Light-emitting element and display device

Abstract

The present invention is provided with: an anode (3); a cathode pattern (CP) including a cathode part (8), which comprises a conductor, and one or more openings (9); a light-emitting layer (5) positioned between the anode and the cathode pattern; and an electron transport layer (7) positioned between the light-emitting layer and the cathode pattern.

Description

Light-emitting element, display device

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

[0002] Patent Document 1 discloses a configuration in which an electron blocking layer is included in an electron transport layer located between a quantum dot light emitting layer and an electrode.

[0003] Japanese Patent Publication: JP2023-534085

[0004] In light-emitting devices, improvement in luminous efficiency is desired.

[0005] The light-emitting element according to the present disclosure includes an anode, a cathode pattern including a cathode portion made of a conductor and one or more openings, a light-emitting layer located between the anode and the cathode pattern, and an electron transport layer located between the light-emitting layer and the cathode pattern.

[0006] The light emitting efficiency of the light emitting element can be improved.

[0007] FIG. 1 is a cross-sectional view showing a configuration example of a light-emitting device according to the present embodiment; FIG. 2 is a cross-sectional view showing electron injection according to the present embodiment; FIG. 3 is a cross-sectional view showing a configuration example of a light-emitting device according to the present embodiment; FIG. 4 is a cross-sectional view showing a configuration example of a light-emitting device according to the present embodiment; FIG. 5 is a combined view including a plan view of a cathode pattern and its Aa cross-sectional view; FIG. 6 is a combined view including a plan view of a cathode pattern and its Aa cross-sectional view; FIG. 7 is a combined view including a plan view of a cathode pattern and its Aa cross-sectional view; FIG. 8 is a combined view including a plan view of a cathode pattern and its Aa cross-sectional view; FIG. 9 is a flowchart showing a method for manufacturing a light-emitting device; FIG. 10 is a graph showing voltage-current characteristics of a light-emitting device; FIG. 11 is a graph showing current density-EQE characteristics of a light-emitting device; FIG. 12 is a graph showing wavelength-reflectance characteristics of ITO and Al; FIG. 13 is a graph showing wavelength-extinction coefficient characteristics of ITO and Al; FIG. 14 is a graph showing Al thickness-LEE (external emissivity) characteristics and Al thickness-effective refractive index characteristics; FIG. 15 is a graph showing ITO thickness-LEE characteristics and ITO thickness-effective refractive index characteristics. 1 is a diagram showing the results of ray tracing of a model in which the left half region has no cathode and the right half region has a cathode pattern including a 2 nm thick striped Al electrode. FIG. 2 is a diagram showing the results of ray tracing of a model in which the left half region has a cathode pattern including a 20 nm thick striped ITO electrode and the right half region has a cathode pattern including a 2 nm thick striped Al electrode. FIG. 3 is a diagram showing the results of ray tracing of a model in which the left half region has a cathode pattern including a 2 nm thick striped ITO electrode and the right half region has a cathode pattern including a 2 nm thick striped Al electrode. FIG. 4 is a cross-sectional view showing an example of the configuration of a light-emitting device according to the present embodiment. FIG. 5 is a cross-sectional view showing an example of the configuration of a light-emitting device according to the present embodiment. FIG. 6 is a table showing the refractive index of each material for each color. FIG. 7 is a schematic diagram showing an example of the configuration of a display device according to the present embodiment.

[0008] FIG. 1 is a cross-sectional view showing an example of the configuration of a light-emitting device according to this embodiment. FIG. 2 is a cross-sectional view showing electron injection according to this embodiment. As shown in FIG. 1 , a light-emitting device 10 according to this embodiment includes an anode 3, a cathode pattern CP including a cathode portion 8 made of a conductor and which is a conductive region, and one or more openings 9 which are non-conductive regions, a light-emitting layer 5 located between the anode 3 and the cathode pattern CP, and an electron transport layer 7 located between the light-emitting layer 5 and the cathode pattern CP. The electron transport layer 7 may be in contact with the cathode portion 8 or may be in contact with the light-emitting layer 5. The light-emitting layer 5 may be a quantum dot light-emitting layer containing light-emitting quantum dots Q.

[0009] As shown in FIGS. 1 and 2 , the light-emitting element 10 has a cathode pattern CP in which the cathode portion 8 is intermittently arranged. Therefore, electrons from the cathode portion 8 diffuse laterally (along the upper surface of the electron transport layer) due to the difference in electron density between the cathode portion 8 and the opening KA. Therefore, electrons injected directly below the cathode portion 8 are suppressed, and electrons can be injected directly below the opening 9. This allows the entire light-emitting layer 5 to emit light while reducing trion Auger (non-radiative recombination) within the quantum dots Q. The reduction in trion Auger improves the EQE (external quantum efficiency) and increases the EQE peak value. Furthermore, the opening 9 in the cathode pattern CP allows light emitted in the light-emitting layer 5 to be emitted through the opening, thereby improving the upward light extraction efficiency. Trion Auger is a phenomenon that occurs in semiconductor particles with a quantum size effect, such as quantum dots Q, and causes a sudden decrease in EQE (so-called roll-off) in the high-brightness region (high-concentration injection region).

[0010] The cathode 8 may be a metal having a thickness of 3 nm or less. The cathode 8 may include at least one of an Al film, an Ag film, and an Ag nanowire. Metals are good materials because of their low electrical resistance, but the amount of light emitted by the light-emitting layer 5 is attenuated when it passes through the metal. To prevent this, it is desirable to set the thickness to 3 nm or less.

[0011] The light-emitting element 10 may include a hole transport layer (HTL) 4 located between the anode 3 and the light-emitting layer 5, and an electron injection layer may also be provided between the anode 3 and the hole transport layer 4. The light-emitting element 10 may have a top-emission structure in which, from the bottom, the anode 3, the hole transport layer (HTL) 4, the light-emitting layer 5, the electron transport layer 7, and the cathode pattern CP are arranged in this order. The electron transport layer 7 may contain a metal oxide (e.g., magnesium zinc oxide). The hole transport layer 4 may contain polyvinylcarbazole (PVK).

[0012] A light-emitting element layer 6 including an anode 3, a bank BK, a hole transport layer (HTL) 4, a light-emitting layer 5, an electron transport layer 7, and a cathode pattern CP may be formed on a substrate 2 (TFT substrate, pixel circuit substrate). The light-emitting element 10 may be formed within the bank BK, and the bank BK may be an edge cover film that covers the edge of the anode 3. The bank BK may be an organic film such as a photosensitive polyimide.

[0013] The light-emitting layer 5 may include an inorganic medium MX in contact with the quantum dots Q. The inorganic medium MX may be a matrix material that encapsulates a plurality of quantum dots Q. The inorganic medium MX may be a semiconductor or an insulator having a band gap larger than that of the cores of the quantum dots Q. The inorganic medium MX may be a sulfide such as ZnS or a silicon compound such as silicon oxide. The cores of the quantum dots Q may be InP (indium phosphide), and the shells of the quantum dots Q may be ZnS (zinc sulfide).

[0014] The cathode portion 8 may be made of a material having a work function smaller than that of Ag. The cathode portion 8 may be a metal oxide having a thickness of 100 nm or less. The cathode portion 8 may include any one of indium tin oxide (ITO), aluminum zinc oxide (AZO), and indium zinc oxide (IZO). In the case of a metal oxide, the attenuation of the amount of light emitted by the light-emitting layer 5 when it passes through is relatively small, so a certain thickness is acceptable. However, if the metal oxide is too thin, the electrical resistance increases, so to suppress this, it is desirable to keep the thickness to 100 nm or less.

[0015] 3A and 3B are cross-sectional views showing an example of the configuration of a light-emitting element according to this embodiment. In the light-emitting element 10 of FIG. 1, the cathode pattern CP is located above the anode 3, but this is not limiting. As in the light-emitting element 10 of FIG. 3, the cathode pattern CP, the electron transport layer 7, the light-emitting layer 5, the hole transport layer 4, and the anode 3 may be arranged in this order from the bottom.

[0016] 4 is a cross-sectional view showing an example of the configuration of the light-emitting device according to this embodiment. As shown in FIG. 4 , the electron transport layer 7 may have a portion 7b located under the opening 9 that is thinner than the portion 7a located under the cathode 8. This configuration can be obtained, for example, as shown in FIG. 4 by etching (by RIE or the like) the surface of the electron transport layer 7 using the cathode 8 as a mask. In this way, the effective refractive index of the portion 7b located under the opening 9 becomes smaller than that of the portion 7a (i.e., the difference in refractive index with the atmosphere becomes smaller), thereby increasing the light extraction efficiency and improving the front brightness of the light-emitting device 10.

[0017] 5 to 7 are combined diagrams including a plan view of the cathode pattern and its Aa cross-sectional view. As shown in FIG. 5, the cathode portion 8 may include a mesh electrode ME. The cathode pattern CP includes a plurality of openings 9 arranged in a matrix in a first direction D1 and a second direction D2 (orthogonal to the first direction D1), and the openings 9 may be rectangular. The maximum width of the openings 9 (the size in the first direction D1 or the second direction D2) may be 1.0 μm to 10 μm. The openings 9 are not limited to being rectangular, and may be circular, polygonal, or the like.

[0018] As shown in Figures 5 and 6, the cathode pattern CP may have a plurality of openings 9 that intersect with a straight line extending from its center KC to its peripheral edge KS in a plan view. As shown in Figure 6, the plurality of openings 9 includes two openings 9c and 9s with different opening areas, and one of the two openings, opening 9s, may be closer to the peripheral edge KS and have a smaller opening area than the other opening, opening 9c. The number and arrangement of the plurality of openings 9 are free, and they do not need to be arranged in a matrix. It is sufficient that the area of ​​the outermost opening (closest to the peripheral edge KS) is smaller than the area of ​​the central opening.

[0019] The cathode pattern CP has a first region A1 including one or more openings (e.g., 9c) and a second region A2 including one or more openings (e.g., 9s) and having an area equal to that of the first region A1, the second region A2 being closer to the periphery KS than the first region A1, and the opening occupancy rate in the second region A2 may be set to be smaller than that in the first region A1. The areas of the first and second regions A1 and A2 may be 1 / 12 to 1 / 5 (e.g., about 1 / 9) of the light-emitting area of ​​the light-emitting element 10.

[0020] The peripheral portion of the light-emitting element 10 is closer to the slope of the bank BK and tends to have a thicker layer thickness. Therefore, for example, when the light-emitting element 10 is used as a subpixel of a display device, the resonance conditions of light may differ between the central portion and the peripheral portion of the element, resulting in a change in color. Therefore, as shown in FIG. 6 , by making the opening area of ​​the peripheral opening 9s smaller than that of the central opening 9c, the light from the opening 9s spreads over a wider area, reducing the amount of light emitted from the opening 9s in the forward direction. This suppresses the change in color from the central portion to the peripheral portion of the light-emitting element 10.

[0021] 7, the cathode section 8 may include stripe-shaped electrodes SE extending in a first direction D1. The cathode pattern CP includes a plurality of openings 9 extending in the first direction D1, and the openings 9 may be rectangular. The gap width between the stripe-shaped electrodes SE (the width of the openings 9) may be 1.0 μm to 10 μm.

[0022] 8 and 9 are combined diagrams including a plan view of the cathode pattern and its A-a cross-sectional view. As shown in FIG. 8, the cathode section 8 includes a plurality of electrically connected electrodes EC extending in a first direction D1, and the length (width) of each electrode EC in a second direction D2 perpendicular to the first direction D1 may vary periodically along the first direction D1. In the electrodes EC, wide portions WL and narrow portions WS may be alternately arranged along the first direction D1. The portions WL may have a width that is two or three times or more times that of the portions WS.

[0023] 9, the cathode portion 8 may include an annular electrode LE. The annular electrode LE may have any one of a circular shape, an elliptical shape, and a frame shape. The annular electrode LE may have a frame shape including a portion B1 along the first direction D1 and a portion B2 along the second direction D2.

[0024] When the cathode section 8 includes a plurality of electrodes, it is desirable that these electrodes are connected by a connecting portion. The connecting portion may be located on the light-emitting region or on a non-light-emitting region such as on the bank BK.

[0025] 7 to 9, the opening area may be designed to be smaller in the region closer to the periphery. As with the effect described above, the light from the periphery spreads over a wider area than that from the center, reducing the amount of light emitted in the front direction. As a result, it is possible to suppress color shifts from the center to the periphery of the light-emitting element.

[0026] The quantum dots Q contained in the light-emitting layer 5 may be light-emitting particles having a maximum width of 100 nm or less. The shape of the quantum dots Q is not particularly limited as long as it satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, the quantum dots Q may have a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, or a three-dimensional shape having an uneven surface, or a combination thereof. The quantum dots Q may be semiconductor single crystals and may have a particle size of 1.0 nm to 50 nm. The quantum dots Q may have at least one of crystals of II-VI group semiconductor compounds such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, and HgTe, crystals of III-V group semiconductor compounds such as GaAs, GaP, InN, InAs, InP, and InSb, and crystals of Group IV semiconductor compounds such as Si and Ge. The quantum dots Q may be, for example, a core-shell type in which the above crystal is used as a core and the core is overcoated with a shell material having a high band gap, or a shell-less type constituted only by a core.

[0027] Materials for the hole transport layer 4 or the hole injection layer include metal oxides such as nickel oxide (NiO), as well 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"). These materials may be used alone or in combination of two or more. An inorganic material such as a metal oxide may be used for the HIL on the anode 3, and an organic material may be used for the hole transport layer 4 located on the HIL and in contact with the light-emitting layer 5. Nanoparticles of metal oxides such as nickel oxide may also be used in the hole injection layer or hole transport layer 4 .

[0028] The electron transport layer 7 may be made of zinc oxide (ZnO), magnesium zinc oxide (MgZnO), titanium oxide (TiO ２ In addition to metal oxides such as zinc oxide, compounds or complexes containing one or more nitrogen-containing heterocycles such as an oxadiazole ring, a triazole ring, a triazine ring, a quinoline ring, a phenanthroline ring, a pyrimidine ring, a pyridine ring, an imidazole ring, or a carbazole ring may be used in the electron transport layer 7.

[0029] 10 is a flowchart showing a method for manufacturing a light-emitting element. As shown in FIGS. 1 and 10, in step S10, an anode 3 and a bank BK that covers the edge of the anode 3 and separates elements are formed on the TFT substrate 2. The anode 3 is formed, for example, by film formation using a sputtering method or vacuum deposition method and patterning using a photolithography method. A resin material such as polyimide may be used for the bank BK. Materials such as indium tin oxide (ITO), indium zinc oxide (IZO), indium gallium zinc oxide, aluminum, and silver may be used for the anode 3.

[0030] Next, a hole injection layer (HIL) such as a NiO layer is formed on the anode 3. The NiO layer can be formed by applying and heating a colloidal solution of dispersed nanoparticles. The particle size of the NiO nanoparticles is preferably approximately 6 nm or more, so that the quantum size effect does not occur. The NiO layer can also be formed by a sputtering method, a vacuum deposition method, or the like. Either method can form a NiO layer of approximately uniform thickness over the entire panel, including the slopes of the banks BK.

[0031] In step S20, a hole transport layer 4 (HTL) is formed on the hole injection layer. For example, a cross-linkable TFB is applied to a NiO layer and cross-linked to form the hole transport layer 4. The hole transport layer 4 is preferably made of a material such as TFB, PVK, or p-TPD, which has a HOMO not significantly different from the VBM of the quantum dots and a LUMO shallower than the CBM of the quantum dots. The HOMO of the hole transport layer 4 is used to lower the hole injection barrier, and the LUMO is used as a barrier to suppress electron overflow from the quantum dots.

[0032] In step S30, a colloidal solution containing quantum dots Q is applied to the hole transport layer 4 and heated to form the light-emitting layer 5. The light-emitting layer 5 may contain an organic ligand, or the organic ligand may be removed and the quantum dots Q may be protected with an inorganic material such as a semiconductor or silica. Conventional techniques can be used to remove the ligand and protect the quantum dots Q with the inorganic medium MX. The light-emitting layer 5 may be patterned using a photolithography method or the like. When forming a light-emitting element of multiple colors, the light-emitting layer 5 may be formed and patterned for each color (e.g., red, green, and blue).

[0033] In step S40, a colloidal solution containing particles such as ZnO and ZnMgO is applied to the light-emitting layer 5 and heated to form the electron transport layer 7 (ETL). As with the NiO layer, the particle size of the ZnO and ZnMgO particles is set to a value that does not cause a quantum size effect. The thickness of the electron transport layer 7 may be approximately 20 nm.

[0034] In step S50, the cathode pattern CP (cathode portion 8 and opening 9) can be formed by film formation using a sputtering method or a vacuum deposition method and patterning using a photolithography method. The cathode portion 8 may be made of a common metal material such as Al or Ag, or a degenerate semiconductor material such as ITO. The thickness of the cathode portion 8 may be 10 nm or less. The cathode pattern CP can also be formed using a lift-off method, an etching method such as ICP or RIE, flexographic printing using a water-based ink containing nanoparticle-like cathode material, or an inkjet method.

[0035] FIG. 11 is a graph showing the voltage-current characteristics of a light-emitting device. FIG. 12 is a graph showing the current density-EQE characteristics of a light-emitting device. Generally, when a light-emitting device having a quantum dot light-emitting layer operates in an electron-excess and density-distributed state, the probability of two or more electrons being injected into a quantum dot cannot be ignored. This phenomenon, called trion Auger, occurs when two or more electrons injected into a single quantum dot interact with each other to generate a single high-energy electron, reducing the light-emitting efficiency. Furthermore, the generated high-energy electrons overflow beyond the barrier between the quantum dot and the HTL, further reducing the light-emitting efficiency. Thus, roll-off of the light-emitting device (a rapid drop in EQE in a high-concentration injection region) is thought to be due to trion Auger of excess electrons. By restricting the electron injection into the light-emitting layer 5, roll-off of the light-emitting device can be suppressed and the light-emitting efficiency can be increased.

[0036] One method for restricting electron injection is to use an n-type nitride with a deep CBM in the ETL to increase the injection barrier (a similar method is used in Patent Document 1), but this method has the problem of increasing the drive voltage.Another method for restricting electron injection is to introduce electron traps into the ETL by irradiating it with an electron beam, heavy ions, or the like (Comparative Example 2 in FIG. 11), but this method has the problem of changing the diode characteristics (voltage-current characteristics) and significantly reducing the EQE.

[0037] In the light-emitting device 10, the cathode portion 8 is discontinuous, allowing electrons to diffuse from the cathode portion 8 to directly below the opening 9 without forming a barrier to electron injection or an electron trap. As a result, as shown in this embodiment in FIG. 11 , the total current can be reduced without changing the diode characteristics (the slope of the voltage-current characteristics) compared to the case of a planar cathode (Comparative Example 1 in FIG. 11 ). In other words, the current injected into the quantum dots Q is reduced at the same rate as the decrease in the total current, and the electron density in the light-emitting layer 5 is reduced. As a result, as shown in FIG. 12 , the roll-off is improved compared to Comparative Example 1, which uses a planar cathode (solid electrode), and the EQE of the light-emitting device 10 is significantly improved.

[0038] FIG. 13 is a graph showing the wavelength-reflectance characteristics of ITO and Al. FIG. 14 is a graph showing the wavelength-extinction coefficient characteristics of ITO and Al. FIG. 15 is a graph showing the Al thickness-LEE (light extraction efficiency) characteristics and the Al thickness-effective refractive index characteristics. FIG. 16 is a graph showing the ITO thickness-LEE characteristics and the ITO thickness-effective refractive index characteristics. The effective refractive index is a refractive index that takes thickness into consideration. FIG. 17 is a diagram showing the results of ray tracing for a model in which the left half region has no cathode and the right half region has a cathode pattern including a 2-nm-thick striped Al electrode. FIG. 18 is a diagram showing the results of ray tracing for a model in which the left half region has a cathode pattern including a 20-nm-thick striped ITO electrode and the right half region has a cathode pattern including a 2-nm-thick striped Al electrode. 19 shows the results of ray tracing for a model in which the left half of the cathode pattern includes a 2-nm-thick striped ITO electrode and the right half of the cathode pattern includes a 2-nm-thick striped Al electrode. Here, 108 rays are traced per element (per subpixel).

[0039] If the LEE (light extraction efficiency) of the left half region (no cathode) in Figure 17 is 1.0, the LEE of the right half region (striped Al electrode) in Figure 17 is 0.5, and the LEE of the region where the Al electrode is present is 0.1. In other words, it can be seen that the use of striped Al electrodes increases the LEE by five times compared to a planar electrode (solid electrode). In this way, by employing a cathode pattern CP having openings 9 such as those in the light-emitting element 10, not only is the EQE improved but the LEE (light extraction efficiency) of the cathode is also improved, resulting in a significant increase in the luminous efficiency of the light-emitting element 10.

[0040] 18 and 19 show that even a 20-nm-thick ITO exhibits 1.7 times the LEE of a 2-nm-thick Al. Furthermore, a 2-nm ITO exhibits 1.8 times the LEE of a 2-nm-thick Al. This is because the extinction coefficient of ITO is approximately 1 / 1000 that of Al (FIG. 14), suppressing light absorption at the cathode. This result indicates a greater influence of light absorption than the LEE calculated using only the effective refractive index (FIGS. 15 and 16). Therefore, although metals such as Al and Ag can be used for the cathode pattern, it may be preferable to use a metal oxide with a small extinction coefficient, such as ITO.

[0041] 20 and 21 are cross-sectional views showing examples of the configuration of a light-emitting element according to this embodiment. As shown in Fig. 20, the light-emitting element 10 may include a protective layer 11 (surface layer) in contact with the cathode pattern CP or the electron transport layer 7. The protective layer 11 is formed so as to fill the opening of the cathode pattern CP, has light-transmitting properties, and has a higher electrical resistance than the cathode part 8. The protective layer 11 may be insulating.

[0042] The light-emitting element 10 also includes an electron transport layer 7, and the protective layer 11 may have a refractive index smaller than that of the electron transport layer 7. The protective layer 11 may be made of Al ２ O ３ , AlON, CaF ２ , MgF, MgO, SiO ２ , dimethyl silicone, and acrylic.

[0043] The protective layer 11 can prevent the intrusion of foreign substances such as oxygen and water. The larger the difference in refractive index between the atmosphere and the ETL, and the greater the light absorption of the cathode, the worse the LEE of the cathode. Therefore, as shown in Figure 20, by covering the cathode pattern CP with a protective layer 11 that is chemically stable, optically transparent, and has a refractive index smaller than that of the ETL 7, the light extraction efficiency and reliability of the light-emitting element 10 can be improved.

[0044] The protective layer 11 may be formed on the cathode pattern as shown in FIG. 20 (formed to cover the cathode portion 8 and fill the opening 9), or may be formed to fill the opening 9 as shown in FIG.

[0045] 22 is a table showing the refractive index of each material for each color. When ZnO is used for the electron transport layer 7, the protective layer 11 is made of a material (e.g., acrylic, DMS, AlN, Al) having a refractive index smaller than 2.200 of ZnO for each of R (red), G (green), and B (blue) lights. ２ O ３ , AlON, CaF ２ , MgF, MgO, SiN, SiON, SiO ２ It is preferable to use a

[0046] When forming light-emitting elements 10 of multiple colors, the protective layer 11 can be formed in a common process, and even when formed in separate processes, the same material can be used. Therefore, it is desirable that the material of the protective layer 11 does not have a large difference in refractive index for each of the R, G, and B wavelengths.

[0047] 23 is a schematic diagram showing an example of the configuration of a display device according to this embodiment. The display device 20 includes a display unit DA, a first driver circuit X1 (e.g., a data signal line drive circuit) and a second driver circuit X2 (e.g., a scanning signal line drive circuit, a light-emitting control line drive circuit) that drive the display unit DA, and a control circuit CL that controls the first driver circuit X1 and the second driver circuit X2. The display unit DA may include a substrate (pixel circuit substrate) 2 and a light-emitting element layer 6, as shown in FIG. 1. The light-emitting element layer 6 may include a light-emitting element 10R (10) that emits red light, a light-emitting element 10G (10) that emits green light, and a light-emitting element 10B (10) that emits blue light, and the light-emitting elements 10R, 10G, and 10B may each be connected to a pixel circuit PC formed in the pixel circuit layer.

[0048] The above-described embodiments are intended to be illustrative and explanatory, and not limiting, and many variations will be apparent to those skilled in the art based on these examples and descriptions.

[0049] 2 Substrate (pixel circuit substrate) 3 Anode 4 Hole transport layer (HTL) 5 Light-emitting layer 6 Light-emitting element layer 7 Electron transport layer (ETL) 8 Cathode portion 9 Opening 10 Light-emitting element 11 Protective layer 20 Display device Q Quantum dots CP Cathode pattern

Claims

1. A light-emitting element comprising: an anode; a cathode pattern including a cathode portion made of a conductive material and one or more openings; a light-emitting layer located between the anode and the cathode pattern; and an electron transport layer located between the light-emitting layer and the cathode pattern.

2. The light-emitting device of claim 1, wherein the light-emitting layer includes quantum dots.

3. The light-emitting element according to claim 1 or 2, wherein, in plan view, the cathode pattern has a plurality of openings that intersect with a straight line extending from the center to the periphery of the cathode pattern.

4. The light-emitting element according to claim 3, wherein the plurality of openings include two openings with different opening areas, one of the two openings being closer to the periphery and having a smaller opening area than the other opening.

5. The light-emitting element described in claim 3, wherein the cathode pattern has a first region including one or more openings and a second region including one or more openings and having an area equal to that of the first region, the second region being closer to the periphery than the first region, and the opening occupancy rate in the second region being smaller than that in the first region.

6. The light-emitting device according to any one of claims 1 to 5, wherein the thickness of the electron transport layer at a portion located below the opening is smaller than the thickness of the portion located below the cathode portion.

7. The light-emitting element according to any one of claims 1 to 6, wherein the cathode portion is made of a metal and has a thickness of 3 nm or less.

8. The light-emitting element according to any one of claims 1 to 7, wherein the cathode portion is an Al film or an Ag film.

9. The light-emitting device according to any one of claims 1 to 7, wherein the cathode portion has a work function smaller than that of Ag.

10. The light-emitting element according to any one of claims 1 to 6, wherein the cathode portion is a metal oxide having a thickness of 100 nm or less.

11. The light-emitting element according to any one of claims 1 to 6, wherein the cathode portion includes any one of indium tin oxide, aluminum zinc oxide, and indium zinc oxide.

12. The light-emitting element according to any one of claims 1 to 11, wherein the cathode portion includes a mesh electrode.

13. The light-emitting element according to any one of claims 1 to 11, wherein the cathode section includes a stripe-shaped electrode extending in a first direction.

14. A light-emitting element described in any one of claims 1 to 11, wherein the cathode section includes a plurality of electrically connected electrodes extending in a first direction, and the width of each electrode in a second direction perpendicular to the first direction varies periodically along the first direction.

15. The light-emitting element according to any one of claims 1 to 11, wherein the cathode portion includes a ring-shaped electrode.

16. The light-emitting device according to claim 15, wherein the annular electrode has one of a circular shape, an elliptical shape, and a frame shape.

17. The light-emitting element according to claim 12, wherein the opening has a maximum width of 1.0 μm to 10 μm.

18. The light-emitting device according to claim 13, wherein the gap width between the stripe-shaped electrodes is 1.0 μm to 10 μm.

19. The light-emitting device according to any one of claims 1 to 18, further comprising a protective layer located over the cathode pattern.

20. The light-emitting device according to claim 19, wherein the protective layer has insulating properties.

21. The light-emitting device according to claim 19 or 20, wherein the protective layer is light-transmitting.

22. The light-emitting device according to any one of claims 19 to 21, wherein the electron transport layer and the protective layer are in contact with each other, and the protective layer has a refractive index smaller than that of the electron transport layer.

23. The protective layer is Al ２ O ３ , AlON, CaF ２ , MgF, MgO, SiO ２ The light-emitting device according to any one of claims 19 to 22, comprising at least one of dimethyl silicone and acrylic.

24. The light-emitting device according to any one of claims 1 to 23, wherein the electron transport layer comprises a metal oxide.

25. The light-emitting device of claim 2, wherein the light-emitting layer comprises an inorganic medium in contact with the quantum dots.

26. A display device comprising a light-emitting element according to any one of claims 1 to 25.

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