Electric field light-emitting device, manufacturing method thereof, and display device

Abstract

The electric field light-emitting device (13) includes electric field light-emitting layers (n > = 2) of first to n-th colors in a direction intersecting the stacking direction, the electric field light-emitting layers emitting light of mutually different colors being disposed, and includes, in the stacking direction, a first electric field light-emitting layer (34) on the anode layer side and a second electric field light-emitting layer (53) on the cathode layer side, with a charge generation layer (40) interposed between the first electric field light-emitting layer (34) and the second electric field light-emitting layer (53). The thickness of the second electroluminescent layer (53) is thinner than the thickness of the first electroluminescent layer (34).

Description

Technical Field

[0001] The present disclosure relates to an electroluminescent device, a manufacturing method thereof, and a display device. Background Art

[0002] Mass production of displays equipped with organic EL elements (also known as "Organic Light Emitting Diode," "OLED") has begun in earnest, starting with thin displays for high-end smartphones and TVs. Displays using organic EL elements are now widespread and are becoming a core component of ultra-thin displays that are replacing LCDs.

[0003] Thin-film stacked organic EL devices using an aluminum quinolate complex (Alq3) for both the electron transport layer and the electroluminescent layer are known. However, in order to further improve the luminous efficiency of organic EL devices, development has been carried out in the following order (1) to (3).

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

[0005] (2) As the guest compound (dopant) for the electroluminescent layer, a fluorescent material, or a fluorescent material and a phosphorescent material is used.

[0006] (3) Using modified guest compounds such as thermally activated delayed fluorescence (TADF) materials or superfluorescent materials as dopants for the electric field luminescence layer.

[0007] Furthermore, from the viewpoint of improving the current efficiency and device life of the organic EL device, the following (4) and (5) were further studied.

[0008] (4) Improve carrier balance by studying carrier transport layers or carrier injection layers.

[0009] (5) The element structure of the light-emitting element adopts a tandem structure (for example, see Patent Document 1).

[0010] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Laid-Open No. 2015-32582 Summary of the Invention Problems to be solved by the invention However, when light-emitting layers of respective colors of RGB are applied so as to enable full-color display and a tandem structure is adopted, the advantages of the tandem structure may not be fully realized.

[0011] One aspect of the present disclosure is to provide a technology capable of fully demonstrating the advantages of adopting a tandem structure in an electroluminescent device capable of full-color display.

[0012] Solutions for solving problems One aspect of the present disclosure relates to an electroluminescent device comprising: an anode layer; a cathode layer, arranged opposite to the anode layer in a stacking direction; a plurality of electroluminescent layers, respectively arranged between the anode layer and the cathode layer in the stacking direction and in a plurality in a direction crossing the stacking direction; a charge generation layer, arranged between two adjacent electroluminescent layers in the stacking direction, wherein in the electroluminescent layers, a plurality of electroluminescent layers emitting light of the same color are arranged in the stacking direction, and in a direction crossing the stacking direction, electroluminescent layers of a first color to an nth color emitting light of different colors are arranged, wherein n is an integer ≥2, and in at least one of the groups consisting of two adjacent electroluminescent layers separated by the charge generation layer in the stacking direction, the thickness of the electroluminescent layer on the cathode layer side is thinner than the thickness of the electroluminescent layer on the anode layer side.

[0013] One aspect of the present disclosure relates to a display device including the above-mentioned electroluminescent device.

[0014] In addition, one aspect of the present disclosure involves a method for manufacturing an electroluminescent device, which is a method for manufacturing the above-mentioned electroluminescent device, including the process of alternately forming the electroluminescent layer and the charge generation layer on the anode layer or the cathode layer and in the stacking direction, and forming the electroluminescent layer by evaporation.

[0015] Effects of the Invention According to one aspect of the present disclosure, an electroluminescent device capable of full-color display is provided that can fully demonstrate the advantages of adopting a tandem structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a plan view schematically showing the configuration of the display device according to the first embodiment of the present invention.

[0017] Figure 2 It is schematically represented Figure 1 Schematic diagram of the layer structure of a display device.

[0018] Figure 3 It is schematically shown Figure 2 Schematic diagram of the layer structure of the electroluminescent element in the layer structure shown.

[0019] Figure 4 It shows Figure 3Flowchart of an example of a method for manufacturing an electroluminescent element shown in FIG.

[0020] Figure 5 Is used to illustrate Figure 2 Schematic diagram of the light-emitting mechanism of the electroluminescent element of the electroluminescent device shown.

[0021] Figure 6 This is a schematic diagram for explaining the light emission mechanism of the electroluminescent element of the electroluminescent device according to Embodiment 2 of the present disclosure. DETAILED DESCRIPTION

[0022] [Electroluminescent element] The electroluminescent element of an embodiment of the present invention has an anode layer, a cathode layer, an electroluminescent layer and a charge generation layer. The electroluminescent element disclosed in the present invention has a plurality of electroluminescent layers overlapping in the stacking direction. In addition, in at least one group of two adjacent electroluminescent layers separated by the charge generation layer, the thickness of the electroluminescent layer on the cathode layer side is thinner than the thickness of the electroluminescent layer on the anode layer side. The electroluminescent element disclosed in the present invention can adopt a known element structure of a light-emitting element within the range of layers that meet these conditions. In the following, the layer structure of the electroluminescent element disclosed in the present invention is mainly described by taking OLED as an example. It should be noted that, in the present invention, "electroluminescent element" refers to a group of arrangements of electroluminescent layers and various carrier functional layers in the stacking direction. In addition, in the present invention, "electroluminescent device" refers to a group of multiple electroluminescent elements in a direction intersecting the stacking direction.

[0023] [Anode Layer] The anode layer is one of a pair of electrode layers, the anode and cathode. In the present disclosure, it is used to supply holes to the various layers that make up the electroluminescent element. The anode layer is conductive. Furthermore, the anode layer has optical properties such as reflecting a portion of visible light and transmitting the remainder. Typically, the anode layer includes both electrode materials that reflect visible light and electrode materials that transmit visible light.

[0024] To improve hole injection, the anode layer preferably uses a material with a relatively high work function (e.g., a material with a work function of 4.5 eV or higher). Examples of electrode materials with a high work function include Pt (5.65 eV), Ir (5.25 eV), Ni (5.2 eV), Au and Pd (5.15 eV), and indium tin oxide (In-Sn-O).

[0025] Examples of electrode materials that reflect visible light include metal materials such as Al, Mg, Li, Ag, Pd, and Cu, and alloys of these metal materials (eg, APC (Ag—Pd—Cu) alloy).

[0026] Examples of electrode materials that transmit visible light include thin films of transparent metal oxides (e.g., indium tinoxide (In-Sn-O), indium zinc oxide (In-Zn-O), and indium gallium zinc oxide (In-Ga-Zn-O)), thin films composed of metal materials such as Al, Mg, and Ag, and nanowires (NWs) composed of these metal materials.

[0027] Among transparent metal oxides, In-Sn-O has a relatively high work function of 4.6 to 5.0 eV, making it suitable for use as anode layer materials. Furthermore, in order to improve the conductivity of the electrode layer or to add a visible light reflection function, a stacked structure with In-Sn-O formed on the surface of a metal material (e.g., In-Sn-O / Ag) can be used in the anode layer.

[0028] [Cathode Layer] The cathode layer is the other electrode layer in a pair of anode and cathode electrodes. In the present disclosure, it is used to supply electrons to the layers that make up the electroluminescent element. The cathode layer is arranged opposite the anode layer in the stacking direction. The cathode layer has, for example, electrical conductivity and visible light transmittance.

[0029] For example, to improve electron injection, the cathode layer preferably uses a material with a relatively low work function. Examples of electrode materials for the cathode layer 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 alloys of Mg and Ag, and Al doped with a small amount of Li.

[0030] [Electroluminescent Layer] An electroluminescent layer is a layer that emits light of a specified color when an electric field is applied. An electroluminescent layer is typically composed of a luminescent material, but may also be a stacked structure of multiple functional layers, such as an immediate luminescent layer and a delayed luminescent layer, with two or more functional layers corresponding to two or more functions of electroluminescence in a known electroluminescent layer overlapping each other, so that the entire structure exhibits electroluminescent function. In the present disclosure, multiple electroluminescent layers are disposed between the anode layer and the cathode layer in the stacking direction and in a direction intersecting the stacking direction.

[0031] In the stacking direction, the electroluminescent layer is configured with multiple electroluminescent layers emitting light of the same color. The number of electroluminescent layers emitting light of the same color that overlap in the stacking direction is not limited; however, from the perspective of improving luminous efficiency and extending the life of the device, it is preferably two or more, and more preferably three or more. On the other hand, from the perspective of suppressing a rise in driving voltage, achieving a withstand voltage of the driver corresponding to the driving voltage, and maintaining the flexibility of the electroluminescent device (suppressing an increase in the total thickness of the electroluminescent device), the number of electroluminescent layers emitting light of the same color that overlap in the stacking direction is preferably five or less, and more preferably four or less.

[0032] Here, the same color refers to the same color of light where, when there are two or more luminous peak wavelengths, all of the luminous peak wavelengths are within the range of ±5nm, and the maximum value of the half-value full width among all the luminous peak wavelengths is less than 1.25 times the minimum value of the half-value full width among the remaining luminous peak wavelengths. Basically, when the host material and the guest compound constituting the electric field luminescent layer are the same material or similar materials with the same skeleton, the same color is emitted. However, in the top emission structure described later, due to the difference in the microcavity structure of each color, the luminous peak wavelength of each color sometimes varies. Therefore, in the top emission structure, the same color refers to the same color of light where all the luminous peak wavelengths are within the range of ±10nm and satisfy the above-mentioned range of the half-value full width.

[0033] In addition, in the direction intersecting the stacking direction, the electric field luminescent layer is configured with an electric field luminescent layer of the first color to an electric field luminescent layer of the nth color (n is an integer of 2) that emits light of different colors from each other. Here, different colors refer to the same color of light that is not included in the range of the above-mentioned same color. As a representative well-known example, as a multi-color electric field luminescent layer for full-color display, three color luminescent layers are known, namely a red luminescent layer, a green luminescent layer, and a blue luminescent layer. In this way, configuring electric field luminescent layers of multiple colors in a direction intersecting the stacking direction is called "split coating". In addition, it is preferred that the number of electric field luminescent layers of each color in the stacking direction is the same for all luminescent colors. In the following, the electric field luminescent layer in the present invention is mainly explained by taking the above-mentioned three-color luminescent layers as an example, but the present disclosure is not limited to this. It should be noted that the electric field luminescent layers of different colors in the intersecting direction can be at the same position (height) or at different positions (heights) (or staggered) in the stacking direction.

[0034] That is, in the present disclosure, when the electric field light emitting device includes electric field light emitting layers of red, green and blue colors, the electric field light emitting elements of each color are independently configured in a direction intersecting the stacking direction, for example, in a direction orthogonal to the stacking direction. In addition, in the stacking direction, the red electric field light emitting layer overlaps with the red electric field light emitting layer, the green electric field light emitting layer overlaps with the green electric field light emitting layer, and the blue electric field light emitting layer overlaps with the blue electric field light emitting layer. In addition, electric field light emitting layers of different colors can be further stacked in the stacking direction, but from the viewpoint of improving color purity, it is preferred that only a plurality of electric field light emitting layers emitting light of the same color be configured in the stacking direction. From the viewpoint of more easily determining the thickness of the electric field light emitting layer described later, it is advantageous to stack only electric field light emitting layers of the same color in the stacking direction.

[0035] In an EFL element with three or more EFL layers arranged in the stacking direction, if a charge generation layer is interposed between the EFL layers, optimizing the carrier (electron and / or hole) supply in the EFL layer on one side of the stacking direction relative to the charge generation layer can sometimes result in a rate-limited, or insufficient, supply of electrons and / or holes in the EFL layer on the other side. This can result in an imbalance in the carrier balance among the multiple EFL layers. In the present invention, by appropriately reducing the thickness of the EFL layer, which controls the carrier (electron) supply rate, it is possible to optimize the carrier balance in all EFL layers in the stacking direction.

[0036] That is, in the electroluminescent device of the present invention, in at least one set of two electroluminescent layers adjacent to each other in the stacking direction across the charge generation layer, the thickness of the electroluminescent layer on the cathode layer side is thinner than the thickness of the electroluminescent layer on the anode layer side. That is, in the present invention, the thickness of a particular electroluminescent layer is thinner than the thickness of the electroluminescent layer on the anode layer side. It should be noted that the term "adjacent" in the electroluminescent layer refers to the positional relationship of the electroluminescent layers included in the electroluminescent element that are adjacent in the stacking direction. That is, other layers may be sandwiched between electroluminescent layers that are adjacent in the stacking direction.

[0037] Furthermore, the electroluminescent device of the present disclosure may be configured to include an electroluminescent layer whose thickness gradually decreases from the anode layer side toward the cathode layer side in the stacking direction.

[0038] By adopting such a configuration, the electroluminescent device of the present disclosure achieves an appropriate carrier balance in each electroluminescent layer along the stacking direction. The thickness of each electroluminescent layer along the stacking direction can be appropriately determined based on various factors, such as the material combination of each layer in the electroluminescent element and the purpose of changing the thickness of the electroluminescent layer, as long as the technical concept of the present disclosure is followed.

[0039] Furthermore, when the thickness of the electroluminescent layer closest to the anode layer is set to 1, from the perspective of extending the device life and reducing the residual carriers (holes) described later, the thickness of the electroluminescent layer on the cathode layer side is preferably 0.1 or more, more preferably 0.3 or more. On the other hand, from the perspective of balancing improvement in luminous efficiency and reduction in driving voltage (power consumption), the thickness is preferably 0.9 or less, more preferably 0.8 or less.

[0040] In the present invention, when three or more electroluminescent layers are arranged in the stacking direction with charge generation layers interposed therebetween, the thickness of each electroluminescent layer can be determined so that the thickness decreases from the anode layer side to the cathode layer side according to a linear function, a quadratic function, or another function. Alternatively, the thickness of each layer can be determined based on factors other than the aforementioned correlation (e.g., the function of the intervening charge generation layer).

[0041] For example, the thickness of a plurality of electroluminescent layers overlapping in the stacking direction of the present disclosure can be determined by the following method. That is, the applied voltage, luminous efficiency, or device life of an electroluminescent element having an electroluminescent layer of the same thickness in the stacking direction is measured and used as a reference value. On the other hand, an electroluminescent element is produced in which the thickness of the electroluminescent layer close to the cathode layer is thinner, and the applied voltage, luminous efficiency, or device life is measured. Based on the obtained measured value and the reference value, the appropriate thickness that meets the purpose is determined.

[0042] In addition, the thickness of each electroluminescent layer in the stacking direction can be determined to be the thickness corresponding to the purpose by a simulation evaluation based on the carrier injection and / or carrier transport properties of each layer in the electroluminescent element and a verification experiment based on the evaluation. In this case, by setting the multiple electroluminescent layers stacked in the stacking direction to only the same color, the parameters of the carrier injection and carrier transport properties between the different electroluminescent layers in the stacking direction can be made the same. Therefore, simulation becomes easier and the thickness of each electroluminescent layer can be determined more simply.

[0043] Preferred electroluminescent layers disclosed herein include host-guest systems comprising a host compound and a guest compound. In a host-guest electroluminescent layer, a solid medium containing the host compound contains a trace amount (e.g., 0.1 to several mol%) of a fluorescent dopant, etc., as the guest compound. In an electroluminescent layer doped with a guest compound, the fluorescence of the host compound completely disappears, replaced by intense luminescence consistent with the fluorescence spectrum of the doped guest compound. This is because the excitation energy of the host compound is transferred to the guest compound. This transfer of excitation energy enables the host-guest electroluminescent layer to produce luminescence from the guest compound with higher quantum efficiency.

[0044] Furthermore, by doping the EFL layer with a fluorescent dopant as a guest compound, the device lifespan of the EFL element is dramatically improved. This is because the dopant, acting as a guest compound, acts as a carrier (electron or hole) trap within the solid medium of the host compound, becoming a recombination center for these carriers and directly generating excitons within the solid medium. The process by which these generated excitons deactivate to their ground state is called the deactivation process. The deactivation process can involve either a non-radiative process (thermal deactivation) or a radiative process (luminescence). The phenomenon of luminescence generated during the radiative process is EFL. By having the guest compound act as a carrier trap, not only is the quantum efficiency of the EFL layer improved, but the device lifespan is also extended due to the increased probability of carrier recombination. Consequently, both the luminous efficiency of the EFL layer and the device lifespan of the EFL element are improved.

[0045] Thus, since carriers can be effectively utilized in the host-guest system electroluminescent layer, the electroluminescent device of the present application can achieve high luminous efficiency of the electroluminescent layer and improve the life of the electroluminescent element.

[0046] In addition, the excitons generated when carriers recombine include singlet excitons and triplet excitons. When a fluorescent dopant is used as a guest compound, the singlet exciton contributes to luminescence. Here, when a phosphorescent dopant is used instead of a fluorescent dopant, the triplet exciton contributes to luminescence. According to the spin statistics law, the generation ratio of singlet excitons to triplet excitons is 25% for singlet excitons and 75% for triplet excitons. Therefore, when a fluorescent dopant is used as a guest compound, that is, in the luminescence process of "fluorescence" emitted only from singlet excitons, the probability of exciton generation that can contribute to luminescence is limited to a maximum of 25%.

[0047] In contrast, using a phosphorescent dopant as a guest compound allows light to be extracted from triplet excitons, resulting in a quantum efficiency three times higher than that of a fluorescent dopant. Furthermore, by utilizing intersystem crossing (ISC), a spin reversal from singlet excitons to triplet excitons, all generated excitons can theoretically emit "phosphorescence" from triplet excitons. Therefore, using a phosphorescent dopant as a guest compound can improve quantum efficiency by up to four times compared to using a fluorescent dopant.

[0048] The luminescent materials for the electric field luminescent layer can be known materials. For example, examples of luminescent materials for the blue electric field luminescent layer include pyrene compounds and anthracene compounds as fluorescent dopants. Furthermore, examples of luminescent materials for the red and green electric field luminescent layers include iridium complexes and palladium complexes as phosphorescent dopants.

[0049] Furthermore, complexes containing platinum-group elements such as iridium and palladium used as phosphorescent dopants are often very expensive, even in trace amounts, due to the low and uneven production of platinum-group elements. This makes stable supply difficult. Therefore, reducing the amount of these platinum-group complexes used as phosphorescent dopants is extremely important from the perspective of cost reduction and economic security.

[0050] Thus, a host-guest system electroluminescent layer can be formed by doping a host compound with a guest compound. A host-guest system electroluminescent layer can be formed by a co-evaporation method using multiple evaporation sources.

[0051] The materials for the host-guest electroluminescent layer can be various well-known examples. Examples of host compounds include well-known luminescent layer materials of various colors. Examples of guest compounds, in addition to the aforementioned fluorescent and phosphorescent dopants, also include TADF and superfluorescent materials. Further examples of fluorescent dopants include perylene, DPT, Coumarin 6, PMDFB, quinacridone, rubrene, BTX, ABTX, DCM, and DCJT. Another example of a phosphorescent dopant includes: Ir(ppy)3, Ir(thpy)3, Ir(t5m-thpy)3, Ir(t-5CF3-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.

[0052] Furthermore, in currently mainstream electroluminescent elements, fluorescent dopants are used as guest compounds in the blue electroluminescent layer, while phosphorescent dopants are used as guest compounds in the red and green electroluminescent layers. In electroluminescent devices incorporating these elements, the quantum efficiency of fluorescent dopants is lower than that of phosphorescent dopants, both theoretically and practically. Therefore, in these electroluminescent devices, a balance in luminescence is achieved by flowing a higher current through the blue electroluminescent layer than through the red and green electroluminescent layers.

[0053] However, if only the amount of current flowing in the blue electric field luminescent layer is increased, the life of the blue electric field luminescent layer will inevitably be shortened (deterioration rate is fast), wherein the blue electric field luminescent layer is the fluorescent electric field luminescent layer mentioned above that uses only fluorescent dopants as guest compounds. In order to address this problem, the total number of blue electric field luminescent layers stacked in the stacking direction can be made greater than the total number of layers of the phosphorescent electric field luminescent layers, i.e., the red and green electric field luminescent layers, in which the guest compounds are phosphorescent dopants. In other words, the total number of layers of the fluorescent electric field luminescent layers can be made greater than the total number of layers of the phosphorescent electric field luminescent layers. Such a structure is conducive to achieving a balance between the life of the electric field luminescent layer and the amount of light emitted between the fluorescent electric field luminescent layer and the phosphorescent electric field luminescent layer in the electric field luminescent element. The total number of layers of the fluorescent electric field luminescent layer is preferably 1 or 2 more than the total number of layers of the phosphorescent electric field luminescent layer. If the number of fluorescent electric field luminescent layers is 3 or more more than the number of phosphorescent electric field luminescent layers, it will be difficult to achieve a balance between the life and the amount of light emitted between the phosphorescent electric field luminescent layers of different colors. Alternatively, the balance of the element structure of the electroluminescent device may be deteriorated, thereby reducing the manufacturing yield.

[0054] [Charge Generation Layer] The charge generation layer is positioned between two adjacent electroluminescent layers in the stacking direction. The charge generation layer generates one or both electrons and holes. The charges (charges or carriers) generated by the charge generation layer are supplied to the electroluminescent layers located on the anode and cathode sides of the stacking direction, respectively. The charge generation layer can employ known charge generation materials that exhibit the aforementioned functions.

[0055] The charge generation layer can be composed of an electron generation layer that generates electrons and a hole generation layer that generates holes. Examples of the electron generation layer include an n-type charge generation layer, and examples of the hole generation layer include a p-type charge generation layer. When holes are supplied from the anode layer and electrons are supplied from the cathode layer, the n-type charge generation layer generates electrons, and the p-type charge generation layer generates holes.

[0056] The p-type charge generation layer can use a material containing an organic hole transport material and an organic electron accepting material (hole supply material) added in an amount ranging from 1% to 10%. The organic hole transport material can be a well-known triarylamine-based organic compound. An example of an organic electron accepting material is tetracyanoquinodimethane tetrafluoride (TCNQ-4F). The p-type charge generation layer uses the aforementioned hole transport material and electron accepting material, all of which are organic materials, to achieve sufficient hole generation capacity.

[0057] For example, the n-type charge generation layer can contain an organic electron transport material and an inorganic metal material (i.e., Yb (ytterbium) or Li (lithium)) added in a range of 5-20% to function as an electron donor. Examples of organic electron transport materials include oxadiazole compounds. Development is also underway to use organic materials for both the electron transport and electron donor materials in the n-type charge generation layer. For example, development of organic electron donor materials such as BUPH1, BPen, p-MeO-Phen, p-NMe2-Phen, and p-Pyrrd-Phen is underway.

[0058] Currently, no organic electron-donating materials with sufficient electron-donating properties suitable for use in n-type charge generation layers have been discovered. Consequently, no n-type charge generation layer composed entirely of organic materials and exhibiting sufficient properties has been discovered. According to the present disclosure, by setting the thickness of each electroluminescent layer in the stacking direction as described above, it is possible to optimize the balance (carrier balance) between the electrons and / or holes supplied from the charge generation layer and the holes and / or electrons supplied by each electrode layer. Therefore, the present invention suppresses the generation of excess carriers, achieving an electroluminescent device having a tandem structure of multiple electroluminescent layers in the stacking direction with excellent power consumption.

[0059] [Other Configurations] The electroluminescent element of the present disclosure may further include other layers within the scope of achieving the effects of the present disclosure. Examples of other configurations include carrier functional layers such as a hole injection layer, an electron injection layer, a hole transport layer, an electron blocking layer, a hole blocking layer, and an electron transport layer.

[0060] The hole injection layer is, for example, disposed adjacent to the anode layer. The hole injection layer may be composed of a hole transport material and an electron accepting material. These materials are the same organic materials as those described for the p-type charge generation layer. The specific material of the hole injection layer in the electroluminescent element may be the same as or different from that of the p-type charge generation layer.

[0061] The electron injection layer is, for example, disposed adjacent to the cathode layer. The electron injection layer can be composed of an electron transport material. Examples of electron transport materials for the electron injection layer include lithium fluoride (LiF), an inorganic material. Similarly to the n-type charge generation layer, the electron injection layer can also be composed of an organic material, such as an oxadiazole compound, doped with a metal material (e.g., Li or Yb).

[0062] LiF used in the electron injection layer exhibits excellent electron injection properties. On the other hand, the film formation of the carrier functional layer containing inorganic materials such as Yb, not limited to LiF, is usually carried out at a higher temperature than the film formation of the electroluminescent layer and the carrier functional layer composed of organic materials due to the high melting point of these inorganic materials. Therefore, there is a possibility of thermal damage to the organic material formed first. Therefore, if possible, it is preferable to form the electroluminescent element only from organic materials.

[0063] Therefore, organic electron-injecting materials such as BUPH1, BPen, p-MeO-Phen, p-NMe2-Phen, and p-Pyrrd-Phen are being developed to achieve sufficient properties by combining them with a cathode layer composed of aluminum (Al) or other materials that form a vapor-deposited layer at a relatively low temperature. However, the electron injection capability of electron-injecting layers using organic materials is inferior to that of electron-injecting layers using inorganic materials such as LiF. Therefore, when an electron-injecting layer composed of an organic material is arranged adjacent to the cathode layer, the electron supply to the electroluminescent layer formed on the cathode layer side may be reduced. In such cases, by reducing the thickness of the electroluminescent layer on the cathode layer side compared to the theoretical value, the effect of the reduced electron supply can be reduced, thereby fully realizing the advantages of adopting a tandem structure.

[0064] The hole transport layer can be composed of an organic hole transport material, for example, a triarylamine organic compound.

[0065] The electron blocking layer may also be composed of an organic hole transport material, similarly to the hole transport layer. The material of the electron blocking layer may be the same as or different from that of the hole transport layer.

[0066] The hole blocking layer may be formed of an organic electron transport material, such as an oxadiazole compound. The material of the hole blocking layer may contain lithium quinoline (Liq) in addition to the electron transport material.

[0067] The electron transport layer, like the hole blocking layer, may also be composed of the above-mentioned organic electron transport material. The material of the electron transport layer may be the same as or different from that of the hole blocking layer.

[0068] The hole injection layer and electron injection layer may be arranged corresponding to the electrode layers, and are typically arranged adjacent to each electrode layer in the stacking direction. Multiple hole transport layers, electron blocking layers, the aforementioned electroluminescent layer, hole blocking layers, electron transport layers, and the aforementioned charge generation layer may be repeatedly arranged in overlapping fashion in the stacking direction of the electroluminescent element.

[0069] The electroluminescent device disclosed in the present invention is suitable for an electroluminescent device capable of top-emitting full-color display. In a top-emitting electroluminescent device, the distance between the electrode layers is adjusted according to the wavelength of light from the light-emitting layers of each color, thereby utilizing the microcavity effect to improve the light extraction efficiency. For this purpose, any layer of the carrier functional layer is sometimes thickened. The electroluminescent device disclosed in the present invention has a so-called series structure having a plurality of electroluminescent layers and carrier functional layers corresponding to each electroluminescent layer in the stacking direction. Therefore, the thickness of the carrier functional layer for adjusting the distance between the electrode layers is suppressed, which can further suppress the consumption of functionally unnecessary materials.

[0070] [Laminate] A laminate is a collection of layers including an electroluminescent layer disposed between the anode layer and the charge generation layer, between the charge generation layers, and between the charge generation layer and the cathode layer in the stacking direction. In addition to the electroluminescent layer, the laminate may also include a carrier-functional layer. Multiple laminates may also be disposed between the anode layer and the cathode layer in the stacking direction. In the present invention, the laminate does not include an anode layer, a cathode layer, or a charge generation layer.

[0071] The thickness of the stack is determined to be a value such that the luminescence amount in the electric field luminescent layer is a theoretical value or a value close to the theoretical value. In the present disclosure, the thickness of each electric field luminescent layer in the stacking direction can be set within the range of the above ratio. Therefore, from the viewpoint of improving the luminous efficiency of the electric field luminescent element, it is preferably set to the thickness of the stack corresponding to the thickness of the electric field luminescent layer set in this way. From such a viewpoint, the ratio of the thickness of the electric field luminescent layer in the stacking direction to the thickness of the stack is preferably 0.05 or more, and preferably 0.35 or less. In addition, the thickness of the stack is obtained by the sum of the thickness of the electric field luminescent layer and the carrier functional layer in the stack, but for the layer with a very small thickness in the electric field luminescent layer and the carrier functional layer (for example, a layer with a thickness that may be less than 1nm), it can also be ignored when calculating the thickness of the stack.

[0072] [Method for Manufacturing an Electroluminescent Device] In manufacturing the electroluminescent device disclosed herein, the thickness of each electroluminescent layer is controlled so that the thickness of the electroluminescent layer on the cathode layer side, adjacent across the charge generation layer in the stacking direction, is thinner than the thickness of the electroluminescent layer on the anode layer side. Alternatively, the electroluminescent device of the present invention can be manufactured using a known method capable of manufacturing an electroluminescent element having multiple electroluminescent layers (tandem structure). The method for manufacturing the electroluminescent device may include alternating formation of electroluminescent layers and charge generation layers on the anode layer or cathode layer in the stacking direction. Furthermore, from the perspective of precisely controlling the thickness of each electroluminescent layer in the electroluminescent device disclosed herein, it is preferred that at least the electroluminescent layer be formed by vapor deposition in this manufacturing method. Electroluminescent layers formed by vapor deposition are generally preferred from the perspectives of achieving high brightness and low voltage operation. Furthermore, since electroluminescent elements composed of fine pixels can be formed with high precision, they are also preferred from the perspective of realizing high-definition display devices. Furthermore, a co-evaporation method using a plurality of evaporation sources is more preferable because a host-guest system electroluminescent layer can also be formed.

[0073] Since the electroluminescent device disclosed in the present invention has a specific layer structure, it can be manufactured by repeatedly forming a specific layer. In the present disclosure, it is preferred to form the electroluminescent layer having different thicknesses in the stacking direction by simply changing the evaporation time. According to such a manufacturing method, the conditions other than the evaporation time in the formation of the electroluminescent layer (for example, the evaporation rate controlled by the temperature of the crucible (evaporation temperature) or the evaporation temperature, the ratio of the host compound to the guest compound (the doping concentration of the guest compound), and the evaporation mask that specifies the pixel shape, etc.) can be fixed. Therefore, the characteristic deviation caused by the change of the conditions of each electroluminescent layer in the stacking direction can be suppressed, and the effect caused by the difference in the thickness of the electroluminescent layer in the stacking direction can be more significantly manifested.

[0074] [Display Device] The display device disclosed herein includes the aforementioned electroluminescent device. In addition to including the aforementioned electroluminescent device, the display device disclosed herein can be configured similarly to a conventional display device including a conventional light-emitting device. Examples of display devices include televisions and smartphones.

[0075] [Specific Description] The following describes the electroluminescent device, its manufacturing method, and display device disclosed herein in more detail using an organic light-emitting diode (OLED) as an example. In this specification, components associated with different colors within the same basic structure are represented by adding a symbol representing the color. For example, components associated with red are further labeled with R, components associated with green are further labeled with G, and components associated with blue are further labeled with B.

[0076] [Implementation Method 1] <Composition> Figure 1 1 is a plan view schematically showing the structure of the display device 100 according to the first embodiment of the present disclosure. Figure 1 FIG. 4 shows a smartphone as an example of a display device. Figure 1 As shown, the display device 100 includes a frame area NDA and a display area DA. The display area DA of the display device 100 includes a plurality of pixels PIX, each pixel PIX including a red sub-pixel RSP, a green sub-pixel GSP, and a blue sub-pixel BSP.

[0077] In addition, the pixel structure of the display device of the present disclosure is not limited to the above structure. In the display device of the present disclosure, for example, a pixel PIX may include sub-pixels of other colors in addition to the red sub-pixel RSP, the green sub-pixel GSP, and the blue sub-pixel BSP.

[0078] Figure 2 It is a schematic representation Figure 1 FIG. 1 is a diagram showing a layer structure of the display device 100. Figure 2 As shown, in the display device 100 , a substrate 11 , a buffer layer 12 , a TFT (thin film transistor) layer 20 including a pixel circuit, an electroluminescent device 13 , an edge cover film 16 , a sealing layer 14 , and an external functional layer 15 are sequentially stacked.

[0079] The substrate 11 is a glass substrate or a flexible substrate primarily composed of a resin such as polyimide. For example, the substrate 11 may be composed of two layers of polyimide film with an inorganic film sandwiched between them. The barrier layer 12 may be an inorganic insulating layer that prevents the intrusion of foreign matter such as water and oxygen. The TFT layer 20 includes pixel circuits that control the red electroluminescent element 10R, the green electroluminescent element 10G, and the blue electroluminescent element 10B.

[0080] The electroluminescent device 13 includes a red electroluminescent element 10R, a green electroluminescent element 10G, and a blue electroluminescent element 10B. The red electroluminescent element 10R includes an anode layer 21R and a cathode layer 22R, with a first electroluminescent layer 34R and a second electroluminescent layer 53R located between these electrode layers. Similarly, the green electroluminescent element 10G includes an anode layer 21G, a first electroluminescent layer 34G, a second electroluminescent layer 53G, and a cathode layer 22G, and the blue electroluminescent element 10B includes an anode layer 21B, a first electroluminescent layer 34B, a second electroluminescent layer 53B, and a cathode layer 22B.

[0081] Here, in Figure 2 , a configuration is shown in which cathode layers 22R, 22G, and 22B are provided on the red, green, and blue electric field light-emitting elements 10R, 10G, and 10B, respectively. The electric field light-emitting device 13 disclosed herein is not limited to this configuration. For example, the cathode layers 22R, 22G, and 22B may also be a common electrode layer provided across the red, green, and blue electric field light-emitting elements 10R, 10G, and 10B.

[0082] The sealing layer 14 covering the electroluminescent device 13 prevents foreign matter such as water and oxygen from penetrating the electroluminescent device 13. For example, it can be composed of two inorganic sealing films and an organic film formed between them. The external functional layer 15 adds various functions to the display device 100, such as optical control, touch sensor, and surface protection.

[0083] The edge cover film 16 is insulating and covers the edges of each anode layer 21R, 21G, and 21B. The edge cover 16 is formed by applying an organic material such as polyimide or acrylic resin, followed by patterning using photolithography. The red, green, and blue electroluminescent elements 10R, 10G, and 10B are, for example, organic light-emitting diodes (OLEDs).

[0084] Reference Figure 3 ,right Figure 2 The device structure of the electroluminescent device 10 shown will be described. Figure 3 It indicates schematically Figure 2 The layer structure of the electroluminescent element is shown in the diagram.

[0085] like Figure 3As shown, the substrate 11, buffer layer 12, and TFT layer 20 are stacked in this order. The electroluminescent element 10 is constructed by stacking an anode layer 21, a layer assembly 30, a first charge generation layer 40, a layer assembly 50, and a cathode layer 22 in this order on the TFT layer 20. The electroluminescent element 10 according to the present disclosure is a top-emission type (a structure in which light is extracted from the upper side, i.e., the cathode layer 22). In the electroluminescent element 10, for example, the anode layer 21 functions as an anode, and the cathode layer 22 functions as a cathode.

[0086] The layer set 30 is composed of a hole injection layer 31, a first hole transport layer 32, a first electron blocking layer 33, a first electroluminescent layer 34, a first hole blocking layer 35, and a first electron transport layer 36. The layer set 50 is composed of a second hole transport layer 51, a second electron blocking layer 52, a second electroluminescent layer 53, a second hole blocking layer 54, a second electron transport layer 55, and an electron injection layer 56. A first charge generation layer 40 including an n-type first charge generation layer (electron generation layer) 41 and a p-type first charge generation layer (hole generation layer) 42 is arranged between the layer set 30 and the layer set 50. Figure 3 In the electroluminescent element 10 , the layer assembly 30 is also referred to as a “first stack”, and the layer assembly 50 is also referred to as a “second stack.” The layer assembly 30 , the first charge generation layer 40 , and the layer assembly 50 constitute an organic stack 60 .

[0087] The hole injection layer 31, the first hole transport layer 32, the first electron blocking layer 33, the first hole blocking layer 35, the first electron transport layer 36, the n-type first charge generation layer 41, the p-type first charge generation layer 42, the second hole transport layer 51, the second electron blocking layer 52, the second hole blocking layer 54, the second electron transport layer 55 and the electron injection layer 56 are carrier functional layers that facilitate at least one of the injection, movement and generation of carriers (electrons or holes).

[0088] The electroluminescent element 10 is a so-called tandem structure electroluminescent element in which two electroluminescent layers, a first electroluminescent layer 34 and a second electroluminescent layer 53, are arranged between the anode layer 21 and the cathode layer 22 in the stacking direction. The first electroluminescent layer 34 and the second electroluminescent layer 53, which overlap in the stacking direction, both emit light of the same color.

[0089] The thickness of the first electric field luminescent layer 34 varies depending on the luminescent color. For example, the thickness of the first electric field luminescent layer 34 of the red electric field luminescent element and the green electric field luminescent element is 25 nm to 50 nm, and the thickness of the first electric field luminescent layer 34 of the blue electric field luminescent element is 10 nm to 25 nm. The thickness of the second electric field luminescent layer 53 is thinner than the thickness of the first electric field luminescent layer 34. For example, the thickness of the second electric field luminescent layer 53 is 0.1 to 0.9 times the thickness of the first electric field luminescent layer 34. Both the first electric field luminescent layer 34 and the second electric field luminescent layer 53 are electric field luminescent layers of a host-guest system.

[0090] <Method for Manufacturing Electroluminescent Element> Next, referring to Figure 4 An example of a method for manufacturing the electroluminescent element 10 will be described. Figure 4 It shows Figure 3 FIG. 1 is a flow chart showing an example of a method for manufacturing the electroluminescent element 5 .

[0091] like Figure 4 As shown, in step S1, the anode layer 21 is formed on the TFT layer 20. Specifically, an Ag layer and an In-Sn-O layer are sequentially formed using a sputtering method.

[0092] In step S2, a hole injection layer 31 is formed on the anode layer 21. Specifically, the hole transport material and the electron accepting material are co-deposited at a predetermined deposition rate by adjusting the respective deposition temperatures and deposition times to achieve a predetermined film thickness and ratio. A uniform deposition film is formed over the entire surface of the workpiece without using a fine metal mask.

[0093] In addition, based on Figure 4 In the detailed description of the manufacturing method, a portion of the carrier functional layer is formed as a common layer among all the color electroluminescent elements, but the manufacturing method of the present invention is not limited to this. The thickness of each carrier functional layer can be set differently for each color, for example, depending on the electroluminescent layer. In this way, carrier functional layers with locally varying thicknesses can be formed through vapor deposition through a mask.

[0094] In step S3, a first hole transport layer 32 is formed on the hole injection layer 31. Specifically, the deposition temperature and deposition time are adjusted so that the hole transport material is deposited to a predetermined thickness at a predetermined deposition rate. Here, the deposited film is formed without using a fine metal mask.

[0095] In step S4, a first electron blocking layer 33 is formed on the first hole transport layer 32. Specifically, the hole transport material is deposited at a predetermined rate by adjusting the evaporation temperature and time, so that the hole transport material is deposited to a predetermined thickness. Here, a fine metal mask is used to deposit the first thickness corresponding to each color. The first thickness can be the same or different for each color of the electroluminescent element.

[0096] In step S5, the first electroluminescent layer 34 is formed on the first electron blocking layer 33. Specifically, the evaporation temperature and time are adjusted to ensure that the host compound and the guest compound (dopant) are co-evaporated at a predetermined rate, resulting in a layer with a predetermined film thickness and guest compound concentration (dopant concentration). Using a fine metal mask, the deposition is performed under conditions that precisely control the thickness of each layer and the guest compound concentration for each color.

[0097] In step S6, the first hole-blocking layer 35 is formed on the first electroluminescent layer 34. Specifically, the electron transport material is deposited at a predetermined rate by adjusting the deposition temperature and time, so that the electron transport material is deposited to a predetermined thickness. Here, the deposited film is formed without using a fine metal mask.

[0098] In step S7, the first electron transport layer 36 is formed on the first hole blocking layer 35. Specifically, the evaporation temperature and evaporation time are adjusted to evaporate the electron transport material at a predetermined evaporation rate, so that the electron transport material is stacked to a predetermined film thickness. This evaporation can also be a co-evaporation of the electron transport material and lithium quinoline. In this case, the evaporation film is formed without using a fine metal mask.

[0099] In step S8, an n-type first charge generation layer 41 is formed on the first electron transport layer 36. Specifically, an organic electron transport material and an inorganic metal material (Yb or Li) serving as an electron donor material are co-deposited at a predetermined deposition rate by adjusting the respective deposition temperatures and deposition times so that the layers are stacked at predetermined film thicknesses and ratios. Here, the deposited film is formed without using a fine metal mask.

[0100] In step S9, a p-type first charge generation layer 42 is formed on the n-type first charge generation layer 41. Specifically, the organic hole transport material and the organic electron accepting material are co-deposited at a predetermined deposition rate by adjusting the respective deposition temperatures and deposition times so that the layers are stacked at predetermined film thicknesses and ratios. Here, the deposited film is formed without using a fine metal mask.

[0101] In step S10, the second hole transport layer 51 is formed on the p-type first charge generation layer 42. Specifically, the hole transport material is deposited at a predetermined rate by adjusting the deposition temperature and time, so that the hole transport material is deposited to a predetermined thickness. Here, the deposited film is formed without using a fine metal mask.

[0102] In step S11, a second electron blocking layer 52 is formed on the second hole transport layer 51. Specifically, the evaporation temperature and evaporation time are adjusted to evaporate the hole transport material at a specified evaporation rate so that the hole transport material is stacked with a specified film thickness. Here, a fine metal mask is used to evaporate to a second thickness corresponding to each color. The second thickness can also be the same as the first thickness, and can be the same or different in the electroluminescent element of each color.

[0103] In step S12, a second electroluminescent layer 53 is formed on the second electron-blocking layer 52. Specifically, the evaporation temperature and time are adjusted to ensure that the host compound and the guest compound (dopant) are co-evaporated at a predetermined rate, resulting in a layer with a predetermined film thickness and guest compound concentration (dopant concentration). Using a fine metal mask, the deposition is performed under conditions that precisely control the thickness of each layer and the guest compound concentration for each color. The second electroluminescent layer 53 is deposited so that its thickness is thinner than that of the first electroluminescent layer 34.

[0104] In step S13, the second hole-blocking layer 54 is formed on the second electroluminescent layer 53. Specifically, the electron transport material is deposited at a predetermined rate by adjusting the deposition temperature and time, so that the electron transport material is deposited to a predetermined thickness. Here, the deposited film is formed without using a fine metal mask.

[0105] In step S14, a second electron transport layer 55 is formed on the second hole blocking layer 54. Specifically, the electron transport material is deposited at a predetermined deposition rate by adjusting the deposition temperature and deposition time, so that the electron transport material is deposited to a predetermined film thickness. This deposition can also be a co-deposition of the electron transport material and lithium quinoline. In this case, the deposited film is formed without using a fine metal mask.

[0106] In step S15, the electron injection layer 56 is formed on the second electron transport layer 55. Specifically, lithium fluoride is deposited at a predetermined rate by adjusting the deposition temperature and deposition time, so that the lithium fluoride is deposited to a predetermined film thickness. Here, the deposited film is formed without using a fine metal mask.

[0107] In step S16, the cathode layer 22 is formed on the electron injection layer 56. Specifically, a magnesium-silver alloy thin film is formed by vapor deposition, for example.

[0108] <Light Emitting Mechanism> Figure 5 , the light emission mechanism of the electroluminescent element 10 of the electroluminescent device 13 capable of full-color display will be described. Figure 5 It is used for Figure 2 FIG1 is a diagram illustrating the light emitting mechanism of the electroluminescent element 10 of the electroluminescent device 13 shown in FIG1. Figure 5 , only the main parts of the structure of the electroluminescent element 10 are shown.

[0109] Figure 5 The electroluminescent element 10 shown is an organic EL element having a series structure of two electroluminescent layers, a first electroluminescent layer 34 and a second electroluminescent layer 53, formed between an anode layer 21 and a cathode layer 22. A first charge generation layer 40 is disposed between the first electroluminescent layer 34 and the second electroluminescent layer 53. Figure 5 In the illustrated example, each of the red electroluminescent element 10R, the green electroluminescent element 10G, and the blue electroluminescent element 10B includes a stacked first electroluminescent layer 34 and a second electroluminescent layer 53 that emit light of the same color.

[0110] In more detail, Figure 5 As shown, in the red electroluminescent element 10R, an anode layer 21R, a first electroluminescent layer 34R, a first charge generation layer 40R, a second electroluminescent layer 53R, and a cathode layer 22R are sequentially arranged. In the red electroluminescent element 10R, a set 30R of layers including the first electroluminescent layer 34R, arranged between the anode layer 21R and the first charge generation layer 40R in the stacking direction, constitutes a first stack. A set 50R of layers including the second electroluminescent layer 53R, arranged between the first charge generation layer 40R and the cathode layer 22R, constitutes a second stack.

[0111] Similarly, in the green electroluminescent element 10G, an anode layer 21G, a first electroluminescent layer 34G, a first charge generation layer 40G, a second electroluminescent layer 53G, and a cathode layer 22G are arranged in this order. The first stack in the green electroluminescent element 10G is a set of layers 30G, including the first electroluminescent layer 34G, arranged between the anode layer 21G and the first charge generation layer 40G in the stacking direction. The second stack in the green electroluminescent element 10G is a set of layers 50G, including the second electroluminescent layer 53G, arranged between the first charge generation layer 40G and the cathode layer 22G.

[0112] In the blue electroluminescent element 10B, the anode layer 21B, the first electroluminescent layer 34B, the first charge generation layer 40B, the second electroluminescent layer 53B, and the cathode layer 22B are stacked in this order. The first stack in the blue electroluminescent element 10B is a set 30B of layers including the first electroluminescent layer 34B, disposed between the anode layer 21B and the first charge generation layer 40B in the stacking direction. The second stack in the blue electroluminescent element 10B is a set 50B of layers including the second electroluminescent layer 53B, disposed between the first charge generation layer 40B and the cathode layer 22B.

[0113] Here, the cathode layers 22R, 22G, and 22B are provided in the red electric field light emitting element 10R, the green electric field light emitting element 10G, and the blue electric field light emitting element 10B, respectively. For example, the cathode layers 22R, 22G, and 22B may also be a common electrode layer provided across the red electric field light emitting element 10R, the green electric field light emitting element 10G, and the blue electric field light emitting element 10B.

[0114] Furthermore, in Figure 5 , a sealing layer 14 is shown provided on the uppermost portion of each of the red electric field light emitting element 10R, the green electric field light emitting element 10G, and the blue electric field light emitting element 10B to prevent the intrusion of oxygen and moisture. For example, the sealing layer 14 may be a common layer provided across the red electric field light emitting element 10R, the green electric field light emitting element 10G, and the blue electric field light emitting element 10B.

[0115] Furthermore, carrier functional layers (electron injection layer, electron transport layer, hole transport layer, hole injection layer, etc.) not shown are provided in the layer assemblies 30R, 30G, 30B, 50R, 50G, and 50B included in the electroluminescent elements 10R, 10G, and 10B of each color.

[0116] The following further describes the light-emitting mechanism of the electroluminescent element 10. In the following description, since the red electroluminescent element 10R, the green electroluminescent element 10G, and the blue electroluminescent element 10B all have the same light-emitting mechanism, the color symbols R, G, and B added to the symbols representing each basic structure are omitted for explanation.

[0117] When current flows through the electroluminescent element 10, holes are supplied from the anode layer 21 to the first electroluminescent layer 34, and electrons are supplied from the cathode layer 22 to the second electroluminescent layer 53. Furthermore, when current flows through the electroluminescent element 10, electrons generated by the n-type first charge generation layer 41 are supplied to the first electroluminescent layer 34, and holes generated by the p-type first charge generation layer 42 are supplied to the second electroluminescent layer 53.

[0118] As a result, electrons and holes recombine in the first EFL layer 34 to generate electron / hole pairs (also known as excitons), which then transition to the ground state and emit light in a predetermined wavelength range. Furthermore, electrons and holes recombine in the second EFL layer 53 to generate electron / hole pairs, which then transition to the ground state and emit light in a predetermined wavelength range (light of the same color as the first EFL layer 34). For example, the first EFL layer 34R and the second EFL layer 53R of the red EFL element 10R each emit red light. Similarly, the first EFL layer 34G and the second EFL layer 53G of the green EFL element 10G each emit green light, and the first EFL layer 34B and the second EFL layer 53B of the blue EFL element 10B each emit blue light.

[0119] At this time, both the first electroluminescent layer 34 and the second electroluminescent layer 53 can emit light at a luminous efficiency substantially equal to the theoretical value. Therefore, the multiple light-emitting layers of the same color arranged along the stacking direction can emit light at substantially the same efficiency as the theoretical value, thereby achieving the formation of a high-brightness and high-definition full-color image.

[0120] However, the luminescence intensity of an existing electroluminescent element that does not use an electroluminescent layer as described in the present disclosure, that is, an electroluminescent element having an existing tandem structure in which two host-guest electroluminescent layers emitting light of the same color are stacked with the same thickness, sometimes cannot reach twice the luminescence intensity of an electroluminescent element having a single electroluminescent layer (i.e., the theoretical value).

[0121] Here, we introduce the results of our verification. First, we produced an electroluminescent element (ELE) with a single blue EL layer (also called a single layer; single-layer structure) (single-layer prototype) and an ELE with a two-layer tandem structure (comparative tandem prototype). The single-layer prototype was manufactured under the following conditions. The comparative tandem prototype was manufactured under three conditions: conditions i through iii. The single-layer prototype had the same layer structure between the cathode and anode layers as the first stack under condition i. The comparative tandem prototype had a conventional tandem structure, with the thickness of each EL layer stacked in the stacking direction being the same. For each prototype, the device life and driving voltage were measured, and the current efficiency was calculated using the Blue Index (unit: cd / A / y, where y is one side of the chromaticity coordinates according to CIE 1931).

[0122] (Single-layer prototype) Layer structure: Cathode layer / first stack (electron transport layer / hole blocking layer / first blue light-emitting layer (thickness: 15nm) / electron blocking layer / hole transport layer / hole injection layer) / anode layer. Thickness ratio: The ratio of the thickness of the first light-emitting layer (15nm) to the thickness of the first stack (165nm) is 0.091.

[0123] (Condition i) Layer structure: cathode layer / second stack (electron injection layer / electron transport layer / hole blocking layer / second blue electric field luminescent layer (thickness: 15 nm) / hole transport layer / hole injection layer) / charge generation layer / first stack (electron transport layer / hole blocking layer / first blue electric field luminescent layer (thickness: 15 nm) / electron blocking layer / hole transport layer / hole injection layer) / anode layer. Thickness ratios: The ratio of the thickness of the second electric field luminescent layer (15 nm) to the thickness of the second stack (70 nm) was 0.21, and the ratio of the thickness of the first electric field luminescent layer (15 nm) to the thickness of the first stack (165 nm) was 0.091.

[0124] (Condition ii) Layer structure: Same as Condition i.

[0125] Thickness ratio: Same as condition i, except adjusting the thickness of the carrier functional layer in the second stacked layer to a total thickness of 80 nm. The ratio of the thickness of the second electroluminescent layer (15 nm) to the thickness of the second stacked layer (80 nm) was 0.188.

[0126] (Condition iii) Layer structure: Same as condition i.

[0127] Thickness ratio: Same as condition i, except adjusting the thickness of the carrier functional layer within the second stack to 90 nm. The ratio of the thickness of the second electroluminescent layer (15 nm) to the thickness of the second stacked layer (90 nm) is 0.167.

[0128] The results showed that the current efficiency of the single-layer prototype was 206 cd / A / y. In contrast, the current efficiency of the comparative series-connected prototype was 305 cd / A / y (1.48 times the current efficiency of the single-layer prototype) under (condition i), 320 cd / A / y (1.55 times the current efficiency) under (condition ii), and 219 cd / A / y (1.1 times the current efficiency) under (condition iii). Furthermore, device lifespan measurements showed that the comparative series-connected prototype had a lifespan 2.01 times that of the single-layer prototype under (condition i), 2.12 times under (condition ii), and 1.92 times under (condition iii). Furthermore, driving voltage measurements showed that the comparative series-connected prototype had a driving voltage 1.9 times that of the single-layer prototype under (condition i), 1.9 times under (condition ii), and 2.0 times under (condition iii).

[0129] The above results show that conventional tandem-structured EL devices with two EL layers, each with the same EL layer thickness and modified conditions for the carrier functional layer other than the EL layer, show an approximately two-fold improvement in device life compared to single-layer EL devices with a single EL layer. Furthermore, conventional tandem-structured EL devices with two EL layers of identical thickness show a smaller increase in current efficiency than single-layer EL devices, indicating that even with modified conditions for the carrier functional layer, the luminous efficiency does not significantly increase to twice that of single-layer EL devices, even though the driving voltage is approximately doubled.

[0130] Based on these results, a possible solution to achieving twice the luminous efficiency of an existing two-layer ELE device (tandem structure) compared to a single-layer ELE device (i.e., an ELE device with a single ELE layer) is to apply a higher drive voltage and supply more current. This, however, will clearly result in increased power consumption and a reduced device lifespan. This suggests that further research is needed to fully realize the advantages of adopting a tandem structure over existing structures. The present inventors' research suggests the following reasons.

[0131] In organic materials, the mobility of holes is often higher than that of electrons. As a result, the supply of electrons is often insufficient during the generation of excitons. Conversely, the supply of holes is often excessive. In existing electroluminescent devices with a single-layer electroluminescent layer, efforts have been made to achieve a uniform supply of carriers in the electroluminescent layer, i.e., to achieve carrier balance, by optimizing the material selection or thickness of the carrier functional layer outside the electroluminescent layer. In addition, research has been conducted on the issue of carrier balance in each electroluminescent layer in existing tandem-structured electroluminescent devices: the same countermeasures as in electroluminescent devices with a single-layer electroluminescent layer, i.e., optimization of the carrier functional layer around the electroluminescent layer outside the electroluminescent layer as described above, have been adopted. However, in tandem-structured electroluminescent devices, a charge generation layer exists between two adjacent electroluminescent layers in the stacking direction, but the balance between electrons and holes generated by the charge generation layer is generally not 1:1. Therefore, in an electroluminescent element having a tandem structure, it is difficult to make the supply amount of electrons uniform between two electroluminescent layers adjacent to each other in the stacking direction with the charge generation layer interposed therebetween.

[0132] Specifically, as demonstrated by the aforementioned verification results, the optimization effect of the carrier functional layer surrounding the tandem-structured EL device, as previously implemented, cannot be considered sufficient. Furthermore, there is room for research to address the new issue of conventional tandem-structured EL devices, where the luminescence output of two EL layers of equal thickness does not reach twice that of EL devices with a single EL layer.

[0133] To address this issue, the inventors focused on the carrier mobility and carrier injection properties in the stacking direction of an EFL element having multiple EFL layers (tandem structure), and furthermore, on the carrier supply and excess carrier generation within each EFL layer. As a result, the inventors discovered that in an EFL element having a tandem structure, in addition to ensuring that the supply of electrons and holes, i.e., the carrier balance, must be consistent within each of the multiple EFL layers, they also need to consider the carrier balance and carrier supply between the EFL layers, which is not necessary in an EFL element having a single EFL layer. Furthermore, they discovered that, among EFL layers stacked with a charge generation layer interposed therebetween, the amount of carriers (electrons) supplied to the EFL layer stacked on the anode layer side is less than the amount of carriers (electrons) supplied to the EFL layer stacked on the cathode layer side. Therefore, in the E-light emitting layer stacked closer to the cathode layer, the supply of electrons capable of combining with holes decreases, and the number of electron-hole pairs (excitons) generated by recombination decreases relatively. In other words, even if there are multiple E-light emitting layers (even if the thickness of the E-light emitting layer is multiplied), the number of excitons does not increase by that multiple. Furthermore, the inventors found that in an E-light emitting element having two E-light emitting layers of the same thickness, the amount of light emitted does not double. Furthermore, the inventors discovered that in an E-light emitting element having a conventional tandem structure with two E-light emitting layers of the same thickness, excess holes are generated in the E-light emitting layer formed closer to the cathode layer, which is the reason why the current efficiency of the E-light emitting element does not double.

[0134] The present inventors have incorporated a novel design concept into an electroluminescent element with a tandem structure comprising multiple electroluminescent layers, as disclosed herein. This concept involves varying the composition (thickness) of each electroluminescent layer to achieve carrier balance among the layers and address the issue of uneven carrier supply. This design eliminates the generation of excess carriers found in conventional tandem electroluminescent elements, allowing for the generation of an appropriate and balanced amount of excitons in each electroluminescent layer along the stacking direction. As a result, the present invention achieves an electroluminescent device with a tandem structure that reduces current consumption and driving voltage while improving luminous efficiency.

[0135] Specifically, in the electroluminescent element disclosed herein, the thickness of the electroluminescent layer formed on the cathode layer side is thinner than the electroluminescent layer formed on the anode layer side. As a result, holes that match the thickness of the electroluminescent layer on the cathode layer side are supplied to the electroluminescent layer on the cathode layer side. Therefore, there are no residual holes that cannot combine with electrons to generate electron / hole pairs (excitons), and in the electroluminescent layer on the anode layer side, electron / hole pairs (excitons) are generated in an amount substantially as the theoretical value. Therefore, any electroluminescent layer that overlaps in the stacking direction emits light with a brightness corresponding to its thickness. Moreover, the generation of residual holes can be prevented in any electroluminescent layer, thereby reducing current consumption and, therefore, reducing power consumption.

[0136] Furthermore, especially in the case of an ELE device with a top-emission structure where light is extracted from the cathode layer, even slight defects in the sealing layer formed on the cathode layer can lead to degradation of the cathode layer due to the intrusion of oxygen or moisture, reducing electron injection properties. This results in a decrease in the amount of electrons supplied to the ELE layer directly below the cathode layer. However, by anticipating such a situation and making the thickness of the ELE layer on the cathode layer side thinner than the theoretical value from the initial design stage, it is possible to prevent the generation of excess holes in the ELE layer on the cathode layer side.

[0137] Here, we describe simulation evaluations of the disclosed embodiments and comparative examples for a full-color electroluminescent device having two electroluminescent layers (tandem structure). The electroluminescent device was designed with a cathode-side electroluminescent layer thickness of 28 nm for red and green electroluminescent elements and 10 nm for blue electroluminescent elements. The anode-side electroluminescent layer thickness was 35 nm for red and green electroluminescent elements and 15 nm for blue electroluminescent elements.

[0138] The electroluminescent device of the example has the layer structure of this embodiment. The electroluminescent device of the comparative example has each layer having the same thickness as the layers of the stack on the anode layer side described above, and is a full-color electroluminescent device having a single electroluminescent layer for each color (non-tandem structure).

[0139] Simulation results based on the above conditions show that the full-color ELE device of the embodiment has a current efficiency (also called "luminous efficiency") that is 1.8 times that of the full-color ELE device of the comparative example, a device lifespan that is 2.7 times longer, and a driving voltage that is 1.7 times lower. Therefore, the ELE device having the disclosed tandem structure can suppress increases in driving voltage, extend device lifespan, and achieve an improvement in luminous efficiency commensurate with the increase in driving voltage, compared to conventional full-color ELE devices having a tandem structure.

[0140] Furthermore, under the conditions used in the simulations of the aforementioned examples, the driving voltage was further increased to further improve the current efficiency (luminous efficiency). As a result, the driving voltage was doubled, and the current efficiency was also increased by 2.1. Furthermore, the device lifetime under these conditions was increased by 2.6. This demonstrates that a full-color electroluminescent device having two electroluminescent layers (tandem structure) in the stacking direction according to the present invention can achieve characteristics that are more than double those of a single-layer full-color electroluminescent device.

[0141] Furthermore, compared to the blue EL elements in the above-described embodiment and comparative example, the EL device in the above-described embodiment achieved a 12.5% ​​increase in current efficiency, a 13.6% increase in device lifetime, and a 12.5% ​​reduction in driving voltage compared to the EL device in the comparative example. These results demonstrate that the EL device of this embodiment can achieve significant improvements in characteristics. Furthermore, the EL device of this embodiment can reduce the amount of guest compound (dopant) used compared to conventional EL devices having multiple EL layers of equal thickness in a tandem structure.

[0142] [Implementation Method 2] The following reference Figure 6 Embodiment 2 of the present disclosure will be described. Figure 6 This figure illustrates the light-emitting mechanism of electroluminescent element 10A in electroluminescent device 13A according to Embodiment 2 of the present disclosure. Electroluminescent device 13A according to Embodiment 2 differs from electroluminescent device 13 described above in that it includes electroluminescent element 10A having three electroluminescent layers in the stacking direction.

[0143] In addition, Figure 6 , only the main components of the electroluminescent element 10A included in the electroluminescent device 13A are shown. Furthermore, for ease of description, in the subsequent embodiments, components having the same functions as those described in Embodiment 1 are denoted by the same reference numerals, and their descriptions are not repeated. Components having the same functions as those described in the preceding embodiments are denoted by the same reference numerals, and their descriptions are not repeated.

[0144] like Figure 6As shown, in the red electroluminescent element 10AR, a third electroluminescent layer 71R and a second charge generation layer 80R are further arranged between the cathode layer 22R and the second electroluminescent layer 53R. In the red electroluminescent element 10AR, the set of layers 50R including the second electroluminescent layer 53R, arranged between the first charge generation layer 40R and the second charge generation layer 80R in the stacking direction, constitutes the second stack. The set of layers 70R including the third electroluminescent layer 71R, arranged between the second charge generation layer 80R and the cathode layer 22R, constitutes the third stack.

[0145] Similarly, in the green electroluminescent element 10AG, a third electroluminescent layer 71G and a second charge generation layer 80G are further arranged between the cathode layer 22G and the second electroluminescent layer 53G. In the green electroluminescent element 10AG, the set of layers 50G including the second electroluminescent layer 53G, arranged between the first charge generation layer 40G and the second charge generation layer 80G in the stacking direction, constitutes the second stack. Furthermore, the set of layers 70G including the third electroluminescent layer 71G, arranged between the second charge generation layer 80G and the cathode layer 22G, constitutes the third stack.

[0146] In addition, in the blue electroluminescent element 10AB, a third electroluminescent layer 71B and a second charge generation layer 80B are arranged between the cathode layer 22B and the second electroluminescent layer 53B. In the blue electroluminescent element 10AB, the set of layers 50B including the second electroluminescent layer 53B, arranged between the first charge generation layer 40B and the second charge generation layer 80B in the stacking direction, constitutes the second stack. Furthermore, the set of layers 70B including the third electroluminescent layer 71B, arranged between the second charge generation layer 80B and the cathode layer 22B, constitutes the third stack.

[0147] Furthermore, carrier functional layers (not shown) (electron injection layer, electron transport layer, hole transport layer, hole injection layer, etc.) are disposed in the layer assemblies 30R, 30G, 30B, 50R, 50G, 50B, and 70R, 70G, and 70B included in the electroluminescent elements 10AR, 10AG, and 10AB of each color. In the following description, the third electroluminescent layers 71R, 71G, and 71B included in the electroluminescent elements 10AR, 10AG, and 10AB of each color are collectively referred to as the "third electroluminescent layer 71."

[0148] In the stacking direction, when the thickness of the first electroluminescent layer 34 is set to 1, the thickness of the second electroluminescent layer 53 is, for example, 0.1 to 0.9, more preferably 0.3 to 0.8. Furthermore, when the thickness of the second electroluminescent layer 53 is set to 1, the thickness of the third electroluminescent layer 71 is, for example, 0.1 to 0.9, more preferably 0.3 to 0.8. Within the above range, the thickness of the electroluminescent layers 34, 53, and 71 included in the electroluminescent element 10A is thicker on the anode layer 21 side and thinner on the cathode layer 22 side.

[0149] In addition, Figure 6 In the embodiment, the cathode layer 22 may be a common electrode layer provided across the red electric field light emitting element 10AR, the green electric field light emitting element 10AG, and the blue electric field light emitting element 10AB. Similarly, the sealing layer 14 may be a common layer provided across the red electric field light emitting element 10AR, the green electric field light emitting element 10AG, and the blue electric field light emitting element 10AB.

[0150] Figure 6 In the case where the electroluminescent layer in the stacking direction is three layers, Figure 5 The display device 100 shown similarly prevents the supply of carriers (electrons or holes) that would otherwise become excess in the electroluminescent layer on the cathode layer side, and both electroluminescent layers emit light with a brightness and luminous efficiency substantially equal to theoretical values.

[0151] This embodiment is the same as the above embodiment 2 except that, among the three electroluminescent layers in the above embodiment 2, the electroluminescent layer on the cathode side of two adjacent electroluminescent layers in the stacking direction is thinner than the electroluminescent layer on the anode side. Figure 6 The thickness of the electroluminescent layer 34 and the electroluminescent layer 53 are the same, and the thickness of the electroluminescent layer 71 is changed to be thinner than that of the electroluminescent layer 53 .

[0152] As described above, in this embodiment, in two adjacent stacks of three stacks, carrier balance is adjusted by a method other than controlling the thickness of the electroluminescent layer disclosed herein. As a result, if good carrier balance cannot be achieved in the remaining stack, the carrier balance in the remaining stack is preferably adjusted. As an example of such an electroluminescent device configuration, an electroluminescent device comprising one or more configurations selected from the group consisting of the following configurations further comprises a configuration in which the ratio of the thickness of the electroluminescent layer between the second stack and the third stack is the ratio of the thickness of the electroluminescent layer described in the present disclosure, wherein the group consisting of the following configurations includes: a configuration in which the thicknesses of the corresponding carrier functional layers in the first stack and the second stack are different, a configuration in which the corresponding carrier functional layers in the first stack and the second stack are made of different materials, and a configuration in which the material of the first electroluminescent layer in the first stack is different from the material of the second electroluminescent layer in the second stack.

[0153] In this embodiment, the same effects as those of the first embodiment are achieved in the two electroluminescent layers adjacent to each other in the stacking direction in the second embodiment.

[0154] [Main Effects] In the electroluminescent device disclosed herein, multiple electroluminescent layers are stacked in the stacking direction according to the emission color, with thickness increasing toward the anode layer and decreasing toward the cathode layer. This configuration prevents the generation of excess carriers in each electroluminescent layer along the stacking direction, achieving luminescence with brightness and efficiency approximately equal to theoretical values.

[0155] Furthermore, because the luminous efficiency (the ratio of brightness to applied voltage) of each E-light emitting layer in the stacking direction is consistent with the theoretical value, the total thickness of the E-light emitting layer from the anode layer to the cathode layer is reduced by an amount equivalent to the thickness of the E-light emitting layer on the cathode side, compared to achieving the same brightness with an E-light emitting device with a constant thickness of each E-light emitting layer in the stacking direction. Therefore, while maintaining the same electric field (unit: V / m) applied to each E-light emitting layer in the stacking direction, the driving voltage (unit: V) can be reduced. Furthermore, since the generation of residual carriers (holes) in each stacked E-light emitting layer can be suppressed, current consumption can be reduced. Consequently, power consumption (unit: W = V × A) can also be reduced.

[0156] Therefore, compared to conventional tandem-structured EL devices in which each EL layer has the same thickness in the stacking direction, the EL device of the present disclosure achieves higher-brightness emission, low-voltage operation, and reduced power consumption. Therefore, according to the present disclosure, the high-brightness and / or power-saving emission, which are advantages of the tandem structure, can be achieved in an EL device capable of full-color display without the use of color filters or the like.

[0157] Furthermore, by gradually reducing the thickness of the electroluminescent layer from one side to the other in the stacking direction, the aforementioned effects of improving brightness (luminous efficiency) and reducing power consumption can be achieved over the entire electroluminescent element in the stacking direction.

[0158] In addition, by using the electroluminescent layer as an electroluminescent layer of a host-guest system, it is possible to achieve high luminous efficiency and improvement in device life. However, according to the present disclosure, it is possible to further improve the carrier balance (balance of electrons and holes) in each electroluminescent layer. Therefore, from the perspective of being able to give full play to the performance of each electroluminescent layer of the host-guest system with high luminous efficiency and excellent life, it is advantageous. In addition, it is also advantageous from the perspective of being able to reduce the amount of expensive and rare phosphorescent dopants used as guest compounds.

[0159] Furthermore, when the electric field luminescence layer includes a fluorescent electric field luminescence layer containing a fluorescent dopant and a phosphorescent electric field luminescence layer containing a phosphorescent dopant, the number of fluorescent electric field luminescence layers in the stacking direction can be greater than the number of phosphorescent electric field luminescence layers, for example, greater than 1 or 2. This structure is more effective from the perspective of optimizing the balance between the lifespan and the amount of light emitted by the fluorescent electric field luminescence layer and the phosphorescent electric field luminescence layer.

[0160] Furthermore, by ensuring that the multiple ELE layers stacked along the stacking direction are of the same color, the ability to apply each of the RGB colors separately for full-color display is advantageous from the perspective of improving color purity. Furthermore, by stacking the ELE layers with the same material emitting the same color, simulations facilitate the evaluation of carrier injection and transport properties between the ELE layers. Thus, the above structure is more effective in achieving a more simplified full-color display-capable ELE device comprising ELE elements having desired characteristics.

[0161] The number of electroluminescent layers in the stacking direction may be 2 or more and 5 or less. This configuration is more effective from the viewpoint of achieving improved luminous efficiency, longer life, and lower driving voltage.

[0162] Furthermore, in the stacking direction, the ratio of the thickness of the other electroluminescent layers to the thickness of the electroluminescent layer closest to the anode layer is 0.1 to 0.9. This structure is more effective in terms of achieving longer life, improved luminous efficiency, and lower driving voltage.

[0163] Furthermore, the electroluminescent device of the present disclosure may be a top emission type. This structure is more effective from the viewpoint of optimizing the thickness of the carrier function layer.

[0164] Furthermore, the display device disclosed herein includes the aforementioned electroluminescent device. Therefore, the thickness of the electroluminescent layer on the cathode side can be set to a thickness obtained by reducing the thickness of the portion that does not contribute to luminescence. Therefore, compared to display devices equipped with conventional electroluminescent devices that do not reduce the thickness of this portion that does not contribute to luminescence, this device offers advantages in achieving high-brightness, high-definition image display and energy conservation. Therefore, according to the present disclosure, high-brightness, energy-saving luminescence is achieved in a display device, fully demonstrating the advantages of using a tandem structure in an electroluminescent device.

[0165] In addition, in the electroluminescent device disclosed herein, at least the electroluminescent layer is formed by vapor deposition. Compared to the case where the electroluminescent layer is formed by other methods, this method is advantageous in realizing an electroluminescent device capable of full-color display because it can form an electroluminescent layer of a host-guest system and separate coating of a high-precision luminescent layer. Moreover, it is advantageous to achieve high-precision control of the thickness of each electroluminescent layer. In particular, in the formation of the electroluminescent layer by a coating method using an inkjet device or the like, it is difficult to form the electroluminescent layer while doping the host compound with a guest compound and to control the thickness of the electroluminescent layer on the order of several nanometers. Therefore, it is believed that the coating method is difficult to form the electroluminescent device capable of full-color display disclosed herein.

[0166] Furthermore, in the manufacture of the electroluminescent device of the present invention, it is also possible to form electroluminescent layers of varying thicknesses in the stacking direction by simply varying the vapor deposition time. This configuration allows electroluminescent layers of varying thicknesses to be formed using the same manufacturing equipment, applying the same conditions except for the deposition time. This is more effective from the perspective of reducing manufacturing costs and improving productivity.

[0167] Furthermore, in an electroluminescent device comprising an electroluminescent element having multiple electroluminescent layers (a tandem structure), the thickness of the electroluminescent layer that emits light of the same color in the stacking direction is generally constant. On the other hand, technologies have also been discovered in which the thickness of the electroluminescent layer varies in the stacking direction (Japanese Patent Publication No. 2007-329054, Japanese Patent No. 5180369, Japanese Patent Publication No. 2015-153587, and Japanese Patent Publication No. 2015-32582). Among these technologies, there are also technologies that have a thicker electroluminescent layer on the anode side and a thinner electroluminescent layer on the cathode side (Japanese Patent Publication No. 2015-153587 and Japanese Patent Publication No. 2015-32582). However, these prior arts do not clearly explain the reason for varying the thickness of each electroluminescent layer in the stacking direction, and the aforementioned publications do not disclose achieving full-color display by applying each RGB color separately.

[0168] According to the present disclosure, in an electroluminescent display device, by controlling the thickness of each electroluminescent layer in the stacking direction, it is possible to achieve further improved luminous efficiency, high brightness, and / or energy savings. Therefore, the electroluminescent device and display device of the present disclosure can enhance sustainability, for example, by achieving Goal 9.4 of the United Nations Sustainable Development Goals (SDGs): "Improving infrastructure and industry through increased resource efficiency and the introduction and expansion of clean and environmentally friendly technologies and industrial processes."

[0169] The present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the claims. Embodiments obtained by appropriately combining the technical methods disclosed in different embodiments are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical methods disclosed in various embodiments.

[0170] Description of Reference Numerals 10, 10A electroluminescent element 11 base plate 12 Buffer layer 13 Electroluminescent Device 14 Sealing layer 15 External functional layer 16 Edge Covering Film 20 TFT layers 21 Anode layer 22 cathode layer 30, 50, 70-layer collections 31 hole injection layer 32 first hole transport layer 33 First electron blocking layer 34. First electroluminescent layer 35. First hole blocking layer 36 First electron transport layer 40 first charge generation layer 41 n-type first charge generation layer 42 p-type first charge generation layer 51 Second hole transport layer 52 Second electron blocking layer 53. Second electroluminescent layer 54 second hole blocking layer 55 Second electron transport layer 60 organic laminate 71 third electroluminescent layer 80 Second charge generation layer 100, 100A display device DA display area NDA border area PIX pixels.

Claims

1. An electroluminescent device, characterized in that: include: Anode layer; a cathode layer, arranged opposite to the anode layer in a stacking direction; a plurality of electroluminescent layers, which are respectively arranged between the anode layer and the cathode layer in the stacking direction and in a direction crossing the stacking direction; as well as a charge generation layer disposed between two adjacent electroluminescent layers in the stacking direction; In the electroluminescent layer, A plurality of electroluminescent layers emitting light of the same color are arranged in the stacking direction. In a direction intersecting the stacking direction, first to n-th color electroluminescent layers emitting light of different colors are arranged, where n is an integer ≥ 2. In at least one of the groups of two electroluminescent layers adjacent to each other in the stacking direction with the charge generation layer interposed therebetween, the electroluminescent layer on the cathode layer side is thinner than the electroluminescent layer on the anode layer side.

2. The electroluminescent device according to claim 1, wherein: The electric field luminescent layer is an electric field luminescent layer of a host-guest system including a host compound and a guest compound.

3. The electroluminescent device according to claim 2, wherein: The electric field luminescent layer includes, according to the luminescent color, a fluorescent electric field luminescent layer, wherein the guest compound is a fluorescent dopant; and a phosphorescent electric field luminescent layer, wherein the guest compound is a phosphorescent dopant. The number of the fluorescent electroluminescent layers in the stacking direction is greater than the number of the phosphorescent electroluminescent layers in the stacking direction.

4. The electroluminescent device according to claim 3, wherein: The number of the fluorescent electroluminescent layers in the stacking direction is one or two more than the number of the phosphorescent electroluminescent layers in the stacking direction.

5. The electroluminescent device according to any one of claims 1 to 4, characterized in that: In the stacking direction, only a plurality of electroluminescent layers emitting light of the same color are arranged.

6. The electroluminescent device according to any one of claims 1 to 5, characterized in that: The number of the electroluminescent layers in the stacking direction is 2 or more and 5 or less.

7. The electroluminescent device according to any one of claims 1 to 6, characterized in that: In the stacking direction, a ratio of the thickness of the other electroluminescent layers to the thickness of the electroluminescent layer closest to the anode layer is 0.1 or more and 0.9 or less.

8. The electroluminescent device according to any one of claims 1 to 7, characterized in that: The electroluminescent device is a top-emitting type.

9. A display device, characterized in that: It comprises the electroluminescent device according to any one of claims 1 to 8.

10. A method for manufacturing an electroluminescent device, the method being a method for manufacturing the electroluminescent device according to any one of claims 1 to 8, characterized in that: The method comprises the steps of alternately forming the electroluminescent layer and the charge generation layer on the anode layer or the cathode layer in the stacking direction, Wherein, the electroluminescent layer is formed by an evaporation method.

11. The method for manufacturing an electroluminescent device according to claim 10, wherein: The electroluminescent layers having different thicknesses in the stacking direction are formed by simply changing the evaporation time.

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