Organic light emitting device and display device using the same

Abstract

Disclosed are an organic light emitting device and a display device using the same, wherein a light emitting layer includes a host and a plurality of dopants. In the light-emitting layer, energy is transferred from a host and other dopants other than one dopant to the one dopant through an energy transfer system, so that the light-emitting efficiency of a monochrome can be increased and the emission lifetime can be prolonged.

Description

[0001] This application is a divisional application of the invention patent application with application number 202011275292.1, application date November 13, 2020, and invention name “Organic light-emitting device and display device using the organic light-emitting device”.

[0002] This application claims the benefit of Korean Patent Application No. 10-2019-0147065, filed on November 15, 2019, which is hereby incorporated by reference as if fully set forth herein. Technical Field

[0003] The present invention relates to a light-emitting device, and more particularly, to an organic light-emitting device and a display device using the same, wherein the organic light-emitting device includes different kinds of dopants in at least one light-emitting layer and ensures light-emitting characteristics of one color and achieves improved lifespan by transferring energy to one of the different kinds of dopants. Background Art

[0004] As society has recently entered the information age, the field of displays for visually displaying electrical information signals has developed rapidly, and in order to meet this development, various flat panel display devices with excellent performance (e.g., slimness, light weight, and low power consumption) have been developed and have rapidly replaced conventional cathode ray tubes (CRTs).

[0005] Examples of such flat panel display devices include a liquid crystal display (LCD) device, a plasma display panel (PDP) device, a field emission display (FED) device, an organic light emitting diode (OLED) display device, a quantum dot display device, and the like.

[0006] Among them, an organic light emitting diode (OLED) display device, which does not require a separate light source and achieves compactness and clear color display, is considered as a competitive application.

[0007] In an organic light emitting diode (OLED) display device, a plurality of sub-pixels are provided, and an organic light emitting diode including a light emitting layer between electrodes facing each other is arranged in each sub-pixel. In addition, the organic light emitting diode in the sub-pixel emits light due to the formation of an electric field between the electrodes, thereby exhibiting a display function.

[0008] Such a light-emitting layer includes a host as a main component and also includes a dopant that can determine the color of the emitted light. In addition, the dopant is divided into a fluorescent dopant and a phosphorescent dopant according to the light emission method. The characteristics of the fluorescent dopant and the characteristics of the phosphorescent dopant are different according to the color of the emitted light, and in particular, in the case of a blue light-emitting layer, both the known fluorescent dopant and the phosphorescent dopant cannot show excellent performance in terms of life span and efficiency. Summary of the invention

[0009] The inventors of the present disclosure have recognized that there are difficulties in constructing materials for a blue light-emitting layer while satisfying improved lifespan and color efficiency compared to light-emitting layers of other colors. Therefore, since the blue light-emitting layer has relatively lower efficiency and reduced lifespan among light-emitting layers of different colors, and these changes become apparent over time, the inventors have developed materials for a blue light-emitting layer that can satisfy both efficiency and lifespan. One or more embodiments of the present disclosure provide an organic light-emitting display device that can achieve full-color display in the entire visible range and can also satisfy both efficiency and lifespan in all colors.

[0010] Additionally, the present invention is directed to an organic light emitting device and a display device using the same that substantially obviate one or more problems due to limitations and disadvantages of the related art.

[0011] One or more embodiments of the present invention provide an organic light-emitting device and a display device using the same, which includes different kinds of dopants in one light-emitting layer and ensures light-emitting characteristics of a single color and achieves improved lifespan by transferring energy to one of the different kinds of dopants.

[0012] Another embodiment of the present invention provides an organic light-emitting device and a display device using the same, the organic light-emitting device including different kinds of dopants in one light-emitting layer, and ensuring light-emitting characteristics of a single color and achieving life improvement by transferring energy to one of the different kinds of dopants. Here, the dopant to which the energy is transferred is a dopant capable of achieving thermally activated delayed fluorescence.

[0013] Other advantages, purposes and features of the present invention will be described in part in the following description, and in part will be apparent to those skilled in the art after reviewing the following, or may be understood from the practice of the present invention. The purposes and other advantages of the present invention may be realized and achieved by the structures specifically provided in the written description and claims and the accompanying drawings.

[0014] To achieve these objects and other advantages and in accordance with the purposes of the present invention, an organic light-emitting device according to one embodiment of the present invention, as embodied and broadly described herein, may include a light-emitting layer disposed between a first electrode and a second electrode arranged relative to each other. The light-emitting layer may include at least one host, a first dopant to which energy is transferred from the host, and a second dopant to which energy is transferred from the host and the first dopant. Thermally activated delayed fluorescence (TADF) may be generated by reverse intersystem crossing transfer from a triplet excited state to a singlet excited state in the second dopant.

[0015] In addition, in order to achieve similar technical benefits, a display device according to the present invention may include: a substrate including a plurality of sub-pixels; a thin film transistor in each sub-pixel; and an organic light-emitting device connected to the thin film transistor in each sub-pixel. The organic light-emitting device may include a first electrode and a second electrode arranged opposite to each other, and at least one light-emitting layer located between the first electrode and the second electrode. The at least one light-emitting layer may include at least one host, a first dopant to which energy is transferred from the host, and a second dopant to which energy is transferred from the host and the first dopant, wherein thermally activated delayed fluorescence is generated by anti-intersystem crossing transfer from a triplet excited state to a singlet excited state in the second dopant.

[0016] The organic light emitting device may include a plurality of stacks separated by charge generation layers therebetween, and each stack includes at least one common layer. The at least one light emitting layer may be in at least one stack of the plurality of stacks. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this application, illustrate embodiments of the present invention and together with the description serve to explain the principle of the present invention. In the drawings:

[0018] Figure 1 is a cross-sectional view showing an organic light emitting device according to the present invention.

[0019] Figure 2 It is shown Figure 1 View of the energy transfer relationship in the light-emitting layer.

[0020] Figure 3 It is shown Figure 1 Graphs showing a PL (photoluminescence) spectrum of a first dopant in a light-emitting layer and a PL spectrum and an absorption spectrum of a second dopant.

[0021] Figure 4A is a diagram showing an energy transfer relationship in the light emitting layer according to the first experimental example.

[0022] Figure 4B is a graph showing PL spectra of different dopants according to the first experimental example.

[0023] Figure 5 is a cross-sectional view showing an organic light emitting device according to a first embodiment of the present invention.

[0024] Figure 6 is a cross-sectional view showing an organic light emitting device according to a second embodiment of the present invention.

[0025] Figure 7 is a cross-sectional view showing an organic light emitting device according to a third embodiment of the present invention.

[0026] Figure 8 is a cross-sectional view showing an organic light emitting device according to a fourth embodiment of the present invention.

[0027] Fig. 9A is a cross-sectional view showing an organic light emitting device according to a fifth embodiment of the present invention.

[0028] Fig. 9B is a cross-sectional view showing an organic light emitting device according to a sixth embodiment of the present invention.

[0029] Fig.10 is a graph showing PL spectra in modified embodiments of the present invention, wherein the modified embodiments have different Stokes shift characteristics of the second dopant.

[0030] Fig.11A and 11B It is shown in Fig.10 0047] Figure 2 is a diagram of the energy transfer relationship in a modified embodiment of FIG.

[0031] Fig. 12A and Fig. 12B : are a view showing an energy transfer relationship in a light emitting layer according to a seventh embodiment of the present invention and a graph showing a PL spectrum therein.

[0032] Fig.13A and Fig. 13B 2 is a view showing an energy transfer relationship in a light emitting layer according to an eighth embodiment of the present invention and a graph showing a PL spectrum therein.

[0033] Fig.14A and Fig. 14B : are a view showing an energy transfer relationship in a light emitting layer according to a ninth embodiment of the present invention and a graph showing a PL spectrum therein.

[0034] Fig.15A and Fig. 15B2 is a view showing an energy transfer relationship in a light emitting layer according to a tenth embodiment of the present invention and a graph showing a PL spectrum therein.

[0035] Fig.16A and Fig. 16B 2 is a view showing an energy transfer relationship in a light emitting layer according to an eleventh embodiment of the present invention and a graph showing a PL spectrum therein.

[0036] Fig.17A and Fig. 17B 2 is a view showing an energy transfer relationship in a light emitting layer according to a twelfth embodiment of the present invention and a graph showing a PL spectrum therein.

[0037] Fig.18 is a cross-sectional view showing a display device according to the present invention.

[0038] FIG. 19A to FIG. 19D are cross-sectional views according to the fourth to seventh experimental examples.

[0039] Fig. 20 is a graph showing external quantum efficiencies according to fourth to sixth experimental examples.

[0040] Fig.21 : is a graph showing EL (electroluminescence) characteristics of the fourth to sixth experimental examples. DETAILED DESCRIPTION

[0041] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are shown in the accompanying drawings. In the following description of the embodiments and drawings, identical or similar elements are represented by the same reference numerals throughout the specification. In the following description of the embodiments of the present invention, when the detailed description of the known functions and configurations incorporated herein may make the subject matter of the present invention unclear, the detailed description will be omitted. In addition, the names of the elements used in the following description of the embodiments of the present invention are selected with consideration of the ease of preparation of the specification and may therefore differ from the names of the components of the actual product.

[0042] The shapes, sizes, ratios, angles and quantities of the elements used to describe the embodiments of the present invention given in the drawings are exemplary only, and therefore, the present invention is not limited to the details shown. In the following description of the embodiments, the terms "including", "comprising" and "having" will be interpreted as indicating the presence of one or more other features, quantities, steps, operations, elements or parts or combinations thereof stated in the specification, and do not exclude the presence of other features, quantities, steps, operations, elements, parts or combinations thereof, or the possibility of adding the above items, unless the term "only" is used. It should be understood that, unless the context clearly indicates otherwise, the singular expression of an element covers the plural expression.

[0043] When explaining elements included in various embodiments of the present invention, unless otherwise specified, the elements should be interpreted as including a range of errors.

[0044] In the following description of embodiments of the present invention, it should be understood that when expressing a positional relationship, for example, when an element is referred to as being "on another element," "above another element," "below another element," or "beside another element," the two elements may be in direct contact with each other, or one or more other elements may be inserted between the two elements, unless the terms "only" or "directly" are used.

[0045] In the following description of embodiments of the present invention, it should be understood that when expressing a temporal relationship, for example, when using terms that express the order of events, such as "after," "following," "after," and "before," unless the term "just" or "directly" is used, the term includes both continuous and discontinuous relationships between events.

[0046] In the following description of the embodiments of the present invention, it should be understood that when the terms "first", "second", etc. are used to describe various elements, these terms are only used to distinguish the same or similar elements. Therefore, without departing from the technical scope of the present invention, the first element described below can be referred to as the second element.

[0047] The various features of the various embodiments of the present invention may be partially or entirely coupled or combined with each other and may be interlocked or driven in various technical ways, and the various embodiments may be implemented independently of each other or together through the connection therebetween.

[0048] In the following description of the embodiments, the terms “lowest unoccupied molecular orbital (LUMO) energy level” and “highest occupied molecular orbital (HOMO) energy level” of a layer refer to the LUMO energy level and HOMO energy level of the material occupying most of the weight of the corresponding layer, for example, the host material, unless they refer to the LUMO energy level and HOMO energy level of the dopant material doped with the corresponding layer.

[0049] In the following description of the embodiments, it should be understood that the term "HOMO energy level" refers to an energy level measured by cyclic voltammetry (CV), wherein the energy level is determined from a potential value relative to a reference electrode having a known electrode potential value. For example, the HOMO energy level of any material can be measured using ferrocene having known oxidation potential values ​​and reduction potential values ​​as a reference electrode.

[0050] In the following description of the embodiment, the term "doped" refers to a material having a different characteristic from the material occupying most of the weight of the corresponding layer, and the content of the material (the material having different characteristics is, for example, N-type and P-type materials, or organic materials and inorganic materials) is added to the material occupying most of the weight of the corresponding layer. In other words, a "doped" layer refers to a layer in which the host material and the dopant material can be distinguished from each other based on the ratio of their weight percentages. In addition, the term "undoped" refers to all cases except the case corresponding to the term "doped". For example, if a layer is formed by a single material or a mixture of materials having the same or similar characteristics, the layer can be an "undoped" layer. For example, if some of the materials forming a layer are P-type (or N-type), and none of the other materials forming the layer are P-type (or N-type), the layer can be regarded as a layer "doped with" a P-type material. For example, if some of the materials forming a layer are a small amount of inorganic materials, and the remaining materials (i.e., the main materials) forming the layer are organic materials, the layer can be regarded as a layer "doped with" an inorganic material.

[0051] In the following description of the embodiments, an electroluminescence (EL) spectrum is calculated by multiplying (1) a photoluminescence (PL) spectrum, wherein the intrinsic characteristics of a light-emitting material (e.g., a dopant material or a host material included in an organic light-emitting layer) are reflected by (2) an out-coupled emission spectrum curve, which is determined by the structure and optical characteristics of the organic light-emitting element (including the thickness of the organic layer, such as the thickness of the hole transport layer and the electron transport layer).

[0052] Hereinafter, an organic light emitting device according to the present invention and a display device using the same will be described with reference to the accompanying drawings.

[0053] Figure 1 is a cross-sectional view showing an organic light emitting device according to the present invention. Figure 2 It is shown Figure 1 A view of the energy transfer relationship in the light-emitting layer, Figure 3 It is shown Figure 1 PL spectrum of the first dopant in the light-emitting layer and a graph of the PL spectrum and absorption spectrum of the second dopant.

[0054] like Figure 1 As shown, the organic light emitting device according to the present invention includes a light emitting layer 130 disposed between a first electrode 110 and a second electrode 120 arranged opposite to each other.

[0055] At least one first common layer CML1 associated with hole transport may be disposed between the first electrode 110 and the light emitting layer 130 , and / or at least one second common layer CML2 associated with electron transport may be disposed between the light emitting layer 130 and the second electrode 120 .

[0056] Here, the first common layer CML1 and the second common layer CML2 are respectively in contact with the light emitting layer 130. The main material constituting the first common layer CML1 or the second common layer CML2 has a triplet excited state whose energy level is higher than or equal to the triplet excited state of the host in the light emitting layer 130. Therefore, the excitons (singlet or triplet) entering the light emitting layer 130 through the first common layer CML1 or the second common layer CML2 from the electrode 110 or 120 can be confined in the light emitting layer 130 and can be used to emit light.

[0057] like Figure 1 and Figure 2 As shown, the light emitting layer 130 includes a host Host, a first dopant D1 to which energy is transferred from the host, and a second dopant D2 to which energy is transferred from the host and the first dopant. Here, thermally activated delayed fluorescence (TADF) is generated by reverse intersystem crossing (RISC) transfer from a triplet excited state to a singlet excited state in the second dopant D2.

[0058] In the light emitting layer 130 of the organic light emitting device, the formation of excitons by charge recombination may occur in the host Host, the first dopant D1, and the second dopant D2, respectively. Energy transfer ( Energy transfer) FET1 and FET3 transfer the singlet excitons generated at the host Host into the singlet excited states of the first dopant D1 and the second dopant D2. Dexter energy transfer (Dexter energy transfer) DET1 and DET3 transfer the triplet excitons generated at the host Host into the triplet excited states of the first dopant D1 and the second dopant D2. The triplet excitons generated at the first dopant D1 are transferred to the triplet excited states of the first dopant D1 and the second dopant D2. The energy transfer FET4 is transferred to the singlet excited state of the second dopant D2 as a fluorescent dopant, thereby emitting fluorescence from the second dopant D2. Moreover, the triplet exciton generated at the second dopant D2 is transferred to the singlet excited state of the second dopant D2 by reverse intersystem crossing (RISC) transfer, thereby generating thermally activated delayed fluorescence (TADF) at the second dopant D2. Therefore, the second dopant D2 theoretically has an internal quantum efficiency of 100%.

[0059] The light emitting layer 130 includes a host Host as a main material in an amount of 50 wt % or more. The host Host controls carriers such as holes and electrons injected from the adjacent first and second electrodes 110 and 120, and transfers energy from singlet excited states and triplet excited states of excitons (which are generated by recombination of holes and electrons) into the first and second dopants D1 and D2.

[0060] In the host Host, the excitons generated within itself are not directly used for emission. Instead, the photoluminescence (PL) spectrum of the host Host overlaps with the absorption spectra of the first dopant D1 and the second dopant D2, so that the energy from the host Host is transferred to the first dopant D1 and the second dopant D2. The energy transfer of the first dopant D1 and the second dopant D2 to the triplet excited state T1 is called "Dexter energy transfer (DET)", and the energy transfer of the first dopant D1 and the second dopant D2 to the singlet excited state S1 is called " Energy transfer (FET). The first dopant D1 is generated from the singlet excited state of the host Host to the singlet excited state of the first dopant D1. Energy transfer FET1 generates a first Dexter energy transfer DET1 from the triplet excited state of the host Host to the triplet excited state of the first dopant D1. To facilitate these energy transfers, the singlet excited state S1 of the host Host is higher than or equal to the singlet excited state S1 of the first dopant D1, and the triplet excited state T1 of the host Host is higher than or equal to the triplet excited state T1 of the first dopant D1.

[0061] Here, the energy levels of the singlet excited state S1 and the triplet excited state T1 are compared with the ground state S0. Therefore, a high energy level means that the excited state is far from the ground state S0. On the contrary, a low energy level means that the excited state is close to the ground state S0.

[0062] like Figure 2 As shown, each of the singlet excited states S1 of the host Host and the first and second dopants D1 and D2 is higher than each of the triplet excited states T1 of the host Host and the first and second dopants D1 and D2.

[0063] and, Figure 2 The singlet excited state S1 and triplet excited state T1 of the first dopant D1 are shown. The second dopant D2 is generated from the singlet excited state of the first dopant D1 to the singlet excited state of the second dopant D2. The energy transfer FET2 generates a second Dexter energy transfer DET2 from the triplet excited state of the first dopant D1 to the triplet excited state of the second dopant D2.

[0064] Energy transfer FET1 and DET1 from the host Host to the first dopant D1 and direct energy transfer from the host Host to the second dopant D2 are generated. That is, a third energy transfer is generated from the singlet excited state of the host Host to the singlet excited state of the second dopant D2. Energy transfer FET3, and a third Dexter energy transfer DET3 is generated from the triplet excited state of the host Host to the triplet excited state of the second dopant D2. That is, the second dopant D2 receives energy from the host Host and the first dopant D1.

[0065] Moreover, since the giving side is in a higher energy level state than the receiving side, it is beneficial for the first to third Energy transfer FET1 to FET3 and first to third Dexter energy transfer DET1 to DET3.

[0066] In the light-emitting layer 130 of the organic light-emitting device, as Figure 3 As shown, the first dopant D1 is a phosphorescent dopant and the second dopant D2 is a fluorescent dopant. At the spectral overlap between the PL spectrum 221 of the first dopant D1 and the absorption spectrum 212 of the second dopant D2, energy transfer from the first dopant D1 to the second dopant D2 occurs. When the spectral overlap between the PL spectrum 221 of the first dopant D1 and the absorption spectrum 212 of the second dopant D2 is large, energy transfer is effectively performed. During the energy transfer process, due to the large spectral overlap between the PL spectrum 221 of the first dopant D1 and the absorption spectrum 212 of the second dopant D2, in particular, the second dopant D2 is not affected by the PL spectrum 221 of the first dopant D1. Energy transfer FET2 and Energy transfer FET4 is effectively generated. The energy transfer is carried out through a long-distance (<10 nm) energy transfer process under the dipole-dipole exchange interaction, so when the energy transfer length becomes longer due to the spectral overlap between the PL spectrum 221 of the first dopant D1 and the absorption spectrum 212 of the second dopant D2, the energy transfer is effectively generated. Energy transfer. In contrast, since Dexter energy transfer DET is possible when the orbitals of heterogeneous dopants D1 and D2 physically overlap, the energy transfer length of Dexter energy transfer DET is very short, on the order of 1 nm or less.

[0067] In the light-emitting layer 130 of the organic light-emitting device of the present invention, in order to improve the fluorescence emission effect of the second dopant D2, the doping concentrations of the first dopant D1 and the second dopant D2 are adjusted so that The energy transfer FET is greater than the Dexter energy transfer DET. That is, the concentration of the first dopant D1 is greater than the concentration of the second dopant D2. The doping concentration of the first dopant D1 is 1wt% to 40wt%, and the doping concentration of the second dopant D2 is 0.01wt% to 10wt%, and then the distance between the first dopant D1 and the second dopant D2 can be adjusted so that Energy transfer FET is easily feasible, and Dexter energy transfer DET can easily occur. In addition, since the doping concentration of the second dopant D2 is set to be small in the light emitting layer 130, recombination in the triplet excited state T1 in the second dopant D2 is difficult to proceed, so the triplet state directly generated at the second dopant D2 can be limited, and the efficiency of forming a singlet state in the singlet excited state S1 is improved as much as possible.

[0068] At the same time, a fourth excited state T1 of the first dopant D1 may be generated from a singlet excited state S1 of the second dopant D2. Energy transfer FET 4. When the spectral overlap between the PL spectrum 221 of the first dopant D1 and the absorption spectrum 212 of the second dopant D2 is greater, more fourth dopant is generated in the light emitting layer 130. The energy is transferred to FET4, and the light emitting efficiency of the second dopant D2 is increased because of the larger amount of fluorescent emission.

[0069] Moreover, in the second dopant D2, due to the small energy level difference ΔEst between the singlet excited state S1 and the triplet excited state T1, anti-intersystem crossing RISC transfer can be generated. Therefore, in the second dopant D2, the energy transferred to the triplet excited state T1 through the second Dexter energy transfer DET2 and the third Dexter energy transfer DET3 is transferred to the singlet excited state S1 again through RISC transfer. At this time, the energy generated by RISC transfer can be used to thermally activate delayed fluorescence TADF. Compared with TADF, the energy generated by the second Dexter energy transfer DET2 and the third Dexter energy transfer DET3 can be transferred to the singlet excited state S1 again through RISC transfer. Energy transfer and third Energy transfer The energy transferred from the host Host and the first dopant D1 to the singlet excited state S1 of the second dopant D2 can be used for fluorescence emission FL. Here, the difference between the triplet energy level T1 and the singlet energy level S1 in the second dopant D2 is preferably 0.4 eV or less. In the second dopant D2, there must be an energy level difference between the singlet excited state S1 and the triplet excited state T1, and it can be about 0.01 eV or more.

[0070] That is, in the light emitting layer 130 of the organic light emitting device of the present invention, fluorescence emission FL and thermally activated delayed fluorescence TADF are generated together at the second dopant D2, and therefore, the same second dopant D2 emits light having fluorescence characteristics, thereby having enhanced monochromatic color emission characteristics.

[0071] pass The fluorescence FL of the energy transfer FET emits immediately within nanoseconds, and the thermally activated delayed fluorescence TADF emits light after a delay of several microseconds. However, there is no difference in perception by the human eye between the fluorescence FL and TADF.

[0072] refer to Figure 2 , at the first dopant D1, the energy transfer from the singlet excited state S1 to the triplet excited state T1 is partially generated by intersystem crossing ISC transfer. However, the energy transferred to the triplet excited state T1 of the first dopant D1 by the ISC transfer and the first DET1 transfer is partially transferred again to the triplet excited state T1 of the second dopant D2, and then transferred to the singlet excited state S1 of the second dopant D2 by RISC transfer, and the energy transferred to the singlet excited state S1 of the second dopant D2 is finally used in thermally activated delayed fluorescence TADF. In the light-emitting layer 130 of the present invention, since there is a difference in doping concentration between the first dopant D1 and the second dopant D2, the Dexter energy transfer DET between the first dopant D1 and the second dopant D2 is minimized, The energy transfer FET is maximized. Also, the recombination rate at the second dopant D2 is minimized, thereby suppressing the generation of triplet states and inducing the generation of singlet states in the second dopant D2, so that the duration of the triplet state is shortened. Therefore, phenomena such as triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA) can be prevented, and the emission lifetime of the light-emitting layer 130 can be improved. That is, the present invention achieves a long lifetime and stability of the organic light-emitting device.

[0073] Moreover, the energy transferred to the triplet excited state T1 of the second dopant D2 through Dexter energy transfers DET2 and DET3 can be fully used in TADF, so theoretically 100% internal quantum efficiency is possible.

[0074] In the light emitting layer 130 of the present invention, the second dopant D2 may be a fluorescent dopant capable of achieving TADF, and the first dopant D1 may be a phosphorescent dopant. In some cases, the first dopant D1 may not be a phosphorescent dopant. If the first dopant D1 can smoothly transfer energy to the second dopant D2, it may be selected as a non-phosphorescent dopant.

[0075] The first dopant D1 uses, for example, a metal complex including iridium (Ir), platinum (Pt), osmium (Os), gold (Au), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), palladium (Pd), or thulium (Tm).

[0076] The second dopant D2 may be, for example, a boron-based compound shown in the following Chemical Formulas 1 to 9 or a modified example thereof.

[0077] [Chemical formula 1]

[0078]

[0079] [Chemical formula 2]

[0080]

[0081] [Chemical formula 3]

[0082]

[0083] [Chemical formula 4]

[0084]

[0085] [Chemical formula 5]

[0086]

[0087] [Chemical formula 6]

[0088]

[0089] [Chemical formula 7]

[0090]

[0091] [Chemical formula 8]

[0092]

[0093] [Chemical formula 9]

[0094]

[0095] In the light-emitting layer of the organic light-emitting device according to the present invention, the first dopant D1 does not emit light directly, but transfers the energy received from the host and its own excitation energy to the second dopant D2, and in order to achieve maximum efficiency of the light-emitting layer, it is expected that the first dopant D1 does not emit light or hardly emits light.

[0096] In the test example to be described below, a phosphorescent dopant is used as the first dopant D1, and a fluorescent dopant is used as the second dopant D2. An iridium complex or a platinum complex is used as the phosphorescent dopant PD, and a boron-based compound is used as the fluorescent dopant FD. In this case, it has been confirmed that the phosphorescent dopant PD effectively transfers the energy received from the host and its own excitation energy to the triplet excited state of the fluorescent dopant, and the fluorescent dopant FD formed of the boron-based compound simultaneously generates single-color fluorescence and thermally activated delayed fluorescence (TADF), as shown in FIG. Figure 2 As shown, and wherein mainly monochromatic fluorescence occurs.

[0097] In the light-emitting layer of the organic light-emitting device according to the present invention, a comparison is made between the intrinsic PL spectrum of the phosphorescent dopant PD and the intrinsic PL spectrum of the fluorescent dopant FD, as shown in FIG. Figure 3As shown, the fluorescent dopant FD may have a narrow full width at half maximum (FWHM). In the organic light-emitting device according to the present invention, light emission is concentrated on the fluorescent dopant FD, and therefore, according to the characteristics of the fluorescent dopant FD, light emission is achieved based on the fluorescent characteristics with a narrow full width at half maximum (FWHM), and this means that high color purity in light emission can be achieved.

[0098] Meanwhile, in the organic light-emitting device of the present invention, due to the small Stokes shift characteristic of the second dopant D2, the fourth dopant D2 used in the light-emitting layer 130 is used for the The energy level of the triplet excited state T1 of the first dopant D1 of the energy transfer FET4 can be set to a value similar to the singlet excited state S1 of the second dopant D2. In addition, for example, when the full width at half maximum (FWHM) based on the same color coordinates is small, the energy of the excited state is reduced compared to when the FWHM based on the same color coordinates is long. In other words, the triplet excited state T1 required for the first dopant D1 as a phosphorescent dopant can be reduced to a value similar to the singlet excited state S1 of the second dopant D2. Since the triplet excited state T1 of the first dopant D1 of the present invention is not higher than that of a conventional phosphorescent light-emitting device using a single phosphorescent dopant with a wider FWHM, a material with a low triplet excited state T1 can be selected as the first dopant D1 as a phosphorescent dopant, thereby achieving material stability of the first dopant D1 and expanding the range of material selection for the first dopant. As a result, the stability of the organic light-emitting device can be improved. In particular, even for a blue light emitting device, the light emitting layer 130 uses a first dopant (phosphorescent dopant) having a low triplet excited state, so that a single color can be stably achieved.

[0099] Meanwhile, the total amount of the first dopant D1 and the second dopant D2 in the light emitting layer is 50 wt% or less. The concentration of the first dopant D1 giving energy is 1 wt% to 40 wt%, and the concentration of the second dopant D2 receiving energy is 0.01 wt% to 10 wt%. In the light emitting layer 130, the concentration of the second dopant D2 is less than that of the first dopant D1. However, due to the Energy transfer FET and Dexter energy transfer DET, energy is transferred to the second dopant D2, and the second dopant D2 emits light with 100% internal quantum efficiency even at a low concentration, so the light-emitting layer including the host Host and the first dopant D1 and the second dopant D2 has sufficient light-emitting efficiency.

[0100] In the light emitting layer of the present invention, since the first dopant D1 transfers energy to the second dopant D2, spontaneous phosphorescence is hardly generated or is negligible compared to the fluorescence FL and thermally activated delayed fluorescence TADF at the second dopant D2.

[0101] The first dopant D1 may be a phosphorescent dopant, and the second dopant D2 may be a fluorescent dopant. When energy is released from the singlet excited state S1 to the ground state S0 in the second dopant D2 of the light emitting layer 130, fluorescence FL and thermally activated delayed fluorescence (TADF) may be generated together at the second dopant. In this case, since fluorescence is generated at the second dopant by transferring energy from the first dopant D1 formed by the phosphorescent dopant, this is also referred to as phosphorescence-sensitized fluorescence PSF emission.

[0102] In the energy transfer from the host Host and the first dopant D1 to the second dopant D2, The amount of energy transfer (FET2+FET3+FET4) may be greater than the amount of Dexter energy transfer (DET2+DET3).

[0103] The reverse intersystem crossing (RISC) transfer from the triplet excited state to the singlet excited state in the second dopant D2 may be proportional to the Dexter energy transfer (DET2+DET3) from the host Host and the first dopant D1 to the second dopant D2 and the energy of the triplet excitons generated in the second dopant D2.

[0104] like Figure 3 As shown, the absorption spectrum 212 of the second dopant D2 in the light emitting layer 130 and the PL spectrum 221 of the first dopant D1 spectrally overlap with each other in a wavelength range of 10 nm or more. The maximum wavelength of the absorption spectrum 212 of the second dopant D2 is greater than the minimum wavelength of the PL spectrum 221 of the first dopant D1, so the absorption spectrum 212 of the second dopant D2 overlaps with the PL spectrum 221 of the first dopant D1. Through this spectral overlap, the transition from the triplet excited state T1 of the first dopant D1 to the singlet excited state S1 of the second dopant D2 is Energy transfer FETs are possible.

[0105] In the light-emitting layer 130 of the organic light-emitting device of the present invention, the peak wavelength of the absorption spectrum 212 of the second dopant D2 receiving energy is located at a wavelength shorter than the peak wavelength of the PL spectrum 221 of the first dopant D1 giving energy. This means that the PL spectrum 221 of the first dopant D1 is located between the absorption spectrum 212 of the second dopant D2 and the PL spectrum 211 of the second dopant D2, and thus the spectral overlap between the absorption spectrum 212 of the second dopant D2 and the PL spectrum 221 of the first dopant D1 can be promoted. To this end, the area of ​​the "spectral overlap" should exceed a certain level. In order to determine the area (integrated value) of the spectral overlap between the absorption spectrum 212 of the second dopant D2 and the PL spectrum 221 of the first dopant D1, the distance between the first wavelength λAb_edge_FD intersecting with the main slope on the longer wavelength side of the absorption spectrum 212 of the second dopant D2 and the second wavelength λPL_onset_FD intersecting with the main slope on the shorter wavelength side of the PL spectrum 221 of the second dopant D1, as well as the height of the spectral overlap with the absorption spectrum 212 of the second dopant D2 are meaningful.

[0106] Meanwhile, "Stokes shift" refers to the difference between the wavelength representing the peak of the absorption spectrum 212 of the second dopant D2 and the wavelength representing the peak of the PL spectrum 211 of the second dopant D2. The value of the Stokes shift varies depending on the characteristics of the second dopant D2. In particular, as the value of the Stokes shift becomes smaller, the full width at half maximum FWHM tends to become smaller.

[0107] like Figure 3 As shown, the emission peak wavelength of the PL spectrum 221 of the first dopant D1 may be located between the peak wavelength of the absorption spectrum 212 of the second dopant D2 and the emission peak wavelength of the PL spectrum 211 of the second dopant D2. Also, the PL spectrum 221 of the first dopant D1 may have a spectrum overlap at an overlap region with the absorption spectrum 212 of the second dopant D2.

[0108] The difference in emission peak wavelength between the PL spectrum 221 of the first dopant D1 and the PL spectrum 211 of the second dopant D2 may be within 30 nm, and thus light emission uniformity between the first dopant D1 and the second dopant D2 may be maintained even if there is a small amount of emission from the first dopant D1 during energy transfer from the first dopant D1 to the second dopant D2.

[0109] at the same time, Figure 3 The PL spectrum 221 of the first dopant D1 and the second PL spectrum 211 of the second dopant D2 represent blue emission. However, the present invention is not limited thereto. In the following embodiments, first dopants and second dopants representing different color emissions will be described.

[0110] First, a first experimental example of the phosphor sensitized fluorescence PSF method will be described. In the first experimental example, the light emitting layer includes a host, a fluorescent dopant, and a phosphorescent dopant in the emission layer. Since the color emitted by the fluorescent dopant is different from the emission color of the phosphorescent dopant (there is a large difference between the wavelengths of the fluorescent dopant and the phosphorescent dopant), and the fluorescent dopant in the first experimental example does not have TADF (thermally activated delayed fluorescence) characteristics, the first experimental example exhibits the same performance as that according to Figure 3 The embodiments have different characteristics.

[0111] Figure 4A is a view showing an energy transfer relationship in a light emitting layer according to a first experimental example, Figure 4B is a graph showing PL spectra of different dopants according to the first experimental example.

[0112] like Figure 4A As shown, in the light emitting layer according to the first experimental example, energy is transferred from the host Host to the phosphorescent dopant PD and the fluorescent dopant FD, and from the phosphorescent dopant PD to the fluorescent dopant FD, respectively.

[0113] That is, the singlet excitons generated in the host pass through Energy transfer FET5 and FET7 are transferred into the singlet excited state of the phosphorescent dopant PD and the fluorescent dopant FD. Moreover, the singlet excitons generated at the phosphorescent dopant PD pass The energy transfer FET6 is transferred into the singlet excited state of the fluorescent dopant FD.

[0114] Moreover, the triplet excitons generated at the host Host are transferred into the triplet excited states of the phosphorescent dopant PD and the fluorescent dopant FD through Dexter energy transfers DET4 and DET 6. In addition, the triplet excitons generated at the phosphorescent dopant PD are transferred into the triplet excited state of the fluorescent dopant FD through Dexter energy transfer DET5. Here, in the phosphorescent dopant PD, energy transfer from the singlet excited state S1 to the triplet excited state T1 can be partially generated by intersystem crossing (ISC) transfer, and then the energy transferred from the triplet excited state T1 to the ground state S0 is released, and part of the phosphorescent luminescence can also be emitted from the phosphorescent dopant PD.

[0115] In addition, the energy of the triplet excited state T1 of the phosphorescent dopant PD is The energy transfer FET8 is partially transferred into the singlet excited state S1 of the fluorescent dopant FD, and partially transferred into the triplet excited state T1 of the fluorescent dopant PD through the Dexter energy transfer DET5. In the fluorescent dopant FD, the energy of the Dexter energy transfers DET4 to DET6 is transferred into the triplet excited state T1, and triplet excitons are generated by recombination in the fluorescent dopant FD. In the fluorescent dopant FD, when the triplet excited state T1 drops to the ground state S0, non-radiative decay occurs due to heat loss instead of light emission.

[0116] That is, even though the first experimental example uses a different type of dopant, since reverse intersystem crossing (RISC) transfer does not occur at the fluorescent dopant, non-radiative decay occurs in the fluorescence at the fluorescent dopant FD. Moreover, in the first experimental example, some phosphorescent emission is generated at the phosphorescent dopant PD, so the color purity of the light emission is low, because part of the phosphorescence and part of the fluorescence are mixed in the light-emitting layer, where the fluorescence exhibits a different color characteristic from the phosphorescence.

[0117] Moreover, if Figure 4B As shown, the light emitting layer in the first experimental example should be set for energy transfer from the phosphorescent dopant PD to the fluorescent dopant FD so that the PL spectrum 321 of the phosphorescent dopant PD almost overlaps with the absorption spectrum 312 of the fluorescent dopant. In this case, the difference in Stokes shift between the absorption spectrum 312 and the PL spectrum 311 of the fluorescent dopant is large, so the emission peak characteristics between the phosphorescent dopant PD and the fluorescent dopant FD are different. In particular, as Figure 4A As shown, when phosphorescence from a phosphorescent dopant and fluorescence from a fluorescent dopant occur simultaneously, light emissions of different colors are mixed, and thus it is difficult to achieve monochromatic emission.

[0118] As described above, in the first experimental example in which the light-emitting layer contains a phosphorescent dopant and a fluorescent dopant having different emission colors, by using Energy transfer converts some triplet excitons of the phosphorescent dopant into singlet excitons of the fluorescent dopant to partially generate fluorescence, and phosphorescence is simultaneously generated in the excitation from the triplet excited state to the ground state in the phosphorescent dopant, thereby inducing mixed color light emission in the light emitting layer. In the first experimental example, the concentration of triplet excitons in the light emitting layer can be reduced, so that the lifetime can be increased compared to a phosphorescent light emitting device having only a single phosphorescent dopant, and high efficiency can be achieved compared to a fluorescent light emitting device having a single fluorescent dopant.

[0119] In the first experimental example, triplet excitons formed by Dexter energy transfer (from the triplet excited state of the phosphorescent dopant and the host to the triplet excited state of the fluorescent dopant) or by charge recombination may be quenched due to non-radiative decay, so the efficiency of the first experimental example tends to be reduced compared to the phosphorescent device.

[0120] For the transition from the triplet excited state of the phosphorescent dopant to the singlet excited state of the fluorescent dopant Energy transfer, the overlap between the PL spectrum of the phosphorescent dopant and the absorption spectrum of the fluorescent dopant is beneficial. Since the fluorescent dopant generally known has a large Stokes shift, for the overlap between the PL spectrum of the phosphorescent dopant and the absorption spectrum of the fluorescent dopant, the emission wavelength of the PL spectrum of the phosphorescent dopant should be at a shorter wavelength than the emission wavelength of the fluorescent dopant. Therefore, as Figure 4B As shown, the first experimental example indicates that the phosphorescent dopant has blue emission, while the fluorescent dopant has green emission, which has a certain gap with the blue emission. In this case, for blue emission, the triplet excited state of the phosphorescent dopant should be higher than the singlet excited state of the blue fluorescent dopant. That is, a phosphorescent dopant with a higher triplet state is beneficial. However, a phosphorescent dopant with a higher triplet state must be formed by adjusting at least one substituent, and the phosphorescent dopant with an adjusted substituent has an unstable nature, thereby greatly reducing the stability of the device.

[0121] On the contrary, Figures 1 to 3 The light-emitting layer of the organic light-emitting device described in the invention simultaneously utilizes the higher efficiency of phosphorescence and the higher color purity and longer lifetime of fluorescence. Figures 1 to 3 In the light-emitting layer, the second dopant as a fluorescent dopant realizes thermally activated delayed fluorescence (TADF) and has a small Stokes shift, so that the triplet excited state of the phosphorescent dopant (the first dopant) is not higher and is sufficient to provide the generation of spectral overlap between the PL spectrum of the first dopant and the absorption spectrum of the second dopant. Finally, by Energy transfer provides energy to the second dopant easily. Moreover, by the second dopant having a small Stokes shift, the spectral overlap between the PL spectrum of the first dopant and the absorption spectrum of the second dopant is maximized, so that the first dopant transfers energy to the second dopant with almost no self-luminescence. In addition, the second dopant generates fluorescent emission and thermally activated delayed fluorescence (TADF) through anti-intersystem crossing transfer, thereby reducing the loss of excitons in the light-emitting layer and improving efficiency.

[0122] The organic light-emitting device of the present invention includes a host Host as a main matrix material in a single light-emitting layer. The host Host may include a single type of organic material or different organic materials. In the light-emitting layer, the host Host is used for the internal movement of holes and electron carriers transmitted through at least one common layer. The total amount of the first dopant D1 and the second dopant D2 is within 40wt% of the host Host. The first dopant D1 may be included in an amount of 1wt% to 30wt% of the host Host, and the second dopant D2 may be included in an amount of 0.01wt% to 10wt%.

[0123] The first dopant D1 may be a phosphorescent dopant. In this case, for example, the first dopant D1 may be a metal complex including iridium (Ir), platinum (Pt), or osmium (Os) as a core. However, the core metal of the first dopant D1 is not limited to the examples listed, and if it has a relative phosphorescent dopant to the second dopant D2 (fluorescent dopant), the first dopant D1 may be a metal complex including iridium (Ir), platinum (Pt), or osmium (Os) as a core. Figure 2 relationship, it can be changed to another metal.

[0124] The second dopant D2 may be a material having a small difference (ΔEst) between a singlet excited state and a triplet excited state and capable of achieving TADF. For example, the second dopant D2 may be a boron-based compound.

[0125] The host Host in the organic light-emitting device of the present invention may include at least one material that controls the transport and balance of internal carriers (electrons and holes) and transfers energy to the first dopant D1 and the second dopant D2. If the host Host acts as a single material to control the transport and balance of internal carriers, the host Host may be formed of a single material. Or the host Host may be formed of a plurality of materials to control the transport and balance of internal carriers. There are two types of p-type hosts with high hole transport mobility and n-type hosts with high electron transport mobility. The light-emitting layer of the present invention may use both p-type hosts and n-type hosts, or may use two or more hosts with the same host type but with different mobilities. In the light-emitting layer, the host Host may be selected in consideration of the composition of the first dopant D1 and the second dopant D2 and the arrangement of the common layers above and below the light-emitting layer.

[0126] Meanwhile, the organic light-emitting device of the present invention may use a phosphorescent dopant as a first dopant and a fluorescent dopant as a second dopant, and the first dopant D1 and the second dopant D2 have the following characteristics: Figure 2 The relationship between the singlet state and the triplet state is shown. Therefore, it is characterized in that light emission is concentrated at the second dopant D2 through energy transfer, thereby achieving monochromatic emission in the organic light-emitting device of the present invention.

[0127] Hereinafter, various embodiments of the organic light emitting device of the present invention will be described. Figure 1 The explanation is described by comparing the device and its modified examples.

[0128] Figure 5 is a cross-sectional view showing an organic light emitting device according to a first embodiment of the present invention.

[0129] like Figure 5 As shown, the organic light-emitting device A according to the first embodiment of the present invention includes a light-emitting layer 130a disposed between a first electrode 110 and a second electrode 120 arranged opposite to each other. The first common layer is located between the first electrode 110 and the light-emitting layer 130a, and the first common layer may include a hole injection layer (HIL) 111, a hole transport layer (HTL) 112, and an electron blocking layer (EBL) 113. The second common layer is located between the light-emitting layer 130a and the second electrode 120, and the second common layer may include a hole blocking layer (HBL) 114, an electron transport layer (ETL) 115, and an electron injection layer (EIL) 116. Because the triplet energy level and the singlet energy level of the electron blocking layer 113 and the hole blocking layer 114 are higher than or equal to the triplet energy level and the singlet energy level of the host in the light-emitting layer 130a, the electron blocking layer 113 and the hole blocking layer 114 are used to block electrons and holes and confine excitons in the light-emitting layer 130a.

[0130] The light emitting layer 130a uses two hosts Host1 and Host2 and a phosphorescent dopant PD for a first dopant and a fluorescent dopant FD for a second dopant. As described above, the two hosts Host1 and Host2 may be a p-type host and an n-type host, respectively. The first host Host1 and the second host Host2 have PL spectra for transferring energy to the first dopant PD and the second dopant FD.

[0131] The structure between the first electrode 110 and the second electrode 120 may be an organic stacked body OS mainly having an organic material therein. In some cases, the hole injection layer 111 and the electron injection layer 116 may include an inorganic material or an inorganic compound, and in the hole injection layer 111 and the electron injection layer 116, the amount of the inorganic material included or the amount of the inorganic compound included may be greater than the amount of the organic material, or may be composed only of the inorganic material or the inorganic compound.

[0132] Furthermore, each functional layer in the organic stack OS may be a single layer or a multi-layer.

[0133] Figure 6 is a cross-sectional view showing an organic light emitting device according to a second embodiment of the present invention.

[0134] like Figure 6As shown in FIG. 1 , the organic light-emitting device B according to the second embodiment of the present invention has the same structure except for the light-emitting layer 130 b. The organic light-emitting device according to the second embodiment of the present invention has a single host in the light-emitting layer 130 b. In this case, the single host Host can be selected from the first dopant PD and the second dopant FD. Energy transfer and Dexter energy transfer in multiple materials.

[0135] Figure 7 is a cross-sectional view showing an organic light emitting device according to a third embodiment of the present invention.

[0136] like Figure 7 As shown, the organic light-emitting device C according to the third embodiment of the present invention does not have an electron blocking layer under the light-emitting layer 130 c , and the light-emitting layer 130 c is in contact with the hole transport layer 112 .

[0137] Figure 8 is a cross-sectional view showing an organic light emitting device according to a fourth embodiment of the present invention.

[0138] like Figure 8 As shown, the organic light-emitting device D according to the fourth embodiment of the present invention is different only in that it does not have a hole blocking layer on the light-emitting layer 130d and is the same as the second embodiment. The light-emitting layer 130d of the fourth embodiment of the present invention is in contact with the electron transport layer 115.

[0139] In the organic light-emitting devices according to the third and fourth embodiments described above, the host provided in the light-emitting layer may include a plurality of hosts having different characteristics.

[0140] The organic light-emitting devices according to the first to fourth embodiments have a common feature, namely, using a first dopant and a second dopant with different characteristics, and selecting a second dopant capable of fluorescent emission using TADF. Therefore, the organic light-emitting devices according to the first to fourth embodiments have a common effect of emitting monochromatic light.

[0141] The organic light-emitting device of the present invention can be applied to a tandem device including a plurality of stacks as well as a single stack configuration having a single light-emitting layer as the above-mentioned light-emitting layer.

[0142] In the case of a tandem device, light of mixed colors emitted from the provided light-emitting layers may eventually appear on the emission side. Also, the tandem device can be used as a white light-emitting device by providing light-emitting layers of different colors.

[0143] Hereinafter, the fifth embodiment and the sixth embodiment of the present invention are described as white light emitting devices.

[0144] Fig. 9Ais a cross-sectional view showing an organic light emitting device according to a fifth embodiment of the present invention, Fig. 9B is a cross-sectional view showing an organic light emitting device according to a sixth embodiment of the present invention.

[0145] like Fig. 9A As shown, the organic light emitting device according to the fifth embodiment of the present invention includes first and second electrodes 110 and 120 arranged opposite to each other, first and second stacks S1 and S2, and a charge generation layer (CGL) 170 between the first and second stacks S1 and S2.

[0146] The first stacked body S1 includes a first hole transport-related common layer 161 , a red light emitting layer 140 , a green or yellow-green light emitting layer 150 , and a first electron transport-related common layer 162 stacked on the first electrode 110 .

[0147] The second stacked body S2 includes a second hole transport-related common layer 163 , a blue light emitting layer 130 , and a second electron transport-related common layer 164 stacked on the charge generation layer 170 .

[0148] The charge generation layer 170 may be a single layer doped with a p-type dopant and an n-type dopant, or may be formed of an n-type charge generation layer and a p-type charge generation layer stacked.

[0149] For example, the first hole transport-related common layer 161 and the second hole transport-related common layer 163 may be at least one of the hole injection layer, the hole transport layer, and the electron blocking layer described in the first example.

[0150] For example, the first electron transport-related common layer 162 and the second electron transport-related common layer 164 may be at least one of the hole blocking layer, the electron transport layer, and the electron injection layer described in the first example.

[0151] The organic light emitting device according to the fifth embodiment of the present invention includes in the second stack body S2: Figures 1 to 3 The light emitting layer 130 is configured as a light emitting layer. The light emitting layer 130 includes a host Host, a first dopant D1 formed by a phosphorescent dopant, and a second dopant D2 formed by a fluorescent dopant. Energy transfer and Dexter energy transfer. In particular, the energy of the triplet excited state transferred to the second dopant D2 by Dexter energy transfer is transferred again into the singlet excited state in the second dopant D2 by reverse intersystem crossing (RISC) and used in TADF. That is, the first dopant D1 formed of the phosphorescent dopant is sensitized, and then fluorescence is generated in the light-emitting layer by the phosphorescence sensitized fluorescence (PSF) method. Figure 3As shown, the second dopant D2 represents blue emission.

[0152] The red light emitting layer 140 and the green or yellow-green light emitting layer 150 disposed in the first stack body S1 may be phosphor layers or fluorescent layers, respectively. In some cases, at least one of the red light emitting layer 140 and the green or yellow-green light emitting layer 150 may include a different type of dopant to enable the following example: Figures 2 to 3 Phosphorescence-sensitized fluorescence (PSF) is shown.

[0153] like Fig. 9B As shown, the organic light emitting device according to the sixth embodiment of the present invention includes a first blue stack S1 and a second blue stack S3 disposed above and below the long wavelength stack S2. Compared with the fifth embodiment, the sixth embodiment requires an additional blue stack.

[0154] The charge generation layers 172 and 173 are located between adjacent stacks S1 , S2 , S3 .

[0155] The first blue stack S1 and the second blue stack S3 include first hole transport-related common layers 161 and 165 , blue light emitting layers 130 e and 130 f , and second electron transport-related common layers 162 and 166 .

[0156] The long wavelength stack S2 includes: Fig. 9A The third hole transport related common layer 163, the red light emitting layer 140, the green or yellow-green light emitting layer 150 and the fourth electron transport related common layer 164 are stacked as described above.

[0157] Since the organic light emitting device according to the sixth embodiment has an additional blue stack compared to the fifth embodiment, the organic light emitting device according to the sixth embodiment can efficiently realize deep blue emission by compensating for the light emitting efficiency of the blue light emitting layer.

[0158] In the case of a blue light-emitting layer capable of achieving PSF of the present invention, energy transfer from the first dopant to the second dopant is additionally performed according to the energy transfer mechanism, and its own TADF is generated in the second dopant, so that theoretically 100% internal quantum efficiency can be achieved. That is, the efficiency can be increased to 1.5 to 2 times the efficiency of the structure with a single fluorescent dopant. Even if the blue stack is configured as a single unit, the organic light-emitting device according to the fifth embodiment can have the same or higher effect as the organic light-emitting device having two blue fluorescent stacks formed by a single fluorescent dopant.

[0159] Compared with a structure having a single fluorescent dopant as a dopant in the light-emitting layer, the present invention can have excellent efficiency, and compared with a structure having a phosphorescent dopant as a dopant in the light-emitting layer, the present invention has an improved lifespan. In addition, even if the stacking structure is simplified to 2 stacks, the present invention has similar efficiency to 3 stacks having two blue stacks, each of which uses a blue light-emitting layer having a single fluorescent dopant as a dopant. Therefore, the present invention according to the fifth embodiment can have high efficiency even when driven by a small voltage.

[0160] Fig.10 is a graph showing PL spectra in a modified example of the present invention having a different Stokes shift characteristic of a second dopant, Fig.11A and 11B It is shown Fig.10 0047] Figure 2 is a diagram of an energy transfer relationship in a modified embodiment of FIG.

[0161] Fig.10 Spectral characteristics according to the dopants used in the second experimental example and the third experimental example are shown.

[0162] exist Fig.10 In FIG. 2 , a Stokes shift is generated in the fluorescent dopant having the main emission, which means a difference between the peak wavelength of the absorption spectrum 232 and the peak wavelength of the PL spectrum 231 in the fluorescent dopant.

[0163] The second experimental example (E) shows the spectrum of the light-emitting layer of the fluorescent dopant having a small Stokes shift characteristic, and the third experimental example (F) shows the spectrum of the light-emitting layer of the fluorescent dopant having a large Stokes shift characteristic. Fig.10 As shown, the second experimental example (E) and the third experimental example (F) have similar spectral overlap between the PL spectrum 241, 261 of the first dopant (phosphorescent dopant) and the absorption spectrum 232, 253 of the second dopant (fluorescent dopant), and have similar energy transfer due to the spectral overlap.

[0164] Compare Fig.11A The second experimental example (E) and Fig. 11B The third experimental example (F) of the second experimental example (E) can relatively reduce the energy levels of the triplet excited states of the main body 431 and the first dopant 432. That is, the triplet excited state of the main body 431 in the second experimental example (E) is reduced by the first energy level difference ΔT1 compared with the triplet excited state of the main body 441 in the third experimental example (F). Similarly, the triplet excited state of the first dopant 432 in the second experimental example (E) is reduced by the first energy level difference ΔT2 compared with the triplet excited state of the first dopant 442 in the third experimental example (F).

[0165] exist FIG. 4A to FIG. 4B In the first experimental example, the internal quantum efficiency is reduced due to the non-radiative decay generated in the fluorescent dopant. Figure 2 and Figure 3 As shown, the light-emitting layer of the present invention uses a second dopant using a fluorescent dopant capable of achieving TADF, and converts the generated triplet excitons into singlet excitons through RISC transfer in the second dopant, thereby suppressing the loss of internal quantum efficiency.

[0166] Although boron-based fluorescent dopants emit in a region similar to the emission wavelength of phosphorescent dopants, Fig.10 In the second experimental example shown, a spectral overlap is generated between the absorption spectrum of the fluorescent dopant and the PL spectrum of the phosphorescent dopant, thereby causing the fluorescent dopant to enter a singlet excited state from a triplet excited state. Energy transfer. That is, the spectral overlap between the absorption spectrum of the fluorescent dopant and the PL spectrum of the phosphorescent dopant is promoted by the small Stokes shift of the fluorescent dopant.

[0167] like Fig.10 As shown in the third experimental example, in the case where the fluorescent dopant has a relatively large Stokes shift, since the PL spectrum of the phosphorescent dopant should be shifted to a shorter wavelength for spectral overlap between the absorption spectrum of the fluorescent dopant and the PL spectrum of the phosphorescent dopant, the triplet excited state of the phosphorescent dopant in the third experimental example is required to be higher than the triplet excited state of the phosphorescent dopant in the second experimental example. In the third experimental example, this higher triplet excited state in the phosphorescent dopant also requires a higher triplet excited state of the host for energy transfer from the host Host to the dopants PD and FD. This required higher triplet excited state increases the difficulty of molecular design of the host and the phosphorescent dopant PD. Therefore, this means that it is difficult to select the host Host and the phosphorescent dopant PD used in the light-emitting layer of the third experimental example, and the third experimental example (F) with a large Stokes shift will reduce electrical stability and optical stability.

[0168] As shown in the second experimental example, the light-emitting layer of the present invention can improve the electrical and optical stability of the device by minimizing the triplet excited state required by the first dopant (phosphorescent dopant).

[0169] Moreover, in the light-emitting layer of the present invention, by increasing the spectral overlap between the absorption spectrum of the fluorescent dopant and the PL spectrum of the phosphorescent dopant, the triplet excitons of the phosphorescent dopant are rapidly converted to the singlet excited state of the fluorescent dopant, thereby reducing the lifetime of the triplet excitons and improving the stability of the device.

[0170] Compared with a fluorescent blue dopant having a wide FWHM in a fluorescent emitting device, in the present invention, each of triplet excited states of a phosphorescent dopant and a host can be reduced, thereby ensuring electrical stability and optical stability, and color purity is improved.

[0171] In the following, various embodiments of the present invention will be described with respect to energy transfer and spectral characteristics.

[0172] Fig. 12A and Fig. 12B : are a view showing an energy transfer relationship in a light emitting layer according to a seventh embodiment of the present invention and a graph showing a PL spectrum therein.

[0173] like Fig. 12A As shown, the organic light emitting device according to the seventh embodiment of the present invention includes a blue light emitting layer 130. Moreover, the blue light emitting layer 130 includes at least one host Host, a first dopant PD (blue) to which energy is transferred from the host, and a second dopant FD (blue) to which energy is transferred from the host and the first dopant.

[0174] The energy transfer and excitation mechanism of each component in the light emitting layer 130 is similar to Figures 1 to 3 , and description of the same parts is omitted.

[0175] like Fig. 12B As shown, in the blue light-emitting layer 130 of the organic light-emitting device according to the seventh embodiment of the present invention, the peak wavelength of the PL spectrum 281 of the first dopant PD (blue) and the peak wavelength of the PL spectrum 271 of the second dopant FD (blue) are within 30 nm, and the PL spectrum 281 of the first dopant PD (blue) and the absorption spectrum 272 of the second dopant FD (blue) overlap spectrally with a large area. Because the Stokes shift between the absorption spectrum 272 and the PL spectrum 271 in the second dopant FD (blue) is small, the energy transfer from the first dopant PD to the second dopant FD is promoted by the large spectral overlap.

[0176] Since the energy from the first dopant PD is transferred to the second dopant FD, and fluorescence and thermally activated delayed fluorescence (TADF) are jointly generated in the singlet excited state of the second dopant FD, the organic light-emitting device according to the seventh embodiment of the present invention can emit uniform blue light. The first dopant PD is a phosphorescent dopant having the above-mentioned metal core, and the second dopant FD is a fluorescent dopant capable of achieving TADF. The second dopant FD can be selected from Chemical Formulas 1 to 9. The light-emitting layer of the organic light-emitting device according to the seventh embodiment represents an emission of about 430nm to 480nm.

[0177] Fig.13A and Fig. 13B2 is a view showing an energy transfer relationship in a light emitting layer according to an eighth embodiment of the present invention and a graph showing a PL spectrum therein.

[0178] like Fig.13A As shown, the organic light-emitting device according to the eighth embodiment of the present invention includes a green light-emitting layer 510. In addition, the green light-emitting layer 510 includes at least one host Host, a first dopant PD (green) to which energy is transferred from the host, and a second dopant FD (green) to which energy is transferred from the host and the first dopant.

[0179] For example, the second dopant D2 may be selected from those shown in the following Chemical Formulas 10 to 13 or modified examples thereof.

[0180] [Chemical formula 10]

[0181]

[0182] [Chemical formula 11]

[0183]

[0184] [Chemical formula 12]

[0185]

[0186] [Chemical formula 13]

[0187]

[0188] The energy transfer and excitation mechanism of each component in the light-emitting layer 510 is similar to Figures 1 to 3 , and description of the same parts is omitted.

[0189] like Fig. 13B As shown, in the green light-emitting layer 510 of the organic light-emitting device according to the eighth embodiment of the present invention, the peak wavelength of the PL spectrum 521 of the first dopant PD (green) and the PL peak wavelength of the PL spectrum 511 of the second dopant FD (green) are within 30 nm, and since the Stokes shift between the absorption spectrum 512 and the PL spectrum 511 in the second dopant FD (green) is small, the PL spectrum 521 of the first dopant PD (green) and the absorption spectrum 512 of the second dopant FD (green) overlap spectrally with a large area, thereby promoting energy transfer from the first dopant PD to the second dopant FD through the large spectral overlap.

[0190] Since the energy from the first dopant PD is transferred to the second dopant FD, and fluorescence and thermally activated delayed fluorescence (TADF) are jointly generated in the singlet excited state of the second dopant FD, the organic light-emitting device according to the eighth embodiment of the present invention can emit uniform green light. The first dopant PD is a phosphorescent dopant having the above-mentioned metal core, and the second dopant FD is a fluorescent dopant capable of achieving TADF. The second dopant FD can be selected from Chemical Formulas 10 to 13. The green light-emitting layer of the organic light-emitting device according to the eighth embodiment represents an emission of about 500nm to 560nm.

[0191] Fig.14A and Fig. 14B : are a view showing an energy transfer relationship in a light emitting layer according to a ninth embodiment of the present invention and a graph showing a PL spectrum therein.

[0192] like Fig.14A As shown, the organic light-emitting device according to the ninth embodiment of the present invention includes a green light-emitting layer 530. In addition, the green light-emitting layer 530 includes at least one host Host, a first dopant PD (blue) to which energy is transferred from the host, and a second dopant FD (green) to which energy is transferred from the host and the first dopant.

[0193] The ninth embodiment is different from the eighth embodiment in that the first dopant PD (blue) has a blue emission characteristic but does not have a green emission characteristic. Fig. 14B As shown, in the green light emitting layer 530 of the organic light emitting device according to the ninth embodiment of the present invention, the peak wavelength of the PL spectrum 531 of the second dopant FD (green) differs from the PL peak wavelength of the PL spectrum 541 of the first dopant PD (blue) by 35nm to 60nm, and the first dopant PD (blue) and the second dopant FD (green) have different emission characteristics. However, in the organic light emitting device according to the ninth embodiment of the present invention, from the first dopant PD (blue) to the second dopant FD (green), the spectral overlap is large, and the spectral overlap is large. Energy transfer promotes energy transfer from the first dopant PD (blue) to the second dopant FD, thereby generating fluorescence at the second dopant. In addition, in the second dopant FD (green), TADF is generated by using Dexter energy transfer DET2 based on electron exchange between triplet excitons between the host Host and the first dopant PD (blue) and the second dopant FD (green) and reverse intersystem crossing (RISC) transfer from the triplet excited state T1 to the singlet excited state S1. Therefore, the green light emitting layer of the organic light emitting device according to the ninth embodiment can represent an emission of about 500nm to 560nm.

[0194] The energy transfer and excitation mechanism of each component in the light emitting layer 530 is similar to Figures 1 to 3 , and description of the same parts is omitted.

[0195] Fig.15A and Fig. 15B 2 is a view showing an energy transfer relationship in a light emitting layer according to a tenth embodiment of the present invention and a graph showing a PL spectrum therein.

[0196] like Fig.15A As shown, the organic light-emitting device according to the tenth embodiment of the present invention includes a red light-emitting layer 550. In addition, the red light-emitting layer 550 includes at least one host Host, a first dopant PD (red) to which energy is transferred from the host, and a second dopant FD (red) to which energy is transferred from the host and the first dopant.

[0197] The energy transfer and excitation mechanism of each component in the light-emitting layer 550 is similar to Figures 1 to 3 , and description of the same parts is omitted.

[0198] like Fig. 15B As shown, in the red light-emitting layer 550 of the organic light-emitting device according to the tenth embodiment of the present invention, the peak wavelength of the PL spectrum 561 of the first dopant PD (red) and the PL peak wavelength of the PL spectrum 551 of the second dopant FD (red) are within 30 nm, and since the Stokes shift between the absorption spectrum 552 and the PL spectrum 551 in the second dopant FD (red) is small, the PL spectrum 561 of the first dopant PD (red) and the absorption spectrum 552 of the second dopant FD (red) overlap spectrally with a large area, thereby promoting energy transfer from the first dopant PD to the second dopant FD through the large spectral overlap.

[0199] Since the energy from the first dopant PD is transferred to the second dopant FD, and fluorescence and thermally activated delayed fluorescence (TADF) are jointly generated in the singlet excited state of the second dopant FD, the organic light-emitting device according to the tenth embodiment of the present invention can emit uniform red light. The first dopant PD is a phosphorescent dopant having the above-mentioned metal core, and the second dopant FD is a fluorescent dopant capable of achieving TADF. The red light-emitting layer of the organic light-emitting device according to the tenth embodiment represents an emission of about 600nm to 700nm.

[0200] Fig.16A and Fig. 16B 2 is a view showing an energy transfer relationship in a light emitting layer according to an eleventh embodiment of the present invention and a graph showing a PL spectrum therein.

[0201] like Fig.16AAs shown, the organic light emitting device according to the eleventh embodiment of the present invention includes a red light emitting layer 570. In addition, the red light emitting layer 560 includes at least one host Host, a first dopant PD (green) to which energy is transferred from the host, and a second dopant FD (red) to which energy is transferred from the host and the first dopant.

[0202] The eleventh embodiment is different from the tenth embodiment in that the first dopant PD (green) has green light emitting characteristics but does not have red light emitting characteristics. Fig. 16B As shown, in the red light emitting layer 570 of the organic light emitting device according to the eleventh embodiment of the present invention, the peak wavelength of the PL spectrum 571 of the second dopant FD (red) differs from the peak wavelength of the PL spectrum 581 of the first dopant PD (green) by 30nm to 60nm, and the first dopant PD (green) and the second dopant FD (red) have different emission characteristics. However, in the organic light emitting device according to the eleventh embodiment of the present invention, from the first dopant PD (green) to the second dopant FD (red), the spectral overlap is large, and the spectral overlap is large. Energy transfer promotes the transfer of energy from the first dopant PD (green) to the second dopant FD (red), thereby generating fluorescence at the second dopant. In addition, in the second dopant FD (red), TADF is generated by using Dexter energy transfer DET2 according to the electron exchange of triplet excitons between the host Host and the first dopant PD (green) and the second dopant FD (red) and reverse intersystem crossing (RISC) transfer from the triplet excited state T1 to the single excited state S1. Therefore, the red light emitting layer of the organic light emitting device according to the eleventh embodiment can represent an emission of about 600nm to 700nm.

[0203] The energy transfer and excitation mechanism of each component in the light emitting layer 570 is similar to Figures 1 to 3 Those are the same as those of FIG. 1 , and description of the same parts is omitted.

[0204] Fig.17A and Fig. 17B 2 is a view showing an energy transfer relationship in a light emitting layer according to a twelfth embodiment of the present invention and a graph showing a PL spectrum therein.

[0205] like Fig.17A As shown, the organic light-emitting device according to the twelfth embodiment of the present invention includes a red light-emitting layer 590. In addition, the red light-emitting layer 590 includes at least one host Host, a first dopant PD (blue) to which energy is transferred from the host, and a second dopant FD (red) to which energy is transferred from the host and the first dopant PD (blue).

[0206] The twelfth embodiment is different from the tenth embodiment in that the first dopant PD (blue) has a blue emission characteristic but does not have a red emission characteristic. Fig. 17B As shown, in the red light emitting layer 590 of the organic light emitting device according to the twelfth embodiment of the present invention, the peak wavelength of the PL spectrum 591 of the second dopant FD (red) differs from the PL peak wavelength of the PL spectrum 601 of the first dopant PD (blue) by 100nm to 160nm, and the first dopant PD (blue) and the second dopant FD (red) have different emission characteristics. However, in the organic light emitting device according to the twelfth embodiment of the present invention, from the first dopant PD (blue) to the second dopant FD (red), the spectral overlap is large, and the spectral overlap is large. Energy transfer promotes the transfer of energy from the first dopant PD (blue) to the second dopant FD (red), thereby generating fluorescence at the second dopant. In addition, in the second dopant FD (red), TADF is generated by using Dexter energy transfer DET2 according to the electron exchange between the host Host and the triplet excitons between the first dopant PD (blue) and the second dopant FD (red) and the reverse intersystem crossing (RISC) transfer from the triplet excited state T1 to the singlet excited state S1. Therefore, the red light emitting layer of the organic light emitting device according to the twelfth embodiment can represent an emission of about 600nm to 700nm.

[0207] The energy transfer and excitation mechanism of each component in the light emitting layer 590 is similar to Figures 1 to 3 , and description of the same parts is omitted.

[0208] Hereinafter, the present invention will be described including Fig. 9A and 9B The fifth or sixth embodiment is shown as an implementation example of a display device of a white organic light emitting device in a series device.

[0209] Fig.18 is a cross-sectional view showing a display device according to the present invention.

[0210] like Fig.18 As shown, the display device according to the present invention may include a substrate 100 having a plurality of sub-pixels R_SP, G_SP, B_SP, and W_SP, and a substrate 100 disposed on the substrate 100. Fig. 9A or Fig. 9B an organic light emitting diode OLED, thin film transistors TFT respectively disposed in the sub-pixels and connected to the first electrodes 110 of the organic light emitting diode OLED, and color filter layers 109R, 109G and 109B disposed under the first electrode 110 of at least one sub-pixel.

[0211] Although the illustrated example shows that the display device includes a white sub-pixel W_SP, the present disclosure is not limited thereto, and the display device may have a structure including only a red sub-pixel R_SP, a green sub-pixel G_SP, and a blue sub-pixel B_SP without a white sub-pixel W_SP. As circumstances require, a cyan sub-pixel, a magenta sub-pixel, and a yellow sub-pixel combined to represent white may be used as a substitute for the red sub-pixel R_SP, the green sub-pixel G_SP, and the blue sub-pixel B_SP.

[0212] The thin film transistor TFT includes, for example, a gate electrode 102 , a semiconductor layer 104 , and a source electrode 106 a and a drain electrode 106 b connected to both sides of the semiconductor layer 104 .

[0213] The gate insulating film 103 is provided between the gate electrode 102 and the semiconductor layer 104 .

[0214] The semiconductor layer 104 may be formed of, for example, amorphous silicon, polycrystalline silicon, an oxide semiconductor, or a combination of two or more thereof. For example, if the semiconductor layer 104 is formed of an oxide semiconductor, an edge stopper 105 directly contacting the upper surface of the semiconductor layer 104 may be further provided to prevent damage to the channel region of the semiconductor layer 104.

[0215] In addition, the drain electrode 106 b of the thin film transistor TFT may be connected to the first electrode 110 through a contact hole CT formed in the first protection film 107 and the second protection film 108 .

[0216] The first protective film 107 is provided to mainly protect the thin film transistor TFT, and color filters 109R, 109G, and 109B may be provided on an upper surface of the first protective film 107 .

[0217] When the sub-pixel includes a red sub-pixel R_SP, a green sub-pixel G_SP, a blue sub-pixel B_SP, and a white sub-pixel W_SP, first to third color filters 109R, 109G, and 109B divided from the color filter layer are provided in the remaining sub-pixels R_SP, G_SP, and B_SP except the white sub-pixel W_SP, and transmit the corresponding wavelengths of the white light emitted via the first electrode 110. In addition, the second protective film 108 is provided on the lower surface of the first electrode 110 to cover the first to third color filters 109R, 109G, and 109B. The first electrode 110 is formed on the surface of the second protective film 108 except the contact hole CT.

[0218] Here, the white organic light emitting diode OLED may include a first electrode 110 as a transparent electrode, a second electrode 120 as a reflective electrode arranged opposite to the first electrode 110, and Fig. 9AAs shown, a two-stack structure including a blue light-emitting stack and a long wavelength (R / G or YG) light-emitting stack, or as Fig. 9B The three-stack structure shown includes a first blue light-emitting stack, a long-wavelength light-emitting stack, and a second blue light-emitting stack.

[0219] Here, undescribed reference numeral 119 denotes a bank, and BH between the banks 119 denotes a bank hole. Light is emitted through an opening area in the bank hole BH, and the bank hole BH defines an emission area of ​​each sub-pixel.

[0220] For example, Fig.18 The display device shown Fig.18 It may be a bottom emission type display device.

[0221] However, the display device according to the present invention is not limited thereto and may be Fig.18 In the structure of the display device shown, a color filter layer is positioned on the upper surface of the second electrode 120, the first electrode 110 is formed of a reflective metal, and the second electrode 120 is formed of a transparent metal or a transflective metal to realize a top emission type display device.

[0222] Alternatively, in Fig.18 In a display device, the color filter layer can be omitted. Fig.18 In the display device, both the first electrode 110 and the second electrode 120 can be transparent electrodes to realize a transparent light-emitting device.

[0223] Hereinafter, in a fourth experimental example to which the first embodiment of the present invention is applied, and in comparison with first to seventh experimental examples in which the structures of the light emitting layers are different, internal quantum efficiency and emission spectrum characteristics are discussed.

[0224] FIG. 19A to FIG. 19D are cross-sectional views according to the fourth to seventh experimental examples.

[0225] like Fig.19A As shown, the fourth experimental example of the present invention has Figure 5 The same structure as the first embodiment. In addition, except for the light-emitting layer, FIG. 19B to FIG. 19D The fifth to seventh experimental examples have the same structure as the first embodiment of FIG. 15 .

[0226] refer to Fig.19A , describes an organic light-emitting device according to a fourth experimental example of the present invention.

[0227] like Fig.19A As shown, the fourth experimental example of the present invention can be formed in the following order.

[0228] On a substrate (not shown), the first electrode 110 is formed to a thickness of 50 nm by depositing indium tin oxide (ITO).

[0229] On the first electrode 110, a hole injection layer 111 with a thickness of 15 nm is formed of a phthalocyanine compound or a starburst amine derivative, which includes a p-type dopant for promoting hole injection. For example, the p-type dopant may be an organic compound such as HAT-CN, or may include a metal or a metal oxide.

[0230] On the hole injection layer 111, a hole transport layer 112 is formed with a thickness of 25 nm from an amine derivative such as NPB or NPD.

[0231] On the hole transport layer 112, an electron blocking layer 113 is formed with a thickness of 10 nm from an electron blocking material such as TAPC to block electrons or excitons from the light emitting layer.

[0232] On the electron blocking layer 113, a light-emitting layer 130a with a thickness of 30 nm is formed, which includes a p-type host Host1 with high hole transport properties and an n-type host Host2 with high electron transport properties in the same ratio of 1:1, and 0.5 wt% of a fluorescent dopant capable of achieving TADF with a small ΔEst and 10 wt% of a phosphorescent dopant capable of transferring energy to the fluorescent dopant.

[0233] On the light emitting layer 130a, a hole blocking layer 114 is formed of a material such as B3PYMPM or phenanthroline to a thickness of 10 nm.

[0234] On the hole blocking layer 114, the electron transport layer 115 is formed of an anthracene compound with a thickness of 25 nm, and then the electron injection layer 116 is formed of an anthracene compound and an inorganic material such as Li, LiF, and MgF or an inorganic compound with a thickness of 1 nm.

[0235] On the electron injection layer 116 , the second electrode 120 is formed of Al or an Al alloy.

[0236] The electron blocking layer 113 and the hole blocking layer 114 respectively have materials that confine excitons within the light emitting layer 130a. That is, each singlet excited state and each triplet excited state of the materials of the electron blocking layer 113 and the hole blocking layer 114 are higher than or equal to the singlet excited state and triplet excited state of the p-type host Host1 and the n-type host Host2, respectively.

[0237] The light emitting layers 130 g , 130 h , and 130 i of the fifth to seventh experimental examples are different from the light emitting layer 130 a .

[0238] The phosphorescent dopant PD of the light-emitting layer according to the fourth experimental example uses, for example, a metal complex including iridium (Ir), platinum (Pt), osmium (Os), gold (Au), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), palladium (Pd) or thulium (Tm) as a core.

[0239] Also, the fluorescent dopant FD may be a boron-based compound, and in the experimental example, the above-described Chemical Formula 6 is used.

[0240] The light emitting layer 130g having a thickness of 30 nm according to the fifth experimental example was formed to include a p-type host Host1 having a high hole transport characteristic and an n-type host Host2 having a high electron transport characteristic in the same ratio of 1:1, and 10 wt % of a single phosphorescent dopant as a dopant.

[0241] The light emitting layer 130h having a thickness of 30 nm according to the sixth experimental example is formed to include a p-type host Host1 having a high hole transport characteristic and an n-type host Host2 having a high electron transport characteristic at the same ratio of 1:1, and 0.5 wt% of a single fluorescent dopant as a dopant. The fluorescent dopant FD in the sixth experimental example has the same characteristics as the fluorescent dopant in the fourth experimental example, and is formed of a boron-based compound capable of realizing TADF as in the above Chemical Formula 6.

[0242] The light emitting layer 130i having a thickness of 30 nm according to the seventh experimental example was formed to include a p-type host Host1 having high hole transport characteristics and an n-type host Host2 having high electron transport characteristics in the same ratio of 1:1, and 10 wt % of a phosphorescent dopant and 0.5 wt % of a fluorescent dopant without TADF as dopants.

[0243] [Table 1]

[0244]

[0245] As shown in Table 1, compared with the fifth experimental example using a single phosphorescent dopant or the sixth experimental example using a single fluorescent dopant, in the fourth experimental example (A) of the first embodiment of the present invention, the main Energy transfer, therefore, can improve the lifetime of the device due to the reduction of the duration of the triplet state, and improve efficiency by using the excess triplet state generated by the fluorescent dopant in the TADF emission. That is, the CIEy color coordinates of the fourth experimental example (A) are almost similar to the case of using the fluorescent dopant of the sixth experimental example (H), and the efficiency is similar to the case of using the phosphorescent dopant of the fifth experimental example (G). As a result, the fourth experimental example can achieve excellent color purity of the fluorescent dopant and excellent efficiency of the phosphorescent dopant.

[0246] In particular, considering the blue index value expressed as efficiency / CIEy, the fourth experimental example (A) is the best, and the lifetime determined as 90% brightness compared to the initial state is more than twice that of the fifth experimental example (G), and almost three times that of the sixth experimental example (H). This means that there is a significant improvement in lifetime. On the other hand, compared with the fourth experimental example (A), the seventh experimental example (I) uses a fluorescent dopant without TADF. In the seventh experimental example (I), because the fluorescent dopant without TADF represents a wide FWHM, the blue efficiency decreases due to the increase in the CIEy value. In addition, the transition from the phosphorescent dopant to the fluorescent dopant is significantly improved. The energy transfer reduces the lifetime of triplet excitons, thereby increasing the device lifetime, while the triplet excitons of the fluorescent dopant are non-luminescent and disappear, thereby reducing the efficiency compared to the pure phosphorescent device of the fifth experimental example G. Fig. 20 is a graph showing external quantum efficiencies according to fourth to sixth experimental examples, Fig.21 is a graph showing EL characteristics of the fourth to sixth experimental examples.

[0247] like Fig. 20 As shown, when comparing the external quantum efficiency (EQE) characteristics in the fourth to sixth experimental examples (A, G, H), the change in the external quantum efficiency (EQE) characteristics according to the change in current density is the largest in the sixth experimental example using a fluorescent dopant. Relatively speaking, the fourth and fifth experimental examples (A and G) show a gentle change in the change in the external quantum efficiency (EQE) characteristics. That is, it can be seen that in the fourth experimental example (A) among the experimental examples, the external quantum efficiency is optimal and the characteristics of the color coordinates are not reversed.

[0248] like Fig.21 As shown, the EL spectra of the fourth to sixth experimental examples (A, G, H) show different emission characteristics even though a single blue light emitting layer is provided.

[0249] In the fifth experimental example (G), only a phosphorescent dopant is provided as a dopant. In this case, the phosphorescent blue dopant has a vibration peak characteristic, and the main peak and the secondary peak appear at the same time. Therefore, the spectral wavelength range is wide and the color purity is poor. In addition, partial light emission occurs in the green wavelength.

[0250] On the other hand, in the fourth experimental example (A) and the sixth experimental example (H), high color purity can be exhibited by using a fluorescent dopant having such a narrow spectrum. Here, the fourth experimental example (A) and the sixth experimental example (H) have almost the same spectral shape. Similarly, this means that most of the energy of the phosphorescent dopant inside the light-emitting layer is transferred to the fluorescent dopant, so fluorescent emission occurs in the fourth experimental example (A).

[0251] As described above, the fourth experimental example (A) to which the first embodiment of the present invention is applied is excellent in high color purity, long life, and high efficiency.

[0252] In addition, for the fourth experimental example (A) and the fifth experimental example (G) of the first embodiment of the present invention, the decay time of the exciton used for luminescence was compared. The decay time of the fourth experimental example (A) was 0.7 μs, and the decay time of the fifth experimental example (G) was 4.2 μs. The fourth experimental example (A) including a fluorescent dopant and a phosphorescent dopant capable of realizing TADF as dopants has a faster time of more than 6 times than the fifth experimental example (G) including only a phosphorescent dopant. Therefore, the fourth experimental example (A) has the possibility of transferring the triplet excited state of the phosphorescent dopant to the singlet excited state of the fluorescent dopant in a short time. And, it is expected that the fourth experimental example (A) solves the problem that the triplet excitons of the phosphorescent dopant remain in the light-emitting layer and the retained triplet excitons shorten the life of the light-emitting layer. As described above, the organic light-emitting device of the present invention and the display device using the organic light-emitting device are characterized in that the light-emitting layer includes a phosphorescent dopant and a fluorescent dopant having the same or different colors, so that the excitons formed by the phosphorescent dopant are completely or almost transferred to the fluorescent dopant to induce monochromatic fluorescence.

[0253] The organic light-emitting devices according to the first to fourth embodiments have a common feature, namely, using a first dopant and a second dopant with different characteristics, and selecting a second dopant capable of fluorescent emission using TADF. Therefore, the organic light-emitting devices according to the first to fourth embodiments of the present invention have a common effect of emitting monochromatic light.

[0254] As described above, the organic light-emitting device according to the present invention may include a light-emitting layer disposed between a first electrode and a second electrode arranged opposite to each other. The light-emitting layer may include at least one host, a first dopant to which energy is transferred from the host, and a second dopant to which energy is transferred from the host and the first dopant. Thermally activated delayed fluorescence (TADF) may be generated by anti-intersystem crossing transfer from a triplet excited state to a singlet excited state in the second dopant.

[0255] The first dopant may be a phosphorescent dopant, and the second dopant may be a fluorescent dopant. Also, in the light emitting layer, the main emission may be generated from the second dopant.

[0256] When energy is emitted from the singlet excited state of the second dopant into the ground state, TADF and fluorescence emission can be generated together.

[0257] An absorption spectrum of the second dopant and a PL (photoluminescence) spectrum of the first dopant may overlap by at least 15 nm or more, and a maximum wavelength of the absorption spectrum of the second dopant may be longer than a minimum wavelength of the PL spectrum of the first dopant.

[0258] By overlapping the absorption spectrum of the second dopant with the PL spectrum of the first dopant, energy can be transferred from the first dopant to the second dopant.

[0259] An emission peak wavelength of a PL spectrum of the first dopant may be located between a peak wavelength of an absorption spectrum of the second dopant and an emission peak wavelength of a PL spectrum of the second dopant.

[0260] An emission peak wavelength of a PL spectrum of the first dopant may have a difference within 30 nm from an emission peak wavelength of a PL spectrum of the second dopant.

[0261] The second dopant may have a singlet energy level that is different from a triplet energy level of the second dopant by 0.4 eV or less.

[0262] In the energy transfer from the first dopant to the second dopant, The energy transfer (FET) can be greater than the Dexter energy transfer (DET).

[0263] The reverse intersystem crossing (RISC) transfer from the triplet excited state to the singlet excited state in the second dopant may be proportional to the Dexter energy transfer from the host and the first dopant to the second dopant and the energy of the triplet excitons generated in the second dopant.

[0264] The triplet energy state of the host may be higher than or equal to the triplet energy state of the first dopant, and the triplet energy state of the first dopant may be greater than or equal to the triplet energy state of the second dopant.

[0265] The triplet energy state of the first dopant may be higher than or equal to the singlet energy state of the second dopant.

[0266] A first difference between the singlet energy state and the triplet energy state of the second dopant may be smaller than a second difference between the singlet energy state and the triplet energy state of the host and a third difference between the singlet energy state and the triplet energy state of the first dopant, respectively.

[0267] The organic light-emitting device may further include at least one common layer between the first electrode and the light-emitting layer and between the second electrode and the light-emitting layer. The at least one common layer contacting the light-emitting layer may include a material whose triplet energy level is higher than or equal to the triplet energy level of the at least one host.

[0268] The light emitting layer may include 50 wt % or more of at least one host, 1 wt % to 40 wt % of a first dopant, and 0.01 wt % to 10 wt % of a second dopant.

[0269] The at least one host may include a plurality of hosts having different carrier transport properties.

[0270] In addition, in order to achieve the same purpose, the display device according to the present invention may include: a substrate including a plurality of sub-pixels; a thin film transistor in each sub-pixel; and an organic light-emitting device connected to the thin film transistor in each pixel. The organic light-emitting device may include a first electrode and a second electrode arranged relative to each other, and at least one light-emitting layer located between the first electrode and the second electrode. The at least one light-emitting layer may include at least one host, a first dopant to which energy is transferred from the host, and a second dopant to which energy is transferred from the host and the first dopant. TADF (thermally activated delayed fluorescence) is generated by reverse intersystem crossing (RISC) transfer from a triplet excited state to a singlet excited state in the second dopant.

[0271] The organic light emitting device may include a plurality of stacks separated by charge generation layers therebetween, and each stack includes at least one common layer. The at least one light emitting layer may be located in at least one stack of the plurality of stacks.

[0272] The light-emitting layer in at least one stack may include at least one host, a first dopant to which energy is transferred from the host, and a second dopant to which energy is transferred from the host and the first dopant. Thermally activated delayed fluorescence (TADF) may be generated by anti-intersystem crossing transfer from a triplet excited state to a singlet excited state in the second dopant.

[0273] The first dopant may be a phosphorescent dopant, the second dopant may be a fluorescent dopant, and, in the light emitting layer, main emission may be generated from the second dopant.

[0274] When energy is emitted from the singlet excited state of the second dopant into the ground state, TADF and fluorescence emission can be generated together.

[0275] An absorption spectrum of the second dopant and a PL (photoluminescence) spectrum of the first dopant may overlap by at least 15 nm or more, and a maximum wavelength of the absorption spectrum of the second dopant may be longer than a minimum wavelength of the PL spectrum of the first dopant.

[0276] In a display device, a plurality of stacks may include: a blue light-emitting stack including at least one blue light-emitting layer including a main body, a first dopant and a second dopant; and a long-wavelength light-emitting stack arranged opposite to the blue light-emitting stack, with a charge generation layer interposed between the blue light-emitting stack and the long-wavelength light-emitting stack, the long-wavelength light-emitting stack emitting light with a wavelength longer than that of the blue light-emitting stack.

[0277] The display device may further include a plurality of color filter layers under the first electrode or over the second electrode to emit light of different colors in corresponding sub-pixels.

[0278] The long wavelength light emitting stack may include a red light emitting layer and a green light emitting layer, and at least one of the red light emitting layer and the green light emitting layer may include a host and a plurality of dopants. Energy may be transferred from the host and the other dopants except one dopant to the one dopant.

[0279] The plurality of stacks may include a plurality of blue light emitting stacks.

[0280] As apparent from the above description, the organic light emitting device according to the present invention and the display device using the same have the following effects.

[0281] First, different kinds of dopants, namely phosphorescent dopants and fluorescent dopants, are used, energy transfer is concentrated on the fluorescent dopant, and almost all light emission is due to excitation in the singlet energy level of the fluorescent dopant through the fluorescence and delayed fluorescence of the fluorescent dopant itself, thereby being able to improve the luminous efficiency of the monochromatic light. Therefore, even when different kinds of dopants are used, the emission of monochromatic light can be achieved and the color purity of the organic light-emitting device can be improved. Energy can be concentrated from the triplet energy level of the fluorescent dopant to the singlet energy level of the fluorescent dopant through reverse intersystem crossing (RISC) transfer.

[0282] Second, fluorescent dopants can be synthesized through Dexter energy transfer (DET) and The energy transfer (FET) mechanism receives energy from the phosphorescent dopant and the host, and fluorescence of the fluorescent dopant itself caused by the transition of excitons from the singlet energy level to the ground state occurs in the fluorescent dopant, as well as thermally activated delayed fluorescence (TADF) caused by anti-system crossing (RISC) transfer due to the small energy level difference ΔEst between the triplet excited state and the singlet excited state, thereby being able to improve the internal quantum efficiency of the excitons.

[0283] Third, when a phosphorescent dopant is used as a dopant configured to transmit energy and a fluorescent dopant is used as a dopant configured to receive energy, energy transfer between different types of dopants is achieved through Dexter energy transfer (DET), and thus the triplet energy level of the phosphorescent dopant does not need to be higher than the singlet energy level of the fluorescent dopant, so that energy can be transferred from the phosphorescent dopant having a lower triplet energy level to the fluorescent dopant, where thermally activated delayed fluorescence (TADF) can occur. Therefore, the phosphorescent dopant is not limited to a high triplet energy level, and thus a phosphorescent dopant structure having stability in its material can be ensured.

[0284] Fourth, in the present invention, due to the small Stokes shift between the peak wavelength of the PL spectrum and the peak wavelength of the absorption spectrum in the fluorescent dopant, the spectral overlap between the absorption spectrum of the fluorescent dopant and the PL spectrum of the phosphorescent dopant can be increased for energy transfer. Therefore, the triplet state generated in the phosphorescent dopant is quickly transferred to the fluorescent dopant, and therefore, the duration of the triplet state can be shortened, which can increase the life of the device.

[0285] It is obvious to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the present invention. Therefore, the present invention is intended to cover modifications and variations of the present invention as long as they fall within the scope of the appended claims and their equivalents.

Claims

1. An organic light-emitting device, comprising: a first electrode and a second electrode arranged opposite to each other; as well as a light-emitting layer located on the first electrode, wherein the light-emitting layer is a single layer, wherein the light-emitting layer comprises at least one host, a first dopant having a phosphorescent dopant, and a second dopant having a fluorescent dopant, wherein the main emission in the light emitting layer is generated from the second dopant, and The PL spectrum of the first dopant is located between the peak wavelength of the absorption spectrum of the second dopant and the emission peak wavelength of the PL spectrum of the second dopant.

2. The organic light-emitting device according to claim 1, wherein: An absorption spectrum of the second dopant and a photoluminescence (PL) spectrum of the first dopant overlap by at least 15 nm or more.

3. The organic light-emitting device according to claim 1, wherein: A maximum wavelength of an absorption spectrum of the second dopant is longer than a minimum wavelength of a PL spectrum of the first dopant.

4. The organic light-emitting device according to claim 1, wherein: An emission peak of a PL spectrum of the first dopant and an emission peak of a PL spectrum of the second dopant have a difference within 30 nm.

5. The organic light-emitting device according to claim 1, wherein: The second dopant has a singlet energy level that is different from a triplet energy level of the second dopant by 0.4 eV or less.

6. The organic light emitting device according to claim 1, wherein: The triplet energy state of the host is higher than or equal to the triplet energy state of the first dopant; and A triplet energy state of the first dopant is higher than or equal to a triplet energy state of the second dopant.

7. The organic light-emitting device according to claim 6, wherein: A triplet energy state of the first dopant is higher than or equal to a singlet energy state of the second dopant.

8. The organic light-emitting device according to claim 6, wherein: A first difference between the singlet energy state and the triplet energy state of the second dopant is smaller than a second difference between the singlet energy state and the triplet energy state of the host and a third difference between the singlet energy state and the triplet energy state of the first dopant, respectively.

9. The organic light-emitting device according to claim 1, wherein: The organic light-emitting device further includes at least one common layer between the first electrode and the light-emitting layer and between the second electrode and the light-emitting layer. The at least one common layer in contact with the light-emitting layer includes a material whose triplet energy level is higher than or equal to the triplet energy level of the at least one host.

10. The organic light-emitting device according to claim 1, wherein: The light-emitting layer comprises: 50 wt % or more of the at least one host; 1 wt % to 40 wt % of the first dopant; and 0.01 wt % to 10 wt % of the second dopant.

11. The organic light-emitting device according to claim 1, wherein: The host includes a plurality of hosts having different carrier transport properties.

12. A display device, comprising: a substrate having a plurality of sub-pixels; a thin film transistor in each of the sub-pixels; and an organic light emitting device connected to the thin film transistor in each of the sub-pixels, The organic light-emitting device includes a first electrode and a second electrode arranged opposite to each other, and at least one light-emitting layer located between the first electrode and the second electrode. Wherein, the at least one light-emitting layer as a single layer comprises: At least one subject; a first dopant comprising a phosphorescent dopant; and a second dopant comprising a fluorescent dopant, and wherein the main emission of the light-emitting layer is generated from the second dopant, and The photoluminescence (PL) spectrum of the first dopant is between the peak wavelength of the absorption spectrum of the second dopant and the emission peak wavelength of the PL spectrum of the second dopant.

13. The display device according to claim 12, wherein: The organic light emitting device includes a plurality of stacks separated by charge generating layers therebetween, Each of the stacks comprises at least one common layer, and The at least one light emitting layer is located in at least one stack among the plurality of stacks.

14. The display device according to claim 12, wherein: The plurality of stacks include at least one of the first blue light emitting stacks.

15. The display device according to claim 12, wherein: The display device further includes a plurality of color filter layers located under the first electrode or on the second electrode to emit light of different colors in the plurality of sub-pixels.

16. A display device, comprising: A first electrode located on the sub-pixel of the substrate; a first light-emitting layer on the first electrode, the first light-emitting layer being a single layer emitting a first color; as well as a second electrode located on the first light-emitting layer, Wherein, the first light-emitting layer includes a first host, a first phosphorescent dopant and a first fluorescent dopant, wherein the first phosphorescent dopant and the first fluorescent dopant are materials for the first color, and Wherein, the main emission of the first light-emitting layer is generated from the first fluorescent dopant.

17. The display device according to claim 16, wherein: The absorption spectrum of the first fluorescent dopant and the photoluminescence (PL) spectrum of the first phosphorescent dopant overlap by at least 15 nm or more.

18. The display device according to claim 16, wherein: The display device further includes: a second light-emitting layer between the first light-emitting layer and the second electrode, the second light-emitting layer being a single layer emitting a second color different from the first color; a third light-emitting layer between the second light-emitting layer and the second electrode, the third light-emitting layer being a single layer emitting a third color different from the first color and the second color; and a charge generation layer located between the first light-emitting layer and the second light-emitting layer, The wavelengths of the second color and the third color are longer than that of the first color.

19. The display device according to claim 18, wherein: The first color is blue.

20. The display device according to claim 18, wherein: At least one of the second light emitting layer and the third light emitting layer includes a second phosphorescent dopant and a second fluorescent dopant, the second phosphorescent dopant and the second fluorescent dopant are materials for the same color, and main emission is generated from the second fluorescent dopant.

21. The display device according to claim 16, wherein: The first light emitting layer further includes a second host having a carrier transport property different from that of the first host.

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