Preparation and liquid-phase ligand exchange method of sulfydryl-free silver telluride colloidal quantum dots

Abstract

The invention discloses a preparation and liquid-phase ligand exchange method of a sulfydryl-free silver telluride colloidal quantum dot, and the sulfydryl-free silver telluride colloidal quantum dot is prepared by adopting oleylamine as a solvent and a ligand for quantum dot synthesis, silver halide as a cationic precursor and organic lithium modified TOP-Te as an anionic precursor through a thermal injection method. The size and the absorption spectrum of the silver telluride quantum dots are adjusted by accurately regulating and controlling the reaction time, the temperature, the halogen type and the organic lithium content. The method is simple to operate and good in repeatability, and the prepared silver telluride quantum dots have excellent size distribution and adjustable absorption wavelength (856-1589 nm). On the basis of oleylamine coordinated silver telluride quantum dots, conductive ink dispersed in polar solvent colloid is obtained by adopting a liquid-phase ligand exchange method which is simple to operate, a flat, compact, crack-free and few-defect high-quality thin film is prepared through a single spin-coating process, and the thin film has application potential in the field of short-wave infrared detectors.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor nanomaterials, and in particular to a preparation method of mercapto-free silver telluride colloidal quantum dots and a liquid phase ligand exchange method. Background Art

[0002] Short-wave infrared detection technology has the characteristics of rich and clear detection information and strong penetration ability, and has broad application prospects in many fields such as military and civilian use. Compared with traditional bulk semiconductor materials, colloidal infrared quantum dot materials have the advantages of adjustable spectral response, low preparation cost, and integrated integration with silicon-based readout circuits. They are the hot spot and frontier of current infrared detection technology research. At present, short-wave infrared detectors are mainly based on lead sulfide and mercury telluride, but these materials contain heavy metal elements such as lead and mercury, which are difficult to meet the environmental protection standards in the consumer electronics field.

[0003] Currently, silver telluride (Ag 2 Te) quantum dots have excellent light absorption properties and a spectral range that covers the entire short-wave infrared (1-2.5 μm), making them ideal candidate materials for environmentally friendly quantum dot infrared detection technology and attracting extensive attention from researchers. 2 Te quantum dot infrared detection technology is still in its early stages, and high-performance Ag 2 The preparation technology of Te quantum dot thin film still needs to be developed. 2 In the preparation process of Te quantum dot photosensitive film, the solid-phase ligand exchange process is conventionally used. By spin coating layer by layer and solid-phase ligand treatment layer by layer, the insulating long-chain ligands on the surface of the quantum dots are replaced with conductive short-chain ligands to improve the conductivity of the film and prepare a quantum dot film of target thickness. This method is cumbersome, requires multiple quantum dot spin coatings (10-20 layers), and requires the use of a large amount of solvent. Most importantly, the film prepared by this method has many defects and low mobility.

[0004] For traditional infrared quantum dots such as lead sulfide, the liquid-phase ligand exchange process is the mainstream technical choice for the preparation of high-performance quantum dot films. Specifically, by adding a long-chain ligand-coated quantum dot octane solution to a polar solvent containing short-chain ligands (such as N,N-dimethylformamide), the long-chain ligands on the surface of the quantum dots are replaced with short-chain ligands by oscillation to prepare a conductive quantum dot ink that can be colloidally dispersed in a polar solvent. Then, a single spin coating or scraping process is used to prepare a quantum dot film with a target thickness (100-1000nm), a flat and dense surface, and high mobility. However, this liquid-phase ligand exchange process has not yet been applied to Ag films. 2 Te quantum dot film preparation has been effectively applied. The reason is that Ag 2The synthesis method of Te quantum dots is incompatible with the liquid phase ligand exchange process. 2 The conventional synthesis of Te quantum dots uses long-chain thiol groups as ligands to assist the nucleation and growth of quantum dots, and is used to prepare colloid-stabilized quantum dot materials. Due to the strong binding force between the thiol ligands and the Ag atoms on the surface of silver telluride quantum dots, it is difficult to completely exchange them into short-chain ligands through a liquid-phase ligand exchange process, and it is impossible to prepare colloid-stabilized conductive inks and high-quality quantum dot films. Therefore, the development of a thiol-free synthesis method for silver telluride quantum dots and the development of a liquid-phase ligand exchange process for silver telluride quantum dots are of great significance for the preparation of high-performance silver telluride quantum dot films. Summary of the invention

[0005] The present invention overcomes the shortcomings of the prior art and provides a method for preparing mercapto-free silver telluride colloidal quantum dots and liquid-phase ligand exchange. First, a mercapto-free synthesis system is adopted, oleylamine is selected as the solvent and ligand for quantum dot synthesis, silver halide is used as a cationic precursor, and trioctylphosphine telluride modified with organic lithium is used as an anionic precursor, and mercapto-free ligand silver telluride quantum dots are prepared by a hot injection method. Then, by precisely controlling reaction parameters such as reaction time, temperature, halogen type, and organic lithium content, the size and absorption spectrum of the silver telluride quantum dots are adjusted. Finally, based on the silver telluride quantum dots, a liquid-phase ligand exchange method is used to obtain a colloidal dispersed silver telluride quantum dot conductive ink, and a high-quality silver telluride quantum dot film is prepared by a single spin coating process.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing mercapto-free silver telluride colloidal quantum dots, comprising the following steps:

[0007] S1, adding a silver source to oleylamine, mixing evenly, and then heating under an inert gas atmosphere to prepare a solution A;

[0008] S2, adding the organic lithium reagent to the oleylamine solution, mixing evenly, to obtain solution B;

[0009] S3, adding the solution B prepared in step S2 to the TOP-Te solution, mixing evenly, to obtain a solution C;

[0010] S4. In an inert atmosphere, heating solution A to a first temperature, rapidly hot-injecting the freshly prepared solution C into solution A to form a first mixed solution, and reacting for 10 to 60 minutes;

[0011] S5, quickly adding a quenching liquid to the first mixed solution prepared in step S4, then adding a polar solvent for washing, centrifuging to separate the silver telluride quantum dots, and dispersing the silver telluride quantum dots in a non-polar solvent.

[0012] In a preferred embodiment of the present invention, the oleylamine solution in steps S1 and S2 needs to undergo the following heat treatment: the oleylamine solution is added to a three-necked flask, heated to 90-110° C., and vacuumed at this temperature to remove water vapor and impurities in the solution, and the vacuuming time is 1-2 hours.

[0013] In a preferred embodiment of the present invention, the silver source in step S1 is one of silver iodide, silver bromide and silver chloride.

[0014] In a preferred embodiment of the present invention, the organic lithium reagent in step S2 is one of lithium bistrimethylsilylamide, n-butyllithium, and lithium diisopropylamide, preferably lithium bistrimethylsilylamide.

[0015] In a preferred embodiment of the present invention, the mass of the organic lithium in step S2 is 0.9-1.5 mmol.

[0016] In a preferred embodiment of the present invention, the mass ratio of the silver source in step S1 to the tellurium source in step S3 is 10-40 mmol:9 mmol.

[0017] In a preferred embodiment of the present invention, the method for preparing the TOP-Te solution in step S3 is specifically as follows: adding Te powder to the TOP solution, mixing evenly, and heating; the treatment temperature is 120-140° C., and the time is 4-6 hours.

[0018] In a preferred embodiment of the present invention, in step S4, the quantum dot growth process is adjusted by adjusting the reaction time of the first mixed solution, thereby obtaining quantum dots with different absorption spectra.

[0019] In a preferred embodiment of the present invention, the first temperature in step S4 is 60-130°C.

[0020] In a preferred embodiment of the present invention, the quenching liquid in step S5 is at least one of tetrachloroethylene, toluene, n-hexane, cyclohexane, and n-octane.

[0021] In a preferred embodiment of the present invention, the polar solution in step S5 is at least one of methanol, ethanol, isopropanol and acetone.

[0022] In a preferred embodiment of the present invention, the volume ratio of the polar solution to the silver telluride quantum dot solution in step S5 is 1 to 4:1, preferably 2 to 3:1.

[0023] In a preferred embodiment of the present invention, the non-polar solvent in step S5 is at least one of n-octane, n-hexane, cyclohexane and tetrachloroethylene.

[0024] A silver telluride quantum dot is prepared based on the method for preparing mercapto-free silver telluride colloidal quantum dots described in any of the above items. The silver telluride quantum dot has the characteristics of sharp absorption peak, adjustable size, excellent size distribution and the like.

[0025] In a preferred embodiment of the present invention, the absorption peak wavelength range of the silver telluride quantum dots is 856-1589 nm.

[0026] A liquid phase ligand exchange method for mercapto-free silver telluride colloidal quantum dots, based on the silver telluride quantum dots, a silver telluride quantum dot conductive ink is obtained, and a silver telluride quantum dot film is prepared by a single spin coating process. The liquid phase ligand exchange method comprises the following steps:

[0027] Step 1: Add the silver telluride quantum dots to a non-polar solvent for dispersion to prepare a silver telluride quantum dot solution, then add the silver telluride quantum dot solution to a centrifuge tube containing a ligand exchange solution. Since the polarity of the quantum dot solution and the ligand exchange solution is greatly different, the two solutions are mixed and obvious stratification will occur; then the mixed solution is oscillated for 2 to 3 minutes, and the long-chain ligands on the surface of the quantum dots are replaced and enter the lower solution, and the mixture is allowed to stand for 1 to 2 minutes. After the exchange solution and the quantum dot solution are separated again, the upper clear solution is gently discarded to obtain a first silver telluride quantum dot solution;

[0028] Step 2: adding a non-polar solvent to the first silver telluride quantum dot solution, shaking for 2 to 3 minutes, standing for 1 to 2 minutes, absorbing the upper clear solution, and continuing to add a non-polar solution to the lower quantum dot solution for washing 2 to 3 times to remove free ligands, and finally discarding the upper solution to obtain a second silver telluride quantum dot solution;

[0029] Step 3: Add a non-polar solvent to the second silver telluride quantum dot solution in step 2, centrifuge at 6000 rpm / min for 2 min, discard the supernatant solution, drain the quantum dot precipitate under vacuum conditions, and finally disperse it into the dispersion to obtain silver telluride quantum dot ink;

[0030] Step 4: Take 20uL of the silver telluride ink solution in step 3 and drop it on a glass substrate, and spin-coat it at a speed of 2500rpm / min for 40s to obtain a silver telluride quantum dot film.

[0031] In a preferred embodiment of the present invention, the concentration of the silver telluride quantum dot solution in step 1 is 10-50 mg / mL.

[0032] In a preferred embodiment of the present invention, the wavelength of the silver telluride quantum dots in step 1 is 856-1589 nm.

[0033] In a preferred embodiment of the present invention, the method for preparing the ligand exchange solution in step 1 is specifically: adding silver iodide (AgI) to a mixed solution of n-butylamine (BTA), 2-mercaptoethanol (ME) and N,N-dimethylformamide (DMF), and stirring and dissolving at room temperature.

[0034] In a preferred embodiment of the present invention, the mass of AgI in the ligand exchange solution in step 1 is 0.25-1 mmol;

[0035] In a preferred embodiment of the present invention, the volume ratio of BTA:ME:DMF in step 1 is 100-200:70-140:5000.

[0036] In a preferred embodiment of the present invention, the non-polar solution in step 1 and step 2 is at least one of n-hexane, cyclohexane and n-octane.

[0037] In a preferred embodiment of the present invention, the volume ratio of the silver telluride quantum dots to the non-polar solvent in step 2 is 1-2:3-1, preferably 1:1.

[0038] In a preferred embodiment of the present invention, the method for preparing the dispersion in step 3 is specifically as follows: iodinated amine (NH 4 I) is dissolved in a mixed solution of DMF and 2-phenylethylamine (PEA), and dissolved by stirring at room temperature.

[0039] In a preferred embodiment of the present invention, in step 3, the NH 4 The mass of I is 1 to 1.5 mmol.

[0040] In a preferred embodiment of the present invention, the volume ratio of PEA:DMF in the ligand exchange solution in step 3 is 20-100:980-900.

[0041] In a preferred embodiment of the present invention, the volume ratio of the silver telluride quantum dots to the exchange liquid is 1-3:3-1, preferably 1:1.

[0042] In a preferred embodiment of the present invention, the non-polar solution in step 3 is at least one of tetrachloroethylene and toluene.

[0043] In a preferred embodiment of the present invention, after liquid phase exchange, the concentration of the dispersed silver telluride conductive ink is 100-500 mg / mL.

[0044] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0045] (1) The present invention provides a method for preparing mercapto-free silver telluride colloidal quantum dots, using oleylamine as a synthetic solvent and ligand, and utilizing the weak binding force between oleylamine and the surface of silver telluride to prepare silver telluride quantum dots that are easy to exchange liquid phase ligands.

[0046] (2) Utilizing the nucleophilicity of organic lithium, TOP-Te is modified to improve the activity of TOP-Te, achieve fine control of quantum dot nucleation and growth, and optimize the size distribution of quantum dots. The size and absorption spectrum of silver telluride quantum dots are controlled by controlling parameters such as reaction time, temperature, halogen type, and organic lithium content. The present invention is simple to operate and has good repeatability. The prepared silver telluride quantum dots have excellent size distribution characteristics, sharp exciton absorption peaks, and the absorption peak wavelength is adjustable within the range of 856nm to 1589nm.

[0047] (3) The present invention provides a liquid phase ligand exchange method for silver telluride quantum dots. The method is simple to operate, avoids the use of conventional complex solid phase ligand exchange methods, saves time, and improves experimental repeatability. At the same time, liquid phase ligand exchange can achieve a single spin coating to prepare a quantum dot film of ideal thickness. The quantum dot film has good quality and few defects, and has application potential in the field of short-wave infrared detectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0049] Figure 1 These are photos of TOP-Te solution before and after the addition of organolithium reagent;

[0050] Figure 2 is a photo of the silver telluride quantum dot solution of Example 1 of the present invention;

[0051] Figure 3 is the absorption spectrum of the silver telluride quantum dots of Example 1 of the present invention;

[0052] Figure 4 a and Figure 4 b are low-magnification and high-magnification transmission electron microscope photos of silver telluride quantum dots with a wavelength of about 1589 nm in Example 1 of the present invention, respectively. Figure 4 c is the statistical distribution diagram of its particle size, Figure 4 d is its energy spectrum distribution diagram and atomic ratio;

[0053] Figure 5 is the absorption spectrum of the silver telluride quantum dots of Comparative Example 1 of the present invention;

[0054] Figure 6 is the absorption spectrum of silver telluride quantum dots in Example 2 of the present invention;

[0055] Figure 7 is the absorption spectrum of silver telluride quantum dots in Example 3 of the present invention;

[0056] Figure 8 is the absorption spectrum of the silver telluride quantum dots of Example 4 of the present invention;

[0057] Fig. 9 This is a picture of the liquid phase ligand exchange process of silver telluride quantum dots in Example 5 of the present invention;

[0058] Fig.10 is a picture of a silver telluride quantum dot film and a scanning electron microscope (SEM) picture of Example 5 of the present invention;

[0059] Fig.11 is a Fourier infrared spectrum of the silver telluride quantum dot film of Example 5 of the present invention;

[0060] Fig.12 The present invention is a flow chart of a method for preparing mercapto-free silver telluride colloidal quantum dots and a liquid phase ligand exchange method.

[0061] Fig.13 It is the absorption spectrum of the mercapto-coordinated silver telluride quantum dots and the liquid phase exchange process diagram of comparative example 2 of the present invention. DETAILED DESCRIPTION

[0062] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 creative work are within the scope of protection of the present invention.

[0063] like Fig.12 As shown, the present invention adopts a thiol-free synthesis system, selects oleylamine as the solvent and ligand for quantum dot synthesis, takes silver halide as the cationic precursor, and uses organic lithium-modified TOP-Te as the anionic precursor to prepare thiol-free ligand silver telluride quantum dots by hot injection. By accurately controlling the reaction parameters such as reaction time, temperature, halogen type, and organic lithium content, the size and absorption spectrum of the silver telluride quantum dots can be adjusted. Based on the quantum dot material coordinated by oleylamine, a liquid phase ligand exchange method is used to obtain a colloid-dispersed silver telluride quantum dot conductive ink, and a high-quality silver telluride quantum dot film is prepared by a single spin coating process.

[0064] Example 1

[0065] This embodiment provides a method for preparing mercapto-free silver telluride colloidal quantum dots, comprising the following steps:

[0066] 1. Heat the heating table to 100°C in advance, add 2mmol silver iodide and 12mL oleylamine into a 50mL glass bottle, mix well, and stir at this temperature for 10min to fully dissolve the silver iodide.

[0067] 2. In a 10 mL centrifuge tube, add 200.8 mg of lithium bis(trimethylsilyl)amide and 2.8 mL of oleylamine and stir at room temperature for 5 min to prepare an organic lithium mixed solution.

[0068] 3. Add 1.2 mL of TOP-Te solution to the organic lithium mixed solution in step 2 and oscillate for 2 to 3 minutes to fully mix to prepare a TOP-Te source solution.

[0069] 4. Adjust the heating stage to 80°C, wait until the temperature stabilizes, use a syringe to take 3 mL of the tellurium precursor solution in step 3, and quickly inject it into the silver precursor solution in step 1. React for 60 minutes. During the reaction, take a sample every 10 minutes to obtain a mixed solution of silver telluride quantum dots with different reaction times.

[0070] 5. After the reaction is completed, 10 mL of low-temperature tetrachloroethylene quenching liquid is quickly injected into the silver telluride quantum dot mixed solution to stop the reaction.

[0071] 6. Add 2 times the volume of methanol solvent to the silver telluride quantum dot mixed solution, centrifuge at 6000 rpm / min for 2 minutes, discard the supernatant solution, and obtain the quantum dot product.

[0072] 7. Disperse the quantum dot product into 12 mL of n-octane solvent to obtain a silver telluride quantum dot solution.

[0073] Figure 1 These are photos of the TOP-Te precursor solution before and after the addition of the organic lithium reagent. It can be seen that after the addition of the organic lithium reagent, the TOP-Te precursor solution becomes darker, which confirms that the organic lithium activates the TOP-Te source.

[0074] Figure 2 This is a photograph of the solution of silver telluride quantum dots in Example 1. It can be seen that the prepared quantum dots show good solution dispersibility.

[0075] In order to better characterize the properties of the silver telluride quantum dots prepared in this embodiment, the present invention uses a spectrophotometer and a transmission electron microscope to characterize and analyze the quantum dots. Figure 3This is the absorption spectrum of silver telluride quantum dots prepared in Example 1. As can be seen from the figure, the absorption peak is sharp, indicating that the size of the prepared quantum dots is uniform. As the reaction time increases, the absorption peak shows an obvious red shift, which indicates that the size of the quantum dots gradually increases over time. After 60 minutes, the size of the silver telluride quantum dots basically no longer increases.

[0076] Figure 4 (ac) are transmission electron microscope images and particle size distribution statistics of silver telluride quantum dots with an absorption peak position of approximately 1589 nm. It can be seen that the silver telluride quantum dots exhibit excellent monodispersity and size distribution characteristics. Figure 4 d is the energy dispersive X-ray spectrum of the quantum dots. The spectrum analysis shows that the molar ratio of Ag / Te in the quantum dots is about 2.3:1, slightly higher than the stoichiometric ratio of 2:1, which indicates that the surface of the quantum dots is Ag-enriched. This Ag-enriched surface will be beneficial to the colloidal stability of silver telluride quantum dots.

[0077] Comparative Example 1

[0078] In order to better illustrate the effect of adding an organic lithium reagent, a silver telluride quantum dot was prepared in this comparative example. The preparation process was compared with that in Example 1, and the only difference was that in step 2, the amount of organic lithium reagent added was 0, and the remaining steps were the same.

[0079] from Figure 5 a It can be seen that when the amount of organic lithium reagent added is 0, the solution at the end of the reaction is black, indicating the formation of silver telluride quantum dots. The quantum dot solution was centrifuged and cleaned and then characterized and analyzed by spectrophotometer. Figure 5 b It can be seen that the quantum dot absorption spectrum is very broad, and there is no obvious exciton absorption peak, which indicates that the prepared silver telluride quantum dots are severely agglomerated. This result can explain that it is difficult to obtain silver telluride quantum dots of uniform size when only TOP-Te is used as the Te source because of its low activity.

[0080] Example 2

[0081] The technical solution of this embodiment is basically similar to that of embodiment 1, except that the first temperature is different, and the embodiment includes the following steps:

[0082] 1. Heat the heating table to 100°C in advance, add 2mmol silver iodide and 12mL oleylamine into a 50mL glass bottle, mix well, and stir at this temperature for 10min to fully dissolve the silver iodide.

[0083] 2. In a 10 mL centrifuge tube, add 200.8 mg of lithium bis(trimethylsilyl)amide and 2.8 mL of oleylamine and stir at room temperature for 5 min to prepare an organic lithium mixed solution.

[0084] 3. Add 1.2 mL of TOP-Te solution to the organic lithium mixed solution in step 2 and oscillate for 2 to 3 minutes to fully mix to prepare a TOP-Te source solution.

[0085] 4. Adjust the heating stage to the first temperature, wait until the temperature stabilizes, use a syringe to take 3 mL of the tellurium precursor solution in step 3, quickly inject it into the silver precursor solution in step 1, and maintain it at the reaction temperature for 10 minutes.

[0086] The first temperature is 60° C., 90° C. or 100° C. for synthesis.

[0087] 5. After the reaction is completed, 10 mL of low-temperature tetrachloroethylene quenching liquid is quickly injected into the silver telluride quantum dot mixed solution to stop the reaction.

[0088] 6. Add 2 times the volume of methanol solvent to the silver telluride quantum dot mixed solution, centrifuge at 600 rpm / min for 2 min, discard the supernatant solution, and obtain a quantum dot product.

[0089] 7. Disperse the quantum dot product into 12 mL of n-octane solvent to obtain a quantum dot solution.

[0090] The absorption spectrum of the prepared product is shown in Figure 6 As shown, it can be seen that the size of silver telluride quantum dots can be controlled by regulating the reaction temperature.

[0091] Example 3

[0092] The technical scheme of this embodiment is basically similar to that of embodiment 1, except that the type of silver source used is different, and the method includes the following steps:

[0093] 1. Heat the heating table to 100°C in advance, add 2 mmol of silver source and 12 mL of oleylamine into a 50 mL glass bottle, mix well, and stir at this temperature for 10 min to fully dissolve the silver source.

[0094] Among them, the silver source is prepared using silver iodide, silver bromide and silver chloride respectively.

[0095] 2. In a 10 mL centrifuge tube, add 200.8 mg of lithium bis(trimethylsilyl)amide and 2.8 mL of oleylamine and stir at room temperature for 5 min to prepare an organic lithium mixed solution.

[0096] 3. Add 1.2 mL of TOP-Te solution to the organic lithium mixed solution in step 2 and oscillate for 2 to 3 minutes to fully mix to prepare a TOP-Te source solution.

[0097] 4. Adjust the heating stage to 80°C. When the temperature stabilizes, use a syringe to take 3 mL of the tellurium precursor solution in step 3, quickly inject it into the solution in step 1, and maintain it at the reaction temperature for 10 minutes.

[0098] 5. After the reaction is completed, quickly inject 10 mL of low-temperature tetrachloroethylene quenching liquid into the silver telluride quantum dot mixed solution to stop the reaction.

[0099] 6. Add 2 times the volume of methanol solvent to the silver telluride quantum dot mixed solution, centrifuge at 6000 rpm / min for 2 min, and discard the supernatant solution to obtain quantum dot precipitation.

[0100] 7. Disperse the quantum dot precipitate in 12 mL of n-octane solvent to obtain a quantum dot solution.

[0101] The absorption spectrum of the prepared product is shown in Figure 7 As shown in the spectrum, it can be seen that silver telluride quantum dots with sharp absorption peaks can be prepared by using different types of silver sources.

[0102] Example 4

[0103] The technical scheme of this embodiment is basically similar to that of embodiment 1, except that the concentration of organic lithium is different, and comprises the following steps:

[0104] 1. Heat the heating table to 100°C in advance, add 2mmol silver iodide and 12mL oleylamine into a 50mL glass bottle, mix well, and stir at this temperature for 10min to fully dissolve the silver iodide.

[0105] 2. In a 10 mL centrifuge tube, add lithium bis(trimethylsilyl)amide and 2.8 mL oleylamine and stir at room temperature for 5 min.

[0106] The content of lithium bis(trimethylsilyl)amide is 200.8 mg, 267.7 mg or 334.67 mg respectively. Due to the limited solubility of organic lithium in oleylamine, the present invention does not conduct experiments with higher content.

[0107] 3. Add 1.2 mL of TOP-Te solution to the organic lithium mixed solution in step 2 and oscillate for 2 to 3 minutes to fully mix to prepare a TOP-Te source solution.

[0108] 4. Adjust the heating stage to 80°C, wait until the temperature is stable, use a syringe to take 3 mL of the tellurium precursor solution in step 3, quickly inject it into the silver precursor solution in step 1, and react for 30 minutes to obtain a mixed solution of silver telluride quantum dots.

[0109] 5. After the reaction is completed, 10 mL of low-temperature tetrachloroethylene quenching liquid is quickly injected into the silver telluride quantum dot mixed solution to stop the reaction.

[0110] 6. Add 2 times the volume of methanol solvent to the silver telluride quantum dot mixed solution, centrifuge at 6000 rpm / min for 2 min, and discard the supernatant solution to obtain quantum dot precipitation.

[0111] S6. Disperse the quantum dot precipitate into 12 mL of n-octane solvent to obtain a quantum dot solution.

[0112] The absorption spectrum of the prepared product is shown in Figure 8 As shown, it can be seen that when the organic lithium reagent increases, the absorption peak position of the silver telluride quantum dots blue shifts, which indicates that with the increase of the organic lithium content, the activity of the TOP-Te source will gradually increase, resulting in faster nucleation of quantum dots and smaller quantum dot size.

[0113] Example 5

[0114] This embodiment provides a liquid phase ligand exchange method for silver telluride quantum dots, comprising the following steps:

[0115] 1. The silver telluride quantum dots with an absorption peak wavelength of about 1589 nm prepared in Example 1 are dispersed in n-octane to prepare a quantum dot solution with a concentration of about 20 mg / mL.

[0116] 2. In a 10 mL centrifuge tube, first add 2 mL of ligand exchange solution, then add 2 mL of the silver telluride quantum dot solution, place the centrifuge tube on an oscillator and fully shake for 2 to 3 minutes, let it stand for 1 to 2 minutes, wait for the solution to separate, and discard the upper clear solution.

[0117] 3. Add an equal volume of n-octane to the lower quantum dot solution, place the centrifuge tube on an oscillator and shake it thoroughly for 2 to 3 minutes, then let it stand for 1 to 2 minutes, wait for the solution to separate into layers, remove the upper clear solution, and continue to add non-polar solution to the lower quantum dot solution for 2 to 3 times to fully remove the free ligands in the solution.

[0118] 4. Add 1 volume of tetrachloroethylene to the silver telluride quantum dot solution layer in step 3, mix well, centrifuge at 6000 rpm / min for 2 min, discard the supernatant solution, drain the silver telluride quantum dot precipitate under vacuum conditions, and finally disperse the quantum dot precipitate into the dispersion to obtain silver telluride quantum dot conductive ink with a concentration of about 300 mg / mL.

[0119] 5. Take 20uL of the silver telluride ink solution and drop it on a glass substrate, and spin-coat it at a speed of 2500rpm / min for 40s to prepare a silver telluride quantum dot film.

[0120] Fig. 9This is a picture of the liquid phase ligand exchange process of silver telluride quantum dots. It can be seen that after the quantum dot solution is added to the ligand exchange liquid layer and fully mixed, the quantum dots undergo ligand exchange and gradually enter the lower layer and finally all enter the ligand exchange liquid layer, indicating that the long-chain ligands on the surface of the quantum dots have been replaced by short-chain ligands.

[0121] Fig.10 The following are photos and scanning electron microscope (SEM) images of silver telluride quantum dot films. It can be seen from the figures that the silver telluride quantum dot film prepared by the liquid phase ligand exchange method of the present invention is flat and dense, has no cracks and holes, and has good film quality. Compared with the solid phase exchange method of the prior art, the liquid phase ligand exchange method proposed in the present invention is simple to operate, does not require cumbersome exchange steps, saves time, and has better experimental repeatability. The liquid phase ligand exchange method can achieve a single spin coating to prepare a film of ideal thickness, avoids the waste of raw materials, and the prepared film is denser and of better quality. In addition, through the liquid phase ligand exchange method, the ligand exchange on the surface of the quantum dots is more thorough and has fewer defects.

[0122] Fig.11 This is a Fourier infrared spectrum of the silver telluride quantum dot film. After the ligands on the quantum dot surface are exchanged, the spectrum still shows a sharp absorption peak, indicating that the liquid phase ligand exchange method of the present invention is gentle and does not damage the quantum dots. The quantum dots after exchange can still maintain a high stability.

[0123] Comparative Example 2

[0124] This comparative example provides a preparation method of mercapto-coordinated silver telluride quantum dots and a liquid phase exchange method, comprising the following steps:

[0125] 1. In a 50 mL three-necked flask, add 1 mmol of silver acetate, 1.3 mL of 1-octanethiol (OTT) and 10 mL of ODE, and then evacuate the flask at 80 °C for 10 min.

[0126] 2. Fill the three-necked flask with argon and raise the temperature to 160°C. When the temperature stabilizes, quickly inject 0.2 mL of 1MTOP-Te. After reacting for 10 minutes, quench the reaction with tetrafluoroethylene.

[0127] 3. Add methanol for centrifugal washing, and finally disperse the quantum dot product in n-octane with a concentration of about 20 mg / mL.

[0128] 4. In a 10mL centrifuge tube, first add 1mL of ligand exchange solution, and then add 1mL of the above-mentioned OTT-coordinated silver telluride quantum dot solution. Place the centrifuge tube on an oscillator and shake it thoroughly for 2 to 3 minutes. Let it stand for 1 to 2 minutes and observe the exchange of quantum dots.

[0129] Fig.13a is the absorption spectrum of silver telluride quantum dots prepared using OTT ligands. It can be seen from the figure that the absorption peak of quantum dots is about 1044nm. Fig.13 b is OTT-Ag 2 Diagram of the liquid phase exchange process of Te quantum dots. It can be seen from the figure that when the quantum dot solution and the ligand exchange solution are mixed, the solution does not stratify, indicating that the long-chain ligands on the surface of the quantum dots are not completely replaced by short-chain ligands. This is mainly because OTT has a stronger coordination ability with Ag, which makes it difficult to completely replace the long-chain ligands on the surface with short-chain ligands.

[0130] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing mercapto-free silver telluride colloidal quantum dots, characterized in that: The following steps are involved: S1, adding a silver source to oleylamine, mixing evenly, and then heating under an inert gas atmosphere to prepare a solution A; S2, adding the organic lithium reagent to the oleylamine solution, mixing evenly, to obtain solution B; S3, adding the solution B obtained in step S2 to the TOP-Te solution, mixing evenly, to obtain a solution C; S4. In an inert atmosphere, heating solution A to a first temperature, rapidly hot-injecting the freshly prepared solution C into solution A to form a first mixed solution, and reacting for 10 to 60 minutes; S5, quickly adding a quenching liquid to the first mixed solution prepared in step S4, then adding a polar solvent for washing, centrifuging to separate the silver telluride quantum dots, and dispersing the silver telluride quantum dots in a non-polar solvent.

2. The method for preparing mercapto-free silver telluride colloidal quantum dots according to claim 1, characterized in that: In step S1, the silver source is one of silver iodide, silver bromide and silver chloride.

3. The method for preparing mercapto-free silver telluride colloidal quantum dots according to claim 1, characterized in that: The organic lithium reagent in step S2 is one of lithium bis(trimethylsilyl)amide, n-butyl lithium and lithium diisopropylamide.

4. The method for preparing mercapto-free silver telluride colloidal quantum dots according to claim 1, characterized in that: The mass of the organic lithium in step S2 is 0.9-1.5 mmol.

5. The method for preparing mercapto-free silver telluride colloidal quantum dots according to claim 1, characterized in that: In the step S4, the first temperature is 60-130°C.

6. The method for preparing mercapto-free silver telluride colloidal quantum dots according to claim 1, characterized in that: In step S5, the volume ratio of the polar solution to the silver telluride quantum dot solution is 1 to 4:

1.

7. A method for preparing mercapto-free silver telluride colloidal quantum dots according to any one of claims 1 to 6, wherein: The absorption peak wavelength range of the silver telluride quantum dots is 856-1589 nm.

8. A liquid phase ligand exchange method for mercapto-free silver telluride colloidal quantum dots, using the silver telluride quantum dots described in claim 7 to prepare a silver telluride quantum dot film, characterized in that: The liquid phase ligand exchange method comprises the following steps: Step 1: Add the silver telluride quantum dots to a non-polar solvent for dispersion to prepare a silver telluride quantum dot solution, then add the silver telluride quantum dot solution to a centrifuge tube containing a ligand exchange solution. Since the polarity of the quantum dot solution and the ligand exchange solution is greatly different, the two solutions are mixed and obvious stratification will occur; then the mixed solution is oscillated for 2 to 3 minutes, and the long-chain ligands on the surface of the quantum dots are replaced and enter the lower solution, and the mixture is allowed to stand for 1 to 2 minutes. After the exchange solution and the quantum dot solution are separated again, the upper clear solution is gently discarded to obtain a first silver telluride quantum dot solution; Step 2: adding a non-polar solvent to the first silver telluride quantum dot solution, shaking for 2 to 3 minutes, standing for 1 to 2 minutes, absorbing the upper clear solution, and continuing to add a non-polar solution to the lower quantum dot solution for washing 2 to 3 times to remove free ligands, and finally discarding the upper solution to obtain a second silver telluride quantum dot solution; Step 3: Add a non-polar solvent to the second silver telluride quantum dot solution in step 2, centrifuge at 6000 rpm / min for 2 min, discard the supernatant solution, drain the quantum dot precipitate under vacuum conditions, and finally disperse it into the dispersion to obtain silver telluride quantum dot ink; Step 4: Take 20uL of the silver telluride quantum dot ink solution in step 3 and drop it on a glass substrate, and spin-coat it at a speed of 2500rpm / min for 40s to obtain a silver telluride quantum dot film.

9. The liquid phase ligand exchange method of mercapto-free silver telluride colloidal quantum dots according to claim 8, characterized in that: The concentration of the silver telluride quantum dot solution in step 1 is 10-50 mg / mL.

10. The liquid phase ligand exchange method of mercapto-free silver telluride colloidal quantum dots according to claim 8, characterized in that: The concentration of the silver telluride conductive ink after liquid phase exchange is 100-500 mg / mL.

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