Light emitting device and display apparatus including the same

Abstract

The present invention relates to light emitting devices and display apparatuses including the same. The light emitting device includes an emissive layer including a plurality of quantum dots, and an electron auxiliary layer disposed on the emissive layer, the electron auxiliary layer transporting electrons to the emissive layer, wherein the electron auxiliary layer includes a plurality of metal oxide nanoparticles, wherein the metal oxide nanoparticles include zinc and a dopant metal, wherein the dopant metal includes Mg, Mn, Ni, Sn, Al, Y, Ga, Zr, Li, Co, or a combination thereof, wherein a concentration of the dopant metal in at least one of the metal oxide nanoparticles increases in a direction from an inner portion to an outer portion of the nanoparticle, or increases in a direction from an outer portion to an inner portion of the nanoparticle.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority and benefits to Korean Patent Application No. 10-2019-0107636, filed on August 30, 2019, with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The light-emitting device and display device were disclosed. Background Technology

[0004] Unlike bulk materials, the intrinsic physical properties of nanoparticles (e.g., band gap energy, melting point, etc.) can be controlled by changing the particle size. For example, semiconductor nanocrystals, also known as quantum dots, can be supplied with light or electrical energy and can emit light at wavelengths corresponding to the size of the quantum dot. Therefore, quantum dots can be used as light-emitting elements that emit light at specific wavelengths. Summary of the Invention

[0005] Quantum dots can be used in light-emitting devices. However, new methods are needed to improve the performance of light-emitting devices that include quantum dots.

[0006] The implementation provides a light-emitting device that enables improved performance.

[0007] The embodiments provide a display device including the light-emitting device.

[0008] According to an embodiment, the light-emitting device includes,

[0009] The device comprises an emitter layer containing multiple quantum dots and an electron-assisted layer disposed on the emitter layer, the electron-assisted layer transmitting and / or injecting electrons into the emitter layer, wherein the electron-assisted layer comprises multiple metal oxide nanoparticles, wherein the metal oxide nanoparticles comprise zinc and a dopant metal, wherein the dopant metal comprises Mg, Mn, Ni, Sn, Al, Y, Ga, Zr, Li, Co, or combinations thereof, and wherein in at least one of the metal oxide nanoparticles, the dopant metal is included (e.g., distributed) to have a concentration gradient in the metal oxide nanoparticles.

[0010] In one embodiment, the concentration of the dopant metal in at least one of the metal oxide nanoparticles may increase in the direction from the inner portion to the outer portion of the nanoparticle.

[0011] In another embodiment, the concentration of the dopant metal may be increased in the direction from the outer portion to the inner portion of the nanoparticle.

[0012] In an embodiment, the molar amount of dopant metal in the internal portion may be different from (greater than or less than) the molar amount of dopant metal in the external portion.

[0013] The dopant metal may be predominantly (mainly) present (e.g., distributed) in the inner portion of the metal oxide nanoparticles. For example, in at least one of the metal oxide nanoparticles, the concentration (or molar amount, hereinafter concentration) of the dopant metal may increase in the direction from the outer portion to the inner portion of the nanoparticle.

[0014] The dopant metal may be predominantly (mainly) present (e.g., distributed) in the outer portion of the metal oxide nanoparticles. For example, in at least one of the metal oxide nanoparticles, the concentration of the dopant metal may increase in the direction from the inner portion to the outer portion of the nanoparticle.

[0015] The metal oxide nanoparticles may include a first layer and a second layer disposed on the first layer.

[0016] The first layer may have a higher concentration of dopant metal, for example, a higher molar amount, than the second layer. The second layer may not include the dopant metal.

[0017] The second layer may be the outermost layer of the metal oxide nanoparticles.

[0018] The plurality of quantum dots may not include cadmium, lead, or combinations thereof.

[0019] The plurality of quantum dots may include II-VI group compounds, III-V group compounds, IV-VI group compounds, group IV elements or compounds, I-III-VI group compounds, II-III-VI group compounds, I-II-IV-VI group compounds, or combinations thereof.

[0020] The dopant metal may include magnesium, aluminum, lithium, or a combination thereof.

[0021] The dopant metal may not include sodium.

[0022] The molar ratio of the dopant metal to zinc in the metal oxide nanoparticles may be greater than or equal to about 0.005:1.

[0023] The molar ratio of the dopant metal to zinc in the metal oxide nanoparticles may be greater than or equal to about 0.01:1.

[0024] The molar ratio of the dopant metal to zinc in the metal oxide nanoparticles may be greater than or equal to about 0.05:1.

[0025] The molar ratio of the dopant metal to zinc in the metal oxide nanoparticles may be greater than or equal to about 0.1:1.

[0026] The molar ratio of the dopant metal to zinc in the metal oxide nanoparticles may be less than or equal to about 0.5:1.

[0027] The molar ratio of the dopant metal to zinc in the metal oxide nanoparticles may be less than or equal to about 0.4:1.

[0028] The molar ratio of the dopant metal to zinc in the metal oxide nanoparticles may be less than or equal to about 0.3:1.

[0029] The molar ratio of the dopant metal to zinc in the metal oxide nanoparticles may be less than or equal to about 0.25:1.

[0030] The metal oxide nanoparticles may have a first ultraviolet (UV) absorption peak wavelength of less than or equal to about 350 nanometers (nm), less than or equal to about 345 nm, or less than or equal to about 340 nm.

[0031] The metal oxide nanoparticles may have a first UV absorption peak wavelength greater than or equal to about 320 nm, greater than or equal to about 325 nm, or greater than or equal to about 330 nm.

[0032] The metal oxide nanoparticles may have a trap emission peak with a center wavelength greater than or equal to about 500 nm or greater than or equal to about 510 nm (e.g., in the photoluminescence spectrum at room temperature or at 77 K). The center wavelength of the trap emission peak may be less than or equal to about 600 nm or less than or equal to about 560 nm.

[0033] The metal oxide nanoparticles can be configured to exhibit a band-edge emission peak with a center wavelength of less than or equal to about 400 nm or less than or equal to about 390 nm in a photoluminescence spectrum (e.g. at 77 K).

[0034] The center wavelength of the band-edge emission peak in the photoluminescence spectrum (e.g., at 77 K) may be greater than or equal to about 200 nm, greater than or equal to about 300 nm, or greater than or equal to about 350 nm.

[0035] The intensity ratio of the trap emission peak to the band-edge emission peak may be greater than or equal to about 2.9:1 (e.g., in a low-temperature photoluminescence (PL) spectrum at about 77 K). The intensity ratio of the trap emission peak to the band-edge emission peak may be greater than or equal to about 5:1. The intensity ratio of the trap emission peak to the band-edge emission peak may be greater than or equal to about 7:1. The intensity ratio of the trap emission peak to the band-edge emission peak may be greater than or equal to about 9:1.

[0036] The metal oxide nanoparticles may have an organic content of about 20% by weight, as determined by thermogravimetric analysis, for example, the amount of organic matter.

[0037] The metal oxide nanoparticles may have an amount of organic matter greater than or equal to about 24% by weight, as determined by thermogravimetric analysis.

[0038] The resistivity of the electronic auxiliary layer can be greater than or equal to approximately 1 × 10⁻⁶. 4 ohm·cm (ohm·cm), greater than or equal to about 1×10 5 ohm·cm, greater than or equal to approximately 3 × 10 8 ohm·cm, or greater than or equal to approximately 3.5 × 10⁻⁶. 8 ohm·cm.

[0039] The contact resistance of the electronic auxiliary layer can be less than or equal to approximately 5 × 10⁻⁶. 11 ohm·cm 2 Less than or equal to approximately 4 × 10 11 ohm·cm 2 Less than or equal to approximately 3 × 10 11 ohm·cm 2 Less than or equal to approximately 2 × 10 11 ohm·cm 2 Less than or equal to approximately 1.5 × 10 11 ohm·cm 2 Less than or equal to approximately 1.4 × 10 11 ohm·cm 2 Less than or equal to approximately 1 × 10 11 ohm·cm 2 Or less than or equal to approximately 1 × 10 10 ohm·cm 2 .

[0040] The metal oxide nanoparticles may include a core and a shell disposed on the core, the core comprising a first metal oxide, the shell comprising a second metal oxide, and the second metal oxide may have a composition different from that of the first metal oxide.

[0041] The first metal oxide may include zinc and optionally a first metal.

[0042] The second metal oxide may include zinc and optionally a second metal.

[0043] The first metal may include magnesium, aluminum, lithium, yttrium, gallium, zirconium, nickel, cobalt, or combinations thereof. The second metal may include magnesium, aluminum, lithium, yttrium, gallium, zirconium, nickel, cobalt, or combinations thereof.

[0044] The band gap energy of the first metal oxide may be greater than or equal to the band gap energy of the second metal oxide.

[0045] The first metal oxide may include the first metal, and the molar ratio of the first metal to zinc may be less than about 1:1, or less than or equal to about 0.5:1. The first metal oxide may include magnesium, and the molar ratio of magnesium to zinc may be less than about 1:1, less than or equal to about 0.5:1, or less than or equal to about 0.3:1.

[0046] The second metal oxide may include a compound represented by chemical formula 2:

[0047] Chemical formula 2

[0048] Zn 1-y M y O

[0049] Where M is Mg, Al, Li, Y, Ga, Zr, Ni, Co or a combination thereof, and 0≤y<1 or 0≤y≤0.5.

[0050] The first metal oxide may include zinc oxide and magnesium oxide, and the second metal oxide may include zinc oxide. The second metal oxide may not include magnesium, aluminum, lithium, yttrium, gallium, zirconium, nickel, cobalt, or combinations thereof.

[0051] The average size of the metal oxide nanoparticles can be greater than or equal to about 2 nm.

[0052] The average size of the metal oxide nanoparticles may be less than or equal to about 10 nm.

[0053] The average size of the metal oxide nanoparticles can be greater than or equal to about 3 nm and less than or equal to about 6 nm.

[0054] The light-emitting device can emit blue light and can have a maximum external quantum efficiency (max EQE) greater than or equal to about 14%.

[0055] The light-emitting device (e.g., capable of emitting blue light) may have a maximum brightness greater than or equal to about 35,000 candela per square meter.

[0056] The light-emitting device can emit blue light and has a T50 of more than about 50 hours.

[0057] The metal oxide nanoparticles may include a core and a shell disposed on the core, and based on the total molar number of the dopant metal present in the metal oxide nanoparticles, greater than or equal to about 70 mol% of the dopant metal may be present in the core.

[0058] The metal oxide nanoparticles may include a core and a shell disposed on the core, and based on the total molar number of the dopant metal present in the metal oxide nanoparticles, greater than or equal to about 70 mol% of the dopant metal may be present in the shell.

[0059] According to an embodiment, a method for preparing zinc oxide nanoparticles includes: providing a first organic solution comprising a first zinc precursor, a first organic solvent, and optionally a first dopant precursor; adding a first hydroxide solution to the first organic solution to form a first mixture; stirring the first mixture to form a precipitate; separating the precipitate to provide a separated precipitate; dispersing the separated precipitate in a dispersion solvent to form a dispersion; mixing the dispersion with a second organic solution comprising a second zinc precursor, a second organic solvent, and optionally a second dopant precursor to form a second mixture; adding a second hydroxide solution to the second mixture to form a third mixture; and stirring the third mixture to prepare the zinc oxide nanoparticles, wherein the first organic solution comprises the first dopant precursor, the second organic solution comprises the second dopant precursor, or a combination thereof.

[0060] In the devices of the embodiments (e.g., electroluminescent devices), the electron mobility in the electron auxiliary layer can be appropriately controlled, and the resistance between the emitting layer and the electron auxiliary layer can be reduced, thereby enabling efficient electron injection / transport and effectively preventing hole movement (or hole extraction) towards the cathode. Therefore, the devices of the embodiments can exhibit increased luminance efficiency and improved lifetime properties. The stacked structure included in the devices of the embodiments can also be used in light-emitting diodes, sensors, lasers, solar cell devices, or any suitable semiconductor device. Attached Figure Description

[0061] The above and other advantages and features of this disclosure will become clearer from a further detailed description of exemplary embodiments thereof with reference to the accompanying drawings, in which:

[0062] Figure 1A This is a schematic cross-sectional view of the light-emitting device according to an embodiment.

[0063] Figure 1BThis is a schematic cross-sectional view of the light-emitting device according to an embodiment.

[0064] Figure 1C This is a schematic cross-sectional view of the light-emitting device according to an embodiment.

[0065] Figure 2 This is a schematic cross-sectional view of the metal oxide nanoparticles included in the electronic auxiliary layer of the light-emitting device according to an embodiment.

[0066] Figure 3 The graph shows absorbance (arbitrary units (au)) versus wavelength (nm), displaying the UV-Vis spectra of the metal oxide nanoparticles prepared in Comparative Examples 1 and 2, and Preparation Examples 1 and 2.

[0067] Figure 4A The graph shows the photoluminescence spectra of the metal oxide nanoparticles prepared in Comparative Examples 1 and 2 and Preparation Examples 1 and 2, at room temperature, as well as the photoluminescence spectra of PL intensity (arbitrary units) versus wavelength (nm).

[0068] Figure 4B The graph shows the PL intensity (arbitrary units) versus wavelength (nm), which illustrates the low-temperature photoluminescence spectra of the metal oxide nanoparticles prepared in Comparative Example 1 and Preparation Example 1.

[0069] Figure 5 This is an electron microscope image of the cross-section of the device prepared in Example 1. Detailed Implementation

[0070] In the following, exemplary embodiments of this disclosure will be described in detail so that those skilled in the art will understand them. However, this disclosure may be embodied in many different forms and is not to be construed as limited to the exemplary embodiments set forth herein.

[0071] In the accompanying drawings, the thicknesses of layers, films, panels, regions, etc., are enlarged for clarity. The same reference numerals throughout the specification denote the same elements. 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 may be directly on said other element or there may be intermediate elements present. Conversely, when an element is referred to as being "directly on" another element, there are no intermediate elements.

[0072] 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 parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or part from another. Therefore, without departing from the teachings herein, the “first element,” “component,” “region,” “layer,” or “part” discussed below may be referred to as a second element, component, region, layer, or part.

[0073] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a” and “the” are intended to include the plural forms, including “at least one”, unless the content clearly indicates otherwise. “At least one” will not be construed as limiting “a”. “Or” means “and / or”. As used herein, the term “and / or” includes any and all combinations of one or more of the associated enumerated items. It will be further understood that the terms “comprising” or “including” as used in this specification indicate the presence of the stated features, regions, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more additional features, regions, integrals, steps, operations, elements, components, and / or sets thereof.

[0074] As used herein, “about” includes the stated value and means within an acceptable range of deviations from the specific value, as determined by one of ordinary skill in the art taking into account the measurement in question and the errors associated with the measurement of the specific quantity (i.e., limitations of the measurement system). For example, “about” may mean within one or more standard deviations relative to the stated value, or within ±10% or 5%.

[0075] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in common dictionaries, should be interpreted as having a meaning consistent with their meaning in the context of the relevant field and in this disclosure, and will not be interpreted in an idealized or overly formal sense unless clearly defined herein.

[0076] Exemplary embodiments are described herein with reference to cross-sectional views that serve as schematic representations of idealized embodiments. Thus, deviations from the shapes shown in the figures will be expected as a result of, for example, manufacturing techniques and / or tolerances. Therefore, the embodiments described herein should not be construed as limited to the specific shapes of the regions shown herein, but rather include deviations in shape caused, for example, by manufacturing processes. For example, regions illustrated or described as flat may typically have rough and / or non-linear characteristics. Furthermore, sharp corners illustrated may be rounded. Therefore, the regions shown in the figures are schematic in nature, and their shapes are not intended to illustrate the precise shapes of the regions, nor are they intended to limit the scope of the claims.

[0077] As used herein, the expression "excluding cadmium (or other harmful heavy metals)" can refer to situations where the concentration of cadmium (or harmful heavy metals) is less than or equal to about 100 parts per million (ppmw), less than or equal to about 50 ppmw, less than or equal to about 10 ppmw, less than or equal to about 1 ppmw, less than or equal to about 0.1 ppmw, less than or equal to about 0.01 ppmw, or about zero. In embodiments, substantially no cadmium (or other heavy metals) may be present, or if present, the amount of cadmium (or other heavy metals) may be less than or equal to the detection limit of a given analytical tool (e.g., inductively coupled plasma atomic emission spectrometry) or as its impurity level.

[0078] As used herein, the terms work function, conduction band edge (CB), valence band edge (VB), highest occupied molecular orbital (“HOMO”), or lowest unoccupied molecular orbital (“LUMO”) level are expressed as absolute values ​​relative to vacuum. If a work function, CB, VB, HOMO, or LUMO level is referred to as “deep,” “high,” or “large,” then the work function, CB / VB level, or HOMO / LUMO level has a large absolute value relative to “0 eV” (i.e., the vacuum level). Conversely, if a work function, CB, VB, HOMO, or LUMO level is referred to as “shallow,” “low,” or “small,” then the work function, CB / VB level, or HOMO / LUMO level has a small absolute value relative to “0 eV” (i.e., the vacuum level).

[0079] LUMO / HOMO levels, CB / VB levels, work function, or combinations thereof can be measured using appropriate methods, which are not particularly limited. In embodiments, the LUMO / HOMO levels, CB / VB levels, work function, or combinations thereof of a given material can be measured by: cyclic voltammetry (CV), spectroscopic analysis (e.g., ultraviolet photoelectron spectroscopy (UPS), UV-Vis spectroscopy, or combinations thereof), photoelectron spectroscopy in air (e.g., using AC-3), Kelvin probe force microscopy, or combinations thereof.

[0080] As used in this article, the term "family" may refer to a family of elements in the periodic table.

[0081] As used herein, “family I” may refer to families IA and IB, and examples may include, but are not limited to, Li, Na, K, Rb, and Cs.

[0082] As used in this article, “Group II” may refer to Group IIA and Group IIB, and examples of Group II metals may be Cd, Zn, Hg, and Mg, but are not limited thereto.

[0083] As used in this article, “Group III” may refer to Group IIIA and Group IIIB, and examples of Group III metals may be Al, In, Ga, and Tl, but are not limited thereto.

[0084] As used herein, “Group IV” may refer to Group IVA and Group IVB, and examples of Group IV metals may be, but are not limited to, Si, Ge, and Sn. As used herein, the term “metal” may include half-metals such as Si.

[0085] As used herein, “group V” may refer to group VA, and examples may include, but are not limited to, nitrogen, phosphorus, arsenic, antimony, and bismuth.

[0086] As used herein, “VI group” may refer to VIA group, and examples may include, but are not limited to, sulfur, selenium, and tellurium.

[0087] As used herein, unless otherwise defined, “substituted” may refer to a compound, group, or portion of which hydrogen is replaced by: C1-C30 alkyl, C2-C30 alkenyl, C2-C30 alkynyl, C2-C30 epoxy, C2-C30 alkyl ester, C3-C30 alkenyl ester (e.g., acrylate, methacrylate), C6-C30 aryl, C7-C30 alkylaryl, C1-C30 alkoxy, C1-C30 heteroalkyl, C3-C40 heteroaryl, C3-C30 heteroalkylaryl, C3-C30 cycloalkyl, C3-C15 cycloalkenyl, C6-C30 cycloalkynyl, C2-C30 heterocycloalkyl, halogen (-F, -Cl, -Br, or -I), hydroxyl (-OH), nitro (-NO2), cyano (-CN). ), amino (-NRR', where R and R' are independently hydrogen or C1-C6 alkyl), azide (-N3), amidine (-C(=NH)NH2), hydrazine (-NHNH2), hydrazone (=N(NH2)), aldehyde (-C(=O)H), carbamoyl (-C(O)NH2), thiol (-SH), ester (-C(=O)OR, where R is C1-C6 alkyl or C6-C12 aryl), carboxyl (-COOH) or its salt (-C(=O)OM, where M is an organic or inorganic cation), sulfonic acid (-SO3H) or its salt (-SO3M, where M is an organic or inorganic cation), phosphate (-PO3H2) or its salt (-PO3MH or -PO3M2, where M is an organic or inorganic cation), or combinations thereof.

[0088] The term "hydrocarbon" can refer to a group comprising carbon and hydrogen (e.g., aliphatic groups such as alkyl, alkenyl, alkynyl, or aromatic groups such as aryl). A hydrocarbon group can be a group having a valence of at least 1 formed by removing at least one hydrogen atom from it (e.g., an alkane, alkene, alkynyl, or aromatic hydrocarbon). At least one methylene group in an aliphatic group can be replaced by an oxygen moiety, a carbonyl moiety, an ester moiety, -NH-, or a combination thereof. Unless otherwise specified, a hydrocarbon group (e.g., alkyl, alkenyl, alkynyl, or aryl) can have any suitable number of carbon atoms, for example, 1-60 carbon atoms, or 2-32 carbon atoms, or 3-24 carbon atoms, or 4-12 carbon atoms.

[0089] As used herein, unless otherwise defined, "alkyl" may refer to a straight-chain or branched saturated monovalent hydrocarbon group (methyl, ethyl, hexyl, etc.).

[0090] As used herein, unless otherwise defined, "alkenyl" may refer to a straight-chain or branched monovalent hydrocarbon group having one or more carbon-carbon double bonds.

[0091] As used herein, unless otherwise defined, "alkynyl" can refer to a straight-chain or branched monovalent hydrocarbon group having one or more carbon-carbon triple bonds.

[0092] As used herein, unless otherwise defined, “aryl” may refer to a group (e.g., phenyl or naphthyl) formed by removing at least one hydrogen atom from an aromatic hydrocarbon.

[0093] As used herein, “heterogeneous” can refer to one or more (e.g., 1-3) heteroatoms including N, O, S, Si, P, or combinations thereof.

[0094] As used herein, unless otherwise defined, “alkoxy” may refer to an alkyl group linked via oxygen (i.e., alkyl-O-), such as methoxy, ethoxy, and sec-butoxy.

[0095] As used herein, unless otherwise defined, the "amine" group has the general formula -NRR, wherein each R is independently hydrogen, C1-C12 alkyl, C7-C20 alkylaryl, C7-C20 aralkyl, or C6-C18 aryl.

[0096] In the following description, a light-emitting device according to an embodiment is described with reference to the accompanying drawings.

[0097] Figure 1A This is a schematic cross-sectional view of a light-emitting device according to an embodiment. (Refer to...) Figure 1A The light-emitting device 1 according to the embodiment includes: an emitting layer 13 comprising a plurality of quantum dots; and an electronic auxiliary layer 14 for transmitting and injecting electrons into the emitting layer 13.

[0098] The emitting layer 13 includes (e.g., multiple) quantum dots. In some embodiments, the quantum dots may not include cadmium, lead, mercury, or combinations thereof. The quantum dots may have a core-shell structure comprising: a core including a first semiconductor nanocrystal, and a shell disposed on the core and including a second semiconductor nanocrystal. The second semiconductor nanocrystal may have a different composition than the first semiconductor nanocrystal.

[0099] The quantum dots (e.g., the first and second semiconductor nanocrystals in the core-shell structure) may include group II-VI compounds, group III-V compounds, group IV-VI compounds, group IV elements or compounds, group I-III-VI compounds, group II-III-VI compounds, group I-II-IV-VI compounds, or combinations thereof. The emitting layer may not include harmful heavy metals such as cadmium, lead, mercury, or combinations thereof.

[0100] The group II-VI compounds may be: binary compounds such as CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, or combinations thereof; ternary compounds such as CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, Cd HgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, or combinations thereof; quaternary compounds such as ZnSeSTe, HgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, or combinations thereof; or combinations thereof. The group II-VI compounds may further include group III metals. The group III-V compounds may be: binary compounds such as GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, or combinations thereof; ternary compounds such as GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, or combinations thereof; quaternary compounds such as GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, or combinations thereof; or combinations thereof. The group III-V compounds may further include group II metals (e.g., InZnP). The group IV-VI compounds may be: binary compounds such as SnS, SnSe, SnTe, PbS, PbSe, PbTe, or combinations thereof; ternary compounds such as SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, or combinations thereof; quaternary compounds such as SnPbSSe, SnPbSeTe, SnPbSTe, or combinations thereof; or combinations thereof. Examples of group I-III-VI compounds may include, but are not limited to, CuInSe2, CuInS2, CuInGaSe, and CuInGaS. Examples of group I-II-IV-VI compounds may include, but are not limited to, CuZnSnSe and CuZnSnS.Examples of the group IV elements or compounds may be: elements such as Si, Ge, or combinations thereof; binary compounds such as SiC, SiGe, or combinations thereof; or combinations thereof.

[0101] In one embodiment, the quantum dot or the core (e.g., the first semiconductor nanocrystal) may comprise a metal and a nonmetal, wherein the metal comprises indium, zinc, or combinations thereof, and the nonmetal comprises phosphorus, selenium, tellurium, sulfur, or combinations thereof. The core may be an emission center. In another embodiment, the second semiconductor nanocrystal may comprise a metal and a nonmetal, wherein the metal comprises indium, zinc, or combinations thereof, and the nonmetal comprises phosphorus, selenium, tellurium, sulfur, or combinations thereof. In another embodiment, the first semiconductor nanocrystal may comprise InP, InZnP, ZnSe, ZnSeS, ZnSeTe, or combinations thereof. In yet another embodiment, the second semiconductor nanocrystal may comprise ZnSe, ZnSeS, ZnS, ZnTeSe, or combinations thereof.

[0102] In one embodiment, the quantum dot may emit blue or green light and may include a core and a shell, the core comprising ZnSeTe, ZnSe, or combinations thereof, and the shell comprising zinc, selenium, and sulfur (e.g., ZnSeS). The amount of sulfur in the shell may vary radially (e.g., increasing or decreasing from the core to the surface of the quantum dot). In another embodiment, the shell may comprise zinc, sulfur, and optionally selenium in its outermost layer. In yet another embodiment, the quantum dot may emit red or green light and may include a core comprising InP, InZnP, or combinations thereof, and the shell may comprise a Group II metal and a nonmetal, the Group II metal including zinc and the nonmetal including sulfur, selenium, or combinations thereof.

[0103] In one embodiment, the quantum dot may have a core-shell structure, and an alloyed layer may or may not be present at the interface between the core and the shell. The alloyed layer may include a homogeneous alloy. The alloyed layer may include a gradient alloy. In a gradient alloy, the concentration of elements present in the shell may have a radially varying gradient (e.g., increasing or decreasing towards the core).

[0104] In one embodiment, the shell may have a radially varying composition. In another embodiment, the shell may be a multilayer shell having at least two layers. In the multilayer shell, adjacent layers may have different compositions. In the multilayer shell, at least one layer may independently have semiconductor nanocrystals of a single composition. In the multilayer shell, at least one layer may independently have alloyed semiconductor nanocrystals. In the multilayer shell, at least one layer may independently exhibit a radially varying concentration gradient with respect to the composition of the semiconductor nanocrystals.

[0105] In the core-shell structured quantum dot, the shell material and the core material may have different bandgap energies. For example, the bandgap energy of the shell material may be greater than that of the core material, but is not limited thereto. According to an embodiment, the bandgap energy of the shell material may be less than that of the core material. In the multilayer shell, the bandgap energy of the outermost layer may be greater than that of the core and the inner layers (i.e., the layers closer to the core). In the multilayer shell, the bandgap energy of each layer may be appropriately selected for effective quantum confinement.

[0106] The quantum dots may include organic ligands and optionally halogen (e.g., chlorine) moieties (e.g., bound to or coordinated on a surface).

[0107] The organic ligand may include RCOOH, RNH2, R2NH, R3N, RSH, R3PO, R3P, ROH, RCOOR, RPO(OH)2, RHPOOH, R2POOH, or combinations thereof, wherein each R is independently a C3-C40 or C5-C40 substituted or unsubstituted aliphatic hydrocarbon group (e.g., alkyl, alkenyl, or alkynyl), a C6-C40 substituted or unsubstituted aromatic hydrocarbon group (e.g., aryl), or combinations thereof.

[0108] Examples of the organic ligands may be: thiols such as methanethiol, ethanethiol, propanethiol, butanethiol, pentylenetetil, hexanethiol, octylthiol, dodecylthiol, hexadecylthiol, octadecylthiol, or benzylthiol; amines such as methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, nonylamine, decylamine, dodecylamine, hexadecylamine, octadecylamine, dimethylamine, diethylamine, dipropylamine, tributylamine, or trioctylamine; carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, dodecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid, or benzoic acid; and phosphine compounds such as methylphosphine, ethylphosphine, propylphosphine, butylphosphine, pentylphosphine, octylphosphine, etc. Dioctylphosphine, tributylphosphine, diphenylphosphine, triphenylphosphine, or trioctylphosphine; phosphine oxide compounds such as methylphosphine oxide, ethylphosphine oxide, propylphosphine oxide, butylphosphine oxide, pentylphosphine oxide, tributylphosphine oxide, octylphosphine oxide, dioctylphosphine oxide, diphenylphosphine oxide, triphenylphosphine oxide, or trioctylphosphine oxide; C5-C20 alkylphosphino acids such as hexylphosphino acid, octylphosphino acid, dodecylphosphino acid, tetradecylphosphino acid, hexadecylphosphino acid, octadecylphosphino acid; alkylphosphino acids such as C5-C20 alkylphosphino acids, such as hexylphosphino acid, octylphosphino acid, dodecylphosphino acid, tetradecylphosphino acid, hexadecylphosphino acid, or octadecylphosphino acid; and so on, but not limited thereto. The quantum dots may include the same hydrophobic organic ligand, or a mixture of at least two different hydrophobic organic ligands. The hydrophobic organic ligand may not include a photopolymerizable portion (e.g., acrylate groups, methacrylate groups, etc.).

[0109] The halogen portion may include chlorine, iodine, or a combination thereof.

[0110] In an embodiment, the quantum dot may include a first organic ligand and a halogen, for example, on its surface. The first organic ligand may include a C6-C40 aliphatic carboxylic acid compound (e.g., myristic acid, oleic acid, stearic acid, etc.). The carboxylic acid compound may include a compound represented by RCOOH (where R is a C12 or larger alkyl group or a C12 or larger alkenyl group).

[0111] In an embodiment, the quantum dot may include a halogen portion (or halogen), and the amount of the halogen (portion) per 1 mg of the quantum dot may be greater than or equal to about 1 microgram (μg), for example greater than or equal to about 2 μg, greater than or equal to about 3 μg, greater than or equal to about 4 μg, greater than or equal to about 5 μg, greater than or equal to about 6 μg, or greater than or equal to about 7 μg and less than or equal to about 12.5 μg, and for example less than or equal to about 12.4 μg, less than or equal to about 12.3 μg, less than or equal to about 12.2 μg, less than or equal to about 12.1 μg, less than or equal to about 12 μg, less than or equal to about 11.9 μg, or less than or equal to about 11.8 μg. The molar ratio of the halogen (e.g., chlorine) to the organic ligand (e.g., a fatty acid such as oleic acid) may be less than about 2.2:1, for example less than or equal to about 2:1, less than or equal to about 1.9:1, less than or equal to about 1.8:1, less than or equal to about 1.7:1, or less than or equal to about 1.6:1. The molar ratio of the halogen to the organic ligand may be greater than or equal to about 0.5:1, for example greater than or equal to about 0.6:1, greater than or equal to about 0.7:1, greater than or equal to about 0.8:1, or greater than or equal to about 0.9:1.

[0112] Quantum dots further comprising a halogen moiety can be obtained by contacting the quantum dots in an organic dispersion with a halogen or a halogen-containing alcohol solution at elevated temperatures, for example, greater than or equal to about 30°C, greater than or equal to about 35°C, greater than or equal to about 40°C, greater than or equal to about 45°C, greater than or equal to about 50°C, greater than or equal to about 55°C, or greater than or equal to about 60°C. The halogen-containing alcohol solution can be obtained by dissolving a metal halide compound in a C1-C10 alcohol.

[0113] The absorption / photoluminescence wavelength of the quantum dot can be controlled by adjusting the composition and size of the quantum dot. The maximum photoluminescence peak wavelength of the quantum dot can be in the ultraviolet (UV) to infrared range or a range greater than the UV to infrared range. For example, the maximum photoluminescence peak wavelength of the quantum dot may be greater than or equal to about 300 nm, such as greater than or equal to about 440 nm, greater than or equal to about 445 nm, greater than or equal to about 450 nm, greater than or equal to about 455 nm, greater than or equal to about 460 nm, greater than or equal to about 465 nm, greater than or equal to about 470 nm, greater than or equal to about 475 nm, greater than or equal to about 480 nm, greater than or equal to about 490 nm, greater than or equal to about 500 nm, greater than or equal to about 510 nm, greater than or equal to about 520 nm, greater than or equal to about 530 nm, greater than or equal to about 540 nm, greater than or equal to about 550 nm, greater than or equal to about 560 nm, greater than or equal to about 570 nm, greater than or equal to about 580 nm, greater than or equal to about 590 nm, greater than or equal to about 600 nm, or greater than or equal to about 610 nm. The maximum photoluminescence wavelength of the quantum dot can be less than or equal to about 800 nm, for example, less than or equal to about 650 nm, less than or equal to about 640 nm, less than or equal to about 630 nm, less than or equal to about 620 nm, less than or equal to about 610 nm, less than or equal to about 600 nm, less than or equal to about 590 nm, less than or equal to about 580 nm, less than or equal to about 570 nm, less than or equal to about 560 nm, less than or equal to about 550 nm, or less than or equal to about 540 nm. The maximum photoluminescence wavelength of the quantum dot can be in the range of about 500 nm to about 650 nm. In one embodiment, the quantum dot can emit green light, and the maximum photoluminescence wavelength of the quantum dot can be in the range of about 500 nm to about 560 nm. In another embodiment, the quantum dot can emit red light, and the maximum photoluminescence wavelength of the quantum dot can be in the range of about 600 nm to about 650 nm. In one embodiment, the quantum dot can emit blue light, and the maximum photoluminescence wavelength of the quantum dot can be in the range of about 400 nm to about 480 nm.

[0114] The quantum dots may have a quantum efficiency of about 10%, for example, about 30%, about 50%, about 60%, about 70%, about 90%, or even about 100%. The quantum dots may have a relatively narrow spectrum. The quantum dots may have a half-width (FWHM) of the photoluminescence wavelength spectrum, for example, less than or equal to about 55 nm, for example, less than or equal to about 50 nm, less than or equal to about 45 nm, less than or equal to about 40 nm, or less than or equal to about 30 nm.

[0115] The quantum dots may have an average particle size greater than or equal to about 1 nm and less than or equal to about 100 nm (e.g., diameter or equivalent diameter obtained under the assumption of a circle, determined by electron microscopy images).

[0116] The size (or average size) of the quantum dot can be from about 1 nm to about 50 nm. The size (or average size) of the quantum dot can be, for example, greater than or equal to about 2 nm, greater than or equal to about 3 nm, greater than or equal to about 4 nm, greater than or equal to about 5 nm, greater than or equal to about 6 nm, greater than or equal to about 7 nm, greater than or equal to about 8 nm, greater than or equal to about 9 nm, greater than or equal to about 10 nm, greater than or equal to about 11 nm, greater than or equal to about 12 nm, greater than or equal to about 13 nm, greater than or equal to about 14 nm, or greater than or equal to about 15 nm. The size (or average size) of the quantum dot can be less than or equal to about 50 nm, less than or equal to about 40 nm, less than or equal to about 30 nm, less than or equal to about 20 nm, less than or equal to about 15 nm, or less than or equal to about 10 nm.

[0117] In some embodiments, particle size (e.g., for quantum dots or for metal oxide nanoparticles) can be measured using electron microscopy analysis (e.g., transmission electron microscopy (TEM)). In some embodiments, particle size can be measured from two-dimensional images obtained by electron microscopy (e.g., calculated using a commercial image analysis program such as ImageJ). In some embodiments, particle size (e.g., for quantum dots or for metal oxide nanoparticles) can be an average (e.g., mean, mode, or median average) size.

[0118] There are no particular limitations on the shape of the quantum dots. For example, the shape of the quantum dots may be a sphere, polyhedron, pyramid, multi-legged object, cube, cuboid, nanotube, nanorod, nanowire, nanosheet, or a combination thereof, but is not limited thereto.

[0119] The quantum dots may not include thiol-containing organic compounds or their salts bound to the surface of the plurality of quantum dots. The organic compounds containing thiols or their salts may include butylthiol, pentylethiol, hexylthiol, heptylthiol, octylthiol, nonylthiol, decanethiol, undecylthiol, dodecanethiol, octadecylthiol, 2-(2-methoxyethoxy)ethanethiol, 3-methoxybutyl 3-mercaptopropionic acid, 3-methoxybutyl 3-mercaptoacetic acid, mercaptoacetic acid, 3-mercaptopropionic acid, thioproline (N-(2-mercaptopropionyl)glycine), 2-mercaptopropionic acid, 2-mercaptopropionate, 2-mercaptoethanol, cysteine, 1-thioglycerol, mercaptosuccinic acid, L-cysteine, dihydrolipoic acid, 2-(dimethylamino)ethanethiol, 5-mercaptomethyltetrazole, 2,3-dimercapto-1-propanol, glutathione, methoxypoly(ethylene glycol)thiol (m(PEG)-SH), dialkyl dithiocarbamate, their metal salts, or combinations thereof.

[0120] In one embodiment, the emitting layer 13 may comprise a monolayer of quantum dots. In another embodiment, the emitting layer 13 may comprise at least one monolayer of quantum dots, such as two or more monolayers, three or more monolayers, or four or more monolayers and 20 or fewer monolayers, and 10 or fewer monolayers, nine or fewer monolayers, eight or fewer monolayers, seven or fewer monolayers, or six or fewer monolayers. The emitting layer 13 may have a thickness greater than or equal to about 5 nm, such as greater than or equal to about 10 nm, greater than or equal to about 20 nm, or greater than or equal to about 30 nm and less than or equal to about 200 nm, such as less than or equal to about 150 nm, less than or equal to about 100 nm, less than or equal to about 90 nm, less than or equal to about 80 nm, less than or equal to about 70 nm, less than or equal to about 60 nm, or less than or equal to about 50 nm. The emitter layer 13 may have a thickness of, for example, about 10 nm to about 150 nm, for example, about 20 nm to about 100 nm, for example, about 30 nm to about 50 nm.

[0121] The emitter layer may have a single-layer structure or a multilayer structure in which at least two layers are stacked. In the multilayer structure, adjacent layers (e.g., a first emitter layer and a second emitter layer) may have different properties or compositions from each other. In an embodiment, the emitter layer may have a halogen amount (e.g., halogen concentration) varying in the thickness direction. In an embodiment, the halogen amount (concentration) may increase toward the electron-assisted layer. In an embodiment, the halogen amount (concentration) may decrease toward the electron-assisted layer.

[0122] In one embodiment, the emission layer may have a first quantum dot emission layer whose surface is replaced or treated with halogen (e.g., chlorine), and a second quantum dot emission layer disposed on the first quantum dot emission layer and having an increased amount of organic ligands. The first quantum dot emission layer may have an increased amount (concentration) of halogen (e.g., the surface of the emission layer may be halogen-treated or the emission layer may comprise halogen-treated quantum dots). The amount of halogen (or chlorine) or organic matter in the emission layer, such as organic content, can be controlled by appropriate means (e.g., post-processing of the layer formed in, for example, the first quantum dot emission layer, or including varying amounts of organic ligands during, for example, the fabrication of the second quantum dot emission layer).

[0123] The emitter layer 13 may have HOMO energy levels greater than or equal to about 5.4 eV, greater than or equal to about 5.6 eV, greater than or equal to about 5.7 eV, greater than or equal to about 5.8 eV, greater than or equal to about 5.9 eV, or greater than or equal to about 6.0 eV. The emitter layer 13 may also have HOMO energy levels less than or equal to about 7.0 eV, less than or equal to about 6.8 eV, less than or equal to about 6.7 eV, less than or equal to about 6.5 eV, less than or equal to about 6.3 eV, or less than or equal to about 6.2 eV. In one embodiment, the emitter layer 13 may have HOMO energy levels ranging from about 5.6 eV to about 6.0 eV.

[0124] The emitter layer 13 may have a LUMO energy level, for example, less than or equal to about 3.8 eV, less than or equal to about 3.7 eV, less than or equal to about 3.6 eV, less than or equal to about 3.5 eV, less than or equal to about 3.4 eV, less than or equal to about 3.3 eV, less than or equal to about 3.2 eV, or less than or equal to about 3.0 eV. The emitter layer 13 may also have a LUMO energy level greater than or equal to about 2.5 eV. In some embodiments, the emitter layer 13 may have a bandgap energy of about 2.4 eV to about 2.9 eV.

[0125] The device of the embodiment has an electronic auxiliary layer 14 disposed on (or directly on) the emitting layer. In the device of the embodiment, the electronic auxiliary layer, which will be described in detail below, enables the device to have improved electroluminescence properties, lifetime properties, or a combination thereof.

[0126] The electron-assisted layer comprises a plurality of metal oxide nanoparticles. The electron-assisted layer transports and injects electrons into the emitter layer. The metal oxide nanoparticles may include zinc and a dopant metal, and the dopant metal may include Mg, Mn, Ni, Sn, Li, Al, Y, Ga, Zr, Co, or combinations thereof. The dopant metal is distributed in a controlled manner within the metal oxide nanoparticles. In embodiments, the controlled distribution of the dopant metal can be confirmed by the properties of the metal oxide nanoparticles (e.g., room temperature or low temperature PL spectral properties of the metal oxide nanoparticles, the composition of the metal oxide nanoparticles, or combinations thereof) as described below.

[0127] The metal oxide nanoparticles may be crystalline or amorphous.

[0128] The dopant metal may include magnesium, aluminum, lithium, or a combination thereof.

[0129] In the metal oxide nanoparticles, the molar ratio of the dopant metal (e.g., magnesium, aluminum, lithium, or a combination thereof) to zinc in the metal oxide nanoparticles may be greater than or equal to about 0.005:1, greater than or equal to about 0.01:1, greater than or equal to about 0.02:1, greater than or equal to about 0.03:1, greater than or equal to about 0.04:1, greater than or equal to about 0.05:1, greater than or equal to about 0.06:1, greater than or equal to about 0.07:1, greater than or equal to about 0.08:1, or greater than or equal to about 0.08:1. Greater than or equal to approximately 0.09:1, greater than or equal to approximately 0.1:1, greater than or equal to approximately 0.11:1, greater than or equal to approximately 0.12:1, greater than or equal to approximately 0.13:1, greater than or equal to approximately 0.14:1, greater than or equal to approximately 0.15:1, greater than or equal to approximately 0.16:1, greater than or equal to approximately 0.17:1, greater than or equal to approximately 0.18:1, greater than or equal to approximately 0.19:1, greater than or equal to approximately 0.2:1, greater than or equal to approximately 0.21:1, greater than or equal to approximately 0.22 :1, greater than or equal to approximately 0.23:1, greater than or equal to approximately 0.24:1, greater than or equal to approximately 0.25:1, greater than or equal to approximately 0.26:1, greater than or equal to approximately 0.27:1, greater than or equal to approximately 0.28:1, greater than or equal to approximately 0.29:1, greater than or equal to approximately 0.3:1, greater than or equal to approximately 0.31:1, greater than or equal to approximately 0.32:1, greater than or equal to approximately 0.33:1, greater than or equal to approximately 0.34:1, greater than or equal to approximately 0.35:1, greater than or equal to approximately 0.36:1, greater than or equal to about 0.37:1, greater than or equal to about 0.38:1, greater than or equal to about 0.39:1, greater than or equal to about 0.4:1, greater than or equal to about 0.41:1, greater than or equal to about 0.42:1, greater than or equal to about 0.43:1, greater than or equal to about 0.44:1, greater than or equal to about 0.45:1, greater than or equal to about 0.46:1, greater than or equal to about 0.47:1, greater than or equal to about 0.48:1, or greater than or equal to about 0.49:1.

[0130] In the metal oxide nanoparticles, the molar ratio of the dopant metal to the metal (i.e., zinc) in the metal oxide nanoparticles may be less than or equal to about 0.5:1, less than or equal to about 0.49:1, less than or equal to about 0.48:1, less than or equal to about 0.47:1, less than or equal to about 0.46:1, less than or equal to about 0.45:1, less than or equal to about 0.44:1, less than or equal to about 0.43:1, less than or equal to about 0.42:1, less than or equal to about 0.41:1, less than or equal to about 0.4:1, less than or equal to about 0.39:1, less than or equal to about 0.38:1, less than or equal to about 0.37:1, less than or equal to about 0.36:1, less than or equal to about 0.35:1, less than or equal to about 0.36:1, less than or equal to about 0.35:1, less than or equal to about 0.37 ... Equal to approximately 0.34:1, less than or equal to approximately 0.33:1, less than or equal to approximately 0.32:1, less than or equal to approximately 0.31:1, less than or equal to approximately 0.3:1, less than or equal to approximately 0.29:1, less than or equal to approximately 0.28:1, less than or equal to approximately 0.27:1, less than or equal to approximately 0.26:1, less than or equal to approximately 0.25:1, less than or equal to approximately 0.24:1, less than or equal to approximately 0.23:1, less than or equal to approximately 0.22:1, less than or equal to approximately 0.21:1, less than or equal to approximately 0.2:1, less than or equal to approximately 0.19:1, less than or equal to approximately 0.18:1, less than or equal to approximately 0.17:1, less than or equal to approximately 0.16:1, or less than or equal to approximately 0.15:1.

[0131] In the device, the absolute value of the difference between the work function at the conduction band edge of the electron-assisted layer and the second electrode may be less than or equal to about 0.4 eV, less than or equal to about 0.3 eV, less than or equal to about 0.2 eV, or less than or equal to about 0.1 eV. In the device, the absolute value of the difference between the conduction band edge of the electron-assisted layer and the LUMO energy level of the emitter layer may be less than or equal to about 0.4 eV, less than or equal to about 0.3 eV, less than or equal to about 0.2 eV, or less than or equal to about 0.1 eV.

[0132] Quantum dot light-emitting devices (QD-LEDs), including quantum dots, can emit light by applying a voltage. In the case of QD-LEDs, the specific operating principle differs from that of organic light-emitting diodes (OLEDs). QD-LEDs can achieve, for example, the emission of light with higher color purity (red, green, blue), resulting in improved color reproduction. Next-generation display devices may include QD-LEDs. During the manufacturing of QD-LEDs, many steps can be performed in a solution-based manner, thereby reducing the manufacturing cost. QD-LEDs are based on inorganic light-emitting materials that provide enhanced stability. However, it is desirable to develop technologies that can improve the luminescent and lifetime properties of QD-LEDs.

[0133] In QD-LEDs, holes and electrons supplied from two opposing electrodes (e.g., cathode and anode) can recombine through a hole-assisted layer (e.g., hole transport layer) and an electron-assisted layer (e.g., electron transport layer) and reach the emitter layer (EML) to emit light. Nanoparticle-based electron-assisted layers can be formed on the quantum dot EML via solution processing at relatively low temperatures.

[0134] QD-LEDs exhibiting desired properties, for example, may include toxic heavy metals such as cadmium in the quantum dots of the EML. However, in the case of QD-LEDs based on environmentally friendly materials, such as cadmium-free quantum dots, achieving the desired level of luminescence properties can be difficult, for example challenging. The inventors have found that it is difficult to achieve the desired level of luminescence properties in an emitter layer comprising cadmium-free quantum dots, even when combined with an electron-assisted layer (e.g., an electron transport layer) containing zinc metal oxide nanoparticles. Without wishing to be bound by any theory, it is considered that zinc metal oxides can have relatively low resistivity and can exhibit (e.g., uncontrollably) increased electron mobility, and that it is difficult to achieve the desired charge balance between the electron-assisted layer comprising zinc metal oxide nanoparticles and the emitter layer comprising cadmium-free quantum dots.

[0135] The nanoparticles may include metal dopants, and the energy levels of the nanoparticles may be affected by the metal dopants. Therefore, dopants can be added to the zinc metal oxide nanoparticles to achieve charge balance with the emitter layer. The inventors have found that QD-LEDs including zinc metal oxide nanoparticles with dopants can also be difficult to improve in terms of desired properties. Without being bound by any theory, it is believed that the addition of dopants can lead not only to an increase in resistivity but also to an increase in contact resistance, the latter of which can have a seriously detrimental effect on the efficiency of electron mobility between the electron auxiliary layer and the emitter layer (or electrode).

[0136] Contact resistance is a parameter distinct from resistivity. Contact resistance is a type of resistance that resists current due to surface conditions and other factors, occurring upon contact. Without being bound by any theory, in the case of QD-LEDs, traps present in the electron assist layer material can have a positive impact on electron flow toward the emitter layer, and the addition of dopants can alter the bandgap energy of the electron assist layer material and simultaneously affect (e.g., reduce) the number of traps present in the metal oxide nanoparticles. When dopants are added to change the bandgap energy to a desired level, the number of traps in the electron assist layer material can be significantly reduced, thereby adversely affecting electron movement within the electron assist layer.

[0137] In the light-emitting device of the embodiment, the zinc-containing metal oxide included in the electronic auxiliary layer (e.g., by means of a spatially controlled distribution of the dopant) comprises the dopant. In at least one of the metal oxide nanoparticles, the dopant metal is included in the metal oxide nanoparticles to have a concentration gradient. In the embodiment, the concentration gradient of a given substance may refer to a situation where, in a given object, the given substance is more concentrated (more concentrated) in one region (e.g., interior, center, or core region) than in another region (e.g., exterior, periphery, or shell). In the metal oxide, the distribution of the dopant throughout the nanoparticle may not be random or uniform.

[0138] In one embodiment, in at least one of the metal oxide nanoparticles, the molar amount or concentration (e.g., moles per volume or weight per volume) of the dopant in the inner (central) portion of the particle may differ from (e.g., be greater than or less than) the molar amount or concentration of the dopant in the outer (or peripheral) portion of the particle. For example, the molar amount or concentration of the dopant may increase in the direction from the inner portion to the outer portion of the nanoparticle, or in the direction from the outer portion to the inner portion of the nanoparticle. In other embodiments, the molar amount or concentration of the dopant in at least one of the metal oxide nanoparticles may increase in the direction from the core to the shell of the nanoparticle, or in the direction from the shell to the core of the nanoparticle. When a core or at least one shell with a controlled distribution is present, a core, inner shell, intermediate shell, or outer shell in the metal oxide nanoparticle may also be present, wherein the spatial distribution of the dopant is uncontrolled.

[0139] In an embodiment, the dopant (e.g., magnesium) may be more predominantly distributed within the internal portion (e.g., the core) of the metal oxide nanoparticles. Based on the overall size (or diameter) of the particle, the size (or diameter) of the internal portion (e.g., the core) may be a range of about 1% to about 99%, about 5% to about 95%, about 10% to about 90%, about 15% to about 85%, about 20% to about 80%, about 25% to about 75%, about 30% to about 70%, about 35% to about 65%, about 40% to about 60%, or about 45% to about 55%, or any combination of the listed limits (upper and lower limits). For example, based on the total molar number of the dopant present in the metal oxide nanoparticles, greater than or equal to about 70 mol% to about 100 mol%, greater than or equal to about 80 mol%, greater than or equal to about 90 mol%, greater than or equal to about 95 mol%, or 100 mol% of the dopant metal may be present in the internal portion (e.g., the core) of the metal oxide nanoparticles. In embodiments, the dopant (e.g., magnesium) may be substantially not distributed (present) in the external or surface portion (e.g., the shell) of the metal oxide nanoparticles.

[0140] In an embodiment, the dopant (e.g., magnesium) may be substantially distributed in the outer or surface portion (e.g., shell) of the metal oxide nanoparticles. Based on the total size (or diameter) of the particle, the size (or thickness) of the outer portion (e.g., shell) may be a range of about 1% to about 99%, about 5% to about 95%, about 10% to about 90%, about 15% to about 85%, about 20% to about 80%, about 25% to about 75%, about 30% to about 70%, about 35% to about 65%, about 40% to about 60%, or about 45% to about 55%, or any combination of the listed limits (upper and lower limits). In an embodiment, the metal oxide nanoparticles consist of the inner portion and the outer portion, and the thickness of the outer shell portion may be about 1% (or 5%) to about 20% (or 15%), based on the total size (or diameter) of the particle. For example, based on the total number of moles of the dopant present in the metal oxide nanoparticles, greater than or equal to about 70 mol% to about 100 mol%, greater than or equal to about 80 mol%, greater than or equal to about 90 mol%, greater than or equal to about 95 mol%, or 100 mol% of the dopant metal may be present in the outer or surface portion (e.g., shell) of the metal oxide nanoparticles.

[0141] In some embodiments, the dopant (e.g., magnesium) may be substantially absent from the interior or central portion (e.g., the core) of the metal oxide nanoparticles.

[0142] In embodiments, the metal oxide nanoparticles may include at least two dopants (e.g., a first dopant and a second dopant), wherein the concentrations of the dopants may differ in the internal and external portions of the metal oxide nanoparticles. For example, the first dopant may be dominant in the internal portion (e.g., the core) of the metal oxide nanoparticles, and the second dopant may be dominant in the external portion (e.g., the shell). Examples of the first and second dopants are the same as those described herein.

[0143] The inventors have discovered that such a controlled distribution of the dopant can be confirmed by the properties of the resulting metal oxide nanoparticles. In other words, the properties (or combinations of properties) of the resulting metal oxide nanoparticles can represent the distribution of the dopant therein (e.g., taking into account the composition of the metal oxide nanoparticles). When zinc-containing (e.g., zinc oxide) nanoparticles include a predetermined amount of the dopant distributed in a controlled manner, the zinc-containing nanoparticles can exhibit different electrical and optical properties than particles including the same amount of the dopant in an uncontrolled manner. In the metal oxide nanoparticles included in the electronic auxiliary layer of the device of the embodiment, the distribution of the dopant is spatially controlled, e.g., non-random, thereby the number of traps included in the metal oxide nanoparticles (e.g., at their surface) can be controlled (e.g., increased), and the controlled (increased) number of traps can act as an electron movement path toward the emitter layer.

[0144] In the light-emitting device of the embodiment, the metal oxide nanoparticles included in the electronic auxiliary layer include a controlled distribution of dopants of a predetermined type / amount, thereby altering their optical properties (e.g., trap emission can be increased).

[0145] The metal oxide nanoparticles may have a first UV-Vis absorption peak wavelength of less than or equal to about 350 nm, less than or equal to about 345 nm, or less than or equal to about 340 nm. The metal oxide nanoparticles may also have a first UV absorption peak wavelength of greater than or equal to about 300 nm, greater than or equal to about 310 nm, greater than or equal to about 315 nm, greater than or equal to about 320 nm, greater than or equal to about 325 nm, or greater than or equal to about 330 nm.

[0146] The metal oxide nanoparticles may be configured to exhibit a trapped emission peak with a center wavelength greater than or equal to about 500 nm, or greater than or equal to about 510 nm (e.g., in room temperature or low temperature PL analysis). The center wavelength of the trapped emission peak may be less than or equal to about 600 nm, or less than or equal to about 560 nm. The metal oxide nanoparticles may be configured to exhibit a band-edge emission peak with a center wavelength less than or equal to about 400 nm, or less than or equal to about 390 nm. The center wavelength of the band-edge emission peak may be greater than or equal to about 200 nm to 350 nm or greater.

[0147] The maximum intensity ratio of the trap emission peak to the edge emission peak can be greater than or equal to about 2.9:1, greater than or equal to about 3:1, greater than or equal to about 3.5:1, greater than or equal to about 4:1, greater than or equal to about 4.5:1, greater than or equal to about 5:1, greater than or equal to about 5.5:1, greater than or equal to about 6:1, greater than or equal to about 6.5:1, greater than or equal to about 7:1, greater than or equal to about 7.5:1, greater than or equal to about 8:1, greater than or equal to about 8.5:1, or greater than or equal to about 9:1.

[0148] The maximum intensity ratio of the trap emission peak to the edge emission peak may be less than or equal to about 50:1, less than or equal to about 40:1, less than or equal to about 30:1, less than or equal to about 20:1, or less than or equal to about 15:1.

[0149] The maximum intensity ratio of the trap emission peak to the band-edge emission peak can be determined using, for example, low-temperature photoluminescence measurements at 77 K.

[0150] In the light-emitting device of the embodiment, the metal oxide nanoparticles included in the electronic auxiliary layer include the dopants with controlled distribution and the electrical properties can be changed to exhibit a desired combination of resistivity and contact resistance.

[0151] The resistivity of the metal oxide nanoparticles can be greater than or equal to about 1 × 10⁻⁶. 4 ohm·cm, greater than or equal to approximately 1×10 5 ohm·cm, greater than or equal to approximately 3 × 10 8 ohm·cm, greater than or equal to approximately 3.3 × 10⁻⁶ 8 ohm·cm, greater than or equal to approximately 3.5 × 10⁻⁶ 8 ohm·cm, greater than or equal to approximately 3.7 × 10⁻⁶ 8 ohm·cm, greater than or equal to approximately 3.9 × 10⁻⁶ 8 ohm·cm.

[0152] The contact resistance of the metal oxide nanoparticles can be less than or equal to approximately 5 × 10⁻⁶. 11 ohm·cm 2 Less than or equal to approximately 4 × 10 11 ohm·cm 2 Less than or equal to approximately 3 × 10 11 ohm·cm 2 Less than or equal to approximately 2 × 10 11 ohm·cm 2 Less than or equal to approximately 1.5 × 10 11 ohm·cm 2 Less than or equal to approximately 1.4 × 10 11 ohm·cm 2 Less than or equal to approximately 1.3 × 10 11 ohm·cm 2 Less than or equal to approximately 1.2 × 10 11 ohm·cm 2 Less than or equal to approximately 1.1 × 10 11 ohm·cm 2 Less than or equal to approximately 1 × 10 11 ohm·cm 2 Or less than or equal to approximately 1 × 10 10 ohm·cm 2 .

[0153] In the light-emitting device of the embodiment, the metal oxide nanoparticles included in the electronic auxiliary layer may have an amount of organic matter greater than or equal to about 20%, greater than or equal to about 24%, or greater than or equal to about 25%, as determined by thermogravimetric analysis. The metal oxide nanoparticles included in the electronic auxiliary layer may have an amount of organic matter less than or equal to about 40%, less than or equal to about 35%, or less than or equal to about 30%, as determined by thermogravimetric analysis.

[0154] In one embodiment, the metal oxide nanoparticles (e.g., including zinc) may have a core-shell structure. The core-shell structure may include: a core comprising a first metal oxide, and a shell disposed on the core and comprising a second metal oxide having a composition different from the first metal oxide. The first metal oxide may include zinc and a first metal, and the first metal may include magnesium, aluminum, lithium, yttrium, gallium, zirconium, nickel, cobalt, or combinations thereof. The second metal oxide may include zinc and a second metal, and the second metal may include magnesium, aluminum, lithium, yttrium, gallium, zirconium, nickel, cobalt, or combinations thereof. In one embodiment, the band gap energy of the first metal oxide may be greater than the band gap energy of the second metal oxide. In another embodiment, the band gap energy of the second metal oxide may be greater than the band gap energy of the first metal oxide.

[0155] The first metal oxide may include a compound represented by Chemical Formula 1:

[0156] Chemical Formula 1

[0157] Zn 1-x A x O

[0158] In Chemical Formula 1, A is Mg, Mn, Ni, Li, Sn, Al, Y, Ga, Zr, Co, or a combination thereof, and 0 ≤ x < 1, for example, 0 ≤ x ≤ 0.5.

[0159] The second metal oxide may include a compound represented by Chemical Formula 2:

[0160] Chemical Formula 2

[0161] Zn 1-y M y O

[0162] In Chemical Formula 2, M is Mg, Mn, Ni, Li, Sn, Al, Y, Ga, Zr, Co or a combination thereof, and 0 ≤ y < 1, for example, 0 ≤ y ≤ 0.5.

[0163] The first metal oxide may include metal A, the second metal oxide may include metal M, or a combination thereof.

[0164] In an embodiment, the first metal oxide includes the first metal, and the molar ratio of the first metal to zinc may be less than or equal to about 0.5:1, for example, less than or equal to about 0.4:1, less than or equal to about 0.3:1. The first metal oxide includes magnesium, and the molar ratio of magnesium to zinc may be less than or equal to about 0.3:1.

[0165] Reference Figure 2 , in the metal oxide nanoparticles, the core may include a first metal oxide containing zinc and a first metal dopant (A). The shell may include a second metal oxide containing zinc and a second metal dopant (M). The first metal oxide may include the first metal dopant (A), the second metal oxide may include the second metal dopant (M), or a combination thereof. In an embodiment, the first metal oxide may include Zn 1-x Mg x O (0 ≤ x < 1, for example 0 < x ≤ 0.5), and the second metal oxide may include zinc oxide represented by ZnO. In an embodiment, the second metal oxide may include Zn 1-x Mg x O (0 ≤ x < 1, for example 0 < x ≤ 0.5), and the first metal oxide may include zinc oxide represented by ZnO.

[0166] In the metal oxide nanoparticles, the core size may be greater than or equal to about 1 nm, greater than or equal to about 1.5 nm, greater than or equal to about 2 nm, greater than or equal to about 2.5 nm, or greater than or equal to about 3 nm. In the metal oxide nanoparticles, the core size may be less than or equal to about 9 nm, less than or equal to about 8 nm, less than or equal to about 7 nm, less than or equal to about 6 nm, less than or equal to about 5 nm, or less than or equal to about 4 nm. In the metal oxide nanoparticles, the shell thickness may be greater than or equal to about 0.1 nm, greater than or equal to about 0.2 nm, greater than or equal to about 0.3 nm, greater than or equal to about 0.4 nm, or greater than or equal to about 0.5 nm. In the metal oxide nanoparticles, the shell thickness may be less than or equal to about 1 nm, less than or equal to about 0.9 nm, less than or equal to about 0.8 nm, less than or equal to about 0.7 nm, or less than or equal to about 0.6 nm.

[0167] The first metal oxide may include zinc oxide and magnesium oxide, and the second metal oxide may include zinc oxide. The second metal oxide may not include magnesium, aluminum, lithium, yttrium, gallium, zirconium, nickel, cobalt, or combinations thereof.

[0168] The average size of the metal oxide nanoparticles may be greater than or equal to about 2 nm, or greater than or equal to about 2.5 nm. The average size of the metal oxide nanoparticles may be less than or equal to about 10 nm, less than or equal to about 8 nm, less than or equal to about 6 nm, or less than or equal to about 4 nm. The average size of the metal oxide nanoparticles may be between about 3 nm and about 6 nm.

[0169] In an embodiment, the metal oxide nanoparticles (e.g., comprising the first metal oxide and the second metal oxide) can be prepared as follows:

[0170] A first organic solution is provided, comprising a first zinc precursor, a first organic solvent, and optionally a first dopant precursor;

[0171] A solution containing hydroxide is added to the first organic solution and the resulting mixture is stirred to form a precipitate.

[0172] Separate the precipitate as formed;

[0173] The separated precipitates are dispersed to form a dispersion;

[0174] The dispersion is mixed with a second organic solution comprising a second zinc precursor, a second organic solvent, and optionally a second dopant precursor, and a solution containing hydroxide is added to the mixture and stirred to form zinc oxide nanoparticles containing zinc, wherein the first organic solution comprises the first dopant precursor; the second organic solution comprises the second dopant precursor; or the first organic solution comprises the first dopant precursor and the second organic solution comprises the second dopant precursor.

[0175] The details of the metal oxide nanoparticles are the same as those described herein.

[0176] In an embodiment, the first organic solution may optionally be heated to a first temperature. The dispersion may optionally be heated to a second temperature. The first temperature and the second temperature may be the same or different. The first temperature and the second temperature may each be independently greater than or equal to about 30°C, greater than or equal to about 40°C, or greater than or equal to about 50°C. The first temperature and the second temperature may each be independently less than or equal to about 100°C, less than or equal to about 80°C, or less than or equal to about 70°C.

[0177] The precipitate formed may optionally be washed with the following: C1-C10 alcohol solvents such as ethanol, methanol, propanol, etc.; C1-C10 ester solvents such as alkyl acetate; C1-C20 amine solvents; C1-C20 amide solvents such as dimethylformamide (DMF); C1-C20 sulfoxides such as dimethyl sulfoxide (DMSO); or combinations thereof.

[0178] The first zinc precursor and the second zinc precursor (hereinafter referred to as zinc precursors) may be the same or different. The zinc precursor may include C1-C30 carboxylic acids (e.g., zinc acetate).

[0179] The type and amount of the first dopant precursor and the second dopant precursor can be selected independently, taking into account the desired distribution of the dopant.

[0180] The first dopant precursor may include the dopant metal. The second dopant precursor may include the dopant metal. The first and second dopant precursors (hereinafter, dopant precursors) may be the same or different. The dopant precursor may include a metal C1-C30 carboxylate (e.g., an acetate). The dopant precursor may include magnesium.

[0181] In one embodiment, the first organic solution may include the first dopant precursor, and the second organic solution may not include the second dopant precursor. In another embodiment, the first organic solution may not include the first dopant precursor, and the second organic solution may include the second dopant precursor. In yet another embodiment, the first organic solution may include the first dopant precursor, and the second organic solution may include the second dopant precursor. The concentration of the dopant precursor included in the first organic solution, the second organic solution, or a combination thereof may be determined taking into account the desired composition of the final metal oxide nanoparticles and the desired distribution of the dopant therein.

[0182] The types of the dispersion solvent, the first organic solvent, and the second organic solvent can be appropriately determined taking into account the type of zinc / dopane precursor and the reaction temperature.

[0183] The first organic solvent and the second organic solvent (hereinafter, organic solvent) may be the same or different. The organic solvent may include C1-C30 alcohol solvents, amide solvents such as DMF, sulfoxide solvents such as DMSO, ether solvents, alkyl ester solvents, or combinations thereof.

[0184] The concentration of the precursor (e.g., the zinc precursor, the first dopant precursor, or a combination thereof) in the first organic solution can be appropriately controlled taking into account the type of precursor used, the reaction temperature, and the composition of the final nanoparticles. The concentration of the precursor (e.g., the zinc precursor, the second dopant precursor, or a combination thereof) in the second organic solution can be appropriately controlled taking into account the amount of precipitate from the dispersion and the composition of the final nanoparticles. In embodiments, the concentration of the zinc precursor can be in the range of about 0.01M to about 10M, about 0.05M to about 5M, about 0.07M to about 1M, 0.1M to 0.5M, or any combination of the limits listed herein. The concentration of the dopant precursor can be controlled according to the desired combination of the zinc precursor and the metal oxide nanoparticles.

[0185] The hydroxide-containing solution may include a hydroxide compound. The hydroxide compound may include alkali metal hydroxides (e.g., NaOH, KOH, etc.), alkaline earth metal hydroxides, alkylammonium hydroxides (e.g., trimethylammonium hydroxide), or combinations thereof. The amount of the hydroxide compound may be adjusted taking into account the amount of the metal precursor used. In embodiments, the hydroxide compound may be used in stoichiometric amounts, but is not limited thereto.

[0186] The thickness of the electronic auxiliary layer can be appropriately selected taking into account the emission wavelength of the quantum dot emission layer, the thickness of the emission layer, etc. The thickness of the electronic auxiliary layer can be greater than or equal to about 10 nm, greater than or equal to about 11 nm, greater than or equal to about 12 nm, greater than or equal to about 15 nm, greater than or equal to about 20 nm, greater than or equal to about 25 nm and less than or equal to about 100 nm, less than or equal to about 90 nm, less than or equal to about 80 nm, less than or equal to about 70 nm, less than or equal to about 60 nm, or less than or equal to about 50 nm.

[0187] The light-emitting device 1 may further include a first electrode and a second electrode facing each other, and the emitting layer may be disposed between the first electrode 11 and the second electrode 15. One of the first electrode 11 and the second electrode 15 may be an anode and the other may be a cathode. In the following description, the case in which the first electrode is an anode is described, but it is not limited thereto.

[0188] A hole auxiliary layer 12 may be disposed between the first electrode 11 and the emitter layer 13. An electron auxiliary layer 14 may be disposed between the second electrode 15 and the emitter layer 13.

[0189] The light-emitting device 1 may further include a substrate. The substrate may be disposed on the main surface of the first electrode 11 or the main surface of the second electrode 15. In an embodiment, the substrate may be disposed on the main surface of the first electrode (e.g., below the first electrode). The substrate may be a substrate comprising an insulating material. The substrate may be insulating, transparent, or a combination thereof. The substrate may include: glass; various polymers such as polyesters (e.g., polyethylene terephthalate (PET), polyethylene naphthalate (PEN)), polycarbonate, polyacrylate, polyimide, and polyamide-imide); polysiloxanes (e.g., polydimethylsiloxane (PDMS)); inorganic materials such as Al₂O₃ and ZnO; or combinations thereof, but not limited thereto. The substrate may be made of a silicon wafer. Here, "transparent" can refer to a transmittance of about 85%, for example, about 88%, about 90%, about 95%, about 97%, or about 99% for light of a predetermined wavelength (e.g., light emitted from a quantum dot). The thickness of the substrate can be appropriately selected with consideration of the substrate material, but is not particularly limited. The transparent substrate may be flexible. The substrate may be omitted.

[0190] The first electrode 11 may be made of a conductor, such as a metal, a conductive metal oxide, or a combination thereof. The first electrode 11 may be made, for example, of a metal or alloy thereof, such as nickel, platinum, vanadium, chromium, copper, zinc, and gold; a conductive metal oxide, such as zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or fluorine-doped tin oxide; or a combination of a metal and a metal oxide, such as ZnO and Al, or SnO2 and Sb, but is not limited thereto. In embodiments, the first electrode may include a transparent conductive metal oxide, such as indium tin oxide. The work function of the first electrode may be higher than that of the second electrode, which will be described later. The work function of the first electrode may be lower than that of the second electrode.

[0191] The second electrode 15 may be made of a conductor such as a metal, a conductive metal oxide, a conductive polymer, or a combination thereof. The second electrode 15 may be, for example, a metal or alloy thereof such as aluminum, magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, silver, tin, lead, cesium, or barium; a multilayer material such as LiF / Al, Li₂O / Al, lithium 8-hydroxyquinoline (Liq) / Al, LiF / Ca, and BaF₂ / Ca, but is not limited thereto. In embodiments, the second electrode may include a transparent conductive metal oxide such as indium tin oxide. Examples of such conductive metal oxides are the same as those described herein.

[0192] In an embodiment, the work function of the first electrode (e.g., the anode) may be greater than or equal to about 4.0 eV, greater than or equal to about 4.1 eV, greater than or equal to about 4.2 eV, greater than or equal to about 4.3 eV, greater than or equal to about 4.4 eV, greater than or equal to about 4.5 eV, greater than or equal to about 4.6 eV, greater than or equal to about 4.7 eV, or greater than or equal to about 4.8 eV and less than or equal to about 5.5 eV, less than or equal to about 5.4 eV, less than or equal to about 5.3 eV, less than or equal to about 5.2 eV, less than or equal to about 5.1 eV, less than or equal to about 5.0 eV, or less than or equal to about 4.9 eV.

[0193] In an embodiment, the work function of the second electrode (e.g., a cathode) may be greater than or equal to about 3.4 eV, greater than or equal to about 3.5 eV, greater than or equal to about 3.6 eV, greater than or equal to about 3.7 eV, greater than or equal to about 3.8 eV, greater than or equal to about 3.9 eV, greater than or equal to about 4.0 eV, greater than or equal to about 4.1 eV, greater than or equal to about 4.2 eV, greater than or equal to about 4.3 eV, greater than or equal to about 4.4 eV, or greater than or equal to about 4.5 eV and less than or equal to about 5.0 eV, less than or equal to about 4.9 eV, less than or equal to about 4.8 eV, less than or equal to about 4.7 eV, less than or equal to about 4.6 eV, less than or equal to about 4.5 eV, or less than or equal to about 4.4 eV.

[0194] The first electrode 11, the second electrode 15, or a combination thereof may be light-transmitting electrodes, and the light-transmitting electrodes may be made, for example, of conductive oxides such as zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or fluorine-doped tin oxide, or single or multiple metal thin layers. When one of the first electrode 11 and the second electrode 15 is a non-light-transmitting electrode, the non-light-transmitting electrode may be made of, for example, an opaque conductor such as aluminum (Al), silver (Ag), or gold (Au).

[0195] The thickness of the electrode (first electrode, second electrode, or combination thereof) is not particularly limited and can be appropriately selected with consideration of device efficiency. For example, the thickness of the electrode can be greater than or equal to about 5 nm, such as greater than or equal to about 50 nm. For example, the thickness of the electrode can be less than or equal to about 100 micrometers (μm), such as less than or equal to about 10 μm, less than or equal to about 1 μm, less than or equal to about 900 nm, less than or equal to about 500 nm, or less than or equal to about 100 nm.

[0196] The hole auxiliary layer 12 may be disposed between the first electrode 11 and the emitter layer 13. The hole auxiliary layer 12 may have one layer or two or more layers, and may include, for example, a hole injection layer (HIL), a hole transport layer (HTL), an electron blocking layer, or a combination thereof.

[0197] Hole auxiliary layer 12 may have HOMO energy levels that match the HOMO energy levels of emitter layer 13, and may enhance, for example, the migration of holes from hole auxiliary layer 12 to emitter layer 13.

[0198] The HOMO level of the hole auxiliary layer 12 (e.g., hole transport layer (HTL)) in contact with the emitter layer can be appropriately tuned to take into account the HOMO of the emitter layer 13. In an embodiment, the hole auxiliary layer may include a hole injection layer near the first electrode 11 and a hole transport layer near the emitter layer 13.

[0199] The materials included in the hole auxiliary layer 12 are not particularly limited and may include, for example, poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), polyarylamines (polyarylamines), poly(N-vinylcarbazole), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene):polysulfonated styrene (PEDOT:PSS), polyaniline, polypyrrole, N,N,N',N'-tetra(4-methoxyphenyl)-benzidine (TPD), 4 ,4'-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), m-MTDATA (4,4',4”-tris[phenyl(m-tolyl)amino]triphenylamine), 4,4',4”-tris(N-carbazolyl)triphenylamine (TCTA), 1,1-bis[(bis-4-tolylamino)phenyl]cyclohexane (TAPC), p-type metal oxides (e.g., NiO, WO3, MoO3, etc.), carbon-based materials such as graphene oxides, or combinations thereof, but not limited thereto.

[0200] In an embodiment, the thickness of the hole assist layer (e.g., hole transport layer, hole injection layer, or a combination thereof) may be greater than or equal to about 10 nm, for example greater than or equal to about 15 nm, greater than or equal to about 20 nm and less than or equal to about 100 nm, for example less than or equal to about 90 nm, less than or equal to about 80 nm, less than or equal to about 70 nm, less than or equal to about 60 nm, or less than or equal to about 50 nm, but is not limited thereto.

[0201] The hole injection layer, the hole transport layer, or a combination thereof may be formed by a solution process (e.g., spin coating). The hole injection layer, the hole transport layer, or a combination thereof may be formed by a deposition process (e.g., physical or chemical deposition).

[0202] The device according to the embodiment may have a normal structure. In the device of the embodiment, the anode 10 disposed on the transparent substrate 100 may include a transparent electrode based on a metal oxide (e.g., an ITO electrode), and the cathode 50 facing the anode may include a metal (Mg, Al, etc.) with relatively low work function. For example, the hole assist layer 20 may include a hole transport layer such as TFB, poly(9-vinylcarbazole) (PVK), or a combination thereof; a hole injection layer such as PEDOT:PSS, p-type metal oxide, or a combination thereof; or a combination thereof may be disposed between the transparent electrode 10 and the emitter layer 30. The electron assist layer 40, such as an electron injection layer / transport layer, may be disposed between the quantum dot (QD) emitter layer 30 and the cathode 50. (See See...) Figure 1B )

[0203] The device according to the embodiment has an inverted structure. Here, the cathode 50 disposed on the transparent substrate 100 may include a transparent electrode based on a metal oxide (e.g., ITO), and the anode 10 facing the cathode may include a metal with a relatively high work function (e.g., Au, Ag, etc.). For example, an n-type metal oxide (ZnO) may be disposed between the transparent electrode 50 and the emitter layer 30 as an electron auxiliary layer 40 (e.g., an electron transport layer (ETL)). A hole auxiliary layer 20 (e.g., a hole transport layer (HTL) including TFB, PVK, or combinations thereof, a hole injection layer (HIL) including MoO3 or other p-type metal oxides, or combinations thereof) may be disposed between the metal anode 10 and the quantum dot emitter layer 30. (See See...) Figure 1C )

[0204] The device of the embodiment can be fabricated in a suitable manner. In the embodiment, the electroluminescent device can be fabricated by forming a charge (e.g., hole) auxiliary layer on a substrate having electrodes thereon (e.g., via deposition or coating), forming an emission layer comprising quantum dots (e.g., a pattern of the aforementioned quantum dots) thereon (e.g., via deposition or coating), and forming electrodes thereon (optionally together with the charge (e.g., electron) auxiliary layer) (e.g., via deposition or coating). The formation of the electrode / hole auxiliary layer / electron auxiliary layer is not particularly limited and can be suitably selected.

[0205] In an embodiment, the method of manufacturing the aforementioned light-emitting device includes: providing a first electrode, optionally forming a hole-assisted layer on the first electrode, forming an emission layer on the first electrode (or optionally the hole-assisted layer), forming an electron-assisted layer on the emission layer as described herein, and forming a second electrode (e.g., a cathode) on the electron-assisted layer, wherein the formation of the electron-assisted layer includes depositing zinc-containing metal oxide nanoparticles as described herein on the emission layer.

[0206] Details of the first electrode, hole-assist layer, and second electrode are as described herein. The techniques for forming these device structural elements are well known to those skilled in the art, and are appropriately selected considering the materials used in forming each structural device element, as well as the thicknesses of the electrodes and the hole-assist layer. Formation methods may include solution processes, deposition processes, or combinations thereof. In embodiments, the aforementioned hole-assist layer 12, the quantum dot-based emitter layer 13, and the electron-assist layer 14 may be formed using solution processes such as spin coating, slot coating, inkjet printing, nozzle printing, jetting, blade coating, or combinations thereof, but are not limited thereto.

[0207] The formation of the emission layer can be performed by dispersing the quantum dots in a solvent (e.g., an organic solvent) to obtain a quantum dot dispersion, and applying or depositing the quantum dot dispersion onto the substrate or the charge-assisted layer in a suitable manner (e.g., spin coating, inkjet printing, etc.). The formation of the emission layer may further include heat-treating the applied or deposited quantum dot layer. The heat treatment temperature is not particularly limited and can be appropriately selected taking into account the boiling point of the organic solvent. For example, the heat treatment temperature may be greater than or equal to about 60°C. The organic solvent for the quantum dot dispersion is not particularly limited and can be appropriately selected. In embodiments, the organic solvent may include (substituted or unsubstituted) aliphatic hydrocarbon organic solvents, (substituted or unsubstituted) aromatic hydrocarbon organic solvents, acetate solvents, or combinations thereof.

[0208] The electronic auxiliary layer 14 can be formed by a wet process. The wet process may include a sol-gel process. In one embodiment, the wet process may include: dispersing nanoparticles of a metal oxide in a polar solvent to obtain a dispersion; applying the dispersion to the quantum dot emission layer, for example by spin coating; and drying and annealing the resulting film. The polar solvent may include, but is not limited to, C1-C10 alcohol solvents such as methanol or ethanol, C2-C20 sulfoxide solvents such as dimethyl sulfoxide, C2-C20 amide solvents such as dimethylformamide, or combinations thereof.

[0209] The annealing can be performed under vacuum at a predetermined temperature (e.g., greater than or equal to about 60°C, or greater than or equal to about 70°C and less than or equal to about 100°C, such as less than or equal to about 90°C, less than or equal to about 80°C, or less than or equal to about 75°C), but is not limited thereto.

[0210] The light-emitting device can exhibit improved properties and lifetime properties. The light-emitting device can (e.g., emit blue light) exhibit a value greater than or equal to about 35,000 cd / m². 2 For example, greater than or equal to approximately 36,000 cd / m³ 2 Or greater than or equal to approximately 37,000 cd / m³ 2 The maximum brightness. The light-emitting device may have a T50 of more than about 50 hours, for example, more than or equal to about 55 hours, more than or equal to about 60 hours, more than or equal to about 65 hours, or more than or equal to about 70 hours, while emitting blue light.

[0211] The light-emitting device can be used in a variety of electronic devices. These electronic devices can be applied to various electronic equipment, such as display devices or lighting devices.

[0212] In implementation, PL properties (e.g., for trap emission and band-edge emission of quantum dots or metal oxide nanoparticles) can be readily and reproducibly determined using a commercially available spectrophotometer (e.g., from Hitach Co. Ltd or Hammamatsu Co. Ltd) at the desired temperature (e.g., room temperature or low temperature such as 77 K).

[0213] The irradiation wavelength can be, for example, about 200 nm to about 400 nm, or about 250 nm to about 390 nm, or about 280 nm to about 380 nm, or about 300 nm to about 375 nm. Sample separation can be performed according to the manual provided by the manufacturer (e.g., dispersion in an organic solvent such as a hydrocarbon solvent, such as toluene, hexane, etc.).

[0214] In this implementation, the UV-Vis absorption properties can be easily determined using a commercially available spectrophotometer (e.g., a Hitachi U-series spectrophotometer or an Agilent Cary-series spectrophotometer).

[0215] In the following description, implementation methods are illustrated in more detail with reference to embodiments. However, these embodiments are exemplary and the scope is not limited thereto.

[0216] Analytical methods

[0217] 1. Photoluminescence analysis

[0218] The photoluminescence (PL) spectra of the prepared nanocrystals or metal oxide nanoparticles were obtained using a Hitachi F-7000 spectrophotometer at irradiation wavelengths of 372 nm (for quantum dots) and 300 nm (for metal oxide nanoparticles) in the solution (solvent: hexane).

[0219] 2. Ultraviolet-Vis (UV-Vis) Spectroscopic Analysis

[0220] Ultraviolet (UV) spectral analysis and UV-visible absorption spectra were performed using a Hitachi U-3310 spectrophotometer.

[0221] 3. Transmission electron microscopy (TEM) analysis

[0222] Transmission electron microscopy images of nanocrystals were obtained using a UT F30 Tecnai electron microscope.

[0223] 4. Transmission Line Measurement (TLM) Analysis

[0224] TLM analysis was performed using a MacScience JVL instrument. Multiple metal electrodes were formed at intervals at different locations on the surface of a thin film of the semiconductor whose conductivity was to be measured. Then, any two electrodes were selected, and a voltage was applied between them to measure the current. By doing so, resistance values ​​dependent on the distance between the metal electrodes were obtained, and from such data, resistivity and conductivity could be determined.

[0225] 5. Low-temperature photoluminescence analysis

[0226] The photoluminescence (PL) spectra of the prepared nanocrystals or the prepared metal oxide nanoparticles (in hexane) were obtained using a Hitachi F-7000 spectrometer at an irradiation wavelength of 300 nm at 77 K.

[0227] 6. Electroluminescence spectroscopy

[0228] The electroluminescence properties of the obtained light-emitting devices were evaluated using a Keithley 2200 source measurement apparatus and a Minolta CS2000 spectroradiometer (current-voltage-luminance measurement apparatus). The current, luminance, and electroluminescence (EL), which depend on the voltage applied to the device, were measured using the current-voltage-luminance measurement apparatus, thereby determining the external quantum efficiency (EQE).

[0229] 7. Lifetime Analysis

[0230] (1) T50 (hours): The time taken for a given device operating at 100 nits to exhibit a 50% reduction in its initial brightness (100%).

[0231] (2) T95 (hours): The time taken for a given device operating at 100 nits to exhibit 95% of its initial brightness (100%).

[0232] 8. TGA Analysis

[0233] Thermogravimetric analysis was performed using TA Instruments Q5000.

[0234] Quantum dot synthesis

[0235] Reference example: Preparation of red luminescent quantum dots

[0236] Example 1 for reference:

[0237] (1) Selenium (Se) and tellurium (Te) were dispersed in trioctylphosphine (TOP) to obtain a 2 M Se / TOP stock solution and a 0.1 M Te / TOP stock solution. 0.125 mmol zinc acetate was added to a reactor containing trioctylphosphine along with oleic acid and hexadecylamine, and the resulting solution was heated at 120 °C under vacuum. After one hour, a nitrogen atmosphere was added to the reactor.

[0238] The reactor was then heated to 300°C, and the prepared Se / TOP and Te / TOP stock solutions were rapidly injected into the reactor at a Te:Se molar ratio of 1:25. After 60 minutes, acetone was added to the reaction solution, and the reaction mixture was rapidly cooled to room temperature. The precipitate obtained after centrifugation was dispersed in toluene to obtain ZnTeSe cores.

[0239] (2) 1.8 mmol (0.336 g) of zinc acetate was added to a reaction flask containing trioctylamine along with oleic acid, and then the mixture was vacuum-treated at 120 °C for 10 min. Nitrogen was then introduced into the reaction flask, and the temperature was raised to 180 °C. The ZnTeSe core obtained above was added to the reaction flask, along with Se / TOP stock solution, and the temperature was raised to 280 °C. Then, 1 M S / TOP stock solution was added, the temperature was raised to 320 °C, and the Se / TOP and S / TOP stock solutions were added to the reaction flask in predetermined amounts. After the reaction was complete, the reactor was cooled, ethanol was added, and the mixture was centrifuged. The collected nanocrystals were dispersed in toluene to obtain a toluene dispersion of ZnTeSe / ZnSeS core / shell quantum dots.

[0240] According to one mole of the zinc precursor, the amounts of the S precursor and the Se precursor used are approximately 0.25 moles and 0.6 moles, respectively.

[0241] Reference Example 2:

[0242] The quantum dots prepared in Reference Example 1 were dispersed in 5 mL of octane at a concentration of 20 mg / mL to obtain an organic dispersion of quantum dots. Zinc chloride was dissolved in ethanol to obtain a zinc chloride solution with a concentration of 10 wt%. 0.01 mL of the obtained zinc chloride solution was added to the prepared organic dispersion of quantum dots, and then the mixture was stirred at 60 °C for 30 min to carry out a surface exchange reaction. After the reaction, ethanol was added to induce precipitation, and the quantum dots were collected by centrifugation.

[0243] Synthesis of metal oxide nanoparticles

[0244] Preparation of Comparative Example 1: Synthesis of ZnMgO

[0245] Zinc acetate dihydrate and magnesium acetate tetrahydrate were added to a reactor containing dimethyl sulfoxide and heated at 60°C in air. Subsequently, an ethanol solution of tetramethylammonium hydroxide pentahydrate was added dropwise to the reactor in stoichiometric amounts. After stirring for 1 hour, the resulting solution containing Zn... 1-x Mg x The precipitate of O (x = 0.15) nanoparticles was centrifuged and dispersed in ethanol to obtain Zn. 1-x Mg x O nanoparticles.

[0246] The obtained nanoparticles were analyzed by transmission electron microscopy, and the results showed that the particles had an average size of about 3 nm.

[0247] Thermogravimetric analysis was performed on the obtained nanoparticles, and the results confirmed that the residual content (amount of organic matter) in the nanoparticles was approximately 72.6% by weight.

[0248] Preparation of Comparative Example 2: Synthesis of ZnO

[0249] ZnO particles were synthesized in the same manner as described in Comparative Example 1, except that magnesium acetate tetrahydrate was not used.

[0250] The obtained nanoparticles were analyzed by transmission electron microscopy, and the results showed that the particles had an average size of about 3.7 nm.

[0251] Thermogravimetric analysis was performed on the obtained nanoparticles, and the results confirmed that the residual content (amount of organic matter) in the nanoparticles was approximately 84.7% by weight.

[0252] Preparation Example 1: Zn 1-x Mg x Preparation of O / ZnO

[0253] Nanoparticles are prepared in which the dopant distribution is dominant in the internal portion of the particle.

[0254] Zn was prepared in a manner similar to that described in Comparative Example 1. 1-x Mg x O particles (x = 0.15) (average size: 3 nm). The Zn... 1-x Mg x O particles were dispersed in a reactor containing DMSO solvent. A second solution with a concentration of 0.1 M, prepared by dissolving zinc acetate dihydrate in DMSO solvent, was added to the reactor, and the reaction was carried out for 60 minutes to obtain a solution with Zn. 1-x Mg xO / ZnO structured nanoparticles, wherein magnesium dopant is predominantly distributed in the internal portion of the particles.

[0255] TEM analysis was performed on the obtained nanoparticles, and the results showed that the average size of the particles was about 3.3 nm.

[0256] Thermogravimetric analysis was performed on the obtained nanoparticles, and the results confirmed that the residual content (amount of organic matter) in the nanoparticles was approximately 74.1% by weight.

[0257] Preparation Example 2: ZnO / Zn 1-x Mg x Preparation of O

[0258] Nanoparticles are prepared in which the dopant distribution is dominant in the outer part of the particle.

[0259] ZnO particles (average size: 3.7 nm) were prepared in a manner similar to that described in Comparative Example 2.

[0260] The ZnO particles were dispersed in a reactor containing DMSO solvent. A second solution (zinc concentration: 0.1 M), prepared by dissolving zinc acetate dihydrate and magnesium acetate tetrahydrate in DMSO solvent, was added to the reactor, and the reaction was carried out for 60 minutes to obtain a ZnO / ZnO ratio. 1-x Mg x Nanoparticles with an O (x = 0.15) structure, wherein the magnesium dopant is predominantly distributed in the outer portion or layer of the particles (i.e., on their surface).

[0261] TEM analysis was performed on the obtained nanoparticles, and the results showed that the average size of the particles was about 4.1 nm.

[0262] Thermogravimetric analysis was performed on the obtained nanoparticles, and the results confirmed that the residual content (amount of organic matter) in the nanoparticles was approximately 80.8% by weight.

[0263] Experimental Example 1: Evaluation of the electrical properties of metal oxide nanoparticles

[0264] For the nanoparticles prepared in Comparative Example 1, Comparative Example 2, and Example 1, resistivity and contact resistance were measured using the TLM method, and the results are summarized in Table 1.

[0265] Table 1

[0266] Resistivity (unit: ohm·cm) <![CDATA[Contact resistance (unit: ohm·cm 2 )]]> Preparation of Comparative Example 1 (ZnMgO) <![CDATA[3×10 8 ]]> <![CDATA[1.4×10 11 ]]> Preparation of Comparative Example 2 (ZnO) <![CDATA[3×10 8 ]]> <![CDATA[1×10 11 ]]> Preparation Example 1 (ZnMgO / ZnO) <![CDATA[4×10 8 ]]> <![CDATA[1×10 11 ]]>

[0267] The results in Table 1 confirm that the nanoparticles prepared in Example 1 exhibit a low level of contact resistance comparable to that of the nanoparticles prepared in Comparative Example 2.

[0268] Evaluation of the optical properties of metal oxide nanoparticles

[0269] Experimental Example 2-1:

[0270] The prepared metal oxide nanoparticles were analyzed by UV-Vis absorption spectroscopy and photoluminescence spectroscopy, and the results are shown in... Figure 3 and Figure 4A middle.

[0271] exist Figure 3 and Figure 4A In the wavelength region greater than 500 nm, the emission peak is the peak of trap emission. Figure 3 and Figure 4A The results confirmed that when the magnesium dopant is distributed over substantially the entire portion of the particle or predominantly distributed in the outer portion of the particle, the trap emission of zinc oxide nanoparticles can be significantly reduced, and when the distribution of the magnesium dopant is predominantly confined to the inner portion of the particle, the trap emission can be maintained at a level similar to that of particles without metal dopant.

[0272] Experimental Example 2-2:

[0273] The metal oxide nanoparticles prepared in Comparative Example 1 and Preparation Example 1 were analyzed by low-temperature photoluminescence spectroscopy, and the results are shown in... Figure 4B middle.

[0274] Figure 4B The results confirmed that, compared with those prepared in Comparative Example 1, the nanoparticles prepared in Example 1 exhibited a significantly increased trap emission ratio.

[0275] Example 1

[0276] The device is fabricated in the following manner:

[0277] A glass substrate with indium tin oxide (ITO) deposition was surface-treated with UV-ozone for 15 minutes, then spin-coated with a poly(3,4-ethylenedioxythiophene):polysulfonated styrene (PEDOT:PSS) solution (HCStarks) and heated at 150°C for 10 minutes in air. It was then heat-treated again at 150°C in N2 atmosphere for 20-30 minutes to provide a hole injection layer with a thickness of 30 nm. Subsequently, a poly[(9,9-dioctylfluorene-2,7-diyl-co-(4,4'-(N-4-butylphenyl)diphenylamine] solution (TFB) (Sumitomo) was spin-coated onto the hole injection layer and heated at 150°C for 30 minutes to provide a hole transport layer with a thickness of 25 nm.

[0278] The quantum dot dispersion obtained by Reference Example 1 was spin-coated onto the hole transport layer obtained above, and a zinc chloride ethanol solution was dropped onto it and evaporated. The resulting structure was then heat-treated at 80°C for 30 minutes. Then, the quantum dot dispersion obtained by Reference Example 2 was spin-coated onto it to provide an emission layer with a thickness of 20 nm.

[0279] An ethanol dispersion comprising the nanoparticles obtained in Preparation Example 1 was prepared. The obtained dispersion was spin-coated onto the emission layer and heated at 80°C for 30 minutes to provide an electron-assisted layer with a thickness of 20 nm.

[0280] A 100 nm layer of aluminum (Al) is vacuum deposited on the obtained electron-assisted layer to provide a second electrode, thereby obtaining a light-emitting device.

[0281] Cross-sectional samples of the fabricated devices were prepared using FIB (Focused Ion Beam) and then analyzed by TEM. The results are shown in... Figure 5 middle.

[0282] The electroluminescence properties of the obtained quantum dot light-emitting devices were evaluated. The results are shown in Table 2.

[0283] Comparative Example 1

[0284] The light-emitting device was obtained according to the same procedure as in Example 1, except that the nanoparticles used to prepare Comparative Example 1 were used instead of those used to form the electron-assisted layer in Example 1. The electroluminescent properties of the obtained light-emitting device were evaluated, and the results are shown in Table 2.

[0285] Comparative Example 2

[0286] The light-emitting device was obtained according to the same procedure as in Example 1, except that the nanoparticles used to prepare Comparative Example 2 were used instead of those used to form the electron-assisted layer in Example 1. The electroluminescent properties of the obtained light-emitting device were evaluated, and the results are shown in Table 2.

[0287] Table 2

[0288]

[0289] *EQE@5,000 nits: External quantum efficiency at a brightness of 5,000 nits (candela / m²).

[0290] *Max. Brightness: Maximum brightness

[0291] The results in Table 2 confirm that the device according to Example 1 exhibits improved electroluminescence properties, and the lifetime of the device according to Example 1 is significantly increased.

[0292] Although this disclosure has been described with respect to exemplary embodiments which are now considered to be practical, it will be understood that the invention is not limited to the disclosed embodiments, but rather is intended to cover a variety of variations and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. Light-emitting devices, including: Including an emission layer of multiple quantum dots, and An electron auxiliary layer disposed on the emitter layer, the electron auxiliary layer transmitting or injecting electrons into the emitter layer. The electronic auxiliary layer comprises multiple metal oxide nanoparticles. The metal oxide nanoparticles comprise zinc and a dopant metal, wherein the dopant metal comprises Mg, Mn, Ni, Sn, Al, Y, Ga, Zr, Li, Co, or combinations thereof, and The dopant metal in at least one of the metal oxide nanoparticles is included in the metal oxide nanoparticles to have a concentration gradient of the dopant metal. The average size of the metal oxide nanoparticles is greater than or equal to 3 nm and less than or equal to 6 nm. In at least one of the metal oxide nanoparticles, the concentration of the dopant metal increases either in the direction from the inner portion to the outer portion of the nanoparticle, or in the direction from the outer portion to the inner portion of the nanoparticle.

2. The light-emitting device of claim 1, wherein the quantum dot does not include cadmium, lead, or a combination thereof.

3. The light-emitting device of claim 1, wherein the plurality of quantum dots comprises II-VI compounds, III-V compounds, IV-VI compounds, group IV elements or compounds, I-III-VI compounds, II-III-VI compounds, I-II-IV-VI compounds, or combinations thereof.

4. The light-emitting device of claim 1, wherein the dopant metal comprises magnesium, aluminum, lithium, or a combination thereof.

5. The light-emitting device of claim 1, wherein the molar ratio of the dopant metal to zinc in the metal oxide nanoparticles is greater than or equal to 0.01:1 and less than or equal to 0.5:

1.

6. The light-emitting device of claim 1, wherein the metal oxide nanoparticles have a trap emission peak having a center wavelength greater than or equal to 500 nanometers.

7. The light-emitting device of claim 1, wherein the metal oxide nanoparticles have a band-edge emission peak with a center wavelength of less than or equal to 400 nanometers in the photoluminescence spectrum at 77K.

8. The light-emitting device of claim 1, wherein in the photoluminescence spectrum of the metal oxide nanoparticles at 77K, the maximum intensity ratio of the trap emission peak to the band-edge emission peak is greater than or equal to 2.9:

1.

9. The light-emitting device of claim 1, wherein the metal oxide nanoparticles have a first ultraviolet absorption peak wavelength of less than or equal to 350 nanometers.

10. The light-emitting device of claim 1, wherein the metal oxide nanoparticles have an organic content of greater than or equal to 20% by weight, as determined by thermogravimetric analysis.

11. The light-emitting device of claim 1, wherein the electronic auxiliary layer has a density of less than or equal to 5 × 10⁻⁶. 11 ohm·cm 2 Contact resistance greater than or equal to 1×10 4 Resistivity in ohm·cm, or a combination thereof.

12. The light-emitting device of claim 1, wherein the metal oxide nanoparticles comprise a core and a shell disposed on the core, the core comprising a first metal oxide, and the shell comprising a second metal oxide. The second metal oxide has a composition different from that of the first metal oxide. The first metal oxide comprises zinc and a first metal. The second metal oxide includes zinc and optionally a second metal. The first metal includes magnesium, aluminum, lithium, yttrium, gallium, zirconium, nickel, cobalt, or combinations thereof. The second metal includes magnesium, aluminum, lithium, yttrium, gallium, zirconium, nickel, cobalt, or combinations thereof. Wherein the band gap energy of the first metal oxide is greater than or equal to the band gap energy of the second metal oxide, and The molar ratio of the first metal to zinc in the metal oxide nanoparticles is less than 1:

1.

13. The light-emitting device of claim 12, wherein the first metal comprises magnesium.

14. The light-emitting device of claim 12, wherein the second metal oxide comprises a compound represented by chemical formula 2: Chemical formula 2 Zn 1-y M y O in, M is Mg, Al, Y, Li, Ga, Zr, Ni, Co, or a combination thereof, and 0 ≤ y < 1.

15. The light-emitting device of claim 12, wherein the first metal oxide comprises zinc magnesium oxide and the second metal oxide comprises zinc oxide.

16. The light-emitting device of claim 1, wherein the average size of the metal oxide nanoparticles is greater than or equal to 3 nanometers and less than or equal to 4 nanometers.

17. The light-emitting device of claim 1, wherein the light-emitting device emits blue light and has a maximum external quantum efficiency of 10% or greater.

18. The light-emitting device of claim 1, wherein the light-emitting device emits blue light and has a maximum brightness of 35,000 candela / square meter or greater.

19. The light-emitting device of claim 1, wherein the light-emitting device emits blue light and has a T50 of more than 50 hours.

20. A display device comprising a light-emitting device as claimed in any one of claims 1-19.

Images