature to 160℃~180℃, Cs source precursor solution is added and reacted for 5~15s, then cooled to room temperature in an ice bath, centrifuged, and the precipitate obtained by centrifugation is dispersed or dissolved in a solvent to obtain quantum dot solution or dispersion. 2) Prepare a surface ligand solution, wherein the surface ligand solution comprises n-dodecyl mercaptan and lecithin; 3) Mix the surface ligand solution and the perovskite quantum dot solution or dispersion to bind the ligands to the quantum dots and obtain passivated quantum dots; the molar ratio of ligands to quantum dots in the mixture is 0.005~0.2:1; 4) The passivated quantum dots are mixed in a solvent to obtain red quantum dot ink, wherein the solvent includes an octane solution of polybutadiene and xylene solvent; the concentration of quantum dots in the red quantum dot ink is 5 mg / ml-60 mg / ml.

2. The application of the electrohydrodynamic inkjet printing process according to claim 1 in full-color Micro-LED displays, characterized in that: The minimum nozzle tip size for inkjet printing is 2 μm.

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