Lead salt quantum dot ink and preparation method thereof

Abstract

The invention provides lead salt quantum dot ink and a preparation method thereof. The preparation method comprises the following steps: preparing a sulfur-containing additive solution; carrying out ligand exchange on the lead salt quantum dots wrapped by the long-carbon-chain oil-phase organic ligands to obtain lead salt quantum dot powder wrapped by short-chain halogen ligands; and after the lead salt quantum dot powder wrapped by the short-chain halogen ligand is prepared, adding the sulfur-containing additive solution into the lead salt quantum dot powder wrapped by the short-chain halogen ligand within 3 minutes, and dissolving to obtain the lead salt quantum dot ink. According to the lead salt quantum dot ink prepared through the preparation method, the stability of the lead salt quantum dot ink can be maintained, meanwhile, residues of ligands in the lead salt quantum dot ink are reduced, the film forming property of the lead salt quantum dot ink is improved, and the film surface defect of a quantum dot film is reduced.

Description

Technical Field

[0001] This application relates to the field of quantum dot ink technology, and in particular to a lead salt quantum dot ink and its preparation method. Background Technology

[0002] Currently, the mainstream synthesis method for lead salt quantum dots encapsulated by long-chain oil-phase organic ligands is the hot-injection method. This involves synthesizing a long-chain coordinated lead precursor in the presence of long-chain organic ligands (hereinafter referred to as oil-soluble ligands), followed by the injection of active materials containing sulfur (S) and selenium (Se). Due to the presence of numerous long carbon chains in the reaction system, the generated quantum dots are encapsulated by the oil-soluble ligands. Because of the large chain length and significant steric hindrance between the oil-soluble ligands, the quantum dots are kept apart, resulting in a large inter-dot distance and reducing the likelihood of collisions and aggregation. However, the charge carriers generated by the excited quantum dots are also difficult to transport, leading to poor conductivity. Therefore, although lead salt quantum dots encapsulated by oil-soluble ligands possess good stability and are easy to store and transport, they are difficult to directly apply in actual device manufacturing.

[0003] Quantum dot materials synthesized by hot-injection polymerization often have oil-soluble organic compounds (such as oleic acid and oleylamine ligands) adhering to their surfaces. To reduce the spacing between quantum dots, ligand exchange processes are typically used to replace these oil-soluble ligands with halide ion ligands (such as PbI₂, PbBr₂, and PbCl₂) to increase their conductivity in optoelectronic devices. However, ligand exchange processes can result in excessive residual PbI₂, PbBr₂, and other ligands, which cannot be effectively removed during purification. During the fabrication of optoelectronic devices, residual ligands precipitate out during spin-coating and drying, generating a large number of solid particles that disrupt the uniformity of the quantum dot film, causing defects and affecting device performance. Furthermore, quantum dot inks typically have poor stability and tend to agglomerate under common process conditions (such as 25°C and 40±10% relative humidity), forming a jelly-like colloid that is unsuitable for device fabrication. Summary of the Invention

[0004] The purpose of this application is to provide a lead salt quantum dot ink and its preparation method, so as to ensure the stability of the lead salt quantum dot ink, reduce the residual ligands in the lead salt quantum dot ink, improve the film-forming properties of the lead salt quantum dot ink, and reduce the surface defects of the quantum dot film. The specific technical solution is as follows:

[0005] The first aspect of this application provides a method for preparing lead salt quantum dot ink, comprising the following steps:

[0006] Prepare a sulfur-containing additive solution; the sulfur-containing additive is selected from at least one of thiourea, methylthiourea, diphenylthiourea, pyridylthiourea, dimethylthiourea, polythiourea, elemental sulfur, carbon disulfide, and sodium sulfide;

[0007] Lead salt quantum dots encapsulated with long-chain oil-phase organic ligands were exchanged to obtain lead salt quantum dot powder encapsulated with short-chain halogen ligands.

[0008] After obtaining the lead salt quantum dot powder coated with the short-chain halogen ligand, the sulfur-containing additive solution is added to the lead salt quantum dot powder coated with the short-chain halogen ligand within 3 minutes to dissolve and obtain the lead salt quantum dot ink.

[0009] In one embodiment, the preparation step of the sulfur-containing additive solution includes: dispersing the sulfur-containing additive in a first organic solvent, filtering after uniform dispersion to obtain the sulfur-containing additive solution; the molar amount of the sulfur-containing additive to the volume ratio of the first organic solvent is 0.01-1 mmol: 200-1500 μL, and the first organic solvent is selected from at least one of N,N-dimethylformamide (DMF), methanol, ethylene glycol, dimethyl sulfoxide, aniline, butylamine, methylamine, and benzyl alcohol (BA).

[0010] In one embodiment, the first organic solvent is a mixed solution of N,N-dimethylformamide and benzyl alcohol, wherein the volume ratio of N,N-dimethylformamide to benzyl alcohol is 1:1 to 1:12.

[0011] In one embodiment, the uniform dispersion includes vortexing and ultrasonic dispersion for 10-20 minutes.

[0012] In one embodiment, the mass-to-volume ratio of the lead salt quantum dot powder encapsulated by the short-chain halogen ligand to the sulfur-containing additive solution is 60-80 mg: 200-1500 μL.

[0013] In one embodiment, the ligand exchange step includes: adding a second organic solvent containing lead salt quantum dots coated with the long-chain oil-phase organic ligand to a first solution containing PbI2, PbBr2, and NH4Ac, shaking vigorously, and separating the layers; taking the lower layer solution for extraction, purification, and separation to obtain lead salt quantum dot powder coated with the short-chain halogen ligand;

[0014] The mass ratio of the lead salt quantum dots encapsulated by the long-chain oil-phase organic ligand, the volume of the second organic solvent, the mass of PbI2, the mass of PbBr2, the mass of NH4Ac, to the volume of the solvent in the first solution is 100mg: 20-100mL: 2.3-6.9g: 0.73-2.19g: 0.05-0.20g: 20-80mL;

[0015] The second organic solvent is selected from at least one of n-hexane, n-octane, and n-heptane;

[0016] The solvent of the first solution is selected from at least one of N,N-dimethylformamide, methanol, ethylene glycol, dimethyl sulfoxide, aniline, butylamine, and methylamine.

[0017] In one embodiment, the extraction, purification, and separation of the lower layer solution includes: extracting the lower layer solution with a third organic solvent 2-4 times, then purifying it with a fourth organic solvent, and performing solid-liquid separation.

[0018] The third organic solvent and the fourth organic solvent are each independently selected from at least one of isopentane, n-pentane, n-hexane, cyclohexane, n-octane, trifluoroacetic acid, n-heptane, cycloheptane, and toluene.

[0019] In one embodiment, the solid-liquid separation is centrifugal separation.

[0020] In one embodiment, the dissolving step includes shaking for 1-3 minutes, vortexing for 3-5 minutes, and sonicating for 1-3 minutes.

[0021] The second aspect of this application provides a lead salt quantum dot ink prepared according to the preparation method provided in the first aspect of this application.

[0022] The third aspect of this application provides a method for preparing a quantum dot film, which uses lead salt quantum dot ink prepared according to the preparation method provided in the first aspect of this application, and coats the quantum dot film within 30 minutes after the lead salt quantum dot ink is prepared to obtain the quantum dot film.

[0023] The fourth aspect of this application provides a quantum dot thin film prepared according to the preparation method provided in the third aspect of this application.

[0024] The beneficial effects of this application are:

[0025] This application provides a lead salt quantum dot ink and its preparation method. The preparation method includes: preparing a sulfur-containing additive solution; exchanging lead salt quantum dots coated with long-chain oil-phase organic ligands to obtain lead salt quantum dot powder coated with short-chain halogen ligands; after obtaining the lead salt quantum dot powder coated with short-chain halogen ligands, adding the sulfur-containing additive solution to the lead salt quantum dot powder coated with short-chain halogen ligands within 3 minutes to dissolve it, thereby obtaining the lead salt quantum dot ink. The lead salt quantum dot ink prepared by the method of this application can maintain the stability of the lead salt quantum dot ink, while reducing the residual ligands in the lead salt quantum dot ink, improving the film-forming properties of the lead salt quantum dot ink, reducing the film surface defects of the quantum dot film, and thus improving the quality of the quantum dot film.

[0026] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0028] Figure 1A An optical microscope image of the quantum dot film in Example 1;

[0029] Figure 1B An optical microscope image of the quantum dot thin film in Comparative Example 1;

[0030] Figure 1C Comparative Example 2: Optical microscope image of quantum dot thin film;

[0031] Figure 2A An atomic force microscope image of the quantum dot film in Example 1;

[0032] Figure 2B An atomic force microscope image of the quantum dot thin film in Comparative Example 1;

[0033] Figure 3A Orthogonal photographs of the lead salt quantum dot ink prepared for Example 1 placed under common process conditions (25°C, relative humidity 40±10%) for 0 minutes and 3 hours.

[0034] Figure 3B Inverted photographs of the lead salt quantum dot ink prepared for Example 1 after being placed under common process conditions (25°C, relative humidity 40±10%) for 0 minutes and 3 hours.

[0035] Figure 4A An optical microscope image of a quantum dot film obtained by spin coating after the lead salt quantum dot ink prepared for Example 1 was placed under common process conditions (25°C, relative humidity 40±10%) for 0 minutes.

[0036] Figure 4B An optical microscope image of a quantum dot film obtained by spin coating after the lead salt quantum dot ink prepared for Example 1 was placed under common process conditions (25°C, relative humidity 40±10%) for 30 minutes.

[0037] Figure 4C An optical microscope image of a quantum dot film obtained by spin coating after the lead salt quantum dot ink prepared for Example 1 was placed under common process conditions (25°C, relative humidity 40±10%) for 60 minutes.

[0038] Figure 4DAn optical microscope image of the quantum dot film obtained by spin coating after the lead salt quantum dot ink prepared in Example 1 was placed under common process conditions (25°C, relative humidity 40±10%) for 3 hours.

[0039] Figure 5 The images show the lead salt quantum dot powder coated with short-chain halogen ligands prepared in Example 1 after being placed under common process conditions (25°C, relative humidity 40±10%) for 0 minutes and 30 minutes, respectively, and then after the addition of sulfur-containing additive solutions. Detailed Implementation

[0040] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0041] The first aspect of this application provides a method for preparing lead salt quantum dot ink, comprising the following steps:

[0042] Prepare a sulfur-containing additive solution; the sulfur-containing additive is selected from at least one of thiourea, methylthiourea, diphenylthiourea, pyridylthiourea, dimethylthiourea, polythiourea, elemental sulfur, carbon disulfide, and sodium sulfide;

[0043] Lead salt quantum dots encapsulated with long-chain oil-phase organic ligands were exchanged to obtain lead salt quantum dot powder encapsulated with short-chain halogen ligands.

[0044] After obtaining the lead salt quantum dot powder coated with the short-chain halogen ligand, the sulfur-containing additive solution is added to the lead salt quantum dot powder coated with the short-chain halogen ligand within 3 minutes to dissolve and obtain the lead salt quantum dot ink.

[0045] This application incorporates a sulfur-containing additive during the preparation of lead-salt quantum dot ink. This additive reacts with excess ligand residues such as PbI2 and PbBr2 generated during ligand exchange. The sulfur-containing additive solution is added to lead-salt quantum dot powder coated with short-chain halogen ligands. The sulfur-containing additive releases sulfur ions and simultaneously reacts to generate a small amount of PbS quantum dots. This innovative process converts residual ligands into quantum dots, allowing them to participate normally in the film formation process. This eliminates surface defects in quantum dot films caused by the precipitation of residual ligands in existing processes and removes the impact of residual ligands on the performance of optoelectronic devices. Furthermore, this application limits the process time for using the short-chain halogen ligand-coated lead-salt quantum dot powder obtained after the ligand exchange process to prepare lead-salt quantum dot ink, preventing the powder from failing to disperse properly in the sulfur-containing additive solution and causing significant sedimentation. The lead salt quantum dot ink prepared by the method of this application reduces the residual ligands in the lead salt quantum dot ink, improves the film-forming properties of the lead salt quantum dot ink, reduces the surface defects of the quantum dot film, and at the same time ensures the stability of the lead salt quantum dot ink.

[0046] In one embodiment, the preparation step of the sulfur-containing additive solution includes: dispersing the sulfur-containing additive in a first organic solvent, filtering after uniform dispersion to obtain the sulfur-containing additive solution; the molar amount of the sulfur-containing additive to the volume ratio of the first organic solvent is 0.01-1 mmol: 200-1500 μL, and the first organic solvent is selected from at least one of N,N-dimethylformamide, methanol, ethylene glycol, dimethyl sulfoxide, aniline, butylamine, methylamine, and benzyl alcohol. For example, the molar amount of the sulfur-containing additive can be 0.01 mmol, 0.05 mmol, 0.1 mmol, 0.3 mmol, 0.5 mmol, 0.6 mmol, 0.8 mmol, 1 mmol, or a range of any two of these values; the volume of the first organic solvent can be 200 μL, 300 μL, 400 μL, 500 μL, 600 μL, 700 μL, 800 μL, 900 μL, 1000 μL, 1100 μL, 1200 μL, 1300 μL, 1400 μL, 1500 μL, or a range of any two of these values.

[0047] In one embodiment, the first organic solvent is a mixed solution of N,N-dimethylformamide and benzyl alcohol, wherein the volume ratio of N,N-dimethylformamide to benzyl alcohol is 1:1 to 1:12. For example, the volume ratio can be 1:1, 1:2, 1:3, 1:5, 1:6, 1:8, 1:10, 1:12, or a range of any two of these values.

[0048] In one embodiment, the uniform dispersion includes vortexing and ultrasonic dispersion for 10-20 minutes; the filtration uses a 0.22 μm filter membrane. For example, the ultrasonic dispersion time can be 10 minutes, 15 minutes, 20 minutes, or a range of any two of these values.

[0049] In one embodiment, the mass-to-volume ratio of the lead salt quantum dot powder encapsulated by the short-chain halogen ligand to the sulfur-containing additive solution is 60-80 mg: 200-1500 μL. For example, the mass-to-volume ratio can be 60 mg: 200 μL, 60 mg: 500 μL, 60 mg: 800 μL, 60 mg: 1000 μL, 60 mg: 1200 μL, 60 mg: 1500 μL, 80 mg: 200 μL, 80 mg: 500 μL, 80 mg: 800 μL, 80 mg: 1000 μL, 80 mg: 1200 μL, 80 mg: 1500 μL, or a range consisting of any two of these values.

[0050] In one embodiment, the ligand exchange step includes: adding a second organic solvent containing lead salt quantum dots encapsulated by the long-chain oil-phase organic ligand to a first solution containing PbI2, PbBr2, and NH4Ac, shaking vigorously to separate the layers; taking the lower layer solution for extraction, purification, and separation to obtain lead salt quantum dot powder encapsulated by the short-chain halogen ligand; the mass ratio of the lead salt quantum dots encapsulated by the long-chain oil-phase organic ligand, the volume of the second organic solvent, the mass of PbI2, the mass of PbBr2, the mass of NH4Ac, to the volume of the solvent in the first solution is 100mg: 20-100mL: 2.3-6.9g: 0.73-2.19g: 0.05-0.20g: 20-80mL; the second organic solvent is selected from at least one of n-hexane, n-octane, and n-heptane; the solvent of the first solution is selected from at least one of N,N-dimethylformamide, methanol, ethylene glycol, dimethyl sulfoxide, aniline, butylamine, and methylamine. For example, the volume of the second organic solvent can be 20 mL, 30 mL, 50 mL, 60 mL, 70 mL, 80 mL, 90 mL, 100 mL, or any combination of two such values; the volume of the first solution can be 20 mL, 30 mL, 40 mL, 50 mL, 60 mL, 70 mL, 80 mL, or any combination of two such values; the mass of PbI2 can be 2.3 g, 3 g, 4 g, 5 g, 6 g, 6.9 g, or any combination of two such values; the mass of PbBr2 can be 0.73 g, 1 g, 1.2 g, 1.5 g, 1.7 g, 2.0 g, 2.19 g, or any combination of two such values; and the mass of NH4Ac can be 0.05 g, 0.08 g, 0.1 g, 0.13 g, 0.15 g, 0.18 g, 0.2 g, or any combination of two such values. In one embodiment, the extraction, purification, and separation of the lower layer solution includes: extracting the lower layer solution 2-4 times with a third organic solvent, then purifying it with a fourth organic solvent, and performing solid-liquid separation; the third and fourth organic solvents are each independently selected from at least one of isopentane, n-pentane, n-hexane, cyclohexane, n-octane, trifluoroacetic acid, n-heptane, cycloheptane, and toluene. For example, the number of extractions can be 2, 3, or 4. In this application, ligand exchange is based on the different solubilities of quantum dots with different ligands in different solvents. Through ligand exchange, quantum dots undergo phase transfer between immiscible solvents of different polarities, thereby extracting quantum dots with different ligands.As described in this application, lead salt quantum dots encapsulated by long-chain oil-phase organic ligands are dispersed in nonpolar solvents such as n-hexane, n-octane, and n-heptane, and then mixed with a solution containing halogen ligands such as DMF. During the process, the halogen ligands in the polar solvent solution replace the oil-soluble ligands and promote the lead salt quantum dots encapsulated by short-chain halogen ligands to enter the polar solvent solution. Since the nonpolar solvent and the polar solvent are immiscible, the mixed solution will separate into layers (phase separation) after standing. The lead salt quantum dots encapsulated by short-chain halogen ligands enter the polar solvent phase, realizing ligand exchange.

[0051] In one embodiment, the solid-liquid separation is centrifugal separation.

[0052] In one embodiment, the preparation steps of the first solution include: adding PbI2, PbBr2, and NH4Ac to the solvent of the first solution, heating to 50-70°C and stirring for 10-20 minutes, and then cooling to room temperature to obtain the first solution.

[0053] In one embodiment, the dissolving step includes shaking for 1-3 minutes, vortexing for 3-5 minutes, and sonication for 1-3 minutes. For example, the shaking time can be 1 minute, 2 minutes, 3 minutes, or a range of any two of these values; the vortexing time can be 3 minutes, 4 minutes, 5 minutes, or a range of any two of these values; and the sonication time can be 1 minute, 2 minutes, 3 minutes, or a range of any two of these values.

[0054] In one embodiment, the long-chain oil-phase organic ligand encapsulated in the lead salt quantum dots is at least one of oleic acid and oleylamine. This application does not particularly limit the source of the lead salt quantum dots encapsulated in the long-chain oil-phase organic ligand, as long as it achieves the purpose of this application; for example, it can be commercially available.

[0055] The second aspect of this application provides a lead salt quantum dot ink prepared according to the preparation method provided in the first aspect of this application.

[0056] The third aspect of this application provides a method for preparing a quantum dot film, which uses lead salt quantum dot ink prepared according to the preparation method provided in the first aspect of this application, and coats the quantum dot film within 30 minutes after the lead salt quantum dot ink is prepared to obtain the quantum dot film.

[0057] The fourth aspect of this application provides a quantum dot thin film prepared according to the preparation method provided in the third aspect of this application.

[0058] The fifth aspect of this application provides an optoelectronic device comprising the quantum dot thin film provided in the fourth aspect of this application.

[0059] This application does not impose a particular limitation on the thickness of the quantum dot film, as long as it achieves the purpose of this application; in one embodiment, the thickness of the quantum dot film can be 100-400 nm. For example, the thickness of the quantum dot film can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, or a range of any two values ​​therein.

[0060] Test methods and equipment:

[0061] Roughness test:

[0062] The quantum dot film was characterized using the tapping mode of an atomic force microscope (AFM, Bruker, Dimension Icon). The surface condition of the quantum dot film was observed, and the spm data generated by the AFM test was imported into the NanoScope Analysis software of the instrument for analysis. The software directly displayed the roughness data Rq of the 20μm×20μm measured area.

[0063] Example

[0064] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were performed according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality bases. The term "about" is defined as close to as understood by those skilled in the art. In a non-limiting embodiment, this term is defined as less than 10%, preferably less than 5%, more preferably less than 1%, and even more preferably less than 0.5%.

[0065] Example 1

[0066] Take 0.06 mmol of sulfur-containing additive diphenylthiourea and mix it thoroughly with 300 μL of a mixed solution of DMF and BA (DMF to BA volume ratio 1:3). Vortex and ultrasonically disperse for 15 min. After uniform dispersion, filter through a 0.22 μm filter until the solution is clear to obtain the prepared sulfur-containing additive solution.

[0067] A 60 mL solution of DMF containing 6.9 g PbI₂, 2.19 g PbBr₂, and 0.20 g NH₄Ac was heated to 60 °C and stirred for 15 min, then cooled to room temperature to obtain the first solution. 100 mL of n-hexane containing 100 mg of lead salt quantum dots (oleic acid) coated with a long-chain oil-phase organic ligand was added to the first solution. At this point, the black solution was in the upper layer, and the yellow solution was in the lower layer. The mixture was vigorously shaken and allowed to stand for 5 min to separate into layers; the upper layer was clear and transparent, while the lower layer turned black (the quantum dots transferred to the lower layer). The lower layer was extracted three times with n-hexane, then purified with toluene. After centrifugation, the supernatant was discarded, and the mixture was inverted and placed in a vacuum chamber under negative pressure to remove residual solvent. The mixture was then weighed to obtain lead salt quantum dot powder coated with short-chain halogen ligands, with a yield of approximately 60 mg.

[0068] Immediately (recorded as 0 minutes), 300 μL of sulfur-containing additive solution was added to 60 mg of lead salt quantum dot powder coated with short-chain halogen ligands. The mixture was shaken thoroughly for 2 minutes, vortexed for 4 minutes, and sonicated for 2 minutes to dissolve the lead salt quantum dot ink to obtain 200 mg / mL.

[0069] Immediately spin-coat the lead salt quantum dot ink onto a commercially available 4-inch diameter, 500μm thick, undoped bare silicon wafer, and then anneal it at 70°C on a heating plate to obtain a quantum dot film with a thickness of 200±25nm.

[0070] Examples 2 to 5

[0071] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as in Example 1, and lead salt quantum dot ink and quantum dot film are obtained.

[0072] Comparative Example 1

[0073] Except for adding 300 μL of a mixed solution of DMF and BA (DMF to BA volume ratio 1:3) directly to 60 mg of lead salt quantum dot powder coated with short-chain halogen ligands without adding sulfur-containing additives, the rest was the same as in Example 1, resulting in lead salt quantum dot ink and quantum dot film without removing ionic ligands.

[0074] Comparative Example 2

[0075] Except for replacing diphenylthiourea with 2-aminoethanethiol (CTA) containing an amino group, the rest is the same as in Example 1, and lead salt quantum dot ink and quantum dot film are obtained.

[0076] Table 1

[0077] Note: " / " indicates that there are no corresponding preparation parameters.

[0078] Film surface particle defect and roughness test:

[0079] The quantum dot film was examined in dark field using a high-powered optical microscope (Olympus CX43). The number of white bright spots on its surface was observed under dark conditions; fewer white bright spots indicated fewer particle defects. The optical microscope image of the quantum dot film in Example 1 is shown below. Figure 1A As shown (magnification 10X, scale bar 50μm), the optical microscope image of the quantum dot film in Comparative Example 1 is as follows. Figure 1B As shown (magnification 10X, scale bar 50μm), the optical microscope image of the quantum dot film in Comparative Example 2 is as follows: Figure 1C As shown, Figure 1C The small image in the lower left corner is a photo with increased contrast. It can be seen that the quantum dot film prepared with lead salt quantum dot ink without the removal of ionic ligands in Comparative Example 1 shows many white bright spots, which are the presence of particle defects. The quantum dot film prepared with lead salt quantum dot ink treated with CTA as an additive in Comparative Example 2, although somewhat improved compared to Comparative Example 1, still has an uneven film surface and more white bright spots than in this application; while the quantum dot film prepared with lead salt quantum dot ink treated with the sulfur-containing additive of this application in Example 1 shows a significant reduction in the number of white bright spots. This may be related to the difference in coordinating atoms and their binding ability. The sulfur-containing additive ligand of this application has a stronger and more stable binding to the lead salt quantum dot surface, and can promote more ordered "self-assembly" of the lead salt quantum dots during film formation, thereby obtaining a smoother and denser quantum dot film; while the interaction force between amino-containing ligands (such as CTA in Comparative Example 2) and the lead salt quantum dot surface is relatively weak or too dynamic, resulting in poor controllability of the film formation process and a larger roughness of the quantum dot film. Specifically, amino ligands are mostly hard Lewis bases, and tend to react with hard Lewis acids (such as Cd). 2+ ) reaction, while Pb 2+ It belongs to the category of weak Lewis acids, and according to the hard-soft acid-base theory, its affinity is relatively weak. However, the coordinating atom S in the sulfur-containing additive of this application is a weak Lewis base, making it more likely to react with Pb. 2+ Therefore, amino-containing ligands may detach, making lead salt quantum dots prone to uncontrolled collisions and aggregation, resulting in an uneven and rough surface of the quantum dot film.

[0080] The quantum dot film was characterized using the tapping mode of AFM, and its specific surface condition was observed and the roughness data Rq was obtained through analysis. Example 1: Atomic force microscopy image of the quantum dot film is shown below. Figure 2A As shown, the atomic force microscope image of the quantum dot thin film in Comparative Example 1 is as follows: Figure 2B As shown, the Height Sensor is the height sensor, and the right column is the height scale. Figure 2AThe maximum value for medium-height wavelength is 7.9 nm, and the minimum value is -7.4 nm. Figure 2B The maximum height is 8.5 nm and the minimum is -7.8 nm. It is evident that the quantum dot film prepared with lead salt quantum dot ink without removing ionic ligands has a rough, agglomerated morphology with numerous particles; software analysis yielded a roughness Rq = 2.34 nm. In contrast, the quantum dot film prepared with lead salt quantum dot ink using the method described in this application has a uniform morphology, no obvious large particles were observed, and its roughness Rq = 2.16 nm is significantly smaller than that of Comparative Example 1.

[0081] The roughness test results of the quantum dot films of each embodiment and comparative example are shown in Table 1. The above results show that the lead salt quantum dot ink prepared by the preparation method of this application can significantly reduce the residual ligands in the lead salt quantum dot ink. When used for spin coating of quantum dot films, it can significantly reduce the surface defects of quantum dot films, improve the film-forming properties of lead salt quantum dot ink, and obtain smooth and flat quantum dot films.

[0082] The effect of dwell time after obtaining lead salt quantum dot ink:

[0083] The lead salt quantum dot ink prepared in Example 1 was placed under common process conditions (25°C, relative humidity 40±10%) for 0 minutes, 30 minutes, 60 minutes, and 3 hours, respectively, and then spin-coated (the lead salt quantum dot ink placed for 3 hours was dispersed before spin-coating) to obtain quantum dot films. Orthogonal photographs of the lead salt quantum dot ink placed for 0 minutes (i.e., immediately after preparation and not yet placed) and 3 hours are shown below. Figure 3A As shown, the inverted photo is as follows Figure 3B As shown, Figure 3A and Figure 3B The left side shows lead salt quantum dot ink that has been left for 3 hours, while the right side shows lead salt quantum dot ink that has been left for 0 minutes. It can be seen that the inverted lead salt quantum dot ink that has been left for 3 hours has completely solidified into a viscous colloid-like state. After forcibly breaking it up, it was spin-coated to obtain a quantum dot film.

[0084] High-magnification optical microscopy was used to examine each quantum dot film under bright-field conditions, observing the number of visible particles on the surface under bright-field conditions. The results are as follows: Figure 4A , Figure 4B , Figure 4C , Figure 4D As shown, the quantum dot film obtained by spin-coating immediately after preparing the lead salt quantum dot ink has no obvious particles on its surface; the quantum dot film obtained after 30 minutes of inactivity under common process conditions has a small number of particles on its surface; the quantum dot film obtained after 60 minutes of inactivity under common process conditions has a significantly larger number of particles on its surface; and the quantum dot film obtained after 3 hours of inactivity under common process conditions has a large number of uneven particles on its surface.

[0085] The above results indicate that coating within 30 minutes after the lead salt quantum dot ink is prepared in this application is beneficial to maintaining the stability of the lead salt quantum dot ink and can reduce the surface defects of the quantum dot film.

[0086] The effect of dwell time on the preparation of lead salt quantum dot powders coated with short-chain halogen ligands:

[0087] The lead salt quantum dot powder coated with short-chain halogen ligands prepared in Example 1 was placed under common process conditions (25°C, relative humidity 40±10%) for 0 minutes (i.e., immediately after preparation and before placement) and 30 minutes, respectively. Then, 300 μL of sulfur-containing additive solution was added to it. The resulting solution is shown in the photograph. Figure 5 As shown, after 30 minutes (left side), the lead salt quantum dot powder coated with short-chain halogen ligands is almost impossible to disperse, while the fresh lead salt quantum dot powder coated with short-chain halogen ligands (right side) can be effectively dispersed in the sulfur-containing additive solution. Therefore, this application controls the addition of the sulfur-containing additive solution to the lead salt quantum dot powder coated with short-chain halogen ligands within 3 minutes after obtaining the powder to prepare lead salt quantum dot ink, thereby obtaining lead salt quantum dot ink with good stability and high film-forming properties, and ultimately obtaining a quantum dot film with uniform morphology and smooth surface.

[0088] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0089] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0090] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing lead salt quantum dot ink, characterized in that, Includes the following steps: Prepare a sulfur-containing additive solution; the sulfur-containing additive is selected from at least one of thiourea, methylthiourea, diphenylthiourea, pyridylthiourea, dimethylthiourea, polythiourea, elemental sulfur, carbon disulfide, and sodium sulfide; Lead salt quantum dots encapsulated with long-chain oil-phase organic ligands were exchanged to obtain lead salt quantum dot powder encapsulated with short-chain halogen ligands. After obtaining the lead salt quantum dot powder coated with the short-chain halogen ligand, the sulfur-containing additive solution is added to the lead salt quantum dot powder coated with the short-chain halogen ligand within 3 minutes to dissolve and obtain the lead salt quantum dot ink.

2. The preparation method according to claim 1, characterized in that, The preparation steps of the sulfur-containing additive solution include: dispersing the sulfur-containing additive in a first organic solvent, filtering after uniform dispersion to obtain the sulfur-containing additive solution; the molar amount of the sulfur-containing additive to the volume ratio of the first organic solvent is 0.01-1 mmol: 200-1500 μL, and the first organic solvent is selected from at least one of N,N-dimethylformamide, methanol, ethylene glycol, dimethyl sulfoxide, aniline, butylamine, methylamine, and benzyl alcohol.

3. The preparation method according to claim 2, characterized in that, The first organic solvent is a mixed solution of N,N-dimethylformamide and benzyl alcohol, with a volume ratio of N,N-dimethylformamide to benzyl alcohol of 1:1 to 1:

12.

4. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the lead salt quantum dot powder encapsulated by the short-chain halogen ligand to the sulfur-containing additive solution is 60-80 mg: 200-1500 μL.

5. The preparation method according to claim 1, characterized in that, The ligand exchange step includes: adding a second organic solvent containing lead salt quantum dots coated with the long-chain oil phase organic ligand to a first solution containing PbI2, PbBr2, and NH4Ac, shaking vigorously, and separating the layers; taking the lower layer solution for extraction, purification, and separation to obtain lead salt quantum dot powder coated with the short-chain halogen ligand; The mass ratio of the lead salt quantum dots encapsulated by the long-chain oil-phase organic ligand, the volume of the second organic solvent, the mass of PbI2, the mass of PbBr2, the mass of NH4Ac, to the volume of the solvent in the first solution is 100mg: 20-100mL: 2.3-6.9g: 0.73-2.19g: 0.05-0.20g: 20-80mL; The second organic solvent is selected from at least one of n-hexane, n-octane, and n-heptane; The solvent of the first solution is selected from at least one of N,N-dimethylformamide, methanol, ethylene glycol, dimethyl sulfoxide, aniline, butylamine, and methylamine.

6. The preparation method according to claim 5, characterized in that, The extraction, purification, and separation of the lower layer solution includes: extracting the lower layer solution with a third organic solvent 2-4 times, then purifying it with a fourth organic solvent, and performing solid-liquid separation. The third organic solvent and the fourth organic solvent are each independently selected from at least one of isopentane, n-pentane, n-hexane, cyclohexane, n-octane, trifluoroacetic acid, n-heptane, cycloheptane, and toluene.

7. The preparation method according to claim 1, characterized in that, The dissolution process includes shaking for 1-3 minutes, vortexing for 3-5 minutes, and sonication for 1-3 minutes.

8. Lead salt quantum dot ink prepared by any one of claims 1-7.

9. A method for preparing a quantum dot thin film, characterized in that, The lead salt quantum dot ink prepared by any one of claims 1-7 is coated within 30 minutes after the preparation of the lead salt quantum dot ink to obtain the quantum dot film.

10. The quantum dot thin film prepared by the preparation method according to claim 9.

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