Light-emitting element and display device

Abstract

A blue-light-emitting element (31B) includes: a lower electrode (4B); an upper electrode (9); a blue-light-emitting layer (7B) which is provided between the lower electrode (4B) and the upper electrode (9); and a nanoparticle layer (5) which is provided between the lower electrode (4B) and the blue-light-emitting layer (7B) and which is in contact with the lower electrode (4B). The nanoparticle layer (5) is composed of a plurality of first inorganic oxide nanoparticles. In a cross-section obtained by cutting along the thickness direction of a laminate including the lower electrode (4B) and the nanoparticle layer (5), a surface of the lower electrode (4B) on the nanoparticle layer (5) side includes a plurality of protrusions (3a) and a plurality of recesses (3b). The difference between the maximum height portion of the plurality of protrusions (3a) and the maximum depth portion of the plurality of recesses (3b) is smaller than the particle diameter of the nanoparticles contained in the nanoparticle layer (5).

Description

Light-emitting element and display device

[0001] The present disclosure relates to a light-emitting device and a display device.

[0002] In recent years, various display devices equipped with light-emitting elements have been developed, and in particular, display devices equipped with QLEDs (Quantum dot Light Emitting Diodes) or OLEDs (Organic Light Emitting Diodes) have attracted much attention because of their ability to achieve low power consumption, thinness, high image quality, and the like.

[0003] For example, Patent Document 1 describes a display device that includes multiple light-emitting units, which are light-emitting elements, and describes that the viewing angle of the display device can be improved by providing irregularities on the substrate side on which the light-emitting units are mounted or on the film that covers the light-emitting units.

[0004] U.S. Patent Publication "US 10,149,366 B1"

[0005] Patent Document 1 does not describe how to improve the reliability, luminous efficiency, and driving voltage of the light-emitting units, which are light-emitting elements, to realize a display device with improved reliability and power consumption.

[0006] The inventors of the present disclosure have noticed that, in order to improve the reliability of a light-emitting element, when a layer composed of inorganic oxide nanoparticles or a laminated film including a layer composed of inorganic oxide nanoparticles is used as a carrier transport layer, for example, an electron transport layer, an electron injection layer, a hole transport layer, and a hole injection layer, the layer composed of inorganic oxide nanoparticles has poor film-forming or coatability on the anode or cathode, which is the lower electrode of the light-emitting element, and therefore, when there are convex portions and concave portions with a relatively large difference in height on the layer composed of inorganic oxide nanoparticles of the lower electrode, i.e., when the roughness is high, the number of portions where it is difficult for the inorganic oxide nanoparticles to penetrate to the bottom of the concave portions increases, and as a result, the contact area between the layer composed of inorganic oxide nanoparticles and the lower electrode becomes smaller, which deteriorates the carrier injection characteristics and increases the driving voltage of the light-emitting element.

[0007] An object of one embodiment of the present disclosure is to provide a light-emitting element that achieves high reliability, high luminous efficiency, and low driving voltage, and a display device that achieves high reliability and low power consumption.

[0008] In order to solve the above-mentioned problems, the light-emitting element of the present disclosure includes a lower electrode, an upper electrode, a light-emitting layer provided between the lower electrode and the upper electrode, and a nanoparticle layer provided between the lower electrode and the light-emitting layer and in contact with the lower electrode, wherein the nanoparticle layer is composed of a plurality of nanoparticles of a first inorganic oxide, and the surface of the lower electrode facing the nanoparticle layer in a cross section cut along the thickness direction of a laminate including the lower electrode and the nanoparticle layer includes a plurality of convex portions and a plurality of concave portions, and the difference between the maximum height portion of the plurality of convex portions and the maximum depth portion of the plurality of concave portions is smaller than the particle diameter of the nanoparticles included in the nanoparticle layer.

[0009] In order to solve the above-mentioned problems, the light-emitting element of the present disclosure includes a lower electrode, an upper electrode, a light-emitting layer provided between the lower electrode and the upper electrode, a nanoparticle layer provided between the lower electrode and the light-emitting layer and composed of a plurality of nanoparticles of a first inorganic oxide, and a continuous film of a second inorganic oxide provided between the lower electrode and the nanoparticle layer and in contact with the lower electrode.

[0010] In order to solve the above-mentioned problems, the display device of the present disclosure includes a plurality of light-emitting elements, each including a lower electrode, an upper electrode, a light-emitting layer provided between the lower electrode and the upper electrode, and a nanoparticle layer provided between the lower electrode and the light-emitting layer, in contact with the lower electrode, and composed of a plurality of nanoparticles of a first inorganic oxide; the plurality of light-emitting elements include a first light-emitting element, a second light-emitting element, and a third light-emitting element; the first light-emitting element is a red light-emitting element having a first lower electrode as the lower electrode and a red light-emitting layer as the light-emitting layer; the second light-emitting element is a green light-emitting element having a second lower electrode as the lower electrode and a green light-emitting layer as the light-emitting layer; and the third light-emitting element is a blue light-emitting element having a third lower electrode as the lower electrode and a blue light-emitting layer as the light-emitting layer; and a surface of the first lower electrode on the nanoparticle layer side in a first cross section cut along a thickness direction of the first light-emitting element includes a plurality of first convex portions and a plurality of first concave portions, The surface of the second lower electrode facing the nanoparticle layer in a second cross section cut along the thickness direction of the second light-emitting element includes a plurality of second convex portions and a plurality of second concave portions, and the surface of the third lower electrode facing the nanoparticle layer in a third cross section cut along the thickness direction of the third light-emitting element includes a plurality of third convex portions and a plurality of third concave portions, and the difference between the maximum height portion of the plurality of second convex portions and the maximum depth portion of the plurality of second concave portions and the difference between the maximum height portion of the plurality of third convex portions and the maximum depth portion of the plurality of third concave portions are each smaller than the difference between the maximum height portion of the plurality of first convex portions and the maximum depth portion of the plurality of first concave portions.

[0011] In order to solve the above-mentioned problems, the display device of the present disclosure includes a plurality of light-emitting elements, each including a lower electrode, an upper electrode, a light-emitting layer provided between the lower electrode and the upper electrode, and a nanoparticle layer provided between the lower electrode and the light-emitting layer and composed of a plurality of nanoparticles of a first inorganic oxide; the plurality of light-emitting elements include a first light-emitting element, a second light-emitting element, and a third light-emitting element; the first light-emitting element is a red light-emitting element having a first lower electrode as the lower electrode and a red light-emitting layer as the light-emitting layer; the second light-emitting element is a green light-emitting element having a second lower electrode as the lower electrode, a continuous film of a second inorganic oxide provided between the second lower electrode and the nanoparticle layer and in contact with the second lower electrode, and a green light-emitting layer as the light-emitting layer; and the third light-emitting element is a blue light-emitting element having a third lower electrode as the lower electrode, a continuous film of a second inorganic oxide provided between the third lower electrode and the nanoparticle layer and in contact with the third lower electrode, and a blue light-emitting layer as the light-emitting layer.

[0012] According to one embodiment of the present disclosure, it is possible to provide a light-emitting element that achieves high reliability, high luminous efficiency, and low driving voltage, and a display device that achieves high reliability and low power consumption.

[0013] 1 is a cross-sectional view showing a schematic configuration of a blue light-emitting device of embodiment 1. FIG. 2 is a cross-sectional view of a lower electrode schematically showing the shape of the surface on the nanoparticle layer side of the lower electrode provided in the blue light-emitting device of embodiment 1. FIG. 3 is a diagram showing the results of measuring the roughness of the surface on the nanoparticle layer side of the lower electrode provided in the blue light-emitting device of embodiment 1 using an AFM (Atomic Force Microscope), and the roughness at a straight line portion 1000 nm connecting arrows X and X' in the figure obtained from the measurement results. FIG. 4 is a diagram showing the results of measuring the roughness of the surface on the nanoparticle layer side of the lower electrode of comparative example 1 using an AFM (Atomic Force Microscope), and the roughness at a straight line portion 1000 nm connecting arrows Y and Y' in the figure obtained from the measurement results. FIG. 5 is a diagram comparing the characteristics of an HOD (Hole Only Device) produced using a transparent metal oxide layer having the roughness shown in FIG. 3 provided in the blue light-emitting device of embodiment 1 and an HOD (Hole Only Device) produced using a transparent metal oxide layer having the roughness shown in FIG. 4, which is the lower electrode of comparative example 1. 4 is a diagram comparing the external quantum efficiency (EQE) of a blue light-emitting element fabricated using a transparent metal oxide layer having the roughness shown in FIG. 3 that is provided in the blue light-emitting element of Embodiment 1, with the external quantum efficiency (EQE) of a blue light-emitting element fabricated using a transparent metal oxide layer having the roughness shown in FIG. 4 that is the lower electrode of Comparative Example 1. FIG. 5 is a diagram comparing the emission luminance of a blue light-emitting element fabricated using a transparent metal oxide layer having the roughness shown in FIG. 3 that is provided in the blue light-emitting element of Embodiment 1, with the emission luminance of a blue light-emitting element fabricated using a transparent metal oxide layer having the roughness shown in FIG. 4 that is the lower electrode of Comparative Example 1, at the same current density. FIG. 6 is a cross-sectional view showing a schematic configuration of a blue light-emitting element of Embodiment 2. FIG. 7 is a plan view showing a schematic configuration of a display device of Embodiment 3. FIG. 8 is a cross-sectional view showing a schematic configuration of a display region of the display device of Embodiment 3. FIG. 9 is a cross-sectional view showing a schematic configuration of a display region of the display device of Embodiment 4.

[0014] The following describes an embodiment of the present disclosure with reference to Figures 1 to 11. For the sake of convenience, components having the same functions as those described in a specific embodiment will be denoted by the same reference numerals, and their description may be omitted.

[0015] 1 is a cross-sectional view showing a schematic configuration of a blue light-emitting element 31B of embodiment 1. Fig. 2 is a cross-sectional view of a lower electrode 4B provided in the blue light-emitting element 31B of embodiment 1, showing a schematic shape of the surface of the lower electrode 4B on the nanoparticle layer 5 side.

[0016] 1, blue light-emitting element 31B includes a lower electrode 4B, an upper electrode 9, a blue light-emitting layer 7B provided between the lower electrode 4B and the upper electrode 9, and a nanoparticle layer 5 provided between the lower electrode 4B and the blue light-emitting layer 7B and in contact with the lower electrode 4B. Nanoparticle layer 5 is composed of a plurality of nanoparticles of a first inorganic oxide.

[0017] As shown in FIG. 1, in this embodiment, the surface of the lower electrode 4B on the nanoparticle layer 5 side in a cross section cut along the thickness direction of the blue light emitting element 31B includes a plurality of protrusions 3a and a plurality of recesses 3b.

[0018] As shown in Figure 2, the difference between the maximum height of the plurality of convex portions 3a and the maximum depth of the plurality of concave portions 3b can be determined from the shape of the surface of the lower electrode 4B on the nanoparticle layer 5 side in a cross section cut along the thickness direction of the blue light-emitting element 31B. As shown in Figure 2, in a cross-sectional view including the shape of the surface on the nanoparticle layer 5 side of the lower electrode 4B provided in the blue light-emitting element 31B, the difference between the maximum height of the plurality of convex portions 3a (upper dotted line shown in Figure 2) and the maximum depth of the plurality of concave portions 3b (lower dotted line shown in Figure 2) is smaller than the particle size of the nanoparticles contained in the nanoparticle layer 5 shown in Figure 1. The cross-sectional view including the shape of the surface on the nanoparticle layer 5 side of the lower electrode 4B provided in the blue light-emitting element 31B as shown in Figure 2 may be, for example, a cross-sectional photograph taken with a scanning electron microscope (SEM). The cross-sectional photograph of the scanning electron microscope (SEM) preferably includes, for example, the nanoparticles contained in the nanoparticle layer 5 shown in Fig. 1 and the plurality of convex portions 3a and the plurality of concave portions 3b on the surface of the lower electrode 4B on the nanoparticle layer 5 side, and is enlarged to a magnification sufficient to determine the difference between the maximum height of the plurality of convex portions 3a of the lower electrode 4B and the maximum depth of the plurality of concave portions 3b, and the particle size of the nanoparticles contained in the nanoparticle layer 5 shown in Fig. 1. For example, the lateral width of the cross-sectional photograph of the scanning electron microscope (SEM) described above, i.e., the lateral observation range, is preferably about 1 µm (1000 nm).

[0019] Generally, a layer made of inorganic oxide nanoparticles has poor film-forming or coating properties on a lower electrode made of, for example, ITO (indium tin oxide). Therefore, if there are convex portions and concave portions with a relatively large difference in height on the side of the lower electrode where the layer made of inorganic oxide nanoparticles is located, i.e., if the roughness is large, the areas where the inorganic oxide nanoparticles have difficulty penetrating to the bottom of the concave portions increase, resulting in a smaller contact area between the layer made of inorganic oxide nanoparticles and the lower electrode and a deterioration in carrier injection characteristics. On the other hand, in the above-described blue light-emitting device 31B, in a cross-sectional view including the shape of the surface of the lower electrode 4B facing the nanoparticle layer 5, the difference between the maximum height of the plurality of convex portions 3a and the maximum depth of the plurality of concave portions 3b is smaller than the particle diameter of the nanoparticles contained in the nanoparticle layer 5. Therefore, even if the nanoparticle layer 5 formed on the lower electrode 4B and composed of a plurality of nanoparticles of the first inorganic oxide has poor film-forming or coating properties, the nanoparticles contained in the nanoparticle layer 5 can be prevented from penetrating to the bottom of the concave portions 3b. As a result, the contact area between the nanoparticle layer 5 and the lower electrode 4B can be increased, thereby improving carrier injection characteristics and suppressing an increase in the driving voltage of the blue light-emitting device 31B. Therefore, a blue light-emitting device 31B that achieves high reliability, high luminous efficiency, and low driving voltage can be realized. In this embodiment, the blue light-emitting device 31B is described as an example, but is not limited thereto. By adopting the shape of the surface of the lower electrode 4B facing the nanoparticle layer 5 and the nanoparticle layer 5 provided in the blue light-emitting device 31B, high reliability, high luminous efficiency, and low driving voltage can also be achieved, for example, in red and green light-emitting devices. The particle size of the nanoparticles contained in the nanoparticle layer 5 may be examined by cross-sectional analysis using a SEM or a TEM (transmission electron microscope). In this case, if the shape of the crystal particles is not spherical, the diameter when the particles are deformed into a spherical shape with equal volume can be taken as the particle size. In addition, if there is a particle size distribution, for example, the particle size D50 at which the cumulative number reaches 50% in the particle size distribution of all crystal particles (e.g., 10 to 100 particles) within the observation field of view can be taken as the overall crystal particle size.Here, "the difference between the maximum height portion of the plurality of convex portions 3 a and the maximum depth portion of the plurality of concave portions 3 b is smaller than the particle diameter of the nanoparticles contained in the nanoparticle layer 5" means that the difference between the maximum height portion of the plurality of convex portions 3 a and the maximum depth portion of the plurality of concave portions 3 b may be smaller than the particle diameter D50 at which the cumulative number reaches 50%, may be smaller than the particle diameter D25 at which the cumulative number reaches 25%, may be smaller than the particle diameter D10 at which the cumulative number reaches 10%, or may be smaller than the particle diameters of all crystal particles within the observation field.

[0020] In the present embodiment, the case where the lower electrode 4B provided in the blue light-emitting element 31B is an anode and the upper electrode 9 is a cathode will be described as an example, but the present invention is not limited thereto, and the lower electrode 4B provided in the blue light-emitting element 31B may be a cathode and the upper electrode 9 may be an anode. When the lower electrode 4B provided in the blue light-emitting element 31B is an anode and the upper electrode 9 is a cathode, the shape of the surface of the lower electrode 4B on the nanoparticle layer 5 side described above can increase the contact area between the nanoparticle layer 5 and the lower electrode 4B, thereby improving the injection characteristics of holes, which are carriers. Therefore, in general, in light-emitting elements that are prone to electron excess, particularly in green and blue light-emitting elements, the carrier balance can be improved, and improvements in external quantum efficiency (EQE) and reliability can be realized. In the blue light-emitting element 31B, the difference between the maximum height of the plurality of convex portions 3 a of the lower electrode 4B and the maximum depth of the plurality of concave portions 3 b is formed to be smaller than the particle diameter of the nanoparticles contained in the nanoparticle layer 5. Therefore, the nanoparticle layer 5 composed of the plurality of nanoparticles of the first inorganic oxide formed on the lower electrode 4B can be formed to a more uniform film thickness that is optimal for hole transport. On the other hand, if the difference between the maximum height of the plurality of convex portions 3 a of the lower electrode 4B and the maximum depth of the plurality of concave portions 3 b is large, the film thickness of the nanoparticle layer 5 composed of the plurality of nanoparticles of the first inorganic oxide formed on the lower electrode 4B will also vary greatly, and the nanoparticle layer 5 will have an increased portion that is not optimal for hole transport, resulting in a deterioration in hole transport properties.

[0021] In this embodiment, a case where the first inorganic oxide constituting the nanoparticles of the nanoparticle layer 5 formed on the lower electrode 4B contains nickel oxide will be described as an example, but the present invention is not limited thereto. The first inorganic oxide constituting the nanoparticles of the nanoparticle layer 5 may contain at least one of Ni, Mg, Mo, Cu, Co, Cr, and Ti. The first inorganic oxide constituting the nanoparticles of the nanoparticle layer 5 is not particularly limited as long as it contains a hole transport material. When the first inorganic oxide constituting the nanoparticles of the nanoparticle layer 5 formed on the lower electrode 4B contains nickel oxide or is composed of nickel oxide, as in this embodiment, the hole injection characteristics via the nanoparticle layer 5 can be improved. This can generally improve the carrier balance in light-emitting elements prone to electron excess, particularly green and blue light-emitting elements, and can realize improved external quantum efficiency (EQE) and reliability.

[0022] 1 may be a top-emission type or a bottom-emission type. Blue light-emitting element 31B has a forward-laid structure in which upper electrode 9 (cathode) is disposed above lower electrode 4B (anode). To make it a top-emission type, lower electrode 4B (anode) should be formed from an electrode material that reflects visible light, and upper electrode 9 (cathode) should be formed from an electrode material that transmits visible light. To make it a bottom-emission type, lower electrode 22 (anode) should be formed from an electrode material that transmits visible light, and upper electrode 9 (cathode) should be formed from an electrode material that reflects visible light. On the other hand, in the case of an inverted stack structure in which the upper electrode 9, the anode, is arranged as a layer above the lower electrode 4B, the cathode, in order to make it a top emission type, the lower electrode 4B, the cathode, can be formed from an electrode material that reflects visible light, and the upper electrode 9, the anode, can be formed from an electrode material that transmits visible light, and in order to make it a bottom emission type, the lower electrode 4B, the cathode, can be formed from an electrode material that transmits visible light, and the upper electrode 9, the anode, can be formed from an electrode material that reflects visible light.

[0023] The electrode material that reflects visible light is not particularly limited as long as it can reflect visible light and has electrical conductivity, and examples thereof include metal materials such as Al, Mg, Li, Ag, Cu, and Au, alloys of the metal materials, laminates of the metal materials and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), and laminates of the alloys and the transparent metal oxides.

[0024] On the other hand, the electrode material that transmits visible light is not particularly limited as long as it can transmit visible light and has conductivity, and examples thereof include transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), thin films made of metal materials such as Al and Ag, and nanowires made of metal materials such as Al and Ag.

[0025] As described above, the blue light-emitting element 31B has a sequentially stacked structure in which the upper electrode 9 (cathode) is disposed above the lower electrode 4B (anode). Therefore, in this embodiment, a laminate in which a transparent metal oxide, a metal material, and a transparent metal oxide are laminated in this order as shown in FIG. 1 is used as the lower electrode 4B (anode). However, the present invention is not limited to this. In this embodiment, the lower electrode 4B is configured as follows: a transparent metal oxide layer 1 made of indium tin oxide (ITO) and having a thickness of 20 nm as the bottom layer of the laminate; a transparent metal oxide layer 3 made of indium tin oxide and having a thickness of 65 nm as the top layer of the laminate; and a metal layer 2 made of Ag and having a thickness of 100 nm provided between the transparent metal oxide layer 1 and the transparent metal oxide layer 3 so as to contact the transparent metal oxide layer 1 and the transparent metal oxide layer 3. The transparent metal oxide layer 1, the metal layer 2, and the transparent metal oxide layer 3 can be formed by, for example, sputtering or vapor deposition.

[0026] Fig. 3 is a diagram showing the results of measuring the roughness of the surface on the nanoparticle layer 5 side of the lower electrode 4B provided in the blue light-emitting element 31B of embodiment 1 using an AFM (Atomic Force Microscope), and the roughness at a distance of 1000 nm obtained from the measurement results, connecting the arrows X and X' in the figure. Fig. 4 is a diagram showing the results of measuring the roughness of the surface on the nanoparticle layer side of the lower electrode of comparative example 1 using an AFM (Atomic Force Microscope), and the roughness at a distance of 1000 nm obtained from the measurement results, connecting the arrows Y and Y' in the figure.

[0027] In the blue light-emitting element 31B of the first embodiment, the difference between the maximum height of the plurality of convex portions 3a of the lower electrode 4B and the maximum depth of the plurality of concave portions 3b is formed to be smaller than the particle size of the nanoparticles contained in the nanoparticle layer 5. The roughness of the surface on the nanoparticle layer 5 side of the lower electrode 4B provided in the blue light-emitting element 31B of the first embodiment shown in Fig. 3, i.e., the roughness of the surface on the nanoparticle layer 5 side of the transparent metal oxide layer 3 made of ITO (indium tin oxide), may be reduced by a known method, for example, mechanical polishing, chemical polishing such as etching, or a combination of mechanical polishing and chemical polishing. The roughness of the surface on the nanoparticle layer 5 side of the lower electrode 4B provided in the blue light-emitting element 31B of embodiment 1 shown in FIG. 3 , i.e., the roughness of the surface on the nanoparticle layer 5 side of the transparent metal oxide layer 3 made of ITO (indium tin oxide), was measured using an AFM (Atomic Force Microscope). The roughness was determined from the results of measuring the surface roughness at a distance of 1000 nm connecting the arrows X and X′ in FIG. 3 . The difference between the height of the plurality of convex portions 3 a of the lower electrode 4B and the depth of the plurality of concave portions 3 b of the transparent metal oxide layer 3 made of ITO (indium tin oxide) was 5.1 nm. The difference between the height of the plurality of protrusions 3 a of the lower electrode 4B and the depth of the plurality of recesses 3 b, i.e., the difference between the height of the plurality of protrusions 3 a of the lower electrode 4B and the depth of the plurality of recesses 3 b of the transparent metal oxide layer 3 made of ITO (indium tin oxide), is preferably 8 nm or less. Note that the difference between the height of the plurality of protrusions 3 a of the lower electrode 4B and the depth of the plurality of recesses 3 b in the cross-sectional photograph taken with a scanning electron microscope (SEM) described above substantially matches the difference between the height of the plurality of protrusions 3 a of the lower electrode 4B and the depth of the plurality of recesses 3 b in the results of measurement using an AFM (Atomic Force Microscope).

[0028] On the other hand, the surface of the nanoparticle layer side of the lower electrode of Comparative Example 1 was not subjected to mechanical polishing, chemical polishing such as etching, or a combination of mechanical polishing and chemical polishing, and therefore the roughness of the surface of the nanoparticle layer side of the lower electrode of Comparative Example 1 was large, as shown in Fig. 4. As shown in Fig. 4, the roughness of the surface of the nanoparticle layer side of the lower electrode of Comparative Example 1 was measured using an AFM (Atomic Force Microscope). In the roughness at a distance of 1000 nm connecting the arrows Y and Y' in Fig. 4, the difference between the maximum height of the plurality of convex portions of the lower electrode and the maximum depth of the plurality of concave portions, i.e., the difference between the maximum height of the plurality of convex portions of the transparent metal oxide layer made of ITO (indium tin oxide) and the maximum depth of the plurality of concave portions, was 10.2 nm.

[0029] In this embodiment, nickel oxide nanoparticles are used as the nanoparticles of the nanoparticle layer 5 formed on the lower electrode 4B shown in FIG. 1 . The nanoparticle layer 5 can be formed to a thickness of, for example, 40 nm by performing a coating process in which a dispersion solution of nickel oxide nanoparticles, obtained by dispersing nickel oxide nanoparticles in a solvent consisting of an equal volume mixture of water and 2-methoxyethanol, is applied by a spin coating method or the like in the atmosphere, followed by a heat treatment process of baking at 200°C. Note that, in order to form the nanoparticle layer 5 to a predetermined thickness, the coating process of the dispersion solution of nickel oxide nanoparticles and the heat treatment process may be repeated, for example, one or more times and up to five times. In the blue light-emitting element 31B shown in FIG. 1 , the nanoparticle layer 5 functions, for example, as a hole injection layer.

[0030] Furthermore, a layer made of a self-assembled monolayer (SAM) (not shown) may be formed between the nanoparticle layer 5 and the first charge transport layer 6 shown in FIG. Examples of self-assembled single molecules (SAMs) include [4-(9H-carbazol-9-yl)butyl]phosphonic Acid (4PACz), [4-(3,6-Dimethoxy-9H-carbazol-9-yl)butyl]phosphonic Acid (MeO-4PACz), and [4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl]phosphonic Acid. (Me-4PACz), [4-(3,6-Dichloro-9H-carbazol-9-yl)butyl]phosphonic Acid (Cl-4PACz), [4-(3,6-Dibromo-9H-carbazol-9-yl)butyl]phosphonic Acid (Br-4PACz), [2-(9H-carbazol-9-yl)ethyl]phosphonic Acid (2PACz), [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic Acid (MeO-2PACz), [2-(3,6-Dimethyl-9H-carbazol-9-yl)ethyl]phosphonic Acid (Me-2PACz), [2-(3,6-Dichloro-9H-carbazol-9-yl)ethyl]phosphonic Acid (Cl-2PACz), or [2-(3,6-Dibromo-9H-carbazol-9-yl)ethyl]phosphonic Acid (Br-2PACz) can be used. A layer consisting of self-assembled monolayers (SAMs) can be formed by applying a 0.01 M ethanol solution of the self-assembled monolayers (SAMs) to the nanoparticle layer 5 in a nitrogen atmosphere using a spin coating method or the like, followed by volatilizing the solvent by baking in a heat treatment step.

[0031] 1, the first charge transport layer 6 provided between the nanoparticle layer 5 and the blue light-emitting layer 7B functions as, for example, a hole transport layer in the blue light-emitting element 31B shown in Fig. 1. The first charge transport layer 6 can be formed to a thickness of, for example, 30 nm by applying a solution obtained by dispersing hole transport materials such as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (abbreviated as "TFB"), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (abbreviated as "Poly-TPD"), polyvinylcarbazole (abbreviated as "PVK"), and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (abbreviated as "PTAA") in a chlorobenzene solvent by spin coating or the like under a nitrogen atmosphere.

[0032] In this embodiment, the blue light-emitting layer 7B shown in FIG. 1 is described as an example of a light-emitting layer containing quantum dots (QDs). However, the present invention is not limited to this example and may be, for example, a light-emitting layer containing an organic light-emitting material. The organic light-emitting material can be formed, for example, by vapor deposition. The blue light-emitting layer 7B, which is a light-emitting layer containing quantum dots (QDs), can be formed to a thickness of, for example, 30 nm by applying a quantum dot dispersion solution in which quantum dots (QDs) are dispersed in octane at a concentration of 20 mg / mL using a spin coating method or the like under a nitrogen atmosphere. The quantum dots (QDs) may have, for example, a core structure, a core / shell structure, a core / shell / shell structure, or a shell structure in which the core / shell ratio is continuously varied. Note that the shell may cover only a portion of the core, but it is preferable for the shell to completely cover the core. The core material of the quantum dot QD is, for example, a crystal of a II-VI group semiconductor such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, or HgTe; a crystal of a III-V group semiconductor such as GaN, GaAs, GaP, InN, InAs, InP, or InSb; Ga ２ S ３ , Ga ２ Se ３, In ２ S ３ , In ２ Se ３ crystals of III-VI group semiconductors such as PbS, PbSe, PbTe, etc., crystals of IV-VI group semiconductors such as CuInGaS ２ (CIGS), AgInGaS ２ (AIGS), AgInGaZnS, CuInGaSe ２ , AgInGaSe ２ , CuInGaTe ２ , AgInGaTe ２ , CuAlS ２ , CuAlSe ２ , CuAlTe ２ , AgAlS ２ , AgAlSe ２ , AgAlTe ２ crystals of group I-III-VI semiconductors such as C and Si, crystals of group IV semiconductors such as CsPbI ３ , CsPbBr ３ , CsPbCl ３ , CsSnI ３ , CsSnBr ３ , CsSnCl ３ , C.H. ３ NH ３ PbI ３ , C.H. ３ NH ３ PbBr ３ , C.H. ３ NH ３ PbCl ３ , C.H. ３ NH ３ SnI ３ , C.H. ３ NH ３ SnBr ３ , C.H. ３ NH ３ SnCl ３ The shell material can be selected from the same material group as the core material, and preferably has a lattice constant close to that of the core material and a larger band gap than the core material.

[0033] The light-emitting layer, for example, the blue light-emitting layer 7B, may contain a halogen element and a metal element, and the value of (the number of halogen elements / the number of metal elements) × 100% may be 0.5% or more. By coating the light-emitting layer containing quantum dots QDs with a halogen ligand containing a halogen element, defects in the quantum dots QDs can be efficiently covered. This is because the halogen ligand is small and less susceptible to steric hindrance, allowing it to be coordinated to the surface of the quantum dots QDs at high density. Furthermore, since the halogen ligand has a high charge density, it has a strong bond to the surface of the quantum dots QDs and is less likely to detach, thereby improving reliability. However, when a halogen element is bonded to or coordinated to the quantum dots QDs, the energy level of the valence band top (VBM) of the quantum dots QDs becomes deeper, thereby deteriorating the hole injection characteristics into the quantum dots QDs. Similarly, when a halogen element is bonded or coordinated to an emitting layer containing an organic light-emitting material, the energy level of the valence band top (VBM) of the emitting layer containing the organic light-emitting material becomes deeper, and the hole injection characteristics into the emitting layer containing the organic light-emitting material become worse. Therefore, in the blue light-emitting layer 7B containing a halogen element and a metal element, when the value of (the number of halogen elements / the number of metal elements) × 100% is 0.5% or more, that is, when the content of halogen elements in the blue light-emitting layer 7B is high and the energy level of the valence band top (VBM) of the emitting layer becomes deeper, the hole injection characteristics can be improved by reducing the surface roughness of the nanoparticle layer 5 side of the lower electrode 4B provided in the blue light-emitting element 31B. This can alleviate the deterioration of the hole injection characteristics caused by the deepening of the energy level of the valence band top (VBM) of the emitting layer, and can achieve both the effect of the halogen ligand and an appropriate carrier balance.

[0034] The light-emitting layer, for example, the blue light-emitting layer 7B, may contain quantum dots QDs, and the energy level of the valence band upper limit (VBM) of the quantum dots QDs may be 0.3 eV or more deeper than the energy level of the valence band upper limit (VBM) of the nanoparticle layer 5. In this way, when the energy level of the valence band upper limit (VBM) of the quantum dots QDs is 0.3 eV or more deeper than the energy level of the valence band upper limit (VBM) of the nanoparticle layer 5 and hole injection characteristics from the nanoparticle layer 5 to the quantum dots QDs are deteriorated due to an energy barrier, the hole injection characteristics can be improved by reducing the roughness of the surface of the lower electrode 4B provided in the blue light-emitting element 31B on the nanoparticle layer 5 side, thereby mitigating the deterioration of hole injection characteristics caused by the energy level of the valence band upper limit (VBM) of the quantum dots QDs being 0.3 eV or more deeper than the energy level of the valence band upper limit (VBM) of the nanoparticle layer 5.

[0035] As shown in FIG. 1 , a second charge transport layer 8 is provided between the blue light-emitting layer 7B and the upper electrode 9. The second charge transport layer 8 can be formed to a thickness of, for example, 50 nm by applying a solution of ZnO nanoparticles doped with Mg, for example, dispersed in ethanol, using a spin coating method or the like under a nitrogen atmosphere. In the blue light-emitting element 31B shown in FIG. 1 , the second charge transport layer 8 functions as, for example, an electron transport layer. The second charge transport layer 8 may be formed of any material having electron transport properties. For example, the second charge transport layer 8 may be formed using a solution of undoped ZnO nanoparticles dispersed in ethanol, or a solution of ZnO nanoparticles doped with at least one of Li, Al, Ti, Ga, and Zr in addition to Mg, dispersed in ethanol. Alternatively, TiO nanoparticles may be used instead of the ZnO nanoparticles. ２ Nanoparticles or ZrO ２ Nanoparticles may be used, and metal oxide nanoparticles containing at least one of Zn, Mg, Ti, Si, Sn, W, Ta, Ba, Zr, Al, Y, and Hf may be used.

[0036] In the blue light-emitting element 31B shown in FIG. 1, a case where the blue light-emitting element 31B includes a second charge transport layer 8 that functions as an electron transport layer will be described as an example, but this is not limited to this. For example, the blue light-emitting element 31B may include a second charge transport layer 8 that functions as an electron injection layer, a second charge transport layer 8 that functions as an electron injection layer and an electron transport layer, or no second charge transport layer 8 may be included.

[0037] In this embodiment, as shown in FIG. 1, a transparent metal oxide layer made of ITO (indium tin oxide) having a thickness of 100 nm and formed by a sputtering method is formed as the upper electrode 9 provided on the second charge transport layer 8. However, the present invention is not limited to this, and a metal layer that transmits visible light and is made of silver or gold having a thickness of about 20 nm and formed by a vapor deposition method may also be formed.

[0038] FIG. 5 is a diagram comparing the characteristics of an HOD (Hole Only Device) fabricated using the transparent metal oxide layer 3 having the roughness shown in FIG. 3 and provided in the blue light-emitting element 31B of embodiment 1, and an HOD (Hole Only Device) fabricated using the transparent metal oxide layer having the roughness shown in FIG. 4, which is the lower electrode of Comparative Example 1. The HOD (Hole Only Device) that is Sample 1 shown in FIG. 5 has a configuration in which the following are stacked in the thickness direction in this order: ITO (indium tin oxide) as the transparent metal oxide layer 3 having the roughness shown in FIG. 3; a 40-nm-thick nanoparticle layer 5 composed of nickel oxide nanoparticles with a particle size of approximately 8 nm; a layer of [2-(3,6-Dibromo-9H-carbazol-9-yl)ethyl]phosphonic Acid (Br-2PACz) as a self-assembled monolayer (SAM); a 30-nm-thick first charge transport layer 6 composed of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)]; a 30-nm-thick blue light-emitting layer 7B containing blue-light-emitting quantum dots; a 15-nm-thick molybdenum oxide layer; and a 50-nm-thick silver layer. On the other hand, the HOD (Hole Only Device) of Sample 2 shown in FIG. 5 has the same configuration as the HOD (Hole Only Device) of Sample 1 shown in FIG. 5 described above, except that the lower electrode of Comparative Example 1 uses ITO (indium tin oxide), which is a transparent metal oxide layer having the roughness shown in FIG. 4 , instead of the ITO (indium tin oxide), which is the transparent metal oxide layer 3 having the roughness shown in FIG. 3 . In the case of the HOD (Hole Only Device) described above, a molybdenum oxide layer is provided instead of a material having electron transport properties, such as ZnMgO, to achieve a structure in which only holes flow. The molybdenum oxide layer having a thickness of 15 nm was formed by applying a solution of molybdo(VI) phosphate hydrate in isopropyl alcohol, for example, by spin coating, and then baking at 120° C. for 10 minutes.

[0039] Fig. 6 is a graph comparing the external quantum efficiency (EQE) of a blue light-emitting element (Sample 3) prepared using the transparent metal oxide layer 3 having the roughness shown in Fig. 3 provided in the blue light-emitting element 31B of Embodiment 1 with the external quantum efficiency (EQE) of a blue light-emitting element (Sample 4) prepared using the transparent metal oxide layer having the roughness shown in Fig. 4 that is the lower electrode of Comparative Example 1. Fig. 7 is a graph comparing the emission luminance, at the same current density, of the blue light-emitting element (Sample 3) prepared using the transparent metal oxide layer 3 having the roughness shown in Fig. 3 provided in the blue light-emitting element 31B of Embodiment 1 with the emission luminance of the blue light-emitting element (Sample 4) prepared using the transparent metal oxide layer having the roughness shown in Fig. 4 that is the lower electrode of Comparative Example 1. The blue light-emitting device (Sample 3) manufactured using the transparent metal oxide layer 3 having the roughness shown in FIG. 3 and provided in the blue light-emitting device 31B of Embodiment 1 shown in FIGS. 6 and 7 includes ITO (indium tin oxide) as the transparent metal oxide layer 3 having the roughness shown in FIG. 3, a nanoparticle layer 5 having a thickness of 40 nm and composed of nickel oxide nanoparticles with a particle size of approximately 8 nm, and a self-assembled monolayer (SAM) of [2-(3,6-Dibromo-9H-carbazol-9-yl)ethyl]phosphonic Acid This is a bottom-emission light-emitting device in which a layer made of (Br-2PACz), a 30-nm-thick first charge transport layer 6 made of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)], a 30-nm-thick blue light-emitting layer 7B containing blue-light-emitting quantum dots, a 50-nm-thick second charge transport layer 8 made of ZnMgO nanoparticles, and a 50-nm-thick silver layer are laminated in this order in the thickness direction. On the other hand, a blue light-emitting device (Sample 4) fabricated using the transparent metal oxide layer having the roughness shown in FIG. 4 , which is the lower electrode of Comparative Example 1, has the same configuration as the blue light-emitting device (Sample 3) shown in FIGS. 6 and 7 described above, except that ITO (indium tin oxide), which is the transparent metal oxide layer having the roughness shown in FIG. 4 , which is the lower electrode of Comparative Example 1, is used instead of ITO (indium tin oxide), which is the transparent metal oxide layer having the roughness shown in FIG. 3 .

[0040] As shown in Figure 5, in the case of an HOD (Hole Only Device) fabricated using the transparent metal oxide layer 3 having the roughness shown in Figure 3 which is provided in the blue light-emitting element 31B of embodiment 1, the hole injection characteristics are significantly improved compared to an HOD (Hole Only Device) fabricated using the transparent metal oxide layer having the roughness shown in Figure 4 which is the lower electrode of Comparative Example 1.

[0041] As shown in Fig. 6 , the external quantum efficiency (EQE) of a blue light-emitting element (Sample 3) fabricated using the transparent metal oxide layer 3 having the roughness shown in Fig. 3 provided in the blue light-emitting element 31B of Embodiment 1 is significantly improved compared to the external quantum efficiency (EQE) of a blue light-emitting element (Sample 4) fabricated using the transparent metal oxide layer having the roughness shown in Fig. 4 , which is the lower electrode of Comparative Example 1. As described above, Fig. 6 shows the evaluation results using a bottom-emission light-emitting element, but it goes without saying that similar evaluation results can also be obtained in the case of a top-emission light-emitting element such as the blue light-emitting element 31B of Embodiment 1. In the top-emission blue light-emitting element 31B shown in Fig. 1 , for example, the anode, which is the lower electrode 4B, can be formed from an electrode material that reflects visible light, and the cathode, which is the upper electrode 9, can be formed from an electrode material that transmits visible light. The lower electrode 4B may be, for example, a laminate in which a transparent metal oxide layer 1 made of ITO (indium tin oxide) and having a thickness of 20 nm, a metal layer 2 made of Ag and having a thickness of 100 nm, and a transparent metal oxide layer 3 made of ITO (indium tin oxide) and having a thickness of 65 nm are laminated in this order.

[0042] 7, the luminance of the blue light-emitting element (sample 3) fabricated using the transparent metal oxide layer 3 having the roughness shown in Fig. 3 provided in the blue light-emitting element 31B of embodiment 1 at the same current density is significantly improved compared to the luminance of the blue light-emitting element (sample 4) fabricated using the transparent metal oxide layer having the roughness shown in Fig. 4 that is the lower electrode of comparative example 1. As described above, Fig. 7 shows the evaluation results using a bottom-emission type light-emitting element, but it goes without saying that similar evaluation results can also be obtained in the case of a top-emission type light-emitting element such as the blue light-emitting element 31B of embodiment 1.

[0043] As described above, in this embodiment, the case where the lower electrode 4B provided in the blue light-emitting element 31B is an anode and the upper electrode 9 is a cathode has been described as an example, but this is not limited thereto, and the lower electrode 4B provided in the blue light-emitting element 31B may be a cathode and the upper electrode 9 may be an anode. When the lower electrode 4B provided in the blue light-emitting element 31B is a cathode and the upper electrode 9 is an anode, the shape of the surface of the lower electrode 4B on the nanoparticle layer 5 side described above can increase the contact area between the nanoparticle layer 5 and the lower electrode 4B, thereby improving the injection characteristics of electrons, which are carriers. In this case, the nanoparticles contained in the nanoparticle layer 5 are nanoparticles that have electron transport properties.

[0044] Second Embodiment FIG. 8 is a cross-sectional view showing a schematic configuration of a blue light-emitting element 41B according to a second embodiment.

[0045] As shown in Figure 8, the blue light-emitting element 41B includes a lower electrode 4B', an upper electrode 9, a blue light-emitting layer 7B provided between the lower electrode 4B' and the upper electrode 9, a nanoparticle layer 5 provided between the lower electrode 4B' and the blue light-emitting layer 7B and composed of a plurality of nanoparticles of a first inorganic oxide, and a continuous film 10 of a second inorganic oxide provided between the lower electrode 4B' and the nanoparticle layer 5 and in contact with the lower electrode 4B'.

[0046] 8, the roughness of the surface of the lower electrode 4B' on the nanoparticle layer 5 side, i.e., the roughness of the surface of the transparent metal oxide layer 3' made of ITO (indium tin oxide) on the nanoparticle layer 5 side, is reduced by forming a continuous film 10 of a second inorganic oxide in contact with the lower electrode 4B' without using, for example, mechanical polishing, chemical polishing such as etching, or a combination of mechanical polishing and chemical polishing, as described in embodiment 1. Therefore, in the blue light-emitting element 41B of embodiment 2, there is a large difference between the maximum height portions of the plurality of protrusions 3a' and the maximum depth portions of the plurality of recesses 3b' of the lower electrode 4B'.

[0047] The second inorganic oxide continuous film 10 is, for example, nickel acetate tetrahydrate (Ni(CH ３ COOH) ２ ・4H ２ The second inorganic oxide continuous film 10 can be formed by a coating process in which a 0.04 M ethanol solution of 0.04 M ethanol is applied by spin coating or the like, followed by a heat treatment process in which the film is baked at 250° C. for 1 hour, for example. In this embodiment, the second inorganic oxide continuous film 10 will be described as a continuous nickel oxide film as an example, but is not limited to this. Note that the continuous film means a film that is not divided in one plane by materials other than the material that constitutes the continuous film.

[0048] In the above-described blue light-emitting device 41B, the continuous film 10 of the second inorganic oxide is formed to cover and planarize the multiple convex portions 3a' and multiple concave portions 3b' on the surface of the lower electrode 4B' facing the nanoparticle layer 5. This increases the contact area between the lower electrode 4B' and the continuous film 10 of the second inorganic oxide, as well as the contact area between the continuous film 10 of the second inorganic oxide and the nanoparticle layer 5 composed of multiple nanoparticles of the first inorganic oxide. This improves carrier injection characteristics and prevents an increase in the driving voltage of the blue light-emitting device 41B. This allows for the realization of a blue light-emitting device 41B that achieves high reliability, high luminous efficiency, and low driving voltage. In this embodiment, the blue light-emitting device 41B is described as an example, but is not limited thereto. By employing the continuous film 10 of the second inorganic oxide and the nanoparticle layer 5 provided in the blue light-emitting device 41B, high reliability, high luminous efficiency, and low driving voltage can be achieved, for example, in red and green light-emitting devices as well.

[0049] In this embodiment, an example is given in which the lower electrode 4B' provided in the blue light-emitting element 41B is an anode and the upper electrode 9 is a cathode, but this is not limited to this, and the lower electrode 4B' provided in the blue light-emitting element 41B may be a cathode and the upper electrode 9 may be an anode.

[0050] When the lower electrode 4B' provided in the blue light-emitting element 41B is an anode and the upper electrode 9 is a cathode, a continuous film 10 of the second inorganic oxide is formed. Therefore, the contact area between the lower electrode 4B' and the continuous film 10 of the second inorganic oxide and the contact area between the continuous film 10 of the second inorganic oxide and the nanoparticle layer 5 composed of a plurality of nanoparticles of the first inorganic oxide can be increased, thereby improving the hole injection characteristics. This generally improves the carrier balance in light-emitting elements prone to electron excess, particularly green and blue light-emitting elements, thereby achieving improved external quantum efficiency (EQE) and reliability. Furthermore, the continuous film 10 of the second inorganic oxide is formed so as to cover and planarize the plurality of convex portions 3a' and the plurality of concave portions 3b' on the surface of the lower electrode 4B' facing the nanoparticle layer 5. This allows the nanoparticle layer 5 composed of a plurality of nanoparticles of the first inorganic oxide formed on the lower electrode 4B' to be formed with a more uniform thickness that is optimal for hole transport.

[0051] The thickness of the continuous film 10 of the second inorganic oxide is preferably 5 nm or more and 15 nm or less. In consideration of the heat resistance of the lower electrode 4B', the continuous film 10 of the second inorganic oxide is generally heat-treated at a temperature of 300°C or less in many cases. Therefore, the crystallinity of the continuous film 10 of the second inorganic oxide is poorer than that of the nanoparticles contained in the nanoparticle layer 5, and the resistivity of the continuous film 10 of the second inorganic oxide is often higher than that of the nanoparticle layer 5. Therefore, in order to prevent an excessive increase in the driving voltage, the thickness of the continuous film 10 of the second inorganic oxide is preferably 15 nm or less. On the other hand, in order to cover and planarize the multiple convex portions 3a' and multiple concave portions 3b' on the surface of the lower electrode 4B' facing the nanoparticle layer 5, the thickness of the continuous film 10 of the second inorganic oxide is preferably 5 nm or more.

[0052] Furthermore, the second inorganic oxide in the continuous film 10 of the second inorganic oxide and the first inorganic oxide constituting the nanoparticles of the nanoparticle layer 5 are preferably the same type of inorganic oxide, and in this embodiment, nickel oxide was used as both the first inorganic oxide and the second inorganic oxide. When the second inorganic oxide in the continuous film 10 of the second inorganic oxide and the first inorganic oxide constituting the nanoparticles of the nanoparticle layer 5 are the same type of inorganic oxide, the contact between the continuous film 10 of the second inorganic oxide and the nanoparticle layer 5 is improved, and the hole injection characteristics can be improved. Note that the above-mentioned "same type of inorganic oxide" means that at least one same element other than oxygen is contained, and the same element is preferably a metal element, and the metal element may be, for example, nickel.

[0053] As described above, in this embodiment, the case where the lower electrode 4B' provided in the blue light-emitting element 41B is an anode and the upper electrode 9 is a cathode has been described as an example. However, this is not limited thereto, and the lower electrode 4B' provided in the blue light-emitting element 41B may be a cathode and the upper electrode 9 may be an anode. When the lower electrode 4B' provided in the blue light-emitting element 41B is a cathode and the upper electrode 9 is an anode, the continuous film 10 of the second inorganic oxide is formed so as to cover and planarize the multiple convex portions 3a' and multiple concave portions 3b' on the surface of the lower electrode 4B' facing the nanoparticle layer 5. This increases the contact area between the lower electrode 4B' and the continuous film 10 of the second inorganic oxide, and the contact area between the continuous film 10 of the second inorganic oxide and the nanoparticle layer 5 composed of multiple nanoparticles of the first inorganic oxide, thereby improving the electron injection characteristics. In this case, the nanoparticles contained in the nanoparticle layer 5 are nanoparticles having electron transport properties.

[0054] 9 is a plan view showing a schematic configuration of a display device 51 of embodiment 3. FIG. 10 is a cross-sectional view showing a schematic configuration of a display area DA of the display device 51 of embodiment 3.

[0055] As shown in Fig. 9, the display device 51 includes a frame area NDA and a display area DA. The display area DA of the display device 51 includes a plurality of display units PIX, each of which includes a red pixel RSP, a green pixel GSP, and a blue pixel BSP. In this embodiment, a case where one display unit PIX is configured with a red pixel RSP, a green pixel GSP, and a blue pixel BSP is described as an example, but this is not limiting. For example, one display unit PIX may include pixels of other colors in addition to the red pixel RSP, the green pixel GSP, and the blue pixel BSP.

[0056] 10 , the display device 51 includes a substrate 12, and on the substrate 12, the red pixel RSP includes a red light-emitting element 31R, the green pixel GSP includes a green light-emitting element 31G, and the blue pixel BSP includes a blue light-emitting element 31B. The substrate 12 may be, for example, a resin substrate made of a resin material such as polyimide, or a glass substrate. In this embodiment, since the display device 51 is a flexible display device, a case where a resin substrate made of a resin material such as polyimide is used as the substrate 12 will be described as an example, but this is not limiting. If the display device 51 is a non-flexible display device, a glass substrate can be used as the substrate 12.

[0057] 10 , the display device 51 includes a red light-emitting element (first light-emitting element) 31R, a green light-emitting element (second light-emitting element) 31G, and a blue light-emitting element (third light-emitting element) 31B. The red light-emitting element 31R includes a first lower electrode 4R, an upper electrode 9, a red light-emitting layer 7R provided between the first lower electrode 4R and the upper electrode 9, and a nanoparticle layer 5 provided between the first lower electrode 4R and the red light-emitting layer 7R and in contact with the first lower electrode 4R, the nanoparticle layer 5 being composed of a plurality of nanoparticles of a first inorganic oxide. The green light-emitting element 31G includes a second lower electrode 4G, an upper electrode 9, a green light-emitting layer 7G provided between the second lower electrode 4G and the upper electrode 9, and a nanoparticle layer 5 provided between the second lower electrode 4G and the green light-emitting layer 7G and in contact with the second lower electrode 4G, the nanoparticle layer 5 being composed of a plurality of nanoparticles of the first inorganic oxide. The blue light-emitting element 31B includes a third lower electrode 4B, an upper electrode 9, a blue light-emitting layer 7B provided between the third lower electrode 4B and the upper electrode 9, and a nanoparticle layer 5 provided between the third lower electrode 4B and the blue light-emitting layer 7B, in contact with the third lower electrode 4B, and composed of a plurality of nanoparticles of a first inorganic oxide.

[0058] As shown in Figure 10, the surface of the first lower electrode 4R facing the nanoparticle layer 5 in a first cross section taken along the thickness direction of the red light-emitting element 31R includes a plurality of first convex portions 23a and a plurality of first concave portions 23b, the surface of the second lower electrode 4G facing the nanoparticle layer 5 in a second cross section taken along the thickness direction of the green light-emitting element 31G includes a plurality of second convex portions 13a and a plurality of second concave portions 13b, and the surface of the third lower electrode 4B facing the nanoparticle layer 5 in a third cross section taken along the thickness direction of the blue light-emitting element 31B includes a plurality of third convex portions 3a and a plurality of third concave portions 3b.

[0059] 10 , in the display device 51, the difference between the maximum height of the second convex portions 13a and the maximum depth of the second concave portions 13b, and the difference between the maximum height of the third convex portions 3a and the maximum depth of the third concave portions 3b are each smaller than the difference between the maximum height of the first convex portions 23a and the maximum depth of the first concave portions 23b. That is, in the display device 51, the roughness of the surface of the lower electrode on the nanoparticle layer 5 side is reduced in the green light-emitting element 31G and the blue light-emitting element 31B so as to improve the hole injection characteristics. The energy levels of the valence band upper edge (VBM) of the quantum dots QDs contained in the blue light-emitting layer 7B and the quantum dots QDs contained in the green light-emitting layer 7G are deeper than the energy level of the valence band upper edge (VBM) of the quantum dots QDs contained in the red light-emitting layer 7R, and therefore the green light-emitting element 31G and the blue light-emitting element 31B have poorer hole injection characteristics than the red light-emitting element 31R. Therefore, in the display device 51, the difference between the maximum height of the second convex portions 13a and the maximum depth of the second concave portions 13b and the difference between the maximum height of the third convex portions 3a and the maximum depth of the third concave portions 3b are each smaller than the difference between the maximum height of the first convex portions 23a and the maximum depth of the first concave portions 23b. Therefore, in the green light-emitting element 31G, the contact area between the nanoparticle layer 5 composed of a plurality of first inorganic oxide nanoparticles formed on the second lower electrode 4G and the second lower electrode 4G can be increased, thereby improving carrier injection characteristics and suppressing an increase in driving voltage. Furthermore, in the blue light-emitting element 31B, the contact area between the nanoparticle layer 5 composed of a plurality of first inorganic oxide nanoparticles formed on the third lower electrode 4B and the third lower electrode 4B can be increased, thereby improving carrier injection characteristics and suppressing an increase in driving voltage. Therefore, a display device 51 with high reliability and low power consumption can be realized.

[0060] In the green light-emitting element 31G provided in the display device 51, the difference between the maximum height of the plurality of second convex portions 13a and the maximum depth of the plurality of second concave portions 13b is preferably smaller than the particle diameter of the nanoparticles contained in the nanoparticle layer 5 in the second cross section. In the blue light-emitting element 31B provided in the display device 51, the difference between the maximum height of the plurality of third convex portions 3a and the maximum depth of the plurality of third concave portions 3b is preferably smaller than the particle diameter of the nanoparticles contained in the nanoparticle layer 5 in the third cross section. According to the above configuration, in the green light-emitting element 31G, the contact area between the nanoparticle layer 5 formed on the second lower electrode 4G and the second lower electrode 4G, which is composed of a plurality of nanoparticles of the first inorganic oxide, can be increased, thereby improving carrier injection characteristics and suppressing an increase in driving voltage. Furthermore, in the blue light-emitting element 31B, the contact area between the nanoparticle layer 5 formed on the third lower electrode 4B and the third lower electrode 4B, which is composed of a plurality of nanoparticles of the first inorganic oxide, can be increased, thereby improving carrier injection characteristics and suppressing an increase in driving voltage. Therefore, a display device 51 with high reliability and low power consumption can be realized.

[0061] As described above, in the present embodiment, a case where the surface roughness of the lower electrode on the nanoparticle layer 5 side is reduced so as to improve the hole injection characteristics in the green light-emitting element 31G and the blue light-emitting element 31B of the display device 51 is described as an example, but the present invention is not limited to this, and the surface roughness of the lower electrode on the nanoparticle layer 5 side may be reduced so as to improve the hole injection characteristics in one or more of the red light-emitting element 31R, the green light-emitting element 31G, and the blue light-emitting element 31B of the display device 51. Note that when reducing the surface roughness of the lower electrode on the nanoparticle layer 5 side so as to improve the hole injection characteristics in only some of the red light-emitting element 31R, the green light-emitting element 31G, and the blue light-emitting element 31B of the display device 51, for example, a resist film may be formed in areas other than the target area for reducing the roughness, and then mechanical polishing, chemical polishing such as etching, or a combination of mechanical polishing and chemical polishing may be performed.

[0062] In the present embodiment, a case where the first lower electrode 4R, the second lower electrode 4G, and the third lower electrode 4B are each an anode and the upper electrode 9 is a cathode will be described as an example, but the present invention is not limited to this, and the first lower electrode 4R, the second lower electrode 4G, and the third lower electrode 4B may each be a cathode and the upper electrode 9 may be an anode. In the display device 51, when the first lower electrode 4R, the second lower electrode 4G, and the third lower electrode 4B are each an anode and the upper electrode 9 is a cathode, the hole injection characteristics can be improved in the green light-emitting element 31G and the blue light-emitting element 31B, which generally tend to have an excess of electrons. Therefore, the carrier balance can be improved in the green light-emitting element 31G and the blue light-emitting element 31B, which are prone to electron excess, and improvements in external quantum efficiency (EQE) and reliability can be realized.

[0063] In the display device 51, it is preferable that at least one of the difference between the maximum height portion of the plurality of second convex portions 13a and the maximum depth portion of the plurality of second concave portions 13b and the difference between the maximum height portion of the plurality of third convex portions 3a and the maximum depth portion of the plurality of third concave portions 3b is 8 nm or less.

[0064] In the display device 51, it is preferable that the difference between the maximum height portion of the plurality of second convex portions 13a and the maximum depth portion of the plurality of second concave portions 13b, and the difference between the maximum height portion of the plurality of third convex portions 3a and the maximum depth portion of the plurality of third concave portions 3b are each 8 nm or less.

[0065] Furthermore, in the display device 51, it is preferable that the difference between the maximum height portions of the plurality of third convex portions 3 a and the maximum depth portions of the plurality of third concave portions 3 b is smaller than the difference between the maximum height portions of the plurality of second convex portions 13 a and the maximum depth portions of the plurality of second concave portions 13 b. The energy level of the valence band upper edge (VBM) of the quantum dots QD contained in the blue light-emitting layer 7B is deeper than the energy level of the valence band upper edge (VBM) of the quantum dots QD contained in the green light-emitting layer 7G, and the blue light-emitting element 31B has poorer hole injection characteristics than the green light-emitting element 31G. Therefore, by making the difference between the maximum height portion of the plurality of third convex portions 3a and the maximum depth portion of the plurality of third concave portions 3b smaller than the difference between the maximum height portion of the plurality of second convex portions 13a and the maximum depth portion of the plurality of second concave portions 13b, the contact area between the nanoparticle layer 5 composed of a plurality of first inorganic oxide nanoparticles formed on the third lower electrode 4B and the third lower electrode 4B can be made larger in the blue light-emitting element 31B compared to the green light-emitting element 31G, thereby improving the carrier injection characteristics and further suppressing an increase in driving voltage.

[0066] 10 , in the display device 51, the nanoparticle layer 5 is preferably a continuous film formed as a common layer for the red light-emitting element 31R, the green light-emitting element 31G, and the blue light-emitting element 31B. This configuration eliminates the need to form the nanoparticle layer 5 using a separate coating process, thereby reducing the manufacturing cost of the display device 51. The first inorganic oxide constituting the nanoparticles contained in the nanoparticle layer 5 preferably contains nickel oxide.

[0067] In the display device 51, one of the green light-emitting layer 7G and the blue light-emitting layer 7B may contain a first halogen element and a first metal element, and a value of (the number of the first halogen elements / the number of the first metal elements) × 100% may be 0.5% or more. When one of the green light-emitting layer 7G and the blue light-emitting layer 7B contains a first halogen element and a first metal element, and a value of (the number of the first halogen elements / the number of the first metal elements) × 100% is 0.5% or more, i.e., when the content of the first halogen element in one of the green light-emitting layer 7G and the blue light-emitting layer 7B is high and the energy level of the valence band upper limit (VBM) of the corresponding light-emitting layer is deepened, deterioration of the hole injection characteristics due to the deepening of the energy level of the valence band upper limit (VBM) of the corresponding light-emitting layer can be alleviated by reducing the roughness of the surface of the lower electrode on the nanoparticle layer 5 side so as to improve the hole injection characteristics. The green light emitting element 31G and the blue light emitting element 31B emit light with high energy, and therefore are more susceptible to element degradation than the red light emitting element 31R, so the effect of improving reliability by the halogen ligand is particularly significant.

[0068] In the display device 51, the other of the green light-emitting layer 7G and the blue light-emitting layer 7B may contain a second halogen element and a second metal element, and a value of (the number of the second halogen elements / the number of the second metal elements) × 100% may be 0.5% or more. When the other of the green light-emitting layer 7G and the blue light-emitting layer 7B contains a second halogen element and a second metal element, and a value of (the number of the second halogen elements / the number of the second metal elements) × 100% is 0.5% or more, that is, when the content of the second halogen element in the other of the green light-emitting layer 7G and the blue light-emitting layer 7B is high and the energy level of the valence band upper limit (VBM) of the corresponding light-emitting layer is deepened, deterioration of the hole injection characteristics due to the deepening of the energy level of the valence band upper limit (VBM) of the corresponding light-emitting layer can be alleviated by reducing the roughness of the surface of the lower electrode on the nanoparticle layer 5 side so as to improve the hole injection characteristics.

[0069] In the display device 51, the red light-emitting element 31R, the green light-emitting element 31G, and the blue light-emitting element 31B may each include the nanoparticle layer 5 and the upper electrode 9 as common layers, and may also each include the first charge transport layer 6 and the second charge transport layer 8 as common layers. In this case, although hole injection in the green light-emitting element 31G and the blue light-emitting element 31B is more difficult than hole injection in the red light-emitting element 31R, because a common charge transport layer is used, at least one of the following cases is likely to occur: a first case in which the red light-emitting element 31R has an excess of holes; and a second case in which the green light-emitting element 31G and the blue light-emitting element 31B have an excess of electrons. This makes it difficult to maintain a carrier balance in all the light-emitting elements. However, by making the difference between the maximum height portions of the plurality of second convex portions 13 a and the maximum depth portions of the plurality of second concave portions 13 b and the difference between the maximum height portions of the plurality of third convex portions 3 a and the maximum depth portions of the plurality of third concave portions 3 b smaller than the difference between the maximum height portions of the plurality of first convex portions 23 a and the maximum depth portions of the plurality of first concave portions 23 b, hole injection in the green light-emitting element 31G and the blue light-emitting element 31B can be promoted compared to hole injection in the red light-emitting element 31R. This makes it possible to adjust the carrier balance in all of the red light-emitting element 31R, green light-emitting element 31G, and blue light-emitting element 31B while enjoying the benefits of the simple process and low cost that come from using a common charge transport layer, which is a great economic advantage.

[0070] The nanoparticle layer 5 provided in the display device 51 is a continuous film formed as a common layer for the red light-emitting element 31R, the green light-emitting element 31G, and the blue light-emitting element 31B, and one of the green light-emitting layer 7G and the blue light-emitting layer 7B contains quantum dots (first quantum dots) QD, and the energy level of the upper valence band (VBM) of the quantum dots (first quantum dots) QD may be 0.3 eV or more deeper than the energy level of the upper valence band (VBM) of the nanoparticle layer 5. In this way, when the energy level of the valence band upper limit (VBM) of the quantum dot (first quantum dot) QD is 0.3 eV or more deeper than the energy level of the valence band upper limit (VBM) of the nanoparticle layer 5 and the hole injection characteristics from the nanoparticle layer 5 to the quantum dot (first quantum dot) QD are deteriorated due to an energy barrier, the roughness of the surface of the lower electrode on the nanoparticle layer 5 side can be reduced to improve the hole injection characteristics, thereby mitigating the deterioration of the hole injection characteristics caused by the energy level of the valence band upper limit (VBM) of the quantum dot (first quantum dot) QD being 0.3 eV or more deeper than the energy level of the valence band upper limit (VBM) of the nanoparticle layer 5.

[0071] The other of the green light-emitting layer 7G and the blue light-emitting layer 7B provided in the display device 51 includes quantum dots (second quantum dots) QDs, and the energy level of the upper valence band (VBM) of the quantum dots (second quantum dots) QDs may be deeper by 0.3 eV or more than the energy level of the upper valence band (VBM) of the nanoparticle layer 5. In this way, when the energy level of the valence band upper limit (VBM) of the quantum dot (second quantum dot) QD is 0.3 eV or more deeper than the energy level of the valence band upper limit (VBM) of the nanoparticle layer 5 and the hole injection characteristics from the nanoparticle layer 5 to the quantum dot (second quantum dot) QD are deteriorated due to an energy barrier, the roughness of the surface of the lower electrode on the nanoparticle layer 5 side can be reduced to improve the hole injection characteristics, thereby mitigating the deterioration of the hole injection characteristics caused by the energy level of the valence band upper limit (VBM) of the quantum dot (second quantum dot) QD being 0.3 eV or more deeper than the energy level of the valence band upper limit (VBM) of the nanoparticle layer 5.

[0072] The red light-emitting layer 7R provided in the display device 51 includes quantum dots (third quantum dots) QDs, and the energy level of the valence band upper edge (VBM) of the quantum dots (third quantum dots) QDs may be shallower by 0.1 eV or more than the energy level of the valence band upper edge (VBM) of the nanoparticle layer 5. In this way, if the energy level of the valence band upper edge (VBM) of the quantum dots (third quantum dots) QDs is shallower by 0.1 eV or more than the energy level of the valence band upper edge (VBM) of the nanoparticle layer 5, the effect of optimizing the carrier balance of holes and electrons in the red light-emitting element 31R can be increased.

[0073] In this embodiment, the transparent metal oxide layer 23 of the first lower electrode 4R provided in the red light-emitting element 31R is formed, for example, from a layer made of ITO (indium tin oxide) with a thickness of 160 nm, the transparent metal oxide layer 13 of the second lower electrode 4G provided in the green light-emitting element 31G is formed, for example, from a layer made of ITO (indium tin oxide) with a thickness of 100 nm, and the transparent metal oxide layer 3 of the third lower electrode 4B provided in the blue light-emitting element 31B is formed, for example, from a layer made of ITO (indium tin oxide) with a thickness of 65 nm, thereby optimizing the light extraction efficiency in each of the red pixel RSP, green pixel GSP, and blue pixel BSP of the display device 51. Without being limited thereto, the film thickness of the transparent metal oxide layer 23 of the first lower electrode 4R provided in the red light emitting element 31R, the film thickness of the transparent metal oxide layer 13 of the second lower electrode 4G provided in the green light emitting element 31G, and the film thickness of the transparent metal oxide layer 3 of the third lower electrode 4B provided in the blue light emitting element 31B may be appropriately adjusted so as to improve the light extraction efficiency in each of the red pixel RSP, green pixel GSP, and blue pixel BSP of the display device 51. Note that the film thickness of the transparent metal oxide layer 23 of the first lower electrode 4R provided in the red light emitting element 31R, the film thickness of the transparent metal oxide layer 13 of the second lower electrode 4G provided in the green light emitting element 31G, and the film thickness of the transparent metal oxide layer 3 of the third lower electrode 4B provided in the blue light emitting element 31B may be the same.

[0074] In this embodiment, the red light-emitting layer 7R provided in the red light-emitting element 31R is formed to a thickness of 15 nm, the green light-emitting layer 7G provided in the green light-emitting element 31G is formed to a thickness of 15 nm, and the blue light-emitting layer 7B provided in the blue light-emitting element 31B is formed to a thickness of 30 nm, but the present invention is not limited to these.

[0075] As described above, in this embodiment, the first lower electrode 4R, the second lower electrode 4G, and the third lower electrode 4B are each an anode, and the upper electrode 9 is a cathode. However, this is not limited thereto. The first lower electrode 4R, the second lower electrode 4G, and the third lower electrode 4B may each be a cathode, and the upper electrode 9 may be an anode. When the first lower electrode 4R, the second lower electrode 4G, and the third lower electrode 4B are each a cathode, and the upper electrode 9 is an anode, the contact area between the nanoparticle layer 5, which is composed of a plurality of first inorganic oxide nanoparticles formed on the first lower electrode 4R, the second lower electrode 4G, and the third lower electrode 4B, and the second lower electrode 4G and the third lower electrode 4B, respectively, can be increased, thereby improving electron injection characteristics. In this case, the nanoparticles contained in the nanoparticle layer 5 are nanoparticles having electron transport properties.

[0076] Fourth Embodiment FIG. 11 is a cross-sectional view showing a schematic configuration of a display area DA of a display device 61 according to a fourth embodiment.

[0077] 11 , the display device 61 includes a substrate 12, and on the substrate 12, the red pixel RSP includes a red light-emitting element 31R, the green pixel GSP includes a green light-emitting element 41G, and the blue pixel BSP includes a blue light-emitting element 41B. The red light-emitting element 41R includes a first lower electrode 4R, an upper electrode 9, a red light-emitting layer 7R provided between the first lower electrode 4R and the upper electrode 9, and a nanoparticle layer 5 provided between the first lower electrode 4R and the red light-emitting layer 7R, in contact with the first lower electrode 4R, and composed of a plurality of nanoparticles of a first inorganic oxide. The green light-emitting element 41G includes a second lower electrode 4G', an upper electrode 9, a green light-emitting layer 7G provided between the second lower electrode 4G' and the upper electrode 9, a nanoparticle layer 5 provided between the second lower electrode 4G' and the green light-emitting layer 7G and composed of a plurality of nanoparticles of a first inorganic oxide, and a continuous film 10 of a second inorganic oxide provided between the second lower electrode 4G' and the nanoparticle layer 5 and in contact with the second lower electrode 4G'. The blue light-emitting element 41B includes a third lower electrode 4B', an upper electrode 9, a blue light-emitting layer 7B provided between the third lower electrode 4B' and the upper electrode 9, a nanoparticle layer 5 provided between the third lower electrode 4B' and the blue light-emitting layer 7B and composed of a plurality of nanoparticles of the first inorganic oxide, and a continuous film 10 of a second inorganic oxide provided between the third lower electrode 4B' and the nanoparticle layer 5 and in contact with the third lower electrode 4B'. In the above-described green light-emitting element 41G, the second inorganic oxide continuous film 10 is formed so as to cover and planarize the plurality of second protrusions 13a' and the plurality of second recesses 13b' on the surface of the second lower electrode 4G' facing the nanoparticle layer 5. This increases the contact area between the second lower electrode 4G' and the second inorganic oxide continuous film 10, as well as the contact area between the second inorganic oxide continuous film 10 and the nanoparticle layer 5 composed of a plurality of nanoparticles of the first inorganic oxide. This improves the carrier injection characteristics, thereby preventing an increase in the driving voltage of the green light-emitting element 41G. Therefore, a green light-emitting element 41G can be realized that has high reliability, high luminous efficiency, and a low driving voltage.Furthermore, in the above-described blue light-emitting device 41B, the continuous film 10 of the second inorganic oxide is formed to cover and planarize the multiple third convex portions 3a' and multiple third concave portions 3b' on the surface of the third lower electrode 4B' facing the nanoparticle layer 5. This increases the contact area between the third lower electrode 4B' and the continuous film 10 of the second inorganic oxide, as well as the contact area between the continuous film 10 of the second inorganic oxide and the nanoparticle layer 5 composed of multiple nanoparticles of the first inorganic oxide. This improves carrier injection characteristics and suppresses an increase in the driving voltage of the blue light-emitting device 41B. Therefore, a blue light-emitting device 41B that achieves high reliability, high luminous efficiency, and low driving voltage can be realized. Therefore, a display device 61 including the green light-emitting device 41G and the blue light-emitting device 41B can achieve high reliability and low power consumption. Furthermore, hole injection in the green light-emitting device 41G and the blue light-emitting device 41B can be promoted compared to hole injection in the red light-emitting device 31R, thereby optimizing the carrier balance in all of the red light-emitting device 31R, the green light-emitting device 41G, and the blue light-emitting device 41B.

[0078] 11 , the surface roughness of the second lower electrode 4G′ on the nanoparticle layer 5 side and the surface roughness of the third lower electrode 4B′ on the nanoparticle layer 5 side are reduced by forming a second inorganic oxide continuous film 10 in contact with the second lower electrode 4G′ and a second inorganic oxide continuous film 10 in contact with the third lower electrode 4B′ without using, for example, mechanical polishing, chemical polishing such as etching, or a combination of mechanical polishing and chemical polishing. However, the present invention is not limited to this. In one or more of the red light-emitting element 31R, green light-emitting element 41G, and blue light-emitting element 41B of the display device 61, the second inorganic oxide continuous film 10 may be formed to reduce the surface roughness of the lower electrode on the nanoparticle layer 5 side. In addition, when forming the continuous film 10 of the second inorganic oxide only in some of the light-emitting elements of the red light-emitting element 31R, the green light-emitting element 41G, and the blue light-emitting element 41B of the display device 61 and reducing the surface roughness of the nanoparticle layer 5 side of the lower electrode, for example, a photosensitive resist material may be used to form a resist film having an opening in a specific region, and then the continuous film 10 of the second inorganic oxide may be formed in the opening and on the resist film, and then the resist film may be peeled off and the continuous film 10 of the second inorganic oxide formed on the resist film may be peeled off, thereby forming the continuous film 10 of the second inorganic oxide only in the specific region.

[0079] In the present embodiment, a case where the first lower electrode 4R, the second lower electrode 4G', and the third lower electrode 4B' are each an anode and the upper electrode 9 is a cathode will be described as an example, but the present invention is not limited thereto, and the first lower electrode 4R, the second lower electrode 4G', and the third lower electrode 4B' may each be a cathode and the upper electrode 9 may be an anode. In the display device 61, when the first lower electrode 4R, the second lower electrode 4G', and the third lower electrode 4B' are each an anode and the upper electrode 9 is a cathode, the hole injection characteristics can be improved in the green light-emitting element 41G and the blue light-emitting element 41B, which generally tend to have an excess of electrons. Therefore, the carrier balance can be improved in the green light-emitting element 41G and the blue light-emitting element 41B, which are prone to electron excess, and improvements in external quantum efficiency (EQE) and reliability can be realized.

[0080] In the display device 61 shown in FIG. 11, the green light emitting element 41G and the blue light emitting element 41B preferably include a second continuous inorganic oxide film 10 formed as a common layer.

[0081] The thickness of the second inorganic oxide continuous film 10 is preferably 5 nm or more and 15 nm or less.

[0082] Furthermore, the first inorganic oxide constituting the nanoparticles contained in the nanoparticle layer 5 and the second inorganic oxide in the continuous film 10 of the second inorganic oxide are preferably the same type of inorganic oxide.

[0083] In this embodiment, the transparent metal oxide layer 23 of the first lower electrode 4R provided in the red light-emitting element 31R is formed, for example, from a layer made of ITO (indium tin oxide) with a thickness of 160 nm, the transparent metal oxide layer 13' of the second lower electrode 4G' provided in the green light-emitting element 41G is formed, for example, from a layer made of ITO (indium tin oxide) with a thickness of 100 nm, and the transparent metal oxide layer 3' of the third lower electrode 4B' provided in the blue light-emitting element 41B is formed, for example, from a layer made of ITO (indium tin oxide) with a thickness of 65 nm, thereby optimizing the light extraction efficiency in each of the red pixel RSP, green pixel GSP, and blue pixel BSP of the display device 61. Without being limited thereto, the film thickness of the transparent metal oxide layer 23 of the first lower electrode 4R provided in the red light emitting element 31R, the film thickness of the transparent metal oxide layer 13' of the second lower electrode 4G' provided in the green light emitting element 41G, and the film thickness of the transparent metal oxide layer 3' of the third lower electrode 4B' provided in the blue light emitting element 41B may be appropriately adjusted so as to improve the light extraction efficiency in each of the red pixel RSP, green pixel GSP, and blue pixel BSP of the display device 61. Note that the film thickness of the transparent metal oxide layer 23 of the first lower electrode 4R provided in the red light emitting element 31R, the film thickness of the transparent metal oxide layer 13' of the second lower electrode 4G' provided in the green light emitting element 41G, and the film thickness of the transparent metal oxide layer 3' of the third lower electrode 4B' provided in the blue light emitting element 41B may be the same.

[0084] As described above, in this embodiment, the first lower electrode 4R, the second lower electrode 4G', and the third lower electrode 4B' are each an anode, and the upper electrode 9 is a cathode, but this is not limited to this, and the first lower electrode 4R, the second lower electrode 4G', and the third lower electrode 4B' may each be a cathode, and the upper electrode 9 may be an anode. When the first lower electrode 4R, the second lower electrode 4G', and the third lower electrode 4B' are each a cathode and the upper electrode 9 is an anode, the second inorganic oxide continuous film 10 is formed to cover and planarize the multiple second convex portions 13a' and multiple second concave portions 13b' on the surface of the second lower electrode 4G' facing the nanoparticle layer 5, and the multiple third convex portions 3a' and multiple third concave portions 3b' on the surface of the third lower electrode 4B' facing the nanoparticle layer 5. This increases the contact area between the second lower electrode 4G' and the continuous film 10 of the second inorganic oxide, the contact area between the third lower electrode 4B' and the continuous film 10 of the second inorganic oxide, and the contact area between the continuous film 10 of the second inorganic oxide and the nanoparticle layer 5, thereby improving the electron injection characteristics. In this case, the nanoparticles contained in the nanoparticle layer 5 are nanoparticles having electron transport properties.

[0085] [Additional Notes] 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 the technical means disclosed in different 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 each embodiment.

[0086] The present disclosure can be used in light-emitting devices and display devices.

[0087] DESCRIPTION OF SYMBOLS 1, 3, 3', 13, 13', 23 Transparent metal oxide layer 2 Metal layer 3a Convex portion (third convex portion) 3b Concave portion (third concave portion) 3a' Convex portion (third convex portion) 3b' Concave portion (third concave portion) 4B, 4B' Third lower electrode (lower electrode) 4G, 4G' Second lower electrode 4R First lower electrode 5 Nanoparticle layer 6 First charge transport layer 7B Blue light-emitting layer (light-emitting layer) 7G Green light-emitting layer (light-emitting layer) 7R Red light-emitting layer (light-emitting layer) 8 Second charge transport layer 9 Upper electrode 10 Second continuous film of inorganic oxide 13a, 13a' Second convex portion 13b, 13b' Second concave portion 23a First convex portion 23b First concave portion 31B, 41B Blue light-emitting element (light-emitting element) 31G, 41G Green light-emitting element (light-emitting element) 31R Red light emitting element 51, 61 Display device PIX Display unit RSP Red pixel GSP Green pixel BSP Blue pixel DA Display area NDA Frame area

Claims

1. A light-emitting device comprising: a lower electrode; an upper electrode; a light-emitting layer provided between the lower electrode and the upper electrode; and a nanoparticle layer provided between the lower electrode and the light-emitting layer and in contact with the lower electrode, wherein the nanoparticle layer is composed of a plurality of nanoparticles of a first inorganic oxide, and a surface of the lower electrode facing the nanoparticle layer in a cross section cut along the thickness direction of a laminate including the lower electrode and the nanoparticle layer comprises a plurality of convex portions and a plurality of concave portions, and the difference between the maximum height of the plurality of convex portions and the maximum depth of the plurality of concave portions is smaller than the particle diameter of the nanoparticles contained in the nanoparticle layer.

2. The light-emitting element according to claim 1, wherein the lower electrode is an anode and the upper electrode is a cathode.

3. The light-emitting element according to claim 1 or 2, wherein the difference between the maximum height of the plurality of convex portions and the maximum depth of the plurality of concave portions is 8 nm or less.

4. A light-emitting element comprising: a lower electrode; an upper electrode; a light-emitting layer provided between the lower electrode and the upper electrode; a nanoparticle layer provided between the lower electrode and the light-emitting layer and composed of a plurality of nanoparticles of a first inorganic oxide; and a continuous film of a second inorganic oxide provided between the lower electrode and the nanoparticle layer and in contact with the lower electrode.

5. The light-emitting element according to claim 4, wherein the lower electrode is an anode and the upper electrode is a cathode.

6. The light-emitting element according to claim 4 or 5, wherein the continuous film of the second inorganic oxide has a thickness of 5 nm or more and 15 nm or less.

7. The light-emitting element according to any one of claims 4 to 6, wherein the first inorganic oxide and the second inorganic oxide are the same type of inorganic oxide.

8. The light-emitting element according to any one of claims 1 to 7, wherein the first inorganic oxide includes nickel oxide.

9. The light-emitting element according to any one of claims 1 to 8, wherein the light-emitting layer contains a halogen element and a metal element, and the value of (number of the halogen elements / number of the metal elements) x 100% is 0.5% or more.

10. A light-emitting element according to any one of claims 1 to 9, wherein the light-emitting layer contains quantum dots, and the energy level of the upper end of the valence band of the quantum dots is 0.3 eV or more deeper than the energy level of the upper end of the valence band of the nanoparticle layer.

11. A light-emitting device comprising a plurality of light-emitting elements, each light-emitting element including a lower electrode, an upper electrode, a light-emitting layer provided between the lower electrode and the upper electrode, and a nanoparticle layer provided between the lower electrode and the light-emitting layer, in contact with the lower electrode, the nanoparticle layer being composed of a plurality of nanoparticles of a first inorganic oxide, wherein the plurality of light-emitting elements include a first light-emitting element, a second light-emitting element, and a third light-emitting element, wherein the first light-emitting element is a red light-emitting element having a first lower electrode as the lower electrode and a red light-emitting layer as the light-emitting layer, the second light-emitting element is a green light-emitting element having a second lower electrode as the lower electrode and a green light-emitting layer as the light-emitting layer, and the third light-emitting element is a blue light-emitting element having a third lower electrode as the lower electrode and a blue light-emitting layer as the light-emitting layer, and wherein a surface of the first lower electrode on the nanoparticle layer side in a first cross section cut along the thickness direction of the first light-emitting element includes a plurality of first convex portions and a plurality of first concave portions, a surface of the second lower electrode on the nanoparticle layer side in a second cross section cut along the thickness direction of the second light-emitting element includes a plurality of second convex portions and a plurality of second concave portions; a surface of the third lower electrode on the nanoparticle layer side in a third cross section cut along the thickness direction of the third light-emitting element includes a plurality of third convex portions and a plurality of third concave portions; and a difference between a maximum height portion of the plurality of second convex portions and a maximum depth portion of the plurality of second concave portions and a difference between a maximum height portion of the plurality of third convex portions and a maximum depth portion of the plurality of third concave portions are each smaller than a difference between a maximum height portion of the plurality of first convex portions and a maximum depth portion of the plurality of first concave portions.

12. The display device described in claim 11, wherein the difference between the maximum height portion of the plurality of second convex portions and the maximum depth portion of the plurality of second concave portions is smaller than the particle size of the nanoparticles contained in the nanoparticle layer in the second cross section, and the difference between the maximum height portion of the plurality of third convex portions and the maximum depth portion of the plurality of third concave portions is smaller than the particle size of the nanoparticles contained in the nanoparticle layer in the third cross section.

13. The display device according to claim 11 or 12, wherein the first lower electrode, the second lower electrode and the third lower electrode are anodes, and the upper electrode is a cathode.

14. A display device described in any one of claims 11 to 13, wherein at least one of the difference between the maximum height portion of the plurality of second convex portions and the maximum depth portion of the plurality of second concave portions and the difference between the maximum height portion of the plurality of third convex portions and the maximum depth portion of the plurality of third concave portions is 8 nm or less.

15. A display device described in any one of claims 11 to 13, wherein the difference between the maximum height portion of the plurality of second convex portions and the maximum depth portion of the plurality of second concave portions, and the difference between the maximum height portion of the plurality of third convex portions and the maximum depth portion of the plurality of third concave portions, are each 8 nm or less.

16. A display device described in any one of claims 11 to 15, wherein the difference between the maximum height portion of the plurality of third convex portions and the maximum depth portion of the plurality of third concave portions is smaller than the difference between the maximum height portion of the plurality of second convex portions and the maximum depth portion of the plurality of second concave portions.

17. A display device comprising a plurality of light-emitting elements, each including a lower electrode, an upper electrode, a light-emitting layer provided between the lower electrode and the upper electrode, and a nanoparticle layer provided between the lower electrode and the light-emitting layer and composed of a plurality of nanoparticles of a first inorganic oxide, wherein the plurality of light-emitting elements include a first light-emitting element, a second light-emitting element, and a third light-emitting element, wherein the first light-emitting element is a red light-emitting element having a first lower electrode as the lower electrode and a red light-emitting layer as the light-emitting layer, the second light-emitting element is a green light-emitting element having a second lower electrode as the lower electrode, a continuous film of a second inorganic oxide provided between the second lower electrode and the nanoparticle layer and in contact with the second lower electrode, and a green light-emitting layer as the light-emitting layer, and the third light-emitting element is a blue light-emitting element having a third lower electrode as the lower electrode, a continuous film of a second inorganic oxide provided between the third lower electrode and the nanoparticle layer and in contact with the third lower electrode, and a blue light-emitting layer as the light-emitting layer.

18. The display device according to claim 17, wherein the first lower electrode, the second lower electrode and the third lower electrode are anodes, and the upper electrode is a cathode.

19. The display device according to claim 17 or 18, wherein the second light-emitting element and the third light-emitting element each comprise a continuous film of the second inorganic oxide formed as a common layer.

20. The display device according to any one of claims 17 to 19, wherein the film thickness of the continuous film of the second inorganic oxide is 5 nm or more and 15 nm or less.

21. The display device according to any one of claims 17 to 20, wherein the first inorganic oxide and the second inorganic oxide are the same type of inorganic oxide.

22. The display device according to any one of claims 11 to 21, wherein the nanoparticle layer is a continuous film formed as a common layer in the first light-emitting element, the second light-emitting element, and the third light-emitting element.

23. The display device according to any one of claims 11 to 22, wherein the first inorganic oxide includes nickel oxide.

24. A display device described in any one of claims 11 to 23, wherein one of the green light-emitting layer and the blue light-emitting layer contains a first halogen element and a first metal element, and the value of (number of the first halogen elements / number of the first metal elements) x 100% is 0.5% or more.

25. The display device described in claim 24, wherein the other of the green light-emitting layer and the blue light-emitting layer contains a second halogen element and a second metal element, and the value of (number of second halogen elements / number of second metal elements) x 100% is 0.5% or more.

26. A display device according to any one of claims 11 to 25, wherein the first light-emitting element, the second light-emitting element, and the third light-emitting element each have the nanoparticle layer and the upper electrode as a common layer.

27. A display device described in any one of claims 11 to 26, wherein the nanoparticle layer is a continuous film formed as a layer common to the first light-emitting element, the second light-emitting element, and the third light-emitting element, and one of the green light-emitting layer and the blue light-emitting layer includes first quantum dots, and the energy level of the upper end of the valence band of the first quantum dots is 0.3 eV or more deeper than the energy level of the upper end of the valence band of the nanoparticle layer.

28. The display device described in claim 27, wherein the other of the green light-emitting layer and the blue light-emitting layer includes a second quantum dot, and the energy level of the upper end of the valence band of the second quantum dot is deeper than the energy level of the upper end of the valence band of the nanoparticle layer by 0.3 eV or more.

29. The display device described in claim 27 or 28, wherein the red light-emitting layer includes third quantum dots, and the energy level of the upper end of the valence band of the third quantum dots is shallower by 0.1 eV or more than the energy level of the upper end of the valence band of the nanoparticle layer.

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