Light-emitting device and the same containing a light-emitting display device

Abstract

A light-emitting device and a light-emitting display device incorporating the same are discussed. The light-emitting device comprises a first electrode and a second electrode facing each other, and a first common layer, a light-emitting layer, and a second common layer arranged between the first and second electrodes. The light-emitting layer is divided into an odd number of layers, the odd-numbered layers of which contain a first host and a dopant, and the even-numbered layers of which contain a second host and the dopant. Furthermore, the first host has a triplet energy level higher than that of the second host.The first common layer and the second common layer contact a first layer and a last layer, each containing the first host and the dopant.

Description

BACKGROUND Technical area

[0001] The present invention relates to a light-emitting device with improved efficiency and lifespan and a light-emitting display device incorporating the same. Description of the related technique

[0002] With the rise of the information society, displays for the visual representation of electrical information signals have rapidly evolved. In response to this need, a variety of display devices with excellent performance characteristics, such as slim design, light weight, and low power consumption, are being produced.

[0003] Among such light-emitting devices, a light-emitting display device that does not require a separate light source to achieve compactness and clear color, and that incorporates a light-emitting device in a display field, has proven to be a competitive application.

[0004] The light-emitting device may include an anode and a cathode facing each other as electrodes, a light-emitting layer between the anode and the cathode, and a common layer for transferring holes and electrons to the light-emitting layer.

[0005] The light-emitting device can include various functional layers to perform a variety of functions, for example, within a single layer. These functional layers include a hole transport layer for transferring holes to the light-emitting layer and an electron transport layer for transferring electrons to the light-emitting layer.

[0006] Light-emitting devices incorporate color-emitting layers to express different colors. The efficiency and lifetime characteristics of these color-emitting layers vary, requiring the development of a different device structure for each layer.

[0007] Furthermore, research is being conducted on the application of light-emitting devices that include color-emitting layers with relatively short lifetimes in order to ensure uniform color representation of display devices. SUMMARY OF THE INVENTION

[0008] Accordingly, the present invention relates to a light-emitting device and a light-emitting display device containing the same, which essentially avoid one or more problems due to limitations and disadvantages of the related technology.

[0009] It is an object of the present invention to provide a light-emitting device and a light-emitting display device comprising a plurality of light-emitting layers with improved efficiency and reduced operating voltage.

[0010] A further object of the present invention is to provide a light-emitting device and a light-emitting display device with improved efficiency and service life.

[0011] It is a further object of the present invention to provide a light-emitting device and a light-emitting display device which, through a design in which a plurality of light-emitting stacks have different multilayer light-emitting layer structures, are provided with improved efficiency and lifetime.

[0012] A further object of the present invention is to provide a light-emitting display device which includes a blue light-emitting device with improved efficiency and lifetime in order to provide color stability without color change over time.

[0013] These problems are solved by the features of independent claim 1 and independent claim 13. Advantageous embodiments of the invention are defined in the dependent claims.

[0014] To achieve these tasks and other advantages, and in accordance with the purpose of the invention as set out and described in detail herein, a light-emitting device comprises a first electrode and a second electrode facing each other, and a first common layer, a first light-emitting layer and a second common layer between the first electrode and the second electrode, wherein the first light-emitting layer is divided into an odd number of layers, odd-numbered layers of the first light-emitting layer contain a first host and a first dopant, and the even-numbered layers of the first light-emitting layer contain a second host and the first dopant, the first host has a triplet energy level higher than that of the second host, and the first common layer and the second common layer contact a first layer and a last layer.each containing the first host and the first dopant.

[0015] In other words, the present invention provides a light-emitting device comprising a first electrode and a second electrode facing each other, and a first common layer, a light-emitting layer, and a second common layer between the first electrode and the second electrode, wherein the light-emitting layer is divided into an odd number of layers, odd-numbered layers of the light-emitting layer containing a first host and a dopant, and the even-numbered layers of the light-emitting layer containing a second host and the dopant, the first host having a triplet energy level higher than that of the second host, and the first common layer and the second common layer contact a first layer and a last layer, respectively, each containing the first host and the dopant.

[0016] In other words, the present invention provides a light-emitting device comprising a first electrode and a second electrode facing each other, and a first common layer, a first light-emitting layer, and a second common layer between the first electrode and the second electrode, wherein the first light-emitting layer comprises an odd number of layers, wherein, if the layers are consecutively numbered, odd-numbered layers of the first light-emitting layer contain a first host and a first dopant, and even-numbered layers of the first light-emitting layer contain a second host and the first dopant, furthermore wherein the first host has a triplet energy level higher than that of the second host, and the first common layer and the second common layer each contact a first layer and a last layer, respectively.each containing the first host and the first dopant.

[0017] In other words, the present invention provides a light-emitting device comprising a first electrode and a second electrode facing each other, and a first common layer, a light-emitting layer, and a second common layer between the first electrode and the second electrode, wherein the light-emitting layer comprises an odd number of layers, wherein, if the layers are consecutively numbered, odd-numbered layers of the light-emitting layer contain a first host and a dopant, and even-numbered layers of the light-emitting layer contain a second host and the dopant, furthermore wherein the first host has a triplet energy level higher than that of the second host, and the first common layer and the second common layer contact a first layer and a last layer, respectively, each containing the first host and the dopant.Referring to the foregoing, when it is stated that a light-emitting layer is subdivided into or comprises an odd number of layers, this may also be referred to as subdividing the light-emitting layer into an odd number of sublayers, elements, layers or the like, or as comprising the aforementioned.

[0018] In a light-emitting device according to an embodiment of the present invention, a triplet energy level of the dopant can be greater than a triplet energy level of the first host. Preferably, the absolute value of the difference between the triplet energy level of the dopant and the triplet energy level of the first host can be 0.4 to 1.2 eV.

[0019] In a light-emitting device according to an embodiment of the present invention, the dopant contained in the light-emitting layer can comprise or consist of a fluorescent dopant, preferably a fluorescent dopant with an emission peak at a wavelength of 430 nm to 495 nm, more preferably a thermally activated, delayed fluorescent dopant with an emission peak at a wavelength of 450 nm to 480 nm.

[0020] In a light-emitting device according to one embodiment of the present invention, the first common layer preferably contacts the first layer of the light-emitting layer, while the second common layer preferably contacts the second layer of the light-emitting layer. In a light-emitting device according to another embodiment of the present invention, the first common layer can comprise a hole transport layer that contacts the first layer of the light-emitting layer, and the second common layer can comprise an electron transport layer that contacts the last layer of the light-emitting layer. Preferably, at least one of the following conditions can be met: The hole transport layer can have a LUMO energy level that is higher than the LUMO energy level of the dopant and a HOMO energy level that is lower than the HOMO energy level of the dopant.The electron transport layer can have a LUMO energy level lower than the LUMO energy level of the dopant. The thickness of each of the odd-numbered and even-numbered layers of the light-emitting layer can be from 2 to 15 nm, preferably from 2 to 10 nm. The thickness of the last layer of the light-emitting layer contacting the second common layer can be less than the thickness of the first layer of the light-emitting layer contacting the first common layer.

[0021] In a light-emitting device according to an embodiment of the present invention, the content of the dopant in the odd-numbered layers can be the same as the content of the dopant in the even-numbered layers in the light-emitting layer.

[0022] In a light-emitting device according to an embodiment of the present invention, a LUMO energy level of the dopant can be higher than a LUMO energy level of each of the first and second hosts.

[0023] In a light-emitting device according to an embodiment of the present invention, the HOMO energy level of the dopant can be higher than the HOMO energy level of each of the first and second hosts.

[0024] A light-emitting device according to an embodiment of the present invention, wherein the light-emitting layer is a first light-emitting layer and the dopant is a first dopant, may further comprise a charge-generating layer, a third common layer, a second light-emitting layer, and a fourth common layer arranged sequentially between the second common layer and the second electrode. Preferably, the second light-emitting layer may emit light of the same color as the first light-emitting layer. Alternatively, the second light-emitting layer may be a light-emitting layer configured to emit light of a different color than light emitted by the first light-emitting layer.

[0025] In a light-emitting device according to one embodiment of the present invention, the second light-emitting layer can be divided into an odd number of layers. Provided that the layers are consecutively numbered, the odd-numbered layers of the second light-emitting layer can contain a third host and a second dopant, and the even-numbered layers of the second light-emitting layer can contain a fourth host and the second dopant. The third host can have a triplet energy level higher than that of the fourth host. The third common layer and the fourth common layer can each contact the first layer or the last layer containing the third host and the second dopant, respectively.Preferably, the second light-emitting layer can be configured to emit light of the same color as the first light-emitting layer, and the first dopant and the second dopant can be the same.

[0026] In a light-emitting device according to an embodiment of the present invention, the first dopant and the second dopant can be the same.

[0027] In a light-emitting device according to an embodiment of the present invention, the thickness of the last layer of the second light-emitting layer contacting the fourth common layer can be less than the thickness of the last layer of the first light-emitting layer contacting the second common layer.

[0028] In a light-emitting device according to an embodiment of the present invention, the thickness of the last layer of the second light-emitting layer, which contacts the fourth common layer, can be less than the thickness of the even-numbered layer, which contacts the last layer of the second light-emitting layer.

[0029] In a light-emitting device according to an embodiment of the present invention, the thickness of the last layer of the second light-emitting layer, which contacts the fourth common layer, can be less than the thickness of the first layer of the second light-emitting layer, which contacts the third common layer.

[0030] In a light-emitting device according to an embodiment of the present invention, the intensity of light emitted by the first light-emitting layer can be highest at an interface between the first layer contacting the first common layer and an even-numbered layer contacting the first common layer. The intensity of light emitted by the second light-emitting layer can be highest at the interface between the first layer contacting the third common layer and the even-numbered layer contacting the first common layer.

[0031] In a light-emitting device according to an embodiment of the present invention, the total thickness of the first light-emitting layer can be the same as the total thickness of the second light-emitting layer.

[0032] In a light-emitting device according to an embodiment of the present invention, the content of the second dopant in the odd-numbered layer can be the same as the content of the second dopant in the even-numbered layer in the second light-emitting layer.

[0033] In a light-emitting device according to an embodiment of the present invention, the thickness of the even-numbered layer in the second light-emitting layer can be greater than the thickness of the odd-numbered layer that contacts the even-numbered layer.

[0034] A light-emitting device according to one embodiment of the present invention can further comprise a charge-generating layer, a third common layer, a second light-emitting layer, and a fourth common layer, arranged successively between the second common layer and the second electrode. The second light-emitting layer can be a light-emitting layer that emits light of a different color than light emitted by the first light-emitting layer.

[0035] According to a further aspect of the present invention, a light-emitting display device comprises a substrate containing a blue subpixel, a green subpixel, and a red subpixel; a pixel circuit provided at each of the blue subpixel, the green subpixel, and the red subpixel; a first electrode connected to a thin-film transistor of the pixel circuit in each of the blue subpixel, the green subpixel, and the red subpixel; a second electrode facing the first electrode; and a first common layer and a second common layer arranged between the first electrode and the second electrode, wherein the blue subpixel includes a blue light-emitting layer containing a blue dopant between the first common layer and the second common layer, and the green subpixel includes a green light-emitting layer.which contains a green dopant between the first common layer and the second common layer, and the red subpixel contains a red light-emitting layer which contains a red dopant between the first common layer and the second common layer, wherein the blue light-emitting layer is divided into an odd number of layers, odd-numbered layers of the blue light-emitting layer containing a first blue host and a blue dopant, and even-numbered layers of the blue light-emitting layer containing a second blue host and the blue dopant, the first blue host having a triplet energy level higher than that of the second blue host, and the first common layer and the second common layer at the blue subpixel contact a first layer and a last layer, respectively, each containing the first blue host and the blue dopant.

[0036] Light-emitting display device according to an embodiment of the present invention, wherein the light-emitting layer is a first light-emitting layer, the blue light-emitting layer is a first blue light-emitting layer, the green light-emitting layer is a first green light-emitting layer, the red light-emitting layer is a first red light-emitting layer, and the blue dopant is a first blue dopant, and wherein the light-emitting device may further comprise a charge-generating layer, a third common layer, a second light-emitting layer, and a fourth common layer, which are arranged successively between the second common layer and the second electrode.The second light-emitting layer can include a second blue light-emitting layer at the blue subpixel, a second green light-emitting layer at the green subpixel, and a second red light-emitting layer at the red subpixel. The second blue light-emitting layer can be subdivided into an odd number of layers, where, if the layers are numbered consecutively, odd-numbered layers of the second blue light-emitting layer contain a third blue host and a second blue dopant, and even-numbered layers of the second blue light-emitting layer contain a fourth blue host and the second blue dopant. The third blue host can have a triplet energy level higher than that of the fourth blue host.The third common layer and the fourth common layer at the blue subpixel can contact the first layer and the last layer, which each contain the third blue host and the second blue dopant.

[0037] In a light-emitting display device according to an embodiment of the present invention, the thickness of the last layer of the second blue light-emitting layer contacting the fourth common layer may be less than the thickness of the last layer of the first blue light-emitting layer contacting the second common layer.

[0038] In a light-emitting display device according to an embodiment of the present invention, the thickness of the last layer of the second blue light-emitting layer, which contacts the fourth common layer, can be less than the thickness of an even-numbered layer, which contacts the last layer of the second blue light-emitting layer.

[0039] In a light-emitting display device according to an embodiment of the present invention, the thickness of the last layer contacting the fourth common layer in the second light-emitting layer may be less than the thickness of the first layer contacting the third common layer.

[0040] Alternatively, a light-emitting display device can be provided which includes the light-emitting device as described above and may further include a substrate containing a plurality of subpixels, wherein a pixel circuit is provided in each of the plurality of subpixels and wherein the light-emitting device is connected to a thin-film transistor of the pixel circuit.

[0041] The light-emitting device of the present invention and the light-emitting display device containing it exhibit the following effects.

[0042] The light-emitting device according to the embodiments of the present invention is configured such that the host layers are arranged alternately and the number of light-emitting layers is odd, so that the host of the first layer is the same as that of the last layer in the light-emitting layer. Additionally, the odd-numbered layer of the light-emitting layer contains a host with a high triplet energy level, and the even-numbered layer of the light-emitting layer contains a host with a low triplet energy level.As a result, the efficiency of delayed fluorescence is increased by the TTF (triplet-triplet fusion) mechanism in the inner even-numbered layer of the light-emitting layer, which is located between the first and last layers, situated at both interfaces of the light-emitting layer, and which do not contact both interfaces of the light-emitting layer, thereby improving the light-emitting efficiency and increasing the efficiency of the light-emitting device and the light-emitting display device.

[0043] The lifetime of the light-emitting device and the light-emitting display device containing it can be effectively improved by reducing the extinction ratio of the excitons generated in the light-emitting layer and increasing the ratio used for direct or delayed light emission.

[0044] If the blue light emitting layer of the blue light emitting device has a multi-layer structure, it is possible to prevent an increase in the operating voltage and improve the lifetime by adjusting the thickness of the first layer and the last layer.

[0045] The light-emitting device and the light-emitting display device containing it, according to the embodiments of the present invention, can improve the efficiency of the light-emitting layer, thereby reducing the operating voltage and extending its service life. Accordingly, the light-emitting device and the light-emitting display device can be used continuously, thus achieving ESG (environmental, social, and governance) objectives.

[0046] It is understood that both the preceding general description and the following detailed description of the present invention are examples and explanations and are intended to provide a further explanation of the claimed invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings, which are attached to provide a further understanding of the invention and which are included in this application and form part thereof, illustrate embodiment(s) of the invention and, together with the description, serve to explain the principle of the invention. The drawings show: Fig. Figure 1 is a cross-sectional view illustrating a light-emitting device according to one or more embodiments of the present invention; Fig. Figure 2 is a cross-sectional view illustrating an example where the light-emitting layer of Fig. 1 has a three-layered structure; Fig. 3 is an energy band diagram of the light-emitting layer and adjacent layers of Fig. 1; Fig. Figure 4 illustrates light-emitting layers of experimental examples 1 and 2; Fig. Figure 5 is a graph showing the 95 lifetime of light-emitting devices according to experimental examples 1 and 2; Fig. Figure 6 is a graph showing the luminance efficiency as a function of the CIEy of the light-emitting devices according to experimental examples 1 and 2; Fig. Figure 7 is a cross-sectional view illustrating an example in which the light-emitting layer has a five-layer structure according to another embodiment of the present invention; Fig. Figure 8 is a cross-sectional view illustrating a light-emitting device according to another embodiment of the present invention; Fig. Figure 9 is a cross-sectional view illustrating a light-emitting device according to another embodiment of the present invention; Fig. 10A and Fig. Figure 10B illustrates layered structures of the first blue light-emitting layer and the second blue light-emitting layer of Fig. 8 or Fig. 9 according to an embodiment of the present invention; Fig. Figure 11 is an example of an energy band diagram of the first blue light-emitting stack of Fig. 8 or Fig. 9; Fig. Figure 12 is an example of an energy band diagram of the second blue light-emitting stack of Fig. 8 or Fig. 9; Fig. Figure 13 is an example of a graph showing a comparison of lifetime between experimental examples 4, 5 and 6; Fig. Figure 14 is an example of a graph showing a comparison of lifetime between experimental examples 5 and 7; Fig. Figure 15 is an example of a graph showing a comparison of lifetime between experimental examples 8 and 9; Fig. Figure 16 is a cross-sectional view illustrating light-emitting devices of a red subpixel, a green subpixel and a blue subpixel in the light-emitting display device according to an embodiment of the present invention; and Fig. Figure 17 is a cross-sectional view illustrating a light-emitting display device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EXECUTION FORMS

[0048] The advantages and features of the present invention and a method for achieving these advantages and features will become apparent with reference to the embodiments described in detail herein, together with the accompanying drawings. The present invention should not be construed as being limited to the embodiments disclosed below and can be implemented in various different forms. Therefore, these embodiments are presented only to make the present invention sufficiently complete and to assist those skilled in the art in fully understanding its scope. The protected scope of the present invention is defined by the claims and their equivalents.

[0049] In the following description of the present invention, where a detailed description of the relevant known steps, elements, functions, technologies, and configurations could unnecessarily obscure an important aspect of the invention, such a detailed description may be omitted. Furthermore, the names of elements used in the following description are chosen for the clarity of the patent specification and may differ from the names of elements in actual products. In addition, numerous specific details are set forth in the following detailed description of the present invention to provide a sufficiently thorough understanding of the invention. It is understood, however, that the present invention can be exercised without these specific details.In other cases, known methods, procedures, components and circuits were not described in detail in order to avoid unnecessarily obscuring aspects of the present invention.

[0050] The shapes, sizes, ratios, angles, numbers, and the like illustrated in the drawings to describe various embodiments of the present invention are given only as examples. The invention is not limited to the representations in the drawings.

[0051] In the present patent specification, where terms such as "including," "featuring," "comprising," and the like are used, one or more components may be added unless the term "only" is used. As used herein, the term "and / or" includes a single related listed element and any and all combinations of two or more of the related listed elements. Furthermore, the term "may" fully encompasses all meanings and coverings of the term "may" and vice versa.

[0052] An expression like "at least one of," when preceding a list of elements, can modify the entire list of elements but cannot modify any individual element within it. The phrase "at least one" should be understood to encompass any and all combinations of one or more of the listed elements. For example, the meaning of "at least one of a first element, a second element, and a third element" includes combinations of all three listed elements, combinations of any two of the three elements, and each individual element—that is, the first element, the second element, and the third element.

[0053] The terminology used herein serves to describe certain aspects and is not intended to limit the present invention. As used herein, the terms "a" and "an," used to describe an element in the singular, are intended to encompass a plurality of elements. An element described in the singular is intended to encompass a plurality of elements, and vice versa, unless the context clearly indicates otherwise.

[0054] When designing a component or numeric value, the component or numeric value should be designed to include a fault or tolerance range, even if no explicit description of such a fault or tolerance range is provided.

[0055] When describing the various exemplary embodiments of the present invention, where the positional relationship between two elements is described using terms such as "on," "above," "below," and "next to," at least one intermediate element may be present between the two elements, unless "immediately," "directly," or "near" is used. It is understood that when an element or layer is described as "connected to" or "coupled with" another element or layer, it may be directly connected or coupled to the other element or layer, or one or more intermediate elements or layers may be present.

[0056] When describing the various exemplary embodiments of the present invention, when terms such as "after", "subsequently", "next" and "before" are used to describe the temporal relationship between two events, another event may occur in between unless a limiting term such as "only", "immediately" or "directly" is used.

[0057] When describing the various exemplary embodiments of the present invention, terms such as "first" and "second" may be used to describe a variety of components. These terms are intended to distinguish identical or similar components from one another and do not restrict the components. Accordingly, throughout the description, a "first" component may be the same as a "second" component within the technical concept of the present invention, unless expressly stated otherwise.

[0058] Features of different embodiments of the present invention can be partially or completely coupled or combined with one another and can interact and be technically controlled in different ways, as a person skilled in the art can readily understand. The embodiments of the present invention can be implemented independently of one another or can be implemented together in a dependent relationship.

[0059] As used herein, terms such as LUMO (lowest unoccupied molecular orbital) energy level, HOMO (highest occupied molecular orbital) energy level, and triplet energy level of a layer refer to the LUMO energy level and HOMO energy level of a material that constitutes the majority of the layer's weight ratio, for example, a host material, unless the context explicitly states that the LUMO energy level and HOMO energy level refer to the LUMO energy level and HOMO energy level, respectively, of a dopant material with which the layer is doped. In the context of the present invention, the HOMO energy level is obtained by measuring the voltage corresponding to a first peak at which electrons are discharged from a target material by cyclic voltammetry (CV) while being compared with a reference material whose HOMO energy level is known.For example, the HOMO energy level of a substance can be measured based on a substance whose oxidation and reduction potentials are known. The LUMO energy level can be measured analogously. The triplet energy level T1 can be measured by a phosphorescence spectrum at a low temperature (77 K) or can be derived by analyzing delayed fluorescence.

[0060] As used herein, the term "doped" layer refers to a layer containing a first material and a second material (for example, n-type and p-type materials, or organic and inorganic substances) that has physical properties different from those of the first material. Aside from the differences in properties, the first and second materials may also differ in their amounts within the doped layer. For example, the host material may be a major component, while the dopant material may be a minor component. The first material constitutes the majority of the doped layer's weight. The second material may be added in an amount of less than 30 wt%, based on the total weight of the first material in the doped layer.A "doped" layer can be a layer used to distinguish a host material from a dopant material of a particular layer based on their weight ratio. For example, if all the materials forming a particular layer are organic materials, at least one of the materials forming the layer will be n-type and the other will be p-type. If the n-type material is present in an amount of less than 30 wt%, or if the p-type material is present in an amount of less than 30 wt%, the layer is considered a "doped" layer.

[0061] Furthermore, the term "undoped" refers to layers that are not "doped." For example, a layer can be "undoped" if it contains a single material or a mixture of materials with the same properties. For instance, if at least one of the materials forming a particular layer is of the p-type and none of the materials forming the layer are of the n-type, the layer is considered "undoped." Similarly, if at least one of the materials forming a layer is an organic material and none of the materials forming the layer are inorganic, the layer is considered "undoped."

[0062] In this present invention, an electroluminescence (EL) spectrum can be calculated by (a) multiplying a photoluminescence (PL) spectrum applying the inherent properties of an emitting material, such as a dopant material or a host material contained in an organic emission layer, with (b) an outcoupling or emission spectrum curve determined by the structure and optical properties of an organic light-emitting element, including the thicknesses of organic layers, such as an electron transport layer.

[0063] Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. If reference numerals are added to elements in each of the drawings, even though the same elements are shown in other drawings, the same reference numerals may refer to the same elements. All components of each device / apparatus according to all embodiments of the present invention are coupled and configured for operation.

[0064] Fig. Figure 1 is a cross-sectional view illustrating a light-emitting device according to an embodiment of the present invention. Fig. Figure 2 is a cross-sectional view illustrating an example where the light-emitting layer of Fig. 1 has a three-layered structure. Fig. 3 is an energy band diagram of the light-emitting layer and adjacent layers of Fig. 1.

[0065] As in Fig. As shown in Figure 1, the light-emitting device ED1 according to an embodiment of the present invention comprises a first electrode AND and a second electrode CAT facing each other, and a first common layer CML1, a light-emitting layer EML and a second common layer CML2 arranged successively between the first electrode AND and the second electrode CAT.

[0066] At least one of the first electrode AND and the second electrode CAT is transparent or semi-transparent, and light generated in the light-emitting device ED1 is transmitted through the transparent or semi-transparent electrode. For example, if the first electrode AND is a reflective electrode and the second electrode CAT is a semi-transparent or transparent electrode, the light-emitting device ED1 can be of a top-emission type. As another example, if the first electrode AND is a semi-transparent or transparent electrode and the second electrode CAT is a reflective electrode, the light-emitting device ED1 can be of a bottom-emission type. As yet another example, the first electrode AND and the second electrode CAT can be transparent or semi-transparent electrodes, allowing the light-emitting device ED1 to emit light in both directions.

[0067] The first electrode, AND, can function as the anode, and the second electrode, CAT, can function as the cathode. The first electrode, AND, can be connected to the thin-film transistor of the pixel circuit, which is provided in each subpixel on the substrate. The second electrode, CAT, can be shared by all subpixels and can receive a common voltage signal from at least one inactive area.

[0068] The first common layer CML1 can, for example, include at least one hole injection layer, one hole transport layer, or one electron blocking layer. Each of the hole injection layer, hole transport layer, and electron blocking layer can be selected from a material that includes a hole transport material or a material that does not impede the flow of holes. The configuration of the first common layer CML1, which contacts one side of the light-emitting layer EML (the lower surface of the light-emitting layer EML in Fig. 1) can be a hole transport layer or an electron blocking layer.

[0069] The second common layer CML2 can, for example, include at least one hole-blocking layer, an electron transport layer, or an electron injection layer. The second common layer CML2 contacts the other side of the light-emitting layer EML (the top surface of the light-emitting layer EML in the Fig. 1) can be a hole-blocking layer or an electron transport layer. The hole-blocking layer and the electron transport layer can each contain an electron transport material or can be selected from a material that does not impede the flow of electrons.

[0070] The light-emitting device ED1 of the embodiments of the present invention comprises at least one light-emitting layer EML comprising a plurality of layers, and the number of layers forming the light-emitting layer EML is an odd number, as shown in Fig. 1, Fig. 2 to Fig. 3 shown.

[0071] Additionally, if the layers are consecutively numbered, odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1), where n is 1 or more, preferably 1 to 15, more preferably 1 to 10, even more preferably 1 to 5) of the light-emitting layer EML include a first host BH1 and a dopant BD of the same material, and even-numbered layers (EMA2, ..., EMA(2n)) include a second host BH2 having at least one difference in the triplet energy level between the first host BH1 and a dopant BD.

[0072] The first layer EMA1 of the light-emitting layer EML and the last layer (EMA(2n+1)) of the light-emitting layer EML each contain the same first host BH1 and the same dopant BD.

[0073] For example, the light-emitting layer EML can be a light-emitting layer that emits blue light. For this purpose, the dopant BD can be a fluorescent dopant with an emission peak at a blue wavelength, for example, a wavelength of 430 nm to 495 nm, and can also be a thermally activated delayed fluorescent dopant (TADF).

[0074] Holes transferred from the first common layer CML1 to the light-emitting layer EML, and electrons transferred from the second common layer CML2 to the light-emitting layer EML, recombine in the light-emitting layer EML, generating singlet and triplet excitons in a ratio of 1:3. Singlet excitons generated in the light-emitting layer EML can fluoresce when their energy drops from a low singlet energy level S1_BD of a dopant BD in the light-emitting layer EML to the ground state. The dopant BD is present in an equal amount in each odd-numbered layer (EMA1, EMA3, ..., EMA(2n+1)) of the light-emitting layer EML with respect to the first host BH1, and is present in an equal or similar amount in each even-numbered layer (EMA2, ..., EMA(2n)) with respect to the second host BH2.Additionally, the singlet energy level S1_BH1 of the first host BH1 and the singlet energy level S1_BH2 of the second host BH2 can each be larger than the singlet energy level of the dopant BD to facilitate the energy transfer of the singlet exciton in each layer.

[0075] Additionally, the first host BH1, present in the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)), and the second host BH2, present in the even-numbered layers (EMA2, ..., EMA(2n)), exhibit differences in triplet energy levels. As in Fig. As shown in Figure 3, the triplet energy level T1_BH1 of the first host BH1 is higher than the triplet energy level T1_BH2 of the second host BH2. Additionally, the triplet energy level T1_BD of the dopant BD is higher than the triplet energy level T1_BH1 of the first host BH1.

[0076] For example, the first host BH1, the second host BH2 and the dopant BD, which are components contained in the light-emitting layer EML, exhibit the following relationship with respect to the triplet energy levels T1. T1_BD<T1_BH1> T1_BH2

[0077] As described above, the first layer EMA1 and the last layer (EMA(2n+1)) of the light-emitting layer EML contain the first host BH1 and the dopant BD of the same material. The second host BH2, with a lower triplet energy level T1_BH2, and the dopant BD are contained in the even-numbered layers (EMA2, ..., EMA(2n)) of the light-emitting layer EML.

[0078] Here, the first common layer CML1 can include a hole transport layer HTL that contacts the first layer EMA1 of the light-emitting layer EML, and the second common layer CML2 can include an electron transport layer ETL that contacts the last layer EMA(2n+1) of the light-emitting layer EML. The first common layer CML1 and the second common layer CML2 can have triplet energy levels T1_CML1 and T1_CML2, respectively, that are higher than the triplet energy levels T1_BH1, T1_BH2, and T1_BD of all materials BH1, BH2, and BD in the light-emitting EML.In one embodiment, the first common layer CML1 can have a triplet energy level T1_CML1 that is greater than the triplet energy levels T1_BH1, T1_BH2 and T1_BD of all materials BH1, BH2 and BD in the light-emitting EML, and the second common layer CML2 can have a triplet energy level T1_CML2 that is greater than the triplet energy levels T1_BH1 and T1_BH2 of materials BH1 and BH2 and equal to the triplet energy level T1_BD of BD in the light-emitting EML.

[0079] The lowest unoccupied molecular orbital (LUMO) energy level LUMO_BD of the dopant BD is higher than the LUMO energy level of each of the first and second hosts (LUMO_BD > LUMO_BH1, LUMO_BD > LUMO_BH2). Additionally, the second common layer CML2 can have a LUMO energy level LUMO_CML2 that is lower than the LUMO energy level LUMO_BD of the dopant BD (LUMO_BD > LUMO_CML2). Electrons injected from the second common layer CML2 through the LUMO energy level LUMO_BD of the dopant BD are readily injected into the LUMO energy levels of the first and second hosts BH1 and BH2 in each layer of the light-emitting layer.

[0080] The first common layer CML1 has a LUMO energy level LUMO_CML1 that is higher than the LUMO energy level LUMO_BD of the dopant BD (LUMO_CML1 > LUMO_BD), and a HOMO energy level HOMO_CML1 that is lower than the highest occupied molecular orbital (HOMO) energy level HOMO_BD of the dopant BD (HOMO_BD > HOMO_CML1). The first common layer CML1 has a higher LUMO energy level LUMO_CML1 than the dopant BD, so electrons transferred into the light-emitting layer EML are trapped within the light-emitting layer EML and serve to emit light. Additionally, the HOMO energy level HOMO_BD of the dopant BD can be higher than the HOMO energy levels HOMO_BH1 and HOMO_BH2 of each of the first and second hosts (HOMO_BD > HOMO_BH1, HOMO_BD > HOMO_BH2). Furthermore, the HOMO energy level HOMO_BD of the dopant BD can also be higher than the HOMO energy level HOMO_CML2 of the second common layer CML2.

[0081] In the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)), which contain the first layer EMA1, electrons and holes recombine, and fluorescence occurs immediately. In the even-numbered layers (EMA2, ..., EMA(2n)), which contain the second layer EMA2, energy is transferred from the triplet energy level T1_BH1 of the first host BH1 of the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) to the triplet energy level T1_BH2 of the second host BH2. Delayed luminescence is caused by the TTF (triplet-triplet fusion) mechanism, in which triplet excitons collide, generating singlet excitons. For example, in the light-emitting layer EML, odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) and even-numbered layers (EMA2, ..., EMA(2n)) are regionally separated by the distinction between host components BH1 and BH2 with differences in triplet energy levels (T1_BH1, T1_BH2), and odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) perform optimal immediate fluorescence, and even-numbered layers (EMA2, ..., EMA(2n)) perform optimal delayed fluorescence.

[0082] Fig. 2 and Fig. Three examples are given where a multilayer structure of a light-emitting layer (EML) is a three-layer structure. In the following experiments, the three-layer EML is a blue light-emitting layer. The luminescence mechanism is described based on the three-layer structure example.

[0083] In the first layer EMA1 and the third layer EMA3, electrons and holes recombine to generate singlet and triplet excitons. Theoretically, singlet and triplet excitons are generated in a ratio of 1:3. The singlet excitons generated in the odd-numbered layers EMA1 and EMA3 decay from the singlet energy level S1_BD of the dopant BD to the ground state, and fluorescence occurs immediately. To achieve more effective fluorescence within the first layer EMA1 and the third layer EMA3, the dopant BD can have a triplet energy level T1_BD that is higher than the triplet energy level T1_BH1 of the first host BH1 (T1_BD > T1_BH1), but can have a singlet energy level that is lower than the singlet energy level S1_BH1 of the first host BH1 (S1_BD < S1_BH1).

[0084] Singlet excitons generated by the recombination of holes and electrons within the first layer EMA1 and the third layer EMA3 are easily moved to the lower singlet energy level S1_BD of the dopant BD due to the lower singlet energy level of the dopant BD, thus contributing to the fluorescence of the dopant BD in the first layer EMA1 and the third layer EMA3.

[0085] In addition, the triplet excitons generated in the first layer EMA1 and the third layer EMA3 are not transferred to the dopant BD with a high triplet energy level in the odd-numbered layers EMA1 and EMA3, but are transferred to the first host BH1 with a lower triplet energy level than the dopant BD. Then, due to the relationship of the triplet energy level difference (T1_BH1 > T1_BH2) between the first host BH1 and the second host BH2, the triplet excitons can be transferred molecularly from the first host BH1 of the odd-numbered layers EMA1 and EMA3 to the second host BH2 of the even-numbered layers EMA2 with a relatively lower triplet energy level, and the triplet excitons transferred to the even-numbered layers EMA2 collide with each other and generate singlet excitons through the TTF mechanism, causing them to undergo delayed fluorescence in the even-numbered layers EMA2.Here, in the even-numbered layer EMA2, singlet and triplet excitons can be generated together within the second layer EMA2 by the supply of holes through the first common layer CML1 and the supply of electrons through the second common layer CML2. Fluorescence is produced by the singlet excitons generated in the even-numbered layer EMA2 itself, and delayed fluorescence is caused by the TTF mechanism, in which the triplet excitons generated directly by the second host BH2 and the triplet excitons that have crossed the triplet energy level from the first host BH1 collide, generating singlet excitons. This causes additional delayed fluorescence along with the immediate fluorescence in the even-numbered layer EMA2, thus increasing the light yield.

[0086] Meanwhile, if excitons in the light-emitting layer are not used for light emission, they can interact with neighboring polarons and be annihilated. This annihilation can be a major factor in reducing the efficiency of the light-emitting layer. Additionally, if excitons not used for light emission accumulate at the interface contacting the first common layer CML1 or the second common layer CML2 in the light-emitting layer, it can severely impact the lifetime of the light-emitting device.

[0087] The light-emitting device according to the embodiment of the present invention is designed such that the triplet energy level T1_BH1 of the first host BH1, which is provided in the odd-numbered layers EMA1 and EMA3, is higher than the triplet energy level T1_BH2 of the second host BH2, which is provided in the even-numbered layers EMA2, so that the energy transfer of the triplet excitons is easily carried out from the first host BH1 to the second host BH2 and the triplet exciton that is not used for light emission is not accumulated in the region of the first layer EMA1 of the light-emitting layer EML, which contacts the first common layer CML1 or the third layer EMA3, which is the last layer that contacts the second common layer CML2, and the triplet excitons are directed to the second layer EMA2, which is the even-numbered layer.Energy is transferred through the difference in triplet energy levels between the first and second hosts BH1 and BH2, thereby maximizing TTF efficiency in the second layer EMA2, increasing the exciton recycling rate, increasing the light yield in the light-emitting layer EML, and improving lifetime.

[0088] Here, the even-numbered layers of the light-emitting layer EML can contain a second host BH2 with a lower triplet energy level, so that the triplet excitons can easily move to the even-numbered layers of the light-emitting layer EML that are not adjacent to the first and second common layers CML1 and CML2 by energy transfer, thereby improving the light yield.

[0089] On the other hand, if the light-emitting layer is applied as a single emitting layer without layer differentiation, lifetime degradation is prominent due to exciton accumulation at the interface between the light-emitting layer and the common layer, especially at the interface where the light-emitting layer and the hole transport layer come into contact.

[0090] Accordingly, the light-emitting device ED1, according to the embodiment of the present invention, generates light emission from odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) and even-numbered layers (EMA2, ..., EMA(2n)) within the light-emitting layer EML. In particular, the quenching of triplet excitons can be reduced or prevented, and triplet excitons can be used to the maximum extent for light emission, thereby improving the light yield compared to a single-layer light-emitting layer structure. Additionally, since the triplet excitons do not remain in the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) but rather migrate from the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) to the even-numbered layers (EMA2, ..., EMA(2n)) by energy transfer due to the triplet energy level difference (T1_BH1-T1_BH2>0) between the first and second host BH1 and BH2 of the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) and the even-numbered layers (EMA2, ..., EMA(2n)) and are recycled for delayed fluorescence, the quenched excitons are not generated at the interface between the first common layer CML1, the second common layer CML2 and the light-emitting layer EML, thus improving the lifetime of the light-emitting layer EML.

[0091] Meanwhile, if the light-emitting layer (EML) is divided into an odd number of layers, and if the layers are consecutively numbered, with the odd-numbered layers containing a first host BH1 with a relatively high triplet energy level and the even-numbered layers containing a second host BH2 with a relatively low triplet energy level, the luminescence intensity within the EML can be highest at the interface between the first layer EMA1 and the second layer EMA2. Additionally, the emission zone of the EML can be concentrated in the first layer EMA1 and the second layer EMA2.This is because the third layer EMA3, adjacent to the second common layer CML2 in the light-emitting layer EML, has a lower supply of holes than the first layer EMA1 and the second layer EMA2, and thus the generation rate of excitons produced by the recombination of electrons and holes can be reduced.

[0092] The luminescence intensity in the light-emitting layer (EML) can vary depending on the recombination rate of holes and electrons. For example, the interface between the first layer (EMA1) and the second layer (EMA2), which has a high recombination rate, exhibits the strongest luminescence intensity, and the recombination rate can gradually decrease with increasing distance from this interface. To effectively ensure a luminescent area, the thickness of the first layer (EMA1) and the second layer (EMA2), which have a high recombination rate, can be greater than the thickness of the third layer (EMA3).

[0093] The first host BH1 can, for example, be a compound containing a pyrene derivative, such as a pyrene derivative.

[0094] The second host BH2 can, for example, be a compound containing an anthracene derivative, such as an anthracene derivative.

[0095] The examples of compounds of the first and second host BH1 and BH2 are not limited to the examples described above, and if the first host BH1, the second host BH2 and the dopant BD have a relationship of T1_BD > T1_BH1 > T1_BH2 in the triplet energy level T1, they can be modified to other compounds.

[0096] The dopant BD in the light-emitting layer EML is a fluorescent dopant with an emission peak at a wavelength of 430 nm to 495 nm. For example, the dopant BD can be a boron-based dopant, as shown in Formulas 1 to 9 below, but this is provided only as an example, and the dopant in embodiments of the present invention is not limited to the following materials. Any fluorescent dopant capable of fluorescence and delayed fluorescence, with an emission peak at a wavelength of visible light of 495 nm or less and with a high triplet energy level, can be used.

[0097] Additionally, the triplet energy level of the dopant can be adjusted to be higher by changing the substituent in at least part of any of the compounds of formulas 1 to 9 described above in the light-emitting device according to the embodiment of the present invention.

[0098] Here, in the light-emitting layer EML, the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) contain the first host BH1 and the dopant BD, and the even-numbered layers (EMA2, ..., EMA(2n)) contain the second host BH2 and the dopant BD.

[0099] The odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) and the even-numbered layers (EMA2, ..., EMA(2n)) differ in their host components. The odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) and the even-numbered layers (EMA2, ..., EMA(2n)) can each contain the first host BH1 and the second host BH2 in major proportions. The odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) preferably contain 50 wt% or more of the first host BH1, and the even-numbered layers (EMA2, ..., EMA(2n)) contain 50 wt% or more of the second host BH2. Even more preferably, the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) can contain 70 wt% or more of the first host BH1 and the even-numbered layers (EMA2, ..., EMA(2n)) can contain 70 wt% or more of the second host BH2.

[0100] Even more preferentially, the first host BH1 can be present in a proportion of 90 wt% or more in the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)), and the second host BH2 can be present in a proportion of 90 wt% or more in the even-numbered layers (EMA2, ..., EMA(2n)). In this case, the dopant BD can be present in a proportion of 10 wt% or less in both the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) and the even-numbered layers (EMA2, ..., EMA(2n)).

[0101] In some cases, the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) may contain 90 wt% or more of the first host BH1 and 10 wt% or less of the dopant BD within the layer, and the even-numbered layers (EMA2, ..., EMA(2n)) may contain 70 wt% or more of the second host BH2, 20 wt% or more of a host other than the second host BH2, and 10 wt% or less of the dopant BD. The triplet energy level of the additional host other than the second host BH2, present in the even-numbered layers (EMA2, ..., EMA(2n)), may be lower than or equal to the triplet energy level of the first host BH1.

[0102] Among the components contained in the light-emitting layer EML, the triplet energy level T1_BD of the dopant BD is the highest, and the triplet energy level T1_BH1 of the first host BH1, present in the odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)), is higher than the triplet energy level T1_BH2 of the second host BH2, present in the even-numbered layers (EMA2, ..., EMA(2n)). The materials for the light-emitting layer EML exhibit at least the relationship T1_BD > T1_BH1 > T1_BH2 with respect to the triplet energy levels.

[0103] The dopant BD, which is typically included in each layer (EMA1, EMA2, EMA3, ...) of the light-emitting layer EML, can be a fluorescent dopant and can be a dopant capable of delayed fluorescence. For example, the dopant BD can be a thermally activated delayed fluorescent dopant (TADF). In a particularly preferred embodiment, the dopant BD is a multiresonant thermally activated delayed fluorescent dopant (MR-TADF).

[0104] In contrast to the ones described above Fig. 1, Fig. 2 to Fig. 3. If the light-emitting layer is designed as a multi-light-emitting layer and the first layer adjacent to the first common layer CML1 contains a host with a lower triplet energy level than the triplet energy level of the host of the second layer, triplet excitons can move to the first layer and concentrate at the interface contacting the first common layer, causing an increase in excitons that are not used for light emission and are quenched, which can have a negative impact on both the light output and the lifetime.

[0105] The light-emitting device according to an embodiment of the present invention can include a light-emitting layer EML with odd-numbered layers (EMA1, EMA3, ..., EMA(2n+1)) containing different first hosts BH1, and even-numbered layers (EMA2, ..., EMA(2n)) containing second hosts BH2, and can be formed in a single chamber.

[0106] Meanwhile, according to one embodiment of the present invention, the light-emitting device includes a light-emitting layer EML that emits light with a wavelength of 430 nm to 495 nm, which corresponds approximately to blue light.

[0107] A blue light-emitting device exhibits low visibility and a short lifespan. Therefore, improving the efficiency and lifespan of blue light-emitting devices compared to light-emitting devices of other colors is a significant technical challenge. The light-emitting device according to the embodiment of the present invention comprises a plurality of blue light-emitting layers, but the internal materials are different to separate the layers, thereby improving both the light output and the lifespan.

[0108] However, the present invention is not limited thereto. Even if a light-emitting dopant emitting light of a different color is included, the multiple light-emitting layers are divided into an odd number of layers, and if the layers are numbered consecutively, the odd-numbered layers contain a first host, and the even-numbered layers contain a second host with a lower triplet energy level than the first host, thereby separating the common layer adjacent to both interfaces of the light-emitting layer and the layer of the light-emitting layer that emits delayed fluorescence based on the TTF mechanism, thus preventing excitons from accumulating at both interfaces of the light-emitting layers and improving the lifetime.

[0109] In the light-emitting device according to an embodiment of the present invention, the light-emitting layer is divided into an odd number of layers, different first and second hosts are arranged alternately, and the dopant is provided jointly in each layer, such that the first and last layers of the light-emitting layer contain the first host and the dopant, and the layers containing the first host and the dopant come into contact with the first common layer and the second common layer at the two interfaces of the light-emitting layer EML.

[0110] The light-emitting layer of the present invention can be formed according to the following manufacturing process.

[0111] The host materials of the multiple light-emitting layers of the light-emitting device according to an embodiment of the present invention can be changed by controlling a deposition area in the same chamber.

[0112] According to one embodiment of the present invention, the light-emitting device can be divided into several light-emitting layers using a single chamber. For example, when odd-numbered layers are formed in the light-emitting layer, the deposition gas injection area of ​​the delivery source of the first host BH1 faces the substrate to selectively supply the first host, and when even-numbered layers are formed, the deposition gas injection area of ​​the second host BH2 faces the substrate to selectively supply the second host BH2. For example, the injection areas of the first host BH1 and the second host BH2 do not overlap, and the dopant BD overlaps the injection areas of both the first and second hosts BH1 and BH2, so that the hosts of the odd-numbered and even-numbered layers are different.

[0113] As a result, the light-emitting device according to one embodiment of the present invention can include a light-emitting layer that is formed using different hosts for the odd-numbered layers and the even-numbered layers using a single chamber. Therefore, the light-emitting device according to this embodiment of the present invention is able to solve the problems of reduced yield and additional process equipment that arise when each chamber is arranged to form multiple layers of the light-emitting layer using multiple chambers.

[0114] The light-emitting device according to an embodiment of the present invention has a configuration in which the layer in which the delayed fluorescence is concentrated by the TTF mechanism is arranged in the even layer within the odd-numbered emission layers, so that the excitons that are extinguished in the light-emitting layer are recycled, the light-emitting efficiency is improved, and the lifetime degradation caused by exciton accumulation at the interface between the common layer and the light-emitting layer is prevented.

[0115] The effect of the light-emitting device according to the present invention is described below with reference to experiments. In the following experiments, the first host BH1 has a triplet energy level of 2.1 eV, the second host BH2 has a triplet energy level of 1.8 eV, and the dopant BD has a triplet energy level of 2.7 eV, as shown in Table 1 below. Specifically, in the following experiments, the first host BH1, the first second host BH2, the dopant BD, the first common layer CML1, and the second common layer exhibit triplet energy levels, HOMO energy levels, and LUMO energy levels, as shown in Table 3 below. For example, in the following experiments, the first host BH1 is a compound containing a pyrene and having a triplet energy level of 2.1 eV, and the second host BH2 is a compound containing an anthracene and having a triplet energy level of 1.8 eV.The dopant BD comprises a boron-based compound selected from one of the formulas 1 to 9 mentioned above. Formulas 1 to 9 exhibit higher triplet energy levels than the triplet energy levels of the first host BH1 and the second host BH2. The hosts and the dopant can be replaced by other materials, provided they exhibit a triplet level relationship and an energy band gap property at the odd- and even-numbered layers in the light-emitting layer, such as those described in [reference missing]. Fig. 3 is shown.

[0116] Fig. Figure 4 illustrates light-emitting layers of experimental comparison example 1 and experimental example 2.

[0117] As in Fig. As shown in Figure 4, the experimental comparison example 1 EX1 has the same configuration as in the light-emitting device of Fig. 1, except that the light-emitting layer is formed as a single layer and the second host BH2 and a blue light-emitting dopant BD are contained within the single light-emitting layer. Here, the total thickness of the light-emitting layer EML of experimental comparison example 1 EX1 is 180 Å.

[0118] Experimental example 2 EX2 has the same configuration as in the light-emitting device of Fig. 1. Accordingly, the first layer EMA1 contains the first host BH1 and the dopant BD, the second layer EMA2 contains the second host BH2 and the dopant BD, and the third layer EMA3 contains the first host BH1 and the dopant BD. The layer thicknesses of the first to third layers EMA1, EMA2, and EMA3 were each set at 60 Å.

[0119] The triplet energy levels of the first host BH1, the second host BH2 and the dopant BD used in the experiment are as shown in Table 1. [Table 1] Element BD BH1 BH2 T1[eV] 2,7 2,1 1,8

[0120] First, with reference to Fig. 5 and Fig. 6. The effects between experimental comparison example 1 EX1, which includes a single light-emitting layer containing a single host, and experimental example 2 EX2, in which the odd-numbered and even-numbered layers of the light-emitting layer EML contain different hosts, were compared.

[0121] Fig. Figure 5 is a graph showing the 95 lifetime of light-emitting devices according to experimental comparison example 1 and experimental example 2. Fig. Figure 6 is a graph showing the luminous efficiency as a function of the CIEy of light-emitting devices according to experimental comparison example 1 and experimental example 2.

[0122] The 95 lifetime refers to the time after which the luminance has decreased to 95% of the initial luminance.

[0123] As from Fig. As can be seen in Figure 5, the 95 lifetime of experimental example 2 EX2, which contains the first host BH1 in the odd-numbered layers and the second host BH2 in the even-numbered layers, is more than three times that of the experimental comparison example 1 EX1, which contains a single host.

[0124] Fig. Figure 6 shows the luminous efficacy of experimental comparison example 1 EX1 and experimental example 2 EX2 at a CIEy of 0.0290 to 0.0390, where pure blue luminance occurs. The luminous efficacy of experimental example 2 EX2 is improved compared to the luminous efficacy of experimental comparison example 1 EX1 across the entire CIEy range from 0.0290 to 0.0390. As can be seen from Table 2, experimental example 2 EX2 shows an increase in blue index efficiency (%) to 126.1% compared to experimental comparison example 1 EX1. The blue index efficiency is obtained by subdividing a maximum luminous efficacy into a color coordinate value CIEy at which the maximum luminous efficacy occurs in each of the first and second experimental examples EX1 and EX2.

[0125] The experiments showed that experimental example 2 EX2, which includes a first and second layer each containing a host and a single dopant, and which includes a third layer as a top layer, showed an improvement in both lifetime and pure color efficiency compared to the experimental comparison example 1 EX1, which includes the light-emitting layer containing a single host material. [Table 2] Element Lichtemittierende Schicht Betriebsspannung(V) Blauindex(%) 95-Lebensdauer (%) EX1 (BH2 + BD) Vr 100 100 EX2 (BH1 + BD) / (BH2 + BD) / (BH1 +BD) Vr-0,150 126,1 363

[0126] Furthermore, the results from Table 2 show that the operating voltage in experimental example 2 EX2 is reduced by 0.150 V compared to the experimental comparison example 1 EX1.

[0127] As shown in Table 2 and Fig. 5 and Fig. As can be seen in Figure 6, the operating voltage in experimental example 2 EX2 is significantly reduced compared to experimental comparison example 1 EX1, and the blue index efficiency is improved. Furthermore, it is evident that the lifetime in experimental example 2 EX2 is more than three times that of experimental comparison example 1 EX1.

[0128] Meanwhile, the multilayer structure of the light-emitting layer in the light-emitting device of the present invention is divided into an odd number of layers and is not limited to the one described in Fig. 2 and Fig. 3 revealed a three-layered structure limited.

[0129] Fig. Figure 7 is a cross-sectional view illustrating an example in which the light-emitting layer has a five-layer structure according to another embodiment of the present invention.

[0130] With reference to Fig. 7. The light-emitting layer EML can also be divided into five layers.

[0131] The first, third and fifth layers EMA1, EMA3 and EMA5 contain a first host BH1 and a dopant BD, and the second and fourth layers EMA2 and EMA4 contain a second host BH2 and a dopant BD.

[0132] Due to the difference between the triplet energy level T1_BH1 of the first host BH1 of the first, third and fifth layers EMA1, EMA3 and EMA5 and the triplet energy level T1_BH2 of the second host BH2 of the second and fourth layers EMA2 and EMA4, the delayed fluorescence by the TTF mechanism is more dominant in the second and fourth layers EMA2 and EMA4 than in the first, third and fifth layers EMA1, EMA3 and EMA5.

[0133] Although the light-emitting layer EML of Fig. If the 7 is divided into five layers, the effects of reduced operating voltage, improved efficiency and improved lifetime can be achieved in the same way as in the case where the light-emitting layer EML described above is divided into three layers.

[0134] The example in which a single light-emitting stack is provided between the first electrode AND and the second electrode CAT has been described above.

[0135] For example, in a light-emitting device comprising multiple stacks, the light-emitting layer of at least one stack can be configured as multiple layers, as described in reference to Fig. 1, Fig. 2, Fig. 3 to Fig. 4 described in order to achieve the effects of improved lifespan and efficiency. A light-emitting device according to another embodiment is described below.

[0136] Fig. Figure 8 is a cross-sectional view illustrating a light-emitting device according to another embodiment of the present invention.

[0137] As in Fig. As shown in Figure 8, the light-emitting device ED2 according to another embodiment of the present invention comprises a first stack S1, a charge-generating layer CGL, and a second stack S2, arranged successively between the first electrode AND and the second electrode CAT, which face each other. The first stack S1 and the second stack S2 each comprise a first common layer CML11 and CML12, a blue light-emitting layer BEML1 and BEML2, and a second common layer CML21 and CML22. The first common layer CML11 and CML12 may comprise hole-transport material, and the second common layer CML21 and CML22 may comprise electron-transport material.

[0138] The first stack S1 and the second stack S2 each contain a first common layer CML11 and CML12, which serves to transport holes, a blue light emitting layer BEML1 and BEML2, and a second common layer CML21 and CML22, which serves to transport electrons.

[0139] The first common layer CML11 and CML12 may include a hole injection layer, a hole transport layer, an electron blocking layer, and the like.

[0140] The second common layer CML21 and CML22 may include a hole-blocking layer, an electron transport layer, an electron injection layer, and the like.

[0141] In the multi-stack structure, the hole injection layer can be provided in the first stack S1, which contacts the first electrode AND, and the electron injection layer can be provided in the second stack S2, which contacts the second electrode CAT.

[0142] The charge-generating layer CGL can be formed by laminating a p-type charge-generating layer PCGL and an n-type charge-generating layer NCGL.

[0143] Here, the first stack S1 contains a first blue light emitting layer BEML1 and the second stack S2 contains a second blue light emitting layer BEML2.

[0144] At least one of the first and second blue light-emitting layers BEML1 and BEML2 can have a multilayer structure with an odd number of layers, for example, including the first to third layers EMA1, EMA2, and EMA3, as described above. Fig. 1, Fig. 2, Fig. 3 to Fig. 4 described. The first to third layers EMA1, EMA2 and EMA3 together contain a dopant BD. The first layer EMA1 and the third layer EMA3, which are odd-numbered layers, contain a first host BH1, and the second layer EMA2 contains a second host BH2 with a lower triplet energy level than the first host.

[0145] Fig. Figure 9 is a cross-sectional view illustrating a light-emitting device according to another embodiment of the present invention.

[0146] As in Fig. As shown in Figure 9, the light-emitting device ED3 according to another embodiment of the present invention includes three or more stacks between a first electrode AND and a second electrode CAT.

[0147] A charge-generating layer CGL1 to CGLN-1 can be provided between the three or more stacks S1, SPE, and SN. The charge-generating layer CGL1 to CGLN-1 can include a laminate of an n-type charge-generating layer NCGL and a p-type charge-generating layer PCGL.

[0148] Two stacks S1 and SN among the three or more stacks provided between the first and second electrodes AND and CAT include blue light emitting layers BEML1 and BEML2.

[0149] The illustrated example is a case in which the first stack S1 and the Nth stack SN have blue light emitting layers BEML1 and BEML2, but the embodiment is not limited thereto.

[0150] Between the first stack S1 and the nth stack SN, one or more phosphorescent light-emitting stacks SPE, including a phosphorescent light-emitting layer PEML, may be included. In some cases, the phosphorescent light-emitting layer PEML may be a laminate of phosphorescent light-emitting layers emitting light of different colors.

[0151] In each stack S1, SPE or SN, a first common layer CML11, CML1A or CML1N, used for hole transport, can be provided on the underside of each light-emitting layer BEML1, PEML, BEML2, and a second common layer CML21, CML2A or CML2N, used for electron transport, can be provided on the top side of each light-emitting layer BEML1, PEML, BEML2.

[0152] For example, the first stack S1 contains a first blue light emitting layer BEML1 and the Nth stack SN contains a second blue light emitting layer BEML2.

[0153] At least one of the first and second blue light-emitting layers BEML1 and BEML2 can have a multilayer structure with an odd number of layers, for example, including the first to third layers EMA1, EMA2, and EMA3, as described above. Fig. 1, Fig. 2, Fig. 3 to Fig. 4 described. The first to third layers EMA1, EMA2 and EMA3 together contain a dopant BD. The first layer EMA1 and the third layer EMA3, which are odd-numbered layers, contain a first host BH1, and the second layer EMA2 contains a second host BH2 with a lower triplet energy level than the first host.

[0154] Meanwhile, an example and its significance are described, in which another structure is applied to the first blue light-emitting layer BEML1 adjacent to the first electrode AND and the second blue light-emitting layer BEML2 adjacent to the second electrode CAT, and to the first and second blue light-emitting layers BEML1 and BEML2 with the multilayer structure of Fig. 8 or Fig. 9 is applied.

[0155] Fig. 10A and Fig. Figure 10B illustrates layered structures of the first blue light-emitting layer and the second blue light-emitting layer of Fig. 8 or Fig. 9 according to an embodiment of the present invention. Fig. Figure 11 is an energy band diagram of the first blue light-emitting stack of Fig. 8 or Fig. 9. Fig. Figure 12 is an energy band diagram of the second blue light-emitting stack of Fig. 8 or Fig. 9.

[0156] As in Fig. As shown in Figure 10A, the first blue light-emitting layer BEML1, which is adjacent to the first electrode AND, can have thicknesses A1, A2, A3 of several layers that are the same or similar (A1≒A2≒A3). This is shown in Fig. The illustrated example in Figure 10A is that the first blue light-emitting layer, BEML1, is configured as a three-layer structure. The first layer, EMA1, and the third layer, EMA3, contain the first blue host, BH1, with high triplet energy levels T1_BH1 and the first blue dopant, BD1, respectively. The second layer, EMA2, contains the second blue host, BH2, with relatively low triplet energy levels T1_BH2, and the first blue dopant, BD1. In this example, the thicknesses A1, A2, and A3 can be equal or similar to each other, and each can be in the range of 2 nanometers to 15 nanometers (20–150 Å), 3 nanometers to 10 nanometers, 4 nanometers to 9 nanometers, or 5 nanometers to 8 nanometers.In another example, the thicknesses A1, A2, and A3 can be the same or different from each other, and each can independently range from 2 to 15 nanometers, from 3 to 10 nanometers, from 4 to 9 nanometers, or from 5 to 8 nanometers. For example, thickness A1 can be 4 nanometers or more, 5 nanometers or more, 6 nanometers or more, 7 nanometers or more, or 8 nanometers or more; thickness A2 can be 6 nanometers or more, 7 nanometers or more, or 8 nanometers or more; thickness A3 can be 8 nanometers or less, 7 nanometers or less, 5 nanometers or less, or 3 nanometers or less.

[0157] As in Fig. As shown in Figure 10B, the second blue light-emitting layer BEML2, adjacent to the second electrode CAT, can have different thicknesses B1, B2, and B3. The second layer EMA2, which is a straight layer within the second blue light-emitting layer BEML2, can be the thickest, and the third layer EMA3, adjacent to the second electrode CAT, can be the thinnest. For example, the second layer thickness B2 of the second layer EMA2 can be greater than the first layer thickness B1 of the first layer EMA1, and the third layer thickness B3 of the third layer EMA3 can be less than the first layer thickness B1. In the figure shown in Fig. In the illustrated example 10B, the second blue light-emitting layer, BEML2, has a three-layer structure. The first layer, EMA1, and the third layer, EMA3, contain a third blue host, BH3, with a high triplet energy level, T1_BH3, and a second blue dopant, BD2, respectively. The second layer, EMA2, contains a fourth blue host, BH4, with a relatively low triplet energy level, T1_BH4, and the second blue dopant, BD2. The second blue dopant, BD2, can also be referred to more generally as the second dopant if it is not specifically used in a second blue light-emitting layer, BEML2, but rather in a second light-emitting layer in general. For example, the thickness B1 can range from 3 nanometers to 10 nanometers, the thickness B2 can range from 5 nanometers to 12 nanometers, and the thickness B3 can range from 2 nanometers to 8 nanometers.

[0158] Here, the total thickness A of the multilayer structure of the first blue light-emitting layer BEML1 and the total thickness B of the multilayer structure of the second blue light-emitting layer BEML2 can be the same or different from each other. For example, the total thickness A and the total thickness B can each independently range from 6 nanometers to 50 nanometers, from 8 nanometers to 40 nanometers, from 10 nanometers to 30 nanometers, or from 12 nanometers to 24 nanometers.

[0159] The first blue host BH1 of the first blue light-emitting layer BEML1 can be the same as the third blue host BH3 of the second blue light-emitting layer BEML2, and the second blue host BH2 of the first blue light-emitting layer BEML1 can be the same as the fourth blue host BH4 of the second blue light-emitting layer BEML2.

[0160] The first blue dopant BD1 of the first blue light emitting layer BEML1 can be the same as the second blue dopant BD2 of the second blue light emitting layer BEML2, but the embodiments of the present invention are not limited thereto.

[0161] Provided that the triplet energy levels T1_BD1, T1_BH1, T1_BH2 in the first blue light emitting layer BEML1 decrease in the order of the first blue dopant, the first blue host and the second blue host (T1_BD1 > T1_BH1 > T1_BH2), and the triplet energy levels T1_BD2, T1_BH3, T1_BH4 in the second blue light emitting layer BEML2 decrease in the order of the second blue dopant, the third blue host and the fourth blue host (T1_BD2 > T1_BH3 > T1_BH4), the materials for the first blue light emitting layer and the second blue light emitting layer can be changed or freely selected.

[0162] Here, the thickness B3 of the third layer EMA3 of the last layer of the second blue light emitting layer BEML2, which contacts the second common layer CML22 of the second blue light emitting stack, can be less than the thickness A3 of the third layer EMA3 of the last layer of the first blue light emitting layer BEML1, which contacts the second common layer CML21 of the first blue light emitting stack (A3 > B3).

[0163] In the second blue light emitting stack, the thickness B3 of the third layer EMA3 of the second blue light emitting layer BEML2, which contacts the second common layer CML22, can be less than the thickness B2 of the second layer EMA2, which contacts the third layer EMA3 (B2 > B3).

[0164] In the second blue light-emitting stack, the thickness B3 of the third layer EMA3 of the second blue light-emitting layer BEML2, which contacts the second common layer CML22, can be less than the thickness B1 of the first layer EMA1 of the second blue light-emitting layer BEML2, which contacts the first common layer CML12 (B1 > B3). For example, the thickness B1 of the first layer EMA1 can be 1.5 times or more, 1.7 times or more, 1.8 times or more, or even twice or more, the thickness B3 of the third layer EMA3. Therefore, while the overall thickness of the light-emitting layer remains unchanged, the recombination region can be expanded, and the region where exciton generation and the TTF mechanism occur can be secured, thus improving lifetime and increasing efficiency.

[0165] Here, the first blue light emitting layer BEML1 and the second blue light emitting layer BEML2 have a multilayered structure with a difference in thickness, because the neighboring electrodes are different, the transfer velocities of holes and electrons are different, and thus the recombination areas formed are different.

[0166] The first blue light-emitting layer BEML1 of the first blue light-emitting stack, which contacts the first electrode AND, is located a short distance from the first electrode AND, resulting in a very high number of injected holes. However, the vertical distance from the second electrode CAT to the first blue light-emitting layer BEML1 is longer than the vertical distance from the first electrode AND to the first blue light-emitting layer BEML1. Therefore, the electron movement distance is longer than the hole movement distance, and the electron delivery rate to the first blue light-emitting layer BEML1 is slow. As shown in Fig. 8 and Fig. As shown in Figure 9, the first blue light-emitting stack can receive electrons through the charge-generating layer of the adjacent light-emitting stack, in particular the n-type charge-generating layer, but the electron transfer rate may be slower than that of the second blue light-emitting layer BEML2, which is relatively adjacent to the second electrode CAT. In this case, as shown in Fig. 11 and Fig. As shown in Figure 12, since there is a difference in the transport rate of holes and electrons between the first blue-light-emitting layer BEML1 and the second blue-light-emitting layer BEML2, the recombination region occurs over a wider area in the first blue-light-emitting layer BEML1 than in the second blue-light-emitting layer BEML2. Even within the first blue-light-emitting layer BEML1, the intensity of hole and electron recombination can be highest between the first layer EMA1 and the second layer EMA2. However, if the thickness of the first layer EMA1 in the first blue-light-emitting layer BEML1 is increased, the location where the recombination region occurs moves to the center of the first blue-light-emitting layer BEML1, and in this case, the TTF efficiency in the second layer EMA2 can decrease. Therefore, as shown in Figure 12, the recombination region can be significantly reduced in the first blue-light-emitting layer BEML1. Fig. 10A and Fig. Figure 11 shows that the thicknesses of each layer EMA1, EMA2 and EMA3 of the first blue light emitting layer BEML1 are equal or similar.

[0167] Meanwhile, as in Fig. 10B and Fig. As shown in Figure 12, the second blue light-emitting layer BEML2 adjacent to the second electrode CAT exhibits a high electron injection rate. Therefore, if each layer of the second blue light-emitting layer BEML2 has the same thickness, a recombination region can form in a local area adjacent to the first common layer CML12, which serves for hole transport. Accordingly, the recombination region is formed closer to the center of the second blue light-emitting layer BEML2, the interface between the first layer EMA1 and the second layer EMA2 with a large distribution of recombination regions is located closer to the center of the second blue light-emitting layer BEML2, and the thickness B1 of the first layer EMA1 of the second blue light-emitting layer BEML2 is greater than the thickness A1 of the first layer EMA1 of the first blue light-emitting layer BEML1.Additionally, the first layer EMA1 and the second layer EMA2 of the second blue light-emitting layer BEML2 undergo energy transfer from the third blue host BH3 to the fourth blue host BH4 due to the difference in triplet energy levels. This results in delayed fluorescence in the second layer EMA2 via the TTF mechanism. Therefore, to maximize TTF efficiency, and thus light yield and lifetime, the thickness B2 of the second layer EMA2 in the second blue light-emitting layer BEML2 can be made as thick as possible (B2 > B1, B2 > B3).

[0168] In the second blue light-emitting layer BEML2, the third layer EMA3, the last layer where recombination is unlikely to occur due to the fast electron transfer rate, is thin, while the first and second layers, where the recombination region distribution is large, are relatively thick. Regarding the occurrence of a recombination region, the thickness B1 of the first layer EMA1 of the second blue light-emitting layer BEML2 must be at least at a predetermined level to ensure performance. The first layer EMA1 of the second blue light-emitting layer BEML2 exhibits greater thickness sensitivity than the first layer A1 of the first blue light-emitting layer BEML1. Therefore, the thickness B1 of the first layer EMA1 of the second blue light-emitting layer BEML2 can be greater than or equal to the first layer A1 of the first blue light-emitting layer BEML1 (B1 ≥ A1).

[0169] Meanwhile, the concentration of the first blue dopant BD1 in each layer of the first blue light emitting layer BEML1 is the same.

[0170] The concentration of the second blue dopant BD2 in each layer of the second blue light-emitting layer BEML2 is also the same.

[0171] Therefore, the recombination range of each layer of the first blue light emitting layer BEML1 and each layer of the second blue light emitting layer BEML2 can be adjusted by the thickness and material of the host.

[0172] With reference to Fig. In the first stack S1, which contacts the first electrode AND, the first common layer CML11 contains a hole transport layer that contacts the first layer EMA1 of the first blue light-emitting layer BEML1 as a common hole transport layer. The second common layer CML21 contains an electron transport layer that contacts the last layer EMA3 of the first blue light-emitting layer BEML1 as a common electron transport layer. With reference to Fig. 8 or Fig. 9 the second common layer CML21 can contact a charge generation layer of the n-type charge generation layer.

[0173] The LUMO energy level LUMO_BD1 of the first blue dopant BD1 is higher than the LUMO energy levels LUMO_BH1 and LUMO_BH2 of each of the first and second hosts (LUMO_BD1 > LUMO_BH1, LUMO_BD1 > LUMO_BH2). Electrons injected from the second common layer CML21 through the LUMO energy level LUMO_BD1 of the first blue dopant BD1 are readily injected into the LUMO energy levels LUMO_BH1 and LUMO_BH2 of the first and second hosts BH1 and BH2 in each layer of the light-emitting layer.

[0174] Either the triplet energy level T1_CML11 of the first common layer CML11 or the triplet energy level T1_CML21 of the second common layer CML21 is higher than the triplet energy level T1_BD1 of the first blue dopant BD1. The first common layer CML11 has a LUMO energy level LUMO_CML11 that is higher than the LUMO energy level LUMO_BD1 of the first blue dopant BD1 (LUMO_CML11 > LUMO_BD1), and a HOMO energy level HOMO_CML11 that is lower than the HOMO energy level HOMO_BD1 of the first blue dopant BD1 (HOMO_CML11 < HOMO_BD1). The second common layer CML21 can have a LUMO energy level LUMO_CML21 that is lower than the LUMO energy level LUMO_BD1 of the first blue dopant BD1, and a HOMO energy level HOMO_CML21 that is lower than the HOMO energy level HOMO_BD1 of the first blue dopant BD1.

[0175] The HOMO energy level HOMO_BD1 of the first blue dopant BD1 can be higher than the HOMO energy level HOMO_BH1, HOMO_BH2 of each of the first and second hosts (HOMO_BD1 > HOMO_BH1, HOMO_BD1 > HOMO_BH2).

[0176] With reference to Fig. In the second stack S2 or the Nth stack SN, which contacts the second electrode CAT, the first common layer CML12 contains a hole transport layer that contacts the first layer EMA1 of the second blue light-emitting layer BEML2 as a common hole transport layer. The second common layer CML22 contains an electron transport layer that contacts the last layer EMA3 of the second blue light-emitting layer BEML2 as a common electron transport layer. The second common layer CML22 can contact the electron injection layer or directly contact the second electrode CAT.

[0177] The LUMO energy level LUMO_BD2 of the second blue dopant BD2 is higher than the LUMO energy levels LUMO_BH3 and LUMO_BH4 of each third and fourth host (LUMO_BD2 > LUMO_BH3, LUMO_BD2 > LUMO_BH4). Electrons injected from the second common layer CML22 through the LUMO energy level LUMO_BD2 of the second blue dopant BD2 can readily be injected into the LUMO energy levels LUMO_BH3 and LUMO_BH4 of the third and fourth hosts BH3 and BH4 in each layer of the light-emitting layer.

[0178] Either the triplet energy level T1_CML12 of the first common layer CML12 or the triplet energy level T1_CML22 of the second common layer CML22 is higher than the triplet energy level T1_BD2 of the second blue dopant BD2. The first common layer CML12, which has hole transport properties, has a LUMO energy level LUMO_CML12 that is higher than the LUMO energy level LUMO_BD2 of the second blue dopant BD2 (LUMO_CML12 > LUMO_BD2), and an HOMO energy level HOMO_CML12 that is lower than the HOMO energy level HOMO_BD2 of the second blue dopant BD2 (HOMO_CML12 < HOMO_BD2). The second common layer CML22 can have a LUMO energy level LUMO_CML22 that is lower than the LUMO energy level LUMO_BD2 of the second blue dopant BD2, and a HOMO energy level HOMO_CML22 that is lower than the HOMO energy level HOMO_BD2 of the second blue dopant BD2.

[0179] The HOMO energy level HOMO_BD2 of the second blue dopant BD2 can be higher than the HOMO energy levels HOMO_BH3 and HOMO_BH4 of the third and fourth host (HOMO_BD2 > HOMO_BH3, HOMO_BD2 > HOMO_BH4).

[0180] Meanwhile, the HOMO energy level and LUMO energy level described above have negative values ​​based on the vacuum level, which means that when comparing one material with another, if the HOMO energy level or the LUMO energy level of one material is higher than that of the other material, its absolute value is smaller.

[0181] The following is based on the light-emitting device of the structure of Fig. 8. The first blue light-emitting layer BEML1 and the second blue light-emitting layer BEML2 have the same multilayer structure. The thickness of the second layer, which is the even-numbered layer, is assumed to be the greatest, and the significance of the thickness difference of the odd-numbered layers is described. The first blue light-emitting layer BEML1 and the second blue light-emitting layer BEML2 each contain three layers. In the first blue light-emitting layer BEML1, the first layer EMA1 and the third layer EMA3 contain a first blue host BH1 with high triplet energy levels and a first blue dopant BD1. The second layer EMA2 contains a second blue host BH2 with relatively low triplet energy levels and the first blue dopant BD1.The triplet energy levels of the first blue host BH1, the second blue host BH2 and the first blue dopant BD1 have the following relationship: T1_BD1 > T1_BH1 > T1_BH2.

[0182] In the second blue light-emitting layer BEML2, the first layer EMA1 and the third layer EMA3 contain a third blue host BH3 with high triplet energy levels and a second blue dopant BD2, and the second layer EMA2 contains a fourth blue host BH4 with lower triplet energy levels and a second blue dopant BD2. The triplet energy levels of the third blue host BH3, the fourth blue host BH4, and the second blue dopant BD2 exhibit the following relationship: T1_BD2 > T1_BH3 > T1_BH4.

[0183] In the following experiments, the first blue dopant BD1 is the same material as the second blue dopant BD2, the first blue host BH1 and the third blue host BH3 are the same, and the second blue host BH2 and the fourth blue host BH4 are the same.

[0184] Experimental examples 4, 5, and 6 (EX4, EX5, and EX6) exhibit differences in the thickness of the light-emitting layer. In each blue light-emitting layer, the first layer (EMA1) has a thickness of 50 Å, and the second layer (EMA2) has a thickness of 80 Å. In experimental example 4 (EX4), the thickness of the third layer (EMA3) is 30 Å; in experimental example 5 (EX5), the thickness of the third layer (EMA3) is 50 Å; and in experimental example 6 (EX6), the thickness of the third layer (EMA3) is 70 Å.

[0185] In experimental example 7 EX7, the thickness of the first layer EMA1 in each blue light emitting layer is 70 Å, the thickness of the second layer EMA2 is 80 Å, and the thickness of the third layer EMA3 is 30 Å.

[0186] In the following experiments, the LUMO energy level, HOMO energy level and triplet energy level T1 of each material are shown in Table 3. [Table 3] BD1, BD2 BH1, BH3 BH2, BH4 CML11,CML12 CML21,CML22 LUMO[eV] -2,80 -3,06 -3,11 -2,61 -3,04 HOMO[eV] -5,60 -6,11 -6,12 -5,70 -6,54 T1 [eV] 2,7 2,1 1,8 2,9 2,7

[0187] Fig. Figure 13 is a graph showing a comparison of lifetime between experimental examples 4, 5 and 6; Fig. Figure 14 is a graph showing a comparison of lifetime between experimental examples 5 and 7. [Table 4] EMA1 / EMA2 / EMA3[Å] Betriebsspannung(V) Blauindex (%) 99-Lebensdauer(%) EX4 50 / 80 / 30 V1 100 100 EX5 50 / 80 / 50 V1+0,1V 101,0 100 EX6 50 / 80 / 70 V1+0,2V 100,3 100 EX7 70 / 80 / 30 V1+0,06V 103,5 139

[0188] As shown in Table 4 and Fig. As can be seen in Figure 13, experimental examples 4, 5, and 6 (EX4, EX5, EX6) have a configuration in which the first layer (EMA1) and the second layer (EMA2) have the same thickness, while the third layer (EMA3) has a different thickness. Consequently, there is almost no difference in the blue index efficiency or lifetime. This is because the operating voltage and the thickness of the organic material in the light-emitting device have increased. These results demonstrate that increasing the thickness of the third layer, which is the last layer in the multilayer light-emitting device, is not a factor that causes changes in lifetime or efficiency.

[0189] From Table 4 and Fig. Section 14 describes experimental example 5EX5, in which the thicknesses of the first layer EMA1 and the third layer EMA3 are equal, and experimental example 7EX7, in which the thickness of the first layer EMA1 is greater than that of the third layer EMA3, resulting in a difference in thickness between the first layer EMA1 and the third layer EMA3. In experimental example 5EX5, the thicknesses of the first layer EMA1 and the third layer EMA3 are each set to 50 Å, and in experimental example 7EX7, the thickness of the first layer EMA1 is set to 70 Å and the thickness of the third layer EMA3 is set to 30 Å, so that the total thickness of the blue light-emitting layer in experimental example 5EX5 and experimental example 7EX7 is the same.

[0190] In comparison to experimental example 5 EX5, experimental example 7 EX7 exhibits a reduced operating voltage, an increased blue index efficiency and an improved lifetime.

[0191] In other words, if the thickness of the first layer contacting the common layer that serves to transport holes for the light-emitting layer is increased between odd-numbered layers, the recombination area can be expanded, and the area where the exciton generation area and the TTF mechanism occur can be secured, thus improving lifetime and increasing efficiency.

[0192] In the following experiments, the significance of the thickness difference in the multilayer structure of the second blue light emitting layer BEML2 is described by experimental example 8 EX8, in which the first blue light emitting layer BEML1 and the second blue light emitting layer BEML2 are the same, and the structure in which there is a difference in thickness between the first blue light emitting layer BEML1 and the second blue light emitting layer BEML2.

[0193] Based on the light-emitting device of the structure of Fig. In experimental example 8EX8, the first blue light-emitting layer BEML1 and the second blue light-emitting layer BEML2 have the same three-layer structure, and the thicknesses of the first, second, and third layers are 50 Å, 80 Å, and 50 Å, respectively. In experimental example 9EX9, the thicknesses of the first, second, and third layers of the first blue light-emitting layer BEML1 are 50 Å, 80 Å, and 50 Å, respectively, and the thicknesses of the first, second, and third layers of the second blue light-emitting layer BEML2 are 70 Å, 80 Å, and 30 Å, respectively.

[0194] The first blue light-emitting layer BEML1 and the second blue light-emitting layer BEML2 each contain three layers. In the first blue light-emitting layer BEML1, the first layer EMA1 and the third layer EMA3 contain a first blue host BH1 with a high triplet energy level and a first blue dopant BD1, and the second layer EMA2 contains a second blue host BH2 with a relatively low triplet energy level and a first blue dopant BD1. The triplet energy levels of the first blue host BH1, the second blue host BH2, and the first blue dopant BD1 exhibit the following relationship: T1_BD1 > T1_BH1 > T1_BH2.

[0195] The first blue dopant BD1 is formed from the same material as the second blue dopant BD2, the first blue host BH1 and the third blue host BH3 are formed from the same material, and the second blue host BH2 and the fourth blue host BH4 are formed from the same material.

[0196] Fig. Figure 15 is a graph showing a comparison of lifetime between experimental examples 8 and 9. [Table 5] Elemen t BEML1 (EMA1 / EMA2 / EMA3)[Å] BEML2 (EMA1 / EMA2 / EMA3) [Å] Betriebs Spannung (V) Blauinde x (%) 99-Lebensdaue r (%) EX8 50 / 80 / 50 50 / 80 / 50 V2 100 100 EX9 50 / 80 / 50 70 / 80 / 30 V2-0,05 103,3 110

[0197] As shown in Table 5 and Fig. As can be seen in 15, if the thickness of the first layer EMA1 of the second blue light emitting layer BEML2 is greater than that of the third layer EMA3, as in experimental example 9 EX9, the operating voltage is reduced, the blue index efficiency is increased and the lifetime is also improved.

[0198] This means that if the thickness of the first layer EMA1 is greater than that of the third layer EMA3, so that the recombination area is closer to the center, taking into account the fast electron transfer rate in the second blue light emitting layer BEML2, the degree of exciton annihilation can be reduced by adjusting the recombination area, the operating voltage can be reduced while maintaining the same thickness of the blue light emitting layer, and the efficiency and lifetime can be improved.

[0199] An example of a light-emitting display device using the light-emitting device according to an embodiment of the present invention is described below.

[0200] Fig. Figure 16 is a cross-sectional view illustrating light-emitting devices of a red subpixel, a green subpixel and a blue subpixel in the light-emitting display device according to an embodiment of the present invention.

[0201] As in Fig. As shown in Figure 16, the light-emitting display device according to an embodiment of the present invention can include a first electrode AND and a second electrode CAT, each facing a red subpixel R_SP, a green subpixel G_SP and a blue subpixel B_SP, a plurality of stacks between the first electrode AND and the second electrode CAT and light-emitting layers that emit light of the same color, overlapping each other in the plurality of stacks.For example, the red subpixel R_SP can have red light emitting layers REML1 and REML2 in separate stacks with a charge generation layer CGL in between, the green subpixel G_SP can have green light emitting layers GEML1 and GEML2 in separate stacks with a charge generation layer CGL in between, and the blue subpixel B_SP can have blue light emitting layers BEML1 and BEML2 in separate stacks with a charge generation layer CGL in between.

[0202] Here, a first common layer CML11, relating to hole injection and hole transport, is provided between the first electrode AND and the first red light emitting layer REML1, the first green light emitting layer GEML1 and the first blue light emitting layer BEML1, and a second common layer CML21, relating to electron transport, is provided between the first red light emitting layer REML1, the first green light emitting layer GEML1 and the first blue light emitting layer BEML1 and the charge generation layer CGL.

[0203] The charge generation layer CGL can be provided by laminating an n-type charge generation layer NCGL and a p-type charge generation layer PCGL.

[0204] Additionally, a third common layer CML12, relating to hole injection and hole transport, can be provided between the charge generation layer CGL and the second red light emitting layer REML2, the second green light emitting layer GEML2 and the second blue light emitting layer BEML2, and a fourth common layer CML22, which includes an electron transport layer and an electron injection layer, can be provided between the second red light emitting layer REML2, the second green light emitting layer GEML2 and the second blue light emitting layer BEML2 and the second electrode CAT.

[0205] The first common layer CML11 and the third common layer CML12, relating to hole injection and transport, may include at least one hole injection layer, one hole transport layer and one electron blocking layer, and the second common layer CML21 and the fourth common layer CML22, relating to electron transport and injection, may include at least one hole blocking layer, one electron transport layer and one electron injection layer.

[0206] Here, at least the first and second blue light emitting layers BEML1 and BEML2, which are provided at the blue subpixel B_SP, are divided into an odd number of layers, as described above, and each layer is provided with the same dopant, but the odd-numbered layer contacting the common layer can contain the first host BH1 or the third host BH3 with a high triplet energy level, and the even-numbered layer can contain the second host BH2 or the fourth host BH4 with a lower triplet energy level.

[0207] As a result, the light-emitting display device according to an embodiment of the present invention can exhibit the effects of improved lifetime and efficiency and reduced operating voltage.

[0208] In addition, the light-emitting device and the light-emitting display device containing it, according to one embodiment of the present invention, include odd-numbered and even-numbered layers containing hosts with different properties. Delayed fluorescence is induced in the even-numbered layers by the TTF mechanism, and the layer in which the TTF mechanism is caused by energy transfer is located within the light-emitting layer and is separated from both interfaces of the light-emitting layer, thus solving the problem of lifetime reduction caused by exciton accumulation at the interface between the light-emitting layer and the common layer.

[0209] In addition, the light-emitting device and the light-emitting display device containing the same, according to one embodiment of the present invention, include the light-emitting layer such that layers having different hosts are arranged alternately, and the number of light-emitting layers is odd, so that the hosts of the first layer and the last layer of the light-emitting layer are the same. Furthermore, the odd-numbered layers of the light-emitting layer contain a host with a high triplet energy level, and the even-numbered layers of the light-emitting layer contain a host with a low triplet energy level.As a result, the efficiency of delayed fluorescence through the TTF mechanism is increased in the inner even-numbered layer of the light-emitting layer, which is located within the first and last layers that are at both interfaces of the light-emitting layer and does not come into contact with both interfaces of the light-emitting layer, thereby increasing the light emission efficiency and improving the efficiency of the light-emitting device and the efficiency of the light-emitting display device.

[0210] In addition, according to one embodiment of the present invention, the light-emitting device and the light-emitting display device containing it can effectively improve the lifetime by reducing the extinction ratio of excitons generated in the light-emitting layer and increasing the ratio used for direct light emission or delayed light emission.

[0211] In addition, according to one embodiment of the present invention, the light-emitting device and the light-emitting display device containing it can prevent an increase in the operating voltage and improve the service life by adjusting the thickness of the first and last layers, particularly when the blue light-emitting layer of the blue light-emitting device is formed in several layers with relatively low efficiency.

[0212] The light-emitting device and the light-emitting display device containing it, according to one embodiment of the present invention, can improve the efficiency of the light-emitting layer, reduce the operating voltage, and extend its service life. Therefore, the light-emitting device and the light-emitting display device containing it are continuously applicable, thereby achieving ESG (environmental, social, and governance) objectives.

[0213] Fig. Figure 17 is a cross-sectional view illustrating a light-emitting display device according to an embodiment of the present invention.

[0214] As in Fig. As shown in Figure 17, the light-emitting display device according to an embodiment of the present invention can emit light through a first electrode AND on an emission side by applying the light-emitting device described above to at least one of a plurality of subpixels R_SP, G_SP, B_SP and W_SP.

[0215] The light-emitting device (ED) of each subpixel can include a first electrode (AND), a second electrode (CAT), and an intermediate layer (OS). The intermediate layer (OS) can contain multiple stacks and have the same configuration in the multiple subpixels (R_SP, G_SP, B_SP, W_SP). Additionally, the intermediate layer (OS) can include the electron transport stack between the multiple stacks and the charge generation layer.

[0216] The light-emitting display device according to an embodiment of the present invention can include a substrate 100 with a plurality of subpixels R_SP, G_SP, B_SP, W_SP, a light-emitting device ED provided jointly on the substrate 100, a thin-film transistor TFT provided on each of the subpixels R_SP, G_SP, B_SP, W_SP and connected to the first electrode AND of the light-emitting device ED, and a color filter 109R, 109G, 109B provided under the first electrode AND of at least one of the subpixels.

[0217] The example in Fig. Figure 17 shows a case in which a white subpixel W_SP is included in the light-emitting display device, but the present invention is not limited to this, and a structure in which the white subpixel W_SP is omitted and only red, green, and blue subpixels R_SP, G_SP, and B_SP are provided is also possible. In some cases, a combination of cyan, magenta, and yellow subpixels, which can represent white by replacing the red, green, and blue subpixels, is also possible.

[0218] The thin-film transistor (TFT) includes, for example, a gate electrode 102, a semiconductor layer 104, and a source electrode 106a and a drain electrode 106b, which are connected to both sides of the semiconductor layer 104. Additionally, a channel protection layer can be provided on the upper part of a section containing a channel of the semiconductor layer 104 to prevent direct contact between the source / drain electrodes 106a, 106b, and the semiconductor layer 104. A buffer layer 101 can be included on a substrate 100, and the thin-film transistor (TFT) can be located on the buffer layer 101.

[0219] A gate insulating film 103 is provided between the gate electrode 102 and the semiconductor layer 104.

[0220] The semiconductor layer 104 can be formed, for example, from an oxide semiconductor, amorphous silicon, polycrystalline silicon, or a combination of two or more of these. If, for example, the semiconductor layer 104 is an oxide semiconductor, the heating temperature required to form a thin-film transistor can be reduced, allowing the substrate 100 to be used with a high degree of freedom, which makes it advantageous for application to a flexible display device.

[0221] A gate electrode 102 can be provided on the gate insulating film 103 and an intermediate layer insulating film 105 can further be provided between the gate electrode 102 and the source electrode 106a / drain electrode 106b.

[0222] Additionally, the drain electrode 106b of the thin-film transistor TFT can be connected to the first electrode AND and the contact hole CT provided in the first and second protective films 107 and 108.

[0223] The first protective film 107 is primarily provided to protect the thin-film transistor TFT, and a color filter 109R, 109G, 109B may be provided on the first protective film 107.

[0224] A second protective film 108 is provided on top of the first protective film 107, which includes the color filter 109R, 109G, 109B.

[0225] If a multitude of subpixels includes a red subpixel R_SP, a green subpixel G_SP, a blue subpixel B_SP, and a white subpixel W_SP, as in Fig. As shown in Figure 17, the color filters are provided as first to third color filters 109R, 109G, 109B for the remaining subpixels R_SP, G_SP, B_SP, with the exception of the white subpixel W_SP, to allow white light emitted by the first electrode AND to pass through at each wavelength. Additionally, a second protective film 108 is formed under the first electrode AND to cover the first to third color filters 109R, 109G, 109B. The first electrode AND is formed on the surface of the second protective film 108, except for the contact hole CT, and is connected to one of the drain electrodes 106b and the source electrode 106a of the thin-film transistor TFT to receive an electrical signal from the thin-film transistor TFT.

[0226] Here, the thin-film transistor array substrate 1000 can include the substrate 100, the thin-film transistor TFT, the color filters 109R, 109G, 109B, and the first and second protective films 107 and 108. A light-emitting device ED can be arranged on the thin-film transistor array substrate 1000.

[0227] The light-emitting device ED is formed on a thin-film transistor array substrate 1000, which includes a ridge or bank 119 defining a light-emitting section BH. The light-emitting device ED can include a transparent first electrode AND, a second electrode CAT of the type of a reflective electrode facing the first electrode AND, a first common layer CML1 serving for hole transport, a blue light-emitting layer BEML, and a second common layer CML2 serving for electron transport in at least one of the first and second blue stacks between the first electrode AND and the second electrode CAT, wherein the blue light-emitting layer BEML can be formed as a multiple layer, as described with reference to Fig. 1, Fig. 2, Fig. 3 to Fig. 4 described. For example, the blue light-emitting layer BEML can be divided into an odd number of layers containing the same dopant and different hosts, with the odd-numbered layers containing a first host with a relatively high triplet energy level, and the even-numbered layers containing a second host with a relatively low triplet energy level.As a result, the TTF efficiency is increased in the even-numbered layers spaced from the two interfaces of the blue light-emitting layer BEML, and the recombination area is separated by a predetermined distance from the interface of the blue light-emitting layer BEML and the common layer, thus preventing the reduction in lifetime caused by the accumulation of excitons at the interface of the light-emitting layer and the common layer, thereby enabling the recycling of excitons by the TTF mechanism to be used for light emission, and providing increased efficiency and reduced operating voltage.

[0228] The first electrode AND is subdivided into each subpixel, and the remaining layers, with the exception of the first electrode AND of the light-emitting device ED, can be provided as an integral part in the entire display area without differentiation by subpixels.

[0229] Either the first electrode AND or the second electrode CAT can be connected to a thin-film transistor TFT.

[0230] Meanwhile, the light-emitting display device described above is of Fig. Figure 17 illustrates a structure in which light is emitted downwards, but the present invention is not limited to this. For example, if the first electrode AND comprises a reflective electrode, the second electrode CAT is a transparent electrode or a reflective-transparent electrode, and the color filter is arranged above the second electrode CAT, the light-emitting display device can implement top-down emission.

[0231] In the structure described above, the intermediate layer OS of the light-emitting device ED is common to each subpixel, but the light-emitting display device of the embodiment of the present invention is not limited to this. For example, as in the light-emitting display device of Fig. 16 described that the light-emitting layers are formed separately from each other in the red, green and blue subpixels.

Claims

[1] Light-emitting device comprising: a first electrode and a second electrode facing each other; and a first common layer, a light-emitting layer and a second common layer arranged between the first electrode and the second electrode, where the light-emitting layer is divided into an odd number of layers, odd-numbered layers of the light-emitting layer contain a first host and a dopant, even-numbered layers of the light-emitting layer contain a second host and the dopant, the first host has a triplet energy level that is higher than a triplet energy level of the second host, and the first common layer and the second common layer contact a first layer and a last layer, each containing the first host and the dopant. [2] Light-emitting device according to claim 1, wherein a triplet energy level of the dopant is greater than the triplet energy level of the first host, wherein preferably the absolute value of a difference between the triplet energy level of the dopant and the triplet energy level of the first host is 0.4 to 1.2 eV. [3] Light-emitting device according to one of claims 1 or 2, wherein the dopant contained in the light-emitting layer comprises or consists of a fluorescent dopant, preferably a fluorescent dopant with an emission peak at a wavelength of 430 nm to 495 nm, more preferably a thermally activated, delayed fluorescent dopant with an emission peak at a wavelength of 450 nm to 480 nm. [4] Light-emitting device according to any of the preceding claims, wherein the first common layer comprises a hole transport layer contacting the first layer of the light-emitting layer, and the second common layer comprises an electron transport layer contacting the last layer of the light-emitting layer, wherein preferably at least one of the following conditions is met: The hole transport layer has a lowest unoccupied molecular orbital (LUMO) energy level that is higher than the LUMO energy level of the dopant, and a highest occupied molecular orbital (HOMO) energy level that is lower than the HOMO energy level of the dopant. The electron transport layer has a LUMO energy level that is lower than the LUMO energy level of the dopant. The thickness of each of the odd-numbered and each of the even-numbered layers of the light-emitting layer is from 2 to 15 nm, preferably from 2 to 10 nm, and The thickness of the last layer of the light-emitting layer that contacts the second common layer is less than the thickness of the first layer of the light-emitting layer that contacts the first common layer. [5] Light-emitting device according to one of the preceding claims, wherein the content of the dopant in the odd-numbered layers is the same as the content of the dopant in the even-numbered layers in the light-emitting layer. [6] Light-emitting device according to any of the preceding claims, wherein a LUMO energy level of the dopant is higher than a LUMO energy level of each of the first and second host, and / or a HOMO energy level of the dopant is higher than a HOMO energy level of each of the first and second host. [7] Light-emitting device according to any of the preceding claims, wherein the light-emitting layer is a first light-emitting layer and the dopant is a first dopant and wherein the light-emitting device further comprises a charge-generating layer, a third common layer, a second light-emitting layer and a fourth common layer, which are arranged successively between the second common layer and the second electrode, wherein preferably the second light-emitting layer is configured to emit light of the same color as the first light-emitting layer, or wherein preferably the second light-emitting layer is a light-emitting layer configured to emit light of a different color than light emitted by the first light-emitting layer. [8] Light-emitting device according to claim 7, wherein the second light-emitting layer is divided into an odd number of layers, odd-numbered layers of the second light-emitting layer contain a third host and a second dopant, and even-numbered layers of the second light-emitting layer contain a fourth host and the second dopant, the third host has a triplet energy level that is higher than a triplet energy level of the fourth host, and the third common layer and the fourth common layer contact the first layer and the last layer, each of which contains the third host and the second dopant, wherein preferably the second light-emitting layer is configured to emit light of the same color as the first light-emitting layer, and the first dopant and the second dopant are the same. [9] Light-emitting device according to claim 8, wherein the thickness of the last layer of the second light-emitting layer contacting the fourth common layer is less than the thickness of the last layer of the first light-emitting layer contacting the second common layer, and / or wherein the thickness of the last layer of the second light-emitting layer contacting the fourth common layer is less than the thickness of the even-numbered layer contacting the last layer of the second light-emitting layer, and / or wherein the thickness of the last layer of the second light-emitting layer contacting the fourth common layer is less than the thickness of the first layer of the second light-emitting layer contacting the third common layer. [10] Light-emitting device according to any one of claims 7 to 9, wherein the total thickness of the first light-emitting layer is the same as the total thickness of the second light-emitting layer. [11] Light-emitting device according to any one of claims 7 to 10, wherein the content of the second dopant in the odd-numbered layer is the same as the content of the second dopant in the even-numbered layer in the second light-emitting layer. [12] Light-emitting device according to any one of claims 7 to 11, wherein in the second light-emitting layer the thickness of the even-numbered layer is greater than the thickness of the odd-numbered layer that contacts the even-numbered layer. [13] Light-emitting display device comprising: a substrate containing a blue subpixel, a green subpixel, and a red subpixel; a pixel circuit provided at each of the blue subpixel, the green subpixel and the red subpixel; a first electrode connected to a thin-film transistor of the pixel circuit at each of the blue subpixel, the green subpixel and the red subpixel; a second electrode facing the first electrode; and a first common layer and a second common layer between the first electrode and the second electrode, wherein the blue subpixel comprises a blue light-emitting layer containing a blue dopant between the first common layer and the second common layer, The green subpixel comprises a green light-emitting layer containing a green dopant between the first common layer and the second common layer. The red subpixel comprises a red light-emitting layer containing a red dopant between the first common layer and the second common layer. the blue light-emitting layer is divided into an odd number of layers, Odd-numbered layers of the blue light-emitting layer contain a first blue host and a blue dopant, even-numbered layers of the blue light-emitting layer contain a second blue host and the blue dopant, the first blue host has a triplet energy level that is higher than a triplet energy level of the second blue host, and The first common layer and the second common layer at the blue subpixel contact a first layer and a last layer, each containing the first blue host and the blue dopant. [14] Light-emitting display device according to claim 13, wherein the light-emitting layer is a first light-emitting layer, the blue light-emitting layer is a first blue light-emitting layer, the green light-emitting layer is a first green light-emitting layer, the red light-emitting layer is a first red light-emitting layer, and the blue dopant is a first blue dopant, and wherein the light-emitting device further comprises a charge-generating layer, a third common layer, a second light-emitting layer, and a fourth common layer, which are arranged successively between the second common layer and the second electrode, wherein: the second light-emitting layer comprises a second blue light-emitting layer at the blue subpixel, a second green light-emitting layer at the green subpixel, and a second red light-emitting layer at the red subpixel. the second blue light-emitting layer is divided into an odd number of layers, odd-numbered layers of the second blue light-emitting layer contain a third blue host and a second blue dopant, and even-numbered layers of the second blue light-emitting layer contain a fourth blue host and the second blue dopant. the third blue host has a triplet energy level that is higher than a triplet energy level of the fourth blue host, and The third common layer and the fourth common layer at the blue subpixel contact the first layer and the last layer, each containing the third blue host and the second blue dopant. [15] Light-emitting display device according to claim 14, wherein the thickness of the last layer of the second blue light-emitting layer contacting the fourth common layer is less than the thickness of the last layer of the first blue light-emitting layer contacting the second common layer, and / or wherein the thickness of the last layer of the second blue light-emitting layer contacting the fourth common layer is less than the thickness of an even-numbered layer contacting the second blue light-emitting layer, and / or where the thickness of the last layer contacting the fourth common layer in the second light-emitting layer is less than the thickness of the first layer contacting the third common layer.

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