Thin film, electroluminescent device and preparation method thereof

Abstract

The present invention discloses a thin film, an electroluminescent device and a preparation method thereof. The preparation method of the thin film comprises the following steps: providing a substrate having pixel pits; transferring ink into the pixel pits on the substrate by a solution method; applying ultrasonic waves to the ink in the pixel pits, and obtaining the thin film by drying. In the present invention, after the ink is transferred into the pixel pits by a solution method, ultrasonic waves are applied to the ink in the pixel pits during the volatilization process of the ink. The ultrasonic waves have a certain amount of energy, which can accelerate the fluidity inside the ink, so that the concentration of the ink in each area of ​​the pixel pit remains relatively consistent during the volatilization process, thereby improving the uniformity of the formed thin film. In addition, the energy possessed by the ultrasonic waves can also increase the internal energy of the ink, increase the volatilization rate of the ink to a certain extent, and avoid the uneven film phenomenon caused by the uneven distribution of ink concentration due to the capillary effect of the ink.

Description

Technical Field

[0001] The present invention relates to the field of electroluminescent devices, and in particular to a thin film, an electroluminescent device and a preparation method thereof. Background Art

[0002] As a new type of luminescent material, quantum dots have the advantages of high luminescent color purity and a wide color gamut, and therefore have gradually broken the monopoly of LCD in the display field. At present, the two most cutting-edge applications of quantum dots as self-luminescent panels are QLED display panels with electro-induced quantum dots as the light-emitting layer and Micro-LED display panels with photo-induced quantum dots as the light-color conversion layer. Both of the above panels require the deposition of a uniform and flat quantum dot layer to improve device performance, prevent light-color crosstalk, and thus achieve a high-resolution display with uniform light output. Inkjet printing, as a new solution processing technology, has the advantages of being able to recycle the remaining ink after a single print, a simple film-forming environment, patterning without the assistance of a mask, and high resolution.

[0003] Inkjet printing is a film-forming method in which ink of functional materials is sprayed drop by drop onto corresponding positions as needed under computer control to form a pattern. It has the advantages of simple operation, non-contact, mask-free, low equipment cost, and high material utilization. It is considered to be an effective way to achieve flexible large-area OLED / QLED displays.

[0004] Inkjet printing for display fabrication has garnered widespread attention and development in recent years, but uniformity of the printed film remains a key issue. During the inkjet printing process, the printed ink often exhibits a coffee ring phenomenon during drying, resulting in an uneven film that is thicker at the edges and thinner in the center. This unevenness and coffee ring phenomenon during the printing and drying processes can severely degrade display performance and visual quality.

[0005] The existing printing process mainly improves the uniformity of the printed film by optimizing the ink solvent composition, the properties and shape of the pixel definition layer, the drying equipment and conditions, etc., but the uniformity of the film is still poor.

[0006] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0007] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a thin film, an electroluminescent device and a method for preparing the same, in order to solve the problem of poor uniformity of the thin film formed after the existing inkjet printing.

[0008] The technical solutions of the present invention are as follows:

[0009] A method for preparing a thin film, comprising the steps of:

[0010] providing a substrate having pixel pits;

[0011] The ink is transferred into the pixel pits on the substrate by a solution method;

[0012] Ultrasonic waves are applied to the ink in the pixel pits, and the thin film is obtained through drying.

[0013] Optionally, the step of applying ultrasonic waves to the ink in the pixel pit specifically includes: emitting ultrasonic waves from top to bottom directly above the pixel pit.

[0014] Optionally, after applying the ultrasonic wave for a preset time, the intensity of the ultrasonic wave is gradually reduced until the intensity of the ultrasonic wave is zero.

[0015] Optionally, the step of applying ultrasonic waves to the ink in the pixel pit is specifically: emitting ultrasonic waves simultaneously from top to bottom, from left to right, and from right to left directly above, to the left, and to the right of the pixel pit.

[0016] Optionally, the intensity of the ultrasonic wave is: frequency 20-24 kHz, power 0.2-0.6 W / cm 2 .

[0017] Optionally, the total drying time is 20-40 minutes.

[0018] A film is prepared by the film preparation method of the present invention.

[0019] A method for preparing an electroluminescent device, comprising the steps of:

[0020] Providing a preform, wherein the surface of the preform has pixel pits;

[0021] The luminescent layer ink is transferred into the pixel pits on the surface of the preform by a solution method, ultrasonic waves are applied to the luminescent layer ink in the pixel pits, and the solvent in the luminescent layer ink is completely dried to obtain a luminescent layer.

[0022] Optionally, the preform includes a first electrode and a first functional layer stacked together, the surface of the first electrode has pixel pits, and the preparation method of the preform includes the steps of:

[0023] The first functional layer ink is transferred into the pixel pit of the first electrode by a solution method, ultrasonic waves are applied to the first functional layer ink in the pixel pit, and the solvent in the first functional layer ink is completely dried to obtain the first functional layer.

[0024] Optionally, the method for preparing the electroluminescent device further comprises the steps of:

[0025] Transferring the second functional layer ink into the pixel pits of the light-emitting layer by a solution method, applying ultrasonic waves to the second functional layer ink in the pixel pits, and waiting for the solvent in the second functional layer ink to completely dry, thereby obtaining the second functional layer;

[0026] The second electrode is formed on the second functional layer.

[0027] An electroluminescent device is prepared by the method for preparing an electroluminescent device of the present invention.

[0028] Beneficial Effects: After the ink is transferred to the pixel pits via a solution method, ultrasonic waves are applied to the ink within the pixel pits during the evaporation process. This ultrasonic wave has a certain amount of energy, which can accelerate the fluidity of the ink, so that the concentration of the ink in each area of ​​the pixel pit remains relatively consistent during the evaporation process, thereby improving the uniformity of the formed film. In addition, the energy of the ultrasonic wave can also increase the internal energy of the ink, which increases the evaporation rate of the ink to a certain extent and avoids the uneven film caused by uneven ink concentration distribution due to the capillary effect. This method is low-cost and simple to process. There is no need to change the type of solvent. Only the intensity of the ultrasonic wave needs to be adjusted to achieve good film uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic flow chart of a method for preparing a thin film provided in an embodiment of the present invention.

[0030] Figure 2 This is a schematic diagram of transmitting ultrasonic waves from top to bottom directly above the pixel pit.

[0031] Figure 3 This is a schematic diagram of simultaneously emitting ultrasonic waves from top to bottom, from left to right, and from right to left toward the top, left, and right of the pixel pit.

[0032] Figure 4 A schematic flow chart of a method for preparing an electroluminescent device provided in an embodiment of the present invention.

[0033] Figure 5 A schematic structural diagram of an electroluminescent device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention provides a thin film, an electroluminescent device, and a method for preparing the same. To make the objectives, technical solutions, and effects of the present invention more clear and explicit, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0035] During inkjet printing, a layer of material is used to define pixels, which is usually called a pixel definition layer. The pixel definition layer has recessed areas as "containers" for the printing ink, called pixel pits.

[0036] During inkjet printing, the ink is first printed in the pixel pit as droplets, and then dries to form a thin film. However, the ink evaporates unevenly during the drying process. At the edges with small curvatures, the vapor pressure on the liquid surface is greater, and the solvent molecules in the ink are more likely to escape into the air, resulting in a greater evaporation intensity. Therefore, the evaporation rate at the edge of the droplet is greater than that at the center of the droplet, resulting in inconsistent evaporation rates in different areas within the pixel pit, resulting in poor film uniformity.

[0037] Since the evaporation rate at the edge of the droplet is greater than that at the center of the droplet, in order to compensate for the loss caused by the inconsistent evaporation rates between the center and the edge, capillary flow is generated from the middle to the edge of the droplet during the evaporation process, causing the suspended solute particles to continuously gather toward the edge of the droplet, eventually forming a "coffee ring" that is thin in the middle and thick at the edge, seriously affecting the final performance and display effect of the device.

[0038] Based on this, an embodiment of the present invention provides a method for preparing a thin film, such as Figure 1 As shown, the steps include:

[0039] S11, providing a substrate having pixel pits;

[0040] S12, transferring ink into pixel pits on the substrate by a solution method;

[0041] S13, applying ultrasonic waves to the ink in the pixel pits, and obtaining the thin film through drying.

[0042] It should be noted that the step of applying ultrasound to the ink in the pixel pits can be performed during the natural drying of the ink (i.e., without applying external heat source heating treatment, the ink is allowed to dry, and the ultrasonic wave energy is used to accelerate the volatilization of the ink) or during the annealing and drying of the ink. In one embodiment, the step of applying ultrasound to the ink in the pixel pits is performed during the natural drying of the ink. This is because the energy of ultrasound can accelerate the volatilization rate of the ink.

[0043] In this embodiment, after the ink is transferred to the pixel pits via a solution method (such as inkjet printing or spin coating), ultrasonic waves are applied to the ink within the pixel pits during the evaporation process. This ultrasonic wave has a certain amount of energy, which can accelerate the fluidity of the ink within the pixel pits, so that the concentration of the ink in each area of ​​the pixel pit remains relatively consistent during the evaporation process, thereby improving the uniformity of the formed film. In addition, the energy of the ultrasonic wave can also increase the internal energy of the ink, which to a certain extent increases the evaporation rate of the ink and avoids the uneven film caused by uneven ink concentration distribution due to the capillary effect. This method is low-cost and simple to process. There is no need to change the type of solvent. Only the intensity of the ultrasonic wave needs to be adjusted to achieve good film uniformity.

[0044] In one embodiment, the intensity of the ultrasound is: frequency f is 20-24 kHz, power P is 0.2-0.6 W / cm 2 By using ultrasonic waves of this intensity, the formed film can have better uniformity.

[0045] In one embodiment, the total drying time is 20-40 minutes, during which the solvent in the ink can be completely evaporated.

[0046] In one embodiment, the step of applying ultrasonic waves to the ink in the pixel pit specifically includes: emitting ultrasonic waves from top to bottom directly above the pixel pit, as shown in FIG. Figure 2 shown.

[0047] In one embodiment, after applying ultrasound for a preset time, the intensity of the ultrasound is gradually reduced until the intensity of the ultrasound is zero. In one embodiment, the preset time is the last third of the total drying time. Since the solvent in the ink becomes less and less in the later stage of drying, the fluidity inside the ink does not need to be faster. Therefore, in the last third of the ink drying time, the energy of the ultrasound is gradually reduced to reduce the cavitation effect of the ultrasound on the ink, so that the fluidity inside the ink becomes slower, which is conducive to making the surface of the film smoother. It should be noted that the total drying time refers to the time from the start of applying ultrasound to the complete volatilization of the solvent to form a film. This time can be determined in advance through multiple experiments, so that the intensity of the ultrasound can be controlled to gradually reduce in the last third of the total drying time.

[0048] In one embodiment, the step of applying ultrasonic waves to the ink in the pixel pit is specifically: emitting ultrasonic waves simultaneously from top to bottom, from left to right, and from right to left, directly above, to the left, and to the right of the pixel pit, as shown in FIG. Figure 3As shown. That is to say, ultrasonic waves are emitted from top to bottom directly above the pixel pit; ultrasonic waves are emitted from left to right to the left of the pixel pit; and ultrasonic waves are emitted from right to left to the right of the pixel pit. Ultrasonic waves are emitted simultaneously in three directions: directly above, to the left, and to the right of the pixel pit. Due to the high directivity of ultrasonic waves, ultrasonic waves surround and act on the ink in the pixel pit in three directions: directly above, to the left, and to the right of the pixel pit. Under the action of ultrasonic waves in different directions, the ink flows more obviously, causing the concentration of ink in each area to be more consistent, which is conducive to further improving the uniformity of the film. In addition, under the action of ultrasonic waves in different directions, the internal energy of the ink is further improved, which further accelerates the volatilization rate of the ink and avoids the uneven film phenomenon caused by uneven ink concentration distribution due to capillary effect.

[0049] An embodiment of the present invention provides a thin film, wherein the thin film is prepared using the thin film preparation method described in the embodiment of the present invention.

[0050] The present invention provides a method for preparing an electroluminescent device, such as Figure 4 As shown, the steps include:

[0051] S21, providing a preform, wherein the surface of the preform has pixel pits;

[0052] S22 , transferring the light-emitting layer ink into the pixel pits on the surface of the preform by a solution method, applying ultrasonic waves to the light-emitting layer ink in the pixel pits, and waiting for the solvent in the light-emitting layer ink to dry completely to obtain a light-emitting layer.

[0053] In this embodiment, after the luminescent layer ink is transferred into the pixel pits on the preform via a solution method (such as inkjet printing or spin coating), ultrasonic waves are applied to the luminescent layer ink within the pixel pits during the evaporation process. This ultrasonic wave has a certain amount of energy, which can accelerate the fluidity of the luminescent layer ink within the pixel pits, so that the concentration of the luminescent layer ink in each area within the pixel pit remains relatively consistent during the evaporation process, thereby improving the uniformity of the formed luminescent layer. In addition, the energy of the ultrasonic wave can also increase the internal energy of the luminescent layer ink, to a certain extent increasing the evaporation rate of the luminescent layer ink, thereby avoiding the uneven luminescent layer caused by the capillary effect. This method is low-cost and simple to process. Without changing the solvent type, only the intensity of the ultrasonic wave can be adjusted to achieve good uniformity of the luminescent layer, thereby obtaining a luminescent layer with uniform thickness, making the pixels emit light uniformly, and achieving a good display effect of the electroluminescent device.

[0054] In one embodiment, the solvent in the luminescent layer ink is a blended solvent comprising a high-boiling-point non-polar organic solvent and a low-boiling-point polar solvent. During evaporation, the high-boiling-point non-polar organic solvent generates a tension gradient with low edges and high centers, inducing inward flow. This ultimately results in more uniform solvent evaporation, which helps improve film flatness. Low-boiling-point polar solvents evaporate quickly and exhibit weak capillary properties.

[0055] In one embodiment, the high-boiling-point non-polar organic solvent is selected from one or more of halogenated aromatic hydrocarbons and their derivatives; in one embodiment, the low-boiling-point polar solvent is selected from one or more of alcohols, esters, and ethers. For example, the high-boiling-point non-polar organic solvent is selected from one or more of o-dichlorobenzene, m-dichlorobenzene, and o-bromotoluene; and the low-boiling-point polar solvent is selected from one or more of methanol, isopropanol, 2-methoxyethanol, ethyl acetate, butyl acetate, ethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether.

[0056] In this embodiment, the electroluminescent devices can be divided into two types based on their light-emitting type: upright electroluminescent devices and inverted electroluminescent devices, and each type of device has multiple forms. In one embodiment, the preform includes a first electrode. In one embodiment, the preform includes a stacked first electrode and a first functional layer. In this embodiment, the first electrode is disposed on a substrate. When the electroluminescent device has an upright structure, the first electrode is an anode; when the electroluminescent device has an inverted structure, the first electrode is a cathode.

[0057] In one embodiment, the electroluminescent device may further include: a second electrode disposed on the side surface of the light-emitting layer away from the first electrode, and a second functional layer disposed between the second electrode and the light-emitting layer. When the electroluminescent device is in an upright structure, the first functional layer is a hole functional layer, and the hole functional layer includes at least one of a hole injection layer and a hole transport layer; the second functional layer is an electron functional layer, and the electron functional layer includes at least one of an electron injection layer and an electron transport layer. When the electroluminescent device is in an inverted structure, the first functional layer is an electron functional layer, and the electron functional layer includes at least one of an electron injection layer and an electron transport layer; the second functional layer is a hole functional layer, and the hole functional layer includes at least one of a hole injection layer and a hole transport layer. The method of applying ultrasonic waves to the light-emitting layer ink in this embodiment is also applicable to different functional layers.

[0058] The following is Figure 5 Taking the electroluminescent device with the structure shown in FIG as an example, the preparation method of the electroluminescent device is introduced. Figure 5As shown, the electroluminescent device includes a substrate, an anode, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode stacked from bottom to top. The preparation method of the electroluminescent device includes the following steps:

[0059] S31, providing a substrate including an anode, wherein the anode has a pixel pit;

[0060] S32, transferring the hole transport layer ink into the pixel pits on the anode by a solution method, applying ultrasonic waves to the hole transport layer ink in the pixel pits, and waiting for the solvent in the hole transport layer ink to completely dry, thereby obtaining a hole transport layer;

[0061] S33, transferring the light-emitting layer ink into the pixel pits of the hole transport layer by a solution method, applying ultrasonic waves to the light-emitting layer ink in the pixel pits, and waiting for the solvent in the light-emitting layer ink to completely dry, thereby obtaining the light-emitting layer;

[0062] S34, transferring electron transport layer ink into the pixel pits of the light-emitting layer by a solution method, applying ultrasonic waves to the electron transport layer ink in the pixel pits, and waiting for the solvent in the electron transport layer ink to completely dry to obtain an electron transport layer;

[0063] S35, forming a cathode on the electron transport layer.

[0064] This embodiment applies ultrasonic waves to each ink in the pixel pit, thereby forming a hole transport layer, a light emitting layer, and an electron transport layer with uniform thickness, so that the pixel points emit light uniformly and the electroluminescent device has a good display effect. This embodiment method is low-cost and simple.

[0065] The relevant details about ultrasound are mentioned above and will not be repeated here.

[0066] An embodiment of the present invention provides an electroluminescent device, wherein the electroluminescent device is prepared using the method for preparing the electroluminescent device described in the embodiment of the present invention.

[0067] In this embodiment, the electroluminescent device can be divided into two types according to the type of luminescent material: organic light emitting diodes and quantum dot light emitting diodes. The specific structure of organic light emitting diodes and quantum dot light emitting diodes and the selection of materials for each layer are prior art and will not be described in detail here.

[0068] The present invention is further described in detail below through specific examples.

[0069] Example 1

[0070] This embodiment provides a method for preparing an inkjet printing film, comprising the following steps:

[0071] (1) Prepare a substrate with pixel pits for inkjet printing;

[0072] (2) using inkjet printing technology to drop ink into pixel pits on the substrate to form ink droplets;

[0073] (3) placing the printed substrate in the ultrasonic generating chamber;

[0074] (4) applying ultrasound to the ink in the pixel pits on the substrate;

[0075] Specifically, the direction of the ultrasonic wave is from top to bottom, facing the top of the pixel pit, and the ultrasonic wave intensity is f = 22kHz, P = 0.4W / cm 2 .

[0076] Example 2

[0077] This embodiment provides a method for preparing an inkjet printing film, comprising the following steps:

[0078] (1) Prepare a substrate with pixel pits for inkjet printing;

[0079] (2) using inkjet printing technology to drop ink into pixel pits on the substrate to form ink droplets;

[0080] (3) placing the printed substrate in the cavity of the ultrasonic generator;

[0081] (4) applying ultrasound to the ink in the pixel pits on the substrate;

[0082] Specifically, the direction of the ultrasonic wave is from top to bottom, facing the top of the pixel pit, and the ultrasonic wave intensity is f = 22kHz, P = 0.4W / cm 2 During the last third of the drying process, the ultrasonic power is gradually increased from P = 0.4 W / cm 2 Reduced to 0;

[0083] (5) Wait for the ink in the pixel pit to dry and form a thin film.

[0084] Example 3

[0085] This embodiment provides a method for preparing an inkjet printing film, comprising the following steps:

[0086] (1) Prepare a substrate with pixel pits for inkjet printing;

[0087] (2) using inkjet printing technology to drop ink into pixel pits on the substrate to form ink droplets;

[0088] (3) placing the printed substrate in the cavity of the ultrasonic generator;

[0089] (4) applying ultrasound to the ink in the pixel pits on the substrate;

[0090] Specifically, the ultrasonic wave is emitted from three directions, namely above, to the left, and to the right of the pixel pit, with an ultrasonic intensity of f = 22kHz and P = 0.4W / cm 2 During the last third of the drying process, the ultrasonic power is gradually increased from P = 0.4 W / cm 2 Reduced to 0;

[0091] (5) Wait for the solution in the pixel pit to dry and form a thin film.

[0092] Comparative Example:

[0093] This comparative example provides a method for treating a solution after inkjet printing, comprising the following steps:

[0094] (1) Prepare a substrate with pixel pits for inkjet printing;

[0095] (2) using inkjet printing technology to drop ink into pixel pits on the substrate to form ink droplets;

[0096] (3) Wait for the ink in the pixel pit to dry and form a thin film.

[0097] In summary, the present invention provides a thin film, an electroluminescent device, and a preparation method thereof. After the ink is transferred to the pixel pit by a solution method, the present invention applies ultrasonic waves to the ink in the pixel pit during the volatilization process of the ink. The ultrasonic waves have a certain amount of energy, which can accelerate the fluidity inside the ink, so that the concentration of the ink in each area of ​​the pixel pit remains relatively consistent during the volatilization process, thereby improving the uniformity of the formed thin film. In addition, the energy possessed by the ultrasonic waves can also increase the internal energy of the ink, increase the volatilization rate of the ink to a certain extent, and avoid the phenomenon of uneven film formed by uneven ink concentration distribution due to the capillary effect of the ink. This method is low-cost and simple in process. There is no need to change the type of solvent. The film can achieve good uniformity by simply adjusting the intensity of the ultrasonic waves.

[0098] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a thin film, characterized in that: Including steps: providing a substrate having pixel pits; Transferring ink into pixel pits on a substrate using a solution method; applying ultrasonic waves to the ink in the pixel pits to obtain the thin film through drying; The step of applying ultrasonic waves to the ink in the pixel pit specifically includes: emitting ultrasonic waves from top to bottom directly above the pixel pit; After applying the ultrasonic wave for a preset time, the intensity of the ultrasonic wave is gradually reduced until the intensity of the ultrasonic wave is zero.

2. The method for preparing a thin film according to claim 1, wherein: The step of applying ultrasonic waves to the ink in the pixel pit is specifically: emitting ultrasonic waves simultaneously from top to bottom, from left to right, and from right to left towards the top, left, and right of the pixel pit.

3. The method for preparing a thin film according to claim 1, wherein: The intensity of the ultrasonic wave: the frequency is 20-24 kHz, the power is 0.2-0.6 W / cm 2 .

4. The method for preparing a thin film according to claim 1, wherein: The total drying time is 20-40 minutes.

5. A film, characterized in that The film is prepared by the method for preparing the film according to any one of claims 1 to 4.

6. A method for preparing an electroluminescent device, characterized in that: Including steps: Providing a preform, wherein the surface of the preform has pixel pits; Transferring the light-emitting layer ink into the pixel pits on the surface of the preform by a solution method, applying ultrasonic waves to the light-emitting layer ink in the pixel pits, and waiting for the solvent in the light-emitting layer ink to completely dry to obtain a light-emitting layer; The step of applying ultrasonic waves to the light-emitting layer ink in the pixel pit specifically includes: emitting ultrasonic waves from top to bottom directly above the pixel pit; After applying the ultrasonic wave for a preset time, the intensity of the ultrasonic wave is gradually reduced until the intensity of the ultrasonic wave is zero.

7. The method for preparing an electroluminescent device according to claim 6, wherein: The preform includes a first electrode and a first functional layer stacked in layers, wherein a surface of the first electrode has pixel pits. The preparation method of the preform includes the following steps: The first functional layer ink is transferred into the pixel pit of the first electrode by a solution method, ultrasonic waves are applied to the first functional layer ink in the pixel pit, and the solvent in the first functional layer ink is completely dried to obtain the first functional layer.

8. The method for preparing an electroluminescent device according to claim 7, wherein: The method for preparing the electroluminescent device further comprises the steps of: Transferring the second functional layer ink into the pixel pits of the light-emitting layer by a solution method, applying ultrasonic waves to the second functional layer ink in the pixel pits, and waiting for the solvent in the second functional layer ink to completely dry, thereby obtaining the second functional layer; The second electrode is formed on the second functional layer.

9. An electroluminescent device, characterized in that The electroluminescent device is prepared by the preparation method of any one of claims 6 to 8.

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