Novel synthesis of colloidal quantum dot inks and their application in semiconductor devices.

Abstract

The present invention provides a method for producing a nanocrystalline composition containing an inorganic ligand by one-pot synthesis. The present invention also provides nanocrystals containing novel inorganic ligands and uses of these nanocrystals. The present invention further provides the use of novel inorganic ligands in the preparation of nanocrystals.

Description

[Technical Field]

[0001] This invention generally relates to nanocrystals. More specifically, it relates to a method for producing nanocrystalline compositions containing inorganic ligands by one-pot synthesis. This invention also extends to nanocrystals containing novel inorganic ligands, the use of these nanocrystals, and the use of novel inorganic ligands in the preparation of nanocrystals. [Background technology]

[0002] Nanocrystals are useful in a wide range of applications because, for example, their optical properties can be fine-tuned to provide desired characteristics. The optical properties of nanocrystals (e.g., absorption and emission properties) can be fine-tuned by controlling their size. The largest nanocrystals yield the longest wavelengths (and lowest frequencies), while the smallest nanocrystals yield the shortest wavelengths (and highest frequencies). The size of nanocrystals can be controlled by the method in which they are manufactured. This ability to fine-tune the optical properties of nanocrystals by controlling their size makes them suitable for use in a wide range of applications, including, for example, photodetectors, sensors, solar cells, bioimaging and biosensing, photovoltaic technologies, displays, lighting, security and counterfeiting, batteries, wired high-speed communications, quantum dot (QD) lasers, photocatalysts, spectrometers, injectable compositions, field-effect transistors, light-emitting diodes, lasers, photonic or optical switching devices, hydrogen production, and metamaterials.

[0003] Unmodified (pristine) lead and lead-free colloidal quantum dots (CQDs) are typically synthesized by wet chemical processes using long-chain organic ligands to control nanocrystal growth and stabilize the colloidal system in the solvent. To construct high-performance CQD devices, it is necessary to replace the long-chain insulating organic ligands with shorter organic ligands or conductive inorganic ligands to improve charge transfer in the system.

[0004] In conventional methods, several purification steps are performed on the crude mixture containing nanocrystals to remove by-products from the initial nanocrystal synthesis before the ligand substitution reaction (ligand exchange) occurs. Figure 1 shows a flowchart of the conventional method for nanocrystal synthesis, illustrating the formation of unmodified nanocrystals, the purification steps, and then the ligand exchange reaction. Finally, an ink composition containing the nanocrystals is formed. The conductive semiconductor nanocrystals can then be used in optical devices.

[0005] The purification process described above has been previously reported as an essential step for achieving optimally performing quantum dots, for example, by King et al. (Importance of QD Purification Procedure on Surface Adsorbance of QDs and Performance of QD Sensitized Photoanode, J. Phys. Chem. C 2012, 116, 3349~3355) and Chen et al. (IEEE Access, Vol. 8, pp. 159415~159423, 2020). For example, King et al. explained that before sensitization, QDs are subjected to general purification, i.e., alternating precipitation / non-solvent / redispersion in solvent. King et al. concluded that the purification process is extremely important and that improved purification can increase the surface-bound QD concentration by a factor of five.

[0006] However, these purification processes are extremely time-consuming and require large amounts of solvent. Furthermore, conventional semiconductor nanocrystals contain partially oxidized surfaces, which is thought to contribute to their low reproducibility and poor optoelectronic properties. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Importance of QD Purification Procedure on Surface Adsorbance of QDs and Performance of QD Sensitized Photoanode, J. Phys. Chem. C 2012, 116, 3349~3355

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, there is an unmet need for a method of manufacturing nanocrystals with reduced surface oxidation. Furthermore, there is an unmet need for a method of manufacturing nanocrystals that is faster and generates less waste.

[0009] In addition, the use of lead and other heavy metals in nanocrystals can be a problem in some industries due to their toxicity. However, current alternative materials and ligand systems are not as performant as lead-based systems. Therefore, there is a further need in the industry to provide alternative ligand systems that confer excellent optoelectronic properties while avoiding the use of toxic heavy metals such as lead.

Means for Solving the Problems

[0010] The inventors have found a method for manufacturing nanocrystals having improved optical properties. In particular, the inventors have found that a method of manufacturing nanocrystals that does not include a purification step after the first synthesis step and before the ligand exchange reaction results in improved optical properties of the resulting nanocrystals.

[0011] Therefore, according to a first aspect, the present invention is a method for manufacturing a nanocrystal composition, comprising a) A contacting step carried out in a non-polar solvent, comprising: a plurality of first organic ligand compounds; a metal-containing compound containing a metal element; and at least one reactant containing a pnictogen element or a chalcogen element are contacted to form a mixture containing a plurality of nanocrystals, the nanocrystals of which comprise a crystalline core and a plurality of first organic ligand compounds coordinated to the surface of the crystalline core, and the crystalline core comprises (i) a metal element and (ii) a pnictogen element or a chalcogen element, the contacting step; b) adding an exchange composition containing an exchange ligand precursor and a polar solvent to the above mixture, comprising, there is no purification step between step a) and step b), A method is provided.

[0012] According to a second aspect, the present invention provides a nanocrystal composition obtainable by the method of the first aspect.

[0013] According to a third aspect, the present invention provides an ink composition comprising the nanocrystal composition of the second aspect. The ink composition generally comprises the nanocrystals of the nanocrystal composition and a polar solvent used to dissolve the nanocrystals.

Brief Description of the Drawings

[0014] [Figure 1] Figure 1 shows a simplified flow diagram of a prior art method for quantum dot synthesis, which is compared with the method of the present invention. [Figure 2] Figure 2 shows a simplified diagram of an in-situ ligand exchange process for PbS quantum dots using a novel inorganic ligand. [Figure 3] Figure 3 shows the absorption spectra of quantum dots at various stages of synthesis, comparing the prior art method of quantum dot synthesis with the method of the present invention. [Figure 4]Figure 4 shows a photograph of the phase-separated quantum dots in the polar inorganic phase along with the final ink. [Figure 5] Figure 5 shows the absorption spectrum and its change over time of nanocrystals produced according to the method of the present invention (in-situ). [Figure 6] Figure 6 shows the absorption spectrum and its change over time of nanocrystals produced according to the conventional method (ex-situ). [Figure 7] Figure 7 shows the absorption spectra of in-situ and ex-situ PbS quantum dots using CsPbI3 as an inorganic ligand. [Figure 8] Figure 8 shows the absorption spectrum of an in-situ PbS quantum dot using CsZnI3 as an inorganic ligand. [Figure 9] Figure 9 shows the absorption spectrum of a PbS quantum dot using AsI3 as an inorganic ligand. [Figure 10] Figure 10 shows photographs of ligand-exchanged QD inks using CsI (left) and ZnI2 (right) as inorganic ligands. [Figure 11] Figure 11 shows the current density-voltage characteristics of (a) photodiode devices fabricated using in-situ and ex-situ PbS QDs, and (b) EQE spectra of photodiode devices fabricated using in-situ and ex-situ QDs, using the same device architecture within the same batch. [Figure 12] Figure 12 shows (a) the absorption spectrum of ligand-exchanged InAs QDs in 2,6-difluoropyridine, and (b) a photograph of the film immediately after manufacturing, along with an AFM image, to show the film quality. [Figure 13] Figure 13 shows the current density-voltage characteristics of (a) photodiode devices fabricated using in-situ and ex-situ InAs QDs, and (b) EQE spectra of photodiode devices fabricated using in-situ and ex-situ QDs, using the same device architecture within the same batch. [Figure 14] Figure 14 shows the absorption spectrum of an InAs nanocrystalline ink using a CsI-InBr3 ligand system. [Figure 15] Figure 15 shows a thermogravimetric analysis (TGA) curve of an InAs nanocrystal, illustrating how the range of inorganic ligand exchange can be measured. [Figure 16] Figure 16 shows the X-ray diffraction (XRD) data of PbS nanocrystals containing the CsPbI3 ligand. [Figure 17] Figure 17 shows a high-resolution TEM micrograph of a PbS nanocrystal containing a CsPbI3 ligand, illustrating the formation of a superlattice structure on the surface of the nanocrystal. [Figure 18] Figure 18 shows inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF MS) of a PbS nanocrystal containing a CsPbI3 ligand, which supports the presence of CsPbI3. [Figure 19] Figure 19 shows the absorption spectrum of nanocrystals produced according to the method of the present invention (in situ). [Modes for carrying out the invention]

[0015] When describing aspects of the present invention, terms used should be interpreted according to the following definitions unless otherwise indicated in the context.

[0016] Where used herein and in the appended claims, unless the context explicitly states otherwise, the singular form (as used in the foreign language specification and claims of this application, "a," "an," and "the") includes both singular and plural designations. For example, "nanocrystal" means one nanocrystal or two or more nanocrystals. For example, "indium-containing compound" means one indium-containing compound or two or more indium-containing compounds. When used in conjunction with a comprising language, any reference to a number includes compositions containing or exceeding that number.

[0017] The terms “comprising,” “comprises,” and “comprised of,” as used herein, are synonymous with “including,” “includes,” or “containing,” and are inclusive or non-restrictive, not excluding any additional unlisted components, elements, or process steps. The terms “comprising,” “comprises,” and “comprised of” also include the term “consisting of.”

[0018] As used herein, the term "and / or" means, when used in a list of two or more items, that any one of the listed items may be used alone, or any combination of two or more of the listed items may be used. For example, if a list is described as containing group A, B, and / or C, the list may contain A alone, B alone, C alone, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B, and C.

[0019] Where used herein, unless otherwise explicitly stated, all numbers, including values, ranges, quantities, or percentages, may be interpreted as if preceded by the word "approximately," even if the word is not explicitly indicated.

[0020] When used herein, the term "approximately" refers to a measurable value, such as a parameter, quantity, or duration, and indicates that the value includes the standard deviation of the error of the device or method used to determine the value. The term "approximately" means that it includes variations of a specified value and variations of + / -10%, + / -5%, or + / -0.1% or less from that value, insofar as such variations are appropriate for implementation in this disclosure. It should be understood that the value to which the modifier "approximately" refers is also to be specifically disclosed.

[0021] The enumeration of a numerical range by endpoints includes all integers and, where appropriate, decimals included within that range (e.g., 1 to 5 includes, for example, 1, 2, 3, 4 when referring to the number of elements, and may also include 1.5, 2, 2.75, and 3.80 when referring to measured values). The enumeration of endpoints also includes the endpoint values themselves (e.g., 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0022] Unless otherwise defined, all terms used in this disclosure, including technical and scientific terms, have the meanings commonly understood by one of ordinary skill in the art to which this disclosure pertains. Definitions of terms used herein are included to better understand the teachings of this disclosure using additional guidance. All publications referenced herein are incorporated by reference.

[0023] As used herein, unless otherwise defined, the term "composition" may be either non-limiting or limiting. For example, a "composition" may include the specified material, i.e., the nanocrystal, and further unspecified materials, or may consist of the specified material, i.e., may substantially exclude unspecified materials.

[0024] <in situ synthesis> According to a first aspect, the present invention is a method for producing a nanocrystal composition, comprising: a) a contacting step conducted in a non-polar solvent, a plurality of first organic ligand compounds; a metal-containing compound containing a metal element; and at least one reactant containing a pnictogen element or a chalcogen element are contacted to form a mixture containing a plurality of nanocrystals, The nanocrystal comprises a crystalline core and a plurality of first organic ligand compounds coordinated to the surface of the crystalline core, wherein the crystalline core comprises (i) a metal element and (ii) a pnictogenic element or a chalcogen element, and the process involves a contact step. b) A step of adding an exchange composition containing an exchange ligand precursor and a polar solvent to the above mixture. Includes, There is no refining step between step a) and step b). Provide a method.

[0025] The method of the present invention does not involve the purification steps of the prior art, while surprisingly offering several advantages. In other words, the present invention provides a one-pot method for producing nanocrystals.

[0026] Conventional ink formation processes are time-consuming and expensive due to the repeated processing / purification of nanocrystals. Furthermore, the purification process can cause surface oxidation, resulting in low reproducibility and poor photoelectronic properties of nanocrystal ink formation. The inventors of this invention have discovered a simple and cost-effective ligand exchange process using an in-situ technique in which the ligand exchange process is performed directly on unmodified (pristine) nanocrystals immediately after synthesis, without prior purification of the nanocrystals. The inventors estimate that this method enables improved optical properties of the resulting nanocrystals and results in a 30% cost reduction in nanocrystal ink production thanks to the use of less solvent, energy, and labor, as well as a simpler process for expansion. Moreover, inks prepared by this technique exhibit excellent photoelectronic properties with high reproducibility, along with good colloidal stability in polar solvents.

[0027] These results are surprising, as it has been accepted in this field that purification after the initial formation of nanocrystals is an essential step to achieve optimal performance of nanocrystals. Conventionally, unmodified (pristine) nanocrystals, particularly quantum dots (QDs), are purified by solvent / poor solvent methods, dissolved in a nonpolar solvent, and then subjected to ligand exchange processes with more electrically conductive short-chain organic or inorganic ligands to achieve nanocrystalline inks for use in devices.

[0028] Conventional purification processes using solvents / poor solvents are not only time-consuming but also less efficient and more costly. While we do not wish to be bound by theory, solvent / poor solvent purification after the synthesis of unmodified nanocrystals also causes surface oxidation of the nanocrystals, resulting in poor device performance and an inconsistent shift to lower wavelengths in the absorption spectrum. Here, we introduce in-situ ligand exchange, in which exchange ligands are introduced into a crude solution containing unmodified nanocrystals without any purification steps in between. As described above, this route provides a more cost-effective and efficient solution. The present invention provides a stable colloidal ink composition containing nanocrystals with improved performance by a method that is not only much cheaper but also more scalable. Generally, the final ink composition is then used to manufacture devices by single-step deposition techniques.

[0029] The advantages of this method include preventing surface oxidation of nanocrystals, providing higher quality nanocrystal compositions and devices, significantly lower manufacturing costs, providing a less time-consuming process, and providing a process that is easy to scale up.

[0030] As used herein, the term "nanocrystal" is used to refer to crystalline particles having at least one dimension less than 100 nanometers (nm).

[0031] As used herein, the term “semiconductor nanocrystal” is used synonymously with the term “quantum dot” and refers to a semiconductor crystalline material that exhibits a quantum confinement effect, enabling it to mimic the properties of atoms. Quantum dots may also be known as zero-dimensional nanocrystals. As used herein, the term “semiconductor nanocrystal composition” is used to refer to a composition comprising at least one semiconductor nanocrystal. The nanocrystals of the present invention are generally semiconductor nanocrystals and quantum dots.

[0032] As used herein, the term "Group I metals" refers to the metals of Groups IA and IB of the periodic table. For example, Group IA metals may be lithium, sodium, potassium, rubidium, or cesium, and Group IB metals may be copper, silver, or gold.

[0033] As used herein, the term "Group II metal" refers to a metal of Group IIA or Group IIB of the periodic table. For example, a Group IIA metal may be beryllium, magnesium, calcium, strontium, or barium, and a Group IIB metal may be zinc, cadmium, or mercury.

[0034] As used herein, the term “Group III metal” refers to the metals of Group 13 of the periodic table. For example, Group III metals may be aluminum, gallium, indium, or thallium.

[0035] As used herein, the term "Group IV metals" refers to the metals of Group 14 of the periodic table. For example, Group IV metals may be silicon, germanium, tin, or lead.

[0036] As used herein, the terms “Group V elements” and “pnictogen” refer to the elements of Group 15 of the periodic table. For example, a pnictogen may be nitrogen, phosphorus, arsenic, antimony, or bismuth.

[0037] As used herein, the term "indium pnictogenide semiconductor nanocrystal" is used to refer to a semiconductor nanocrystal containing indium and pnictogen.

[0038] As used herein, the terms “Group VI elements” and “chalcogen” refer to the elements of Group 16 of the periodic table. For example, a chalcogen may be oxygen, sulfur, selenium, tellurium, or polonium.

[0039] As used herein, the term “ligand” refers to a compound that can form a complex with a nanocrystal by coordinating to the surface of the nanocrystal. Nanocrystals generally contain a crystalline core having dimensions on the order of tens of nanometers. They are typically stabilized as a colloidal solution by surface-capping ligands that can coordinate to the crystalline core as Lewis acids (Z-type), Lewis bases (L-type), or anionic (X-type) species.

[0040] As used herein, the term “organic compound” is used to refer to a compound containing a carbon atom covalently bonded to another atom. x ~C y The term "organic compound" (wherein x and y are integers) is used to refer to an organic compound containing at least x and y or fewer carbon atoms.

[0041] As used herein, the term "inorganic compound" is used to refer to compounds other than organic compounds.

[0042] As used herein, the term “purification process” is used to mean any method that results in the isolation of nanocrystals from a solution, or any method that reduces the ratio of impurities to nanocrystals in a mixture. As used herein, the term “impurity” is used to mean components in the solvent other than nanocrystals (excluding the solvent). For example, impurities may be free organic ligands or free inorganic ligands in a solution, or salts thereof. In particular, the term “purification process” includes purification processes disclosed in the prior art, such as alternating precipitation / non-solvent / redispersion cycles. These purification processes generally involve precipitation of nanocrystals by centrifugation using a solvent / non-solvent followed by redispersion into a solvent.

[0043] As used herein, the letter "X" is used to refer to a halide. When X is a halide, X is preferably Cl, Br, or I. X may be a mixed halide or not; for example, X4 may be I4 or Br3I.

[0044] Preferably, the nanocrystals produced by the method of the first embodiment are semiconductor nanocrystals, such as colloidal quantum dots. More specifically, the present invention produces colloidal quantum dot ink.

[0045] Preferably, steps a) and b) are carried out in a reaction vessel, and the mixture remains in the reaction vessel between steps a) and b). Preferably, step b) is carried out immediately after step a). In other words, preferably, there are no further steps between steps a) and b). Preferably, the method is a one-pot method. Preferably, no components are removed from the mixture between steps a) and b). Preferably, no components are added to the mixture between steps a) and b).

[0046] As used herein, the term “reaction vessel” is used to refer to a vessel that isolates one reaction (e.g., a contact step) from another reaction, or a vessel that provides a space in which a reaction may occur. As used herein, the term “step b) is carried out immediately after step a)” is used to refer to a series of steps in which no further reaction steps are taken between step a) and step b). As used herein, the terms “one-pot method” and “in situ method” are used to refer to a reaction in which all steps are carried out in the same reaction vessel. As used herein, the term “component” is used to refer to a compound that forms a mixture.

[0047] Preferably, steps a) and b) are carried out under inert conditions. For example, the reaction may be carried out under argon or nitrogen gas. Typically, inert conditions are used to avoid surface oxidation of the nanocrystals. After the ligand exchange reaction with the exchange ligand, the nanocrystals may be exposed to air as they become less sensitive to oxygen.

[0048] The metal element of the present invention may be any suitable metal element for preparing nanocrystals, as will be understood by those skilled in the art. For example, the metal element may be any suitable post-transition metal element or transition metal element.

[0049] Preferably, the metal element is selected from the group consisting of Group I metals, Group II metals, Group III metals, Group IV metals and mixtures thereof, and the metal-containing compound is selected from the group consisting of elemental metals, metal halides, metal acetates, metal nitrates, metal carbonates, metal oleates, metal oxides, metal peroxides, metal alkoxides, metal hydroxides, metal sulfates, metal acetylacetonates, metal perchlorates, metal carboxylates, metal cyanides, or mixtures thereof. Preferably, the metal element is selected from the group consisting of indium, gallium, lead, and silver.

[0050] In a preferred embodiment, step a) includes contacting a plurality of first organic ligand compounds with a metal-containing compound comprising a metal element, wherein the metal element is indium or gallium, and with at least one reagent comprising a pnictogen element. In other words, in a preferred embodiment, the metal element is indium or gallium, and the at least one reagent comprises a pnictogen element. As shown in Example 10, photodiode devices with excellent EQE characteristics can be manufactured using InAs quantum dots produced by the method of the present invention.

[0051] In a preferred embodiment, the metal element is indium. When the metal element is indium, the metal-containing compound is preferably selected from the group consisting of indium halides, indium acetate, indium nitrate, indium carbonate, indium oleate, and mixtures thereof. In a particularly preferred embodiment, the metal-containing compound is indium acetate.

[0052] In an alternative embodiment, the metallic element is gallium. When the metallic element is gallium, the metal-containing compound is preferably selected from the group consisting of gallium halides, gallium acetate, gallium nitrate, gallium carbonate, gallium oleate, and mixtures thereof.

[0053] The inventors have found that nanocrystals can be prepared using a range of suitable pnictogenic elements according to the method of the present invention. Preferably, the pnictogenic element is selected from the group consisting of phosphorus, arsenic, and antimony.

[0054] In one embodiment, the pnictogenic element is phosphorus. When the pnictogenic element is phosphorus, at least one reactant may be any suitable phosphorus-containing precursor, but preferably, at least one reactant is selected from the group consisting of triphenylphosphine, tris(trimethylsilyl)phosphine, tris(dimethylamino)phosphine, triethylphosphine, tributylphosphine, tricyclohexylphosphine, trioctylphosphine, and mixtures thereof.

[0055] In a preferred embodiment, the pnictogenic element is arsenic or antimony. In a particularly preferred embodiment, the pnictogenic element is arsenic. When the pnictogenic element is arsenic, preferably at least one reactant is selected from the group consisting of arsenic halides, tris(trimethylsilyl)arsenic, arsenic oxide, arsenic sulfate, and mixtures thereof. In a preferred embodiment, the pnictogenic element is antimony. When the pnictogenic element is antimony, preferably at least one reactant is antimony halide or tris(trimethylsilyl)antimony.

[0056] When the metallic element is indium or gallium, the method of the present invention is particularly useful for preparing binary, ternary, and quaternary nanocrystals. For example, the method is suitable for preparing indium pnictogenide and gallium pnictogenide nanocrystals. For example, the present invention can be used to prepare InAs, InSb, InAsSb, GaAs, GaSb, InGaAs, InGaSb, and InGaAsSb nanocrystals.

[0057] In one embodiment, in which at least one reactant contains a pnictogen element, the contact step may also include contacting the other component with a compound selected from the group consisting of secondary amines, zinc carboxylates, and mixtures thereof, preferably the compound being dioctylamine. This compound is used to further enhance the control of the nanocrystal shape by complexing with the pnictogen-containing compound. In this way, it is possible to reduce the reactivity of the pnictogen-containing compound, which results in better control over the size and size distribution of the nanocrystals. Preferably, this compound is used when the pnictogen-containing compound is tris(trimethylsilyl)arsenide or tris(trimethylsilyl)antimony, because these compounds are particularly reactive.

[0058] In one embodiment, step a) includes contacting a plurality of first organic ligand compounds with a metal-containing compound comprising a metal element, wherein the metal element is lead or silver, and with at least one reagent comprising a chalcogen element. In other words, in a preferred embodiment, the metal element is lead or silver, and at least one reagent comprises a chalcogen element.

[0059] In a preferred embodiment, the metal element is lead. Preferably, the metal-containing compound is lead oxide or lead acetate. Preferably, the metal-containing compound is lead oxide. Preferably, the metal-containing compound is selected from the group consisting of PbO, Pb3O4, PbO2, and mixtures thereof. In an alternative embodiment, the metal-containing compound is lead acetate.

[0060] In an alternative embodiment, the metallic element is silver. Preferably, the metal-containing compound is selected from the group consisting of silver acetate, silver nitrate, silver oxide, silver halide, and mixtures thereof.

[0061] The inventors have found that nanocrystals can be prepared using a range of suitable chalcogen elements according to the method of the present invention. Any suitable chalcogen-containing precursor can be used. Preferably, the chalcogen element is selected from the group consisting of sulfur, selenium, and tellurium.

[0062] In one embodiment, the chalcogen element is sulfur. Examples of suitable sulfur-containing reagents include bis(trialkylsilyl) sulfide compounds, e.g., bis(trimethylsilyl) sulfide, bis(triethylsilyl) sulfide and bis(tripropylsilyl) sulfide, thioacetamides, tri-n-octylphosphine sulfide, tributylphosphine sulfide, alkyl-substituted and / or phenylthiourea compounds, e.g., N,N'-disubstituted and N,N,N'-trisubstituted thioureas, alkyl-substituted thioamide compounds, elemental sulfur, mercaptopropylsilane, sulfur-triphenylphosphine ("S-TPP"), sulfur-trioctylamine ("S-TOA"), ammonium sulfide, sodium sulfide, hexanethiol, octanthiol, decanethiol, dodecanethiol, hexadecanethiol, and mixtures thereof.

[0063] In alternative embodiments, the chalcogen element is selenium. Examples of suitable selenium-containing compounds include bis(trimethylsilyl)selenide, trioctylphosphine selenide, 1-octadeceneselenium, tributylphosphine selenide, selenium-triphenylphosphine, and mixtures thereof.

[0064] In alternative embodiments, the chalcogen element is tellurium. Suitable examples of tellurium-containing compounds include tellurium powder, triphenylphosphine telllide, tri-n-octylphosphine telllide, tributylphosphine telllide, and mixtures thereof.

[0065] When the metallic element is lead or silver, the method of the present invention is suitable for preparing binary and ternary nanocrystals. For example, the method is suitable for preparing lead chalcogenide and silver chalcogenide nanocrystals. For example, the present invention can be used to prepare PbS, PbSe, PbTe, Ag2S, and Ag2Se nanocrystals.

[0066] Preferably, lead chalcogenide nanocrystals or lead chalcogenide nanocrystal compositions exhibit absorption in the visible and near-infrared range, preferably in the range of 500 to 4500 nm, more preferably in the range of 500 to 2400 nm, more preferably in the range of 950 to 1600 nm, and more preferably in the range of 1350 to 1600 nm. In a preferred embodiment, lead chalcogenide nanocrystals or lead chalcogenide nanocrystal compositions exhibit absorption above 1300 nm.

[0067] The first organic ligand compound can form a complex with the nanocrystal by coordinating to the surface of the crystalline core of the nanocrystal. Generally, the first organic ligand compound coordinates to the surface of the nanocrystal via the functional group of the organic ligand as a Lewis acid (Z-type), Lewis base (L-type), or anionic (X-type) species. Generally, the organic ligand coordinates to the surface of the nanocrystal via the functional group of the organic ligand.

[0068] Typically, metal-containing compounds can be contacted with organic ligands in molar excess. For example, the molar ratio of metal atoms (from the metal-containing compound) to organic ligands may be in the range of 1:1.5 to 1:200, for example, 1:1.5 to 1:60.

[0069] The first organic ligand compound may be any suitable organic compound known in the art. In a preferred embodiment, the first organic ligand compound has a formula selected from the group consisting of RH2PO, R2HPO, R3PO, RPO(OH)2, or R2POOH, RH2P, R2HP, R3P, ROH, RCOOH, RCOOR', RSH, RNH2, R2NH, and R3N, where R and R' are each independently C1-C 24 Alkyl, C2~C 24Alkenil, C6~C 24 Selected from the group consisting of aryls and mixtures thereof. Preferably, the first organic ligand compound is a C2-C2 compound containing a functional group selected from the group consisting of aminos, thiols, hydroxyls, and carboxylic acids. 24 It is an organic compound. Examples of preferred first organic ligand compounds include, but are not limited to, aminobenzoic acid, dicarboxylic acid, aminoalkylcarboxylic acid, mercaptopropionic acid, mercaptobenzoic acid, thioalkane, dithioalkane, thiocarboxylic acid, thioglycolic acid, poly(ethylene glycol), bis(3-aminopropyl)-terminated poly(ethylene glycol), didodecyldimethylammonium bromide, n-dodecylammonium bromide, dodecyltrimethylammonium bromide, dimercaptosuccinic acid, oleic acid, oleylamine, bis(diphenylphosphin)methane, and alkylamine.

[0070] Preferably, the first organic ligand compound is an organic acid or an organic amine. Preferably, the first organic ligand compound is a compound selected from the group consisting of mercaptopropionic acid, mercaptobenzoic acid, thioglycolic acid, dimercaptosuccinic acid, oleic acid, and oleylamine. Preferably, the first organic ligand compound is oleic acid or oleylamine. In a preferred embodiment, the first organic ligand compound is oleic acid. In a preferred embodiment, the first organic ligand compound is oleylamine.

[0071] The exchange ligand precursor forms a ligand that can form a complex with the nanocrystal by coordinating to the surface of the crystalline core of the nanocrystal, as is known in the art. The exchange ligand precursor may include any suitable compound, such as an organic or inorganic compound.

[0072] In some embodiments, the exchange ligand precursor comprises a second organic ligand compound. A preferred second organic ligand compound is generally the same as that for the first organic ligand compound as described above. However, preferably, the first and second organic ligand compounds used in any individual reaction are different compounds.

[0073] In a particularly preferred embodiment, the second organic ligand compound is a C2-C2 compound containing a functional group selected from the group consisting of aminos and thiols. 24 It is an organic compound. Preferably, the second organic ligand compound is selected from the group consisting of 3-mercaptopropionic acid, thioglycerol, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, ethane-1,2-dithiol, meso-2,3-dimercaptosuccinic acid, dimercaptopropanol, 5-(trifluoromethyl)pyridine-2-thiol, 3-(trifluoromethyl)pyridine-2-thiol, butylamine, phenethylamine, benzylamine, amylamine, and mixtures thereof. In a preferred embodiment, the thiol contains an aromatic group. Preferably, the thiol is selected from the group consisting of 5-(trifluoromethyl)pyridine-2-thiol, 3-(trifluoromethyl)pyridine-2-thiol, and mixtures thereof.

[0074] In some embodiments, the exchange ligand precursor comprises an inorganic ligand precursor containing one or more inorganic compounds. For example, the inorganic ligand precursor may contain one or more metal halide compounds. Furthermore, the inventors have discovered that several inorganic compounds not previously used in the preparation of nanocrystals can be used as inorganic ligands. The use of these novel inorganic ligands results in nanocrystals with excellent photoelectronic properties.

[0075] While we do not wish to be bound by theory, the inorganic ligands of the present invention are thought to form a shell surrounding the nanocrystal during step b). Thus, the nanocrystal formed in the nanocrystalline composition of the first embodiment comprises a core-shell structure, the nanocrystal comprising a crystalline core containing (i) a metallic element and (ii) a pnictogenic or chalcogenic element, and a shell surrounding the crystalline core, the shell being formed from the inorganic ligand precursor during step b) of the reaction. The structure of the shell may be amorphous or crystalline. Preferably, the shell is crystalline and / or forms a lattice layer surrounding the crystalline core. As used herein, the term “lattice” is used to refer to a regular array of points describing the arrangement of particles forming a crystal.

[0076] Crystalline cores of all embodiments disclosed herein typically comprise (i) a metallic element and (ii) a pnictogenic or chalcogenous element. The crystalline core has a different chemical composition from the shell so that the shell surrounding the crystalline core is structurally distinct from the crystalline core. In other words, the crystalline core has a different chemical composition from the shell or lattice layer surrounding the crystalline core. Preferably, the crystalline core does not contain halides. Preferably, the crystalline core substantially comprises (i) a metallic element and (ii) a pnictogenic or chalcogenous element. More preferably, the crystalline core consists solely of (i) a metallic element and (ii) a pnictogenic or chalcogenous element.

[0077] The composition and structure of the inorganic ligand precursors and the resulting inorganic ligands in the shell may be the same or they may be different. In other words, the inorganic compounds in the inorganic ligand precursors can react with each other and / or with the nanocrystals to form a shell surrounding the crystalline core, whereby they can change from their original composition and structure that they had when first added to form the inorganic ligand precursors. For example, the inorganic compounds added to the inorganic ligand precursors may be CsI and ZnI2. These compounds may be present in the inorganic ligand precursors as ions in solution, or as CsI and ZnI2, or as CsZnI3. The inorganic compounds can then react with each other and / or with the nanocrystals to form a shell surrounding the crystalline core, and the shell can include amorphous or crystalline CsZnI3. In certain embodiments, the shell may include crystalline CsZnI3, optionally having a perovskite crystal structure, formed from an inorganic ligand precursor initially containing CsI and ZnI2.

[0078] Examples of suitable inorganic compounds in the inorganic ligand precursors include PbX2, CsX, InBr3, MgBr3, AgBr, FeX3, AsX3, TlX, CsZnI3, CsInBr3I, CsPbI3, ZnX2, or CsI (where X is a halide). In a preferred embodiment, the inorganic ligand precursor includes CsI and ZnI2. In a preferred embodiment, the inorganic ligand precursor includes CsI and InBr3. In particular, it should be noted that the present invention discloses the advantageous use of the novel pure inorganic ligands (a) CsI and ZnI2 and (b) AsI3 for colloidal lead-based and lead-free quantum dots. Both of these ligand systems, like other novel inorganic ligand systems disclosed herein such as TlX and CsInBr3I, result in complete surface passivation and high charge carrier mobility.

[0079] In one embodiment, the inorganic ligand precursor has the formula A p Zn q X rThe formula includes a metal halide (wherein A is a group IA metal or an organic ammonium salt, X is a halide, and p, q, and r are independently 1, 2, or 3). Examples of suitable organic ammonium salts include methylammonium and formamidinium.

[0080] In a preferred embodiment, the inorganic ligand precursor comprises a metal halide of formula AMX3 (wherein A is a group IA metal, thallium, or an organic ammonium salt, M is a metal having a +2 oxidation state, and X is a halide). In a preferred embodiment, the inorganic ligand precursor comprises a metal halide of formula AMX3 (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, potassium, lithium, thallium, and sodium, M is Pb, Sn, Cu, or Zn, and X is a halide). Preferably, the inorganic ligand precursor comprises a metal halide of formula AMX3 (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, potassium, lithium, and sodium, M is Pb or Zn, and X is a halide).

[0081] In a preferred embodiment, M is Pb. When M is Pb, the metal halide is preferably CsPbI3. In a preferred embodiment, M is Zn. When M is Zn, the metal halide is preferably CsZnI3.

[0082] In one embodiment, the inorganic ligand precursor is CsZn x As y The formula contains an inorganic compound I3 (wherein the sum of x and y is equal to 1, and y is in the range of 0 to 0.1). In one embodiment, y is less than 0.01 or in the range of 0.01 to 0.1.

[0083] In one embodiment, the inorganic ligand precursor is Cs3Zn x As yIt contains an inorganic compound I5 (wherein the formula, the sum of x and y is equal to 1, and y is in the range of 0 to 0.1). In one embodiment, y is in the range of 0.01 to 0.1.

[0084] In an alternative embodiment, the inorganic ligand precursor comprises an inorganic compound of the formula Cs3BX6 (wherein B is indium or antimony, and X is a halide).

[0085] In one embodiment, the metal halide has a perovskite crystal structure. As used herein, the term "perovskite" has its standard meaning in the art. Accordingly, the term "perovskite" is used to refer to inorganic compounds containing a three-dimensional crystal structure related to the three-dimensional crystal structure of CaTiO3, such as CsZnI3 and CsPbI3.

[0086] Further examples of suitable metal halide inorganic ligand precursors include inorganic compounds having a perovskite-like crystal structure, such as Cs3InX6, CsInX4, and Cs2InX5 (wherein X is a halide). In one embodiment, the inorganic ligand precursor comprises a metal halide of the formula Cs3InX6, CsInX4, or Cs2InX5 (wherein X is a halide). Preferably, the shell comprises CsInBr3I.

[0087] Step b) includes adding the exchange composition to the mixture. Upon addition of the exchange composition, a reaction generally occurs between the exchange ligand precursor and the nanocrystals capped with the first organic ligand compound.

[0088] When the replacement composition contains a second inorganic ligand compound, a reaction generally occurs between the second organic ligand compound and the nanocrystals capped with the first organic ligand compound. Specifically, a reaction occurs that removes the first organic ligand compound from the surface of the nanocrystals. The first organic ligand compound is replaced by the second organic ligand compound.

[0089] Therefore, this method is preferably, c) The process further includes replacing at least a portion of the first organic ligand compound coordinated to the surface of the crystalline core to form a nanocrystal comprising the crystalline core and a plurality of second organic ligand compounds coordinated to the surface of the crystalline core.

[0090] When the exchange composition contains an inorganic ligand precursor, a reaction generally occurs between the inorganic compound in the inorganic ligand precursor and the nanocrystal capped with the first organic ligand compound. Specifically, a reaction occurs that removes the first organic ligand compound from the surface of the nanocrystal. The first organic ligand compound is replaced by a ligand formed from the inorganic compound of the inorganic ligand precursor.

[0091] Therefore, this method is preferably, c) A step of forming a nanocrystal comprising a crystalline core and a shell surrounding the crystalline core by replacing at least a portion of a first organic ligand compound coordinated to the surface of a crystalline core, further comprising the step of forming the shell from an inorganic ligand precursor.

[0092] Preferably, step c) is carried out under inert conditions. Preferably, all of steps a), b) and c) are carried out under inert conditions.

[0093] Preferably, step c) includes stirring the mixture for at least 2 hours, preferably 2 to 18 hours, preferably 4 to 18 hours.

[0094] Preferably, if the replacement composition contains an inorganic ligand precursor, step c) comprises replacing at least 10%, preferably at least 20%, more preferably at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, and more preferably at least 90% of the first organic ligand compound coordinated to the surface of the crystalline core, as determined by thermogravimetric analysis (TGA) in air at a ramp rate of 10°C / min, to form a nanocrystal comprising a crystalline core and a shell surrounding the crystalline core, wherein the shell is formed from the inorganic ligand precursor.

[0095] The mass percentages of various ligands on the surface of nanocrystals are obtained from characteristic traces of the TGA curves of these nanocrystals, as illustrated in Figure 15. The first mass loss (generally between 0°C and 200°C) is presumed to correspond to the evaporation of the solvent. The second mass loss (generally between 200°C and 450°C) is presumed to correspond to the decomposition of organic ligands. The third mass loss (generally between 450°C and 750°C) is presumed to correspond to the decomposition of inorganic ligands. Further mass losses (generally above 750°C) are presumed to correspond to the decomposition of the crystalline core of the nanocrystal, such as PbS.

[0096] As described above, the inorganic compound in the inorganic ligand precursor is preferably a metal halide. Generally, the inorganic compound in the inorganic ligand precursor reacts to form a shell layer that partially surrounds the crystalline core of the nanocrystal. This shell may be amorphous or crystalline. Preferably, the shell is crystalline. When the shell is crystalline, it may have a perovskite crystal structure. The core-shell structure of the nanocrystal obtained in the nanocrystal composition is described above.

[0097] As described above, the composition and structure of the inorganic ligand obtained in the inorganic ligand precursor and the shell may be the same, or they may be different. Therefore, the inorganic ligand precursor and the shell may have the same composition. Therefore, the inorganic ligand precursor and the shell may have the same structure.

[0098] Preferably, the shell contains a metal halide. The shell may contain any suitable metal halide known in the art. Examples of suitable metal halides include PbX2, CsX, InBr3, MgBr3, AgBr, FeX3, AsX3, TlX, CsZnI3, CsInBr3I, CsPbI3, ZnX2, or CsI (wherein X is a halide). In a preferred embodiment, the shell contains CsI and ZnI2. In a preferred embodiment, the shell contains CsI and InBr3.

[0099] In one embodiment, the shell is, Formula A p Zn q X r The formula contains a metal halide (wherein A is a group IA metal or an organic ammonium salt, X is a halide, and p, q, and r are each independently 1, 2, or 3). Preferably, the organic ammonium salt is methylammonium or formamidinium.

[0100] In one embodiment, the shell comprises a metal halide of formula AMX3 (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, thallium, and sodium, M is Pb, Sn, Cu, or Zn, and X is a halide). Preferably, the shell comprises a metal halide of formula AMX3 (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, and sodium, M is Pb or Zn, and X is a halide). In a preferred embodiment, M is Pb. When M is Pb, the metal halide is preferably CsPbI3. In a preferred embodiment, M is Zn. When M is Zn, the metal halide is preferably CsZnI3.

[0101] In one embodiment, the shell is made of the formula CsZn x As y It contains a metal halide of I3 (wherein the formula, the sum of x and y is equal to 1, and y is in the range of 0 to 0.1). Preferably, y is in the range of 0.01 to 0.1.

[0102] In one embodiment, the shell is made of the formula Cs3Zn x As y It contains a metal halide of I5 (wherein the formula, the sum of x and y is equal to 1, and y is in the range of 0 to 0.1). Preferably, y is in the range of 0.01 to 0.1.

[0103] In one embodiment, the shell comprises a metal halide of the formula Cs3BX6 (wherein B is indium or antimony, and X is a halide).

[0104] In one embodiment, the shell comprises a metal halide of the formula CsInX4 (wherein X is a halide). Preferably, the shell comprises CsInBr3I.

[0105] In some embodiments, the shell has a perovskite crystal structure, and in particular, the shell is a shell of formula AMX3 as defined above. In particular, if the shell contains CsPbI3 and / or CsZnI3, the shell may contain a perovskite crystal structure.

[0106] While lead-based nanocrystals are presented in this application for their excellent performance, their use may be problematic in some industries due to their toxicity. There is an industrial need for alternative ligand systems that avoid the use of toxic heavy metals such as lead. The lead-free metal halides described above solve this problem, providing superior performance while exhibiting reduced toxicity.

[0107] When the inorganic ligand precursor is lead-free, it preferably comprises CsI and ZnI2. The mixture of these two components is thought to form CsZnI3 on ​​the nanocrystalline surface during step b), and the mixture is preferably prepared by dissolving ZnI2, CsI, and a stabilizer, such as ammonium acetate, in a solvent such as dimethylformamide (DMF). In an alternative embodiment where the inorganic ligand precursor is lead-free, the inorganic ligand precursor may comprise AsX3 or TlX (wherein X is a halide).

[0108] A possible way to determine whether any purification process has been performed is to examine whether the solution containing the ligand-exchanged nanocrystals contains impurities resulting from any other prior steps in the contact or reaction. These impurities may be salts of metal elements and organic ligands, or multiple free organic ligands remaining in the solution that are not coordinated to the surface of the crystalline core of the nanocrystals. Therefore, preferably, the mixture formed in step c) (containing the ligand-exchanged nanocrystals) a) Salts containing a metal element and a first organic ligand compound; and b) A second plurality of first organic ligand compounds which are not coordinated to the surface of the crystalline core. It further includes at least one of the following.

[0109] Preferably, the second plurality of first organic ligand compounds are free in the solution. Preferably, the second plurality of first organic ligand compounds are present in an amount of at least 2% by mass, preferably at least 3% by mass, preferably at least 4% by mass, preferably at least 5% by mass, preferably at least 10% by mass, and preferably at least 20% by mass, relative to the total mass of the first organic ligand compounds in the mixture. The total mass of organic ligands in the mixture includes the mass of organic ligands coordinated to the surface of the nanocrystals and the mass of the organic ligand salts in the solution. Again, this can be determined by the TGA in air at a ramp rate of 10°C / min.

[0110] In a preferred embodiment, forming the second composition further comprises adding a stabilizer to a polar solvent, the stabilizer being selected from the group consisting of sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, and mixtures thereof. Thus, the exchange composition preferably further comprises a stabilizer being selected from the group consisting of sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, trimethylsilyl halide, and mixtures thereof. In a particularly preferred embodiment, the stabilizer is selected from the group consisting of sodium acetate, ammonium acetate, trimethylsilyl halide, and mixtures thereof. The stabilizers, particularly sodium acetate and ammonium acetate, help remove long-chain organic ligands from the nanocrystals of the first nanocrystalline composition during the contact step and also help to provide colloidal stability during this ligand exchange process. Trimethylsilyl halide acts in a manner very similar to ammonium acetate and sodium acetate, and is a stronger chemical than ammonium acetate, which makes trimethylsilyl halide a particularly preferred stabilizer for concentrated nanocrystalline crude solutions.

[0111] In preferred embodiments, the nonpolar solvent has a relative permittivity at 20°C of less than 3, preferably less than 2.5. As used herein, the term “relative permittivity” refers to the ratio of the permittivity of a substance to the permittivity of vacuum, which is a dimensionless number. As defined in Christian Wohlfarth’s Permittivity (Dielectric Constant) of Liquids, the permittivity of a substance (often called the dielectric constant) is the ratio of the electric displacement D to the electric field strength E when an external electric field is applied to the substance. The relative permittivity is measured using a BI-870 Dielectric Constant Meter, available from Brookhaven Instruments, with a sensitivity range of 1 to 200. The instrument can be calibrated using liquids with known relative permittivity.

[0112] Nonpolar solvents include any C6-C 30 It may be an aliphatic or aromatic organic compound. Preferably, the nonpolar solvent is C6-C6 30 Amines, C6~C 30 Acid, C6~C 30 Phosphine, C6~C 30 The solvent is selected from the group consisting of ethers and mixtures thereof. Examples of suitable nonpolar solvents include octadecene, oleylamine, oleic acid, octylamine, butylamine, dioctylamine, diphenylphosphine, trioctylphosphine, heptadecane, hexadecane, and mixtures thereof.

[0113] Preferably, the polar solvent has a dielectric constant at 20°C greater than 3, more preferably greater than 5, and more preferably greater than 10. Examples of suitable polar solvents include octylamine, ethylene glycol, N,N-dimethylformamide, dimethyl sulfoxide, triphenylphosphine, 1,2-dichlorobenzene, hexamethylphosphoramide, trioctylphosphine, trioctylphosphine oxide, diphenyl ether, glycerol, propylene carbonate, dipropylene glycol, tetraethylene glycol, dihydrolevoglucocenone, dimethyl isosorbide, glycoflore, sulfolane, gammabutyrolactone, diformylxylose, and mixtures thereof.

[0114] The contact process may be carried out in several different forms, as described below. All of these methods are used to produce nanocrystals and are largely known in the prior art. In one embodiment, nanocrystals are produced by a simple addition method. In an alternative embodiment, nanocrystals are produced by a heating method, optionally combined with continuous addition. In an alternative embodiment, nanocrystals are produced by a high-temperature addition method, optionally combined with continuous addition. In an alternative embodiment, nanocrystals are produced by continuous addition. In an alternative embodiment, nanocrystals are produced by a combination of available methods. This method generally includes the steps of heating the components of the mixture to a crystal growth temperature in the range of 200°C to 350°C and maintaining this growth temperature for a predetermined length of time. However, this method is subject to variation depending on the order of addition of the components, the temperature at which each component is added, the timing, etc.

[0115] Typically, a metal-containing compound and several organic ligands are mixed in a suitable solvent until the reaction (i.e., salt formation) is substantially complete and a solution of the salt in the solvent is produced. At least one reagent may then be added to the salt solution and reacted to form nanocrystals and / or compositions thereof. The at least one reagent may be added with or without the solvent.

[0116] Various aspects of the method of the present invention, such as specific reagents and / or reaction conditions, may be modified to provide nanocrystals of a desired size to achieve desired optical properties, such as desired absorbance and luminescence (for example, for specific uses of nanocrystals).

[0117] For example, the reagents (particularly metal-containing compounds) used in this method may be modified to produce nanocrystals of a desired size in order to achieve desired optical properties, such as desired absorption and emission (for example, for specific uses of nanocrystals).

[0118] For example, the reaction conditions of this method may be modified to yield nanocrystals of a desired size in order to achieve desired optical properties, such as desired absorbance and emission (for example, for specific uses of nanocrystals).

[0119] In other words, the uses and methods of the present invention can be used to prepare nanocrystals having size-adjustable optical properties. Examples of modifiable reagents and / or reaction conditions are discussed herein.

[0120] The method of the present invention specifies at least one reagent. Two or more reagents containing the same pnictogen or chalcogen element, or different pnictogen or chalcogen elements, may be used.

[0121] Simple addition method A simple addition method for preparing nanocrystals is a preferred embodiment. This method generally involves contacting the components of the mixture at a temperature higher than 50°C in step a). Preferably, this contact step involves contacting a plurality of organic ligands, a metal-containing compound, and at least one reagent at a temperature of at least 50°C, preferably at least 60°C, preferably at least 70°C, preferably at least 80°C, and preferably at least 90°C.

[0122] In the first step of the simple addition method, the metal-containing compound and several organic ligands are preferably dissolved in a nonpolar solvent. Generally, this is done under an inert atmosphere. The solution is then preferably degassed. Typically, degassing is carried out at 50°C to 150°C, for example, about 100°C, for a period ranging from 0.5 to 1.5 hours.

[0123] In a further step, the temperature of the mixture may then be raised to above 200°C, which typically forms salts of the metal element and organic ligand. The temperature may be lowered to 50°C to 150°C, preferably about 100°C, for the addition of at least one reactant, which is generally added by injection. The reactants may preferably be added by a series of injections. The reaction is cooled after the final injection, preferably for about 3 to 15 minutes after the final injection.

[0124] In the simple additive method, preferably, the contact step is A) Mixing a metal-containing compound and a plurality of first organic ligand compounds in a nonpolar solvent to form a precursor mixture; B) Degassing the precursor mixture; C) Heating the precursor mixture to a temperature higher than 150°C; D) Cool the mixture to below 150°C and add at least one reactant to the precursor mixture. Includes.

[0125] Preferably, the contact step includes contacting a plurality of first organic ligand compounds, a metal-containing compound, and at least one reactant at a temperature of at least 50°C, preferably at least 60°C, preferably at least 70°C, preferably at least 80°C, and preferably at least 90°C.

[0126] Next, an exchange ligand (e.g., an inorganic ligand dissolved in a polar solvent) is added to the reaction mixture. The reaction mixture is then generally left to stand for several hours (e.g., 6 to 18 hours) with stirring in an inert atmosphere. In other words, in the simple addition method, the method preferably further includes stirring the mixture for at least 2 hours, preferably 2 to 18 hours, preferably 4 to 18 hours. This is usually part of step c), as described below. The temperature of the mixture is preferably in the range of 0°C to 150°C, preferably in the range of 20°C to 50°C.

[0127] The resulting nanocrystals contain exchange ligands (e.g., inorganic ligand shells) coordinated to the surface of the crystalline core of the nanocrystal. These nanocrystals are typically then washed and dissolved in further polar solvents for use as ink.

[0128] High temperature addition method As described in the review by Tamang et al. (Chem. Rev. 2016, 116, 10731~10819), in the case of the high-temperature addition method, separation of nucleation and growth can be achieved by rapid injection of the reagent into a high-temperature solvent that raises the concentration in the reaction flask above the nucleation threshold. This high-temperature injection results in a nucleation burst, which is rapidly quenched by two factors: (i) rapid cooling of the reaction mixture, enhanced by the fact that the injected solution is at room temperature; and (ii) a decrease in supersaturation due to precursor / monomer consumption during nucleation.

[0129] When the high-temperature addition method is used, the contact step is: A) A step of heating a precursor mixture to a first temperature, wherein the precursor mixture includes a metal-containing compound and a plurality of first organic ligand compounds, B) A step of adding at least one reactant to the precursor mixture, C) A step of maintaining a precursor mixture at a first temperature for a first predetermined period to form a plurality of seed particles. Includes.

[0130] The precursor mixture may be optionally degassed before heating to the first temperature. Typically, degassing is carried out at 50°C to 150°C, for example, approximately 100°C, for a period ranging from 0.5 to 1.5 hours.

[0131] Preferably, the first temperature is in the range of 275°C to 350°C, preferably in the range of 275°C to 325°C, and preferably in the range of 290°C to 310°C.

[0132] Preferably, before being added to the precursor mixture in step B), at least one reactant is at a temperature in the range of 5°C to 50°C, preferably in the range of 10°C to 35°C, preferably in the range of 15°C to 25°C, and preferably approximately room temperature.

[0133] Preferably, the first predetermined period is within the range of 10 to 60 minutes, preferably within the range of 15 to 50 minutes, preferably within the range of 20 to 40 minutes, and preferably within the range of 25 to 35 minutes.

[0134] Preferably, the contact step is D) A step of lowering the temperature of the precursor mixture to a second temperature, E) A step of continuously adding at least one reactant to the precursor mixture for a second predetermined period to produce the mixture of step a), It also includes.

[0135] Preferably, the second temperature is lower than the first temperature and within the range of 200°C to 275°C, preferably within the range of 225°C to 275°C, and preferably within the range of 240°C to 260°C.

[0136] Preferably, the second predetermined period is within the range of 60 to 180 minutes, preferably within the range of 90 to 150 minutes, preferably within the range of 100 to 140 minutes, and preferably within the range of 110 to 130 minutes.

[0137] Continuous addition method When the contact process uses a continuous additive method, the contact process is: A) A step of heating a precursor mixture to a third temperature, wherein the precursor mixture includes a metal-containing compound and a plurality of first organic ligand compounds, B) A step of continuously adding at least one reactant to the precursor mixture for a third predetermined period to produce the mixture of step a), Includes.

[0138] Preferably, the third temperature is in the range of 200°C to 275°C, preferably in the range of 225°C to 275°C, and preferably in the range of 240°C to 260°C.

[0139] Preferably, the third predetermined period is within the range of 60 to 180 minutes, preferably within the range of 90 to 150 minutes, preferably within the range of 100 to 140 minutes, and preferably within the range of 110 to 130 minutes.

[0140] heating method As outlined by Tamang et al., the heating method relies on achieving the degree of supersaturation necessary for homogeneous nucleation through in situ formation of reactive species during the supply of thermal energy.

[0141] In one embodiment, the contact step is: A) A step of adding at least one reactant to a precursor mixture, wherein the precursor mixture comprises a metal-containing compound and a plurality of first organic ligand compounds, B) A step of heating the precursor mixture to a fourth temperature. Includes.

[0142] The precursor mixture may be optionally degassed. Typically, degassing is carried out at a temperature of 50°C to 150°C, for example, approximately 100°C, for a period ranging from 0.5 to 1.5 hours.

[0143] Preferably, the fourth temperature is in the range of 200°C to 275°C, preferably in the range of 225°C to 275°C, and preferably in the range of 240°C to 260°C.

[0144] Preferably, the contact step is C) A step of maintaining the precursor mixture at a fourth temperature for a fourth predetermined period. It also includes.

[0145] Preferably, the fourth predetermined period is within the range of 60 to 180 minutes, preferably within the range of 90 to 150 minutes, preferably within the range of 100 to 140 minutes, and preferably within the range of 110 to 130 minutes.

[0146] Heating + continuous addition method When the heating method is used in combination with the continuous addition method, the contact step is: D) A fifth step of continuously adding at least one reactant to the precursor mixture for a predetermined period to produce the mixture of step a). It also includes.

[0147] Preferably, the fifth predetermined period is within the range of 60 to 180 minutes, preferably within the range of 90 to 150 minutes, preferably within the range of 100 to 140 minutes, and preferably within the range of 110 to 130 minutes.

[0148] According to a second aspect, the present invention provides a nanocrystalline composition that can be obtained by the method of the first aspect.

[0149] The method of the present invention is particularly useful for preparing nanocrystalline ink compositions, especially quantum dot ink compositions. These ink compositions have a wide range of applications in optoelectronic devices. These ink compositions are generally formed by dissolving nanocrystals containing inorganic ligands in a polar solvent. Prior to this dissolution, the nanocrystals are generally washed to remove impurities from the solution containing the ligand-exchanged nanocrystalline composition.

[0150] When the method of the present invention is used to produce nanocrystalline ink, this method is d) A step of washing the nanocrystalline composition with a solution containing at least one of acetone, methyl acetate, ethyl acetate, and acetonitrile, e) A step of dissolving the nanocrystalline composition in a second polar solvent to form a nanocrystalline ink composition. The following are further included. Preferably, the second polar solvent is selected from the group consisting of 2,6-difluoropyridine, gamma-butyrolactone, propylene carbonate, dimethylformamide, sulfolane, and combinations thereof.

[0151] Ink quality can be improved by using an in-situ ligand exchange process. Final QD inks produced by the in-situ method using conductive inorganic ligands exhibit superior performance in devices.

[0152] According to a third aspect, the present invention provides an ink composition comprising the nanocrystalline composition of the second aspect. The ink composition generally comprises nanocrystals of the nanocrystalline composition and a polar solvent used to dissolve the nanocrystals.

[0153] <Novel metal halide ligands> According to a fourth aspect, the present invention provides a nanocrystal comprising a crystalline core and a lead-free inorganic shell that at least partially surrounds the crystalline core. The present invention also provides a nanocrystal composition comprising a plurality of nanocrystals according to a fourth aspect. While not wishing to be bound by theory, the nanocrystals of the fourth aspect are thought to comprise a core-shell structure, and the nanocrystals are thought to comprise a crystalline core comprising (i) a metallic element and (ii) a pnictogenic or chalcogenous element, and a lead-free inorganic shell that at least partially surrounds the crystalline core. Preferably, the shell surrounds the crystalline core.

[0154] As used herein, the term “lead-free” refers to a component that does not contain lead. For example, “lead-free inorganic ligand precursor” refers to an inorganic ligand precursor that does not contain any lead-containing compounds.

[0155] As described above, in the fourth embodiment, the crystalline core typically comprises (i) a metallic element and (ii) a pnictogenic element or a chalcogenous element. Preferred embodiments of the metallic element, pnictogenic element and chalcogenous element are the same as those for each embodiment of the present invention.

[0156] As discussed above, there is an industrial need to provide nanocrystals, particularly nanocrystal ligand systems, that avoid the use of toxic heavy metals, such as lead. The inventors of this invention have found that lead-free inorganic compounds can be used as ligands on the surface of all types of nanocrystals to produce nanocrystals with improved performance. For example, the nanocrystals of this invention are stable in air for several months and have an excellent P / V ratio. To date, cesium-containing metal halide ligands have shown particularly remarkable performance.

[0157] Nanocrystals containing lead-free inorganic shells can be prepared by the methods of the present invention or by any other suitable method. For example, a method for preparing nanocrystals according to the fourth embodiment may include a step for purifying unmodified (pristine) nanocrystals. The simple addition method, heating method, high-temperature addition method, and continuous addition method described above are all suitable for preparing nanocrystals containing lead-free perovskite ligands, as understood in the art.

[0158] Preferably, the shell comprises a metal halide ligand. In a preferred embodiment, the shell comprises a metal halide selected from the group consisting of CsX, AsX3, TlX, CsZnI3, CsInBr3I, ZnX2, CsI, and mixtures thereof (wherein X is a halide).

[0159] In particular, the inventors have found that arsenic halide (AsX3) and thallium halide (TlX) can be used as inorganic ligands for nanocrystals. These inorganic ligands have also been found to form a shell layer surrounding a crystalline core. In a preferred embodiment, the shell comprises AsX3 or TlX. In one embodiment, the shell comprises AsX3. In one embodiment, the shell comprises TlX.

[0160] While we do not wish to be bound by theory, due to the high mobility of AsI3, nanocrystals containing AsX3 ligands also favorably result in very high charge carrier extraction, and therefore high external quantum efficiency (EQE) in devices. Preferably, X is Cl, Br, or I, and more preferably, X is I.

[0161] While we do not wish to be bound by theory, the use of thallium halide ligands is thought to result in lower dark currents in optical devices. Preferably, X is Cl, Br, or I, and more preferably I.

[0162] In a preferred embodiment, the shell comprises CsI and ZnI2. In a preferred embodiment, the shell comprises CsI and InBr3.

[0163] In a preferred embodiment, the shell is made of formula A p Zn q X r The formula contains a metal halide of (wherein A is a group IA metal or an organic ammonium salt, X is a halide, and p, q, and r are each independently 1, 2, or 3). Preferably, the organic ammonium salt is methylammonium or formamidinium.

[0164] In a preferred embodiment, the shell comprises a metal halide of formula AMX3 (wherein A is a group IA metal, thallium, or an organic ammonium salt, M is a metal having a +2 oxidation state, and X is a halide). In a preferred embodiment, the shell comprises a metal halide of formula AMX3 (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, thallium, and sodium, M is Sn, Cu, or Zn, and X is a halide). Preferably, the shell comprises a metal halide of formula AMX3 (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, and sodium, M is Zn, and X is a halide). Preferably, the metal halide is CsZnI3.

[0165] In a preferred embodiment, the shell is made of the formula CsZn x As y It contains a metal halide of I3 (wherein the formula, the sum of x and y is equal to 1, and y is in the range of 0 to 0.1). Preferably, y is in the range of 0.01 to 0.1.

[0166] In a preferred embodiment, the shell is made of the formula Cs3Zn x As y It contains a metal halide of I5 (wherein the formula, the sum of x and y is equal to 1, and y is in the range of 0 to 0.1). Preferably, y is in the range of 0.01 to 0.1.

[0167] In a preferred embodiment, the shell comprises a metal halide of the formula Cs3BX6 (wherein B is indium or antimony, and X is a halide). In a preferred embodiment, the shell comprises a metal halide of the formula Cs3InX6, CsInX4, or Cs2InX5 (wherein X is a halide).

[0168] In a preferred embodiment, the shell contains CsInBr3I.

[0169] As described above, the shell structure may be amorphous or crystalline. Preferably, the shell is crystalline and / or forms a lattice layer surrounding a crystalline core. As used herein, the term “lattice” is used to refer to a regular arrangement (array) of points that describe the arrangement of particles forming a crystal.

[0170] Preferably, the metal halide has a perovskite crystal structure.

[0171] The shell is typically positioned on the surface of a crystalline core and coordinated to the nanocrystalline core. Preferably, the shell surrounds the crystalline core. In a preferred embodiment, the crystalline core has a radius, and the shell has a thickness, the thickness of which is less than the radius of the crystalline core.

[0172] In a preferred embodiment, the nanocrystal has at least one dimension of less than 50 nm, or less than 40 nm, or less than 30 nm, or less than 20 nm, or less than 10 nm.

[0173] In a preferred embodiment, the nanocrystal is a semiconductor nanocrystal. In a preferred embodiment, the nanocrystal is a quantum dot.

[0174] According to a fifth aspect, the present invention provides a nanocrystalline composition comprising a plurality of nanocrystals according to a fourth aspect.

[0175] In a preferred embodiment, the nanocrystals of the nanocrystalline composition have an average particle size in the range of 2 nm to 20 nm, or 2 nm to 17 nm, or 2 nm to 15 nm, or 2 nm to 12 nm, or 2 nm to 10 nm, or 5 nm to 20 nm, or 5 nm to 17 nm, or 5 nm to 15 nm, or 5 nm to 12 nm, or 5 nm to 10 nm.

[0176] In preferred embodiments, the nanocrystals have a relative size dispersion of less than 25%, preferably less than 22%, preferably less than 20%, preferably less than 17%, preferably less than 15%, preferably less than 12%, and preferably less than 10%.

[0177] In preferred embodiments, the nanocrystalline composition exhibits an absorption full width at half maximum (FWHM) value of less than 250 nm, preferably less than 225 nm, preferably less than 200 nm, and preferably less than 175 nm. As used herein, the term “full width at half maximum” (or “FWHM”) refers to the width of the absorption peak at half its maximum amplitude. The FWHM value is preferably measured by UV-vis spectroscopy. In particular, the FWHM value of an absorption peak is determined by measuring the distance between two points on the y-axis (absorbance) where the intensity of the curve is half of its peak value.

[0178] In preferred embodiments, the nanocrystalline composition exhibits an emission full width at half maximum (FWHM) value of less than 250 nm, preferably less than 225 nm, preferably less than 200 nm, and preferably less than 175 nm.

[0179] According to a sixth aspect, the present invention provides an ink composition comprising a nanocrystalline composition and a polar solvent according to a fifth aspect.

[0180] Preferably, the polar solvent is selected from the group consisting of 2,6-difluoropyridine, gamma-butyrolactone, propylene carbonate, dimethylformamide, sulfolane, and combinations thereof.

[0181] The present invention also provides a device selected from the group consisting of IR sensors, photodetectors, sensors, solar cells, bioimaging or biosensing compositions, photovoltaic systems, displays, batteries, lasers, photocatalysts, spectrometers, injection compositions, field-effect transistors, light-emitting diodes, photonic or optical switching devices or metamaterials, fiber amplifiers, optical gain media, optical fibers, infrared LEDs, lasers, and electroluminescent devices, comprising a nanocrystalline composition according to a fourth embodiment.

[0182] In a preferred embodiment, IR sensors or photodetectors are modified for use as 3D cameras and 3D time-of-flight cameras in mobile and consumer goods, automotive, medical, industrial, defense, or aerospace applications. In a preferred embodiment, bioimaging or biosensing compositions are modified for use as biolabels or biotags in in vitro or ex vivo applications. In a preferred embodiment, infrared LEDs and electroluminescent devices are modified for use in telecommunications devices, night vision devices, solar energy conversion, thermoelectric, or energy generation applications.

[0183] According to a seventh aspect, the present invention provides the use of lead-free metal halide ligands in the preparation of nanocrystals. In other words, the seventh aspect provides a method for preparing nanocrystals, comprising the step of contacting nanocrystals with lead-free metal halide ligands. The nanocrystals may contain any type of unmodified (native) ligand, such as organic or inorganic ligands. These unmodified ligands coordinate to the surface of the crystalline core of the nanocrystal.

[0184] According to the eighth aspect, the present invention relates to a method for exchanging nanocrystalline ligands, (i) A first nanocrystalline composition comprising a plurality of nanocrystals, wherein the nanocrystals comprise a crystalline core and a plurality of unmodified ligand compounds coordinated to the surface of the crystalline core, (ii) A second composition comprising a lead-free inorganic ligand precursor, wherein the inorganic ligand precursor comprises one or more metal halide compounds. The present invention provides a method that includes a contact step, which involves bringing the two parts into contact.

[0185] Similar to the method of the first embodiment, this method generally involves a reaction between a metal halide compound in an inorganic ligand precursor and a nanocrystal, resulting in the formation of a shell layer located on the surface of a crystalline core. This shell layer is formed from the metal halide compound in the inorganic ligand precursor. Further information regarding this reaction is described above in relation to the first embodiment.

[0186] The method of the eighth embodiment is typically carried out under inert conditions, for example, under the conditions described above in relation to the first embodiment.

[0187] In preferred embodiments, the native ligand compound does not contain a metal halide compound. In other words, the native ligand compound and the inorganic ligand precursor are different. Preferably, the native ligand compound and the inorganic ligand precursor have different chemical compositions and / or different structures.

[0188] In a preferred embodiment, the unmodified ligand compound is an organic ligand compound. In this embodiment, the first nanocrystalline composition preferably further comprises a nonpolar solvent. The organic ligand compound is as described above in relation to the first organic ligand compound of the first embodiment. The preferred dielectric constant of the nonpolar solvent is the same for each embodiment of the present invention. The preferred nonpolar solvent is the same for each embodiment of the present invention.

[0189] In alternative embodiments, the unmodified ligand compound is an inorganic ligand compound. In this embodiment, the first nanocrystalline composition preferably further comprises a polar solvent. Preferably, the polar solvent has a dielectric constant at 20°C greater than 3, more preferably greater than 5, and more preferably greater than 10. Preferably, the polar solvent is selected from the group consisting of octylamine, ethylene glycol, N,N-dimethylformamide, dimethyl sulfoxide, triphenylphosphine, 1,2-dichlorobenzene, hexamethylphosphoramide, trioctylphosphine, trioctylphosphine oxide, diphenyl ether, glycerol, propylene carbonate, dipropylene glycol, tetraethylene glycol, dihydrolevoglucocenone, dimethyl isosorbide, glycoflor, sulfolane, gammabutyrolactone, diformylxylose, and mixtures thereof.

[0190] As described above, the inorganic compound in the inorganic ligand precursor is preferably a metal halide. Generally, the inorganic compound in the inorganic ligand precursor reacts to form a shell layer that partially surrounds the crystalline core of the nanocrystal. This shell may be amorphous or crystalline. Preferably, the shell is crystalline. When the shell is crystalline, it may have a perovskite crystalline structure. The core-shell structure of the nanocrystal obtained in the nanocrystalline composition is described above.

[0191] In a preferred embodiment, the inorganic ligand precursor includes CsX, AsX3, TlX, CsZnI3, CsInBr3I, ZnX2, or CsI (wherein X is a halide). These halides may all be the same halide; for example, X3 may represent I3, or a mixed halide, such as Br2I.

[0192] In a preferred embodiment, the inorganic ligand precursor comprises CsI and ZnI2.

[0193] In a preferred embodiment, the inorganic ligand precursor comprises CsI and InBr3.

[0194] In a preferred embodiment, the inorganic ligand precursor is of formula A p Zn q X r The formula includes a metal halide (wherein A is a group IA metal or an organic ammonium salt, X is a halide, and p, q, and r are independently 1, 2, or 3). Examples of suitable organic ammonium salts include methylammonium and formamidinium.

[0195] In a preferred embodiment, the inorganic ligand precursor comprises a metal halide of formula AMX3 (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, thallium, and sodium, M is Sn, Cu, or Zn, and X is a halide). In a preferred embodiment, the metal halide is CsZnI3. This CsZnI3 precursor is generally formed by adding CsI and ZnI2 to a non-solvent (e.g., DMF) to form a second composition, which preferably additionally comprises a stabilizer, such as ammonium acetate or other suitable compounds.

[0196] In a preferred embodiment, the inorganic ligand precursor comprises CsInBr3I.

[0197] In a preferred embodiment, the metal halide has a perovskite crystal structure.

[0198] As described above in relation to the first aspect, when the second composition is added, a reaction generally occurs between the inorganic compound in the inorganic ligand precursor and the nanocrystals capped with the organic ligand compound. Specifically, a reaction occurs that removes the organic ligand compound from the surface of the nanocrystals. The organic ligand compound is replaced by a ligand formed from the inorganic compound of the inorganic ligand precursor.

[0199] Therefore, the contact step further includes replacing at least a portion of the unmodified ligand compound coordinated to the surface of the crystalline core to form a nanocrystal comprising a crystalline core and a shell surrounding the crystalline core, wherein the shell is formed from an inorganic ligand precursor. Preferably, the contact step includes stirring the composition for at least 2 hours, preferably 2 to 18 hours, preferably 4 to 18 hours. Preferably, the contact step includes replacing at least 10%, preferably at least 20%, more preferably at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, and more preferably at least 90% of the unmodified ligand compound coordinated to the surface of the crystalline core, as determined by thermogravimetric analysis (TGA) in air at a ramp rate of 10°C / min, to form a nanocrystal comprising a crystalline core and a shell surrounding the crystalline core, wherein the shell is formed from an inorganic ligand precursor.

[0200] As in all aspects of the present invention, the shell may be amorphous or crystalline. Preferably, the shell is crystalline.

[0201] In preferred embodiments, the second composition further comprises a stabilizer selected from the group consisting of sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, trimethylsilyl halide, and mixtures thereof. Preferably, the stabilizer is selected from the group consisting of sodium acetate, ammonium acetate, trimethylsilyl halide, and mixtures thereof. The stabilizer is as described above in relation to the first embodiment. [Examples]

[0202] The following sections describe examples illustrating the method described herein.

[0203] While specific embodiments of the present invention are described below for illustrative purposes, it will be apparent to those skilled in the art that numerous modifications to the details of the present invention can be made without departing from the invention as defined in the appended claims.

[0204] Unless otherwise specified, in the following embodiments and throughout the specification, all parts and percentages are parts by mass or percentages by mass, respectively.

[0205] The absorption spectra of colloidal quantum dots or quantum dot films were obtained using a JASCO V-770 UV-Vis / NIR spectrometer, which is capable of providing measurements at wavelengths of 400–3200 nm.

[0206] XRD data were collected using a Panalytical X'Pert PRO MPD diffractometer at room temperature over the range of 10 < 2q < 90° using Cu Ka1 X radiation (l = 1.5406 Å). In each case, several drops of dispersed sample were placed on a glass microscope slide and evaporated. Data were analyzed using Rigaku SmartLab Studio II software, and search and matching were performed using the Crystallographic Open Database.

[0207] TEM and high-resolution transmission electron microscope (HRTEM) images were obtained using an FEI Talos F200X microscope equipped with an X-FEG electron source. Experiments were performed using an accelerating voltage of 200 kV and a beam current of approximately 5 nA. Images were recorded using an FEI CETA 4k×4k CMOS camera. In each case, several drops of dispersed quantum dots in solvent were dropped onto a carbon-coated copper grid and evaporated. The samples were used as is, or treated with acetone and then methanol to remove unwanted organic materials before imaging.

[0208] Thermogravimetric analysis (TGA) measurements were performed using a Hitachi STA200-RV TGA. Samples were prepared by first drying them under vacuum and then placing them in an alumina crucible. Measurements were performed at 25°C to 900°C under a nitrogen gas flow at a ramp rate of 10°C / min.

[0209] For ICP-TOF MS measurements, all imaging data were acquired using an ImageBIO 266nm laser ablation system equipped with a TwoVolume 3 sample chamber coupled to an ICP-ToF-MS 2R (TOFWERK, Thun) and dual concentric injectors (ESL, Bozeman). A summary of the instrument parameters can be seen in the table below. Aerosol particles were transported to the ICP by a 0.9 L / min He gas stream, and data acquisition was performed in standard mode without the addition of reaction gases.

[0210] [Table 1]

[0211] For the sample, a 10 nm quantum dot layer was selected for imaging due to the high Pb content of the sample. Three regions across the sample were measured (x=2.1 mm, y=0.2 mm, spacing between mapped regions=1 mm), with each region having a corresponding mapped area. Database line subtraction and mass calibration were performed on all images using TofWare (version 3.2.0).

[0212] (Example 1 - In situ preparation of PbS nanocrystals using PCsZnI3) To demonstrate the advantages of the in-situ ligand exchange process, PbS nanocrystals were synthesized in a large flask. The resulting mixture was divided into two parts, and in-situ ligand exchange (Example 1) and ex-situ purification and ligand exchange process (Comparative Example 2) were performed. Figure 2 shows a simplified diagram of the ligand exchange reaction.

[0213] All processing and ligand exchange procedures were performed in an N2-filled glove box using anhydrous solvent.

[0214] Part 1: 1.765 g of Pb3O4, 14.6 mL of oleic acid, and 200 mL of 1-octadecene were placed in a three-necked round-bottom flask under an inert atmosphere. The reaction mixture was degassed at 100°C for 1 hour, then the temperature was raised to 220°C to form lead oleate. Once a clear solution was formed, the reaction temperature was lowered to 100°C for the injection of the bis(trimethylsilyl) sulfide solution. To prepare the bis(trimethylsilyl) sulfide solution, first 1 mL of bis(trimethylsilyl) sulfide was dissolved in 50 mL of ODE, which is called solution A. Next, 17.8 mL of solution A was measured out and dissolved in 32.2 mL of ODE to prepare solution B. Once the reaction temperature stabilized at 100°C, 11.8 mL of solution A was injected into the reaction flask, followed by 12.8 mL of solution B after 8 minutes. Five minutes after the injection of solution B, an additional 12.8 mL of solution B is injected into the reaction medium, and finally, five minutes later, another 6.4 mL of solution B is injected to achieve the desired wavelength. Six minutes after the last injection, the reaction is cooled.

[0215] Part 2: Once the reaction is complete, half of the colloidal solution is weighed out and an ex-situ test is performed (Comparative Example 2). The remaining half (this example) is treated with a CsZnI3 inorganic ligand precursor prepared by dissolving 3.1 g of ZnI2, 2.5 g of CsI, and 305 mg of ammonium acetate in 100 mL of dimethylformamide (DMF). The solution is added to the crude reaction mixture, and phase transfer from the long-chain unstable organic ligand to the inorganic stable ligand is performed in the same flask. The reaction mixture is left to stand for 12 hours under an inert atmosphere with stirring. After 12 hours, there is a clear phase transfer of QDs from the ODE to the DMF phase, and these are then washed with 100 mL of hexane and then 100 mL of acetone by centrifugation at 6,000 RPM for 10 minutes. The resulting precipitate is dissolved in 2,6-difluoropyridine and used as an ink.

[0216] The same reaction can be carried out using heating and continuous injection, and it should be noted that the bis(trimethylsilyl) sulfide-ODE solution is added before heating or continuously during synthesis if the temperature is reduced to 100°C after the formation of lead oleate. Once the PbS QDs are synthesized by either of the above methods, the rest of the ligand exchange process (i.e., washing and ink formation) remains the same. This also applies to Comparative Example 2. As can be observed from the results of these examples, no particular method of contact step is required to form nanocrystals, and generally, contact of components is sufficient to produce the desired nanocrystals.

[0217] Figure 3 shows the absorption characteristics of the obtained QDs, which are also shown in Table 1 below. The unmodified (pristine) nanocrystals exhibit an absorption wavelength of 1450 nm, an FWHM of 92 nm, and a P / V of 6.4. After in-situ ligand exchange, the obtained QDs show significantly better solubility in 2,6-difluoropyridine compared to ex-situ ligand-exchanged QDs. Furthermore, the absorption wavelength and FWHM of the absorption peak remain the same, namely the absorption wavelength of 1448 nm and the FWHM of 91 nm.

[0218] (Comparative Example 2 - Ex-situ preparation of PbS nanocrystals using CsZnI3) Part 1: Same as Example 1.

[0219] Part 2: Once the reaction was complete, half of the colloidal solution was weighed out and tested ex-situ. The unpurified solution was purified twice by centrifugation at 6,000 RPM using a mixture of unpurified solution:acetone:isopropyl alcohol (IPA) in a 1:1:1 ratio. The precipitate was dissolved in octane to form a purified, unmodified nanocrystalline solution. This process was carried out in a nitrogen-filled glove box. For ex-situ ligand exchange, a CsZnI3 inorganic ligand precursor, prepared by dissolving 3.1 g of ZnI2, 2.5 g of CsI, and 305 mg of ammonium acetate in 100 mL of dimethylformamide (DMF), was added to 100 mL of a 7 mg / mL QD-octane solution. The reaction mixture was left to stand for 12 hours under an inert atmosphere with stirring. After 12 hours, there is a clear interphase transfer of QDs from the ODE to the DMF phase, which are then washed with 100 mL of hexane and then 100 mL of acetone by centrifugation at 6,000 RPM for 10 minutes. The resulting precipitate is dissolved in 2,6-difluoropyridine and used as an ink.

[0220] Referring to Figure 3, it can be observed that ex-situ ligand-exchanged QDs exhibit a 30 nm blue shift for every 10 nm increment of FWHM, indicating lower QD quality compared to in-situ QDs. In contrast, nanocrystals formed by the in-situ method show no blue shift or broadening of the FWHM, and these nanocrystals also have a higher P / V ratio than conventional ex-situ nanocrystals. This demonstrates that the in-situ ligand-exchange process results in better quality QDs.

[0221] [Table 2]

[0222] (Example 3 - In situ preparation of PbS nanocrystals using CsPbI3) Part 1: 0.88 g of Pb3O4, 7.3 mL of oleic acid, and 100 mL of 1-octadecene were placed in a three-necked round-bottom flask under an inert atmosphere. The reaction mixture was degassed at 100°C for 1 hour, then the temperature was raised to 220°C to form lead oleate. Once a clear solution was formed, the reaction temperature was lowered to 100°C for the injection of the bis(trimethylsilyl) sulfide solution. To prepare the bis(trimethylsilyl) sulfide solution, first 0.5 mL of bis(trimethylsilyl) sulfide was dissolved in 25 mL of ODE, which is called solution A. Next, 8.9 mL of solution A was measured out and dissolved in 16.1 mL of ODE to prepare solution B. Once the reaction temperature stabilized at 100°C, 5.9 mL of solution A was injected into the reaction flask, followed by 6.4 mL of solution B after 8 minutes. Five minutes after the injection of solution B, an additional 6.4 mL of solution B is injected into the reaction medium, and finally, five minutes later, an additional 3.2 mL of solution B is injected to achieve the desired wavelength. Six minutes after the last injection, the reaction is cooled.

[0223] Part 2: Once the reaction was complete, the reaction mixture was treated with a CsPbI3 inorganic ligand precursor prepared by dissolving 4.57 g of PbI2, 2.5 g of CsI, and 305 mg of ammonium acetate in 100 mL of dimethylformamide (DMF). The solution was added to the crude reaction mixture to allow phase transfer from the long-chain unstable organic ligand to the inorganic stable ligand in the same flask. The reaction mixture was left to stand for 12 hours under an inert atmosphere with stirring. After 12 hours, there was a clear phase transfer of QDs from the ODE to the DMF phase, which were then washed with 100 mL of hexane and purified by centrifugation at 6,000 RPM for 10 minutes using 100 mL of acetone. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0224] The same reaction can be carried out using the heating method and continuous injection, and it should be noted that the bis(trimethylsilyl) sulfide-ODE solution is added before heating or, if the temperature is reduced to 100°C after the formation of lead oleate, it is added continuously during the synthesis. Once PbS QDs are synthesized by either of the above methods, the rest of the ligand exchange process (i.e., washing and ink formation) remains the same.

[0225] Once clear phase separation occurs, these QDs are then washed with acetone and finally dissolved in a polar solvent such as 2,6-difluoropyridine, propylene carbonate, and / or DMF. Figure 4 shows a photograph of the phase-separated QDs in a centrifuge tube and a photograph of the final colloidal nanocrystalline ink. As is evident from the photograph of the colloidal ink, the QDs exhibit excellent colloidal stability in polar solvents after the ligand exchange process.

[0226] Nanocrystals were generated by the method of Example 3 to produce an ink composition having an absorption wavelength of approximately 1400 nm (Sample 3A) and an ink composition having an absorption wavelength of approximately 1200 nm (Sample 3B). This demonstrates the versatility of the method of the present invention. Furthermore, as shown in Figure 19, nanocrystalline ink compositions exhibiting absorption peaks at 1550 nm, 1650 nm, 2000 nm, and 2300 nm were generated according to Example 3. Different absorption peaks were obtained by changing the timing in Part 1. Here again, this further demonstrates the versatility of the method of the present invention.

[0227] The optical properties of the resulting inks are remarkable. The ink composition maintains its exciton properties with a high peak-to-valley ratio (P / V), which indicates the high quality of the ligand-exchanged colloidal QD ink. Table 2 below shows the optical air stability of sample 3B of these quantum dots.

[0228] As used herein, the term “peak-to-valley ratio” (or “P / V” ratio) refers to the ratio between the maximum absorption value of an absorption peak and the lowest absorption value within 150 nm of the maximum absorption peak. The P / V ratio is preferably measured by UV-vis spectroscopy.

[0229] (Comparative Example 4 - Ex-situ preparation of PbS nanocrystals using CsPbI3) Part 1: This is the same as Example 3.

[0230] Part 2: The unpurified solution was purified twice by centrifugation at 6,000 RPM using unpurified solution:acetone:IPA:1:1. The precipitate was dissolved in octane to form a purified QD solution. This process was carried out in a nitrogen-filled glove box. For ex-situ ligand exchange, a CsPbI3 inorganic ligand precursor prepared by dissolving 4.5 g PbI2, 2.5 g CsI, and 305 mg ammonium acetate in 100 mL of dimethylformamide (DMF) was added to a 100 mL solution of 7 mg / mL QD-octane solution. The reaction mixture was left to stand for 12 hours under an inert atmosphere with stirring. After 12 hours, there was a clear interphase transfer of QD from the ODE to the DMF phase, which was then washed with 100 mL of hexane and purified by centrifugation at 6,000 RPM for 10 minutes using 100 mL of acetone. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0231] Nanocrystals were produced by the method of Comparative Example 4 to create an ink composition having an absorption wavelength of approximately 1400 nm (comparative sample 4A) and an ink composition having an absorption wavelength of approximately 1520 nm (comparative sample 4B).

[0232] As is evident in Table 2 and Figure 7, in-situ ligand exchange QDs yield a higher P / V ratio compared to post-synthesis (ex-situ) ligand exchange with similar absorption wavelengths, indicating improved surface passivation and solubility of these in-situ QDs in solvents.

[0233]

Table 3

[0234] The aerobic stability of the nanocrystal ink composition sample 3B and the comparative sample 4B was also analyzed. As previously discussed, in-situ ligand exchange acts more efficiently than the ex-situ method, prevents surface oxidation of pristine QDs, and provides higher quality QDs than the ex-situ method. Figures 5 (in situ) and 6 (ex situ) show the absorption spectra of the QDs and how they change over time. Figures 5 and 6 show that the QDs produced according to the above method are stable. As is clear from Table 3 and Figures 5 and 6, the obtained ink formed by the method of the present invention exhibits air stability up to 97 days, which is the same as the ink formed by the ex-situ method (post-ligand exchange QD ink) because the CsPbI3 ligand system is very stable. Therefore, it can be concluded that the in-situ ligand exchange process produces a nanocrystal ink composition that is at least as air-stable as conventional nanocrystal inks while providing several additional advantages discussed in further sections.

[0235]

Table 4

[0236] Generally, the longer the absorption wavelength of the nanocrystals, the higher the P / V ratio. Therefore, since there is a large difference in absorption wavelength (>200 nm) between sample 3B and comparative sample 4B, the P / V ratios of these samples are not directly comparable.

[0237] (Example 5 - In-situ preparation of PbS nanocrystals using CsZnI3) Part 1: The same as Example 1.

[0238] Part 2: The same as Example 1.

[0239] The same type of in-situ ligand exchange was performed using a CsI and ZnI2 ligand system, which demonstrated successful phase transfer and resulted in high-quality quantum dot ink. CsI and ZnI2 led to successful phase transfer into the polar inorganic phase. The obtained QDs showed good colloidal stability in 2,6-difluoropyridine.

[0240] Figure 8 shows the absorption spectrum of PbS QDs that underwent in-situ ligand exchange based on CsI-ZnI2, which exhibits promising optical absorption properties. The same ligand exchange method can also be implemented for AsX3 (X = Cl, Br, I) and TlX (X = Cl, Br, I). Both of these materials offer unique advantages. For example, due to the high mobility of AsI3, its use often results in very high charge carrier extraction and thus nanocrystals with high external quantum efficiency in devices. On the other hand, the use of ligands based on thallium halides should result in suitable nanocrystals due to lower dark current.

[0241] (Example 6 - Ligand Exchange of Synthesized PbS Nanocrystals with AsI3) Part 1: The same as Example 1.

[0242] Part 2: The same as Comparative Example 2, except that the ligand exchange DMF solution contained 0.070 M AsI3 together with 21 mg of ammonium acetate in 7 mL of DMF, and the amount of nanocrystals was 7 mL at 7 mg / mL.

[0243] This test involved ex-situ ligand exchange with AsI3 ligands, demonstrating that AsI3 is an acceptable inorganic ligand. AsI3 can also be simply applied using an in-situ ligand exchange system. Figure 9 shows the absorption spectrum of PbS QDs based on AsI3 ligands in 2,6-difluoropyridine.

[0244] (Example 7 - Monitoring of CsI and ZnI2 ligand systems) To investigate the roles of CsI and ZnI2, controlled ligand exchange tests were conducted using CsI and ZnI2 to observe how these ligands behave individually and in combination.

[0245] Part 1: Same as Example 1.

[0246] Part 2: This is the same as Comparative Example 2, except that CsI, ZnI2, and CsZnI3 were used in separate ligand exchange reactions. For CsI, the same molar amount of CsI solution as in Comparative Example 2 was prepared, and for ZnI2, the same amount of ZnI2 was used in the exact same amount of DMF.

[0247] The inventors found that CsI as an inorganic ligand can induce phase separation from the non-polar phase to the polar phase of unmodified QDs, but the resulting QD ink precipitates and cannot form a suitable colloidal solution (Figure 10). When ZnI2 was used, a stable quantum dot ink was formed, but its optical properties were not as good as those obtained with ligand exchange using CsI and ZnI2, which is likely due to better surface passivation. This result suggests that CsI combined with ZnI2 forms a crystalline ligand structure with excellent optical properties around the nanocrystal.

[0248] Figure 10 shows photographs of ligand-exchanged QDs using CsI (left) and ZnI2 (right). It is clear that the QD ink is less stable when using the CsI ligand compared to when using both CsI and ZnI2 together, although the final ink was stable in the case of ZnI2, at least in the case of a diluted solution.

[0249] Table 4 shows the optical properties of the final inks formed using three different types of ligands. As is clear, the QD system based on the CsI-ZnI2(CsZnI3) ligand yields the best optical properties.

[0250] [Table 5]

[0251] (Example 8 - Fabrication of a photodiode device incorporating PbS-CsPbI3 prepared by in situ method) The in-situ ligand exchange base QD was also implemented in a photodiode device containing ITO / ZnO / PbS QD / organic ligand-exchanged PbS QD / MoO / Au. In this example, PbS ink was prepared using CsPbI3 as the ligand system using the method of Example 3 (in-situ ligand exchange).

[0252] Device Manufacturing Method: The manufacturing of the photodiode device involves several steps. First, a ZnO sol-gel solution is prepared by dissolving 1.09 g of zinc acetate dihydrate in 10 mL of methoxyethanol and 0.3 mL of ethanolamine. The ZnO solution is spin-coated onto a cleaned ITO substrate at 1,500 RPM for 60 seconds, followed by heating at 210°C for 15 minutes. A second layer of ZnO is then coated on top, followed by heating at 210°C for 30 minutes. The ZnO-coated film is then transferred to a nitrogen-filled glove box for PbS ink addition, and the PbS ink is spin-coated at 1,500 RPM for 60 seconds, followed by spin-coating of a further layer at the same spin rate, this time containing quantum dot ink with organic ligands coordinated to the surface. The device is then transferred to a thermal evaporator for MoO and Au deposition under shadow masking.

[0253] First, CsPbI3 was used as the inorganic ligand for the PbS QDs implemented in the photodiode devices. The nanocrystals in the photodiode devices were prepared using the in-situ (Example 8) or ex-situ (Comparative Example 9) method as described in the above examples, and the performance of each device was analyzed.

[0254] Figure 11 shows a comparison between an in-situ photodiode device and an ex-situ photodiode device. In particular, Figure 11 shows (a) the current density-voltage characteristics of photodiodes fabricated using in-situ and post-synthetically ligand-exchanged PbS QDs, and (b) the EQE spectra of photodiodes immediately after fabrication using in-situ and post-synthetically ligand-exchanged base QDs with the same device architecture in the same batch.

[0255] When in-situ ligand-exchanged QDs were used, a dark current density of 1.6E-5 A / cm² was achieved with an EQE of 16.6% at -1V. 2 This EQE spectrum shows the excitonic feature of PbS QDs at 1300 nm, indicating that the QDs maintained quantum confinement during the in-situ ligand exchange and the entire device fabrication process.

[0256] (Comparative Example 9 - Fabrication of a Photodiode Device Incorporating PbS-CsPbI3 Prepared by the Ex-situ Method) For comparison, ex-situ ligand-exchanged QDs were implemented in a photodiode device comprising ITO / ZnO / PbS QD / Organic ligand-exchanged PbS QD / MoO / Au. In this example, PbS ink was prepared using CsPbI3 as the ligand system using the method of Comparative Example 4 (ex-situ ligand exchange).

[0257] Device fabrication method: The same as in Example 8.

[0258] With the same type of device structure, this time with optimized post-synthetically ligand-exchanged QDs (ex-situ), the photodiode device showed relatively low device performance, with an EQE of 13.8%.

[0259] Table 5 summarizes the device data for in-situ versus post-synthesis ligand-exchanged QDs. As is clear, the in-situ ligand-exchanged QD devices exhibit significantly higher external quantum efficiency and similar dark current, demonstrating that the in-situ ligand-exchange process is not only cost-effective but also yields high-quality products, including QD inks and devices.

[0260] [Table 6]

[0261] (Example 10 - Fabrication of a photodiode device incorporating InAs-CsZnI3) To further expand this research, InAs QDs based on the CsI-ZnI2 ligand were also implemented in photodiode devices and showed promising performance.

[0262] The dark current and light current ratio (Table 6) clearly support the photodiode behavior of the device.

[0263] [Table 7]

[0264] In this example, CsZnI3 is demonstrated to be an acceptable inorganic ligand for InAs nanocrystals. Here, the InAs nanocrystals and devices containing these nanocrystals are prepared using the ex-situ method described below.

[0265] Step 1: Preparation of amorphous InAs clusters 3.0 mmol of In(OAc)3, 9.2 mmol of oleic acid, and 15 mL of heptadecane were weighed into a 250 mL three-necked flask and evacuated under vacuum (approximately 0.1 mbar) at 110 °C for 90 minutes. During this process, indium oleate was formed, and 9 mmol of acetic acid was collected in a cooling trap. In(OAc)3+R-COOH(R=C 17H 33 )→In-COOR+CH3COOH

[0266] The flask was switched to a nitrogen atmosphere and slowly cooled to room temperature. The flask was moved into a glove box. In the glove box, 0.96 mmol of tris(trimethylsilyl)arsenide ((TMSi)3As), 1.98 mmol of dioctylamine, and 2.5 mL of degassed heptadecane were weighed into a 10 mL vial and thoroughly vortexed. Under constant stirring, the indium oleate solution was mixed with the TMSi-As solution to produce a composition containing InAs clusters.

[0267] A composition containing InAs clusters, manufactured according to Step 1, was used in Step 2 as a composition containing group III-V clusters.

[0268] Step 2: Preparation of InAs nanocrystals having an absorption peak at approximately 1400 nm. In step 2, the preparation of InAs nanocrystals is divided into two crystal growth periods, followed by purification, ligand exchange with CsZnI3, ink formation, and then device fabrication. First, InAs nanocrystals exhibiting an absorption peak around 1100 nm are formed (first growth period of 4.5 hours). The UV-vis spectra of these nanocrystals are shown in Figure 2. Next, these nanocrystals are used to prepare nanocrystals exhibiting an absorption peak around 1400 nm (second growth period of 8 hours). The UV-vis spectra of these nanocrystals are shown in Figure 1. The total growth time is 12.5 hours.

[0269] 1100nm QD 0.4 mmol of In(OAc)3, 1.2 mmol of oleic acid, and 6 mL of heptadecane were weighed into a 250 mL three-necked flask and degassed under vacuum at 110 °C for 90 minutes (approximately 0.1 mbar). During this process, indium oleate was formed, and 1.2 mmol of acetic acid was collected in a cooling trap. In(OAc)3+R-COOH(R=C 17 H 33)→In-COOR+CH3COOH

[0270] The flask was switched to a nitrogen atmosphere and the temperature was maintained at 100°C. In a glove box, 0.32 mmol of (TMSi)3As, 0.56 mmol of dioctylamine, and 1 mL of degassed heptadecane were loaded into a syringe. This solution was added to the indium oleate solution at 100°C. A color change was observed immediately after the injection of the arsenic precursor solution. The solution was simply heated to 287°C, and once the temperature reached 287°C, growth was continued for 15 minutes. 10 mL of the amorphous cluster solution from Example 1 was loaded into a syringe (20 mm in diameter) and added at an injection rate of 2.230 mL / hour for approximately 4 hours and 30 minutes. After all of the amorphous cluster solution had been injected, the solution was maintained at 287°C for a further 10 minutes. During cluster addition, 270 μL of dilute HBr solution in acetone (prepared by diluting 40 μL of HBr in 2 mL of acetone solution) was added over 4 hours and 30 minutes. Heating was turned off, and the solution was allowed to cool naturally. The CQDs were transferred to a glove box for further use. CQD growth was monitored by taking aliquots and measuring the absorption spectra.

[0271] 1400nm QD Under vacuum, 6 mL of InAs CQD (50 mg / mL) (with maximum absorption around 1100 nm) and 4 mL of degassed heptadecane were placed in a connected 250 mL three-necked flask. The contents of the flask were evacuated under vacuum (approximately 0.1 mbar) at 100 °C for 30 minutes. The flask was then switched to nitrogen. 200 μL of dilute HBr solution was added to the flask and maintained at 100 °C for 10 minutes. The temperature was then raised to 285 °C. Once the temperature reached approximately 285 °C, amorphous InAs clusters were loaded into a syringe and added using a syringe pump at a rate of 1.16 mL / hour for approximately 8 hours. During cluster addition, 120 μL of dilute HBr was added over 8 hours. Heating was turned off and the solution was allowed to cool naturally. The CQD was transferred to a glove box for further use. CQD growth was monitored by taking aliquots and measuring the absorption spectrum.

[0272] Step 2 is the same as above, except that a second growth period of 14 hours and the addition of amorphous cluster solution at a rate of 1.16 mL / hour are required to prepare InAs nanocrystals having an absorption peak around 1550 nm to 1600 nm.

[0273] purification The contents of the flask were transferred to a glove box. 5 mL of hexane was added to the QDs, followed by 40 mL of acetone. The solution was divided into centrifuge tubes and centrifuged at 6000 RPM for 10 minutes. The clear supernatant was discarded, and the CQD pellet was redispersed in hexane. Acetone and IPA were added in a 2:1 volume ratio, and the quantum dots were again centrifuged at 6000 RPM for 10 minutes. The supernatant was discarded, and the CQD pellet was redispersed in n-octane. The CQD in the octane was centrifuged at 6000 RPM for 10 minutes to remove any solid impurities. The precipitate was discarded, and the clear QD solution was filtered through 0.1 μm PTFE to obtain the product.

[0274] Ligand exchange and ink formation After purification, the InAs nanocrystals contain oleic acid capping the surface and are dissolved in octane. This organic ligand is replaced with CsZnI3 as described below.

[0275] A CsZnI3 inorganic ligand precursor was prepared by dissolving 3.1 g of ZnI2, 2.5 g of CsI, and 305 mg of ammonium acetate in 100 mL of dimethylformamide (DMF). This precursor was added to 100 mL of a 7 mg / mL QD-octane solution. The reaction mixture was left to stand under an inert atmosphere with stirring for 12 hours. After 12 hours, there was a clear interphase transfer of QD from the ODE to the DMF phase, which was then washed with 100 mL of hexane and then 100 mL of acetone by centrifugation at 6,000 RPM for 10 minutes. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0276] Device Manufacturing The device stack structure can be described as ITO / ETL / active layer (InAs-CsZnI3 ink) / HTL / Au. ETL is used to refer to the electron transport layer. HTL is used to refer to the hole transport layer.

[0277] An advantage of perovskite-like systems based on cesium zinc halides is that they are heavy metal-free and therefore can be used for ligand exchange for environmentally friendly QD systems. For example, zinc cesium iodide can be used for InAs QD ligand exchange, where precursor solutions of cesium iodide and zinc iodide are dissolved in DMF, added to a hexane QD solution, and then stirred for 15 minutes. This results in a clear interphase transfer of the InAs QD from a nonpolar phase to a polar inorganic ligand system. Figure 12 shows the optical properties and atomic force microscopy images of the ligand-exchanged QD. As is clear, the resulting QD exhibits excitonic features along with high-quality ink (Figure 12a). Figure 12b shows a photograph of the film immediately after fabrication using spin-coating technology, along with an AFM image showing an RMS roughness of less than 10 nm.

[0278] Furthermore, dark current and EQE were measured for InAs-CsZnI3 nanocrystals. These results are shown in Table 7 and Figure 13 below. As is clear, when the CsZnI3 ligand was used, the dark current density was 170 μA / cm². 2 ~9.2 μA / cm 2 This resulted in a reduction and a significant increase in EQE from 15.3% to 16.5%. These results are promising and demonstrate excellent surface passivation using our novel CsZnI3 system for lead-free InAs QDs.

[0279] (Comparative Example 11 - Manufacturing of a photodiode device incorporating InAs-InBr3) For comparison, photodiode devices were prepared using a conventionally used InBr3 inorganic ligand system. To ensure consistency, these devices were fabricated from the same batch of InAs nanocrystals as in Example 10, but with a different ligand (InBr3) instead of CsZnI3. The device stack structure can be described as ITO / ETL / active layer (InAs-InBr3 ink) / HTL / Au. The performance of these devices is compared in Table 7 and Figure 13.

[0280] [Table 8]

[0281] These results are discussed in Example 10 above.

[0282] (Example 12 - In situ preparation of InAs nanocrystals using CsI-InBr3) In this example, CsZnI3 is demonstrated to be an acceptable inorganic ligand for nanocrystals, particularly InAs nanocrystals. Here, these InAs nanocrystals and devices containing these nanocrystals are prepared using the ex-situ method described below.

[0283] Furthermore, the photodiode device was also prepared using a novel CsI-InBr3 inorganic ligand system. In this example, the method was the same as in Example 10, but a new ligand (CsI-InBr3) was used instead of CsZnI3, and different ligand exchange and ink manufacturing processes were used as described below. The device stack structure can be described as ITO / ETL / active layer (InAs-(CsI-InBr3) ink) / HTL / Au.

[0284] Ligand exchange and ink formation After purification, the InAs nanocrystals contain oleic acid that caps the surface and is dissolved in octane. This organic ligand is replaced with CsI-InBr3 as described below.

[0285] The QD-octane mixture was treated with a CsInBr3I inorganic ligand precursor prepared by dissolving 90 mmol of InBr3, 90 mmol of CsI, and 77 mmol of ammonium acetate in 10 mL of dimethylformamide (DMF) in a reaction vessel. This solution was added to the QD-octane mixture to induce phase transfer from the long-chain unstable organic ligand to the inorganic stable ligand. The reaction mixture was left to stand under an inert atmosphere with stirring for 12 hours. After 12 hours, there was a clear phase transfer of QD from the ODE to the DMF phase, which was then washed with 100 mL of hexane and purified by centrifugation at 6,000 RPM for 10 minutes using 100 mL of acetone. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0286] Ligand exchange demonstrated successful phase transfer, resulting in a high-quality quantum dot ink. Therefore, the use of CsI-InBr3 as a ligand leads to successful phase transfer to the polar inorganic phase. The resulting QDs exhibited good colloidal stability in 2,6-difluoropyridine. The resulting solution forms a highly stable ink with concentrations higher than 80 mg / mL and a high P / V of 1.30, as shown by the absorption spectrum in Figure 14.

[0287] (Example 13 - Further analysis of PbS-CsPbI3 nanocrystals) PbS-CsPbI3 nanocrystals were prepared according to the method in Example 3.

[0288] TGA: The nanocrystals were further analyzed to determine the extent of ligand exchange, i.e., how much organic ligand remains on the nanocrystal surface after the inorganic ligand exchange reaction. This can be determined by TGA using the method described above (illustrated in Figure 15).

[0289] Samples were prepared by drying a small solution containing nanocrystals under high vacuum for several hours until further mass loss ceased and it became a powder. The samples were then transferred to a TGA furnace for measurement.

[0290] For this ligand exchange, Figure 15 suggests that the ratio of inorganic ligands to organic ligands on the surface of the nanocrystal is 19.3:0.9 (21.4:1) by mass. This indicates that the ligand exchange reaction involved exchanging 95.5% by mass of organic ligands coordinated to the surface of the crystalline core with the inorganic ligand system shell.

[0291] XRD: Figure 16 shows the XRD pattern of the PbS-CsPbI3 nanocrystal. The diffraction pattern demonstrates that the nanocrystal has a cubic crystal structure. However, due to the overlap between the cubic perovskite crystal structure and PbS, it is difficult to identify the presence of CsPbI3.

[0292] HRTEM: Figure 17 shows an HRTEM micrograph of a PbS-CsPbI3 nanocrystal. As can be observed from the micrograph, CsPbI3 forms a superlattice surrounding the nanocrystal surface.

[0293] ICP-TOF MS: The MS graph in Figure 18 supports the presence of CsPbI3 at this elemental ratio. The estimated Cs:I ratio is 1:3, which corresponds to the perovskite formula CsPbI3. This supports the formation of a core-shell structure in the nanocrystal. Furthermore, the uniform distribution of cesium and iodine demonstrates that the ligand uniformly coats the surface of the nanocrystal in this system, and also indicates that corresponding ligand systems in other examples also form a core-shell structure.

[0294] (References) King et al., Importance of QD Purification Procedure on Surface Absorbance of QDs and Performance of QD Sensitized Photoanode, J. Phys. Chem. C 2012, 116, 3349-3355 Chen et al., IEEE Access, Vol. 8, pp. 159415-159423, 2020. Tamang et al., Chem, Rev. 2016, 116, 10731-10819

Claims

1. A method for producing a nanocrystalline composition, comprising the following steps: a) A contact step carried out in a nonpolar solvent, Multiple first organic ligand compounds; Metal-containing compounds that include metallic elements; and At least one reagent containing a pnictogenic element or a chalcogen element This includes bringing them into contact to form a mixture containing multiple nanocrystals, The nanocrystal comprises a crystalline core and a plurality of first organic ligand compounds coordinated to the surface of the crystalline core, wherein the crystalline core comprises (i) a metal element and (ii) a pnictogenic element or a chalcogen element, and the process involves a contact step. b) A step of adding an exchange composition containing an exchange ligand precursor and a polar solvent to the mixture. Includes, A method in which there is no purification step between step a) and step b).

2. The metallic element is selected from the group consisting of Group I metals, Group II metals, Group III metals, Group IV metals, and mixtures thereof. The metal-containing compound is selected from the group consisting of elemental metals, metal halides, metal acetates, metal nitrates, metal carbonates, metal oleates, metal oxides, metal peroxides, metal alkoxides, metal hydroxides, metal sulfates, metal acetylacetonates, metal perchlorates, metal carboxylates, metal cyanides, or mixtures thereof. The method according to claim 1.

3. The method according to claim 1 or 2, wherein the metallic element is selected from the group consisting of indium, gallium, lead, and silver.

4. The metallic element is indium or gallium, and at least one reactant contains a pnictogenic element. The aforementioned pnictogen element is selected from the group consisting of phosphorus, arsenic, and antimony. The method according to any one of claims 1 to 3.

5. The metallic element is lead or silver, and at least one reactant contains a chalcogen element. The chalcogen element is selected from the group consisting of sulfur, selenium, and tellurium. The method according to any one of claims 1 to 4.

6. The first organic ligand compound is RH ２ PO, R ２ HPO, R ３ PO, RPO(OH) ２ , or R ２ POOH, RH ２ P, R ２ HP, R ３ P, ROH, RCOOH, RCOOR', RSH, RNH ２ , R ２ NH, and R ３ has a formula selected from the group consisting of N, In the formula, R and R' are independent of C １ ~C ２４ Alkyl, C ２ ~C ２４ Alkenil, C ６ ~C ２４ Selected from the group consisting of aryls and mixtures thereof, The method according to any one of claims 1 to 5.

7. The method according to any one of claims 1 to 6, wherein the exchange ligand precursor comprises a second organic ligand compound.

8. The method according to any one of claims 1 to 7, wherein the exchange ligand precursor comprises an inorganic ligand precursor comprising one or more inorganic compounds.

9. The method according to claim 8, wherein the inorganic ligand precursor comprises one or more metal halide compounds.

10. The inorganic ligand precursor is PbX ２ , CsX, InBr ３ MgBr ３ AgBr, FeX ３ AsX ３ , TlX, CsZnI ３ , CsInBr ３ I, CsPbI ３ , ZnX ２ Or containing CsI (wherein X is a halide), The inorganic ligand precursors are CsI and ZnI ２ including, or The inorganic ligand precursors are CsI and InBr ３ including, The method according to claim 9.

11. The inorganic ligand precursor is, Formula A ｐ Zn ｑ X ｒ The method according to claim 9, comprising a metal halide (wherein A is a group IA metal or an organic ammonium salt, X is a halide, and p, q, and r are each independently 1, 2, or 3).

12. The inorganic ligand precursor is given by formula AMX ３ (wherein A is a group IA metal, thallium, or an organic ammonium salt, M is a metal having a +2 oxidation state, and X is a halide) containing a metal halide, The inorganic ligand precursor is given by formula AMX ３ (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, potassium, lithium, thallium, and sodium, M is Pb, Sn, Cu, or Zn, and X is a halide) containing a metal halide, or The inorganic ligand precursor is given by formula AMX ３ (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, potassium, lithium, and sodium, M is Pb or Zn, and X is a halide) containing a metal halide, The method according to claim 9.

13. c) A step of forming a nanocrystal comprising a crystalline core and a shell surrounding the crystalline core by replacing at least a portion of a first organic ligand compound coordinated to the surface of a crystalline core, further comprising the step of forming the shell from an inorganic ligand precursor, Preferably, step c) includes stirring the mixture for at least 2 hours, preferably 2 to 18 hours, preferably 4 to 18 hours. Preferably, the shell contains a metal halide. The method according to any one of claims 1 to 12.

14. The mixture formed in step c) a) Salts containing a metal element and a first organic ligand compound; and b) A second plurality of first organic ligand compounds which are not coordinated to the surface of the crystalline core. It further includes at least one of the following: Preferably, a second plurality of the first organic ligand compounds are free in the solution. The method according to claim 13.

15. The replacement composition further comprises a stabilizer, The stabilizer is selected from the group consisting of sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, trimethylsilyl halide, and mixtures thereof, or The stabilizer is selected from the group consisting of sodium acetate, ammonium acetate, trimethylsilyl halide, and mixtures thereof. The method according to any one of claims 1 to 14.

16. Nonpolar solvents, C ６ ~C ３０ It is an aliphatic or aromatic organic compound, Optionally, the nonpolar solvent may be C ６ ~C ３０ Amine, C ６ ~C ３０ acid, C ６ ~C ３０ Phosphine, C ６ ~C ３０ Selected from the group consisting of ethers and mixtures thereof, The method according to any one of claims 1 to 15.

17. A nanocrystalline composition that can be obtained by the method described in any one of claims 1 to 16.

18. d) A step of washing the nanocrystalline composition with a solution containing at least one of acetone, methyl acetate, ethyl acetate, and acetonitrile, e) A step of dissolving the nanocrystalline composition in a second polar solvent to form a nanocrystalline ink composition. It further includes, Optionally, the second polar solvent may be selected from the group consisting of 2,6-difluoropyridine, gamma-butyrolactone, propylene carbonate, dimethylformamide, sulfolane, and combinations thereof. The method according to any one of claims 1 to 16.

19. An ink composition comprising the nanocrystalline composition defined in claim 18.

20. A nanocrystal comprising a crystalline core and a lead-free inorganic shell that at least partially surrounds the crystalline core.

21. The nanocrystal according to claim 20, wherein the shell comprises a metal halide ligand.

22. The shell is CsX, AsX ３ , TlX, CsZnI ３ , CsInBr ３ I, ZnX ２ It includes a metal halide selected from the group consisting of CsI and mixtures thereof (wherein X is a halide), or The shell is AsX ３ or including TLS, The shell, CsI and ZnI ２ including, or The shell, CsI and InBr ３ including, The nanocrystal according to claim 20 or 21.

23. Shell, Equation A ｐ Zn ｑ X ｒ The nanocrystal according to claim 20 or 21, comprising a metal halide of (wherein A is a group IA metal or an organic ammonium salt, X is a halide, p, q and r are each independently 1, 2 or 3, and optionally the organic ammonium salt is methylammonium or formamidinium).

24. The shell is, formula AMX ３ (wherein A is a group IA metal, thallium, or an organic ammonium salt, M is a metal having a +2 oxidation state, and X is a halide) containing a metal halide, The shell is, formula AMX ３ (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, thallium, and sodium, M is Sn, Cu, or Zn, and X is a halide) containing a metal halide, The shell is, formula AMX ３ (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, and sodium, M is Zn, and X is a halide) containing a metal halide, or Metal halides, CsZnI ３ That is, The nanocrystal according to claim 20 or 21.

25. The shell, expression CsZn ｘ As ｙ I ３ A metal halide containing (wherein the formula, the sum of x and y is equal to 1, y is in the range of 0 to 0.1, and optionally y is in the range of 0.01 to 0.1), or The shell, expression Cs ３ Zn ｘ As ｙ I ５ (In the formula, the sum of x and y is equal to 1, y is in the range of 0 to 0.1, and optionally y is in the range of 0.01 to 0.1) containing a metal halide, The nanocrystal according to claim 20 or 21.

26. The shell, expression Cs ３ BX ６ A metal halide containing (wherein B is indium or antimony and X is a halide), or The shell, expression Cs ３ InX ６ , CsInX ４ , or Cs ２ InX ５ Contains a metal halide (wherein X is a halide), or The shell, CsInBr ３ Including I, The nanocrystal according to claim 20 or 21.

27. A nanocrystalline composition comprising a plurality of nanocrystals according to any one of claims 20 to 26.

28. An ink composition comprising the nanocrystalline composition according to claim 27 and a polar solvent.

29. A device comprising the nanocrystalline composition described in claim 27, selected from the group consisting of an IR sensor, a photodetector, a sensor, a solar cell, a bioimaging or biosensing composition, a photovoltaic system, a display, a battery, a laser, a photocatalyst, a spectrometer, an injection composition, a field-effect transistor, a light-emitting diode, a photonic or optical switching device or metamaterial, a fiber amplifier, an optical gain medium, an optical fiber, an infrared LED, a laser, and an electroluminescent device, Optionally, the IR sensor or photodetector may be modified for applications as a 3D camera and 3D time-of-flight camera in mobile and consumer goods, automotive, medical, industrial, defense, or aerospace applications. Optionally, the bioimaging or biosensing composition may be modified for use as a biolabel or biotag in in vitro or ex vivo applications. Optionally, infrared LEDs and electroluminescent devices may be modified for use in telecommunications devices, night vision devices, solar energy conversion, thermoelectric, or energy generation applications.

30. A method for exchanging nanocrystalline ligands, (i) A first nanocrystalline composition comprising a plurality of nanocrystals, wherein the nanocrystals comprise a crystalline core and a plurality of unmodified ligand compounds coordinated to the surface of the crystalline core, and (ii) A second composition comprising a lead-free inorganic ligand precursor, wherein the inorganic ligand precursor comprises one or more metal halide compounds. A method comprising a contact step, which includes bringing into contact with a part.

31. The method according to claim 30, wherein the unmodified ligand compound is an organic ligand compound, and the first nanocrystalline composition further comprises a nonpolar solvent.

32. The inorganic ligand precursors are CsX and AsX ３ , TlX, CsZnI ３ , CsInBr ３ I, ZnX ２ , or containing CsI (wherein X is a halide), The inorganic ligand precursor is AsX ３ or including TLS, The inorganic ligand precursors are CsI and ZnI ２ including, or The inorganic ligand precursors are CsI and InBr ３ including, The method according to claim 30 or claim 31.

33. The inorganic ligand precursor is, Formula A ｐ Zn ｑ X ｒ The method according to claim 30 or 31, comprising a metal halide of (wherein A is a group IA metal or an organic ammonium salt, X is a halide, and p, q, and r are each independently 1, 2, or 3, and optionally the organic ammonium salt is methylammonium or formamidinium).

34. The inorganic ligand precursor is given by formula AMX ３ (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, thallium, and sodium, M is Sn, Cu, or Zn, and X is a halide) containing a metal halide, The inorganic ligand precursor is given by formula AMX ３ (wherein A is selected from the group consisting of cesium, methylammonium, rubidium, and sodium, M is Zn, and X is a halide) containing a metal halide, or Metal halides, CsZnI ３ That is, The method according to claim 30 or 31.

35. The inorganic ligand precursor is CsInBr ３ The method according to claim 30 or 31, comprising I.

36. A step of forming a nanocrystal comprising a crystalline core and a shell surrounding the crystalline core by replacing at least a portion of an unmodified ligand compound coordinated to the surface of a crystalline core, further comprising the step of forming the shell from an inorganic ligand precursor, The method according to any one of claims 30 to 35, wherein the contact step optionally includes stirring the composition for at least two hours, preferably two to eighteen hours, preferably four to eighteen hours.

37. The second composition further comprises a stabilizer, the stabilizer being selected from the group consisting of sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, trimethylsilyl halide, and mixtures thereof, or The stabilizer is selected from the group consisting of sodium acetate, ammonium acetate, trimethylsilyl halide, and mixtures thereof. The method according to any one of claims 30 to 36.

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