JP2022076513A - Quantum dot, quantum dot aggregate, and production method thereof - Google Patents

Abstract

To provide a silver bismuth chalcogenide quantum dot in which uniformization of particle diameter can be attained and a production method of the silver bismuth chalcogenide quantum dot which is simple, has high safety, and uses a raw material easy to handle.SOLUTION: A quantum dot is a nanocrystal represented by AgBiE2 (E is at least one of tellurium, selenium, or sulfur) containing silver, bismuth, and chalcogen. The quantum dot has an average particle diameter of 1 nm or more and 15 nm or less.SELECTED DRAWING: None

Description

The present invention relates to indirect transitioning quantum dots, quantum dot aggregates, and methods for manufacturing the same.

Quantum dots are nanoparticles having a particle size of several nm to several tens of nm and are composed of hundreds to several thousand atoms. Quantum dots are also called fluorescent nanoparticles, semiconductor nanoparticles, or nanocrystals.

The emission wavelength of the quantum dots can be variously changed depending on the particle size and composition of the nanoparticles. Further, examples of the performance of the quantum dots include a fluorescence quantum yield (Quantum Yield: QY), a full width at half maximum (FULL Width at Half Maximum: FWHM), an absorption wavelength, and a fluorescence wavelength.

The following patent documents and non-patent documents describe solar cells using AgBiS ₂ quantum dots.

Japanese Unexamined Patent Publication No. 2017-28267

ACS Applied Nano Materials, 2020, 3, 5, pp 4014 Cubic AgBiS2 Colloidal Nanocrystals for SolarCells Nature Photonics, 2016, 10, pp521 Solution-processed solar cells based on environmentally friendly AgBiS2nanocrystals J. Mater. Chem. C, 2018, 6, pp 731 Enhanced optoelectronic performancein AgBiS2 nanocrystals obtained via an improved amine-based synthesis route

However, no research and development has been reported in line with the practical application of silver bismuth chalcogenide quantum dots. For example, in the synthesis of the silver bismascarcogenide quantum dots described in Non-Patent Documents 1 to 3 and Patent Document 1, S (TMS) ₂ (hexamethyldisilatian) is used as a sulfur source. Is a reagent that, when used in the atmosphere, easily reacts with moisture in the air and releases toxic _H2S .

From the above background, the synthesis of silver bismuth chalcogenide quantum dots by a mass-producible method using simple and easy-to-handle raw materials, and the physical characteristics of silver bismuth chalcogenide quantum dots synthesized by such a method. Clarification is strongly required.

The present invention has been made in view of this point, and an object of the present invention is to provide a silver bismuth scalcogenide quantum dot and a quantum dot aggregate capable of making the particle size uniform.

Another object of the present invention is to provide a method for producing silver bismuth chalcogenide quantum dots using a simple, highly safe, and easy-to-handle raw material.

The quantum dot in the present invention is a nanocrystal represented by AgBiE ₂ (E is at least one of tellurium, selenium, or sulfur) containing silver, bismuth, and chalcogen, and is a quantum dot. The average particle size is 1 nm or more and 15 nm or less.
For the quantum dots in the present invention, it is preferable that the surface of the quantum dots is covered with a ligand.

In the present invention, the ligand is preferably selected from at least one or two of phosphine-based, aliphatic thiol-based, aliphatic amine-based, and aliphatic carboxylic acid-based.

In the present invention, it is preferable to obtain an optical bandgap of 0.90 to 1.10 eV in the TauC plot.

The quantum dot aggregate in the present invention contains a large number of the quantum dots described above, and the particle size distribution in STEM includes the quantum dots of 2/3 or more of the whole within ± 20% of the average particle size. It is a feature.

The method for producing quantum dots in the present invention comprises AgBiE ₂ (E is tellurium or selenium) from a silver raw material, a bismuth raw material, and a chalcogenide raw material (chalcogenide is at least one of tellurium, selenium, or sulfur). Or, it is characterized by synthesizing quantum dots represented as at least one of sulfur).

In the present invention, it is preferable to synthesize the quantum dots in a solvent containing thiol.
In the present invention, it is preferable to synthesize the raw material solution by reacting at a reaction temperature of about 100 ° C to about 150 ° C.

In the present invention, the silver raw material, the bismuth raw material, and the ligand are sequentially added to a high boiling point solvent having a boiling point of 150 ° C. or higher, reacted at a predetermined reaction temperature, the chalcogenide raw material is added, and then the same. It is preferable to react at warm temperature.

In the present invention, a step of dissolving the silver raw material, the bismuth raw material, and one or two raw materials of the ligand in the high boiling point solvent heated to 100 ° C. to 150 ° C., and the chalcogenide raw material are used. It is preferable to have a step of sequentially adding other raw materials including the raw materials, and a step of adding all the raw materials and then continuously reacting them at the same reaction temperature to synthesize the quantum dots.

According to the quantum dots of the present invention, the particle size distribution in STEM can be narrowed, and silver bismuth scalcogenide quantum dots having the same particle size can be synthesized.

Further, according to the quantum dot manufacturing method of the present invention, silver bismuth scalcogenide quantum dots can be directly mass-produced simply and safely without using an easy-to-handle reactant and without using an intermediate or the like. be.

It is a schematic diagram of the quantum dot in embodiment of this invention. It is a schematic diagram of the quantum dot in embodiment of this invention. 9 is an absorption spectrum of AgBiS ₂ in Example 1. 9 is a TauC plot of AgBiS ₂ in Example 1. FIG. 3 is a scanning transmission electron microscope (STEM) photograph and a particle size analysis diagram of AgBiS ₂ in Example 1. It is a differential thermal analysis figure of AgBiS ₂ in Example 1. FIG. It is an X-ray diffraction (XRD) spectrum of AgBiS ₂ in Example 1. FIG. 9 is an absorption spectrum of AgBiS ₂ in Example 2. 9 is a TauC plot of AgBiS ₂ in Example 2. FIG. 3 is a scanning transmission electron microscope (STEM) photograph and a particle size analysis diagram of AgBiS ₂ in Example 2. It is a differential thermal analysis figure of AgBiS ₂ in Example 2. FIG. It is an X-ray diffraction (XRD) spectrum of AgBiS ₂ in Example 2. FIG. FIG. 3 is an Absorption spectrum of AgBiS ₂ in Example 3. 9 is a TauC plot of AgBiS ₂ in Example 3. FIG. 3 is a scanning transmission electron microscope (STEM) photograph and a particle size analysis diagram of AgBiS ₂ in Example 3. FIG. It is a differential thermal analysis figure of AgBiS ₂ in Example 3. FIG. 5 is an X-ray diffraction (XRD) spectrum of AgBiS ₂ in Example 3. 9 is an absorption spectrum of AgBiS ₂ in Example 4. 9 is a TauC plot of AgBiS ₂ in Example 4. FIG. 3 is a scanning transmission electron microscope (STEM) photograph and a particle size analysis diagram of AgBiS ₂ in Example 4. It is a differential thermal analysis figure of AgBiS ₂ in Example 4. FIG. It is an X-ray diffraction (XRD) spectrum of AgBiS ₂ in Example 4. FIG. 9 is an absorption spectrum of AgBiS ₂ in Example 5. 9 is a TauC plot of AgBiS ₂ in Example 5. FIG. 5 is a scanning transmission electron microscope (STEM) photograph and a particle size analysis diagram of AgBiS ₂ in Example 5. It is a differential thermal analysis diagram of AgBiS ₂ in Example 5. 5 is an X-ray diffraction (XRD) spectrum of AgBiS ₂ in Example 5.

In recent years, near-infrared emission quantum dots that do not contain heavy metals subject to toxic regulation such as Cd and Pb have been attracting attention. Among them, the present inventors focused on silver bismuth scalcogenide (AgBiE ₂ (E is at least one of tellurium, selenium, or sulfur)) ternary quantum dots, and used a reactant that is easy to handle. , Silver bismuth scalcogenide quantum dots were mildly synthesized without passing through intermediates, etc., directly and in a safe manner in the atmosphere, and the physical characteristics were elucidated.

Hereinafter, an embodiment of the present invention (hereinafter, abbreviated as “embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

1A and 1B are schematic views of quantum dots in this embodiment. The quantum dots 1 shown in FIGS. 1A and 1B are nanocrystals that are directly synthesized using an easy-to-handle reactant and without passing through an intermediate or the like.

In the present embodiment, the quantum dot 1 contains silver (Ag), bismuth (Bi), and chalcogen ₍ E is tellurium (Te), selenium (Se), or sulfur (S)). It is preferable that the nanocrystal is represented by at least one of the above. This compound undergoes an indirect transition and emits very weak light.

Here, the "nanocrystal" refers to nanoparticles having a particle size of about 1 nm to several tens of nm. In this embodiment, a large number of quantum dots can be generated with a uniform particle size. "Uniform" refers to a state in which two-thirds or more of the particles are contained within ± 20% of the average particle size. As described above, in the present embodiment, it is possible to mass-produce fine and uniform high-quality quantum dots. In this embodiment, the particle size of the quantum dots can be adjusted in the range of 1 nm or more and 15 nm or less. It is preferably 2 nm or more and 10 nm or less, more preferably 3 nm or more and 7 nm or less, and further preferably 4 nm or more and 5 nm or less.

Ag, Bi, and chalcogen contained in the quantum dots are the main components, and elements other than these elements may be contained. However, when producing quantum dots, the reactants must be easy to handle, they do not pass through intermediates, etc., and after the raw materials are added in sequence, they react in a high boiling point solvent at a temperature of around 100 ° C to around 150 ° C. Therefore, it is preferable to satisfy the condition that the quantum dots can be synthesized.

By using such a synthesis method, it is possible to stably mass-produce quantum dots without incurring an increase in manufacturing cost, restrictions on the handling of reactants, and complexity of the manufacturing process.

In the present embodiment, as described later, as a reaction system for synthesizing quantum dots, Ag raw materials, Bi raw materials, and ligands, which are raw materials, are sequentially added to a high boiling point solvent, and finally chalcogenide. After adding the raw material, the reaction is carried out at around 100 ° C to around 150 ° C. By manufacturing quantum dots based on such a direct and simple synthetic reaction, the particle size of the quantum dots can be made uniform. Specifically, particles of 2/3 or more of the entire quantum dots can be produced. It can be contained within ± 20% of the average particle size.

As shown in FIG. 1A, it is preferable that a large number of organic ligands 2 are coordinated on the surface of the quantum dots 1. As a result, the aggregation of the quantum dots 1 can be suppressed and the desired optical characteristics can be exhibited. The ligand that can be used in the reaction is not particularly limited, and for example, the following ligands are typical examples.

(1) Aliphatic primary amine-based oleylamine: C ₁₈ H ₃₅ NH ₂ , stearyl (octadecyl) amine: C ₁₈ H ₃₇ NH ₂ , dodecyl (lauryl) amine: C ₁₂ H ₂₅ NH ₂ , decyl amine: C ₁₀ H ₂₁ NH ₂ , Octylamine: C ₈ H ₁₇ NH ₂

(2) Fatty acids Oleic acid: C ₁₇ H ₃₃ COOH, stearic acid: C ₁₇ H ₃₅ COOH, palmitic acid: C ₁₅ H ₃₁ COOH, myristic acid: C ₁₃ H ₂₇ COOH, lauric acid: C ₁₁ H ₂₃ COOH, decane Acid: C ₉ H ₁₉ COOH, Octanoic acid: C ₇ H ₁₅ COOH

(3) Thiol-based octadecane thiol: C ₁₈ H ₃₇ SH, hexane decane thiol: C ₁₆ H ₃₃ SH, tetradecane thiol: C ₁₄ H ₂₉ SH, dodecane thiol: C ₁₂ H ₂₅ SH, decane thiol: C ₁₀ H ₂₁ SH , Octadecane Thiol: C ₈ H ₁₇ SH
(4) Phosphine-based trioctylphosphine: (C ₈ H ₁₇ ) ₃ P, triphenylphosphine: (C ₆ H ₅ ) ₃ P, tributylphosphine: (C ₄ H ₉ ) ₃ P

(5) Phosphine oxide system Trioctylphosphine oxide: (C ₈ H ₁₇ ) ₃ P = O, triphenylphosphine oxide: (C ₆ H ₅ ) ₃ P = O, tributylphosphine oxide: (C ₄ H ₉ ) ₃ P = O

In the present embodiment, as shown in FIG. 1B, the quantum dot 1 may have a core-shell structure including a core 1a and a shell 1b coated on the surface of the core 1a. As shown in FIG. 1B, it is preferable that a large number of organic ligands 2 are coordinated on the surface of the quantum dots 1.

The core 1a shown in FIG. 1B is AgBiE ₂ . Like the core 1a, the shell 1b does not contain regulated heavy metals such as Cd, Hg, and Pb, and substances derived from highly reactive reactants typified by silicon compounds.

The shell 1b may be in a state of being solid-dissolved on the surface of the core 1a. However, in the present embodiment, it is possible to obtain an optical bandgap of 0.90 to 1.10 eV in the TauC plot with only the core 1a, that is, the quantum dot 1 of the core alone in FIG. 1A without using the shell 1b. ..

Next, a method for manufacturing quantum dots according to the present embodiment will be described. In this embodiment, from a silver raw material, a bismuth raw material, and a chalcogenide raw material (chalcogenide is at least one of tellurium, selenium, or sulfur), AgBiE ₂ (E is tellurium, selenium, or sulfur). Quantum dots represented as at least one of these) are synthesized.

Here, in the present embodiment, the Ag raw material of AgBiE ₂ is not particularly limited, but for example, the following organic silver reagent or inorganic silver reagent can be used. That is, silver acetate (I): Ag (OAc) as an acetate, silver stearate: Ag (OC (= O) C ₁₇ H ₃₅ ) as a fatty acid salt, silver oleate: Ag (OC (= O) C ₁₇ ). H ₃₃ ), silver myristate: Ag (OC (= O) C ₁₃ H ₂₇ ), silver dodecanoate: Ag (OC (= O) C ₁₁ H ₂₃ ), silver acetylacetonate: Ag (acac), halides As a monovalent compound, silver chloride (I): AgCl, silver bromide (I): AgBr, silver iodide (I): AgI and the like can be used.

Here, in the present embodiment, the Bi raw material of AgBiE ₂ is not particularly limited, but for example, the following organic bismuth reagent or inorganic bismuth reagent can be used. That is, as the fatty acid salt, bismuth oxide (III): BiO (OC (= O) CH ₃ ), bismuth acetate (III): Bi (OC (= O) CH ₃ ) ₃ , 2-ethylhexanate bismuth (III). ): Bi (OC (= O) C ₂₁ H ₄₅ ) ₃ , bismuth neodecanoate (III): Bi (OC (= O) C ₂₇ H ₅₇ ) ₃ , bismuth hypophagic acid (III): Bi (C ₇ O) ₆ H ₅ ), trivalent compounds can be used as halides, bismuth fluoride (III): BiF ₃ , bismuth chloride (III): BiCl ₃ , bismuth bromide (III): BiBr ₃ , inorganic acid salt. As bismuth nitrate, pentahydrate (III): Bi (NO ₃ ) _{3.5H 2} O, bismuth oxycarbonate (III): (BiO) ₂ CO ₃ , bismuth oxide (III): Bi ₂ O ₃ , etc. Can be used.

In the present embodiment, tellurium (Te) uses an organic tellurium compound (organotellurium compound) or an inorganic tellurium compound as a solid or dissolved in a high boiling point solvent as a raw material. Although the structure of the compound is not particularly limited, for example, trioctylphosphine terlide in which tellur is dissolved in trioctylphosphine: ( _{C8H 17} ) ₃ P = Te, tributylphosphine in which tellurium is dissolved in tributylphosphine. Telluride: (C ₄ H ₉ ) ₃ P = Te, or a solution in which tellurium is dissolved at a high temperature in a high boiling point solvent which is a long-chain hydrocarbon such as octadecene can be used.

Further, in the present embodiment, when selenium (Se) is dissolved as a solid solution, the selenium is a raw material obtained by dissolving an organic selenium compound (organoselenium compound) or an inorganic selenium compound in a solid state or in a high boiling point solvent. Used as. In particular, although the structure is not limited, for example, trioctylphosphine serenide in which selenium is dissolved in trioctylphosphine: ( _{C8H 17} ) ₃ P = Se, tributylphosphine serenide in which selenium is dissolved in tributylphosphine. : (C ₄ H ₉ ) ₃ P = Se, or a solution in which selenium is dissolved in a high boiling solvent which is a long-chain hydrocarbon such as octadecene at a high temperature can be used.

Further, in the present embodiment, when sulfur (S) is dissolved as a solid solution, the sulfur is an organic sulfur compound (organic chalcogen compound) or an inorganic sulfur compound dissolved in a solid state or a high boiling point solvent. Used as a raw material. In particular, although the structure is not limited, for example, trioctylphosphine sulfide in which sulfur is dissolved in trioctylphosphine: ( _{C8H 17} ) ₃ P = S, or tributylphosphine sulfide in which sulfur is dissolved in tributylphosphine. : (C ₄ H ₉ ) ₃ P = S, or a solution in which sulfur is dissolved at a high temperature in a high boiling point solvent which is a long-chain hydrocarbon such as octadecene can be used.

In this embodiment, an organic bismuth compound or an inorganic bismuth compound is added to a high boiling point solvent to dissolve it. As the solvent, octadecene can be used as a saturated hydrocarbon having a boiling point of 150 ° C. or higher or an unsaturated hydrocarbon. In addition to this, dodecylbenzene: C ₆ H ₅ (CH ₂ ) ₁₁ CH ₃ as an aromatic high boiling point solvent, and butyl butyrate: C ₄ H ₉ COOC ₄ H ₉ as a high boiling point ester solvent. , Benzyl butyrate: C ₆ H ₅ CH ₂ COOC ₄ H ₉ , etc. can be used, but an aliphatic thiol-based, an aliphatic amine-based, or a fatty acid-based compound or an aliphatic phosphorus-based compound is used as a solvent. It can also be used as.

At this time, the reaction temperature is set in the range of 100 ° C. or higher and 200 ° C. or lower to dissolve the silver compound. The reaction temperature is preferably 175 ° C. or lower at a lower temperature of 100 ° C. or higher, and more preferably 150 ° C. or lower at a lower temperature of 100 ° C. or higher.

Further, in the present embodiment, the reaction conditions are not particularly limited, but in order to obtain quantum dots having the same particle size, the reaction is carried out at a low temperature of about 100 ° C. to a high temperature of about 140 ° C., AgBiTe ₂ and AgBiSe. ₂ and is important in synthesizing _AgBiS2 . Therefore, one or two kinds of raw materials are dissolved in a high boiling point solvent heated to about 100 ° C., other raw materials are sequentially added to the solution, and then the reaction is continued at the same temperature to obtain quantum dots. It is preferable to synthesize dots.

Further, in the present embodiment, in order to obtain AgBiE ₂ having the same particle size, in the reaction of the precursor silver raw material, bismuth raw material, and chalcogen raw material, the thiol is 1 with respect to Te, Se or S. It is preferable to add up to 200 equivalents, more preferably 5 to 1000 equivalents, and even more preferably 50 to 10000 equivalents. In particular, the thiol is not limited, but for example, octadecane thiol: C ₁₈ H ₃₇ SH, hexane decane thiol: C ₁₆ H ₃₃ SH, tetradecane thiol: C ₁₄ H ₂₉ SH, dodecane thiol: C ₁₂ H ₂₅ SH, decane. Thiol: C ₁₀ H ₂₁ SH, octane thiol: C ₈ H ₁₇ SH and the like can be used.

Further, in the present embodiment, when each raw material is added and reacted, a compound having an auxiliary role of releasing the precursor metal into the reaction solution by coordination or chelation is required.

Examples of the compound having the above-mentioned role include a ligand capable of forming a complex with silver. For example, phosphorus-based ligands, amine-based ligands, thiol-based ligands, and carboxylic acid-based ligands are preferable, and among them, thiol-based ligands are particularly preferable because of their high efficiency.

As a result, the reaction between Ag, Bi and chalcogen is appropriately carried out, and based on Ag, Bi and chalcogen, it has an optical bandgap of 0.90 to 1.10 eV and a uniform particle size. It is possible to manufacture AgBiE ₂ quantum dots having the above.

In the method for producing quantum dots of the present embodiment, the high boiling point solvent obtained by heating one or two of the above-mentioned silver raw material, bismuth raw material, chalcogenide raw material, and ligand to 100 ° C to 150 ° C. It is preferable to have a step of dissolving in, a step of sequentially adding other raw materials, and a step of continuously synthesizing quantum dots at the same reaction temperature after adding all the raw materials.

This makes it possible to safely mass-produce silver bismuth chalcogenide having a uniform particle size directly without passing through an intermediate or the like using a reactant that is easy to handle.

Hereinafter, the effects of the present invention will be described with reference to Examples and Comparative Examples of the present invention. The present invention is not limited to the following examples.

<Raw materials>
In the present invention, the following raw materials were used for synthesizing the silver chalcogenide compound (AgBiE ₂ system) quantum dots having a uniform particle size.
(solvent)
Octadesen: Made by Aldrich Co., Ltd., manufactured by Idemitsu Kosan Co., Ltd. (raw material for chalcogen)
Sulfur powder (99.0% or more): Made by Kishida Chemical Co., Ltd. (raw material for bismuth)
Bismuth acetate: Kishida Chemical Co., Ltd. Bismuth nitrate / pentahydrate: Fujifilm Wako Pure Chemical Industries, Ltd. Bismuth oxide: Mitsuwa Chemical Co., Ltd. (silver raw material)
Silver acetate: manufactured by Kishida Chemical Co., Ltd. (ligand)
Trioctylphosphine: manufactured by Hokuko Chemical Industry Co., Ltd. Dodecane thiol: manufactured by Arkema Co., Ltd. <Measuring equipment>
Ultraviolet-Visible Light Spectrophotometer: Hitachi, Ltd. V-770
X-ray diffractometer (XRD): Bruker D2 PHASER
Scanning transmission electron microscope (STEM): SU9000 manufactured by Hitachi, Ltd.
Differential thermal balance (TG-DTA): Thermo Plus EVO2 manufactured by Rigaku Co., Ltd.

[Example 1]
In a 300 mL reaction vessel, silver acetate: Ag (OAc) 200.2 mg, dodecanethiol: DDT 30.0 mL, and bismuth nitrate pentahydrate: Bi (NO ₃ ) _{3.5H 2} O 582.2 mg were placed. .. Then, the raw material was dissolved by heating with stirring at 145 ° C. for 5 minutes in an atmosphere of an inert gas (N ₂ ).

To this solution was added 13.0 mL of 0.20 M octadecene sulfide (S-ODE) and heated for an additional 10 minutes at the same temperature with stirring.

The obtained reaction solution was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and centrifugation was performed to recover the precipitate. Then, hexane was added to the precipitate and dispersed to obtain a dispersion solution of AgBiS ₂ particles.

The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible-near-infrared absorption spectrum of FIG. 2 was obtained. Further, it was found that the quantum dots obtained by this synthesis had an optical bandgap of 0.90 eV as shown in the analysis result by the TauC plot in FIG. Further, the average particle size of the quantum dots is about 4.43 nm as shown in FIG. 4, and the particles having 2/3 or more of the total number of particles are within ± 20% of the average particle size. have understood. Further, analysis by a differential thermal balance (TG) revealed that about 15% of the ligands were coordinated to the entire quantum dots as shown in FIG.
Further, from the peak value and peak pattern of the XRD spectrum of the AgBiS ₂ particles shown in FIG. 6, it was proved that the AgBiS ₂ solid solution was produced.

[Example 2]
In a 300 mL reaction vessel, silver acetate: Ag (OAc) 200.2 mg, dodecanethiol: DDT 30.0 mL, and bismuth nitrate pentahydrate: Bi (NO ₃ ) _{3.5H 2} O 582.2 mg were placed. .. Then, the raw material was dissolved by heating with stirring at 145 ° C. for 5 minutes in an atmosphere of an inert gas (N ₂ ).

To this solution was added 13.0 mL of 0.20 M octadecene sulfide (S-ODE) and heated for an additional 20 minutes at the same temperature with stirring.

The obtained reaction solution was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and centrifugation was performed to recover the precipitate. Then, hexane was added to the precipitate and dispersed to obtain a dispersion solution of AgBiS ₂ particles.

The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible-near-infrared absorption spectrum of FIG. 7 was obtained. Further, it was found that the quantum dots obtained by this synthesis had an optical bandgap of 1.075 eV as shown in the analysis result by the TauC plot in FIG. Further, the average particle size of the quantum dots is about 4.53 nm as shown in FIG. 9, and the particles having 2/3 or more of the total number of particles are within ± 20% of the average particle size. have understood. Further, analysis by a differential thermal balance revealed that, as shown in FIG. 10, about 18% of the ligands are coordinated to the mass of the entire quantum dot.

Further, from the peak value and peak pattern of the XRD spectrum of the AgBiS ₂ particles shown in FIG. 11, it was proved that the AgBiS ₂ solid solution was produced.

[Example 3]
Silver acetate: Ag (OAc) 200.2 mg, dodecanethiol: DDT 30.0 mL, and bismuth oxide acetate: BiO (OC (= O) CH ₃ ) 340.8 mg were placed in a 300 mL reaction vessel. Then, the raw material was dissolved by heating with stirring at 140 ° C. for 5 minutes in an atmosphere of an inert gas (N ₂ ).

To this solution was added 19.5 mL of 0.20 M octadecene sulfide (S-ODE) and heated for an additional 15 minutes at the same temperature with stirring.

The obtained reaction solution was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and centrifugation was performed to recover the precipitate. Then, hexane was added to the precipitate and dispersed to obtain a dispersion solution of AgBiS ₂ particles.

The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible-near-infrared absorption spectrum of FIG. 12 was obtained. Further, it was found that the quantum dots obtained by this synthesis had an optical bandgap of 1.065 eV as shown in the analysis result by the TauC plot in FIG. Further, as shown in FIG. 14, the average particle size of the quantum dots is about 4.23 nm, and the particles having 2/3 or more of the total number of particles are within ± 20% of the average particle size. have understood. Further, analysis by a differential thermal balance revealed that, as shown in FIG. 15, about 18% of the ligands are coordinated to the mass of the entire quantum dot.

Further, from the peak value and peak pattern of the XRD spectrum of the AgBiS ₂ particles shown in FIG. 16, it was proved that the AgBiS ₂ solid solution was produced.

[Example 4]
Silver acetate: Ag (OAc) 200.2 mg, dodecanethiol: DDT 30.0 mL, and bismuth oxide acetate: BiO (OC (= O) CH ₃ ) 340.8 mg were placed in a 300 mL reaction vessel. Then, the raw material was dissolved by heating with stirring at 100 ° C. for 5 minutes in an atmosphere of an inert gas (N ₂ ).

To this solution was added 13.0 mL of 0.20 M octadecene sulfide (S-ODE) and heated for an additional 15 minutes at the same temperature with stirring.

The obtained reaction solution was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and centrifugation was performed to recover the precipitate. Then, hexane was added to the precipitate and dispersed to obtain a dispersion solution of AgBiS ₂ particles.

The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible-near-infrared absorption spectrum of FIG. 17 was obtained. It was also found that the quantum dots obtained by this synthesis had an optical bandgap of 1.10 eV, as shown in the analysis results by the TauC plot in FIG. Further, as shown in FIG. 19, the average particle size of the quantum dots is about 4.82 nm, and the particles having 2/3 or more of the total number of particles are within ± 20% of the average particle size. have understood. Further, analysis by a differential thermal balance revealed that, as shown in FIG. 20, about 19% of the ligands are coordinated to the mass of the entire quantum dot.

Further, from the peak value and peak pattern of the XRD spectrum of the AgBiS ₂ particles shown in FIG. 21, it was proved that the AgBiS ₂ solid solution was produced.

[Example 5]
In a 300 mL reaction vessel, silver acetate: Ag (OAc) 200.2 mg, dodecanethiol: DDT 30.0 mL, and bismuth nitrate pentahydrate: Bi (NO ₃ ) _{3.5H 2} O 582.2 mg were placed. .. Then, the raw material was dissolved by heating with stirring at 100 ° C. for 5 minutes in an atmosphere of an inert gas (N ₂ ).

To this solution was added 13.0 mL of 0.20 M octadecene sulfide (S-ODE) and heated for an additional 15 minutes at the same temperature with stirring.

The obtained reaction solution was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and centrifugation was performed to recover the precipitate. Then, hexane was added to the precipitate and dispersed to obtain a dispersion solution of AgBiS ₂ particles.

The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible-near-infrared absorption spectrum of FIG. 22 was obtained. Further, it was found that the quantum dots obtained by this synthesis had an optical bandgap of 1.10 eV as shown in the analysis result by the TauC plot in FIG. Further, as shown in FIG. 24, the average particle size of the quantum dots is about 4.52 nm, and the particles having 2/3 or more of the total number of particles are within ± 20% of the average particle size. have understood. Further, analysis by a differential thermal balance revealed that, as shown in FIG. 25, about 22% of the ligands are coordinated to the mass of the entire quantum dot.

Further, from the peak value and peak pattern of the XRD spectrum of the AgBiS ₂ particles shown in FIG. 26, it was proved that the AgBiS ₂ solid solution was produced.

[Comparative Example 1]
Silver acetate: Ag (OAc) 200.2 mg, octadecene: ODE 30.0 mL, and bismuth nitrate pentahydrate: Bi (NO ₃ ) _{3.5H 2} O 582.2 mg were placed in a 300 mL reaction vessel. Then, it was heated with stirring at 150 ° C. for 5 minutes in an atmosphere of an inert gas (N ₂ ).

To this solution was added 13.0 mL of 0.20 M octadecene sulfide (S-ODE) and heated for an additional 15 minutes at the same temperature with stirring.

The obtained reaction solution (AgBiS ₂ ) was cooled to room temperature. The reaction solution did not change in color, and it was confirmed by XRD that the raw material remained as it was from the obtained solution.

[Comparative Example 2]
In a 300 mL reaction vessel, silver acetate: Ag (OAc) 200.2 mg, dodecanethiol: DDT 30.0 mL, and bismuth nitrate pentahydrate: Bi (NO ₃ ) _{3.5H 2} O 582.2 mg were placed. .. Then, the raw material was dissolved by heating with stirring at 250 ° C. for 5 minutes in an atmosphere of an inert gas (N ₂ ).

To this solution was added 13.0 mL of 0.20 M octadecene sulfide (S-ODE) and heated for an additional 15 minutes at the same temperature with stirring.

The obtained reaction solution (AgBiS ₂ ) was cooled to room temperature. The reaction solution changed to a black suspension, and no XRD reflection peak was confirmed from the obtained solution.

In Comparative Example 1, the ligand dodecanethiol is not present in the system, and in Comparative Example 2, the reaction temperature is as high as 250 ° C., so that the _AgBiE2 system quantum dots cannot be properly synthesized. have understood.

From the above, it was found that the _AgBiE2 system quantum dots can be synthesized according to Examples 1 to 5.

According to the present invention, AgBiS ₂ quantum dots having a uniform particle size and an optical bandgap of 0.90 to 1.10 eV are used with an easy-to-handle reactant and do not pass through an intermediate or the like. It can be synthesized by a method that can be directly mass-produced. Then, by applying the quantum dots of the present invention to a light absorption device or the like, excellent solar cell performance or the like can be obtained in the apparatus.

1: Quantum dot 1a: Core 1b: Shell 2: Organic ligand

Claims (10)

A nanocrystal represented by AgBiE ₂ (E is at least one of tellurium, selenium, or sulfur) containing silver, bismuth, and chalcogen, and the average particle size of the quantum dots is 1 nm or more. Quantum dots characterized by being 15 nm or less. The quantum dot according to claim 1, wherein the surface of the quantum dot is covered with a ligand. The second aspect of claim 2, wherein the ligand is selected from at least one or two of phosphine-based, aliphatic thiol-based, aliphatic amine-based, and aliphatic carboxylic acid-based. Quantum dots. The quantum dot according to any one of claims 1 to 3, wherein an optical bandgap of 0.90 to 1.10 eV is obtained in the TauC plot. It is required that a large number of quantum dots according to any one of claims 1 to 4 are contained, and that the particle size distribution in STEM includes 2/3 or more of the quantum dots within ± 20% of the average particle size. A characteristic quantum dot aggregate. From silver raw material, bismuth raw material, chalcogenide raw material (chalcogenide is at least one of tellurium, selenium, or sulfur), AgBiE ₂ (E is at least one of tellurium, selenium, or sulfur). ) Is a method for manufacturing quantum dots, which comprises synthesizing quantum dots. The method for producing quantum dots according to claim 6, wherein the quantum dots are synthesized in a solvent containing thiol. The method for producing quantum dots according to claim 6 or 7, wherein the reaction temperature is in the range of about 100 ° C to about 150 ° C. The silver raw material, the bismuth raw material, and the ligand are sequentially added to a high boiling point solvent having a boiling point of 150 ° C. or higher, reacted at a predetermined reaction temperature, the chalcogenide raw material is added, and then the reaction is continued at the same temperature. The method for manufacturing a quantum dot according to any one of claims 6 to 8, wherein the method is characterized by that. A step of dissolving the silver raw material, the bismuth raw material, and one or two raw materials of the ligand in the high boiling point solvent heated to 100 ° C to 150 ° C.
The step of sequentially adding other raw materials including the chalcogenide raw material, and
After adding all the raw materials, the reaction is continued at the same temperature to synthesize the quantum dots.
9. The method for manufacturing a quantum dot according to claim 9.

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