Inkjet ink composition, electron transport layer, laminate, display device, and method for producing display device

Abstract

Provided is an inkjet ink composition that, in the formation of an electron transport layer (17) through an inkjet printing method, is exceptional in coating properties with respect to a light-emitting layer (16) serving as a body subject to printing, and is less likely to damage the light-emitting layer. This inkjet ink composition contains: metal oxide nanoparticles composed of an electron transport material; and a dispersion medium. The dispersion medium has a Hansen solubility parameter having a polarity term dP of 7.5 or less and a hydrogen bond term dH of 15 or less, has 6-10 carbon atoms per molecule, includes a hydrocarbon group and a functional group bonded to the hydrocarbon group, and has a maximum carbon chain length of 5-10 starting from a carbon atom adjacent to the functional group.

Description

Inkjet ink composition, electron transport layer, laminate, display device, and method for manufacturing the display device.

[0001] This disclosure relates to an inkjet ink composition.

[0002] The layers contained between the anode and cathode in organic electroluminescent elements and semiconductor nanoparticle light-emitting diodes can be formed by inkjet printing. For example, Patent Document 1 describes forming an electron transport layer by inkjet printing. Patent Document 2 also describes forming a hole injection layer, a hole transport layer, and an electron transport layer by inkjet printing.

[0003] Japanese Patent Publication No. 2021-116345, International Publication No. 2022 / 070296

[0004] When an inkjet ink composition containing metal oxide nanoparticles is used to form an electron transport layer that comes into contact with a light-emitting layer, the inkjet ink composition is required to have good coating properties on the light-emitting layer, which is the substrate to be printed on. Furthermore, the inkjet ink composition is required not to damage the light-emitting layer, such as by degrading its light-emitting properties.

[0005] The present invention aims to provide an inkjet ink composition that exhibits excellent coatability on the light-emitting layer of the substrate and is less likely to damage the light-emitting layer when forming an electron transport layer by inkjet printing.

[0006] According to one aspect of the present invention, an inkjet ink composition is provided which comprises metal oxide nanoparticles made of an electron transport material and a dispersion medium, wherein the dispersion medium has a Hansen solubility parameter dP of 7.5 or less and a hydrogen bonding parameter dH of 15 or less, has 6 to 10 carbon atoms per molecule, and comprises a hydrocarbon group and a functional group bonded to the hydrocarbon group, and the hydrocarbon group has a portion in which the maximum carbon chain length starting from a carbon atom adjacent to the functional group is 5 to 10.

[0007] According to another aspect of the present invention, there is provided an inkjet ink composition according to the above aspect, which contains one or more of a plurality of types of nanoparticles each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

[0008] According to still another aspect of the present invention, there is provided an inkjet ink composition according to any one of the above aspects, which contains one or more of nanoparticles containing zinc oxide and nanoparticles containing magnesium-doped zinc oxide.

[0009] According to still another aspect of the present invention, there is provided an inkjet ink composition according to any one of the above aspects, in which the metal oxide nanoparticles have an average particle diameter in the range of 3 nm to 50 nm by the dynamic light scattering method.

[0010] According to still another aspect of the present invention, there is provided an inkjet ink composition according to any one of the above aspects, in which the dispersion medium has a polar term dP of 3 or more and 7.5 or less, and a hydrogen bond term dH of 9 or more and 15 or less.

[0011] According to still another aspect of the present invention, there is provided an inkjet ink composition containing metal oxide nanoparticles made of an electron transport material and a dispersion medium. The metal oxide nanoparticles contain nanoparticles containing zinc oxide. The dispersion medium has a polar term dP of the Hansen solubility parameter of 3 or more and 7.5 or less, a hydrogen bond term dH of 9 or more and 15 or less, has 6 or more and 10 or less carbon atoms per molecule, contains a hydrocarbon group and a functional group bonded to the hydrocarbon group, and the hydrocarbon group has a site where the maximum carbon chain length starting from the carbon atom adjacent to the functional group is 5 or more and 10 or less. The inkjet ink composition contains one or more selected from 2-ethyl-1-hexanol, 2-methyl-1-pentanol, 1-heptanol, 1-nonanol, and 1-decanol.

[0012] According to still another aspect of the present invention, there is provided an electron transport layer made of a cured product of the inkjet ink composition according to any one of the above aspects.

[0013] According to yet another aspect of the present invention, a laminate is provided that includes an emissive layer and an electron transport layer provided on the emissive layer relating to the above aspect.

[0014] According to yet another aspect of the present invention, the light-emitting layer comprises semiconductor nanoparticles, the semiconductor nanoparticles comprising core-shell particles including a core and a shell layer covering the core, and ligands coordinated to the surface of the core-shell particles, the shell layer comprising one or more elements selected from Zn, S, and Te, is provided.

[0015] According to yet another aspect of the present invention, the ligand is provided as a laminate relating to any of the above aspects, comprising a thiol compound.

[0016] According to yet another aspect of the present invention, a display device comprising a laminate relating to any of the above aspects is provided.

[0017] In yet another aspect of the present invention, a method for manufacturing a display device is provided, which includes applying an inkjet ink composition according to any of the above aspects to a light-emitting layer by an inkjet printing method to form a coating film, and curing the coating film to form an electron transport layer.

[0018] According to yet another aspect of the present invention, the light-emitting layer comprises semiconductor nanoparticles, the semiconductor nanoparticles comprising core-shell particles including a core and a shell layer covering the core, and ligands coordinated to the surface of the core-shell particles, and the shell layer comprises one or more elements selected from Zn, S, and Te, a method for manufacturing according to the above aspect is provided.

[0019] According to yet another aspect of the present invention, a method for producing the ligand according to any one of the above aspects is provided, comprising a thiol compound.

[0020] According to this disclosure, an inkjet ink composition is provided that exhibits excellent coatability on the light-emitting layer of the substrate and is less likely to damage the light-emitting layer when forming an electron transport layer by inkjet printing.

[0021] Figure 1 is a cross-sectional view of a display device according to one embodiment of the present invention.

[0022] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are more specific to any of the above aspects. The matters described below can be incorporated into each of the above aspects, individually or in combination.

[0023] Furthermore, the embodiments shown below illustrate configurations for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited by the material, shape, and structure of the components described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims described in the claims.

[0024] Please note that the drawings are schematic, and the relationships between dimensions in one direction and those in another, as well as the relationships between the dimensions of one component and those of other components, may differ from those in reality.

[0025] <1> Display Device Figure 1 is a cross-sectional view of a display device according to the first embodiment of the present invention. The display device 1 shown in Figure 1 employs an active matrix drive method and is a display device capable of displaying color images.

[0026] The display device 1 includes a plurality of pixels arranged in the X and Y directions, as described later. Each pixel includes a first subpixel PXR, a second subpixel PXG, and a third subpixel PXB. Each of the first subpixel PXR, the second subpixel PXG, and the third subpixel PXB includes a light-emitting element and a pixel circuit. Here, as an example, the semiconductor included in the light-emitting element is assumed to be an inorganic material.

[0027] The display device 1 includes a substrate 11, an anode 12, a partition layer 13, a hole injection layer 14, a hole transport layer 15, a light-emitting layer 16, an electron transport layer 17, and a cathode 18. The anode 12, the hole injection layer 14, the hole transport layer 15, the light-emitting layer 16, the electron transport layer 17, and the portion of the cathode 18 facing the anode 12 constitute a light-emitting element.

[0028] In Figure 1, the X and Y directions are parallel to the display surface of the display device 1 and intersect each other. For example, the X and Y directions are orthogonal to each other. The Z direction is perpendicular to the X and Y directions, i.e., the thickness direction of the display device 1.

[0029] In one example, the substrate 11 includes an insulating substrate such as a glass substrate and an array portion provided on one of its main surfaces. In another example, the substrate 11 includes a semiconductor substrate such as a silicon substrate and an array portion provided on one of its surface regions. The array portion includes pixel circuits and wiring that supplies signals and power to the pixel circuits. The pixel circuits are arranged in the X and Y directions. Each pixel circuit includes transistors and capacitors as driving elements and switches, and wiring that connects them to each other. The transistors are, for example, field-effect transistors. Here, as an example, the driving element is a p-channel field-effect transistor and the switch is an n-channel field-effect transistor.

[0030] The anode 12 in this case is a pixel electrode arranged on the substrate 11 in the X and Y directions, corresponding to the pixel circuit. Each anode 12 is connected to the drain of the driving element included in the corresponding pixel circuit.

[0031] If the substrate 11 is light-transmitting, the display device 1 may be a top-emission type or a bottom-emission type. If the substrate 11 is light-shielding, the display device 1 shall be a top-emission type.

[0032] When the display device 1 is of the bottom emission type, the anode 12 is a light-transmitting electrode. As the material for the light-transmitting electrode, transparent conductive oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and fluorine-doped tin oxide (FTO) can be used. The layer made of the transparent conductive oxide can be formed by, for example, a sputtering method.

[0033] When the display device 1 is of the top emission type, it is preferable that the anode 12 includes a light-reflecting layer. The light-reflecting layer is made of, for example, elemental metals such as aluminum and silver, or an alloy containing one or more of them. Layers made of elemental metals and alloys can be formed, for example, by vacuum deposition.

[0034] The anode 12, which includes a light-reflecting layer, may further include a light-transmitting layer on top of the light-reflecting layer. As the material for the light-transmitting layer, for example, those exemplified as materials for light-transmitting electrodes can be used. It is preferable that the material constituting the upper surface of the anode 12 has a large work function.

[0035] The partition layer 13 is provided on the substrate 11 and the anode 12. The partition layer 13 has through holes at the positions of the anode 12. Each of these through holes has a shape that tapers from the upper opening to the lower opening. Each of the anodes 12 has its peripheral edge covered by the partition layer 13, and its central part is exposed in the internal space of the through holes provided in the partition layer 13.

[0036] The partition layer 13 is made of an insulator. In one example, the partition layer 13 is made of an inorganic insulator. In another example, the partition layer 13 is made of a cured resin.

[0037] The hole injection layer 14 covers the central portion of the anode 12 within through-holes provided in the partition layer 13. The ionization energy of the hole injection layer 14 is typically greater than the work function of the anode 12.

[0038] The hole injection layer 14 is made of a hole injection material. The hole injection material is, for example, nickel oxide (NiO), bismuth oxide (Bi ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ O), molybdenum oxide (MoO ３ These are metal oxides such as ) and magnesium oxide (MgO). The hole injection material made of these metal oxides may be included in the hole injection layer 14 in the form of metal oxide nanoparticles.

[0039] Here, "nanoparticles" refers to particles whose average particle diameter, as measured by dynamic light scattering, is in the range of 1 nm to 200 nm. For metal oxide nanoparticles, it is preferable that the average particle diameter, as measured by dynamic light scattering, is in the range of 3 nm to 50 nm.

[0040] The thickness of the hole injection layer 14 is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 5 nm to 50 nm.

[0041] The hole transport layer 15 covers the hole injection layer 14 within through-holes provided in the partition layer 13. Typically, the ionization energy of the hole transport layer 15 is greater than that of the hole injection layer 14.

[0042] The hole transport layer 15 is made of a hole transport material. The hole transport material is, for example, bismuth oxide (Bi ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ O), molybdenum oxide (MoO ３ These are metal oxides such as ), and magnesium oxide (MgO). The hole transport material consisting of these metal oxides may be included in the hole transport layer 15 in the form of metal oxide nanoparticles. It is preferable that the average particle size of these metal oxide nanoparticles, as measured by dynamic light scattering, is within the range described above for the hole injection material.

[0043] The thickness of the hole transport layer 15 is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 10 nm to 50 nm.

[0044] The light-emitting layer 16 covers the hole transport layer 15 within through holes provided in the partition layer 13. Typically, the light-emitting layer 16 has a higher ionization energy and electron affinity compared to the hole transport layer 15.

[0045] The light-emitting layer 16 is made of a light-emitting material. The first subpixel PXR, the second subpixel PXG, and the third subpixel PXB have different light-emitting materials in their light-emitting layers 16. For example, the light-emitting layer 16 of the first subpixel PXR, the light-emitting layer 16 of the second subpixel PXG, and the light-emitting layer 16 of the third subpixel PXB use a red-emitting material, a green-emitting material, and a blue-emitting material, respectively.

[0046] The light-emitting material is, for example, a semiconductor nanoparticle. The particle size of the semiconductor nanoparticle is, for example, in the range of a few nanometers to 10 nanometers.

[0047] The semiconductor nanoparticles include core-shell particles, which consist of a core and a shell layer covering the core, and ligands coordinated to the surface of the core-shell particles.

[0048] The core includes, for example, zinc (Zn), sulfur (S), tellurium (Te), or selenium (Se). The core is, for example, a combination of Zn and Te, a combination of Zn and Se, a combination of Zn, S, and Te, a combination of Zn, Se, and S, a combination of Zn, Te, and Se, or a combination of Zn, Te, Se, and S.

[0049] The shell layer contains, for example, one or more elements selected from Zn, S, and Te. The shell layer may further contain Te. The shell layer contains, for example, a combination of Zn and S, or a combination of Zn, S, and Te. Part of the shell layer may be dissolved in the core. The shell layer may consist of a single layer or multiple layers.

[0050] The core-shell particles may contain elements other than the above elements, but preferably do not contain at least one of cadmium (Cd) and phosphorus (P). Since Cd is a harmful substance, it is preferable that the core-shell particles, semiconductor nanoparticles, and semiconductor nanoparticle compositions do not contain Cd. In addition, when an organic phosphorus compound is used as a raw material for the core-shell particles, the organic phosphorus compound is likely to be oxidized in air, so the synthesis of semiconductor nanoparticles is likely to be destabilized. In this case, an increase in cost, destabilization of fluorescence characteristics, and complication of the manufacturing process are likely to occur. Also, in the above case, the cost is likely to increase because the organic phosphorus compound is expensive.

[0051] The ligand contributes to improving resistance and preventing aggregation in the dispersion. The ligand preferably contains a thiol-based compound. The thiol-based compound contains, for example, a thiol and an alkyl chain. The alkyl chain may be linear or branched. In one form, the alkyl chain is preferably linear. Also, the number of carbon atoms in the main chain of the alkyl chain is preferably 8 or more. When the number of carbon atoms in the main chain of the alkyl chain is 8 or more, the dispersibility of the semiconductor nanoparticles is particularly excellent. The thiol-based compound is, for example, octadecanethiol (C １８ H ３７ SH), hexadecanethiol (C １６ H ３３ SH), tetradecanethiol (C １４ H ２９ SH), dodecanethiol (C １２ H ２５ [[ID=(19]]decane thiol (C １０ H) ２１ SH), or octanethiol (C ８ H １７ SH). The semiconductor nanoparticles preferably contain 1-dodecanethiol as a ligand on the surface of the core-shell particles.

[0052] The ligand preferably contains the thiol compound described above and one or more compounds selected from the group consisting of amines, fatty acids, phosphine compounds, and alcohols. Hereinafter, the thiol compound may be referred to as the first ligand, and one or more compounds selected from the group consisting of amines, fatty acids, phosphine compounds, and alcohols may be referred to as the second ligand. The second ligand preferably contains an alkyl chain. Furthermore, it is preferable that the main chain of the alkyl chain has eight or more carbon atoms. When the main chain of the alkyl chain has eight or more carbon atoms, the dispersibility of semiconductor nanoparticles is excellent.

[0053] The amine is, for example, an aliphatic amine. The aliphatic amine is preferably a primary amine. The aliphatic amine is, for example, oleylamine (C １８ H ３５ NH ２ ), stearyl(octadecyl)amine (C １８ H ３７ NH ２ ), dodecyl(lauryl)amine (C １２ H ２５ NH ２ ), decylamine (C １０ H ２１ NH ２ ), or octylamine (C ８ H １７ NH ２ )

[0054] The fatty acid may be saturated or unsaturated. For example, the fatty acid is oleic acid (C １７ H ３３ COOH), stearic acid (C １７ H ３５ COOH), palmitic acid (C １５ H ３１ COOH), myristic acid (C １３ H ２７ COOH), lauric acid (C １１ H ２３ COOH), decanoic acid (C ９ H １９ COOH), or octanoic acid (C ７ H １５It is COOH. The fatty acid is preferably oleic acid.

[0055] Phosphine compounds are phosphine and compounds containing phosphine. ３ It is a compound represented as (where P is phosphorus and R is a hydrocarbon group). A phosphine is, for example, trioctylphosphine ((C ８ H １７ ) ３ P), triphenylphosphine ((C ６ H ５ ) ３ P), or tributylphosphine ((C) ４ H ９ ) ３ P) is preferred. The phosphine is preferably trioctylphosphine.

[0056] Compounds containing phosphine are, for example, phosphine oxides. Phosphine oxides include, for example, trioctylphosphine oxide ((C) ８ H １７ ) ３ P=O), triphenylphosphine oxide ((C ６ H ５ ) ３ P=O) or tributylphosphine oxide ((C) ４ H ９ ) ３ P=O). The compound containing phosphine is preferably trioctylphosphine oxide.

[0057] Examples of alcohols include octanol, nonanol, decanol, undecanol, and dodecanol.

[0058] The ligand may also be a compound containing multiple different functional groups, such as thiols and alcohols. Examples of compounds containing multiple functional groups include 8-mercapto-1-octanol and 11-mercapto-1-undecanol.

[0059] The semiconductor nanoparticles preferably contain a first ligand (thiol compound) and a second ligand which is a fatty acid, a phosphine compound, or a combination of a fatty acid and a phosphine compound. The first ligand is preferably 1-dodecanethiol, and the second ligand is preferably oleic acid, trioctylphosphine, or a combination of oleic acid and trioctylphosphine.

[0060] The thickness of the light-emitting layer 16 is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 10 nm to 50 nm.

[0061] The electron transport layer 17 covers the light-emitting layer 16 within through-holes provided in the partition layer 13. Typically, the electron transport layer 17 has a higher ionization energy and electron affinity compared to the light-emitting layer 16.

[0062] The electron transport layer 17 is made of an electron transport material. The electron transport material is, for example, bismuth oxide (Bi ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ These are metal oxides such as 0), magnesium oxide (MgO), nickel oxide (NiO), zinc oxide (ZnO), magnesium-doped zinc oxide (MgZnO), and titanium oxide (TiO). These electron transport materials made of metal oxides may be included in the electron transport layer 17 in the form of metal oxide nanoparticles. It is preferable that the average particle size of these metal oxide nanoparticles, as measured by dynamic light scattering, is within the range described above for the hole injection material. The electron transport layer 17 preferably contains, for example, one or more nanoparticles containing zinc oxide and nanoparticles containing magnesium-doped zinc oxide.

[0063] The electron transport layer 17 is formed by an inkjet printing method using an inkjet ink composition according to the second embodiment of the present invention, which will be described later, with the light-emitting layer 16 as the substrate.

[0064] The thickness of the electron transport layer 17 is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 10 nm to 50 nm.

[0065] The cathode 18 covers the electron transport layer 17 and the exposed portion of the partition layer 13. In this case, the cathode 18 is a common electrode facing multiple anodes 12.

[0066] When the display device 1 is of the bottom emission type, it is preferable that the cathode 18 includes a light-reflecting layer. The light-reflecting layer is made of, for example, elemental metals such as aluminum and silver, or an alloy containing one or more of them. Layers made of elemental metals and alloys can be formed, for example, by vacuum deposition.

[0067] When the display device 1 is of the top-emission type, the cathode 18 is a light-transmitting electrode. As the material for the light-transmitting electrode, transparent conductive oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and fluorine-doped tin oxide (FTO) can be used. The layer made of the transparent conductive oxide can be formed by, for example, a sputtering method.

[0068] The work function of the cathode 18 is typically smaller than that of the anode 12 and larger than that of the electron affinity of the electron transport layer 17. The cathode 18 may include a layer made of a material with a low work function, such as an MgAg alloy or an AlLi alloy, between the layer made of a metal or transparent conductive oxide and the electron transport layer 17.

[0069] The display device 1 may further include one or more other elements. For example, the display device 1 may further include an electron injection layer, such as a LiF layer, between the electron transport layer 17 and the cathode 18. The display device 1 may also further include a sealing film or sealing substrate that seals the light-emitting element.

[0070] Furthermore, the display device 1 employs a forward structure for the light-emitting element. The light-emitting element may also employ an inverse structure in which the stacking order of the layers it contains is reversed.

[0071] <2> Method of manufacturing the display device The display device 1 shown in Figure 1 can be manufactured, for example, by the following method.

[0072] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0073] Next, a hole injection layer 14 and a hole transport layer 15 are formed sequentially. Each of the hole injection layer 14 and the hole transport layer 15 can be formed, for example, by an inkjet printing method using an ink composition containing metal oxide nanoparticles and a dispersion medium. Specifically, first, the inkjet ink composition is supplied to the surface of the substrate by an inkjet printing method to form a coating film. Next, this coating film is dried. For example, the coating film is baked. This yields a layer made of cured inkjet ink composition as the printed layer.

[0074] Next, the light-emitting layer 16 is formed. As described above, the first subpixel PXR, the second subpixel PXG, and the third subpixel PXB have different light-emitting materials in their light-emitting layer 16. Therefore, the light-emitting layer 16 of the first subpixel PXR, the light-emitting layer 16 of the second subpixel PXG, and the light-emitting layer 16 of the third subpixel PXB are formed separately. Each of these light-emitting layers 16 can be formed, for example, using the lift-off method.

[0075] Next, the electron transport layer 17 is formed. The electron transport layer 17 can be formed by an inkjet printing method using the inkjet ink composition according to the second embodiment of the present invention, which will be described next, in the same manner as described above for the hole injection layer 14 and the hole transport layer 15. That is, first, the inkjet ink composition according to the second embodiment is supplied to the surface of the light-emitting layer 16, which will be printed, by an inkjet printing method to form a coating film. Next, this coating film is dried. For example, the coating film is baked. This gives the electron transport layer 17, which is made of a cured product of the inkjet ink composition, as a printed layer.

[0076] Next, the cathode 18 is formed. The cathode 18 can be formed by vacuum deposition, sputtering, or a combination thereof. After that, the light-emitting element is sealed as necessary. In this way, the display device 1 shown in the figure is obtained.

[0077] <3> Inkjet Ink Composition As described above, the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17 can be formed by the inkjet printing method. Among these, the ink composition used to form the electron transport layer 17 by the inkjet printing method, i.e., the inkjet ink composition, is required to have excellent coatability with respect to the light-emitting layer 16 which is the substrate. Furthermore, this inkjet ink composition is required to be less susceptible to damage to the light-emitting layer 16 that occurs when the electron transport layer 17 is formed by the inkjet printing method with the light-emitting layer 16 as the substrate.

[0078] From the viewpoint of improving the coatability of the light-emitting layer 16 and reducing damage, it is preferable to form the electron transport layer 17 using an inkjet ink composition according to the second embodiment having the composition described below.

[0079] That is, the inkjet ink composition according to the second embodiment comprises metal oxide nanoparticles made of an electron transport material and a dispersion medium. The dispersion medium satisfies a specific relationship between dP and dH, which are three parameters (dD, dP, dH) that constitute the Hansen solubility parameter (HSP), and contains a specific number of carbon atoms and a specific structural site.

[0080] (Metal Oxide Nanoparticles) Metal oxide nanoparticles are metal oxide nanoparticles made of electron transport materials. Examples of metal oxide nanoparticles include bismuth oxide (Bi ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ The nanoparticles are one or more of several types, each containing, for example, 0), magnesium oxide (MgO), nickel oxide (NiO), zinc oxide (ZnO), magnesium-doped zinc oxide (MgZnO), and titanium oxide (TiO). The inkjet ink composition according to this embodiment preferably contains, for example, one or more nanoparticles containing zinc oxide and one or more nanoparticles containing magnesium-doped zinc oxide.

[0081] It is preferable that the average particle diameter of these metal oxide nanoparticles, as measured by dynamic light scattering, falls within the range described above. That is, "nanoparticles" refers to particles whose average particle diameter, as measured by dynamic light scattering, is in the range of 1 nm to 200 nm. It is preferable that the average particle diameter of metal oxide nanoparticles, as measured by dynamic light scattering, falls within the range of 3 nm to 50 nm.

[0082] The proportion of metal oxide nanoparticles in the inkjet ink composition according to this embodiment, that is, the concentration of metal oxide nanoparticles in the inkjet ink composition, is preferably in the range of 20% to 0.1% by mass, more preferably in the range of 10% to 0.3% by mass, and even more preferably in the range of 5% to 0.5% by mass.

[0083] (Dispersion medium) The dispersion medium disperses or dissolves metal oxide nanoparticles made of electron transport material. The dispersion medium contained in the inkjet ink composition according to this embodiment has a Hansen solubility parameter (HSP) polarity term dP of 7.5 or less and a hydrogen bonding term dH of 15 or less.

[0084] Here, the Hansen solubility parameter (HSP) is derived by dividing the solubility parameter introduced by Hildebrand into three components: the dispersion term dD, the polarity term dP, and the hydrogen bonding term dH. The dispersion term dD represents the energy due to intermolecular dispersion forces, the polarity term dP represents the energy due to intermolecular dipole interactions, and the hydrogen bonding term dH represents the energy due to intermolecular hydrogen bonding.

[0085] Keeping the dP and dH of the dispersion medium low means keeping the polarity and hydrogen bonding properties of the dispersion medium itself low. This increases the affinity between the dispersion medium and highly hydrophobic components such as organic ligands that make up the light-emitting layer 16, improving the wettability of the surface of the light-emitting layer 16.

[0086] This improved affinity suppresses the increase in the contact angle of the inkjet ink composition with respect to the surface of the light-emitting layer 16, resulting in good coating properties and, as a result, a high-quality electron transport layer 17 can be obtained.

[0087] Therefore, the coatability of the inkjet ink composition to the light-emitting layer 16 is improved when the Hansen solubility parameter (HSP) dP of the dispersion medium is 7.5 or less and dH is 15 or less. Here, the coatability of the inkjet ink composition to the light-emitting layer 16 can be evaluated by measuring the contact angle of the inkjet ink composition to the light-emitting layer 16 by the droplet method. That is, when the dP and dH of the Hansen solubility parameter (HSP) of the dispersion medium satisfy the above relationship, the contact angle with the surface of the light-emitting layer 16 is suppressed to become high, and the coatability is improved. The dP of the dispersion medium is 7.5 or less, preferably 7 or less, and more preferably 6.5 or less. Also, the dH of the dispersion medium is 15 or less, preferably 14 or less, and more preferably 13 or less.

[0088] Furthermore, the dP of the dispersion medium may be, for example, 3 or greater. Also, the dH of the dispersion medium may be, for example, 9 or greater.

[0089] The dispersion medium has 6 to 10 carbon atoms per molecule. "Number of carbon atoms per molecule" refers to the total number of carbon atoms contained in one molecule of the dispersion medium (hereinafter also referred to as "total number of carbon atoms").

[0090] The dispersion medium contains a hydrocarbon group and a functional group bonded to the hydrocarbon group. This hydrocarbon group has a portion where the maximum carbon chain length, starting from a carbon atom adjacent to the functional group, is between 5 and 10.

[0091] Here, the hydrocarbon group may be linear or branched. The "carbon chain length" of a hydrocarbon group refers to the number of carbon atoms in the linear portion of the hydrocarbon chain, starting from the carbon atom adjacent to the functional group. The "maximum carbon chain length" refers to the carbon chain length if the hydrocarbon group contains only one carbon chain, and the longest carbon chain length if the hydrocarbon group contains two or more carbon chain lengths. If there are two or more functional groups attached to the hydrocarbon group, the "maximum carbon chain length" refers to the longest carbon chain length when starting from each carbon atom adjacent to each functional group. Hereafter, the "maximum carbon chain length" will also be referred to as the "maximum carbon chain length."

[0092] Specific examples of functional groups include hydroxyl groups, mercapto groups, amine groups, carboxyl groups, and the like.

[0093] The maximum carbon chain length will be explained with specific examples. For example, 4-methyl-2-pentanol, shown below, has a maximum carbon chain length of 4. Also, propylene glycol, shown below, has a maximum carbon chain length of 3. Neither compound meets the requirement of "maximum carbon chain length" (5 to 10).

[0094]

[0095] On the other hand, 2-ethyl-1-hexanol, shown below, has a maximum carbon chain length of 6. Also, 2-methyl-1-pentanol, shown below, has a maximum carbon chain length of 5. Both compounds satisfy the requirement of "maximum carbon chain length" (5 to 10).

[0096]

[0097] Dispersion media having a total of 6 or more carbon atoms and a maximum carbon chain length of 5 or more have relatively long nonpolar chains (hydrophobic regions) within their molecules. By using such a dispersion media, when the ink lands on the surface of the light-emitting layer, it is possible to suppress excessive interaction (e.g., dissolution) between the dispersion media and the carbon chain length in the structure of the ligands in the light-emitting layer 16, thereby preventing the ligands from peeling off or disrupting the structure of the light-emitting layer 16. Therefore, it is possible to reduce damage to the light-emitting layer of the substrate by the inkjet ink composition and suppress a decrease in the light-emitting properties of the light-emitting layer.

[0098] On the other hand, by using a dispersion medium with a total number of carbon atoms of 10 or less and a maximum carbon chain length of 10 or less, it is possible to suppress the decrease in inkjet printability due to increased boiling point and viscosity.

[0099] Examples of dispersion media that satisfy the requirements of having a Hansen solubility parameter (HSP) dP of 7.5 or less, a dH of 15 or less, a total number of carbon atoms of 6 or more and 10 or less, and a maximum carbon chain length of 5 or more and 10 or less include 2-ethyl-1-hexanol, 2-methyl-1-pentanol, 1-heptanol, 1-nonanol, and 1-decanol.

[0100] <Effects> The inkjet ink composition according to the second embodiment of the present invention is suitably used as an inkjet ink composition for forming an electron transport layer 17 that contacts the light-emitting layer 16. That is, the inkjet ink composition according to the second embodiment has excellent coatability with respect to the light-emitting layer 16. Therefore, by using this composition to form an electron transport layer 17 with the light-emitting layer 16 as the substrate by an inkjet printing method, an electron transport layer 17 consisting of a high-quality printed layer can be obtained.

[0101] Furthermore, the inkjet ink composition according to the second embodiment is less likely to cause damage to the light-emitting layer 16 when the electron transport layer 17 is formed on the light-emitting layer 16 by the inkjet printing method. Therefore, by using this composition to form the electron transport layer 17 on the light-emitting layer 16 by the inkjet printing method, adverse effects such as a decrease in the light-emitting properties of the light-emitting layer 16 can be suppressed.

[0102] The tests conducted in connection with the present invention are described below.

[0103] (1) Preparation of inkjet ink composition (1.1) Example 1 An inkjet ink composition containing metal oxide nanoparticles and a dispersion medium was prepared. As the metal oxide nanoparticles, nanoparticles made of zinc oxide with an average particle size of 10 nm were used. The average particle size of the metal oxide nanoparticles was measured by the dynamic light scattering method described later. The amount of metal oxide nanoparticles was adjusted so that their proportion of the inkjet ink composition was 2.5% by mass. 2-ethyl-1-hexanol was used as the dispersion medium.

[0104] (1.2) Example 2 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, 1-heptanol was used instead of 2-ethyl-1-hexanol.

[0105] (1.3) Example 3 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, 2-methyl-1-pentanol was used instead of 2-ethyl-1-hexanol.

[0106] (1.4) Example 4 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, 1-nonanol was used instead of 2-ethyl-1-hexanol.

[0107] (1.5) Example 5 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, 1-decanol was used instead of 2-ethyl-1-hexanol.

[0108] (1.6) Comparative Example 1 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, 4-methyl-2-pentanol was used instead of 2-ethyl-1-hexanol.

[0109] (1.7) Comparative Example 2 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, 2-ethyl-1-butanol was used instead of 2-ethyl-1-hexanol.

[0110] (1.8) Comparative Example 3 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, diethylene glycol monomethyl ether (DGME) was used instead of 2-ethyl-1-hexanol.

[0111] (1.9) Comparative Example 4 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, 1,3-propanediol was used instead of 2-ethyl-1-hexanol.

[0112] (1.10) Comparative Example 5 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, ethylene glycol (EG) was used instead of 2-ethyl-1-hexanol.

[0113] (1.11) Comparative Example 6 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, propylene glycol (PG) was used instead of 2-ethyl-1-hexanol.

[0114] (1.12) Comparative Example 7 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, diacetone alcohol (DAA) was used instead of 2-ethyl-1-hexanol.

[0115] Table 1 shows the dP, dH, total number of carbon atoms, and maximum carbon chain length for the dispersion media used in Examples 1 to 5 and Comparative Examples 1 to 7.

[0116]

[0117] (2) Evaluation (2.1) Average particle size of metal oxide nanoparticles The average particle size of metal oxide nanoparticles was measured immediately after manufacturing for the inkjet ink compositions according to Examples 1 to 5 and Comparative Examples 1 to 7. The average particle size was measured by dynamic light scattering. A NanoTrac® UPA-EX150 particle size analyzer manufactured by Nikkiso Co., Ltd. was used to measure the average particle size. The results are shown in Table 2.

[0118] (2.2) Coatability (contact angle) In order to evaluate the coatability of the inkjet ink compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 7 to the light-emitting layer, the contact angle with respect to the light-emitting layer was measured for these compositions.

[0119] In this study, a light-emitting layer was fabricated using semiconductor nanoparticles in which dodecanethiol, trioctylphosphine, and oleic acid were coordinated as ligands to the surface of core-shell particles, with a zinc selenide (ZnSe) core and a zinc sulfide (ZnS) shell. The light-emitting layer was fabricated by depositing a coating solution containing the above semiconductor nanoparticles onto a glass substrate using a spin-coating method, and then baking it in a glove box under a nitrogen atmosphere at 120°C for 10 minutes.

[0120] A contact angle meter (LSE-ME4, manufactured by NIC Co., Ltd.) was used to measure the contact angle. The measurement was performed with a volume of 1.5 μL of liquid, and the average of the contact angles measured at three locations was calculated. The results are shown in Table 2.

[0121] (2.3) Effect on the light-emitting layer (rate of change in light intensity) For the inkjet ink compositions of Examples 1 to 5 and Comparative Examples 1 and 2, which showed good coatability in the evaluation of "(2.2) Coatability" above, the effect on the light-emitting layer was evaluated using the following method.

[0122] A light-emitting layer was prepared using the same method as described in "(2.2) Coatability" above. The fluorescence intensity of this light-emitting layer was measured using an F7100 manufactured by Hitachi High-Tech Science Corporation. The excitation wavelength was 350 nm.

[0123] The light-emitting layer whose fluorescence intensity was measured was placed in a spin coater. Next, an inkjet ink composition was dropped onto the light-emitting layer, allowed to stand for 20 seconds, and then spin-coated at 1200 rpm for 60 seconds. The fluorescence intensity of the light-emitting layer after spin-coating was measured to determine the fluorescence intensity of the light-emitting layer after dropping the inkjet ink composition.

[0124] The fluorescence intensity change rate was calculated using the following formula: Fluorescence intensity change rate (%) = 100 × (1 - (Maximum fluorescence intensity after dropping the inkjet ink composition / Maximum fluorescence intensity before dropping the inkjet ink composition)). For samples where the fluorescence intensity change rate showed a negative value (samples where the maximum fluorescence intensity after dropping the inkjet ink composition was greater than the maximum fluorescence intensity before dropping the inkjet ink composition), the fluorescence intensity change rate was set to 0%.

[0125] A smaller rate of change in luminescence intensity indicates less damage to the luminescent layer. A change in fluorescence intensity of 5% or less was rated as A, between 5% and 10% as B, and above 10% as C. The evaluation results are shown in Table 2.

[0126]

[0127] As shown in Table 2, the inkjet ink compositions of Examples 1 to 5 and Comparative Examples 1 and 2, in which the Hansen solubility parameter (HSP) dP was 7.5 or less and dH was 15 or less, exhibited a low contact angle and excellent coating properties for the light-emitting layer. The inkjet ink compositions of Comparative Examples 3 to 7, in which neither dP nor dH met the above conditions, exhibited a high contact angle.

[0128] Furthermore, as shown in Table 2, among the inkjet ink compositions of Examples 1 to 5 and Comparative Examples 1 and 2, which exhibited good coatability, the inkjet ink compositions of Examples 1 to 5, in which the total number of carbon atoms was 6 or more and 10 or less, and the maximum carbon chain length was 5 or more and 10 or less, had little impact (damage) on the light-emitting layer, and the light-emitting layer maintained good light-emitting properties. On the other hand, the inkjet ink compositions of Comparative Examples 1 and 2, in which the maximum carbon chain length did not meet the above conditions, had a large impact (damage) on the light-emitting layer, and the fluorescence properties of the light-emitting layer deteriorated.

[0129] 1...Display device, 11...Substrate, 12...Anode, 13...Blocking layer, 14...Hole injection layer, 15...Hole transport layer, 16...Light-emitting layer, 17...Electron transport layer, 18...Cathode, PXB...Third subpixel, PXG...Second subpixel, PXR...First subpixel.

Claims

1. An inkjet ink composition comprising metal oxide nanoparticles made of an electron transport material and a dispersion medium, wherein the dispersion medium has a Hansen solubility parameter polarity term dP of 7.5 or less and a hydrogen bonding term dH of 15 or less, has 6 to 10 carbon atoms per molecule, and comprises a hydrocarbon group and a functional group bonded to the hydrocarbon group, and the hydrocarbon group has a portion where the maximum carbon chain length starting from a carbon atom adjacent to the functional group is 5 to 10.

2. The inkjet ink composition according to claim 1, wherein the metal oxide nanoparticles comprise one or more of several types of nanoparticles, each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

3. The inkjet ink composition according to claim 1, wherein the metal oxide nanoparticles comprise one or more nanoparticles containing zinc oxide and nanoparticles containing magnesium-doped zinc oxide.

4. The inkjet ink composition according to any one of claims 1 to 3, wherein the metal oxide nanoparticles have an average particle size in the range of 3 nm to 50 nm as determined by dynamic light scattering.

5. The inkjet ink composition according to any one of claims 1 to 4, wherein the dispersion medium has a polarity term dP of 3 or more and 7.5 or less, and a hydrogen bonding term dH of 9 or more and 15 or less.

6. An inkjet ink composition comprising metal oxide nanoparticles made of an electron transport material and a dispersion medium, wherein the metal oxide nanoparticles include nanoparticles containing zinc oxide, and the dispersion medium is a solvent having a Hansen solubility parameter polarity term dP of 3 to 7.5 and a hydrogen bonding term dH of 9 to 15, with 6 to 10 carbon atoms per molecule, comprising a hydrocarbon group and a functional group bonded to the hydrocarbon group, wherein the hydrocarbon group has a portion where the maximum carbon chain length starting from a carbon atom adjacent to the functional group is 5 to 10, and comprises one or more selected from 2-ethyl-1-hexanol, 2-methyl-1-pentanol, 1-heptanol, 1-nonanol, and 1-decanol.

7. An electron transport layer comprising a cured product of an inkjet ink composition according to any one of claims 1 to 6.

8. A laminate comprising an emissive layer and an electron transport layer according to claim 7 provided on the emissive layer.

9. The laminate according to claim 8, wherein the light-emitting layer comprises semiconductor nanoparticles, the semiconductor nanoparticles comprising core-shell particles including a core and a shell layer covering the core, and ligands coordinated to the surface of the core-shell particles, and the shell layer comprising one or more elements selected from Zn, S, and Te.

10. The laminate according to claim 9, wherein the ligand comprises a thiol compound.

11. A display device comprising the laminate according to any one of claims 8 to 10.

12. A method for manufacturing a display device, comprising: applying an inkjet ink composition according to any one of claims 1 to 6 to a light-emitting layer by an inkjet printing method to form a coating film; and curing the coating film to form an electron transport layer.

13. The manufacturing method according to claim 12, wherein the light-emitting layer comprises semiconductor nanoparticles, the semiconductor nanoparticles comprising core-shell particles including a core and a shell layer covering the core, and ligands coordinated to the surface of the core-shell particles, and the shell layer comprises one or more elements selected from Zn, S and Te.

14. The manufacturing method according to claim 13, wherein the ligand comprises a thiol compound.

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