KR102421872B1 - PbS quantum-dot having subnanometer size and Manufacturing method thereof - Google Patents

Abstract

The present invention relates to a sub-nanometer-sized lead sulfide quantum dot and a method for manufacturing the same, a method for producing a lead sulfide quantum dot through a low-temperature synthesis method, and amorphous lead sulfide quantum dots having a sub-nanometer diameter manufactured by this method will be.

Description

Sub-nanometer-sized lead sulfide quantum dots and their manufacturing method {PbS quantum-dot having subnanometer size and Manufacturing method thereof}

The present invention relates to lead sulfide quantum dots prepared through low-temperature synthesis and a method for manufacturing the same, to sub-nanometer-sized lead sulfide quantum dots having a diameter of 3 nm or less, and a method for efficiently manufacturing the same.

Quantum dots are small semiconductor crystals with a size of several nanometers and are applied to medical imaging, solar cells, and light emitting devices due to their unique light-receiving/emission properties. Quantum dots have optical and electro-electric properties that are clearly distinguished from bulk-sized semiconductors because electrons and holes present therein strongly interact with each other. The semiconductor band spacing of quantum dots can be easily modulated by changing the chemical composition of the materials constituting it or by changing the size of the quantum dots. can be applied as

Quantum dots can be divided into I-type and II-type quantum dots. When two different semiconductors (No. 1 and No. 2) are physically in contact, the conduction band of semiconductor No. 1 depends on the energy level position of the two semiconductors. , CB) The lowest energy exists at a position lower than the lowest energy of the conduction band of semiconductor No. 2, and the highest energy of the valence band (VB) of semiconductor No. The case is called I-type, where the lowest energy in the conduction band of semiconductor 1 is higher than the lowest energy in the conduction band of semiconductor 2, and the highest energy in the valence band of semiconductor 1 is higher than the highest energy in the outermost band of semiconductor 2. A case in which the energy level of a semiconductor exists as a staggered gap is called type II-type.

The characteristics of quantum dots are different in optical and physical characteristics expressed depending on their size and semiconductor composition. Existing quantum dots are sub-nano-sized due to the lack of understanding and research on the control of the growth process of the quantum dot nucleus, understanding of the growth principle, and synthesis conditions. It is difficult to synthesize quantum dots, and even if synthesized, there is a problem that the yield is very low.

Korean Patent Registration No. 10-1891391 (published on September 28, 2018)

Gebauer, D.; Volkel, A.; Colfen, H. Stable prenucleation calcium carbonate clusters. Science 2008, 322,1819-1822.

The present invention controls the nucleation and growth of lead sulfide (PbS) quantum dots in the process of conducting research on the crystal nucleation and growth of various quantum dots, and learns a method for stably synthesizing sub-nano-sized lead sulfide quantum dots. and completed the present invention. That is, the present invention is to provide a sub-nano-sized lead sulfide quantum dots and a method for manufacturing the same.

The present invention for solving the above problems relates to lead sulfide quantum dots, which may have a sub-nano size.

As a preferred embodiment of the present invention, the lead sulfide quantum dots of the present invention have a diameter of 3.0 nm or less, and include lead sulfide quantum dots satisfying Equation 1 below.

[Equation 1]

5.8 ≤ A/B ≤ 6.2

In Equation 1, A is the number of atoms of lead atoms (Pb) in the quantum dot, and B is the number of atoms of sulfur atoms (S).

As a preferred embodiment of the present invention, the lead sulfide quantum dots of the present invention have a full width half maximum (FWHM) of 3.50 to 3.60 of Pb 4f _7/2 related to lead (Pb) and sulfur (S) bonding during XPS analysis. , the FWHM of Pb 4f _5/2 may be 3.40 to 3.49.

As a preferred embodiment of the present invention, the lead sulfide quantum dots of the present invention may have an absorption wavelength peak at 570 to 585 nm when measuring the UV-Vis spectrum.

As a preferred embodiment of the present invention, the lead sulfide quantum dots of the present invention may be amorphous.

Another object of the present invention relates to a method for manufacturing the lead sulfide quantum dots described above, the first step of preparing a lead precursor solution and a sulfur precursor solution, respectively; a second step of preparing a mixed solution by dropwise adding the sulfur precursor solution to the lead precursor solution; A third step of forming a reaction product by stirring and reacting the mixed solution for 1 minute to 15 minutes at a reaction temperature of 25 to 40 °C; After purifying the reaction product, 4 steps of isolating and obtaining quantum dots satisfying Equation 1 below from the purified product; a process including a process may be performed.

[Equation 1]

5.8 ≤ A/B ≤ 6.2

In Equation 1, A is the number of atoms of lead atoms (Pb) in the quantum dot, and B is the number of atoms of sulfur atoms (S).

As a preferred embodiment of the present invention, in the method for manufacturing lead sulfide quantum dots of the present invention, the lead precursor solution in step 1 is a PbO stock solution in which lead oxide (PbO), oleic acid, oleylamine and a solvent are mixed. Step 1-1 of degassing; 1-2 steps of heating the degassed PbO stock solution to 80 ~ 100 ℃; and steps 1-3 of cooling the heated PbO stock solution to 20 to 30° C.; may be prepared by performing a process comprising a.

As a preferred embodiment of the present invention, the PbO stock solution may include the lead oxide, the oleic acid, and the oleylamine in a molar ratio of 1:2.0 to 2.5:0.20 to 0.35.

As a preferred embodiment of the present invention, in the method of manufacturing the lead sulfide quantum dots of the present invention, the sulfur precursor solution of step 1 is step 1-1 of degassing the solvent under 70 ~ 90 ℃; 1-2 steps of preparing a sulfur stock solution by mixing and stirring bis(trimethylsilyl)sulfide in a degassed solvent; and steps 1-3 of cooling the sulfur stock solution to 20 to 30° C.; may be prepared by performing a process comprising a.

As a preferred embodiment of the present invention, the sulfur stock solution may include bis(trimethylsilyl)sulfide in a volume ratio of 1:2.00 to 2.50 by volume with respect to 100 volume ratio of the solvent.

As a preferred embodiment of the present invention, in the method for manufacturing lead sulfide quantum dots of the present invention, the purified product of step 4 includes lead sulfide quantum dots having various diameters, and the purified product is MEIS (medium energy ion scattering) As measured with a spectrometer, it contains 2.0 to 3.0% of lead sulfide quantum dots having a diameter of more than 2.0 nm to 3.0 nm or less, 5.0 to 6.0% of lead sulfide quantum dots having a diameter of more than 1.0 nm to 2.0 nm or less, and sulfide having a diameter of 1.0 nm or less Lead quantum dots may be included as the remaining balance %.

As a preferred embodiment of the present invention, the quantum dots represented by Formula 1 in step 4 may have a diameter of 3.0 nm or less.

As a preferred embodiment of the present invention, the manufacturing method of the present invention may further include; step 5 of separating and obtaining quantum dots having a diameter of 1 nm or less from the quantum dots in step 4 with an ultracentrifuge.

The PbS quantum dot manufacturing method of the present invention is different from the conventional production of PbS quantum dots by reacting at a high temperature (90 ~ 120 ℃), by controlling the reaction and reaction time at a low temperature of 40 ℃ or less, quantum dots with a diameter of 3 nm or less efficiently In this way, the PbS quantum dots of the present invention prepared in this way can commercially provide sub-nanometer-sized PbS having optical and physical properties different from those of crystalline PbS quantum dots having a size of 4 to 5 nm or larger. .

1a is a TEM image of the sub-nanometer-sized lead sulfide quantum dots prepared in Example 1, and b is a MEIS spectroscopic measurement result.
FIG. 2 c is an HR-TEM image of the sub-nanometer-sized lead sulfide quantum dots prepared in Example 1, and d is HR-TEM measurement of the crystallized lead sulfide quantum dots prepared in Comparative Example 4 (90° C.) It is an image.
FIG. 3 e is a result of measuring the size distribution of quantum dots in the purified product before separation of sub-nanometer-sized lead sulfide quantum dots in the manufacturing process of sub-nanometer-sized lead sulfide quantum dots of Example 1 using MEIS, f is Pb 4f is the measurement result of the XPS spectrum.
4A is an XRD pattern measurement result of the sub-nanometer-sized lead sulfide quantum dots prepared in Example 1, and b is a UV-Vis spectrum measurement result.
5 is a MEIS spectra measurement result by adding 80 KeV He ⁺ ions to the sub-nanometer-sized lead sulfide quantum dots prepared in Example 1. FIG.
6 is an XPS measurement result, where a is a measurement result for the entire range (survey), and b is a measurement result for S 2s of the sub-nanometer-sized lead sulfide quantum dots prepared in Example 1.

Hereinafter, the present invention will be described in more detail.

The present invention relates to lead sulfide (PbS) quantum dots of sub-nanometer size, wherein the PbS quantum dots of the present invention have a diameter of 3.0 nm or less, preferably 2.0 nm or less, more preferably 1.0 nm or less, even more preferably It may be 0.8 nm or less.

Pb and S of the PbS quantum dots of the present invention may satisfy Equation 1 below non-stoichiometrically.

[Equation 1]

5.8 ≤ A/B ≤ 6.2, preferably 5.85 ≤ A/B ≤ 6.17, more preferably 5.90 ≤ A/B ≤ 6.12

In Equation 1, A is the number of atoms of lead atoms (Pb) in the quantum dot, and B is the number of atoms of sulfur atoms (S).

In addition, the sub-nanomit-sized PbS quantum dots of the present invention may be amorphous.

In addition, the PbS quantum dot of the present invention has a full width half maximum (FWHM) of 3.50 to 3.60, preferably 3.54 to 3.60, of Pb 4f _7/2 related to lead (Pb) and sulfur (S) bonding during XPS analysis, The FWHM of Pb 4f _5/2 may be 3.40 to 3.49, preferably 3.43 to 3.49.

In addition, the PbS quantum dots of the present invention may have an absorption wavelength peak at 570 to 585 nm, preferably at 575 to 585 nm, when measuring the UV-Vis spectrum.

The PbS quantum dot of the present invention is a first step of preparing a lead precursor solution and a sulfur precursor solution, respectively; a second step of preparing a mixed solution by dropwise adding the sulfur precursor solution to the lead precursor solution; A third step of forming a reaction product by stirring and reacting the mixed solution for 1 minute to 15 minutes at a reaction temperature of 25 to 40 °C; After purifying the reaction product, 4 steps of separating and obtaining quantum dots satisfying Equation 1 from the purified product; a process including a process may be performed.

In addition, the present invention may further include; step 5 of separating and obtaining quantum dots having a diameter of 1 nm or less from the quantum dots in the step by an ultracentrifuge.

Step 1-1 of degassing the PbO stock solution in which the lead precursor solution of step 1 is mixed with lead oxide (PbO), oleic acid, oleylamine and a solvent; 1-2 steps of heating the degassed PbO stock solution; and steps 1-3 of cooling the heated PbO stock solution.

The PbO stock solution may contain lead oxide, oleic acid, and oleylamine in a molar ratio of 1: 2.0 to 2.5: 0.20 to 0.35, preferably 1: 2.20 to 2.45: 0.22 to 0.30 by molar ratio.

At this time, the oleic acid acts as a surface stabilizer, and when its usage is less than 2.0 molar ratio or exceeds 2.5 molar ratio, there may be a problem in that a reaction product in the form of a bar and/or sheet is formed rather than in the form of quantum dots. In addition, oleylamine acts as a reducing agent for the reaction, and if its usage is less than 0.20 molar ratio or exceeds 0.35 molar ratio, there may be a problem that a reaction product in the form of a bar and/or sheet is formed rather than in the form of quantum dots.

In addition, the solvent includes at least one selected from 1-octadecene, 1-pentadecene, 1-hexadecene, and 1-tetradecene. It may include, and preferably may include one or more selected from 1-octadecene (1-octadecene), 1-pentadecene (1-pentadecene) and 1-hexadecene (1-hexadecene).

In addition, the 1-2 steps of the lead precursor solution preparation process heat the PbO low crystal to about 80 to 100 ° C, preferably to about 85 to 95 ° C. At this time, if the heating temperature is less than 80 ° C, it is used for precursor synthesis. There may be a problem in that the solvent cannot remove moisture or gas, and if it exceeds 100°C, it has too high potential energy, which speeds up the nuclear growth rate, so there may be a problem in that quantum dots of 1 nm or less cannot be synthesized. have.

In addition, steps 1-3 of the lead precursor solution preparation process are a process of cooling the PbO stock solution heated in steps 1-2 to room temperature, preferably 20° C. to 30° C., in this way, by heating the PbO stock solution. After minimizing the nucleation energy, it is cooled for the effect of effectively growing and separating quantum dot nuclei by controlling the initial growth rate.

Next, step 1-1 of degassing the solvent in the sulfur precursor solution of step 1; 1-2 steps of preparing a sulfur stock solution by mixing and stirring bis(trimethylsilyl)sulfide in a degassed solvent; and steps 1-3 of cooling the sulfur stock solution.

Step 1-1 in the process of preparing the sulfur precursor solution is prepared by heating the solvent to 70°C to 90°C, preferably 75°C to 90°C, and then degassing. In this case, the solvent is one or more selected from 1-octadecene, 1-pentadecene, 1-hexadecene, and 1-tetradecene. It may include, and preferably may include one or more selected from 1-octadecene (1-octadecene), 1-pentadecene (1-pentadecene) and 1-hexadecene (1-hexadecene). At this time, if the heating temperature is less than 70 ℃, there may be a problem that the moisture and gas contained in the initial cannot be removed, and if it exceeds 90 ℃, there may be a problem that makes it difficult to control the growth rate by increasing the potential energy of the precursor. .

In addition, in steps 1-2 in the process of preparing the sulfur precursor solution, a sulfur stock solution is prepared by mixing and stirring bis(trimethylsilyl)sulfide in a degassed solvent, and in this case, the solvent is maintained at a temperature of 70 to 90°C. In addition, the bis(trimethylsilyl)sulfide mixing amount may be bis(trimethylsilyl)sulfide in a volume ratio of 1:2.00 to 2.50, preferably in a volume ratio of 2.0 to 2.35, with respect to 100 volume ratio of the solvent. At this time, if the bis(trimethylsilyl)sulfide mixing amount is less than 2.00 volume ratio, the amount of Pb becomes relatively large, so there may be a problem in showing a change in the amount of finally synthesized lead sulfide quantum dots. Since there may be a problem of showing a change in reaction rate and production amount by showing a change in

And, in the process of preparing the sulfur precursor solution, steps 1-3 are a process of cooling the sulfur stock solution to room temperature, preferably 20°C to 30°C. The effect of increasing the yield of quantum dots of 1 nm or less can be obtained.

Next, step 2 is a step of preparing a mixed solution by dropwise adding a sulfur precursor solution to a lead precursor solution, and the dropwise addition method may be performed using a general method used in the art.

Next, step 3 is a process of stirring and reacting the mixed solution prepared in step 2 at a reaction temperature to form a reaction product, wherein the stirring and reaction is carried out at 25 to 40° C. for 1 minute to 15 minutes, preferably at 27° C. to It is preferable to carry out for 1 minute to 5 minutes at 35° C., more preferably 1 minute to 3 minutes at 28° C. to 35° C. At this time, if the reaction temperature exceeds 40 °C or the reaction time exceeds 15 minutes, the particles of the synthesized PbS quantum dots are large, and there may be a problem that crystallinity is greatly increased, and the reaction temperature is less than 25 °C or the reaction time is 1 If it is less than a minute, there may be a problem in that a large amount of unreacted product is generated or quantum dots and nucleation are not generated.

Next, step 4 is a process of purifying the reaction product of step 3 to obtain a purified product, and then separating and obtaining PbS quantum dots from the purified product.

In this case, the purification may be performed by a general method used in the art, and for example, the purification may be performed by dissolving the remaining unreacted reagent through acetone and acetone/hexane.

And, it is possible to obtain sub-nanometer-sized quantum dots having the characteristics described above through a general separation process used in the art, for example, a centrifugation process, and the like for the obtained purified product.

Hereinafter, the present invention will be described with reference to the following examples. At this time, the following examples are only presented to illustrate the invention, and the scope of the present invention is not limited by the following examples.

[Example]

Example 1: Preparation of PbS quantum dots

(1) Preparation of lead precursor solution

Purity 99.999% lead oxide (PbO, 2.016 mmol) 0.45 g, oleic acid (4.75 mmol, technical grade, 90%) 1.5 ㎖, oleylamine (oleylamine, 0.502 mmol, technical grade, 70%) 0.165 ㎖ and 18 ml of 1-octadecene (ODE) were mixed to prepare a PbO stock solution, and then the prepared PbO stock solution was degassed in a 100 ml three-necked flask under vacuum and room temperature for 24 hours. .

Then, the degassed PbO stock solution was heated to 90° C. under an Ar atmosphere, and this temperature was maintained for 5 minutes until the color of the solution changed to pure yellow and lead oleate was formed.

Next, the solution was cooled to ambient temperature (about 23° C.) to prepare a lead precursor solution in which the nucleation energy of lead oleate was minimized.

(2) Preparation of sulfur precursor solution

10 mL of degassed 1-octadecine (ODE) was prepared in a 100 mL three-necked flask under vacuum and 80° C. for 24 hours.

After degassing, 0.213 ml of bis(trimethylsilyl)sulfide (TMS, [(Me ₃ Si)] ₂ S, Sigma-Aldrich) was added to 10 ml of the ODE and stirred, followed by cooling to ambient temperature (about 23° C.) to prepare a sulfur precursor solution.

(3) Sub-nanometer-sized PbS quantum dots production

0.5 ml of the sulfur precursor solution was added dropwise to the lead precursor solution using a syringe. During the dropwise addition process, the solution color changed from yellow to orange, from orange to red-orange, from red-orange to bright red, and then from crimson red.

Next, after stirring slowly at ambient temperature for 30 minutes, heating to 30° C., stirring and reaction for 2 minutes to form a reaction product.

Next, the reaction product was purified through acetone and acetone/hexane to obtain a purified product.

Next, the purified product was centrifuged at 15,000 rpm for 10 minutes to separate and obtain sub-nanometer (diameter 1 nm or less) PbS quantum dots from the purified product. Then, the obtained sub-nanometer-sized PbS quantum dots were dispersed in hexane.

Comparative Example 1 ~ Comparative Example 4

PbS quantum dots were prepared in the same manner as in Example 1, but after the sulfur precursor solution was added dropwise to the lead precursor solution, the reaction was performed under the conditions shown in Table 1 below to obtain a reaction product, and then purified and separated by the same method to obtain PbS quantum dots.

division reaction conditions temperature hour Example 1 30℃ 2 minutes Comparative Example 1 30℃ 30 minutes Comparative Example 2 50℃ 30 minutes Comparative Example 3 70℃ 30 minutes Comparative Example 4 90℃ 30 minutes

Experimental Example 1: MEIS spectroscopy, TEM and HR-TEM measurement

MEIS (medium energy ion scattering) spectra, TEM (Transmission electron microscope), and HR-TEM (High resolution-Transmission electron microscope) of the sub-nanometer-sized PbS quantum dots prepared in Example 1 were measured. did.

Here, MEIS spectroscopic measurements analyzed PbS quantum dot samples cast on diamondoid carbon-coated silicon substrates (DLC Si) using a MEIS spectrometer operated with a He ⁺ ion source accelerated to 80 keV. And, the measurement data was analyzed using POWERMEIS 2.0 simulation software. The MEIS spectroscopic measurements can provide information on the shape, size, composition, stoichiometry and size distribution characterization of nanoparticle structures.

And, the TEM image of the PbS quantum dots was measured using a Hitachi HF-3300 FE-TEM (Hitachi, Tokyo, Japan) with an acceleration voltage of 300 kV. HR-TEM images were measured using a Titan G2 ChemiSTEM Cs probe (FEI, Hillsboro, USA) with an accelerating voltage of 200 kV. And, when measuring the image, the PbS quantum dot sample was drop-casting on a carbon-coated Cu 200 megrid.

FIG. 1 a) is a TEM image of PbS quantum dots in Example 1, and FIG. 2 c) is an HR-TEM image of PbS quantum dots, confirming that PbS quantum dots of homogeneous size were obtained.

And, b) of FIG. 1 is a MEIS spectrum measurement result, and the Pb signal appears at a scattering energy of 77.2 keV according to 80 keV He ⁺ ion acceleration, indicating the range of the Pb peak. Then, lower energy tails are observed, which are due to the aggregation of particles of various sizes on diamondoid carbon coated silicon substrates (DLC Si).

In the PbS quantum dots obtained in Example 1, the number of Pb atoms was 0.85, S was 0.14 (Pb _0.85 S _0.14 ), and it was confirmed that the ratio of the number of atoms of Pb to S was 1:6.071 non-stoichiometrically. These results suggest that there is a large amount of Pb ²⁺ ions on the surface of the PbS quantum dots and the surface-to-volume ratio is high.

2 d) is an HR-TEM image of the PbS quantum dots prepared in Comparative Example 4 (90° C., 30 minutes), and it can be seen that the d ₁₁₁ value is 0.34. This d ₁₁₁ value is the interatomic spacing seen when it has crystallinity, and d) If you look at the image arrangement in the upper right corner of the image, it can be confirmed that it has crystallinity. On the other hand, it was confirmed that there is no arrangement having the crystallinity as in d) in the image c) of FIG. 2 .

3e) is a particle size distribution diagram of the PbS quantum dots obtained in Example 1 through MEIS analysis, and 83.8% of the particles having a diameter of about 0.8 nm or less were about 83.8%, and the particles with a diameter of about 0.8 to 1.0 nm were 8.1%. , it was confirmed that 5.4% of particles with a diameter of about 2 nm or less and 2.7% of particles with a diameter of about 3 nm or less were found.

And, the MEIS particle size distribution for the PbS quantum dots of Example 1 is shown in Table 2 below.

division 0.8nm or less More than 0.8 nm to 1.0 nm or less More than 1.0 nm to 2.0 nm or less > 2.0 nm to 3.0 nm or less Example 1 83.8% 8.1% 5.4% 2.7%

Referring to Table 2, it can be seen that the distribution of PbS quantum dots having a size of 1.0 nm or less is very high.

Experimental Example 2: XPS measurement

Among the PbS quantum dots prepared in Example 1, PbS quantum dots having a size of 0.8 nm or less were separated and XPS measurement was performed thereon, and the results are shown in f) of FIG. 3 . In addition, the XPS measurement results for Comparative Examples 1 to 4 are shown in Table 3 below.

X-ray photoelectron spectra (XPS) were acquired using an ESCALAB 250Xi (Thermo Fisher Scientific, MA, USA, MA, USA), and each PbS quantum dot sample was drop-cast on a glass substrate in an Ar-filled glove box. Based on the binding energy obtained for the PbS quantum dots, the analysis results were derived by correcting the C1s peak located at 284.5 eV.

Fig. 3f) is a Pb 4f XPS spectrum, showing Pb 4f _7/2 and Pb 4f _5/2 associated with Pb-S bonding around the binding energies of 137.48 eV (FWHM: 3.57) and 142.9 eV (FWHM: 3.47). You can check the Pb 4f core level spectrum showing the characteristic peak of , and the broadness of the peak indicates the connection between Pb ^{2 +} and oleic acid COO ^- anion.

In addition, the XPS measurement results for Comparative Examples 1 to 4 are shown in Table 3 below.

division element binding energy
(eV) FWHM peak area
(peak area) Example 1
(30℃, 2 minutes) Pb 4f _7/2 137.48 3.57 58647 Pb 4f _5/2 142.9 3.47 33163 S 2s 223.7 3 1110 Comparative Example 1
(30℃, 30min) Pb 4f _7/2 137.51 2.4 4900 Pb 4f _5/2 142.38 2.3 3700 S 2s 224.5 3 119.54 Comparative Example 2
(50℃, 30min) Pb 4f _7/2 137.4 2.4 5500 Pb 4f _5/2 142.24 2.3 4300 S 2s 224.5 3 141.31 Comparative Example 3
(70℃, 30min) Pb 4f _7/2 137.5 2.4 5700 Pb 4f _5/2 142.4 2.4 4400 S 2s 224.5 3 148.6 Comparative Example 4
(90℃, 30min) Pb 4f _7/2 137.38 2.3 5400 Pb 4f _5/2 142.3 2.3 4400 S 2s 224.5 3 149.27

Experimental Example 3: XRD (X-ray powder diffraction spectroscopy) and UV-vis spectrum measurement

The XRD patterns and UV-vis spectra of the quantum dots of Example 1 and Comparative Examples 1 to 4 were measured through X-ray diffraction analysis, and the results are shown in a) and b) of FIG. 4 , respectively.

Here, XRD patterns were performed using an X-ray diffraction analyzer (Rigaku, Osaka, Japan, MiniFlex 600/300), and XRD samples were each sample (with a known concentration in hexane) on a cleaned glass substrate. After the drop casting was performed, a product that was completely dried was used.

And, the UV-vis spectrum was measured using an ultraviolet visible near-infrared (UV-vis-NIR) spectrophotometer (Agilent Technologies, Cary 5000, Santa Clara, CA).

Looking at the XRD pattern of FIG. 4 a), the peaks (111), (200), (220), and (331) representing the characteristics of lead sulfide quantum dots according to the change in reaction temperature and time are clearly separated, so that the amorphous phase is different. It can be seen that the crystal phase is clearly transformed. It can be seen that the PbS quantum dots of Example 1 exhibit a broad peak in the range of 2θ = 20° to 30°, which may be related to the bound (111) and (200) sides of PbS.

At the initial stage of nucleation, lead ions and sulfur ions have strong attractive forces leading to crystallization and formation of metastable clusters due to incomplete octahedral clusters and high surface-to-volume ratio. Looking at the peaks in the range of 2θ = 20° to 30°, wide peak splitting is observed when the reaction temperature is increased to 70°C or higher, which is an incomplete octahedral pronuclear cluster (almost amorphous) and at a high reaction temperature. It represents the combination of subsequent growth into a cubic crystal structure due to the thermal energy provided. This is a result consistent with the HR-TEM image for Comparative Example 4 of FIG. 2 d).

Looking at the UV-vis spectrum measurement result of FIG. 4 b), the quantum dots of Example 1 have a peak at about 580 nm, and as the reaction temperature or reaction time increases, the peak shifts in the red direction, that is, the red shift is (Peak = Comparative Example 1: 610 nm, Comparative Example 2: 640 nm, Comparative Example 3: 670 nm, Comparative Example 4: 750 nm).

Through the above examples and experimental examples, it is possible to efficiently provide sub-nanometer-sized PbS quantum dots through low-temperature synthesis, and the manufactured sub-nanometer-sized PbS quantum dots are different from the existing PbS quantum dots with optical properties, physical properties, etc. was able to confirm that it has The sub-nanometer-sized PbS quantum dots of the present invention are expected to be applied and applied as materials in various fields such as optical devices and solar cells.

Claims (11)

Step 1 of preparing a lead precursor solution and a sulfur precursor solution, respectively;
Step 2 of preparing a mixed solution by dropwise adding the sulfur precursor solution to the lead precursor solution;
A third step of forming a reaction product by stirring and reacting the mixed solution for 1 minute to 15 minutes at a reaction temperature of 25 to 40 °C; and
After purifying the reaction product, 4 steps of separating and obtaining quantum dots satisfying Equation 1 below from the purified product;
Step 5 of separating and obtaining quantum dots with a diameter of 1 nm or less from the quantum dots of step 4 with an ultracentrifuge; further comprising,
The lead precursor solution of step 1 is
Step 1-1 of degassing a PbO stock solution in which lead oxide (PbO), oleic acid, oleylamine, and a solvent are mixed;
1-2 steps of heating the degassed PbO stock solution to 80 ~ 100 ℃; and
1-3 steps of cooling the heated PbO stock solution to 20 ~ 30 ℃; prepared by performing a process comprising;
The sulfur precursor solution of step 1 is
1-1' step of degassing the solvent under 70 ~ 90 ℃;
1-2' step of preparing a sulfur stock solution by mixing and stirring bis (trimethylsilyl) sulfide in a degassed solvent; and
A method of producing sub-nanometer-sized lead sulfide quantum dots, characterized in that the manufacturing process is carried out by performing a process comprising;
[Equation 1]
5.8 ≤ A/B ≤ 6.2
In Equation 1, A is the number of atoms of lead atoms (Pb) in the quantum dot, and B is the number of atoms of sulfur atoms (S).
delete delete The method of claim 1, wherein the PbO stock solution contains the lead oxide, the oleic acid, and the oleylamine in a molar ratio of 1: 2.0 to 2.5: 0.20 to 0.35. How to manufacture.
delete The method of claim 1, wherein the sulfur stock solution contains bis(trimethylsilyl)sulfide in a volume ratio of 1:2.00 to 2.50 with respect to 100 volume ratio of the solvent.
The method of claim 1, wherein the lead sulfide quantum dots in step 4 contain 2.0 to 3.0% of lead sulfide quantum dots having a diameter of more than 2.0 nm to 3.0 nm or less, as measured by a medium energy ion scattering (MEIS) spectrometer, and a diameter of more than 1.0 nm to A method for producing a sub-nanometer-sized lead sulfide quantum dot, comprising 5.0 to 6.0% of lead sulfide quantum dots having a diameter of 2.0 nm or less, and lead sulfide quantum dots having a diameter of 1.0 nm or less as the remaining balance.
The method of claim 1, wherein the quantum dots represented by Equation 1 have a diameter of 3.0 nm or less.
[Claim 9] The method of any one of claims 1, 4, and 6 to 8, wherein the lead sulfide quantum dots are amorphous. delete delete

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