Ink composition for electron transport layer, electron transport layer manufactured using the same, and light-emitting device including the same

Abstract

The present invention relates to an ink composition for an electron transport layer, an electron transport layer formed therefrom, and a light-emitting device employing the same. The ink composition for an electron transport layer of the present invention has excellent ejection reproducibility by mixing three or more specific solvents, thereby enabling mass production of the electron transport layer.

Description

Technology Field

[0001] The present invention provides an ink composition for an electron transport layer, an electron transport layer manufactured using the same, and a light-emitting device employing the same. Specifically, the invention provides an ink composition for an electron transport layer that is used in an inkjet printing device and has excellent reproducibility, an electron transport layer manufactured using the same, and a light-emitting device employing the same. Background Technology

[0002] The Electron Transport Layer (ETL) is used as an essential component in the development of Quantum Dot Light-Emitting Diodes (QD-LEDs), which primarily contain Quantum Dots (QDs). While ETLs generally exist in the form of conductive polymers or organic materials, metal oxides are widely utilized. In particular, metal oxide-based ETLs are attracting attention as a technology that provides not only high efficiency but also excellent stability, and active development is currently underway.

[0003] Recently, as QD-LED displays have begun to establish themselves in the market, the demand for metal oxide-based electron transport layers has been rapidly increasing. Accordingly, research is actively being conducted to consider the feasibility of commercialization and mass production, and inkjet printing is attracting attention as an important alternative in the manufacturing process of electron transport layers.

[0004] Inkjet printing offers significant advantages in terms of process simplification, improved manufacturing efficiency, and reduced material waste, but research on electron transport layers has been relatively insufficient to date, and there are technical limitations in terms of inks for inkjet printing, process stability, and reproducibility.

[0005] In particular, ink compositions for inkjet printing are known to have various problems, such as reproducibility issues, nozzle clogging issues, drying speed issues, and film formation issues.

[0006] Therefore, in order to prevent nozzle clogging of the ink composition, ensure reproducibility, improve stability, and resolve compatibility issues, it is possible to achieve mass production using inkjet printing and realize a high-quality electron transport layer. Prior art literature

[0007] Korean Published Patent Application No. 10-2023-0011528 (January 25, 2023) The problem to be solved

[0008] To overcome the above-mentioned problems, the present invention provides an ink composition for an electron transport layer with excellent reproducibility and an electron transport layer manufactured using the same.

[0009] In addition, the present invention provides a light-emitting device employing an electron transport layer prepared from the ink composition of the present invention. means of solving the problem

[0010] The present invention provides an ink composition for an electron transport layer in which nozzle clogging is prevented and reproducibility is ensured by employing a specific solvent.

[0011] The ink composition of the present invention is, Metal oxide nanoparticles; and It includes three or more different glycol ether-based solvents.

[0012] Preferably, a glycol ether-based solvent according to one embodiment of the present invention can be represented by the following chemical formula 1.

[0013] [Chemical Formula 1]

[0014] R 1 -(OR) n -OR 2

[0015] (In the above chemical formula 1,

[0016] R is a C2-C10 alkylene, and

[0017] R 1 and R 2 are independently hydrogen or C1-C10 alkyl, and

[0018] n is an integer from 1 to 10.

[0019] In Formula 1 according to one embodiment of the present invention, R is a C2-C7 alkylene, and R 1 and R 2 are independently hydrogen or C1-C7 alkyl, and R 1 and R 2 This excludes cases where it is hydrogen, and n can be an integer from 1 to 5.

[0020] A glycol ether-based solvent according to one embodiment of the present invention can be represented by the following chemical formula 2, the following chemical formula 3, and the following chemical formula 4.

[0021] [Chemical Formula 2]

[0022] R 11 -(OCH2CH2) p -OH

[0023] [Chemical Formula 3]

[0024] H-(OCH2CH2) q -OH

[0025] [Chemical Formula 4]

[0026] R 12 -(OCH2CR 13 H) r -OH

[0027] (In the above chemical formulas 2 to 4,

[0028] The above R 11 and R 12 are independently C1-C7 alkyls, and

[0029] R 13 It is a C1-C5 alkyl, and

[0030] p and q are independent integers from 2 to 5, and r is an integer from 1 to 5.

[0031] Preferably, a solvent according to one embodiment of the present invention comprises compounds represented by chemical formulas 2, 3, and 4, respectively, and the compounds represented by chemical formulas 2, 3, and 4 may be included in a volume ratio of 4 to 8: 0.5 to 3: 0.5 to 3.5.

[0032] A glycol ether-based solvent according to one embodiment of the present invention may have a boiling point of 150°C or higher, and specifically may be di(ethylene glycol)n-hexyl ether, propylene glycol n-butyl ether, tri(ethylene glycol), tri(ethylene glycol) monobutyl ether, tri(ethylene glycol) monomethyl ether, tri(ethylene glycol) dimethyl ether, tri(propylene glycol) monoethyl ether, tri(propylene glycol) butyl ether, tri(propylene glycol) monomethyl ether, di(propylene glycol)n-butyl ether, di(propylene glycol)n-butyl ether, di(ethylene glycol), di(ethylene glycol)n-butyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol n-propyl ether, or di(propylene glycol)n-propyl ether.

[0033] An electron transport layer ink composition according to one embodiment of the present invention may contain 5 to 30 weight percent of metal oxide nanoparticles, a surface tension of 50 dyn / cm or less, and a viscosity of 20 cP or less.

[0034] A metal oxide nanoparticle according to one embodiment of the present invention may be an oxide comprising a transition metal and an alkaline earth metal, and preferably may be a Zn-containing oxide.

[0035] An ink composition for an electron transport layer according to one embodiment of the present invention may be used for inkjet printing.

[0036] In addition, the present invention provides an electron transport layer manufactured using an ink composition for an electron transport layer according to one embodiment of the present invention.

[0037] In addition, the present invention provides a light-emitting device employing an electron transport layer according to one embodiment of the present invention. Effects of the invention

[0038] The ink composition for the electron transport layer of the present invention uses three or more glycol ether-based solvents, thereby significantly increasing the ejection reproducibility, particularly in the inkjet printing process.

[0039] Therefore, the ink composition for the electron transport layer of the present invention enables mass production of a high-quality electron transport layer through an inkjet printing process.

[0040] The ink composition for the electron transport layer of the present invention can obtain a uniform film by mixing and using three or more glycol ether-based solvents, and the electron transport layer using this has excellent characteristics.

[0041] Therefore, a light-emitting device employing an electron transport layer formed using an ink composition for an electron transport layer according to one embodiment of the present invention has excellent light-emitting characteristics. Brief explanation of the drawing

[0042] FIG. 1 is a diagram showing the absorption spectra of ink compositions for electron transport layers prepared in Example 1 and Comparative Examples 1 to 3 of the present invention. FIG. 2 is a drawing showing the discharge images of ink compositions for an electron transport layer prepared in Examples 1 to 3 and Comparative Examples 1 to 6 of the present invention. Specific details for implementing the invention

[0043] The terms used herein are merely for describing exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to indicate the presence of the implemented features, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, steps, components, or combinations thereof.

[0044] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0045] In the present invention, "alkyl" refers to a linear or branched saturated monovalent hydrocarbon radical. "alkyl" also includes both linear and branched alkyls unless otherwise specified. In one embodiment, the alkyl is a linear saturated monovalent hydrocarbon radical having 1 to 10 (C1-10), 1 to 7 (C1-7), 1 to 5 (C1-5), or 1 to 4 (C1-4) carbon atoms, or a branched saturated monovalent hydrocarbon radical consisting of 3 to 10 (C3-10), 3 to 7 (C3-7), or 3 to 5 (C3-5) carbon atoms. As used in the present invention, linear C1-6 and branched C3-6 alkyl groups are also referred to as "lower alkyls."

[0046] In the present invention, "alkylene" refers to a linear or branched saturated divalent hydrocarbon radical. Like the alkyl, it includes both linear and branched alkylenes unless otherwise specified. In one embodiment, the alkylene is a linear saturated monovalent hydrocarbon divalent radical having 1 to 10 (C2-10), 1 to 7 (C2-7), 1 to 5 (C2-5), or 1 to 4 (C2-4) carbon atoms, or a branched saturated monovalent hydrocarbon divalent radical consisting of 3 to 10 (C3-10), 3 to 7 (C3-7), or 3 to 5 (C3-5) carbon atoms.

[0047] In the present invention, "glycol ether-based" refers to a compound having both an ether and an alcohol functional group, which can be prepared by the reaction of an alcohol with an alkylene oxide (e.g., ethylene oxide or propylene oxide, etc.) or by the reaction of a glycol (e.g., ethylene glycol, propylene glycol) with an alcohol, etc.

[0049] The present invention will be described in detail below.

[0050] The present invention provides an ink composition for an electron transport layer with excellent reproducibility, enabling mass production of high-quality electron transport layers.

[0051] The ink composition for an electron transport layer of the present invention is, Metal oxide nanoparticles; and It includes three or more different glycol ether-based solvents.

[0052] Specifically, the ink composition for the electron transport layer of the present invention is used by mixing three or more different types of glycol ether-based solvents, thereby having excellent physical properties for use in an inkjet printing process and significantly improving ejection reproducibility.

[0053] A glycol ether-based solvent according to one embodiment of the present invention is not limited but can be represented by the following chemical formula 1.

[0054] [Chemical Formula 1]

[0055] R 1 -(OR) n -OR 2

[0056] (In the above chemical formula 1,

[0057] R is a C2-C10 alkylene, and

[0058] R 1 and R 2 are independently hydrogen or C1-C10 alkyl, and

[0059] n is an integer from 1 to 10.

[0060] In Formula 1 according to one embodiment of the present invention, R is a C2-C7 alkylene, and R 1 and R 2 are independently hydrogen or C1-C7 alkyl, and R 1 and R 2 This excludes cases where it is hydrogen, and n can be an integer from 1 to 5.

[0061] Preferably, in the above chemical formula 1, R is a C2-C3 alkylene, and R 1 and R 2 are independently hydrogen or C1-C7 alkyl, and R 1 and R 2 This excludes cases where it is hydrogen, and n can be an integer from 1 to 4.

[0062] A glycol ether-based solvent according to one embodiment of the present invention can be represented by the following chemical formula 2, the following chemical formula 3, and the following chemical formula 4.

[0063] [Chemical Formula 2]

[0064] R 11 -(OCH2CH2) p -OH

[0065] [Chemical Formula 3]

[0066] H-(OCH2CH2) q -OH

[0067] [Chemical Formula 4]

[0068] R 12 -(OCH2CR 13 H) r -OH

[0069] (In the above chemical formulas 2 to 4,

[0070] The above R 11 and R 12 are independently C1-C7 alkyls, and

[0071] R 13 It is a C1-C5 alkyl, and

[0072] p and q are independent integers from 2 to 5, and r is an integer from 1 to 5.

[0073] Preferably, a glycol ether-based solvent according to one embodiment of the present invention may each include a compound represented by the chemical formulas 2, 3, and 4.

[0074] That is, it may include one or more compounds represented by Chemical Formula 2, one or more compounds represented by Chemical Formula 3, and one or more compounds represented by Chemical Formula 4, and specifically, may essentially include three types of solvents such as one compound of Chemical Formula 2, one compound represented by Chemical Formula 3, and one compound represented by Chemical Formula 4.

[0075] The mixing ratio of one compound of Chemical Formula 2, one compound represented by Chemical Formula 3, and the compound represented by Chemical Formula 4 may be included in a volume ratio of 4 to 7: 0.5 to 3: 0.5 to 3.5, and may be included in a volume ratio of 5 to 7: 0.5 to 2.5: 1 to 3.

[0076] A glycol ether-based solvent according to one embodiment of the present invention may have a boiling point of 150°C or higher, preferably 150°C to 350°C, and preferably 150°C to 300°C.

[0077] A glycol ether-based solvent according to one embodiment of the present invention is not limited to, but may be di(ethylene glycol)n-hexyl ether, propylene glycol n-butyl ether, tri(ethylene glycol), di(propylene glycol)n-butyl ether, tri(ethylene glycol), tri(ethylene glycol) monobutyl ether, tri(ethylene glycol) monomethyl ether, tri(ethylene glycol) dimethyl ether, tri(propylene glycol) monoethyl ether, tri(propylene glycol) butyl ether, tri(propylene glycol) monomethyl ether, di(propylene glycol)n-butyl ether, di(ethylene glycol), di(ethylene glycol)n-butyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol n-propyl ether, or di(propylene glycol)n-propyl ether.

[0078] The metal oxide nanoparticles according to one embodiment of the present invention can be used without limitation as long as they are materials used in the electron transport layer in the technical field of the present invention.

[0079] The metal oxide nanoparticles may be oxides containing transition metals, preferably oxides containing transition metals and alkaline earth metals, and may be oxides containing zinc.

[0080] For example, conventional metal oxide nanoparticles used as dopant materials may be used, and non-limiting examples thereof may include ZnMgO, In2S3, Cu2S, Ag2S, ZnSe, ZnS, ZnO, ZnTe, ZnSe, TiO2, SnO2, ZnS, or forms in which at least one element is added to the aforementioned components.

[0081] To explain with a more specific example, the metal oxide nanoparticles are Zn-containing metal oxide nanoparticles, and more specifically, may be alloyed with a metal (M) capable of increasing the ZnO bandgap [ZnMO(M = Ca, Mg)]. The metal (M) capable of increasing the ZnO bandgap is Ca or Mg. These metals have ionic radii similar to those of Zn, so they can be incorporated into the ZnO lattice without inducing stress and can increase the ZnO bandgap by reducing the size of ZnO. Preferably, it may be ZnMgO.

[0082] As described above, when the bandgap of ZnO nanoparticles is increased through alloying and applied as an electron transport layer, an upshift occurs at the conduction band minimum (CBM) level. This brings about energy proximity between the CBM of the quantum dot emissive layer and the electron transport layer, thereby lowering the electron energy barrier and consequently promoting electron injection into the quantum dot region. Consequently, light-emitting devices equipped with an electron transport layer containing alloyed ZnO nanoparticles exhibit superior brightness and efficiency compared to devices equipped with an electron transport layer containing ZnO nanoparticles, and can achieve higher luminous efficiency even at lower driving voltages. In other words, applying the aforementioned electron transport layer reduces the electron injection barrier, thereby enabling a reduction in QLED driving voltage, improved efficiency, and further power consumption. A decrease in the device's driving voltage leads to a reduction in heat generation, which in turn allows for an expected increase in lifespan.

[0083] A metal oxide nanoparticle according to one embodiment of the present invention may have an organic ligand having a hydrophilic moiety attached to part or all of its surface. The organic ligand may be any known in the art without limitation and may include, for example, C5 to C20 alkyl carboxylic acids, C5 to C20 alkenyl carboxylic acids or C5 to C20 alkynyl carboxylic acids; pyridine; mercapto alcohol; thiol; phosphine; phosphine oxide; primary amine; secondary amine; or combinations thereof. Specifically, the organic ligand may include at least two hydrophilic moietyes selected from carboxyl groups and hydroxyl groups, and more specifically, a ligand material having the aforementioned carboxyl group and / or hydroxyl group hydrophilic moiety at both ends of the molecular structure is preferred. Non-limiting examples of available organic ligands include mono(2-acryloyloxyethyl) succinate (MAES), mono-2-(methacryloyloxy)ethylsuccinate (MMES), 2-(2-methoxyethoxy)acetic acid (MEAA), or mixtures thereof.

[0084] An organic ligand according to one embodiment of the present invention is attached to the surface of metal oxide nanoparticles and can play a role in ensuring film uniformity by exhibiting an effect that improves the Coffee Ring Effect (CRF) during inkjet ejection. Here, the Coffee Ring Effect (CRF) refers to a phenomenon in which colloidal particles move to the edges due to hydrodynamic effects during the evaporation process, resulting in a non-uniform density distribution of particles. That is, the smaller the particle size, the further it can move to the edges, so small particles are distributed closer to the edges of the droplet, while relatively large particles are distributed closer to the center of the droplet. By introducing a predetermined organic ligand and / or a monomer described below into an ink composition for an electron transport layer according to one embodiment of the present invention, the coffee ring effect can be minimized and the uniformity of the film can be maximized.

[0085] The content of the organic ligand is not particularly limited and can be appropriately adjusted within the content range known in the art. Considering dispersibility and membrane uniformity, it may be included in a range of 0.0001 to 10 mol relative to 1 mol of the metal, such as zinc (Zn), contained in the metal oxide nanoparticles, and specifically, in a range of 0.001 to 5 mol.

[0086] In addition, metal oxide nanoparticles according to one embodiment of the present invention may include a polymer coating layer formed on part or all of the surface. The composition of the polymer coating layer is not particularly limited, and conventional polymers known in the art may be applied. For example, it may be formed using acrylic or methacrylic polymers known in the molecule or polyethylene glycol without limitation. Specifically, it is preferable to use a (meth)acrylic polymer containing polar functional groups within the molecule in a predetermined range and / or polyethylene glycol having a hydrophilic moiety. These functional groups may react with certain chemicals, and this reaction is used to induce a polymer coating on the surface of the metal oxide nanoparticles.

[0087] Conventional (meth)acrylate monomers known in the art may be used as the monomer (monomer) forming the above polymer coating layer. However, they are not particularly limited thereto. Non-limiting examples of usable monomers include monofunctional (meth)acrylate monomers such as caprolactone acrylate, ortho-phenylphenol ethoxyacrylate, lauryl acrylate, isodecyl acrylate, tetrahydrofurfuryl acrylate, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, ethoxyethoxyethyl acrylate, isobornyl (meth)acrylate, alkoxylated tetrahydrofurfuryl (meth)acrylate, and 2-ethylhexyl acrylate; Ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyolefin glycol di(meth)acrylate, ethoxylated polypropylene glycol di(meth)acrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, 2-hydroxy-1,3-dimethacryloxypropane, dioxane glycol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, glycerin di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, Di(meth)acrylates having an aromatic ring, such as 2-methyl-1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, butylethylpropanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, triethylene glycol diacrylate, and trichlorodecane dimethanol diacrylate;Trifunctional (meth)acrylate monomers such as ethoxylated glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane (ethylene oxide) modified triacrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane (propylene oxide) modified triacrylate, and tris(2-hydroxyethyl)isothiaurate triacrylate; tetrafunctional (meth)acrylate monomers such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate (tetrafunctional monomer), or mixtures thereof; There are pentafunctional (meth)acrylate monomers such as dipentaerythritol pentaacrylate, propionic acid-modified dipentaerythritol pentaacrylate, dipentaerythritol pentamethacrylate, propionic acid-modified dipentaerythritol pentamethacrylate, or mixtures thereof; and hexafunctional (meth)acrylate monomers such as dipentaerythritol hexaacrylate, caprolactone-modified dipentaerythritol hexaacrylate, dipentaerythritol hexamethacrylate, caprolactone-modified dipentaerythritol hexamethacrylate, or mixtures thereof.

[0088] The above polymer coating layer is formed on the surface of metal oxide nanoparticles, and can ensure film uniformity by improving the Coffee Ring Effect (CRF) during inkjet ejection.

[0089] The content of metal oxide nanoparticles included in the ink composition for an electron transport layer according to one embodiment of the present invention is not particularly limited and can be appropriately adjusted within a range known in the art.

[0090] The ink composition for the electron transport layer of the present invention may use at least one additive known in the art without limitation within a range that does not impede the effect of the invention.

[0091] Examples of usable additives include light stabilizers, thermal stabilizers, photoinitiation promoters, thermal initiation promoters, smoothing agents, toughening agents, thickeners, coloring agents, reactive diluents, coupling agents, dispersants, solvents, etc. These may be used alone or in combination of two or more. In this case, the content of the additives can be appropriately adjusted within a range known in the art and is not particularly limited. For example, at least one of the above additives may be included in an amount of 0.01 to 5 weight%, specifically 0.01 to 2 weight%, based on the total weight of the ink composition for the electron transport layer.

[0092] An ink composition for an electron transport layer according to one embodiment of the present invention can be prepared by mixing and stirring, in accordance with conventional methods known in the art, a ligand, a monomer, and other additives that are formulated as necessary in addition to the aforementioned metal oxide nanoparticles and three or more glycol ether-based solvents.

[0093] Specifically, the preparation of an ink composition for an electron transport layer according to one embodiment of the present invention may comprise: a first step of preparing metal oxide nanoparticles by adding a basic substance to a reaction solution in which a zinc-containing compound and a metal-containing compound capable of increasing the ZnO bandgap are dissolved in a solvent, and then precipitating the result; and a second step of preparing an ink composition for an electron transport layer by adding three or more types of glycol ether-based solvents to the prepared metal oxide nanoparticle dispersion and then mixing.

[0094] In the first step above, the zinc-containing compound and the metal-containing compound are not particularly limited, and materials known in the art may be used without limitation. For example, zinc acetate dihydrate, zinc chloride, zinc nitrate, zinc sulfate, magnesium acetate tetrahydrate, etc. may be used.

[0095] In addition, basic substances are not particularly limited, and substances known in the art may be used without limitation. For example, at least one substance selected from the group consisting of tetramethyl ammonium hydroxide (TMAH), potassium hydroxide (KOH), sodium hydroxide (NaOH), and amines may be used.

[0096] In the first step above, the metal oxide nanoparticles may further include an organic ligand. In this case, the organic ligand may be included in a range of 0 to 10 weight% relative to the total weight (e.g., 100 weight%) of the metal oxide nanoparticles, and specifically, may be included in an amount greater than 0 and less than or equal to 5 weight%.

[0097] Additionally, in the first step, the metal oxide nanoparticles may further comprise a polymer. Such a polymer may comprise a conventional hydrophilic moiety known in the art, and, for example, may comprise at least two hydrophilic moietyes selected from carboxyl groups and hydroxyl groups. Examples of usable polymers include Polyethyleneglycol (PEG) having carboxyl groups. The polymer may be included in a range of 0 to 10 weight percent relative to the total weight (e.g., 100 weight%) of the metal oxide nanoparticles, but is not particularly limited thereto. When the metal oxide nanoparticles contain an organic ligand and a polymer, this becomes a dispersion of metal oxide nanoparticles.

[0098] After adding a basic substance, the temperature is raised to 55 to 65°C, and then the nanoparticles are precipitated by stirring and reacting at a uniform rate for approximately 0.5 to 2 hours. Then, the metal oxide nanoparticles are separated using the properties of the solvent and non-solvent, and the metal oxide nanoparticles are prepared.

[0099] Non-limiting examples of solvents that can be used at this time include hexane, benzene, xylene, toluene, octane, chloroform, chlorobenzene, tetrahydrofuran (THF), methylene chloride, 1,4-dioxane, diethyl ether, cyclohexane, dichlorobenzene, etc., and these may be used individually or in combination of two or more. In addition, non-limiting examples of non-solvents that can be used include acetone, ethanol, methanol, butanol, propanol, isopropyl alcohol, tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, etc., and these may be used individually or in combination of two or more.

[0100] In the second step above, the mixing ratio between the metal oxide nanoparticles and the at least three types of solvents may be 1 to 30:99 to 70 by weight. However, this is not particularly limited thereto and can be appropriately adjusted within a range known in the art.

[0101] In addition, the mixing method is not particularly limited, and for example, conventional homodispersers, homomixers, universal mixers, planetary mixers, kneaders, three-roll mixers, etc. known in the field may be used.

[0102] The ink composition for an electron transport layer prepared in the second step above may further include at least one of a monomer and a dispersant. In this case, the monomer and / or dispersant may be included in a range of 0 to 10 volume% relative to 100 volume% of the ink composition for an electron transport layer, and specifically, may be included in a range greater than 0 and less than or equal to 5 volume%.

[0103] The ink composition for an electron transport layer of the present invention, configured as described above, can provide excellent workability and processability as viscosity and vapor pressure characteristics are optimized, and in particular, it can be usefully applied to inkjet printing methods as it ensures uniformity and stability in terms of inkjet ejection, the shape of the ejected ink, and the shape of the ink formed on the substrate.

[0104] An ink composition for an electron transport layer according to one embodiment of the present invention may contain 1 to 30 weight% of metal oxide nanoparticles, preferably 1 to 20 weight%.

[0105] An ink composition for an electron transport layer according to one embodiment of the present invention may have a surface tension of 50 dyn / cm or less, a viscosity of 20 cP or less, preferably 40 dyn / cm or less, a viscosity of 3 to 20 cP, more preferably 20 to 40 dyn / cm, a viscosity of 5 to 20 cP, and even better 25 to 35 dyn / cm, and a viscosity of 5 to 25 cP.

[0106] In addition, the present invention provides an electron transport layer prepared from an ink composition for an electron transport layer according to one embodiment of the present invention.

[0107] In addition, the present invention provides a light-emitting device employing an electron transport layer according to one embodiment of the present invention.

[0108] A light-emitting element according to one embodiment of the present invention comprises: a first electrode; a second electrode disposed opposite to the first electrode; a light-emitting layer disposed between the first electrode and the second electrode; a hole transport layer disposed between the first electrode and the light-emitting layer; and an electron transport layer disposed between the light-emitting layer and the second electrode and formed by inkjet printing an ink composition for an electron transport layer described above. If necessary, the light-emitting element may further comprise at least one of a hole injection layer and an electron injection layer.

[0109] Hereinafter, the present invention is described using a quantum dot light-emitting device as an example. However, the invention is not limited thereto and can be applied to various types of light-emitting devices, such as organic light-emitting devices.

[0110] The first electrode is positioned on a substrate. This substrate may be a transparent, flat-surfaced glass substrate or a transparent plastic substrate. The substrate can be used after ultrasonically cleaning with a solvent such as isopropyl alcohol, acetone, or methanol to remove contaminants and then treating it with UV-ozone.

[0111] The first electrode may be provided as an anode. For example, the anode may be composed of a metal, a metal oxide suitable for each transparent / opaque condition, or other non-oxide inorganic materials. For bottom light emission, the first electrode may be composed of a transparent conductive metal such as transparent ITO, IZO, ITZO, or AZO.

[0112] The hole injection layer and the hole transport layer are located on the first electrode. These hole injection layer and the hole transport layer facilitate hole injection from the first electrode and serve to transport holes to the emissive layer. The hole transport layer can be an organic or inorganic material. If it is an organic material, it may be CBP (4,4'-N,N'-dicarbazole-biphenyl), α-NPD (N,N'-diphenyl-N,N'-bis(1=naphtyl)-1,1'-biphenyl-4,4''-diamine), TCTA (4,4',4''-tris(N-carbazolyl)-triphenylamine), TFB, or DNTPD (N,N'-di(4-(N,N'-diphenyl-amino)phenyl)-N.N'-diphenylbenzidine). If it is an inorganic material, it may be composed of an oxide of NiO or MoO3. For example, the hole injection layer may be provided as poly(ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). In addition, the hole transport layer may be provided as TFB or poly(9-vinlycarbazole) (PVK), etc.

[0113] The emissive layer is located on the hole transport layer, and quantum dots can be provided as the emissive layer. For example, the emissive layer can be formed by coating the hole transport layer with a dispersion solution in which quantum dots are dispersed in a solvent, and then volatilizing the solvent.

[0114] Examples of the above coating methods include dropcasting, spin coating, dip coating, spray coating, flow coating, screen printing, or inkjet printing, which can be used individually or in combination.

[0115] Quantum dots (QDs) constituting the light-emitting layer can refer to nano-sized semiconductor materials. Atoms form molecules, and molecules form aggregates of small molecules called clusters to form nanoparticles; when these nanoparticles exhibit semiconductor properties, they are called quantum dots. When the quantum dots receive energy from the outside and reach an excited state, they emit energy according to the corresponding energy bandgap of the quantum dots themselves.

[0116] These quantum dots may have a homogeneous single-layer structure; a multilayer structure such as a core-shell form, a gradient structure, etc.; or a mixed structure thereof.

[0117] A single-layer quantum dot (QD) or a multilayer shell component, excluding the core and / or surface (outermost layer) constituting the multilayer structure, can be freely selected from the group II-VI compounds, group III-V compounds, group IV-VI compounds, group IV elements, group IV compounds, and combinations thereof described below, respectively. In the case where the shell is multilayer, each layer may contain different components, such as (quasi)metal oxides, and may be freely composed of the components exemplified below.

[0118] For example, group II-VI compounds are diatomic compounds selected from the group consisting of CdO, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, MgSe, MgS, and mixtures thereof; ternary compounds selected from the group consisting of CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and mixtures thereof; and may be selected from the group consisting of four element compounds selected from the group consisting of CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe and mixtures thereof.

[0119] As another example, group III-V compounds may be selected from the group consisting of diatomic compounds selected from GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; ternary compounds selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, and mixtures thereof; and quaternary compounds selected from the group consisting of GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and mixtures thereof.

[0120] As another example, group IV-VI compounds may be selected from the group consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe and mixtures thereof; ternary compounds selected from the group consisting of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe and mixtures thereof; and quaternary compounds selected from the group consisting of SnPbSSe, SnPbSeTe, SnPbSTe and mixtures thereof.

[0121] As another example, the Group IV element may be selected from the group consisting of Si, Ge, and mixtures thereof. The Group IV compound may be a binary compound selected from the group consisting of SiC, SiGe, and mixtures thereof.

[0122] The aforementioned binary, ternary, or quaternary compounds may exist within the particle at a uniform concentration, or they may exist within the same particle with concentration distributions divided into partially different states. Additionally, they may have a core / shell structure in which one quantum dot surrounds another. The interface between the core and the shell may have a concentration gradient in which the concentration of the element present in the shell decreases toward the center.

[0123] The shape of the quantum dots is not particularly limited as long as it is a shape commonly used in the field. For example, shapes such as spherical, rod-shaped, pyramidal, disc-shaped, multi-arm, or cubic nanoparticles, nanotubes, nanowires, nanofibers, and nanoplate particles may be used.

[0124] In addition, the size of the quantum dots is not particularly limited and can be appropriately adjusted within the usual range known in the field.

[0125] For example, the average particle size (D50) of the quantum dot may be 1 to 20 nm, specifically 2 to 15 nm. When the particle size of the quantum dot is controlled to a range of approximately 1 to 20 nm in this way, light of a desired color can be emitted. For example, blue-emitting quantum dots (QDs) may be used in the present invention. As a specific example, as blue-emitting quantum dots (Quantum dots), Cd-based II-VI group QDs (e.g., CdZnS, CdZnSSe, CdZnSe, CdS, CdSe), non-Cd-based II-VI group QDs (e.g., ZnSe, ZnTe, ZnS, HgS), or non-Cd-based III-V group QDs (e.g., InP, InGaP, InZnP, GaN, GaAs, GaP) may be used.

[0126] The electron transport layer facilitates electron injection from the second electrode and serves to transfer electrons to the light-emitting layer. This electron transport layer includes metal alloyed Zn-containing metal oxide nanoparticles capable of increasing the ZnO bandgap.

[0127] For example, the electron transport layer can be formed by inkjet printing the aforementioned ink composition for the electron transport layer onto the light-emitting layer and then volatilizing the solvent. The electron transport layer of the present invention may be provided as a single-layer structure that also serves as an electron injection layer, or the electron injection layer may be formed as a stacked structure separately.

[0128] The second electrode is located on the electron injection / transport layer and can be provided as a cathode. The second electrode may be composed of metals, metal oxides suitable for each transparent / opaque condition, or other non-oxide inorganic materials. In particular, the second electrode may be a metal electrode having a low work function and excellent internal reflectivity to facilitate electron injection into the LUMO level of the light-emitting layer. Specifically, metals with a small work function to facilitate electron injection, such as I, Ca, Ba, Ca / Al, LiF / Ca, LiF / Al, BaF2 / Al, BaF2 / Ca / Al, Al, Mg, Ag:Mg alloys, etc., may be used.

[0129] As described above, the light-emitting device according to the embodiment is described as a quantum dot light-emitting device. However, unlike what is described above, the light-emitting device may be of various types. For example, the light-emitting device may be an organic light-emitting device. Furthermore, although the electron injection / transport layer is described as being composed of a single material in the embodiment, the electron injection layer and the electron transport layer may be provided separately.

[0131] The present invention will be described in detail below through examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited by the following examples.

[0132] <Preparation Example 1> Preparation of metal oxide nanoparticles

[0133] 8.5 mmol (1.756) g of zinc acetate dehydrate (Zn(OAc)22H2O) and 1.5 mmol (0.321) g of magnesium acetate tetrahydrate were dissolved in 40 ml of dimethyl sulfoxide (DMSO), and then 10 mmol (1.812) g of tetramethyl ammonium hydroxide pentahydrate (TMAH), a basic substance, was added. The mixture was heated to 60°C and reacted for approximately 1 hour. The prepared nanoparticles were purified with acetone-hexane, separated by centrifugation for 5 minutes to remove the solution layer, thereby obtaining zinc magnesium oxide nanoparticles.

[0135] <Comparative Example 1> Preparation of an ink composition for an electron transport layer

[0136] zinc magnesium oxide nanoparticles prepared in the preparation example An ink composition for an electron transport layer was prepared by dispersing zinc magnesium oxide nanoparticles in a Di(ethylene glycol) hexyl ether (DEGHE) solvent to a content of 4.3 wt%.

[0138] <Comparative Example 2> Preparation of an ink composition for an electron transport layer

[0139] An ink composition for an electron transport layer was prepared in the same manner as in Comparative Example 1, except that Di(ethylene glycol) hexyl ether (DEGHE) and Tri(ethylene glycol) (TEG) were mixed in a volume ratio of 8:2 and used instead of the DEGHE solvent in Comparative Example 1.

[0141] <Comparative Example 3> Preparation of an ink composition for an electron transport layer

[0142] An ink composition for an electron transport layer was prepared in the same manner as in Comparative Example 1, except that a solvent mixed with DMSO, ethanol, 2-methoxyethanol, and butanol in a volume ratio of 5:3:1:1 was used instead of the DEGHE solvent in Comparative Example 1.

[0144] <Comparative Examples 4 to 6> Preparation of ink compositions for electron transport layers

[0145] Ink compositions for an electron transport layer were prepared in the same manner as in Comparative Example 1, except that four solvents of DMSO, ethanol, 2-methoxyethanol, and butanol were mixed in volume ratios of 4:3:1:2 (Comparative Example 4), 3:3:1:3 (Comparative Example 5), and 2:3:1:4 (Comparative Example 6), respectively.

[0147] <Example 1> Preparation of an ink composition for an electron transport layer

[0148] An ink composition for an electron transport layer was prepared in the same manner as in Comparative Example 1, except that Di(ethylene glycol) hexyl ether (DEGHE), Tri(ethylene glycol) (TEG), and Di(propylene glycol) butyl ether (DPGBE) were mixed in a volume ratio of 7:0.5:2.5 instead of the DEGHE solvent in Comparative Example 1.

[0150] <Example 2> Preparation of an ink composition for an electron transport layer

[0151] An ink composition for an electron transport layer was prepared in the same manner as in Example 1, except that Di(ethylene glycol) hexyl ether (DEGHE), Tri(ethylene glycol) (TEG), and Di(propylene glycol) butyl ether (DPGBE) were mixed in a volume ratio of 7:1:2.

[0153] <Example 3> Preparation of an ink composition for an electron transport layer

[0154] An ink composition for an electron transport layer was prepared in the same manner as in Example 1, except that Di(ethylene glycol) hexyl ether (DEGHE), Tri(ethylene glycol) (TEG), and Di(propylene glycol) butyl ether (DPGBE) were mixed in a volume ratio of 7:2:1.

[0156] <Experiment 1> Evaluation of Spectroscopic Characteristics

[0157] Absorption spectra were measured using ink compositions for electron transport layers prepared in Example 1 and Comparative Examples 1 to 3, and the results are shown in Figure 1.

[0158] From FIG. 1, it can be seen that the ink compositions for electron transport layers prepared in Example 1 and Comparative Examples 1 to 3 have nearly similar absorption spectra, indicating that the compositions of Example 1 and Comparative Examples 1 to 3 contain the same metal oxide nanoparticles. Additionally, the maximum absorption wavelength is approximately 310 nm, indicating a broad absorption band in the ultraviolet region. Accordingly, it can be confirmed that the same spectral characteristics are exhibited even when used as a composition for spin coating and a composition for inkjet.

[0160] <Experimental Example 2> Evaluation of Physical Properties of Ink Composition for Electron Transport Layer

[0161] The physical properties of the ink compositions for electron transport layers prepared in Examples 1 to 3 of the present invention and the ink compositions for electron transport layers prepared in Comparative Examples 3 to 6 were measured, and the results are shown in Table 1 below.

[0162] Viscosity was measured using REOMETER MARS-40, and surface tension was measured using KRUSS K100C at 25℃.

[0163] Viscosity (cP) Surface tension (dyn / cm) Solvent boiling point (°C) DEGHE, TEG, DPGBE Example 1 7.19 28.14 260, 285, 230 Example 2 8.48 29.05 260, 285, 230 Example 3 10.05 30.86 260, 285, 230 DMSO, ethanol, 2-methoxyethanol, butanol Comparative Example 3 1.83 34.05 189, 78, 125, 117 Comparative Example 4 1.92 32.25 189, 78, 125, 117 Comparative Example 5 2.01 30.45 189, 78, 125, 117 Comparative Example 6 2.10 28.65 189, 78, 125, 117

[0164] It can be seen that the ink composition for an electron transport layer of the present invention has a higher viscosity but lower surface tension compared to the ink compositions for an electron transport layer of Comparative Examples 3 to 6, making it more advantageous for inkjet printing.

[0165] In addition, the physical properties of the electron transport layer compositions of Examples 1 to 3 manufactured are shown in Table 2 below.

[0166]

[0168] <Experimental Example 3> Inkjet Printing Dispensing and Shape Evaluation

[0169] Ejection evaluation was performed using an inkjet printing device (OMNIJET200) with the electron transport layer compositions of Examples 1 to 3 of the present invention and the electron transport layer ink compositions of Comparative Examples 1 to 6. At this time, the presence or absence of a tail and a 2-drop shape were observed, and the ejection images are shown in FIG. 2.

[0170] As shown in FIG. 2, it can be seen that the ink compositions for the electron transport layer of Examples 1 to 3 of the present invention have no nozzle clogging, no tail, almost no 2-drop shape, and excellent discharge reproducibility.

[0171] On the other hand, it can be seen that the ink compositions for the electron transport layer of Comparative Examples 1 to 6 frequently have intermittent nozzle clogging, have tails, or exhibit a 2-drop shape, resulting in significantly reduced reproducibility.

[0172] It is presumed that these results are achieved by using a specific solvent with a high boiling point, such as a glycol ether-based solvent, and by mixing three or more different glycol ether-based solvents, as shown in Figure 2.

Claims

Claim 1 An ink composition for an electron transport layer comprising metal oxide nanoparticles; and three or more different glycol ether-based solvents. Claim 2 In claim 1, the glycol ether-based solvent is an ink composition for an electron transport layer represented by the following chemical formula 1. [Chemical Formula 1]R 1 -(OR) n -OR 2 (In the above chemical formula 1, R is a C2-C10 alkylene, and R 1 and R 2 ε₀ are independently hydrogen or C1-C10 alkyl, and n is an integer from 1 to 10. Claim 3 In claim 2, in the above chemical formula 1, R is a C2-C7 alkylene, and R 1 and R 2 are independently hydrogen or C1-C7 alkyl, and R 1 and R 2 An ink composition for an electron transport layer, wherein the case where it is simultaneously hydrogen is excluded, and n is an integer from 1 to 5. Claim 4 In claim 1, the glycol ether-based solvent is an ink composition for an electron transport layer represented by the following Chemical Formula 2, the following Chemical Formula 3, and the following Chemical Formula 4. [Chemical Formula 2]R 11 -(OCH2CH2) p -OH[Chemical Formula 3]H-(OCH2CH2) q -OH[Chemical Formula 4]R 12 -(OCH2CR 13 H) r -OH(in the above chemical formulas 2 to 4, the R 11 and R 12 are independently C1-C7 alkyls, and R 13 ...is a C1-C5 alkyl, p and q are independently integers from 2 to 5, and r is an integer from 1 to 5. Claim 5 An ink composition for an electron transport layer according to claim 4, wherein the glycol ether-based solvent comprises formulas 2, 3, and 4, respectively, and formulas 2, 3, and 4 are included in a volume ratio of 4 to 8: 0.5 to 3: 0.5 to 3.

5. Claim 6 An ink composition for an electron transport layer according to claim 3, wherein the glycol ether-based solvent is di(ethylene glycol)n-hexyl ether, propylene glycol n-butyl ether, tri(ethylene glycol), tri(ethylene glycol) monobutyl ether, tri(ethylene glycol) monomethyl ether, tri(ethylene glycol) dimethyl ether, tri(propylene glycol) monoethyl ether, tri(propylene glycol) butyl ether, tri(propylene glycol) monomethyl ether, di(propylene glycol)n-butyl ether, di(ethylene glycol), di(ethylene glycol)n-butyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol n-propyl ether, or di(propylene glycol)n-propyl ether. Claim 7 In claim 1, the electron transport layer ink composition comprises 1 to 30 weight percent of metal oxide nanoparticles. Claim 8 In claim 1, the above glycol ether-based solvent is an ink composition for an electron transport layer having a boiling point of 150°C or higher. Claim 9 In claim 1, the electron transport layer ink composition is an ink composition for an electron transport layer having a surface tension of 50 dyn / cm or less and a viscosity of 20 cP or less. Claim 10 In claim 1, the ink composition for an electron transport layer, wherein the metal oxide nanoparticles are oxides comprising transition metals and alkaline earth metals. Claim 11 In claim 1, the metal oxide nanoparticles are Zn-containing oxides, an ink composition for an electron transport layer. Claim 12 In paragraph 2, the ink composition for the electron transport layer is an ink composition for the electron transport layer used for inkjet printing. Claim 13 An electron transport layer formed using an electron transport layer ink composition selected from any one of claims 1 to 12. Claim 14 A light-emitting device comprising the electron transport layer of claim 13.

Images