Zinc-based oxide nanoparticles, method of preparing same, and electroluminescent diode and display device including same

Abstract

Disclosed are zinc-based oxide nanoparticles, a method of preparing the same, and an electroluminescent diode and a display device including the same. The zinc-based oxide nanoparticles include zinc and a further metal different from zinc, and have oxygen-containing anions of vanadium (V) on their surfaces.

Description

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority and all benefits arising therefrom to Korean Patent Application No. 10-2024-0011773, filed with the Korean Intellectual Property Office on January 25, 2024, the entire content of which is incorporated herein by reference. Technical field

[0003] The present disclosure relates to surface-modified zinc-based oxide nanoparticles, a method for preparing the same, and an electroluminescent diode and a display device (device) including the nanoparticles. Background art

[0004] Semiconductor nanoparticles having a nanoscale size (e.g., semiconductor nanocrystal particles) can emit light. For example, quantum dots including semiconductor nanocrystals can exhibit a quantum confinement effect. For example, when electrons in an excited state obtained by light excitation or an applied voltage transition from the conduction band to the valence band, light emission from the semiconductor nanoparticles can occur. The semiconductor nanoparticles can be configured to emit light in a desired wavelength region by adjusting the size and / or composition of the semiconductor nanoparticles. The semiconductor nanoparticles can be used in light-emitting diodes (e.g., electroluminescent diodes) and display devices including the same. Summary of the invention

[0005] Embodiments relate to a light-emitting diode that emits light by itself by applying a voltage to semiconductor nanoparticles (e.g., quantum dots) and a method for manufacturing the same.

[0006] Embodiments relate to surface-modified zinc-based oxide nanoparticles that can be used as an electron transport layer material for the light-emitting diode and a method for manufacturing the same.

[0007] Embodiments provide a display device (e.g., a QD-LED display) that includes semiconductor nanoparticles (e.g., quantum dots) as a light-emitting material in one or more pixels, wherein the display device includes the aforementioned light-emitting diode.

[0008] The zinc-based oxide nanoparticles according to one embodiment include zinc and another metal different from zinc (other than zinc), and include an oxo anion of vanadium (V) on their surface.

[0009] The other metal includes an alkaline earth metal, zirconium (Zr), tungsten (W), titanium (Ti), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), tin (Sn), cobalt (Co), vanadium (V), or a combination thereof.

[0010] The other metal includes magnesium.

[0011] The molar ratio of zinc to the additional metal in the zinc-based oxide nanoparticles is from about 99.9:0.1 to about 70:30.

[0012] The vanadium oxyanions include one or more of those represented by the chemical formulas shown in Group 1:

[0013] (Group 1)

[0014] VO3 - , VO4 3- , V2O7 4- , V3O9 3- , V4O 12 4- , V5O 14 3- , V5O 15 5- , V6O 18 6- , V 10 O 28 6- , V 12 O 32 4- , V 13 O 34 3- , V 18 O 42 12- , VO2(OH) - 2, VO3(OH) 2- .

[0015] The zinc-based oxide nanoparticles can have a particle size greater than or equal to about 1 nm and less than or equal to about 30 nm.

[0016] According to another embodiment, a method of preparing zinc-based oxide nanoparticles comprising zinc and an additional metal different from zinc and comprising vanadium (V) oxyanions on its surface includes: dissolving a compound comprising vanadium oxyanions in a first organic solvent in which a basic compound is dissolved to obtain a first solution, dissolving a zinc precursor and a precursor of the additional metal different from zinc in a second organic solvent to obtain a second solution, and mixing and reacting the first solution and the second solution.

[0017] The additional metal includes an alkaline earth metal, zirconium (Zr), tungsten (W), titanium (Ti), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), tin (Sn), cobalt (Co), vanadium (V), or a combination thereof.

[0018] The compound comprising vanadium oxyanions is a salt comprising vanadium oxyanions and alkali metal cations.

[0019] The vanadium-containing oxyanions include one or more of those represented by the chemical formulas shown in Group 1:

[0020] (Group 1)

[0021] VO3 - 、VO4 3- 、V2O7 4- 、V3O9 3- 、V4O 12 4- 、V5O 14 3- 、V5O 15 5- 、V6O 18 6- 、V 10 O 28 6- 、V 12 O 32 4- 、V 13 O 34 3- 、V 18 O 42 12- 、VO2(OH) - 2、VO3(OH) 2- 。

[0022] The basic compound includes an organic base containing an organic group, an inorganic base containing an alkali metal or an alkaline earth metal, or a combination thereof.

[0023] Each of the first organic solvent and the second organic solvent independently includes a C1-C10 alcohol solvent, dimethyl sulfoxide, a C3-C15 hydrocarbon solvent, or a combination thereof, and the first organic solvent and the second organic solvent are different solvents from each other.

[0024] Mixing and reacting the first solution and the second solution includes heating and stirring the first solution and the second solution.

[0025] The method for preparing the zinc-based oxide nanoparticles further includes, after mixing and reacting the first solution and the second solution, adding a third solvent immiscible with the first organic solvent and the second organic solvent to the reaction mixture to form a precipitate.

[0026] An electroluminescent diode according to another embodiment includes:

[0027] A first electrode and a second electrode facing each other,

[0028] A light-emitting layer disposed between the first electrode and the second electrode and including semiconductor nanoparticles, and

[0029] An electron transport layer between the light-emitting layer and the second electrode,

[0030] wherein the electron transport layer includes zinc-based oxide nanoparticles, the zinc-based oxide nanoparticles include zinc and another metal different from zinc, and include an oxygen-containing anion of vanadium (V) on its surface.

[0031] The another metal different from zinc includes an alkaline earth metal, zirconium (Zr), tungsten (W), titanium (Ti), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), tin (Sn), cobalt (Co), vanadium (V), or a combination thereof.

[0032] The oxygen-containing anion of vanadium includes one or more of those represented by the chemical formulas shown in Group 1:

[0033] (Group 1)

[0034] VO3 - 、VO4 3- 、V2O7 4- 、V3O9 3- 、V4O 12 4- 、V5O 14 3- 、V5O 15 5- 、V6O 18 6- 、V 10 O 28 6- 、V 12 O 32 4- 、V 13 O 34 3- 、V 18 O 42 12- 、VO2(OH) - 2、VO3(OH) 2- 。

[0035] The average particle size of the zinc-based oxide nanoparticles in the electron transport layer is greater than or equal to about 1 nm and less than or equal to about 30 nm.

[0036] The thickness of the electron transport layer is greater than or equal to about 5 nm and less than or equal to about 60 nm.

[0037] The electroluminescent diode further includes a hole auxiliary layer between the first electrode and the light-emitting layer.

[0038] A display device according to another embodiment includes the aforementioned electroluminescent diodes.

[0039] Zinc-based oxide nanoparticles according to an embodiment, which include zinc and another metal different from zinc and include vanadium-containing oxyanions on their surfaces, effectively passivate defects in the zinc-based oxide nanoparticles. Therefore, by introducing the zinc-based oxide nanoparticles according to the embodiment into the electron transport layer of an electroluminescent diode including semiconductor nanoparticles in a light-emitting layer, an electroluminescent diode having improved external quantum efficiency, brightness, and a significantly increased lifespan can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic cross-sectional view showing an electroluminescent diode according to an embodiment.

[0041] Figure 2 Schematic cross-sectional view showing an electroluminescent diode according to an embodiment.

[0042] Figure 3 Schematic cross-sectional view showing an electroluminescent diode according to an embodiment.

[0043] Figure 4 is a schematic front view of a display panel according to an embodiment.

[0044] Figure 5 is Figure 4 schematic cross-sectional view taken along line IV-IV of the display panel of

[0045] Figure 6 is a transmission electron microscopy (TEM) image of zinc oxide nanoparticles prepared in Preparation Example 1.

[0046] Figure 7 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis results of zinc magnesium oxide nanoparticles synthesized in Preparation Example 1 and Preparation Comparative Example 1.

[0047] Figure 8 is a TEM-energy dispersive spectroscopy (TEM-EDS) surface scan image of zinc magnesium oxide nanoparticles having vanadate ions provided on their surfaces, prepared in Preparation Example 1.

[0048] Figure 9 is showing Figure 8 graph of the TEM-EDS analysis results of

[0049] Figure 10 is the ultraviolet-visible (UV-Vis) absorption spectrum of the nanoparticles prepared in Preparation Example 1.

[0050] Figure 11 is the ultraviolet-visible (UV-Vis) absorption spectrum of the nanoparticles prepared in Preparation Example 2.

[0051] Figure 12 is the ultraviolet-visible (UV-Vis) absorption spectrum of the nanoparticles prepared in Preparation Example 3.

[0052] Figure 13 is a schematic diagram showing the energy band arrangements of the diodes of Comparative Example 1, Example 2, and Example 4 calculated from the measurement results of ultraviolet photoelectron spectroscopy (UPS). Detailed Embodiments

[0053] Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, so that those of ordinary skill in the art can easily implement the present disclosure. The present disclosure can be embodied in many different forms and is not limited to the embodiments described herein.

[0054] To clearly illustrate the present disclosure, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar elements throughout the specification.

[0055] For better understanding and ease of description, the sizes and thicknesses of the respective constituent elements shown in the drawings are arbitrarily shown, and the present disclosure is not necessarily limited to those shown. In the drawings, the thicknesses of layers, films, panels, regions, etc. are enlarged for clarity. Also, in the drawings, the thicknesses of some layers and regions are enlarged for ease of description.

[0056] In addition, it will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or there can also be an intermediate element. In contrast, when an element is referred to as being "directly on" another element, there is no intermediate element. Further, being "on" a reference part means being above or below the reference part, and does not necessarily mean "above" in the opposite direction of gravity.

[0057] In addition, unless explicitly described to the contrary, the words "comprising" and variations such as "including" or "containing" will be understood to imply the inclusion of the stated elements but not the exclusion of any other elements.

[0058] Here, a "cross-section" may refer to a cross-section that vertically (perpendicularly) penetrates a target part substantially when viewed from the side.

[0059] In addition, the singular includes the plural unless otherwise noted. For example, the term particle may refer to a single particle or a plurality of particles. Thus, herein, "zinc-based oxide nanoparticles" may refer to one zinc-based oxide nanoparticle or a plurality of zinc-based oxide nanoparticles. Herein, "semiconductor nanoparticles" may refer to one semiconductor nanoparticle or a plurality of semiconductor nanoparticles.

[0060] In the drawings, for clarity, the thicknesses of layers, films, panels, regions, etc. are enlarged. Like reference numerals throughout the specification denote like elements.

[0061] Hereinafter, the work function or the values of the HOMO or LUMO energy levels are expressed as absolute values from the vacuum energy level. Additionally, when the work function or energy level is referred to as "deep", "high", or "large", the work function or energy level has a large absolute value based on the vacuum energy level of "0 eV", while when the work function or energy level is referred to as "shallow", "low", or "small", the work function or energy level has a small absolute value based on the vacuum energy level of "0 eV".

[0062] As used herein, when no definition is otherwise provided, "substituted" means that at least one hydrogen of a compound or the corresponding moiety is replaced by a substituent selected from the following: C1-C30 alkyl, C1-C30 alkenyl, C2-C30 alkynyl, C6-C30 aryl, C7-C30 alkylaryl, C1-C30 alkoxy, C1-C30 heteroalkyl, C3-C30 heteroalkylaryl, C3-C30 cycloalkyl, C3-C15 cycloalkenyl, C6-C30 cycloalkynyl, C2-C30 heterocycloalkyl, halogen (-F, -Cl, -Br, or -I), hydroxy (-OH), nitro (-NO2), cyano (-CN), amino (-NRR', where R and R' are independently hydrogen or C1-C6 alkyl), azido (-N3), amidino (-C(=NH)NH2), hydrazino (-NHNH2), hydrazono (=N(NH2)), aldehyde (-C(=O)H), carbamoyl (-C(O)NH2), mercapto (-SH), ester (-C(=O)OR, where R is C1-C6 alkyl or C6-C12 aryl), carboxy (-COOH) or its salt (-C(=O)OM, where M is an organic or inorganic cation), sulfonic acid group (-SO3H) or its salt (-SO3M, where M is an organic or inorganic cation), phosphoric acid group (-PO3H2) or its salt (-PO3MH or -PO3M2, where M is an organic or inorganic cation), and combinations thereof. The explicitly specified number or range of carbon atoms in a compound or moiety does not include any substituents.

[0063] Here, a hydrocarbon group refers to a group composed of carbon and hydrogen (e.g., an aliphatic group such as an alkyl, alkenyl, or alkynyl group, or an aromatic group such as an aryl group). A hydrocarbon group can be a monovalent or higher-valent group formed by removing one or more hydrogen atoms from an alkane, alkene, alkyne, or aromatic hydrocarbon. In the hydrocarbon group, at least one methylene group can be replaced by an oxygen moiety (-O-), a carbonyl moiety, an ester moiety (-C(=O)-O-), -NH-, or a combination thereof. Unless otherwise stated to the contrary, a hydrocarbon (alkyl, alkenyl, alkynyl, or aryl) group can have 1 to 60, 2 to 32, 3 to 24, 4 to 12, or 6 to 10 carbon atoms.

[0064] As used herein, "alkyl" refers to a straight-chain or branched saturated monovalent hydrocarbon group (e.g., methyl, ethyl, hexyl, etc.).

[0065] As used herein, "alkenyl" refers to a straight-chain or branched monovalent hydrocarbon group having one or more carbon-carbon double bonds.

[0066] As used herein, "alkynyl" refers to a straight-chain or branched monovalent hydrocarbon group having one or more carbon-carbon triple bonds.

[0067] As used herein, "aryl" refers to a group formed by removing at least one hydrogen from an aromatic group (e.g., phenyl or naphthyl).

[0068] As used herein, "hetero" refers to 1 to 3 heteroatoms including N, O, S, Si, P, or a combination thereof.

[0069] As used herein, "alkoxy" means an alkyl group attached via oxygen (i.e., alkyl-O-), such as methoxy, ethoxy, or sec-butoxy.

[0070] "Amino" can be -NRR, where each R is independently hydrogen, a C1 to C12 alkyl group, a C7 to C20 alkaryl group, a C7 to C20 aralkyl group, or a C6 to C18 aryl group.

[0071] Here, the description that it does not include cadmium (or other toxic heavy metals) can refer to a cadmium (or other heavy metals) concentration of less than or equal to about 100 ppm, less than or equal to about 50 ppm, less than or equal to about 10 ppm, or almost zero. In an embodiment, there is substantially no cadmium (or other heavy metals), or if present, it is present in an amount or impurity level below the detection limit of a given detection means.

[0072] Unless otherwise stated, the numerical ranges stated herein include the endpoints.

[0073] Unless otherwise stated, the words "substantially" or "about" or "approximately" are omitted in front of the values in the numerical ranges stated herein.

[0074] As used herein, "substantially" or "about" or "approximate" not only means the stated value, but also means within an acceptable deviation range considering the errors associated with the corresponding measurement and the measurement results of the measured value. For example, "substantially" or "about" or "approximate" may mean a deviation within ±10%, ±5%, ±3% or ±1% of the stated value or within the standard deviation.

[0075] Here, a nanostructure refers to a structure having a nanoscale dimension or characteristic dimension in at least one direction. In an embodiment, the size of the nanoparticle may be less than about 300 nm, less than about 250 nm, less than about 150 nm, less than about 100 nm, less than about 50 nm, or less than about 30 nm. The nanostructure may have any shape. Unless specifically stated otherwise herein, the nanoparticle or semiconductor nanoparticle may have any shape, such as a nanowire, a nanorod, a nanotube, a multi-legged shape having two or more legs, a nanodot (or quantum dot), etc., but there is no particular limitation. The nanoparticle may be, for example, substantially crystalline, substantially single crystal, polycrystalline, amorphous (non-crystalline), or a combination thereof.

[0076] For example, semiconductor nanoparticles such as quantum dots may exhibit quantum confinement or exciton confinement. In this specification, the terms nanoparticle or quantum dot are not limited in terms of shape unless otherwise defined. Semiconductor nanoparticles such as quantum dots may have a size smaller than the Bohr diameter in a bulk crystal of the same material and may exhibit a quantum confinement effect. Quantum dots can emit light corresponding to their bandgap energy by controlling the size of the luminescent centers of the nanocrystals.

[0077] Here, the size or average size (hereinafter referred to as "size") of a nanoparticle such as a quantum dot or a zinc oxide nanoparticle may be the particle diameter (or average diameter). The particle size of the nanoparticle may be an equivalent diameter obtained by calculation, and the calculation includes converting the two-dimensional area confirmed by transmission electron microscopy analysis into a circle. The size of a luminescent semiconductor nanoparticle such as a quantum dot may be a nominal size, and the nominal size may be calculated from the composition of the semiconductor nanoparticle (for example, the composition of the particle determined by appropriate analytical means such as inductively coupled plasma-atomic emission spectrometry (ICP-AES)) and the emission peak wavelength.

[0078] Here, T50 refers to the time it takes for the brightness of a given device to decrease to 50% of the initial brightness based on 100% when the device is driven at a predetermined initial brightness.

[0079] Here, T90 refers to the time it takes for the brightness of a given device to decrease to 90% of the initial brightness based on 100% when the device is driven at a predetermined initial brightness.

[0080] Here, the term "external quantum efficiency (EQE)" refers to the ratio of the number of photons emitted from a light-emitting diode (LED) to the number of electrons passing through the device. The EQE can be a measure of how effectively the LED converts electrons into photons and allows them to escape. In an embodiment, the EQE can be determined based on the following equation:

[0081] EQE = [injection efficiency] × [solid-state quantum yield] × [extraction efficiency]

[0082] where the injection efficiency is the proportion of electrons passing through the device that are injected into the active region;

[0083] the solid-state quantum yield is the proportion of all electron-hole recombinations in the active region that are radiative and thus produce photons; and

[0084] the extraction efficiency is the proportion of photons generated in the active region that escape from the device.

[0085] Here, the maximum external quantum efficiency refers to the maximum value of the external quantum efficiency.

[0086] Here, the maximum brightness refers to the maximum value of the brightness that the device can achieve.

[0087] Here, quantum efficiency is a term that can be used interchangeably with quantum yield. The quantum efficiency (or quantum yield) can be measured in solution or in the solid state (in a complex). In an embodiment, the quantum efficiency (or quantum yield) is the ratio of the photons emitted by a nanostructure or a group thereof to the photons absorbed by it. In an embodiment, the quantum efficiency can be measured by any method. For example, for fluorescence quantum yield or efficiency, there can be two methods: an absolute method and a relative method.

[0088] In the absolute method, the quantum efficiency is obtained by detecting the fluorescence of all samples with an integrating sphere. In the relative method, the quantum efficiency of an unknown sample is calculated by comparing the fluorescence intensity of a standard dye (standard sample) with the fluorescence intensity of the unknown sample. Coumarin 153, Coumarin 545, Rhodamine 101 inner salt, Anthracene, Rhodamine 6G, etc. can be used as standard dyes according to their PL wavelengths, but the present disclosure is not limited thereto.

[0089] Here, the emission peak wavelength refers to the wavelength at which the emission spectrum of light reaches a maximum.

[0090] Here, the full width at half maximum (FWHM) is defined as the wavelength width corresponding to half of the maximum intensity value of a given peak.

[0091] The bandgap of quantum dots can be altered according to the size, structure, and composition of the nanocrystals. For example, as the size of the quantum dots increases, the semiconductor nanocrystals can have a narrow bandgap and an increased emission wavelength. Semiconductor nanocrystals are attracting attention as luminescent materials in various fields such as display devices, energy devices, and bioluminescent diodes.

[0092] A light-emitting diode based on semiconductor nanocrystal particles that emits light when a voltage is applied (hereinafter referred to as QD-LED) includes semiconductor nanocrystal particles as a luminescent material. QD-LEDs employ an emission principle different from that of organic light-emitting diodes (OLEDs) that emit light by using organic materials as emission centers, but can achieve purer colors (red, green, or blue) and improved color reproducibility, and thus are being considered as next-generation display device apparatuses. QD-LEDs can be produced at a reduced cost by a solution process and can be expected to achieve increased stability because they are based on inorganic materials, but require technological development for improving device performance and lifetime characteristics. Additionally, quantum dots having electroluminescent properties at a practically applicable level may include harmful heavy metals such as cadmium (Cd), lead, mercury, or a combination thereof. Therefore, it is desirable to provide a light-emitting diode or a display device having a light-emitting layer that includes environmentally friendly quantum dots substantially free of harmful heavy metals, for example, quantum dots not including cadmium.

[0093] Metal oxide nanoparticles, such as zinc oxide (ZnO) nanoparticles, are used as electron transport layer materials in QD-LED devices. Solution-based processes such as sol-gel or solution-precipitation are being used to introduce these metal oxide nanoparticles into the electron transport layer of QD-LED devices. The colloidal particles of the metal oxide formed during the synthesis process may include organic substances derived from the precursors used to form the colloidal particles as stabilizing ligands on the particle surface. However, the nanoparticles prepared by the aforementioned bottom-up synthesis method may have their own surface defects, such as Zn interstitial (Zni) and / or oxygen vacancy (V O ) defects, and depending on the degree of these defects, the efficiency of the electron transport layer within the device may be reduced, or there may be problems of device deterioration. It is known that the defects in zinc-based oxide nanoparticles are very diverse in type and form and are very difficult to control in a desired direction.

[0094] In addition, although Cd quantum dot-based LED structures including metal oxide nanoparticles in the electron transport layer (ETL) show high efficiency, in Cd-free QD-LED structures, there are the following problems: the charge balance between holes moving through the hole transport layer (HTL) and electrons moving through the ETL including metal oxide nanoparticles such as zinc-based oxide nanoparticles is not smoothly maintained. This results in a reduction in the efficiency of Cd-free QD-LEDs and also causes device degradation due to charge imbalance. Therefore, attempts have been reported to control the moving speed of holes or electrons by coating a polymer such as polymethyl methacrylate (PMMA) within the LED structure to optimize the charge balance; however, there are many limitations in applying this to commercial processes because the composition and content of the polymer and the thickness of the formed layer can affect the operation of the device.

[0095] Attempts have also been made to control the particle size, distribution, amount of surface organic material, and degree of surface defect passivation by adjusting the synthesis steps of zinc-based oxide nanoparticles or the final dispersion state of the prepared nanoparticles before they are applied to the device. The dispersion of zinc-based oxide nanoparticles manufactured in this way can be made into a thin film by a coating process and applied as the ETL, and thus it has the following advantages: it can enhance the characteristics of QD-LEDs without significant process limitations. However, as described above, it is very difficult to control the defects of zinc-based oxide nanoparticles in the desired direction.

[0096] To solve this, it has been reported to introduce or incorporate alkali metal carbonates to improve conductivity, electrical properties, bandgap control, and thermal stability, thereby improving QD-LED performance. However, this is unfortunate because it does not control the defects of the particles themselves, and thus there are limitations in improving the device, and it is difficult to determine the precise mechanism because the device characteristics change depending on the characteristics of the alkali metal.

[0097] The inventors of the present invention have completed the present invention by the following: confirming that by introducing an oxygen-containing anion of vanadium (V) onto the surface of zinc-based oxide nanoparticles (for example, zinc-based oxide nanoparticles including zinc and another metal other than zinc), the bandgap of the nanoparticles expands and the minimum conduction band (CBM: conduction band bottom) moves upward, thereby reducing the electron conduction barrier from the electron transport layer to the light-emitting layer including quantum dots to enhance conduction characteristics, and thus significantly improving the performance and lifetime of quantum dot light-emitting diodes including the nanoparticles in the electron transport layer. Therefore, the zinc-based oxide nanoparticles according to an embodiment include zinc and another metal different from zinc, and include an oxygen-containing anion of vanadium on their surface.

[0098] The other metals different from zinc may include alkaline earth metals, for example, magnesium, calcium, beryllium, barium, strontium, or a combination thereof. Although not intending to be bound by a particular theory, it is believed that the presence of alkaline earth metals may contribute to suppressing exciton quenching in the quantum dot-based light-emitting layer and improving electron transport in the quantum dot-based light-emitting layer by reducing oxygen vacancies or defects in the electron transport layer. In an embodiment, the alkaline earth metal may include magnesium. In addition to the alkaline earth metals, the other metals different from zinc may optionally further include zirconium (Zr), tungsten (W), titanium (Ti), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), tin (Sn), cobalt (Co), vanadium (V), or a combination thereof. The oxide nanoparticles may or may not further include alkali metals. The Zn-based oxide nanoparticles or the alkali metals may further include sodium (Na), potassium (K), cesium (Cs), rubidium (Rb), francium (Fr), or a combination thereof. The Zn-based oxide nanoparticles or the alkali metals may or may not include lithium (Li).

[0099] In an embodiment, the zinc-based oxide nanoparticles may include Zn 1-x M 1 x O (where M 1is an alkaline earth metal and optionally zirconium (Zr), tungsten (W), lithium (Li), titanium (Ti), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), sodium (Na), potassium (K), cesium (Cs), tin (Sn), cobalt (Co), vanadium (V), or a combination thereof, and x is greater than 0 and less than or equal to 0.3). Here, in the above chemical formula, x can be greater than or equal to about 0.01, greater than or equal to about 0.03, greater than or equal to about 0.05, greater than or equal to about 0.07, greater than or equal to about 0.1, greater than or equal to about 0.13, greater than or equal to about 0.15, greater than or equal to about 0.17, greater than or equal to about 0.18, greater than or equal to about 0.19, greater than or equal to about 0.2, greater than or equal to about 0.21, greater than or equal to about 0.22, greater than or equal to about 0.23, greater than or equal to about 0.25, greater than or equal to about 0.27, or greater than or equal to about 0.29. x can be less than or equal to about 0.3, less than or equal to about 0.27, less than or equal to about 0.25, less than or equal to about 0.23, less than or equal to about 0.20, less than or equal to about 0.18, less than or equal to about 0.16, less than or equal to about 0.15, less than or equal to about 0.14, less than or equal to about 0.13, less than or equal to about 0.12, less than or equal to about 0.11, less than or equal to about 0.10, less than or equal to about 0.09, less than or equal to about 0.08, less than or equal to about 0.07, less than or equal to about 0.06, or less than or equal to about 0.05. That is, the molar ratio of zinc to the other metal different from zinc in the zinc-based oxide nanoparticles according to the embodiment can be about 99.9:0.01 to about 70:30, such as about 99:1 to about 70:30, about 95:5 to about 70:30, about 90:10 to about 75:25, about 90:10 to about 80:20, or about 90:10 to about 85:15, but is not limited to these ranges.

[0100] According to an embodiment, the zinc-based oxide nanoparticles include vanadium oxyanions on their surfaces. Vanadium oxyanions are generally also referred to as "vanadate", and "vanadium oxyanions" and "vanadate" can be used interchangeably with the same meaning. The vanadium oxyanions can include, for example, one or more of those represented by the chemical formulas shown in Group 1:

[0101] (Group 1)

[0102] VO3 - 、VO4 3- 、V2O7 4- 、V3O9 3- 、V4O 12 4- 、V5O 14 3- 、V5O 155- , V6O 18 6- , V 10 O 28 6- , V 12 O 32 4- , V 13 O 34 3- , V 18 O 42 12- , VO2(OH) - 2, VO3(OH) 2- .

[0103] In an embodiment, the vanadium oxyanion may be VO3 - , VO4 3- , V2O7 4- , V3O9 3- , VO3(OH) 2- , or a combination thereof, but not limited thereto.

[0104] Methods have been reported for introducing metal elements such as magnesium or vanadium into the lattice of zinc oxide to broaden the bandgap energy of zinc-based oxide nanoparticles. However, the zinc-based oxide nanoparticles according to the embodiment are not nanoparticles in which a metal element is introduced into the lattice, but nanoparticles that include a vanadium oxyanion on their surface, which were unknown prior to the priority date of this application.

[0105] The average particle size of the zinc-based oxide nanoparticles according to an embodiment can be greater than or equal to about 1 nm and less than or equal to about 30 nm, such as greater than or equal to about 1 nm, greater than or equal to about 2 nm, greater than or equal to about 2.5 nm, greater than or equal to about 3 nm, greater than or equal to about 3.5 nm, greater than or equal to about 4 nm, greater than or equal to about 4.5 nm, greater than or equal to about 5 nm, greater than or equal to about 5.5 nm, greater than or equal to about 6 nm, greater than or equal to about 6.5 nm, greater than or equal to about 7 nm, greater than or equal to about 7.5 nm, greater than or equal to about 8 nm, greater than or equal to about 8.5 nm, greater than or equal to about 9 nm, greater than or equal to about 9.5 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 15 nm, greater than or equal to about 17 nm, greater than or equal to about 20 nm, greater than or equal to about 22 nm, greater than or equal to about 25 nm, or greater than or equal to about 27 nm and less than or equal to about 30 nm, less than or equal to about 25 nm, less than or equal to about 23 nm, less than or equal to about 20 nm, less than or equal to about 18 nm, less than or equal to about 15 nm, less than or equal to about 13 nm, less than or equal to about 12 nm, less than or equal to about 10 nm, 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, less than or equal to about 4 nm, less than or equal to about 3 nm, less than or equal to about 2.5 nm, less than or equal to about 2 nm, or less than or equal to about 1 nm. For example, the average size of the zinc-based oxide nanoparticles according to an embodiment can be from about 2 nm to about 20 nm, such as from about 3 nm to about 20 nm, from about 3 nm to about 15 nm, or from about 5 nm to about 10 nm, but is not limited thereto.

[0106] According to an embodiment, a method for preparing zinc-based oxide nanoparticles comprising zinc and at least one additional metal different from zinc and comprising an oxyanion of vanadium on its surface can include: dissolving a compound comprising an oxyanion of vanadium in a first organic solvent in which a basic compound is dissolved to obtain a first solution, dissolving a zinc precursor and a precursor of the at least one additional metal different from zinc in a second organic solvent to obtain a second solution, and mixing and reacting the first solution and the second solution.

[0107] The basic compound can include a strong basic compound having a pH greater than or equal to about 8, such as greater than or equal to about 8.5, greater than or equal to about 9, greater than or equal to about 9.5, greater than or equal to about 10, greater than or equal to about 10.5, or greater than or equal to about 11. For example, the basic compound can include an organic base comprising an organic group, an inorganic base comprising an alkali metal or an alkaline earth metal, or a combination thereof.

[0108] For example, the organic base may include an organic base containing an aliphatic hydrocarbon group having a C1 to C50 organic group such as an alkyl group, and may be an organic base containing one, two, three, or four substituted or unsubstituted aliphatic hydrocarbon groups (such as alkyl, alkenyl, or alkynyl) having carbon atoms in the range of, for example, C1-C50, C2-C40, C3-C30, C4-C25, C5-C20, C6-C15, C7-C14, C8-C12, C9-C1, or a combination thereof. The organic base may include a quaternary ammonium base, for example, trialkylammonium hydroxide (such as trimethylammonium hydroxide, diethylmethylammonium hydroxide, dimethylethylammonium hydroxide, or a combination thereof).

[0109] For example, the inorganic base may include hydroxides of alkali metals (such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, rubidium hydroxide, francium hydroxide, or a combination thereof). The inorganic base may include two or more alkali metal hydroxides selected from, for example, the following: potassium hydroxide, cesium hydroxide, rubidium hydroxide, or a combination thereof, and may be used, for example, together with an organic base or without an organic base. In an embodiment, when the basic compound includes an inorganic base, the resulting zinc-based oxide nanoparticles may further include an alkali metal (such as lithium, potassium, sodium, rubidium, cesium, or a combination thereof).

[0110] The basic compound may be dissolved in the first organic solvent at a concentration of about 0.1M to about 1M. For example, the basic compound may be included in the first organic solvent at a concentration of about 0.1M to about 0.8M, about 0.1M to about 0.7M, about 0.2M to about 0.8M, about 0.2M to about 0.7M, about 0.3M to about 0.8M, about 0.3M to about 0.7M, about 0.3M to about 0.6M, about 0.4M to about 0.8M, about 0.4M to about 0.7M, or about 0.4M to about 0.6M, but is not limited to these ranges.

[0111] The compound including an oxygen-containing anion of vanadium may include a salt compound containing a cation of an alkali metal or an alkaline earth metal and the oxygen-containing anion of vanadium described in Group 1. For example, the compound including an oxygen-containing anion of vanadium may include a compound containing a cation of lithium, sodium, potassium, rubidium, cesium, francium, magnesium, calcium, beryllium, strontium, barium, or a combination thereof. For example, the compound including an oxygen-containing anion of vanadium may include a cation of potassium, rubidium, cesium, or a combination thereof. For example, the compound including an oxygen-containing anion of vanadium may include potassium metavanadate, but is not limited thereto.

[0112] The compound comprising an oxygen-containing anion of vanadium can be included in the mixture of the first solution and the second solution such that the oxygen-containing anion of vanadium separated therefrom is present on the surface of the zinc-based oxide nanoparticles in the following amounts relative to the total number of moles of zinc in the zinc-based oxide nanoparticles to be produced by the reaction: for example, less than or equal to about 30 moles based on 100 moles of zinc, such as less than or equal to about 25 moles based on 100 moles of zinc, less than or equal to about 20 moles based on 100 moles of zinc, less than or equal to about 15 moles based on 100 moles of zinc, or less than or equal to about 10 moles based on 100 moles of zinc. For example, the oxygen-containing anion of vanadium can be included in the mixture of the first solution and the second solution so as to be present on the surface of the zinc-based oxide nanoparticles in the following amounts: greater than or equal to about 1 mole, greater than or equal to about 2 moles, greater than or equal to about 3 moles, greater than or equal to about 5 moles, greater than or equal to about 7 moles, greater than or equal to about 8 moles, greater than or equal to about 9 moles, greater than or equal to about 10 moles, greater than or equal to about 12 moles, or greater than or equal to about 15 moles based on 100 moles of zinc in the zinc-based oxide nanoparticles to be produced by the reaction.

[0113] The zinc precursor can be an organic compound comprising zinc, and the precursor of the additional metal different from zinc can be an organic compound comprising an additional metal different from zinc. The zinc precursor and the precursor of the additional metal can include a carboxylate moiety, such as an acetate moiety. For example, the zinc precursor can include zinc carboxylate, such as zinc acetate; zinc acetylacetonate; zinc halide, such as zinc chloride, zinc bromide, zinc iodide, or zinc fluoride; zinc nitrate; zinc oxide (zinc oxide); or a combination thereof.

[0114] The additional metal different from zinc can be an alkaline earth metal, and the precursor of the additional metal different from zinc can be an organic compound comprising the additional metal, such as a carboxylate compound (e.g., acetate), an acetylacetonate compound, a halide, a nitride, an oxide, or a combination thereof. In an embodiment, the additional metal can include magnesium, and the precursor of magnesium can include magnesium carboxylate (e.g., magnesium acetate), magnesium acetylacetonate, magnesium halide (e.g., magnesium chloride, magnesium bromide, magnesium fluoride, or magnesium iodide), magnesium nitrate, magnesium oxide, or a combination thereof. In an embodiment, the precursor of the additional metal can further include gallium carboxylate (e.g., gallium acetate), gallium acetylacetonate, gallium halide, gallium nitride, gallium oxide, or a combination thereof. Here, the halide can include chloride, fluoride, bromide, or iodide.

[0115] The molar ratio between the zinc precursor and the precursor of the additional metal can be appropriately selected in consideration of the desired composition of the zinc-based oxide nanoparticles. In an embodiment, the molar amount of the precursor of the additional metal based on 1 mole of the zinc precursor can be about 0.1 mole to about 1.5 moles, about 0.2 mole to about 1 mole, about 0.3 mole to about 0.9 mole, about 0.4 mole to about 0.8 mole, about 0.5 mole to about 0.7 mole, or a combination thereof.

[0116] The first organic solvent and the second organic solvent may each independently include a C1 to C10 alcohol solvent, dimethyl sulfoxide, a substituted or unsubstituted hydrocarbon solvent having a carbon number in the range of C1 to C30, C3 to C15, or a combination thereof (e.g., a substituted or unsubstituted aliphatic hydrocarbon, a substituted or unsubstituted alicyclic hydrocarbon, a substituted or unsubstituted aromatic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon in which at least one double bond is hydrogenated, etc.), or a combination thereof, and in an embodiment, the first organic solvent and the second organic solvent may be the same as or different from each other. The first organic solvent and the second organic solvent may each independently include a C1 to C10 alcohol solvent (e.g., methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, or a combination thereof), a sulfoxide solvent (e.g., dimethyl sulfoxide), a C3 to C15 hydrocarbon solvent (e.g., an aliphatic, aromatic, or alicyclic solvent, or an alicyclic compound obtained by hydrogenation of an aromatic hydrocarbon), or a combination thereof, and in an embodiment, the first organic solvent and the second organic solvent may be the same as or different from each other.

[0117] In an embodiment, the first organic solvent and the second organic solvent may be different solvents from each other. In an embodiment, the first organic solvent and the second organic solvent may be solvents having a relative polarity difference of greater than or equal to about 0.3 and less than or equal to about 0.9. When the first organic solvent and the second organic solvent having such a relative polarity difference are used in combination, and when the first solution and the second solution are mixed and reacted, the synthesis of nanoparticles occurring therein may involve the normal phase transition and separation mechanisms occurring at the interfaces of the liquid phase, solid phase, and solution phase present in the reaction system (e.g., liquid-solid-solution synthesis, hereinafter referred to as LSS). Without wishing to be bound by a particular theory, in an embodiment, it is believed that the polarity difference between the two solvents may cause the formation of nanobubbles within the reaction solution (e.g., liquid or solution), and at the interface between the mixture (e.g., liquid or solution) and the nanobubbles, the precursors (solids) may migrate and react (e.g., phase transfer and / or phase separation) to form nanoparticles including oxides of zinc and the other metal (e.g., magnesium), and at the same time, the oxyanions of vanadium derived from the compound including the oxyanions of vanadium may be adsorbed onto the surface of the formed zinc-based oxide nanoparticles. At the same time, the cations of the alkali metal or alkaline earth metal derived from the compound including the oxyanions of vanadium may be separated and removed from the reaction mixture of the zinc-based oxide nanoparticles as the final product during the washing process described below after forming salts with the carboxylate groups or halogen anions of the zinc precursor and / or the precursor of the other metal.

[0118] The first organic solvent and the second organic solvent may have a relative polarity difference of greater than or equal to about 0.35, greater than or equal to about 0.4, greater than or equal to about 0.45, greater than or equal to about 0.5, or greater than or equal to about 0.55. The relative polarity difference may be less than or equal to about 0.85, less than or equal to about 0.8, less than or equal to about 0.75, less than or equal to about 0.7, less than or equal to about 0.65, less than or equal to about 0.6, less than or equal to about 0.55, less than or equal to about 0.5, or less than or equal to about 0.45. The relative polarity of solvents can be obtained from the literature (e.g., Solvents and solvent Effects in organicchemistry, Wiliey VCH publisher, 3rd edition, 2003). The relative polarity value of water is 1.

[0119] The first organic solvent may include a C1 to C10 alcohol solvent, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, or a combination thereof. The relative polarity value of the first organic solvent may be greater than or equal to about 0.4, greater than or equal to about 0.45, greater than or equal to about 0.5, greater than or equal to about 0.55, greater than or equal to about 0.6, greater than or equal to about 0.65, greater than or equal to about 0.7, or greater than or equal to about 0.75. The relative polarity value of the first organic solvent may be less than or equal to about 1, or less than or equal to about 0.9.

[0120] The second organic solvent may be a C3 to C30 (e.g., C3 to C15) hydrocarbon solvent (e.g., an aliphatic hydrocarbon solvent, an aromatic hydrocarbon solvent, an alicyclic hydrocarbon solvent, or a solvent having a benzene ring with one or more double bonds hydrogenated), dimethyl sulfoxide, etc. The second organic solvent may include, for example, cyclohexane, hexane, heptane, nonane, octane, toluene, cyclohexene, xylene, etc. The relative polarity value of the second organic solvent may be greater than or equal to about 0.001, greater than or equal to about 0.003, greater than or equal to about 0.006, greater than or equal to about 0.009, greater than or equal to about 0.01, or greater than or equal to about 0.012.

[0121] The relative polarity value of the second organic solvent may be less than or equal to about 4, less than or equal to about 3.5, less than or equal to about 3, less than or equal to about 2.5, less than or equal to about 2, less than or equal to about 1.5, less than or equal to about 1, or less than or equal to about 0.5.

[0122] The second organic solvent may form nano-bubbles within the first organic solvent. The volume ratio of the first organic solvent to the second organic solvent (i.e., the first organic solvent: the second organic solvent) may be about 1:0.2 to about 1:5, about 1:0.3 to about 1:3, about 1:0.5 to about 1:2, about 1:0.8 or about 1:1.25, about 1:1 to about 1:1.5, or a combination thereof.

[0123] The organic solvent (or the composition for forming the ETL described below) may not include butylamine, ethylamine, ethanolamine, hexamethylenediamine, aniline, hexylamine, or a combination thereof. The above organic solvent (or the composition for forming the ETL described below) may not include an organic amine having C1 to C12, an aromatic amine having a benzene group, or a combination thereof.

[0124] Mixing and reacting the first solution and the second solution may include stirring and reacting the mixture at a predetermined temperature, for example, a temperature greater than or equal to about 40 °C and less than or equal to about 80 °C. The stirring may be carried out, for example, at a rate greater than or equal to about 100 revolutions per minute (rpm), greater than or equal to about 150 rpm, greater than or equal to about 200 rpm, greater than or equal to about 250 rpm, greater than or equal to about 300 rpm, greater than or equal to about 350 rpm, greater than or equal to about 400 rpm, greater than or equal to about 450 rpm, or greater than or equal to about 500 rpm. The stirring may be carried out, for example, at a rate less than or equal to about 800 rpm, less than or equal to about 700 rpm, or less than or equal to about 600 rpm. The temperature may be greater than or equal to about 40 °C, for example, greater than or equal to about 50 °C, or greater than or equal to about 60 °C. The temperature may be less than or equal to the boiling point of the first organic solvent and / or the second organic solvent, or less than or equal to about 78 °C, less than or equal to about 75 °C, for example, less than or equal to about 70 °C, less than or equal to about 65 °C, or less than or equal to about 60 °C.

[0125] The preparation method may further include, after reacting the first solution and the second solution, adding a third solvent immiscible with the first organic solvent and the second organic solvent to the reaction mixture to form a precipitate. The third solvent is an anti-solvent that does not mix (is immiscible) with the first organic solvent and the second organic solvent, and enables the zinc-based oxide nanoparticles formed from the reaction solution to be precipitated and separated. By adding the third solvent to the solution in which the reaction is completed and stirring, precipitation of the zinc-based oxide nanoparticles is induced, and the resulting precipitate can be separated, for example, by centrifugation. After separating the precipitate, the precipitate can be further washed with the third solvent and dried to obtain the finally produced zinc-based oxide nanoparticles. The third solvent may be ethyl acetate.

[0126] The zinc-based oxide nanoparticles prepared as described above include, in addition to zinc, further metals such as alkaline earth metals, zirconium (Zr), tungsten (W), titanium (Ti), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), tin (Sn), cobalt (Co), vanadium (V), or combinations thereof, and have vanadate anions on their surface. It can be confirmed by XPS analysis etc. that the zinc-based oxide nanoparticles prepared in this way include vanadate anions on their surface. That is, as demonstrated by the examples described below, the zinc-based oxide nanoparticles prepared by the method according to the embodiment exhibit a V2p3 peak intensity (3.64) derived from vanadate anions that is significantly greater than the K2p peak intensity (0.08) of potassium in XPS analysis. Potassium is an alkali metal derived from a compound including vanadate anions such as potassium metavanadate. That is, it can be seen that the vanadate anions derived from potassium metavanadate passivate well the surface of the zinc-based oxide nanoparticles according to the embodiment prepared by the said preparation method. On the other hand, as in the preparation of the comparative example described below, when zinc-based oxide nanoparticles are first synthesized and then potassium metavanadate powder is simply added thereto, the XPS results of the obtained nanoparticles show that both the K2p peak intensity of potassium (3.06) and the V2p3 peak intensity of vanadium (4.22) are high. This indicates that the potassium metavanadate added in powder form does not undergo any additional reaction with the previously prepared zinc-based oxide nanoparticles, but exists in a simple mixed state.

[0127] In addition, the prepared zinc-based oxide nanoparticles may have a first absorption peak in a wavelength range as follows: greater than or equal to about 285 nm, greater than or equal to about 289 nm, greater than or equal to about 292 nm, or greater than or equal to about 295 nm and less than or equal to about 330 nm, less than or equal to about 315 nm, less than or equal to about 302 nm, less than or equal to about 300 nm, less than or equal to about 299 nm, less than or equal to about 298 nm, or less than or equal to about 297 nm. The zinc oxide nanoparticles may have a first absorption peak wavelength in a UV-Vis absorption spectrum as follows: less than or equal to about 320 nm, less than or equal to about 319 nm, less than or equal to about 318 nm, less than or equal to about 317 nm, less than or equal to about 316 nm, less than or equal to about 315 nm, less than or equal to about 314 nm, less than or equal to about 313 nm, less than or equal to about 312 nm, or less than or equal to about 311 nm. The first absorption peak wavelength may be greater than or equal to about 290 nm. The first absorption peak wavelength may be greater than or equal to about 295 nm, greater than or equal to about 300 nm, greater than or equal to about 301 nm, greater than or equal to about 302 nm, or greater than or equal to about 303 nm.

[0128] The zinc oxide nanoparticles may exhibit a valley adjacent to the first absorption peak in the UV-Vis absorption spectrum and may have a valley depth (VD) defined by the following equation that is greater than or equal to about 0.01, greater than or equal to about 0.02, greater than or equal to about 0.027, greater than or equal to about 0.03, greater than or equal to about 0.035, greater than or equal to about 0.04, greater than or equal to about 0.045, greater than or equal to about 0.05, greater than or equal to about 0.055, or greater than or equal to about 0.06:

[0129] 1-(Abs 谷 / Abs 第一 )=VD

[0130] In this equation, Abs 第一 is the absorption at the first absorption peak, and Abs 谷 is the absorption at the lowest point of the valley adjacent to the first absorption peak.

[0131] The valley depth may be less than or equal to about 0.2, less than or equal to about 0.15, less than or equal to about 0.1, less than or equal to about 0.08, less than or equal to about 0.07, or less than or equal to about 0.06.

[0132] The zinc oxide nanoparticles may have a bandgap energy determined by the x-intercept value in the UV-Vis absorption spectrum as follows: greater than or equal to about 3.6 eV, greater than or equal to about 3.65 eV, greater than or equal to about 3.7 eV, greater than or equal to about 3.75 eV, greater than or equal to about 3.77 eV, greater than or equal to about 3.78 eV and less than or equal to about 3.95 eV, less than or equal to about 3.94 eV, less than or equal to about 3.9 eV, less than or equal to about 3.85 eV, less than or equal to about 3.8 eV, less than or equal to about 3.78 eV, less than or equal to about 3.77 eV, less than or equal to about 3.75 eV, or less than or equal to about 3.7 eV.

[0133] As demonstrated in the examples described below, compared to zinc-based oxide nanoparticles that do not include vanadium-containing oxygen anions on the surface, the zinc-based oxide nanoparticles prepared as described above have a wider bandgap and an upshifted conduction band minimum (CBM), such that an electroluminescent diode including the zinc-based oxide nanoparticles in the electron transport layer can have significantly improved performance and lifetime by: reducing the electron conduction barrier from the electron transport layer to the light-emitting layer including quantum dots, and thus enhancing the conduction characteristics.

[0134] Not wishing to be bound by a particular theory, it is believed that the zinc-based oxide nanoparticles according to the embodiments have surface passivation through the carboxylate moieties included in the zinc precursor and / or the precursor of the additional metal, the hydroxyl moieties derived from the basic compound, etc., and surface passivation through the oxyanions of vanadium, thereby more effectively passivating the zinc dangling bonds present on the surface of the nanoparticles. In addition, the zinc-based oxide nanoparticles according to the embodiments may have a composition of surface ligands different from those of the prior art, and thus, it is believed that the leakage current of the device can be reduced by trap passivation of the particles, the balance between electrons and holes can be maintained, and thus the efficiency and lifetime of the electroluminescent diode can be improved.

[0135] Therefore, the zinc-based oxide nanoparticles according to the embodiments can be applied as a material for forming an electron transport layer of an electroluminescent diode including quantum dots in a light-emitting layer. The electroluminescent diode according to the embodiments is a self-luminous type light-emitting diode configured to emit desired light by voltage application without a separate light source. Hereinafter, the electroluminescent diode according to the embodiments will be described in detail with reference to the accompanying drawings.

[0136] Reference Figure 1 , the electroluminescent diode includes a first electrode 1 and a second electrode 5 spaced apart from each other (e.g., facing each other); a light-emitting layer 3 disposed between the first electrode and the second electrode and including a plurality of semiconductor nanoparticles; and an electron transport layer 4 between the light-emitting layer 3 and the second electrode 5. The above electroluminescent diode may further include a hole assisting layer 2 between the light-emitting layer and the first electrode. The hole assisting layer may include a hole transport layer (e.g., including an organic compound), a hole injection layer, an electron blocking layer, or a combination thereof.

[0137] The first electrode or the second electrode may be an anode or a cathode. In an embodiment, the first electrode may be a cathode (or an anode), and the second electrode may be an anode (or a cathode). In an embodiment, the second electrode is a cathode.

[0138] Reference Figure 2 and 3 , in the electroluminescent diode, the first electrode or the second electrode may be disposed on a (transparent) substrate 100. The transparent substrate may be a light extraction surface.

[0139] In Figure 2 and 3In this case, the light-emitting layer 30 can be disposed between the first electrode (e.g., anode) 10 and the second electrode (e.g., cathode) 50. The second electrode or cathode 50 can include an electron injection conductor. The first electrode or anode 10 can include a hole injection conductor. The work functions of the electron / hole injection conductors included in the second electrode and the first electrode can be appropriately controlled and are not particularly limited. For example, the second electrode can have a small work function, and the first electrode can have a relatively large work function, or vice versa.

[0140] The electron / hole injection conductor can include a metal-based material (e.g., metal, metal compound, alloy, or a combination thereof) (e.g., aluminum, magnesium, tungsten, nickel, cobalt, platinum, palladium, calcium, LiF, etc.), a metal oxide such as indium gallium oxide or indium tin oxide (ITO), or a conductive polymer (e.g., having a relatively high work function) such as polyethylenedioxythiophene, but is not limited thereto.

[0141] At least one of the first electrode and the second electrode can be a light-transmissive electrode or a transparent electrode. In an embodiment, both the first electrode and the second electrode can be light-transmissive electrodes. The electrodes can be patterned. The first electrode and / or the second electrode can be disposed on (e.g., an insulating) substrate 100. The substrate 100 can be optically transparent (e.g., can have a light transmittance of greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, greater than or equal to about 80%, greater than or equal to about 85%, or greater than or equal to about 90% and, for example, less than or equal to about 99%, or less than or equal to about 95%). The substrate can include regions for blue pixels, regions for red pixels, regions for green pixels, or a combination thereof. Thin-film transistors can be disposed in each region of the substrate, and one of the source electrode and the drain electrode of the thin-film transistor can be electrically connected to the first electrode or the second electrode.

[0142] The light-transmissive electrode can be disposed on (e.g., an insulating) transparent substrate. The substrate can be rigid or flexible. The substrate can be plastic, glass, or metal.

[0143] The light-transmissive electrode can be made of, for example, a transparent conductor such as indium tin oxide (ITO) or indium zinc oxide (IZO), indium gallium tin oxide, indium zinc tin oxide, titanium nitride, polyaniline, LiF / Mg:Ag, etc., or a thin metal film of a single layer or multiple layers, but is not limited thereto. When one of the first electrode and the second electrode is an opaque electrode, it can be made of an opaque conductor such as aluminum (Al), lithium-aluminum (Li:Al) alloy, magnesium-silver alloy (Mg:Ag), and lithium fluoride-aluminum (LiF:Al).

[0144] The thickness of the electrode (the first electrode and / or the second electrode) is not particularly limited and can be appropriately selected considering 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 10 nm, greater than or equal to about 20 nm, greater than or equal to about 30 nm, greater than or equal to about 40 nm, or greater than or equal to about 50 nm. For example, the thickness of the electrode can be less than or equal to about 100 μm, such as less than or equal to about 90 μm, less than or equal to about 80 μm, less than or equal to about 70 μm, less than or equal to about 60 μm, less than or equal to about 50 μm, less than or equal to about 40 μm, less than or equal to about 30 μm, less than or equal to about 20 μm, 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.

[0145] The method of forming the electrode is not particularly limited and can be appropriately selected depending on the material. In an embodiment, the electrode can be formed by, but not limited to, deposition, coating, or a combination thereof.

[0146] In Figures 1 to 3 it, a light-emitting layer (EML) 3 or 30 is disposed between a first electrode (e.g., an anode) 1 or 10 and a second electrode (e.g., a cathode) 5 or 50. The light-emitting layer includes semiconductor nanoparticles (e.g., nanoparticles emitting blue light, nanoparticles emitting red light, or nanoparticles emitting green light). The light-emitting layer can include one or more (e.g., 2 or more or 3 or more and 10 or less) monolayers of a plurality of nanoparticles.

[0147] The light-emitting layer can be patterned. In an embodiment, the patterned light-emitting layer can include a layer emitting blue light (e.g., disposed within a blue pixel in a display device to be described later), a layer emitting red light (e.g., disposed within a red pixel in a display device to be described later), and a layer emitting green light (e.g., disposed within a green pixel in a display device to be described later)), or a combination thereof. Each light-emitting layer can be separated from an adjacent light-emitting layer (e.g., optically) by a partition wall. In an embodiment, a partition wall such as a black matrix can be disposed between the layer emitting red light, the layer emitting green light, and the layer emitting blue light. In a non-limiting example, the layer emitting red light, the layer emitting green light, and the layer emitting blue light can each be isolated.

[0148] The light-emitting layer or the semiconductor nanoparticles may not include cadmium. The light-emitting layer or the semiconductor nanoparticles may not include mercury, lead, or a combination thereof.

[0149] In an embodiment, the semiconductor nanoparticles may have a core-shell structure. The semiconductor nanoparticles may include a core and a shell, the core including a first semiconductor nanocrystal and the shell including a second semiconductor nanocrystal disposed on the core and having a composition different from that of the first semiconductor nanocrystal.

[0150] The semiconductor nanoparticles (e.g., the first semiconductor nanocrystal and / or the second semiconductor nanocrystal) may include a semiconductor compound or material, such as a II-VI compound, a III-V compound, a IV-VI compound, a Group IV element or compound, a I-III-VI compound, a I-II-IV-VI compound, or a combination thereof. The light-emitting layer (or the semiconductor nanoparticles, the first semiconductor nanocrystal, or the second semiconductor nanocrystal) may not include harmful heavy metals, such as cadmium, lead, mercury, or a combination thereof.

[0151] The II-VI compound may be a binary compound selected from ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and mixtures thereof; a ternary compound selected from ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and mixtures thereof; and a quaternary compound selected from HgZnTeS, HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof. The II-VI compound may further include a Group III metal.

[0152] The III-V compound may be a binary compound selected from GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; a ternary compound selected from GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, and mixtures thereof; and a quaternary compound selected from GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and mixtures thereof. The III-V compound may further include a Group II element. An example of such a semiconductor nanocrystal is InZnP.

[0153] The Group IV-VI compounds can be binary compounds selected from SnS, SnSe, SnTe, and mixtures thereof; ternary compounds selected from SnSeS, SnSeTe, SnSTe, and mixtures thereof; and quaternary compounds such as SnSSeTe.

[0154] Examples of the Group I-III-VI compounds include, but are not limited to, CuInSe2, CuInS2, CuInGaSe, and CuInGaS. Examples of the Group I-III-VI semiconductor compounds include ternary compounds such as AgInS, AgInS2, AgInSe2, AgGaS, AgGaS2, AgGaSe2, CuInS, CuInS2, CuInSe2, CuGaS2, CuGaSe2, CuGaO2, AgGaO2, AgAlO2, etc.; quaternary compounds such as AgInGaS2, AgInGaSe2, etc.; or any combination thereof.

[0155] Examples of the Group I-II-IV-VI compounds include, but are not limited to, CuZnSnSe and CuZnSnS.

[0156] The Group IV element or compound is a single element (elemental substance) selected from Si, Ge, and mixtures thereof; and binary compounds selected from SiC, SiGe, and mixtures thereof.

[0157] Each element included in a multi-element compound such as the binary compound, ternary compound, or quaternary compound may be present in the particle at a uniform or non-uniform concentration. For example, the above chemical formulas represent the types of elements included in the compound, and the element ratios within the compound may vary. For example, AgInGaS2 may mean AgIn x Ga 1-x S2 (where x is a real number between 0 and 1).

[0158] In an embodiment, the first semiconductor nanocrystal may include a metal and a non-metal, the metal including indium, zinc, or a combination thereof, and the non-metal including phosphorus, selenium, tellurium, sulfur, or a combination thereof. In an embodiment, the second semiconductor nanocrystal may include a metal and a non-metal, the metal including indium, zinc, or a combination thereof, and the non-metal including phosphorus, selenium, tellurium, sulfur, or a combination thereof.

[0159] In an embodiment, the first semiconductor nanocrystal may include InP, InZnP, ZnSe, ZnSeS, ZnSeTe, or a combination thereof, and / or the second semiconductor nanocrystal may include ZnSe, ZnSeS, ZnS, ZnTeSe, or a combination thereof. In an embodiment, the shell may include zinc, sulfur, and optionally selenium in the outermost layer.

[0160] In an embodiment, the semiconductor nanoparticles can emit blue or green light and have a core comprising ZnSeTe, ZnSe, or a combination thereof and a shell comprising a zinc chalcogenide (e.g., ZnS, ZnSe, and / or ZnSeS). The content of sulfur in the shell can increase or decrease in the radial direction (from the core towards the surface).

[0161] In an embodiment, the semiconductor nanoparticles can emit red or green light, the core can comprise InP, InZnP, or a combination thereof, and the shell can comprise a Group 2 metal and a non-metal, the Group 2 metal including zinc and the non-metal including at least one of sulfur and selenium.

[0162] The plurality of semiconductor nanoparticles can include a first semiconductor nanocrystal comprising zinc, selenium, and tellurium and a second semiconductor nanocrystal comprising a zinc chalcogenide and different from the first semiconductor nanocrystal.

[0163] The plurality of semiconductor nanoparticles can include a first semiconductor nanocrystal and a second semiconductor nanocrystal, the first semiconductor nanocrystal comprising indium, phosphorus, and optionally zinc, the second semiconductor nanocrystal comprising a zinc chalcogenide and different from the first semiconductor nanocrystal. The plurality of semiconductor nanoparticles includes a zinc chalcogenide that includes tellurium, and optionally, the plurality of semiconductor nanoparticles can be configured to emit blue light. The plurality of semiconductor nanoparticles can include a core and a shell, the core comprising the first semiconductor nanocrystal and the shell disposed on the core and comprising the second semiconductor nanocrystal.

[0164] In an embodiment, when the semiconductor nanoparticles have a core / shell structure, an alloyed layer may or may not be present at the interface between the core and the shell. The alloyed layer can be a homogeneous alloy or can be a gradient alloy. In a gradient alloy, the concentration of the elements present in the shell can have a concentration gradient that varies in the radial direction (e.g., decreasing or increasing towards the center).

[0165] In an embodiment, the shell can have a composition that varies in the radial direction. In an embodiment, the shell can be a multi-layer shell comprising two or more layers. In a multi-layer shell, two adjacent layers can have different compositions from each other. In a multi-layer shell, at least one layer can independently comprise semiconductor nanocrystals having a single composition. In a multi-layer shell, at least one layer can independently have alloyed semiconductor nanocrystals. In a multi-layer shell, at least one layer can have a concentration gradient that varies radially in terms of the composition of the semiconductor nanocrystals.

[0166] In a core / shell structured semiconductor nanoparticle, the bandgap energy of the shell material can be greater than that of the core material, but is not limited thereto. The bandgap energy of the shell material can be less than that of the core material. In the case of a multi-layer shell, the energy bandgap of the outermost layer material of the shell can be greater than that of the core and the inner layer materials (the layer closer to the core) of the shell. In a multi-layer shell, semiconductor nanocrystals of each layer are selected to have an appropriate bandgap so as to effectively exhibit the quantum confinement effect.

[0167] The semiconductor nanoparticles of the embodiment can include, for example, organic ligands in a state where they are bound or coordinated to the surface of the semiconductor nanoparticles. The organic ligands are as described below.

[0168] In an embodiment, the semiconductor nanoparticles can control the absorption / emission wavelength, for example, by adjusting their composition and / or size. The semiconductor nanoparticles included in the light-emitting layer 3 or 30 can be configured to emit light of a desired color. The semiconductor nanoparticles can include semiconductor nanoparticles that emit blue light, semiconductor nanoparticles that emit green light, or semiconductor nanoparticles that emit red light.

[0169] The maximum emission peak wavelength of the semiconductor nanoparticles can have a wavelength range from ultraviolet to infrared wavelength or higher. For example, the maximum emission peak wavelength of the semiconductor nanoparticles can be greater than or equal to about 300 nm, such as 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 emission wavelength of the semiconductor nanoparticles can be in the range of less than or equal to about 800 nm, such as 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 emission wavelength of the semiconductor nanoparticles can be in the range of about 500 nm to about 650 nm.

[0170] The semiconductor nanoparticles can emit green light, and the maximum emission wavelength can be in the range of greater than or equal to about 500 nm (e.g., greater than or equal to about 520 nm) and less than or equal to about 560 nm (e.g., less than or equal to about 540 nm, or less than or equal to about 530 nm). The semiconductor nanoparticles can emit red light, and the maximum emission wavelength can be in the range of greater than or equal to about 600 nm (e.g., greater than or equal to about 610 nm) and less than or equal to about 650 nm (e.g., less than or equal to about 640 nm). The semiconductor nanoparticles can emit blue light and the maximum emission wavelength can be greater than or equal to about 440 nm (e.g., greater than or equal to about 450 nm, or greater than or equal to about 455 nm) and less than or equal to about 480 nm (e.g., less than or equal to about 470 nm, or less than or equal to about 465 nm).

[0171] The semiconductor nanoparticles can exhibit a photoluminescence spectrum with a relatively narrow full width at half maximum (FWHM). In an embodiment, the semiconductor nanoparticles can have an FWHM of less than or equal to about 45 nm, such as less than or equal to about 44 nm, less than or equal to about 43 nm, less than or equal to about 42 nm, less than or equal to about 41 nm, less than or equal to about 40 nm, less than or equal to about 39 nm, less than or equal to about 38 nm, less than or equal to about 37 nm, less than or equal to about 36 nm, or less than or equal to about 35 nm in their photoluminescence spectrum.

[0172] The semiconductor nanoparticles can have (e.g., configured to achieve) a quantum yield of greater than or equal to about 10%, such as greater than or equal to about 20%, greater than or equal to about 30%, greater than or equal to about 40%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, greater than or equal to about 80%, greater than or equal to about 90%, or even about 100%.

[0173] The semiconductor nanoparticles may have a size greater than or equal to about 1 nm and less than or equal to about 100 nm (e.g., the particle diameter or, in the case of non-spherical particles, the equivalent particle diameter calculated from the two-dimensional area confirmed by analysis using electron microscopy). In an embodiment, the semiconductor nanoparticles may have a size of about 1 nm to about 50 nm, such as about 2 nm (or about 3 nm) to about 35 nm. In an embodiment, the size of the semiconductor nanoparticles may be greater than or equal to about 1 nm, greater than or equal to about 2 nm, greater than or equal to about 3 nm, greater than or equal to about 4 nm, or greater than or equal to about 5 nm. In an embodiment, the size of the semiconductor nanoparticles may 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 25 nm, less than or equal to about 20 nm, less than or equal to about 19 nm, less than or equal to about 18 nm, less than or equal to about 17 nm, less than or equal to about 16 nm, or less than or equal to about 15 nm.

[0174] The semiconductor nanoparticles may have any shape. In an embodiment, the shape of the semiconductor nanoparticles may be a sphere, polyhedron, pyramid, multi-legged body, cube, nanotube, nanowire, nanofiber, nanosheet, nanoplate, or a combination thereof.

[0175] The semiconductor nanoparticles may be synthesized by any method. For example, semiconductor nanocrystals having several nanometer sizes may be synthesized by a wet chemical process. In the wet chemical process, crystal particles are grown by reacting precursor materials in an organic solvent, and the growth of the crystals can be controlled by coordinating the organic solvent or ligand compound on the surface of the semiconductor nanocrystals.

[0176] In an embodiment, for example, a method for preparing semiconductor nanoparticles having a core / shell structure may include: obtaining a core; preparing a first shell precursor solution including a metal (e.g., zinc) and an organic ligand; preparing a second shell precursor including a non-metallic element (e.g., sulfur, selenium, or a combination thereof); and heating the first shell precursor solution at a reaction temperature (e.g., greater than or equal to about 180 °C, greater than or equal to about 200 °C, greater than or equal to about 240 °C, or greater than or equal to about 280 °C and less than or equal to about 360 °C, less than or equal to about 340 °C, or less than or equal to about 320 °C), and then adding the core and the second shell precursor thereto (e.g., once or multiple times, or two or more times) to form a shell of a second semiconductor nanocrystal on the first semiconductor nanocrystal core. The method may further include preparing a core solution by separating the core from the reaction system for preparing the core and then dispersing it in an organic solvent.

[0177] In an embodiment, to form the shell, the solvent and optionally the ligand compound are heated (or vacuum treated) under vacuum at a predetermined temperature (e.g., greater than or equal to about 100 °C), and then, after replacing the atmosphere with an inert gas atmosphere, heat treatment is performed again at a predetermined temperature (e.g., greater than or equal to 100 °C). Subsequently, the core is added thereto, and the shell precursor is added thereto sequentially or simultaneously, and then, heating is performed at a predetermined reaction temperature to carry out the reaction. The shell precursor may be introduced sequentially as a mixture in different ratios during the reaction time.

[0178] In an embodiment of the semiconductor nanoparticles, the core can be prepared by a suitable method. The organic solvent may include C6 to C22 primary amines such as hexadecylamine, C6 to C22 secondary amines such as dioctylamine, C6 to C40 tertiary amines such as trioctylamine, nitrogen-containing heterocyclic compounds such as pyridine, C6 to C40 olefins such as octadecene, C6 to C40 aliphatic hydrocarbons such as hexadecane, octadecane or squalane, aromatic hydrocarbons substituted with C6 to C30 alkyl groups such as phenyldodecane, phenyltetradecane or phenylhexadecane, primary, secondary or tertiary phosphines substituted with at least one (e.g., 1, 2 or 3) C6 to C22 alkyl groups (e.g., trioctylphosphine), phosphine oxides substituted with (e.g., 1, 2 or 3) C6 to C22 alkyl groups (e.g., trioctylphosphine oxide), C12 to C22 aromatic ethers such as phenyl ether or benzyl ether, or a combination thereof.

[0179] The organic ligand coordinates to the surface of the fabricated semiconductor nanoparticles and can enable the semiconductor nanoparticles to be well dispersed in the solution. The organic ligand may include RCOOH, RNH2, R2NH, R3N, RSH, RH2PO, R2HPO, R3PO, RH2P, R2HP, R3P, ROH, RCOOR', RPO(OH)2, R2POOH, wherein R and R' each independently include (or are) a substituted or unsubstituted aliphatic hydrocarbon group having 1 or more, 6 or more, or 10 or more and 40 or less, 35 or less, or 25 or less carbon atoms, or a substituted or unsubstituted C6 to C40 aromatic hydrocarbon group, or a combination thereof), or a combination thereof. The ligand may be used alone or as a mixture of two or more compounds.

[0180] Examples of the organic ligand may be thiol compounds such as methanethiol, ethanethiol, propanethiol, butanethiol, pentanethiol, hexanethiol, octanethiol, dodecanethiol, hexadecanethiol, octadecanethiol, benzyl mercaptan, etc.; amines such as methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, nonylamine, decylamine, dodecylamine, hexadecylamine, octadecylamine, dimethylamine, diethylamine, dipropylamine, tributylamine, trioctylamine, etc.; carboxylic acid compounds 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, myristic acid, stearic acid, lauric acid, benzoic acid, etc.; phosphine compounds such as methylphosphine, ethylphosphine, propylphosphine, butylphosphine, pentylphosphine, octylphosphine, dioctylphosphine, tributylphosphine, trioctylphosphine, etc.; their phosphine oxide compounds such as methylphosphine oxide, ethylphosphine oxide, propylphosphine oxide, butylphosphine oxide, pentylphosphine oxide, tributylphosphine oxide, octylphosphine oxide, dioctylphosphine oxide, trioctylphosphine oxide, etc.; diphenylphosphine (DPP), triphenylphosphine compounds, or their oxide compounds; C5 to C20 alkylphosphinic acids such as hexylphosphinic acid, octylphosphinic acid, dodecylphosphinic acid, tetradecylphosphinic acid, hexadecylphosphinic acid, octadecylphosphinic acid; C5 to C20 alkylphosphonic acids; and so on, but not limited thereto.

[0181] The semiconductor nanocrystals can be collected by pouring into an excess of a non-solvent to remove the excess organic substances uncoordinated on the surface and centrifuging the resulting mixture. For example, after the reaction is completed, if a non-solvent is added to the reaction product, the semiconductor nanoparticles coordinated with the ligand compound can be separated. The non-solvent can be a polar solvent that is miscible with the solvent used in the core formation and / or shell formation reaction and is not capable of dispersing the prepared nanocrystals. The non-solvent can be selected depending on the solvent used in the reaction and can include, for example, acetone, ethanol, butanol, isopropanol, ethylene glycol, water, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), diethyl ether, formaldehyde, acetaldehyde, ethylene glycol, solvents having solubility parameters similar to the foregoing solvents, or a combination thereof. The semiconductor nanocrystals can be separated by centrifugation, sedimentation, chromatography, or distillation. If necessary, the separated nanocrystals can be added to a washing solvent and washed. The washing solvent is not particularly limited and can have solubility parameters similar to those of the ligand and can include, for example, hexane, heptane, octane, chloroform, toluene, benzene, etc.

[0182] The semiconductor nanoparticles may be non-dispersible or insoluble in water, the aforementioned non-solvent, or a combination thereof. The semiconductor nanoparticles can be dispersed in the aforementioned organic solvents. In an embodiment, the semiconductor nanoparticles can be dispersed on a C6 to C40 aliphatic hydrocarbon, a substituted or unsubstituted C6 to C40 aromatic hydrocarbon, or a combination thereof.

[0183] In a display device or a light-emitting diode, the thickness of the light-emitting layer can be appropriately selected. In one embodiment, the light-emitting layer may include a single layer of semiconductor nanoparticles. In another embodiment, the light-emitting layer may include one or more, for example, two or more, three or more, or four or more and 20 or less, 10 or less, 9 or less, 8 or less, 7 or less, or 6 or less single layers of semiconductor nanoparticles. The light-emitting layer may have a thickness greater than or equal to about 5 nm, for example greater than or equal to about 10 nm, greater than or equal to about 20 nm, greater than or equal to about 25 nm, or greater than or equal to about 30 nm and less than or equal to about 200 nm, for example 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, and the light-emitting layer 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.

[0184] The formation of the light-emitting layer 3 or 30 can be carried out as follows: obtaining a composition including semiconductor nanoparticles (configured to emit desired light), and applying or depositing it on a substrate (e.g., an electrode) or a charge-assisting layer (e.g., a hole-assisting layer or an electron-assisting layer) by an appropriate method (e.g., by spin coating, inkjet printing, etc.).

[0185] The formation of the light-emitting layer may further include contacting the applied or deposited layer of semiconductor nanoparticles with an organic solution (e.g., an alcohol solution) of a metal halide (e.g., zinc chloride), for example.

[0186] The formation of the light-emitting layer may further include heat-treating the applied or deposited layer of semiconductor nanoparticles. The heat-treatment temperature is not particularly limited and can be appropriately selected considering the boiling point of the organic solvent, etc. For example, the heat-treatment temperature may be greater than or equal to about 60 °C. The type of the organic solvent for the semiconductor nanoparticle dispersion is not particularly limited and can be appropriately selected. In an embodiment, the organic solvent may include an (un)substituted aliphatic hydrocarbon organic solvent, an (un)substituted aromatic hydrocarbon organic solvent, an acetate solvent, or a combination thereof.

[0187] The light-emitting layer may have a single-layer structure or a multi-layer structure in which two or more layers are stacked. Adjacent layers in the multi-layer structure (e.g., the first light-emitting layer and the second light-emitting layer) may be configured to emit the same color. In the multi-layer structure, adjacent layers (e.g., the first light-emitting layer and the second light-emitting layer) may have the same or different compositions and / or ligands from each other. In an embodiment, the light-emitting layer or the multi-layer light-emitting layer including two or more layers may have a halogen content that varies in the thickness direction. In the (multi-layer) light-emitting layer according to an embodiment, the halogen content may increase toward the electron-assisted layer. In the (multi-layer) light-emitting layer according to an embodiment, the organic ligand content may decrease toward the electron-assisted layer. In the light-emitting layer according to an embodiment, the halogen content may decrease toward the electron-assisted layer. In the (multi-layer) light-emitting layer according to an embodiment, the organic ligand content may increase toward the electron-assisted layer.

[0188] In an embodiment, the light-emitting layer may include a first semiconductor nanoparticle light-emitting layer in which the surface is substituted with a halogen (e.g., chlorine), and a second semiconductor nanoparticle light-emitting layer provided on the first semiconductor nanoparticle light-emitting layer and having an increased organic ligand content. The halogen (e.g., chlorine) content and the organic material content of the light-emitting layer may be controlled by appropriate means (post-treatment of the formed layer). For example, the amount of the organic ligand of the semiconductor nanoparticles in the light-emitting layer may be controlled (reduced) by treating the layer with an alcohol solution of a metal halide (e.g., zinc halide such as zinc chloride). The layer treated in this way may have an increased halogen content and may exhibit changed solubility properties for organic solvents. Therefore, a layer of semiconductor nanoparticles (e.g., halogen-treated semiconductor nanoparticles or semiconductor nanoparticles having a ligand containing a carboxylic acid) having different amounts of organic ligands may be subsequently formed on the treated light-emitting layer.

[0189] The electron transport layer 4 or 40 is provided between the second electrode and the light-emitting layer. The electron transport layer may be adjacent to the light-emitting layer (e.g., directly provided on the light-emitting layer). In an embodiment, the electron transport layer may be in contact with the light-emitting layer. An electron injection layer may be further provided between the second electrode and the electron transport layer.

[0190] The electron transport layer includes zinc-based oxide nanoparticles according to an embodiment. Since the zinc-based oxide nanoparticles have been described above, their detailed description will be omitted.

[0191] As described above, the zinc-based oxide nanoparticles according to the embodiment can effectively passivate the zinc dangling bonds on the surface of the nanoparticles by including an oxygen-containing anion of vanadium on the surface, and thus, it is considered that the band gap is widened and the conduction band minimum (CBM) moves upward compared to the zinc-based oxide nanoparticles that do not include the oxygen-containing anion of vanadium on the surface. Therefore, an electroluminescent diode including the zinc-based oxide nanoparticles according to the embodiment in the electron transport layer can have significantly improved device performance and lifespan by reducing the electron conduction barrier from the electron transport layer to the light-emitting layer containing quantum dots, thereby enhancing the conductivity characteristics.

[0192] The electron transport layer can be formed by obtaining a composition including the zinc-based oxide nanoparticles according to the embodiment, for example, a composition for forming an electron transport layer prepared by dispersing the zinc-based oxide nanoparticles in an organic solvent (e.g., a polar organic solvent, a non-polar organic solvent, or a combination thereof), and applying the same to form a film. The composition for the electron transport layer can be applied on the light-emitting layer. The solution process can further include removing the organic solvent from the formed film (e.g., by evaporation, etc.) or heat treatment. The heat treatment can be performed at a temperature of greater than or equal to about 50°C, greater than or equal to about 60°C, greater than or equal to about 70°C, or greater than or equal to about 85°C and less than or equal to about 100°C. The composition can be, for example, a dispersion in which the zinc-based oxide nanoparticles according to the embodiment are dispersed in an organic solvent.

[0193] The zinc-based oxide nanoparticles according to the embodiment can exhibit the dispersibility required for the process. For example, the zinc-based oxide nanoparticles can have an average particle diameter (hereinafter referred to as "dynamic light scattering (DLS) average particle diameter") of greater than or equal to about 4.5 nm, greater than or equal to about 5 nm, greater than or equal to about 5.5 nm, greater than or equal to about 6 nm, greater than or equal to about 6.5 nm, greater than or equal to about 7 nm, or greater than or equal to about 7.5 nm, which is measured by DLS analysis by dispersing the zinc-based oxide nanoparticles in an alcohol solvent. The DLS average particle diameter of the zinc oxide nanoparticles can be less than or equal to about 500 nm, less than or equal to about 300 nm, less than or equal to about 150 nm, less than or equal to about 100 nm, 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 10 nm, less than or equal to about 9 nm, less than or equal to about 8.5 nm, less than or equal to about 8 nm, less than or equal to about 7.5 nm, or less than or equal to about 7 nm.

[0194] The size or average size (hereinafter referred to as "size") of the zinc-based oxide nanoparticles according to the embodiment may be greater than or equal to about 1 nm, greater than or equal to about 2 nm, greater than or equal to about 3 nm, greater than or equal to about 3.5 nm, greater than or equal to about 4 nm, greater than or equal to about 4.5 nm, greater than or equal to about 5 nm, greater than or equal to about 5.5 nm, greater than or equal to about 6 nm, greater than or equal to about 6.5 nm, or greater than or equal to about 7 nm, and the average size of the zinc-based oxide nanoparticles may be less than or equal to about 30 nm, such as less than or equal to about 25 nm, less than or equal to about 20 nm, less than or equal to about 15 nm, less than or equal to about 10 nm, less than or equal to about 9 nm, less than or equal to about 8 nm, less than or equal to about 7 nm, or less than or equal to about 6 nm, but is not limited to these ranges.

[0195] In an embodiment, the thickness of the electron transport layer may be 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, greater than or equal to about 15 nm, greater than or equal to about 16 nm, greater than or equal to about 17 nm, greater than or equal to about 18 nm, greater than or equal to about 19 nm, or greater than or equal to about 20 nm and less than or equal to about 120 nm, less than or equal to about 110 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, less than or equal to about 50 nm, less than or equal to about 40 nm, less than or equal to about 30 nm, or less than or equal to about 25 nm, but is not limited thereto.

[0196] In an embodiment, an electron injection layer may be further disposed between the electron transport layer and the second electrode. The material of the electron injection layer is not particularly limited and may be appropriately selected.

[0197] The electroluminescent diode according to the embodiment may further include a hole auxiliary layer. The hole auxiliary layer 2 or 20 is located between the first electrode 1 or 10 and the light emitting layer 3 or 30. The hole auxiliary layer 2 or 20 may include a hole injection layer, a hole transport layer, and / or an electron blocking layer. The hole auxiliary layer 12 may be a single-layer structure or a multi-layer structure in which adjacent layers include different components.

[0198] The hole auxiliary layer 2 or 20 may have a HOMO level that can match the HOMO level of the light emitting layer 3 or 30 to enhance the mobility of holes transferred from the hole auxiliary layer to the light emitting layer 3 or 30. In an embodiment, the hole auxiliary layer 2 or 20 may include a hole injection layer close to the first electrode 1 or 10 and a hole transport layer close to the light emitting layer 3 or 30.

[0199] There is no particular limitation on the material included in the hole auxiliary layer 2 or 20 (for example, a hole transport layer, a hole injection layer, or an electron blocking layer), and it may include, for example, poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), polyarylamine (polyaryl amine), poly(N-vinylcarbazole), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS), polyaniline, polypyrrole, N,N,N',N'-tetrakis(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[(di-4-tolylamino)phenyl]cyclohexane (TAPC), p-type metal oxides (for example, NiO, WO3, MoO3, etc.), carbon-based materials such as graphene oxide, or a combination thereof, but not limited thereto.

[0200] In the hole auxiliary layer, the thickness of each layer can be appropriately selected. For example, the thickness of each layer can be greater than or equal to about 5 nm, greater than or equal to about 10 nm, greater than or equal to about 15 nm, or greater than or equal to about 20 nm, and the thickness of each layer can be 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, less than or equal to about 50 nm, for example less than or equal to about 40 nm, less than or equal to about 35 nm, or less than or equal to about 30 nm, but not limited thereto.

[0201] The device according to one embodiment may have a normal structure. In an embodiment, in the device, the anode 10 disposed on the transparent substrate 100 may include a metal oxide-based transparent electrode (for example, an ITO electrode), and the cathode 50 facing the anode 10 may include a conductive metal (for example, having a relatively low work function, such as Mg, Al, etc.). A hole auxiliary layer 20 (for example, a hole injection layer such as PEDOT:PSS and / or a p-type metal oxide and / or a hole transport layer such as TFB and / or PVK) may be disposed between the transparent electrode 10 and the light-emitting layer 30. The hole injection layer can be close to the transparent electrode, and the hole transport layer can be close to the light-emitting layer. An electron auxiliary layer 40 may be disposed between the light-emitting layer 30 and the cathode 50.

[0202] Devices according to another embodiment may have 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 50 may include a metal (e.g., Au, Ag, etc.) (having a relatively high work function). For example, an n-type metal oxide (e.g., crystalline Zn metal oxide) (optionally doped) may be provided between the transparent electrode 50 and the light-emitting layer 30 as an electron assisting layer (e.g., an electron transport layer) 40. Between the metal anode 10 and the light-emitting layer 30, MoO3 or another p-type metal oxide may be provided as a hole assisting layer (e.g., a hole transport layer including TFB and / or PVK and / or a hole injection layer including MoO3 or another p-type metal oxide) 20.

[0203] The above-described devices may be fabricated by a suitable method. For example, an electroluminescent diode may be fabricated by: optionally forming a hole assisting layer (e.g., by deposition or coating) on a substrate on which an electrode is formed, forming a light-emitting layer including semiconductor nanoparticles (e.g., a pattern of the semiconductor nanoparticles described above), and forming an electron transport layer and an electrode on the light-emitting layer (e.g., by deposition or coating). The method of forming the electrode / hole assisting layer / electron assisting layer may be appropriately selected and is not particularly limited.

[0204] The electroluminescent diodes of the embodiments may exhibit improved electroluminescent properties, e.g., along with a longer lifetime as described above.

[0205] The electroluminescent diodes of the embodiments may have a maximum external quantum efficiency (EQE Max) of greater than or equal to about 5%, greater than or equal to about 5.5%, greater than or equal to about 6%, greater than or equal to about 6.5%, greater than or equal to about 7%, greater than or equal to about 7.5%, greater than or equal to about 7.7%, greater than or equal to about 8%, greater than or equal to about 8.5%, greater than or equal to about 9%, greater than or equal to about 9.5%, greater than or equal to about 10%, greater than or equal to about 10.5%, greater than or equal to about 11%, greater than or equal to about 11.5%, greater than or equal to about 12%, greater than or equal to about 12.5%, greater than or equal to about 13%, greater than or equal to about 13.5%, or greater than or equal to about 14%. The light-emitting layer may have a maximum external quantum efficiency (EQE Max) of less than or equal to about 40%, less than or equal to about 30%, or less than or equal to about 20%.

[0206] The electroluminescent diode may have a luminance of greater than or equal to about 50,000 cd / m 2 、greater than or equal to about 60,000 cd / m 2 、greater than or equal to about 70,000 cd / m 2 、greater than or equal to about 80,000 cd / m 2, greater than or equal to about 90,000 cd / m 2 , greater than or equal to about 100,000 cd / m 2 , greater than or equal to about 150,000 cd / m 2 , greater than or equal to about 200,000 cd / m 2 , greater than or equal to about 250,000 cd / m 2 , greater than or equal to about 300,000 cd / m 2 , greater than or equal to about 310,000 cd / m 2 , greater than or equal to about 320,000 cd / m 2 , greater than or equal to about 330,000 cd / m 2 , greater than or equal to about 340,000 cd / m 2 , greater than or equal to about 350,000 cd / m 2 , greater than or equal to about 360,000 cd / m 2 , greater than or equal to about 370,000 cd / m 2 , greater than or equal to about 380,000 cd / m 2 , greater than or equal to about 390,000 cd / m 2 , greater than or equal to about 400,000 cd / m 2 , greater than or equal to about 440,000 cd / m 2 , greater than or equal to about 500,000 cd / m 2 , or greater than or equal to about 550,000 cd / m 2 The maximum luminance (LUMMax). The maximum luminance of the light-emitting layer in a light-emitting diode or a display device may be less than or equal to about 1,000,000 cd / m 2 , or less than or equal to about 600,000 cd / m 2 .

[0207] The electroluminescent diode may be configured to emit blue light, green light or red light. The peak emission wavelengths of the blue light, green light and red light are as described herein.

[0208] In addition, when driven at a predetermined brightness (e.g., 650 nits), the electroluminescent diode of the embodiment may have a T50 that is greater than or equal to about 100 hours, greater than or equal to about 150 hours, greater than or equal to about 200 hours, greater than or equal to about 250 hours, greater than or equal to about 300 hours, greater than or equal to about 350 hours, greater than or equal to about 400 hours, greater than or equal to about 500 hours, greater than or equal to about 600 hours, or greater than or equal to about 700 hours. The T50 may be from about 270 hours to about 4000 hours, from about 270 hours to about 2000 hours, from about 280 hours to about 1500 hours, from about 300 hours to about 1000 hours, or from about 300 hours to about 900 hours.

[0209] The electroluminescent diode may have a T90 (when driven at a predetermined brightness such as 650 nits) that is greater than or equal to about 10 hours, greater than or equal to about 20 hours, greater than or equal to about 30 hours, greater than or equal to about 40 hours, greater than or equal to about 50 hours, greater than or equal to about 60 hours, greater than or equal to about 70 hours, greater than or equal to about 80 hours, greater than or equal to about 90 hours, greater than or equal to about 100 hours, greater than or equal to about 110 hours, greater than or equal to about 120 hours, greater than or equal to about 130 hours, greater than or equal to about 140 hours, greater than or equal to about 150 hours, greater than or equal to about 160 hours, greater than or equal to about 170 hours, greater than or equal to about 180 hours, greater than or equal to about 190 hours, or greater than or equal to about 200 hours. The electroluminescent diode may have a T90 (when driven at a predetermined brightness such as 650 nits) that is from about 10 hours to about 1000 hours, from about 15 hours to about 1000 hours, from about 15 hours to about 800 hours, from about 20 hours to about 700 hours, or a combination thereof.

[0210] The electroluminescent diode may have an initial voltage (when driven at a predetermined brightness such as 650 nits) that is less than or equal to about 3 volts, such as less than or equal to about 2.9 volts, or less than or equal to about 2.88 volts. The initial voltage may be greater than or equal to about 2.5 volts, greater than or equal to about 2.6 volts, or greater than or equal to about 2.7 volts.

[0211] Another embodiment relates to a display device including the aforementioned electroluminescent diode.

[0212] The display device may include a first pixel and a second pixel, and the second pixel is configured to emit light of a color different from that of the first pixel. An electroluminescent diode according to an embodiment may be provided in the first pixel, the second pixel, or a combination thereof. In an embodiment, the display device may further include a blue pixel, a red pixel, a green pixel, or a combination thereof. In the display device, the red pixel may include a red light-emitting layer including a plurality of semiconductor nanoparticles that emit red light, the green pixel may include a green light-emitting layer including a plurality of semiconductor nanoparticles that emit green light, and the blue pixel may include a blue light-emitting layer including a plurality of semiconductor nanoparticles that emit blue light.

[0213] Reference Figure 4 , a display panel 1000 according to an embodiment may include a display area 1000D for displaying an image, and a non-display area 1000P optionally provided around the display area 1000D and in which bonding elements (not shown) may be provided. The display area 1000D may include a plurality of pixels PX arranged along rows (e.g., the x direction) and / or columns (e.g., the y direction), and each pixel PX may include a plurality of sub-pixels PX1, PX2, and PX3 that display different colors. Herein, as an example, a configuration in which three sub-pixels PX1, PX2, and PX3 constitute one pixel PX is illustrated, but the configuration is not limited thereto. It may further include additional sub-pixels such as white sub-pixels, and may include one or more sub-pixels that display the same color. The plurality of pixels PX may be arranged, for example, in a Bayer matrix, a PenTile matrix, and / or a diamond matrix, but is not limited thereto.

[0214] Each of the sub-pixels PX1, PX2, and PX3 may be configured to display a color of a primary color or a combination of primary colors, for example, red, green, blue, or a combination thereof. For example, the first sub-pixel PX1 may be configured to display red, the second sub-pixel PX2 may be configured to display green, and the third sub-pixel PX3 may be configured to display blue.

[0215] In Figure 4 , an example in which all sub-pixels have the same size is illustrated, but the present disclosure is not limited thereto. At least one of the sub-pixels may be larger or smaller than the other sub-pixels. In Figure 4 , an example in which all sub-pixels have the same shape is illustrated, but the present disclosure is not limited thereto. At least one of the sub-pixels may have a shape different from that of the other sub-pixels.

[0216] Reference Figure 5 , in an embodiment, the display panel may include a substrate 110, a buffer layer 111, a thin film transistor TFT, and a light-emitting diode 180. The display panel may include circuit elements configured to switch and / or drive each light-emitting device.

[0217] The light-emitting diodes 180 may be disposed in each of the sub-pixels PX1, PX2, and PX3, and the light-emitting diodes 180 disposed in the sub-pixels PX1, PX2, and PX3 may be independently driven. The sub-pixels may include blue pixels, red pixels, or green pixels. At least one of the light-emitting diodes 180 may be an electroluminescent diode according to an embodiment.

[0218] The substrate 110 is as described above. The buffer layer 111 may include an organic material, an inorganic material, or an organic-inorganic material. The buffer layer 111 may include, for example, an oxide, a nitride, or an oxynitride, and may include, for example, silicon oxide, silicon nitride, silicon oxynitride, or a combination thereof, but is not limited thereto. The buffer layer 111 may be one layer or two or more layers, and may cover the entire surface of the lower substrate 110. The buffer layer 111 may be omitted.

[0219] The thin-film transistor TFT may be a three-terminal element for switching and / or driving the light-emitting diode 180, and one or two or more may be included for each sub-pixel. The thin-film transistor TFT may include a gate electrode 124, a semiconductor layer 154 overlapping with the gate electrode 124, a gate insulating layer 140 between the gate electrode 124 and the semiconductor layer 154, and a source electrode 173 and a drain electrode 175 electrically connected to the semiconductor layer 154. In Figure 5 it, a coplanar top-gate structure is shown as an example, but the structure is not limited thereto and may have various structures.

[0220] The gate electrode 124 is electrically connected to a gate line (not shown), and may include, for example, a low-resistance metal such as aluminum (Al), molybdenum (Mo), copper (Cu), titanium (Ti), silver (Ag), gold (Au), an alloy thereof, or a combination thereof, but is not limited thereto.

[0221] The semiconductor layer 154 may be an inorganic semiconductor, such as amorphous silicon, polycrystalline silicon, or an oxide semiconductor; an organic semiconductor; an organic-inorganic semiconductor; or a combination thereof. For example, the semiconductor layer 154 may include an oxide semiconductor containing at least one of indium (In), zinc (Zn), tin (Sn), and gallium (Ga), and the oxide semiconductor may include, for example, indium-gallium-zinc oxide, zinc-tin oxide, or a combination thereof, but is not limited thereto. The semiconductor layer 154 may include a channel region and doping regions, and the doping regions are disposed on both sides of the channel region and are electrically connected to the source electrode 173 and the drain electrode 175, respectively.

[0222] The gate insulating layer 140 may include an organic material, an inorganic material, or an organic-inorganic material, and may include, for example, an oxide, a nitride, or an oxynitride, and may include, for example, silicon oxide, silicon nitride, silicon oxynitride, or a combination thereof, but is not limited thereto. In Figure 5In [the figure], an example is illustrated in which the gate insulating layer 140 is formed on the entire surface of the lower substrate 110. However, the present disclosure is not limited thereto, and the gate insulating layer 140 may optionally be formed between the gate electrode 124 and the semiconductor layer 154. The gate insulating layer 140 may be formed of one or two or more layers.

[0223] The source electrode 173 and the drain electrode 175 may include, for example, a low-resistance metal such as aluminum (Al), molybdenum (Mo), copper (Cu), titanium (Ti), silver (Ag), gold (Au), an alloy thereof, or a combination thereof, but is not limited thereto. The source electrode 173 and the drain electrode 175 may be electrically connected to the doped regions of the semiconductor layer 154, respectively. The source electrode 173 is electrically connected to a data line (not shown), and the drain electrode 175 is electrically connected to the light-emitting diode 180 described above.

[0224] In addition, an interlayer insulating layer 145 is formed between the gate electrode 124 and the source / drain electrodes 173 and 175. The interlayer insulating layer 145 may include an organic material, an inorganic material, or an organic-inorganic material, such as an oxide, a nitride, or an oxynitride, such as silicon oxide, silicon nitride, silicon oxynitride, or a combination thereof, but is not limited thereto. The interlayer insulating layer 145 may be formed of one or two or more layers.

[0225] In an embodiment, a protective film 160 is formed on the thin-film transistor TFT. The protective film 160 may be, for example, a passivation layer, but is not limited thereto. The protective film 160 may include an organic material, an inorganic material, or an organic-inorganic material, such as polyacrylic acid, polyimide, polyamide, polyamideimide, or a combination thereof, but is not limited thereto. The protective film 160 may be formed of one or two or more layers.

[0226] In an embodiment, one of the first electrodes 1 and 10 and the second electrodes 5 and 50 may be a pixel electrode connected to the TFT, and the other may be a common electrode.

[0227] The display device according to the embodiment may be used as a top-emission type display panel, a bottom-emission type display panel, or a dual-sided emission type display panel.

[0228] In an embodiment, the first electrodes 1 and 10 may be light-transmissive electrodes, and the second electrodes 5 and 50 may be reflective electrodes, and the display panel may be a bottom-emission type display panel that emits light toward the first electrodes 1 and 10 and the substrate 110 if present. In an embodiment, the first electrodes 1 and 10 may be reflective electrodes, and the second electrodes 5 and 50 may be light-transmissive electrodes, and the display panel may be a top-emission type display panel that emits light to the opposite side of the first electrodes 1 and 10 and the substrate 100 if present. In an embodiment, both the first electrode and the second electrode may be light-transmissive electrodes, and the display panel 1000 may be a dual-emission type display panel that emits light to the substrate 110 side and the side opposite to the substrate 110.

[0229] The display device may include a portable terminal device, a monitor (e.g., a portable monitor), a laptop computer, a television, an electronic signage, a camera, or an electronic component.

[0230] Specific embodiments are described below. However, the embodiments described below are only for specifically exemplifying or illustrating the present disclosure, and the scope of the present disclosure is not limited thereto.

[0231] [Embodiment]

[0232] Analysis method

[0233] [1] Electroluminescence spectroscopy analysis

[0234] While applying a voltage, the current according to the voltage was measured using a Keithley 2635B source meter, and the EL properties (e.g., luminance and EQE, etc.) were measured using a CS2000 spectrometer.

[0235] [2] Lifetime characteristics

[0236] T90 (h): When starting operation at a given initial luminance (e.g., 650 nits), the time (hr) taken for the luminance to reach 90% of the initial luminance (100%) was measured.

[0237] T50 (h): When starting operation at a given initial luminance (e.g., 650 nits), the time (hr) taken for the luminance to reach 50% of the initial luminance of 100% was measured.

[0238] [3] XPS analysis

[0239] XPS analysis was performed using an X-ray photoelectron spectrometer (manufacturer: Physical Electronics, model: Quantum2000).

[0240] [4] ICP-AES analysis

[0241] Inductively coupled plasma atomic emission spectrometry (ICP-AES) was performed using a Shimadzu ICPS-8100.

[0242] [5] TEM analysis

[0243] Transmission electron microscopy analysis of the prepared nanoparticles was carried out using a UT F30 Tecnai electron microscope.

[0244] [6] Photoluminescence analysis

[0245] Photoluminescence (PL) analysis was performed using a Hitachi F-7100 spectrophotometer.

[0246] [7] UV-Vis spectroscopy

[0247] UV spectral analysis was performed using a Shimadzu UV-2600 spectrometer to obtain the ultraviolet-visible absorption spectrum. The band gap energy (eV) can be obtained from the x-intercept wavelength (nm) of the obtained ultraviolet-visible absorption spectrum using the following equation:

[0248] Band gap energy (eV) = 1240 (nm) / x-intercept wavelength (nm)

[0249] [8] TGA analysis

[0250] TGA analysis was carried out using a Trios V3.2 system (TA Instruments) from 20 °C to 600 °C at a heating rate of 10 °C / min in an N2 atmosphere.

[0251] [9] Dynamic light scattering (DLS) analysis

[0252] DLS analysis was performed using an Otsuka, ELSZ-2000.

[0253] The following syntheses were carried out under an inert gas atmosphere (under nitrogen flow conditions) unless otherwise stated. The precursor contents are in molar amounts unless otherwise stated.

[0254] Synthesis Example 1: Preparation of ZnSeTe / ZnSeS Quantum Dots Emitting Blue Light

[0255] Stock solutions of S / TOP, Se / TOP, and Te / TOP were prepared by dispersing sulfur (S), selenium (Se), and tellurium (Te) in trioctylphosphine (TOP), respectively. 0.125 mmol of zinc acetate, oleylamine, and oleic acid were added to a reactor containing trioctylamine, and then heated at 120 °C under vacuum. After 1 hour, the atmosphere in the reactor was replaced with nitrogen.

[0256] After heating the reactor at 240 °C, a Se / TOP stock solution and a Te / TOP stock solution with a Te / Se molar ratio of 1 / 15 were rapidly injected into it. When the reaction was completed, after rapidly cooling the reaction solution to room temperature, acetone was added to it, and then centrifuged to obtain a precipitate. Then, the precipitate was dispersed in toluene to obtain a ZnSeTe core.

[0257] 1.8 mmol of zinc acetate and oleic acid were placed in a flask containing trioctylamine, and then vacuum-treated at 120 °C for 10 minutes. The inside of the flask was replaced with nitrogen (N2), and then heated to 220 °C. Subsequently, the obtained ZnSeTe core was added to it, and Se / TOP and S / TOP were injected into it. The reaction temperature was set at about 280 °C. Optionally, precursors could be additionally injected at the reaction temperature. When the reaction was completed, the reactor was cooled, and the prepared nanocrystals were centrifuged with ethanol and then dispersed in toluene to obtain ZnSeTe / ZnSeS semiconductor nanoparticles emitting blue light.

[0258] Through photoluminescence analysis, it was found that the semiconductor nanoparticles had a maximum emission peak wavelength of 460 nm.

[0259] Preparation of Zinc-Based Oxide Nanoparticles

[0260] Preparation Example 1: Preparation of zinc magnesium oxide nanoparticles with vanadate (VO3 - ) disposed on the surface of the nanoparticles

[0261] Potassium hydroxide (KOH) was dissolved in ethanol at a concentration of 0.5 M. 14.7 ml of this solution was mixed with 0.5 mmol of potassium vanadate (KVO3, Cas No.: 13769 - 43 - 2) to prepare a first solution.

[0262] Zinc acetate dihydrate (powder) as a zinc precursor and magnesium acetate tetrahydrate (powder) as a magnesium precursor were dissolved in dimethyl sulfoxide in a flask, and then heated to 50 °C and held for 5 minutes to prepare a second solution. The zinc precursor and magnesium precursor in the second solution had a molar ratio of 0.85:0.15 between zinc and magnesium.

[0263] The first solution was mixed with the second solution at 50 °C, and then stirred for 60 minutes while maintaining the temperature. In the mixed solution, according to 100 moles of zinc, the amount of vanadate (VO3 - ) was equivalent to 10 moles. When the stirring was completed, the solution was centrifuged to remove the precipitate and separate the supernatant.

[0264] Subsequently, ethyl acetate was added to the separated supernatant to form a precipitate, which was centrifuged. The obtained particles were washed with ethyl acetate more than 2 times to obtain zinc magnesium oxide nanoparticles.

[0265] The obtained nanoparticles were redistributed / redispersed in ethanol, and then, transmission electron microscopy (TEM) analysis was performed. As a result, the nanoparticles had an average size of about 5 nm to about 10 nm (see Figure 6 ).

[0266] Production Example 2: Preparation of zinc magnesium oxide nanoparticles having vanadate (VO3 - ) on the surface thereof

[0267] The zinc magnesium oxide nanoparticles according to Production Example 2 were produced in the same manner as in Production Example 1, except that: a first solution was prepared as follows: potassium hydroxide (KOH) was dissolved in ethanol at a concentration of 0.4 M, and then, 25 ml of this solution was mixed with 0.425 mmol of potassium vanadate (KVO3, Cas No.: 13769-43-2).

[0268] Production Example 3: Preparation of zinc magnesium oxide nanoparticles having vanadate (VO3 - ) on the surface thereof

[0269] The zinc magnesium oxide nanoparticles according to Production Example 3 were produced in the same manner as in Production Example 1, except that: a first solution was prepared as follows: cesium hydroxide (CsOH) was dissolved in ethanol at a concentration of 0.4 M, and then, 25 ml of this solution was mixed with 0.425 mmol of potassium vanadate (KVO3, Cas No.: 13769-43-2).

[0270] Comparative Example 1: Preparation of zinc magnesium oxide nanoparticles

[0271] Zinc acetate dihydrate (powder) as a zinc precursor and magnesium acetate tetrahydrate (powder) as a magnesium precursor were dissolved in dimethyl sulfoxide in a flask, and then, the mixture was heated to 50 °C and maintained at the same temperature for 5 minutes.

[0272] 0.5 mmol of potassium vanadate (KVO3, Cas No.: 13769-43-2) in powder form was added to the solution, and then, the mixture was stirred for 60 minutes while maintaining the temperature at 50 °C.

[0273] In the solution, the zinc precursor and the magnesium precursor were mixed so as to include zinc and magnesium in a molar ratio of 0.85:0.15, and based on 100 moles of zinc, the amount of vanadate (VO3 - ) was equivalent to 10 moles.

[0274] When the stirring is completed, the solution is centrifuged to remove the precipitate and separate the supernatant. Then, ethyl acetate is added to the separated supernatant to form a precipitate, which is centrifuged. The obtained particles are washed with ethyl acetate more than twice to obtain zinc magnesium oxide nanoparticles.

[0275] Preparation of Comparative Example 2: Preparation of zinc magnesium oxide nanoparticles

[0276] Tetramethylammonium hydroxide (N(CH3)4OH) is dissolved in ethanol at a concentration of 0.5 M to prepare an alkaline solution.

[0277] A 0.1 M rubidium carbonate solution is prepared by dissolving rubidium carbonate (Cas No.: 584-09-8) in ethanol.

[0278] A second solution is prepared by dissolving zinc acetate dihydrate (powder) as a zinc precursor and magnesium acetate tetrahydrate (powder) as a magnesium precursor in dimethyl sulfoxide in a flask. In the second solution, the zinc precursor and the magnesium precursor are mixed so as to include zinc and magnesium in a molar ratio of 0.85:0.15.

[0279] The prepared alkaline solution and rubidium carbonate solution are added to the second solution, and then, stirred at room temperature for 60 minutes. In the mixed solution, the amount of rubidium carbonate is equivalent to 5 moles per 100 moles of zinc.

[0280] When the stirring is completed, ethyl acetate is added to the solution to form a precipitate, which is centrifuged. The obtained particles are washed with ethyl acetate more than twice to obtain zinc magnesium oxide nanoparticles.

[0281] The obtained nanoparticles are redispersed in ethanol, and then, subjected to transmission electron microscopy (TEM) analysis. As a result, the nanoparticles have an average size of about 3 nm to about 4.5 nm.

[0282] Evaluation 1: Characterization of zinc magnesium oxide nanoparticles

[0283] (1) XPS analysis results of the nanoparticles prepared in Preparation Example 1 and Preparation Comparative Example 1

[0284] XPS analysis was performed on the zinc magnesium oxide nanoparticles synthesized in Preparation Example 1 and Preparation Comparative Example 1, and the results are shown in Figure 7 the figures and Table 1.

[0285] Figure 7 is an intensity diagram showing the binding energies of C1s, K2p (left figure) and O1s, V2p (right figure) of XPS. Refer to Figure 7In the O1s peak, the nanoparticles of Preparation Example 1 and Preparation Comparative Example 1 showed metal oxide peaks (affected by Zn-O and Mg-O bonds) at the same position of 532 eV. However, compared with those of Preparation Comparative Example 1, the nanoparticles of Preparation Example 1 showed metal oxide peaks with stronger intensities and also showed V2p peaks with relatively stronger intensities. Additionally, referring to Figure 7 the left figure of, Preparation Comparative Example 1 showed a higher K2p peak caused by the KVO3 powder added for introducing vanadate, but Preparation Example 1 showed a K2p peak with a weaker intensity. And as shown in the right figure, V (vanadium) alone showed a large atomic %.

[0286] These results were also clear from the XPS data in Table 1. Referring to Table 1, Preparation Comparative Example 1 showed a large atomic content (atomic %) of K (potassium), but Preparation Example 1 showed a very small K atomic content. However, Preparation Example 1 showed a V atomic content much larger than the K atomic content. These results confirmed that in the method of Preparation Example 1, the surface of the zinc-magnesium oxide nanoparticles was effectively passivated by vanadate ions, which could change the energy band of the nanoparticles, and thus, in terms of XPS data, change their binding states, as described later. On the other hand, it was confirmed that the surface of the nanoparticles was not effectively passivated by adding KVO3 powder to the synthesized zinc-magnesium nanoparticles of Preparation Comparative Example 1.

[0287] Table 1

[0288] C1s O1s Mg2p Si2p K2p V2p3 Zn2p3 Preparation of Comparative Example 1 21.54 47.09 2.15 6.82 3.06 4.22 15.13 Preparation of Example 1 20.37 45.99 2.77 2.14 0.08 3.64 25.00

[0289] (In Table 1, the unit of each number is atomic %. )

[0290] (2) TEM-EDS analysis and surface scanning results of the nanoparticles of Preparation Example 1

[0291] Figure 8 are the TEM-EDS surface scanning images of the zinc-magnesium oxide nanoparticles with vanadate ions set on their surfaces prepared in Preparation Example 1, and Figure 9 is the figure showing the TEM-EDS analysis results.

[0292] Referring to Figure 8 the EDS surface scanning image, it can be confirmed that the elements of zinc (Zn), magnesium (Mg), oxygen (O) and vanadium (V) overlap well, and the Figure 9 figure showing the obvious peak intensity of the V element confirmed that vanadate ions were well introduced onto the zinc-magnesium oxide nanoparticles.

[0293] (3) UV-Vis absorption spectrometry and DLS analysis of the nanoparticles of Preparation Examples 1 to 3 and Preparation Comparative Example 1

[0294] UV-Vis absorption spectroscopy analysis and DLS analysis were performed on the nanoparticles prepared according to Preparation Examples 1 to 3 and Preparation Comparative Example 1, and the results are shown in Figures 10 to 12 and Table 2.

[0295] Figure 10 is the UV-Vis absorption spectrum of the nanoparticles prepared in Preparation Example 1, Figure 11 is the UV-Vis absorption spectrum of the nanoparticles prepared in Preparation Example 2, and Figure 12 is the UV-Vis absorption spectrum of the nanoparticles prepared in Preparation Example 3.

[0296] Reference Figures 10 to 12 , in the UV-Vis absorption spectroscopy analysis of the nanoparticles of Preparation Examples 1 to 3, the first absorption peak exists in the range of greater than or equal to about 285 nm and less than or equal to about 330 nm. In addition, it can be seen that there are valleys adjacent to the first absorption peak of each of the nanoparticles. These valleys have a valley depth (VD) defined by the following equation in the range of greater than or equal to about 0.01 and less than or equal to about 0.2:

[0297] 1 - (Abs 谷 / Abs 第一 ) = VD

[0298] (wherein, in the above equation, Abs 第一 is the absorption at the first absorption peak, and Abs 谷 is the absorption at the lowest point of the valley adjacent to the first absorption peak.)

[0299] From Figures 10 to 12 the UV-Vis absorption spectra, the first absorption peak (UV peak), the maximum absorption intensity (UV Max), and the x-intercept of each of the nanoparticles were measured, and the DLS average particle diameter of each of the nanoparticles was measured by the DLS analysis method, and the results are shown in Table 2, respectively.

[0300] Table 2

[0301]

[0302] Manufacture of Electroluminescent Diodes

[0303] Example 1 and Comparative Example 1

[0304] The semiconductor nanoparticles of Synthesis Example 1 were dispersed in octane to prepare a semiconductor nanoparticle solution. The zinc oxide nanoparticles of Preparation Example 1 were dispersed in ethanol to prepare a dispersion for the electron transport layer (ETL).

[0305] An electroluminescent diode (ITO / PEDOT (35 nm) / TFB (25 nm) / QD light-emitting layer (20 nm) / ETL (20 nm) / Al (100 nm)) is fabricated according to the following method:

[0306] After surface-treating the glass substrate deposited with ITO with UV-ozone for 15 minutes, a PEDOT:PSS solution (H.C. Starks) is spin-coated thereon, and then, heat-treated at 150 °C for 10 minutes in an air atmosphere and re-heat-treated at 150 °C for 20 to 30 minutes in an N2 atmosphere to form a 35-nm-thick hole injection layer.

[0307] On the hole injection layer, a solution of poly[(9,9-dioctylfluorene-2,7-diyl-co-(4,4'-(N-4-butylphenyl)diphenylamine)] (TFB) (Sumitomo Corp.) is spin-coated, and then, heat-treated at 150 °C for 30 minutes to form a 25-nm-thick hole transport layer.

[0308] On the hole transport layer, the prepared semiconductor nanoparticle solution is spin-coated to form a 20-nm-thick light-emitting layer.

[0309] A solution of Rb2CO3 in ethanol (EtOH) is added to the prepared ETL dispersion and spin-coated on the light-emitting layer, and then, washed and dried with a mixed solution of citric acid and acetic acid in a ratio of 3:1. Subsequently, heat treatment is carried out for 30 minutes to form an electron transport layer (thickness: 20 nm).

[0310] On the electron transport layer, aluminum (Al) is vacuum-deposited to form a 100-nm-thick second electrode, thereby fabricating the electroluminescent diode according to Example 1.

[0311] On the other hand, an electroluminescent diode according to Comparative Example 1 is fabricated in the same manner as above, except that the ETL dispersion is prepared by dispersing the zinc magnesium oxide nanoparticles of Comparative Example 1 in ethanol.

[0312] The electroluminescent properties and lifetimes of the electroluminescent diodes according to Example 1 and Comparative Example 1 are measured, and the results are shown in Table 3.

[0313] Table 3

[0314]

[0315] (In Table 3, the initial V represents the initial driving voltage)

[0316] As shown in Table 3, the device of Comparative Example 1 exhibited a maximum external quantum efficiency (EQE Max) of 5.3%, but the device of Example 1 exhibited a maximum external quantum efficiency (EQE Max) of 12.0%, which was more than twice as high as 5.3%, and furthermore, the maximum luminance (Lum Max) of the device of Example 1 was almost twice as high as the maximum luminance of Comparative Example 1. Additionally, the device of Example 1 exhibited an EQE that was more than twice as high as the EQE of Comparative Example 1 across the entire luminance range of 5,000 to 20,000 nits, and also exhibited a maximum luminance per current (Cd / A Max) that was more than twice as high as that of Comparative Example 1 per current.

[0317] In terms of lifespan, although the device of Comparative Example 1 exhibited a longer T90 than the device of Example 1, the T50 of the device of Example 1 was almost twice as long as the T50 of the device of Comparative Example 1, indicating that although the device of Example 1 took less time to reduce the luminance by 10% compared to the device of Comparative Example 1, the luminance of the device of Example 1 gradually decreased afterwards and took a longer T50 to reduce the luminance by 50% compared to the device of Comparative Example 1.

[0318] Therefore, the electroluminescent diode of Example 1 exhibited much superior performance and lifespan compared to all of the electroluminescent diodes of Comparative Example 1.

[0319] Example 2 and Comparative Example 2

[0320] The electroluminescent diode according to Example 2 was manufactured in the same manner as in Example 1, except that the electron transport layer (ETL) (thickness: 20 nm) was formed as follows: zinc oxide nanoparticles for preparing Example 2 were dispersed in ethanol to prepare a dispersion for the electron transport layer (ETL), the ETL dispersion was spin-coated on the light-emitting layer, and it was immediately heat-treated for 30 minutes without adding an Rb2CO3 ethanol solution and subsequent washing.

[0321] Additionally, the electroluminescent diode according to Comparative Example 2 was manufactured in the same manner as in Example 2, except that: an ETL dispersion was prepared by dispersing the zinc magnesium oxide nanoparticles of Comparative Example 1 in ethanol.

[0322] The electroluminescent properties and lifespan of the electroluminescent diodes were measured, and the results are shown in Table 4.

[0323] Table 4

[0324]

[0325] (In Table 4, T50 is a prediction based on the trend line, and ΔV / hr represents the voltage change per hour.)

[0326] As shown in Table 4, the devices of Example 2 and Comparative Example 2 exhibited similar maximum external quantum efficiency (EQEMax), but the maximum brightness of the device of Example 2 was higher than that of the device of Comparative Example 2. However, in terms of lifetime, the device of Example 2 exhibited much longer T90 and T50 than the device of Comparative Example 2. In addition, compared with the device of Comparative Example 2, in the device of Example 2, the driving voltage at T50 was lower. In other words, the devices of Example 2 and Comparative Example 2 had some similar light-emitting properties, but the device of Example 2 exhibited much superior lifetime characteristics than the device of Comparative Example 2.

[0327] Example 3 and Comparative Example 3

[0328] The electroluminescent diode of Example 3 was fabricated in the same manner as in Example 1, except that: the ETL dispersion was prepared by dispersing the zinc oxide nanoparticles prepared in Example 2 in ethanol.

[0329] The electroluminescent diode of Comparative Example 3 was fabricated in the same manner as in Example 3, except that: the ETL dispersion was prepared by dispersing the zinc magnesium oxide nanoparticles prepared in Comparative Example 1 in ethanol.

[0330] The electroluminescent characteristics and lifetime of the fabricated electroluminescent diodes were measured, and the results are shown in Table 5.

[0331] Table 5

[0332]

[0333] EL Max@650 nits represents the maximum electroluminescent wavelength when the brightness is 650 nits.

[0334] As shown in Table 5, the device of Example 3 exhibited much higher EQEMax value and LumMax than Comparative Example 3. In particular, the device of Example 3 exhibited an EQEMax that was almost twice as high as that of the device of Comparative Example 3, and also exhibited much better maximum brightness per current (Cd / A) and brightness at a current of 5 mA. In other words, compared with the device of Comparative Example 3, the device of Example 3 exhibited much better light-emitting performance.

[0335] Example 4 and Comparative Example 4

[0336] The electroluminescent diode of Example 4 was fabricated in the same manner as in Example 2, except that: the ETL dispersion was prepared by dispersing the zinc oxide nanoparticles prepared in Example 3 in ethanol to form an electron transport layer (ETL).

[0337] The electroluminescent diode of Comparative Example 4 was fabricated in the same manner as in Example 4, except that: the ETL dispersion was prepared by dispersing the zinc magnesium oxide nanoparticles of Comparative Example 1 in ethanol to form an electron transport layer (ETL).

[0338] The electroluminescent properties and lifetime of the fabricated electroluminescent diode were measured, and the results are shown in Table 6.

[0339] Table 6

[0340]

[0341] As shown in Table 6, the device of Example 4 exhibited an EQE Max and Lum Max that were almost twice as high as those of the device of Comparative Example 4. Additionally, compared to the device of Comparative Example 4, the device of Example 4 exhibited a much higher EQE at both 5,000 nits and 20,000 nits, and also exhibited a much higher maximum brightness per current (Cd / A). In other words, the device of Example 4 exhibited much better luminescence performance than the device of Comparative Example 4.

[0342] Example 5 and Comparative Example 5

[0343] The semiconductor nanoparticles of Synthesis Example 1 were dispersed in octane to prepare a semiconductor nanoparticle solution. The zinc oxide nanoparticles of Preparation Example 3 were dispersed in ethanol to prepare a dispersion for the electron transport layer (ETL).

[0344] An electroluminescent diode (ITO / PEDOT (35 nm) / TFB (25 nm) / QD light-emitting layer (28 nm) / ETL (20 nm) / Al (100 nm)) was fabricated according to the following method:

[0345] After surface-treating the glass substrate deposited with ITO with UV-ozone for 15 minutes, a PEDOT:PSS solution (H.C.Starks) was spin-coated thereon, and heat-treated at 150 °C for 10 minutes in an air atmosphere, and then re-heat-treated at 150 °C for 20 to 30 minutes in an N2 atmosphere to form a 35-nm-thick hole injection layer.

[0346] On the hole injection layer, a solution of poly[(9,9-dioctylfluorene-2,7-diyl-co-(4,4'-(N-4-butylphenyl)diphenylamine)] (TFB) (Sumitomo Corp.) was spin-coated, and then heat-treated at 150 °C for 30 minutes to form a 25-nm-thick hole transport layer.

[0347] On the hole transport layer, the prepared semiconductor nanoparticle solution was spin-coated to form a 28-nm-thick light-emitting layer.

[0348] The ETL dispersion was spin-coated on the light-emitting layer and then heat-treated for 30 minutes to form an electron transport layer (thickness: 20 nm).

[0349] On the electron-assisted layer, aluminum (Al) was vacuum-deposited to form a 100-nm-thick second electrode, thereby fabricating the electroluminescent diode according to Example 5.

[0350] The electroluminescent diode of Comparative Example 5 was fabricated in the same manner as in Example 5, except that: the ETL dispersion was prepared by dispersing the zinc magnesium oxide nanoparticles of Comparative Example 1 in ethanol.

[0351] (Table 7)

[0352]

[0353] As shown in Table 7, the devices of Example 5 and Comparative Example 5 exhibited similar EQE Max and Lum Max, but the device of Example 5 exhibited more excellent T90 and T50 lifetimes than the device of Comparative Example 5. In other words, compared with the device of Comparative Example 5, the device of Example 5 exhibited excellent lifetime characteristics.

[0354] Example 6 and Comparative Example 6

[0355] The semiconductor nanoparticles of Synthesis Example 1 were dispersed in octane to prepare a semiconductor nanoparticle solution. The zinc oxide nanoparticles of Preparation Example 3 were dispersed in ethanol to prepare a dispersion for the electron transport layer (ETL).

[0356] According to the following method, an electroluminescent diode (ITO / PEDOT (35 nm) / TFB (25 nm) / QD light-emitting layer (20 nm) / ETL (20 nm) / Al (100 nm)) was fabricated:

[0357] After surface-treating the glass substrate deposited with ITO with UV-ozone for 15 minutes, a PEDOT:PSS solution (H.C. Starks) was spin-coated thereon and heat-treated at 150 °C for 10 minutes in an air atmosphere, and then re-heat-treated at 150 °C for 20 to 30 minutes in an N2 atmosphere to form a 35-nm-thick hole injection layer.

[0358] On the hole injection layer, a solution of poly[(9,9-dioctylfluorene-2,7-diyl-co-(4,4'-(N-4-butylphenyl)diphenylamine)] (TFB) (Sumitomo Corp.) was spin-coated, and then heat-treated at 150 °C for 30 minutes to form a 25-nm-thick hole transport layer.

[0359] On the obtained hole transport layer, the prepared semiconductor nanoparticle solution was spin-coated to form a 20-nm-thick light-emitting layer.

[0360] After adding the solution of Rb2CO3 in EtOH to the ETL dispersion, the mixture was spin-coated on the light-emitting layer, and then, washed and dried with a mixed solution of citric acid and acetic acid with a ratio of 3:1. Subsequently, heat treatment was carried out for 30 minutes to form an electron transport layer (thickness: 20 nm).

[0361] On the obtained electron transport layer, aluminum (Al) was vacuum-deposited to form a 100-nm-thick second electrode, thereby fabricating the electroluminescent diode according to Example 6.

[0362] The electroluminescent diode of Comparative Example 6 was fabricated in the same manner as in Example 6, except that: the ETL dispersion was prepared by dispersing the zinc magnesium oxide nanoparticles of Comparative Example 1 in ethanol.

[0363] Table 8

[0364]

[0365] Table 9

[0366]

[0367] As shown in Table 8, compared with the device of Comparative Example 6, the device of Example 6 exhibited all excellent EQE Max and Lum Max, as well as excellent EQE in the brightness range of 5000 nits to 20000 nits and brightness at a current of 5 mA. In other words, compared with the device of Comparative Example 6, the device of Example 6 exhibited more excellent device performance.

[0368] In addition, as shown in Table 9, compared with the device of Comparative Example 6, the device of Example 6 exhibited a longer T90 and T50 lifetime, and also exhibited a lower driving voltage at T50 and a smaller voltage change per hour (ΔV / hr). In other words, the device of Example 6 exhibited more excellent lifetime characteristics than the device of Comparative Example 6.

[0369] In summary, the device of Example 6 exhibited more excellent device performance and lifetime characteristics than the device of Comparative Example 6.

[0370] Evaluation 2: Calculation and diagram of the energy band alignment of the electroluminescent diode

[0371] The energy band alignments calculated from the UPS (ultraviolet photoelectron spectroscopy) measurement results of the devices of Comparative Example 1 and Examples 2 and 4 are shown in Figure 13 in.

[0372] As Figure 13As shown, when nanoparticles according to an embodiment prepared by disposing vanadate anions (vanadate ions) on the surface of zinc-based oxide nanoparticles and nanoparticles according to Comparative Example 1 that do not have vanadate anions on their surfaces are respectively introduced as materials for forming an electron transport layer (wherein the surface-modified zinc-based oxide nanoparticles of Examples 2 and 4 have a wider bandgap energy than the nanoparticles of Comparative Example 1 and at the same time have a conduction band bottom (CBM) shifted upward), the electroluminescent diode including such surface-modified zinc-based oxide nanoparticles according to the embodiment in the electron transport layer exhibits greatly enhanced electron transport characteristics, and thus, exhibits more excellent performance and lifetime characteristics.

[0373] Although the present disclosure has been described with respect to what are presently considered to be practical embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. Zinc-based oxide nanoparticles, which comprise zinc and an additional metal different from zinc, and which comprise an oxyanion of vanadium (V) on their surface.

2. The zinc-based oxide nanoparticles according to claim 1, wherein the additional metal comprises an alkaline earth metal, zirconium (Zr), tungsten (W), titanium (Ti), yttrium (Y), aluminum (Al), gallium (Ga), indium (In), tin (Sn), cobalt (Co), vanadium (V), or a combination thereof.

3. The zinc-based oxide nanoparticles according to claim 1, wherein the additional metal comprises magnesium.

4. The zinc-based oxide nanoparticles according to claim 1, wherein the molar ratio of zinc and the additional metal in the zinc-based oxide nanoparticles is from 99.9:0.1 to 70:

30.

5. The zinc-based oxide nanoparticles according to claim 1, wherein the oxyanion of vanadium comprises one or more of those represented by the chemical formulas shown in Group 1: (Group 1) VO3 - 、VO4 3- 、V2O7 4- 、V3O9 3- 、V4O 12 4- 、V5O 14 3- 、V5O 15 5- 、V6O 18 6- 、V 10 O 28 6- 、V 12 O 32 4- 、V 13 O 34 3- 、V 18 O 42 12- 、VO2 + 、VO2(OH) - 2、VO3(OH) 2- 。 6. The zinc-based oxide nanoparticles according to claim 1, wherein the zinc-based oxide nanoparticles have a particle size of greater than or equal to 1 nm and less than or equal to 30 nm.

7. A method for preparing the zinc-based oxide nanoparticles according to any one of claims 1 to 6, comprising dissolving a compound comprising an oxyanion of vanadium in a first organic solvent in which an alkaline compound is dissolved to obtain a first solution, dissolving a zinc precursor and a precursor of an additional metal different from zinc in a second organic solvent to obtain a second solution, and mixing the first solution and the second solution to react with each other.

8. The method according to claim 7, wherein the compound comprising an oxyanion of vanadium is a salt comprising an oxyanion of vanadium and an alkali metal cation.

9. The method according to claim 7, wherein the alkaline compound comprises an organic base comprising an organic group, an inorganic base comprising an alkali metal or an alkaline earth metal, or a combination thereof.

10. The method according to claim 7, wherein the first organic solvent and the second organic solvent each independently comprise a C1 to C10 alcohol solvent, dimethyl sulfoxide, a C3 to C15 hydrocarbon solvent, or a combination thereof, and the first organic solvent and the second organic solvent are different from each other.

11. The method according to claim 7, wherein mixing the first solution and the second solution to react with each other comprises heating and stirring the first solution and the second solution.

12. The method according to claim 7, wherein the method further comprises, after mixing the first solution and the second solution to react with each other, adding a third solvent immiscible with the first organic solvent and the second organic solvent to the reaction mixture of the first solution and the second solution to form a precipitate.

13. An electroluminescent diode, comprising a first electrode and a second electrode facing each other, a light-emitting layer between the first electrode and the second electrode and comprising semiconductor nanoparticles, and an electron transport layer between the light-emitting layer and the second electrode Wherein the electron transport layer comprises zinc-based oxide nanoparticles according to any one of claims 1 to 6.

14. The electroluminescent diode according to claim 13, wherein the thickness of the electron transport layer is greater than or equal to 5 nm and less than or equal to 60 nm.

15. The electroluminescent diode according to claim 13, wherein the electroluminescent diode further comprises a hole auxiliary layer between the first electrode and the light-emitting layer.

16. A display device comprising the electroluminescent diode according to any one of claims 13 to 15.

Images