Light-emitting element, display device, method for producing light-emitting element, and method for producing metal oxide nanoparticles

Abstract

The light-emitting element is provided with a hole transport layer (24HT) as a charge transport layer, the hole transport layer (24HT) containing a plurality of nickel oxide nanoparticles (NP ') having no surface oxygen vacancy portion (DE), and one or more nickel oxide nanoparticles (NP') among the plurality of nickel oxide nanoparticles (NP ') are provided with a coating portion (30) comprising an inorganic oxide on at least a part of the surface (SU) thereof.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a light emitting element, a display device, a manufacturing method of a light emitting element, and a manufacturing method of metal oxide nanoparticles. BACKGROUND

[0002] In recent years, various display devices provided with a light emitting element have been developed, and in particular, display devices provided with an OLED (Organic Light Emitting Diode) or a QLED (Quantum dot Light Emitting Diode) have attracted attention because they can achieve low power consumption, thinness, high image quality, and the like.

[0003] In the field of OLEDs or QLEDs, organic materials are mainly used as hole transport layers, hole injection layers, electron transport layers, and electron injection layers, and the like, because they have high charge transport properties (carrier (hole or electron) transport properties).

[0004] However, in the case of charge transport layers such as hole transport layers, hole injection layers, electron transport layers, and electron injection layers formed of organic materials, there are problems with reliability.

[0005] Therefore, research on inorganic materials that can be used as charge transport layers for OLEDs or QLEDs is actively being conducted.

[0006] Patent Document 1 discloses the use of nanocrystals (nanoparticles) of, for example, nickel oxide, which is an inorganic material, for charge transport layers.

[0007] PRIOR ART DOCUMENTS PATENT DOCUMENTS Patent Document 1: Japanese Patent Publication “Tokukai No. 2019-522367” SUMMARY Technical Problem to be Solved by the Invention Generally, metal oxide nanoparticles have surface oxygen defect portions (oxygen defect portions formed on the surface due to the absence of intermolecular interactions in the surface of the metal oxide nanoparticles) formed at random locations and in random amounts in the manufacturing process thereof. Due to the influence of the surface oxygen defect portions, the energy levels change, resulting in a deviation in the energy levels of each metal oxide nanoparticle. Thus, in the case of a light emitting element provided with a charge transport layer formed using metal oxide nanoparticles having surface oxygen defect portions formed on the surface, there is a problem of a decrease in light emitting efficiency accompanied by a decrease in external quantum efficiency (EQE).

[0008] Patent Document 1 describes a light-emitting element provided with a charge transport layer containing nanocrystals (nanoparticles) of nickel oxide as metal oxide nanoparticles and an organic molecule provided with an electron-withdrawing group.

[0009] However, the nanocrystals (nanoparticles) of nickel oxide contained in the charge transport layer provided in the light-emitting element described in Patent Document 1 still have surface oxygen defect portions, and thus it is not possible to suppress the decrease in the light-emitting efficiency described above, and furthermore, since an organic molecule having an electron-withdrawing group is used, there is a problem in reliability.

[0010] An aspect of the present disclosure, which is made in view of the above-described problems, aims to provide a light-emitting element, a display device, a manufacturing method of a light-emitting element, and a manufacturing method of metal oxide nanoparticles, which have high reliability and can suppress a decrease in light-emitting efficiency accompanying a decrease in external quantum efficiency (EQE).

[0011] Technical Solution for Solving Technical Problem To solve the problem, the light-emitting element of the present disclosure has: an anode; a cathode; a light-emitting layer provided between the anode and the cathode; and a charge transport layer provided between one of the anode and the cathode and the light-emitting layer, the charge transport layer containing a plurality of metal oxide nanoparticles having no surface oxygen defect portions, one or more of the plurality of metal oxide nanoparticles being provided with a coating portion on at least a part of a surface thereof, the coating portion being composed of an inorganic oxide.

[0012] To solve the problem, the display device of the present disclosure contains the light-emitting element.

[0013] To solve the problem, the manufacturing method of a light-emitting element of the present disclosure includes a charge transport layer formation step, the charge transport layer formation step including: a step of providing a coating portion containing an inorganic oxide on a surface of each of a plurality of metal oxide nanoparticles; and a step of, after the step of providing the coating portion, heat-treating the plurality of metal oxide nanoparticles in an oxygen atmosphere.

[0014] To solve the problem, the manufacturing method of metal oxide nanoparticles of the present disclosure includes: a step of providing a coating portion containing an inorganic oxide on a surface of each of a plurality of metal oxide nanoparticles; and a step of, after the step of providing the coating portion, heat-treating the plurality of metal oxide nanoparticles in an oxygen atmosphere. Advantageous Effects An aspect of the present disclosure can provide a light-emitting element, a display device, a manufacturing method of a light-emitting element, and a manufacturing method of metal oxide nanoparticles, which can improve reliability and can suppress a decrease in luminous efficiency accompanying a decrease in external quantum efficiency (EQE). BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a top view showing a schematic configuration of a display device of the first embodiment.

[0016] Figure 2 is a cross-sectional view showing a schematic configuration of a display region of the display device of the first embodiment.

[0017] Figure 3 is a view showing a manufacturing process of the display device of the first embodiment including a manufacturing process of a red light-emitting element, a green light-emitting element, and a blue light-emitting element.

[0018] Figure 4 is a cross-sectional view showing a schematic configuration of the red light-emitting element included in the display device of the first embodiment.

[0019] Figure 5 is a cross-sectional view showing a schematic configuration of the green light-emitting element included in the display device of the first embodiment.

[0020] Figure 6 is a cross-sectional view showing a schematic configuration of the blue light-emitting element included in the display device of the first embodiment.

[0021] Figure 7 is a view showing a manufacturing process of the display device of the first embodiment. Figure 3 is a view showing a manufacturing process of the display device of the first embodiment.

[0022] Figure 8 is a view showing a manufacturing process of metal oxide nanoparticles, i.e., nanoparticles of nickel oxide, having surface oxygen defect portions.

[0023] Figure 9 is a view for explaining a process in which a plurality of nanoparticles of nickel oxide each having a coating portion including an inorganic oxide provided on a surface thereof are manufactured by the manufacturing process of the nanoparticles of nickel oxide shown in Figure 8 is a view for explaining a process in which a plurality of nanoparticles of nickel oxide each having a coating portion including an inorganic oxide provided on a surface thereof are manufactured by the manufacturing process of the nanoparticles of nickel oxide shown in

[0024] Figure 10 is a view showing a schematic state of the nanoparticles of nickel oxide in each process shown in Figure 9

[0025] Figure 11 ​is a cross-sectional view showing the schematic configuration of a charge transport layer, i.e., a hole transport layer, included in each of a red light emitting element, a green light emitting element, and a blue light emitting element included in the display device of the first embodiment.

[0026] Figure 12 is a cross-sectional view showing the schematic configuration of a red light emitting element included in the display device of the second embodiment.

[0027] Figure 13 is a cross-sectional view showing the schematic configuration of a charge transport layer, i.e., an electron transport layer, included in the red light emitting element shown in FIG. 8. Figure 12

[0028] Figure 14 is a cross-sectional view showing the schematic configuration of a red light emitting element included in the display device of the third embodiment. DETAILED DESCRIPTION

[0029] Based on the above, the present application is described as follows. Hereinafter, for the convenience of explanation, for the configurations having the same functions as the configurations explained in the specific embodiments, the same reference numerals are sometimes marked and the explanation thereof is omitted. Figures 1 to 14

[0030] [First Embodiment] Figure 1 is a plan view showing the schematic configuration of the display device 1 of the first embodiment.

[0031] As shown in FIG. 1, the display device 1 includes a frame region NDA and a display region DA. In the display region DA of the display device 1, a plurality of pixels PIX are included, and each of the pixels PIX includes a red sub-pixel RSP, a green sub-pixel GSP, and a blue sub-pixel BSP. In the present embodiment, a case where one pixel PIX is configured of the red sub-pixel RSP, the green sub-pixel GSP, and the blue sub-pixel BSP is explained as an example, but the present embodiment is not limited thereto. For example, 1 pixel PIX can include sub-pixels of other colors in addition to the red sub-pixel RSP, the green sub-pixel GSP, and the blue sub-pixel BSP. Figure 1

[0032] Figure 2 is a cross-sectional view showing the schematic configuration of the display region DA of the display device 1 of the first embodiment.

[0033] As shown in FIG. 10, in the display region DA of the display device 1, on the substrate 12, from the substrate 12 side, the following are included in order: the barrier layer 3; the thin film transistor layer 4 including the transistor TR; the red light emitting element 5R, the green light emitting element 5G, the blue light emitting element 5B, and the bank 23; the sealing layer 6; and the functional film 39. Figure 2 ​​​​

[0034] The red sub-pixel RSP provided in the display region DA of the display device 1 includes the red light emitting element 5R as the light emitting element, the green sub-pixel GSP provided in the display region DA of the display device 1 includes the green light emitting element 5G as the light emitting element, and the blue sub-pixel BSP provided in the display region DA of the display device 1 includes the blue light emitting element 5B as the light emitting element.

[0035] The substrate 12 can be a resin substrate composed of a resin material such as polyimide, or a glass substrate. In the present embodiment, the case where, for example, a resin substrate composed of a resin material such as polyimide is used as the substrate 12 is exemplified as an example of the case where the display device 1 is a flexible display device, but is not limited thereto. In the case where the display device 1 is a non-flexible display device, for example, a glass substrate can be used as the substrate 12.

[0036] The barrier layer 3 is a layer for preventing invasion of foreign matters such as water and oxygen into the transistor TR, the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B, and can be composed of, for example, a silicon oxide film, a silicon nitride film, or a silicon oxynitride film formed by a CVD method, or a laminated film thereof.

[0037] The transistor TR portion of the thin film transistor layer 4 including the transistor TR includes the semiconductor film SEM and the doped semiconductor films SEM', SEM", the inorganic insulating film 16, the gate electrode G, the inorganic insulating film 18, the inorganic insulating film 20, the source electrode S and the drain electrode D, and the planarization film 21, and the portion of the thin film transistor layer 4 including the transistor TR other than the transistor TR portion includes the inorganic insulating film 16, the inorganic insulating film 18, the inorganic insulating film 20, and the planarization film 21.

[0038] The semiconductor films SEM, SEM', and SEM" can be composed of, for example, low temperature polysilicon (LTPS) or an oxide semiconductor (for example, an In-Ga-Zn-O-based semiconductor). In the present embodiment, the case where the transistor TR is of a top gate structure is exemplified, but is not limited thereto, and the transistor TR can be of a bottom gate structure.

[0039] The gate electrode G and the source electrode S and the drain electrode D can be composed of, for example, a single layer film or a laminated film of a metal including at least one of aluminum, tungsten, molybdenum, tantalum, chromium, titanium, and copper.

[0040] The inorganic insulating film 16, the inorganic insulating film 18, and the inorganic insulating film 20 can be composed of, for example, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film thereof formed by a CVD method.

[0041] The planarization film 21 can be composed of, for example, a coatable organic material such as polyimide or acrylic.

[0042] The red light emitting element 5R included in the red sub-pixel RSP includes an anode 22 which is upper than the planarization film 21, a functional layer 24R including a red light emitting layer, and a cathode 25. The green light emitting element 5G included in the green sub-pixel GSP includes an anode 22 which is upper than the planarization film 21, a functional layer 24G including a green light emitting layer, and a cathode 25. The blue light emitting element 5B included in the blue sub-pixel BSP includes an anode 22 which is upper than the planarization film 21, a functional layer 24B including a blue light emitting layer, and a cathode 25. In addition, the insulating bank 23 which covers the edge of the anode 22 can be formed by, for example, patterning using photolithography after coating an organic material such as polyimide or acrylic.

[0043] In the present embodiment, a case where the functional layer 24R including the red light emitting layer is configured by sequentially stacking a hole transport layer, a red light emitting layer, and an electron transport layer from the anode 22 side is described as an example, but is not limited thereto. The functional layer 24R including the red light emitting layer can be configured by, for example, sequentially stacking a hole injection layer, a hole transport layer, a red light emitting layer, an electron transport layer, and an electron injection layer from the anode 22 side, or can be configured to have the red light emitting layer and one or more layers selected from a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer as a charge transport layer, for example.

[0044] In the present embodiment, a case where the functional layer 24G including the green light emitting layer is configured by sequentially stacking a hole transport layer, a green light emitting layer, and an electron transport layer from the anode 22 side is described as an example, but is not limited thereto. The functional layer 24G including the green light emitting layer can be configured by, for example, sequentially stacking a hole injection layer, a hole transport layer, a green light emitting layer, an electron transport layer, and an electron injection layer from the anode 22 side, or can be configured to have the green light emitting layer and one or more layers selected from a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer as a charge transport layer, for example.

[0045] In the present embodiment, a case where the functional layer 24B including the blue light emitting layer is configured by sequentially stacking a hole transport layer, a blue light emitting layer, and an electron transport layer from the anode 22 side is described as an example, but is not limited thereto. The functional layer 24B including the blue light emitting layer can be configured by, for example, sequentially stacking a hole injection layer, a hole transport layer, a blue light emitting layer, an electron transport layer, and an electron injection layer from the anode 22 side, or can be configured to have the blue light emitting layer and one or more layers selected from a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer as a charge transport layer, for example.

[0046] In this embodiment, a case where the functional layer 24R including the red light-emitting layer, the functional layer 24G including the green light-emitting layer, and the functional layer 24B including the blue light-emitting layer each have a hole-transport layer formed using the same material in the same process and an electron-transport layer formed using the same material in the same process is described as an example, but is not limited thereto.

[0047] For example, each of the hole-transport layers included in each of the functional layers 24R, 24G, and 24B can be formed of mutually different materials, and for example, the hole-transport layers included in two of the functional layers 24R, 24G, and 24B can be formed using the same material in the same process, and the hole-transport layer included in the remaining one of the functional layers can be formed using a different material in another process.

[0048] Further, for example, each of the electron-transport layers included in each of the functional layers 24R, 24G, and 24B can be formed of mutually different materials, and for example, the electron-transport layers included in two of the functional layers 24R, 24G, and 24B can be formed using the same material in the same process, and the electron-transport layer included in the remaining one of the functional layers can be formed using a different material in another process.

[0049] In this embodiment, a case where the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B each are a QLED (quantum dot light-emitting diode) having a light-emitting layer containing quantum dots is described as an example, but is not limited thereto, and each of the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B can be an OLED (organic light-emitting diode) having an organic light-emitting layer, and further, part of the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B can be a QLED, and the remaining part of the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B can be an OLED.

[0050] The control circuit including the transistor TR that controls the red light-emitting element 5R, the control circuit including the transistor TR that controls the green light-emitting element 5G, and the control circuit including the transistor TR that controls the blue light-emitting element 5B are each provided in the thin film transistor layer 4 including the transistor TR for each subpixel of each of the red subpixels RSP, the green subpixels GSP, and the blue subpixels BSP. Note that the control circuit including the transistor TR provided for each of the red subpixels RSP, the green subpixels GSP, and the blue subpixels BSP and the light-emitting element are collectively referred to as a subpixel circuit.

[0051] Figure 2The red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B shown are either a top emission type or a bottom emission type. The red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B have a stack structure in which an anode 22, each functional layer 24R, 24G, 24B, and a cathode 25 are formed in this order from the substrate 12 side, and therefore the cathode 25 is disposed more on the upper layer than the anode 22, and therefore in order to be a top emission type, the anode 22 is formed of an electrode material that reflects visible light, and the cathode 25 is formed of an electrode material that transmits visible light, and in order to be a bottom emission type, the anode 22 is formed of an electrode material that transmits visible light, and the cathode 25 is formed of an electrode material that reflects visible light.

[0052] Although not shown, the red light emitting element 5R, the green light emitting element 5G, and the blue light emitting element 5B can be an inverse stack structure in which the cathode 25, each functional layer (for example, an electron transport layer, a light emitting layer, and a hole transport layer are sequentially stacked from the substrate 12 side), and the anode 22 are formed in this order from the substrate 12 side, and in the case of the inverse stack structure, the anode 22 is disposed more on the upper layer than the cathode 25, and therefore in order to be a top emission type, the cathode 25 is formed of an electrode material that reflects visible light, and the anode 22 is formed of an electrode material that transmits visible light, and in order to be a bottom emission type, the cathode 25 is formed of an electrode material that transmits visible light, and the anode 22 is formed of an electrode material that reflects visible light.

[0053] As the electrode material that reflects visible light, an electrode material that can reflect visible light, as long as it has conductivity, is not particularly limited, and for example, a metal material such as Al, Mg, Li, Ag, or an alloy of the metal material or a laminate of the metal material and a transparent metal oxide such as indium tin oxide, indium zinc oxide, indium gallium zinc oxide, or a laminate of the alloy and the transparent metal oxide can be cited.

[0054] On the other hand, as the electrode material that transmits visible light, an electrode material that can transmit visible light, as long as it has conductivity, is not particularly limited, and for example, a transparent metal oxide such as indium tin oxide, indium zinc oxide, indium gallium zinc oxide, or a thin film composed of a metal material such as Al or Ag or a nano wire composed of a metal material such as Al or Ag can be cited.

[0055] In this embodiment, the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B are top-emitting types with a superposition structure. Therefore, the example given is that the anode 22 is formed by a laminated film of electrode material that reflects visible light, namely ITO (indium tin oxide) / Ag / ITO, and the cathode 25 is formed by a thin film of electrode material that transmits visible light, namely Ag. However, this is not the only example.

[0056] The sealing layer 6 is a light-transmitting membrane, which may be composed of, for example, an inorganic sealing membrane 26 covering the cathode 25, an organic membrane 27 positioned above the inorganic sealing membrane 26, and an inorganic sealing membrane 28 positioned above the organic membrane 27. The sealing layer 6 prevents foreign matter such as water and oxygen from penetrating into the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B.

[0057] Inorganic sealing films 26 and 28 are inorganic films, such as silicon oxide films, silicon nitride films, or silicon oxynitride films formed by CVD, or laminates thereof. Organic film 27 is a light-transmitting organic film with a planarization effect, such as being made of a material that can be coated with organic cloth, such as acrylic. Organic film 27 can be formed, for example, by inkjet printing. In this embodiment, the sealing layer 6 is illustrated by forming a sealing layer 6 with two inorganic films and an organic film disposed between the two inorganic films, but the stacking order of the two inorganic films and the organic film is not limited to this. Furthermore, the sealing layer 6 can be composed of only inorganic films, only organic films, one inorganic film and two organic films, or two or more inorganic films and two or more organic films.

[0058] The functional film 39 is, for example, a thin film having at least one of optical compensation function, touch sensor function, and protection function.

[0059] Figure 3 This is a diagram illustrating the manufacturing process of a display device 1 according to a first embodiment, which includes a red light-emitting element 5R, a green light-emitting element 5G, and a blue light-emitting element 5B.

[0060] like Figure 3 As shown, the light-emitting element with a product structure Figure 2The manufacturing process of the display device 1 shown includes: a process of forming a barrier layer 3 and a thin-film transistor layer 4 on a substrate 12 (S1); a process of forming an anode 22 (S2); a process of forming a barrier 23 (S3); a process of forming a functional layer 24R including a red light-emitting layer contained in a red light-emitting element 5R, a functional layer 24G including a green light-emitting layer contained in a green light-emitting element 5G, and a functional layer 24B including a blue light-emitting layer contained in a blue light-emitting element 5B (S4); a process of forming a cathode 25 (S5); a process of forming a sealing layer 6 (S6); and a process of forming a functional film 39 (S7). On the other hand, although not shown, the manufacturing process of a display device with a light-emitting element having an inverse phase structure is similar to that of a display device with an inverse phase structure, except for the change in the order of the process of forming the anode 22 (S2) and the process of forming the cathode 25 (S5). Figure 3 The manufacturing process of the display device 1 with the light-emitting element of the superposition structure shown is the same.

[0061] Figure 4 This is a cross-sectional view showing the schematic configuration of the red light-emitting element 5R included in the display device 1 of the first embodiment.

[0062] Figure 5 This is a cross-sectional view showing the schematic configuration of the green light-emitting element 5G included in the display device 1 of the first embodiment.

[0063] Figure 6 This is a cross-sectional view showing the schematic configuration of the blue light-emitting element 5B included in the display device 1 of the first embodiment.

[0064] Figure 7 It indicates formation Figure 3 The diagram shows the process flow of each functional layer 24R, 24G, 24B in the manufacturing process of the display device 1 of the first embodiment.

[0065] like Figure 7 As shown, the process of forming the functional layer 24R of the red light-emitting element 5R, the functional layer 24G of the green light-emitting element 5G, and the functional layer 24B of the blue light-emitting element 5B includes: forming a hole transport layer 24HT on the anode 22 (S11), forming a light-emitting layer 24REM (red light-emitting layer) (S12), forming a light-emitting layer 24GEM (green light-emitting layer) (S13), forming a light-emitting layer 24BEM (blue light-emitting layer) (S14), and forming an electron transport layer 24ET (S15).

[0066] In the present embodiment, the formation of the light-emitting layer 24REM (red light-emitting layer), the light-emitting layer 24GEM (green light-emitting layer), and the light-emitting layer 24BEM (blue light-emitting layer) in this order is described as an example, but the present embodiment is not limited thereto. These light-emitting layers can be formed in any order.

[0067] In the present embodiment, as described above, the functional layer 24R, the functional layer 24G, and the functional layer 24B each have the hole-transporting layer 24HT formed using the same material in the same process, so in the process (S11) of forming the hole-transporting layer 24HT on the anode 22, the hole-transporting layer 24HT is formed on the anode 22 having the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B, as illustrated in FIG. 6A. Figure 4 Figure 5 Figure 6 In the present embodiment, as described above, the functional layer 24R, the functional layer 24G, and the functional layer 24B each have the hole-transporting layer 24HT formed using the same material in the same process, so in the process (S11) of forming the hole-transporting layer 24HT on the anode 22, the hole-transporting layer 24HT is formed on the anode 22 having the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B, as illustrated in FIG. 6A.

[0068] In the present embodiment, as described above, the functional layer 24R, the functional layer 24G, and the functional layer 24B each have the hole-transporting layer 24HT formed using the same material in the same process, so in the process (S11) of forming the hole-transporting layer 24HT on the anode 22, the hole-transporting layer 24HT is formed on the anode 22 having the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B, as illustrated in FIG. 6A. Figure 4 Figure 6 In the present embodiment, as described above, the functional layer 24R, the functional layer 24G, and the functional layer 24B each have the hole-transporting layer 24HT formed using the same material in the same process, so in the process (S11) of forming the hole-transporting layer 24HT on the anode 22, the hole-transporting layer 24HT is formed on the anode 22 having the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B, as illustrated in FIG. 6A.

[0069] In addition, the anode 22 can be formed, for example, to have a film thickness of 100 nm or more and 300 nm or less, but is not limited thereto. The cathode 25 can be formed, for example, to have a film thickness of 10 nm or more and 100 nm or less, but is not limited thereto. The hole-transporting layer 24HT can be formed, for example, to have a film thickness of 10 nm or more and 150 nm or less, but is not limited thereto. The light-emitting layer 24REM (red light-emitting layer), the light-emitting layer 24GEM (green light-emitting layer), and the light-emitting layer 24BEM (blue light-emitting layer) can be formed, for example, to have a film thickness of 20 nm or more and 50 nm or less, but are not limited thereto. The electron-transporting layer 24ET can be formed, for example, to have a film thickness of 30 nm or more and 120 nm or less, but is not limited thereto.

[0070] In the present embodiment, the electron-transporting layer 24ET can be formed, for example, using the nanoparticles of zinc oxide having the surface oxygen defect portion DE.

[0071] According to Figures 8 to 11 , a method for manufacturing the nanoparticles of nickel oxide, which is used in the process (S11) of forming the hole-transporting layer 24HT on the anode 22 described above, will be described.​​​

[0072] In the present embodiment, as one example of the metal oxide nanoparticles used in the step (S11) of forming the hole transport layer 24HT on the anode 22, one example of nickel oxide nanoparticles is described, but as long as the metal oxide nanoparticles used in at least one of the steps of forming the hole transport layer 24HT and the hole injection layer provided between the anode 22 and the light-emitting layers 24REM, 24GEM, 24BEM are metal oxide nanoparticles as a hole transport material, there is no particular limitation. For example, the metal oxide nanoparticles as a hole transport material can also be nanoparticles of a metal oxide containing at least one of Ni, Mg, Mo, Cu, Co, Cr, and Ti.

[0073] Further, as shown in the second embodiment (see Figure 12 ) described later, the metal oxide nanoparticles can also be metal oxide nanoparticles as an electron transport material used in at least one of the steps of forming the electron transport layer 24ET' and the electron injection layer provided between the cathode 25 and the light-emitting layer 24REM, for example, the metal oxide nanoparticles as an electron transport material can also be nanoparticles of a metal oxide containing at least one of Zn, Mg, Ti, Si, Sn, W, Ta, Ba, Zr, Al, Y, and Hf, for example, the metal oxide nanoparticles as an electron transport material can also be nanoparticles of zinc oxide or magnesium zinc oxide.

[0074] In addition, the particle diameter of the metal oxide nanoparticles described above is not particularly limited, and for example, it is preferably 1 nm or more and 1000 nm or less. By making the particle diameter of the metal oxide nanoparticles 1 nm or more, the control of the particle diameter of the metal oxide nanoparticles becomes easy. Furthermore, by making the particle diameter of the metal oxide nanoparticles 1000 nm or less, the efficiency of injecting holes from the anode 22 or injecting electrons from the cathode 25 can be improved.

[0075] Figure 8 is a view showing a manufacturing step of metal oxide nanoparticles, that is, nickel oxide nanoparticles NP having surface oxygen defect portions DE.

[0076] As shown in Figure 8 , the manufacturing step of the metal oxide nanoparticles, that is, nickel oxide nanoparticles NP having surface oxygen defect portions DE includes a step (S21) of preparing an aqueous solution containing a nickel element, a step (S22) of adding an alkali solution, a stirring step (S23), a drying step (S24), a heat treatment step (S25), and a filter treatment step (S26).

[0077] In the process (S21) of preparing an aqueous solution containing a nickel element, for example, an aqueous solution containing a nickel element in which 7.27 g of Ni(NO3)2-6H2O is dispersed in 10 ml of pure water is prepared. Then, in the process (S22) of adding an alkali solution, for example, 5.85 to 5.9 ml of an aqueous solution of NaOH of 10 N (N is Normality) is added. The aqueous solution of NaOH can also be added while stirring at a rate of, for example, 0.3 to 0.4 ml / minute until the pH value reaches about 10. Then, in the stirring process (S23), for example, stirring is performed for about 5 minutes. From the above processes, nanoparticles of nickel oxide can be obtained in an alkaline environment by a chemical precipitation method. A washing process of washing the nanoparticles of nickel oxide can also be performed before the drying process (S24). Then, in the drying process (S24), for example, heat treatment at 80°C for 15 to 24 hours is performed to dry the nanoparticles of nickel oxide. Then, as necessary, a pulverization process of pulverizing the nanoparticles of nickel oxide can be performed. Then, in the heat treatment process (S25), for example, heat treatment at 250 to 270°C in the presence of oxygen for 2 to 4 hours is performed, and the nanoparticles of nickel oxide are fired. Then, in the filter treatment process (S26), after the nanoparticles of nickel oxide after firing are pulverized, the pulverized nanoparticles of nickel oxide are put into pure water, stirred to disperse them, and, for example, a PTFE filter having a pore diameter of 1 μm is used to obtain nanoparticles of nickel oxide having a particle diameter of 1000 nm or less.

[0078] In the case of the nanoparticles of nickel oxide NP manufactured by the manufacturing process of the nanoparticles of nickel oxide NP shown in Figure 8 In the case of the nanoparticles of nickel oxide NP manufactured by the manufacturing process of the nanoparticles of nickel oxide NP shown in

[0079] In the present embodiment, the case of the nanoparticles of nickel oxide NP manufactured by the manufacturing process of the nanoparticles of nickel oxide NP shown in Figure 8 In the present embodiment, the case of the nanoparticles of nickel oxide NP manufactured by the manufacturing process of the nanoparticles of nickel oxide NP shown in

[0080] As shown in the manufacturing process of the nanoparticles of nickel oxide NP shown in Figure 8As shown in the manufacturing process of nickel oxide nanoparticles NP, a random number of surface oxygen defects DE are formed at random positions on the surface SU of the nickel oxide nanoparticles NP. Due to the influence of these surface oxygen defects DE, the energy level changes. In the case of a light-emitting element with a charge transport layer formed by using nickel oxide nanoparticles NP in which the energy level of each nickel oxide nanoparticle NP will be deviated, there is a problem of reduced luminous efficiency along with the decrease in external quantum efficiency (EQE).

[0081] Figure 9 It is used to explain in passing Figure 8 The diagram shows the manufacturing process of nickel oxide nanoparticles NP, including the process of setting an inorganic oxide coating 30 on the surface of each of the multiple nickel oxide nanoparticles NP (S31-S39), the process of heat-treating the multiple nickel oxide nanoparticles NP under an oxygen atmosphere after setting the coating 30 (S40), and the process of removing the coating 30 (S41).

[0082] Figure 10 To indicate Figure 9 The diagram shows the approximate states of nickel oxide nanoparticles NP and NP' in each process step.

[0083] Figure 11 This is a cross-sectional view showing the schematic configuration of the charge transport layer, i.e. the hole transport layer 24HT, of each of the red light-emitting element 5R, the green light-emitting element 5G, and the blue light-emitting element 5B in the display device 1 of the first embodiment.

[0084] Therefore, in this embodiment, as Figure 10 As shown, by the manufacturing method of nickel oxide nanoparticles NP' including the following steps, it is possible to obtain multiple metal oxide nanoparticles, i.e., nickel oxide nanoparticles NP', that do not have surface oxygen defect portions DE. Specifically, the method includes a step (S31 to S39) of providing a coating portion 30 containing inorganic oxide on the surface SU of the nickel oxide nanoparticles NP, i.e., the nickel oxide nanoparticles NP whose surface SU has surface oxygen defect portions DE, and a step (S40) of heat-treating the nickel oxide nanoparticles NP in an oxygen atmosphere after the step of providing the coating portion 30.

[0085] According to the above-described method for manufacturing nickel oxide nanoparticles NP', since it has a coating portion 30 composed of inorganic oxide, it has high reliability. Since it does not have surface oxygen defect portions DE, it is possible to obtain metal oxide nanoparticles, i.e., nickel oxide nanoparticles NP', which can suppress the decrease in luminescence efficiency associated with the decrease in external quantum efficiency (EQE).

[0086] Furthermore, in the above-mentioned method for manufacturing nickel oxide nanoparticles NP', it is preferable to include a step (S41) of removing the coating portion 30 after the heat treatment step (S40).

[0087] The degree of energy level change in metal oxide nanoparticles caused by the influence of surface oxygen defects DE formed at random positions on the surface of metal oxide nanoparticles is smaller than that caused by the influence of the coating portion 30, which is composed of the same oxide as the metal oxide nanoparticles, i.e., inorganic oxide. Therefore, in the process of removing the coating portion 30 (S41), the coating portion 30 composed of inorganic oxide can also be removed, but a portion of the coating portion 30 composed of inorganic oxide, which plays a role in inhibiting the aggregation of nickel oxide nanoparticles NP', can remain. Alternatively, the process of removing the coating portion 30 (S41) can be omitted, and the entire coating portion 30 composed of inorganic oxide can be retained.

[0088] The manufacturing method of the light-emitting elements (red light-emitting element 5R, green light-emitting element 5G, and blue light-emitting element 5B) of the above-mentioned display device 1 includes a process of forming a hole transport layer 24HT as a charge transport layer. The process of forming the hole transport layer 24HT includes: a process of setting a coating portion 30 containing inorganic oxide (S31~S39); and a process of heat-treating nickel oxide nanoparticles NP in an oxygen atmosphere after the process of setting the coating portion 30 (S40).

[0089] Furthermore, the process of forming the hole transport layer 24HT is preferably performed after the heat treatment process (S40), and includes the process of removing the coating portion 30 (S41).

[0090] like Figure 9 As shown, the steps (S31-S39) for setting the coating portion 30 containing inorganic oxides include: a step of preparing a nickel oxide nanoparticle dispersion solution (S31, first step); a step of stirring the nickel oxide nanoparticle dispersion solution (S32); a step of adding a catalyst solution containing water and a catalyst for hydrolysis reaction (S33); a step of stirring the nickel oxide nanoparticle dispersion solution containing the catalyst solution (S34); a step of adding a precursor solution containing an alcohol solvent and a precursor of the inorganic oxide constituting the coating portion 30 (S35); a step of stirring the nickel oxide nanoparticle dispersion solution containing the catalyst and the precursor (S36); a step of centrifuging the nickel oxide nanoparticle dispersion solution containing the catalyst and the precursor to remove the solvent (S37, fourth step); a step of washing with alcohol (S38, fifth step); and a drying step (S39, third step).

[0091] In the process (S31) of preparing the dispersion solution of nickel oxide nanoparticles, for example, the nickel oxide nanoparticles having the surface oxygen defect portions DE are added to a surface SU in a dispersant, that is, an alcohol solvent, that is, 1 L of ethanol containing 10 g of N-vinyl-2-pyrrolidone. In the process (S32) of stirring the dispersion solution of nickel oxide nanoparticles, the dispersion solution of nickel oxide nanoparticles is stirred for, for example, 12 hours. In the process (S33) of adding a catalyst solution containing water and a catalyst for a hydrolysis reaction, for example, 100 ml of water and 25% ammonia solution containing 25 wt% of NH3 with respect to 100 ml of water are added. In the present embodiment, a case where an alkaline catalyst is used as the catalyst for the hydrolysis reaction is described as an example, but an acidic catalyst can be used as the catalyst for the hydrolysis reaction. In the process (S34) of stirring the dispersion solution of nickel oxide nanoparticles to which the catalyst solution is added, for example, the stirring is performed for 30 minutes using ultrasonic waves. In the process (S35) of adding a precursor solution containing an alcohol solvent and a precursor of an inorganic oxide constituting the coating portion 30, for example, 50 ml of a precursor solution containing 49 ml of ethanol as the alcohol solvent and 1 ml of tetraethoxysilane (TEOS) as the precursor of the inorganic oxide constituting the coating portion 30 is added. In the present embodiment, a case where tetraethoxysilane (TEOS) is used as the precursor of the inorganic oxide constituting the coating portion 30 is described as an example, but the present embodiment is not limited thereto, and a precursor represented by the following Chemical Formula (1) can be used.

[0092] Si(OR)4(R is an alkyl group) Chemical Formula (1) Further, as the precursor of the inorganic oxide constituting the coating portion 30, a precursor represented by the following Chemical Formula (2) can be used.

[0093] M(OR)4Chemical Formula (2) In Chemical Formula (2), M is a metal element or a semi-metal element other than Si, and R is an alkyl group.

[0094] In addition, the processes S33 to S35 described above are processes (second processes) of preparing a dispersion solution (sol) of nickel oxide nanoparticles containing a catalyst and a precursor.

[0095] In the process (S36) of stirring the dispersion solution of nickel oxide nanoparticles containing the catalyst and the precursor, the stirring is performed for 1 hour and 30 minutes using ultrasonic waves. In the process (S37) of removing a solvent by centrifugation of the dispersion solution of nickel oxide nanoparticles containing the catalyst and the precursor, ethanol as the solvent is removed using a centrifugal separator. In the process (S38) of cleaning with an alcohol, for example, cleaning is performed one or more times using ethanol. In the drying process (S39), for example, drying is performed by heat treatment at 70°C for 5 hours.

[0096] Further, in each of the stirring processes of S32, S34, and S36 described above, stirring can be performed using a stirrer, or stirring can be performed using ultrasonic waves.

[0097] Further, in the present embodiment, as described above, the case where the process of providing the coating portion 30 containing the inorganic oxide (S31 to S39) includes processes of stirring a total of three times is described as an example, but the present embodiment is not limited thereto. The number of times of the stirring processes can be more than three, can be less than three, or the processes of stirring can be omitted.

[0098] Further, in the present embodiment, as described above, the case where the process of providing the coating portion 30 containing the inorganic oxide (S31 to S39) includes processes of stirring a total of three times is described as an example, but the present embodiment is not limited thereto. The number of times of the stirring processes can be more than three, can be less than three, or the processes of stirring can be omitted.

[0099] Further, in the present embodiment, as described above, the case where the process of providing the coating portion 30 containing the inorganic oxide (S31 to S39) includes processes of stirring a total of three times is described as an example, but the present embodiment is not limited thereto. The number of times of the stirring processes can be more than three, can be less than three, or the processes of stirring can be omitted.

[0100] Further, in the process of providing the coating portion 30 containing the inorganic oxide (S31 to S39), the reason for using an alcohol solvent (for example, ethanol) as a common solvent is that ethoxy groups (OCH2CH3) of tetraethoxysilane (TEOS) are hydrophobic, and it is difficult to mix with water added in the process of adding a catalyst solution containing water and a catalyst for a hydrolysis reaction (S33). Therefore, an alcohol solvent that mixes with both the hydrophobic ethoxy groups (OCH2CH3) and water is used.

[0101] In this embodiment, by providing a coating portion 30 containing inorganic oxide (S31-S39), the precursor of the inorganic oxide constituting the coating portion 30, namely tetraethoxysilane (TEOS), can be gelled. In the step (S36) of stirring the nickel oxide nanoparticle dispersion containing the catalyst and precursor, gelation of tetraethoxysilane (TEOS) also occurs. However, in the steps (S37) of centrifuging the nickel oxide nanoparticle dispersion containing the catalyst and precursor to remove the solvent, and the drying step (S39), by removing the solvent, the gelation of tetraethoxysilane (TEOS) can be further performed.

[0102] like Figure 10 As shown, the coating portion 30 after the drying process (S39) is composed of a portion containing O-Si-O bonds as inorganic oxides and a portion not shown but containing residual ethoxy groups (OCH2CH3) and residual OH groups bonded to Si, and is composed of porous inorganic oxides containing organic groups.

[0103] like Figure 10 As shown, by using a coating portion 30 made of porous inorganic oxide containing organic groups, the aggregation of nickel oxide nanoparticles NP with surface oxygen defect portions DE can be suppressed, thereby separating the distance between nickel oxide nanoparticles NP.

[0104] like Figure 9 and Figure 10 As shown, in the coating portion 30 composed of porous inorganic oxide containing organic groups, a process (S40) is performed on multiple metal oxide nanoparticles, namely nickel oxide nanoparticles NP, under an oxygen atmosphere while the distance between nickel oxide nanoparticles NP having surface oxygen defect portions DE is separated.

[0105] In this embodiment, in the step (S40) of heat treating multiple metal oxide nanoparticles, namely nickel oxide nanoparticles NP, under an oxygen atmosphere, as follows: Figure 10 As shown, heat treatment is performed while oxygen (O2) is supplied at a specified flow rate, but it is not limited to this. For example, heat treatment can also be performed in an atmosphere with an oxygen atmosphere.

[0106] When heat treatment is performed while supplying oxygen (O2) at a specified flow rate, by appropriately adjusting the flow rate, the ratio of nickel to oxygen in the nickel oxide nanoparticles NP' can be made to be 1:1.

[0107] In the process (S40) of heat treatment of multiple metal oxide nanoparticles, i.e. nickel oxide nanoparticles NP, under an oxygen atmosphere, as described above, since the coating portion 30 is composed of a porous inorganic oxide containing organic groups, oxygen O2 is smoothly supplied to the surface oxygen defect portion DE of the nickel oxide nanoparticles NP, which can repair the surface oxygen defect portion DE, and multiple metal oxide nanoparticles, i.e. nickel oxide nanoparticles NP', without the surface oxygen defect portion DE can be obtained.

[0108] Furthermore, the process (S40) of heat-treating multiple metal oxide nanoparticles, namely nickel oxide nanoparticles NP, under an oxygen atmosphere is preferably performed at a temperature of 500°C or higher for 3 hours or more. By performing heat treatment at a temperature of 500°C or higher for 3 hours or more, the coating portion 30 can be formed from silicon oxide, which is an inorganic oxide, and reliability can be improved even if at least a portion of the coating portion 30 is not removed and remains.

[0109] like Figure 9 and Figure 10 As shown, after the heat treatment step (S40), in the step (S41) of removing the coating portion 30, the coating portion 30 can be removed by washing the nickel oxide nanoparticles NP', which are multiple metal oxide nanoparticles, with an alkaline solution. For example, an aqueous NaOH solution can be used as the alkaline solution. By appropriately controlling the concentration of the alkaline solution, the number of times the alkaline solution is used for washing, and the contact time between the nickel oxide nanoparticles NP' and the alkaline solution, the number of remaining coating portions 30 can be appropriately adjusted.

[0110] like Figure 11 As shown, in the charge transport layer, i.e. hole transport layer 24HT, of each of the red light-emitting element 5R, green light-emitting element 5G and blue light-emitting element 5B in the display device 1 of the first embodiment, a portion of the nickel oxide nanoparticles NP' may also have a coating portion 30 provided on at least a portion of their surface SU.

[0111] Figure 11 If the cross-sectional view is of a specified size for the hole transport layer 24HT, then when the total number of nickel oxide nanoparticles NP' contained in the cross-section of the specified size is set as A, and the number of nickel oxide nanoparticles NP' with the coating portion 30 contained in the cross-section of the specified size is set as B, (B / A) is preferably 0.1 or less. Figure 11 In the figure, A is 11, B is 1, and (B / A) is 0.09. In addition, if a portion of the nickel oxide nanoparticle NP' is included in the cross-section of a specified size, it can be counted as one; if only the coating portion 30 is included in the cross-section of a specified size, it can be counted as the nickel oxide nanoparticle NP' provided with the coating portion 30.

[0112] according to Figure 11 The display device 1 shown, which has a hole transport layer 24HT and includes a red light-emitting element 5R, a green light-emitting element 5G, and a blue light-emitting element 5B, has high reliability and can suppress the decrease in luminous efficiency associated with the decrease in external quantum efficiency (EQE).

[0113] [Second Implementation] Next, according to Figure 12 and Figure 13 The second embodiment of the present invention will now be described. The red light-emitting element 5R' of this embodiment differs from that of the first embodiment described above in that it includes an electron transport layer 24ET' comprising zinc oxide nanoparticles NP1' which are multiple metal oxide nanoparticles without surface oxygen defect portions DE. Otherwise, it functions as described in the first embodiment. For ease of explanation, components having the same functions as those shown in the figures of the first embodiment are labeled with the same reference numerals, and their descriptions are omitted.

[0114] Figure 12 This is a cross-sectional view showing the schematic configuration of the red light-emitting element 5R' included in the display device of the second embodiment.

[0115] Figure 13 It means Figure 12 The diagram shows a cross-sectional view of the charge transport layer, i.e. the electron transport layer 24ET', of the red light-emitting element 5R'.

[0116] like Figure 13 As shown, Figure 12 The red light-emitting element 5R' shown includes an electron transport layer 24ET', which contains multiple zinc oxide nanoparticles NP1' that do not have surface oxygen defects DE. Furthermore, when the zinc oxide nanoparticles are heat-treated while oxygen (O2) is supplied at a predetermined flow rate, the ratio of metal element (zinc) to oxygen in the zinc oxide nanoparticles NP1' can be adjusted to a 1:1 ratio. In this embodiment, the use of zinc oxide nanoparticles NP1' is described as an example, but it is not limited to this; for example, magnesium zinc oxide nanoparticles can also be used. Furthermore, when the magnesium zinc oxide nanoparticles are heat-treated while oxygen (O2) is supplied at a predetermined flow rate, the ratio of metal element (zinc + magnesium) to oxygen in the magnesium zinc oxide nanoparticles can be adjusted to a 1:1 ratio. The electron transport layer 24ET' can be formed with a film thickness of 30 nm or more and 120 nm or less, but it is not limited to this.

[0117] also, Figure 12 The hole transport layer 24HT' of the red light-emitting element 5R' shown can be formed, for example, using nickel oxide nanoparticles NP with surface oxygen defect portions DE. Furthermore, the hole transport layer 24HT' can be formed, for example, with a film thickness of 10 nm or more and 150 nm or less, but is not limited thereto.

[0118] like Figure 13 As shown, in the charge transport layer, i.e., the electron transport layer 24ET', of the red light-emitting element 5R' in the display device of the second embodiment, a portion of the zinc oxide nanoparticles NP1' may also have a coating portion 30 provided on at least a portion of their surface SU.

[0119] Figure 13 When the cross-sectional view of the electron transport layer 24ET' of a specified size is given as A, and the number of zinc oxide nanoparticles NP1' contained in the cross-section of the specified size is given as B, (B / A) is preferably 0.1 or less. Figure 13 In the figure, A is 11, B is 1, and (B / A) is 0.09. In addition, when a portion of zinc oxide nanoparticles NP1' is included in a cross-section of a specified size, it can also be counted as such. When only the coated portion 30 is included in a cross-section of a specified size, it can also be counted as zinc oxide nanoparticles NP1' with the coated portion 30.

[0120] according to Figure 13 The display device shown, which includes a red light-emitting element 5R' with an electron transport layer 24ET' and a second embodiment with a red light-emitting element 5R', has high reliability and can suppress the decrease in luminous efficiency that accompanies the decrease in external quantum efficiency (EQE).

[0121] [Third Implementation Method] Next, based on Figure 14 The third embodiment of the present invention will be described. The red light-emitting element 5R” in this embodiment differs from the first and second embodiments described above in that it comprises: a hole transport layer 24HT including a plurality of metal oxide nanoparticles (i.e., nickel oxide nanoparticles NP') without surface oxygen defect portions DE, and an electron transport layer 24ET’ including a plurality of metal oxide nanoparticles (i.e., zinc oxide nanoparticles NP1') without surface oxygen defect portions DE. Otherwise, it is as described in the first and second embodiments. For ease of explanation, components having the same functions as those shown in the drawings of the first and second embodiments are labeled with the same reference numerals, and their descriptions are omitted.

[0122] Figure 14 is a cross-sectional view showing a schematic configuration of a red light emitting element 5R" provided in the display device of the third embodiment.

[0123] As shown in Figure 14 , the red light emitting element 5R" is provided with a hole transport layer 24HT which is a charge transport layer (first charge transport layer) including a plurality of metal oxide nanoparticles, namely nickel oxide nanoparticles NP' having no surface oxygen defect portion DE, and an electron transport layer 24ET' which is a charge transport layer (second charge transport layer) including a plurality of second metal oxide nanoparticles, namely zinc oxide nanoparticles NP1' having no surface oxygen defect portion DE.

[0124] According to the red light emitting element 5R" having the hole transport layer 24HT and the electron transport layer 24ET' shown in Figure 14 , and the display device of the third embodiment provided with the red light emitting element 5R", the reliability is higher, and reduction in light emitting efficiency accompanying reduction in external quantum efficiency (EQE) can be further suppressed.

[0125] 〔Matters〕 The present application is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims, and embodiments obtained by appropriately combining the technical means respectively disclosed in different embodiments are also included in the technical scope of the present application. Furthermore, by combining the technical means respectively disclosed in the embodiments, new technical features can be formed.

[0126] Industrial Applicability The present application can be used for a light emitting element, a display device, a manufacturing method of a light emitting element, and a manufacturing method of a metal oxide nanoparticle.

[0127] Explanation of Reference Numerals 1: display device; 3: barrier layer; 4: thin film transistor layer; 5R, 5R', 5R": red light emitting element (light emitting element); 5G: green light emitting element (light emitting element); 5B: blue light emitting element (light emitting element); 6: sealing layer; 12: substrate; 16, 18, 20: inorganic insulating film; 21: planarization film; 22: anode; 23: bank; 24R, 24R', 24R": functional layer including a red light-emitting layer; 24G: functional layer including a green light-emitting layer; 24B: functional layer including a blue light-emitting layer; 24HT: hole transport layer (charge transport layer); 24HT': hole transport layer; 24REM: red light-emitting layer (light-emitting layer); 24GEM: green light-emitting layer (light-emitting layer); 24BEM: blue light-emitting layer (light-emitting layer); 24ET: electron transport layer; 24ET': electron transport layer (charge transport layer); 25: cathode; 26, 28: inorganic sealing film; 27: organic film; 30: covering portion; 39: functional film; NP, NP': nanoparticle of nickel oxide (nanoparticle of metal oxide); NP1': nanoparticle of zinc oxide (nanoparticle of metal oxide); SU: surface of nanoparticle of nickel oxide; DE: surface oxygen defect portion; PIX: pixel; RSP: red sub-pixel; GSP: green sub-pixel; BSP: blue sub-pixel; TR: transistor; SEM, SEM', SEM": semiconductor film; G: gate; D: drain; S: source; DA: display area; NDA: frame area.

Claims

1. A light-emitting element, characterized in that, It possesses: anode; cathode; A light-emitting layer disposed between the anode and the cathode; and A charge transport layer is disposed between one of the anode and the cathode and the light-emitting layer. The charge transport layer comprises multiple metal oxide nanoparticles that do not have surface oxygen defects. One or more of the plurality of metal oxide nanoparticles have a coating portion on at least a portion of their surface, the coating portion being composed of inorganic oxide.

2. The light-emitting element according to claim 1, characterized in that, A portion of the plurality of metal oxide nanoparticles has the coating portion disposed on at least a portion of its surface.

3. The light-emitting element according to claim 2, characterized in that, When the total number of metal oxide nanoparticles contained in a cross section of a predetermined size of the charge transport layer is set as A, and the number of metal oxide nanoparticles with the coating portion contained in the cross section of the predetermined size of the charge transport layer is set as B, (B / A) is 0.1 or less.

4. The light-emitting element according to any one of claims 1 to 3, characterized in that, The coating is made of silicon dioxide.

5. The light-emitting element according to any one of claims 1 to 4, characterized in that, The charge transport layer is at least one of a hole transport layer and a hole injection layer disposed between the anode and the light-emitting layer. The metal oxide nanoparticles are hole transport materials.

6. The light-emitting element according to claim 5, characterized in that, The metal oxide nanoparticles are nanoparticles containing at least one of the metal oxides selected from Ni, Mg, Mo, Cu, Co, Cr, and Ti.

7. The light-emitting element according to claim 6, characterized in that, The metal oxide nanoparticles are nickel oxide nanoparticles.

8. The light-emitting element according to claim 7, characterized in that, The nickel oxide nanoparticles contain nickel to oxygen in a ratio of 1:

1.

9. The light-emitting element according to any one of claims 1 to 4, characterized in that, The charge transport layer is at least one of an electron transport layer and an electron injection layer disposed between the cathode and the light-emitting layer. The metal oxide nanoparticles are electron transport materials.

10. The light-emitting element according to claim 9, characterized in that, The metal oxide nanoparticles are nanoparticles containing at least one of the metal oxides selected from Zn, Mg, Ti, Si, Sn, W, Ta, Ba, Zr, Al, Y, and Hf.

11. The light-emitting element according to claim 10, characterized in that, The metal oxide nanoparticles are zinc oxide or magnesium zinc oxide nanoparticles.

12. The light-emitting element according to claim 11, characterized in that, The ratio of metal elements to oxygen elements in the zinc oxide nanoparticles or the magnesium zinc oxide nanoparticles is 1:

1.

13. The light-emitting element according to any one of claims 5 to 8, characterized in that, It also includes a second charge transport layer, which is at least one of an electron transport layer and an electron injection layer disposed between the cathode and the light-emitting layer. The second charge transport layer contains multiple second metal oxide nanoparticles that do not have surface oxygen defects. The second metal oxide nanoparticle is an electron transport material. One or more of the plurality of second metal oxide nanoparticles have a coating composed of inorganic oxides on at least a portion of their surface.

14. A display device, characterized in that, It contains the light-emitting element as described in any one of claims 1 to 13.

15. A method for manufacturing a light-emitting element, characterized in that, It includes the process of forming a charge transport layer. The process for forming the charge transport layer includes: The process of forming an inorganic oxide coating on the surface of multiple metal oxide nanoparticles; and After the process of setting the coating, a process of heat-treating the plurality of metal oxide nanoparticles in an oxygen atmosphere.

16. The method for manufacturing a light-emitting element according to claim 15, characterized in that, The process of forming the charge transport layer includes a process of removing the coating portion after the heat treatment process.

17. The method for manufacturing a light-emitting element according to claim 16, characterized in that, In the process of removing the coating, the plurality of metal oxide nanoparticles are cleaned with an alkaline solution.

18. A method for manufacturing a light-emitting element according to any one of claims 15 to 17, characterized in that, The process of setting the covered portion includes: The first step is to prepare a nickel oxide nanoparticle dispersion solution, which contains the metal oxide nanoparticles, i.e., nickel oxide nanoparticles, an alcohol solvent, and a dispersant. The second step involves preparing a nickel oxide nanoparticle dispersion solution containing a catalyst and a precursor. This second step includes adding a catalyst solution containing water and a hydrolysis reaction catalyst to the nickel oxide nanoparticle dispersion solution, and adding a precursor solution containing an alcohol solvent and an inorganic oxide constituting the coating, represented by the following chemical formula (1). Si(OR)4 (R is an alkyl group) chemical formula (1); and The third step involves drying the nickel oxide nanoparticle dispersion solution containing the catalyst and precursor.

19. The method for manufacturing a light-emitting element according to claim 18, characterized in that, The process of setting the coating portion, at least before the second process, includes a process of stirring the nickel oxide nanoparticle dispersion solution prepared in the first process.

20. The method for manufacturing a light-emitting element according to claim 18 or 19, characterized in that, In the second process, The catalyst solution is added before the precursor solution is added. At least before the step of adding the precursor solution, there is a step of stirring the nickel oxide nanoparticle dispersion solution in which the catalyst solution has been added.

21. A method for manufacturing a light-emitting element according to any one of claims 18 to 20, characterized in that, The process of setting the coating includes a fourth step between the second and third steps: centrifuging the nickel oxide nanoparticle dispersion solution containing the catalyst and precursor and removing the solvent.

22. The method for manufacturing a light-emitting element according to claim 21, characterized in that, In the process of setting the coating, a fifth step of cleaning with alcohol is included between the fourth step and the third step.

23. The method for manufacturing a light-emitting element according to claim 21 or 22, characterized in that, Prior to the fourth step, there is a step of stirring the nickel oxide nanoparticle dispersion solution containing the catalyst and precursor prepared in the second step.

24. The method for manufacturing a light-emitting element according to any one of claims 18 to 23, characterized in that, The dispersant used in the first step is N-vinyl-2-pyrrolidone. The precursor used in the second step of adding the precursor solution is tetraethoxysilane.

25. The method for manufacturing a light-emitting element according to any one of claims 18 to 24, characterized in that, The process of forming the charge transport layer includes, prior to the process of setting the coating portion, a process of manufacturing the nickel oxide nanoparticles used in the process of setting the coating portion. The process of manufacturing the nickel oxide nanoparticles includes: manufacturing nickel oxide nanoparticles by chemical precipitation using an aqueous solution and an alkaline solution containing nickel.

26. The method for manufacturing a light-emitting element according to any one of claims 15 to 25, characterized in that, In the process of heat-treating the plurality of metal oxide nanoparticles, heat treatment is performed while oxygen is supplied at a specified flow rate.

27. The method for manufacturing a light-emitting element according to any one of claims 15 to 26, characterized in that, The heat treatment process for the plurality of metal oxide nanoparticles is carried out at a temperature above 500°C for more than 3 hours.

28. A method for manufacturing metal oxide nanoparticles, characterized in that, It includes: A process of setting a coating containing inorganic oxides on the surface of each of multiple metal oxide nanoparticles; as well as Following the process of setting the coating, a process of heat-treating the plurality of metal oxide nanoparticles in an oxygen atmosphere.

29. The method for manufacturing metal oxide nanoparticles according to claim 28, characterized in that, The process following the heat treatment step includes a step of removing the coating.

30. The method for manufacturing metal oxide nanoparticles according to claim 28 or 29, characterized in that, The metal oxide nanoparticles used in the process of setting the coating are nickel oxide nanoparticles.

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