KR102585546B1 - Quantum dot precursor - Google Patents

Abstract

This application relates to quantum dot precursors. The quantum dot precursor of the present application can maintain high optical properties and have excellent solubility even when using a solvent with a high boiling point. Accordingly, unreacted precursors can be maintained homogeneously without precipitating even at low temperatures, so the quantum dots can be maintained homogeneously. It can be purified with high yield.

Description

Quantum dot precursor

This application relates to quantum dot precursors.

Quantum dot display is a self-luminous technology that does not require a separate light source and is similar to OLED technology, but the difference is that while OLED's light-emitting layer is composed of organic materials, quantum dot display's light-emitting layer is composed of quantum dots. Quantum dots have the advantage of free conversion of optical properties through size control, high color purity provided by a narrow color wavelength, and the ability to proceed with the process by dissolving in a solvent. Since they are not organic materials, they also have characteristics that can guarantee light stability. have

Cadmium (Cd)-based quantum dots are capable of the highest internal quantum efficiency of over 90%, but are toxic when used in large quantities, and their use is regulated by the Restriction of Hazardous Substances Directive (RoHS). As an alternative, technology to create InP-based red and green quantum dots from non-cadmium quantum dots is being researched, and can achieve an internal quantum efficiency of 80%.

As for blue quantum dots, research on forming ZnSe-based quantum dots using a Zn precursor whose ligand is formed of saturated fatty acid has been reported. In order to synthesize ZnSe-based quantum dots with high quantum efficiency, a high temperature reaction is required, making it necessary to use a solvent such as octadecene with a high boiling point. However, Zn precursors to which saturated fatty acids are bound have low solubility, and unreacted Zn precursors precipitate during the purification process, making purification of quantum dots difficult.

Republic of Korea Patent Registration No. 10-1468985

This application shows that while maintaining high optical properties, it can have excellent solubility even when using a solvent with a high boiling point, and thus unreacted precursors can be maintained homogeneously without precipitating even at low temperatures, thereby producing quantum dots in high yield. A quantum dot precursor that can be purified is provided.

This application relates to quantum dot precursors. In this application, quantum dots may refer to nanometer (nm)-sized semiconductor crystals that emit light on their own manufactured through a chemical synthesis process. In the present application, quantum dot precursor may refer to a material in the previous step for synthesizing the quantum dot.

The quantum dot precursor of the present application may include a compound in which two monovalent organic anions are bonded to a divalent Zn metal cation. In this specification, the above compound may be abbreviated as “Zn precursor.” According to the present application, at least one of the two organic anions may include an unsaturated hydrocarbon group in the molecular structure.

By applying an organic anion containing at least one unsaturated hydrocarbon group as the Zn ligand, the quantum dot precursor of the present application can maintain high optical properties and have excellent solubility even when using a solvent with a high boiling point, and thus even at low temperatures. Since unreacted precursors can be maintained uniformly without precipitating, quantum dots can be purified with high yield. Hereinafter, the quantum dot precursor of the present application will be described in detail.

The quantum dot precursor of the present application may include a Zn precursor represented by the following formula (1). That is, the quantum dot precursor may include a Zn precursor in which one organic anion containing an unsaturated hydrocarbon group is bound to a Zn ligand and one organic anion containing a saturated hydrocarbon group is bound to one organic anion containing a saturated hydrocarbon group.

[Formula 1]

Zn ^{2 +} ·[R ₁ ] ^- [R ₂ ] ^-

In Formula 1, Zn ²⁺ is a divalent zinc metal cation, [R ₁ ] ^- and [R ₂ ] ^- are each monovalent organic anions, and [R ₁ ^{] -} and [R ₂ ] ^- are each Zn ²⁺ , R ₁ is X-COO-, X is a saturated hydrocarbon group, R ₂ is Y-COO-, and Y is ^an unsaturated hydrocarbon group.

The quantum dot precursor may further include a Zn precursor represented by the following formula (2). That is, the quantum dot precursor may further include a Zn precursor in which two organic anions containing an unsaturated hydrocarbon group are bonded as Zn ligands.

[Formula 2]

Zn ^{2 +} ·[R ₂ ] ^- [R ₂ ] ^-

In Formula 2, Zn ²⁺ is a divalent zinc metal cation, [ ^R ₂ ] ^- is a monovalent organic anion, · means that two [ _{R 2} ^{] -} are each bonded to Zn ²⁺ , and R ₂ is Y-COO-, and Y is an unsaturated hydrocarbon group.

The component ratio of all Zn precursors included in the quantum dot precursor may satisfy the following formula (3).

[Formula 3]

Zn ^{2 +} [R ₁ ] ^- _x [R ₂ ] ^- _2-x

In Formula 3, Zn ²⁺ is a divalent zinc metal cation, [R ₁ ] ^- and [R ₂ ] ^- are ^each monovalent organic anions, R ₁ is X-COO-, and X is a saturated hydrocarbon group. , R ₂ is Y-COO-, Y is an unsaturated hydrocarbon group, and x is a number from 0 to 2.

The component ratio of [R ₁ ^- ] and [R ₂ ^- ] according to the above x value follows the analysis value using ¹ H-NMR after dissolving the Zn precursor in a solvent. In Formula 3, x may be in the range of 0.1 to 1, specifically, 0.1 to 0.8, and more specifically, 0.2 to 0.6. If x is too low, the optical properties of the quantum dots may be lowered, and if x is too high, solubility may be lowered, so it may be desirable for x to be adjusted within the above range.

As used herein, a hydrocarbon radical may refer to a group consisting of only carbon and hydrogen. As used herein, a saturated hydrocarbon radical may refer to a hydrocarbon group in which all carbon atoms are connected by a single bond. As used herein, an unsaturated hydrocarbon radical may refer to a hydrocarbon group containing at least one unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond.

The saturated and/or unsaturated hydrocarbon group may be a chain hydrocarbon group. More preferably, the saturated and/or unsaturated hydrocarbon group may be a linear chain hydrocarbon group.

In Formulas 1 to 3, each of X may be a linear saturated hydrocarbon group, and Y may be a linear unsaturated hydrocarbon group. In Formulas 1 to 3, each of X may be a saturated hydrocarbon group having 1 to 30 carbon atoms, preferably 5 to 25 carbon atoms, and more preferably 9 to 18 carbon atoms. In Formulas 1 to 3, each of Y may be an unsaturated hydrocarbon group having 1 to 30 carbon atoms, preferably 5 to 25 carbon atoms, and more preferably 9 to 18 carbon atoms. This can be advantageous for purifying quantum dots with high yield by increasing the solubility of the quantum dot precursor. In Formulas 1 to 3, the number of carbon atoms of the saturated hydrocarbon group of X and the number of carbon atoms of the unsaturated hydrocarbon group of Y may be the same. This can be advantageous for purifying quantum dots with high yield by increasing the solubility of the quantum dot precursor.

In Formulas 1 to 3, each Y may be an unsaturated hydrocarbon group having at least one double bond in the hydrocarbon chain. In one example, the at least one double bond may be located at the center of the hydrocarbon chain. For example, when the unsaturated hydrocarbon group has 2n+1 carbon atoms, the n+1 carbon and the n+2 carbon may be connected by a double bond.

The Zn precursor can be prepared, for example, by reacting Zn(acetate) ₂ with a saturated fatty acid of R ₁ of Formulas 1 to 3 and an unsaturated fatty acid of R ₂ of Formulas 1 to 3. At this time, the number of moles of Zn (acetate) ₂ and the number of moles of saturated fatty acid may be the same, and the molar ratio of unsaturated fatty acid to saturated fatty acid may be 1:1.5 to 1:2.5, preferably 1:2. According to an embodiment of the present application, the saturated fatty acid may be steric acid, and the unsaturated fatty acid may be oleic acid.

This application also relates to quantum dot precursor compositions. The precursor composition may include the quantum dot precursor and a solvent. The solvent may be an organic solvent.

As the solvent, a high-temperature reaction is required to synthesize Zn-based quantum dots with high quantum efficiency, so a solvent with a high boiling point can be used. As the solvent, for example, a solvent having a boiling point of 100°C or higher can be used. The upper limit of the boiling point of the solvent is not particularly limited, but may be, for example, 500°C or less or 400°C or less. Representative examples of such solvents include octadecene, trioctylphosphine, and trioctylphosphine oxide, but are not limited thereto.

The quantum dot precursor may be included in a ratio of 0.05 to 50 parts by weight based on 100 parts by weight of the solvent. If the content is too small, the synthesis yield of quantum dots may be low, and if it is too high, uniform synthesis cannot be achieved due to an increase in viscosity, so it may be desirable to adjust the content within the above range.

The present application also relates to a method of producing quantum dots. The method for producing the quantum dot may use the quantum dot precursor or the quantum dot precursor composition.

In one example, the manufacturing method may be a method of manufacturing quantum dots with a core/shell structure. The core-shell structure may include a core portion, which is the central portion of the quantum dot, and a shell portion surrounding the core portion. Depending on the size of the core, different colors can be implemented, and the shell surrounding the core can play a role in improving luminous characteristics.

The manufacturing method may include a first step of reacting the quantum dot precursor composition by injecting a core precursor and a second step of reacting the quantum dot precursor composition by additionally injecting a shell precursor.

In the first step, the composition containing the precursor and the solvent may be raised to a temperature of at least about 150°C or higher, 200°C or higher, 250°C or higher, or 300°C or higher, and then the core precursor may be injected. This can be advantageous for manufacturing Zn-based quantum dots with high quantum efficiency.

In one example, the core precursor may be a selenium (Se) precursor, and the shell precursor may be a sulfur (S) precursor. As a specific example, the selenium (Se) precursor may be a suspension of selenium powder (Se powder), and the sulfur (S) precursor may be TOPS (trioctylphosphine sulphur). In this case, quantum dots with a core/shell structure in which the core part is ZnSe and the shell part is ZnS can be manufactured.

When manufacturing quantum dots using the quantum dot precursor or quantum dot precursor composition of the present application, high optical properties can be maintained while maintaining excellent solubility even when a solvent with a high boiling point is used, and thus unreacted precursors do not precipitate even at low temperatures. Since it can be maintained homogeneous, quantum dots can be purified with high yield. Quantum dots manufactured using the quantum dot precursor or quantum dot precursor composition of the present application can exhibit high quantum efficiency. The quantum efficiency may be 40% or more, 50% or more, 60% or more, or 65% or more.

In the above, a method for manufacturing quantum dots having a core/shell structure using a solution synthesis method has been described by way of example. However, as long as the quantum dot precursor or the quantum dot precursor composition of the present application is used, the method for manufacturing quantum dots and the structure of quantum dots manufactured therefrom are known to those skilled in the art. The design can be changed in various ways according to technical common sense. For example, in addition to the solution synthesis method, gas-phase synthesis methods, micro-fluidic synthesis methods, etc. are known, and in addition to the core/shell structure, alloy quantum dots, doped quantum dots, etc. are known.

The size of the quantum dots can be appropriately adjusted depending on the wavelength of light to be emitted within the range where photoluminescence is possible. In one example, the quantum dots may be spherical and have an average particle diameter of, for example, about 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less. It may be less than or equal to 20 nm or less than or equal to about 15 nm.

The quantum dots can emit various colors by adjusting their size. In one example, quantum dots manufactured using the precursor of the present application may be blue light-emitting quantum dots. Blue light-emitting quantum dots may refer to quantum dots that emit maximum light within a wavelength range of about 380 nm to 440 nm.

The quantum dots may emit light by electroluminescence. Electroluminescence means that a semiconductor material with an optical bandgap emits light when electrons are injected or a strong electric field is applied. The quantum dots can be applied not only to displays, but also to various fields such as solar cells, biosensors, quantum computers, lasers, and lighting.

The quantum dot precursor of the present application can maintain high optical properties and have excellent solubility even when using a solvent with a high boiling point. Accordingly, unreacted precursors can be maintained homogeneously without precipitating even at low temperatures, so the quantum dots can be maintained homogeneously. It can be purified with high yield.

Figure 1 shows the results of ¹ H-NMR analysis of the quantum dot precursor of Example 1.
Figure 2 is an image of the solution after quantum dot synthesis of Example 2 and Comparative Example 2.
Figure 3 is an image of a solution diluted with toluene after synthesizing quantum dots of Example 2 and Comparative Example 2.
Figure 4 shows the results of measuring the emission intensity of quantum dots of Example 2 and Comparative Example 2.

Hereinafter, the present application will be described in detail through examples according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the examples presented below.

Example One. quantum dot precursor

10 mmol of Zn (acetate) ₂ (product of Sigma-Aldrich), 20 mmol of oleic acid (product of Sigma-Aldrich), and 10 mmol of stearic acid (product of TCI) were added to a 2 neck round bottle flask. ), mixed, and reacted at 120°C for 2 hours to synthesize the Zn precursor. After reaction, 30ml DI. Wash with water (de-ionized water) and Ethanol, and finally wash with 2-butanol. The Zn precursor washed with each solvent is dried in vacuum after using a filter. The Zn precursor synthesized in this way is dissolved in dichloromethane-d2 and then analyzed using ¹ H-NMR. Figure 1 is a ¹ H-NMR analysis graph of a Zn precursor. The Zn precursor includes a material of the following formula A. In the graph of FIG. 1, x is NMR peaks corresponding to stearate and y is peaks corresponding to oleate. Since _the equation of x+y=2 can be solved through integration, it can be seen that it has a ratio of Zn (Stearate) _0.4 (Oleate) _1.6 .

[Formula A]

Comparative example One. quantum dot precursor

Commercially available Zn (Stearate) ₂ (manufactured by Sigma-Aldrich) of the following formula B was prepared.

[Formula B]

Example 2. quantum dot synthesis and purification

1.4 mmol of the Zn (Stearate) _0.4 (Oleate) _1.6 precursor prepared in _Example 1 was added to 30 ml of octadecene solvent, and the temperature was raised to 300°C after N ₂ purging. Afterwards, 0.5 mmol of selenium powder (Se powder) (manufactured by AlFA AESAR) is maintained in a suspension form in octadecene solvent and then injected using a 1 ml syringe. After reacting for 2 hours, 0.9M TOPS (trioctylphosphine sulphur) is slowly injected to synthesize quantum dots in the form of a ZnSe/ZnS core/shell. The TOPS is a substance prepared by dissolving 0.009 mol of sulfur powder (S powder) (produced by AlFA AESAR) in 10 ml of TOP (trioctylphosphine) (produced by TCI) in a state in which TOP and S are bonded to each other. The ZnSe/ZnS synthesized in this way was first diluted with toluene, then the quantum dots were settled using a solution of acetone and isopropyl alcohol mixed in a volume ratio of 1:2, and then washed at 8000 rpm for 10 minutes. Purify by centrifugation.

Comparative example 2. quantum dot synthesis and purification

1.4 mmol of Zn (Stearate) ₂ prepared in Comparative Example 1 was added to 30 ml of octadecene solvent and the temperature was raised to 300°C after N ₂ purging. Afterwards, 0.5 mmol of selenium powder (manufactured by AlFA AESAR) is maintained in a suspension form in octadecene solvent and then injected using a 1 ml syringe. After reacting for 2 hours, 0.9M TOPS (trioctylphosphine sulphur) is slowly injected to synthesize quantum dots in the form of a ZnSe/ZnS core/shell. The manufacturing method of TOPS is the same as Example 2. The ZnSe/ZnS synthesized in this way is first diluted with toluene, then the quantum dots are settled using a solution of acetone and isopropyl alcohol in a volume ratio of 1:2, and then purified by centrifugation at 8000 rpm for 10 minutes.

Evaluation example 1. Zn precursor solubility evaluation

Figure 2 is an image of a solution after synthesizing quantum dots of Example 2 and Comparative Example 2, and Figure 3 is an image of a solution diluted with toluene after synthesizing quantum dots of Example 2 and Comparative Example 2. As can be seen from Figures 2 and 3, it can be seen that the solution of Example 2 is more transparent compared to Comparative Example 2. This means that in Example 2, unreacted Zn precursor was not precipitated due to the higher solubility of the Zn precursor compared to Comparative Example 2.

Evaluation example 2. quantum dot Yield evaluation

For Example 2 and Comparative Example 2, the quantum dot yield after purification was evaluated, and the results are shown in Table 1. Specifically, the relative yield was measured by measuring the weight of the material after purification and measuring and comparing the UV-absorbance corresponding to a certain concentration with the UV-absorbance corresponding to a certain concentration of the synthesized material. The UV-absorbance was measured using SHIMADZU's uv-2600 model product. More specifically, prepare Sample 1 by taking 50ul of a solution of synthesized quantum dots and 41mL of solvent (octadecene) and diluting it with 3mL of hexane. Prepare sample 2 by taking 50 mL of a solution of purified quantum dots (about 0.324 g) and 41 mL of solvent (octadecene) and diluting it with 3 mL of hexane. After measuring the UV-absorbance for Samples 1 and 2, respectively, if the UV-absorbance of Sample 1 is about 2 times higher than the UV-absorbance of Sample 2, the amount of initially synthesized quantum dots is greater than that of purified quantum dots. Assuming there are twice as many, the yield can be calculated as 50% by assuming that the initially synthesized quantum dots are 0.648g. As shown in Table 1, it can be seen that Example 2 has a significantly higher yield compared to Comparative Example 2. This means that in Example 2, compared to Comparative Example 2, the unreacted Zn precursor was not precipitated due to the higher solubility of the Zn precursor and was maintained dissolved in the solvent, so quantum dots were obtained at a high yield using a centrifuge.

Evaluation example 3 PL (photoluminescence) measurement

For Example 2 and Comparative Example 2, PL (photoluminescence) was measured, and the results are shown in Figure 4 and Table 1. Specifically, 50 ul was taken from a solution of synthesized quantum dots and 41 mL of solvent (octadecene), and the UV absorbance was measured for a sample diluted with 3 mL of hexane, and then used a PL measuring device (FS-2, manufactured by SCINCO). PL was measured during excitation at a wavelength of 350 nm. As shown in Figure 4, Example 2 and Comparative Example 2 both emit blue light, but it can be seen that Example 2 has a significantly higher emission intensity compared to Comparative Example 2. These experimental results mean that the quantum dots of Example 2 have better performance as quantum dots than the quantum dots of Comparative Example 2.

Evaluation example 4. Quantum efficiency measurement

For the quantum dots prepared in Example 2 and Comparative Example 2, the quantum efficiency was measured, and the results are shown in Table 1. Specifically, using quantum efficiency measurement equipment (C11327-11, manufactured by Hamamatsu), the absolute value of quantum efficiency was measured by acquiring the optical spectrum as sensitivity corrected by a multi-channel detector and calculating the quantum efficiency. As shown in Table 1, it can be seen that Example 2 has significantly higher quantum efficiency compared to Comparative Example 2. These experimental results mean that the quantum dots of Example 2 have better performance as quantum dots than the quantum dots of Comparative Example 2.

Example 2 Comparative Example 2 yield 70% 24% PL intensity max 46,000 19,000 quantum efficiency 68% 32%

Claims (15)

A quantum dot precursor comprising a Zn precursor represented by Formula 1 below and a Zn precursor represented by Formula 2 below:
[Formula 1]
Zn ²⁺ ·[R ₁ ] ^- [R ₂ ] ^-
In Formula 1, Zn ²⁺ is a divalent zinc metal cation, [R ₁ ] ^- and [R ₂ ] ^- are each monovalent organic anions, and [R ₁ ] ^- and [R ₂ ] ^- are each Zn ² means bonding to ⁺ _{, R 1 is} X-COO-, am.
[Formula 2]
Zn ²⁺ ·[R ₂ ] ^- [R ₂ ] ^-
In Formula 2, Zn ²⁺ is a divalent zinc metal cation, [R ₂ ] ^- is a monovalent organic anion, · means that two [R ₂ ] ^- are each bonded to Zn ²⁺ , and R ₂ is Y-COO-, and Y is an unsaturated hydrocarbon group having 5 to 25 carbon atoms. The quantum dot precursor of claim 1, wherein the component ratio of all Zn precursors included in the quantum dot precursor satisfies the following formula (3):
[Formula 3]
Zn ²⁺ [R ₁ ] ^- _x [R ₂ ] ^- _2-x
In Formula 3, Zn ²⁺ is a divalent zinc metal cation, [R ₁ ] ^- and [R ₂ ] ^- are each monovalent organic anions, R ₁ is X-COO-, and X has 5 to 25 carbon atoms. is a saturated hydrocarbon group, R ₂ is Y-COO-, Y is an unsaturated hydrocarbon group having 5 to 25 carbon atoms, and x is a number in the range of 0.1 to 1. The quantum dot precursor of claim 1, wherein X in Formula 1 is a straight-chain saturated hydrocarbon group, and Y in Formulas 1 and 2 are each a straight-chain unsaturated hydrocarbon group. The quantum dot precursor of claim 1, wherein X and Y of Formula 1 are hydrocarbon groups having the same carbon number. The quantum dot precursor of claim 1, wherein Y in Formulas 1 and 2 is each an unsaturated hydrocarbon group having at least one double bond in a hydrocarbon chain. The quantum dot precursor of claim 5, wherein the at least one double bond is located at the center of a hydrocarbon chain. A quantum dot precursor composition comprising the quantum dot precursor of claim 1 and a solvent. The precursor composition of claim 7, wherein the solvent has a boiling point of 100°C or higher. The quantum dot precursor composition of claim 7, wherein the quantum dot precursor is contained in a ratio of 0.05 to 50 parts by weight based on 100 parts by weight of the solvent. A method for producing quantum dots comprising a first step of reacting the quantum dot precursor composition of claim 7 by injecting a core precursor and a second step of reacting the quantum dot precursor composition of claim 7 by additionally injecting a shell precursor. The method of claim 10, wherein the temperature of the quantum dot precursor composition in the first step is raised to at least 150° C. and then the core precursor is injected. The method of claim 10, wherein the quantum dots produced by the method have a core/shell structure and have a quantum efficiency of 30% or more. delete delete delete