KR20210033252A - Method for preparing a quantum dot, and a quantum dot prepared by the same - Google Patents

Abstract

The present invention relates to a method for manufacturing a quantum dot and a quantum dot manufactured thereby. The method for manufacturing a quantum dot comprises the steps of: (S100) heating a first solution containing a first zinc precursor, a first carboxylic acid-based compound, and a first organic solvent; (S200) feeding a first selenium precursor to a second organic solvent to prepare a second solution; (S300) feeding the second solution to the heated first solution to form a ZnSe core; and (S400) forming at least one layered shell on the ZnSe core, wherein the polarity index difference between the second organic solvent and the first organic solvent falls in a range of 0 to 0.4. According to the present invention, it is possible to manufacture a quantum dot having high quantum efficiency.

Description

Quantum dots manufacturing method, and quantum dots manufactured thereby BACKGROUND ART [METHOD FOR PREPARING A QUANTUM DOT PREPARED BY THE SAME}

The present invention relates to a method of manufacturing a quantum dot and a quantum dot manufactured thereby.

Quantum dot (QD) is a material having a crystal structure of several nano to tens of nanometers, and it is easy to adjust the band gap by controlling the size and composition of nanoparticles, and can realize light of various wavelengths. It can have electrical, magnetic, optical, chemical, and mechanical properties. These quantum dots can be applied to various devices such as light-emitting diodes (LEDs), organic-inorganic hybrid electroluminescent devices, inorganic electroluminescent devices, solar cells, and transistors.

For example, an LED display to which a quantum dot is applied, such as a quantum dot TV, uses a blue-emitting LED as a light source, and the quantum dot absorbs light having a predetermined wavelength and emits light having a different wavelength-a quantum dot-polymer composite sheet (QD It is included in the form of a sheet). The LED display to which such quantum dots are applied is drawing attention because of its excellent color purity and efficiency, while the same as the conventional general LED display operating principle.

In addition, OLED displays to which quantum dots are applied, like OLED TVs, are in the spotlight as next-generation light emitting displays because, unlike conventional OLEDs, they have excellent color reproduction and color purity.

However, there is a limit to emitting blue light using quantum dots. In addition, most of the blue light-emitting quantum dots are Cd-based quantum dots, and ZnSe-based quantum dots are known as non-Cd-based quantum dots, but their emission wavelength is about 420 to 430 nm, and ZnSe-based quantum dots with more than about 440 nm are It has not been developed yet. In addition, since conventional ZnSe-based quantum dots have low quantum efficiency, it has been difficult to be used for high-efficiency self-luminous TV materials.

An object of the present invention is to provide a method for manufacturing quantum dots having a light emission wavelength of 440 nm or more and having high quantum efficiency by uniformly controlling the particle diameter of a ZnSe core in synthesizing quantum dots.

In addition, another object of the present invention is to provide a quantum dot having a light emission wavelength of 440 nm or more and high quantum efficiency.

In order to achieve the above object, the present invention includes heating a first solution including a first zinc precursor, a first carboxylic acid compound, and a first organic solvent; Forming a second solution by adding a second organic solvent to the first selenium precursor; Mixing the heated first solution and the second solution to form a ZnSe core; And forming a shell of at least one layer on the ZnSe core, wherein the second organic solvent has a difference in polarity index with the first organic solvent in the range of 0 to 0.4. Provides a way.

In addition, the present invention provides a quantum dot having an emission wavelength of 440 nm or more, including a ZnSe core, and at least one layer of a shell, manufactured by the above-described method.

In the present invention, by uniformly controlling the particle diameter of the ZnSe core, quantum dots having a light emission wavelength of 440 nm or more and high quantum efficiency can be manufactured.

1 is a graph showing an emission spectrum of a quantum dot prepared in Example 1.

Hereinafter, the present invention will be described.

In the present invention, in manufacturing a quantum dot, an organic solvent having the same or similar polarity as the organic solvent used in the zinc precursor-containing solution is added to the zinc precursor-containing solution together with the selenium precursor and reacted to synthesize a ZnSe core. Accordingly, in the present invention, a quantum dot having a light emission wavelength of 440 nm or more and high quantum efficiency can be manufactured.

According to a first embodiment of the present invention, a method of manufacturing a quantum dot includes heating a first solution including a first zinc precursor, a first carboxylic acid compound, and a first organic solvent; Forming a second solution in which a first selenium (Se) precursor is added to a second organic solvent; Mixing the heated first solution and the second solution to form a ZnSe core; And forming at least one shell on the ZnSe core, wherein the second organic solvent has a difference in polarity index with the first organic solvent in the range of 0 to 0.4.

Hereinafter, each step of the method of manufacturing a quantum dot according to the present invention will be described.

(1) Preparation and heating step of the first solution

First, after preparing a first solution including a first zinc (Zn) precursor, a first carboxylic acid compound, and a first organic solvent, the first solution is heated (hereinafter referred to as'step S100').

According to an example of the present invention, the step S100 includes (S110) preparing a first solution by introducing a first zinc precursor and a first carboxylic acid-based compound into a first organic solvent; (S120) It may include heating the first solution under vacuum and then raising the temperature to a higher temperature under a nitrogen gas atmosphere, but is not limited thereto.

The first zinc precursor usable in the present invention is not particularly limited as long as it is a zinc metal itself or a compound containing zinc (Zn), as long as it is commonly known in the art. For example, zinc acetate, dimethyl zinc, diethyl zinc, zinc acetylacetonate, zinc iodide, zinc bromide , Zinc chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide, zinc peroxide peroxide), zinc perchlorate, zinc sulfate, and the like, but are not limited thereto. These may be used alone or in combination of two or more. According to one example, the zinc precursor may be zinc acetate.

The first carboxylic acid-based compound usable in the present invention is a material capable of uniformly dispersing the first zinc precursor in the first organic solvent, such as oleic acid, myristoleic acid, palmitolein _{C 6} ~ C ₃₀ unsaturated fatty acids such as Palmitoleic acid, Linoleic acid, Eicosapentaenoic acid (EPA), Docosapentaenoic acid (DPA), and the like; Lauric acid, palmitic acid, stearic acid, myristic acid, elaidic acid, eicosanoic acid, Heneicos Heneicosanoic acid, tricosanoic acid, docosanoic acid, tetracosanoic acid, hexacosanoic acid, heptacosanoic acid, octacosanoic acid There are saturated fatty acids of _{C 3} to C ₃₀ such as (octacosanoic acid) and cis-13-docosenoic acid, but are not limited thereto. These may be used alone or in combination of two or more. According to an example, the carboxylic acid-based compound may be an unsaturated fatty acid such as oleic acid.

The first organic solvent that can be used in the present invention may be used without limitation, as long as it is an organic solvent used in the synthesis of ZnSe core in the art. For example, C ₆ ~ C ₂₂ primary alkylamines such as hexadecylamine, dioctylamine Amine-based organic solvents such as C ₆ to C ₂₂ secondary alkylamines and C ₆ to C _{40 tertiary alkylamines such as trioctylamine;} Nitrogen (N)-containing heterocyclic compounds such as pyridine; Pentene, hexine, heptene, octadecene, nonene, decene, undecene, dodecene, tridecene, tetra Aliphatic hydrocarbons of _{C 5} to C ₄₀ such as tetradecene, pentadecene, octane, hexadecane, octadecane, octadecene, squalene, and the like; _{C 6} ~ C ₃₀ aromatic hydrocarbons such as phenyldodecane, phenyltetradecane, and phenyl hexadecane; Phosphine substituted with a _{C 6} ~ C ₂₂ alkyl group such as trioctylphosphine; Phosphine oxide substituted with a _{C 6} ~ C ₂₂ alkyl group such as trioctyl phosphine oxide; _{There are aromatic ethers of C 12} ~ C ₂₂ such as phenyl ether and benzyl ether, but are not limited thereto. These may be used alone or in combination of two or more. According to an example, the first organic solvent may be an amine-based organic solvent, specifically a C ₆ ~ C ₄₀ tertiary alkylamine.

In the first solution of the present invention, the contents of the first zinc precursor, the first carboxylic acid compound, and the first organic solvent are not particularly limited. According to an example, the content of the first carboxylic acid-based compound may be about 1 to 5 mol per 1 mol of the first zinc precursor. In this case, the content of the first organic solvent may be about 100 to 50,000 ml per 1 mol of the first zinc precursor.

This first solution is heated under vacuum and then heated to a higher temperature under a nitrogen atmosphere.

The heating temperature and time under vacuum are not particularly limited, and may be heated at, for example, about 100° C. or higher, specifically about 100 to 160° C. for about 0.5 to 24 hours.

In addition, the heating temperature and time are not particularly limited, and for example, the temperature may be raised to about 200° C. or more, specifically about 200 to 350° C.

(2) Formation step of the second solution

This step is a step of forming a second solution containing a selenium precursor by introducing a first selenium (Se) precursor into a second organic solvent (hereinafter referred to as'step S200').

In the present invention, as the second organic solvent, a solvent having the same or similar polarity index as the first organic solvent used in step S100, specifically the same or similar polarity, and the same or similar boiling point (Boiling Point, BP), more specifically the same solvent is used. Here, the polarity index of the solvent generally indicates the polarity of the solvent, and when the polarity of water is 1.000, it means a relative polarity.

According to an example, the second organic solvent is a solvent having a difference in polarity with the first organic solvent in the range of about 0 to 0.4.

According to another example, the second organic solvent may be a solvent having a difference in polarity with the first organic solvent in the range of about 0 to 0.4 and a difference in boiling point with the first organic solvent of about 0 to 100°C.

According to another example, the second organic solvent may be the same solvent as the first organic solvent.

This second organic solvent prevents aggregation of the first selenium precursors during storage and injection of the second solution, and prevents phase separation between the second solution and the first solution when the second solution is added to the first solution to react. In addition, it is possible to induce a uniform reaction by preventing a difference in boiling point (BP) between the second solution and the first solution. Therefore, in the present invention, a ZnSe core having a uniform particle diameter can be synthesized. This step S200 has no temporal relationship to the step S100 described above. For example, it may be performed after step S100, but may be performed before step S100 or may be performed separately at the same time as step S100.

The first selenium precursor used in this step is not particularly limited as long as it is known in the art as a compound containing selenium (Se), and for example, selenium-diphenylphosphine selenide, selenium-trioctylphosphine, It may be selenium-tributylphosphine, selenium-triphenylphosphine, and the like. These may be used alone or in combination of two or more.

The content of selenium in the first selenium (Se) precursor may range from about 0.05 to 2 mol with respect to 1 mol of zinc in the first zinc precursor.

Specific examples of the second organic solvent used in this step are the same as those described for the first organic solvent, and thus are omitted. However, in the present invention, the second organic solvent is a solvent having the same or similar polarity index as the first organic solvent used in step S100 described above, and specifically, the same or similar polarity index. It may be a solvent having a boiling point (BP). More specifically, when the first organic solvent is an amine-based organic solvent, specifically a tertiary alkylamine, in consideration of the difference in polarity with the first organic solvent and further, the difference in boiling point with the first organic solvent, the second organic solvent It may also be an amine-based organic solvent, specifically a tertiary alkylamine. According to an example, both the first organic solvent and the second organic solvent may be _{a tertiary amine containing a C 6} ~ C ₄₀ alkyl group, specifically trioctylamine.

In step S200, the use ratio of the first selenium precursor and the second organic solvent is not particularly limited, and is adjusted according to the content of the first selenium precursor, for example, the use ratio of the first selenium precursor and the second organic solvent (mixing ratio) May be 1: 0.001 ~ 1 volume ratio.

(3) Formation step of ZnSe core

This step is a step of forming a ZnSe core by mixing and reacting the first solution heated in step (S100) with the second solution formed in step (S200) (hereinafter referred to as'step S300').

The use ratio (mixing ratio) of the first solution and the second solution is not particularly limited, and may be in a ratio of 1:0.001 to 1:1.

When the second solution is added, the temperature, speed, and time are not particularly limited, and vary depending on the amount of the second solution. For example, the second solution may be added to the first solution for about 6 hours or less at room temperature or higher, specifically, about 15 to 30°C. At this time, the injection rate is adjusted according to the content of the second solution.

Meanwhile, in the present invention, when the second solution is added to the first solution, a halide solution may be additionally added.

The halide solution is a solution in which halide is dispersed or dissolved in a solvent. By etching and coating the surface of the ZnSe core with the halide in the halide solution, the growth and surface of the ZnSe core are stabilized, leading to high quantum efficiency of the ZnSe core.

Specifically, some or all of the organic material layer (e.g., organic ligand layer) present on the surface of the ZnSe core is removed by the halide of the halide solution, and instead, a material constituting the halide, such as a metal cation-halide anion or a hydrocarbon group-halogen Each group is substituted by bonding with some or all of the surface of the ZnSe core. Accordingly, since the occurrence of defects on the surface of the ZnSe core due to the removal of the organic ligand layer is suppressed by the coating layer formed of halide, the growth of the ZnSe core and stability of the surface are improved, thereby obtaining quantum dots having high quantum efficiency. At this time, the produced quantum dot has a halide layer interposed in some or all of the interface between the ZnSe core and the shell.

The halide usable in the present invention is not particularly limited as long as it is a halide known in the art, and not only inorganic halide such as fluoride, chloride, bromide, iodide, etc., but also halogenated hydrocarbons (eg, C ₁ ~ C ₁₂ alkyl halide) It may be an organic halide such as. Specific examples include, but are not limited to, NH ₄ Cl, NH ₄ Br, NH ₄ I, ZnCl ₂ , ZnBr ₂ , ZnI ₂ , CH ₃ Cl, CH ₃ Br, CH ₃ I, and the like.

In addition, the solvent in the halide solution is not particularly limited as long as it is a polar solvent or non-polar solvent known in the art capable of dissolving or dispersing the halide.

The content of the halide solution is not particularly limited, and may be, for example, in the range of about 0.01 to 100 parts by volume based on 100 parts by volume of the second solution. At this time, the concentration of the halide solution is not particularly limited, and may be, for example, about 1 to 30% by weight, specifically about 5 to 20% by weight, and more specifically about 8 to 15% by weight based on the total amount of the halide solution. . For example, the concentration of the halide solution may be about 10% by weight.

The ZnSe core particles formed through the above-described step (S300) are dissolved together with impurities in a solvent. Thus, optionally, it is possible to purify and separate the ZnSe core particles. For example, after the ZnSe core particles are precipitated by adding an anti-solvent to the solution containing the ZnSe core particles obtained in step (S300), the ZnSe core particles may be separated. At this time, in the present invention, when purifying and separating the ZnSe core particles, a halide may be added together with an anti-solvent. This purification process may be repeatedly performed one or more times.

Non-limiting examples of the anti-solvent include acetone, ethanol, methanol, butanol, propanol, isopropyl alcohol, tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, and the like, and these may be used alone or in combination of two or more. have.

The method of separating the ZnSe core particles is not particularly limited as long as it is known as a liquid-solid separation method in the art, and includes, for example, a centrifugation method.

The halide not only prevents defects on the surface of the ZnSe core from occurring when the ZnSe core particles are separated and purified, but also improves the reaction between the ZnSe core and the shell precursor so that a shell is formed and grown on the ZnSe core. have.

As the halide usable in the present invention, an inorganic halide or an organic halide may be used without limitation. Specifically, inorganic halide is a material containing halogen (X=F, Cl, Br, I, etc.) and one metal known in the art, and specifically, metal fluoride, metal chloride, metal bromide, metal iodide, etc. It may be the same metal halide salt. For example, ZnCl ₂ , ZnBr ₂ , ZnI ₂ , NH ₄ Cl, NH ₄ Br, NH ₄ I, and the like. In addition, the organic halide may be a halogenated hydrocarbon or the like, specifically, a C ₁ ~ C ₁₂ alkyl halide, and the like, such as CH ₃ Cl, CH ₃ Br, CH ₃ I, and the like. These may be used alone or in combination of two or more. According to an example, the halide may be _{ZnCl 2.}

The content of halide is not particularly limited, for example, the ratio _{of the volume (V 2} ) of the solution in which the halide is dissolved (hereinafter,'halide solution') to the volume (V _{1 ) of the ZnSe core dispersion (V 2} /V ₁ ) may be about 0.1 to 5, and the halide content in the halide solution is about 0.1 wt% or more, and the halide can be dissolved up to the solubility limit.

Also, if necessary, the ZnSe core particles separated above may be redispersed in a non-polar solvent. As a result, since the ZnSe core particles exist in a colloidal form in a non-polar solvent, they can be stably stored. Examples of non-polar solvents that can be used at this time include hexane, benzene, xylene, toluene, octane, chloroform, chlorobenzene, tetrahydrofuran (THF), methylene chloride, 1,4 -Dioxane (1,4-dioxane), diethyl ether (diethyl ether), cyclohexane, dichlorobenzene, and the like, but are not limited thereto.

(4) the formation stage of the shell

This step is a step of forming and growing a shell of at least one layer on the ZnSe core formed in step (S300) (hereinafter referred to as'step S400'), in which a shell is formed and grown on the core of quantum dots in the industry. If it is a method, it is not particularly limited. In this case, the shell formation process may be appropriately selected according to the component, thickness, and number of layers of each shell.

According to an example, step S400 may include forming a third solution by mixing the ZnSe core formed in step S410 with a solution containing a second zinc precursor; (S420) adding a first mixture of a second selenium precursor and a first sulfur precursor to the third solution and reacting to form a solution containing first particles having a ZnSe core/ZnSeS shell structure; (S430) Injecting a second mixture of a third selenium precursor and a second sulfur precursor into a solution containing the first particles and reacting to form a solution containing the second particles having a ZnSe core/ZnSeS shell/ZnSeS shell structure step; And (S440) adding and reacting a third sulfur precursor to the solution containing the second particles to form particles having a ZnSe core/ZnSeS shell/ZnSeS shell/ZnS shell structure, but is not limited thereto. Does not.

Specifically, step (S410) is a step of forming a third solution by mixing the ZnSe core formed in step (S300) with a solution containing a second zinc precursor.

The solution containing the second zinc precursor may contain a second zinc precursor and a second carboxylic acid-based compound, and may optionally further contain a third organic solvent. Before the ZnSe core is introduced into the solution containing the second zinc precursor, the solution containing the second zinc precursor may be heated under vacuum and then heated to a higher temperature under a nitrogen gas atmosphere. Accordingly, it is possible to increase the reaction rate between the ZnSe core, the zinc precursor, the selenium precursor, and the sulfur precursor.

The second zinc precursor, the second carboxylic acid compound, and the third organic solvent that can be used in this step are the same as or different from the first zinc precursor, the first carboxylic acid compound, and the first organic solvent used in step S100, respectively, Each of these examples is as already described in step S100.

In the solution containing the second zinc precursor, the contents of the second zinc precursor, the second carboxylic acid-based compound, and the third organic solvent are not particularly limited. According to an example, the content of the second carboxylic acid-based compound may be about 1 to 5 mol per 1 mol of the second zinc precursor. In this case, the content of the third organic solvent may be about 0 to 50,000 ml per 1 mol of the second zinc precursor.

The solution containing this second zinc precursor is heated under vacuum and then heated to a higher temperature under a nitrogen atmosphere.

The heating temperature and time under vacuum are not particularly limited, and may be heated at, for example, about 100° C. or higher, specifically about 100 to 160° C. for about 0.5 to 24 hours.

Further, the temperature and time of raising the temperature in a nitrogen atmosphere are not particularly limited, and the temperature may be raised to, for example, about 200° C. or more, and specifically, about 200 to 350° C.

Thereafter, in step (S420), a first mixture of a second selenium (Se) precursor and a first sulfur (S) precursor is added to the third solution containing the ZnSe core and the Zn precursor prepared in the step (S410), and reacted. In the step of forming a ZnSeS shell on the surface of the ZnSe core, a solution containing particles having a ZnSe core/ZnSeS shell structure can be obtained.

In this case, the first mixture of the second Se precursor and the first S precursor may be added dropwise into the third solution. As described above, by slowly adding the second Se precursor and the first S precursor, it is possible to form and grow a strong, stable and uniform ZnSeS shell on the surface of the ZnSe core without being affected by temperature.

The second selenium precursor usable in step (S420) is a compound containing selenium, and may be the same as or different from the first selenium precursor used in step S200. For example, it may be selenium-diphenylphosphine selenide, selenium-trioctylphosphine, selenium-tributylphosphine, selenium-triphenylphosphine, and the like, but is not limited thereto. These may be used alone or in combination of two or more.

The first sulfur precursor usable in the (S420) step is not particularly limited as long as it is known as a sulfur-containing compound in the art, for example, sulfur-diphenylphosphine sulfide, sulfur-trioctylphosphine, sulfur-t There are pibutylphosphine, sulfur-triphenylphosphine, sulfur-trioctylamine, trimethylsilyl sulfur, ammonium sulfide, sodium sulfide, hexane thiol, octane thiol, decane thiol, dodecane thiol, hexadecane thiol, etc. It doesn't work. These may be used alone or in combination of two or more.

In the first mixture of step (S420), the use ratio (mixing ratio) of the second selenium precursor and the first sulfur precursor is not particularly limited, and may be, for example, 0.99:0.01 to 0.01:0.99 molar ratio.

The content of the first mixture can be adjusted according to the thickness and components of the ZnSeS shell. For example, the first mixture and the second zinc precursor in the third solution may be used in a molar ratio of 1:1 to 1:100.

In step (S420), when the first mixture is added, the temperature, speed, and time are not particularly limited, and may vary depending on the amount of the first mixture added. For example, the first mixture may be added to the third solution for about 6 hours or less at room temperature or higher, specifically, about 15 to 30°C. At this time, the input rate is adjusted according to the content of the first mixture.

Subsequently, in step (S430), a second mixture of Se precursor and S precursor is additionally added and reacted to the solution containing particles of the ZnSe core/ZnSeS shell structure formed in step (S420), thereby reacting the ZnSeS shell (hereinafter, ' A ZnSeS shell (hereinafter, a'second ZnSeS shell') is formed on the surface of the first ZnSeS shell') to obtain a solution containing particles having a ZnSe core/first ZnSeS shell/second ZnSeS shell structure.

In this case, the rate of addition of the second mixture is not particularly limited, and may be the same as, similar to, or faster than the rate of addition of the first mixture. In this way, when the second mixture of the Se precursor and the S precursor is added to a solution containing particles of a ZnSe core/first ZnSeS shell structure and reacted, a second ZnSeS shell can be formed and grown on the surface of the first ZnSeS shell. have. In this case, the second ZnSeS shell has a smaller Zn content than the first ZnSeS shell.

The third selenium precursor usable in step (S430) may be the same as or different from the first selenium precursor and the second selenium precursor used in steps (S200) and (S420), respectively, examples of which are the steps (S420). Since it is the same as described in, it will be omitted.

In addition, the second sulfur precursor may be the same as or different from the first sulfur precursor used in the step (S420), and examples thereof are the same as those described in the step (S420), and thus will be omitted.

In the second mixture of step (S430), the use ratio (mixing ratio) of the third selenium precursor and the second sulfur precursor is not particularly limited, and may be, for example, 0.99:0.01 to 0.01:0.99 molar ratio.

The content of the second mixture may be adjusted according to the thickness of the second ZnSeS shell. For example, the second mixture may be used by mixing with the particles of the ZnSe core/first ZnSeS shell structure in the solution formed in the step (S420) at a molar ratio of 1:0.01 to 2. In this case, the thickness of the second ZnSeS shell may be about 0.1 to 5 nm.

In step (S430), when the second mixture is added, the temperature, speed, and time are not particularly limited, and may vary depending on the amount of the second mixture added. For example, the second mixture may be added to the solution obtained in step (S420) for about 6 hours or less at room temperature or higher, specifically, about 15 to 30°C. At this time, the input rate is adjusted according to the content of the second mixture.

Thereafter, in step (S440), a third sulfur precursor is added to the solution containing particles of the ZnSe core / first ZnSeS shell / second ZnSeS shell structure formed in step (S430) and reacted to form the second ZnSeS shell. A ZnS shell is formed on the surface to form a quantum dot having a ZnSe core/first ZnSeS shell/second ZnSeS shell/ZnS shell structure. At this time, the content of Zn and Se in the quantum dot has a concentration gradient that gradually decreases from the center toward the surface (outermost layer), and the content of S has a concentration gradient that gradually increases from the center toward the surface (outermost layer). .

The third sulfur precursor usable in step (S440) may be the same as or different from the first sulfur precursor and the second sulfur precursor used in steps (S420) and (S430), respectively, examples of which are the above (S420) Since it is the same as described in the step, it will be omitted.

The content of the third sulfur precursor is controlled according to the thickness of the S shell. According to an example, the thickness of the S shell may be about 0.1 to 5 nm.

Meanwhile, optionally, in the present invention, the quantum dots formed through the step (S400) may be purified and separated. For example, after cooling after the reaction in step (S400) is completed, an anti-solvent is added to the quantum dots formed in step (S400) to precipitate the quantum dots, and then the ZnSe core particles may be separated. This purification process may be repeatedly performed one or more times.

The quantum dots are cooled to room temperature, specifically about 15 to 30°C, and more specifically about 23 to 28°C, thereby preventing the quantum dots from becoming excessively large. Accordingly, the particle diameter of the quantum dot particles may be uniform.

Examples of anti-solvents that can be used in the present invention include acetone, ethanol, methanol, butanol, propanol, isopropyl alcohol, tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, and the like, and these are used alone or in combination of two or more. I can.

The method of separating the quantum dots is not particularly limited as long as it is known as a liquid-solid separation method in the art, and includes, for example, a centrifugal separation method.

In addition, if necessary, the quantum dots may be redispersed in a non-polar solvent and stored. As a result, since the quantum dots are colloidally dispersed in a non-polar solvent, they can be stably stored. Examples of non-polar solvents that can be used at this time include hexane, benzene, xylene, toluene, octane, chloroform, chlorobenzene, tetrahydrofuran (THF), methylene chloride, 1,4 -Dioxane (1,4-dioxane), diethyl ether (diethyl ether), cyclohexane, dichlorobenzene, and the like, but are not limited thereto.

The quantum dot of the present invention manufactured according to the above-described method includes a ZnSe core, and at least one layer of a shell. It has an emission wavelength. Further, the quantum dot according to the present invention may have a full width at half maximum (FWHM) of about 14 nm or less, an average particle diameter of about 5 to 20 nm, and a quantum efficiency of about 55% or more.

According to an example, the quantum dot of the present invention includes a ZnSe core; And a first ZnSeS shell, a second ZnSeS shell, and a ZnS shell continuously formed on the ZnSe core. At this time, each shell has a layered gradient composition. That is, Zn, Se, and S in each shell may have different contents. Specifically, the Zn and Se content has a concentration gradient that gradually decreases from the center of the quantum dot to the surface (outermost layer) side, and the content of S is a concentration gradient that gradually increases from the center to the surface (outermost layer) side. Have.

Such quantum dots can be variously applied to various electronic devices such as light emitting diode (LED) displays, organic light emitting diode (OLED) displays, sensors, imaging sensors, solar cells, and the like.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are for illustrative purposes only, and the scope of the present invention is not limited to the examples.

<Example 1>-Preparation of quantum dots

1-1. Synthesis of ZnSe core

A first solution was formed by adding 20 mmol _{of Zn acetate[Zn(CH 3} COO) ₂ ] to a solution of 100 ml of oleic acid 60 mmol and trioctylamine(TOA) (boiling point at 1 atm: about 365~367 ℃). After that, the first solution was heated to about 120° C. under vacuum and then heated to a temperature of about 300° C. under a nitrogen gas atmosphere. A Se precursor was formed by dissolving 16 mmol of selenium (Se) powder in 16 ml of diphenylphosphine, and then TOA was mixed with the Se precursor in a volume ratio of 1:1 to obtain a second solution. The second solution was slowly injected into the heated first solution using an injection pump and reacted at 300° C. for 120 minutes to synthesize a ZnSe core, and then the ZnSe core was centrifuged using _{Acetone, Ethanol, and ZnCl 2.} Then, the separated ZnSe core was dispersed in Hexane to obtain a dispersion solution in which the ZnSe core was dispersed.

1-2. Shell formation

20 mmol of Zn acetate was added to a solution of 60 mmol of oleic acid and 100 ml of trioctylamine (TOA) to form a Zn precursor-containing solution, and the Zn precursor-containing solution was heated to 120° C. under vacuum, and then in a nitrogen atmosphere. The temperature was raised to a temperature of about 280°C. Thereafter, the ZnSe core synthesized in Example 1-1 was added to the 280° C. Zn precursor-containing solution to obtain a third solution. Subsequently, 0.13 M Se precursor and 1 M S precursor were mixed so that Se and S were in a 3:1 molar ratio to obtain a first mixture, and then the first mixture was added to a third solution for 4 hours using an injection pump. It was injected (injected) to form a ZnSeS shell on the surface of the ZnSe core. Thereafter, 0.13 M Se precursor and 1 M S precursor were mixed so that Se and S had a molar ratio of 1:20, and then rapidly injected into a solution containing particles of ZnSe core/ZnSeS shell, followed by 20 at 280°C. By reacting for a minute, a ZnSeS shell (hereinafter, a'second ZnSeS shell') was formed on the surface of the ZnSeS shell (hereinafter, referred to as'first ZnSeS shell'). Here, 1 M of the S precursor was further added and reacted to form a ZnS shell on the surface of the second ZnSeS shell. After the reaction was completed, the mixture was cooled to room temperature, and then a mixed solution of Acetone and Ethanol was added and centrifuged to prepare quantum dots having a ZnSe core-first ZnSeS/second ZnSeS/ZnS shell structure. The 0.13 M Se precursor used at this time was obtained by dissolving selenium (Se) powder in Trioctylphosphine, and the 1 M S precursor was obtained by dissolving sulfur (S) powder in Trioctylphosphine.

<Example 2>-Preparation of quantum dots

2-1. Synthesis of ZnSe core

In Example 1-1, when the second solution was slowly injected into the first solution, ZnSe was performed in the same manner as in Example 1-1, except that 0.3 ml of a halide solution (containing HF) was added at regular intervals. The core was synthesized.

2-2. Shell formation

Quantum dots were manufactured in the same manner as in Example 1-2, except that the ZnSe core synthesized in Example 2-1 was used instead of the ZnSe core of Example 1-1 used in Example 1-2. .

<Comparative Example 1>-Preparation of quantum dots

1-1. Synthesis of ZnSe core

In Example 1-1, a ZnSe core was synthesized in the same manner as in Example 1-1, except that the Se precursor solution was rapidly injected into the first solution at once instead of slowly injecting the second solution into the first solution. . At this time, the Se precursor used was obtained by dissolving 16 mmol of selenium (Se) powder in 16 ml of diphenylphosphine.

1-2. Shell formation

Quantum dots were manufactured in the same manner as in Example 1-2, except that the ZnSe core synthesized in Comparative Example 1-1 was used instead of the ZnSe core of Example 1-1 used in Example 1-2. .

<Comparative Example 2>-Preparation of quantum dots

In Example 1-1, instead of the second solution, Example 1, except that a mixture (1:1 volume ratio) of the Se precursor and water (polarity: 1, boiling point at 1 atm: 100 °C) was used. In the same manner as -1, the ZnSe core was synthesized. However, the mixed solution was not mixed with the first solution and phase-separated, and some components (Se precursor) in the mixed solution were solidified and could not be injected, so that the ZnSe core could not be synthesized.

<Comparative Example 3>-Preparation of quantum dots

In Example 1-1, instead of the second solution, except for using a mixture (1:1 volume ratio) of the Se precursor and Toluene (polarity: 0.099, boiling point at 1 atm: about 110 to 111 °C), In the same manner as in Example 1-1, a ZnSe core was synthesized. However, when the mixed solution was injected into the first solution, the reactor was exploded due to the vapor of toluene, so that the ZnSe core could not be synthesized.

<Experimental Example 1>

For the quantum dots prepared in Examples 1 to 2 and Comparative Example 1, respectively, the emission peak (PL peak), half width (FWHM), and quantum efficiency (QE) were measured at an excitation wavelength of 370 nm using a wavelength equipment of Otsuka QE2100, The results are shown in Table 1 and FIG. 1 below. At this time, each quantum dot was measured while being dispersed in octane.

PL peak (nm) FWHM (nm) QE (%) Example 1 444 12 57 Example 2 446 14 75 Comparative Example 1 420 13 60

Both of the quantum dots of Examples 1 and 2 had an emission peak of 440 nm or more, whereas the emission peak of Comparative Example 1 was less than 440 nm.

In addition, both of the quantum dots of Examples 1 and 2 had a small half width like the quantum dots of Comparative Example 1. In addition, the quantum dots of Example 2 had higher quantum efficiency than the quantum dots of Comparative Example 1.

As described above, it was confirmed that the quantum dots synthesized according to the present invention had an emission wavelength of 440 nm or more while having a uniform particle diameter of the core. In addition, it was confirmed that the quantum dots synthesized using the halide solution according to the present invention can further improve the quantum efficiency compared to the quantum dots without the halide solution.

Claims (8)

Heating a first solution including a first zinc (Zn) precursor, a first carboxylic acid compound, and a first organic solvent;
Forming a second solution by injecting a first selenium (Se) precursor into a second organic solvent;
Mixing the heated first solution and the second solution to form a ZnSe core; And
Forming at least one layer of shell on the ZnSe core
Including,
The second organic solvent has a polarity index difference with the first organic solvent in the range of 0 to 0.4, The method of manufacturing a quantum dot. The method of claim 1,
The second organic solvent has a boiling point difference with the first organic solvent in the range of 0 to 100°C. The method of claim 2,
The second solvent is the same as the first organic solvent, the method of manufacturing a quantum dot. The method of claim 1,
When the first solution and the second solution are mixed, a halide solution is additionally added. The method of claim 4,
The halide in the halide solution is one or more selected from the group consisting of inorganic halide and organic halide. The method of claim 1,
After the step of forming the ZnSe core,
Separating the ZnSe core using a halide;
A method of manufacturing a quantum dot further comprising a. The method of claim 1,
Forming the shell,
Forming a third solution by mixing the ZnSe core with a solution containing a second zinc precursor;
Adding a first mixture of a second selenium precursor and a first sulfur precursor to the third solution and reacting to form a solution containing first particles having a ZnSe core/ZnSeS shell structure;
Adding a second mixture of a third selenium precursor and a second sulfur precursor to a solution containing the first particles and reacting to form a solution containing the second particles having a ZnSe core/ZnSeS shell/ZnSeS shell structure; And
Injecting and reacting a third sulfur precursor to the solution containing the second particles to form particles having a ZnSe core/ZnSeS shell/ZnSeS/ZnS shell structure
Containing, a method of manufacturing a quantum dot. A quantum dot manufactured by the method according to any one of claims 1 to 7, and including a ZnSe core, and at least one layer of shell, and having an emission wavelength of 440 nm or more.

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