Novel synthesis of colloidal quantum dot ink and application of colloidal quantum dot ink in semiconductor equipment

Abstract

The present invention provides a method of preparing a nanocrystal composition comprising an inorganic ligand by one-pot synthesis. The invention also provides nanocrystals comprising the novel inorganic ligands and uses thereof. The invention also provides application of the novel inorganic ligand in preparation of nanocrystals.

Description

Technical Field

[0001] This invention generally relates to nanocrystals. Specifically, it relates to a method for preparing nanocrystal compositions comprising inorganic ligands through one-pot synthesis. The invention further extends to nanocrystals comprising novel inorganic ligands and their uses, as well as the use of novel inorganic ligands in the preparation of nanocrystals. Background Technology

[0002] Nanocrystals are useful in a wide range of applications, for example, because their optical properties can be fine-tuned to provide desired performance. The optical properties of nanocrystals (such as light absorption and emission characteristics) can be fine-tuned by controlling their size. The largest nanocrystals produce the longest wavelengths (and lowest frequencies), while the smallest nanocrystals produce shorter wavelengths (and higher frequencies). The size of nanocrystals can be controlled by methods used to fabricate them. This ability to fine-tune the optical properties of nanocrystals by controlling their size makes them suitable for a wide range of applications, including, for example, photodetectors, sensors, solar cells, bioimaging and biosensing, photovoltaics, 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] Primitive lead colloidal quantum dots (CQDs) and lead-free colloidal quantum dots (CQDs) are typically synthesized using wet chemistry, employing long-chain organic ligands to control the growth of nanocrystals and stabilize colloidal systems in solvents. To construct high-performance CQD devices, long-chain insulating organic ligands need to be replaced with shorter-chain organic ligands or conductive inorganic ligands to improve charge transfer in the system.

[0004] In existing methods, a crude mixture containing nanocrystals undergoes multiple purification steps prior to the ligand replacement reaction (ligand exchange) to remove byproducts of the initial nanocrystal synthesis from the mixture. Figure 1 A flowchart illustrating a prior art method for synthesizing nanocrystals is shown, demonstrating the formation of the original nanocrystals, purification steps, and subsequent ligand exchange reactions. Finally, an ink composition containing the nanocrystals is formed. The conductive semiconductor nanocrystals can then be used in optoelectronic devices.

[0005] The purification step has been previously reported as essential for obtaining quantum dots with optimal performance, 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 instance, King et al. explained the routine purification of QDs prior to sensitization, followed by alternating cycles of precipitation / redispersion in non-solvent / solvent environments. King et al. concluded that the purification step is crucial, and that with increased purification, the concentration of surface-bound QDs can potentially increase by up to 5-fold.

[0006] However, these purification steps are very time-consuming and use large amounts of solvent. Furthermore, it is believed that existing semiconductor nanocrystals contain partially oxidized surfaces, which leads to poor reproducibility and poor photoelectric properties.

[0007] Therefore, there is an unmet need for methods to prepare nanocrystals with reduced surface oxidation. Furthermore, there is an unmet need for methods to prepare nanocrystals more quickly and with less waste.

[0008] Furthermore, the use of lead and other heavy metals in nanocrystals presents problems in some industries due to their toxicity. However, current alternative materials and ligand systems are inferior to lead-based systems. Therefore, there is a further industrial need to provide alternative ligand systems that avoid the use of toxic heavy metals (such as lead) while also offering excellent optoelectronic properties. Summary of the Invention

[0009] The inventors have discovered a method for preparing nanocrystals with improved optical properties. In particular, the inventors have discovered that the method for preparing nanocrystals without omitting a purification step after the initial synthesis step and before the ligand exchange reaction achieves improved optical properties in the resulting nanocrystals.

[0010] Therefore, according to a first aspect, the present invention provides a method for preparing a nanocrystalline composition, the method comprising:

[0011] a) A contacting step is performed in a nonpolar solvent, the contacting step comprising contacting the following substances to form a mixture comprising multiple nanocrystals:

[0012] Various first organic ligand compounds;

[0013] Metallic compounds containing metallic elements; and

[0014] A reagent containing at least one pnictogen or chalcogen element.

[0015] The nanocrystals comprise a crystal nucleus and a variety of first organic ligand compounds surface-coordinated to the crystal nucleus, wherein the crystal nucleus comprises (i) a metallic element, and (ii) a nitrogen group element or a chalcogen group element, and

[0016] b) Add the exchange composition, which includes the exchange ligand precursor and the polar solvent, to the mixture.

[0017] There is no purification step between step a) and step b).

[0018] According to a second aspect, the present invention provides a nanocrystal composition that can be obtained by the method of the first aspect.

[0019] According to a third aspect, the present invention provides an ink composition comprising the nanocrystalline composition of the second aspect. The ink composition typically comprises nanocrystals of the nanocrystalline composition and a polar solvent for dissolving the nanocrystals. Attached Figure Description

[0020] Figure 1 A simplified flowchart of a prior art method for quantum dot synthesis is shown and compared with the method of the present invention.

[0021] Figure 2 A simplified diagram of an in-situ ligand exchange method for PbS quantum dots using novel inorganic ligands is shown.

[0022] Figure 3 The absorption spectra of quantum dots at different stages of synthesis are shown, and the methods of the present invention are compared with those of the prior art for quantum dot synthesis.

[0023] Figure 4 A photograph of quantum dots phase-separated in a polar inorganic phase and the resulting ink is shown.

[0024] Figure 5 The absorption spectrum of nanocrystals prepared (in situ) according to the method of the present invention and its variation over time are shown.

[0025] Figure 6 The absorption spectra of nanocrystals prepared according to existing methods (ex-situ) and their changes over time are shown.

[0026] Figure 7 The absorption spectra of in-situ and ex-situ PbS quantum dots with CsPbI3 as inorganic ligands are shown.

[0027] Figure 8 The absorption spectrum of in-situ PbS quantum dots with CsZnI3 as inorganic ligand is shown.

[0028] Figure 9 The absorption spectrum of PbS quantum dots with AsI3 as the inorganic ligand is shown.

[0029] Figure 10 A photograph of a QD ink using CsI (left) and ZnI2 (right) as inorganic ligands for ligand exchange is shown.

[0030] Figure 11 The current density-voltage characteristics of photodiode devices fabricated using in-situ PbS QD and out-of-situ PbS QD are shown, as well as the EQE spectra of photodiode devices fabricated using in-situ QD and out-of-situ QD in the same batch.

[0031] Figure 12 The following are shown: (a) the absorption spectrum of InAs QD with ligand exchange in 2,6-difluoropyridine, and (b) a photograph of the fabricated membrane and an AFM image showing the membrane quality.

[0032] Figure 13 The following are shown: (a) the current density-voltage characteristics of photodiode devices fabricated using in-situ InAs QD and out-of-situ InAs QD, and (b) the EQE spectra of photodiode devices fabricated in the same batch using in-situ QD and out-of-situ QD with the same device structure.

[0033] Figure 14 The absorption spectrum of InAs nanocrystal ink using the CsI-InBr3 ligand system is shown.

[0034] Figure 15 Thermogravimetric analysis (TGA) curves of InAs nanocrystals are shown, illustrating how the degree of inorganic ligand exchange can be measured.

[0035] Figure 16 X-ray diffraction (XRD) data of PbS nanocrystals with CsPbI3 ligands are shown.

[0036] Figure 17 A high-resolution TEM micrograph of PbS nanocrystals with CsPbI3 ligands is shown, illustrating the formation of a superlattice structure on the surface of the nanocrystals.

[0037] Figure 18 Inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF MS) of PbS nanocrystals with CsPbI3 ligands was shown, confirming the presence of CsPbI3.

[0038] Figure 19 The absorption spectrum of nanocrystals prepared (in situ) according to the method of the present invention is shown. Detailed Implementation

[0039] When describing various aspects of the invention, the terminology used will be interpreted according to the following definitions unless the context otherwise requires.

[0040] As used in the specification and appended claims, the singular forms “a,” “an,” and “the” include both singular and plural indicators, unless the context clearly specifies otherwise. For example, “nanocrystal” refers to one or more nanocrystals. For example, “indium-containing compound” refers to one or more indium-containing compounds. When used in conjunction with inclusive language, references to quantities include those containing the stated quantity or combinations of quantities greater than the stated quantity.

[0041] As used herein, the terms “comprising,” “comprises,” and “comprised of” are synonymous with “including,” “includes,” or “containing,” and are inclusive or open-ended, and do not exclude additional, unlisted components, elements, or method steps. The terms “comprising,” “comprises,” and “comprised of” also include the term “consisting of.”

[0042] As used herein, the term "and / or," when used in a list of two or more items, means that any one of the listed items may be used individually, or any combination of two or more of the listed items may be used. For example, if a list is described as including groups A, B, and / or C, then the list may include 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.

[0043] As used herein, unless otherwise expressly stated, all numbers, such as those representing numerical values, ranges, or percentages, may be understood to begin with the word “about,” even if the term is not explicitly stated.

[0044] As used herein, when referring to a measurable value (such as a parameter, quantity, duration, etc.), the term "about" indicates that the value includes the standard deviation of the error of the apparatus or method used to determine the value. The term "about" is intended to include variations of + / -10% or less, + / -5% or less, or + / -0.1% or less in a particular value, provided such variations are suitable for implementation in this disclosure. It should be understood that the value referred to by the modifier "about" is itself specifically disclosed.

[0045] The range of values ​​listed by endpoints includes all integers, and, where appropriate, fractions within that range (e.g., when dealing with multiple elements, 1 to 5 may include 1, 2, 3, 4, and when dealing with measurements, it may include 1.5, 2, 2.75, and 3.80). The listing of endpoints also includes the endpoint values ​​themselves (e.g., 1.0 to 5.0, inclusive of 1.0 and 5.0). Any range of values ​​listed herein is intended to include all subranges contained therein.

[0046] Unless otherwise defined, all terms used in this disclosure, including technical and scientific terms, shall have the meanings commonly understood by one of ordinary skill in the art to which this disclosure pertains. Further guidance is provided by including definitions of terms used in the specification to better understand the teachings of this invention. All publications cited herein are incorporated by reference.

[0047] As used herein, unless otherwise defined, the term "composition" can be open-ended or closed-ended. For example, a "composition" may include specific materials, i.e., nanocrystals, and additional non-specific materials, or may consist of specific materials, i.e., substantially excluding non-specific materials.

[0048] In situ synthesis

[0049] According to a first aspect, the present invention provides a method for preparing a nanocrystalline composition, the method comprising:

[0050] a) A contacting step is performed in a nonpolar solvent, the contacting step comprising contacting the following substances to form a mixture comprising multiple nanocrystals:

[0051] Various first organic ligand compounds;

[0052] Metallic compounds containing metallic elements; and

[0053] A reagent containing at least one nitrogen group element or chalcogen group element.

[0054] The nanocrystals comprise a crystal nucleus and a variety of first organic ligand compounds surface-coordinated to the crystal nucleus, wherein the crystal nucleus comprises (i) a metallic element, and (ii) a nitrogen group element or a chalcogen group element, and

[0055] b) Add the exchange composition, which includes the exchange ligand precursor and the polar solvent, to the mixture.

[0056] There is no purification step between step a) and step b).

[0057] The method of this invention does not include the purification steps of prior art, and in turn surprisingly offers several advantages. In other words, this invention provides a one-pot method for preparing nanocrystals.

[0058] Existing ink-forming methods are time-consuming and expensive due to the reproducible processing / purification of nanocrystals. Furthermore, the purification process can lead to surface oxidation, resulting in poor reproducibility and photoelectric properties in the nanocrystal ink formation. The inventors of this invention have discovered a simple and cost-effective ligand exchange method using an in-situ technique, wherein the ligand exchange is performed directly on the synthesized pristine nanocrystals without prior purification. The inventors determine that this method improves the optical properties of the resulting nanocrystals and reduces the cost of nanocrystal ink preparation by 30% due to reduced solvent, energy, and labor usage, as well as a simpler scaling-up process. Moreover, the ink prepared using this technique exhibits good colloidal stability in polar solvents, as well as excellent photoelectric properties and high reproducibility.

[0059] These results are surprising because it is generally accepted in the field that purification is a necessary step after the initial formation of nanocrystals in order to obtain optimal performance. Traditionally, pristine nanocrystals, especially quantum dots (QDs), are purified and dissolved in nonpolar solvents using solvent / antisolvent methods, and then subjected to a ligand exchange process with more conductive short-chain organic or inorganic ligands to obtain nanocrystal inks for use in devices.

[0060] Traditional solvent / antisolvent purification methods are not only time-consuming but also inefficient and costly. It is undesirable to be bound by the theory that post-synthesis solvent / antisolvent purification of the original nanocrystals also leads to surface oxidation of the nanocrystals, resulting in poor device performance and an inconsistent shift of the absorption spectrum to lower wavelengths. In this paper, we introduce in-situ ligand exchange, where exchanged ligands are introduced into the crude solution containing the original nanocrystals without any intermediate purification steps. As mentioned above, this method provides a more cost-effective and efficient solution. This invention provides a stable colloidal ink composition containing nanocrystals with improved performance through a method that is not only cheaper but also easier to scale. The final ink composition is then typically used to manufacture devices via a single-step deposition technique.

[0061] The advantages of this method include: preventing surface oxidation of nanocrystals, providing higher quality nanocrystal compositions and equipment, significantly reducing production costs, providing a less time-consuming method, and providing a method that is easy to scale up.

[0062] As used herein, the term “nanocrystal” refers to crystal particles having at least one size measurement of less than 100 nanometers (nm).

[0063] As used herein, the term "semiconductor nanocrystal" is used interchangeably with the term "quantum dot" and is used to refer to semiconductor crystalline materials that exhibit a quantum confinement effect, which allows them to mimic the properties of atoms. Quantum dots can also be referred to 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.

[0064] As used herein, the term "Group I metal" refers to metals in Groups IA and IB of the periodic table. For example, Group IA metals can be lithium, sodium, potassium, rubidium, or cesium, and Group IB metals can be copper, silver, or gold.

[0065] As used herein, the term "Group II metal" refers to metals in Group IIA or Group IIB of the periodic table. For example, Group IIA metals may be beryllium, magnesium, calcium, strontium, or barium, while Group IIB metals may be zinc, cadmium, or mercury.

[0066] As used herein, the term "Group III metal" refers to metals belonging to Group 13 of the periodic table. For example, Group III metals can be aluminum, gallium, indium, or thallium.

[0067] As used herein, the term "Group IV metal" refers to metals in Group 14 of the periodic table. For example, Group IV metals can be silicon, germanium, tin, or lead.

[0068] As used herein, the terms "Group V elements" and "Nitrogen Group elements" refer to elements in Group 15 of the periodic table. For example, Nitrogen Group elements can be nitrogen, phosphorus, arsenic, antimony, or bismuth.

[0069] As used herein, the term "indium pnictogenide semiconductor nanocrystal" refers to semiconductor nanocrystals containing indium and nitrogen group elements.

[0070] As used herein, the terms "Group VI elements" and "chalcogen elements" are used to refer to elements in Group 16 of the periodic table. For example, chalcogen elements can be oxygen, sulfur, selenium, tellurium, or polonium.

[0071] As used herein, the term "ligand" refers to a compound capable of forming a complex with nanocrystals through surface coordination. Nanocrystals typically comprise crystal nuclei on the order of tens of nanometers in size. They are usually stabilized into colloidal solutions by surface-capped ligands, which can coordinate with the crystal nuclei as Lewis acidic (Z-type), Lewis basic (L-type), or anionic (X-type) substances.

[0072] As used herein, the term "organic compound" refers to a compound containing a carbon atom covalently bonded to other atoms. As used herein, the term "C" refers to a compound containing a carbon atom covalently bonded to other atoms. x -C y "Organic compounds, where x and y are integers, are used to refer to organic compounds containing at least x and no more than y carbon atoms."

[0073] As used in this article, the term "inorganic compound" refers to compounds other than organic compounds.

[0074] As used herein, the term "purification step" refers to any method that results in the separation of nanocrystals in solution, or any method that reduces the ratio of impurities to nanocrystals in a mixture. As used herein, the term "impurity" refers to components in a solvent other than the nanocrystals (excluding the solvent itself). For example, an impurity can be a free organic or inorganic ligand in solution, or a salt thereof. In particular, the term "purification step" includes purification steps disclosed in the art, such as cycles of alternating precipitation / redispersion in a non-solvent / solvent environment. These purification steps typically involve precipitating the nanocrystals by centrifugation with a solvent / non-solvent, followed by redispersion in a solvent.

[0075] As used herein, the letter "X" refers to a halide. X is a halide, preferably Cl, Br, or I. X may or may not be a mixed halide; for example, X4 may be I4 or Br3I.

[0076] Preferably, the nanocrystals prepared by the method of the first aspect are semiconductor nanocrystals, such as colloidal quantum dots. More specifically, the present invention prepares colloidal quantum dot inks.

[0077] 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 no other steps are taken between steps a) and b). Preferably, the method is a one-pot process. 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).

[0078] As used herein, the term "reaction vessel" refers to a container that isolates one reaction (e.g., a contact step) from another reaction, or a container that provides space in which a reaction may occur. As used herein, the term "step b) immediately after step a)" refers to a series of steps in which no other reactive steps occur between steps a) and b). As used herein, the terms "one-pot" and "in-situ" refer to reactions in which all steps are carried out in the same reaction vessel. As used herein, the term "component" refers to a compound that forms a mixture.

[0079] Preferably, steps a) and b) are carried out under inert conditions. For example, the reaction can be carried out under argon or nitrogen. Typically, inert conditions are used to avoid surface oxidation of the nanocrystals. After the ligand exchange reaction with the exchange ligand, the nanocrystals can be exposed to air because they become less sensitive to oxygen.

[0080] The metallic element of this invention can be any suitable metallic element used to prepare nanocrystals, as understood by those skilled in the art. For example, the metallic element can be any suitable post-transition metal element or transition metal element.

[0081] Preferably, the metal element is selected from Group I metals, Group II metals, Group III metals, Group IV metals, and mixtures thereof, and the metal compound is selected from 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 indium, gallium, lead, and silver.

[0082] In a preferred embodiment, step a) includes contacting a plurality of first organic ligand compounds, a metal-containing compound containing a metal element, and at least one reagent containing a nitrogen group element, wherein the metal element is indium or gallium. In other words, in a preferred embodiment, the metal element is indium or gallium, and at least one reagent contains a nitrogen group element. As shown in Example 10, InAs quantum dots prepared by the method of the present invention can be used to produce photodiode devices with excellent EQE characteristics.

[0083] In a preferred embodiment, the metal element is indium. When the metal element is indium, preferably, the metal-containing compound is selected from 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.

[0084] In another embodiment, the metal element is gallium. When the metal element is gallium, preferably, the metal-containing compound is selected from gallium halide, gallium acetate, gallium nitrate, gallium carbonate, gallium oleate, and mixtures thereof.

[0085] The inventors have discovered that, according to the method of the present invention, a range of suitable nitrogen group elements can be used to prepare nanocrystals. Preferably, the nitrogen group elements are selected from phosphorus, arsenic, and antimony.

[0086] In one embodiment, the nitrogen group element is phosphorus. When the nitrogen group element is phosphorus, at least one reagent can be any suitable phosphorus-containing precursor, but preferably at least one reagent is selected from triphenylphosphine, tris(trimethylsilyl)phosphine, tris(dimethylamino)phosphine, triethylphosphine, tributylphosphine, tricyclohexylphosphine, trioctylphosphine, and mixtures thereof.

[0087] In a preferred embodiment, the nitrogen group element is arsenic or antimony. In a particularly preferred embodiment, the nitrogen group element is arsenic. When the nitrogen group element is arsenic, preferably, at least one reagent is selected from arsenic halides, tris(trimethylsilyl)arsenic, arsenic oxide, arsenic sulfate, and mixtures thereof. In a preferred embodiment, the nitrogen group element is antimony. When the nitrogen group element is antimony, preferably, at least one reagent is antimony halide or tris(trimethylsilyl)antimony.

[0088] When the metal element is indium or gallium, the method of the present invention is particularly suitable for preparing binary, ternary, and quaternary nanocrystals. For example, the method is suitable for preparing indium-based nitride and gallium-based nitride nanocrystals. For example, the present invention can be used to prepare InAs, InSb, InAsSb, GaAs, GaSb, InGaAs, InGaSb, and InGaAsSb nanocrystals.

[0089] In one embodiment, at least one reagent comprises a nitrogen group element, and the contacting step may further include contacting other components with a compound selected from secondary amines, zinc carboxylate, and mixtures thereof, preferably wherein the compound is dioctylamine. This compound is used to further enhance the shape control of the nanocrystals by complexing with the nitrogen group element-containing compound. In this way, the reactivity of the nitrogen group element-containing compound can be reduced, thereby allowing for better control over the size and size distribution of the nanocrystals. Preferably, the compound is used when the nitrogen group element-containing compound is tris(trimethylsilyl)arsenic or tris(trimethylsilyl)antimony, because these compounds are particularly reactive.

[0090] In one embodiment, step a) includes contacting a plurality of first organic ligand compounds, a metal-containing compound comprising a metal element, and at least one reagent comprising a chalcogenide element, wherein the metal element is lead or silver. In other words, in a preferred embodiment, the metal element is lead or silver, and at least one reagent comprises a chalcogenide element.

[0091] 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 PbO, Pb3O4, PbO2, and mixtures thereof. In another embodiment, the metal-containing compound is lead acetate.

[0092] In another embodiment, the metal element is silver. Preferably, the metal-containing compound is selected from silver acetate, silver nitrate, silver oxide, silver halides, and mixtures thereof.

[0093] The inventors have discovered that, according to the method of the present invention, a range of suitable chalcogen elements can be used to prepare nanocrystals. Any suitable chalcogen element precursor can be used. Preferably, the chalcogen elements are selected from sulfur, selenium, and tellurium.

[0094] In one embodiment, the chalcogen element is sulfur. Examples of suitable sulfur-containing agents include bis(trialkylsilyl) sulfide compounds, such as bis(trimethylsilyl) sulfide, bis(triethylsilyl) sulfide and bis(tripropylsilyl) sulfide, thioacetamide, trioctylphosphine sulfide, tributylphosphine sulfide, alkyl-substituted and / or phenylthiourea compounds, such as N,N'-disubstituted and N,N,N'-trisubstituted thioureas, alkyl-substituted thioamide compounds, elemental sulfur, mercaptopropylsilane, thio-triphenylphosphine (“S-TPP”), thio-trioctylamine (“S-TOA”), ammonium sulfide, sodium sulfide, hexamethylenetetramine, octylthiol, decaalkylthiol, dodecathiol, hexadecylthiol and mixtures thereof.

[0095] In another embodiment, the chalcogenide is selenium. Examples of suitable selenium-containing compounds include bis(trimethylsilyl)selenide, trioctylphosphine selenide, 1-octadecene selenide, tributylphosphine selenide, selenium-triphenylphosphine, and mixtures thereof.

[0096] In another embodiment, the chalcogenide is tellurium. Examples of suitable tellurium-containing compounds include tellurium powder, triphenylphosphine telluride, trioctylphosphine telluride, tributylphosphine telluride, and mixtures thereof.

[0097] When the metallic element is lead or silver, the method of the present invention is applicable to the preparation of binary and ternary nanocrystals. For example, the method is applicable to the preparation of lead-based chalcogenide nanocrystals and silver-based chalcogenide nanocrystals. For example, the present invention can be used to prepare PbS, PbSe, PbTe, Ag₂S, and Ag₂Se nanocrystals.

[0098] Suitablely, lead-based chalcogenide nanocrystals or compositions thereof exhibit absorption in the visible and near-infrared range, suitably in the range of 500 nm to 4500 nm, preferably in the range of 500 nm to 2400 nm, more preferably in the range of 950 nm to 1600 nm, and most preferably in the range of 1350 nm to 1600 nm. In a preferred embodiment, the lead-based chalcogenide nanocrystals or compositions thereof exhibit absorption greater than 1300 nm.

[0099] The first organic ligand compound can form a complex with the nanocrystal by surface coordination with the crystallization nucleus of the nanocrystal. Typically, the first organic ligand compound coordinates with the surface of the nanocrystal as a Lewis acid (Z-type), Lewis basic (L-type), or anionic (X-type) substance through the functional group of the organic ligand.

[0100] Typically, metal-containing compounds can be contacted with a molar excess of organic ligands. For example, the molar ratio of metal atoms (from the metal-containing compound) to organic ligands can be from 1:1.5 to 1:200, such as from 1:1.5 to 1:60.

[0101] The first organic ligand compound can be any suitable organic compound known in the art. In a preferred embodiment, the first organic ligand compound has a chemical formula selected from: RH2PO, R2HPO, R3PO, RPO(OH)2 or R2POOH, RH2P, R2HP, R3P, ROH, RCOOH, RCOOR', RSH, RNH2, R2NH and R3N, wherein R and R' are each independently selected from C1-C1. 24 Alkyl, C2-C 24 alkenyl, C6-C 24 Aryl groups and mixtures thereof. Preferably, the first organic ligand compound is a C2-C compound containing a functional group selected from amino, thiol, hydroxyl, and carboxylic acid groups. 24 Organic compounds. Examples of suitable first organic ligand compounds include, but are not limited to, aminobenzoic acid, dicarboxylic acid, aminoalkylcarboxylic acid, mercaptopropionic acid, mercaptobenzoic acid, thioalkanes, dithioalkanes, thiocarboxylic acids, mercaptoacetic acid, poly(ethylene glycol), poly(ethylene glycol) bis(3-aminopropyl)-terminated, bis(dodecyl dimethyl ammonium bromide, n-dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dimercaptosuccinic acid, oleic acid, oleylamine, bis(diphenylphosphine)methane, and alkylamines.

[0102] Preferably, the first organic ligand compound is an organic acid or an organic amine. More preferably, the first organic ligand compound is selected from compounds including mercaptopropionic acid, mercaptobenzoic acid, mercaptoacetic acid, dimercaptosuccinic acid, oleic acid, and oleylamine. More 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.

[0103] As is known in the art, exchange ligand precursors form ligands capable of forming complexes with nanocrystals through surface coordination with the crystallization nucleus of nanocrystals. Exchange ligand precursors can comprise any suitable compound, such as organic or inorganic compounds.

[0104] In some embodiments, the exchange ligand precursor comprises a second organic ligand compound. The preferred second organic ligand compound is generally the same as the first organic ligand compound described above. However, preferably, the first and second organic ligand compounds used in any individual reaction are different compounds.

[0105] In a particularly preferred embodiment, the second organic ligand compound is a C2-C compound containing a functional group selected from amino and thiols. 24 An organic compound. Preferably, the second organic ligand compound is selected from 3-mercaptopropionic acid, thioglycerol, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 1,2-ethanedithiol, meso-2,3-dimercaptosuccinic acid, dimercaprol, 5-(trifluoromethyl)pyridine-2-thiol, 3-(trifluoromethyl)pyridine-2-thiol, butylamine, phenethylamine, benzylamine, pentylamine, and mixtures thereof. In a preferred embodiment, the thiol comprises an aryl group. Preferably, the thiol is selected from 5-(trifluoromethyl)pyridine-2-thiol, 3-(trifluoromethyl)pyridine-2-thiol, and mixtures thereof.

[0106] 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 comprise one or more metal halides. 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 exhibiting excellent photoelectric properties.

[0107] Without being bound by theory, it is considered that the inorganic ligands of the present invention form a shell encapsulating the nanocrystals during step b). In this way, the nanocrystals formed in the nanocrystal composition of the first aspect comprise a core-shell structure, wherein the nanocrystals include a crystallizing nucleus and a shell encapsulating the crystallizing nucleus, wherein the crystallizing nucleus contains (i) a metallic element and (ii) a nitrogen group element or a chalcogenide group element, wherein the shell is formed by the inorganic ligand precursor during step b) of the reaction. The shell structure can be amorphous or crystalline. Preferably, the shell is crystalline and / or forms a lattice layer encapsulating the crystallizing nucleus. As used herein, the term "lattice" is used to describe an ordered lattice describing the arrangement of particles forming a crystal.

[0108] The crystal nuclei disclosed herein for all purposes generally comprise (i) a metallic element and (ii) a nitrogen group element or a chalcogenide element. The crystal nucleus has a different chemical composition from the shell, such that the shell covering the crystal nucleus is structurally different from the crystal nucleus. In other words, the crystal nucleus has a different chemical composition from the shell or lattice layer covering the crystal nucleus. Preferably, the crystal nucleus does not contain halides. Preferably, the crystal nucleus substantially comprises (i) a metallic element and (ii) a nitrogen group element or a chalcogenide element. More preferably, the crystal nucleus is composed of (i) a metallic element and (ii) a nitrogen group element or a chalcogenide element.

[0109] The composition and structure of the inorganic ligand precursor and the resulting inorganic ligand can be the same or different. In other words, the inorganic compounds in the inorganic ligand precursor can react with each other and / or with nanocrystals to form a shell encapsulating the crystal nucleus, thereby altering their original composition and structure when initially added to form the inorganic ligand precursor. For example, the inorganic compounds added to the inorganic ligand precursor can be CsI and ZnI2. These compounds can exist as ions in solution, or as CsI and ZnI2, or as CsZnI3 in the inorganic ligand precursor. The inorganic compounds can then react with each other and / or with nanocrystals to form a shell encapsulating the crystal nucleus, wherein the shell contains amorphous CsZnI3 or crystalline CsZnI3. In a specific embodiment, the shell can contain crystalline CsZnI3, optionally having a perovskite crystal structure, formed from the inorganic ligand precursor initially containing CsI and ZnI2.

[0110] Examples of suitable inorganic compounds as 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 comprises CsI and ZnI2. In a preferred embodiment, the inorganic ligand precursor comprises CsI and InBr3. Of particular note is the advantageous use of novel pure inorganic ligands (a) CsI and ZnI2, and (b) AsI3, for colloidal lead-based quantum dots and lead-free quantum dots. These two ligand systems, as well as other novel inorganic ligand systems disclosed herein, such as TlX and CsInBr3I, provide complete surface passivation and high charge carrier mobility.

[0111] In one implementation, the inorganic ligand precursor includes formula A p Zn q X r The metal halide, wherein A is a Group IA metal or an organoammonium salt, X is a halide, and p, q, and r are each independently 1, 2, or 3. Examples of suitable organoammonium salts include methylammonium and formamidinium.

[0112] In a preferred embodiment, the inorganic ligand precursor comprises a metal halide of the formula AMX3, wherein A is a Group IA metal, thallium, or an organoammonium 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 the formula AMX3, wherein A is selected from 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 the formula AMX3, wherein A is selected from cesium, methylammonium, rubidium, potassium, lithium, and sodium, M is Pb or Zn, and X is a halide.

[0113] 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.

[0114] In one implementation, the inorganic ligand precursor includes the formula CsZn. x As y An inorganic compound of I3, wherein the sum of x and y equals 1, and y is from 0 to 0.1. In one embodiment, y is less than 0.01 or is from 0.01 to 0.1.

[0115] In one implementation, the inorganic ligand precursor includes the formula Cs3Zn. x As yAn inorganic compound of I5, wherein the sum of x and y equals 1, and y is from 0 to 0.1. In one embodiment, y is from 0.01 to 0.1.

[0116] In another embodiment, the inorganic ligand precursor comprises an inorganic compound of the formula Cs3BX6, wherein B is indium or antimony and X is a halide.

[0117] In one embodiment, the metal halide has a perovskite crystal structure. As used herein, the term "perovskite" takes on its standard meaning in the art. Thus, the term "perovskite" is used to refer to inorganic compounds containing a three-dimensional crystal structure associated with CaTiO3, such as CsZnI3 and CsPbI3.

[0118] Other examples of suitable inorganic metal halide ligand precursors include inorganic compounds having a perovskite-like crystal structure, such as Cs3InX6, CsInX4, and Cs2InX5, where X is a halide. In one embodiment, the inorganic ligand precursor comprises a metal halide of the formula Cs3InX6, CsInX4, or Cs2InX5, where X is a halide. Preferably, the shell comprises CsInBr3I.

[0119] Step b) involves adding the exchange composition to the mixture. Once the exchange composition is added, a reaction typically occurs between the exchange ligand precursor and the nanocrystals capped with the first organic ligand compound.

[0120] When the exchange composition contains a second inorganic ligand compound, a reaction typically occurs between the second organic ligand compound and the nanocrystals capped with a first organic ligand compound. Specifically, a reaction occurs to remove the first organic ligand compound from the surface of the nanocrystals. The first organic ligand compound is then replaced by the second organic ligand compound.

[0121] Therefore, the method preferably further includes:

[0122] c) Replace at least a portion of the first organic ligand compound that is surface-coordinated with the crystallization nucleus to form a nanocrystal comprising the crystallization nucleus and a plurality of second organic ligand compounds that are surface-coordinated with the crystallization nucleus.

[0123] When the exchange composition contains an inorganic ligand precursor, a reaction typically occurs between the inorganic compound in the inorganic ligand precursor and the nanocrystals capped with a first organic ligand compound. Specifically, a reaction occurs to remove the first organic ligand compound from the surface of the nanocrystals. The first organic ligand compound is replaced by a ligand formed from the inorganic compound of the inorganic ligand precursor.

[0124] Therefore, the method preferably further includes:

[0125] c) Displacing at least a portion of a first organic ligand compound that is surface-coordinated with the crystallization nucleus to form a nanocrystal comprising a crystallization nucleus and a shell encapsulating the crystallization nucleus, wherein the shell is formed from an inorganic ligand precursor.

[0126] Preferably, step c) is performed under inert conditions. Preferably, steps a), b) and c) are all performed under inert conditions.

[0127] Preferably, step c) includes stirring the mixture for at least 2 hours, more preferably 2 to 18 hours, and more preferably 4 to 18 hours.

[0128] Preferably, when the exchange 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%, more preferably at least 90% of a first organic ligand compound that is surface-coordinated with the crystal nucleus to form a nanocrystal comprising a crystal nucleus and a shell encapsulating the crystal nucleus, wherein the shell is formed by the inorganic ligand precursor, which is determined by thermogravimetric analysis (TGA) in air at a heating rate of 10 °C / min.

[0129] like Figure 15 As shown, the weight percentage of different ligands on the surface of the nanocrystals is derived from the characteristic trajectories of the TGA curves of these nanocrystals. It is assumed that the first mass reduction (typically between 0°C and 200°C) corresponds to solvent evaporation. It is assumed that the second mass reduction (typically between 200°C and 450°C) corresponds to the decomposition of organic ligands. It is assumed that the third mass reduction (typically between 450°C and 750°C) corresponds to the decomposition of inorganic ligands. It is assumed that any further mass reduction (typically above 750°C) corresponds to the decomposition of the nanocrystal nuclei (e.g., PbS).

[0130] As described above, the inorganic compound in the inorganic ligand precursor is preferably a metal halide. The inorganic compound in the inorganic ligand precursor typically reacts to form a shell partially encapsulating the crystal nucleus of the nanocrystals. This shell can be amorphous or crystalline. Preferably, the shell is crystalline. When the shell is crystalline, it can have a perovskite crystal structure. The core-shell structure of the nanocrystals in the resulting nanocrystal composition is as described above.

[0131] As mentioned above, the composition and structure of the inorganic ligand precursor in the shell and the resulting inorganic ligand can be the same or different. Therefore, the inorganic ligand precursor and the shell can have the same composition. Therefore, the inorganic ligand precursor and the shell can have the same structure.

[0132] Preferably, the shell comprises a metal halide. The shell may comprise 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, where X is a halide. In a preferred embodiment, the shell comprises CsI and ZnI2. In a preferred embodiment, the shell comprises CsI and InBr3.

[0133] In one implementation, shell-enclosed A p Zn q X r The metal halide, wherein A is a Group IA metal or an organoammonium salt, X is a halide, and p, q, and r are each independently 1, 2, or 3. Preferably, the organoammonium salt is methylammonium or formamidinium.

[0134] In one embodiment, the shell contains a metal halide of the form AMX3, wherein A is selected from cesium, methylammonium, rubidium, thallium, and sodium, M is Pb, Sn, Cu, or Zn, and X is a halide. Preferably, the shell contains a metal halide of the form AMX3, wherein A is selected from 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.

[0135] In one implementation, the shell-containing CsZn x As y Metal halide of I3, wherein the sum of x and y is equal to 1, and y is from 0 to 0.1. Preferably, y is from 0.01 to 0.1.

[0136] In one implementation, the shell contains Cs3Zn x As y Metal halide of I5, wherein the sum of x and y is equal to 1, and y is from 0 to 0.1. Preferably, y is from 0.01 to 0.1.

[0137] In one embodiment, the shell contains a metal halide of the form Cs3BX6, wherein B is indium or antimony and X is a halide.

[0138] In one embodiment, the shell comprises a metal halide of the formula CsInX4, where X is a halide. Preferably, the shell comprises CsInBr3I.

[0139] In some embodiments, the shell has a perovskite crystal structure, particularly when the shell has the formula AMX3 as defined above. In particular, the shell may contain a perovskite crystal structure when it comprises CsPbI3 and / or CsZnI3.

[0140] While lead-based nanocrystals exhibit excellent performance in this application, their use in some industries may be problematic due to their toxicity. There is a need in industry for alternative ligand systems that avoid the use of toxic heavy metals (such as lead). The lead-free metal halides described above address this issue, providing excellent performance while reducing toxicity.

[0141] When the inorganic ligand precursor is lead-free, the preferred inorganic ligand precursor comprises CsI and ZnI2. It is assumed that the mixing of these two components forms CsZnI3 on ​​the surface of the nanocrystals during step b), and this mixture is preferably prepared by dissolving ZnI2, CsI, and a stabilizer (such as ammonium acetate) in a solvent (such as dimethylformamide (DMF)). In another embodiment of the lead-free inorganic ligand precursor, the inorganic ligand precursor may comprise AsX3 or TlX, where X is a halide.

[0142] A potential method to determine whether any purification steps have occurred is to verify whether the solution containing the ligand-exchanged nanocrystals contains impurities generated by the contact step or any other prior steps in the reaction. These impurities can be salts of metal elements and organic ligands, or multiple free organic ligands remaining in solution (which are not surface-coordinated to the crystallization nuclei of the nanocrystals). Therefore, preferably, the mixture formed in step c) (containing the ligand-exchanged nanocrystals) also contains at least one of the following components:

[0143] a) Salts containing a metallic element and a first organic ligand compound; and

[0144] b) A second plurality of first organic ligand compounds, wherein the second plurality of first organic ligand compounds are not coordinated to the surface of the crystallization nucleus.

[0145] Preferably, the second plurality of first organic ligand compounds are free in solution. Preferably, the second plurality of first organic ligand compounds are present in an amount of at least 2 wt%, preferably at least 3 wt%, preferably at least 4 wt%, preferably at least 5 wt%, preferably at least 10 wt%, preferably at least 20 wt%, relative to the total weight of the first organic ligand compounds in the mixture. The total weight of the organic ligands in the mixture includes the weight of the organic ligands coordinated to the surface of the nanocrystals and the weight of the salts of the organic ligands in solution. This can also be determined by TGA in air at a heating rate of 10 °C / min.

[0146] In a preferred embodiment, forming the second compound further includes adding a stabilizer to the polar solvent, wherein the stabilizer is selected from sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, and mixtures thereof. Therefore, the exchange composition preferably also contains a stabilizer, wherein the stabilizer is selected from sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, trimethylsilyl halides, and mixtures thereof. In a particularly preferred embodiment, the stabilizer is selected from sodium acetate, ammonium acetate, trimethylsilyl halides, and mixtures thereof. Stabilizers, particularly sodium acetate and ammonium acetate, facilitate the removal of long-chain organic ligands from the nanocrystals of the first nanocrystal composition during the contact step and also contribute to providing colloidal stability during the ligand exchange process. Trimethylsilyl halides act in a manner very similar to ammonium acetate and sodium acetate and are a more potent chemical than ammonium acetate, making them a particularly preferred stabilizer for concentrated crude solutions of nanocrystals.

[0147] In a preferred embodiment, the relative permittivity of the nonpolar solvent at 20°C is less than 3, preferably less than 2.5. As used herein, the term "relative permittivity" refers to the ratio of the dielectric constant of a substance to the dielectric constant of vacuum; it is a dimensionless number. As defined by Christian Wohlfarth in *Permittivity (Dielectric Constant) of Liquids*, the dielectric constant of a substance (commonly referred to as the dielectric constant) is the ratio of the electric displacement D to the electric field strength E when an external field is applied to the substance. The relative permittivity is measured using a BI-870 dielectric constant meter purchased from Brookhaven Instruments, with a sensitivity range of 1 to 200. This instrument can be calibrated with liquids whose relative permittivity is known.

[0148] Nonpolar solvents can be any C6-C 30 Aliphatic or aromatic organic compounds. Preferably, the nonpolar solvent is selected from C6-C6. 30 Amines, C6-C 30 Acids, C6-C 30 Phosphine, C6-C 30 Ethers and mixtures thereof. Examples of suitable nonpolar solvents include octadecene, oleylamine, oleic acid, octylamine, butylamine, dioctylamine, diphenylphosphine, trioctylphosphine, heptadecane, hexadecane, and mixtures thereof.

[0149] Preferably, the polar solvent has a relative permittivity greater than 3 at 20°C, more preferably greater than 5, and even more preferably greater than 10. Examples of suitable polar solvents include octylamine, ethylene glycol, N,N-dimethylformamide, dimethyl sulfoxide, triphenyl phosphite, 1,2-dichlorobenzene, hexamethylphosphamide, trioctylphosphine, trioctylphosphine oxide, diphenyl ether, glycerol, propylene carbonate, dipropylene glycol, tetraethylene glycol, dihydro-L-glucanone, isosorbide dimethyl ether, tetraethylene glycol trioxide, sulfolane, γ-butyrolactone, diformylxylose, and mixtures thereof.

[0150] As described below, the contact step can be performed in a variety of different ways. These methods are all used to prepare nanocrystals and are well known in the art. In one embodiment, nanocrystals are prepared by a simple addition method. In another embodiment, nanocrystals are prepared by a heating method, optionally combined with continuous addition. In another embodiment, nanocrystals are prepared by a thermal addition method, optionally combined with continuous addition. In another embodiment, nanocrystals are prepared by continuous addition. In yet another embodiment, nanocrystals are prepared by a combination of available methods. This method typically involves heating the components of the mixture to a crystal growth temperature of 200°C to 350°C and maintaining this growth temperature for a predetermined duration. However, these methods differ in the order of component addition, the temperature at which each component is added, and the time required for addition.

[0151] Typically, a metal compound and multiple organic ligands are mixed in a suitable solvent until the reaction (i.e., salt formation) is substantially complete, producing a solution of the salt in the solvent. At least one reagent can then be added to the salt solution, causing the reaction to form nanocrystals and / or combinations thereof. This at least one reagent can be added with or without a solvent.

[0152] Various aspects of the method of the present invention can be modified, such as specific reagents and / or reaction conditions, to provide nanocrystals of the desired size, thereby obtaining the desired optical properties, such as desired absorption and emission (e.g., for a specific purpose of the nanocrystals).

[0153] For example, the reagents used in the method (especially metal-containing compounds) can be varied to provide nanocrystals of the desired size, thereby obtaining the desired optical properties, such as the desired absorption and emission (e.g., for the specific use of nanocrystals).

[0154] For example, the reaction conditions of these methods can be modified to provide nanocrystals of the desired size, thereby obtaining the desired optical properties, such as the desired absorption and emission (e.g., for specific applications of nanocrystals).

[0155] In other words, the uses and methods of this invention can be used to prepare nanocrystals with size-tunable optical properties. Examples of reagents and / or reaction conditions that can be varied are discussed herein.

[0156] The method of the present invention specifies at least one reagent. More than one reagent may be used, which may comprise the same nitrogen group element or chalcogen element, or different nitrogen group elements or chalcogen elements.

[0157] Simple addition method

[0158] A simple addition method for preparing nanocrystals is a preferred embodiment. This method typically involves contacting the components of the mixture in step a) at a temperature above 50°C. Preferably, the contacting step involves contacting a variety 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, preferably at least 90°C.

[0159] In the first step of the simple addition method, the metal-containing compound and various organic ligands are preferably dissolved in a nonpolar solvent. This is typically carried out under an inert atmosphere. The solution is then preferably degassed. Degasting is typically performed at 50°C to 150°C (e.g., about 100°C) for 0.5 to 1.5 hours.

[0160] In a further step, the temperature of the mixture can be raised to above 200°C, which typically forms salts of metal elements and organic ligands. To add at least one reagent by injection, the temperature can be lowered to 50°C to 150°C, preferably about 100°C. The reagent can preferably be added via a series of injections. After the last injection, preferably about 3 to 15 minutes later, the reaction is cooled.

[0161] In the simple addition method, preferably, the contact step includes:

[0162] A) Mixing a metal-containing compound and multiple first organic ligand compounds in a nonpolar solvent to form a precursor mixture;

[0163] B) Degas the precursor mixture;

[0164] C) Heating the precursor mixture to above 150°C; and

[0165] D) Cool the mixture to below 150°C and add at least one reagent to the precursor mixture.

[0166] Preferably, the contacting step includes contacting a plurality of first organic ligand compounds, 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, preferably at least 90°C.

[0167] The exchange ligand (e.g., an inorganic ligand dissolved in a polar solvent) is then added to the reaction mixture. The reaction mixture is then typically left to stand under an inert atmosphere with stirring for several hours (e.g., 6 to 18 hours). In other words, in the simple addition method, the method preferably also includes stirring the mixture for at least 2 hours, preferably 2 to 18 hours, and more preferably 4 to 18 hours. This is typically part of step c), as described below. The temperature of the mixture is preferably from 0°C to 150°C, more preferably from 20°C to 50°C.

[0168] The resulting nanocrystals contain exchange ligands (e.g., inorganic ligand shells) that are surface-coordinated to the crystallization nucleus of the nanocrystals. These nanocrystals are then typically washed and dissolved in another polar solvent for use in inks.

[0169] Hot addition method

[0170] Such as Tamang and others ( Chem. Rev. As described in the review (2016, 116, 10731-10819), in the case of the hot-addition method, the separation of nucleation and growth can be achieved by rapidly injecting the reagent into a hot solvent, which raises the concentration in the reaction flask above the nucleation threshold. Hot injection leads to a nucleation burst, which is rapidly quenched by two factors: (i) rapid cooling of the reaction mixture, enhanced by the fact that the solution to be injected is at room temperature; and (ii) reduced supersaturation due to the consumption of precursors / monomers during nucleation.

[0171] When using the heat-applied method, the contact steps include:

[0172] A) Heating the precursor mixture to a first temperature, wherein the precursor mixture comprises a metal-containing compound and multiple first organic ligand compounds.

[0173] B) Add at least one reagent to the precursor mixture.

[0174] C) The precursor mixture is held at a first temperature for a first predetermined time to form a variety of seed particles.

[0175] The precursor mixture may optionally be degassed before heating to the first temperature. Typically, degassing is carried out at 50°C to 150°C (e.g., about 100°C) for 0.5 to 1.5 hours.

[0176] Preferably, the first temperature is 275°C to 350°C, more preferably 275°C to 325°C, and even more preferably 290°C to 310°C.

[0177] Preferably, before being added to the precursor mixture in step B), the temperature of at least one reagent is 5°C to 50°C, preferably 10°C to 35°C, preferably 15°C to 25°C, and preferably about room temperature.

[0178] Preferably, the first predetermined time length is 10 to 60 minutes, more preferably 15 to 50 minutes, more preferably 20 to 40 minutes, and more preferably 25 to 35 minutes.

[0179] Preferably, the contact step further includes:

[0180] D) Lower the temperature of the precursor mixture to a second temperature.

[0181] E) During a second predetermined time period, at least one reagent is continuously added to the precursor mixture to prepare the mixture of step a).

[0182] Preferably, the second temperature is lower than the first temperature, and is between 200°C and 275°C, more preferably between 225°C and 275°C, and more preferably between 240°C and 260°C.

[0183] Preferably, the second predetermined time length is 60 to 180 minutes, more preferably 90 to 150 minutes, more preferably 100 to 140 minutes, and more preferably 110 to 130 minutes.

[0184] Continuous addition method

[0185] When the contact step uses a continuous addition method, the contact step includes:

[0186] A) Heating the precursor mixture to a third temperature, wherein the precursor mixture contains a metal-containing compound and multiple first organic ligand compounds.

[0187] B) During a third predetermined time period, at least one reagent is continuously added to the precursor mixture to prepare the mixture of step a).

[0188] Preferably, the third temperature is 200°C to 275°C, more preferably 225°C to 275°C, and even more preferably 240°C to 260°C.

[0189] Preferably, the third predetermined time length is 60 to 180 minutes, more preferably 90 to 150 minutes, more preferably 100 to 140 minutes, and more preferably 110 to 130 minutes.

[0190] Heating method

[0191] As outlined by Tamang et al., heating methods rely on obtaining the supersaturation required for uniform nucleation by forming active material in situ when thermal energy is provided.

[0192] In one implementation, the contact step includes:

[0193] A) Adding at least one reagent to a precursor mixture, wherein the precursor mixture comprises a metal-containing compound and multiple first organic ligand compounds, and

[0194] B) Heat the precursor mixture to the fourth temperature.

[0195] The precursor mixture may optionally be degassed. Typically, degassing is carried out at 50°C to 150°C (e.g., about 100°C) for 0.5 to 1.5 hours.

[0196] Preferably, the fourth temperature is 200°C to 275°C, more preferably 225°C to 275°C, and more preferably 240°C to 260°C.

[0197] Preferably, the contact step further includes:

[0198] C) The precursor mixture is held at a fourth temperature for a fourth predetermined time length.

[0199] Preferably, the fourth predetermined time length is 60 to 180 minutes, more preferably 90 to 150 minutes, more preferably 100 to 140 minutes, and more preferably 110 to 130 minutes.

[0200] Heating + Continuous Addition Method

[0201] When the heating method is used in combination with the continuous addition method, the contact step also includes:

[0202] D) During a fifth predetermined time period, at least one reagent is continuously added to the precursor mixture to prepare the mixture of step a).

[0203] Preferably, the fifth predetermined time length is 60 to 180 minutes, more preferably 90 to 150 minutes, more preferably 100 to 140 minutes, and more preferably 110 to 130 minutes.

[0204] According to a second aspect, the present invention provides a nanocrystal composition that can be obtained by the method of the first aspect.

[0205] The method of this invention is particularly suitable for preparing nanocrystalline ink compositions, especially quantum dot ink compositions. These ink compositions have wide applications in optoelectronic devices. The ink compositions are typically formed by dissolving nanocrystals containing inorganic ligands in a polar solvent. Prior to dissolution, the nanocrystals are typically washed to remove impurities from the solution containing the ligand-exchanged nanocrystalline composition.

[0206] When the method of the present invention is used to manufacture nanocrystalline ink, the method further includes:

[0207] d) Wash the nanocrystalline composition with a solution containing at least one of acetone, methyl acetate, ethyl acetate, and acetonitrile, and

[0208] e) Dissolve the nanocrystalline composition in a second polar solvent to form a nanocrystalline ink composition. Preferably, the second polar solvent is selected from 2,6-difluoropyridine, γ-butyrolactone, propylene carbonate, dimethylformamide, sulfolane, and combinations thereof.

[0209] Ink quality can be improved by using in-situ ligand exchange methods. The final QD ink obtained by using the in-situ method with conductive inorganic ligands exhibits excellent performance in devices.

[0210] According to a third aspect, the present invention provides an ink composition comprising the nanocrystalline composition of the second aspect. The ink composition typically comprises nanocrystals of the nanocrystalline composition and a polar solvent for dissolving the nanocrystals.

[0211] Novel metal halide ligands

[0212] According to a fourth aspect, the present invention provides a nanocrystal comprising a crystal nucleus and a lead-free inorganic shell at least partially enclosing the crystal nucleus. The present invention also provides a nanocrystal composition comprising various nanocrystals according to the fourth aspect. Without being bound by theory, it is considered that the nanocrystal of the fourth aspect comprises a core-shell structure, wherein the nanocrystal comprises: a crystal nucleus comprising (i) a metallic element and (ii) a nitrogen group element or a chalcogen group element, and a lead-free inorganic shell at least partially enclosing the crystal nucleus. Preferably, the shell encloses the crystal nucleus.

[0213] As used herein, the term "lead-free" refers to a component that does not contain lead. For example, a lead-free inorganic ligand precursor is an inorganic ligand precursor that does not contain any lead-containing compounds.

[0214] As described above, in the fourth aspect, the crystal nucleus typically comprises (i) a metallic element and (ii) a nitrogen group element or a chalcogen group element. For each aspect of the invention, the preferred metallic element, nitrogen group element, and chalcogen group element are the same.

[0215] As mentioned above, there is an industrial need for nanocrystals, particularly nanocrystal ligand systems, that avoid the use of toxic heavy metals such as lead. The inventors of this invention have discovered that lead-free inorganic compounds can be used as ligands on the surface of all types of nanocrystals to prepare nanocrystals with enhanced properties. For example, the nanocrystals of this invention are stable in air for months and exhibit an excellent P / V ratio. To date, cesium-containing metal halide ligands have shown particularly impressive properties.

[0216] Nanocrystals containing a lead-free inorganic shell can be prepared by the method of the present invention or any other suitable method. For example, a method for preparing nanocrystals according to the fourth aspect may include the step of purifying the original nanocrystals. As understood in the art, the simple addition method, heating method, hot addition method, and continuous addition method described above are all suitable for preparing nanocrystals containing lead-free perovskite ligands.

[0217] Preferably, the shell comprises a metal halide ligand. In a preferred embodiment, the shell comprises a metal halide selected from CsX, AsX3, TlX, CsZnI3, CsInBr3I, ZnX2, CsI, and mixtures thereof, wherein X is a halide.

[0218] In particular, the inventors discovered that arsenic halides (AsX3) and thallium halides (TlX) can be used as inorganic ligands for nanocrystals. They further discovered that these inorganic ligands form a shell encapsulating the crystal nucleus. In a preferred embodiment, the shell comprises AsX3 or TlX. In one embodiment, the shell comprises AsX3. In one embodiment, the shell comprises TlX.

[0219] Without being bound by theory, nanocrystals containing AsX3 ligands advantageously provide very high charge carrier extraction due to the high mobility of AsI3, and thus provide high external quantum efficiency (EQE) in the device. Preferably, X is Cl, Br, or I, more preferably X is I.

[0220] We do not wish to be bound by theory, but believe that the use of thallium halide ligands results in lower dark current in optoelectronic devices. Preferably, X is Cl, Br, or I, more preferably I.

[0221] In a preferred embodiment, the shell comprises CsI and ZnI2. In a preferred embodiment, the shell comprises CsI and InBr3.

[0222] In a preferred embodiment, shell-containing A p Zn q X r The metal halide, wherein A is a Group IA metal or an organoammonium salt, X is a halide, and p, q, and r are each independently 1, 2, or 3. Preferably, the organoammonium salt is methylammonium or formamidinium.

[0223] In a preferred embodiment, the shell contains a metal halide of the form AMX3, wherein A is a Group IA metal, thallium, or an organoammonium salt, M is a metal having a +2 oxidation state, and X is a halide. In a preferred embodiment, the shell contains a metal halide of the form AMX3, wherein A is selected from cesium, methylammonium, rubidium, thallium, and sodium, M is Sn, Cu, or Zn, and X is a halide. Preferably, the shell contains a metal halide of the form AMX3, wherein A is selected from cesium, methylammonium, rubidium, and sodium, M is Zn, and X is a halide. Preferably, the metal halide is CsZnI3.

[0224] In a preferred embodiment, the shell-containing CsZn x As y Metal halide of I3, wherein the sum of x and y is equal to 1, and y is from 0 to 0.1. Preferably, y is from 0.01 to 0.1.

[0225] In a preferred embodiment, the shell-containing Cs3Zn x As y Metal halide of I5, wherein the sum of x and y is equal to 1, and y is from 0 to 0.1. Preferably, y is from 0.01 to 0.1.

[0226] In a preferred embodiment, the shell comprises a metal halide of the form Cs3BX6, wherein B is indium or antimony, and X is a halide. In a preferred embodiment, the shell comprises a metal halide of the form Cs3InX6, CsInX4, or Cs2InX5, wherein X is a halide.

[0227] In a preferred embodiment, the shell comprises CsInBr3I.

[0228] As described above, the shell structure can be amorphous or crystalline. Preferably, the shell is crystalline and / or forms a lattice layer that covers the crystal nuclei. As used herein, the term "lattice" is used to describe an ordered lattice of points that describes the arrangement of particles forming a crystal.

[0229] Preferably, the metal halide has a perovskite crystal structure.

[0230] The shell typically resides on the surface of the crystal nucleus and coordinates with it. Preferably, the shell encapsulates the crystal nucleus. In a preferred embodiment, the crystal nucleus has a radius and the shell has a thickness, with the thickness of the shell being less than the radius of the crystal nucleus.

[0231] In a preferred embodiment, the nanocrystals have at least one size measurement 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.

[0232] In a preferred embodiment, the nanocrystal is a semiconductor nanocrystal. In a preferred embodiment, the nanocrystal is a quantum dot.

[0233] According to a fifth aspect, the present invention provides a nanocrystal composition comprising a plurality of nanocrystals according to a fourth aspect.

[0234] In a preferred embodiment, the average particle size of the nanocrystals in the nanocrystal composition is 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.

[0235] In a preferred embodiment, the relative size dispersion of the nanocrystals is 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%.

[0236] In a preferred embodiment, 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 an absorption peak at half its maximum amplitude. The FWHM value is preferably measured by UV-Vis spectroscopy. In particular, the FWHM value of the absorption peak is determined by measuring the distance between two points on the y-axis (absorbance) curve where the intensity is half of the peak value.

[0237] In a preferred embodiment, the nanocrystal 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.

[0238] According to a sixth aspect, the present invention provides an ink composition comprising the nanocrystalline composition of the fifth aspect and a polar solvent.

[0239] Preferably, the polar solvent is selected from 2,6-difluoropyridine, γ-butyrolactone, propylene carbonate, dimethylformamide, sulfolane, and combinations thereof.

[0240] The present invention also provides an apparatus selected from infrared (IR) sensors, photodetectors, sensors, solar cells, bioimaging or biosensing compositions, photovoltaic systems, displays, batteries, lasers, photocatalysts, spectrometers, injectable 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 the nanocrystalline composition of the fourth aspect.

[0241] In preferred embodiments, the IR sensor or photodetector is modified for use as a 3D camera and 3D time-of-flight camera in mobile and consumer, automotive, medical, industrial, defense, or aerospace applications. In preferred embodiments, the bioimaging or biosensing composition is modified for use as a biomarker or biotag in in vitro or biological applications. In preferred embodiments, infrared light-emitting diodes (LEDs) and electroluminescent devices are modified for use in telecommunications equipment, night vision devices, solar energy conversion, thermoelectric, or energy production applications.

[0242] 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 contacting the nanocrystals with lead-free metal halide ligands. The nanocrystals may contain any type of native ligand, such as organic or inorganic ligands. These native ligands are surface-coordinated with the crystallization nucleus of the nanocrystals.

[0243] According to an eighth aspect, the present invention provides a method for ligand exchange in nanocrystals, the method comprising a contacting step, the contacting step including contacting:

[0244] (i) A first nanocrystal composition comprising multiple nanocrystals, wherein the nanocrystals comprise a crystallization nucleus and multiple native ligand compounds surface-coordinated to the crystallization nucleus, and

[0245] (ii) A second composition comprising a lead-free inorganic ligand precursor, wherein the inorganic ligand precursor comprises one or more metal halides.

[0246] Similar to the method in the first aspect, this method typically involves a reaction between a metal halide in an inorganic ligand precursor and nanocrystals, resulting in the formation of a shell disposed on the surface of the crystallization nucleus. The shell is formed by the metal halide in the inorganic ligand precursor. More information about this reaction is given in the first aspect above.

[0247] The method of the eighth aspect is usually carried out under inert conditions, such as those described above with respect to the first aspect.

[0248] In a preferred embodiment, the native ligand compound does not contain metal halides. 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.

[0249] In a preferred embodiment, the native ligand compound is an organic ligand compound. In this embodiment, the first nanocrystal composition preferably further comprises a nonpolar solvent. The organic ligand compound is as described above with respect to the first organic ligand compound of the first aspect. For each aspect of the invention, the preferred relative permittivity of the nonpolar solvent is the same. For each aspect of the invention, the preferred nonpolar solvent is the same.

[0250] In another embodiment, the native ligand compound is an inorganic ligand compound. In this embodiment, the first nanocrystal composition preferably further comprises a polar solvent. Preferably, the polar solvent has a relative permittivity greater than 3 at 20°C, more preferably greater than 5, and even more preferably greater than 10. Preferably, the polar solvent is selected from octylamine, ethylene glycol, N,N-dimethylformamide, dimethyl sulfoxide, triphenyl phosphite, 1,2-dichlorobenzene, hexamethylphosphamide, trioctylphosphine, trioctylphosphine oxide, diphenyl ether, glycerol, propylene carbonate, dipropylene glycol, tetraethylene glycol, dihydro-L-glucanone, isosorbide dimethyl ether, tetraethylene glycol trioxide, sulfolane, γ-butyrolactone, xylaldehyde dialdehyde, and mixtures thereof.

[0251] As described above, the inorganic compound in the inorganic ligand precursor is preferably a metal halide. The inorganic compound in the inorganic ligand precursor typically reacts to form a shell partially encapsulating the crystal nucleus of the nanocrystal. This shell can be amorphous or crystalline. Preferably, the shell is crystalline. When the shell is crystalline, it can have a perovskite crystal structure. The core-shell structure of the nanocrystals obtained in the nanocrystal composition is as described above.

[0252] In a preferred embodiment, the inorganic ligand precursor comprises CsX, AsX3, TlX, CsZnI3, CsInBr3I, ZnX2, or CsI, where X is a halide. The halides can all be the same halide, for example, X3 can represent I3, or they can be a mixture of halides, such as Br2I.

[0253] In a preferred embodiment, the inorganic ligand precursor comprises CsI and ZnI2.

[0254] In a preferred embodiment, the inorganic ligand precursor comprises CsI and InBr3.

[0255] In a preferred embodiment, the inorganic ligand precursor includes formula A. p Zn q X r The metal halide, wherein A is a Group IA metal or an organoammonium salt, X is a halide, and p, q, and r are each independently 1, 2, or 3. Examples of suitable organoammonium salts include methylammonium and formamidinium.

[0256] In a preferred embodiment, the inorganic ligand precursor comprises a metal halide of the formula AMX3, wherein A is selected from cesium, methylammonium, rubidium, thallium, and sodium, M is Sn, Cu, or Zn, and X is a halide. In a preferred embodiment, the inorganic ligand precursor comprises a metal halide of the formula AMX3, wherein A is selected from cesium, methylammonium, rubidium, and sodium, M is Zn, and X is a halide. In a preferred embodiment, the metal halide is CsZnI3. The CsZnI3 precursor is typically formed by adding CsI and ZnI2 to a non-solvent (e.g., DMF) to form a second composition, wherein the second composition preferably additionally comprises a stabilizer, such as ammonium acetate or other suitable compound.

[0257] In a preferred embodiment, the inorganic ligand precursor comprises CsInBr3I.

[0258] In a preferred embodiment, the metal halide has a perovskite crystal structure.

[0259] As explained above regarding the first aspect, once the second composition is added, a reaction typically occurs between the inorganic compound in the inorganic ligand precursor and the nanocrystals capped with the organic ligand compound. Specifically, a reaction occurs to remove 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.

[0260] Therefore, the contacting step further includes replacing at least a portion of the native ligand compound that is surface-coordinated with the crystallization nucleus to form nanocrystals comprising a crystallization nucleus and a shell encapsulating the crystallization nucleus, wherein the shell is formed from an inorganic ligand precursor. Preferably, the contacting step includes stirring the composition for at least 2 hours, more preferably 2 to 18 hours, and more preferably 4 to 18 hours. Preferably, the contacting 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 native ligand compound that is surface-coordinated with the crystallization nucleus to form nanocrystals comprising a crystallization nucleus and a shell encapsulating the crystallization nucleus, wherein the shell is formed from an inorganic ligand precursor, as determined by thermogravimetric analysis (TGA) in air at a heating rate of 10°C.

[0261] As in all aspects of the invention, the shell can be amorphous or crystalline. Preferably, the shell is crystalline.

[0262] In a preferred embodiment, the second composition further comprises a stabilizer selected from sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, trimethylsilyl halides, and mixtures thereof. Preferably, the stabilizer is selected from sodium acetate, ammonium acetate, trimethylsilyl halides, and mixtures thereof. The stabilizer is as described above with respect to the first aspect.

[0263] Example

[0264] The embodiments described below illustrate the method of the present invention.

[0265] Although specific embodiments of the invention have been described below for illustrative purposes, it will be apparent to those skilled in the art that various changes can be made to the details of the invention without departing from the invention as defined by the appended claims.

[0266] Unless otherwise stated, all parts and percentages in the following examples and throughout the specification are parts by weight or weight percentages.

[0267] Absorption spectra of colloidal quantum dots or quantum dot films were obtained on a JASCO V-770UV-visible / NIR (ultraviolet-visible / near-infrared) spectrometer, which provides measurements in the wavelength range of 400 nm to 3200 nm.

[0268] XRD data were collected at room temperature in the range of 10 < 2q < 90° using Cu Ka1 X-rays (l = 1.5406 Å) on a Panalytical X'pert PRO MPD diffractometer. In each case, a few drops of dispersed sample were placed on a glass microscope slide and allowed to evaporate. Data were analyzed using Rigaku SmartLab Studio II software, and searches and matches were performed using open crystallography databases.

[0269] TEM and high-resolution transmission electron microscopy (HRTEM) images were obtained using a FEITalos F200X microscope equipped with an X-FEG electron source. Experiments were conducted using an accelerating voltage of 200 kV and a beam current of approximately 5 nA. Images were recorded using a FEI CETA 4k x 4k CMOS camera. In each case, a few drops of quantum dots dispersed in a solvent were dropped onto a carbon-coated copper grid and allowed to evaporate. Samples were used as is or treated with acetone followed by methanol to remove unwanted organic matter before imaging.

[0270] Thermogravimetric analysis (TGA) measurements were performed using a Hitachi STA200-RV TGA. Samples were prepared by first drying under vacuum and then placing them in an alumina crucible. Measurements were performed under a nitrogen flow at a heating rate of 10 °C / min from 25 °C to 900 °C.

[0271] For ICP-TOF MS measurements, all imaging data were acquired using an ImageBIO 266nm laser ablation system equipped with a dual-volume 3-sample chamber and dual concentric injectors (ESL, Bozeman), coupled to an ICP-ToF-MS 2R (TOFWERK, Thun). Instrument parameters are summarized in the table below. Aerosol particles were transferred to the ICP via a 0.9 L / min helium flow. Data acquisition was performed in standard mode without the addition of reactive gases.

[0272] For the sample, a 10 nm quantum dot layer was chosen for imaging due to its high Pb content. Three regions on the sample were measured (x = 2.1 mm, y = 0.2 mm, spacing between mapped regions = 1 mm), each with a corresponding mapped area. For all images, baseline subtraction and quality calibration were performed using TofWare (version 3.2.0).

[0273] Example 1 - In-situ preparation of PbS nanocrystals using CsZnI3

[0274] To consolidate the advantages of the in-situ ligand exchange method, PbS nanocrystals were synthesized in a large flask. The resulting mixture was divided into two halves for in-situ ligand exchange (Example 1) and ex-situ purification and ligand exchange (Comparative Example 2). Figure 2 A simplified diagram of the ligand exchange reaction is shown.

[0275] All processing and ligand exchange procedures were carried out in an N2 glove box containing anhydrous solvents.

[0276] Part 1: Under an inert atmosphere, 1.765 g of Pb3O4, 14.6 mL of oleic acid, and 200 mL of 1-octadecene were added to a three-necked round-bottom flask. The reaction mixture was degassed at 100 °C for 1 h, and 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 to inject a bis(trimethylsilyl) sulfide solution. To prepare the bis(trimethylsilyl) sulfide solution, 1 mL of bis(trimethylsilyl) sulfide was first dissolved in 50 mL of ODE, referred to as solution A. Then, 17.8 mL of solution A was taken and dissolved in 32.2 mL of ODE to prepare solution B. When the reaction temperature stabilized at 100 °C, 11.8 mL of solution A was injected into the reaction flask, and 12.8 mL of solution B was injected 8 minutes later. Five minutes after injecting solution B, another 12.8 mL of solution B was injected into the reaction medium. Five minutes later, another 6.4 mL of solution B was injected to obtain the desired wavelength. The reaction was cooled six minutes after the final injection.

[0277] Part 2: Once the reaction was complete, half of the colloidal solution was taken for ex-situ experiments (Comparative Example 2). The remaining half (in this example) was treated with a CsZnI3 inorganic ligand precursor prepared by dissolving 3.1 g ZnI2, 2.5 g CsI, and 305 mg ammonium acetate in 100 mL dimethylformamide (DMF). This solution was added to the crude reaction mixture, and a phase transfer from the long-chain unstable organic ligand to the inorganic stable ligand was carried out in the same flask. The reaction mixture was stirred under an inert atmosphere for 12 hours. After 12 hours, QD clearly transferred from the ODE phase to the DMF phase, was washed with 100 mL hexane, and further centrifuged at 6,000 RPM for 10 min using 100 mL acetone. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0278] It should be noted that the same reaction can be performed using heating methods as well as continuous injection, wherein a bis(trimethylsilyl) sulfide solution is added before heating, or a bis(trimethylsilyl) sulfide solution is added continuously during the synthesis process after lead oleate formation when the temperature is lowered to 100°C. Once PbSQD has been synthesized by any of the above methods, the remainder of the ligand exchange method (i.e., washing and ink formation) remains unchanged. This also applies to Comparative Example 2. The results from these examples demonstrate that no specific contact step method is required to form nanocrystals, and the contact components are generally sufficient to produce the desired nanocrystals.

[0279] Figure 3 The absorption properties of the obtained QD are shown and are also presented in Table 1 below. The original nanocrystals showed an absorption wavelength of 1450 nm, an FWHM of 92 nm, and a P / V of 6.4. Furthermore, after in-situ ligand exchange, the obtained QD exhibited excellent solubility in 2,6-difluoropyridine compared to the ecto-ligand-exchanged QD. Moreover, the absorption wavelength and the FWHM of the absorption peak remained unchanged, namely an absorption wavelength of 1448 nm and an FWHM of 91 nm.

[0280] Comparative Example 2 - Preparation of PbS nanocrystals using CsZnI3 in situ

[0281] Part 1: Same as Example 1.

[0282] Part 2: Once the reaction was complete, half of the colloidal solution was used for ectopic experiments. The crude solution was purified by centrifugation twice at 6,000 RPM using a crude solution:acetone:isopropanol (IPA) 1:1:1. The precipitate was dissolved in octane to form a purified original nanocrystal solution. This method was performed in a nitrogen-filled glove box. For ectopic ligand exchange, a CsZnI3 inorganic ligand precursor, prepared by dissolving 3.1 g ZnI2, 2.5 g CsI, and 305 mg 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 stirred for 12 hours under an inert atmosphere. After 12 hours, QD transferred from the ODE phase to the DMF phase, was washed with 100 mL of hexane, and further centrifuged at 6,000 RPM for 10 min using 100 mL of acetone. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as ink.

[0283] from Figure 3 As can be seen, the ecto-ligand exchange QD exhibits a 30 nm blue shift and a 10 nm increase in FWHM, indicating that the QD quality is inferior compared to the in-situ QD. In contrast, nanocrystals formed by the in-situ method do not show a blue shift or FWHM broadening, and these nanocrystals also have a higher P / V ratio than the ecto-situ nanocrystals of the prior art. This demonstrates that the in-situ ligand exchange method provides higher quality QD.

[0284] Table 1: Absorption spectral data of nanocrystals prepared according to Example 1 and Comparative Example 2.

[0285] Example 3 - In-situ preparation of PbS nanocrystals using CsPbI3

[0286] Part 1: Under an inert atmosphere, 0.88 g of Pb₃O₄, 7.3 mL of oleic acid, and 100 mL of 1-octadecene were added to a three-necked round-bottom flask. The reaction mixture was degassed at 100 °C for 1 h, and 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 to inject a bis(trimethylsilyl) sulfide solution. To prepare the bis(trimethylsilyl) sulfide solution, 0.5 mL of bis(trimethylsilyl) sulfide was first dissolved in 25 mL of ODE, referred to as solution A. Then, 8.9 mL of solution A was taken and dissolved in 16.1 mL of ODE to prepare solution B. When 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 injecting solution B, inject another 6.4 mL of solution B into the reaction medium. Five minutes later, inject another 3.2 mL of solution B to obtain the desired wavelength. Cool the reaction 6 minutes after the final injection.

[0287] Part 2: Once the reaction was complete, the reaction mixture was treated with a CsPbI3 inorganic ligand precursor prepared by dissolving 4.57 g PbI2, 2.5 g CsI, and 305 mg ammonium acetate in 100 mL dimethylformamide (DMF). This solution was added to the crude reaction mixture, and a phase transfer from the long-chain unstable organic ligand to the inorganic stable ligand was carried out in the same flask. The reaction mixture was stirred for 12 h under an inert atmosphere. After 12 h, QD clearly transferred from the ODE phase to the DMF phase, was washed with 100 mL hexane, purified with 100 mL acetone, and centrifuged at 6,000 RPM for 10 min. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0288] It should be noted that the same reaction can be performed using heating methods as well as continuous injection, wherein a bis(trimethylsilyl) sulfide solution is added before heating, or a bis(trimethylsilyl) sulfide solution is added continuously during the synthesis process after lead oleate formation when the temperature is lowered to 100°C. Once PbSQD has been synthesized by any of the above methods, the remainder of the ligand exchange method (i.e., washing and ink formation) remains unchanged.

[0289] Once significant phase separation occurs, these QDs are washed with acetone and finally dissolved in a polar solvent such as 2,6-difluoropyridine, propylene carbonate, and / or DMF. Figure 4 Photographs of the phase-separated QD in centrifuge tubes and the final colloidal nanocrystal ink are shown. The photographs of the colloidal ink clearly demonstrate that the QD exhibits excellent colloidal stability in polar solvents after the ligand exchange process.

[0290] Nanocrystals were prepared using the method of Example 3 to prepare ink compositions with an absorption wavelength of approximately 1400 nm (Sample 3A) and approximately 1200 nm (Sample 3B). This demonstrates the versatility of the method of the present invention. Figure 19 As shown, another nanocrystalline ink composition was prepared according to Example 3, exhibiting absorption peaks at 1550 nm, 1650 nm, 2000 nm, and 2300 nm. Different absorption peaks were obtained by changing the time in Part 1. Again, this demonstrates the versatility of the method of the present invention.

[0291] The resulting ink exhibits impressive optical properties. The ink composition retains its exciton properties with a high peak-to-valence ratio (P / V), indicating the high quality of the ligand-exchanged colloidal QD ink. Table 2 below shows the optical aerobic stability of these quantum dot samples 3B.

[0292] As used herein, the term "peak-to-valley ratio" (or "P / V ratio") refers to the ratio between the maximum absorbance of an absorption peak and the lowest absorbance within a 150 nm range preceding the maximum absorbance. The P / V ratio is preferably measured by UV-Vis spectroscopy.

[0293] Comparative Example 4 - Preparation of PbS nanocrystals using CsPbI3 in situ

[0294] Part 1: Same as Example 3.

[0295] Part 2: The crude solution was purified by centrifugation twice at 6,000 RPM using a crude solution:acetone:IPA ratio of 1:1:1. The precipitate was dissolved in octane to form a purified QD solution. This method was performed in a nitrogen-filled glove box. For heteroligand exchange, 100 mL of a 7 mg / mL QD-octane solution was added to a CsPbI3 inorganic ligand precursor prepared by dissolving 4.5 g PbI2, 2.5 g CsI, and 305 mg ammonium acetate in 100 mL dimethylformamide (DMF). The reaction mixture was stirred for 12 h under an inert atmosphere. After 12 h, QD transferred from the ODE phase to the DMF phase, was washed with 100 mL hexane, purified with 100 mL acetone, and centrifuged at 6,000 RPM for 10 min. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0296] Nanocrystals were prepared using the method described in Comparative Example 4 to prepare ink compositions with an absorption wavelength of approximately 1400 nm (Comparative Sample 4A) and approximately 1520 nm (Comparative Sample 4B).

[0297] As shown in Table 2 and Figure 7As shown, in-situ ligand exchange QDs provide a higher P / V compared to post-synthetic (ex-situ) ligand exchange with similar absorption wavelengths, which suggests improved surface passivation and solubility of these in-situ QDs in solvents.

[0298] Table 2: Optical properties of in-situ ligand-exchanged (CsPbI3) QD (sample 3A) and synthesized ligand-exchanged QD (ex-situ comparison sample 4A).

[0299] The oxygen stability of nanocrystalline ink composition sample 3B and control sample 4B was further analyzed. As previously stated, in-situ ligand exchange is more effective than the ex-situ method and prevents surface oxidation of the original QD, providing a higher quality QD than the ex-situ method. Figure 5 (in situ) and Figure 6 (Extraterrestrial) shows the absorption spectrum of QD and its variation over time. Figure 5 and Figure 6 This indicates that the QD prepared according to the above method is stable. (From Table 3 and...) Figure 5 and Figure 6 As can be clearly seen, the ink obtained by the method of the present invention exhibits aerobic stability for up to 97 days, which is similar to the ink formed by the ex-situ method (QD ink after ligand exchange), because the CsPbI3 ligand system is very stable. Therefore, it can be concluded that the nanocrystalline ink composition prepared by the in-situ ligand exchange method has at least the same aerobic stability as prior art nanocrystalline inks, while providing some additional advantages, which will be discussed in later sections.

[0300] Table 3: Absorption spectral parameters of PbS QD with in-situ and post-synthetic ligand exchange

[0301] Generally, the longer the absorption wavelength of nanocrystals, the higher the P / V ratio. Therefore, since there is a significant difference in the absorption wavelength between sample 3B and control sample 4B (>200 nm), the P / V ratios of these samples cannot be directly compared.

[0302] Example 5 - In-situ preparation of PbS nanocrystals using CsZnI3

[0303] Part 1: Same as Example 1.

[0304] Part 2: Same as Example 1.

[0305] A similar in-situ ligand exchange system using CsI and ZnI2 ligands demonstrated successful phase transfer, yielding high-quality quantum dot inks. CsI and ZnI2 achieved successful phase transfer to a polar inorganic phase. The resulting QDs exhibited good colloidal stability in 2,6-difluoropyridine.

[0306] Figure 8 Absorption spectra of in-situ ligand-exchanged PbS QD based on CsI-ZnI2 are shown, demonstrating promising optical absorption properties. Similar ligand-exchange methods can also be implemented on AsX3 (X = Cl, Br, I) and TlX (X = Cl, Br, I). Both materials offer their own advantages; for example, the use of AsI3 should provide nanocrystals with very high charge carrier extraction due to its high mobility, thus resulting in high external quantum efficiency in devices, while the use of thallium halide-based ligands should yield nanocrystals suitable for lower dark currents.

[0307] Example 6 - Ligand Exchange of Synthesized PbS Nanocrystals with AsI3

[0308] Part 1: Same as Example 1.

[0309] Part 2: Same as Comparative Example 2, except that the ligand exchange DMF solution contains 0.070 M AsI3 and 21 mg ammonium acetate in 7 mL of DMF, and the amount of nanocrystals is 7 mg / mL in 7 mL.

[0310] Although this experiment involved ectopic ligand exchange with AsI3 ligands, this embodiment demonstrates that AsI3 is an acceptable inorganic ligand. AsI3 can also be easily applied using in-situ ligand exchange systems. Figure 9 The absorption spectrum of PbSQD based on the AsI3 ligand in 2,6-difluoropyridine is shown.

[0311] Example 7 - Monitoring CsI and ZnI2 ligand systems

[0312] To verify the effects of CsI and ZnI2, controlled ligand exchange experiments were conducted using CsI and ZnI2 to observe the performance of the ligands alone and in combination.

[0313] Part 1: Same as Example 1.

[0314] Part 2: Same as Comparative Example 2, except that CsI, ZnI2, and CsZnI3 were each used for separate ligand exchange reactions. For CsI, the same molar amount of CsI solution was prepared as in Comparative Example 2, and for ZnI2, the same amount of ZnI2 was used in exactly the same amount of DMF.

[0315] The inventors discovered that CsI, as an inorganic ligand, can induce phase separation from the nonpolar phase of the original QD to the polar phase of the original QD; however, the resulting QD ink precipitates and cannot form a stable colloidal solution. Figure 10 When ZnI2 is used, a stable quantum dot ink is formed, but its optical properties are not as good as those using ligands exchanged between CsI and ZnI2, which may be due to better surface passivation. This result indicates that CsI combined with ZnI2 forms a crystalline ligand structure around the nanocrystals, exhibiting excellent optical properties.

[0316] Figure 10 Photographs of QD inks using ligands of CsI (left) and ZnI2 (right). It is clear that the QD ink using the CsI ligand is unstable, but in the case of ZnI2, the final ink is stable compared to that using CsI and ZnI2 together, although it is a diluted solution.

[0317] Table 4 shows the optical properties of the final inks formed using three different types of ligands. Clearly, the QD system based on the CsI-ZnI2 (CsZnI3) ligand produces the best optical properties.

[0318] Table 4: Absorption performance of QD inks with ligand exchange using different inorganic ligands.

[0319] Example 8 - Fabrication of a photodiode device comprising PbS-CsPbI3 prepared by in-situ method

[0320] In-situ ligand exchange-based QDs are also used in photodiode devices with ITO / ZnO / PbS QD / organic ligand exchange-based PbS QD / MoO / Au structures. In this embodiment, the method of Example 3—in-situ ligand exchange—is used to prepare PbS ink with CsPbI3 as the ligand system.

[0321] Device Manufacturing Method: The fabrication 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 clean ITO substrate at 1,500 RPM for 60 s, followed by heating at 210 °C for 15 min. A second layer of ZnO is then coated on top, followed by heating at 210 °C for 30 min. The ZnO-coated film is then transferred to a nitrogen-filled glove box for the addition of PbS ink, which is spin-coated at 1,500 RPM for 60 s, followed by spin-coating another layer at the same speed, this time containing quantum dot ink with organic ligands coordinated to the surface. The device is then transferred to a thermal evaporator for the deposition of MoO and Au under a mask.

[0322] First, CsPbI3 was used as an inorganic ligand for PbS QD in photodiode devices. As described in the examples above, nanocrystals in photodiode devices were prepared using in-situ (Example 8) or ex-situ (Comparative Example 9) methods, and the performance of each device was analyzed.

[0323] Figure 11 A comparison between in-situ and out-of-situ photodiode devices is shown. Specifically, Figure 11 The following are shown: (a) the current density-voltage characteristics of photodiodes fabricated using in-situ PbS QD and synthesized ligand-exchanged PbS QD, and (b) the EQE spectra of photodiodes fabricated in the same batch using the same device structure, using in-situ QD and synthesized ligand-exchanged QD.

[0324] When using in-situ ligand-exchanged QD, 1.6E-5 A / cm was obtained at -1V. 2 The dark current density is 16.6% with an EQE of 16.6%. The EQE spectrum shows the exciton characteristics of the PbS QD at 1300 nm, indicating that the QD maintains the quantum confinement effect throughout the in-situ ligand exchange and device fabrication process.

[0325] Comparative Example 9 - Fabrication of a photodiode device comprising PbS-CsPbI3 prepared by an ex-situ method

[0326] For comparison, an ectopic ligand-exchanged QD is applied in a photodiode device with an ITO / ZnO / PbS QD / organic ligand-exchanged PbS QD / MoO / Au structure. In this embodiment, the method of Comparative Example 4—ectopic ligand exchange—is used to prepare PbS ink with CsPbI3 as the ligand system.

[0327] Equipment manufacturing method: Same as in Example 8.

[0328] Using the same type of device structure, this time with an optimized post-synthetic ligand-exchanged QD (extra-situ), the photodiode device exhibits relatively low device performance, with an EQE of 13.8%.

[0329] Table 5 summarizes the device data for in-situ QD and post-synthetic ligand exchange QD. Clearly, the in-situ ligand exchange QD device offers significantly higher external quantum efficiency and similar dark current, demonstrating that the in-situ ligand exchange method is not only low-cost but also produces high-quality products, including QD inks and devices.

[0330] Table 5: Comparison of equipment specifications between in-situ QD and post-synthetic ligand exchange (ex-situ) QD

[0331] Example 10 - Manufacturing of a photodiode device containing InAs-CsZnI3

[0332] To further extend this work, InAs QD based on CsI-ZnI2 ligands has also been applied to photodiode devices and has shown promising performance.

[0333] The ratio of dark current to photocurrent (Table 6) clearly demonstrates the performance of the device's photodiode.

[0334] Table 6: Device performance of photodiodes using QDs based on CsI-ZnI2 ligands

[0335] In this embodiment, CsZnI3 is demonstrated to be an acceptable inorganic ligand for InAs nanocrystals. In this document, the InAs nanocrystals and devices comprising these nanocrystals are prepared using the ex-situ method described below.

[0336] Step 1: Preparation of amorphous InAs clusters

[0337] In a 250 mL three-necked flask, 3.0 mmol In(OAc)3, 9.2 mmol oleic acid, and 15 mL heptadecane were added, and the mixture was evacuated at 110 °C under vacuum (~0.1 mbar) for 90 minutes. In this step, indium oleate was formed, and 9 mmol acetic acid was collected in a cold trap.

[0338] In(OAc)3+ R-COOH (R= C 17 H 33 ) ->In-COOR + CH3COOH

[0339] Switch the flask to a nitrogen atmosphere and slowly cool it to room temperature. Transfer the flask to a glove box. In the glove box, add 0.96 mmol of tris(trimethylsilyl)arsenic ((TMSi)3As), 1.98 mmol of dioctylamine, and 2.5 mL of degassed heptadecane to a 10 mL vial and vortex thoroughly. Under continuous stirring, mix the indium oleate solution with the TMSi-As solution to provide a composition containing InAs clusters.

[0340] The composition containing InAs clusters prepared according to step 1 is used as the composition containing group III-V clusters in step 2.

[0341] Step 2: Preparation of InAs nanocrystals with an absorption peak of approximately 1400 nm

[0342] In step 2, the preparation of InAs nanocrystals consists of two crystal growth stages, followed by purification, ligand exchange with CsZnI3, ink formation, and then device fabrication. First, InAs nanocrystals exhibiting an absorption peak at approximately 1100 nm were formed (the first growth stage lasted 4.5 hours). The UV-Vis spectra of these nanocrystals are as follows... Figure 2 As shown. Second, these nanocrystals were used to prepare nanocrystals exhibiting an absorption peak at approximately 1400 nm (the second growth stage lasted 8 hours). The UV-Vis spectra of these nanocrystals are as follows. Figure 1 As shown. The total growth time was 12.5 hours.

[0343] 1100 nm QD

[0344] In a 250 mL three-necked flask, 0.4 mmol In(OAc)3, 1.2 mmol oleic acid, and 6 mL heptadecane were added, and the mixture was degassed at 110 °C under vacuum (~0.1 mbar) for 90 min. In this step, indium oleate was formed, and 1.2 mmol acetic acid was collected in a cold trap.

[0345] In(OAc)3+ R-COOH (R= C 17 H 33 ) ->In-COOR + CH3COOH

[0346] Switch the flask to a nitrogen atmosphere and maintain the temperature at 100°C. In a glove box, load 0.32 mmol (TMSi)₃As, 0.56 mmol dioctylamine, and 1 mL degassed heptadecane into a syringe. Add this solution to the indium oleate solution at 100°C. A color change occurs immediately after the injection of the arsenic precursor solution. Simply heat the solution to 287°C and continue growth for 15 minutes once the temperature reaches 287°C. Load 10 mL of the amorphous cluster solution from Example 1 into a syringe (20 mm diameter) and inject at a rate of 2.230 mL / hour for approximately 4 hours and 30 minutes. After injecting all the amorphous cluster solution, maintain the solution at 287°C for another 10 minutes. Simultaneously with the addition of clusters, add 270 µL of diluted HBr-acetone solution (the diluted HBr solution was prepared by diluting 40 µL of HBr in 2 mL of acetone solution) over 4 hours and 30 minutes. Turn off the heating and allow the solution to cool naturally. Transfer the CQD to a glove box for later use. CQD growth was monitored by taking equal portions of the sample and measuring the absorption spectrum.

[0347] 1400 nm QD

[0348] In a 250 mL three-necked flask connected under vacuum, add 6 mL of InAs CQD (50 mg / mL) (maximum absorption at approximately 1100 nm) and 4 mL of degassed heptadecane. Evacuate the contents of the flask at 100 °C under vacuum (~0.1 mbar) for 30 minutes. Switch the flask to nitrogen. Add 200 µL of diluted HBr solution to the flask and maintain at 100 °C for 10 minutes. Then raise the temperature to 285 °C. When the temperature reaches approximately 285 °C, load amorphous InAs clusters into a syringe and add them using a syringe pump at a rate of 1.16 mL / h for approximately 8 hours. Simultaneously with the addition of the clusters, add 120 µL of diluted HBr over 8 hours. Turn off the heating and allow the solution to cool naturally. Transfer the CQD to a glove box for later use. Monitor CQD growth by taking aliquots and measuring the absorption spectra.

[0349] To prepare InAs nanocrystals with absorption peaks at approximately 1550 nm to 1600 nm, step 2 is the same as described above, except that a second growth stage of 14 hours is required and the amorphous cluster solution is added at a rate of 1.16 mL / hour.

[0350] purification

[0351] Transfer the contents of the flask to a glove box. Add 5 mL of hexane to the QD, followed by 40 mL of acetone. Aliquot the solution into centrifuge tubes and centrifuge at 6000 RPM for 10 minutes. Discard the clear supernatant and redisperse the CQD precipitate in hexane. Add acetone and IPA at a 2:1 volume ratio and centrifuge again at 6000 RPM for 10 minutes. Discard the supernatant and redisperse the CQD precipitate in n-octane. Centrifuge the CQD in octane at 6000 RPM for 10 minutes to remove any solid impurities. Discard the precipitate and filter the clear QD solution through a 0.1 μm PTFE filter to obtain the product.

[0352] Ligand exchange and ink formation

[0353] After purification, the InAs nanocrystals contained oleic acid covering the surface and dissolved in octane. The organic ligand was exchanged for CsZnI3, as described below.

[0354] An inorganic ligand precursor, CsZnI3, prepared by dissolving 3.1 g ZnI2, 2.5 g CsI, and 305 mg ammonium acetate in 100 mL dimethylformamide (DMF), was added to 100 mL of a 7 mg / mL QD-octane solution. The reaction mixture was stirred for 12 h under an inert atmosphere. After 12 h, QD clearly transferred from the ODE phase to the DMF phase, was washed with 100 mL hexane, and further centrifuged at 6,000 RPM for 10 min using 100 mL acetone. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0355] Equipment manufacturing

[0356] The device stack structure can be described as ITO / ETL / active layer (InAs-CsZnI3 ink) / HTL / Au. ETL refers to the electron transport layer. HTL refers to the hole transport layer.

[0357] The advantage of cesium zinc halide-based perovskite-like systems is their absence of heavy metals, making them suitable for ligand exchange in environmentally friendly QD systems. For example, cesium zinc iodide can be used for InAs QD ligand exchange, where precursor solutions of cesium iodide and zinc iodide are dissolved in DMF and added to a hexane QD solution, followed by stirring for 15 minutes. This results in a significant phase transfer in InAs QD from a nonpolar phase to a polar inorganic ligand system. Figure 12 The optical properties and atomic force microscopy images of the ligand-exchanged QD are shown. Clearly, the resulting QD exhibits exciton characteristics and high-quality ink (…). Figure 12 a). Figure 12 b shows a photograph and AFM image of the film fabricated using spin coating technology, which shows a roughness of less than 10 nm RMS.

[0358] In addition, the dark current and EQE of the InAs-CsZnI3 nanocrystals were measured. These results are shown in Table 7 below. Figure 13 As shown in the figure. Clearly, when using the CsZnI3 ligand, the dark current density increases from 170 µA / cm². 2 Reduced to 9.2 µA / cm 2 The EQE increased significantly from 15.3% to 16.5%. These results are encouraging, demonstrating that the novel CsZnI3 system provides excellent surface passivation for lead-free InAs QD.

[0359] Comparative Example 11 - Manufacturing of a photodiode device containing InAs-InBr3

[0360] For comparison, photodiode devices were fabricated using the 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. Table 7 and Figure 13 The performance of these devices was compared.

[0361] Table 7: Device performance of photodiodes using existing InBr3 ligands and photodiodes using the CsZnI3 ligands of the present invention.

[0362] These results will be discussed in Example 10 above.

[0363] Example 12 - In-situ preparation of InAs nanocrystals using CsI-InBr3

[0364] In this embodiment, CsZnI3 is demonstrated to be an acceptable inorganic ligand for nanocrystals, particularly InAs nanocrystals. In this document, these InAs nanocrystals and the devices comprising them are prepared using the ex-situ method described below.

[0365] A photodiode device was further fabricated using a novel CsI-InBr3 inorganic ligand system. For this embodiment, the method is the same as in Example 10, but a new ligand (CsI-InBr3) is used instead of CsZnI3, and the different ligand exchange and ink fabrication steps are described below. The device stack structure can be described as ITO / ETL / active layer (InAs-(CsI-InBr3) ink) / HTL / Au.

[0366] Ligand exchange and ink formation

[0367] After purification, the InAs nanocrystals contained oleic acid covering the surface and dissolved in octane. The organic ligand exchanged for CsI-InBr3, as described below.

[0368] The QD-octane mixture was treated with a CsInBr3I inorganic ligand precursor, prepared by dissolving 90 mmol InBr3, 90 mmol g CsI, and 77 mmol ammonium acetate in 10 mL dimethylformamide (DMF) in a reaction vessel. This solution was added to the QD-octane mixture to induce a phase transfer from a long-chain unstable organic ligand to a stable inorganic ligand. The reaction mixture was stirred for 12 h under an inert atmosphere. After 12 h, the QD clearly transferred from the ODE phase to the DMF phase, was washed with 100 mL hexane, purified with 100 mL acetone, and centrifuged at 6,000 RPM for 10 min. The resulting precipitate was dissolved in 2,6-difluoropyridine and used as an ink.

[0369] Ligand exchange demonstrated successful phase transfer, yielding high-quality quantum dot inks. Therefore, successful phase transfer to a polar inorganic phase was achieved using CsI-InBr3 as a ligand. The resulting QDs exhibited good colloidal stability in 2,6-difluoropyridine. Figure 14 The absorption spectrum shows that the resulting solution forms a very stable ink with a concentration higher than 80 mg / mL and a P / V as high as 1.30.

[0370] Example 13 - Further Analysis of PbS-CsPbI3 Nanocrystals

[0371] PbS-CsPbI3 nanocrystals were prepared according to the method in Example 3.

[0372] TGA:

[0373] Further analysis of the nanocrystals is needed 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 via the methods described above (e.g., Figure 15 (As shown).

[0374] Samples were prepared by drying a small amount of solution containing nanocrystals under high vacuum for several hours until it ceased to lose further weight and turned into powder. The samples were then transferred to a TGA furnace for measurement.

[0375] For this kind of ligand exchange Figure 15 The results indicate that the weight ratio of inorganic ligands to organic ligands on the nanocrystal surface is 19.3:0.9 (21.4:1). This suggests that the ligand exchange reaction involves 95.5% by weight of shell exchange between the organic ligands coordinated to the crystal nucleus surface and the inorganic ligand system.

[0376] XRD:

[0377] Figure 16The XRD pattern of PbS-CsPbI3 nanocrystals is shown. The diffraction pattern indicates that the nanocrystals have 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.

[0378] HRTEM:

[0379] Figure 17 An HRTEM image of PbS-CsPbI3 nanocrystals is shown. The image reveals that CsPbI3 forms a superlattice coating the surface of the nanocrystals.

[0380] ICP-TOF MS:

[0381] Figure 18 The MS plot confirmed the presence of CsPbI3 in this elemental ratio. The estimated Cs:I ratio is 1:3, which corresponds to the CsPbI3 molecular formula of perovskite. This confirms the formation of a core-shell structure in the nanocrystals. Furthermore, the uniform distribution of cesium and iodine indicates that, for this system, the ligands uniformly cover the surface of the nanocrystals, and suggests that the corresponding ligand systems in other embodiments also form core-shell structures.

[0382] References

[0383] King et al., Importance of QD Purification Procedure on SurfaceAdsorbance of QDs and Performance of QD Sensitized Photoanode, J. Phys. Chem.C 2012, 116, 3349-3355.

[0384] Chen et al., IEEE Access, vol. 8, pp. 159415-159423, 2020.

[0385] Tamang et al., Chem. Rev. 2016, 116, 10731-10819.

Claims

1. A method for preparing a nanocrystalline composition, the method comprising: a) A contacting step is performed in a nonpolar solvent, said contacting step comprising contacting the following substances to form a mixture comprising multiple nanocrystals: Various first organic ligand compounds; Metallic compounds containing metallic elements; and A reagent containing at least one nitrogen group element or chalcogen group element. The nanocrystal comprises a crystallization nucleus and a plurality of first organic ligand compounds surface-coordinated to the crystallization nucleus, wherein the crystallization nucleus comprises (i) the metal element, and (ii) the nitrogen group element or the chalcogen group element, and b) Add an exchange composition comprising an exchange ligand precursor and a polar solvent to the mixture. There is no purification step between step a) and step b).

2. The method of claim 1, wherein the metallic element is selected from Group I metals, Group II metals, Group III metals, Group IV metals, and mixtures thereof. The metal-containing compound is selected from 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.

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

4. The method according to any one of the preceding claims, wherein the metal element is indium or gallium, and wherein the at least one reagent comprises a nitrogen group element, and The nitrogen group elements mentioned therein are selected from phosphorus, arsenic and antimony.

5. The method according to any one of the preceding claims, wherein the metallic element is lead or silver, and wherein the at least one reagent comprises a chalcogenide element, and The chalcogens are selected from sulfur, selenium, and tellurium.

6. The method according to any one of the preceding claims, wherein the first organic ligand compound has a chemical formula selected from: RH2PO, R2HPO, R3PO, RPO(OH)2 or R2POOH, RH2P, R2HP, R3P, ROH, RCOOH, RCOOR', RSH, RNH2, R2NH and R3N, wherein R and R' are each independently selected from the group consisting of C1-C 24 alkyl, C2-C 24 alkenyl, C6-C 24 aryl, and mixtures thereof.

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

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

9. The method of claim 8, wherein the inorganic ligand precursor comprises one or more metal halides.

10. The method according to claim 9, wherein the inorganic ligand precursor comprises PbX2, CsX, InBr3, MgBr3, AgBr, FeX3, AsX3, TlX, CsZnI3, CsInBr3I, CsPbI3, ZnX2, or CsI, wherein X is a halide, or The inorganic ligand precursors described herein comprise CsI and ZnI2, or The inorganic ligand precursors mentioned above contain CsI and InBr3.

11. The method of claim 9, wherein the inorganic ligand precursor comprises a metal halide of the formula A p Zn q X r 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 method of claim 9, wherein the inorganic ligand precursor comprises a metal halide of the 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, or The inorganic ligand precursor comprises a metal halide of formula AMX3, wherein A is selected from cesium, methylammonium, rubidium, potassium, lithium, thallium, and sodium, M is Pb, Sn, Cu, or Zn, and X is a halide, or The inorganic ligand precursor comprises a metal halide of the formula AMX3, wherein A is selected from cesium, methylammonium, rubidium, potassium, lithium and sodium, M is Pb or Zn, and X is a halide.

13. The method according to any one of the preceding claims, wherein the method further comprises: c) Replacing at least a portion of the first organic ligand compound that is surface-coordinated with the crystallization nucleus to form a nanocrystal comprising the crystallization nucleus and a shell encapsulating the crystallization nucleus, wherein the shell is formed from the inorganic ligand precursor. Preferably, step c) includes stirring the mixture for at least 2 hours, preferably 2 to 18 hours, and more preferably 4 to 18 hours. Preferably, the shell comprises a metal halide.

14. The method of claim 13, wherein the mixture formed in step c) further comprises at least one of the following: a) A salt comprising the metal element and the first organic ligand compound; and b) A second plurality of first organic ligand compounds, wherein the second plurality of first organic ligand compounds are not coordinated to the surface of the crystallization nucleus. Preferably, the second plurality of first organic ligand compounds are free in solution.

15. The method according to any one of the preceding claims, wherein the exchange composition further comprises a stabilizer. The stabilizer is selected from sodium acetate, lithium acetate, rubidium acetate, cesium acetate, ammonium acetate, butylamine, trimethylsilyl halides and mixtures thereof, or The stabilizer is selected from sodium acetate, ammonium acetate, trimethylsilyl halides and mixtures thereof.

16. The method according to any one of the preceding claims, wherein the nonpolar solvent is C6-C. 30 Aliphatic organic compounds or C6-C 30 Aromatic organic compounds, Optionally, the nonpolar solvent is selected from C6-C. 30 Amines, C6-C 30 Acids, C6-C 30 Phosphine, C6-C 30 Ethers and mixtures thereof.

17. A nanocrystalline composition obtained by the method of any one of the preceding claims.

18. The method according to any one of claims 1 to 16, wherein the method further comprises: d) Wash the nanocrystalline composition with a solution containing at least one of acetone, methyl acetate, ethyl acetate, and acetonitrile, and e) Dissolve the nanocrystalline composition in a second polar solvent to form a nanocrystalline ink composition. Optionally, the second polar solvent is selected from 2,6-difluoropyridine, γ-butyrolactone, propylene carbonate, dimethylformamide, sulfolane, and combinations thereof.

19. An ink composition comprising the nanocrystalline composition of claim 18.

20. A nanocrystal comprising a crystallization nucleus and a lead-free, inorganic shell at least partially enclosing the crystallization nucleus.

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

22. The nanocrystal of claim 20 or 21, wherein 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, or The shell contains AsX3 or TlX, or The shell contains CsI and ZnI2, or The shell contains CsI and InBr3.

23. The nanocrystal of claim 20 or 21, wherein the shell-containing type A p Zn q X r The metal halide, wherein A is a Group IA metal or an organoammonium salt, X is a halide, and p, q and r are each independently 1, 2 or 3, optionally wherein the organoammonium salt is methylammonium or formamidinium.

24. The nanocrystal of claim 20 or 21, wherein the shell comprises a metal halide of the formula AMX3, wherein A is a Group IA metal, thallium, or an organoammonium salt, M is a metal having a +2 oxidation state, and X is a halide, or The shell contains a metal halide of the form AMX3, wherein A is selected from cesium, methylammonium, rubidium, thallium, and sodium, M is Sn, Cu, or Zn, and X is a halide, or The shell contains a metal halide of the form AMX3, wherein A is selected from cesium, methylammonium, rubidium, and sodium, M is Zn, and X is a halide, or The metal halide mentioned therein is CsZnI3.

25. The nanocrystal according to claim 20 or 21, wherein the shell-containing CsZn x As y Metal halides of I3, wherein the sum of x and y equals 1, wherein y is from 0 to 0.1, optionally wherein y is from 0.01 to 0.1, or The shell-containing Cs3Zn x As y Metal halides of I5, wherein the sum of x and y is equal to 1, wherein y is from 0 to 0.1, and optionally, wherein y is from 0.01 to 0.

1.

26. The nanocrystal of claim 20 or 21, wherein the shell comprises a metal halide of formula Cs3BX6, wherein B is indium or antimony, and X is a halide, or The shell comprises a metal halide of the formula Cs3InX6, CsInX4, or Cs2InX5, wherein X is a halide, or The shell contains CsInBr3I.

27. A nanocrystal composition comprising any one of the nanocrystals according to claims 20 to 26.

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

29. An apparatus selected from IR sensors, photodetectors, sensors, solar cells, bioimaging or biosensing compositions, photovoltaic systems, displays, batteries, lasers, photocatalysts, spectrometers, injectable compositions, field-effect transistors, light-emitting diodes, photonic or optical switching devices or metamaterials, fiber optic amplifiers, optical gain media, optical fibers, infrared LEDs, lasers, and electroluminescent devices, said apparatus comprising the nanocrystalline composition of claim 27. Optionally, the IR sensor or photodetector is modified for use as a 3D camera and a 3D time-of-flight camera in mobile and consumer, automotive, medical, industrial, defense, or aerospace applications. Optionally, the bioimaging or biosensing composition is modified for use as a biomarker or biotag in in vitro or biological applications. Optionally, the infrared LEDs and electroluminescent devices are modified for use in telecommunications equipment, night vision equipment, solar energy conversion, thermoelectric or energy production applications.

30. A method for ligand exchange in nanocrystals, the method comprising a contacting step, the contacting step comprising contacting the following substances: (i) A first nanocrystal composition comprising multiple nanocrystals, wherein the nanocrystals comprise a crystallization nucleus and multiple native ligand compounds surface-coordinated to the crystallization nucleus, and (ii) A second composition comprising a lead-free inorganic ligand precursor, wherein the inorganic ligand precursor comprises one or more metal halides.

31. The method of claim 30, wherein the native ligand compound is an organic ligand compound, and wherein the first nanocrystal composition further comprises a nonpolar solvent.

32. The method according to claim 30 or 31, wherein the inorganic ligand precursor comprises CsX, AsX3, TlX, CsZnI3, CsInBr3I, ZnX2, or CsI, wherein X is a halide, or The inorganic ligand precursor contains AsX3 or TlX, or The inorganic ligand precursors mentioned above comprise CsI and ZnI2, or The inorganic ligand precursors mentioned above contain CsI and InBr3.

33. The method according to claim 30 or 31, wherein the inorganic ligand precursor comprises formula A p Zn q X r The metal halide, wherein A is a Group IA metal or an organoammonium salt, X is a halide, and p, q and r are each independently 1, 2 or 3, optionally wherein the organoammonium salt is methylammonium or formamidinium.

34. The method according to claim 30 or 31, wherein the inorganic ligand precursor comprises a metal halide of the formula AMX3, wherein A is selected from cesium, methylammonium, rubidium, thallium, and sodium, M is Sn, Cu, or Zn, and X is a halide, or The inorganic ligand precursor comprises a metal halide of the formula AMX3, wherein A is selected from cesium, methylammonium, rubidium, and sodium, M is Zn, and X is a halide, or The metal halide is CsZnI3.

35. The method according to claim 30 or 31, wherein the inorganic ligand precursor comprises CsInBr3I.

36. The method according to any one of claims 30 to 35, wherein the method further comprises replacing at least a portion of the native ligand compound surface-coordinated with the crystallization nucleus to form a nanocrystal comprising the crystallization nucleus and a shell encapsulating the crystallization nucleus, wherein the shell is formed from the inorganic ligand precursor. Optionally, the contact step includes stirring the composition for at least 2 hours, preferably 2 to 18 hours, and more preferably 4 to 18 hours.

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

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