A method for preparing lead sulfide quantum dots, lead sulfide quantum dots and applications

Abstract

The application relates to a lead sulfide quantum dot preparation method, which specifically comprises the following steps: rapidly injecting a ZnS quantum dot solution into a mixed solution of lead chloride and oleylamine to make the solution nucleate; after maintaining for a certain time, rapidly injecting an amine solution of zinc dithiocarbamate; and controlling the size of the synthesized PbS quantum dots by controlling the temperature and the concentration of the sulfur source. The application provides a single precursor zinc dithiocarbamate to replace the ZnS quantum dots as the growth sulfur source, so that the time is saved, and the complex steps of synthesizing the ZnS quantum dots are omitted.

Description

Technical Field

[0001] This invention relates to the field of semiconductor nanomaterials technology, and in particular to a method for preparing lead sulfide quantum dots, lead sulfide quantum dots, and their applications. Background Technology

[0002] Currently, the main methods for synthesizing PbS quantum dots include hydrothermal / solvothermal methods, hot-injection methods, heat-up methods, co-precipitation methods, sol-gel methods, microemulsion methods, and pyrolysis methods. Cation exchange is a type of hot-injection method. Although this synthesis method is complex, it yields quantum dots with precisely controllable peak positions, uniform size, and good luminescence efficiency and stability. Therefore, quantum dots prepared by cation exchange are more suitable for fabricating optoelectronic devices.

[0003] The cation exchange method generally involves first synthesizing zinc sulfide (ZnS) quantum dots of different sizes, which are then used for the nucleation and dropwise growth of PbS quantum dots, respectively.

[0004] The synthesis of ZnS quantum dots uses zinc stearate as the zinc source and thioacetamide as the sulfur source, and is carried out under a nitrogen atmosphere by heating. Compared with the synthesis, the cleaning of ZnS quantum dots is more complex. The cleaning steps for ZnS quantum dots of different sizes are not entirely the same. Generally, anhydrous ethanol is used as the antisolvent. After centrifugation, the supernatant in each tube is aspirated with a dropper, leaving the viscous liquid at the bottom. This step is repeated several times to obtain pure, oily ZnS quantum dots. However, ZnS quantum dots obtained by this method not only require a large amount of antisolvent, manpower, and time, but also make it difficult to guarantee the reproducibility of ZnS quantum dot concentration.

[0005] To optimize the cation exchange method, it is desirable to find a sulfur precursor that can replace the ZnS quantum dots used for dropwise growth, which can synthesize PbS quantum dots with better size distribution while saving time, manpower and other costs. Summary of the Invention

[0006] In the prior art, the synthesis and cleaning steps of ZnS quantum dots used for growth are very complicated, the concentration is difficult to control, and the drop-injection method is time-consuming. The present invention provides a single precursor, zinc dithiocarbamate, to replace ZnS quantum dots as the sulfur source for growth. This not only eliminates the need for drop-injection, saving time, but also eliminates the complicated steps of synthesizing ZnS quantum dots.

[0007] In view of the problems existing in the prior art, the present invention aims to provide a method for preparing lead sulfide quantum dots, the method comprising:

[0008] S1. Dissolve lead chloride in oleylamine to form a first solution in which the lead chloride reaches a first concentration;

[0009] S2. Dissolve zinc dithiocarbamate in oleylamine to form a second solution of zinc dithiocarbamate at a second concentration; the zinc dithiocarbamate includes zinc diethyl dithiocarbamate, zinc dimethyl dithiocarbamate, or zinc dibutyl dithiocarbamate.

[0010] S3. Rapidly inject zinc sulfide quantum dots into the first solution and maintain for a first time. Rapidly inject the second solution into the first solution to form a first mixture and maintain for a second time, so that the quantum dots in the mixture can nucleate and grow, thereby obtaining lead sulfide quantum dots of a predetermined size.

[0011] According to one embodiment of the present invention, the second concentration is greater than the first concentration, and the mass ratio of the zinc sulfide quantum dots to the zinc dithiocarbamate is less than 6.

[0012] According to an embodiment of the present invention, after step S3, the method further includes:

[0013] S4. Cool the first mixture in a water bath, injecting hexane and oleic acid during the cooling process, and then centrifuge. Extract the supernatant of the first mixture and wash it with a polar solvent to separate the lead sulfide quantum dots. The polar solvent includes solvents such as acetone or ethanol.

[0014] According to one embodiment of the present invention, the centrifugation speed in step S4 is 4000-7000 r / min.

[0015] According to an embodiment of the present invention, step S1 further includes:

[0016] After the first solution is formed, a vacuum is drawn and a protective gas is introduced. The temperature is raised and allowed to stand, then the temperature is lowered to 100℃-130℃.

[0017] According to one embodiment of the present invention, the protective gas includes an inert gas, nitrogen, or argon.

[0018] According to one embodiment of the present invention, the first time ranges from 15 seconds to 60 seconds.

[0019] According to one embodiment of the present invention, the value of the second time is no greater than 120 minutes.

[0020] The present invention also provides a lead sulfide quantum dot, comprising: the lead sulfide quantum dot being prepared by the method described in any one of the above embodiments.

[0021] The present invention also provides an application of lead sulfide quantum dots prepared by any of the methods described in the above embodiments, characterized in that the lead sulfide quantum dots are applied to colloidal quantum dot infrared detectors, solar cells, or light-emitting devices.

[0022] The beneficial effects of this invention are as follows: By rapidly injecting a ZnS quantum dot solution into a mixture of lead chloride and oleylamine to induce nucleation, and maintaining this state for a certain period, a zinc dithiocarbamate amine solution is rapidly injected. The size of the synthesized PbS quantum dots can be controlled by adjusting the temperature and sulfur source concentration. This invention provides a single precursor, zinc dithiocarbamate, to replace ZnS quantum dots as the sulfur source for growth. This not only eliminates the need for dropwise injection, saving time, but also simplifies the complex steps involved in synthesizing ZnS quantum dots. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments or prior art, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is the growth absorption curve of PbS quantum dots in Embodiment 1 of the present invention;

[0025] Figure 2 This is the growth absorption curve of PbS quantum dots in Embodiment 2 of the present invention;

[0026] Figure 3 This is the growth absorption curve of PbS quantum dots in Example 3 of the present invention;

[0027] Figure 4 This is the growth absorption curve of PbS quantum dots in Example 4 of the present invention;

[0028] Figure 5 This is the growth absorption curve of PbS quantum dots in Example 5 of the present invention;

[0029] Figure 6 This is the growth absorption curve of PbS quantum dots in Example 6 of the present invention;

[0030] Figure 7 This is an X-ray diffraction pattern of PbS quantum dots according to an embodiment of the present invention;

[0031] Figure 8 This is a TEM image of the PbS quantum dots in an embodiment of the present invention. Detailed Implementation

[0032] The following descriptions of the embodiments are made with reference to the accompanying illustrations to illustrate specific embodiments in which the invention can be implemented.

[0033] Since the concentration of ZnS quantum dots is a key factor affecting the synthesis of PbS quantum dots, it is necessary to dilute them to the same concentration using absorption spectroscopy before each cation exchange to ensure experimental repeatability, which makes the synthesis of PbS quantum dots more complicated.

[0034] The typical method involves rapidly injecting a ZnS quantum dot solution into a mixture of lead chloride and oleylamine to induce nucleation. After maintaining this state for 1 minute, small-sized ZnS quantum dot solution is continuously and slowly added dropwise at varying rates to continue growth. Growth is stopped after approximately 60 minutes of dropwise addition, followed by cooling in a water bath, injection of n-hexane and oleic acid, and washing with acetone. While this method can synthesize PbS quantum dots with good size distribution and high stability in air, it requires a significant amount of time and reagents.

[0035] Example 1

[0036] To address the shortcomings of existing technologies, an embodiment of the present invention provides a method for preparing lead sulfide quantum dots, the specific steps of which include:

[0037] Before the synthesis of lead sulfide quantum dots, the ZnS quantum dots used for nucleation of lead sulfide quantum dots are synthesized first, specifically as follows:

[0038] First, weigh out thioacetamide and zinc stearate in a molar ratio of 1:2, then add an appropriate amount of oleylamine to make the concentration of zinc stearate 1 mmol / ml. Finally, add excess octadecene (molar ratio of 2:1 with oleylamine), evacuate the vacuum, purge with nitrogen, raise the temperature to 90-220℃, and maintain for 15-80 minutes.

[0039] Secondly, heat the solution in a water bath to 30-40℃ until it becomes cloudy. Then, add an appropriate amount of n-octylamine to clarify it.

[0040] Next, after clarification, add the solution to a polar solvent, shake well, and centrifuge at 4000-7000 rpm for 3 minutes. Repeat twice.

[0041] Finally, the supernatant was removed with a dropper, and octadecene was added for dilution to obtain zinc sulfide quantum dots.

[0042] The synthesis steps of lead sulfide quantum dots also include:

[0043] S1. Dissolve lead chloride in oleylamine to form a first solution in which the lead chloride reaches a first concentration;

[0044] After the first solution is formed, a vacuum is drawn and a protective gas is introduced. The temperature is raised to 140°C and held for 30 minutes, then cooled to 100-300°C. The protective gas is preferably nitrogen, argon, or another inert gas.

[0045] S2. Dissolve zinc diethyldithiocarbamate in oleylamine to form a second solution of zinc diethyldithiocarbamate at a second concentration.

[0046] Wherein, the second concentration is greater than the value of the first concentration; preferably, the first concentration is 0.3 mol / L, the second concentration is preferably 0.6 mol / L, and the ratio of the first concentration to the second concentration is preferably 1:2. Under this ratio, quantum dots that absorb in the range of 1200 nm to 2000 nm can be obtained, and the size distribution is better.

[0047] S3. Rapidly inject 0.5 ml of zinc sulfide quantum dots into the first solution and maintain for a first time. Then rapidly inject the second solution into the first solution to form a first mixture and maintain for a second time, so that the quantum dots in the mixture can nucleate and grow, thereby obtaining lead sulfide quantum dots of a predetermined size.

[0048] In this process, 0.5 ml of the previously prepared zinc sulfide quantum dots are rapidly injected into the first solution to allow nucleation for a first time, preferably 15-60 seconds. Then, the second solution is mixed with the first solution, and the growth of the lead sulfide quantum dots is controlled for a second time. Preferably, the molar ratio of ZnS to Zn(S₂CNEt₂)₂ is maintained at 3:1. The second time is preferably no more than 120 minutes, and the required second time duration is determined according to the desired size of the lead sulfide quantum dots. Generally, the longer the growth time, the larger the size of the obtained lead sulfide quantum dots. However, after 120 minutes, the size of the lead sulfide quantum dots stops growing, and their size distribution begins to deteriorate.

[0049] Following step S3, the method further includes:

[0050] S4. Cool the first mixture in a water bath, inject hexane and oleic acid during the cooling process, and centrifuge; extract the supernatant of the first mixture and add a polar solvent for washing to separate the lead sulfide quantum dots.

[0051] After the lead sulfide quantum dots have grown to the desired size, the first mixture is rapidly cooled in a water bath. When the temperature drops to approximately 70°C, 90 ml of n-hexane is injected, and when the temperature drops further to approximately 40°C, 40 ml of oleic acid is injected. After the injection is completed, the mixture is maintained at room temperature for at least 10 minutes. Next, the first mixture is centrifuged at a speed preferably of 4000-7000 r / min for at least 3 minutes. The supernatant of the first mixture is extracted and washed with acetone or ethanol. The centrifugation process is repeated twice to separate the lead sulfide quantum dots.

[0052] Example 2

[0053] This embodiment is basically similar to the technical solution of Embodiment 1, except that the ratio of zinc sulfide quantum dots to zinc diethyldithiocarbamate is different.

[0054] The synthesis steps of lead sulfide quantum dots also include:

[0055] S3. Rapidly inject 0.25 ml of zinc sulfide quantum dots into the first solution and maintain for a first time. Then rapidly inject the second solution into the first solution to form a first mixture and maintain for a second time, so that the quantum dots in the mixture can nucleate and grow, thereby obtaining lead sulfide quantum dots of a predetermined size.

[0056] In this process, 0.25 ml of the previously prepared zinc sulfide quantum dots are rapidly injected into the first solution to allow nucleation for a first time, preferably 15-60 seconds. Then, the second solution is mixed with the first solution, and the growth of the lead sulfide quantum dots is controlled for a second time. Preferably, the molar ratio of ZnS to Zn(S₂CNEt₂)₂ is maintained at 1.5:1. The second time is preferably no more than 120 minutes, and the duration of the second time required for growth is determined according to the desired size of the lead sulfide quantum dots. Generally, the longer the growth time, the larger the size of the obtained lead sulfide quantum dots. However, after 120 minutes, the size of the lead sulfide quantum dots stops growing, and their size distribution begins to deteriorate.

[0057] Example 3

[0058] This embodiment is basically similar to the technical solution of Embodiment 1, except that the ratio of zinc sulfide quantum dots to zinc diethyldithiocarbamate is different.

[0059] The synthesis steps of lead sulfide quantum dots also include:

[0060] S3. Rapidly inject 0.125 ml of zinc sulfide quantum dots into the first solution and maintain for a first time. Then rapidly inject the second solution into the first solution to form a first mixture and maintain for a second time, so that the quantum dots in the mixture can nucleate and grow, thereby obtaining lead sulfide quantum dots of a predetermined size.

[0061] In this process, 0.125 ml of the previously prepared zinc sulfide quantum dots are rapidly injected into the first solution to allow nucleation for a first time, preferably 15-60 seconds. Then, the second solution is mixed with the first solution, and the size growth of the lead sulfide quantum dots is controlled for a second time. The molar ratio of ZnS:Zn(S₂CNEt₂)₂ is maintained at 0.75:1. The second time is preferably no more than 120 minutes, and the required second time duration is determined based on the desired size of the lead sulfide quantum dots. Generally, the longer the growth time, the larger the size of the obtained lead sulfide quantum dots. However, after 120 minutes, the size of the lead sulfide quantum dots stops growing, and their size distribution begins to deteriorate.

[0062] Example 4

[0063] This embodiment is basically similar to the technical solution of Embodiment 1, except that the ratio of zinc sulfide quantum dots to zinc diethyldithiocarbamate is different.

[0064] The synthesis steps of lead sulfide quantum dots also include:

[0065] S3. Rapidly inject 0.05 ml of zinc sulfide quantum dots into the first solution and maintain for a first time. Then rapidly inject the second solution into the first solution to form a first mixture and maintain for a second time, so that the quantum dots in the mixture can nucleate and grow, thereby obtaining lead sulfide quantum dots of a predetermined size.

[0066] In this process, 0.05 ml of the previously prepared zinc sulfide quantum dots are rapidly injected into the first solution to allow nucleation for a first time, preferably 15-60 seconds. Then, the second solution is mixed with the first solution, and the size growth of the lead sulfide quantum dots is controlled for a second time. Preferably, the molar ratio of ZnS to Zn(S₂CNEt₂)₂ is maintained at 0.3:1. The second time is preferably no more than 120 minutes, and the required second time duration is determined according to the desired size of the lead sulfide quantum dots. Generally, the longer the growth time, the larger the size of the obtained lead sulfide quantum dots. However, after 120 minutes, the size of the lead sulfide quantum dots stops growing, and their size distribution begins to deteriorate.

[0067] Example 5

[0068] This embodiment is basically similar to the technical solution of Embodiment 1, except that the single precursor is zinc dimethyl dithiocarbamate.

[0069] The synthesis steps of lead sulfide quantum dots also include:

[0070] S2. Dissolve zinc dimethyldithiocarbamate in oleylamine to form a second solution of zinc dimethyldithiocarbamate at a second concentration.

[0071] S3. Rapidly inject 0.5 ml of zinc sulfide quantum dots into the first solution and maintain for a first time. Then rapidly inject the second solution into the first solution to form a first mixture and maintain for a second time, so that the quantum dots in the mixture can nucleate and grow, thereby obtaining lead sulfide quantum dots of a predetermined size.

[0072] Example 6

[0073] This embodiment is basically similar to the technical solution of Embodiment 1, except that the single precursor is zinc dibutyldithiocarbamate.

[0074] The synthesis steps of lead sulfide quantum dots also include:

[0075] S2. Dissolve zinc dibutyldithiocarbamate in oleylamine to form a second solution of zinc dibutyldithiocarbamate at a second concentration.

[0076] S3. Rapidly inject 0.5 ml of zinc sulfide quantum dots into the first solution and maintain for a first time. Then rapidly inject the second solution into the first solution to form a first mixture and maintain for a second time, so that the quantum dots in the mixture can nucleate and grow, thereby obtaining lead sulfide quantum dots of a predetermined size.

[0077] One embodiment of the present invention also provides a lead sulfide quantum dot, comprising the lead sulfide quantum dot prepared by the method described in any of the above embodiments.

[0078] like Figure 1-8 As shown, the growth absorption curves of lead sulfide quantum dots directly obtained by the preparation methods described in Examples 1 to 6 of the present invention, as well as the X-ray diffraction pattern and TEM image of the lead sulfide quantum dots with an absorption peak at 1700 nm, demonstrate that the lead sulfide quantum dots synthesized by the preparation method of the present invention have high stability and good size distribution.

[0079] This invention also protects the specific applications of the lead sulfide quantum dots prepared in the above embodiments.

[0080] Semiconductor quantum dots are quasi-zero-dimensional nanomaterials. When the particle size enters the nanoscale, size confinement induces size effects, quantum confinement effects, macroscopic quantum tunneling effects, and surface effects. This results in low-dimensional properties in nanoscale systems that differ from macroscopic and microscopic systems, exhibiting many physicochemical properties unlike those of bulk materials. All properties of quantum dots change with their size; for example, the emission and absorption wavelengths of quantum dots can be tuned by adjusting their size. Furthermore, colloidal quantum dots prepared through solution processing offer advantages such as low cost and large-scale production capabilities, making them widely used in optoelectronic devices such as solar cells, light-emitting diodes, field-effect transistors, and photodetectors.

[0081] One embodiment of this invention, a colloidal quantum dot infrared detector, as a new generation of near-infrared detectors, possesses characteristics such as simple material preparation, tunable bandgap, low cost, and ease of integration with various readout circuits, and is expected to occupy a place in the field of near-infrared detectors. Since the IV-VI group binary compound PbS is a narrow bandgap semiconductor material with advantages such as a large dielectric constant, a narrow bandgap (0.41 eV), a wide absorption spectrum (<800 nm), and a high absorption coefficient, PbS quantum dots have broad market prospects in optoelectronic devices and communications.

[0082] A colloidal quantum dot infrared detector is also provided, comprising lead sulfide quantum dots prepared by the method described in any of the above embodiments. The lead sulfide quantum dots exhibit high stability and good size distribution, making them suitable for use in colloidal quantum dot infrared detectors. Furthermore, as a next-generation near-infrared detector, the colloidal quantum dot infrared detector possesses advantages such as simple material preparation, adjustable material bandgap, low cost, and ease of integration with various readout circuits, and is expected to gain a foothold in the near-infrared detector field.

[0083] In summary, this invention provides a method for preparing lead sulfide quantum dots, lead sulfide quantum dots, and a detector. The method involves rapidly injecting a ZnS quantum dot solution into a mixture of lead chloride and oleylamine to induce nucleation. After maintaining this state for a certain period, an amine solution of zinc dithiocarbamate is rapidly injected. The size of the synthesized PbS quantum dots is controlled by adjusting the temperature and sulfur source concentration. This invention provides a single precursor, zinc dithiocarbamate, to replace ZnS quantum dots as the sulfur source for growth, eliminating the need for dropwise injection, saving time, and simplifying the complex steps involved in synthesizing ZnS quantum dots.

[0084] It should be noted that although the present invention has been disclosed above with specific embodiments, the above embodiments are not intended to limit the present invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope defined in the claims.

Claims

1. A method for preparing lead sulfide quantum dots, characterized in that, The preparation method includes: S1. Dissolve lead chloride in oleylamine to form a first solution in which the lead chloride reaches a first concentration; Step S1 further includes: after the first solution is formed, evacuating and then filling with protective gas, heating and letting stand, and then cooling to 100℃-130℃; S2. Dissolve zinc dithiocarbamate in oleylamine to form a second solution of zinc dithiocarbamate at a second concentration. S3. Rapidly inject zinc sulfide quantum dots into the first solution and maintain for a first time. Rapidly inject the second solution into the first solution to form a first mixture and maintain for a second time, so that the quantum dots in the mixture can nucleate and grow, and obtain lead sulfide quantum dots of a predetermined size. The first time interval is between 15 seconds and 60 seconds. The value of the second time is no greater than 120 minutes; The second concentration is greater than the first concentration, and the mass ratio of the zinc sulfide quantum dots to the zinc dithiocarbamate is less than 6.

2. The method for preparing lead sulfide quantum dots according to claim 1, characterized in that, After step S3, the method further includes: S4. Cool the first mixture in a water bath, injecting hexane and oleic acid during the cooling process, and centrifuge; extract the supernatant of the first mixture and add a polar solvent for washing to separate the lead sulfide quantum dots.

3. The method for preparing lead sulfide quantum dots according to claim 2, characterized in that, The centrifugation speed in step S4 is 4000-7000 r / min.

4. The method for preparing lead sulfide quantum dots according to claim 1, characterized in that, The protective gas includes an inert gas.

5. The method for preparing lead sulfide quantum dots according to claim 1, characterized in that, The protective gas includes nitrogen.

6. The method for preparing lead sulfide quantum dots according to claim 4, characterized in that, The inert gas is argon.

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