Quantum dot aggregate

Abstract

To provide silver bismuth chalcogenide quantum dots capable of uniformizing the particle diameter and provide a method for producing silver bismuth chalcogenide quantum dots using a simple, highly safe and easily handleable raw material.SOLUTION: The quantum dots in the present invention are nanocrystals represented by AgBiE2 (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 and 15 nm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a quantum dot assembly including quantum dots that undergo indirect transitions.

Background Art

[0002] Quantum dots are nanoparticles composed of about several hundred to several thousand atoms and having a particle size of about several nm to several tens of nm. Quantum dots are also called fluorescent nanoparticles, semiconductor nanoparticles, or nanocrystals.

[0003] The emission wavelength of quantum dots can be variously changed depending on the particle size and composition of the nanoparticles. Further, examples of properties representing the performance of quantum dots include fluorescence quantum yield (Quantum Yield: QY), full width at half maximum of fluorescence (Full Width at Half Maximum: FWHM), absorption wavelength, and fluorescence wavelength.

[0004] The following patent documents and non-patent documents describe solar cells using AgBiS2 quantum dots.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

[0007] However, research and development for practical use of silver bismuth chalcogenide quantum dots has not been reported. For example, in the synthesis of silver bismuth chalcogenide quantum dots described in Non-Patent Documents 1 to 3 and Patent Document 1 above, S(TMS)2 (hexamethyldisilathiane) is used as a sulfur source, but when used under the atmosphere, it easily reacts with moisture in the air and releases toxic H2S.

[0008] From the above background, there is a strong demand for the synthesis of silver bismuth chalcogenide quantum dots by a mass-producible method using simple and easy-to-handle raw materials, and for elucidating the physical properties of silver bismuth chalcogenide quantum dots synthesized by such a method.

[0009] The present invention has been made in view of this point, and an object thereof is to provide a quantum dot aggregate containing silver bismuth chalcogenide quantum dots capable of achieving uniform particle size.

[0010] Another object of the present invention is to provide a method for producing silver bismuth chalcogenide quantum dots using simple, highly safe, and easy-to-handle raw materials. [Means for solving the problem]

[0011] In the present invention amount The dot aggregate is a nanocrystal represented by AgBiE2 (where 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 3nm or more and 5nm or less The invention is characterized by containing a large number of quantum dots, and in the particle size distribution observed in STEM, more than two-thirds of the quantum dots are contained within ±20% of the average particle size.

[0012] In the present invention, it is preferable that the surface of the quantum dot is covered with a ligand.

[0013] In the present invention, it is preferable that the ligand is selected from at least one or two of the phosphine-based, aliphatic thiol-based, aliphatic amine-based, and aliphatic carboxylic acid-based types.

[0014] In this invention, it is preferable to obtain an optical band gap of 0.90 to 1.075 eV in the TauC plot. [Effects of the Invention]

[0015] The quantum dots of the present invention allow for a narrower particle size distribution in STEM, enabling the synthesis of silver-bismuth chalcogenide quantum dots with uniform particle sizes.

[0016] Furthermore, according to the quantum dot manufacturing method of the present invention, silver bismuth chalcogenide quantum dots can be mass-produced simply, safely, and directly using an easily handled reagent and without going through intermediates. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram of a quantum dot in an embodiment of the present invention. [Figure 2] This is the absorption spectrum of AgBiS2 in Example 1. [Figure 3] This is the TauC plot of AgBiS2 in Example 1. [Figure 4] These are scanning transmission electron microscope (STEM) images and particle size analysis diagrams of AgBiS2 in Example 1. [Figure 5] This is a differential thermal analysis diagram of AgBiS2 in Example 1. [Figure 6] This is the X-ray diffraction (XRD) spectrum of AgBiS2 in Example 1. [Figure 7] This is the absorption spectrum of AgBiS2 in Example 2. [Figure 8] This is the TauC plot of AgBiS2 in Example 2. [Figure 9] These are scanning transmission electron microscope (STEM) images and particle size analysis diagrams of AgBiS2 in Example 2. [Figure 10] This is a differential thermal analysis diagram of AgBiS2 in Example 2. [Figure 11] This is the X-ray diffraction (XRD) spectrum of AgBiS2 in Example 2. [Figure 12] This is the absorption spectrum of AgBiS2 in Example 3. [Figure 13] This is the TauC plot of AgBiS2 in Example 3. [Figure 14] These are scanning transmission electron microscope (STEM) images and particle size analysis diagrams of AgBiS2 in Example 3. [Figure 15] This is a differential thermal analysis diagram of AgBiS2 in Example 3. [Figure 16] This is the X-ray diffraction (XRD) spectrum of AgBiS2 in Example 3. [Figure 17] This is the absorption spectrum of AgBiS2 in Example 4. [Figure 18] This is the TauC plot of AgBiS2 in Example 4. [Figure 19] These are scanning transmission electron microscope (STEM) images and particle size analysis diagrams of AgBiS2 in Example 4. [Figure 20] This is a differential thermal analysis diagram of AgBiS2 in Example 4. [Figure 21] This is the X-ray diffraction (XRD) spectrum of AgBiS2 in Example 4. [Figure 22] This is the absorption spectrum of AgBiS2 in Example 5. [Figure 23] This is the TauC plot of AgBiS2 in Example 5. [Figure 24] These are scanning transmission electron microscope (STEM) images and particle size analysis diagrams of AgBiS2 in Example 5. [Figure 25] This is a differential thermal analysis diagram of AgBiS2 in Example 5. [Figure 26] This is the X-ray diffraction (XRD) spectrum of AgBiS2 in Example 5. [Modes for carrying out the invention]

[0018] In recent years, near-infrared emitting quantum dots that do not contain toxic heavy metals such as Cd and Pb have attracted attention. The inventors of this invention focused on silver bismuth chalcogenide (AgBiE2 (where E is at least one of tellurium, selenium, or sulfur)) ternary quantum dots, and have successfully synthesized silver bismuth chalcogenide quantum dots mildly and directly in an atmospheric environment using an easily handled reagent, without the need for intermediates, and have elucidated their physical properties.

[0019] Hereinafter, one embodiment of the present invention (hereinafter abbreviated as "Embodiment") will be described in detail. It should be noted that the present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of its gist.

[0020] Figures 1A and 1B are schematic diagrams of quantum dots in this embodiment. The quantum dot 1 shown in Figures 1A and 1B is a nanocrystal synthesized directly using an easily handled reagent and without the need for intermediates.

[0021] In this embodiment, quantum dot 1 is preferably a nanocrystal represented by AgBiE2 (where E is at least one of tellurium (Te), selenium (Se), or sulfur (S)) containing silver (Ag), bismuth (Bi), and chalcogen. This compound undergoes indirect transitions and emits very little light.

[0022] Here, "nanocrystal" refers to nanoparticles having a particle size of approximately 1 nm to several tens of nm. In this embodiment, a large number of quantum dots can be produced with a uniform particle size. "Uniform" means that more than two-thirds of the particles are contained within ±20% of the average particle size. Thus, in this embodiment, fine and uniform high-quality quantum dots can be mass-produced. In this embodiment, the particle size of the quantum dots can be adjusted within the range of 1 nm to 15 nm. Preferably, it is 2 nm to 10 nm, more preferably 3 nm to 7 nm, and even more preferably 4 nm to 5 nm.

[0023] Ag, Bi, and chalcogens contained in the quantum dots are the main components, and other elements may be included. However, when manufacturing the quantum dots, it is preferable to satisfy the conditions that the reactants are easy to handle, do not pass through intermediates, etc., and that the quantum dots can be synthesized by reacting at a temperature of around 100°C to around 150°C in a high-boiling-point solvent after sequentially adding the raw materials.

[0024] By using such a synthesis method, quantum dots can be stably mass-produced without causing an increase in manufacturing cost, restrictions on the handling of reactants, and complexity of the manufacturing process.

[0025] In this embodiment, as will be described later, as a reaction system for synthesizing quantum dots, an Ag raw material, a Bi raw material, and a ligand as raw materials are sequentially added to a high-boiling-point solvent, and finally, after adding a chalcogenide 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 synthesis reaction, the particle size of the quantum dots can be made uniform. Specifically, more than 2 / 3 of the particles of the entire quantum dots can be included within ±20% of the average particle size.

[0026] 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. Thereby, aggregation of the quantum dots 1 can be suppressed, and the desired optical properties can be exhibited. The ligands that can be used in the reaction are not particularly limited, and for example, the following ligands can be cited as representative ones.

[0027] (1) Aliphatic primary amine-based Oleylamine: C 17 , 10 , 21 , 25 H 35 NH2, Stearyl (octadecyl) amine: C 18 H 37 NH2, Dodecyl (lauryl) amine: C 12 ​​​​​​​​​

[0028] (2)Fatty acid 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, Lauryl Acid: C 11 H 23 COOH, Decanoic acid: C9H 19 COOH, Octanoic acid: C7H 15 COOH

[0029] (3) Thiol type Octadecanthiol: C 18 H 37 SH, Hexanedecanethiol:C 16 H 33 SH, Tetradecanethiol:C 14 H 29 SH, Dodecanethiol:C 12 H 25 SH, Decanethiol:C 10 H 21 SH, Octanethiol: C8H 17 SH (4) Phosphine systems Trioctylphosphine:(C8H 17 )3P, Triphenylphosphine:(C6H5)3P, Tributylphosphine:(C4H9)3P

[0030] (5) Phosphine oxide systems Trioctylphosphine oxide: (C8H 17 )3P=O, Triphenylphosphine oxide: (C6H5)3P=O, Tributylphosphine oxide: (C4H9)3P=O

[0031] In this embodiment, as shown in Figure 1B, the quantum dot 1 may have a core-shell structure comprising a core 1a and a shell 1b covering the surface of the core 1a. As shown in Figure 1B, it is preferable that a large number of organic ligands 2 are coordinated to the surface of the quantum dot 1.

[0032] The core 1a shown in Figure 1B is AgBiE2. Like core 1a, shell 1b does not contain regulated heavy metals such as Cd, Hg, and Pb, nor substances derived from highly reactive reagents such as silicon compounds.

[0033] The shell 1b may be in a solid solution state on the surface of the core 1a. However, in this embodiment, an optical band gap of 0.90 to 1.10 eV can be obtained in the TauC plot using only the core 1a, i.e., the quantum dot 1 of the core alone as shown in Figure 1A, without using the shell 1b.

[0034] Next, the method for manufacturing quantum dots according to this embodiment will be described. In this embodiment, quantum dots represented as AgBiE2 (where E is at least one of tellurium, selenium, or sulfur) are synthesized from a silver raw material, a bismuth raw material, and a chalcogenide raw material (a chalcogenide is at least one of tellurium, selenium, or sulfur).

[0035] In this embodiment, the Ag raw material for AgBiE2 is not particularly limited, but for example, the following organosilver reagents and inorganic silver reagents can be used. That is, silver(I) acetate as the acetate salt: Ag(OAc), and silver stearate as the fatty acid salt: Ag(OC(=O)C 17 H 35 ), 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), and monovalent compounds can be used as halides, such as silver(I) chloride: AgCl, silver(I) bromide: AgBr, and silver(I) iodide: AgI.

[0036] In this embodiment, the Bi raw material for AgBiE2 is not particularly limited, but for example, the following organic bismuth reagents or inorganic bismuth reagents can be used. That is, as fatty acid salts, bismuth(III) oxidized acetate:BiO(OC(=O)CH3), bismuth(III) acetate:Bi(OC(=O)CH3)3, bismuth(III) 2-ethylhexanoate:Bi(OC(=O)C 21 H 45 )3, Bismuth(III) neodecanoate:Bi(OC(=O)C 27 H 57 )3. Bismuth(III) subgallate: Bi(C7O6H5) can be used as a halide, and trivalent compounds such as bismuth(III) fluoride: BiF3, bismuth(III) chloride: BiCl3, bismuth(III) bromide: BiBr3 can be used as inorganic salts, such as bismuth(III) nitrate pentahydrate: Bi(NO3)3·5H2O, bismuth(III) oxycarbonate: (BiO)2CO3, bismuth(III) oxide: Bi2O3, etc.

[0037] In this embodiment, tellurium (Te) is used as a raw material in the form of an organic tellurium compound (organo-chalcogen compound) or an inorganic tellurium compound, either in solid form or dissolved in a high-boiling point solvent. The structure of the compound is not particularly limited, but for example, trioctylphosphine telluride (C8H) obtained by dissolving tellurium in trioctylphosphine is used. 17 )3P=Te, tributylphosphine telluride ((C4H9)3P=Te) obtained by dissolving tellurium in tributylphosphine, or a solution obtained by dissolving tellurium at high temperature in a high-boiling point solvent that is a long-chain hydrocarbon such as octadecene can be used.

[0038] Furthermore, in this embodiment, when solid-solution selenium (Se) is used, the selenium used as a raw material is either an organic selenium compound (organo-chalcogen compound) or an inorganic selenium compound, either in its solid state or dissolved in a high-boiling point solvent. While the structure is not particularly limited, for example, trioctylphosphine selenide (C8H) obtained by dissolving selenium in trioctylphosphine is used. 17 )3P=Se, tributylphosphine selenide ((C4H9)3P=Se) obtained by dissolving selenium in tributylphosphine, or a solution obtained by dissolving selenium at high temperature in a high-boiling point solvent that is a long-chain hydrocarbon such as octadecene can be used.

[0039] Furthermore, in this embodiment, when sulfur (S) is dissolved in a solid solution, the sulfur used as a raw material is either an organic sulfur compound (organic chalcogen compound) or an inorganic sulfur compound, either in its solid state or dissolved in a high-boiling point solvent. While the structure is not particularly limited, for example, trioctylphosphine sulfide (C8H) obtained by dissolving sulfur in trioctylphosphine is used. 17 )3P=S, or tributylphosphine sulfide ((C4H9)3P=S) obtained by dissolving sulfur in tributylphosphine, or a solution obtained by dissolving sulfur at high temperature in a high-boiling point solvent that is a long-chain hydrocarbon such as octadecene, can be used.

[0040] In this embodiment, an organic bismuth compound or an inorganic bismuth compound is added to a high-boiling point solvent and dissolved. As the solvent, octadecene can be used as a saturated or unsaturated hydrocarbon with a high boiling point of 150°C or higher. In addition, dodecylbenzene:C6H5(CH2) can be used as an aromatic high-boiling point solvent. 11 As high-boiling point ester solvents, such as butyl butyrate (C4H9COOC4H9) and benzyl butyrate (C6H5CH2COOC4H9), can be used. However, aliphatic thiols, aliphatic amines, fatty acids, and aliphatic phosphorus compounds can also be used as solvents.

[0041] At this time, the reaction temperature is set to a range of 100°C to 200°C, and the silver compound is dissolved. Preferably, the reaction temperature is lower, between 100°C and 175°C, and even more preferably, between 100°C and 150°C.

[0042] Furthermore, in this embodiment, there are no particular limitations on the reaction conditions, but in order to obtain quantum dots with uniform particle sizes, it is important to react at a low temperature of about 100°C to a high temperature of about 140°C in order to synthesize AgBiTe2, AgBiSe2, and AgBiS2. For this reason, it is preferable to dissolve one or two types of raw materials in a high-boiling point solvent heated to about 100°C, sequentially add the other raw materials to the solution, and then continue the reaction at the same temperature to synthesize quantum dots.

[0043] Furthermore, in this embodiment, in order to obtain AgBiE2 with uniform particle size, it is preferable to add 1 to 200 equivalents of thiol relative to Te, Se, or S in the reaction of the precursor silver raw material, bismuth raw material, and chalcogen raw material, more preferably 5 to 1000 equivalents, and even more preferably 50 to 10000 equivalents. In particular, the thiol is not limited, but for example, octadecanethiol:C 18 H 37 SH, Hexanedecanethiol:C 16 H 33 SH, Tetradecanethiol:C 14 H 29 SH, Dodecanethiol:C 12 H 25 SH, Decanethiol:C 10 H 21 SH, Octanethiol:C8H 17 SH, etc., can be used.

[0044] Furthermore, in this embodiment, when each raw material is added and reacted, a compound is needed that plays an auxiliary role in releasing the precursor metal into the reaction solution through coordination or chelation.

[0045] Compounds having the above-mentioned role include ligands that can form complexes with silver. For example, phosphorus ligands, amine ligands, thiol ligands, and carboxylic acid ligands are preferred, and among these, thiol ligands are particularly preferred due to their high efficiency.

[0046] This allows for proper reaction between Ag, Bi, and chalcogen, enabling the production of AgBiE2 quantum dots based on Ag, Bi, and chalcogen, with an optical band gap of 0.90 to 1.10 eV and a uniform particle size.

[0047] In the quantum dot manufacturing method of this embodiment, it is preferable to have the following steps: dissolving one or two of the above-mentioned silver raw material, bismuth raw material, chalcogenide raw material, and ligand in the high-boiling point solvent heated to 100°C to 150°C; then sequentially adding the other raw materials; and after adding all the raw materials, synthesizing quantum dots at a reaction temperature of approximately the same temperature.

[0048] This allows for the safe and rapid mass production of silver bismuth chalcogenide with a uniform particle size, using easily handled reagents and without the need for intermediates. [Examples]

[0049] The effects of the present invention will be explained below with reference to examples and comparative examples of the present invention. However, the present invention is not limited in any way by the following examples.

[0050] <Raw materials> In this invention, the following raw materials were used to synthesize silver chalcogenide compound (AgBiE2-based) quantum dots having a uniform particle size. (solvent) Octadecene: Manufactured by Aldrich Corporation and Idemitsu Kosan Co., Ltd. (Calcogen raw material) Sulfur powder (99.0% or higher): Manufactured by Kishida Chemical Co., Ltd. (Bismuth raw material) Bismuth acetate oxide: Manufactured by Kishida Chemical Co., Ltd. Bismuth nitrate pentahydrate: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Bismuth Oxide: Manufactured by Mitsuwa Chemical Co., Ltd. (Silver raw material) Silver acetate: Manufactured by Kishida Chemical Co., Ltd. (ligand) Trioctylphosphine: Manufactured by Hokko Chemical Co., Ltd. Dodecanethiol: Manufactured by Arkema <Measuring equipment> Ultraviolet-Visible Spectrophotometer: Hitachi V-770 X-ray diffraction device (XRD): Bruker D2 PHASER Scanning transmission electron microscope (STEM): Hitachi SU9000 Differential thermal balance (TG-DTA): Rigaku Corporation Thermo Plus EVO2

[0051] [Example 1] 200.2 mg of silver acetate (Ag(OAc)), 30.0 mL of dodecanethiol (DDT), and 582.2 mg of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) were placed in a 300 mL reaction vessel. The mixture was then heated at 145°C for 5 minutes with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0052] To this solution, 13.0 mL of 0.20 M octadecensulfide (S-ODE) was added, and the mixture was heated with stirring at the same temperature for a further 10 minutes.

[0053] The resulting reaction mixture was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and the precipitate was collected by centrifugation. Then, hexane was added to the precipitate to disperse it and obtain a dispersion solution of AgBiS2 particles.

[0054] The obtained dispersion solution was measured using a UV-Vis spectrometer. As a result, the UV-Vis near-infrared absorption spectrum shown in Figure 2 was obtained. Furthermore, it was found that the quantum dots obtained in this synthesis have an optical band gap of 0.90 eV, as shown in the TauC plot analysis results in Figure 3. In addition, the average particle size of these quantum dots was approximately 4.43 nm, as shown in Figure 4, and it was found that more than two-thirds of the total number of particles fell within ±20% of the average particle size. Furthermore, differential thermal analysis (TG) revealed that approximately 15% of the entire quantum dot was coordinated by ligands, as shown in Figure 5. Furthermore, the peak values ​​and peak patterns of the XRD spectrum of AgBiS2 particles shown in Figure 6 demonstrate that an AgBiS2 solid solution is being formed.

[0055] [Example 2] 200.2 mg of silver acetate (Ag(OAc)), 30.0 mL of dodecanethiol (DDT), and 582.2 mg of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) were placed in a 300 mL reaction vessel. The mixture was then heated at 145°C for 5 minutes with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0056] To this solution, 13.0 mL of 0.20 M octadecensulfide (S-ODE) was added, and the mixture was heated with stirring at the same temperature for a further 20 minutes.

[0057] The resulting reaction mixture was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and the precipitate was collected by centrifugation. Then, hexane was added to the precipitate to disperse it and obtain a dispersion solution of AgBiS2 particles.

[0058] The resulting dispersion solution was measured using an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible near-infrared absorption spectrum shown in Figure 7 was obtained. Furthermore, it was found that the quantum dots obtained in this synthesis have an optical band gap of 1.075 eV, as shown in the TauC plot analysis results in Figure 8. In addition, the average particle size of these quantum dots was approximately 4.53 nm, as shown in Figure 9, and it was found that more than two-thirds of the total number of particles fell within ±20% of the average particle size. Furthermore, analysis using a differential thermal balance revealed that approximately 18% of the total mass of the quantum dots was coordinated by ligands, as shown in Figure 10.

[0059] Furthermore, the peak values ​​and peak patterns of the XRD spectrum of AgBiS2 particles shown in Figure 11 demonstrate that an AgBiS2 solid solution is being formed.

[0060] [Example 3] 200.2 mg of silver acetate (Ag(OAc)), 30.0 mL of dodecanethiol (DDT), and 340.8 mg of bismuth acetate (BiO(OC(=O)CH3)) were placed in a 300 mL reaction vessel. The mixture was then heated at 140 °C for 5 minutes with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0061] To this solution, 19.5 mL of 0.20 M octadecensulfide (S-ODE) was added, and the mixture was heated with stirring at the same temperature for a further 15 minutes.

[0062] The resulting reaction mixture was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and the precipitate was collected by centrifugation. Then, hexane was added to the precipitate to disperse it and obtain a dispersion solution of AgBiS2 particles.

[0063] The obtained dispersion solution was measured using an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible near-infrared absorption spectrum shown in Figure 12 was obtained. Furthermore, it was found that the quantum dots obtained in this synthesis have an optical band gap of 1.065 eV, as shown in the TauC plot analysis results in Figure 13. In addition, the average particle size of these quantum dots was approximately 4.23 nm, as shown in Figure 14, and it was found that more than two-thirds of the total number of particles fell within ±20% of the average particle size. Furthermore, analysis using a differential thermal balance revealed that approximately 18% of the total mass of the quantum dots was coordinated by ligands, as shown in Figure 15.

[0064] Furthermore, the peak values ​​and peak patterns of the XRD spectrum of AgBiS2 particles shown in Figure 16 demonstrate that an AgBiS2 solid solution is being formed.

[0065] [Example 4] 200.2 mg of silver acetate (Ag(OAc)), 30.0 mL of dodecanethiol (DDT), and 340.8 mg of bismuth acetate (BiO(OC(=O)CH3)) were placed in a 300 mL reaction vessel. The mixture was then heated at 100 °C for 5 minutes with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0066] To this solution, 13.0 mL of 0.20 M octadecensulfide (S-ODE) was added, and the mixture was heated with stirring at the same temperature for a further 15 minutes.

[0067] The resulting reaction mixture was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and the precipitate was collected by centrifugation. Then, hexane was added to the precipitate to disperse it and obtain a dispersion solution of AgBiS2 particles.

[0068] The resulting dispersion solution was measured using an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible near-infrared absorption spectrum shown in Figure 17 was obtained. Furthermore, it was found that the quantum dots obtained in this synthesis have an optical band gap of 1.10 eV, as shown in the TauC plot analysis results in Figure 18. In addition, the average particle size of these quantum dots was approximately 4.82 nm, as shown in Figure 19, and it was found that more than two-thirds of the total number of particles fell within ±20% of the average particle size. Furthermore, analysis using a differential thermal balance revealed that approximately 19% of the total mass of the quantum dots was coordinated by ligands, as shown in Figure 20.

[0069] Furthermore, the peak values ​​and peak patterns of the XRD spectrum of AgBiS2 particles shown in Figure 21 demonstrated the formation of an AgBiS2 solid solution.

[0070] [Example 5] 200.2 mg of silver acetate (Ag(OAc)), 30.0 mL of dodecanethiol (DDT), and 582.2 mg of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) were placed in a 300 mL reaction vessel. The mixture was then heated at 100 °C for 5 minutes with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0071] To this solution, 13.0 mL of 0.20 M octadecensulfide (S-ODE) was added, and the mixture was heated with stirring at the same temperature for a further 15 minutes.

[0072] The resulting reaction mixture was cooled to room temperature, toluene and ethanol were added to generate a precipitate, and the precipitate was collected by centrifugation. Then, hexane was added to the precipitate to disperse it and obtain a dispersion solution of AgBiS2 particles.

[0073] The obtained dispersion solution was measured using an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible near-infrared absorption spectrum shown in Figure 22 was obtained. Furthermore, it was found that the quantum dots obtained in this synthesis have an optical band gap of 1.10 eV, as shown in the TauC plot analysis results in Figure 23. In addition, the average particle size of these quantum dots was approximately 4.52 nm, as shown in Figure 24, and it was found that more than two-thirds of the total number of particles fell within ±20% of the average particle size. Furthermore, analysis using a differential thermal balance revealed that approximately 22% of the total mass of the quantum dots was coordinated by ligands, as shown in Figure 25.

[0074] Furthermore, the peak values ​​and peak patterns of the XRD spectrum of AgBiS2 particles shown in Figure 26 demonstrate that an AgBiS2 solid solution is being formed.

[0075] [Comparative Example 1] 200.2 mg of silver acetate (Ag(OAc)), 30.0 mL of octadecene (ODE), and 582.2 mg of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) were placed in a 300 mL reaction vessel. The mixture was then heated at 150 °C for 5 minutes with stirring under an inert gas (N2) atmosphere.

[0076] To this solution, 13.0 mL of 0.20 M octadecensulfide (S-ODE) was added, and the mixture was heated with stirring at the same temperature for a further 15 minutes.

[0077] The resulting reaction solution (AgBiS2) was cooled to room temperature. The reaction solution showed no change in color, and XRD confirmed that the starting materials remained intact in the resulting solution.

[0078] [Comparative Example 2] 200.2 mg of silver acetate (Ag(OAc)), 30.0 mL of dodecanethiol (DDT), and 582.2 mg of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) were placed in a 300 mL reaction vessel. The mixture was then heated at 250 °C for 5 minutes with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0079] To this solution, 13.0 mL of 0.20 M octadecensulfide (S-ODE) was added, and the mixture was heated with stirring at the same temperature for a further 15 minutes.

[0080] The resulting reaction solution (AgBiS2) was cooled to room temperature. The reaction solution changed to a black suspension, and no reflection peaks were observed in the resulting solution by XRD.

[0081] In Comparative Example 1, it was found that the AgBiE2-based quantum dots could not be properly synthesized because the ligand dodecanethiol was not present in the system, and in Comparative Example 2, it was found that the reaction temperature was too high at 250°C.

[0082] Based on the above, it was found that AgBiE2-based quantum dots can be synthesized according to Examples 1 to 5. [Industrial applicability]

[0083] According to the present invention, AgBiS2 quantum dots with a uniform particle size and an optical band gap of 0.90 to 1.10 eV can be synthesized using an easily handled reagent and in a method that allows for direct mass production without the need for intermediates. Furthermore, by applying the quantum dots of the present invention to light absorption devices and the like, excellent solar cell performance can be obtained in the apparatus. [Explanation of symbols]

[0084] 1: Quantum dots 1a: Core 1b: Shell 2 :Organic ligand

Claims

1. AgBiE contains silver, bismuth, and chalcogen. ２ A quantum dot aggregate characterized by being a nanocrystal represented by (E being at least one of tellurium, selenium, or sulfur), containing a large number of quantum dots with an average particle size of 3 nm to 5 nm, and in the particle size distribution in STEM, more than two-thirds of the quantum dots are contained within ±20% of the average particle size.

2. The quantum dot assembly according to claim 1, characterized in that the surface of the quantum dot is covered with a ligand.

3. The quantum dot assembly according to claim 2, characterized in that the ligand is selected from at least one or two of the phosphine-based, aliphatic thiol-based, aliphatic amine-based, and aliphatic carboxylic acid-based types.

4. The quantum dot assembly according to any one of claims 1 to 3, characterized in that an optical band gap of 0.90 to 1.075 eV can be obtained in the TauC plot.

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