Preparation method and application of cation exchange lead sulfide quantum dots

Abstract

The invention discloses a preparation method and application of cation-exchanged lead sulfide quantum dots, and the preparation method of the cation-exchanged lead sulfide quantum dots comprises the following steps: S1, mixing lead halide with oleylamine to form a first solution; heating the first solution in vacuum to form a lead halide precursor, and maintaining the first temperature; s2, introducing inert gas, injecting a second solution into the lead halide precursor to form a quantum dot nucleation initiating solution, and maintaining for a first time; s3, under the heating condition, dropwise adding a third solution into the quantum dot nucleation initiating solution, and reaching a second temperature; maintaining for a second time to finally obtain a lead sulfide quantum dot mixed solution; and S4, cooling and centrifuging the lead sulfide quantum dot mixed solution to obtain the lead sulfide quantum dots. According to the embodiment of the invention, peak position and size control is realized, passivation of surface defects of the quantum dots is met, and preparation of the lead sulfide quantum dots with higher quality is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic materials, and particularly relates to a preparation method of cation-exchanged lead sulfide quantum dots and application thereof. Background Art

[0002] Lead sulfide (PbS) quantum dots have the advantages of multi-exciton effect, high quantum yield, high molar absorption coefficient and solution preparation, and are widely used in the field of near-infrared solar cells and photodetectors. Hot injection is currently the most common and advantageous method for synthesizing lead sulfide quantum dots. As a special hot injection method, the cation exchange method can produce quantum dots with precise peak control, uniform size and better luminous efficiency, so it is widely used. The conventional cation exchange method is used to prepare lead sulfide quantum dots. Lead halide (PbX2) is usually used as the lead source. Zinc sulfide or cadmium sulfide is selected as the single sulfur source under high temperature conditions and injected to synthesize lead sulfide. Among them, quantum dots prepared with cadmium sulfide often have Cd 2+ Passivation can achieve relatively good surface defect passivation and stability, but the size control and repeatability are still not ideal. Another strategy is to use zinc sulfide to prepare quantum dots. Although it can obtain excellent peak position and size control, there is no Zn on the surface of the quantum dots. 2+ In order to further improve the performance of lead sulfide quantum dots prepared by cation exchange, it is hoped to find a quantum dot preparation method with the advantages of both size control and surface passivation, which can achieve peak position and size control while satisfying the passivation of quantum dot surface defects and further improve its stability. Summary of the invention

[0003] The technical problem to be solved by the present invention is that, since the existing lead sulfide quantum dots have various deficiencies, the present invention provides a preparation method of cation-exchanged lead sulfide quantum dots and its application.

[0004] In order to solve the above technical problems, an embodiment of the present invention provides a method for preparing cation-exchanged lead sulfide quantum dots, comprising the following steps:

[0005] S1: mixing lead halide and oleylamine to form a first solution; heating the first solution in vacuum to form a lead halide precursor and maintaining a first temperature;

[0006] S2: introducing an inert gas, injecting a second solution into the lead halide precursor to form a quantum dot nucleation initiation solution, and maintaining the solution for the first time;

[0007] S3: under the condition of increasing temperature, adding the third solution to the quantum dot nucleation initiation solution and reaching the second temperature; maintaining the temperature for the second time to finally obtain the lead sulfide quantum dot mixed solution;

[0008] S4: cooling and centrifuging the lead sulfide quantum dot mixed solution to obtain lead sulfide quantum dots;

[0009] Wherein, the second solution includes zinc sulfide; and the third solution includes zinc sulfide and cadmium sulfide.

[0010] Preferably, the step S4 specifically comprises: cooling the lead sulfide quantum dot mixed solution in a water bath, adding a dispersant and oleic acid to form a mixed solution; extracting the supernatant of the mixed solution into a centrifuge tube, adding an anti-solvent for washing, and separating to obtain the lead sulfide quantum dots.

[0011] Preferably, in the steps S2 and S3, the second solution is a solution formed by dissolving zinc sulfide in octadecene; the third solution is a solution formed by mixing zinc sulfide and cadmium sulfide in a certain proportion and dissolving them in octadecene to form a sulfur source precursor;

[0012] The second solution has a second solubility, and the third solution has a third solubility; the second solubility is greater than the third solubility.

[0013] Preferably, the zinc sulfide and cadmium sulfide in the third solution are mixed in proportion using concentration absorption values, and the concentration ratio of cadmium sulfide to zinc sulfide is less than or equal to 0.3.

[0014] Preferably, in step S1, the lead halide includes: one or any combination of lead chloride, lead bromide and lead iodide.

[0015] Preferably, in steps S1 and S3, the first temperature range is 90°C-120°C, and the second temperature range is 120-160°C.

[0016] Preferably, in steps S2 and S3, the first time ranges from 30s to 120s, and the second time value is less than 150min.

[0017] Preferably, the dispersant includes at least one of n-hexane, n-octane, chloroform and toluene.

[0018] The embodiment of the present invention further provides a lead sulfide quantum dot, which is prepared by using the above-mentioned cation exchange lead sulfide quantum dot preparation method.

[0019] An embodiment of the present invention further provides an application of the lead sulfide quantum dots, wherein the lead sulfide quantum dots are applied to colloidal quantum dot infrared detectors, solar cells or light-emitting devices.

[0020] Implementing the embodiments of the present invention has the following beneficial effects:

[0021] (1) In the embodiment of the present invention, a zinc sulfide quantum dot solution is quickly injected into a lead halide precursor formed by lead halide and oleylamine to nucleate it, and a mixed solution of zinc sulfide and cadmium sulfide is continuously added dropwise after a period of time, and the growth of lead sulfide quantum dots is regulated by controlling the temperature, sulfur source concentration and dropwise acceleration rate. The polysulfur source system is introduced into the cation exchange synthesis method to achieve peak position and size control while also satisfying the passivation of quantum dot surface defects. The lead sulfide quantum dots finally prepared have uniform particle size, good surface passivation, high exciton absorption peak-to-valley ratio, and narrow absorption half-height width. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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 will be briefly introduced below. 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 creative work.

[0023] Figure 1 A flow chart of a method for preparing cation-exchanged lead sulfide quantum dots provided in an embodiment of the present invention;

[0024] Figure 2 This is a fixed absorption curve diagram of different batches of a lead sulfide quantum dot film provided in Example 1 of the present invention;

[0025] Figure 3 A fixed absorption curve diagram of different batches of a lead sulfide quantum dot film provided in Example 2 of the present invention;

[0026] Figure 4 This is an absorption curve diagram of different growth times of a lead sulfide quantum dot film provided in Example 3 of the present invention;

[0027] Figure 5 An absorption curve diagram of absorption change of a lead sulfide quantum dot film during placement time provided in Example 1 of the present invention;

[0028] Figure 6 This is an absorption curve diagram of different growth times of a lead sulfide quantum dot film provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0029] 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 making creative work are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, this embodiment discloses a method for preparing cation-exchanged lead sulfide quantum dots, and the method for preparing cation-exchanged lead sulfide quantum dots comprises the following steps:

[0031] S1: mixing lead halide and oleylamine to form a first solution; heating the first solution in vacuum to form a lead halide precursor and maintaining a first temperature;

[0032] S2: introducing an inert gas, injecting a second solution into the lead halide precursor to form a quantum dot nucleation initiation solution, and maintaining the solution for the first time;

[0033] S3: under the condition of increasing temperature, adding the third solution to the quantum dot nucleation initiation solution and reaching the second temperature; maintaining the temperature for the second time to finally obtain the lead sulfide quantum dot mixed solution;

[0034] S4: cooling and centrifuging the lead sulfide quantum dot mixed solution to obtain lead sulfide quantum dots;

[0035] Wherein, the second solution includes zinc sulfide; and the third solution includes zinc sulfide and cadmium sulfide.

[0036] In the step S1, the lead halide includes one or any combination of lead chloride, lead bromide and lead iodide. The first temperature range is 90°C-120°C.

[0037] In the step S2, the second solution is a solution of zinc sulfide dissolved in octadecene. The first time is in the range of 30s-120s.

[0038] In step S3, the third solution is zinc sulfide and cadmium sulfide mixed in proportion and dissolved in octadecene to form a sulfur source precursor. The zinc sulfide and cadmium sulfide in the third solution are mixed in proportion using concentration absorption values, and the concentration ratio of cadmium sulfide to zinc sulfide is less than or equal to 0.3. The second temperature range is 120-160° C. The second time value is less than 150 min.

[0039] The second solution has a second solubility, and the third solution has a third solubility; the second solubility is greater than the third solubility.

[0040] The step S4 specifically comprises: cooling the lead sulfide quantum dot mixed solution in a water bath, adding a dispersant and oleic acid to form a mixed solution; extracting the supernatant of the mixed solution and putting it into a centrifuge tube, adding an anti-solvent for washing, and separating to obtain the lead sulfide quantum dots.

[0041] Wherein, the dispersant includes at least one of n-hexane, n-octane, chloroform and toluene. The inert gas includes one of nitrogen and argon.

[0042] Specifically, the embodiments of the present invention also provide a clear method for preparing cation exchanged lead sulfide quantum dots as follows:

[0043] Before the step of synthesizing lead sulfide quantum dots, the raw materials of the second solution and the third solution, zinc sulfide and cadmium sulfide, are synthesized first, specifically:

[0044] Preparation of ZnS quantum dots

[0045] Weigh 96mmol zinc stearate and 48mmol thioacetamide into a 1L three-necked flask, then add 280ml octadecene solution and mix evenly. Vacuum and introduce nitrogen. After the temperature rises to 50-80℃, inject an appropriate amount of oleylamine. After the reaction solution continues to heat to 120-220℃, maintain for 40-80min. After the water bath cools to room temperature, inject an appropriate amount of n-octylamine, and the solution becomes clear. Add more than twice the volume of ethanol solvent to the reaction solution, shake evenly, and centrifuge (4000-6000r / min, 5min), repeat twice, and finally use octadecene to further dilute to the specified concentration.

[0046] Preparation of Cadmium Sulfide Quantum Dots

[0047] Weigh 10mmol of cadmium oxide, 8ml of oleic acid and 32ml of octadecene, mix them evenly, evacuate and introduce nitrogen, and continue to heat to 220-280℃ until the reaction solution is clear and transparent. After the reaction is completed, cool the reaction solution naturally to room temperature, inject NH2S solution and continue the reaction for 1h. Add more than twice the volume of ethanol solvent to the reaction solution, shake evenly and centrifuge (4000-6000r / min, 5min), repeat twice, and finally use octadecene to further dilute to the specified concentration.

[0048] Embodiment 1

[0049] The method for preparing cation-exchanged lead sulfide quantum dots comprises the following steps:

[0050] Mix 25mmol lead chloride with 80ml oleylamine, heat to 140℃ and continue to evacuate for 35min, introduce nitrogen and cool to the first temperature range. Rapidly inject 3.26g zinc sulfide quantum dot solution (absorbance value is 0.4) and maintain for the first time. Then gradually add the mixed solution of zinc sulfide and cadmium sulfide (cadmium sulfide: zinc sulfide = 0.3) to the solution and continue to heat to the second temperature, and continue to grow for 30-50min according to the required quantum dot size. Cool the reaction mixture in a water bath, inject 100ml of n-hexane when the temperature drops below 70℃, and then continue to cool to below 40℃ and inject 120ml of oleic acid. After the liquid is added, stabilize at room temperature for 30min. Centrifuge the final reaction solution for 5min (4000r / min) to remove unreacted lead chloride. Wash the supernatant with 2 volumes of acetone, pour out the supernatant after centrifugation, and blow dry the solvent with nitrogen. Add 10 ml of n-hexane to the centrifuge tube to disperse the quantum dots, repeat the above cleaning steps, and finally store the quantum dot powder in a glove box.

[0051] Embodiment 2

[0052] The technical solutions of this embodiment are basically similar to those of the first embodiment, except that the ratio of zinc sulfide quantum dots to cadmium sulfide quantum dots is different.

[0053] Preparation of lead sulfide quantum dots: Mix 25mmol lead chloride with 80ml oleylamine, heat to 140℃ and continue to vacuum for 35min, introduce nitrogen and cool to the first temperature range. Rapidly inject 3.26g of zinc sulfide quantum dot solution (absorbance value is 0.4) and maintain for the first time. Then, a mixed solution of zinc sulfide and cadmium sulfide (cadmium sulfide: zinc sulfide = 0.15) is gradually added dropwise to the solution and continuously heated to the second temperature, and the growth continues for 30-50min according to the required quantum dot size. Cool the reaction mixture in a water bath, inject 100ml of n-hexane when the temperature drops below 70℃, and then continue to cool to below 40℃ and inject 120ml of oleic acid. After the liquid is added, stabilize at room temperature for 30min. Centrifuge the final reaction solution for 5min (4000r / min) to remove unreacted lead chloride. Wash the supernatant with 2 volumes of acetone, pour out the supernatant after centrifugation, and blow dry the solvent with nitrogen. Add 10 ml of n-hexane to the centrifuge tube to disperse the quantum dots, repeat the above cleaning steps, and finally store the quantum dot powder in a glove box.

[0054] Embodiment 3

[0055] The technical solutions of this embodiment are basically similar to those of the first embodiment, except that the second time of the quantum dots is different.

[0056] Preparation of lead sulfide quantum dots: Mix 25mmol lead chloride with 80ml oleylamine, heat to 140℃ and continue to evacuate for 35min, introduce nitrogen and cool to the first temperature range. Rapidly inject 3.26g of zinc sulfide quantum dot solution (absorbance value is 0.4) and maintain for the first time. Then, a mixed solution of zinc sulfide and cadmium sulfide (cadmium sulfide: zinc sulfide = 0.3) is gradually added dropwise to the solution and continuously heated to the second temperature, and the growth continues for 60-120min according to the required quantum dot size. Cool the reaction mixture in a water bath, inject 100ml of n-hexane when the temperature drops below 70℃, and then continue to cool to below 40℃ and inject 120ml of oleic acid. After the liquid is added, stabilize at room temperature for 30min. Centrifuge the final reaction solution for 5min (4000r / min) to remove unreacted lead chloride. Wash the supernatant with 2 volumes of acetone, pour out the supernatant after centrifugation, and blow dry the solvent with nitrogen. Add 10 ml of n-hexane to the centrifuge tube to disperse the quantum dots, repeat the above cleaning steps, and finally store the quantum dot powder in a glove box.

[0057] Embodiment 4

[0058] The technical solutions of this embodiment are basically similar to those of the first embodiment, except that the lead halide used is lead bromide.

[0059] Preparation of lead sulfide quantum dots: Mix 25mmol lead bromide with 80ml oleylamine, heat to 140℃ and continue to vacuum for 35min, introduce nitrogen and cool to the first temperature range. Rapidly inject 3.26g of zinc sulfide quantum dot solution (absorbance value is 0.4) and maintain for the first time. Then, a mixed solution of zinc sulfide and cadmium sulfide (cadmium sulfide: zinc sulfide = 0.3) is gradually added dropwise to the solution and continuously heated to the second temperature, and the growth continues for 30-50min according to the required quantum dot size. Cool the reaction mixture in a water bath, inject 100ml of n-hexane when the temperature drops below 70℃, and then continue to cool to below 40℃ and inject 120ml of oleic acid. After the liquid is added, stabilize at room temperature for 30min. Centrifuge the final reaction solution for 5min (4000r / min) to remove unreacted lead chloride. Wash the supernatant with 2 volumes of acetone, pour out the supernatant after centrifugation, and blow dry the solvent with nitrogen. Add 10 ml of n-hexane to the centrifuge tube to disperse the quantum dots, repeat the above cleaning steps, and finally store the quantum dot powder in a glove box.

[0060] Embodiment 5

[0061] The technical solution of this embodiment is basically similar to that of the first embodiment, except that the lead halide used is lead iodide.

[0062] Preparation of lead sulfide quantum dots: Mix 25mmol lead iodide with 80ml oleylamine, heat to 140℃ and continue to evacuate for 35min, introduce nitrogen and cool to the first temperature range. Rapidly inject 3.26g of zinc sulfide quantum dot solution (absorbance value is 0.4) and maintain for the first time. Then, a mixed solution of zinc sulfide and cadmium sulfide (cadmium sulfide: zinc sulfide = 0.3) is gradually added dropwise to the solution and continuously heated to the second temperature, and the growth continues for 30-50min according to the required quantum dot size. Cool the reaction mixture in a water bath, inject 100ml of n-hexane when the temperature drops below 70℃, and then continue to cool to below 40℃ and inject 120ml of oleic acid. After the liquid is added, stabilize at room temperature for 30min. Centrifuge the final reaction solution for 5min (4000r / min) to remove unreacted lead chloride. Wash the supernatant with 2 volumes of acetone, pour out the supernatant after centrifugation, and blow dry the solvent with nitrogen. Add 10 ml of n-hexane to the centrifuge tube to disperse the quantum dots, repeat the above cleaning steps, and finally store the quantum dot powder in a glove box.

[0063] Embodiment 6

[0064] The technical solutions of this embodiment are basically similar to those of the first embodiment, except that the concentration of the initially injected zinc sulfide quantum dots is different.

[0065] Preparation of lead sulfide quantum dots: Mix 25mmol lead iodide with 80ml oleylamine, heat to 140℃ and continue to vacuum for 35min, introduce nitrogen and cool to the first temperature range. Rapidly inject 3.26g of zinc sulfide quantum dot solution (absorbance value is 0.6) and maintain for the first time. Then, a mixed solution of zinc sulfide and cadmium sulfide (cadmium sulfide: zinc sulfide = 0.3) is gradually added dropwise to the solution and continuously heated to the second temperature, and the growth continues for 45-50min according to the required quantum dot size. Cool the reaction mixture in a water bath, inject 100ml of n-hexane when the temperature drops below 70℃, and then continue to cool to below 40℃ and inject 120ml of oleic acid. After the liquid is added, stabilize at room temperature for 30min. Centrifuge the final reaction solution for 5min (4000r / min) to remove unreacted lead chloride. Wash the supernatant with 2 times the volume of acetone, pour out the supernatant after centrifugation, and blow dry the solvent with nitrogen. Add 10 ml of n-hexane to the centrifuge tube to disperse the quantum dots, repeat the above cleaning steps, and finally store the quantum dot powder in a glove box.

[0066] See also Figure 2-Figure 3 , similar peak positions and sizes can be obtained in lead sulfide quantum dots prepared in different batches, so the lead sulfide quantum dots prepared by the cation exchange lead sulfide quantum dot preparation method of the present invention can achieve precise peak position and size control.

[0067] See also Figure 4 and Figure 6 The lead sulfide quantum dots prepared by the cation exchange lead sulfide quantum dot preparation method of the present invention can control the quantum dot size by adjusting the injection time. Under different injection times, the lead sulfide quantum dots have different sizes, and the maximum size can grow to 2090nm.

[0068] See also Figure 5 The lead sulfide quantum dots prepared by the cation exchange lead sulfide quantum dot preparation method of the present invention are prepared by introducing Cd 2+ , which greatly enhances the surface passivation of quantum dots and enables the quantum dots to be stored for a long time, thus showing excellent stability.

[0069] The embodiment of the present invention also provides a lead sulfide quantum dot, which is prepared by the above-mentioned cation exchange lead sulfide quantum dot preparation method. The lead sulfide quantum dot is used in a colloidal quantum dot infrared detector, a solar cell or a light-emitting device. After experiments, the external quantum efficiency of the infrared detector device reaches 60%.

[0070] In summary, the embodiments of the present invention provide a method for preparing cation exchange lead sulfide quantum dots and its application. By rapidly injecting a zinc sulfide solution into a mixed solution of lead chloride and oleylamine, nucleation is promoted and maintained for a certain period of time. After cadmium sulfide and zinc sulfide quantum dots are mixed evenly in a certain proportion, they are continuously added dropwise to the reaction solution. By controlling the addition time, the peak position and size can be precisely controlled. Since Cd is introduced on the basis of the original zinc sulfide quantum dots as a sulfur source, 2+ The surface of the quantum dots is passivated, and the synthesized lead sulfide quantum dots show excellent stability. In addition, the lead sulfide quantum dots prepared by the present invention are well applied in the device preparation of infrared detectors, and obtain good device performance.

[0071] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for preparing cation exchange lead sulfide quantum dots, characterized in that: The following steps are involved: S1: mixing lead halide and oleylamine to form a first solution; heating the first solution in vacuum to form a lead halide precursor and maintaining a first temperature; S2: introducing an inert gas, injecting a second solution into the lead halide precursor to form a quantum dot nucleation initiation solution, and maintaining the solution for the first time; S3: under the condition of increasing temperature, adding the third solution to the quantum dot nucleation initiation solution and reaching the second temperature; maintaining the temperature for the second time to finally obtain the lead sulfide quantum dot mixed solution; S4: cooling and centrifuging the lead sulfide quantum dot mixed solution to obtain lead sulfide quantum dots; Wherein, the second solution includes zinc sulfide; and the third solution includes zinc sulfide and cadmium sulfide.

2. The method for preparing cation-exchanged lead sulfide quantum dots according to claim 1, characterized in that: The step S4 specifically comprises: cooling the lead sulfide quantum dot mixed solution in a water bath, adding a dispersant and oleic acid to form a mixed solution; extracting the supernatant of the mixed solution and putting it into a centrifuge tube, adding an anti-solvent for washing, and separating to obtain the lead sulfide quantum dots.

3. The method for preparing cation-exchanged lead sulfide quantum dots according to claim 1, characterized in that: In the steps S2 and S3, the second solution is a solution formed by dissolving zinc sulfide in octadecene; the third solution is a solution formed by mixing zinc sulfide and cadmium sulfide in a certain proportion and dissolving them in octadecene to form a sulfur source precursor; The second solution has a second solubility, and the third solution has a third solubility; the second solubility is greater than the third solubility.

4. The method for preparing cation-exchanged lead sulfide quantum dots according to claim 3, characterized in that: The zinc sulfide and cadmium sulfide in the third solution are mixed in proportion using concentration absorption values, and the concentration ratio of cadmium sulfide to zinc sulfide is less than or equal to 0.

3.

5. The method for preparing cation-exchanged lead sulfide quantum dots according to claim 1, characterized in that: In the step S1, the lead halide includes: one or any combination of lead chloride, lead bromide and lead iodide.

6. The method for preparing cation-exchanged lead sulfide quantum dots according to claim 1, characterized in that: In the steps S1 and S3, the first temperature range is 90°C-120°C, and the second temperature range is 120-160°C.

7. The method for preparing cation-exchanged lead sulfide quantum dots according to claim 1, characterized in that: In the steps S2 and S3, the first time ranges from 30s to 120s, and the second time value is less than 150min.

8. The method for preparing cation-exchanged lead sulfide quantum dots according to claim 2, characterized in that: The dispersant includes at least one of n-hexane, n-octane, chloroform and toluene.

9. A lead sulfide quantum dot, characterized in that: The lead sulfide quantum dots are prepared by using any cation exchange lead sulfide quantum dot preparation method as claimed in any one of claims 1 to 8.

10. An application of lead sulfide quantum dots prepared by the method according to any one of claims 1 to 8, characterized in that: The lead sulfide quantum dots are applied to colloidal quantum dot infrared detectors, solar cells or light-emitting devices.

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