Patent Description:
The physical characteristics (e.g., energy bandgaps and melting points) of nanoparticles that are known as intrinsic characteristics depend on their particle size, unlike bulk materials. For example, a semiconductor nanocrystal, also known as a quantum dot (QD), is a semiconductor material having a crystalline structure with a size of several nanometers. Quantum dots have such a small size that they have a large surface area per unit volume and exhibit quantum confinement effects, and thus have different physicochemical characteristics from the characteristics of the bulk material. Quantum dots may absorb light from an excitation source, and may emit energy corresponding to an energy bandgap of the quantum dot. In the quantum dots, the energy bandgap may be selected by controlling the sizes and/or the compositions of the nanocrystals. Also, QDs have desirable photoluminescence properties and have a high color purity. Therefore, QD technology is used for various applications, including a display element, an energy device, a bio-light emitting element, or the like.

The quantum dots may be synthesized in a vapor deposition method such as metal organic chemical vapor deposition (MOCVD) and/or molecular beam epitaxy (MBE), or in a wet chemical method by adding a precursor to an organic solvent to grow crystals. In the wet chemical method, colloidal quantum dots may be prepared, and the quantum dots are coordinated with an organic material such as a dispersing agent on its surface during the crystal growth, and thereby the organic material controls the crystal growth. Therefore, the quantum dots may have a uniform size and shape, and semiconductor nanocrystal particles having various compositions and/or structures (e.g. core/shell) may be more easily synthesized in the wet chemical method than in the vapor deposition method.

The prepared quantum dots are separated and/or rinsed, and may be processed in a form of a composite including the quantum dots dispersed in a matrix such as a polymer for a final application. In the above processes, photoluminescence characteristics of the semiconductor nanocrystals may be degraded. Therefore, there is a need to develop semiconductor nanocrystals having improved stability and photoluminescence characteristic.

<NPL>, discloses cesium lead halide perovskite nanocrystals obtained by anion exchange reactions and tuning of their optical properties.

An embodiment provides quantum dots having improved photoluminescence properties and enhanced stability.

Another embodiment provides a method of producing the quantum dots.

Yet another embodiment provides an electronic device including the quantum dots.

In an embodiment, a quantum dot has a perovskite crystal structure represented by Chemical Formula <NUM>:.

wherein, A is a Group IA metal selected from Rb, Cs, Fr, and a combination thereof, B is a Group IVA metal selected from Si, Ge, Sn, Pb, and a combination thereof, X is a halogen selected from F, Cl, Br, and I, BF<NUM>-, or a combination thereof, and wherein the quantum dot has a size of about <NUM> nanometer to about <NUM> nanometers.

A photoluminescence peak wavelength of the quantum dot may be in a range of about <NUM> to about <NUM>.

The quantum dot further includes at least one of a first dopant and a second dopant, and the first dopant includes potassium (K) or a first metal having a crystal ionic radius of less than about <NUM> picometers (pm) and being different from the Group IA metal and the Group IVA metal, and the second dopant includes a non-metal element that forms a bond with the Group IVA metal.

The first metal may have a crystal ionic radius that is smaller than a crystal ionic radius of the Group IVA metal of the B in Chemical Formula <NUM>.

The first metal may include Zn, Cd, Hg, Ga, In, Tl, Cu, Al, Li, Na, Be, Mg, Ca, Sr, Ag, Pt, Pd, Ni, Co, Fe, Cr, Zr, Mn, Ti, Ce, Gd, or a combination thereof.

In an embodiment, the non-metal element includes S, Se, Te, or a combination thereof.

In an embodiment, the quantum dot includes the first dopant, and an amount of the first dopant may be greater than or equal to about <NUM> parts per million (ppm) when measured by an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis.

In another embodiment, the quantum dot includes the second dopant, and an amount of the second dopant may be greater than or equal to about <NUM> ppm when measured by an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis.

In an embodiment, the quantum dot includes the first dopant and the second dopant and each of an amount of the first dopant and an amount of the second dopant may be greater than or equal to about <NUM> ppm when measured by an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis, respectively.

The quantum dot may include CsPbCl<NUM>, CsPbBr<NUM>, CsPbI<NUM>, CsPb(Cl,I)<NUM>, CsPb(Br,I)<NUM>, CsPb(Br,Cl)<NUM>, or a combination thereof.

In the quantum dot, an atomic ratio of a halogen with respect to the Group IA metal when measured by a transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX) analysis is greater than about <NUM>.

In the quantum dot, an atomic ratio of a halogen with respect to the Group IA metal when measured by a transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX) analysis may be greater than or equal to about <NUM>.

The quantum dot may have an organic ligand compound selected from RCOOH, RNH<NUM>, R<NUM>NH, R<NUM>N, RSH, R<NUM>PO, R<NUM>P, ROH, RCOOR', RPO(OH)<NUM>, R<NUM>POOH, RCOOCOR' (wherein, R and R' are independently a substituted or unsubstituted C1 to C24 aliphatic hydrocarbon group or a substituted or unsubstituted C5 to C24 aromatic hydrocarbon group), and a combination thereof on a surface of the quantum dot.

The quantum dot may have a full width at half maximum (FWHM) of a photoluminescence peak wavelength of less than or equal to about <NUM>.

The quantum dot may have quantum efficiency of greater than or equal to about <NUM> %.

The quantum dot may not exhibit a decrease in quantum efficiency until after about <NUM> hours when it is dispersed in toluene and the resulting solution is allowed to stand in air.

In another embodiment, a method of producing a quantum dot is provided, the method including:.

The first precursor may include NR<NUM>+ (wherein each R independently is a hydrogen atom or a C1 to C10 straight or branched alkyl group) and BF<NUM>-.

The second precursor may include a Pb halide, a Ge halide, a Si halide, a Sn halide, or a combination thereof.

In an embodiment, the first metal is present and includes Zn, Cd, Hg, Ga, In, Tl, Cu, Al, Li, Na, Be, Mg, Ca, Sr, Ag, Pt, Pd, Ni, Co, Fe, Cr, Zr, Mn, Ti, Ce, Gd, or a combination thereof.

The non-metal element may include S, Se, Te, or a combination thereof.

The first precursor may be a metal powder, a metal carbonate, an alkylated metal compound, a metal alkoxide, a metal carboxylate, a metal nitrate, a metal perchlorate, a metal sulfate, a metal acetylacetonate, a metal halide, a metal cyanide, a metal hydroxide, a metal oxide, a metal peroxide, or a combination thereof.

The reaction solution may include the first additive, and the first additive includes a halide of the first metal.

The first additive may include ZnX<NUM>, CdX<NUM>, HgX<NUM>, GaX<NUM>, InX<NUM>, TIX<NUM>, CuX<NUM>, AlX<NUM>, LiX, NaX, BeX<NUM>, MgX<NUM>, CaX<NUM>, SrX<NUM>, AgX, PtX<NUM>, PtX<NUM>, PdX<NUM>, NiX<NUM>, CoX<NUM>, FeX<NUM>, CrX<NUM>, CrX<NUM>, ZrX<NUM>, ZrX<NUM>, MnX<NUM>, TiX<NUM>, CeX<NUM>, GdX<NUM>, or a combination thereof (wherein X is F, Cl, Br, or I).

The reaction solution may include the second additive and the second additive may include sulfur-trioctylphosphine (S-TOP), sulfur-tributylphosphine (S-TBP), sulfur-triphenylphosphine (S-TPP), sulfur-trioctylamine (S-TOA), sulfur-octadecene (S-ODE), sulfur-diphenylphosphine (S-DPP), sulfur-oleylamine (S-oleylamine), sulfur-dodecylamine (S-dodecylamine), dodecanethiol (DDT), octanethiol, selenium-trioctylphosphine (Se-TOP), selenium-tributylphosphine (Se-TBP), selenium-triphenylphosphine (Se-TPP), selenium-octadecene (Se-ODE), selenium-diphenylphosphine (Se-DPP), selenium-dodecylamine (Se-dodecylamine), tellurium-tributylphosphine (Te-TBP), tellurium-triphenylphosphine (Te-TPP), tellurium-trioctylphosphine (Te-TOP), tellurium-octadecene (Te-ODE), tellurium-diphenylphosphine (Te-DPP), tellurium-oleylamine (Te-oleylamine), tellurium-dodecylamine (Te-dodecylamine), or a combination thereof.

The reaction solution may further include a halogen organic ligand compound.

The halogen organic ligand compound may be HF, HCl, HBr, HI, alkyl halide (e.g. CH<NUM>Cl, CH<NUM>Br), dichloroethylene, dibromoethylene, tetrachloroethylene, tetrabromoethylene, hexachloroethane, hexachloro-propylene, chlorohexanol, bromohexanol, C<NUM>H<NUM>Br, C<NUM>H<NUM>Cl, N-bromosuccinimide, or a combination thereof.

The providing the reaction solution may use a solvent selected from a C6 to C22 amine compound, a nitrogen-containing heterocyclic compound, a C6 to C40 aliphatic hydrocarbon, a C6 to C30 aromatic hydrocarbon, a C6 to C22 phosphine oxide compound, a C12 to C22 aromatic ether, and a combination thereof.

The reaction solution may further include at least one organic ligand compound selected from RCOOH, RNH<NUM>, R<NUM>NH, R<NUM>N, RSH, R<NUM>PO, R<NUM>P, ROH, RCOOR', RPO(OH)<NUM>, R<NUM>POOH, RCOOCOR' (wherein, each R and R' are independently a substituted or unsubstituted C1 to C24 aliphatic hydrocarbon group or a substituted or unsubstituted C5 to C24 aromatic hydrocarbon group), and a combination thereof.

The providing of the reaction solution may include:.

In another embodiment, a quantum dot-polymer composite includes.

The polymer matrix may include a thiolene polymer, a (meth)acrylate polymer, a urethane polymer, an epoxy polymer, a vinyl polymer, a silicone polymer resin, or a combination thereof.

The quantum dot-polymer composite may have blue light conversion efficiency of greater than or equal to about <NUM> %.

Another embodiment provides an electronic device including the quantum dot-polymer composite.

Still another embodiment provides an electronic device including the quantum dot.

The electronic device may be a light emitting diode (LED), an organic light emitting diode (OLED), a sensor, an imaging sensor, or a solar cell electronic device, or a liquid crystal display (LCD) device.

The quantum dots of the embodiments may have enhanced photoluminescence properties and stability even when they undergo a separation from the synthesis solvent and/or a washing process after the separation therefrom and/or when they are prepared into a quantum dot-polymer matrix.

Advantages and characteristics of this disclosure, and a method for achieving the same, will become evident referring to the following example embodiments together with the drawings attached hereto. The embodiments may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. If not defined otherwise, all terms (including technical and scientific terms) in the specification may be defined as commonly understood by one skilled in the art. The terms defined in a generally-used dictionary may not be interpreted ideally or exaggeratedly unless clearly defined. In addition, unless explicitly described to the contrary, the word "comprise" and variations such as "comprises" or "comprising," will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

Further, the singular includes the plural, unless mentioned otherwise.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification.

It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present.

It will be understood that, although the terms "first," "second," "third," etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, "a first element," "component," "region," "layer," or "section" discussed below could be termed a second element, component, region, layer, or section without departing from the teachings herein.

As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, including "at least one," unless the content clearly indicates otherwise. " It will be further understood that the terms "comprises" and/or "comprising," or "includes" and/or "including" when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

For example, "about" can mean within one or more standard deviations, or within ± <NUM>%, or <NUM>% of the stated value.

As used herein, when a definition is not otherwise provided, the term "substituted" refers to a group or compound wherein at least one of the hydrogen atoms thereof is substituted with a C1 to C30 alkyl group, a C2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30 alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30 heteroalkyl group, a C3 to C30 heteroalkylaryl group, a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C3 to C30 cycloalkynyl group, a C2 to C30 heterocycloalkyl group, a halogen (-F, -Cl, -Br, or -I), a hydroxy group (-OH), a nitro group (-NO<NUM>), a cyano group (-CN), an amino group (-NRR' wherein R and R' are independently hydrogen or a C1 to C6 alkyl group), an azido group (-N<NUM>), an amidino group (-C(=NH)NH<NUM>), a hydrazino group (-NHNH<NUM>), a hydrazono group (=N(NH<NUM>), an aldehyde group (-C(=O)H), a carbamoyl group (-C(O)NH<NUM>), a thiol group (-SH), an ester group (-C(=O)OR, wherein R is a C1 to C6 alkyl group or a C6 to C12 aryl group), a carboxyl group (-COOH) or a salt thereof (-C(=O)OM, wherein M is an organic or inorganic cation), a sulfonic acid group (-SO<NUM>H) or a salt thereof (-SO<NUM>M, wherein M is an organic or inorganic cation), a phosphoric acid group (-PO<NUM>H<NUM>) or a salt thereof (-PO<NUM>MH or -PO<NUM>M<NUM>, wherein M is an organic or inorganic cation), and a combination thereof.

As used herein, the term "hydrocarbon group" refers to a monovalent group containing carbon and hydrogen (e.g., alkyl group, alkenyl group, alkynyl group, or aryl group) formed by a removal of a hydrogen atom from an aliphatic or aromatic hydrocarbon such as alkane, alkene, alkyne, or arene. In the hydrocarbon group, at least one methylene (-CH<NUM>-) moiety may be replaced with an oxide (-O-) moiety.

As used herein, the term "alkyl" refers to a linear or branched, saturated monovalent hydrocarbon group (e.g., methyl, hexyl, etc.).

As used herein, the term "alkenyl" refers to a linear or branched monovalent hydrocarbon group having at least one carbon-carbon double bond.

As used herein, the term "aryl" refers to a monovalent group formed by removing one hydrogen atom from at least one aromatic ring (e.g., phenyl or naphthyl).

As used herein, when a definition is not otherwise provided, the term "hetero" refers to inclusion of <NUM> to <NUM> heteroatoms that can be N, O, S, Si, P, or a combination thereof.

Further as used herein, when a definition is not otherwise provided, an alkyl group is a C1 to C20 alkyl, or a C1 to C12 alkyl, or a C1 to C6 alkyl.

As used herein, the term "Group" refers to a Group of the Periodic Table.

As used herein, the term "metal" refers to a metal such as an alkali metal, an alkaline earth metal, a transition metal, and a basic metal. The term "metal" also includes a semi-metal such as Si and the like.

As used herein, "doping" refers to the inclusion of a dopant in a crystal structure. In an exemplary embodiment, inclusion of a dopant in the crystal structure does not substantially change the crystal structure. For example, a dopant atom (e.g., a first metal such as Zn, potassium, or a chalcogen) may be substituted for an atom in a crystal structure, or may be present in the interstices of a crystal lattice. In some embodiments, the dopant element may bind with an element constituting the crystal lattice to form a chemical species attached to a surface thereof.

In some embodiments, when the dopant is present in the lattice or as an alloy, an X-ray diffraction spectrum of the quantum dot including the dopant may show a crystalline peak that is shifted to a different diffraction angle relative to an X-ray diffraction spectrum of the quantum dot without the dopant. In other embodiments, the X-ray diffraction spectrum of a quantum dot including the dopant is substantially the same as the X-ray diffraction spectrum of an undoped quantum dot. When the dopant is present as a crystal outside of the lattice of the quantum dot, its inherent peak may be detected in an X-ray diffraction spectrum thereof. In an embodiment, the presence of the dopant may be confirmed, for example, by X-ray photoelectron spectroscopy, energy dispersive X ray spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), or a combination thereof.

As used herein, the term "quantum yield" (QY) or the term "quantum efficiency (QE) is a value determined from a photoluminescence spectrum obtained by dispersing quantum dots in toluene, and may be calculated with respect to the photoluminescent peak of an organic solution of a reference dye (e.g., an ethanol solution of coumarin dye (absorption (optical density) at <NUM> nanometers (nm) is <NUM>)). As used herein, the term "quantum yield (QY)" and the term "quantum efficiency (QE)" may have substantially the same meaning and can be used interchangeably.

wherein A is a Group IA metal selected from Rb, Cs, Fr, and a combination thereof, B is a Group IVA metal selected from Si, Ge, Sn, Pb, and a combination thereof, X is BF<NUM>-, at least one halogen selected from F, Cl, Br, and I, or a combination thereof. In an embodiment, a surface of the quantum dot includes a halogen.

In an embodiment, in the above Chemical Formula <NUM>, A is a Group IA metal (selected from Rb, Cs, Fr, and a combination thereof), NR<NUM>+, wherein, each R independently is a hydrogen atom or a substituted or unsubstituted C1 to C10 straight or branched alkyl group (including but not limited to CH<NUM>NH<NUM>+, NH<NUM>+, or C<NUM>H<NUM>NH<NUM>+),[CH(NH<NUM>)<NUM>]+, or a combination thereof, B is a Group IVA metal (selected from Si, Ge, Sn, Pb, and a combination thereof), X is a halogen (selected from F, Cl, Br, I, and a combination thereof), BF<NUM>-, or a combination thereof, and includes at least one of a first dopant and a second dopant, and the first and the second dopants will be set forth below.

The perovskite crystal structure may have a cubic crystalline lattice and is confirmed by an X-ray diffraction spectrum, and the quantum dot may have a cubic shape and/or a rectangular parallelepiped shape.

The quantum dot represented by Chemical Formula <NUM> may include CsPbCl<NUM>, CsPbBr<NUM>, CsPbI<NUM>, CsPb(Cl,I)<NUM>, CsPb(Br,I) <NUM>, CsPb(Br,Cl)<NUM>, or a combination thereof. As used herein, the expression (X1, X2) (wherein X1 and X2 are each independently a halogen different from each other) such as (Cl,I), (Br,I), and (Br,I), refers to a quantum dot that includes two different halogens (i.e., Cl and I, Br and I, or Br and Cl). When the quantum dot includes two halogens, the mole ratio therebetween is not particularly limited. For example, when the quantum dot includes two halogens, X1 and X2, the amount of the X2 per one mole of X1 is greater than or equal to about <NUM> moles, for example, <NUM> moles, greater than or equal to about <NUM> moles, greater than or equal to about <NUM> moles, greater than or equal to about <NUM> moles, or greater than or equal to about <NUM> moles. In an embodiment, when the quantum dot includes two halogens, X1 and X2, the amount of the X2 per one mole of X1 is less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, less than or equal to about <NUM> moles, or less than or equal to about <NUM> mole. For example, when the quantum dot includes two halogens, X1 and X2, the amount of the X2 per one mole of X1 is about <NUM> moles to about <NUM> moles, about <NUM> moles to about <NUM> moles, or about <NUM> moles to about <NUM> moles, but it is not limited thereto.

In the quantum dot, an atomic ratio of the halogen atoms relative to the Group IA metal atoms when measured by a transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX) analysis is greater than or equal to about <NUM>, for example, greater than about <NUM> or greater than or equal to about <NUM>. The quantum dot includes a greater amount of halogen than a stoichiometric amount for the formation of the perovskite crystal and/or the quantum dot may have a halogen rich surface.

The quantum dot further includes at least one of a first dopant and a second dopant. The first dopant includes potassium (K) or a first metal having a crystal ionic radius of less than about <NUM> picometers (pm) and being different from the Group IA metal and the Group IVA metal. The second dopant includes a non-metal element that forms a bond with the Group IVA metal. For example, the first metal may have a crystal ionic radius of about <NUM> pm to about <NUM> pm. The first metal may have a crystal ionic radius that is less than the crystal ionic radius of the Group IVA metal of B. For example, when B is Pb, the crystal ionic radius of the first metal is less than <NUM> pm. The crystal ionic radius may correspond to the physical size of the ion in a solid, and in this regard, the publication of the revised ionic radius by Shannon may be referred to (e.g., <NPL>).

The first dopant may be a substitute for the metal element (e.g., the Group IA metal such as Cs and Rb, and/or the Group IVA metal such as Pb) in the quantum dot. In an embodiment, the first dopant may include the first metal having a crystal ionic radius that is less than crystal ionic radius of the Group IVA metal. In an embodiment, the first dopant may include a metal ion having the same valency as that of the Group IVA metal or a Group IA metal (e.g., a monovalent ion or a divalent ion). In an embodiment, the first dopant may include a metal element that forms a compound (e.g., a metal oxide) having a lattice structure that is substantially similar to that of the perovskite lattice structure. The second dopant may include an element that may form a chemical bond with the Group IVA metal (e.g., Pb) during the synthesis of a quantum dot, and thereby may be precipitated out of solution. Without wishing to be bound by theory, this may contribute to decreasing the amount of the Group IVA metal in a reaction system during the synthesis. As a result, the resulting quantum dot may include an excess amount of the halogen, or a surface of the quantum dot may include a halogen.

In some embodiments, the first metal may be selected from Zn, Cd, Hg, Ga, In, Tl, Cu, Al, Li, Na, Be, Mg, Ca, Sr, Ag, Pt, Pd, Ni, Co, Fe, Cr, Zr, Mn, Ti, Ce, Gd, and a combination thereof. In some embodiments, the non-metal element may be selected from S, Se, Te, and a combination thereof.

The presence of the first and second dopants may be confirmed by an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis. For example, in the quantum dot, the amount of the first dopant may be greater than or equal to about <NUM> ppm, for example, greater than or equal to about <NUM> ppm as measured by ICP-AES. In the quantum dot, the amount of the second dopant may be greater than or equal to about <NUM> ppm, for example, about <NUM> ppm when measured by ICP-AES.

The quantum dot may be a colloidal quantum dot prepared in a wet chemical method, and thus a surface of the quantum dot may have an organic ligand compound selected from RCOOH, RNH<NUM>, R<NUM>NH, R<NUM>N, RSH, R<NUM>PO, R<NUM>P, ROH, RCOOR', RPO(OH)<NUM>, R<NUM>POOH, RCOOCOR' (wherein, each R and R' are independently a substituted or unsubstituted C1 to C24 aliphatic hydrocarbon group such as an alkyl group, an alkenyl group, or an alkynyl group, or a substituted or unsubstituted C5 to C24 aromatic hydrocarbon group such as an aryl group), and a combination thereof.

Specific examples of the organic ligand compound may include methane thiol, ethane thiol, propane thiol, butane thiol, pentane thiol, hexane thiol, octane thiol, dodecane thiol, hexadecane thiol, octadecane thiol, benzyl thiol; methane amine, ethane amine, propane amine, butane amine, pentane amine, hexane amine, octane amine, dodecane amine, hexadecyl amine, oleyl amine, octadecyl amine, dimethyl amine, diethyl amine, dipropyl amine, dioleylamine; methanoic acid, ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, dodecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid, benzoic acid, palmitic acid, stearic acid; a phosphine such as methyl phosphine, ethyl phosphine, propyl phosphine, butyl phosphine, pentyl phosphine, tributylphosphine, or trioctylphosphine; a phosphine oxide compound such as methyl phosphine oxide, ethyl phosphine oxide, propyl phosphine oxide, butyl phosphine oxide, or trioctylphosphine oxide; diphenyl phosphine, a triphenyl phosphine compound or an oxide compound thereof; phosphonic acid, and the like, but are not limited thereto. The organic ligand compound may be used alone or as a mixture of at least two organic ligands.

In some embodiments, the quantum dot does not include an amine organic ligand having an alkyl group of at least <NUM> carbon atoms, such as at least <NUM> carbon atoms (e.g., n-octyl amine).

The quantum dot (i.e., a nanocrystal particle including a semiconductor material) may have an energy bandgap that varies based on size and composition, and may have desirable photoluminescence properties such as color purity. These compounds may be suitable as a material applicable to various fields such as a display, an energy device, a semiconductor, a bio device, and the like. A colloidal halide perovskite quantum dot may be a suitable quantum dot material due to its photoluminescence properties such as color tunability, desirable bandgap, and the like.

The present inventors have found that the halide perovskite quantum dot of, for instance, a CsPbX<NUM> nanoparticle or a CH<NUM>NHPbX<NUM> nanoparticle, does not have desirable stability. For example, the halide perovskite quantum dot may exhibit an undesirable quantum yield when they are separated from a synthesis solvent and/or washed to remove the solvent, or after dispersion in a dispersion solvent (e.g., toluene). In addition, the dispersibility of the halide perovskite quantum dot may decrease over time. For example, when the halide perovskite quantum dot is separated from the synthesis solvent thereof, dispersed in a dispersion solvent such as toluene, and then allowed to stand in the air, it loses its photoluminescence within one week, and is precipitated.

Without wishing to be bound by any theory, when the halide perovskite quantum dot is separated from their synthesis solvent and washed, they may lose an amount of an organic ligand previously bound to a surface thereof, and due to such a loss of the ligand, the metal elements may be exposed on a surface thereof. The exposed metal elements may be susceptible to an external environment such as oxygen, moisture, or heat, and the metal elements may then be transformed into an oxide or a decomposition product. However, rather than being used directly after the synthesis, the quantum dots may be washed with a non-solvent for the removal of impurities, and then be re-dispersed in a solvent optimized for an applied field. In addition, the quantum dots may go through a surface exchange or may be prepared into a quantum dot-polymer composite. The aforementioned changes on a surface of the quantum dot (i.e., loss of the ligand and exposure of a metal atom) after the washing with the non-solvent and the stability deterioration caused thereby may hinder the subsequent application of the quantum dot.

A quantum dot according to an embodiment may include a first dopant such as Zn and a second dopant such as Se and/or additionally a halogen in an amount that exceeds the amount that is necessary for the formation of the perovskite structure. Accordingly, the quantum dots according to an embodiment may not show a substantial decrease in quantum efficiency (or a quantum yield) when they are removed from a synthesis solvent, washed, and then dispersed again in a dispersion solvent. For example, after being separated from the synthesis solvent, the quantum dots of an embodiment may have a quantum efficiency of greater than or equal to about <NUM> %, for example, greater than or equal to about <NUM> %, greater than or equal to about <NUM> %, or greater than or equal to about <NUM> % of its original quantum efficiency. In addition, the quantum dots of an embodiment may be stable with respect to an external environment such as oxygen, moisture, and the like when they are dispersed in a dispersion solvent (e.g., toluene). For example, the quantum dots of an embodiment may maintain their initial quantum efficiency for about <NUM> hours or longer, or about <NUM> hours or longer, in the air. In addition, the quantum dots of an embodiment may include a surface ligand in at least an amount necessary for maintaining their stability, even when they are separated from the synthesis solvent and washed. Therefore, the quantum dots of an embodiment may be re-dispersed in various dispersion solvents even after being kept in the air. In addition, the perovskite quantum dots according to an embodiment may include an excess amount of a halogen together with a first dopant and/or a second dopant on a surface thereof while keeping the ligand loss at a minimum level or suppressing the same. Therefore, a surface oxidation of the quantum dots and/or loss of constituting elements due to heat, moisture, light, and the like may be minimized. Without wishing to be bound by any theory, inclusion of the excess amount of halogen on a surface thereof together with the first/second dopants may bring forth a change in the elemental composition of the entire and/or the surface of the quantum dot (e.g., the entire and/or the surface compositions of the quantum dot) and this may reduce the amount of the organic ligand that is lost when the quantum dots are washed with a non-solvent. In addition, an individual or combined effect of the halogen element, the dopant, and the ligand on a surface thereof may reduce the amount of oxidation of the metal element constituting the perovskite structure, and thereby may preserve the perovskite structure. The perovskite quantum dot of the aforementioned embodiments of Chemical Formula <NUM> may be an inorganic material, and thus may show desirable long term stability in comparison of the perovskite quantum dot including an organic substance (e.g., an amine salt).

The perovskite quantum dot may have a size of about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. The size of the quantum dot may be measured using any suitable method. For example, the size of the quantum dot may be directly measured from a transmission electron microscopic (TEM) image or may be calculated from the full width at half maximum (FWHM) of the peak of the XRD spectrum and Scherrer equation.

The quantum dot may have a perovskite crystal structure and a cubic or rectangular cuboid shape, but is not limited thereto. The quantum dot may have a FWHM of a photoluminescence peak wavelength of less than or equal to about <NUM>, for example, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>. The quantum dot may have quantum efficiency (QE) or quantum yield (QY) of greater than or equal to about <NUM> %, for example, greater than or equal to about <NUM> %, greater than or equal to about <NUM> %, greater than or equal to about <NUM> %, greater than or equal to about <NUM> %, greater than or equal to about <NUM> %, or greater than or equal to about <NUM> %. The perovskite quantum dot of an embodiment, for example, includes no cadmium but may show desirable photoluminescence characteristics (e.g., a high quantum efficiency, a narrow FWHM, and thus desirable color purity, and the like).

Other embodiments provide a method of preparing a perovskite quantum dot, which includes:.

The halogen may include F, Cl, Br, I, or a combination thereof.

The preparing of the reaction solution may include solvating the first precursor, the second precursor, the first additive, the second additive, or combination thereof in a solvent selected from a C6 to C22 amine compound, a nitrogen-containing heterocyclic compound, a C6 to C40 aliphatic hydrocarbon, a C6 to C30 aromatic hydrocarbon, a C6 to C22 phosphine oxide compound, a C12 to C22 aromatic ether, and a combination thereof.

The reaction solution may further include at least one organic ligand compound selected from RCOOH, RNH<NUM>, R<NUM>NH, R<NUM>N, RSH, R<NUM>PO, R<NUM>P, ROH, RCOOR', RPO(OH)<NUM>, R<NUM>POOH, RCOOCOR' (wherein, each R and R' are independently a substituted or unsubstituted C1 to C24 aliphatic hydrocarbon group or a substituted or unsubstituted C5 to C24 aromatic hydrocarbon group) and a combination thereof.

Referring to <FIG> illustrating non-limiting examples, the preparation of a reaction solution is illustrated in more detail.

Referring to <FIG>, the second precursor (e.g., PbX<NUM>) and the first additive (e.g., ZnX<NUM>) are mixed in a solvent, and the organic ligand (e.g., oleylamine and oleic acid) is injected thereinto to prepare a solution of the second precursor and the first additive.

Aside from the preparation of the aforementioned solution, a compound including a Group IA metal (e.g., Cs<NUM>CO<NUM>) or a quaternary ammonium salt (e.g., a [CH(NH<NUM>)<NUM>]+ salt or a NR<NUM>+ salt such as CH<NUM>NH<NUM>Br or CH<NUM>NH<NUM>BF<NUM>) is dissolved in a solvent and optionally a compound (e.g., oleic acid) for forming the first precursor, and the solution is optionally heated to prepare a first precursor solution including the first precursor (e.g., Cs oleate, that is, Group IA metal-carboxylate or quaternary ammonium salt such as CH<NUM>NH<NUM>Br).

The first precursor solution is added to a solution including the second precursor and the first additive to obtain a reaction solution, and a reaction between the first and the second precursors is carried out in the reaction solution. The reaction may be carried out at a predetermined temperature (e.g., at greater than or equal to about <NUM> (e.g., a temperature of about <NUM> to about <NUM>). If desired, the second additive (e.g., selenium-triphenylphosphine (Se-TOP)) may be added to the reaction solution before the initiation of the reaction or after the progress of the reaction, and before the completion of the reaction.

Referring to <FIG>, the second precursor (e.g., PbX<NUM>) may be mixed with (or dissolved in) a solvent, and the organic ligand (e.g., oleylamine and oleic acid) is injected thereto and the second precursor is solubilized to prepare a second precursor-containing solution.

A first precursor solution including the first precursor (e.g., Cs oleate, that is, a Group IA metal-carboxylate) may be prepared by dissolving a compound including a Group IA metal (e.g., Cs<NUM>CO<NUM>) in a solvent and optionally a compound for forming the first precursor (e.g., oleic acid), and optionally heating the solution.

The first precursor solution is added to the second precursor-containing solution to obtain a reaction solution, and a reaction between the first and the second precursors is carried out, for example, at a temperature of greater than or equal to about <NUM> (e.g., a temperature of about <NUM> to about <NUM>), and the second additive (e.g., Se-TOP) may be added to the reaction solution before the initiation of the reaction or after the progress of the reaction, and before the completion of the reaction. In some embodiments, the first precursor solution may be mixed with the second precursor-containing solution during a process of preparing the second precursor-containing solution or adding materials for the second precursor to the first precursor solution in any order.

Referring to <FIG>, the second precursor (e.g., PbX<NUM>) and the first additive (e.g., ZnX<NUM>) are mixed with (dissolved in) a solvent, and the organic ligand (e.g., oleylamine and oleic acid) is injected thereto to dissolve the second precursor and the first additive and thereby a solution including the second precursor and the first additive is prepared. The solution including the first precursor may be prepared in accordance with the aforementioned manner and may be added to the solution including the second precursor and the first additive to provide the reaction solution. As the reaction solution is heated to a reaction temperature (e.g., a temperature of greater than or equal to about <NUM>, for example, a temperature of about <NUM> to about <NUM>), a reaction between the first and the second precursors is carried out to synthesize the aforementioned quantum dot.

In the method illustrated in <FIG>, the first additive and the second precursor are simultaneously dissolved in a solvent, but it is not limited thereto. The first additive may be prepared as a separate solution from the second precursor and then be added to the reaction solution at any point prior to or during the synthesis of the quantum dot represented by Chemical Formula <NUM>.

In addition, the second additive may be added to the reaction solution at any time prior to or during the synthesis of the quantum dot represented by Chemical Formula <NUM>.

As described above, in the aforementioned method, the reaction solution may include the first additive, the second additive, or both, before the initiation of the reaction or during the progress of the reaction. Accordingly, the reaction solution may include a reduced concentration of the Group IVA metal (e.g. Pb) and a relatively high concentration of the halogen.

Without wishing to be bound by any theory, in the aforementioned method, the first additive may play a role of an additional supply source of the halogen and may contribute to reducing the relative amount of the Group IVA metal in the prepared quantum dot because the metal included therein (e.g., the first metal) may replace the Group IVA metal or may be added (e.g., be injected as an interstitial element or be bound physically on a surface of the quantum dot). In addition, the second additive may form a precipitate together with the Group IVA metal element (e.g., PbSe) during the synthesis of the quantum dot represented by Chemical Formula <NUM>, and thereby may further reduce the relative amount of the Group IVA metal element in the quantum dot. Therefore, the quantum dot prepared according to the aforementioned method may have a halogen rich surface as confirmed by a TEM-EDX analysis without additional process steps such as a ligand assisted re-precipitation (LARP) process. In addition, the quantum dot prepared according to the aforementioned method may include the first dopant originated from the first additive and the second dopant originated from the second additive.

In the aforementioned method, the first precursor includes the Group IA metal (e.g., Cs or Rb), and may be a metal powder, metal carbonate, alkylated metal compound, metal alkoxide, metal carboxylate, metal nitrate, metal perchlorate, metal sulfate, metal acetylacetonate, metal halide, metal cyanide, metal hydroxide, metal oxide, or metal peroxide. The first precursor may be used alone or as a mixture of two or more species. In an embodiment, the first precursor may include NR<NUM>+ (wherein each R independently is a hydrogen atom or a substituted or unsubstituted C1 to C10 straight or branched alkyl group) such as CH<NUM>NH<NUM>+, NH<NUM>+, C<NUM>H<NUM>NH<NUM>+, HC(NH<NUM>)<NUM>+, or a combination thereof. The first precursor may include NR<NUM>+ and BF<NUM>- such CH<NUM>NH<NUM> BF<NUM>.

The first precursor may include the one (e.g., Cs-oleate) obtained by reacting a compound (e.g., Cs<NUM>CO<NUM>) including a Group IA metal with a certain compound (e.g., an organic ligand such as oleic acid) in a reaction solvent. The first precursor may be heated to a temperature of greater than or equal to about <NUM>, for example, greater than or equal to about <NUM>, before the injection to minimize the amount of precipitation from the reaction solution.

The second precursor may include a Pb halide such as PbCl<NUM>, Pbl<NUM>, or PbBr<NUM>, a Ge halide such as GeCl<NUM>, GeCl<NUM>, Gel<NUM>, Gel<NUM>, GeBr<NUM>, or GeBr<NUM>, a Si halide such as SiCl<NUM>, SiCl<NUM>, SiI<NUM>, SiI<NUM>, SiBr<NUM>, SiBr<NUM>, a Sn halide such as SnCl<NUM>, SnI<NUM>, or SnBr<NUM>, or a combination thereof. The second precursor may be used alone or as a mixture of at least two compounds. For the solubilization of the second precursor, the resulting mixture may be heated at a predetermined temperature (e.g., greater than or equal to about <NUM>, for example, greater than or equal to about <NUM>) in the presence of an organic ligand depending on a selected solvent.

The first additive may include a zinc halide such as ZnCl<NUM>, ZnBr<NUM>, or ZnI<NUM>, a Cd halide such as CdCl<NUM>, CdBr<NUM>, or CdI<NUM>, a Hg halide such as HgCl<NUM>, HgBr<NUM>, or HgI<NUM>, a Ga halide such as GaCl<NUM>, GaBr<NUM>, or GaI<NUM>, an In halide such as InCl<NUM>, InBr<NUM>, or InI<NUM>, a Tl halide such as TI Cl, TIBr, or TlI, a Cu halide such as CuCl<NUM>, CuBr<NUM>, or CuI<NUM>, a Al halide such as AlCl<NUM>, AlBr<NUM>, or AlI<NUM>, a Li halide such as LiCl, LiBr, or Lil, a Na halide such as NaCl, NaBr, or Nal, a K halide such as KCI, KBr, or KI, a Be halide such as BeCl<NUM>, BeBr<NUM>, or BeI<NUM>, a Mg halide such as MgCl<NUM>, MgBr<NUM>, or MgI<NUM>, a Ca halide such as CaCl<NUM>, CaBr<NUM>, or CaI<NUM>, a Sr halide such as SrCl<NUM>, SrBr<NUM>, or SrI<NUM>, a Ag halide such as AgCl, AgBr, or AgI, a Pt halide such as PtCl<NUM>, PtBr<NUM>, or PtI<NUM>, a Pd halide such as PdCl<NUM>, PdBr<NUM>, or PdI<NUM>, a Ni halide such as NiCl<NUM>, NiBr<NUM>, or NiI<NUM>, a Co halide such as CoCl<NUM>, CoBr<NUM>, or CoI<NUM>, a Fe halide such as FeCl<NUM>, FeBr<NUM>, or FeI<NUM>, a Cr halide such as CrCl<NUM>, CrBr<NUM>, or CrI<NUM>, a Zr halide such as ZrCl<NUM>, ZrBr<NUM>, or ZrI<NUM>, a Mn halide such as MnCl<NUM>, MnBr<NUM>, or MnI<NUM>, a Ti halide such as TiCl<NUM>, TiBr<NUM>, or TiI<NUM>, a Ce halide such as CeCl<NUM>, CeBr<NUM>, or CeI<NUM>, a Gd halide such as GdCl<NUM>, GdBr<NUM>, or GdI<NUM>, or a combination thereof. The first additive may be used alone or as a mixture of two or more compounds.

The second additive may be sulfur-trioctylphosphine (S-TOP), sulfur-tributylphosphine (S-TBP), sulfur-triphenylphosphine (S-TPP), sulfur-trioctylamine (S-TOA), sulfur-octadecene (S-ODE), sulfur-diphenylphosphine (S-DPP), sulfur-oleylamine (S-oleylamine), sulfur-dodecylamine (S-dodecylamine), dodecanethiol (DDT), octanethiol, selenium-trioctylphosphine (Se-TOP), selenium-tributylphosphine (Se-TBP), selenium-triphenylphosphine (Se-TPP), selenium-octadecene (Se-ODE), selenium-diphenylphosphine (Se-DPP), selenium-dodecylamine(Se-Dodecylamine), tellurium-tributylphosphine (Te-TBP), tellurium-triphenylphosphine (Te-TPP), tellurium-trioctylphosphine (Te-TOP), tellurium-octadecene (Te-ODE), tellurium-diphenylphosphine (Te-DPP), tellurium-oleylamine (Te-Oleylamine), tellurium-dodecylamine (Te-dodecylamine), or a combination thereof.

The solvent may include a C6 to C22 primary alkylamine such as hexadecylamine, a C6 to C22 secondary alkylamine such as dioctylamine, a C6 to C40 tertiary alkylamine such as trioctylamine, a nitrogen-containing heterocyclic compound such as pyridine, a C6 to C40 olefin such as octadecene, a C6 to C40 aliphatic hydrocarbon such as hexadecane, octadecane, or squalane, an aromatic hydrocarbon substituted with a C6 to C30 alkyl group such as phenyldodecane, phenyltetradecane, or phenyl hexadecane, a phosphine substituted with a C6 to C22 alkyl group such as trioctylphosphine, a phosphine oxide substituted with a C6 to C22 alkyl group such as trioctylphosphine oxide, a C12 to C22 aromatic ether such as phenyl ether, or benzyl ether, or a combination thereof. The solvent may be selected considering the precursors and organic ligands.

The reaction may be performed under any suitable conditions such as a temperature or a time without a particular limit. For example, the reaction may be performed at greater than or equal to about <NUM> (e.g., a temperature of about <NUM> to about <NUM>) for greater than or equal to about <NUM> second (e.g., about <NUM> seconds to about <NUM> minutes), but it is not limited thereto. The reaction may be performed under an inert gas atmosphere, in the air, or under a vacuum, but it is not limited thereto.

After the completion of the reaction, a non-solvent is added to the resulting reaction mixture and thereby a quantum dot having the organic ligand coordinated on the surface may be separated therefrom. The non-solvent may include a polar solvent that is miscible with the solvent used in the reaction and nanocrystals are not dispersible therein. The non-solvent may be selected in light of the solvent used in the reaction and for example, it may include acetone, ethanol, butanol, isopropanol, water, tetrahydrofuran (THF), dimethylsulfoxide (DMSO), diethylether, formaldehyde, acetaldehyde, ethylene glycol, a solvent having a similar solubility parameter to the foregoing solvents, or a combination thereof. The separation may be carried out by centrifugation, precipitation, chromatography, or distillation. The separated nanocrystal may be added to a washing solvent for washing if desired. Types of the washing solvent are not particularly limited and may include a solvent having a similar solubility parameter to the ligand. For example, the washing solvent may include hexanes, heptane, octane, chloroform, toluene, benzene, and the like.

A quantum dot manufactured according to the foregoing method may have a perovskite structure and may include a halogen in an excess amount, (e.g., on a surface thereof), as determined by the TEM-EDX analysis. In addition, the quantum dot may further include the first dopant and/or the second dopant, the presence of which are confirmed by the ICP-AES analysis. The quantum dot of an embodiment has this structure and may show improved stability in a dispersion solvent or a polymer matrix after the process of solvent washing and separation as described above.

An amount of the quantum dot in the polymer matrix may be appropriately selected and is not particularly limited. For example, the amount of the quantum dot in the polymer matrix may be greater than or equal to about <NUM> weight percent (wt%) and less than or equal to about <NUM> wt% based on the total weight of the composite, but is not limited thereto.

A method of manufacturing the quantum dot polymer composite may include mixing a dispersion including the quantum dot with a solution including a polymer and, then, removing a solvent therefrom, but is not limited thereto. In an embodiment, the quantum dot polymer composite may be obtained by dispersing the quantum dot in a monomer mixture for forming the polymer and polymerizing the obtained final mixture. This quantum dot-polymer composite may be a quantum dot sheet (QD sheet).

The quantum dot may show stability reinforced in the monomer mixture or the polymer matrix and thus have a desirable luminous efficiency.

Some embodiments are directed to an electronic device including the aforementioned quantum dot polymer composite. Some embodiments are directed to an electronic device including the quantum dot of the aforementioned embodiments. In an embodiment, the electronic device may include a display device wherein the quantum dot polymer composite is used as a photo-conversion layer. In the electronic device, the quantum dot polymer composite may be positioned in a distance (or spaced apart) from a LED light source or may be in the form of a LED on-chip (a LED Package). The quantum dot polymer composite may be included in a wave guide. The quantum dot polymer composite may be included in the form of a rail, a film, or a patterned layer.

In some embodiments, the quantum dot may be used in a luminescent layer of an electro-luminescent (EL) device. In the EL device, the quantum dot may be used together with a light emitting organic or a light emitting polymer. The quantum dot may be used alone in the luminescent layer of the EL device. The structure of the aforementioned electronic devices are described, for example, in <CIT> (a LED on-chip, a LED package, or the like), <CIT> (waveguide), <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

The electronic device may be a light emitting diode (LED), an organic light emitting diode (OLED), a sensor, a solar cell, or an imaging sensor, but is not limited thereto. <FIG> shows a stacking structure of a liquid crystal display (LCD) including the quantum dot sheet among these devices. Referring to <FIG>, the structure of the LCD may include a reflector, a light guide panel (LGP), a blue LED light source (Blue-LED), a quantum dot-polymer composite sheet (QD sheet), optical films (e.g., a prism, and a double brightness enhance film (DBEF) that are stacked), and a liquid crystal panel that is disposed thereon.

However, they are example embodiments of the present invention, and the present invention is not limited thereto.

A Hitachi F-<NUM> spectrometer is used to perform a photoluminescence spectrum analysis when light at <NUM> is radiated. Based on the obtained photoluminescence spectrum, a maximum photoluminescence peak wavelength, quantum efficiency, and a full width at half maximum (FWHM) are evaluated. The quantum efficiency is calculated with respect to the photoluminescent peak of an ethanol solution of coumarin dye (absorption (optical density) at <NUM> nanometers (nm) is <NUM>).

A transmission electron microscope image is obtained by using a TEM-TITAN-<NUM>-<NUM> (FEI) equipment at an acceleration voltage of <NUM> KV. Accordingly, the average diameter of a quantum dot is measured.

An X-ray diffraction spectrum by using a Philips XPert PRO equipment is obtained.

An EDS measuring device mounted on the TEM-TITAN-<NUM>-<NUM> (FEI) is used to perform an energy-dispersing X-ray spectrum analysis.

Quantum <NUM> made by Physical Electronics, Inc. is used to perform an XPS element analysis under a condition of an acceleration voltage: <NUM>-<NUM> keV, <NUM> W, and a minimum analysis area: <NUM> X <NUM><NUM>.

ICPS-<NUM> (Shimadzu Corp. ) is used to perform an inductively-coupled plasma-element releasing spectrum analysis.

Cs<NUM>CO<NUM> (<NUM> grams (g), Sigma-Aldrich, <NUM> %) is put into a <NUM> milliliter (mL) <NUM>-neck flask along with octadecene (<NUM>, Sigma-Aldrich, <NUM> %, ODE) and oleic acid (<NUM>, Sigma-Aldrich, <NUM> %, OA), and the mixture is dried at <NUM> for one hour, and subsequently heated at <NUM> under N<NUM> to react the Cs<NUM>CO<NUM> with the oleic acid and thereby obtain a first precursor of Cs-oleate. The Cs-oleate is precipitated from the ODE at room temperature and heated up to <NUM> before being injected into the reaction solution.

The ODE (<NUM>), PbBr<NUM> (<NUM>, Sigma-Aldrich Co. , <NUM> %), and ZnBr<NUM> (<NUM>, Sigma-Aldrich Co. , <NUM> %) are placed in a <NUM> <NUM>-neck flask and dried at <NUM> for one hour. Then, dry oleylamine (<NUM>, STREM Chemicals, <NUM> %, OLA) and dry OA (<NUM>) are injected thereinto at <NUM> under a nitrogen atmosphere, and the obtained mixture is stirred to dissolve the PbBr<NUM> and the ZnBr<NUM> to prepare a solution containing a second precursor and a first additive.

[<NUM>] The obtained solution containing the second precursor and the first additive is heated at a temperature of <NUM>, the first precursor solution obtained from [<NUM>] is rapidly injected thereto, and then Se-TOP (<NUM> mmol) is added thereto. The Se-TOP is prepared as a <NUM> molar (M) solution by dissolving Se powder (RND Korea Co. , <NUM> %) in Tri-n-octylphosphine (STREM Chemicals, <NUM> %, TOP). After five minutes, the reaction solution is rapidly cooled to room temperature.

Subsequently, as a non-solvent, isopropanol is added to the cooled reaction solution to form a precipitate, which is then washed. The precipitate is centrifuged to obtain a quantum dot, and the obtained quantum dot is dispersed in toluene and laurylmethacrylate, respectively. A Transmission Electron Microscopic (TEM) analysis is carried out for the obtained quantum dots and the results are shown in <FIG>. The results of <FIG> confirm that the obtained quantum dots have a cubic or rectangular cuboid shape and their average size is about <NUM> (i.e., based on the TEM planar image, the length distribution of the long axis is <NUM> ± <NUM>).

For the obtained quantum dots, X-ray diffraction (XRD) analyses are carried out and the results are shown in <FIG>. The results of <FIG> confirm that the prepared quantum dots include a compound having a perovskite structure. The size of the quantum dot is <NUM>, as calculated from the XRD results and the Scherrer equation:<MAT>.

[<NUM>] The toluene dispersion and the laurylmethacrylate dispersion, each including the quantum dots, are kept in the air. A photoluminescence spectrum analysis of the quantum dots for each of the dispersions is performed both after <NUM> hours and after <NUM> hours and the results are summarized in Table <NUM> and Table <NUM>.

A quantum dot doped with Se and including CsPbBr3+α is prepared in the same method as Example <NUM>, except for not using ZnBr<NUM> as a first additive, and the toluene dispersion and the laurylmethacrylate dispersion each including the prepared quantum dots are obtained, respectively.

The obtained quantum dots have a cubic or rectangular cuboid shape and their average size is about <NUM>.

The toluene dispersion and the laurylmethacrylate dispersion, each including the quantum dots, are kept in the air. A photoluminescence spectrum analysis of the quantum dots for each of the dispersion is performed after <NUM> hours and after <NUM> hours, and the results are summarized in Table <NUM> and Table <NUM>.

A quantum dot doped with Zn and including CsPbBr3+α is prepared in the same method as Example <NUM> except for not using the Se-TOP as a second additive, and the toluene dispersion and the laurylmethacrylate dispersion each including the prepared quantum dots are obtained, respectively.

The obtained quantum dots have a cubic or rectangular cuboid shape and their average size is about <NUM>.

The toluene dispersion and the laurylmethacrylate dispersion, each including the quantum dots, are kept in the air. A photoluminescence spectrum analysis of the quantum dot for each of the dispersion is performed after <NUM> hours and after <NUM> hours, and the results are summarized in Table <NUM> and Table <NUM>.

An un-doped quantum dot including CsPbBr<NUM> is prepared in the same method as Example <NUM> except for not using the first and second additives, and the toluene dispersion and the laurylmethacrylate dispersion each including the prepared quantum dots are obtained, respectively.

The quantum dot has a cubic or rectangular cuboid shape and an average size of about <NUM>. For the quantum dot as prepared, an X-ray diffraction analysis is carried out and the results are shown in <FIG>. The results of <FIG> confirm that the prepared quantum dots include a compound having a perovskite structure. The results of <FIG> confirm that the FWHM at the (<NUM>) peak of the quantum dots of Example <NUM> is smaller than that of the quantum dots of Comparative Example <NUM>. That is, the FWHM at the (<NUM>) peak of the quantum dots of Example <NUM> is <NUM> while the FWHM at the (<NUM>) peak of the quantum dots of Comparative Example <NUM> is <NUM>. The size of the quantum dot calculated from the XRD data and the Scherrer equation is about <NUM>.

The toluene dispersion and the laurylmethacrylate dispersion, each including the quantum dots, are kept in the air. Directly after being kept in the air, after the elapse of <NUM> hours therefrom and after <NUM> hours therefrom, respectively, a photoluminescence spectrum analysis of the quantum dot for each of the dispersion is carried out and the results are summarized in Table <NUM> and Table <NUM>.

The results of Tables <NUM> and <NUM> confirm that a quantum dot doped with a first dopant and/or a second dopant may maintain a desirable FWHM when dispersed in either toluene or laurylmethacrylate, and show a suitable improvement in quantum efficiency.

For the quantum dots prepared in Example <NUM> and Comparative Example <NUM>, a TEM-EDX-analysis is carried out. As a result, in the case of the quantum dot of Example <NUM>, an atomic ratio of the Br with respect to the Cs is <NUM>, while in the case of the quantum dot of Comparative Example <NUM>, an atomic ratio of the Br with respect to the Cs is <NUM>.

The aforementioned results confirm that the quantum dots of Example <NUM> include a stoichiometric excess amount of halogen.

For the quantum dots prepared in Example <NUM> and Comparative Example <NUM>, an XPS analysis is carried out.

The results confirm that in case of the quantum dots of Comparative Example <NUM>, an atomic ratio of the Br with respect to the Pb (Pb4f/Br3d) is <NUM> %/<NUM> %, while in case of the quantum dots of Example <NUM>, the atomic ratio of the Br with respect to Pb (Pb4f/Br3d) is <NUM> %/<NUM> %. The results also confirm that the quantum dots of Example <NUM> include a stoichiometric excess amount of the Br.

For the quantum dots of Example <NUM>, an ICP-AES analysis is carried out, and the results are shown below:.

The results confirm that the quantum dots of Example <NUM> include a Zn and/or Se dopant.

<NUM> wt% of lauryl methacrylate, <NUM> wt% of tricyclodecane dimethanol diacrylate, <NUM> wt% of trimethylol propane triacrylate, <NUM> wt% of epoxy diacrylate oligomer (Manufacturer: Sartomer), <NUM> wt% of <NUM>-hydroxy-cyclohexyl-phenyl-ketone, and <NUM> wt% of <NUM>,<NUM>,<NUM>-trimethylbenzoyl-diphenyl-phosphine oxide are mixed to prepare a monomer and an oligomer mixture. The mixture is defoamed under vacuum.

The nanoparticles synthesized in Example <NUM> are centrifuged one time. A toluene dispersion of the semiconductor nanocrystals [concentration: (absorption at <NUM>) X (volume of QD solution (mL)) = <NUM>] thus obtained is mixed again with an excess amount of ethanol, and the semiconductor nanocrystal particles are centrifuged. The separated semiconductor nanocrystals are dispersed in <NUM> (<NUM> wt% of the entire composition except for an initiator) of lauryl methacrylate, the monomer (oligomer) mixture (<NUM>) is added thereto, and the resulting mixture is stirred to prepare a semiconductor nanocrystal composition.

About <NUM> of the semiconductor nanocrystal composition prepared above is drop-cast on a surface of a PET film sputtered with SiOx (purchased from I-component, Hereinafter, a barrier film). On the composition, another barrier film is placed, and then a UV-curing is carried out for <NUM> seconds (photo intensity: <NUM> milliwatts per square centimeter (mW/cm<NUM>)) to provide a light conversion layer. The light conversion layer is inserted between a light guide panel and an optical sheet of a <NUM>-inch TV mounted with a blue LED having a peak wavelength of <NUM>, and the TV is operated and the luminance of the layer is measured at a distance of about <NUM> with spectroradiometer (Konica Minolta Inc. , CS-<NUM>). The results are compiled in Table <NUM>.

A quantum dot-polymer composite is prepared in the same manner as Example <NUM> except for using the quantum dot-LMA dispersion prepared in Example <NUM>.

For the quantum dot-polymer composite, a PL spectroscopy analysis is made, and the results are compiled in Table <NUM>.

A quantum dot-polymer composite is prepared in the same method as Example <NUM> except for using the quantum dot-LMA dispersion of Example <NUM>.

A quantum dot-polymer composite is prepared in the same method as Example <NUM> except for using the quantum dot-LMA dispersion of Comparative Example <NUM>.

For the quantum dot-polymer composites of Examples <NUM>-<NUM> and Comparative Example <NUM>, a PL spectroscopy analysis is made, and the results are compiled in Table <NUM>. The quantum dot-polymer composites are further measured to determine the optical conversion efficiency, and the results are provided in Table <NUM>:.

Referring to Table <NUM>, the quantum dot-polymer composite sheet prepared in the Examples may show significantly improved light conversion efficiency in comparison with the QD sheet of the Comparative Example.

Claim 1:
A quantum dot having a perovskite crystal structure represented by Chemical Formula <NUM>:

        Chemical Formula <NUM>     ABX<NUM>

wherein, A is a Group IA metal selected from Rb, Cs, Fr, and a combination thereof, B is a Group IVA metal selected from Si, Ge, Sn, Pb, and a combination thereof, X is a halogen selected from F, Cl, Br, and I, BF<NUM>, or a combination thereof,;
wherein the quantum dot has a size of <NUM> nanometer to <NUM> nanometers;
wherein in the quantum dot, an atomic ratio of halogen atoms relative to the Group IA metal atoms is greater than <NUM>; and
wherein the quantum dot further comprises at least one of a first dopant and a second dopant,
wherein the first dopant comprises potassium or a first metal having a crystal ionic radius of less than <NUM> picometers, wherein the first metal is different from the Group IA metal and the Group IVA metal, and
wherein the second dopant comprises a non-metal element that forms a bond with the Group IVA metal, preferably wherein the first metal has a smaller crystal ionic radius of the Group IVA metal of the B in Chemical Formula <NUM>.