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

Abstract

The present disclosure provides technology capable of sufficiently expressing the advantage of adopting a tandem structure for light-emitting elements of at least one color in a light-emitting device including light-emitting elements of at least two colors. A light-emitting device (110) includes a blue light-emitting element (111B) having a tandem structure. The blue light-emitting element (111B) includes: specific light-emitting layers (14B, 34B) including a specific guest compound at a specific concentration; and a charge generation layer (20) having a specific carrier generation characteristic.

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 In order to further improve the luminous efficiency of organic EL elements, developments are being made 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 or hole) transport layer, or carrier (electron or hole) injection layer of an organic EL element.

[0005] (2) A fluorescent material, a phosphorescent material, or a combination of 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 device life (the period during which desired characteristics can be maintained) of organic EL devices, the following (4) and (5) have been further investigated.

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

[0009] (5) A tandem structure is adopted for the element structure of the light-emitting element (see, for example, Patent Documents 1 to 4).

[0010] Japanese Patent Publication No. 2007-329054 International Publication No. 2010 / 113493 Japanese Patent Publication No. 2020-4970 Korean Patent Publication No. 10-2018-0013527

[0011] However, when light-emitting elements of two or more colors are regularly arranged in the display area, as in a full-color light-emitting device, and a tandem structure is adopted for the light-emitting layers of some colors, the advantages of adopting a tandem structure may not be fully realized.

[0012] An object of one embodiment of the present disclosure is to provide a technique that can fully utilize the advantages of employing a tandem structure for light-emitting elements of one or more colors in a light-emitting device including light-emitting elements of two or more colors.

[0013] In order to solve the above-described problems, a light-emitting device according to one aspect of the present disclosure includes a plurality of light-emitting elements arranged in a first direction, the light-emitting elements adjacent to each other in the first direction emitting light of different colors, each of the light-emitting elements including a cathode, a light-emitting layer, and an anode, in this order, in a second direction intersecting the first direction, and the light-emitting element emitting light of at least a specific color among a plurality of emission colors of the plurality of light-emitting elements includes a specific light-emitting layer, which is each of two or more light-emitting layers arranged to overlap each other in the second direction and emitting light of the same specific color, and an electron-generating layer located on the anode side between two of the specific light-emitting layers adjacent to each other in the second direction, and generating electrons. and a hole generation layer located on the cathode side between two of the specific light-emitting layers adjacent to each other in the second direction and generating holes, wherein the two or more specific light-emitting layers that emit light of the same specific color all contain the same type of host compound and the same or different types of guest compound, the concentration of the guest compound in each of the two or more specific light-emitting layers is higher in the specific light-emitting layer located closer to the cathode, the guest compound in at least the specific light-emitting layer located closest to the anode is an electron-transporting material, and the amount of holes injected from the hole generation layer into the specific light-emitting layer on the cathode side is greater than the amount of electrons injected from the electron generation layer into the specific light-emitting layer on the anode side.

[0014] In order to solve the above problem, a display device according to one aspect of the present disclosure includes the above light-emitting device.

[0015] In addition, in order to solve the above problem, a manufacturing method for a light-emitting device according to one embodiment of the present disclosure includes a step of alternately stacking the light-emitting layer of the light-emitting element, which emits light in at least one color among a plurality of light-emitting colors of the light-emitting element, and the charge generation layer, and in the stacking step, the light-emitting layer is formed by a vapor deposition method.

[0016] According to one aspect of the present disclosure, it is possible to fully utilize the advantages of employing a tandem structure for light emitting elements of one or more colors in a light emitting device including light emitting elements of two or more colors.

[0017] FIG. 1 is a diagram schematically illustrating the configuration of a display device according to embodiment 1 of the present disclosure. FIG. 2 is a diagram schematically illustrating the configuration of a light-emitting device according to embodiment 1 of the present disclosure. FIG. 3 is a flowchart illustrating an example of a manufacturing method for a light-emitting device according to embodiment 1 of the present disclosure. FIG. 4 is a diagram schematically illustrating the movement of carriers in a tandem light-emitting element according to embodiment 1 of the present disclosure. FIG. 5 is a diagram schematically illustrating the configuration of a light-emitting device according to embodiment 2 of the present disclosure. FIG. 6 is a diagram illustrating a model of a light-emitting element in a reference experimental example in the present disclosure.

[0018] [Summary] In a tandem light-emitting device having two or more light-emitting layers and a charge generation layer (electron generation layer and / or hole generation layer) interposed between two adjacent light-emitting layers, optimizing the carrier (electron and / or hole) supply amount in one light-emitting layer relative to the charge generation layer may result in a deviation from the optimal value in the other light-emitting layer. As a result, an imbalance in carrier balance may occur among multiple light-emitting layers included in the same light-emitting device. Here, in a tandem light-emitting device in which multiple light-emitting layers are arranged in series between a cathode and an anode, according to Kirchhoff's first law, the amount of current flowing through each light-emitting layer is the same. In the present disclosure, the concentration of the guest compound in the anode-side light-emitting layer, which has an insufficient rate-limiting carrier (hole) injection amount, is reduced compared to the concentration of the guest compound in the cathode-side light-emitting layer (the concentration of the guest compound in the cathode-side light-emitting layer is increased compared to the concentration of the guest compound in the anode-side light-emitting layer). This optimizes the carrier balance of all light-emitting layers in the tandem light-emitting device.

[0019] In this disclosure, "concentration" refers to a concentration based on weight unless otherwise specified, and in this case, the concentration is also referred to as "weight concentration." Furthermore, "to" refers to a range including both ends unless otherwise specified.

[0020] [Light-Emitting Device] The light-emitting device according to the present disclosure has a plurality of light-emitting elements arranged in a first direction, and adjacent light-emitting elements in the first direction emit light of different colors. Such an arrangement of the light-emitting elements can be realized in the same manner as a known light-emitting device having a plurality of light-emitting elements that emit light of each of a plurality of colors. For example, the light-emitting elements that emit light of different colors in the light-emitting device may be arranged parallel to each other along the first direction or in a pentile array.

[0021] In the present disclosure, "adjacent" refers to a positional relationship in which specific components in a light-emitting device are adjacent to each other in a specific direction (first direction or second direction). Therefore, adjacent specific components may be adjacent to each other, or another component may be interposed between the specific components.

[0022] In the light-emitting device according to the present disclosure, the light-emitting element that emits light of a specific color may be a light-emitting element having a specific tandem structure, which will be described later. In the light-emitting device according to the present disclosure, the light-emitting element that emits light of other colors may be a light-emitting element having a single structure, a light-emitting element having a normal tandem structure, or a light-emitting element having a specific tandem structure. The single structure and normal tandem structure of the light-emitting element that emits light of other colors may employ the element structure of the light-emitting element known in the art for OLEDs.

[0023] [Light-emitting element] Each light-emitting element in the present disclosure includes a cathode, a light-emitting layer, and an anode, in this order, in a second direction intersecting the first direction. The second direction is also referred to as the "stacking direction." The first direction is a direction intersecting the second direction and is also referred to as the "plane direction."

[0024] In the present disclosure, among a plurality of light-emitting elements, a light-emitting element that emits light of a specific color has a specific tandem structure. Hereinafter, a light-emitting element having a specific tandem structure in the present disclosure (hereinafter also referred to as the "tandem light-emitting element of the present disclosure") will be described.

[0025] The tandem light-emitting device of the present disclosure has two or more specific light-emitting layers that are stacked in the second direction and emit light of the same specific color, and each of the two or more specific light-emitting layers that emit light of the same specific color contains the same host compound and a guest compound that may be different from each other.

[0026] The tandem light-emitting device of the present disclosure also has, as charge generation layers, an electron generation layer located on the anode side between two light-emitting layers adjacent in the second direction and generating electrons, and a hole generation layer located on the cathode side and generating holes. When the tandem light-emitting device of the present disclosure includes a configuration that satisfies the following requirements, the carrier balance in each of the light-emitting layers in the tandem light-emitting device of the present disclosure is optimized. The tandem light-emitting device of the present disclosure can be realized by utilizing a known configuration for an OLED, as long as the following requirements are satisfied.

[0027] First, in the tandem light-emitting device of the present disclosure, the concentration of the guest compound in the specific light-emitting layer is higher toward the cathode (the farther from the anode in the second direction). In the present disclosure, the concentration of the guest compound in the specific light-emitting layer on the cathode side is different from the concentration of the guest compound in the specific light-emitting layer on the anode side, thereby appropriately adjusting the carrier balance in both specific light-emitting layers. As a result, the generation of excess carriers in the specific light-emitting layer is suppressed, resulting in a light-emitting device with reduced power consumption and excellent reliability. The above configuration is preferable from the viewpoint of suppressing excessive carrier injection into either specific light-emitting layer in the tandem light-emitting device of the present disclosure.

[0028] In the tandem light-emitting device of the present disclosure, if the ratio of the concentrations of the guest compound between the specific light-emitting layers is too large, self-quenching may occur in the specific light-emitting layer on the cathode side, where the concentration of the guest compound is higher, and excitons generated in the specific light-emitting layer may be consumed by the self-quenching, and sufficient excitons may not be generated in the specific light-emitting layer on the anode side, where the concentration of the guest compound is lower. From the viewpoint of realizing the consumption and generation of excitons in each specific light-emitting layer, of two specific light-emitting layers adjacent to each other in the second direction, the concentration of the guest compound in the specific light-emitting layer on the cathode side is preferably no more than 2 times, more preferably no more than 1.9 times, and even more preferably no more than 1.7 times the concentration of the guest compound in the specific light-emitting layer on the anode side.

[0029] On the other hand, the concentration of the guest compound in the specific light-emitting layer on the cathode side is preferably higher than that in the specific light-emitting layer on the anode side, more preferably at least 1.1 times, and even more preferably at least 1.3 times. As an optimal range of the weight concentration of the guest compound, the concentration range of the guest compound in the specific light-emitting layer on the cathode side is preferably more than 0.01% and 15% or less, and the concentration range of the guest compound in the specific light-emitting layer on the anode side is preferably 0.01% or more and 10% or less.

[0030] The concentration of the guest compound in the specific light-emitting layer is expressed as the mass of the guest compound relative to the sum of the mass of the host compound and the mass of the guest compound in the specific light-emitting layer. The concentration of the guest compound can be measured using known instrumental analysis. Examples of known instrumental analysis include emission spectrum measurement, emission time-resolved characteristic measurement, absorption spectrum measurement, １ H-NMR, １３ These include C-NMR, mass spectrometry, and a combination of at least two of these techniques.

[0031] The concentration of the guest compound in each specific light-emitting layer in the tandem light-emitting device of the present disclosure can be determined as appropriate based on various factors, such as the combination of materials for each layer in the light-emitting device and the concentration of the guest compound in the specific light-emitting layer, within the scope of the technical concept of the present disclosure.

[0032] The concentration of the guest compound in a specific light-emitting layer of a tandem light-emitting device according to the present disclosure can be determined, for example, by the following method. That is, for a light-emitting device of a specific emission color having two or more light-emitting layers stacked in the second direction, multiple (e.g., 3 to 5) types of light-emitting device samples are prepared by keeping the guest compound concentration in the light-emitting layer closest to the cathode constant and appropriately varying the guest compound concentration in the light-emitting layer closest to the anode, and then measuring the light-emitting characteristics of the samples. This measurement result is designated as the first measurement result. Alternatively, multiple (e.g., 3 to 5) types of light-emitting device samples are prepared by keeping the guest compound concentration in a specific light-emitting layer closest to the anode constant and appropriately varying the guest compound concentration in the light-emitting layer closest to the cathode, and then measuring the light-emitting characteristics of the samples. This measurement result is designated as the second measurement result. Based on at least one of the first measurement result and the second measurement result, a desired (e.g., optimal) combination of guest compound concentrations in the light-emitting layers is selected.

[0033] In the tandem light-emitting device of the present disclosure, the guest compound in at least the specific light-emitting layer closest to the anode is an electron-transporting material. The term "electron-transporting material" refers to a material in which electrons are relatively stable and which is characterized by electron transport in response to an electric field. This configuration is also preferable from the viewpoint of suppressing excessive carrier injection in any of the specific light-emitting layers in the tandem light-emitting device of the present disclosure.

[0034] The guest compounds in each specific light-emitting layer in the tandem light-emitting device of the present disclosure may be the same or different. It is preferable that the guest compounds in the specific light-emitting layers of each color are the same material, from the viewpoint of facilitating the production of the tandem light-emitting device of the present disclosure. In the tandem light-emitting device of the present disclosure, the guest compound in at least the specific light-emitting layer located closest to the cathode in the second direction may be a hole-transporting material. The term "hole-transporting material" refers to a material in which holes exist relatively stably and are transported by an electric field. In this way, by using an electron-transporting material as the guest compound in the specific light-emitting layer on the anode side and a hole-transporting material as the guest compound in the specific light-emitting layer on the cathode side, it becomes easier to adjust the carrier balance between the two specific light-emitting layers. In the tandem light-emitting device of the present disclosure, using a hole-transporting material as the guest compound in the specific light-emitting layer on the cathode side is preferable from the viewpoint of further improving the characteristics (e.g., luminous efficiency and lifespan) of the tandem light-emitting device of the present disclosure.

[0035] Furthermore, in the tandem light-emitting device of the present disclosure, the amount of holes injected from the hole generation layer into the specific light-emitting layer on the cathode side is greater than the amount of electrons injected from the electron generation layer into the specific light-emitting layer on the anode side. Here, "the amount of holes injected is greater than the amount of electrons injected" means that when a specific voltage is applied to the tandem light-emitting device of the present disclosure, the amount of holes generated in the hole generation layer and injected into the specific light-emitting layer closest to it is greater than the amount of electrons generated in the electron generation layer and injected into the specific light-emitting layer closest to it.

[0036] In the tandem light-emitting device of the present disclosure, satisfying such a relationship between the amount of charge injection of the hole generation layer and the electron generation layer into the specific light-emitting layer is preferable from the viewpoint of suppressing excessive injection of carriers into either specific light-emitting layer in the tandem light-emitting device of the present disclosure. Furthermore, since the electron transport property or hole transport property in the specific light-emitting layer is enhanced in the tandem light-emitting device of the present disclosure, it is preferable from the viewpoint of suppressing the device voltage in the tandem light-emitting device of the present disclosure to not more than twice that of a single structure and realizing highly efficient light emission.

[0037] The amount of injected charge can be confirmed by preparing a fabricated sample having an electrode and a charge generation layer (an electron generation layer and a hole generation layer) and detecting the amount of electrons and the amount of holes generated when a specific voltage is applied to the electrodes of the sample. To detect the amount of generated carriers, a common method is to first measure current and then calculate and compare the current densities from the current value and the electrode area. However, the method for detecting the amount of generated carriers in the present disclosure is not limited to this.

[0038] As described above, the tandem light-emitting device of the present disclosure has three characteristics: (1) the amount of holes injected from the hole generation layer into the specific light-emitting layer on the cathode side is greater than the amount of electrons injected from the electron generation layer into the specific light-emitting layer on the anode side; (2) the guest compound in at least the specific light-emitting layer located closest to the anode is an electron-transporting material; and (3) the concentration of the guest compound in the specific light-emitting layer increases toward the cathode side. Therefore, excessive carrier injection into any of the specific light-emitting layers is prevented, and the specific light-emitting layers have high electron-transporting or hole-transporting properties. That is, in the tandem light-emitting device of the present disclosure, the supply of holes to the specific light-emitting layer on the cathode side is promoted, and the electron-transporting properties of the specific light-emitting layer on the anode side are promoted. Therefore, the light-emitting intensity and efficiency of the specific light-emitting layer on the cathode side and the specific light-emitting layer on the anode side are optimized. As a result, the device voltage of the tandem light-emitting device of the present disclosure is kept substantially at most twice that of a single light-emitting device, resulting in highly efficient light emission.

[0039] The light-emitting element of the present disclosure can employ various configurations as long as the above-described requirements are satisfied, and such various configurations can be realized by using materials known in OLEDs in known methods. Specific information on materials that can be used in the present disclosure will be described later.

[0040] For example, each of the light-emitting elements according to the present disclosure may have a fluorescent-emitting layer in which the guest compound is a fluorescent dopant, or a phosphorescent-emitting layer in which the guest compound is a phosphorescent dopant. By employing a light-emitting layer doped with a fluorescent or phosphorescent dopant as a guest compound in a specific light-emitting layer, the device life of the light-emitting element can be dramatically improved. This is because the dopant, which is a guest compound, functions as a trap for carriers (electrons or holes) in the solid medium of the host compound, serves as a carrier recombination center, and directly generates excitons in the solid medium.

[0041] Here, the process by which the exciton relaxes 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 (light emission). Of these, the phenomenon of light emission due to the radiative process is called electroluminescence (EL). The guest compound functions as a carrier trap, which not only improves the quantum efficiency of the light-emitting layer but also improves the carrier recombination probability, thereby improving the device life due to the improved recombination probability. In this way, the luminous efficiency of the light-emitting layer and the device life of the light-emitting device are improved. In this way, the host-guest light-emitting layer effectively utilizes carriers, which is advantageous for improving the high luminous efficiency of the light-emitting layer and the device life of the light-emitting device.

[0042] The excitons generated during carrier recombination are classified into singlet excitons and triplet excitons. In a fluorescent-emitting layer that uses a fluorescent dopant as a guest compound, singlet excitons contribute to light emission. In a phosphorescent-emitting layer that uses a phosphorescent dopant as a guest compound, 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, in the "fluorescence" emission process in a fluorescent-emitting layer that is emitted only from singlet excitons, the generation probability of excitons that can contribute to light emission is at most 25%.

[0043] In contrast, in a phosphorescent-emitting layer, light can be extracted from triplet excitons, thereby increasing the quantum efficiency by three times compared to that of a fluorescent-emitting layer. Furthermore, due to 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, the quantum efficiency of a phosphorescent-emitting layer can be increased by up to four times compared to that of a fluorescent-emitting layer.

[0044] On the other hand, complexes containing platinum-group elements such as iridium or palladium, which are phosphorescent dopants, are very expensive even in small amounts, due to the limited production of platinum-group elements and their uneven distribution in production areas. Therefore, it may be difficult to stably supply them. Therefore, reducing the amount of phosphorescent dopants used, which have the inherent problem of making them difficult to stably supply, may be preferable from the perspective of cost reduction and economic security.

[0045] Any of the specific light-emitting layers in the tandem light-emitting device of the present disclosure may be a fluorescent light-emitting layer. In conventional light-emitting devices, the blue light-emitting layer is typically a fluorescent light-emitting layer, and the red and green light-emitting layers are typically phosphorescent light-emitting layers. As mentioned above, the quantum efficiency of a fluorescent light-emitting layer is lower than that of a phosphorescent light-emitting layer. Therefore, the amount of light emitted may be balanced by increasing the amount of current passed through the blue light-emitting layer relative to the amount of current passed through the red and green light-emitting layers. In this case, only the lifespan of the blue light-emitting layer is shortened (the deterioration rate is accelerated). Using a fluorescent light-emitting layer as the specific light-emitting layer in a tandem light-emitting device is advantageous for balancing the lifespan and the amount of light emitted between the light-emitting device with the fluorescent light-emitting layer and the light-emitting device with the phosphorescent light-emitting layer when both a fluorescent light-emitting layer and a phosphorescent light-emitting layer are used.

[0046] Furthermore, it is preferable that the peak wavelength of the emission spectrum of the specific light-emitting layer in the tandem light-emitting device of the present disclosure be 440 nm or more and 660 nm or less from the viewpoint of application to full-color display with a sufficiently wide color gamut that can be expressed. In the tandem light-emitting device of the present disclosure, each specific light-emitting layer may be a light-emitting layer that emits light with a peak wavelength of 430 nm or more and 470 nm or less. A light-emitting layer that emits light with a peak wavelength of 430 nm or more and 470 nm or less is a so-called blue light-emitting layer. In general, the thickness of the blue light-emitting layer and its associated carrier functional layer is thinner than the thickness of light-emitting layers of other colors, such as red or green, and their associated carrier functional layers. Therefore, applying a blue light-emitting layer as a specific light-emitting layer to a tandem light-emitting device is advantageous from the viewpoint of balancing the thickness with light-emitting elements of other colors.

[0047] In the tandem light-emitting device of the present disclosure, two specific light-emitting layers adjacent to each other in the second direction each emit light of a specific color, i.e., the same color. Basically, 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 light of the same color. However, in the top-emission structure described below, the emission peak wavelength of each specific light-emitting layer in the tandem light-emitting device of the present disclosure may vary due to differences in the microcavity structure of each color. Furthermore, in the tandem light-emitting device of the present disclosure, the guest compound may be different for each specific light-emitting layer, and therefore, the emission spectrum may change due to the different guest compounds.

[0048] In the present disclosure, the term "same color" refers to a commonality in which the emission spectra of two or more specific light-emitting layers have a color that can be said to be substantially the same. From the viewpoint of the isochromaticity of the two or more specific light-emitting layers in the tandem light-emitting device of the present disclosure, the difference in peak wavelengths of the emission spectra of the two or more specific light-emitting layers in the tandem light-emitting device of the present disclosure is preferably 10 nm or less. From the viewpoint of the isochromaticity, the difference in peak wavelength is more preferably ±5 nm or less, and the smaller the difference, the better.

[0049] In addition, a small difference in the peak wavelengths between two specific light-emitting layers adjacent to each other in the second direction in the tandem light-emitting device of the present disclosure is preferable from the viewpoint of improving color purity and widening the color gamut. Therefore, from the viewpoint of further improving the isochromatism, it is more preferable that the difference in the peak wavelengths between two specific light-emitting layers adjacent to each other in the second direction in the tandem light-emitting device of the present disclosure be 10 nm or less. If the difference in peak wavelengths is large, the situation will be equivalent to a broad emission wavelength, and as a result, the color purity will decrease, which may lead to a decrease in the color gamut.

[0050] Furthermore, a small difference in peak wavelength is also advantageous from the viewpoint of suppressing a decrease in efficiency. When the difference in peak wavelength between two light-emitting layers adjacent to each other in the second direction is large, for example, when a blue light-emitting layer and a green light-emitting layer are stacked, a blue color filter is required to extract blue light, and a green color filter is required to extract green light. In this case, the light that is not extracted is absorbed by the color filter, which may result in a decrease in the emission brightness of the tandem light-emitting device, i.e., a decrease in light-emitting efficiency. Tandem light-emitting devices of the same color do not require the above-mentioned color filters, so light absorption by the color filters does not occur and high light-emitting efficiency can be maintained.

[0051] From the viewpoint of isochromaticity, it is preferable that the maximum full width at half maximum at the peak wavelength of all the emission spectra of the plurality of specific light-emitting layers in the tandem light-emitting device of the present disclosure is 1.25 times or less the minimum full width at half maximum. From the viewpoint of isochromaticity, it is more preferable that the ratio of the maximum full width at half maximum to the minimum full width at half maximum is smaller.

[0052] From the viewpoint of further enhancing isochromaticity, in the two specific light-emitting layers adjacent to each other in the second direction in the tandem light-emitting device of the present disclosure, the full width at half maximum at the peak wavelength of the emission spectrum of the specific light-emitting layer on the anode side is preferably 0.75 to 1.25 times the full width at half maximum at the peak wavelength of the emission spectrum of the specific light-emitting layer on the cathode side. From the viewpoint of enhancing isochromaticity, the ratio of the maximum full width at half maximum of the two specific light-emitting layers adjacent to each other to the minimum full width at half maximum is preferably as close to 1 as possible. Note that this full width at half maximum ratio can be increased by, for example, appropriately adjusting the distance between the two electrodes and the distance from the light-emitting layer to the electrode (reflective electrode or semi-reflective electrode).

[0053] In this disclosure, "different colors" refers to the relationship between colors of light that do not fall within the same color range described above. Typical examples of "different colors" include red, green, and blue, which are used in full-color displays.

[0054] The number of specific light-emitting layers in one tandem light-emitting device of the present disclosure may be determined appropriately within a range in which the effects of the present disclosure can be obtained. A large number of specific light-emitting layers is preferable from the viewpoints of improving luminous efficiency and extending device life. From the above viewpoints, the number of specific light-emitting layers per tandem light-emitting device of the present disclosure is preferably 2 or more, and more preferably 3 or more.

[0055] Furthermore, a small number of specific light-emitting layers in one tandem light-emitting device of the present disclosure is preferable from the viewpoints of suppressing an increase in driving voltage, realizing a withstand voltage of a driving 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). From the above viewpoints, the number of specific light-emitting layers per one tandem light-emitting device of the present disclosure is preferably 5 or less, and more preferably 4 or less.

[0056] The light-emitting device according to the present disclosure is suitable for a top-emission type light-emitting device, and is even more suitable for a light-emitting device capable of full-color display. In a top-emission type light-emitting device, the light extraction efficiency can be improved by utilizing the microcavity effect by adjusting the distance between the electrode layers in the light-emitting element of each color according to the wavelength of light from the light-emitting layer. The distance between the electrode layers can be adjusted by the thickness of the carrier functional layer described below. The light-emitting device according to the present disclosure includes the tandem light-emitting element according to the present disclosure, and in the tandem light-emitting element according to the present disclosure, the thickness of the carrier functional layer for adjusting the distance between the electrode layers can be suppressed. Therefore, the present disclosure is suitable from the viewpoint of further suppressing the consumption of functionally unnecessary materials.

[0057] In the light-emitting device according to the present disclosure, the light-emitting layers of the light-emitting elements arranged in the first direction emit light of different colors, and the distance between the electrode layers of each light-emitting element can be adjusted as described above. Therefore, the light-emitting layers in the light-emitting device according to the present disclosure may be at the same position (height) as each other in the second direction, or at different positions (heights) (shifted).

[0058] The various layers constituting the light-emitting device of the present disclosure will be described in more detail below.

[0059] <Anode> The anode is one of a pair of electrodes, an anode and a cathode, and in the present disclosure is an electrode for supplying holes to each layer constituting the light-emitting element. The anode is conductive. Furthermore, the anode may have 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.

[0060] 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).

[0061] 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.).

[0062] 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), indium gallium zinc oxide (In—Ga—Zn—O), etc.), thin films made of metal materials such as Al, Mg, and Ag, and nanowires (NW) made of these metal materials.

[0063] 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 as an electrode or adding the function of reflecting visible light.

[0064] <Cathode> The cathode is the other of a pair of electrodes, an anode and a cathode, and in the present disclosure is an electrode 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.

[0065] For example, a material with a relatively small work function is preferably used as the cathode material, in order to enhance electron injection. Examples of electrode materials constituting the cathode include metal materials such as alkali metals, alkaline earth metals, and Al, alloys containing these, and nanowires (e.g., Ag nanowires). Examples of alloys include an alloy of Mg and Ag, and Al doped with a small amount of Li.

[0066] <Light-emitting layer> The light-emitting layer is a layer that emits light of a desired color when a voltage is applied. The light-emitting layer is usually composed of a light-emitting material, but may also have a laminated structure in which two or more functional layers corresponding to two or more functions for light emission in known light-emitting layers are stacked, such as a layer that emits immediate light and a layer that emits delayed light, and the functional layers as a whole exhibit the light-emitting function.

[0067] The specific light-emitting layer in the tandem light-emitting device of the present disclosure is a so-called host-guest light-emitting layer containing a host compound and a guest compound. The light-emitting layer in a light-emitting device other than the tandem light-emitting device of the present disclosure may be a host-guest light-emitting layer or another type of light-emitting layer. Examples of other types of light-emitting layers include a light-emitting layer containing quantum dots.

[0068] A host-guest emitting layer contains, for example, a small amount (e.g., 0.01 to 10%) of a guest compound in a solid medium that is a host compound. In an emitting layer doped with a guest compound in this way, 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, a host-guest emitting layer can emit light from the guest compound with higher quantum efficiency.

[0069] Various known examples of host-guest emitting layer materials can be used. Examples of host compounds include known specific emitting layer materials for each color.

[0070] Examples of the guest compound of the electron transporting material include pyrene-based compounds, anthracene-based compounds, perylene, DPT, Coumarin 6, PMDFB, quinacridone, rubrene, BTX, ABTX, DCM, and DCJT, spiro-based compounds (spiro-DPVBi, spiro-6P, spiro-BDAVBi (2,7-bis[4-(diphenylamino)styryl]-9,9′-spirofluorene)), distyryl compounds (distyrylbenzene (DSB), distyrylarylene (DSA)), and polyfluorene (polyfluorene, PFO)-based polymers.

[0071] The guest compound of the hole transport material is an iridium ligand complex (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, Ir(ppy), Ir(tpy), Ir(bzq), Ir(thp), Ir(op), Ir(bo), Ir(bt), Ir(bon), Ir(αbsn), Ir(btp), Ir(ppo), Ir(C6), Ir(pq), Ir(β-bsn), Ir(ppz)), platinum-based complexes (such as PtOEP, PtON-TBBI, and PtON7-t-Bu), polyparaphenylene vinylene (poly(phenylene vinylene), PPV)-based polymers, and TADF materials (such as DABNA and v-DABNA).

[0072] Examples of guest compounds include fluorescent dopants, phosphorescent dopants, TADF, and hyperfluorescent materials.

[0073] Examples of fluorescent dopants include delayed fluorescent dopants, thermally activated delayed fluorescent dopants, and fluorescent dopants that emit light via delayed fluorescent materials (hyperfluorescence).

[0074] Further examples of fluorescent dopants include Perylene, DPT, Coumarin 6, PMDFB, quinacridone, Rubrene, BTX, ABTX, DCM, and DCJT.

[0075] 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.

[0076] Examples of electron-transporting fluorescent dopants in the blue-emitting layer include pyrene-based compounds and anthracene-based compounds, and examples of hole-transporting phosphorescent dopants in the red- and green-emitting layers include iridium-based complexes and palladium-based complexes.

[0077] In addition, the host compound and guest compound in the light-emitting layer of any of the emitted colors may contain a TADF material. Usually, the amount of electrons or holes injected from the charge generation layer (electron generation layer and hole generation layer) into the light-emitting layer is lower than the amount of electrons or holes injected from the electrodes (cathode and anode) into the light-emitting layer. The TADF material forms many charge-transfer complexes and has high electron transport properties. Therefore, it is preferable that the host compound or guest compound contains a TADF material, because electrons injected from either the charge generation layer or the electrode can be more effectively contributed to the light emission of the light-emitting layer, thereby further improving the luminous efficiency of the light-emitting device according to the present disclosure.

[0078] <Charge Generation Layer> The tandem light-emitting element of the present disclosure has an electron generation layer that generates electrons and a hole generation layer that generates holes, located between adjacent specific light-emitting layers in the second direction. In the present disclosure, the electron generation layer and the hole generation layer are also collectively referred to as "charge generation layer." When holes are supplied from the anode and electrons are supplied from the cathode, the electron generation layer generates electrons and the hole generation layer generates holes. The electrons generated in the charge generation layer are supplied to the specific light-emitting layer on the anode layer side in the second direction, and the holes generated in the charge generation layer are supplied to the specific light-emitting layer on the cathode layer side. Any known charge generation material that exhibits the above functions can be used as the material for the charge generation layer.

[0079] Examples of electron generation layers include n-type charge generation layers. Examples of materials for n-type charge generation layers include n-type host materials with electron transporting properties and n-type dopant materials capable of injecting electrons and doped into the n-type host material. Examples of n-type host materials include Alq3 (tris(8-hydroxyquinolino)aluminum), Liq (8-hydroxyquinolinolato-lithium), PBD (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4 oxadiazole), TAZ (3-(4-biphenyl)4-phenyl-5-tert-butylphenyl-1,2,4-triazole), spiro-PBD, and BAlq (bis)(2-methyl-8-quinolinolato)-4-(phenylphenolato)aluminum), SAlq, TPBi (2,2′,2-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)), oxadiazole, triazole, phenanthroline, benzoxazole, and benzthiazole.

[0080] Examples of n-type dopant materials include metals from Groups 1 and 2 of the periodic table, organic materials capable of injecting electrons, and mixtures thereof. More specifically, examples of n-type dopant materials include alkali metals such as lithium (Li), sodium (Na), potassium (K), and cesium (Cs); alkaline earth metals such as magnesium (Mg), strontium (Sr), barium (Ba), and radium (Ra); metals with high electron injection properties (e.g., ytterbium (Yb)); metal compounds containing these metals (e.g., lithium fluoride (LiF)); oxadiazole-based compounds; and phenanthroline-based compounds. For example, the above-mentioned metal materials are added as n-type dopant materials in an amount of 3 to 20% of the material for the n-type charge generation layer.

[0081] Examples of hole generation layers include p-type charge generation layers. Examples of materials for p-type charge generation layers include p-type host materials with hole-transporting properties and p-type dopant materials with electron-accepting properties that are doped into the p-type host material. Examples of p-type host materials include organic hole-transporting materials, such as NPD (N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine), TPD (N,N'-bis-(3-methylphenyl)-N,N'-bis-(phenyl)-benzidine), and MTDATA (4,4',4-tris(N-3-methylphenyl-N-phenyl)(-amino)-triphenylamine).

[0082] Examples of p-type dopant materials include organic materials such as F4-TCNQ (tetrafluoro-tetracyanoquinodimethane), HATCN (hexaazatriphenylene-hexacarbonitrile), and hexaazatriphenylene derivatives. ２ O ５ , MoO ｘ , and W.O. ３ Metal oxides such as MoO ｘ In the formula, x is, for example, a value of 3 to 6. When the p-type dopant material is, for example, one of the above organic materials, it is added in an amount of 1 to 10% to the material of the p-type charge generation layer.

[0083] The n-type dopant material LiF exhibits excellent electron injection properties. However, deposition of layers containing inorganic materials such as LiF is generally performed at high temperatures due to the high melting points of these inorganic materials. This may result in thermal damage to previously deposited organic materials. From this perspective, organic materials are preferred for the layers constituting the light-emitting device, and organic electron injection materials such as BUPH1, BPen, p-MeO-Phen, p-NMe2-Phen, and p-Pyrrd-Phen are currently being developed. These organic materials are capable of exhibiting sufficient properties even after exposure to the deposition temperatures of cathodes made of aluminum (Al). On the other hand, the electron injection ability of organic electron injection materials is generally lower than that of inorganic materials such as LiF, and tandem light-emitting devices including an electron generation layer containing an organic electron injection material may experience an insufficient supply of electrons to the light-emitting layer.

[0084] In the present disclosure, since the concentration of the guest compound in the specific light-emitting layer of the tandem light-emitting device is set as described above, even if an electron generation layer with a low electron generation amount is employed, it is possible to substantially supply theoretical electrons to the specific light-emitting layer. Therefore, the light-emitting device of the present disclosure can be applied to light-emitting devices that have a high proportion of organic functional layers or that use an electron generation layer made only of organic materials.

[0085] <Carrier Functional Layer> The light-emitting element of the present disclosure may further include layers other than the layers described above, as long as the effects of the present disclosure can be obtained. Examples of other configurations include 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. Hereinafter, these other layers are also collectively referred to as "carrier functional layers."

[0086] The hole injection layer is disposed adjacent to the anode, for example. The hole injection layer may be composed of the hole transport material and the electron accepting material described above. The specific material of the hole injection layer may be the same as or different from that of the p-type charge generation layer.

[0087] The electron injection layer is disposed adjacent to the cathode, for example. The electron injection layer may be composed of the electron transport material described above. Examples of electron transport materials constituting the electron injection layer include lithium fluoride (LiF), which is an inorganic material. Similarly to the n-type charge generation layer, the electron injection layer may be composed of an organic electron transport material doped with an inorganic electron donor material (e.g., Li or Yb).

[0088] The hole transport layer may be made of an organic hole transport material, such as a triarylamine organic compound.

[0089] The electron blocking layer, like the hole transporting layer, may be made of an organic hole transporting material, and the material of the electron blocking layer may be the same as or different from that of the hole transporting layer.

[0090] The hole-blocking layer may be made of the organic electron-transporting material described above. The material of the hole-blocking layer may contain lithium quinoline (Liq) in addition to the electron-transporting material.

[0091] 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 that of the hole blocking layer. The electron transport layer may also contain lithium quinoline in addition to the electron transport material.

[0092] <Stack> The hole injection layer and the electron injection layer are usually disposed corresponding to the electrodes, for example, adjacent to each electrode in the second direction. In contrast, the hole transport layer, the electron blocking layer, the specific light-emitting layer, the hole blocking layer, the electron transport layer, and the charge generation layer can be repeatedly stacked in the second direction in the tandem light-emitting device of the present disclosure or a typical tandem light-emitting device. In the present disclosure, such a structure in which multiple layers are stacked in the second direction is also referred to as a "stack."

[0093] The stack is a collection of layers including one specific light-emitting layer disposed between the anode and the charge generation layer, between the charge generation layers, and between the charge generation layer and the cathode in the second direction. The stack may typically include the above-mentioned carrier functional layer in addition to the one specific light-emitting layer. The stack is disposed between the anode and the cathode in the second direction. The tandem light-emitting device of the present disclosure or other typical tandem light-emitting devices has two or more stacks. In the present disclosure, the anode, the cathode, and the charge generation layer are not included in the stack.

[0094] The thickness of each stack in each light-emitting element is determined so that the amount of light emitted from the specific light-emitting layer is a theoretical value or a value close to it. In the present disclosure, it is preferable to set the thickness of the stack according to the thickness of the specific light-emitting layer from the viewpoint of improving the light-emitting efficiency of the light-emitting element. Note that the thickness of the stack is calculated as the sum of the thicknesses of the specific light-emitting layer and the carrier functional layer in the stack, but among the specific light-emitting layer and the carrier functional layer, layers with a very small thickness (for example, a layer with a thickness of less than 1 nm) may be ignored when calculating the thickness of the stack.

[0095] [Method for Manufacturing the Light-Emitting Device] The light-emitting device can be manufactured based on known techniques for manufacturing tandem OLEDs. For example, the light-emitting device can be manufactured by a method including a step of alternately stacking a specific light-emitting layer of the tandem light-emitting element (a light-emitting element that emits light of a specific color) of the present disclosure, an electron generation layer, and a hole generation layer.

[0096] In the present disclosure, in the lamination step, it is preferable to form the specific light-emitting layer by a vapor deposition method, from the viewpoint of precisely controlling the thickness and concentration of the specific light-emitting layer and from the viewpoint of appropriately controlling the concentration of the guest compound in the specific light-emitting layer of the tandem light-emitting device of the present disclosure.

[0097] Forming the specific light-emitting layer by a vapor deposition method is preferable from the viewpoint of realizing a specific light-emitting layer with high brightness and low driving voltage, and is also preferable from the viewpoint of realizing a high-definition display device because a light-emitting device with fine pixels can be formed with high precision. Furthermore, forming the specific light-emitting layer by a vapor deposition method is preferable from the viewpoint of forming a host-guest specific light-emitting layer in which the concentration of the guest compound is precisely controlled by using a co-evaporation method using multiple evaporation sources.

[0098] In the lamination process, the specific light-emitting layer can be formed by co-evaporation of a host compound and a guest compound. Therefore, the concentration of the guest compound in the specific light-emitting layer can be controlled by the vapor deposition conditions of the guest compound in the co-evaporation, and the concentration can be increased by changing the vapor deposition conditions to promote vapor deposition.

[0099] From the viewpoint of appropriately controlling the concentration of the guest compound in the specific light-emitting layer, it is preferable to vary at least the vapor deposition time of the guest compound for each specific light-emitting layer in the lamination step.

[0100] Furthermore, among the vapor deposition conditions, only the vapor deposition time of the guest compound in the stacking process may be varied for each specific light-emitting layer. In such a process, when forming two or more specific light-emitting layers overlapping in the second direction, the vapor deposition conditions other than the vapor deposition time (e.g., the crucible temperature (vapor deposition temperature), the vapor deposition rate controlled by these temperatures, and the use of a vapor deposition mask that defines the pixel shape) may be constant. Therefore, the variation in the characteristics of each specific light-emitting layer in the second direction is suppressed, and the effects due to the difference in the concentration (doping concentration) of the guest compound and the difference in carrier transportability of the specific light-emitting layer in the second direction can be more significantly exhibited. For example, in the present disclosure, when forming multiple specific light-emitting layers that emit the same color in the second direction, the specific light-emitting layers can be formed by varying the vapor deposition temperature of the guest compound for each specific light-emitting layer.

[0101] Alternatively, in the lamination step, at least the vapor deposition temperature of the guest compound, i.e., the temperature of the crucible, may be varied for each specific light-emitting layer. Setting of such vapor deposition conditions is suitable for the case where different guest compounds are contained in two or more specific light-emitting layers of the tandem light-emitting device of the present disclosure.

[0102] Alternatively, from the viewpoint of achieving the above-mentioned effects, both the deposition time and the deposition temperature may be appropriately adjusted as the deposition conditions for the guest compound.

[0103] In the above manufacturing method, the manufacturing methods of the anode, cathode, electron generating layer, hole generating layer, and other layers included in the light emitting device may be appropriately determined based on known manufacturing techniques for OLEDs.

[0104] [Display Device] A display device according to the present disclosure includes the above-described light-emitting device. The display device can be configured in the same manner as a known display device having a known light-emitting device, except for having the above-described light-emitting device. Examples of the display device include a television set and a smartphone.

[0105] [Explanation of Specific Embodiments] The light-emitting device, the manufacturing method thereof, and the display device of the present disclosure will be described in more detail below, taking an OLED as an example, with reference to the drawings. In this specification, for configurations related to different colors among similar basic configurations, a symbol indicating the color is further added to the symbol of the basic configuration. For example, a symbol R is further added to a configuration related to red light emission, a symbol G is further added to a configuration related to green light emission, and a symbol B is further added to a configuration related to blue light emission.

[0106] [Embodiment 1] FIG. 1 is a plan view schematically illustrating a configuration of a display device 100 according to embodiment 1 of the present disclosure. FIG. 1 illustrates a smartphone, which is an example of a display device. The display device 100 includes a display area 101 and a frame area 102 surrounding the display area 101. The display area 101 is provided with a plurality of light-emitting devices 110. The light-emitting device 110 includes a red light-emitting element 111R, a green light-emitting element 111G, and a blue light-emitting element 111B. The light-emitting elements 111 of each color are arranged in parallel in the direction indicated by arrow X in the figure. In the display device 100, the light-emitting devices 110 correspond to pixels, and the light-emitting elements 111 of each color correspond to sub-pixels. The X direction indicated by arrow X in the figure corresponds to the first direction described above, and the Y direction indicated by arrow Y corresponds to the first direction described above.

[0107] 2 is a diagram schematically illustrating the layer structure of the light-emitting device 110. The light-emitting device 110 is a so-called top-emission type light-emitting device, which is a light-emitting device having a structure in which light generated in the light-emitting layer is emitted upward in the figure, i.e., in the Y direction. The red light-emitting element 111R and the green light-emitting element 111G are each single-type light-emitting elements having only one first light-emitting layer 14 in the Y direction. The blue light-emitting element 111B is the tandem-type light-emitting element of the present disclosure described above.

[0108] The red light-emitting element 111R and the green light-emitting element 111G each have an anode 1 (anode 1R for the red light-emitting element 111R, and anode 1G for the green light-emitting element 111G), a first stack 10, an electron injection layer 37, a cathode 2, an auxiliary layer 3, a buffer layer 4, and a sealing layer 5, in this order along the Y direction. The blue light-emitting element 111B has an anode 1B, the first stack 10, a first charge generation layer 20, a second stack 30, a cathode 2, an auxiliary layer 3, a buffer layer 4, and a sealing layer 5, in this order along the Y direction.

[0109] The anode 1 is a light-reflective electrode and is the indium tin oxide / Ag laminate described above. The cathode 2 is a light-transmitting electrode and is an Mg / Ag layer in which Mg and Ag are mixed in predetermined amounts. The auxiliary layer 3 is a layer for improving the viewing angle. The buffer layer 4 and the sealing layer 5 are both layers for preventing moisture from penetrating into the light-emitting element 111; for example, the buffer layer 4 is a LiF layer, and the sealing layer 5 is a resin film.

[0110] The anode 1 is formed corresponding to the emitted color and is formed independently for each light-emitting element. Hereinafter, the layers formed corresponding to each color are also referred to as "independent layers." The cathode 2, auxiliary layer 3, buffer layer 4, and sealing layer 5 are all formed integrally across the light-emitting elements of each color in the light-emitting device 110. Hereinafter, the layers formed integrally across the light-emitting elements of different colors are also referred to as "common layers."

[0111] The first stack 10 has, in this order in the Y direction, a hole injection layer 11, a first hole transport layer 12, a first electron blocking layer 13, a first blue light-emitting layer 14B, a first hole blocking layer 15, and a first electron transport layer 16. The hole injection layer 11 and the first hole transport layer 12 are both common layers.

[0112] The first electron blocking layer 13 is an independent layer made of a hole transport material and has a specific thickness according to the emission color of each light-emitting element. For example, the first red electron blocking layer 13R of the red light-emitting element 111R is the thickest, the first green electron blocking layer 13G of the green light-emitting element 111G is the next thickest, and the first blue electron blocking layer 13B of the blue light-emitting element 111B is the thinnest.

[0113] The first light-emitting layer 14 is also an independent layer, and is made of a light-emitting layer material corresponding to the emission color of each light-emitting element, and has a specific thickness corresponding to the emission color. The first red light-emitting layer 14R and the first green light-emitting layer 14G are both phosphorescent light-emitting layers. The first blue light-emitting layer 14B is a fluorescent light-emitting layer. The first hole-blocking layer 15 and the first electron-transporting layer 16 are both common layers.

[0114] In the blue light-emitting element 111B, the first charge generation layer 20 has a first blue electron generation layer 21B and a first blue hole generation layer 22B, in this order in the Y direction. In the blue light-emitting element 111B, the second stack 30 has a second blue hole injection layer 31B, a second blue hole transport layer 32B, a second blue electron blocking layer 33B, a second blue light-emitting layer 34B, a second blue hole blocking layer 35B, a second blue electron transport layer 36B, and an electron injection layer 37, in this order in the Y direction. The second blue light-emitting layer 34B is also a fluorescent light-emitting layer.

[0115] The electron injection layer 37, the cathode 2, the auxiliary layer 3, the buffer layer 4, and the sealing layer 5 are all common layers. The dots in the light-emitting layer schematically represent guest compounds.

[0116] In the blue light-emitting element 111B, as described above, the first blue light-emitting layer 14B and the second blue light-emitting layer 34B are both fluorescent light-emitting layers containing a host compound and a guest compound, and the guest compound in the first blue light-emitting layer 14B is an electron-transporting material, while the guest compound in the second blue light-emitting layer 34B is a hole-transporting material.

[0117] The concentration of the guest compound in the second blue light-emitting layer 34B is higher than the concentration of the guest compound in the first blue light-emitting layer 14B, for example, not more than twice the concentration of the guest compound in the first blue light-emitting layer 14B.

[0118] Furthermore, the difference between the peak wavelength of the emission spectrum of the first blue light-emitting layer 14B and the peak wavelength of the emission spectrum of the second blue light-emitting layer 34B is 10 nm or less, and the full width at half maximum at the peak wavelength of the emission spectrum of the first blue light-emitting layer 14B is 0.75 to 1.25 times the full width at half maximum of the emission spectrum of the second blue light-emitting layer 34B.

[0119] In addition, in the blue light-emitting element 111B, the first blue electron generation layer 21B and the first blue hole generation layer 22B are each configured so that the amount of holes injected from the first blue hole generation layer 22B into the second blue light-emitting layer 34B is greater than the amount of electrons injected from the first blue electron generation layer 21B into the first blue light-emitting layer 14B.

[0120] <Example of Method for Manufacturing Light-Emitting Device> Next, an example of a method for manufacturing the light-emitting device 110 will be described with reference to FIG.

[0121] In step S1, the anode 1 is formed on, for example, a substrate. For example, an Ag layer and an Indium Tin Oxide layer are formed in this order on the substrate by sputtering.

[0122] In step S2, a hole injection layer 11 is formed on the anode 1. For example, a hole transport material and an electron acceptor material are co-evaporated at a predetermined evaporation rate over the entire surface of the workpiece without using a fine metal mask, by adjusting the evaporation temperature and evaporation time so that the material is deposited to a predetermined film thickness and in a predetermined composition ratio.

[0123] In step S3, the first hole transport layer 12 is formed on the hole injection layer 11. For example, the hole transport material is evaporated at a predetermined evaporation rate by adjusting the evaporation temperature and evaporation time so that the layer is deposited to a predetermined film thickness, without using a fine metal mask.

[0124] In step S4, a first electron blocking layer 13 is formed on the first hole transport layer 12. For example, a hole transport material is vapor-deposited at a predetermined vapor deposition rate by adjusting the vapor deposition temperature and vapor deposition time so that a predetermined film thickness is formed. The vapor deposition is performed using a fine metal mask to obtain a first thickness corresponding to each color. The first thickness may be the same or different for each light-emitting element of each color, as long as the effects of the present disclosure are obtained. For example, the thickest first red electron blocking layer 13R may be formed in the portion of the first hole transport layer 12 corresponding to the red light-emitting element 111R, the next thickest first green electron blocking layer 13G may be formed in the portion of the first hole transport layer 12 corresponding to the green light-emitting element 111G, and the thinnest first blue electron blocking layer 13B may be formed in the portion of the first hole transport layer 12 corresponding to the blue light-emitting element 111B.

[0125] In step S5, a first light-emitting layer 14 is formed on the first electron blocking layer 13. For example, co-evaporation of a host compound and a guest compound corresponding to each color is performed for each emitted color using a fine metal mask at a predetermined evaporation rate by adjusting the evaporation temperature and evaporation time so that the layers are stacked to a predetermined film thickness and a predetermined composition ratio (dopant concentration). The thicknesses of the light-emitting layers for each color may be the same or different in electroluminescent devices of each color, as long as the effects of the present disclosure are obtained. For example, a first red light-emitting layer 14R may be formed on the first red electron blocking layer 13R, a first green light-emitting layer 14G may be formed on the first green electron blocking layer 13G, and a first blue light-emitting layer 14B may be formed on the first blue electron blocking layer 13B.

[0126] In step S6, the first hole-blocking layer 15 is formed on the first blue light-emitting layer 14B. For example, the electron-transporting material is evaporated at a predetermined evaporation rate by adjusting the evaporation temperature and evaporation time so that the layer is deposited to a predetermined thickness, without using a fine metal mask.

[0127] In step S7, the first electron transport layer 16 is formed on the first hole blocking layer 15. For example, the electron transport material is evaporated at a predetermined evaporation rate by adjusting the evaporation temperature and evaporation time so that the layer is deposited to a predetermined thickness, without using a fine metal mask.

[0128] In step S8, a first blue electron generating layer 21B is formed on the first electron transport layer 16. For example, a fine metal mask is used to perform co-evaporation of an organic electron transport material and an inorganic metal electron donor material, Yb or Li, at a predetermined evaporation rate by adjusting the evaporation temperature and evaporation time so that a predetermined film thickness and ratio are achieved, only at the position of the blue light emitting element 111B where the second blue light emitting layer 34B is to be formed.

[0129] In step S9, a first blue hole generation layer 22B is formed on the first blue electron generation layer 21B. For example, an organic hole transport material and an organic electron acceptor material are co-deposited at a predetermined deposition rate by adjusting the deposition temperature and deposition time so that a predetermined thickness and ratio are achieved. This is done using a fine metal mask only at the position of the blue light-emitting element 111B where the second blue light-emitting layer 34B is to be formed. In step S9, for example, the introduction of the electron-accepting material is appropriately adjusted so that the amount of holes injected from the first blue hole generation layer 22B into the second blue light-emitting layer 34B is greater than the amount of electrons injected from the first blue electron generation layer 21B into the first blue light-emitting layer 14B.

[0130] In step S10, a second blue hole transport layer 32B is formed on the first blue hole generation layer 22B. For example, a hole transport material is evaporated using a fine metal mask at a predetermined evaporation rate by adjusting the evaporation temperature and evaporation time so that the layer is deposited to a predetermined thickness, only at the position of the blue light emitting element 111B.

[0131] In step S11, second blue electron blocking layer 33B is formed on second blue hole transport layer 32B. For example, a hole transport material is vapor-deposited at a predetermined vapor deposition rate by adjusting the vapor deposition temperature and vapor deposition time so that a layer having a predetermined thickness is formed. The vapor deposition is performed using a fine metal mask to obtain a second thickness corresponding to the blue color.

[0132] In step S12, a second blue light-emitting layer 34B is formed on the second blue electron blocking layer 33B. For example, a host compound and a guest compound (dopant) are co-evaporated at a predetermined evaporation rate using a fine metal mask, adjusting the evaporation temperature and evaporation time so that a predetermined film thickness and composition ratio (dopant concentration) are achieved. This is performed only at the position of the blue light-emitting element 111B. In step S12, the introduction of the guest compound is appropriately adjusted so that the concentration of the guest compound contained in the second blue light-emitting layer 34B is greater than the concentration of the guest compound contained in the first blue light-emitting layer 14B.

[0133] In step S13, a second blue hole-blocking layer 35B is formed on the second blue light-emitting layer 34B. For example, an electron transporting material is evaporated at a predetermined evaporation rate by adjusting the evaporation temperature and evaporation time so that the layer is deposited to a predetermined thickness, using a fine metal mask only at the position of the blue light-emitting element 111B.

[0134] In step S14, a second blue electron transport layer 36B is formed on the second blue hole blocking layer 35B. For example, an electron transport material is evaporated using a fine metal mask at a predetermined evaporation rate by adjusting the evaporation temperature and evaporation time so that the layer is deposited to a predetermined thickness, only at the position of the blue light emitting element 111B.

[0135] In step S15, the electron injection layer 37 is formed on the red light emitting element 111R portion and the green light emitting element 111G portion of the first electron transport layer 16 and on the second blue electron transport layer 36B. For example, lithium fluoride is evaporated at a predetermined evaporation rate without using a fine metal mask by adjusting the evaporation temperature and evaporation time so that a predetermined film thickness is formed.

[0136] In step S16, the cathode 22 is formed on the electron injection layer 37. For example, a magnesium-silver alloy thin film is formed on the electron injection layer 37 by using a vapor deposition method.

[0137] In this manner, a light-emitting device 110 can be manufactured in which only blue light-emitting element 111B is a tandem light-emitting element according to the present disclosure, and red light-emitting element 111R and green light-emitting element 111G are single light-emitting elements. In light-emitting device 110, first red light-emitting layer 14R emits red light having a peak wavelength of 600 nm or more and 660 nm or less in its emission spectrum, and first green light-emitting layer 14G emits green light having a peak wavelength of 500 nm or more and less than 600 nm in its emission spectrum. Furthermore, first blue light-emitting layer 14B and second blue light-emitting layer 34B both emit blue light having a peak wavelength of 430 nm or more and 470 nm or less in its emission spectrum.

[0138] In the above manufacturing example, the hole transport material in step S4 may be the same as or different from that in step S3. In step S5, the first blue light-emitting layer 14B may be formed using a resist mask formed by photolithography instead of a fine metal mask. In step S7, the electron transport material may be the same as or different from that in step S6. The deposition in step S7 may involve deposition of only the electron transport material, or co-deposition of the electron transport material and lithium quinoline. In step S12, the guest compound may be composed of either an electron transport material or a hole transport material, but preferably a hole transport material. In step S12, the second blue light-emitting layer 34B may be formed using a resist mask formed by photolithography instead of a fine metal mask. In step S14, the second blue electron transport layer 36B may be formed by co-deposition of the electron transport material and lithium quinoline.

[0139] 4 is a schematic diagram showing carrier movement in the tandem light-emitting element according to the first embodiment of the present disclosure. A voltage is applied to the anode 1 and the cathode 2 of the blue light-emitting element 111B. The magnitude of the voltage applied to the blue light-emitting element 111B to emit light is the same as the voltage applied to the light-emitting elements of the other colors to emit light.

[0140] When a voltage is applied to the anode 1 and the cathode 2, holes are supplied from the anode 1 and electrons are supplied from the cathode 2. Furthermore, the application of this voltage causes electrons to be generated from the first blue electron generation layer 21B and supplied to the first blue light-emitting layer 14B, and holes to be generated from the first blue hole generation layer 22B and supplied to the second blue light-emitting layer 34B. The charges (electrons and holes) supplied from each electrode and charge generation layer recombine in the first blue light-emitting layer 14B and the second blue light-emitting layer 34B, respectively, to generate excitons and emit blue light.

[0141] In the blue light-emitting element 111B, the concentration of the guest compound in the blue light-emitting layer is lower in the first blue light-emitting layer 14B, and the guest compound in the first blue light-emitting layer 14B is an electron-transporting material. Furthermore, the amount of holes supplied from the first blue hole-generating layer 22B to the second blue light-emitting layer 34B is greater than the amount of electrons supplied from the first blue electron-generating layer 21B to the first blue light-emitting layer 14B. Therefore, excessive carriers are not injected into either blue light-emitting layer, and the carrier balance between the first blue light-emitting layer 14B and the second blue light-emitting layer 34B is optimized. Therefore, the device voltage of the blue light-emitting element 111B is substantially twice or less that of the single-type light-emitting element, and highly efficient light emission is achieved.

[0142] On the other hand, the concentration of the guest compound in the first blue light-emitting layer 14B is lower than that in the second blue light-emitting layer 34B. However, holes are generally more easily generated in a light-emitting element than electrons, and are more easily supplied to the light-emitting layer. Therefore, a sufficient number of holes are supplied to the first blue light-emitting layer 14B, sufficient recombination of electrons and holes occurs, and sufficient excitons are generated. As a result, the first blue light-emitting layer 14B also emits blue light with a desired brightness according to the concentration of the guest compound.

[0143] In the blue light-emitting element 111B, it is preferable that the guest compound in the second blue light-emitting layer 34B is a hole-transporting material, from the viewpoint of further improving the element characteristics (light-emitting efficiency and element life).

[0144] Furthermore, if the concentration of the guest compound in the second blue light-emitting layer 34B is not more than twice the concentration of the guest compound in the first blue light-emitting layer 14B, unintended consumption of carriers in the second blue light-emitting layer 34B is suppressed, and this is preferable from the viewpoint of preventing carrier shortage in the first blue light-emitting layer 14B.

[0145] Furthermore, while first red light-emitting layer 14R and first green light-emitting layer 14G are both phosphorescent light-emitting layers, first blue light-emitting layer 14B and second blue light-emitting layer 34B are fluorescent light-emitting layers having lower luminous efficiency than phosphorescent light-emitting layers. As described above, in blue light-emitting element 111B, first blue light-emitting layer 14B and second blue light-emitting layer 34B each emit light at substantially the desired luminance, and therefore the tandem light-emitting element of the present disclosure having a fluorescent light-emitting layer is suitable for combination with a light-emitting element having a single phosphorescent light-emitting layer.

[0146] Furthermore, blue light-emitting element 111B emits blue light having a peak wavelength of 430 nm or more and 470 nm or less. Currently, materials for the blue phosphorescent light-emitting layer have emission wavelength peaks at relatively long wavelengths, and light-emitting materials compatible with a wide color gamut are still under development. Furthermore, materials for the blue phosphorescent light-emitting layer are expensive and can be difficult to produce stably. In contrast, blue fluorescent light-emitting layers do not have the above problems. From the viewpoint of stable production, it is preferable to apply the tandem light-emitting element of the present disclosure to blue light-emitting elements.

[0147] Furthermore, the difference in peak wavelength of the emission spectrum between the first blue light-emitting layer 14B and the second blue light-emitting layer 34B is 10 nm or less, and the full width at half maximum at the peak wavelength of the emission spectrum of the first blue light-emitting layer 14B is 0.75 to 1.25 times that of the second blue light-emitting layer 34B. Thus, the first blue light-emitting layer 14B and the second blue light-emitting layer 34B have sufficiently high isochromaticity with each other.

[0148] Furthermore, the blue light emitting element 111B is the tandem type light emitting element described above, which has more layers between electrodes than a single type light emitting element, and is therefore suitable for forming a top emission type light emitting device.

[0149] Furthermore, the concentrations of the guest compounds in the first blue light-emitting layer 14B and the second blue light-emitting layer 34B of the blue light-emitting element 111B can be easily and appropriately adjusted by varying the vapor deposition conditions (vapor deposition time, vapor deposition temperature, or both) of these blue light-emitting layers.

[0150] Here, the carrier balance of a light-emitting element will be explained. As mentioned above, in a light-emitting element, the amount of electrons flowing in from the cathode is equal to the amount of electrons flowing out from the anode (Kirchhoff's first law). Current is the amount of charge flowing per unit time (amount of electrons x elementary charge). When the light-emitting layer and carrier functional layer constituting the light-emitting element all have the same injection and transport properties for carriers, the current flowing in the light-emitting element should be proportional to the voltage between the anode and cathode and inversely proportional to the resistance of the entire light-emitting element (Ohm's law).

[0151] However, in the case of a light-emitting element using an organic thin film, the current flowing through the light-emitting element is proportional to the square of the voltage between the anode and cathode and inversely proportional to the cube of the thickness of the organic thin film (space charge limited current). Furthermore, in reality, the carrier injection and transport properties differ between layers. Therefore, the amount of current flowing through the light-emitting element is limited by the layer with the lowest injection and transport properties. Therefore, the amount of current flowing through the light-emitting element is observed to be limited 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 (the amount of electrons flowing into the anode).

[0152] In a single-type light-emitting element having one light-emitting layer, as a measure to suppress excessive generation of carriers and further improve the light-emitting efficiency of the light-emitting element, a material for the carrier functional layer is generally selected and the thickness of the carrier functional layer is adjusted so that the number of holes supplied to the light-emitting layer from the anode is equal to the number of electrons supplied to the light-emitting layer from the cathode. Alternatively, based on the concept of space-charge-limited current, a measure to achieve a suitable carrier balance in the light-emitting layer is also available by changing the thickness of the light-emitting layer so that a current flows through the light-emitting layer at an optimal current density.

[0153] In contrast, in the case of a tandem light-emitting device, the current flowing through each light-emitting layer is the same, and therefore, the same measures as those for a single light-emitting device, such as adjusting the amount of current flowing through a light-emitting layer with an imbalanced carrier content by changing its thickness, cannot be applied to a tandem light-emitting device because the carrier balance between multiple light-emitting layers must be optimized.

[0154] Regarding this issue, the inventors have found that in a tandem light-emitting device having multiple light-emitting layers via a charge generation layer, even if the carrier functional layer conditions described above, which are adjusted to equalize the electron and hole supply amounts, are applied, even if the carrier balance in one light-emitting layer is optimized, it is difficult to simultaneously optimize the carrier balance in the remaining light-emitting layers (i.e., to generate or supply appropriate excitons or 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 to each light-emitting layer from the charge generation layer. That is, carrier generation in the charge generation layer cannot be directly controlled electrically, unlike carrier generation in an anode and cathode directly connected to a power source. Furthermore, in a tandem light-emitting device, according to Kirchhoff's first law, the amount of current flowing through each of the light-emitting layers arranged in series between a pair of cathodes and anodes is the same. Therefore, the above-mentioned conventional measures cannot optimize the carrier balance in each light-emitting layer of a tandem light-emitting device.

[0155] In a tandem light-emitting element, there are two cases where the amount of carrier supply is not balanced: These are collectively referred to as an imbalance in the carrier balance in a tandem light-emitting element.

[0156] The first case is when exciton generation is insufficient or excessive in any of the light-emitting layers. More specifically, the same amount of electrons and holes is supplied to all the light-emitting layers, and electron-hole pairs (excitons) are formed without generating excess carriers, but exciton generation is insufficient or excessive in any of the multiple light-emitting layers.

[0157] In the second case, in addition to the first case, the amount of electrons and / or holes supplied to any of the plurality of light-emitting layers becomes unbalanced. More specifically, this is the case where not only is there a shortage or excess of excitons in any of the light-emitting layers, but also the balance between the supply of electrons and holes to at least any of the light-emitting layers is disrupted, resulting in the formation of excess carriers other than excitons.

[0158] Therefore, to give an example of an imbalance in the carrier balance in a tandem light-emitting element in the above-described embodiment, when the supply amount of carriers (electrons and / or holes) in one of the first blue light-emitting layer 14B and the second blue light-emitting layer 34B is optimized, the supply amount of electrons and / or holes in the other of the first blue light-emitting layer 14B and the second blue light-emitting layer 34B becomes excessive, resulting in an imbalance in the carrier balance between the first blue light-emitting layer 14B and the second blue light-emitting layer 34B.

[0159] In the light-emitting device 110, the guest compound contained in the first blue light-emitting layer 14B of the blue light-emitting element 111B is composed of an electron-transporting material, and the concentration of the guest compound contained in the second blue light-emitting layer 34B, which generates a shortage of excitons, is set higher than the concentration of the guest compound contained in the first blue light-emitting layer 14B. This optimizes the carrier balance between the first blue light-emitting layer 14B and the second blue light-emitting layer 34B. Additionally, the amount of holes generated and injected in the first blue hole-generating layer 22B is set higher than the amount of electrons generated and injected in the first blue electron-generating layer 21B. This more effectively suppresses carrier deficiencies and / or excess carrier generation in each of the two light-emitting layers, thereby optimizing the carrier balance.

[0160] Therefore, according to the light-emitting device 110 of the present disclosure, the generation of excess carriers that cannot contribute to light emission can be suppressed in the multiple specific light-emitting layers (first blue light-emitting layer 14B and second blue light-emitting layer 34B) between the anode 1 and the cathode 2, and an appropriate amount of excitons is generated in both the first blue light-emitting layer 14B and the second blue light-emitting layer 34B. This achieves highly efficient and bright light emission in the blue light-emitting element 111B. Note that excess carriers cannot be eliminated by radiative recombination, but instead generate heat and are deactivated, which can cause degradation of the light-emitting element. Therefore, according to the light-emitting device 110 of the present disclosure, thermal deactivation due to such excess carriers can also be suppressed, thereby improving element reliability.

[0161] The thickness of first blue light-emitting layer 14B and the concentration of the guest compound (dopant concentration) vary depending on the emitted color, but for example, the thickness of first light-emitting layer 14 of red light-emitting element 111R and green light-emitting element 111G is 25 to 50 nm, and the weight concentration of the guest compound is 0.01% or more and 15% or less, while the thickness of first blue light-emitting layer 14B of blue light-emitting element 111B is 10 to 25 nm, and the weight concentration of the guest compound is 0.01% or more and 10% or less. Each guest compound is made of, for example, an electron transport material.

[0162] 5 is a schematic diagram showing the layer structure of a light-emitting device 210 according to this embodiment. The light-emitting device 210 includes a red light-emitting element 211R, a green light-emitting element 211G, and a blue light-emitting element 211B. The light-emitting device 210 has the same structure as the light-emitting device 110 according to the first embodiment, except that the blue light-emitting element 211B further includes a second charge generation layer 40 and a third stack 50.

[0163] The layer structures of the red light emitting element 211R and the green light emitting element 211G are substantially the same as the layer structures of the red light emitting element 111R and the green light emitting element 111G in the first embodiment.

[0164] The blue light-emitting element 211B has a layer structure substantially similar to that of the blue light-emitting element 111B in embodiment 1, except that the second stack 30 does not include the electron injection layer 37, the second charge generation layer 40 is on the second stack 30, the third stack 50 is on the second charge generation layer 40, and the electron injection layer 37 is included in the third stack 50.

[0165] The second charge generation layer 40 has a second blue electron generation layer 41B and a second blue hole generation layer 42B, in this order in the Y direction. These layers are both independent layers. In the blue light emitting element 211B, the second blue electron generation layer 41B and the second blue hole generation layer 42B are configured so that the amount of holes injected from the second blue hole generation layer 42B into the third blue light emitting layer 54B is greater than the amount of electrons injected from the second blue electron generation layer 41B into the second blue light emitting layer 34B.

[0166] The amount of holes injected from the second blue hole generating layer 42B into the third blue light-emitting layer 54B may be smaller than, equal to, or larger than the amount of holes injected from the first blue hole generating layer 22B into the second blue light-emitting layer 34B. Also, the amount of electrons injected from the second blue electron generating layer 41B into the second blue light-emitting layer 34B may be smaller than, equal to, or larger than the amount of electrons injected from the first blue electron generating layer 21B into the first blue light-emitting layer 14B.

[0167] The third stack 50 includes a third blue hole injection layer 51B, a third blue hole transport layer 52B, a third blue electron blocking layer 53B, a third blue light-emitting layer 54B, a third blue hole blocking layer 55B, and a third blue electron transport layer 56B, in this order in the Y direction. These layers are all independent layers. The carrier functional layers in the third stack 50 have the same configuration as those in the first stack 10 and the second stack 30.

[0168] In the blue light-emitting element 211B, the concentration of the guest compound in the blue light-emitting layer is highest in the third blue light-emitting layer 54B, next highest in the second blue light-emitting layer 34B, and lowest in the first blue light-emitting layer 14B. The guest compound in the third blue light-emitting layer 54B is a hole-transporting material. The guest compound in the second blue light-emitting layer 34B may be either a hole-transporting material or an electron-transporting material.

[0169] The third blue light-emitting layer 54B is a fluorescent light-emitting layer, similar to the first blue light-emitting layer 14B and the second blue light-emitting layer 34B, and emits blue light having a peak wavelength of 430 to 470 nm. The difference between the maximum and minimum peak wavelengths of the emission spectra of the first blue light-emitting layer 14B, the second blue light-emitting layer 34B, and the third blue light-emitting layer 54B is 10 nm or less, and the maximum full width at half maximum at the peak wavelength of the emission spectrum is 1.25 times or less the minimum full width at half maximum.

[0170] The blue light-emitting element 211B can be manufactured by, after the above-described step S14, further performing steps similar to steps S8 to S14 to form the second charge generation layer 40 and each layer of the third stack 50. When the materials of each layer of the second charge generation layer 40 and each layer of the first charge generation layer 20 are the same, each layer of the second charge generation layer 40 can be formed by appropriately changing the deposition conditions (deposition time, deposition temperature, or composition ratio) for forming each layer of the first charge generation layer 20.

[0171] In blue light-emitting element 211B, similarly to blue light-emitting element 111B described above, electrons are sufficiently supplied to the blue light-emitting element on the anode 1 side, and holes are sufficiently supplied to the blue light-emitting element on the cathode side. Therefore, in any of the specific light-emitting layers, first blue light-emitting layer 14B, second blue light-emitting layer 34B, and third blue light-emitting layer 54B, blue light of a desired luminance according to the concentration of the guest compound can be emitted.

[0172] Furthermore, since the blue light-emitting element 211B has three specific light-emitting layers to which such carriers are appropriately supplied, it is more advantageous in terms of extending the life of the light-emitting element than the above-mentioned blue light-emitting element 111B.

[0173] Other Embodiments The display device according to the present disclosure may further include sub-pixels of colors other than red, green, and blue in one pixel.

[0174] The layer constituting the surface of the display device of the present disclosure may be an external functional layer, which is a layer that exhibits various functions such as optical control, touch sensor, or surface protection, and can be appropriately selected depending on the application of the display device.

[0175] In the light-emitting device of the present disclosure, some layers are common layers, but any of the layers may be independent layers, which can be formed by vapor deposition using a mask such as a fine metal mask having openings corresponding to the light-emitting elements of each color, as described above.

[0176] In the light-emitting device of the present disclosure, the charge generation layer may be a common layer, i.e., a layer that spans both the single-type light-emitting element and the tandem-type light-emitting element. When the charge generation layer is a common layer, the carrier functional layer and the light-emitting layer of the single-type light-emitting element may be designed to maximize the luminous efficiency of the light-emitting layer or the characteristics related to the element life of the single-type light-emitting element, taking into account the amount of carrier injection from the charge generation layer. The charge generation layer being a common layer is preferable from the viewpoint of increasing the productivity (manufacturing throughput) of the light-emitting device of the present disclosure. The charge generation layer being an independent layer only for the tandem-type light-emitting element is preferable from the viewpoint of improving the characteristics of the tandem-type light-emitting element without affecting the characteristics of the single-type light-emitting element.

[0177] In the light-emitting device of the present disclosure, the light-emitting elements other than the blue light-emitting element may be tandem light-emitting elements. For example, the red light-emitting element may also be a tandem light-emitting element, or the green light-emitting element may also be a tandem light-emitting element. Thus, in the present disclosure, the "specific color" of the light-emitting element and the specific light-emitting layer may be only blue, or both blue and green, or both blue and red, or both green and red, or blue, green, and red.

[0178] The thickness of the second light-emitting layer and the concentration of the guest compound in the light-emitting element of the present disclosure may vary depending on the emitted color. For example, the thickness of the second light-emitting layer of a red light-emitting element and a green light-emitting element may be 25 nm to 50 nm, and the concentration of the guest compound may be 0.01% or more and 10% or less. The thickness of the second light-emitting layer of a blue light-emitting element may be 10 to 25 nm, and the concentration of the guest compound may be 0.01% or more and 10% or less. The guest compounds in the second light-emitting layer may each be made of a hole-transporting material. However, in the present disclosure, for light-emitting elements of any color, the concentration of the guest compound in the second light-emitting layer is set to be greater than that in the first light-emitting layer.

[0179] In the tandem light-emitting device of the present disclosure, the second and third stacks do not need to include an electron blocking layer if the amount of holes injected into the light-emitting layer can be optimally adjusted. Furthermore, since the inter-electrode distance can be appropriately adjusted by the electron blocking layer in the first stack, the absence of an electron blocking layer in the second and third stacks does not substantially reduce the luminous efficiency in the top-emission structure.

[0180] In the light-emitting device of the present disclosure, the blue light-emitting layer may be a phosphorescent light-emitting layer, and the red or green light-emitting layer may be a fluorescent light-emitting layer.

[0181] Reference Experimental Example Light-emitting devices of various structures, including the tandem light-emitting device of the present disclosure, were fabricated, and their light-emitting device characteristics were determined. The configuration of the tandem light-emitting device in this experimental example is shown schematically in FIG.

[0182] The tandem light-emitting device shown in FIG. 6 has an anode 1, which is a reflective electrode, on a substrate 120, and a first stack 10, a first charge generation layer 20, a second stack 30, and a cathode 2, which is a transmissive electrode, on the anode 1, in this order.

[0183] The substrate 120 is a glass substrate or a flexible substrate whose main component is a resin such as polyimide. The substrate 120 may be composed of, for example, two polyimide films and an inorganic film sandwiched between them. The substrate 120 includes a circuit for driving the light-emitting elements.

[0184] In the first stack 10, the hole injection layer 11 is a layer in which a triphenylamine-based compound is doped with 1% of TCNQ-4F, an electron-accepting material. The first hole transport layer 12 is a layer of a triphenylamine-based compound. The first electron blocking layer 13 is a layer of a carbazole-based compound. The first blue light-emitting layer 14B is a layer in which a perylene-based compound, a host compound, is doped with a pyrene-based compound, an electron-transporting material, as a guest compound. The first hole blocking layer 15 is a layer of a phenanthroline-based compound. The first electron transport layer 16 is a layer of an oxadiazole compound, an electron-transporting material, and an equal amount of Liq.

[0185] In the first charge generation layer 20, the first electron generation layer 21 is a layer in which an oxadiazole-based compound is doped with 10% Yb. The first hole generation layer 22 is a layer in which a triphenylamine-based compound is doped with a specific amount of TCNQ-4F. The amount of TCNQ-4F is set so that the number of holes generated in the first hole generation layer 22 exceeds the number of electrons generated in the first electron generation layer 21.

[0186] The second stack 30 has a second hole transport layer 32, a second electron blocking layer 33, a second blue light-emitting layer 34B, a second hole blocking layer 35, a second electron transport layer 36, and an electron injection layer 37. The second hole transport layer 32, the second electron blocking layer 33, the second blue light-emitting layer 34B, the second hole blocking layer 35, and the second electron transport layer 36 have the same structures as the corresponding layers in the first stack 10. The second blue light-emitting layer 34B has the same structure as the first blue light-emitting layer 14B, except for the type and amount of the guest compound. The electron injection layer 37 is a layer of LiF.

[0187] A tandem light-emitting device was fabricated by doping a 2% pyrene-based compound as a guest compound to form a first blue light-emitting layer 14B, doping the first hole-generating layer 22 with 20% TCNQ-4F, and doping a 3% platinum-based compound (platinum-based complex (Pt complex)) with hole-transporting properties as a guest compound to form a second blue light-emitting layer 34B. This light-emitting device is designated as light-emitting device A.

[0188] A tandem light-emitting device was fabricated in the same manner as in the light-emitting device A, except that the guest compound in the second blue light-emitting layer 34B was changed to a pyrene-based compound.

[0189] A tandem light-emitting device was fabricated in the same manner as light-emitting device B, except that the doping amount of the guest compound in first blue light-emitting layer 14B was 1.5% and the doping amount of the guest compound in second blue light-emitting layer 34B was 3.5%. This was designated light-emitting device C.

[0190] A single-type light-emitting device was fabricated in the same manner as in the light-emitting device B, except that an electron injection layer 37 was formed instead of the first charge generation layer 20 and the second stack 30. This was designated as light-emitting device D.

[0191] A tandem light-emitting device was fabricated in the same manner as in the light-emitting device B, except that the doping amount of the guest compound in each of the first blue light-emitting layer 14B and the second blue light-emitting layer 34B was set to 2.5% by weight. This was designated light-emitting device E.

[0192] A tandem light-emitting device was fabricated in the same manner as light-emitting device B, except that the doping amount of TCNQ-4F in first hole-generating layer 22 was changed to 5%.

[0193] A tandem light-emitting device was fabricated in the same manner as light-emitting device B, except that the doping amount of the guest compound in first blue light-emitting layer 14B was 3% and the doping amount of the guest compound in second blue light-emitting layer 34B was 2%. This was designated light-emitting device G.

[0194] For each of the light-emitting elements A to G, (1) 10 mA / cm ２The voltage (ultimate voltage) (V) when a current was applied at 1000 mA / cm, (2) the luminous efficiency (cd / A / y), and the luminous life (LT90) (h) were measured. The luminous efficiency was determined by evaluating the current density-voltage-luminous characteristics, where y is the value of chromaticity y. The luminous life was measured at a constant current density (here, 50 mA / cm). ２ The results are shown in Table 1.

[0195]

[0196] [Discussion] The device characteristics of light-emitting elements A, B, and C, which are tandem-type light-emitting elements, are all about twice or more of the device characteristics of light-emitting element D, which is a single-type light-emitting element. In particular, the luminous efficiency and luminance life of light-emitting elements A and B are greater than those of light-emitting element C. This is thought to be because the dopant concentration in the second emitting layer is less than twice the dopant concentration in the first emitting layer. Furthermore, the luminance life of light-emitting element A is longer than that of light-emitting element B. This is thought to be because the guest compound in the second emitting layer is a hole-transporting compound different from the guest compound in the first emitting layer.

[0197] The dopant concentration in the first emitting layer and the dopant concentration in the second emitting layer of the light-emitting element E are the same, and the light-emitting element E tends to have lower luminous efficiency and luminance lifetime than the light-emitting elements A, B, and C. The doped amount of the guest compound in the hole generation layer of the light-emitting element F is clearly smaller, and the light-emitting element F tends to have lower luminous efficiency and luminance lifetime than the light-emitting elements A, B, and C. The dopant concentration in the first emitting layer of the light-emitting element G is higher than the dopant concentration in the second emitting layer, and the light-emitting element G tends to have lower luminance lifetime than the light-emitting elements A, B, and C.

[0198] The light-emitting device and display device disclosed herein 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 introduction of clean technologies and environmentally friendly technologies and industrial processes."

[0199] 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.

[0200] 1 anode 2 cathode 3 auxiliary layer 4 buffer layer 5 sealing layer 10 first stack 11 hole injection layer 12 first hole transport layer 13 first electron blocking layer 14 first emitting layer 15 first hole blocking layer 16 first electron transport layer 20 first charge generation layer 21B first blue electron generation layer 22B first blue hole generation layer 30 second stack 32B second blue hole transport layer 33B second blue electron blocking layer 34B second blue emitting layer 35B second blue hole blocking layer 36B second blue electron transport layer 37 electron injection layer 40 second charge generation layer 41B second blue electron generation layer 42B second blue hole generation layer 50B third stack 51B third blue hole injection layer 52B third blue hole transport layer 53B third blue electron blocking layer 54B Third blue light-emitting layer 55B Third blue hole-blocking layer 56B Third blue electron-transporting layer 100 Display device 101 Display area 102 Frame area 110, 210 Light-emitting device 111, 211 Light-emitting element 120 Substrate

Claims

1. A light-emitting device comprising a plurality of light-emitting elements arranged in a first direction, wherein adjacent light-emitting elements in the first direction emit light of different colors, and each of the light-emitting elements comprises a cathode, a light-emitting layer, and an anode, in this order, in a second direction intersecting the first direction, and each light-emitting element emitting light of at least a specific color among a plurality of emission colors of the plurality of light-emitting elements comprises: a specific light-emitting layer, which is each of two or more light-emitting layers arranged to overlap in the second direction and emit light of the same specific color; an electron generation layer located on the anode side between two adjacent specific light-emitting layers in the second direction and generating electrons; and a hole generation layer located on the cathode side between two adjacent specific light-emitting layers in the second direction and generating holes, wherein the two or more specific light-emitting layers emitting light of the same specific color all contain the same type of host compound and the same or different types of guest compound, and the concentration of the guest compound in each of the two or more specific light-emitting layers is higher as the specific light-emitting layer is closer to the cathode, a guest compound in at least the specific light-emitting layer closest to the anode is an electron transporting material, and an amount of holes injected from the hole generation layer into the specific light-emitting layer on the cathode side is greater than an amount of electrons injected from the electron generation layer into the specific light-emitting layer on the anode side.

2. The light-emitting device according to claim 1, wherein the guest compound in at least the specific light-emitting layer located closest to the cathode in the second direction is a hole-transporting material.

3. The light-emitting device according to claim 1 or 2, wherein, in two of the specific light-emitting layers adjacent to each other in the second direction, the concentration of the guest compound in the specific light-emitting layer on the cathode side is not more than twice the concentration of the guest compound in the specific light-emitting layer on the anode side.

4. The light-emitting device according to any one of claims 1 to 3, wherein each of the plurality of light-emitting elements has a fluorescent light-emitting layer in which the guest compound is a fluorescent dopant, or a phosphorescent light-emitting layer in which the guest compound is a phosphorescent dopant, and all of the specific light-emitting layers are the fluorescent light-emitting layers.

5. The light emitting device according to any one of claims 1 to 4, wherein each of the specific light emitting layers emits light having a peak wavelength of 430 nm or more and 470 nm or less.

6. The light emitting device according to any one of claims 1 to 5, wherein the difference in peak wavelength of the emission spectrum between two of the specific light emitting layers adjacent to each other in the second direction is 10 nm or less.

7. The light-emitting device according to any one of claims 1 to 6, wherein, in two of the specific light-emitting layers adjacent to each other in the second direction, the full width at half maximum at the peak wavelength of the emission spectrum of the specific light-emitting layer on the anode side is 0.75 to 1.25 times the full width at half maximum at the peak wavelength of the emission spectrum of the specific light-emitting layer on the cathode side.

8. The light-emitting device according to any one of claims 1 to 7, which has three or more of the specific light-emitting layers.

9. The light-emitting device according to any one of claims 1 to 8, which has five or less of the specific light-emitting layers.

10. The light emitting device according to any one of claims 1 to 9, wherein the difference between the maximum and minimum peak wavelengths of the emission spectra of the plurality of specific light emitting layers in the second direction is 10 nm or less.

11. The light-emitting device according to any one of claims 1 to 10, wherein the maximum value of the full width at half maximum at the peak wavelength of the emission spectrum of the plurality of specific light-emitting layers in the second direction is 1.25 times or less the minimum value of the full width at half maximum.

12. The light emitting device according to any one of claims 1 to 11, which is a top emission type.

13. A display device comprising the 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, comprising a step of alternately laminating the specific light-emitting layer, the electron generation layer, and the hole generation layer, wherein in the laminating step, the specific light-emitting layer is formed by a vapor deposition method.

15. The method for manufacturing a light-emitting device according to claim 14, wherein in the laminating step, at least the vapor deposition time of the guest compound is varied for each of the specific light-emitting layers.

16. The method for manufacturing a light-emitting device according to claim 15, wherein in the laminating step, only the vapor deposition time of the guest compound is varied for each of the specific light-emitting layers.

17. The method for manufacturing a light-emitting device according to claim 14 or 15, wherein in the laminating step, at least the vapor deposition temperature of the guest compound is made different for each of the specific light-emitting layers.

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