A method for preparing stable fluorescent PeQD ink suitable for EHD inkjet printing

Abstract

The present invention belongs to the technical field of inkjet printing, and specifically discloses a method for preparing a stable fluorescent PeQD ink suitable for EHD inkjet printing, comprising the following steps: (1) preparing a Cs precursor, (2) preparing PeQD, and (3) preparing PeQD ink. The PeQD ink prepared by the present invention can eliminate the coffee ring effect in inkjet printing, make the thickness of the pixel points of the color conversion layer more uniform, thereby achieving a uniform light emission effect; it can realize three-dimensional printing, and control the pixel point thickness by controlling the voltage application time without changing the pixel point size of the color conversion layer, which can not only make the pixel point light emission more uniform, but also significantly reduce blue light leakage and improve light conversion efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of inkjet printing, and in particular relates to a method for preparing a stable fluorescent PeQD ink suitable for EHD inkjet printing. Background Art

[0002] In recent years, full-color Micro-LED displays with high contrast, fast response, wide color gamut and low power consumption have developed rapidly. Micro-LED can be used in small-sized wearable devices such as AR, VR, and smart watches. As a basic element of display devices, high-pixel-density micro-light-emitting arrays are the key to our research. Not only the pixel size should be guaranteed, but also the uniformity of its luminous stability should be guaranteed. Therefore, in the application of Micro-LED devices, the color conversion layer needs to be reduced to a level comparable to that of the Micro-LED chip. The tiny pixel size negates the traditional thin film manufacturing methods, such as spin coating and dip coating. In view of this problem, some new strategies such as transfer printing, laser direct writing, photolithography, and inkjet printing have been applied. Among them, inkjet printing is the most promising approach because it has obvious advantages, can achieve on-demand printing, and greatly saves materials.

[0003] Electrohydrodynamic (EHD) inkjet printing is an emerging advanced technology that is compatible with conductive nanocolloidal inks for printing high-resolution arrays. Under pulsed voltage, droplets at the liquid-air interface are alternately charged positively or negatively and form a meniscus. Then, the induced electric force, once large enough to overcome the surface tension, drags the droplet downward, producing a large number of small droplets as small as sub-femtoliter due to the Rayleigh limit, ultimately resulting in resolutions up to submicrometers. The realization of such ultra-high resolution requires inks with suitable physical parameters to adapt to the printing process. Therefore, "ink formulation" is crucial for EHD inkjet printing, and traditional II-VI quantum dot inks have been successfully incorporated into quantum dot light-emitting diodes (QLEDs) and micro-LEDs. All-inorganic halide PeQDs are another promising candidate due to their high photoluminescence quantum yield (PLQY), narrow linewidth, easily adjustable spectral range, and easy processing in solution and customizable surface chemistry. There are currently two types of PeQD inks: one is PeQD precursor ink, which forms in-situ crystals after solvent evaporation. However, the PeQD color conversion layer prepared by this method has low crystallinity and many surface defects, which can easily reduce the optical or photoelectric performance; the other is to prepare PeQD ink by dispersing the prepared PeQD in a solvent, which can effectively improve the crystallinity of the ink PeQD and improve the luminescence performance. The prepared PeQD can be stably dispersed in low-boiling point, non-polar solvents, and is prone to fluorescence quenching in high-boiling point solvents. However, inks suitable for EHD printing often require solvents with higher boiling points to prevent evaporation and needle clogging. At the same time, the ink also requires certain dielectric properties, which can drive the ink to form a meniscus at the needle tip under the action of an electric field and break into small droplets that are deposited on the substrate. Inkjet printing also has a common problem. PeQD is not as stable as II-V quantum dots and is easily degraded under oxygen, water and light illumination conditions. At the same time, during the inkjet printing process, the printed pixels are prone to form a coffee ring phenomenon, which affects the uniformity of luminescence. At the same time, if the printed pixels are small, the amount of droplets deposited at the pixel position is small, and the pixels are too thin, resulting in blue light leakage problems, and effective color conversion cannot be achieved. This limits the manufacture, storage and large-scale application of PeQD inks.

[0004] Therefore, it is urgent to develop a method for preparing PeQD ink that has sufficient dielectric properties, stable luminescence, the ability to deposit uniform pixels, stable ink output, and adjustable printed pixel thickness. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a method for preparing a stable fluorescent PeQD ink suitable for EHD inkjet printing. Toluene is used as a single solvent system, and polystyrene polymer is added to the prepared perovskite ink to prepare a passivated PeQD ink, which effectively inhibits ion migration and improves the ink stability and luminous brightness. At the same time, a layer of polymer film is uniformly deposited on the surface of the printed pixel points to isolate the water and oxygen in the environment, play a protective role, and improve the optical properties and stability of the ink.

[0006] The present invention proposes a method of preparing a passivated PeQD ink by adding a polystyrene polymer to a prepared perovskite ink using toluene as a single solvent system, effectively inhibiting the ion migration phenomenon, improving the ink stability and luminous brightness, and uniformly depositing a layer of polymer film on the surface of the printed pixel point to isolate the water and oxygen in the environment, play a protective role, and improve the optical properties and stability of the ink. By changing the addition ratio of polystyrene, the surface tension, dielectric constant, viscosity and other physical parameters of the PeQD ink are optimized. The printing parameters are controlled to adjust the applied electric field strength and the electric field action time to control the ink output, and the EHD inkjet printing effectively adjusts the morphology of the array. Not only can the coffee ring effect be eliminated, but also columnar pixels can be further three-dimensionally printed, and the thickness of the pixel points can be increased without changing the pixel point size, effectively preventing the blue light crosstalk problem and improving the light conversion efficiency. This ink preparation technology has great potential in the high-resolution array structure of Micro-LED.

[0007] In order to achieve the above objectives, one of the technical solutions of the present invention is: a method for preparing a stable fluorescent PeQD ink suitable for EHD inkjet printing, comprising the following steps:

[0008] (1) Preparation of cesium precursor: Cs2CO3 (cesium carbonate) was added to OA (oleic acid) and ODE, and after mixing, the mixture was heated and kept warm in vacuum to fully remove water and oxygen in the flask; nitrogen was then introduced and heated and kept warm to completely dissolve Cs2CO3, thereby obtaining a yellow Cs precursor solution;

[0009] (2) Preparation of PeQD: Add lead halide to ODE, OA and OAm (oleylamine), mix, heat under vacuum and keep warm, then introduce nitrogen to raise the temperature, then add the cesium precursor solution prepared in step (1), react and immediately cool to room temperature in an ice bath, then centrifuge the mixed solution to disperse; take the centrifugal precipitate and disperse it in toluene, then wash it in ethyl acetate and centrifuge it to disperse it, finally collect the precipitate and disperse it in toluene to prepare a PeQD solution;

[0010] (3) Preparation of PeQD ink: The PeQD solution prepared in step (2) is added to the polymer and stirred at room temperature until the polymer is completely dissolved, so that the polymer can be evenly coated on the PeQD surface to obtain an ink with the PeQD surface coated with the polymer. Finally, the prepared ink is filtered to remove the large agglomerated particles in the ink to obtain a PeQD ink suitable for EHD inkjet printing.

[0011] In a preferred embodiment of the present invention, the volume ratio of OA and ODE in step (1) is (0.8-1.2):(8-12), and the amount of Cs2CO3 added to OA and ODE is 0.01-0.03 g / ml.

[0012] In a preferred embodiment of the present invention, the vacuum heating temperature in step (1) is 100-140° C., and the insulation time is 0.5-1.5 h.

[0013] In a preferred embodiment of the present invention, the heating temperature in step (1) is 120-170°C and the insulation time is 8-12 minutes to completely dissolve Cs2CO3.

[0014] In a preferred embodiment of the present invention, the Cs precursor solution in step (1) needs to be refrigerated and protected from light, and heated to 90-110° C. before use.

[0015] In a preferred embodiment of the present invention, the organic solvent 1 in step (2) is a non-polar or weakly polar solvent containing a benzene ring, preferably toluene or xylene, and the organic solvent 2 is an anti-solvent, preferably methyl acetate, tert-butyl alcohol or the like, and the anti-solvent facilitates the precipitation of crystals from the solution.

[0016] In a preferred embodiment of the present invention, the volume ratio of ODE, OA and OAm in step (2) is (8-12)(0.8-1.2):(0.8-1.2).

[0017] In a preferred embodiment of the present invention, the lead halide salt in step (2) is at least one of lead bromide and lead iodide, and the amount of the lead halide salt added to ODE, OA, OAm is 0.01-0.02 g / ml.

[0018] In a preferred embodiment of the present invention, in step (2), the vacuum heating temperature is 100-140°C, the insulation time is 15-45 minutes, and nitrogen is introduced to raise the temperature to 160-180°C.

[0019] In a preferred embodiment of the present invention, the volume ratio of the cesium precursor solution to ODE, OA, and OAm in step (2) is (0.06-0.08): 1

[0020] In a preferred embodiment of the present invention, the reaction time of adding the cesium precursor solution in step (2) is 3-7s.

[0021] In a preferred embodiment of the present invention, the centrifugal dispersion speed in step (2) is 8000-12000 rpm, and the centrifugation time is 3-7 min.

[0022] In a preferred embodiment of the present invention, the polymer in step (3) is polystyrene, and the amount of polymer added to the PeQD solution is 0.02-0.06 g\ml.

[0023] In order to achieve the above objectives, the second technical solution of the present invention is a PeQD ink prepared by the above preparation method.

[0024] In order to achieve the above objectives, the third technical solution of the present invention is the application of PeQD ink in EHD inkjet printing.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The PeQD ink prepared in the present invention can eliminate the coffee ring effect in EHD inkjet printing, making the pixel thickness of the color conversion layer more uniform, thereby achieving a uniform luminescence effect;

[0027] 2. The PeQD ink prepared by the present invention can realize three-dimensional printing. Without changing the size of the pixel points of the color conversion layer, the thickness of the pixel points can be controlled by controlling the voltage application time, which can not only make the pixel points emit light more uniformly but also significantly reduce the blue light crosstalk and improve the light conversion efficiency;

[0028] 3. After adding high molecular polymer, the surface tension and viscosity of the ink are increased. Even if PeQD is dispersed in a low boiling point solvent, it can stably and continuously discharge ink from a needle tip with a diameter of 1.5um without blocking the needle tip or affecting the fluorescent properties of the solution. It can emit light stably. It can achieve stable full-color light emission. After the ink at the pixel position of the EHD inkjet printing is dry, the polystyrene in the ink can evenly cover each pixel, isolating the water and oxygen in the environment, and can effectively improve the stability of the color conversion layer and extend the service life.

[0029] 4. The present invention improves the compatibility of PeQD with solvents. By adding polystyrene high molecular polymers to the PeQD solution, surface defects can be effectively passivated, and PeQD can be stably dispersed in weakly polar solvents, thereby improving the stability and luminescence brightness of PeQD. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the synthesis process of PeQD of the present invention;

[0031] Figure 2 This is a schematic diagram of EHD inkjet printing of the present invention;

[0032] Figure 3 This is the EHD inkjet printing effect diagram of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is described in more detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments. The same reference numerals in the text always represent the same elements, and similar reference numerals represent similar elements.

[0034] In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left",

[0035] The directions or positional relationships indicated by “right”, “horizontal”, “vertical”, “top”, “bottom”, “inside” and “outside”, etc., are based on the directions or positional relationships shown in the stereoscopic diagrams in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0036] A method for preparing a stable fluorescent PeQD ink suitable for EHD inkjet printing comprises the following steps:

[0037] (1) Preparation of cesium precursor: Cs2CO3 (cesium carbonate) was added to OA (oleic acid) and ODE, and after mixing, the mixture was heated and kept warm in vacuum to fully remove water and oxygen in the flask; nitrogen was then introduced and heated and kept warm to completely dissolve Cs2CO3, thereby obtaining a yellow Cs precursor solution;

[0038] (2) Preparation of PeQD: Add lead halide to ODE, OA and OAm (oleylamine), mix, heat under vacuum and keep warm, then introduce nitrogen to raise the temperature, then add the cesium precursor solution prepared in step (1), react and immediately cool to room temperature in an ice bath, then centrifuge the mixed solution to disperse; take the centrifugal precipitate and disperse it in toluene, then wash it in ethyl acetate and centrifuge it to disperse it, finally collect the precipitate and disperse it in toluene to prepare a PeQD solution;

[0039] (3) Preparation of PeQD ink: The PeQD solution prepared in step (2) is added to the polymer and stirred at room temperature until the polymer is completely dissolved, so that the polymer can be evenly coated on the PeQD surface to obtain an ink with the PeQD surface coated with the polymer. Finally, the prepared ink is filtered to remove the large agglomerated particles in the ink to obtain a PeQD ink suitable for EHD inkjet printing.

[0040] The volume ratio of OA and ODE in step (1) is (0.8-1.2):(8-12), and the amount of Cs2CO3 added to OA and ODE is 0.01-0.03 g / ml.

[0041] In the step (1), the vacuum heating temperature is 100-140° C., and the insulation time is 0.5-1.5 h.

[0042] In the step (1), the heating temperature of nitrogen is 120-170° C. and the insulation time is 8-12 min to completely dissolve Cs 2 CO 3 .

[0043] The Cs precursor solution in step (1) needs to be refrigerated and protected from light, and heated to 90-110° C. before use.

[0044] In the step (2), the organic solvent 1 is a non-polar or weakly polar solvent containing a benzene ring, and the organic solvent 2 is an anti-solvent, preferably a solvent such as methyl acetate and tert-butyl alcohol.

[0045] In the step (2), the volume ratio of ODE, OA and OAm is (8-12)(0.8-1.2):(0.8-1.2).

[0046] The lead halide salt in step (2) is at least one of lead bromide and lead iodide, and the amount of the lead halide salt added to ODE, OA, and OAm is 0.01-0.02 g / ml.

[0047] In the step (2), the vacuum heating temperature is 100-140° C., the insulation time is 15-45 min, and nitrogen is introduced to raise the temperature to 160-180° C.

[0048] In the step (2), the volume ratio of the cesium precursor solution to ODE, OA, and OAm is (0.06-0.08): 1

[0049] The reaction time of adding the cesium precursor solution in step (2) is 3-7s.

[0050] In the step (2), the centrifugal dispersion speed is 8000-12000 rpm, and the centrifugal time is 3-7 min.

[0051] The polymer in step (3) is polystyrene, and the amount of polymer added to the PeQD solution is 0.02-0.06 g / ml.

[0052] A PeQD ink.

[0053] Application of a PeQD ink in EHD inkjet printing.

[0054] Example 1

[0055] A stable fluorescent PeQD ink suitable for EHD inkjet printing is prepared by the following preparation method:

[0056] 1. PeQDs were prepared by hot injection in two steps:

[0057] (1) Preparation of cesium precursor: 0.36 g Cs2CO3 (cesium carbonate), 1.5 ml OA (oleic acid), and 15 ml ODE (1-octadecene) were mixed in a 100 ml three-necked flask; then the mixture was evacuated and heated to 120°C and kept warm for 1 h to fully remove the water and oxygen in the flask; then nitrogen was introduced and heated to 150°C for 10 min to completely dissolve Cs2CO3 to obtain a yellow Cs source precursor solution, which was then poured into a brown reagent bottle and stored in a refrigerator away from light. It should be heated to 100°C before use;

[0058] (2) Preparation of PeQD: 15 ml ODE, 0.2 g PbBr2 (lead bromide), 1.5 ml OA and 1.5 ml OAm were added to a 100 ml three-necked flask, evacuated and heated to 120 °C for half an hour; nitrogen was then introduced and the temperature was raised to 180 °C; subsequently, 1.5 ml cesium precursor solution obtained in step (1) was heated to 100 °C and injected into the three-necked flask to react for 5 seconds, and the three-necked flask was immediately ice-bathed to room temperature, and the mixed solution was then centrifuged in a centrifuge at 10,000 rpm for 5 minutes; the precipitate was dispersed in 1:3 toluene:ethyl acetate for washing, and centrifuged at 10,000 rpm for 5 minutes; finally, the precipitate was collected and dispersed in toluene for use.

[0059] 2. Preparation of PeQD ink: Add the prepared PeQD solution to polystyrene particles at a rate of 0.06 g / ml, stir at room temperature until the polymer is completely dissolved, so that the polymer can be evenly coated on the PeQD surface, and finally filter the prepared ink with a 0.22 um filter needle to remove some large particles in the ink, thereby obtaining PeQD ink suitable for EHD inkjet printing.

[0060] Example 2

[0061] A stable fluorescent PeQD ink suitable for EHD inkjet printing, the preparation method is the same as that of Example 1, except that 0.2g PbBr2 (lead bromide) is replaced by 0.3g PbI2 (lead iodide), and the amount of cesium precursor solution added is 1.6ml.

[0062] Example 3

[0063] A stable fluorescent PeQD ink suitable for EHD inkjet printing, the preparation method is the same as that of Example 1, except that 0.2g PbBr2 (lead bromide) is replaced by 0.15g PbI2 (lead iodide) and 0.1g PbBr2 (lead bromide), and the amount of cesium precursor solution added is 1.6ml.

[0064] Example 4

[0065] A stable fluorescent PeQD ink suitable for EHD inkjet printing, the preparation method is the same as that of Example 1, except that 0.2g PbBr2 (lead bromide) is replaced by 0.18g PbI2 (lead iodide) and 0.08g PbBr2 (lead bromide), and the amount of cesium precursor solution added is 1.6ml.

[0066] Example 5

[0067] A stable fluorescent PeQD ink suitable for EHD inkjet printing is used in EHD printing. The PeQD ink prepared in Example 1 is injected into a printing needle tip with a diameter of 1.5 um. The pattern is printed using an EHD printing device. The printing voltage is adjusted to 1000 V and the printing speed is adjusted to 0.05 m / s to eliminate the coffee ring effect of traditional printing and obtain a three-dimensional pixel morphology.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a stable fluorescent PeQD ink suitable for EHD inkjet printing, characterized in that: The steps include: (1) Preparation of Cs precursor: Cs2CO3 was added to OA and ODE, heated and kept warm in vacuum, and then nitrogen was introduced and heated and kept warm to obtain a yellow Cs precursor solution; (2) Preparation of PeQD: Add lead halide to ODE, OA and OAm, heat and keep warm in vacuum, then introduce nitrogen to raise the temperature, then add the Cs precursor solution prepared in step (1) and react, ice bath to room temperature, then centrifuge and disperse the mixed solution; take the centrifugal precipitate and disperse it in organic solvent 1, then wash it in organic solvent 2 and centrifuge and disperse it, finally collect the precipitate and disperse it in toluene to prepare PeQD solution; the volume ratio of ODE, OA and OAm is (8-12)(0.8-1.2):(0.8-1.2), and the volume ratio of cesium precursor solution to ODE, OA and OAm is (0.06-0.08):1; (3) Preparation of PeQD ink: Add the PeQD solution prepared in step (2) to the polymer and stir until the polymer is completely dissolved to obtain an ink with the PeQD surface coated with the polymer. Finally, filter the prepared ink to remove the large agglomerated particles in the ink to obtain a PeQD ink suitable for EHD inkjet printing. The polymer is polystyrene, and the amount of polystyrene added to the PeQD solution is 0.02-0.06 g / ml.

2. The preparation method according to claim 1, characterized in that The volume ratio of OA and ODE in step (1) is (0.8-1.2):(8-12), and the amount of Cs2CO3 added to OA and ODE is 0.01-0.03 g / ml.

3. The preparation method according to claim 1, characterized in that: In the step (1), the vacuum heating temperature is 100-140° C., and the insulation time is 0.5-1.5 h. The nitrogen heating temperature is 120-170° C., and the insulation time is 8-12 min.

4. The preparation method according to claim 1, characterized in that: In the step (2), the organic solvent 1 is a non-polar or weakly polar solvent containing a benzene ring, and the organic solvent 2 is an anti-solvent.

5. The preparation method according to claim 1, characterized in that: In the step (2), the amount of lead halide added to ODE, OA, and OAm is 0.01-0.02 g / ml.

6. The preparation method according to claim 1 or 4, characterized in that: The lead halide salt in step (2) is at least one of lead bromide and lead iodide.

7. The preparation method according to claim 1, characterized in that: In the step (2), the vacuum heating temperature is 100-140° C., the insulation time is 15-45 min, nitrogen is introduced to raise the temperature to 160-180° C., the reaction time of adding the cesium precursor solution is 3-7 s, the centrifugal dispersion speed is 8000-12000 rpm, and the centrifugation time is 3-7 min.

8. A PeQD ink prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the PeQD ink as claimed in claim 8 in EHD inkjet printing.

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