Method for improving structural stability of colloidal quantum dots

Abstract

A method for improving structural stability of colloidal quantum dots comprises the following steps: dissolving a metal salt into a polar phase solution to obtain a metal salt ligand solution, and dissolving a V-VI chalcogenide into n-butylamine to obtain a chalcogenide ligand solution; injecting the chalcogenide ligand solution into the metal salt ligand solution, and rapidly oscillating to fully react to synthesize a small-size metal chalcogenide monomer, so as to obtain a monomer ligand solution; and mixing the quantum dots dissolved in the non-polar phase solution with a monomer ligand solution, and carrying out phase transfer ligand exchange to obtain the quantum dot ink with a stable structure in the polar phase. According to the invention, a small-size monomer is synthesized in a ligand solution, and in a phase transfer process, the small-size monomer is dissolved and grows on the surface of a target quantum dot by using an Ostwald mechanism, so that the size focusing of the quantum dot is realized, the structure of the quantum dot is kept stable, and the long-time colloid stability of the quantum dot ink in a polar phase is realized; the method can be applied to quantum dot materials such as PbX, CdX (X = S, Se) and the like.

Description

Technical Field

[0001] The present invention belongs to the field of low-dimensional semiconductor nanomaterials and short-wave infrared detection technology. More specifically, it relates to a method for improving the structural stability of colloidal quantum dots. The method comprises mixing a metal salt ligand solution with a V-VI group sulfide ligand solution to prepare a small-sized monomer ligand solution, and then using the monomer ligand solution to perform phase transfer on non-polar phase quantum dots, thereby achieving structural stability and colloidal stability of the quantum dots in the polar phase. Background Art

[0002] Colloidal quantum dots (CQDs) are semiconductor nanocrystals synthesized via solution methods, typically ranging in size from a few to tens of nanometers. Due to their tunable band gap, excellent optoelectronic properties, and scalable fabrication, they have garnered widespread attention and application in a variety of fields, including light-emitting diodes, photodetectors, solar cells, and lasers. As a semiconductor nanomaterial exhibiting quantum confinement, CQDs' optical and electrical properties are highly dependent on their size and morphology, a characteristic that significantly distinguishes them from traditional bulk semiconductor materials.

[0003] With the development of solution synthesis technology, CQD has made significant progress in the control of size and size distribution, but it still faces a series of key challenges in the process of high-performance optoelectronic devices. Generally, the surface of the synthesized CQD is coated with long-chain organic ligands. Although these ligands contribute to stability in solution, they significantly inhibit the charge transfer ability. Therefore, during the device manufacturing process, long-chain ligands need to be replaced with short-chain ligands through the phase transfer ligand exchange method to obtain highly conductive CQD ink. However, this treatment process often destroys the surface structure of CQD, resulting in a decrease in the uniformity of quantum dot size and its distribution, which in turn causes significant changes in energy level position and spacing, thereby affecting its electronic structure and optical properties. This structural instability problem induced by surface treatment has not received enough attention in CQD device research so far. The fundamental reason for the structural instability of CQD is its high surface-to-volume ratio, which causes its chemical potential to be significantly higher than that of the corresponding bulk material. According to the Gibbs-Thompson equation, the solubility of CQDs increases significantly as their size decreases. During solution processing and storage of CQDs, this size-dependent solubility is often used to achieve a directional growth mechanism called "size focusing," but it can have negative consequences during device fabrication. For example, CQDs are particularly susceptible to partial dissolution in polar solvents because their surface often contains some ionic bond structures, which are more susceptible to dissociation in polar solvents.

[0004] Therefore, the structural stability of CQD in polar solvent environments directly affects its usability as an electronic-grade material and its application potential in high-performance optoelectronic devices. Solving this problem is crucial for realizing electronic-grade CQD materials and high-performance devices. Summary of the Invention

[0005] Current phase transfer ligand exchange methods often use small molecule metal salts or short-chain organic ligands, which are somewhat destructive to the structural stability of CQDs in the polar phase. To address the above-mentioned deficiencies or improvement needs of the existing technology, the present invention aims to provide a method for improving the structural stability of colloidal quantum dots while ensuring the charge transport capability of quantum dots. This method involves mixing metal salt ligands with Group V-VI sulfide ligands to produce small-sized quantum dot monomers. Phase transfer ligand exchange is then performed on the target quantum dots, and the monomers are decomposed and grown on the target quantum dot surface through Oswald ripening, effectively improving the structural stability of the quantum dots in the polar phase. This invention has the characteristics of improving the optical and electrical properties of quantum dots and is also applicable to a variety of Group IV-VI quantum dot materials.

[0006] To achieve the above objectives, the present invention provides a method for improving the structural stability of colloidal quantum dots, comprising the following steps:

[0007] (1) dissolving a metal salt in a polar solvent to obtain a metal salt ligand solution; dissolving a V-VI group sulfide compound in solvent A to obtain a sulfide ligand solution; mixing the sulfide ligand solution with the metal salt ligand and oscillating the mixture to prepare a ligand solution containing small-sized monomers; dissolving quantum dots with long-chain ligands on their surfaces in a non-polar solvent to obtain a quantum dot solution;

[0008] (2) mixing the ligand solution containing small-sized monomers obtained in step (1) and the quantum dot solution, and rapidly shaking the mixture for 1 to 10 minutes, wherein the quantum dots are transferred from the non-polar phase to the polar phase, and the long-chain ligands on the surface of the quantum dots are removed. The supernatant is removed to obtain a quantum dot ink with a stable structure in the polar phase;

[0009] The steps (1) and (2) are both carried out under an inert atmosphere.

[0010] Preferably, the metal salt in step (1) is one or a mixture of lead iodide, lead bromide, lead chloride, anhydrous lead acetate, cadmium iodide, cadmium bromide, cadmium chloride, anhydrous cadmium acetate, zinc iodide, silver iodide, bismuth iodide, and tin iodide.

[0011] Preferably, the concentration of the metal salt in the metal salt ligand solution in step (1) is 0.2 to 0.7 mol / L.

[0012] Preferably, the Group V-VI chalcogenide compound in step (1) is one or more mixtures of arsenic sulfide, arsenic selenide, bismuth sulfide, and bismuth selenide.

[0013] Preferably, the concentration of the sulfide compound in the sulfide ligand solution in step (1) is 0.01 to 0.05 mol / L.

[0014] Preferably, in step (1), the sulfide ligand solution and the metal salt ligand are mixed and shaken for 0.5 to 5 minutes.

[0015] Preferably, the polar solvent in step (1) is a mixture of one or more of methyl sulfoxide and N,N-dimethylformamide.

[0016] Preferably, the solvent A in step (1) is n-butylamine or a mixture of n-butylamine and mercaptoethanol.

[0017] Preferably, in step (1), the Group V-VI sulfide compound is dissolved in solvent A, and the process is carried out at 40-60° C. with long-term stirring, the dissolution time is 12-24 hours, and the rotation speed is 400-700 rpm.

[0018] Preferably, the long-chain ligand on the surface of the quantum dots in step (1) is a mixture of one or more of oleic acid and oleylamine.

[0019] Preferably, the non-polar solvent in step (1) is one or a mixture of n-hexane and n-octane.

[0020] Preferably, in step (1), the concentration of the quantum dots dissolved in the non-polar solvent is 10 to 50 mg / mL.

[0021] According to another aspect of the present invention, a structurally stable quantum dot prepared by the phase transfer method is provided.

[0022] According to another aspect of the present invention, there is provided an application of the structurally stable quantum dots in the field of 1300-1700 nm short-wave infrared detection.

[0023] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0024] (1) The method for improving the structural stability of colloidal quantum dots described in the present invention is different from the metal salts or short-chain organic ligands commonly used in the existing liquid phase transfer ligand exchange method. Small-sized quantum dot monomers are generated by mixing metal salt ligands and V-VI group sulfide ligands. During the phase transfer process, due to the solubility difference caused by the size difference, the small-sized monomers dissolve and then grow on the surface of the target quantum dots, so that the target quantum dots are focused in size, effectively solving the problem of structural instability of quantum dots caused by the phase transfer process.

[0025] (2) Compared with the original quantum dots, the colloidal quantum dots prepared by the present invention have better optical properties, a narrower half-width at half maximum of the absorption curve, and a higher peak-to-valley ratio.

[0026] (3) Compared with the prior art, the colloidal quantum dots prepared by the present invention have better electrical properties, reduced film defect state density, and improved mobility.

[0027] (4) The colloidal dispersibility of the colloidal quantum dots prepared by the present invention in polar solvents is also significantly improved, and they can be stably stored for more than one month, and their optical properties remain almost unchanged within one month.

[0028] (5) The present invention can synthesize different types of small-sized quantum dot monomer ligands by changing the types of metal salt ligands and V-VI group sulfide ligands, thereby achieving the regulation of the doping characteristics and components of the target quantum dots.

[0029] (6) The colloidal quantum dots prepared by the present invention are applied to photodetector devices, which significantly improves the device performance, as reflected in the reduction of dark current density, the improvement of external quantum dot efficiency and the improvement of specific detection rate.

[0030] (5) The present invention has broad universality and can be applied to different types of IV-VI group quantum dot materials, such as PbS, PbSe, CdS, CdSe, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 The absorption curve graph (1a) and TEM image (1b) of a small-sized PbSe monomer prepared by mixing and oscillating a metal salt lead iodide and lead bromide ligand solution with a Group V-VI arsenic selenide ligand solution in Example 1 of the present invention;

[0033] Figure 2 This is a comparison diagram of the absorption curve (2a) and PL curve (2b) of the structurally stable PbSe quantum dot ink prepared in Example 1 of the present invention (applied to 1276nm PbSe quantum dots) and the quantum dot stock solution;

[0034] Figure 3 3a and PL curve (3b) of the 1276nm PbSe quantum dot ink and the quantum dot stock solution prepared in comparative example 1;

[0035] Figure 4 This is a DLS comparison chart of the small-sized PbSe monomer and the structurally stable PbSe quantum dot ink and the quantum dot stock solution obtained in Example 1 of the present invention;

[0036] Figure 5 This is a graph monitoring the absorption stability of the structurally stable PbSe quantum dot ink prepared in Example 1 of the present invention within one month;

[0037] Figure 6 This is a comparison of absorption curves of the structurally stable PbSe quantum dot thin films and quantum dot stock solutions at different wavelengths prepared in Examples 2-4 of the present invention;

[0038] Figure 7 This is a comparison of the absorption curves of the PbS quantum dot ink and the quantum dot stock solution prepared in Example 5 of the present invention (applied to 1200nm PbS quantum dots) and Comparative Example 3;

[0039] Figure 8 This is a comparison chart of the absorption curves of the structure-stabilized CdSe and CdS quantum dot inks and the quantum dot stock solution prepared in Example 6 (8a) and Example 7 (8b) of the present invention;

[0040] Figure 9 9a and 9b are AFM images of PbSe quantum dot films prepared in Example 2 and Comparative Example 2 of the present invention and the corresponding FET transfer characteristic curves.

[0041] Figure 10 This is a performance comparison of the PbSe quantum dots prepared in Example 2 of the present invention and Comparative Example 2 when used in infrared detectors. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0044] Example 1 (Applicability of the present invention to 1276 nm PbSe quantum dots)

[0045] (1) Preparation of metal halide ligand: 0.737 g of lead iodide and 0.127 g of lead bromide powder were weighed and dissolved in 3 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0046] (2) Preparation of Group V-VI AsSe ligands: 0.185 g of AsSe powder was weighed and dissolved in 15 mL of n-butylamine. The mixture was stirred at 40°C for 12 hours. Undissolved impurities were removed by centrifugal filtration to obtain a clear AsSe ligand solution.

[0047] (3) Rapidly inject 1 mL of arsenic selenide ligand solution into the metal halide ligand obtained in (1). The mixed ligand solution quickly turns black, indicating that PbSe monomers are generated. Then, rapidly shake the mixture for 1 minute to allow it to fully react, thereby obtaining a PbSe monomer ligand solution.

[0048] (4) 1276 nm PbSe quantum dots were dissolved in a non-polar solvent n-octane to a concentration of 10 mg / mL to obtain a PbSe quantum dot stock solution. 5 mL of the PbSe quantum dot stock solution was added to the monomer ligand solution obtained in (3), and then oscillated for 1 minute. The PbSe quantum dots were quickly transferred from the n-octane layer to the N,N-dimethylformamide layer, indicating that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0049] (5) removing the supernatant from the quantum dot solution after exchange in (4), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, and repeating this process twice to obtain a structurally stable and colloidally stable PbSe quantum dot ink in N,N-dimethylformamide;

[0050] Example 2 (Applicability of the present invention to 1565 nm PbSe quantum dots)

[0051] (1) Preparation of metal halide ligand: 0.737 g of lead iodide and 0.127 g of lead bromide powder were weighed and dissolved in 3 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0052] (2) Preparation of Group V-VI AsSe ligands: 0.185 g of AsSe powder was weighed and dissolved in 15 mL of n-butylamine. The mixture was stirred at 40°C for 12 hours. Undissolved impurities were removed by centrifugal filtration to obtain a clear AsSe ligand solution.

[0053] (3) Rapidly inject 1 mL of arsenic selenide ligand solution into the metal halide ligand obtained in (1). The mixed ligand solution quickly turns black, indicating that PbSe monomers are generated. Then, rapidly shake the mixture for 1 minute to allow it to fully react, thereby obtaining a PbSe monomer ligand solution.

[0054] (4) 1565 nm PbSe quantum dots were dissolved in a non-polar solvent n-octane to a concentration of 10 mg / mL to obtain a PbSe quantum dot stock solution. 5 mL of the PbSe quantum dot stock solution was added to the monomer ligand solution obtained in (3), and then oscillated for 1 minute. The PbSe quantum dots were quickly transferred from the n-octane layer to the N,N-dimethylformamide layer, indicating that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0055] (5) removing the supernatant from the quantum dot solution after exchange in (4), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, and repeating this process twice to obtain a structurally stable and colloidally stable PbSe quantum dot ink in N,N-dimethylformamide;

[0056] Example 3 (Application of the present invention to 1940 nm PbSe quantum dots)

[0057] (1) Preparation of metal halide ligand: 0.737 g of lead iodide and 0.127 g of lead bromide powder were weighed and dissolved in 3 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0058] (2) Preparation of Group V-VI AsSe ligands: 0.185 g of AsSe powder was weighed and dissolved in 15 mL of n-butylamine. The mixture was stirred at 40°C for 12 hours. Undissolved impurities were removed by centrifugal filtration to obtain a clear AsSe ligand solution.

[0059] (3) Rapidly inject 1 mL of arsenic selenide ligand solution into the metal halide ligand obtained in (1). The mixed ligand solution quickly turns black, indicating that PbSe monomers are generated. Then, rapidly shake the mixture for 1 minute to allow it to fully react, thereby obtaining a PbSe monomer ligand solution.

[0060] (4) 1940 nm PbSe quantum dots were dissolved in a non-polar solvent n-octane to a concentration of 10 mg / mL to obtain a PbSe quantum dot stock solution. 5 mL of the PbSe quantum dot stock solution was added to the monomer ligand solution obtained in (3), and then oscillated for 1 minute. The PbSe quantum dots were quickly transferred from the n-octane layer to the N,N-dimethylformamide layer, indicating that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0061] (5) removing the supernatant from the quantum dot solution after exchange in (4), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, and repeating this process twice to obtain a structurally stable and colloidally stable PbSe quantum dot ink in N,N-dimethylformamide;

[0062] Example 4 (Applicability of the present invention to 2075 nm PbSe quantum dots)

[0063] (1) Preparation of metal halide ligand: 0.737 g of lead iodide and 0.127 g of lead bromide powder were weighed and dissolved in 3 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0064] (2) Preparation of Group V-VI AsSe ligands: 0.185 g of AsSe powder was weighed and dissolved in 15 mL of n-butylamine. The mixture was stirred at 40°C for 12 hours. Undissolved impurities were removed by centrifugal filtration to obtain a clear AsSe ligand solution.

[0065] (3) Rapidly inject 1 mL of arsenic selenide ligand solution into the metal halide ligand obtained in (1). The mixed ligand solution quickly turns black, indicating that PbSe monomers are generated. Then, rapidly shake the mixture for 1 minute to allow it to fully react, thereby obtaining a PbSe monomer ligand solution.

[0066] (4) 2075 nm PbSe quantum dots were dissolved in a non-polar solvent n-octane to a concentration of 10 mg / mL to obtain a PbSe quantum dot stock solution. 5 mL of the PbSe quantum dot stock solution was added to the monomer ligand solution obtained in (3), and then oscillated for 1 minute. The PbSe quantum dots were quickly transferred from the n-octane layer to the N,N-dimethylformamide layer, indicating that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0067] (5) removing the supernatant from the quantum dot solution after exchange in (4), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, and repeating this process twice to obtain a structurally stable and colloidally stable PbSe quantum dot ink in N,N-dimethylformamide;

[0068] Example 5 (Application of the present invention to 1200nm PbS quantum dots)

[0069] (1) Preparation of metal halide ligand: 0.737 g of lead iodide and 0.127 g of lead bromide powder were weighed and dissolved in 3 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0070] (2) Preparation of Group V-VI arsenic sulfide ligands: 0.06 g of arsenic sulfide powder was dissolved in 15 mL of n-butylamine and stirred at 40°C for 12 hours. Undissolved impurities were removed by centrifugal filtration to obtain a clear arsenic sulfide ligand solution.

[0071] (3) Rapidly inject 1 mL of arsenic sulfide ligand solution into the metal halide ligand obtained in (1). The mixed ligand solution quickly turns black, indicating that PbS monomers are generated. Then, rapidly shake the mixture for 1 minute to allow it to fully react, thereby obtaining a PbS monomer ligand solution.

[0072] (4) 1200 nm PbS quantum dots were dissolved in the non-polar solvent n-octane to a concentration of 10 mg / mL to obtain a PbS quantum dot stock solution. 5 mL of the PbS quantum dot stock solution was added to the monomer ligand solution obtained in (3), and then oscillated for 1 minute. The PbS quantum dots were quickly transferred from the n-octane layer to the N,N-dimethylformamide layer, indicating that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0073] (5) removing the supernatant from the quantum dot solution after exchange in (4), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, and repeating this process twice to obtain a PbS quantum dot ink with structural stability and colloid stability in N,N-dimethylformamide;

[0074] Example 6 (Application of the present invention to 444nm CdSe quantum dots)

[0075] (1) Preparation of metal halide ligand: 0.366 g of cadmium iodide powder was weighed and dissolved in 5 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0076] (2) Preparation of Group V-VI AsSe ligands: 0.185 g of AsSe powder was weighed and dissolved in 15 mL of n-butylamine. The mixture was stirred at 40°C for 12 hours. Undissolved impurities were removed by centrifugal filtration to obtain a clear AsSe ligand solution.

[0077] (3) Rapidly injecting 1 mL of the arsenic selenide ligand solution into the metal halide ligand obtained in (1), and then rapidly shaking for 1 minute to allow it to fully react, to obtain a CdSe monomer ligand solution;

[0078] (4) 444 nm CdSe quantum dots were dissolved in a non-polar solvent n-octane to a concentration of 5 mg / mL to obtain a CdSe quantum dot stock solution. 5 mL of the CdSe quantum dot stock solution was added to the monomer ligand solution obtained in (3), and then oscillated for 1 minute. The CdSe quantum dots were quickly transferred from the n-octane layer to the N,N-dimethylformamide layer, indicating that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0079] (5) removing the supernatant from the quantum dot solution after exchange in (4), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, and repeating this process twice to obtain a structurally stable and colloidally stable CdSe quantum dot ink in N,N-dimethylformamide;

[0080] Example 7 (Application of the present invention to 474nm CdS quantum dots)

[0081] (1) Preparation of metal halide ligand: 0.366 g of cadmium iodide powder was weighed and dissolved in 5 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0082] (2) Preparation of Group V-VI arsenic sulfide ligands: 0.06 g of arsenic sulfide powder was dissolved in 15 mL of n-butylamine and stirred at 40°C for 12 hours. Undissolved impurities were removed by centrifugal filtration to obtain a clear arsenic sulfide ligand solution.

[0083] (3) Rapidly injecting 1 mL of the arsenic sulfide ligand solution into the metal halide ligand obtained in (1), and then rapidly shaking for 1 minute to allow for sufficient reaction, thereby obtaining a CdS monomer ligand solution;

[0084] (4) 474 nm CdS quantum dots were dissolved in a non-polar solvent n-octane to a concentration of 5 mg / mL to obtain a CdS quantum dot stock solution. 5 mL of the CdS quantum dot stock solution was added to the monomer ligand solution obtained in (3), and then oscillated for 1 minute. The CdS quantum dots were quickly transferred from the n-octane layer to the N,N-dimethylformamide layer, indicating that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0085] (5) removing the supernatant from the quantum dot solution after exchange in (4), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, and repeating this process twice to obtain a structurally stable and colloidally stable CdS quantum dot ink in N,N-dimethylformamide;

[0086] Comparative Example 1 (applied to 1276nm PbSe quantum dots, using only metal halide ligands)

[0087] (1) Preparation of metal halide ligand: 0.737 g of lead iodide and 0.127 g of lead bromide powder were weighed and dissolved in 5 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0088] (2) 1276 nm PbSe quantum dots were dissolved in a non-polar solvent n-octane to a concentration of 10 mg / mL to obtain a PbSe quantum dot stock solution. 5 mL of the PbSe quantum dot stock solution was added to the metal halide ligand solution obtained in (1), and then oscillated for 1 minute. The PbSe quantum dots were slowly transferred from the n-octane layer to the N,N-dimethylformamide layer, proving that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0089] (3) removing the supernatant from the quantum dot solution after exchange in (2), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, repeating this process twice, centrifuging the quantum dot solution to obtain a solid, and then dispersing the quantum dot solid in a mixed solution of n-butylamine and N,N-dimethylformamide to obtain PbSe quantum dot ink;

[0090] Comparative Example 2 (applied to 1565nm PbSe quantum dots, using only metal halide ligands)

[0091] (1) Preparation of metal halide ligand: 0.737 g of lead iodide and 0.127 g of lead bromide powder were weighed and dissolved in 5 mL of N,N-dimethylformamide. The mixture was stirred on an oscillator for 10 minutes until the powder was completely dissolved to obtain a metal halide ligand solution.

[0092] (2) 1565 nm PbSe quantum dots were dissolved in a non-polar solvent n-octane to a concentration of 10 mg / mL to obtain a PbSe quantum dot stock solution. 5 mL of the PbSe quantum dot stock solution was added to the metal halide ligand solution obtained in (1), and then oscillated for 1 minute. The PbSe quantum dots were slowly transferred from the n-octane layer to the N,N-dimethylformamide layer, proving that the long-chain organic ligands on the surface had been replaced by short-chain ligands.

[0093] (3) removing the supernatant from the quantum dot solution after exchange in (2), adding 5 mL of n-octane and shaking for 1 minute, removing the supernatant again, repeating this process twice, centrifuging the quantum dot solution to obtain a solid, and then dispersing the quantum dot solid in a mixed solution of n-butylamine, N,N-dimethylformamide, and N,N-dimethylsulfoxide to obtain PbSe quantum dot ink;

[0094] Figure 1 The absorption curve and TEM image of the small-sized PbSe monomer prepared by mixing and oscillating the metal salt lead iodide and lead bromide ligand solution with the V-VI group arsenic selenide ligand solution in Example 1 of the present invention. Figure 1 As shown in a, the exciton absorption peak is less than 900nm, and TEM is as follows Figure 1 As shown in b in the figure, the particle size is about 2.7 nm.

[0095] Figure 2The present invention is applied to 1276nm PbSe quantum dots. The absorption curve of the structure-stable PbSe quantum dot ink prepared in Example 1 and the quantum dot stock solution ( Figure 2 a in the figure) and the PL curve ( Figure 2 As shown in b) comparison chart. Figure 2 As shown in the figure, the absorption and PL curves of the quantum dots prepared by the present invention are narrower than those of the quantum dot stock solution, which indicates that the size distribution of the quantum dots becomes more uniform after the phase transfer process and the structure is well preserved; and the absorption and PL curves are slightly red-shifted, which is because the small-sized PbSe monomers have a higher chemical potential and tend to dissolve and then grow to the 1276nm PbSe surface, causing the quantum dots with stable structure to grow slightly.

[0096] Figure 3 The absorption curves of 1276nm PbSe quantum dot ink and quantum dot stock solution prepared in comparative example 1 are ( Figure 3 a in the figure) and the PL curve ( Figure 3 As shown in b) comparison chart. Figure 3 As shown in the figure, using the existing phase transfer technology, the absorption and PL curves of PbSe quantum dots after metal halide as ligand exchange are greatly broadened compared with the quantum dot original solution. This indicates that there is a quantum dot solution phenomenon in the phase transfer process of quantum dots, which leads to structural instability and worsens the uniformity of the size distribution of quantum dots.

[0097] Figure 4 This is a DLS comparison chart of the small-sized PbSe monomer and the structurally stable PbSe quantum dot ink and the quantum dot stock solution obtained in Example 1 of the present invention. Figure 4 As shown, dynamic light scattering (DLS) tests indicate that after the quantum dots undergo phase transfer, the distribution of small-sized PbSe monomers almost disappears, while the size of the structurally stable quantum dots increases after the exchange, proving that the small-sized PbSe monomers dissolve and grow onto the surface of the 1276nm PbSe quantum dots, and their size distribution curve becomes narrower, further illustrating that the present invention makes the size distribution of quantum dots more uniform and prepares structurally stable colloidal quantum dots.

[0098] Figure 5 This is a graph monitoring the absorption stability of the structurally stable PbSe quantum dot ink prepared in Example 1 of the present invention within one month. Figure 5 As shown in Figure a, the absorption curve of the prepared structurally stable PbSe quantum dots was monitored for aging. The absorption test was performed after aging for 1, 7, 15, and 28 days. It was found that the absorption curve after aging had a high degree of overlap with that before aging. By comparing the exciton absorption peak and HWHM data, as shown in Figure 5, the absorption curve after aging had a high degree of overlap with that before aging. Figure 5 As shown in (b), the exciton absorption peak and HWHM remain almost unchanged, indicating that the quantum dots can maintain structural stability within a month.

[0099] Figure 6 This is a comparison of the absorption curves of the structurally stable PbSe quantum dot film and the quantum dot solution at different wavelengths prepared in Examples 2-4 of the present invention. Figure 6 As shown, the present invention is applied to 1565nm, 1940nm and 2075nm PbSe quantum dots respectively. Compared with the quantum dot original solution, the half-maximum half-width of the absorption curve after phase transfer is narrower, indicating that the size distribution is more uniform, indicating that the present invention can be applied to quantum dot materials of different sizes.

[0100] The absorption curves of the structure-stabilized quantum dots prepared in Examples 5, 6, and 7 are compared with the absorption curves of the quantum dot stock solution. Figure 7 、 8 As shown, the absorption curves of the structurally stable quantum dots are narrower than those of the quantum dot stock solution, indicating that the uniformity of the size distribution is improved, indicating that the present invention can be applied to different types of quantum dot materials such as PbS, CdSe, and CdS.

[0101] Figure 9 a in the figure is an AFM image of the PbSe quantum dot thin films prepared in Example 2 of the present invention and Comparative Example 2. It can be clearly seen that the surface of the film prepared in Example 2 is more uniform and has lower roughness than that of the film prepared in Comparative Example 2. Figure 9 b is the transfer characteristic curve of the field effect transistor based on the two thin films. The film prepared in Example 2 has a higher electron mobility of 0.101 cm 2 V -1 S -1 , compared with comparative example 2, it has increased by several orders of magnitude (0.005cm 2 V -1 S -1 ).

[0102] Figure 10 This is a performance comparison of the PbSe quantum dots prepared in Example 2 of the present invention and Comparative Example 2 when used in infrared detectors. Figure 9 a in the figure is the JV characteristic curve of the PbSe quantum dot infrared detector. Under the reverse bias of -0.5V, the dark current density of the device prepared by the PbSe quantum dots in Example 2 is 4.96×10 -7 A cm -2 , compared with the dark current density of the device in Example 2 (3.0×10 -6 A cm -2 ) is nearly one order of magnitude lower, and the photovoltage increases significantly from 110mV to 190mV; Figure 9 b in the figure is the external quantum efficiency (EQE) spectra of the two devices. The EQE at the exciton absorption peak of the device in comparative example 2 is 36.0%, while the EQE at the exciton absorption peak of the device in embodiment 2 increases to 61.5%. Figure 9c in the figure is the noise current spectrum of the two devices in the frequency range of 1 to 7000 Hz. The noise current density of the device in Example 2 at 500 Hz is reduced by nearly an order of magnitude compared with that in Comparative Example 2. Figure 9 Where d is the specific detectivity (D*) calculated from the noise current of the two devices at 500 Hz. Compared with the device of comparative example 2, the D* of example 2 is increased by nearly an order of magnitude at the exciton absorption peak, reaching 3.1×10 12 Jones.

[0103] In summary, the colloidal quantum dots prepared by the present invention have better optical and electrical properties and colloidal dispersibility. By changing the types of metal salt ligands and V-VI group sulfide ligands, different types of small-sized quantum dot monomer ligands can be synthesized to achieve the regulation of the doping characteristics and components of the target quantum dots, effectively solving the problem of structural instability caused by quantum dots during the phase transfer process. When the colloidal quantum dots prepared by the present invention are applied to photodetector devices, the device performance is significantly improved. It can be applied to different types of IV-VI group quantum dot materials and has wide applicability.

Claims

1. A method for improving the structural stability of colloidal quantum dots, characterized by: The following steps are involved: (1) dissolving a metal salt in a polar solvent to obtain a metal salt ligand solution; dissolving a V-VI group sulfide compound in solvent A to obtain a sulfide ligand solution; mixing the sulfide ligand solution with the metal salt ligand and oscillating the mixture to prepare a ligand solution containing small-sized monomers; dissolving quantum dots with long-chain ligands on their surfaces in a non-polar solvent to obtain a quantum dot solution; (2) mixing the ligand solution containing small-sized monomers obtained in step (1) and the quantum dot solution, and rapidly shaking the mixture for 1 to 10 minutes, wherein the quantum dots are transferred from the non-polar phase to the polar phase, and the long-chain ligands on the surface of the quantum dots are removed. The supernatant is removed to obtain a quantum dot ink with a stable structure in the polar phase; Both step (1) and step (2) are carried out under an inert atmosphere.

2. The method for improving the structural stability of colloidal quantum dots according to claim 1, wherein: The metal salt in step (1) is one or a mixture of lead iodide, lead bromide, lead chloride, anhydrous lead acetate, cadmium iodide, cadmium bromide, cadmium chloride, anhydrous cadmium acetate, zinc iodide, silver iodide, bismuth iodide, and tin iodide, and the concentration of the metal salt in the metal salt ligand solution is 0.2 to 0.7 mol / L.

3. The method for improving the structural stability of colloidal quantum dots according to claim 1, wherein: In the step (1), the V-VI group chalcogenide is a mixture of one or more of arsenic sulfide, arsenic selenide, bismuth sulfide, and bismuth selenide, and the concentration of the chalcogenide in the chalcogenide ligand solution is 0.01 to 0.05 mol / L.

4. The method for improving the structural stability of colloidal quantum dots according to claim 1, wherein: In the step (1), the sulfide ligand solution and the metal salt ligand are mixed and shaken for 0.5 to 5 minutes.

5. The method for improving the structural stability of colloidal quantum dots according to claim 1, wherein: In the step (1), the polar solvent is a mixture of one or more of methyl sulfoxide and N,N-dimethylformamide, and the solvent A is n-butylamine or a mixture of n-butylamine and mercaptoethanol.

6. The method for improving the structural stability of colloidal quantum dots according to claim 1, wherein: In the step (1), the V-VI group sulfide compound is dissolved in solvent A, and the process is carried out at 40-60° C. with long-term stirring, the dissolution time is 12-24 hours, and the rotation speed is 400-700 rpm.

7. The method for improving the structural stability of colloidal quantum dots according to claim 1, wherein: In the step (1), the long-chain ligand on the surface of the quantum dots is a mixture of one or more of oleic acid and oleylamine.

8. The method for improving the structural stability of colloidal quantum dots according to claim 1, wherein: In the step (1), the non-polar solvent is one or a mixture of n-hexane and n-octane, and the concentration of the quantum dots dissolved in the non-polar solvent is 10 to 50 mg / mL.

9. The structurally stable quantum dots prepared by the method according to any one of claims 1 to 8.

10. Use of the structurally stable quantum dots according to claim 9 in the field of 1300-1700 nm short-wave infrared detection.

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