Method for realizing compatible photoetching of quantum dots and commercial photoresist through ligand exchange

Abstract

The invention relates to the technical field of photoelectric materials, particularly discloses a method for improving the stability of perovskite quantum dots through ligand exchange, realizes direct mixing of the perovskite quantum dots and commercial photoresist AZ5214 and simple and efficient patterning, and overcomes the compatibility problem. According to the method, a new ligand n-dodecanethiol is introduced into the CsPbBrI2 quantum dot, and the mercaptan ligand can be bonded to the surface by forming an S-Pb bond to replace a part of original oleic acid and oleylamine ligands, so that the optical performance and the stability of the CsPbBrI2 quantum dot are remarkably improved. After the CsPbBrI2 quantum dots are directly mixed with photoresist, the CsPbBrI2 quantum dots can be prepared through a photoetching process. The quantum dots still maintain excellent luminescence performance in the coating of the photoresist, and can be applied to a color conversion layer of a display.

Description

TECHNICAL FIELD

[0001] The application relates to a patterning method based on a perovskite quantum dot film, and belongs to the technical field of perovskite. BACKGROUND

[0002] Colloidal quantum dots have always been one of the representatives of contemporary high-performance optoelectronic semiconductor materials, among which perovskite quantum dots have entered the field of vision due to their excellent optoelectronic performance, narrow emission spectrum capable of covering the next generation of display standards, adjustable fluorescent spectrum, and super-high photoluminescence quantum yield (PLQY). And most high-tech applications require precise patterning and assembly of quantum dots on solid surfaces and films, one of the most active research application fields is display, which requires various patterned quantum dot film forms to replace traditional color filters.

[0003] Mixing perovskite quantum dots with current mature commercial photoresist and using photolithography process is considered to be one of the best solutions to realize patterning, which perfectly adapts to the current market demand for mass production. However, when photolithography process is applied to perovskite quantum dot patterning, the ionic bond of perovskite structure is easily affected by chemicals, and most solvents of photoresist will have a negative effect on the surface ligand of quantum dots. After mixing ordinary perovskite quantum dots with photoresist, the original excellent luminescent performance will be directly lost, which greatly limits the development of perovskite quantum dot patterning.

[0004] Current research mainly focuses on isolating photoresist from perovskite quantum dots by adding an isolation layer or coating the quantum dots. The above two methods have indeed achieved certain results, but the steps are too cumbersome. Therefore, the most effective method is to regulate the stability of perovskite quantum dots during synthesis, so that they can be directly mixed with photoresist for subsequent photolithography process.

[0005] Direct mixing of perovskite quantum dots and photoresist can solve a series of complex process problems. The two main components after mixing of quantum dot photoresist play an indispensable role in display devices: quantum dots are the core of light emission, responsible for high optical performance, while photoresist serves as an auxiliary material, with functions such as patterning performance and protection of quantum dot optical performance. If successful, the development of photo patterning can enter a new stage. SUMMARY

[0006] The purpose of the present application is to provide a method for solving the compatibility problem of high-performance perovskite quantum dots and mature commercial photoresist. The method improves the stability of perovskite quantum dots through a simple and efficient ligand exchange method, and mixed with commercial photoresist can be patterned according to standard photolithography process, and is used for the preparation of display device color conversion film.

[0007] A method for making quantum dots compatible with commercial photoresist lithography by ligand exchange, comprising the following steps:

[0008] Step 1: adding n-dodecanethiol to the crude solution of CsPbBrI2 quantum dots for ligand exchange and centrifugal purification;

[0009] Step 2: uniformly mixing the obtained quantum dots with AZ5214 photoresist, spin coating to prepare a thin film and drying;

[0010] Step 3: performing high-energy ultraviolet (365 nm) lithography on the thin film under a mask, developing and blowing dry after lithography, and finally the pattern part is left;

[0011] Step 4: using the obtained pattern film as a color conversion layer to light up a blue backlight LED device.

[0012] Preferably, in step 1, in order to ensure the luminescent efficiency of the quantum dots, the molar ratio of (oleic acid + oleylamine) : n-dodecanethiol is (3.3-16.7) : 1.

[0013] Preferably, in step 1, the solvent of the perovskite quantum dot solution is toluene, and the concentration of the perovskite quantum dots is 0.045 mmol / ml.

[0014] Preferably, in step 2, the obtained CsPbBrI2 quantum dots are uniformly mixed with the photoresist, spin coating to prepare a single-layer thin film or not mixing to prepare a two-layer thin film for lithography.

[0015] Preferably, in step 2, the volume ratio of quantum dots to photoresist is 1:2.

[0016] Preferably, in step 2, the thin film is solidified by high-temperature heating, the drying temperature is selected to be 60-180℃, and the heating time is 1-5 minutes.

[0017] Preferably, in step 3, the thickness of the lithographic film is 4-15 μm, and the exposure time is 8-20 seconds.

[0018] Preferably, in step 4, a 530±10 nm narrow-band filter is used to filter out the blue backlight.

[0019] The principle of the present application is that the present application is based on the preparation of CsPbBrI2 quantum dots by hot injection method, by adding n-dodecanethiol ligand in the obtained quantum dot solution, and reasonably adjusting the proportion to realize the successful exchange of the original oleylamine and oleic acid ligand of CsPbBrI2 quantum dots. The introduced n-dodecanethiol ligand can be combined to the surface by forming S-Pb bond, repairing the surface defects of quantum dots, effectively reducing the defect states in quantum dots, improving the radiation recombination ratio, and further improving the luminescence performance and stability of CsPbBrI2 quantum dots. The CsPbBrI2 quantum dots after ligand exchange are mixed into AZ5214 commercial photoresist, and the quantum dots still maintain excellent luminescent performance due to its high stability, and the photoresist is exposed by the mask plate during photoetching, the organic solvent molecular chain in the exposed area is broken, the solubility changes, and the photoresist can be washed away by the developer, and the quantum dots coated in the photoresist are also washed away, achieving the effect of patterning. The obtained pattern film is successfully lit as a color conversion layer on a backlight device.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] (1) The present application successfully solves the compatibility problem of CsPbBrI2 quantum dots and mature and widely used commercial AZ5214 positive photoresist by specific dodecanethiol ligand exchange treatment. Without developing or customizing a special photoresist formula, the existing mature photoetching process and equipment of the semiconductor and display industry can be directly used, which significantly reduces the process complexity, research and development cost and industrialization threshold.

[0022] (2) The ligand exchange strategy of the present application can effectively passivate the surface defects of CsPbBrI2 quantum dots while realizing compatibility with photoresist, improve the luminescent performance of CsPbBrI2 quantum dots, and ensure the high luminescent efficiency of the subsequent color conversion layer.

[0023] (3) The quantum dots after ligand exchange of the present application are uniformly dispersed and have good stability in the photoresist solvent system, avoiding agglomeration or precipitation, which is a key prerequisite for obtaining high-quality, uniform film and fine pattern.

[0024] (4) The quantum dot pattern obtained after development of the present application has sharp edges, good morphology and high contrast with the substrate, and there is no residual quantum dot in the developed area.

[0025] (5) Compared with one-step preparation of quantum dot photoresist, the mixing process of quantum dots and photoresist has high flexibility, and both of them can be adjusted individually to achieve the best performance.

[0026] Therefore, the above-mentioned functionalized quantum dot photoresist composite photoetching system paves the way for the large-scale, low-cost integrated application of perovskite quantum dots in the next generation of displays. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0028] Figure 1 This is a schematic diagram of the ligand exchange process of CsPbBrI2 quantum dots.

[0029] Figure 2 Comparison of photoluminescence spectra of CsPbBrI2 quantum dot solutions with different volumes of n-dodecyl mercaptan ligand.

[0030] Figure 3 TEM images and grain statistics of CsPbBrI2 quantum dots after ligand exchange.

[0031] Figure 4 This is a schematic diagram of the photolithography patterning process.

[0032] Figure 5 This is a TEM image of CsPbBrI2 quantum dots after ligand exchange mixed with photoresist.

[0033] Figure 6 The image and luminescence intensity of the ligand-exchanged quantum dots and the thin film prepared by mixing untreated quantum dots with photoresist are compared under ultraviolet light.

[0034] Figure 7 Images of photolithographic films prepared by spin coating (a) two layers and (b) one layer under a fluorescence microscope.

[0035] Figure 8 The graph shows the decay of luminescence intensity of quantum dot photoresist films at different temperatures.

[0036] Figure 9 This is an image of the patterned film obtained by photolithography under ultraviolet light.

[0037] Figure 10 Images of patterned films obtained by photolithography with different film thicknesses and exposure times under ultraviolet light.

[0038] Figure 11 This describes the structure of an LED device used for lighting.

[0039] Figure 12 (a) The blue backlight illumination pattern of the LED device, and (b) The final display effect of using the patterned film obtained by photolithography as the color conversion layer. Detailed Implementation

[0040] The present application will be further clarified by the following examples which are intended to be purely exemplary of the present application. It is to be understood that the examples are not intended to limit the scope of the present application. Various modifications of the application in accordance with the application, as can be, will be apparent to those skilled in the art, upon reference to the description of the application which follows.

[0041] It should be noted that the terms such as "upper", "lower", "left", "right", "intermediate" and the like as cited in the present specification are merely intended for clear and succinct description and are not intended to limit the range of implementation, and any change in relative relationship or adjustment without substantial change in technical content is also regarded as the scope of implementation of the present application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0043] Unless otherwise specified, the specific conditions in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0044] As used herein, the term "about" is used to provide flexibility to a given term, measurement, or value associated with a given term, measurement, or value. The degree of flexibility of a particular variable can be readily determined by one skilled in the art.

[0045] As used herein, the term "at least one of" is intended to mean one or more of the listed items. For example, "at least one of A, B, and C" includes only A, only B, only C, and combinations thereof.

[0046] The present application optimizes the preparation process, introduces a new ligand into the CsPbBrI2 quantum dots with poor stability, replaces part of the original ligand, realizes stable luminescence and better luminescence performance. Using the ligand exchange treatment method, the CsPbBrI2 quantum dots are successfully mixed with commercial photoresist, and the standard process is carried out for photoetching, and a pattern film for color conversion layer is obtained.

[0047] Examples

[0048] A method for making quantum dots compatible with commercial photoresist for photoetching by ligand exchange, the specific steps are as follows:

[0049] Step 1: Synthesis of CsPbBrI2 quantum dots and ligand exchange, the specific steps are as follows:

[0050] Step 1.1: 1.5 mL of oleic acid, 15 mL of octadecene and 0.36 g of cesium carbonate were mixed and stirred under argon protection, and heated to 150°C to completely dissolve to obtain a cesium oleate solution.

[0051] Step 1.2: 0.1675 g of lead iodide, 0.0667 g of lead bromide, and 1.5 mL of oleic acid, 1.5 mL of oleylamine, 15 mL of octadecene were mixed and stirred under argon protection, and the molar ratio of lead iodide to lead bromide was 2:1.

[0052] Step 1.3: After heating to 120°C for 5 minutes, continue to heat to 160°C for 5 minutes to obtain a precursor solution, then quickly inject 1.5 mL of the previously heated to 140°C cesium oleate solution into the precursor solution, and after 5 seconds of reaction, the reaction container is placed in ice water to cool to room temperature to obtain a crude quantum dot solution.

[0053] Step 1.4: 60 μL of n-dodecanethiol solution was added to the crude quantum dot solution, and stirred for 10 min to mix evenly, and the ligand exchange process and ligand chemical structure were as follows Figure 1 .

[0054] Step 1.5: 40 mL of ethyl acetate was added to the crude quantum dot solution, and after mixing evenly, it was placed in a centrifuge with a speed of 10,000 revolutions per minute for 1 min for centrifugation. After centrifugation, the supernatant was removed, and the obtained precipitate was dispersed in 4 mL of toluene, and then placed in a centrifuge with a speed of 8,000 revolutions per minute for 2 minutes for centrifugation.

[0055] Step 1.6: After centrifugation, the supernatant was retained in a sample bottle, which was the CsPbBrI2 quantum dot solution after ligand exchange.

[0056] The above steps were repeated to prepare CsPbBrI2 quantum dots, with the difference being that 20 μL, 100 μL of n-dodecanethiol was added in step 1.4 for ligand exchange, and no n-dodecanethiol was added. By comparing the photoluminescence intensity of the quantum dots (as shown in Figure 2 ), it can be found that the luminescence intensity of the quantum dots after ligand exchange is significantly improved. This is because the introduced n-dodecanethiol ligand can be combined to the surface by forming S-Pb bonds, repairing the surface defects of the quantum dots, and effectively reducing the defect states in the quantum dots. By comparing different amounts of addition, it is found that the best amount of n-dodecanethiol ligand added is 60 μL, at which the fluorescence intensity is the highest. Excessive n-dodecanethiol ligand leads to a decrease in luminescence intensity due to the distortion of the crystal structure induced by excessive n-dodecanethiol ligand, and the generation of non-luminescent phase. Therefore, the quantum dots used in the subsequent steps are the quantum dots with the ligand added in the amount of 60 μL.

[0057] The CsPbBrI2 quantum dots obtained after ligand exchange were observed under a transmission electron microscope (as shown inFigure 3 ), it was found that the average size of the quantum dots was 9.34 nm, the particle consistency was high, and the particle size of most products was between 6-12 nm, meeting the use requirements.

[0058] Step 2: After uniformly mixing the obtained quantum dots with AZ5214 photoresist, spin coating was performed to prepare a thin film and drying was performed, and the flow chart was as shown in Figure 4 , and the specific steps were as follows:

[0059] Step 2.1: 1 ml of quantum dots and 2 ml of AZ5214 photoresist were taken into a sample bottle, and stirring was performed for 5 min under light shielding to uniformly mix. The TEM image of the mixed quantum dot photoresist compound was as shown in Figure 5 , the quantum dots were still arranged in order in the photoresist, and the lattice stripes were still visible under high resolution, indicating that the photoresist did not cause serious damage to the performance of the CsPbBrI2 quantum dots.

[0060] Step 2.2: The parameters of the spin coater were set, including a rotation speed of 800 rpm and a time of 45 s. The quartz glass substrate was placed on the spin coater rotor using tweezers, the spin coater suction button was turned on, and the quartz glass substrate was adsorbed on the rotor. 150 μL of the quantum dot photoresist compound was quickly dropped on the quartz glass substrate using a pipette, and the spin coater button was quickly turned on to make the rotor quickly rotate to form a film. Compared with the prepared thin film without ligand exchange (as shown in Figure 6 ), the luminescence intensity of the untreated quantum dots was seriously reduced and was seriously damaged, and the surface uniformity was poor, while the luminescence intensity of the quantum dots prepared by the ligand exchange was better.

[0061] Compared with the spin coating of the quantum dots and the photoresist separately, two layers of films were prepared (as shown in Figure 7 a), under the fluorescence microscope, the quantum dots were observed to have agglomeration, and the luminescence intensity in some areas was weakened, which was due to the fact that the surface of the quantum dots was directly in contact with water oxygen in the air during the spin coating process, causing damage. After uniformly mixing the quantum dots with the photoresist, only one layer of film was prepared, and since the photoresist separated the quantum dots from the external environment, the quantum dots were not easily damaged by water oxygen and other environmental factors, and the prepared thin film was more uniform under the fluorescence microscope (as shown in Figure 7 b).

[0062] Step 2.3: The quantum dot photoresist film obtained in step 2.2 was dried on a heating table, and the parameters were set to 120°C and 2 min. As shown in Figure 8 , the luminescence performance test of the quantum dot photoresist film was performed at different temperatures, and it was found that the luminescence intensity did not decrease significantly at 120°C, and the luminescence intensity decreased significantly after 150°C, and therefore, drying was performed at 120°C.

[0063] Step 3: The film was exposed to high-energy UV (365 nm) light under a mask, and after exposure, the film was developed and blown dry, and finally the pattern part was reserved. The specific steps are as follows:

[0064] Step 3.1: The film of the cured quantum dot photoresist was placed under a mask and exposed to high-energy UV (365 nm) light for 14 seconds,

[0065] Step 3.2: After exposure, the film was developed with ZX-238 developer for 45-60 seconds, then washed with deionized water and blown dry. The obtained pattern film is shown in Figure 9 The pattern has good luminescence, high clarity, clear edges, and no residual quantum dots.

[0066] The thickness of the photoresist film and the exposure time are important factors affecting the clarity of the photoresist pattern. As shown in Figure 10 , if the UV exposure time is insufficient (8 seconds), the photoresist reaction is incomplete, and part of the pattern will leave some photoresist that cannot be washed away by development; if the exposure time is too long (20 seconds), the luminescence intensity of the pattern part decreases, resulting in poor uniformity of the film luminescence, and the photoresist is more easily washed away under the condition of overexposure, and a complete pattern cannot be obtained. The thickness of the film affects the adhesion of the quantum dot photoresist to the substrate. When the thickness is less than 10 μm, the adhesion to the substrate is poor, and the developed photoresist pattern is not clear; when the thickness is too large, excess photoresist will be left. The optimal photoresist parameters are a film thickness of 11 μm and an exposure time of 14 s, which can obtain the clearest pattern.

[0067] Step 4: The obtained pattern film was used as a color conversion layer on a blue backlight LED device, and the device structure is shown in Figure 11 The specific steps are as follows:

[0068] Step 4.1: Turn on the power supply and light up the blue backlight LED chip (such as Figure 12 a).

[0069] Step 4.2: The pattern film obtained in step 3.2 was used as a color conversion layer on a blue backlight.

[0070] Step 4.3: A 530±10 nm narrow-band filter was used to filter the pattern in step 2, and the blue backlight with a wavelength not in the range of 530±10 nm was filtered out. The actual effect diagram obtained by shooting is shown in 12b.

Claims

1. A method for photolithography that enables quantum dots to be compatible with commercial photoresists through ligand exchange, characterized in that, Specifically, the following steps are included: Step 1: Add n-dodecyl mercaptan to the crude CsPbBrI2 quantum dot solution for ligand exchange, followed by centrifugation for purification; Step 2: The obtained quantum dots are uniformly mixed with AZ5214 photoresist, then spin-coated to prepare a thin film and dried. Step 3: The thin film is subjected to high-energy ultraviolet 365nm photolithography under a photomask. After photolithography, it is developed and dried, and the patterned part is retained. Step 4: Use the obtained patterned film as a color conversion layer to illuminate the blue backlight LED device.

2. The method as described in claim 1, characterized in that, In step 1, in order to ensure the luminescence efficiency of quantum dots, the molar ratio is (oleic acid + oleylamine): n-dodecyl mercaptan = (3.3-16.7):

1.

3. The method as described in claim 1, characterized in that, In step 1, the solvent for the perovskite quantum dot solution is toluene, and the concentration of the perovskite quantum dots is 0.045 mmol / ml.

4. The method as described in claim 1, characterized in that, In step 2, the obtained CsPbBrI2 quantum dots are uniformly mixed with photoresist and then spin-coated to prepare a single-layer film.

5. The method as described in claim 1, characterized in that, In step 2, the volume ratio of quantum dots to photoresist is 1:

2.

6. The method as described in claim 1, characterized in that, In step 2, the film is cured by high-temperature heating. The drying temperature is selected as 60-180℃ and the heating time is 1-5 minutes.

7. The method as described in claim 1, characterized in that, In step 3, the photolithography film thickness is 4-15 μm, and the exposure time is 8-20 seconds.

8. The method as described in claim 1, characterized in that, In step 4, a 530±10nm narrowband filter is used to filter out the blue backlight.

Images