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

Abstract

A light-emitting device (8) comprises: a first light-emitting layer (29) having a first area (38) on an anode side; and a second light-emitting layer (30) having a second area (39) larger than the first area (38) on a cathode side.

Description

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

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

[0002] Mass production of displays incorporating organic light-emitting diodes (OLEDs) has begun in earnest, starting with flat-panel displays for high-end smartphones and TVs. OLED displays have become so widespread that they can be said to have become a central replacement for LCDs as flat-panel displays.

[0003] Aluminum quinolinol complex (Alq ３ However, in order to further improve the luminous efficiency of organic EL elements, development is being carried out in the order of (1) to (3) below.

[0004] (1) A host-guest material in which a guest compound as a dopant is added to a host compound is used as a material for the light-emitting layer, carrier (electron, hole) transport layer, or carrier (electron, hole) injection layer of an organic EL element.

[0005] (2) A fluorescent material, or a fluorescent material and a phosphorescent material, is used as a guest compound (dopant) for the light-emitting layer.

[0006] (3) Improved guest compounds such as thermally activated delayed fluorescent (TADF) materials or hyperfluorescent materials are used as dopants in the emissive layer.

[0007] Furthermore, from the viewpoint of improving the current efficiency and reliability of organic EL elements, the following (4) and (5) have been further investigated.

[0008] (4) The carrier balance is improved by devising the carrier transport layer and / or the carrier injection layer.

[0009] (5) As a light-emitting device, a light-emitting element (tandem light-emitting element) configuration is adopted in which multiple light-emitting units (light-emitting layers) are arranged in tandem between an anode and a cathode (see, for example, Patent Document 1).

[0010] Japanese Patent Publication No. 2005-285401

[0011] Tandem light-emitting devices have the potential to achieve high-efficiency, high-brightness light emission by having multiple light-emitting layers between an anode and a cathode emit light of the same color. However, at present, this high-efficiency, high-brightness light emission has not been fully achieved.

[0012] An object of one aspect of the present disclosure is to provide a tandem light-emitting device structure that has a charge generation layer and can achieve highly efficient and bright light emission.

[0013] A light-emitting device according to one aspect of the present disclosure is a light-emitting device having a plurality of light-emitting elements that emit light of different colors, wherein the plurality of light-emitting elements include a first light-emitting element, the first light-emitting element having an anode and a cathode, a first light-emitting layer located between the anode and the cathode and emitting light of a first color, a second light-emitting layer located between the first light-emitting layer and the cathode and emitting light of the same color as the first color, and a first charge generation layer located between the first light-emitting layer and the second light-emitting layer, wherein the first light-emitting layer has a first area, and the second light-emitting layer has a second area that is larger than the first area.

[0014] A display device according to an aspect of the present disclosure includes the above-described light-emitting device.

[0015] Furthermore, a manufacturing method for a light-emitting device according to one aspect of the present disclosure is a method for manufacturing the above-described light-emitting device, wherein the light-emitting device has a plurality of the first light-emitting elements and a plurality of second light-emitting elements, and each of the first light-emitting layers is formed using a first vapor deposition mask having a plurality of first openings formed therein, each of which corresponds to the first light-emitting layer, and each of the second light-emitting layers is formed using a second vapor deposition mask having a plurality of second openings formed therein, each of which corresponds to the second light-emitting layer and has an area larger than an area of ​​the first openings.

[0016] According to one aspect of the present disclosure, a tandem light-emitting device having a charge generation layer between multiple light-emitting layers, in which multiple light-emitting layers between an anode and a cathode emit light of the same color, can emit light with high efficiency and high brightness.

[0017] FIG. 1 is a plan view schematically showing the configuration of a display device having a frame region and a display region according to embodiment 1 of the present disclosure. FIG. 2 is a cross-sectional view showing the schematic configuration of one pixel portion of the display device shown in FIG. 1. FIG. 3 is a diagram schematically showing the layer configuration of a light-emitting element in the layer configuration shown in FIG. 2. FIG. 4 is a plan view of a first light-emitting layer and a second light-emitting layer. FIG. 5 is a flowchart showing a method for manufacturing a light-emitting device according to embodiment 1 of the present disclosure. FIG. 6 is a cross-sectional view showing the main configuration of a display device according to embodiment 1 of the present disclosure. FIG. 7 is a cross-sectional view showing only the main configuration of a light-emitting element of a display device (light-emitting device) according to embodiment 2 of the present disclosure. FIG. 8 is a plan view of one light-emitting element provided in a display device according to embodiment 2 of the present disclosure, in which three light-emitting layers are shown overlapping. FIG. 9 is a cross-sectional view showing the schematic configuration of a display device according to embodiment 3 of the present disclosure.

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present disclosure. For convenience of explanation, the same reference numerals are used to designate components having the same functions as those previously described, and the description thereof may not be repeated.

[0019] [Light-Emitting Element] A light-emitting element according to an embodiment of the present disclosure includes an anode, a cathode, a light-emitting layer, and a charge generation layer. The light-emitting element according to the present disclosure includes multiple light-emitting layers stacked in the stacking direction. Furthermore, in at least one pair of two adjacent light-emitting layers separated by the charge generation layer, the area of ​​the light-emitting layer on the cathode side is larger than the area of ​​the light-emitting layer on the anode side. In the present disclosure, the area of ​​the light-emitting layer refers to the area of ​​each light-emitting layer as viewed from the light-emitting side in a planar view. The light-emitting element according to the present disclosure may be a top-emission type that emits light from the cathode side, or a bottom-emission type that emits light from the anode side. The light-emitting element according to the present disclosure may employ a known element configuration for a light-emitting element as long as it includes layers that satisfy these conditions. Hereinafter, the layer configuration of the light-emitting element according to the present disclosure will be described primarily using an OLED as an example. In the present disclosure, the term "light-emitting element" refers to a group of light-emitting layers and various carrier functional layers arranged in the stacking direction. In the present disclosure, the term "light-emitting device" refers to a group of multiple light-emitting elements arranged in a direction intersecting the stacking direction.

[0020] [Anode] The anode is one of a pair of electrode layers, an anode and a cathode, and in the present disclosure is an electrode layer for supplying holes to each layer constituting the light-emitting element. The anode is electrically conductive. Furthermore, the anode has optical properties, for example, of reflecting part of visible light and transmitting the rest. Typically, the anode includes both an electrode material that reflects visible light and an electrode material that transmits visible light.

[0021] To enhance hole injection properties, a material with a relatively high work function (e.g., a material with a work function of 4.5 eV or more) is preferably used as the anode material. Examples of electrode materials with a high work function include Pt (5.65 eV), Ir (5.25 eV), Ni (5.2 eV), Au (5.15 eV), and Pd (5.15 eV), as well as indium tin oxide (In—Sn—O).

[0022] Examples of electrode materials that reflect visible light include metal materials such as Al, Mg, Li, Ag, Pd, and Cu, as well as alloys of these metal materials (e.g., APC (Ag-Pd-Cu) alloy, etc.).

[0023] Examples of electrode materials that transmit visible light include thin films of transparent metal oxides (e.g., indium tin oxide, indium zinc oxide (In—Zn—O), and indium gallium zinc oxide (In—Ga—Zn—O)), thin films made of metal materials such as Al, Mg, and Ag, and nanowires (NW) made of the metal materials.

[0024] Among transparent metal oxides, indium tin oxide has a relatively high work function of 4.6 to 5.0 eV and is therefore suitable for use as an anode material. Furthermore, for the anode, a laminate (e.g., indium tin oxide / Ag) in which indium tin oxide is formed on the surface of a metal material can be used for the purpose of improving the conductivity of the electrode layer or adding the function of reflecting visible light.

[0025] [Cathode] The cathode is the other of a pair of electrode layers, an anode and a cathode, and in the present disclosure is an electrode layer for supplying electrons to each layer constituting the light-emitting element. The cathode is disposed opposite the anode in the stacking direction. The cathode has, for example, electrical conductivity and visible light transparency.

[0026] For example, a material with a relatively small work function is preferably used as the cathode material, from the viewpoint of enhancing electron injection properties. Examples of electrode materials constituting the cathode include metal materials such as alkali metals, alkaline earth metals, and Al, alloys containing these metals, and nanowires (e.g., Ag nanowires). Examples of alloys include alloys of Mg and Ag, and Al doped with a small amount of Li.

[0027] [Light-emitting layer] The light-emitting layer is a layer that electroluminesces light of a predetermined color when an electric field is applied. The light-emitting layer is usually composed of a light-emitting material, but may also have a laminated structure of multiple functional layers in which two or more functional layers corresponding to two or more functions for electroluminescence in known light-emitting layers are stacked, such as an immediate-emitting layer and a delayed-emitting layer, and which as a whole exhibit the function of electroluminescence. In the present disclosure, multiple light-emitting layers are arranged between the anode and the cathode in the stacking direction. Furthermore, multiple light-emitting layers may be arranged in a direction intersecting the stacking direction.

[0028] The light-emitting layer has a plurality of light-emitting layers emitting the same color arranged in the stacking direction. The number of light-emitting layers emitting the same color overlapping in the stacking direction is not limited, but from the viewpoints of increasing the light-emitting efficiency and improving the device reliability, it is preferably 2 or more, and more preferably 3 or more. On the other hand, the number of light-emitting layers emitting the same color overlapping in the stacking direction is preferably 5 or less, and more preferably 4 or less, from the viewpoints of suppressing an increase in the driving voltage, realizing a withstand voltage of the driver according to the driving voltage, and maintaining the flexibility of the light-emitting device (suppressing an increase in the total thickness of the light-emitting device).

[0029] In the present disclosure, the term "same color" refers to light colors in which, when two or more emission peak wavelengths exist, all emission peak wavelengths are within a range of ±5 nm from each other, and the maximum full width at half maximum of all emission peak wavelengths is 1.25 times or less the minimum full width at half maximum of the remaining emission peak wavelengths. Essentially, when both the host material and the guest compound constituting the light-emitting layer are the same material or similar materials having the same skeleton, they emit the same color. However, in tandem light-emitting devices having a top-emission structure, as described below, the emission peak wavelength for each light-emitting layer may vary due to differences in the microcavity structure of each color. Therefore, in a top-emission structure, the term "same color" refers to light colors in which all emission peak wavelengths are within a range of ±10 nm and the full width at half maximum satisfies the above range.

[0030] Furthermore, in the direction intersecting the stacking direction, the light-emitting layers are arranged with a first color light-emitting layer to an nth color light-emitting layer (n being an integer greater than or equal to 2), emitting light of different colors. In the present disclosure, "different colors" refers to light colors that do not fall within the same color range described above. A typical known example is a three-color light-emitting layer, consisting of a red light-emitting layer, a green light-emitting layer, and a blue light-emitting layer, as a multi-color light-emitting layer for full-color display. Arranging multiple color light-emitting layers in a direction intersecting the stacking direction is sometimes referred to as "color separation." It is preferable that the number of light-emitting layers of each color in the stacking direction is the same for all emitted colors. Hereinafter, the light-emitting layers in the present disclosure will be described mainly using the above three color light-emitting layers as an example, but the present disclosure is not limited thereto. The light-emitting layers of different colors in the intersecting direction may be located at the same position (height) or at different positions (heights) (shifted) relative to each other in the stacking direction.

[0031] That is, in the present disclosure, when a light-emitting device includes light-emitting elements of three colors, red, green, and blue, the light-emitting elements of each color are independently arranged in a direction intersecting the stacking direction, for example, a direction perpendicular to the stacking direction. Furthermore, in the stacking direction, red light-emitting layers are overlapped with red light-emitting layers, green light-emitting layers are overlapped with green light-emitting layers, and blue light-emitting layers are overlapped with blue light-emitting layers. Although light-emitting layers of different colors may be further stacked in the stacking direction, from the viewpoint of improving color purity, it is preferable that only a plurality of light-emitting layers emitting the same color are arranged in the stacking direction. Stacking only light-emitting layers of the same color in the stacking direction is advantageous from the viewpoint of more easily determining the area of ​​the light-emitting layer, which will be described later.

[0032] In a tandem light-emitting device having multiple light-emitting layers arranged in the stacking direction, when a charge generation layer is interposed between the light-emitting layers, optimizing the supply of carriers (electrons and / or holes) in the light-emitting layer on one side of the charge generation layer in the stacking direction may result in a deviation from the optimal value of the supply of electrons and / or holes in the light-emitting layer on the other side. As a result, a carrier imbalance may occur between the multiple light-emitting layers in the same light-emitting device. In a tandem light-emitting device having multiple light-emitting layers arranged in series between a pair of cathodes and anodes, according to Kirchhoff's first law, the amount of current flowing through each light-emitting layer is the same. In other words, in a tandem light-emitting device, even if the thicknesses of the light-emitting layers are made different from each other, the amount of current flowing through each light-emitting layer remains the same. Therefore, in a tandem light-emitting device, if a carrier imbalance occurs and the supply of carriers (electrons and / or holes) to one light-emitting layer decreases, not only does the amount of current flowing through that light-emitting layer decrease, but the amount of current flowing through all light-emitting layers, including the other light-emitting layers, arranged between the pair of cathodes and anodes also decreases uniformly. In contrast, the generation of excess carriers cannot be prevented by a measure to maximize the amount of current. In the present disclosure, in order to cope with the situation where the amount of carriers (electrons and / or holes) supplied to the light-emitting layer formed on the cathode side is greater than the amount of carriers (electrons and / or holes) supplied to the light-emitting layer formed on the anode side, the area of ​​the light-emitting layer on the cathode side in plan view is increased as a means for increasing the volume of the light-emitting layer on the cathode side where the carrier supply becomes excessive, thereby optimizing the carrier balance in all light-emitting layers in the stacking direction without generating excess carriers.

[0033] In the light-emitting device of the present disclosure, in at least one pair of two light-emitting layers adjacent to each other in the stacking direction via a charge generation layer, the area of ​​the cathode-side light-emitting layer is larger than the area of ​​the anode-side light-emitting layer. That is, in the present disclosure, the area of ​​a specific light-emitting layer is larger than the area of ​​the anode-side light-emitting layer. Note that "adjacent" in the light-emitting layer refers to a positional relationship in which the light-emitting layers included in the light-emitting element are adjacent to each other in the stacking direction. That is, another layer may be interposed between the light-emitting layers adjacent to each other in the stacking direction.

[0034] Furthermore, the light emitting device of the present disclosure may be configured to include a light emitting layer whose area gradually increases from the anode side toward the cathode side in the stacking direction.

[0035] With this configuration, the light-emitting device of the present disclosure has an optimized carrier balance in each light-emitting layer in the stacking direction. The area of ​​each light-emitting layer in the stacking direction can be appropriately determined based on various factors, such as the combination of materials for each layer in the light-emitting element and the purpose of changing the area of ​​the light-emitting layer, as long as it is in accordance with the technical concept of the present disclosure.

[0036] If the area of ​​the cathode-side light-emitting layer in the stacking direction is too large relative to the area of ​​the anode-side light-emitting layer in the stacking direction, the amount of carriers (which subsequently become electron-hole pairs) corresponding to the volume of the cathode-side light-emitting layer cannot be supplied, resulting in underutilization of the light-emitting layer's capabilities and reduced luminous efficiency. On the other hand, if there is almost no difference in area, the effect of correcting the carrier balance is reduced, resulting in excess carriers in the cathode-side light-emitting layer. This increases the current that does not contribute to light emission, resulting in increased power consumption relative to the amount of light emitted. Therefore, in either case, the effect of the tandem structure with multiple light-emitting layers in the stacking direction is diminished.

[0037] Therefore, the ratio of the area of ​​the anode-side light-emitting layer to the area of ​​the cathode-side light-emitting layer is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more, from the viewpoint of achieving sufficient light-emitting efficiency on the cathode side. Furthermore, from the viewpoint of suppressing the generation of excess carriers and reducing power consumption, the ratio is preferably 90% or less, and even more preferably 80% or less.

[0038] In the present disclosure, when three or more light-emitting layers are arranged in the stacking direction with a charge generation layer interposed therebetween, the area of ​​each light-emitting layer may be determined so that the area increases linearly, quadratically, or in another manner from the anode side to the cathode side. Alternatively, the area of ​​each light-emitting layer may be determined based on factors other than the above correlation (e.g., the performance or function of the intervening charge generation layer).

[0039] By forming the cathode-side light-emitting layer so that its area changes relative to the anode-side light-emitting layer in the stacking direction at the above ratio, even when the carrier supply rate to the cathode-side light-emitting layer is greater than that to the anode-side light-emitting layer, the carrier balance in the cathode-side light-emitting layer can be balanced, and an appropriate amount of carriers can be supplied to the cathode-side light-emitting layer. Therefore, the tandem-structured light-emitting device having multiple light-emitting layers of the present disclosure can reduce power consumption and improve light-emitting efficiency compared to conventional tandem-structured light-emitting devices having multiple light-emitting layers of the same area. Furthermore, by preventing the generation of excess carriers, the possibility of excess carriers deteriorating the materials of the light-emitting layer or the functional layers surrounding the light-emitting layer can be reduced, thereby improving the reliability of the light-emitting device.

[0040] In the light-emitting device of the present disclosure, the area of ​​the light-emitting layer in a planar view is increased as a means of substantially increasing the volume of the light-emitting layer. Therefore, even if a light-shielding material such as a black matrix is ​​formed on the light-emitting layer, the area of ​​the region in which the light-shielding material is formed may also be included in the area of ​​the light-emitting layer, provided that the volume of the light-emitting layer itself does not change.

[0041] The area of ​​the multiple light-emitting layers overlapping in the stacking direction of the present disclosure can be determined, for example, by the following method. That is, the applied voltage, luminous efficiency, or device life of a tandem light-emitting device having light-emitting layers with the same area in the stacking direction is measured and used as a reference value. Meanwhile, a tandem light-emitting device is fabricated in which the area of ​​the light-emitting layer closer to the cathode is increased, and the applied voltage, luminous efficiency, or device life is measured. Based on the obtained measured values ​​and the reference value, an appropriate area according to the purpose is determined.

[0042] The area of ​​each light-emitting layer in the stacking direction can be determined as an area according to the purpose by simulating the carrier injection and / or carrier transport properties between each layer in the light-emitting element and conducting demonstration experiments based on the evaluation. In this case, by setting the multiple light-emitting layers stacked in the stacking direction to be of the same color, the carrier injection and carrier transport parameters between different light-emitting layers in the stacking direction can be made identical. This makes the simulation easier, and the area of ​​the light-emitting layer can be determined more simply. It is also possible to first set the conditions of the carrier functional layer for one light-emitting layer having a specific area so that an appropriate amount of exciton generation can be achieved without generating excess carriers, and then determine the areas of the remaining light-emitting layers.

[0043] In addition, as long as the effects of the present disclosure are obtained, the area of ​​only one light-emitting layer of a light-emitting device having light-emitting layers of multiple colors in a direction intersecting the stacking direction may be changed by the above ratio, or the areas of any two or more colors may be changed uniformly or independently by the above ratio. Furthermore, the ratio of the areas of the light-emitting layers in the stacking direction may be constant for each light-emitting color, or may be different ratios within the above range.

[0044] A preferred light-emitting layer in the present disclosure is a host-guest light-emitting layer containing a host compound and a guest compound. A host-guest light-emitting layer contains a small amount (e.g., about 0.1 to several mol %) of a fluorescent dopant or the like as a guest compound in a solid medium that is a host compound. In a light-emitting layer doped with a guest compound in this manner, the fluorescence of the host compound is completely lost, and instead, strong light emission is obtained that matches the fluorescence spectrum of the doped guest compound. This is because the excitation energy of the host compound is transferred to the guest compound. Due to this transfer of excitation energy, light emission from the guest compound with higher quantum efficiency can be obtained in a host-guest light-emitting layer.

[0045] Furthermore, doping a fluorescent dopant as a guest compound in the light-emitting layer dramatically improves the device life of the light-emitting device. This is because the dopant, which is a guest compound, functions as a carrier (electron or hole) trap in the solid medium of the host compound, becoming a carrier recombination center and directly generating excitons in the solid medium. The process by which these generated excitons relax to the ground state is called the deactivation process. The deactivation process can be classified into a non-radiative process (thermal deactivation) and a radiative process (luminescence). Of these, the phenomenon in which luminescence occurs via the radiative process is called electroluminescence. The guest compound's function as a carrier trap not only improves the quantum efficiency of the light-emitting layer but also improves device reliability due to an increased carrier recombination rate.

[0046] In this way, the host-guest light-emitting layer can effectively utilize carriers, and therefore, the light-emitting device of the present disclosure can achieve high light-emitting efficiency of the light-emitting layer and improved device reliability of the light-emitting element.

[0047] The excitons generated upon carrier recombination include singlet excitons and triplet excitons. When a fluorescent dopant is used as the guest compound, singlet excitons contribute to light emission. When a phosphorescent dopant is used instead of a fluorescent dopant, triplet excitons contribute to light emission. According to the law of spin statistics, the generation ratio of singlet excitons and triplet excitons is 25% and 75%, respectively. Therefore, when a fluorescent dopant is used as the guest compound, i.e., in the process of "fluorescence" emitted only from singlet excitons, the generation probability of excitons that can contribute to light emission is at most 25%.

[0048] In contrast, when a phosphorescent dopant is used as a guest compound, light can be extracted from triplet excitons, thereby increasing the quantum efficiency three times that of a fluorescent dopant. Furthermore, by utilizing intersystem crossing, which is the inversion of the spin from singlet excitons to triplet excitons, theoretically all generated excitons can emit "phosphorescence" from triplet excitons. Therefore, when a phosphorescent dopant is used as a guest compound, the quantum efficiency can be increased up to four times compared to when a fluorescent dopant is used.

[0049] The guest compound contained in the light-emitting layer in the present disclosure may be either a fluorescent dopant or a phosphorescent dopant. The guest compound may be a hole-transporting material or an electron-transporting material. By using a hole-transporting material or an electron-transporting material as the guest compound, it becomes easier to adjust the carrier balance by changing the concentration of the guest compound. In the present disclosure, a hole-transporting material refers to a material characterized by holes being present relatively stably and holes being moved by an electric field. Furthermore, an electron-transporting material refers to a material characterized by electrons being present relatively stably and electrons being moved by an electric field. Note that delayed fluorescent dopants and fluorescent dopants (hyperfluorescence) that emit light via a delayed fluorescent material are also types (improved) of fluorescent dopants.

[0050] Known materials can be used as the light-emitting materials (host compounds and guest compounds) of the light-emitting layer. For example, examples of light-emitting materials constituting the blue light-emitting layer include pyrene-based compounds and anthracene-based compounds, which are fluorescent dopants. Furthermore, examples of light-emitting materials constituting the red and green light-emitting layers include iridium complexes and palladium-based complexes, which are phosphorescent dopants.

[0051] However, complexes containing platinum-group elements such as iridium or palladium, which are used as phosphorescent dopants, are very expensive even in small amounts because the production of platinum-group elements is small and unevenly distributed, and stable supply is sometimes difficult. Therefore, reducing the amount of phosphorescent dopants using these platinum-group complexes is extremely important from the perspectives of cost reduction and economic security.

[0052] The host-guest emitting layer can be formed by doping a host compound with a guest compound, or by a co-evaporation method using a plurality of evaporation sources.

[0053] Various known examples of materials for the host-guest emitting layer can be used. Examples of host compounds include known emitting layer materials for each color. Examples of guest compounds include the fluorescent dopants and phosphorescent dopants described above, as well as TADF and hyperfluorescent materials. Further examples of fluorescent dopants include perylene, DPT, Coumarin 6, PMDFB, quinacridone, rubrene, BTX, ABTX, DCM, and DCJT. Further examples of phosphorescent dopants include Ir(ppy). ３ , Ir(thpy) ３ , Ir(t5m-thpy) ３ , Ir(t-5CF ３ -py) ３ , Ir(t-5t-py) ３ , Ir(mt-5mt-py) ３ , Ir(btpy) ３ , Ir(tflpy) ３ , Ir(piq) ３ , Ir(tiq) ３ , Ir(fliq) ３ , FIrpic, FIr6, ppy, tpy, bzq, thp, op, bo, bt, bon, αbsn, btp, ppo, C6, pq, β-bsn, and ppz.

[0054] In currently mainstream light-emitting elements, a fluorescent dopant is used as a guest compound in the blue-emitting layer, and a phosphorescent dopant is used as a guest compound in the red- and green-emitting layers. In light-emitting devices including these light-emitting elements, the quantum efficiency of the fluorescent dopant is lower than that of the phosphorescent dopant, both theoretically and practically. Therefore, in the above-mentioned light-emitting devices, the amount of current passed through the blue-emitting layer may be made larger than the amount of current passed through the red- and green-emitting layers to balance the amount of light emitted.

[0055] However, increasing the amount of current flowing through the blue-emitting layer, which is a fluorescent-emitting layer using a fluorescent dopant as a guest compound, inevitably shortens the lifespan of the blue-emitting layer (accelerating the rate of deterioration). To address this issue, the total number of blue-emitting layers stacked in the stacking direction may be greater than the total number of red- and green-emitting layers, which are phosphorescent-emitting layers using a phosphorescent dopant as a guest compound. That is, the total number of fluorescent-emitting layers may be greater than the total number of phosphorescent-emitting layers. This configuration is advantageous for balancing the reliability and light emission between the fluorescent-emitting layer and the phosphorescent-emitting layer in the light-emitting element. The total number of fluorescent-emitting layers is preferably greater than the total number of phosphorescent-emitting layers by one or two. Increasing the number of fluorescent-emitting layers by three or more may make it difficult to balance the reliability and light emission between phosphorescent-emitting layers of different colors. Furthermore, the difference in total layer thickness between light-emitting elements having phosphorescent-emitting layers may become too large, resulting in an unbalanced element structure of the light-emitting device and a low manufacturing yield.

[0056] [Charge Generation Layer] The charge generation layer is disposed between two adjacent light-emitting layers in the stacking direction. The charge generation layer is a layer that generates one or both of electrons and holes. The charges (charges or carriers) generated in the charge generation layer are supplied to the light-emitting layers located on the anode and cathode sides in the stacking direction. The charge generation layer can be made of a known charge generation material that exhibits the above-mentioned functions.

[0057] The charge generation layer may be composed of an electron generation layer that generates electrons and a hole generation layer that generates holes. Examples of electron generation layers include n-type charge generation layers, and examples of hole generation layers include p-type charge generation layers. The charge generation layer may have a structure in which an electron generation layer and a hole generation layer are stacked. When holes are supplied from the anode and electrons are supplied from the cathode, the electron generation layer (n-type charge generation layer) generates electrons, and the hole generation layer (p-type charge generation layer) generates holes.

[0058] The hole generation layer can be made of a material containing an organic hole transport material and an organic electron accepting material (hole supply material) added in a range of 1 to 10%. Known triarylamine organic compounds can be used as the organic hole transport material. An example of an organic electron accepting material is tetracyanoquinodimethane tetrafluoride (TCNQ-4F). By using the hole transport material and electron accepting material described above as the hole generation layer material and using all organic materials, a material with sufficient hole generation ability can be achieved.

[0059] The electron generation layer may be made of, for example, an organic electron transport material and an inorganic metal material, Yb (ytterbium) or Li (lithium), added in an amount of 5 to 20% and acting as an electron donor. Examples of organic electron transport materials include oxadiazole-based compounds and phenanthroline-based compounds. Development is underway to use organic materials for both the electron transport layer and the electron donor in the electron generation layer. For example, organic electron donor materials include BUPH1, BPen, p-MeO-Phen, and p-NMe. ２ Development of p-Pyrrd-Phen, p-Pyrrd-Phen, etc. is currently underway.

[0060] Currently, no organic electron donor material has been found that has the same electron supply capacity as inorganic materials. Therefore, no electron generation layer formed entirely of organic materials and with sufficient characteristics has been found. However, even in such cases, the technical concept of the present disclosure can optimize the balance (carrier balance) between the electrons and / or holes supplied from the charge generation layer (electron generation layer and hole generation layer) and the holes and / or electrons supplied from the anode and cathode by reducing the area of ​​the light-emitting layer formed on the anode side of the electron generation layer to match the amount of electrons supplied from the entirely organic electron generation layer. Therefore, the present disclosure provides a tandem light-emitting device having multiple light-emitting layers stacked in the stacking direction, which reduces power consumption and provides excellent reliability, even in a tandem light-emitting device having an electron generation layer formed entirely of organic materials.

[0061] [Other Configurations] The light-emitting element of the present disclosure may further include other layers as long as the effects of the present disclosure are obtained. Examples of other configurations include carrier functional layers such as a hole injection layer, an electron injection layer, a hole transport layer, an electron blocking layer, a hole blocking layer, and an electron transport layer.

[0062] The hole injection layer is disposed adjacent to the anode, for example, and may be composed of a hole transport material and an electron acceptor material. The material of the hole injection layer may be the same organic material as the material described for the hole generation layer. The specific material of the hole injection layer in the light-emitting element may be the same as or different from the material of the hole generation layer.

[0063] The electron injection layer may be disposed adjacent to the cathode, for example, and may be composed of an electron transport material. Examples of electron transport materials constituting the electron injection layer include inorganic materials such as lithium fluoride (LiF). Similarly to the electron generation layer, the electron injection layer may be composed of an organic material such as an oxadiazole-based compound or a phenanthroline-based compound, and doped with a metal material (e.g., Li or Yb).

[0064] LiF used in the electron injection layer exhibits excellent electron injection properties. On the other hand, the formation of a carrier functional layer containing an inorganic material such as Yb, not limited to LiF, is generally carried out at a higher temperature than the formation of an emitting layer and other carrier functional layers made of organic materials due to the high melting point of the inorganic material. Therefore, there is a risk of thermal damage to the organic material that was previously formed. Therefore, if possible, it is preferable to form a light-emitting element using only organic materials, without including inorganic materials.

[0065] Therefore, BUPH1, BPen, p-MeO-Phen, p-NMe, etc. were used as all-organic electron injection layers that can have sufficient properties when combined with a cathode made of aluminum (Al) or the like, which allows the deposition layer to be formed at a relatively low temperature. ２ The development of organic electron-injecting materials such as p-Pyrrd-Phen and p-Pyrrd-Phen is currently underway.

[0066] However, the electron injection ability of an electron injection layer made of an organic material is still inferior to that of an electron injection layer made of an inorganic material such as LiF. Therefore, when an electron injection layer made of an organic material is disposed adjacent to the cathode, the amount of carriers supplied (the amount of electrons supplied) to the light-emitting layer formed on the cathode side may be reduced. In such cases, the advantages of adopting a tandem structure can be fully realized by reducing the area of ​​the light-emitting layer on the cathode side to be smaller than the aforementioned determined value in order to reduce the impact of the reduced electron supply. This configuration may be included in the present disclosure.

[0067] The hole transport layer may be made of an organic hole transport material, such as a triarylamine organic compound.

[0068] The electron blocking layer, like the hole transport layer, may be made of an organic hole transport material. The material of the electron blocking layer may be the same as or different from the material of the hole transport layer.

[0069] The hole blocking layer may be composed of an organic electron transporting material, such as an oxadiazole-based compound or a phenanthroline-based compound, and may contain lithium quinoline (Liq) in addition to the electron transporting material.

[0070] The electron transport layer, like the hole blocking layer, may be composed of the organic electron transport material described above. The material of the electron transport layer may be the same as or different from the material of the hole blocking layer. In addition to the electron transport material, lithium quinoline may be included.

[0071] The hole injection layer and the electron injection layer may be disposed corresponding to the anode and the cathode, respectively. Typically, the hole injection layer and the electron injection layer are disposed adjacent to the anode and the cathode, respectively, in the stacking direction of the multiple layers constituting the light-emitting element. The hole transport layer, the electron blocking layer, the light-emitting layer, the hole blocking layer, the electron transport layer, and the charge generation layer may be disposed in a stacked manner multiple times in the stacking direction of the light-emitting element.

[0072] The light-emitting device of the present disclosure is suitable for a top-emission type light-emitting device capable of full-color display. In a top-emission type light-emitting device, the distance between the anode and cathode can be adjusted according to the wavelength of light from the light-emitting layer of each color, thereby utilizing the microcavity effect to narrow the emission radiation angle from the light-emitting layer and improve light extraction efficiency. In this case, the light-emitting device of the present disclosure can further control the emission radiation angle by making the area of ​​the light-emitting layer on the cathode side different from the area of ​​the light-emitting layer on the anode side.

[0073] In top-emission light-emitting devices, the light extraction efficiency is determined by the resonance conditions of the microcavity structure. The resonance conditions are determined by the position of the light-emitting point in the stacking direction of the organic layers, the total thickness of the organic layers, the emission wavelength, and the refractive index of the organic material. Therefore, if the light-emitting point (light-emitting layer) is stacked at an appropriate position relative to the total thickness of the organic layers, the light extraction efficiency to the outside will improve, but if it is not in an appropriate position, the light extraction efficiency will decrease. Due to this constraint, the position of the light-emitting layer cannot be set arbitrarily and must be located at one of the periodic positions depending on the emission wavelength and refractive index. However, if the light-emitting layer is formed too close to the anode, it will be quenched due to the influence of the interaction between the metal oxide (indium tin oxide) constituting the anode and the light-emitting material (host compound and / or guest compound) (sometimes referred to as the "heavy atom effect" or "plasmon effect"), resulting in a phenomenon of reduced luminous efficiency. Therefore, for example, the light-emitting layer disposed closest to the anode needs to be stacked at a distance from the anode not to the primary peak (the shortest position, e.g., 30 nm) based on the resonance condition, but to the next secondary peak (e.g., 100 nm). To achieve such a stacking configuration, the organic layer (carrier functional layer) other than the light-emitting layer may be thickened, more specifically, the thickness of the hole transport layer on the anode side may be increased, and the light-emitting layer may be stacked at an appropriate position. However, if the thickness of the hole transport layer is increased, the probability of holes being deactivated relative to other hole transport layers may increase, resulting in fewer holes being supplied to the light-emitting layer formed immediately above the anode. In such cases, the advantages of adopting a tandem structure can be fully realized by reducing the area of ​​the anode-side light-emitting layer below the aforementioned determined value. This configuration may also be included in the present disclosure.

[0074] [Stack] A stack is a collection of layers including one light-emitting layer arranged between the anode and the charge generation layer, between the charge generation layers, and between the charge generation layer and the cathode in the stacking direction. The stack may include a carrier functional layer in addition to the one light-emitting layer. Multiple stacks may be arranged between the anode and the cathode in the stacking direction. In the present disclosure, the anode, cathode, and charge generation layer are not included in the stack.

[0075] The thickness of the stack is determined so that the amount of light emitted from the light-emitting layer is a theoretical value or a value close to it. Note that the thickness of the stack is calculated as the sum of the thicknesses of the light-emitting layer and the carrier functional layer in the stack, but among the light-emitting layer and the carrier functional layer, layers with a very small thickness (for example, a layer that may have a thickness of less than 1 nm) may be ignored when calculating the thickness of the stack.

[0076] [Method for Manufacturing Light-Emitting Device] In the manufacturing of the light-emitting device of the present disclosure, the area of ​​the cathode-side light-emitting layer in the stacking direction is formed larger than the area of ​​the adjacent anode-side light-emitting layer with a charge generation layer interposed therebetween. Otherwise, the light-emitting device of the present disclosure can be manufactured by a known manufacturing method capable of manufacturing a light-emitting element having multiple light-emitting layers (tandem structure). The manufacturing method of the light-emitting device may be any method that includes a step of forming light-emitting layers and charge generation layers alternately in the stacking direction on the anode or cathode. Furthermore, from the viewpoint of precisely controlling the area of ​​each light-emitting layer in the light-emitting device of the present disclosure, the manufacturing method preferably forms the light-emitting layer by a vapor deposition method using a vapor deposition mask having at least multiple openings. Light-emitting layers formed by a vapor deposition method are generally preferred from the viewpoints of high brightness and low-voltage operation, and are also preferred from the viewpoint of realizing high-resolution display devices because they enable the formation of light-emitting elements consisting of fine pixels with high precision. Furthermore, a co-evaporation method using multiple evaporation sources is more preferable because it enables the formation of a host-guest light-emitting layer.

[0077] Since the light-emitting device of the present disclosure has a specific layer structure repeatedly, it can be manufactured by repeating the formation of a specific layer multiple times. In the present disclosure, it is preferable to form the light-emitting layers having different areas in the stacking direction by changing only the deposition mask. This manufacturing method makes it possible to keep constant conditions other than the deposition mask when forming the light-emitting layer (e.g., the temperature of the crucible (deposition temperature) or the deposition rate controlled by the deposition temperature, the ratio of the host compound to the guest compound (doping concentration of the guest compound), etc.). Therefore, variation in characteristics due to changes in conditions for each light-emitting layer in the stacking direction is suppressed, and the effect of differences in the areas of the light-emitting layers in the stacking direction can be more significantly exhibited.

[0078] [Display Device] The display device according to the present disclosure includes the above-described light-emitting device. The display device according to the present disclosure can be configured in the same manner as a known display device having a known light-emitting device, except for including the above-described light-emitting device. Examples of the display device include a smartphone and a television set.

[0079] [Description of Specific Embodiments] The light-emitting device, display device, and manufacturing method of the light-emitting device according to the present disclosure will be described in more detail below with reference to the drawings, taking a light-emitting device including an organic light-emitting diode (OLED) as an example. In this specification, for configurations of different colors among similar basic configurations, a symbol indicating the color may be added to the symbol of the basic configuration. For example, a symbol such as R may be added to a configuration related to red, G may be added to a configuration related to green, and B may be added to a configuration related to blue.

[0080] 1 is a plan view schematically illustrating a configuration of a display device 101 including a frame region NDA and a display region DA according to a first embodiment of the present disclosure. The display device 101 is a smartphone, which is an example of a display device. The display region DA of the display device 101 includes a plurality of pixels PIX, each of which includes a red sub-pixel RSP, a green sub-pixel GSP, and a blue sub-pixel BSP.

[0081] Note that the pixel configuration of the display device according to the present disclosure is not limited to the above configuration. In the display device according to the present disclosure, for example, one pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, the green subpixel GSP, and the blue subpixel BSP.

[0082] Fig. 2 is a cross-sectional view showing a schematic configuration of one pixel PIX portion of the display device 101 shown in Fig. 1. The display device 101 includes a substrate 1, a buffer layer 2, a TFT (thin film transistor) layer 3 including a pixel circuit, a light-emitting device 4, an edge cover film 5, a sealing layer 6, and an external functional layer 7 stacked in this order in a stacking direction (first direction X1).

[0083] The substrate 1 is a glass substrate or a flexible substrate whose main component is a resin such as polyimide. In this example, it is composed of two polyimide film layers and an inorganic film sandwiched between them. The buffer layer 2 is an inorganic insulating layer that prevents the intrusion of foreign substances such as water and oxygen. The TFT layer 3 includes pixel circuits that control the light-emitting devices 4.

[0084] The light emitting device 4 includes a plurality of light emitting elements 8 (a first light emitting element 9, a second light emitting element 10, and a third light emitting element 11) arranged in a direction perpendicular to the stacking direction (second direction X2). Each of the light emitting elements 8 includes an anode 12 and a cathode 26, and includes a light emitting layer 16 and a light emitting layer 22 between these electrode layers.

[0085] In addition to the organic light-emitting diode (OLED) elements used in the following description, quantum dot light-emitting diode (QLED) elements can be cited as examples of each of the plurality of light-emitting elements 8 (first light-emitting element 9, second light-emitting element 10, and third light-emitting element 11). When the light-emitting element 8 is an OLED, the light-emitting layers 16 and 22 contain an organic light-emitting material, and when the light-emitting element 8 is a QLED, the light-emitting layers 16 and 22 contain quantum dots. Quantum dots are semiconductor particles with a diameter (particle size) of several nanometers to several tens of nanometers, and can emit light at a desired wavelength by appropriately selecting the particle size and material.

[0086] 2 shows a configuration in which the first light-emitting element 9, the second light-emitting element 10, and the third light-emitting element 11 are each provided with an individual cathode 26. The light-emitting device 4 of the present disclosure is not limited to this configuration. For example, the cathode 26 may be a common cathode provided across the first light-emitting element 9, the second light-emitting element 10, and the third light-emitting element 11.

[0087] The edge cover film 5 is an insulating film that covers the edge of the anode 12 of the light-emitting element 8 and defines the region of each subpixel in a planar view. The edge cover film 5 is formed by applying an acrylic resin and then patterning it using photolithography. The edge cover film may be made of an organic material such as polyimide or an inorganic material such as SiNx. The sealing layer 6 is a layer that covers the light-emitting device 4 and prevents foreign substances such as water and oxygen from penetrating into the light-emitting device 4, and is composed of two inorganic sealing films and an organic film formed between them. The external functional layer 7 is a layer that realizes various functions in the display device 101, such as optical control, touch sensor, and surface protection.

[0088] 3 is a diagram schematically illustrating the layer structure of the light-emitting element 8. The light-emitting element 8 includes a substrate 1, a buffer layer 2, and a TFT layer 3 (not shown) stacked in this order, on which an anode 12, a set of layers 49, a charge generation layer 19, a set of layers 50, and a cathode 26 are stacked. The charge generation layer 19 includes an electron generation layer 27 and a hole generation layer 28. The light-emitting element 8 according to the present disclosure is a top-emission type (i.e., a structure in which light is extracted from the cathode 26 side).

[0089] When the light-emitting element 8 is an OLED, the set of layers 49 is composed of a hole injection layer 13, a hole transport layer 14, an electron blocking layer 15, an emitting layer 16, a hole blocking layer 17, and an electron transport layer 18, and the set of layers 50 is composed of a hole transport layer 20, an electron blocking layer 21, an emitting layer 22, a hole blocking layer 23, an electron transport layer 24, and an electron injection layer 25. When the light-emitting element 8 is a QLED, the emitting layers 16 and 22 included in the sets of layers 49 and 50 may contain quantum dots.

[0090] The hole injection layer 13, the hole transport layer 14, the electron blocking layer 15, the hole blocking layer 17, the electron transport layer 18, the charge generation layer 19 (the electron generation layer 27 and the hole generation layer 28), the hole transport layer 20, the electron blocking layer 21, the hole blocking layer 23, the electron transport layer 24, and the electron injection layer 25 are carrier functional layers that contribute to at least one of the injection, movement, and generation of carriers (electrons or holes).

[0091] The anode 12 has a two-layer structure in which indium tin oxide, which has the function of reflecting visible light and has high hole injection properties, is formed on Ag. The cathode 26 is made of a thin film alloyed with Mg and Ag to ensure visible light transmittance. By configuring the anode 12 and the cathode 26 in this way, the light-emitting element 8 has a top-emission structure in which light generated from the light-emitting layer 16 and the light-emitting layer 22 is extracted from the cathode 26 side.

[0092] The light-emitting element 8 is a light-emitting element (tandem light-emitting element) having a so-called tandem structure in which two light-emitting layers, a light-emitting layer 16 and a light-emitting layer 22, are arranged between an anode 12 and a cathode 26 in the stacking direction. The light-emitting layer 16 and the light-emitting layer 22, which overlap in the stacking direction (first direction X1 in FIG. 3), are layers that emit light of the same predetermined color when an electric field is applied. Note that the light-emitting layer 16 and the light-emitting layer 22 are both host-guest light-emitting layers.

[0093] Hereinafter, when the light-emitting element 8 is a first light-emitting element 9, a second light-emitting element 10, or a third light-emitting element 11, different reference numerals may be assigned to the anode 12, the light-emitting layers 16 and 22, the charge generation layer 19, the electron generation layer 27, the hole generation layer 28, and the cathode 26. In this case, the correspondence is as follows:

[0094] (When the light-emitting element 8 is the first light-emitting element 9) Anode 12: anode 36 Light-emitting layer 16: first light-emitting layer 29 Charge generation layer 19: first charge generation layer 35 Electron generation layer 27: electron generation layer 40, hole generation layer 28: hole generation layer 41 Light-emitting layer 22: second light-emitting layer 30 Cathode 26: cathode 37 (When the light-emitting element 8 is the second light-emitting element 10) Anode 12: anode 52 Light-emitting layer 16: third light-emitting layer 31 Charge generation layer 19: second charge generation layer 42 Light-emitting layer 22: fourth light-emitting layer 32 Cathode 26: cathode 53 (When the light-emitting element 8 is the third light-emitting element 11) Anode 12: anode 54 Light-emitting layer 16: fifth light-emitting layer 33 Charge generation layer 19: third charge generation layer 47 Light-emitting layer 22: sixth light-emitting layer 34 Cathode 26: cathode 55 The first light-emitting element 9 emits light of the same color as the first color. The second light-emitting element 10 emits light of a second color different from the first color. The third light-emitting element 11 emits light of a third color different from both the first color and the second color. One of the first color, the second color, and the third color may be red. Another one of the first color, the second color, and the third color may be green. The remaining one of the first color, the second color, and the third color may be blue. There is no particular limitation on which of the first color, the second color, and the third color is red, which is green, and which is blue. For example, when the first light-emitting element 9 emits red light as the first color, the first light-emitting layer 29 and the second light-emitting layer 30 emit red light; when the second light-emitting element 10 emits green light as the second color, the third light-emitting layer 31 and the fourth light-emitting layer 32 emit green light; and when the third light-emitting element 11 emits blue light as the third color, the fifth light-emitting layer 33 and the sixth light-emitting layer 34 emit blue light.

[0095] The areas of the light-emitting layers 16, 22, 29, 30, 31, 32, 33, and 34 may vary depending on the emitted color. In the case where the display device 101 is a smartphone as in the present disclosure, for example, the size of one red sub-pixel RSP on the anode side included in each of the plurality of pixels PIX included in the display area DA is 10 μm×10 μm (the area of ​​the first light-emitting layer 29 of the first light-emitting element 9 is 100 μm ２ ), the size of one green sub-pixel GSP on the anode side is 11.7 μm×11.7 μm (the area of ​​the third light-emitting layer 31 of the second light-emitting element 10 is 137 μm ２), and the size of one blue sub-pixel BSP on the anode side is 12.5 μm×12.5 μm (the area of ​​the fifth light-emitting layer 33 of the third light-emitting element 11 is 155 μm ２ ) However, two green sub-pixels GSP are provided in one pixel PIX. Therefore, the total area of ​​the green sub-pixels GSP per pixel is 274 μm ２ In contrast, the areas of the red subpixel RSP (second light-emitting layer 30), green subpixel GSP (fourth light-emitting layer 32), and blue subpixel BSP (sixth light-emitting layer 34) on the cathode side are larger than the areas of the first light-emitting layer 29, third light-emitting layer 31, and fifth light-emitting layer 33 on the anode side, respectively. For example, the area of ​​the second light-emitting layer 30 of the first light-emitting element 9 is 144 μm ２ The area of ​​the fourth light-emitting layer 32 of the second light-emitting element 10 (the total area of ​​the two anode-side green sub-pixels GSP) is 392 μm ２ The area of ​​the sixth light-emitting layer 34 of the third light-emitting element 11 is 225 μm ２ The area of ​​the anode-side light-emitting layer is 0.1 times or more and 0.9 times or less the area of ​​the cathode-side light-emitting layer. As the size of the display area DA increases, such as in so-called medium-sized display devices used in notebook PCs and tablet terminals and large-sized display devices used in TVs, the size of one pixel PIX also increases. However, the area of ​​the anode-side light-emitting layer and the area of ​​the cathode-side light-emitting layer in the display device of the present disclosure satisfy the above-mentioned relationship. Generally, in the case of small display devices for smartphones and the like, the pixel size is approximately 5 μm × 5 μm to 60 μm × 60 μm, and in the case of medium-sized display devices, the pixel size is approximately 50 μm × 50 μm to 200 μm × 200 μm. While this embodiment illustrates an example in which each light-emitting layer is square, the present disclosure is not limited thereto. For example, the shape of each light-emitting layer may be rectangular, circular, or other polygonal.

[0096] The charge generation layer 19 is a layer that generates at least one of electrons and holes. The charges (charges or carriers) generated in the charge generation layer 19 are supplied to the light-emitting layers 16 and 22. A known charge generation material can be used for the charge generation layer 19. In the display device 101 of the present disclosure, the charge generation layer 19 has a structure in which an electron generation layer 27 and a hole generation layer 28 are stacked.

[0097] The electron generation layer 27 generates electrons. The hole generation layer 28 generates holes. Examples of the electron generation layer 27 include an n-type charge generation layer, and examples of the hole generation layer 28 include a p-type charge generation layer. When holes are supplied from the anode 12 and electrons are supplied from the cathode 26, the electron generation layer 27 generates electrons and the hole generation layer 28 generates holes.

[0098] The electron generating layer 27 is made of an oxadiazole compound, which is an organic electron transport material, to which Yb (ytterbium), an inorganic metal material that acts as an electron donor, is added.

[0099] The hole generating layer 28 used a triarylamine organic compound as an organic hole transport material and tetracyanoquinodimethane tetrafluoride (TCNQ-4F) as an organic electron accepting material (hole supplying material).

[0100] Hereinafter, the notations "first charge generation layer 35," "second charge generation layer 42," and "third charge generation layer 47" may be used. When the light-emitting element 8 is the first light-emitting element 9, the charge generation layer 19 corresponds to the first charge generation layer 35, and when the light-emitting element 8 is the second light-emitting element 10 or the third light-emitting element 11, the charge generation layer 19 corresponds to the second charge generation layer 42 or the third charge generation layer 47, respectively.

[0101] The first light-emitting element 9 and the second light-emitting element 10 may be adjacent to each other in the second direction X2, and the first charge generation layer 35 may be separated from the second charge generation layer 42. Alternatively, the first charge generation layer 35 and the second charge generation layer 42 may be continuous. Here, the first charge generation layer 35 and the second charge generation layer 42 are formed so as to be continuous.

[0102] The cathodes 26 of at least two of the plurality of light-emitting elements 8 may be separated from each other or may be continuous with each other. In this example, the cathodes 26 of the first light-emitting element 9, the second light-emitting element 10, and the third light-emitting element 11 are formed so as to be continuous with each other.

[0103] The hole injection layer 13 may be composed of an organic hole transport material and an organic electron acceptor material. In the first embodiment, the material of the hole injection layer 13 is the same as the material of the hole generation layer 28.

[0104] Each of the hole transport layers 14 and 20 was made of a triarylamine organic compound, which is an organic hole transport material.

[0105] The electron blocking layers 15 and 21 were each made of the same organic hole transport material (triarylamine organic compound) as the material of the hole transport layers 14 and 20 .

[0106] The hole blocking layers 17 and 23 each used an oxadiazole-based compound, which is an organic electron transport material.

[0107] The electron transport layers 18 and 24 were made of an oxadiazole-based compound, which was an organic electron transport material similar to the material of the hole blocking layers 17 and 23, to which lithium quinoline (Liq) had been added.

[0108] The electron injection layer 25 was made of lithium fluoride (LiF), which is an electron transport material that exhibits excellent electron injection properties.

[0109] The hole injection layer 13 and the electron injection layer 25 are formed adjacent to the anode 12 and the cathode 26, respectively.

[0110] In the first light-emitting element 9, the first light-emitting layer 29, the first charge generation layer 35, and the second light-emitting layer 30 are aligned in a first direction X1. The first direction X1 coincides with the stacking direction of the layers constituting the first light-emitting element 9. The first light-emitting element 9, the second light-emitting element 10, and the third light-emitting element 11 are aligned in a second direction X2 perpendicular to the first direction X1.

[0111] The first light-emitting layer 29 is located between the anode 36 of the first light-emitting element 9 and the cathode 37 of the first light-emitting element 9. The second light-emitting layer 30 is located between the first light-emitting layer 29 and the cathode 37. The first charge generation layer 35 is located between the first light-emitting layer 29 and the second light-emitting layer 30. The first light-emitting layer 29 emits light of a first color. The second light-emitting layer 30 emits light of the same color as the first color.

[0112] 4 is a plan view of the first light-emitting layer 29 and the second light-emitting layer 30. The first light-emitting layer 29 has a first area 38. The second light-emitting layer 30 has a second area 39. The second area 39 is larger than the first area 38.

[0113] Here, we will explain the carrier imbalance that needs to be corrected in a light-emitting element. In a light-emitting element having a cathode and an anode, the amount of electrons flowing from the cathode is equal to the amount of holes flowing from the anode. In other words, the amount of electrons flowing from the cathode is equal to the amount of electrons flowing from the anode (Kirchhoff's first law). Here, the amount of charge flowing per unit time (amount of electrons × elementary charge) is the current. If each layer (light-emitting layer and carrier functional layer) constituting the light-emitting element all has the same carrier injection and transport properties, the current flowing through the light-emitting element should be proportional to the voltage between the anode and cathode and inversely proportional to the overall resistance of the light-emitting element (Ohm's law). However, in the case of a light-emitting element using an organic thin film, the current is proportional to the square of the anode-cathode voltage and inversely proportional to the cube of the thickness of the organic thin film (space charge limited current). In any case, when looking inside the light-emitting element, the carrier injection and transport properties differ for each layer. Therefore, the amount of current flowing through the light-emitting element is rate-limited by the layer with the lowest injection and transport properties. When observed externally, the amount of current flowing through the light-emitting element appears to be determined by the smaller of the amount of electrons injected and transported from the cathode or the amount of holes injected and transported from the anode (in other words, the amount of electrons flowing into the anode).

[0114] In single-element light-emitting devices (not tandem structures) with a single light-emitting layer, in order to further improve light-emitting efficiency by suppressing the generation of unnecessary carriers (electrons or holes), it is common to select the material and adjust the thickness of the carrier functional layer so that the number of holes supplied to the light-emitting layer from the anode is equal to the number of electrons supplied from the cathode. Another approach is to optimize the carrier balance by changing the thickness of the light-emitting layer, taking into account the concept of space-charge-limited current, and thereby changing the current flowing through the light-emitting layer to achieve the optimal current density. This structural design guideline is sometimes referred to as "achieving carrier balance."

[0115] Furthermore, for tandem light-emitting devices, which have an anode, a cathode, a charge generation layer, and multiple light-emitting layers in series, the same approach has been taken as for single light-emitting devices, namely, by selecting the material and adjusting the thickness of the carrier functional layer, a structural design has been made to equalize the amounts of electrons and holes supplied to the light-emitting layers. However, in the case of tandem light-emitting devices, the current value flowing through each of the light-emitting layers arranged in the stacking direction is the same, so the idea of ​​optimizing the carrier balance between light-emitting layers by changing only the current flowing through the light-emitting layer with an imbalanced carrier balance by changing the thickness of one of the light-emitting layers cannot be applied.

[0116] In contrast, the inventors' investigations have revealed that in a tandem light-emitting device having multiple light-emitting layers separated by a charge generation layer, even if the carrier functional layer conditions adjusted to equalize the supply of electrons and holes as described above are used, it is possible to achieve a carrier balance in one of the light-emitting layers, but it is difficult to generate and supply appropriate excitons to the remaining light-emitting layers and prevent the generation of excess carriers. This is because, in a tandem light-emitting device, at least one of the electron and hole carriers is supplied from the charge generation layer to each of the light-emitting layers. Unlike carrier generation in the anode and cathode, which are directly connected to a power source, carrier generation in the charge generation layer cannot be directly controlled electrically. Furthermore, in a tandem light-emitting device, according to Kirchhoff's first law, the amount of current flowing through each light-emitting layer arranged in series between a cathode and anode pair is the same. Therefore, as described above, the prior art has not been able to optimize the carrier balance for each light-emitting layer.

[0117] In a tandem light-emitting element, there are two cases where the carrier supply is unbalanced: one is when the same amount of electrons and holes are supplied to each light-emitting layer, forming electron-hole pairs (excitons) without generating excess carriers, but one of the light-emitting layers has a shortage or excess of excitons; the other is when not only the number of excitons is insufficient or excessive in one of the light-emitting layers, but the balance between the supply of electrons and holes to at least one of the light-emitting layers is disrupted, resulting in the formation of excess carriers other than excitons. These cases are collectively referred to as a carrier imbalance in a tandem light-emitting element. Carrier imbalances include a case where exciton generation is insufficient or excessive in one of the light-emitting layers, and a case where the amount of electrons and / or holes supplied to one of the multiple light-emitting layers formed between a pair of anode and cathode is unbalanced.

[0118] Therefore, optimizing the supply amount of carriers (electrons and / or holes) in one of the first light-emitting layer 29 and the second light-emitting layer 30 may result in an excessive supply of electrons and / or holes in the other of the first light-emitting layer 29 and the second light-emitting layer 30. As a result, an imbalance in the carrier balance occurs between the first light-emitting layer 29 and the second light-emitting layer 30. In the light-emitting device 4 of the present disclosure, the first area 38, which is the area of ​​the first light-emitting layer 29 where an insufficient amount of excitons is generated and / or where excess carriers are generated, is made smaller than the second area 39, which is the area of ​​the second light-emitting layer 30, in the first light-emitting element 9, thereby optimizing the carrier balance between the first light-emitting layer 29 and the second light-emitting layer 30. Therefore, according to the light-emitting device 4, in a tandem light-emitting element (first light-emitting element 9) in which multiple light-emitting layers (first light-emitting layer 29 and second light-emitting layer 30) between the anode 36 and the cathode 37 emit light of the same color, the generation of excess carriers that cannot contribute to light emission can be suppressed, and an appropriate amount of excitons is generated in both the first light-emitting layer 29 and the second light-emitting layer 30, enabling highly efficient and bright light emission. Note that the excess carriers cannot be eliminated by radiative recombination, but rather generate heat and become deactivated, which can cause deterioration of the light-emitting element. Therefore, according to the light-emitting device 4 of the present disclosure, thermal deactivation due to such excess carriers can also be suppressed, thereby improving element reliability.

[0119] The first area 38 and the second area 39 can be determined as appropriate as long as they are in line with the technical idea of ​​the present disclosure, which is to optimize the carrier balance in the first light-emitting layer 29 and the second light-emitting layer 30. From the viewpoint of fully exhibiting the light-emitting characteristics of the second light-emitting layer 30 (from the viewpoint of obtaining sufficient light-emitting efficiency), the first area 38 may be 10% or more of the second area 39. Furthermore, from the viewpoint of obtaining a sufficient amount of light emission, the first area 38 may be 90% or less of the second area 39.

[0120] At least one of the electron generation layer 27 and the hole generation layer 28 constituting the charge generation layer 19 of the light-emitting element 8 may contain an organic material. For example, the first charge generation layer 35 of the first light-emitting element 9 includes an electron generation layer 40 containing an organic material and generating electrons, and a hole generation layer 41 containing an organic material and generating holes, located between the electron generation layer 40 and the second light-emitting layer 30. Similarly, the second charge generation layer 42 of the second light-emitting element 10 and the third charge generation layer 47 of the third light-emitting element 11 contain an organic material.

[0121] A pn junction is not formed at the interface between the electron generation layer 27 and the hole generation layer 28. A pn ​​junction is a semiconductor interface where a p-type semiconductor material and an n-type semiconductor material are metallurgically bonded in a single crystal or near-single crystal state, and is originally formed by a junction between inorganic semiconductor materials. A metallurgical junction between different inorganic semiconductor materials is called a heterojunction. To form a pn junction at the heterojunction interface between different p-type and n-type semiconductor materials, the atoms must be metallurgically bonded so that the atomic arrangements (crystal planes, lattice constants, etc.) match at the junction interface. Therefore, in the case of a heterojunction, a pn junction may not be formed due to differences in lattice constants between the p-type and n-type semiconductor materials, differences in thermal expansion during junction formation, differences in mechanical strength during junction formation, etc. Other reasons why a pn junction is not formed at a heterointerface include edge dislocations, lattice distortion, and uneven distribution of impurity atoms due to interdiffusion across several tens of atomic layers, which behave as an electrically localized level. In any case, when at least one of the electron generating layer 27 and the hole generating layer 28 contains an organic substance, a charge generating layer in which no pn junction is formed at the interface therebetween can be realized.

[0122] The conductivity of the electron generating layer 27 is 1.0×10 －１０ The conductivity of the hole generation layer 28 may be 1.0×10 S / m or more and 1.0 S / m or less. －１０ It may be 1.0 S / m or more and 1.0 S / m or less.

[0123] The conductivity of the electron generating layer 27 is set to 1.0×10 ６It is not preferable to set the conductivity of the electron generation layer 27 to 1.0×10 s / m or more. This is because the material of the electron generation layer 27 must have a conductivity equivalent to that of a so-called conductor, which requires the use of a special organic substance, and further, current leakage from the first light-emitting element 9 to the second light-emitting element 10 and / or the third light-emitting element 11 occurs, making crosstalk unnegligible. The conductivity of the electron generation layer 27 is preferably set to 1.0×10 s / m or more, which is the conductivity of a semiconductor. －６ S / m or more and 1.0 x 10 ６ The conductivity of the electron generating layer 27 may be less than 1.0×10 S / m, which is the conductivity of an insulator. －１６ S / m or more and 1.0 x 10 －６ S / m does not pose any particular problem. A lower conductivity of the electron generation layer 27 is advantageous in terms of life (reliability of the first light-emitting element 9). However, if the conductivity of the electron generation layer 27 is reduced too much, the resistance increases and the electrical characteristics deteriorate (power consumption of the light-emitting element 8 increases). When the conductivity of the electron generation layer 27 is reduced to 1.0×10 －１０ It is preferable to set the conductivity of the hole generation layer 28 to be 1.0 S / m or more and 1.0 S / m or less from the viewpoints of preventing crosstalk, improving the reliability of the light-emitting element, and preventing deterioration of electrical characteristics. The same applies to the setting of the conductivity of the hole generation layer 28.

[0124] [Method for Manufacturing Light-Emitting Element] Next, an example of a method for manufacturing the light-emitting device 4 will be described with reference to Fig. 5. Fig. 5 is a flowchart showing a method for manufacturing the light-emitting device 4 according to the first embodiment of the present disclosure. The method for manufacturing the light-emitting device 4 includes steps S1 to S16. Steps other than steps S5 and S12 of the method for manufacturing the light-emitting device 4 can be realized within the scope of well-known technology.

[0125] Step S1 in the manufacturing method of the present disclosure is a step of forming the anode 12 on the TFT layer 3. Specifically, an Ag layer and an indium tin oxide layer are formed in this order by sputtering.

[0126] Step S2 is a process of forming a hole injection layer 13 on the anode 16. In this process, a hole transport material and an electron acceptor material are co-deposited onto the entire surface of the workpiece without using a fine metal mask, with the deposition temperature and deposition time adjusted so that the materials are laminated to a predetermined thickness and ratio.

[0127] In the specific description of the manufacturing method based on Fig. 5, some of the carrier functional layers are formed as common layers between the respective light-emitting elements, but the manufacturing method of the present disclosure is not limited to this. The thickness of each carrier functional layer may be different for each color depending on, for example, the respective light-emitting layers. Such carrier functional layers with different thicknesses can be formed by vapor deposition using a mask.

[0128] Step S3 is a process of forming the hole transport layer 14 on the hole injection layer 13. In this process, a hole transport material is evaporated using a common mask while adjusting the evaporation temperature and evaporation time so that the hole transport material is deposited to a predetermined film thickness.

[0129] Step S4 is a process of forming the electron blocking layer 15 on the hole transport layer 14. In this process, the hole transport material is deposited using a fine metal mask while adjusting the deposition temperature and deposition time so that the hole transport material is deposited to a predetermined film thickness (first thickness). The first thickness may be the same for each light-emitting element of each color, or may be different.

[0130] Step S5 is a process of forming a first light-emitting layer 29 on the electron blocking layer 15 using a first vapor deposition mask having a plurality of first openings formed therein. Here, the first vapor deposition mask is a fine metal mask. A host compound and a guest compound (dopant) constituting the first light-emitting layer 29 are vapor-deposited by co-evaporation using the first vapor deposition mask to have a predetermined first area 38, film thickness, and guest compound concentration (dopant concentration). Note that the first light-emitting layer 29 may be formed using a resist mask formed by photolithography instead of a fine metal mask.

[0131] Step S6 is a process of forming a hole blocking layer 17 on the first light-emitting layer 29. In this process, an electron transport material is deposited by vapor deposition without using a fine metal mask, while adjusting the deposition temperature and deposition time so that the electron transport material is deposited to a predetermined thickness.

[0132] Step S7 is a process of forming an electron transport layer 18 on the hole blocking layer 17. In this process, an electron transport material is deposited without using a fine metal mask by adjusting the deposition temperature and deposition time so that the electron transport material is deposited to a predetermined thickness. This process may be performed by depositing only the electron transport material, or by co-depositing the electron transport material and an electron donor material (e.g., lithium quinoline).

[0133] Step S8 is a process of forming an electron generation layer 40, which is a part of the first charge generation layer 35, on the electron transport layer 18. In this process, an organic electron transport material and an inorganic metal electron donor material, Yb or Li, are co-deposited without using a fine metal mask by adjusting the deposition temperature and deposition time so that the layers are laminated to a predetermined thickness and ratio.

[0134] Step S9 is a process of forming a hole generation layer 41, which is the remainder of the first charge generation layer 35, on the electron generation layer 40. In this process, an organic hole transport material and an organic electron acceptor material are co-deposited without using a fine metal mask, with the deposition temperature and deposition time adjusted so that the layers are laminated to a predetermined thickness and ratio.

[0135] Step S10 is a process of forming the hole transport layer 20 on the first charge generation layer 35 (hole generation layer 41). In this process, the hole transport material is deposited without using a fine metal mask by adjusting the deposition temperature and deposition time so that the hole transport material is deposited to a predetermined thickness.

[0136] Step S11 is a process of forming an electron blocking layer 21 on the hole transport layer 20. In this process, a hole transport material is deposited to a second thickness corresponding to each color using a fine metal mask, while adjusting the deposition temperature and deposition time so that the hole transport material is deposited to a predetermined film thickness. Like the first thickness, the second thickness may be the same or different for light-emitting elements of each color.

[0137] Step S12 is a process of forming a second light-emitting layer 30 on the electron blocking layer 21 using a second vapor deposition mask in which a plurality of second openings, each having an area larger than that of the first openings, are formed. Here, the second vapor deposition mask is a fine metal mask. A host compound and a guest compound (dopant) constituting the second light-emitting layer 30 are vapor-deposited to a predetermined second area 39, film thickness, and guest compound concentration (dopant concentration) by a co-evaporation method using the second vapor deposition mask. Note that the second light-emitting layer 30 may be formed using a resist mask formed by photolithography instead of a fine metal mask.

[0138] Step S13 is a step of forming a hole blocking layer 23 on the second light-emitting layer 30. In this step, an electron transport material is deposited by vapor deposition without using a fine metal mask, while adjusting the vapor deposition temperature and vapor deposition time so that the electron transport material is deposited to a predetermined film thickness.

[0139] Step S14 is a step of forming an electron transport layer 24 on the hole blocking layer 23. In this step, the electron transport material is deposited without using a fine metal mask by adjusting the deposition temperature and deposition time so that the electron transport material is deposited to a predetermined thickness. This step may be performed by depositing only the electron transport material, or by co-depositing the electron transport material and an electron donor material (e.g., lithium quinoline).

[0140] Step S15 is a process of forming the electron injection layer 25 on the electron transport layer 24. In this process, lithium fluoride is deposited without using a fine metal mask by adjusting the deposition temperature and deposition time so that the layer is deposited to a predetermined thickness.

[0141] Step S16 is a step of forming the cathode 26 on the electron injection layer 25. In this step, for example, a magnesium-silver alloy thin film is formed by vapor deposition.

[0142] [Configuration of Full-Color Light-Emitting Device] Next, the configuration of the light-emitting element 8 of the light-emitting device 4 capable of full-color display will be described with reference to Fig. 6. The light-emitting element 8R corresponds to the first light-emitting element 9 that emits red light, the light-emitting element 8G corresponds to the second light-emitting element 10 that emits green light, and the light-emitting element 8B corresponds to the third light-emitting element 11 that emits blue light. In Fig. 6, only the essential parts of the configuration of the light-emitting element 8 in the light-emitting device 4 are shown.

[0143] The light-emitting device 4 has a high-definition RGB color-separated organic EL element having a tandem structure in which two light-emitting layers, a light-emitting layer 16 and a light-emitting layer 22, are formed between an anode 12 and a cathode 26. A charge generation layer 19 is disposed between the light-emitting layer 16 and the light-emitting layer 22.

[0144] More specifically, the first light-emitting element 9 (light-emitting element 8R) that emits red light has an anode 12R, a light-emitting layer 16R, a charge generation layer 19R, a light-emitting layer 22R, and a cathode 26R arranged in this order. In the light-emitting element 8R, a set of layers 49R including the light-emitting layer 16R that is arranged between the anode 12R and the charge generation layer 19R in the stacking direction constitutes the first stack. Furthermore, a set of layers 50R including the light-emitting layer 22R that is arranged between the charge generation layer 19R and the cathode 26R constitutes the second stack.

[0145] Similarly, the second light-emitting element 10 (light-emitting element 8G) that emits green light has an anode 12G, a light-emitting layer 16G, a charge generation layer 19G, a light-emitting layer 22G, and a cathode 26G arranged in this order. The first stack in light-emitting element 8G is a set of layers 49G including light-emitting layer 16G that is arranged between anode 12G and charge generation layer 19G in the stacking direction. The second stack in light-emitting element 8G is a set of layers 50G including light-emitting layer 22G that is arranged between charge generation layer 19G and cathode 26G.

[0146] The third light-emitting element 11 (light-emitting element 8B) that emits blue light has an anode 12B, a light-emitting layer 16B, a charge generation layer 19B, a light-emitting layer 22B, and a cathode 26B stacked in this order. The first stack in light-emitting element 8B is a set of layers 49B including light-emitting layer 16B that is disposed between anode 12B and charge generation layer 19B in the stacking direction. The second stack in light-emitting element 8B is a set of layers 50B including light-emitting layer 22B that is disposed between charge generation layer 19B and cathode 26B.

[0147] Here, the cathodes 26R, 26G, and 26B are provided for the light-emitting element 8R, the light-emitting element 8G, and the light-emitting element 8B, respectively. However, the cathodes 26R, 26G, and 26B may be a common electrode layer provided across the light-emitting element 8R, the light-emitting element 8G, and the light-emitting element 8B.

[0148] 6, a sealing layer 6 is formed on the top of each of the light-emitting elements 8R, 8G, and 8B to prevent the intrusion of oxygen and moisture. The sealing layer 6 may also be a common layer provided across the light-emitting elements 8R, 8G, and 8B.

[0149] In addition, the groups 49R, 49G, and 49B, and the groups 50R, 50G, and 50B of layers included in the light-emitting elements 8R, 8G, and 8B of each color are provided with carrier function layers (electron injection layer, electron transport layer, hole transport layer, hole injection layer, etc.) not shown.

[0150] [Light Emission Mechanism] Next, a description will be given of the light emission mechanism of the light-emitting element 8. In the following description, since the light-emitting element 8R, the light-emitting element 8G, and the light-emitting element 8B all have the same light-emitting mechanism, the symbols R, G, and B that indicate colors and are added to the symbols indicating the respective basic components will be omitted.

[0151] When a current flows through the light-emitting element 8, holes are supplied from the anode 12 to the light-emitting layer 16, and electrons are supplied from the cathode 26 to the light-emitting layer 22. At this time, electrons generated in the charge generation layer 19 (electron generation layer 27) are supplied to the light-emitting layer 16, and holes generated in the charge generation layer 19 (hole generation layer 28) are supplied to the light-emitting layer 22.

[0152] As a result, in the light-emitting layer 16, electrons supplied from the charge generation layer 19 and holes supplied from the anode 12 recombine to generate electron-hole pairs (also called excitons), which transition to the ground state and emit light of a desired color (predetermined wavelength range). At the same time, in the light-emitting layer 22, electrons supplied from the cathode 26 and holes supplied from the charge generation layer 19 recombine to generate electron-hole pairs, which transition to the ground state and emit light of a desired color (predetermined wavelength range) (light of the same color as the light-emitting layer 16). For example, the light-emitting layers 16R and 22R of the light-emitting element 8R each emit red light. Similarly, the light-emitting layers 16G and 22G of the light-emitting element 8G each emit green light, and the light-emitting layers 16B and 22B of the light-emitting element 8B each emit blue light.

[0153] In this case, both the light-emitting layer 16 and the light-emitting layer 22 can emit light with a luminous efficiency substantially equal to the theoretical value. Therefore, each of the light-emitting layers of the same color arranged in the stacking direction should emit light with a luminous efficiency substantially equal to the theoretical value, contributing to the formation of a full-color image with high efficiency and high brightness.

[0154] However, the light emission amount of a conventional tandem light-emitting element that does not have the light-emitting layer configuration described in the present disclosure, i.e., a conventional tandem light-emitting element in which two light-emitting layers having the same area and emitting the same color are stacked, may not reach twice the light emission amount (i.e., the theoretical value) of a single light-emitting element having a single light-emitting layer.

[0155] Here, we present the results of our verification. First, we fabricated a light-emitting device (single prototype) having one blue-emitting layer (also called a single layer; single structure) and a tandem light-emitting device (comparison tandem prototype) having two blue-emitting layers of the same area. The layer structures of the single prototype and the comparison tandem prototype are as follows. The comparison tandem prototype was fabricated under three conditions, Conditions i to iii, below. The single prototype had the same layer structure between the anode and cathode as the first stack under Condition i. As mentioned above, the comparison tandem prototype had the same area of ​​each light-emitting layer stacked in the stacking direction, i.e., a conventional tandem light-emitting device. The device lifetime and driving voltage of each prototype were then measured, and the current efficiency was calculated using the Blue Index (unit: cd / A / y, where y is one of the chromaticity coordinates in CIE 1931).

[0156] (Single prototype) Layer structure: cathode / first stack (electron transport layer / hole blocking layer / blue light-emitting layer (thickness: 15 nm, light-emitting layer area of ​​one pixel: 50 μm×50 μm) / electron blocking layer / hole transport layer / hole injection layer) / anode Thickness ratio: The ratio of the thickness of the blue light-emitting layer (15 nm) to the thickness of the first stack (165 nm) was 0.091.

[0157] (Comparative tandem prototype) (Condition i) Layer configuration: cathode / second stack (electron injection layer / electron transport layer / hole blocking layer / second blue light-emitting layer (thickness: 15 nm, light-emitting layer area per pixel: 50 μm×50 μm) / hole transport layer / hole injection layer) / charge generation layer / first stack (electron transport layer / hole blocking layer / first blue light-emitting layer (thickness: 15 nm, light-emitting layer area per pixel: 50 μm×50 μm) / electron blocking layer / hole transport layer / hole injection layer) / anode Thickness ratio: the ratio of the thickness of the second blue light-emitting layer (15 nm) to the thickness of the second stack (70 nm) was 0.21, and the ratio of the thickness of the first blue light-emitting layer (15 nm) to the thickness of the first stack (165 nm) was 0.091.

[0158] (Condition ii) Layer structure: Same as condition i. Thickness ratio: Same as condition i, except that the thickness of the carrier functional layer in the second stack layer was adjusted to a total thickness of 80 nm. The ratio of the thickness of the second blue light-emitting layer (15 nm) to the thickness of the second stack layer (80 nm) was 0.188.

[0159] (Condition iii) Layer structure: Same as condition i. Thickness ratio: Same as condition i, except that the thickness of the carrier functional layer in the second stack layer was adjusted to a total thickness of 90 nm. The ratio of the thickness of the second blue light-emitting layer (15 nm) to the thickness of the second stack layer (90 nm) was 0.167.

[0160] As a result of prototyping and evaluation, the current efficiency of the single prototype was 206 cd / A / y. In contrast, the current efficiencies of the comparative tandem prototypes were (condition i) 305 cd / A / y (1.48 times that of the single prototype), (condition ii) 320 cd / A / y (1.55 times), and (condition iii) 219 cd / A / y (1.1 times). Furthermore, when the device lifetimes were measured, the device lifetimes of the comparative tandem prototypes were 2.01 times (condition i), 2.12 times (condition ii), and 1.92 times (condition iii) that of the single prototypes. Furthermore, when the driving voltages were measured, the driving voltages of the comparative tandem prototypes were 1.9 times (condition i), 1.9 times (condition ii), and 2.0 times (condition iii) that of the single prototypes.

[0161] From the above results, it can be seen that in tandem light-emitting devices (comparative tandem prototypes) using the conventional device design concept of adjusting the carrier balance by changing the conditions of the carrier functional layer without changing the conditions of the light-emitting layer (area, thickness, doping concentration, etc.), the device life (device reliability) is improved by approximately twice compared to a single-structure light-emitting device (single prototype) having a single light-emitting layer. On the other hand, in this conventional tandem light-emitting device, even when the conditions of the cathode-side carrier functional layer, which is known to be most effective for adjusting the carrier balance in single light-emitting devices, are variously changed, the current efficiency (light-emitting efficiency) does not reach significantly twice that of a single light-emitting device, even though the driving voltage is approximately doubled, indicating that the improvement in current efficiency is small relative to the increase in driving voltage expected from the characteristics of a single light-emitting device.

[0162] These results demonstrate that conventional tandem light-emitting devices have not achieved the desired high efficiency. One possible solution for doubling the current efficiency of conventional tandem light-emitting devices with two light-emitting layers compared with single light-emitting devices with a single light-emitting layer is to simply apply a higher driving voltage. However, adopting such a solution clearly results in increased power consumption and reduced device reliability. Thus, tandem light-emitting devices constructed according to conventional design concepts do not fully realize the advantages of adopting a tandem structure, and further investigation remains. In other words, as shown by the above-mentioned verification results, the effects of conventionally optimized carrier functional layers around the light-emitting layer other than the light-emitting layer may not be sufficient for tandem light-emitting devices. Furthermore, there remains room for investigation into a new issue: the light emission output of conventional tandem light-emitting devices with two light-emitting layers of the same area may not reach twice that of single light-emitting devices.

[0163] To address this issue, the inventors have conducted research focusing on the carrier mobility and carrier injection properties in the stacking direction of the tandem light-emitting element, as well as the amount of carriers supplied to and the amount of excess carriers generated in each of the multiple light-emitting layers of the tandem light-emitting element. Based on this research, the reasons why the efficiency and light emission amount of conventional tandem light-emitting elements have not improved as expected are considered to be as follows.

[0164] Generally, in organic materials, hole mobility is often higher than electron mobility. In such cases, the electron supply is likely to be insufficient when generating excitons necessary for radiative recombination in the light-emitting layer. However, depending on the organic material selected, electron mobility may be higher than hole mobility. In conventional single-layer light-emitting devices having a single light-emitting layer, efforts have been made to match the amounts of electrons and holes (carrier supply amounts) supplied to the light-emitting layer, i.e., to achieve carrier balance, by optimizing the thickness of the light-emitting layer, the material selection of the carrier functional layer, or the thickness of the carrier functional layer. Furthermore, as mentioned above, in conventional tandem light-emitting devices, efforts have been made to achieve carrier balance by optimizing the carrier functional layer around the light-emitting layer other than the light-emitting layer.

[0165] However, in a tandem light-emitting element having multiple light-emitting layers connected in series, although the current flowing through each light-emitting layer provided between a pair of anode and cathode is equal, in terms of carrier generation and injection, in addition to the anode and cathode directly connected to TFTs including pixel circuits and capable of directly controlling the potential, there is also a charge generation layer that is not directly connected to TFTs, etc. The inventors have found that the amount of carriers (electrons and holes) generated by this charge generation layer is prone to quantitative differences due to differences in the carrier generation and supply capabilities between the electron generation layer and the hole generation layer, and that the potential applied to the charge generation layer can only be indirectly controlled by changing the potential between the anode and cathode, which means that the balance of carriers supplied to each light-emitting layer may not be 1:1.

[0166] Furthermore, the electron generation layer constituting the charge generation layer is typically an organic-inorganic hybrid structure in which a small amount of metal material is doped into an organic electron transport material. However, in recent years, development of electron generation layers containing only organic materials, like the hole generation layer, has been progressing in order to prevent deterioration of the organic materials contained in other layers due to high deposition temperatures. However, currently, the amount of electrons supplied from an electron generation layer made entirely of organic materials can be significantly smaller than the amount of holes supplied from the hole generation layer. In this case, in a tandem light-emitting device, it becomes even more difficult to match the amount of electrons and holes supplied between two light-emitting layers adjacent to each other in the stacking direction via a charge generation layer.

[0167] Furthermore, as mentioned above, when attempting to improve light extraction efficiency using a microcavity structure, the position of the light-emitting layer cannot be arbitrarily determined; it must be located at one of several periodic positions that depend on the emission wavelength and refractive index. Due to the constraints on the position of the light-emitting layer imposed by the microcavity conditions and the phenomenon of quenching due to interactions when the anode and light-emitting layer are formed in close proximity, tandem light-emitting devices are constrained by the requirement that the thickness of the hole transport layer formed between the anode and the light-emitting layer above it must be thicker than the thickness of any other hole transport layer. However, increasing the thickness of this hole transport layer increases the probability of holes being deactivated relative to the other hole transport layers, resulting in a further carrier imbalance in which fewer holes are supplied to the light-emitting layer formed immediately above the anode. These phenomena make it even more difficult to match the supply of electrons and holes between adjacent light-emitting layers in the stacking direction in tandem light-emitting devices using a microcavity structure.

[0168] Thus, the inventors discovered that in a tandem light-emitting device, in addition to matching the electron and hole supply amounts, i.e., carrier balance, in each of the multiple light-emitting layers, it is necessary to consider the difference in exciton generation amount and carrier supply amount between the light-emitting layers, which was not necessary to consider in a single light-emitting device having a single light-emitting layer. Furthermore, they discovered that in light-emitting layers stacked via a charge generation layer, the amount of carriers supplied to the light-emitting layer stacked closer to the cathode may be greater than the amount of carriers supplied to the light-emitting layer stacked closer to the anode. Conversely, the amount of carriers supplied to the light-emitting layer stacked closer to the anode may be less than the amount of carriers supplied to the light-emitting layer stacked closer to the cathode. In this case, the amount of electron-hole pairs (excitons) generated in the light-emitting layer stacked closer to the anode decreases, and excess carriers are generated in the light-emitting layer closer to the anode. As a result, even if there are multiple light-emitting layers (even if the volume of the light-emitting layers is multiple times larger), the amount of excitons does not increase multiple times. As a result, the present inventors have found that in a conventional tandem light emitting device having two light emitting layers of the same area, the current efficiency decreases and the amount of light emitted does not double in some cases.

[0169] Therefore, the present inventors have introduced a new design concept for a tandem light-emitting device having multiple light-emitting layers connected in series. This concept solves the problems of imbalances in carrier supply between the light-emitting layers and excess carrier generation in each light-emitting layer by varying the volume (area) of each light-emitting layer according to the amount and balance of carriers supplied to each light-emitting layer, as described in the present disclosure. This makes it possible to generate an appropriate amount and balance of excitons in each light-emitting layer in the stacking direction without generating the imbalances in carrier balance and excess carriers seen in conventional tandem light-emitting devices. Furthermore, the configuration of the present disclosure also makes it possible to vary the current density (= current / light-emitting layer area) in each light-emitting layer. As described below, the present disclosure realizes a light-emitting device equipped with a tandem light-emitting device that can reduce current consumption and driving voltage and improve light-emitting efficiency and reliability.

[0170] That is, in the light-emitting layer stacked on the anode side, the generation of electron-hole pairs (excitons) is insufficient, and excess carriers that cannot become excitons are generated in this light-emitting layer. In this disclosure, the conditions of the carrier functional layer are first set so that the anode-side light-emitting layer is supplied with an appropriate amount of excitons without generating excess carriers. As a result, excessive carrier supply occurs in the cathode-side light-emitting layer. To address this, the volume (area of ​​the light-emitting layer) of the cathode-side light-emitting layer is appropriately increased. As a result, the anode-side light-emitting layer generates an amount of excitons that is substantially equal to the theoretical value, and the cathode-side light-emitting layer also generates electron-hole pairs (excitons) without generating excess carriers. Therefore, each of the light-emitting layers stacked in the stacking direction emits light with a brightness corresponding to its area. Furthermore, since the appropriate amount of excitons can be formed in each of the light-emitting layers stacked in the stacking direction while preventing the generation of excess carriers, a reduction in current consumption is achieved, thereby achieving reduced power consumption and improved reliability.

[0171] In particular, in the case of a top-emission light-emitting element in which light is extracted from the cathode side, even a slight defect in the sealing layer formed on the cathode can cause the cathode to deteriorate due to the intrusion of oxygen or moisture, resulting in a decrease in electron injection properties and, as a result, a decrease in the amount of electrons supplied to the light-emitting layer directly below the cathode. Taking this into consideration, in the present disclosure, the area of ​​the cathode-side light-emitting layer may be made even smaller than the theoretical area, as long as the effects of the present disclosure are achieved. In this way, by forming the area of ​​the cathode-side light-emitting layer smaller than the theoretical area from the initial design stage, it is possible to prevent the generation of excess holes in the cathode-side light-emitting layer of a top-emission light-emitting element.

[0172] Here, the results of simulation evaluations of examples and comparative examples of full-color light-emitting devices having two light-emitting layers in the stacking direction will be described. In the light-emitting device of the example of the present disclosure, the areas of the light-emitting layers on the anode 12 side were 10 μm × 10 μm for the red-emitting light-emitting layer 16R, 11.7 μm × 11.7 μm for the green-emitting light-emitting layer 16G (however, two green subpixels GSP are provided per pixel), and 12.5 μm × 12.5 μm for the blue-emitting light-emitting layer 16B, and the areas of the light-emitting layers on the cathode side were 12 μm × 12 μm for the red-emitting light-emitting layer 22R, 14 μm × 14 μm for the green-emitting light-emitting layer 22G, and 15 μm × 15 μm for the blue-emitting light-emitting layer 22B. The light-emitting device of the example has the layer configuration of this embodiment. The ratio of the area of ​​the anode-side light-emitting layer 16 to the area of ​​the cathode-side light-emitting layer 22 is 69.4% for the red light-emitting layers 22R and 16R, 70.2% for the green light-emitting layers 22G and 16G, and 68.8% for the blue light-emitting layers 22B and 16B. In other words, in this example, the area ratio of the anode-side light-emitting layer 16 to the cathode-side light-emitting layer 22 for all colors is approximately 70%.

[0173] On the other hand, each light-emitting layer of the comparative light-emitting device (single light-emitting element) has the same area as the cathode-side light-emitting layer 22, and is a full-color light-emitting device in which each color has a single light-emitting layer (not a tandem structure).

[0174] According to the results of a simulation under the above conditions, the current efficiency (also referred to as "luminous efficiency") of the full-color light-emitting device (tandem light-emitting device) of the above example was 1.7 times that of the full-color light-emitting device (single light-emitting device) of the above comparative example, the element life was 2.6 times, and the driving voltage was 1.7 times. These results demonstrate that the light-emitting elements of the above example achieve an improvement in luminous efficiency commensurate with the increase in driving voltage. Therefore, it can be seen that the light-emitting device equipped with the tandem light-emitting elements of the present disclosure can suppress an increase in driving voltage, extend the element life, and achieve an improvement in luminous efficiency commensurate with the increase in driving voltage, compared to a full-color light-emitting device equipped with a conventional tandem light-emitting element.

[0175] Furthermore, when the driving voltage was further increased to further improve the current efficiency (light-emitting efficiency) under the conditions of the simulation of the above example, the current efficiency doubled when the driving voltage was doubled, and the device lifetime under those conditions was also increased by 2.4 times. In other words, it can be seen that the full-color light-emitting device having two light-emitting layers in the stacking direction according to the present disclosure can achieve twice the characteristics of a single-layer full-color light-emitting device.

[0176] Furthermore, when comparing the blue light-emitting device in the above Example with that in the Comparative Example, the current efficiency of the light-emitting device in the Example is increased by 11.6% compared to that of the light-emitting device in the Comparative Example, the device life is increased by 12.1%, and the driving voltage is reduced by 11.2%. As is clear from these results, it is understood that the light-emitting device of this embodiment can achieve significant improvements in characteristics.

[0177] In addition, when a phosphorescent dopant is used in the red light-emitting layers 16R, 22R and the green light-emitting layers 16G, 22G, and a fluorescent dopant is used only in the blue light-emitting layers 16B, 22B, the device may be designed to match the conditions of the carrier functional layer (e.g., hole transport layer, electron transport layer, etc.) formed common to each color to the blue light-emitting layers 16B, 22B in order to maximize the characteristics of the blue light-emitting layers 16B, 22B, which use fluorescent dopants and have poor luminous efficiency. In this case, the configuration of the carrier functional layer for the red light-emitting layer 16R, whose emission wavelength is farther from blue, may deviate significantly from the optimal conditions, resulting in a large imbalance in the carrier balance in the red light-emitting layer 16R. In such cases, the ratio of reduction in the area of ​​the red light-emitting layer 16R on the anode side may be greater than the ratio of reduction in the areas of the green light-emitting layer 16G and blue light-emitting layer 16B on the anode side. Conversely, the ratio of reduction in the area of ​​the anode-side light-emitting layer 16B for the blue light-emitting layer 16B, 22B having inferior characteristics may be greater than the ratio of reduction in the area of ​​the anode-side red light-emitting layer 16R and green light-emitting layer 16G. By doing so, it is possible to correct the imbalance in the carrier balance of the light-emitting layer of a specific emission color, and therefore the light-emitting device of this embodiment can achieve further improvement in characteristics.

[0178] [Embodiment 2] Embodiment 2 of the present disclosure will be described below with reference to the drawings. Fig. 7 is a cross-sectional view showing only the main configuration of a light-emitting element 8A of a display device 101A (light-emitting device 4A) according to Embodiment 2 of the present disclosure. The light-emitting device 4A according to Embodiment 2 differs from the light-emitting device 4 described above in that it includes a light-emitting element 8A that includes three light-emitting layers in the stacking direction and has one charge generation layer between each pair of adjacent light-emitting layers.

[0179] In the following description of the embodiments, for the sake of convenience, the same explanations as those in the above-described embodiments will not be repeated, and components having the same functions as those described in the above-described embodiments will be denoted by the same reference numerals, and their explanations will not be repeated.

[0180] 7 , in a light-emitting element 8AR that emits red light, a light-emitting layer 43R and a charge generation layer 44R are further disposed between the cathode 26R and the light-emitting layer 22R. In the light-emitting element 8AR, a set of layers 50R including the light-emitting layer 22R that is disposed between the charge generation layer 19R and the charge generation layer 44R in the stacking direction constitutes a second stack. Furthermore, a set of layers 51R including the light-emitting layer 43R that is disposed between the charge generation layer 44R and the cathode 26R constitutes a third stack.

[0181] Similarly, in light-emitting element 8AG that emits green light, a light-emitting layer 43G and a charge generation layer 44G are further disposed between cathode 26G and light-emitting layer 22G. In light-emitting element 8AG, a set of layers 50G including light-emitting layer 22G that is disposed between charge generation layer 19G and charge generation layer 44G in the stacking direction constitutes the second stack. Furthermore, a set of layers 51G including light-emitting layer 43G that is disposed between charge generation layer 44G and cathode 26G constitutes the third stack.

[0182] In addition, in light-emitting element 8AB that emits blue light, a light-emitting layer 43B and a charge generation layer 44B are further disposed between cathode 26B and light-emitting layer 22B. In light-emitting element 8AB, a set of layers 50B including light-emitting layer 22B, which is disposed between charge generation layer 19B and charge generation layer 44B in the stacking direction, constitutes the second stack. Furthermore, a set of layers 51B including light-emitting layer 43B, which is disposed between charge generation layer 44B and cathode 26B, constitutes the third stack.

[0183] In addition, the groups 49R, 49G, and 49B, the groups 50R, 50G, and 50B, and the groups 51R, 51G, and 51B of layers included in the light-emitting elements 8AR, 8AG, and 8AB of each color have carrier functional layers (electron injection layer, electron transport layer, hole transport layer, hole injection layer, etc.) arranged therein. In the following description, the light-emitting layers 43R, 43G, and 43B included in the light-emitting elements 8AR, 8AG, and 8AB of each color are collectively referred to as "light-emitting layer 43."

[0184] 7, the cathode 26 may be a common electrode layer provided across the light-emitting elements 8AR, 8AG, and 8AB. Similarly, the sealing layer 6 may be a common layer provided across the light-emitting elements 8AR, 8AG, and 8AB.

[0185] 8 is a plan view of one light-emitting element 8 included in the display device 101A of the second embodiment, and shows three overlapping light-emitting layers, 16, 22, and 43. The minimum area 45 of the three light-emitting layers 16, 22, and 43 may be 10% or more and 90% or less of the maximum area 46 of the three light-emitting layers 16, 22, and 43. This provides the same effect as when the second area 39 is 10% or more and 90% or less of the first area 38 in the display device 101A including the three light-emitting layers 16, 22, and 43.

[0186] In the stacking direction, when the area of ​​the light-emitting layer 43 is taken as 1, the area of ​​the light-emitting layer 22 is, for example, 0.1 to 0.9, more preferably 0.3 to 0.8. Furthermore, when the area of ​​the light-emitting layer 22 is taken as 1, the area of ​​the light-emitting layer 16 is, for example, 0.1 to 0.9, more preferably 0.3 to 0.8. Within the above ranges, the areas of the light-emitting layers 16, 22, and 43 included in the light-emitting element 8A are larger on the cathode 26 side and smaller on the anode 12 side.

[0187] 7 and 8, the display device 101A including the light-emitting element 8A having three light-emitting layers in the stacking direction also prevents the supply of excess carriers (electrons or holes) in the light-emitting layer closer to the anode, and all light-emitting layers emit light with substantially theoretical luminance and luminous efficiency, as in the display device 101 shown in Fig. 6. That is, the display device 101A of this embodiment 2 can suppress an increase in driving voltage, extend the element life, and achieve an improvement in luminous efficiency commensurate with the increase in driving voltage.

[0188] 9 is a cross-sectional view showing a schematic configuration of a display device 101B according to a third embodiment of the present disclosure. In the display device 101B, the first light-emitting element 9 and the second light-emitting element 10 are adjacent to each other in the second direction X2, and the first charge generation layer 35 may be continuous with the charge generation layer 42 of the second light-emitting element 10.

[0189] By adopting a configuration in which the charge generation layer is continuous between a plurality of light emitting elements as in the third embodiment, it is possible to reduce the number of steps in which a mask is used during manufacturing.

[0190] [Major Effects] The light-emitting device of the present disclosure has multiple light-emitting layers stacked in the stacking direction for each emitted color, with the areas of the layers being larger on the cathode side and smaller on the anode side. With this configuration, an appropriate number of excitons are generated in each light-emitting layer in the stacking direction, while preventing the generation of excess carriers, thereby achieving light emission with nearly theoretical brightness and efficiency.

[0191] Furthermore, the excess carriers that are unnecessarily formed cannot be eliminated by radiative recombination, but instead generate heat and become deactivated, which causes deterioration of the light-emitting element. However, the light-emitting device of the present disclosure can suppress the generation of excess carriers in each of the stacked light-emitting layers, thereby suppressing thermal deactivation due to the excess carriers and improving element reliability.

[0192] Therefore, the light emitting device of the present disclosure realizes a tandem light emitting device that is more efficient, brighter, and more reliable than a light emitting device having conventional tandem light emitting elements in which the areas of the light emitting layers in the stacking direction are the same.

[0193] In addition, by gradually increasing the area of ​​the light-emitting layer from the anode side to the cathode side in the stacking direction, the above-mentioned effects of improving the light-emitting efficiency, brightness, reliability, and reducing power consumption can be achieved throughout the entire stacking direction of the light-emitting element.

[0194] Furthermore, by using a host-guest light-emitting layer as the light-emitting layer, high luminous efficiency and improved device life can be achieved, and according to the present disclosure, the carrier balance (balance between electrons and holes) in each light-emitting layer can be further improved, which is advantageous from the viewpoint of being able to fully utilize the performance of each host-guest light-emitting layer, which has high luminous efficiency and excellent life.

[0195] Furthermore, when the light-emitting layer includes a fluorescent-emitting layer containing a fluorescent dopant and a phosphorescent-emitting layer containing a phosphorescent dopant, the number of fluorescent-emitting layers in the stacking direction may be greater than the number of phosphorescent-emitting layers, for example, by 1 or 2. This configuration is even more effective from the viewpoint of optimizing the balance between the lifetime and the amount of light emitted between the fluorescent-emitting layer and the phosphorescent-emitting layer.

[0196] Furthermore, by using only the same color for the multiple light-emitting layers stacked in the stacking direction, it is advantageous in terms of improving color purity in a light-emitting device that enables full-color display by painting each of the RGB colors separately. Furthermore, when the same material that emits the same color is stacked in each light-emitting layer, it becomes easier to evaluate the carrier injection property and carrier transport property between each light-emitting layer by simulation. Thus, the above configuration is even more effective in terms of more easily realizing a light-emitting device capable of full-color display that includes light-emitting elements having desired characteristics.

[0197] The number of light-emitting layers in the stacking direction may be from 2 to 5. This configuration is even more effective in terms of improving light-emitting efficiency, extending life, and reducing driving voltage.

[0198] In addition, the ratio of the area of ​​the light-emitting layer closest to the cathode to the area of ​​the other light-emitting layers in the stacking direction may be 0.1 or more and 0.9 or less, which is even more effective from the viewpoints of realizing a longer life, improved luminous efficiency, and reduced driving voltage.

[0199] The light emitting device of the present disclosure may also be a top-emission type, which is even more effective in terms of optimizing the thickness of the carrier functional layer.

[0200] Furthermore, the display device of the present disclosure includes the light-emitting device described above. Therefore, the area of ​​the anode-side light-emitting layer is reduced by the area that does not contribute to light emission, which is advantageous from the viewpoint of realizing high-brightness, high-resolution image display and power saving compared to display devices including conventional light-emitting devices in which the area that does not contribute to light emission is not reduced. Therefore, according to the present disclosure, the display device achieves high-brightness and power-saving light emission, and the advantages of adopting a tandem structure in the light-emitting device can be fully realized.

[0201] Furthermore, in the light-emitting device of the present disclosure, forming at least the light-emitting layer by vapor deposition is extremely advantageous in that the area of ​​each light-emitting layer can be controlled with high precision compared to forming the light-emitting layer by a coating method using an inkjet device or the like. Furthermore, since it is possible to form a host-guest light-emitting layer, this is advantageous in realizing a light-emitting device capable of full-color display. In addition, it is also advantageous in realizing high-precision control of the thickness of each light-emitting layer. From the perspective of forming the light-emitting layer area with high precision, a photolithography method may also be used.

[0202] Furthermore, in the manufacture of the light-emitting device of the present disclosure, light-emitting layers having different areas in the stacking direction may be formed by changing only the deposition mask. This configuration allows light-emitting layers having different areas to be formed using the same manufacturing equipment while applying the same conditions except for the deposition mask, which is even more effective in terms of reducing manufacturing costs and improving productivity.

[0203] In addition, in light-emitting devices including light-emitting elements having multiple light-emitting layers, the area of ​​the light-emitting layers in the stacking direction is usually constant. On the other hand, there are also technologies in which the areas of the light-emitting layers in the stacking direction vary (e.g., JP 2005-285401 A, JP 2013-229218 A, etc.), and some technologies include a light-emitting layer with a larger area on the cathode side and a light-emitting layer with a smaller area on the anode side (e.g., JP 2005-285401 A, etc.). However, this conventional technology involves providing a charge inversion layer having an inorganic semiconductor pn junction consisting of a p-type semiconductor layer arranged on the cathode (cathode) side and an n-type semiconductor layer arranged on the anode (anode) side between the light-emitting units (light-emitting layers), which differs from the configuration of a light-emitting device equipped with a tandem light-emitting element in which a charge generation layer containing an organic material is provided between the light-emitting layers as disclosed herein. Furthermore, in the above publication, the area of ​​the light-emitting unit is increased upward in the stacking direction in order to prevent the end of the charge inversion layer made of an inorganic semiconductor from shorting out with the electrode, and is not intended to adjust the carrier balance as in the present disclosure. Furthermore, the above publication provides a highly efficient light-emitting element that can replace conventional lighting light sources such as lamps, and does not disclose a display device that achieves a full-color display by painting each of the RGB colors separately with high resolution.

[0204] According to the present disclosure, in an electroluminescent display device, it is possible to achieve even higher luminous efficiency, higher brightness, and / or power saving by controlling the area of ​​each light-emitting layer in the stacking direction. Therefore, the light-emitting device and display device of the present disclosure are expected to contribute to the achievement of, for example, Goal 9.4 of the Sustainable Development Goals (SDGs) proposed by the United Nations, which states, "Improve sustainability by improving infrastructure and industry through increased resource efficiency and the expanded adoption of clean technologies and environmentally friendly technologies and industrial processes."

[0205] [Additional Notes] The present inventors have developed a new design concept for achieving carrier balance among multiple light-emitting layers by varying the area in a planar view as a means for varying the volume of the light-emitting layers, as disclosed herein. This enables exciton generation without excess carrier generation in each light-emitting layer, which was not possible with conventional tandem light-emitting devices. As a result, it has become possible to realize a light-emitting device that can reduce current consumption and driving voltage and improve light-emitting efficiency and reliability.

[0206] Specifically, when the amount of holes supplied from the anode is smaller than the amount of electrons supplied from the charge generation layer (electron generation layer), and / or when the amount of holes supplied from the anode and the amount of electrons supplied from the charge generation layer (electron generation layer) are smaller than the amount of holes supplied from the charge generation layer (hole generation layer) and the amount of electrons supplied from the cathode, the amount of excitons generated in the light-emitting layer formed on the anode side is reduced, and therefore the area of ​​the light-emitting layer formed on the anode side is reduced. In this case, the anode-side light-emitting layer is formed so that the area ratio of the anode-side light-emitting layer to the cathode-side light-emitting layer in the stacking direction is 1 / 10 or more and 9 / 10 or less. More preferably, the area ratio of the anode-side light-emitting layer to the cathode-side light-emitting layer is 3 / 10 or more and 4 / 5 or less.

[0207] 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.

[0208] REFERENCE SIGNS LIST 1 Substrate 2 Buffer layer 3 TFT layer 4 Light-emitting device 5 Edge cover film 6 Sealing layer 7 External functional layer 8 Light-emitting element 9 First light-emitting element 10 Second light-emitting element 11 Third light-emitting element 12, 36 Anode 13 Hole injection layer 14, 20 Hole transport layer 15, 21 Electron blocking layer 16, 22, 43 Light-emitting layer 17, 23 Hole blocking layer 18, 24 Electron transport layer 19, 42, 44 Charge generation layer 25 Electron injection layer 26, 37 Cathode 27, 40 Electron generation layer 28, 41 Hole generation layer 29 First light-emitting layer 30 Second light-emitting layer 31 Third light-emitting layer 32 Fourth light-emitting layer 33 Fifth light-emitting layer 34 Sixth light-emitting layer 35 First charge generation layer 38 First area 39 Second area 42 Second charge generation layer 45 Minimum area of ​​three or more light-emitting layers 46 Maximum area of ​​three or more light-emitting layers 47 Third charge generation layer 49, 50, 51 Collection of layers 101, 101A, 101B Display device X1 First direction X2 Second direction

Claims

1. A light-emitting device having a plurality of light-emitting elements emitting light of different colors, the plurality of light-emitting elements including a first light-emitting element, the first light-emitting element having an anode and a cathode, a first light-emitting layer located between the anode and the cathode and emitting light of a first color, a second light-emitting layer located between the first light-emitting layer and the cathode and emitting light of the same color as the first color, and a first charge generation layer located between the first light-emitting layer and the second light-emitting layer, the first light-emitting layer having a first area and the second light-emitting layer having a second area larger than the first area.

2. The light emitting device of claim 1, wherein the first area is greater than or equal to 10% and less than or equal to 90% of the second area.

3. The light-emitting device according to claim 1 or 2, wherein the first charge generation layer comprises: an electron generation layer containing an organic material and generating electrons; and a hole generation layer located between the electron generation layer and the second light-emitting layer, the hole generation layer containing an organic material and generating holes.

4. The light emitting device according to claim 3, wherein no pn junction is formed at the interface between said electron generating layer and said hole generating layer.

5. The conductivity of the electron generating layer is 1.0×10 －１０ The light emitting device according to claim 3 , wherein the resistivity is equal to or more than 1.0 S / m and equal to or less than 1.0 S / m.

6. The conductivity of the hole generating layer is 1.0×10 －１０ The light emitting device according to claim 3 , wherein the resistivity is equal to or greater than 1.0 S / m and equal to or less than 1.0 S / m.

7. The light-emitting device according to any one of claims 1 to 6, wherein the first light-emitting element has three or more light-emitting layers including the first light-emitting layer and the second light-emitting layer, emitting light of the same color as the first color, and two or more charge generation layers including the first charge generation layer, one charge generation layer being located between every two adjacent ones of the three or more light-emitting layers, and the minimum value of the area of ​​the three or more light-emitting layers is 10% or more and 90% or less of the maximum value of the area of ​​the three or more light-emitting layers.

8. The light emitting device according to any one of claims 1 to 7, wherein the plurality of light emitting elements include a second light emitting element that emits light of a second color different from the first color, and a third light emitting element that emits light of a third color different from both the first color and the second color.

9. The light-emitting device described in claim 8, wherein in the first light-emitting element, the first light-emitting layer, the first charge generation layer, and the second light-emitting layer are positioned side by side in a first direction, and the first light-emitting element, the second light-emitting element, and the third light-emitting element are positioned side by side in a second direction perpendicular to the first direction.

10. The light emitting device according to claim 9, wherein the first light emitting element and the second light emitting element are adjacent to each other in the second direction, and the first charge generation layer is continuous with the charge generation layer of the second light emitting element.

11. The light-emitting device according to claim 9, wherein the first light-emitting element and the second light-emitting element are adjacent to each other in the second direction, and the first charge generation layer is separated from the charge generation layer of the second light-emitting element.

12. The light emitting device of any one of claims 8 to 11, wherein one of the first color, the second color, and the third color is red; another one of the first color, the second color, and the third color is green; and the remaining one of the first color, the second color, and the third color is blue.

13. A display device comprising a light-emitting device according to any one of claims 1 to 12.

14. A method for manufacturing a light-emitting device according to any one of claims 1 to 12, wherein the light-emitting device has a plurality of the first light-emitting elements and a plurality of second light-emitting elements, and each of the first light-emitting layers is formed using a first deposition mask having a plurality of first openings formed therein, each of which corresponds to the first light-emitting layer, and each of the second light-emitting layers is formed using a second deposition mask having a plurality of second openings formed therein, each of which corresponds to the second light-emitting layer and has an area larger than an area of ​​the first openings.

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