Quantum dot assembly

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 hundreds to several thousands of 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. In addition, the performance of quantum dots is represented by fluorescence quantum yield (Quantum Yield: QY), full width at half maximum of fluorescence (Full Width at Half Maximum: FWHM), absorption wavelength, and emission wavelength.

[0004] The following patent documents and non-patent documents describe solar cells using 2 quantum dots.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[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 H 2 2S.

[0008] Against the background as described above, 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 the elucidation of the physical properties of silver bismuth chalcogenide quantum dots synthesized by such a method.

[0009] The present invention has been made in view of such points, 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] The quantum dot quantum dot assembly in the present invention is a nanocrystal represented by AgBiE containing silver, bismuth, and chalcogen 2 (E is at least one of tellurium, selenium, or sulfur), which contains a large number of quantum dots with an average particle size of the quantum dots being 1 nm or more and 15 nm or less, and in the particle size distribution in STEM, 2 / 3 or more of the total number of the quantum dots are included within ±20% of the average particle size.

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

[0013] 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.

[0014] In the present invention, it is preferable that an optical band gap of 0.90 or more and 1.075 eV or less is obtained in the TauC plot. [Advantages of the Invention]

[0015] According to the quantum dots of the present invention, the particle size distribution in STEM can be narrowed, and silver bismuth chalcogenide quantum dots with uniform particle sizes can be synthesized.

[0016] Moreover, according to the method for manufacturing quantum dots of the present invention, using reactants that are easy to handle and directly, simply and safely mass-producible silver bismuth chalcogenide quantum dots can be obtained without going through intermediates or the like. [Brief Description of the Drawings]

[0017]

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Mode for Carrying Out the Invention

[0018] In recent years, near-infrared luminescent quantum dots that do not contain heavy metals subject to toxicity regulations such as Cd and Pb have attracted attention. Among them, the inventors focused on silver bismuth chalcogenide (AgBiE 2(E is at least one of tellurium, selenium, or sulfur)) Focusing on ternary quantum dots, using reagents that are easy to handle, directly and in a safe manner under the atmosphere, without going through intermediates, etc., silver bismuth chalcogenide quantum dots were gently synthesized, and their physical properties were elucidated.

[0019] Hereinafter, an embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail. Note that the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

[0020] FIG. 1A and FIG. 1B are schematic diagrams of quantum dots in the present embodiment. The quantum dot 1 shown in FIGS. 1A and 1B is a nanocrystal directly synthesized using reagents that are easy to handle and without going through intermediates, etc.

[0021] In the present embodiment, the quantum dot 1 contains silver (Ag), bismuth (Bi), and a chalcogen, AgBiE 2 (E is preferably a nanocrystal represented by at least one of tellurium (Te), selenium (Se), or sulfur (S)). This compound has an indirect transition and very weak luminescence.

[0022] Here, "nanocrystal" refers to nanoparticles having a particle size of about 1 nm to several tens of nm. In the present embodiment, a large number of quantum dots can be generated with a uniform particle size. "Uniform" refers to a state in which more than 2 / 3 of the total particles are included within ±20% of the average particle size. Thus, in the present embodiment, fine and uniform high-quality quantum dots can be mass-produced. In the present embodiment, the particle size of the quantum dots can be adjusted in the range of 1 nm or more and 15 nm or less. Preferably, it is 2 nm or more and 10 nm or less, more preferably, 3 nm or more and 7 nm or less, and still more preferably, 4 nm or more and 5 nm or less.

[0023] Ag, Bi, and chalcogen contained in the quantum dots are the main components, and other elements may be contained in addition to these elements. 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 the quantum dots can be synthesized by reacting at a temperature of around 100 °C to around 150 °C in a high-boiling 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 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 between the quantum dots 1 can be suppressed, and the desired optical properties can be expressed. The ligands that can be used in the reaction are not particularly limited. For example, the following ligands can be mentioned as typical ones.

[0027] (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 , Decylamine: C 10 H 21 NH2 , octylamine: C 8 H 17 NH 2

[0028] (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, Decanoic acid: C 9 H 19 COOH, Octanoic acid: C 7 H 15 COOH

[0029] (3) Thiol-based Octadecanethiol: C 18 H 37 SH, Hexadecanethiol: C 16 H 33 SH, Tetradecanethiol: C 14 H 29 SH, Dodecanethiol: C 12 H 25 SH, Decanethiol: C 10 H 21 SH, Octanethiol: 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

[0030] (5) Phosphine oxide-based Trioctylphosphine oxide: (C 8 H17 ) 3 P=O, triphenylphosphine oxide: (C 6 H 5 ) 3 P=O, tributylphosphine oxide: (C 4 H 9 ) 3 P=O

[0031] In this embodiment, as shown in FIG. 1B, the quantum dot 1 may have a core-shell structure having 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 dot 1.

[0032] The core 1a shown in FIG. 1B is AgBiE 2 is. The shell 1b does not contain substances derived from regulated heavy metals such as Cd, Hg, Pb, etc. and highly reactive reactants represented by silicon compounds, similar to the core 1a.

[0033] Note that the shell 1b may be in a state of being solidified on the surface of the core 1a. However, in this embodiment, only the core 1a without using the shell 1b, that is, the quantum dot 1 of the core alone in FIG. 1A, can obtain an optical band gap of 0.90 to 1.10 eV in the TauC plot.

[0034] Next, a method for manufacturing the quantum dot of this 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 at least one of tellurium, selenium, or sulfur) is synthesized as the quantum dot represented.

[0035] Here, in this embodiment, the Ag raw material of AgBiE 2 is not particularly limited, but for example, the following organic silver reagents or inorganic silver reagents can be used. That is, silver(I) acetate: Ag(OAc) as an acetate, and silver stearate: Ag(OC(=O)C 17H 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, silver(I) iodide: AgI, etc.

[0036] Here, in this embodiment, the Bi raw material of AgBiE 2 is not particularly limited, and for example, the following organic bismuth reagents or inorganic bismuth reagents can be used. That is, as fatty acid salts, bismuth(III) acetate oxide: BiO(OC(=O)CH 3 ) bismuth(III) acetate: Bi(OC(=O)CH 3 ) 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) gallate: Bi(C 7 O 6 H 5 ) and trivalent compounds can be used as halides, such as bismuth(III) fluoride: BiF 3 , bismuth(III) chloride: BiCl 3 , bismuth(III) bromide: BiBr 3 , as inorganic acid salts, bismuth(III) nitrate pentahydrate: Bi(NO 3 ) 3 ·5H 2 O, bismuth(III) oxycarbonate: (BiO) 2 CO 3 , bismuth(III) oxide: Bi 2 O 3 etc. can be used.

[0037] In this embodiment, tellurium (Te) is used as a raw material in the form of an organic tellurium compound (organic chalcogen compound) or an inorganic tellurium compound, either in solid form or dissolved in a high-boiling solvent. Although the structure of the compound is not particularly limited, for example, trioctylphosphine telluride obtained by dissolving tellurium in trioctylphosphine: (C 8 H 17 ) 3 P=Te, tributylphosphine telluride obtained by dissolving tellurium in tributylphosphine: (C 4 H 9 ) 3 P=Te, or a solution obtained by dissolving tellurium in a high-boiling solvent such as octadecene, a long-chain hydrocarbon, at a high temperature can be used.

[0038] Further, in this embodiment, when selenium (Se) is to be solid-solved, selenium is used as a raw material in the form of an organic selenium compound (organic chalcogen compound) or an inorganic selenium compound, either in solid form or dissolved in a high-boiling solvent. Although the structure is not particularly limited, for example, trioctylphosphine selenide obtained by dissolving selenium in trioctylphosphine: (C 8 H 17 ) 3 P=Se, tributylphosphine selenide obtained by dissolving selenium in tributylphosphine: (C 4 H 9 ) 3 P=Se, or a solution obtained by dissolving selenium in a high-boiling solvent such as octadecene, a long-chain hydrocarbon, at a high temperature can be used.

[0039] Further, in this embodiment, when sulfur (S) is to be solid-solved, sulfur is used as a raw material in the form of an organic sulfur compound (organic chalcogen compound) or an inorganic sulfur compound, either in solid form or dissolved in a high-boiling solvent. Although the structure is not particularly limited, for example, trioctylphosphine sulfide obtained by dissolving sulfur in trioctylphosphine: (C 8 H 17 ) 3P=S, or tributylphosphine sulfide obtained by dissolving sulfur in tributylphosphine: (C 4 H 9 ) 3 P=S, or a solution obtained by dissolving sulfur at a high temperature in a high-boiling solvent such as a long-chain hydrocarbon like octadecene can be used.

[0040] In this embodiment, an organobismuth compound or an inorganic bismuth compound is added to a high-boiling solvent and dissolved. As the solvent, octadecene can be used as a high-boiling saturated hydrocarbon or unsaturated hydrocarbon of 150 °C or higher. In addition, as an aromatic high-boiling solvent, dodecylbenzene: C 6 H 5 (CH 2 ) 11 CH 3 , as a high-boiling ester solvent, butyl butyrate: C 4 H 9 COOC 4 H 9 , benzyl butyrate: C 6 H 5 CH 2 COOC 4 H 9 etc. can be used, but it is also possible to use compounds of aliphatic thiol, aliphatic amine, or fatty acid, or aliphatic phosphorus compounds as the solvent.

[0041] 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. Note that the reaction temperature is preferably lower, 100 °C or higher and 175 °C or lower, and more preferably even lower, 100 °C or higher and 150 °C or lower.

[0042] Also, 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 possible to react at a low temperature of about 100 °C to a high temperature of about 140 °C for AgBiTe 2 AgBiSe 2 , and AgBiS 2For 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, add the other raw materials to the solution in sequence, and then continue the reaction at the same temperature to synthesize quantum dots.

[0043] In addition, in this embodiment, AgBiE having a uniform particle size 2 In order to obtain the above, in the reaction of the precursors, that is, the silver raw material, the bismuth raw material, and the chalcogen raw material, it is preferable to add 1 to 200 equivalents of thiol relative to Te, Se, or S, 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: C 8 H 17 SH, etc. can be used.

[0044] In addition, in this embodiment, when each raw material is added and reacted, a compound is required that has an auxiliary role of liberating the precursor metal into the reaction solution by coordination or chelating.

[0045] Compounds having the above-mentioned role include ligands capable of forming a complex with silver. For example, phosphorus-based ligands, amine-based ligands, thiol-based ligands, and carboxylic acid-based ligands are preferred, and among these, thiol-based ligands are particularly preferred due to their high efficiency.

[0046] This allows the reaction between Ag, Bi, and chalcogen to proceed appropriately, producing AgBiE, which is based on Ag, Bi, and chalcogen, has an optical band gap of 0.90 to 1.10 eV, and has a uniform particle size.2 Quantum dots can be manufactured.

[0047] In the method for manufacturing quantum dots of the present embodiment, a step of dissolving one or two kinds of raw materials among the above-mentioned silver raw material, bismuth raw material, chalcogenide raw material, and ligand in the high-boiling solvent heated to 100°C to 150°C, and then, a step of sequentially adding the other raw materials, and after adding all the raw materials, a step of continuously synthesizing quantum dots at the same reaction temperature are preferably included.

[0048] Thereby, a reactant that is easy to handle can be used, and silver bismuth chalcogenide having a uniform particle diameter can be safely mass-produced in a short time directly without going through an intermediate or the like.

Example

[0049] Hereinafter, the effects of the present invention will be described with reference to examples and comparative examples of the present invention. Note that the present invention is not limited to the following examples at all.

[0050] <Raw materials> In the present invention, the following raw materials were used to synthesize silver chalcogenide compound (AgBiE 2 system) quantum dots having a uniform particle diameter. (Solvent) Octadecene: manufactured by Aldrich Co., Ltd., manufactured by Idemitsu Kosan Co., Ltd. (Chalcogenide raw material) Sulfur powder (99.0% or more): 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 Corporation Bismuth oxide: manufactured by Mitsuwa Chemical Co., Ltd. (Silver raw material) Silver acetate: manufactured by Kishida Chemical Co., Ltd. (Ligand) Trioctylphosphine: manufactured by Kitakyo Chemical Co., Ltd. Dodecanethiol: manufactured by Arkema <Measuring equipment> Ultraviolet-visible spectrophotometer: V-770 manufactured by Hitachi, Ltd. X-ray diffractometer (XRD): D2 PHASER manufactured by Bruker Scanning transmission electron microscope (STEM): SU9000 manufactured by Hitachi, Ltd. Differential thermal balance (TG-DTA): Thermo Plus EVO2 manufactured by Rigaku Corporation

[0051] [Example 1] In a 300 mL reaction vessel, 200.2 mg of silver acetate: Ag(OAc), 30.0 mL of dodecanethiol: DDT, and 582.2 mg of bismuth nitrate pentahydrate: Bi(NO 3 ) 3 ·5H 2 O were added. Then, under an inert gas (N 2 ) atmosphere, it was heated with stirring at 145 °C for 5 minutes to dissolve the raw materials.

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

[0053] The obtained reaction solution 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 to obtain a dispersion solution of AgBiS 2 particles.

[0054] The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible near-infrared absorption spectrum shown in Figure 2 was obtained. Also, the quantum dots obtained in this synthesis were found to have an optical bandgap of 0.90 eV as shown by the analysis result using the TauC plot in Figure 3. Also, as shown in Figure 4, the average particle size of this quantum dot was about 4.43 nm, and it was found that more than 2 / 3 of the total number of particles were within ±20% of the average particle size. Also, from the analysis by differential thermal balance (TG), as shown in Figure 5, it was revealed that about 15% of the ligands were coordinated to the entire quantum dots. Also, as shown in Figure 6, AgBiS2 From the peak values and peak patterns of the XRD spectra of the particles, it was proven that an AgBiS 2 solid solution was formed.

[0055] [Example 2] Into a 300 mL reaction vessel, 200.2 mg of silver acetate: Ag(OAc), 30.0 mL of dodecanethiol: DDT, and 582.2 mg of bismuth nitrate pentahydrate: Bi(NO 3 ) 3 ·5H 2 O were placed. Then, under an inert gas (N 2 ) atmosphere, it was heated with stirring at 145 °C for 5 minutes to dissolve the raw materials.

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

[0057] The obtained reaction solution 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, obtaining a dispersion solution of AgBiS 2 particles.

[0058] The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible near-infrared absorption spectrum in Figure 7 was obtained. Also, the quantum dots obtained in this synthesis were found to have an optical bandgap of 1.075 eV, as shown by the analysis result in the TauC plot in Figure 8. Moreover, as shown in Figure 9, the average particle size of this quantum dot was approximately 4.53 nm, and it was found that more than 2 / 3 of the total number of particles were within ±20% of the average particle size. Also, from the analysis using a differential thermal balance, as shown in Figure 10, it became clear that approximately 18% of the ligands were coordinated with respect to the mass of the entire quantum dot.

[0059] Also, from the peak values and peak patterns of the XRD spectra of the AgBiS 2 particles shown in Figure 11, AgBiS 2It was proved that a solid solution was formed.

[0060] [Example 3] Into a 300 mL reaction vessel, 200.2 mg of silver acetate: Ag(OAc), 30.0 mL of dodecanethiol: DDT, and 340.8 mg of bismuth acetate oxide: BiO(OC(=O)CH 3 ) were placed. Then, under an inert gas (N 2 ) atmosphere, it was heated with stirring at 140 °C for 5 minutes to dissolve the raw materials.

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

[0062] The obtained reaction solution 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, obtaining a dispersion solution of AgBiS 2 particles.

[0063] 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. Also, the quantum dots obtained in this synthesis were found to have an optical band gap of 1.065 eV as shown by the analysis result according to the TauC plot of Fig. 13. Moreover, as shown in Fig. 14, the average particle size of this quantum dot was about 4.23 nm, and it was found that more than 2 / 3 of the total number of particles were within ±20% of the average particle size. Also, from the analysis by a differential thermal balance, as shown in Fig. 15, it became clear that about 18% of the ligands were coordinated with respect to the mass of the whole quantum dots.

[0064] Also, from the peak values and peak patterns of the XRD spectrum of the AgBiS 2 particles shown in Fig. 16, it was proved that an AgBiS 2 solid solution was formed.

[0065] [Example 4] In a 300 mL reaction vessel, 200.2 mg of silver acetate: Ag(OAc), 30.0 mL of dodecanethiol: DDT, and 340.8 mg of bismuth acetate oxide: BiO(OC(=O)CH 3 ) were placed. Then, under an inert gas (N 2 ) atmosphere, it was heated with stirring at 100 °C for 5 minutes to dissolve the raw materials.

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

[0067] The resulting reaction solution 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, obtaining a dispersion solution of AgBiS 2 particles.

[0068] The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible near-infrared absorption spectrum in Fig. 17 was obtained. Also, the quantum dots obtained in this synthesis were found to have an optical bandgap of 1.10 eV, as shown by the analysis result in the TauC plot in Fig. 18. Moreover, as shown in Fig. 19, the average particle size of this quantum dot was about 4.82 nm, and it was found that more than 2 / 3 of the total number of particles were within ±20% of the average particle size. Also, from the differential thermal balance analysis, as shown in Fig. 20, it was revealed that about 19% of the ligands were coordinated with respect to the mass of the entire quantum dot.

[0069] Also, from the peak values and peak patterns of the XRD spectrum of the AgBiS 2 particles shown in Fig. 21, it was proved that an AgBiS 2 solid solution was formed.

[0070] [Example 5] In a 300 mL reaction vessel, 200.2 mg of silver acetate: Ag(OAc), 30.0 mL of dodecanethiol: DDT, and bismuth nitrate pentahydrate: Bi(NO 3 ) 3·5H 2 582.2 mg of O was added. Then, under an inert gas (N 2 ) atmosphere, it was heated with stirring at 100 °C for 5 minutes to dissolve the raw materials.

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

[0072] The resulting reaction solution 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 a dispersion solution of AgBiS 2 particles was obtained.

[0073] The obtained dispersion solution was measured with an ultraviolet-visible spectrometer. As a result, the ultraviolet-visible near-infrared absorption spectrum of Figure 22 was obtained. Also, as shown in the analysis result by the TauC plot of Figure 23, the quantum dots obtained in this synthesis were found to have an optical bandgap of 1.10 eV. Moreover, as shown in Figure 24, the average particle size of this quantum dot was about 4.52 nm, and it was found that more than 2 / 3 of the total number of particles were within ±20% of the average particle size. Also, from the analysis by a differential thermal balance, as shown in Figure 25, it was clarified that about 22% of the ligands were coordinated with respect to the mass of the entire quantum dots.

[0074] Also, from the peak values and peak patterns of the XRD spectrum of the AgBiS 2 particles shown in Figure 26, it was proved that an AgBiS 2 solid solution was formed.

[0075] [Comparative Example 1] In a 300 mL reaction vessel, 200.2 mg of silver acetate: Ag(OAc), 30.0 mL of octadecene: ODE, and 582.2 mg of bismuth nitrate pentahydrate: Bi(NO 3 ) 3 ·5H 2 O were added. Then, under an inert gas (N 2)It was heated with stirring at 150 °C for 5 minutes under an atmosphere.

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

[0077] The resulting reaction solution (AgBiS 2 ) was cooled to room temperature. There was no color change in the reaction solution, and it was confirmed by XRD that the raw materials remained as they were in the obtained solution.

[0078] [Comparative Example 2] Into a 300 mL reaction vessel, 200.2 mg of silver acetate: Ag(OAc), 30.0 mL of dodecanethiol: DDT, and 582.2 mg of bismuth nitrate pentahydrate: Bi(NO 3 ) 3 ·5H 2 O were placed. Then, it was heated with stirring at 250 °C for 5 minutes under an inert gas (N 2 ) atmosphere to dissolve the raw materials.

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

[0080] The resulting reaction solution (AgBiS 2 ) was cooled to room temperature. The reaction solution changed to a black suspension, and no reflection peaks were confirmed by XRD from the obtained solution.

[0081] In Comparative Example 1, due to the absence of dodecanethiol as a ligand in the system, and in Comparative Example 2, due to the high reaction temperature of 250 °C, it was found that AgBiE 2 system quantum dots could not be synthesized appropriately.

[0082] From the above, according to Examples 1 to 5, it was found that AgBiE 2 system quantum dots could be synthesized. [Industrial Applicability]

[0083] According to the present invention, AgBiS quantum dots having a uniform particle size and an optical band gap of 0.90 to 1.10 eV can be synthesized by using a reagent that is easy to handle and in a method that can be directly mass-produced without going through intermediates or the like. 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 device. 2

Explanation of reference numerals

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

Claims

1. AgBiE containing silver, bismuth, and chalcogen ２ (E is at least one of tellurium, selenium, or sulfur), the quantum dots have an average particle size of 1 nm or more and 15 nm or less, and at least 2 / 3 of the quantum dots are within ±20% of the average particle size in a particle size distribution measured by STEM.

2. 2. The quantum dot ensemble according to claim 1, wherein the surface of the quantum dot is covered with a ligand.

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

4. 4. The quantum dot ensemble according to claim 1, wherein an optical band gap of 0.90 to 1.075 eV is obtained in a TauC plot.

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