Light-emitting element, display device, and method for manufacturing light-emitting element

Abstract

A light-emitting element (2) comprises an anode (21), a hole injection layer (22), a light-emitting layer (24), an electron transport layer (25), and a cathode (26) in the stated order. The electron transport layer contains first metal atoms. The hole injection layer contains the first metal atoms and a chelating agent.

Description

Light-emitting element, display device, and method for manufacturing the same

[0001] The present disclosure relates to a field injection type light emitting device, a display device including the light emitting device, and a method for manufacturing the light emitting device.

[0002] Patent Document 1 discloses a field injection type light emitting device containing nickel oxide (NiO) in a hole injection layer.

[0003] Japanese Patent Application Publication No. 2012-23388

[0004] Because the particle size of materials containing metal atoms, such as nickel oxide, is relatively large, the film-forming properties of the hole injection layer of the light-emitting element described in Patent Document 1 may be deteriorated. Furthermore, because the metal atoms contained in the material of the hole injection layer tend to aggregate, the thickness uniformity of the hole injection layer may be reduced. Furthermore, because the band gap of the material containing metal atoms used in the hole injection layer is different from the band gap of the material used in the electron transport layer, the carrier balance may be deteriorated in the light-emitting layer of the light-emitting element described in Patent Document 1. As a result, the light-emitting efficiency of the light-emitting element described in Patent Document 1 may be reduced.

[0005] A light-emitting element according to one aspect of the present disclosure includes an anode, a cathode facing the anode, a light-emitting layer located between the anode and the cathode, a hole injection layer between the anode and the light-emitting layer, and an electron transport layer between the cathode and the light-emitting layer, wherein the electron transport layer contains a first metal atom, and the hole injection layer contains the first metal atom and a chelating agent.

[0006] A method for manufacturing a light-emitting element according to one aspect of the present disclosure is a method for manufacturing a light-emitting element including an anode, a cathode facing the anode, a light-emitting layer located between the anode and the cathode, a hole injection layer between the anode and the light-emitting layer, and an electron transport layer between the cathode and the light-emitting layer, the method including forming the electron transport layer containing a first metal atom, and forming the hole injection layer containing the first metal atom and a chelating agent.

[0007] In a light-emitting device, the film-forming properties of the hole injection layer are improved, and the carrier balance in the light-emitting layer is improved, thereby improving the light-emitting efficiency.

[0008] FIG. 1 is a schematic side cross-sectional view of a display device according to an embodiment. FIG. 2 is a schematic plan view of a display device according to an embodiment. FIG. 3 is a band diagram of each layer of a light-emitting element according to an embodiment. FIG. 4 is a schematic diagram showing an example of a specific configuration of a material contained in a hole injection layer according to an embodiment. FIG. 5 is a flowchart of a method for manufacturing a display device according to an embodiment. FIG. 6 is a flowchart of a method for forming a hole injection layer according to an embodiment. FIG. 7 is a graph showing FTIR results for hole injection layers according to an example and a comparative example. FIG. 8 is a graph showing XRD measurement results for a hole injection layer according to an example. FIG. 9 is a histogram showing the ratio of the number of microparticles contained in a hole injection layer according to an example, integrated for each particle size of the microparticles.

[0009] [Embodiments] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that in each drawing, similar configurations are assigned the same reference numerals and their description will be omitted. Furthermore, all components shown in each drawing of the present disclosure are merely examples, and the scales thereof are not limited to those shown in the drawings.

[0010] <Overview of Display Device> FIG. 2 is a schematic plan view of a display device 1 according to this embodiment. The display device 1 is a device that can be used, for example, as a display for a television or a smartphone. As shown in FIG. 2, the display device 1 includes a frame region NDA and a display region DA. The display region DA of the display device 1 includes a plurality of pixels PIX, each of which includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. However, this embodiment is not limited to this. For example, the pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, the green subpixel GSP, and the blue subpixel BSP.

[0011] The display device 1 includes a light-emitting element in each of the red subpixels RSP, green subpixels GSP, and blue subpixels BSP. In particular, the light-emitting element in the red subpixel RSP emits red light, the light-emitting element in the green subpixel GSP emits green light, and the light-emitting element in the blue subpixel BSP emits blue light. The display device 1 performs full-color display in the display area DA by controlling the light emission from each light-emitting element in the display area DA via a driver circuit and pixel circuit (not shown). Note that the light-emitting elements included in the display device 1 may have the same configuration, except for the emitted color, regardless of the subpixel in which they are located.

[0012] <Display Element: Overview> The structure of the display area DA of the display device 1, particularly the structure of the light-emitting elements of each subpixel, will be described in more detail with reference to Fig. 1. Fig. 1 is a schematic side cross-sectional view of the display device 1 according to an embodiment of the present disclosure, particularly showing a cross section perpendicular to the display surface of the display device 1 and passing through one of the light-emitting elements. In other words, the cross section shown in Fig. 1 is a cross section parallel to the film thickness direction of, for example, a light-emitting layer 24 described below.

[0013] 1, the display device 1 according to this embodiment includes, in a display area DA, the above-described plurality of light-emitting elements 2 and a substrate 3, and in particular, the plurality of light-emitting elements 2 on the substrate 3. The display device 1 has a structure in which the layers of the light-emitting elements 2 are stacked on the substrate 3 on which, for example, TFTs (Thin Film Transistors) (not shown) are formed as pixel circuits. In this specification, the direction from the light-emitting elements 2 of the display device 1 to the substrate 3 is referred to as the "downward direction," and the direction opposite to the downward direction is referred to as the "upward direction."

[0014] The light-emitting element 2 includes an anode 21, a hole injection layer 22, a hole transport layer 23, a light-emitting layer 24, an electron transport layer 25, and a cathode 26, which are arranged on a substrate 3 in this order from the substrate 3 side. In other words, the light-emitting element 2 includes an anode 21, a cathode 26 facing the anode 21, and a light-emitting layer 24 located between the anode 21 and the cathode 26. The light-emitting element 2 further includes a hole injection layer 22 between the anode 21 and the light-emitting layer 24, and an electron transport layer 25 between the cathode 26 and the light-emitting layer 24. In addition, the light-emitting element 2 includes a hole transport layer 23 between the hole injection layer 22 and the light-emitting layer 24.

[0015] The anode 21 may be formed in an island shape for each subpixel of the display device 1, and may be electrically connected to a pixel circuit on the substrate 3 and driven individually. The cathode 26 may be formed in common to a plurality of subpixels of the display device 1, and may be applied with a common potential via an auxiliary power supply (not shown) or the like of the display device 1. In this way, the display device 1 may drive the light-emitting element 2 for each subpixel individually.

[0016] The structure of each layer of the light emitting element 2 will be described in more detail below.

[0017] <Display Element: Anode and Cathode> The anode 21 and the cathode 26 contain a conductive material and are electrically connected to the hole injection layer 22 and the electron transport layer 25, respectively.

[0018] At least one of the anode 21 and the cathode 26 is a transparent electrode that transmits visible light. Examples of transparent electrodes include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO, AZO (aluminum-doped zinc oxide, also known as ZAO), BZO (boron-doped zinc oxide), and FTO (fluorine-doped tin oxide). Either the anode 21 or the cathode 26 may contain a metal material. As the metal material, Al, Cu, Au, Ag, or Mg, or an alloy thereof, which have high visible light reflectance, are preferred. The anode 21 and the cathode 26 may be formed by sputtering or the like, or may be patterned by dry etching or the like.

[0019] <Display Element: Hole Injection Layer> The hole injection layer 22 is a layer containing a hole transport material that injects holes from the anode 21 into the hole transport layer 23. The hole injection layer 22 may be in contact with the anode 21 from the viewpoint of improving the efficiency of injection of holes from the anode 21 into the hole transport layer 23.

[0020] The hole injection layer 22 includes a first metal atom as a metal element contained in the hole transport material, and a chelating agent. The hole injection layer 22 may further include a second metal atom that is a metal element contained in the hole transport material and is a metal element different from the first metal atom.

[0021] The first metal atoms contained in the hole injection layer 22 include, for example, at least one of Mg, Zn, Cu, and Co. The second metal atoms contained in the hole injection layer 22 include, for example, at least one of Ni, Cu, and Co. Both the first metal atoms and the second metal atoms described above are metal atoms that can be efficiently introduced into a metal oxide by doping.

[0022] The hole injection layer 22 may include, for example, an oxide of an alloy having a first metal atom and a second metal atom. For example, the hole injection layer 22 may include an Mg alloy, in which NiO is doped with Mg, where 0<x<1. ｘ Ni １－ｘ The hole injection layer 22 may contain O as the first metal atom and Mg as the second metal atom. When the hole injection layer 22 contains an oxide of an alloy having the first metal atom and the second metal atom, the light-emitting element 2 has both the first metal atom and the second metal atom and achieves a material that functions as a hole transport material with a simple configuration.

[0023] The chelating agent contained in the hole injection layer 22 may include, for example, at least one of EDTA, NTA, DTPA, GLDA, HEDTA, GEDTA, TTHA, HIDA, and DHEG. In particular, the chelating agent contained in the hole injection layer 22 may form a complex with a second metal atom. The specific materials of the chelating agent described above are all chelating agents that efficiently form complexes with the second metal atom. Whether the chelating agent contained in the hole injection layer 22 forms a complex with the second metal atom may be confirmed, for example, by identifying the type of chelating agent and the type of second metal atom contained in the hole injection layer 22. The material and type of atom contained in the hole injection layer 22 may be identified, for example, by Fourier Transform Infrared Spectroscopy (FTIR).

[0024] For example, as shown in FIG. 1, the hole injection layer 22 may include a plurality of fine particles 31. The fine particles 31 may have at least one of a first metal atom and a chelating agent. For example, the fine particles 31 may contain the above-mentioned Mg ｘ Ni １－ｘThe nanoparticles may include nanoparticles of an oxide of an alloy having first metal atoms and second metal atoms, including nanoparticles of O.

[0025] <Display Element: Hole Transport Layer> The hole transport layer 23 is a layer containing a hole transport material that transports holes from the hole injection layer 22 to the light-emitting layer 24. The hole transport layer 23 improves the efficiency of transporting holes from the hole injection layer 22 to the light-emitting layer 24, thereby improving the hole concentration in the light-emitting layer 24.

[0026] In this embodiment, various organic or inorganic materials, including materials conventionally used in light-emitting devices, can be used for the material of the hole transport layer 23. For example, conductive compounds such as polyvinylcarbazole (PVK), [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD), 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylenevinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT-PSS), and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB) can be used as the organic material of the hole transport layer 23. Examples of inorganic materials that can be used for the hole transport layer 23 include molybdenum oxide, NiO, Cr, and the like. ２ O ３ , MgO, MgZnO, LaNiO ３ , MoO ３ , or W.O. ３ In particular, as the material for the hole transport layer 23, a material having a large electron affinity and ionization potential is suitable.

[0027] <Display Element: Electron Transport Layer> The electron transport layer 25 is a layer containing an electron transport material that transports electrons from the cathode 26 to the light-emitting layer 24. The electron transport layer 25 contains the same type of first metal atoms as the first metal atoms contained in the hole injection layer 22, for example, as metal atoms of the electron transport material.

[0028] The electron transport layer 25 may contain, for example, a metal oxide having the first metal atom. When the electron transport layer 25 contains the oxide of the first metal atom, the light-emitting element 2 has a simple structure and is made of a material that has the first metal atom and functions as an electron transport material.

[0029] For example, the electron transport layer 25 may contain ZnO, in other words, zinc oxide. In this case, the electron transport layer 25 may contain Zn as the first metal atom. Alternatively, the electron transport layer 25 may be an MgO doped Mg layer, where 0<y<1. ｙ Zn １－ｙ The electron transport layer 25 may contain Mg or Zn as the first metal atom, in other words, magnesium zinc oxide. When the electron transport layer 25 contains at least one of zinc oxide and magnesium zinc oxide, the electron transport layer 25 improves the efficiency of electron transport from the cathode 26 to the light-emitting layer 24, thereby improving the electron concentration in the light-emitting layer 24.

[0030] In this embodiment, the hole transport layer 23 and the electron transport layer 25 can be formed by vacuum deposition, sputtering, or a coating method using a colloidal solution using the above-mentioned materials. The light-emitting element 2 may also include an electron injection layer between the cathode 26 and the electron transport layer 25. The light-emitting element 2 may also include an intermediate layer, such as a charge blocking layer, between the hole transport layer 23 and the light-emitting layer 24, or between the electron transport layer 25 and the light-emitting layer 24. These electron injection layers and intermediate layers may be formed by the same method as the hole transport layer 23 or the electron transport layer 25. The method for forming the hole injection layer 22 according to this embodiment will be described in detail later.

[0031] <Display Element: Light-Emitting Layer> The light-emitting layer 24 includes a light-emitting material that emits light due to holes injected from the anode 21 via the hole injection layer 22 and the hole transport layer 23 and electrons injected from the cathode 26 via the electron transport layer 25. For example, the light-emitting material may be a material that emits light such as fluorescence or phosphorescence after being excited by excitons generated by the recombination of the holes and electrons described above. For example, the light-emitting layer 24 may include at least one of a quantum dot material, an organic fluorescent material, and an organic phosphorescent material as the light-emitting material.

[0032] The light-emitting material contained in the light-emitting layer 24 may be selected appropriately depending on the emission color of the subpixel in which the light-emitting element 2 is located. For example, the light-emitting layer 24 of the light-emitting element 2 in each of the red subpixel RSP, the green subpixel GSP, and the blue subpixel BSP may contain light-emitting materials that emit red light, green light, and blue light, respectively.

[0033] When the light-emitting layer 24 contains a quantum dot material, the light-emitting layer 24 may be formed, for example, by applying a dispersion liquid in which quantum dots are dispersed and drying the applied dispersion liquid, or may be patterned by a lift-off method or the like. When the light-emitting layer 24 contains an organic fluorescent material or an organic phosphorescent material, the light-emitting layer 24 may be formed, for example, by a vapor deposition method using a metal mask having an opening for each subpixel. However, the light-emitting layer 24 is not limited to the above, and may be formed by various methods including conventionally known methods.

[0034] <Band Gap of Each Layer of Display Element> Each layer included in the light-emitting element 2 will be described in more detail with reference to FIG. 3. FIG. 3 is a band diagram of each layer of the light-emitting element 2 according to this embodiment. In the band diagram shown in FIG. 3, it is assumed that the level at infinity is located upward as viewed into the paper. Of the layers included in the light-emitting element 2, the anode 21 and the cathode 26 each have their work functions shown in FIG. 3. The band gaps of each layer included in the light-emitting element 2, from the hole injection layer 22 to the electron transport layer 25, are shown in FIG.

[0035] For example, the barrier to hole injection from the anode 21 to the hole injection layer 22 corresponds to the energy difference between the work function of the anode 21 and the lower end level of the band gap of the hole injection layer 22. The barrier to electron injection from the cathode 26 to the electron transport layer 25 corresponds to the energy difference between the work function of the cathode 26 and the upper end level of the band gap of the electron transport layer 25.

[0036] The barriers to hole injection from the hole injection layer 22 to the hole transport layer 23 and from the hole transport layer 23 to the light-emitting layer 24 correspond to the difference in the lower end level of the band gap between the hole injection layer 22 and the hole transport layer 23 and between the hole transport layer 23 and the light-emitting layer 24, respectively. The barrier to electron injection from the electron transport layer 25 to the light-emitting layer 24 corresponds to the difference in the upper end level of the band gap between the electron transport layer 25 and the light-emitting layer 24.

[0037] The carrier balance in the light-emitting layer 24 is improved by reducing the difference between the hole concentration and the electron concentration in the light-emitting layer 24. Improving the carrier balance in the light-emitting layer 24 reduces the generation of charges, such as Auger electrons, that do not contribute to the light emission of the light-emitting layer 24 and that may deteriorate the materials of the light-emitting layer 24 and the layers nearby. Improving the carrier balance in the light-emitting layer 24 also reduces the loss of exciton energy through deactivation processes that do not contribute to the light emission of the light-emitting layer 24. Furthermore, improving the carrier balance in the light-emitting layer 24 increases the probability of recombination between holes and electrons in the light-emitting layer 24, thereby reducing the leakage of holes from the light-emitting layer 24 to the cathode 26 and the leakage of electrons from the light-emitting layer 24 to the anode 21. Therefore, improving the carrier balance in the light-emitting layer 24 contributes to improving the luminous efficiency or extending the life of the light-emitting element 2.

[0038] In order to improve the carrier balance in the light-emitting layer 24, it is conceivable to reduce the difference between the barriers to hole injection from the anode 21 to the light-emitting layer 24 and the barriers to electron injection from the cathode 26 to the light-emitting layer 24. Here, in this embodiment, both the hole injection layer 22 and the electron transport layer 25 contain first metal atoms. Therefore, differences in the band gap profiles of the hole injection layer 22 and the electron transport layer 25 are unlikely to occur, and as a result, differences in the efficiency of hole and electron injection from each electrode to the light-emitting layer 24 are unlikely to occur.

[0039] Therefore, the light-emitting element 2 improves the carrier balance in the light-emitting layer 24, improves the light-emitting efficiency, or extends the lifespan. The display device 1 including the light-emitting element 2 achieves reduced power consumption or extended lifespan.

[0040] 3 , the band gap of the hole injection layer 22 has HOMO22H as the lowest level. The band gap of the hole transport layer 23 has HOMO23H as the lowest level. The band gap of the electron transport layer 25 has HOMO25H as the lowest level. In this embodiment, the difference GH between HOMO22H and HOMO23H may be 0.5 eV or less.

[0041] Since the hole injection layer 22 contains the first metal atoms, the light-emitting element 2 can bring the energy of the lower end level of the band gap of the hole injection layer 22 closer to the energy of the lower end level of the band gap of the electron transport layer 25. This reduces the barrier to hole injection from the hole injection layer 22 to the hole transport layer 23 in the light-emitting element 2. Therefore, the light-emitting element 2 improves the efficiency of hole transport from the anode 21 to the light-emitting layer 24, thereby increasing the carrier concentration of holes in the light-emitting layer 24. In particular, when the carrier balance in the light-emitting layer 24 of the light-emitting element 2 is electron-excessive, the above-mentioned configuration of the light-emitting element 2 is effective in improving the carrier balance in the light-emitting layer 24, thereby more efficiently improving the light-emitting efficiency or extending the lifetime.

[0042] The band gap of the electron transport layer 25 may be larger than the band gap of the light-emitting layer 24. In particular, the HOMO25H of the electron transport layer 25 may be located lower in the band diagram than the lowest energy level of the light-emitting layer 24, or lower than the HOMO22H, HOMO23H, etc. In this case, the barrier to hole injection from the light-emitting layer 24 to the electron transport layer 25 becomes large. Therefore, with the above configuration, the light-emitting element 2 reduces the outflow of holes injected into the light-emitting layer 24 toward the electron transport layer 25, and improves the hole concentration in the light-emitting layer 24, thereby improving luminous efficiency.

[0043] Furthermore, the band gap of the electron transport layer 25 may be larger than the band gap of the light-emitting layer 24. In this case, the barrier to electron injection from the light-emitting layer 24 to the hole transport layer 23 becomes larger. Therefore, with the above configuration, the light-emitting element 2 reduces the outflow of electrons injected into the light-emitting layer 24 to the hole transport layer 23 side, and improves the electron concentration in the light-emitting layer 24, thereby improving the luminous efficiency.

[0044] As described above, for example, the light-emitting layer 24 contains at least one of a quantum dot material, an organic fluorescent material, and an organic phosphorescent material as a light-emitting material. These light-emitting materials efficiently improve the luminous efficiency or extend the lifetime by improving the carrier balance in the light-emitting layer 24. Therefore, the light-emitting element 2 having the light-emitting layer 24 containing at least one of the above-mentioned light-emitting materials more efficiently improves the luminous efficiency or extends the lifetime.

[0045] As described above, the hole injection layer 22 may contain second metal atoms different from the first metal atoms. This makes it possible to easily differentiate the profile at levels different from the HOMO, such as the upper end level of the band gap, while reducing the difference in the band gap profile contributing to charge transport between the hole injection layer 22 and the electron transport layer 25. Therefore, the light-emitting element 2 including the hole injection layer 22 has an increased degree of freedom in designing the hole injection layer 22, enabling a design that can achieve further improvement in luminous efficiency or a longer lifetime, or a simpler manufacturing method.

[0046] <Materials of Hole Injection Layer> Next, examples of specific configurations of materials contained in the hole injection layer 22 according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a schematic diagram showing examples of specific configurations of materials contained in the hole injection layer 22 according to this embodiment.

[0047] 4, for example, the hole injection layer 22 includes a metal oxide 41 having a first metal atom and a second metal atom. In particular, in the example shown in FIG. 4, magnesium nickel oxide, for example, Mg ｘ Ni １－ｘ In this case, the metal oxide 41 contains Mg as the first metal atoms and Ni as the second metal atoms.

[0048] 4, for example, the hole injection layer 22 includes a chelating agent 42. In the example shown in FIG. 4, the chelating agent 42 includes EDTA.

[0049] The chelating agent 42 containing EDTA forms a complex with a second metal atom, for example, Ni. Therefore, the chelating agent 42 containing EDTA forms a complex with a metal oxide 41 having Ni as the second metal atom. In particular, as shown in FIG. 4 , the chelating agent 42 may form a complex so as to surround the periphery of the metal oxide 41, thereby capturing the metal oxide 41.

[0050] As described above, the hole injection layer 22 contains the chelating agent 42 that forms a complex with the metal oxide 41. Therefore, in the hole injection layer 22, the plurality of metal oxides 41 that form a complex with the chelating agent 42 are less likely to come close to each other due to steric hindrance between the metal oxide 41 and the chelating agent 42. Therefore, aggregation of the plurality of metal oxides 41 is reduced in the hole injection layer 22.

[0051] For example, the hole injection layer 22 contains a metal oxide 41 as a hole transport material. Therefore, reducing the aggregation of the metal oxide 41 in the hole injection layer 22 reduces the occurrence of a deactivation process of charges, including holes, in the vicinity of the aggregated metal oxide 41. Furthermore, reducing the aggregation of the metal oxide 41 in the hole injection layer 22 reduces differences in the film thickness of the hole injection layer 22 during the formation of the hole injection layer 22, which will be described later, and improves the film formability of the hole injection layer 22, thereby improving the hole transport properties of the hole injection layer 22.

[0052] Therefore, the light-emitting element 2 including the hole injection layer 22 improves the characteristics of the hole injection layer 22, improving the carrier balance in the light-emitting layer 24 or extending the life of the hole injection layer 22. Therefore, the light-emitting element 2 including the hole injection layer 22 improves the luminous efficiency or extends the life. The display device 1 including the light-emitting element 2 achieves reduced power consumption or extended life.

[0053] The hole injection layer 22 according to this embodiment has both the first metal atom, which is also present in the electron transport layer 25, and the second metal atom, which forms a complex with the chelating agent 42. This reduces the difference in band gap profile between the hole injection layer 22 and the electron transport layer 25, while reducing aggregation of the metal oxide 41 containing the second metal atom. Therefore, the light emitting element 2 having the hole injection layer 22 further improves the luminous efficiency or extends the lifetime.

[0054] In this embodiment, the hole injection layer 22 has second metal atoms that form a complex with the chelating agent 42, but this is not limiting. For example, when the hole injection layer 22 includes first metal atoms and the chelating agent 42, the distance between the first metal atoms may be increased by the chelating agent 42. Therefore, the hole injection layer 22 having the above configuration can also reduce aggregation of metal oxides and the like that contain first metal atoms.

[0055] <Manufacturing Method: Up to Formation of Anode> A manufacturing method for the display device 1 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart of the manufacturing method for the display device 1 according to this embodiment.

[0056] In the manufacturing method of the display device 1 according to this embodiment, first, a substrate 3 is prepared (step S21). The substrate 3 may be formed by forming pixel circuits and drivers for driving the light-emitting elements 2 of each sub-pixel on a substrate such as a glass substrate or a film substrate.

[0057] Next, the anode 21 is formed on the substrate 3 (step S22). The anode 21 may be formed by forming a thin conductive film common to a plurality of sub-pixels by the above-described method, and then patterning the thin film for each sub-pixel.

[0058] <Manufacturing Method: Formation of Hole Injection Layer: Generation of Suspension> Next, the hole injection layer 22 is formed on the anode 21 (step S23). The formation of the hole injection layer will be described in more detail with reference to Fig. 6. Fig. 6 is a flowchart of a manufacturing method of the hole injection layer 22 according to this embodiment.

[0059] In this embodiment, an example will be described in which, in a method for forming a hole injection layer 22, fine particles 31 containing a metal oxide 41 having a first metal atom and a second metal atom and a chelating agent 42 are synthesized, and a thin film containing the fine particles 31 is formed. In particular, in this embodiment, the fine particles 31 contain Mg as the metal oxide 41. ｘ Ni １－ｘ In this embodiment, an example will be described in which the fine particles 31 contain O, and the metal oxide 41 contains Mg as the first metal atom and Ni as the second metal atom. In addition, in this embodiment, an example will be described in which the fine particles 31 contain EDTA as the chelating agent 42.

[0060] In the method for forming the hole injection layer 22 according to this embodiment, first, a mixed aqueous solution containing a first metal atom and a second metal atom is prepared (step S1). For example, in step S1, nickel nitrate hexahydrate and magnesium acetate are dissolved in pure water to prepare a mixed aqueous solution of nickel nitrate and magnesium acetate. This prepares a mixed aqueous solution containing Mg as the first metal atom and Ni as the second metal atom.

[0061] Next, the pH of the mixed aqueous solution prepared in step S1 is adjusted to produce a suspension (step S2). In step S2, a sodium hydroxide aqueous solution is added dropwise to the mixed aqueous solution until the pH of the mixed aqueous solution reaches, for example, 12. As a result, a green suspension is produced in step S2.

[0062] <Manufacturing Method: Formation of Hole Injection Layer: Separation of Precipitate> Next, a chelating agent 42 is added to the suspension produced in step S2, and the suspension is stirred (step S3). In step S3, the suspension is stirred while, for example, an aqueous solution of EDTA as the chelating agent 42 is added dropwise to the suspension. For example, ultrasonic waves may be irradiated onto the suspension during stirring in step S3. For example, stirring of the suspension in step S3 may be carried out for one hour.

[0063] Step S3 generates a green precipitate in the suspension. In this embodiment, the precipitate is, for example, Mg ｘ Ni １－ｘ (OH) ２ In other words, it may contain a complex of magnesium nickel hydroxide and EDTA.

[0064] Next, the precipitate is centrifuged from the suspension (step S4). ｘ Ni １－ｘ (OH) ２ The complex between EDTA and EDTA is separated.

[0065] <Manufacturing Method: Formation of Hole Injection Layer: Precipitate Treatment> Next, the precipitate separated in step S4 is washed (step S5). In step S5, the precipitate may be washed with pure water, for example, to remove any residual suspension adhering to the precipitate. Here, washing of the precipitate in step S5 may be performed multiple times. In particular, in this case, the precipitate that has been washed once in step S5 may be added to pure water again, and centrifuged again to separate the precipitate, and then the precipitate may be washed again. This may result in a precipitate with fewer impurities.

[0066] Next, the precipitate washed in step S5 is dried (step S6). Step S6 may be performed by drying the precipitate in an environment at 80° C. As a result, the precipitate may be changed into a clay-like state in step S6.

[0067] <Manufacturing Method: Formation of Hole Injection Layer: Formation of Fine Particles> Next, the clay-like precipitate obtained in step S6 is pulverized (step S7). The pulverization of the precipitate in step S7 may be performed by subjecting the precipitate to a mill. As a result, the precipitate may become a green powder in step S7.

[0068] Next, the powder obtained in step S7 is heated to form the fine particles 31 (step S8). In step S8, the powder may be heated at 500° C. for 5 hours. In step S8, the Mg contained in the powder is ｘ Ni １－ｘ (OH) ２ From H ２ O is removed and Mg ｘ Ni １－ｘ In other words, step S8 may be a calcination step to remove water from the powder. ｘ Ni １－ｘ Fine particles 31 containing a complex of O and EDTA are obtained.

[0069] <Production Method: Formation of Hole Injection Layer: Coating and Drying of Dispersion Liquid> Next, the obtained fine particles 31 are added to a solvent to prepare a dispersion liquid of the fine particles 31 (step S9). The solvent for the dispersion liquid of the fine particles 31 may contain, for example, toluene, octane, etc. Here, the fine particles 31 are Mg ｘ Ni １－ｘ In this embodiment, since the dispersion contains a complex of O and EDTA, it is possible to reduce aggregation of the fine particles 31 in the dispersion.

[0070] Next, the dispersion liquid of the microparticles 31 obtained in step S9 is applied onto the anode 21 (step S10). In particular, in step S10, the dispersion liquid of the microparticles 31 may be applied by various application methods including conventionally known methods such as spin coating. As a result, a layer of the dispersion liquid containing the microparticles 31 is formed on the anode 21.

[0071] Next, the dispersion of the fine particles 31 applied in step S10 is dried (step S11). As a result, only the solvent in the layer of the dispersion of the fine particles 31 applied in step S10 evaporates, and the fine particles 31 are layered on the anode 21. As a result, a thin film containing the fine particles 31 is formed on the anode 21, and the formation of the hole injection layer 22 on the anode 21 is completed.

[0072] <Manufacturing Method: Formation of Hole Transport Layer and After> Referring back to FIG. 5 , after the formation of the hole injection layer 22, the hole transport layer 23 is formed (step S24). Next, the light-emitting layer 24 is formed (step S25), the electron transport layer 25 is formed (step S26), and the cathode 26 is formed (step S27). Each of steps S24 to S27 may be performed by any of the methods for forming each layer described above. In this way, the light-emitting element 2 is formed on the substrate 3, and the manufacture of the display device 1 is completed.

[0073] The display device 1 manufactured by the above method achieves reduced power consumption and extended life for the same reasons as those described above. Furthermore, the above method can reduce aggregation of the particles 31 in the dispersion of the particles 31 in step S10. Therefore, the above method can not only reduce the deterioration of the hole injection characteristics of the hole injection layer 22 due to aggregation of the particles 31, but also improve the uniformity of the film thickness of the hole injection layer 22.

[0074] <Characteristics Evaluation: Comparison with Hole Injection Layer of Comparative Example> The characteristics of the hole injection layer 22 of the light-emitting element 2 according to this embodiment will be explained using the explanation of the hole injection layer according to the example. The hole injection layer according to the example was formed by the same method as step S23 according to this embodiment described above. However, in the example, the hole injection layer was formed directly on the substrate.

[0075] Furthermore, a hole injection layer according to a comparative example was formed. ｘ Ni １－ｘ The film was formed directly on the substrate by coating and film formation of a dispersion of fine particles containing only O.

[0076] The results of FTIR measurements on the hole injection layers of the Examples and Comparative Examples are summarized in Figure 7. Figure 7 is a graph showing the results of FTIR measurements on the hole injection layers of the Examples and Comparative Examples. In Figure 7, the horizontal axis represents the wave number (unit: cm) of infrared light irradiated onto each hole injection layer. －１ ) and the vertical axis represents the absorbance (arbitrary unit) of infrared light obtained after irradiating each hole injection layer with the infrared light.

[0077] As shown in FIG. 7, the FTIR measurement results for the hole injection layer according to the example show that the wave number of the irradiated infrared light is 1320 to 1330 cm －１ When the wavenumber of the irradiated infrared light is around 1320 to 1330 cm, a dip D indicating absorption of infrared light is observed. This indicates that EDTA, which is a chelating agent contained in the hole injection layer according to the example, absorbs infrared light having the above wavenumber. On the other hand, in the FTIR measurement results for the hole injection layer according to the comparative example, a dip D is not observed around the above wavenumber. From the above, when FTIR is performed on the hole injection layer, it is found that the wavenumber of the irradiated infrared light is 1320 to 1330 cm. －１ Whether or not the hole injection layer contains EDTA as a chelating agent can be confirmed by whether or not absorption of infrared light is observed when the wavelength is in the vicinity of 1000 nm.

[0078] <Characteristics Evaluation: Measurement of Crystallite Size> Next, the hole injection layer according to the example was measured by XRD (X-ray diffraction), and the results are shown in Fig. 8. Fig. 8 is a graph showing the results of the XRD measurement of the hole injection layer according to the example. The horizontal axis of Fig. 8 represents the X-ray irradiation angle 2θ (unit: °), and the vertical axis represents the measured X-ray intensity (arbitrary unit).

[0079] As shown in FIG. 8 , the results of the XRD measurement of the hole injection layer according to the example show peaks P1, P2, and P3 in the measured X-ray intensity when 2θ is 36.99°, 43.07°, and 62.65°, respectively.

[0080] Generally, the half-width of the peak obtained in the results of XRD measurement correlates with the crystallite size of the sample. Therefore, the crystallite size of the sample can be calculated from the half-width of the peak obtained in the results of XRD measurement. For example, when the wavelength of the X-ray irradiated to the sample in XRD is λ (unit: nm), the broadening of the diffraction line width is B (unit: rad), and the Bragg angle is θ (unit: rad), the crystallite size D (unit: nm) of the sample satisfies D = Kλ / B cos θ. Here, the Scherrer constant K depends on the definition of the crystallite size of the sample to be measured. In the present disclosure, the crystallite size to be measured is defined by the volume-weighted average diameter, and thus the case where the Scherrer constant K is 8 / 3π is described.

[0081] The crystallite size of the hole injection layer according to the example calculated from the half width of peak P1 shown in Figure 8 is 4.0 nm. The crystallite size of the hole injection layer according to the example calculated from the half width of peak P2 is 3.7 nm. The crystallite size of the hole injection layer according to the example calculated from the half width of peak P3 is 3.8 nm. The average value of the calculation results of the crystallite sizes of these hole injection layers is 3.8 nm.

[0082] Therefore, it can be seen that the crystallite size of the hole injection layer according to the example is 4.0 nm or less. A hole injection layer with a crystallite size of 4.0 nm or less further reduces the occurrence of aggregation of the contained metal oxides and the like.

[0083] <Characteristics Evaluation: Measurement of Particle Diameter> Next, the particle diameters of the particles contained in the hole injection layer according to the example were measured. The particle diameters of the particles were measured by performing DLS (Dynamic Light Scattering) on ​​the particle dispersion prepared in step S9. The DLS measurement results are summarized in FIG. 9. FIG. 9 is a histogram showing the percentage of the number of particles contained in the hole injection layer according to the example, integrated for each particle diameter. The horizontal axis of FIG. 9 represents the particle diameter (unit: nm) of the particle, and the vertical axis represents the percentage (unit: %) of the number of particles having the corresponding particle diameter relative to the total number of particles contained in the hole injection layer.

[0084] As shown in Figure 9, the particle diameters of the microparticles obtained in the examples are in the range of approximately 6 nm to 24 nm. This shows that the examples reduce the aggregation of the obtained microparticles in the dispersion liquid, which causes an increase in the apparent particle diameter. Furthermore, the average particle diameter of each microparticle measured by the DLS was 10.67 nm, which was 11 nm or less. In the hole injection layer according to the examples containing microparticles with an average particle diameter of 11 nm or less, the occurrence of aggregation of the contained microparticles is sufficiently reduced.

[0085] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining different technical means disclosed in the embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in the embodiments.

[0086] REFERENCE SIGNS LIST 1 Display device 2 Light-emitting element 3 Substrate 21 Anode 22 Hole injection layer 23 Hole transport layer 24 Light-emitting layer 25 Electron transport layer 26 Cathode 31 Fine particles 41 Metal oxide 42 Chelating agent

Claims

1. A light-emitting element comprising: an anode; a cathode facing the anode; a light-emitting layer located between the anode and the cathode; a hole injection layer between the anode and the light-emitting layer; and an electron transport layer between the cathode and the light-emitting layer, wherein the electron transport layer contains a first metal atom; and the hole injection layer contains the first metal atom and a chelating agent.

2. The light-emitting device according to claim 1, wherein the hole injection layer contains second metal atoms different from the first metal atoms.

3. The light-emitting device according to claim 2, wherein the hole injection layer contains an oxide of an alloy having the first metal atoms and the second metal atoms.

4. The light-emitting device according to claim 2 or 3, wherein the chelating agent forms a complex with the second metal atom.

5. The light-emitting device according to any one of claims 2 to 4, wherein the second metal atoms include at least one of Ni, Cu, and Co.

6. The light-emitting device according to any one of claims 1 to 5, wherein the first metal atoms include at least one of Mg, Zn, Cu, and Co.

7. The light-emitting element according to any one of claims 1 to 6, wherein the chelating agent includes at least one of EDTA, NTA, DTPA, GLDA, HEDTA, GEDTA, TTHA, HIDA, and DHEG.

8. The light-emitting element according to any one of claims 1 to 7, wherein the electron transport layer contains a metal oxide having the first metal atoms.

9. The light-emitting device according to any one of claims 1 to 8, wherein the crystallite size of the hole injection layer is 4.0 nm or less.

10. The light-emitting device according to any one of claims 1 to 9, wherein the hole injection layer contains fine particles having at least one of the first metal atoms and the chelating agent and having an average particle size of 11 nm or less.

11. The light-emitting device according to any one of claims 1 to 10, wherein the electron transport layer contains at least one of zinc oxide and magnesium zinc oxide.

12. The light-emitting device according to any one of claims 1 to 11, wherein the hole injection layer is in contact with the anode.

13. The light-emitting device according to any one of claims 1 to 12, further comprising a hole transport layer between the anode and the hole injection layer.

14. The light-emitting device according to claim 13, wherein the difference between the HOMO of the hole injection layer and the HOMO of the hole transport layer is 0.5 eV or less.

15. The light-emitting device according to any one of claims 1 to 14, wherein the light-emitting layer includes at least one of a quantum dot material, an organic fluorescent material, and an organic phosphorescent material.

16. A display device comprising a light-emitting element according to any one of claims 1 to 15.

17. A method for manufacturing a light-emitting element comprising an anode, a cathode facing the anode, a light-emitting layer located between the anode and the cathode, a hole injection layer between the anode and the light-emitting layer, and an electron transport layer between the cathode and the light-emitting layer, the method comprising: forming the electron transport layer containing a first metal atom; and forming the hole injection layer containing the first metal atom and a chelating agent.

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