Light emitting device and display apparatus using the same

Abstract

Disclosed are a light-emitting device and a display device including the same. A light-emitting layer is formed to have a double-layer structure, a triplet energy level of a dopant of a first light-emitting layer adjacent to a hole transport layer is greater than a triplet energy level of a first host in the first light-emitting layer, and the triplet energy level of the first host is greater than a triplet energy level of a second host of a second light-emitting layer, whereby triplet excitons generated in the first light-emitting layer are recycled to the second light-emitting layer for reuse for light emission.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0190049, filed on December 31, 2020, the contents of which are incorporated herein by reference as fully set forth herein. Technical Field

[0003] The present invention relates to light-emitting devices and display devices using the same, and more particularly to light-emitting devices configured such that the structure of the light-emitting layer is altered so that excitons generated in the light-emitting layer are recycled for reuse in light emission, thereby preventing the accumulation of excitons at the interface between adjacent components, thus improving the efficiency and lifespan of the light-emitting device. Background Technology

[0004] Recently, organic light-emitting display devices have been considered competitive applications because they do not require a separate light source and can achieve compact device designs and vibrant color displays.

[0005] Meanwhile, the organic light-emitting display device includes multiple sub-pixels, each of which includes an organic light-emitting device to emit light without a separate light source.

[0006] In recent years, research has been conducted on tandem devices consisting of an organic layer and a light-emitting layer without a deposition mask in organic light-emitting devices.

[0007] In light-emitting devices, a host exhibiting high electron transport capability in the emissive layer pushes electrons toward the hole transport layer, thereby creating a thin recombination region of holes and electrons at the interface between the electron transport layer and the distant emissive layer. In this situation, electrons accumulate at one interface of the emissive layer, potentially causing a sudden degradation in the lifetime of the hole transport layer or the adjacent electron blocking layer. Therefore, it is necessary to address this problem. Summary of the Invention

[0008] Therefore, the present invention provides a light-emitting device and a display device using the same, which substantially eliminates one or more problems caused by the limitations and disadvantages of the prior art.

[0009] A light-emitting device according to one aspect of this disclosure includes: an electron blocking layer, a first light-emitting layer, a second light-emitting layer, and an electron transport layer sequentially disposed between a first electrode and a second electrode, wherein the first electrode and the second electrode are opposite to each other, wherein the first light-emitting layer includes a first body and a first blue dopant, the second light-emitting layer includes a second body and a second blue dopant, the triplet energy level of the first body is greater than the triplet energy level of the second body, and the triplet energy level of the first blue dopant is greater than the triplet energy level of the first body.

[0010] According to another aspect of this disclosure, the display device includes the aforementioned light-emitting device.

[0011] A display device according to another aspect of this disclosure includes: a plurality of sub-pixels; a thin-film transistor disposed for each sub-pixel; and a blue stack connected to the thin-film transistor at each sub-pixel, the blue stack including a hole transport layer, an electron blocking layer, a first light-emitting layer, a second light-emitting layer and an electron transport layer disposed sequentially between a first electrode and a second electrode so as to be adjacent to each other, the first electrode and the second electrode being opposite to each other, wherein the first light-emitting layer includes a first body and a first blue dopant, the second light-emitting layer includes a second body and a second blue dopant, the triplet energy level of the first body is greater than the triplet energy level of the second body, and the triplet energy level of the first blue dopant is greater than the triplet energy level of the first body.

[0012] Further advantages, objects, and features of the invention will be set forth in part in the description which follows, and will in part become apparent to those skilled in the art upon review of the following, or may be learned from practice of the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures particularly pointed out in the written description, its claims, and the accompanying drawings.

[0013] To achieve these and other advantages, and according to the purposes of the invention, as embodied and broadly described herein, the light-emitting device and display apparatus are configured such that the light-emitting layer is formed having a bilayer structure, wherein the triplet energy level of the dopant in the first emissive layer adjacent to the hole transport layer is greater than the triplet energy level of the first host in the first emissive layer, and the triplet energy level of the first host is greater than the triplet energy level of the second host in the second emissive layer, thereby recycling triplet excitons generated in the first emissive layer to the second emissive layer for reuse in light emission.

[0014] It should be understood that the above general description of the invention and the following detailed description are exemplary and illustrative, and are intended to provide further explanation of the claimed invention. Attached Figure Description

[0015] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0016] Figure 1 This is a cross-sectional view showing the light-emitting device according to the present invention.

[0017] Figure 2 yes Figure 1 The energy band diagram of the light-emitting unit and the layer in its vicinity are shown in the figure.

[0018] Figure 3 This is a view showing the relationship between the singlet and triplet energy levels of each material in the light-emitting unit of the light-emitting device according to a first embodiment of the present invention.

[0019] Figure 4 This is a view showing the relationship between the singlet and triplet energy levels of each material in the light-emitting unit of the light-emitting device according to a second embodiment of the present invention.

[0020] Figure 5A and Figure 5B This is a cross-sectional view illustrating a white organic light-emitting device according to another embodiment of the present invention.

[0021] Figure 6 This is a cross-sectional view showing a display device including a white organic light-emitting device according to the present invention. Detailed Implementation

[0022] In the following description, embodiments will be described with reference to the accompanying drawings. In the drawings, even if the same or similar elements are depicted in different figures, they are indicated by the same reference numerals. In the following description, detailed descriptions of known functions and configurations incorporated herein may be omitted where such descriptions could make the subject matter of this disclosure considerably unclear. Furthermore, the names of components used in the following description have been chosen for ease of preparation of the specification and may differ from the names of components in the actual product.

[0023] In the accompanying drawings, which illustrate exemplary embodiments of the invention, shapes, dimensions, ratios, angles, and numbers are given by way of example only and are therefore not intended to limit the scope of the disclosure. Throughout the specification, the same reference numerals designate the same constituent elements. Additionally, in the following description of the invention, detailed descriptions of known functions and configurations incorporated herein will be omitted where such descriptions might make the subject matter of the invention considerably unclear. Unless used with the term "only," the terms "comprising," "including," and / or "having" as used herein do not exclude the presence or addition of other elements. Unless the context clearly indicates otherwise, the singular form also implies the inclusion of the plural form.

[0024] In the explanation of the constituent elements included in the various embodiments of the present invention, even without an explicit description thereof, the constituent elements are interpreted as including a range of error.

[0025] In the description of various embodiments of the present invention, when describing positional relationships, for example, when using terms such as "above," "over," "below," "beside," etc. to describe the positional relationship between two components, one or more other components may be located between the two components unless the terms "directly" or "closely" are used with them.

[0026] In the description of various embodiments of the present invention, when describing temporal relationships, for example, when using terms such as "after", "following", "next", "before" to describe the temporal relationship between two actions, the actions may not occur sequentially unless the terms "immediately" or "directly" are used with them.

[0027] In the description of various embodiments of the present invention, although terms such as "first" and "second" may be used to describe various elements, these terms are only used to distinguish between identical or similar elements. Therefore, in this specification, unless otherwise stated, within the scope of the present invention, an element modified by "first" may be the same as an element modified by "second".

[0028] Various features of the various embodiments of the present invention can be coupled and combined with each other, either partially or entirely, and various technical connections and operating methods between these features are possible. These various embodiments can be performed independently of each other or can be performed in conjunction with each other.

[0029] In this specification, the “lowest unoccupied molecular orbital (LUMO) level” and “highest occupied molecular orbital (HOMO) level” of any layer refer to the LUMO and HOMO levels of the material, such as the host material, that constitute the largest weight percentage of the corresponding layer, unless they are referred to as the LUMO and HOMO levels of the dopant material doped in the corresponding layer.

[0030] In this specification, the "HOMO level" is obtained by irradiating a surface with UV light and measuring the energy required to release electrons from the surface. That is, the emitted photoelectrons are measured using an electrometer, and the threshold of photoelectron emission is inferred from the energy curve of the emitted photoelectrons relative to the irradiated photons, in order to measure the HOMO level.

[0031] Furthermore, the HOMO and LUMO energy levels compared in this specification are based on vacuum energy levels and are negative values. Therefore, one being lower than the other means that the one is based on vacuum energy levels and is lower than the other, and the lower one has a larger absolute value.

[0032] The band gap Eg is obtained by: measuring the UV absorption spectrum; drawing the tangent at the rising edge of the long wavelength with the absorption spectrum; and converting the wavelength, which is the intersection with the horizontal axis, into an energy value (E = hv / λ = h*C / λ, where h is Planck's constant, C is the speed of light, and λ is the wavelength of light).

[0033] In this specification, the term "doped" means the addition of a material having physical properties different from those of the material comprising the maximum weight percentage of the corresponding layer (e.g., N-type and P-type, or organic and inorganic materials) to the material comprising the maximum weight percentage in an amount corresponding to less than 30% by weight. In other words, a "doped" layer is a layer in which the host material and dopant material of any layer are distinguishable from each other by weight percentage. Furthermore, the term "undoped" refers to all cases other than those corresponding to the term "doped." For example, a layer is "undoped" when any layer is formed from a single material or from a mixture of materials having the same or similar properties. For example, a layer is "undoped" when at least one of the constituent materials of any layer is P-type and not all other constituent materials of the layer are N-type. For example, a layer is "undoped" when at least one of the constituent materials of any layer is an organic material and not all other constituent materials of the layer are inorganic. For example, when all the constituent materials of any layer are organic materials, at least one of the constituent materials is N-type, at least another constituent material is P-type, and the weight percentage of N-type material is less than 30% or the weight percentage of P-type material is less than 30%, the layer is a "doped" layer.

[0034] Meanwhile, in this specification, the electroluminescence (EL) spectrum is calculated by multiplying (1) the photoluminescence (PL) spectrum and (2) the output coupled emission spectrum curve, which represents the unique characteristics of the light-emitting material, such as dopants or host materials, contained in the organic light-emitting layer, and the output coupled emission spectrum curve is determined based on the structure and optical properties of the organic light-emitting device, including the thickness of organic layers such as electron transport layers.

[0035] Figure 1 This is a cross-sectional view showing the light-emitting device according to the present invention, and Figure 2 yes Figure 1 The energy band diagram of the light-emitting unit and its surrounding layers are shown in the figure.

[0036] like Figure 1 and Figure 2 As shown, the light-emitting device according to an embodiment of the present invention includes an electron blocking layer (EBL) 124, a first light-emitting layer 131, a second light-emitting layer 132, and an electron transport layer (ETL) 140, which are sequentially disposed between a first electrode (e.g., an anode) 110 and a second electrode (e.g., a cathode) 170 opposite to each other. The first light-emitting layer 131 includes a first body BH1 and a first blue dopant BD1. The second light-emitting layer 132 includes a second body BH2 and a second blue dopant BD2. Hereinafter, the first light-emitting layer 131 may also be referred to as EML1, and the second light-emitting layer 132 may also be referred to as EML2.

[0037] The first light-emitting layer 131 and the second light-emitting layer 132 together emit blue light. Therefore, the first light-emitting layer and the second light-emitting layer are usually referred to as light-emitting unit 130.

[0038] Reference Figure 2 The energy band diagram shows that the light-emitting unit 130 is a set of light-emitting layers configured to emit blue light. The first light-emitting layer 131 and the second light-emitting layer 132 include a first body BH1 and a second body BH2 made of different materials, respectively.

[0039] Since the first host BH1 of the first light-emitting layer 131 has better hole transport characteristics than the second host BH2 of the second light-emitting layer 132, the first host BH1 prevents electrons from accumulating at the interface IF1 of the electron blocking layer 124 located in front of the first light-emitting layer 131, thereby preventing the degradation of the electron blocking layer 124 adjacent to the light-emitting unit 130. Therefore, the lifetime of the light-emitting device can be increased.

[0040] The light-emitting unit 130 is divided into two or more layers, based at least on the host material. Excitons are recycled to one side adjacent to the electron transport layer 140, and the second light-emitting layer 132 adjacent to the electron transport layer 140 uses the recycled excitons for light emission. For this purpose, the triplet energy levels T1(BH1) and T1(BD1) of the first host BH1 and the first blue dopant BD1 constituting the first light-emitting layer 131 are both higher than the triplet energy level T1(BH2) of the second host BH2 of the second light-emitting layer 132.

[0041] Furthermore, triplet-triplet fusion (TTF) is possible in the second host BH2 of the second luminescent layer 132. In the luminescent unit 130, triplet excitons transferred to the second luminescent layer 132 are fused, thereby achieving fluorescence emission as the main emission.

[0042] When multiple light-emitting layers are used in the light-emitting unit 130, the efficiency may decrease due to the increase in hole transport. However, by transferring triplet excitons in the first light-emitting layer 131 to the second light-emitting layer 132, the triplet excitons can be reused for light emission, thereby potentially improving the efficiency.

[0043] The second light-emitting layer 132 may include a second host BH2 with good electron transport properties and a second blue dopant BD2 exhibiting hole trapping properties. In this case, the electron transport layer 140, which increases electron transport, mainly generates a recombination region of holes and electrons at the interface IF2 between the first light-emitting layer 131 and the second light-emitting layer 132, thereby preventing excitons from accumulating at the interface of the electron blocking layer 124 and thus increasing the lifetime of the light-emitting device.

[0044] According to the light-emitting device of the present invention, a second light-emitting layer 132 serving as the main emitter is disposed in the light-emitting unit 130, and a first light-emitting layer 131 exhibiting good hole transport characteristics and recycling excitons for reuse is disposed between the second light-emitting layer 132 and the electron blocking layer 124.

[0045] The first luminescent layer 131, exhibiting high hole transport characteristics, suppresses the degradation of the electron blocking layer 124. For example... Figure 2 As shown, the triplet level T1(BH1) of the first host BH1 is designed to be higher than the triplet level T1(BH2) of the second host BH2, thereby maintaining high efficiency through the reuse of triplet excitons.

[0046] Meanwhile, in the above structure, the first light-emitting layer 131 of the light-emitting unit 130 is adjacent to the electron blocking layer 124.

[0047] However, the present invention is not limited thereto. The light-emitting layer 131 of the light-emitting unit 130 may be directly adjacent to the hole transport layer (HTL) 122 without an electron blocking layer 124. In this case, the hole transport layer 122 may be composed of multiple layers.

[0048] Hole injection layer (HIL) 120 and hole transport layer 122 may also be disposed between the first electrode 110 and the electron blocking layer 124, thereby allowing for the regulation of hole injection and transport from the first electrode (anode) 110.

[0049] The electron transport layer (ETL) 140 and the electron injection layer (EIL) 150 can also be disposed between the light-emitting unit 130 and the second electrode (cathode) 170.

[0050] For example, the emitting unit BU, the hole transport layer 122 and the electron blocking layer 124 disposed below the light-emitting unit 130, and the electron transport layer 140 disposed above the light-emitting unit 130 can constitute a blue stack BU. For example, when multiple stacks are disposed between the first electrode 110 and the second electrode 170 in a state divided by the charge generation layer, the blue stack BU can be set as at least one of the stacks.

[0051] Meanwhile, all components from the first electrode 110 to the second electrode 170 can form an organic light-emitting device (OLED).

[0052] At the same time, Figure 2 In the diagram, arrows indicate the direction of light emission. As an example, downward light emission is shown. The first electrode 110 is a transparent electrode, and the second electrode 170 is a reflective electrode. However, the invention is not limited thereto. Upward light emission is also possible. In upward light emission, the first electrode 110 can be a reflective electrode, and the second electrode 170 can be a transparent electrode or a reflective and transmissive electrode.

[0053] The function of the light-emitting device according to embodiments of the present invention will be described in more detail below.

[0054] The classification of the first and second embodiments is based on whether the dopants BD1 and BD2 of the first and second emission layers are made of the same material.

[0055] First, the case where the dopants BD1 and BD2 of the first and second light-emitting layers are made of the same material will be described through the first embodiment.

[0056] Figure 3 This is a view showing the relationship between the singlet and triplet energy levels of each material in the light-emitting unit of the light-emitting device according to a first embodiment of the present invention.

[0057] like Figure 3As shown, the light-emitting unit according to a first embodiment of the present invention includes a first light-emitting layer EML1 and a second light-emitting layer EML2 configured to emit blue light. The first light-emitting layer EML1 includes a first body BH1 and a first blue dopant BD1. The second light-emitting layer EML2 includes a second body BH2 and a second blue dopant BD2. In the first embodiment, the first blue dopant BD1 and the second blue dopant BD2 are made of the same material. In the following description of the first embodiment, the first blue dopant BD1 and the second blue dopant BD2 are simply referred to as blue dopant BD.

[0058] For the main emission in the second emitting layer EML2, the second host BH2 in the second emitting layer EML2 must successfully receive energy from the first emitting layer EML1.

[0059] In this respect, the triplet level T1(BD) of the blue dopant BD is greater than the triplet level T1(BH1) of the first host BH1, the triplet level T1(BH1) of the first host BH1 is greater than 2.0 eV, and the triplet level T1(BH2) of the second host BH2 is less than 2.0 eV. That is to say, the following relationship must be satisfied.

[0060] T1(BD) > T1(BH1) > 2.0 eV > T1(BH2)

[0061] In addition, the singlet level S1(BH1) of the first host BH1 is greater than the singlet level S1(BH2) of the second host BH2, and the singlet level S1(BH2) of the second host BH2 is greater than the singlet level S1(BD) of the blue dopant BD.

[0062] In other words, the condition S1(BH1)>S1(BH2)>S1(BD) must be satisfied.

[0063] In the light-emitting device according to the first embodiment, each of the first light-emitting layer 131 and the second light-emitting layer 132 may further include a host. However, essentially, the first light-emitting layer 131 and the second light-emitting layer 132 must include a first host, a second host, and a blue dopant having the above-described relationship.

[0064] Here, the triplet energy level T1(BD) of the blue dopant BD included in the first light-emitting layer 131 is greater than the triplet energy levels of the first host BH1 and the second host BH2, and exceeds 2.0 eV.

[0065] Furthermore, the singlet energy level S1(BD) of the blue dopant included in the first luminescent layer 131 is smaller than the singlet energy levels of the first host BH1 and the second host BH2. As a result, the value of ΔEst(S1-T1) of the blue dopant is small.

[0066] In the light-emitting device according to the present invention, although multiple light-emitting layers are provided, the thickness of the light-emitting unit 130 is not increased. For example, the first light-emitting layer 131 and the second light-emitting layer 132 are provided in the light-emitting unit 130 of the present invention, and the materials for the first host (BH1) and blue dopant (BD) included in the first light-emitting layer and the materials for the second host (BH2) and blue dopant (BD) in the second light-emitting layer satisfy the conditions T1(BD)>T1(BH1)>2.0eV>T1(BH2) and S1(BH1)>S1(BH2)>S1(BD). Through the association of triplet and singlet energy levels between the first and second light-emitting layers, electrons or excitons are driven, causing the recombination region to concentrate on the light-emitting layer located at the rear end of the confined light-emitting unit 130. This prevents the accumulation of electrons or excitons at the interface IF1 of the electron blocking layer or hole transport layer, and thus increases the lifetime of the device.

[0067] Meanwhile, the first host BH1 of the first light-emitting layer EML1, which has hole transport capability, can be p-type or bipolar. In order to continuously supply excitons and holes to the second light-emitting layer 132, the hole mobility of the first host BH1 can be greater than that of the second host BH2.

[0068] The first light-emitting layer 131 and the second light-emitting layer 132 can be configured to be adjacent to each other. In this case, the thickness of the second light-emitting layer 132 can be equal to or greater than the thickness of the first light-emitting layer 131.

[0069] Depending on the circumstances, the mixing region where the different main bodies BH1 and BH2 of the two light-emitting layers are mixed with each other can also be set between the first light-emitting layer 131 and the second light-emitting layer 132, so that the composite region is separated from the electron blocking layer or hole transport layer and electron transport layer, thereby further increasing the lifetime of the light-emitting device.

[0070] When the first host BH1 exhibits hole transport properties, its HOMO level can range from -6.0 eV to -5.6 eV, its LUMO level can be higher than -2.6 eV, and the LUMO level of the blue dopant BD can be lower than the LUMO level of the first host BH1. Compared to the vacuum level, all HOMO and LUMO levels are negative.

[0071] The first body BH1 may include a naphthalene moiety, but it is not anthracene, pyrene, or phenanthrene, which are aromatic hydrocarbons. Conversely, the second body BH2 may include one of anthracene, pyrene, and phenanthrene.

[0072] Depending on the requirements, the blue dopant can be of the same type, or different dopant can be used.

[0073] Reference Figure 4 Describe the use of different dopants.

[0074] Figure 4 This is a graph showing the relationship between the singlet and triplet energy levels of each material in the light-emitting unit of the light-emitting device according to the second embodiment of the present invention.

[0075] When different blue dopants BD1 and BD2 are used in the first light-emitting layer 131 and the second light-emitting layer 132, the first blue dopant BD1 included in the first light-emitting layer 131 has the following characteristics.

[0076] In other words, the HOMO level of the first blue dopant BD1 must be greater than -5.3 eV. The emission spectrum of the first blue dopant BD1 is smaller than the absorption spectrum of the second blue dopant BD2. Therefore, in the region where the emission spectrum of the first blue dopant BD1 and the absorption spectrum of the second blue dopant BD2 overlap, energy is mainly transferred from the first blue dopant BD1 to the second blue dopant BD2, thereby causing main emission in the second emitting layer 132.

[0077] In addition, the triplet energy level T1(BD1) of the first blue dopant satisfies the following relationship.

[0078] T1(BD1)>T1(BH1)>T1(BD2)>T1(BH2)

[0079] Due to the relationship between the triplet energy levels of the materials in the first and second light-emitting layers, the accumulation of singlet and triplet excitons is carried to the interface between the first and second light-emitting layers, thereby increasing the lifetime of the light-emitting device.

[0080] The light-emitting device according to the present invention will be described below with reference to various experimental examples.

[0081] In the following experimental example, by including as Figure 1 The first electrode 110 is deposited sequentially on an indium tin oxide (ITO) substrate to form a stacked structure as follows: [thickness information missing] Hole injection layer 120, thickness is Hole transport layer 122, thickness is The electron blocking layer 124 has a thickness of The light-emitting layer or light-emitting unit 130 has a thickness of The electron transport layer 140 has a thickness of The electron injection layer 150 and the cathode 170 serving as a reflective aluminum electrode.

[0082] The concentration of dopant in the first and second light-emitting layers, or a single light-emitting layer, is 2% by volume of the dopant in the light-emitting layer or light-emitting unit, and is within 10 mA / cm². 2 The driving voltage is evaluated under the following conditions.

[0083] [Table 1]

[0084]

[0085] In Experiment 1 through Experiment 6, tests were conducted. Figure 1 The light-emitting device. In the first to third experimental examples Ex1 to Ex3, a single light-emitting layer is used instead of a light-emitting unit. In the fourth to sixth experimental examples Ex4 to Ex6, the first body of the first light-emitting layer is made of a material having a triplet energy level of 2.0 eV or less, therefore the light-emitting unit according to the invention is made of a material with low hole transport. First, the experimental examples shown in Table 1 above and Table 2 below are compared with the first experimental example Ex1 where a single light-emitting layer is applied. In the first to third experimental examples Ex1 to Ex3, the thickness of the single light-emitting layer is The experiment was conducted under the following conditions. In Experiments 4 to 6 (Ex4 to Ex6), the thickness of the light-emitting unit composed of a double-emitting layer was... The experiment was conducted in the same manner under the same conditions.

[0086] In the second experimental example Ex2, the light-emitting layer is a single layer, and the electron transport layer ETL1 adjacent to the light-emitting layer is made of a material exhibiting high electron transport properties. In the first experimental example Ex1 and the third to sixth experimental examples Ex3 to Ex6, an electron transport layer ETLb with general electron transport properties is provided in each light-emitting unit. In the second experimental example Ex2, the device efficiency increases, but the device lifetime decreases significantly. This is because electrons accumulate at the interface between the electron blocking layer and the light-emitting layer, resulting in the degradation of the electron blocking layer.

[0087] In the table, EQE(%) means the external quantum efficiency of each experimental example compared to the external quantum efficiency of the first experimental example Ex1. CIEx and CIEy are the color coordinate values ​​of each experimental example compared to the color coordinate values ​​of the first experimental example Ex1.

[0088] In the third experimental example, Ex3, the emitting layer is a single layer, and the material of the electron blocking layer adjacent to the emitting layer is changed to improve electron transport. In this case, improving electron transport by changing the material of the electron blocking layer increases lifetime but decreases efficiency. This is because the increased hole current leads to the widespread formation of recombination regions, thereby reducing TTF efficiency and thus overall efficiency. The electron density towards the electron blocking layer and the emitting layer decreases, thus reducing the degradation of the electron blocking layer and increasing lifetime.

[0089] In all the first to third experimental examples Ex1 to Ex3, there was no increase in lifetime or efficiency.

[0090] In Experimental Examples 4 through 6 (Ex4 through Ex6), the luminescent layer has a bilayer structure. The main body of the first luminescent layer is made of a material with a triplet energy level of 2.0 eV or less, and the thickness ratio of the first and second luminescent layers is adjusted for evaluation.

[0091] However, in the fourth to sixth experimental examples Ex4 to Ex6, both efficiency and lifetime were reduced compared to the first experimental example Ex1.

[0092] In the seventh to thirteenth experimental examples Ex7 to Ex13 shown in Table 2 below, the materials used for the first host (BH1) and blue dopant (BD) included in the first emitting layer and the materials used for the second host (BH2) and blue dopant (BD) in the second emitting layer satisfy the conditions used in this invention: T1(BD)>T1(BH1)>2.0eV>T1(BH2) and S1(BH1)>S1(BH2)>S1(BD).

[0093] [Table 2]

[0094]

[0095] In the seventh experimental example Ex7, the first emitting layer comprises a first host with a large triplet energy level without dopant, and the thicknesses of the first and second emitting layers are respectively... and In the seventh experimental example Ex7, the efficiency and lifetime are lower than those in the first experimental example Ex1. Furthermore, the lifetime and efficiency are lower than those in the eighth through eleventh experimental examples Ex8 through Ex11.

[0096] Therefore, in Experimental Examples 8 to 11 (Ex8 to Ex11), the function of the blue dopant BD included in the first emitting layer EML1 can be deduced by analogy. That is, it can be deduced that among the excitons generated in the first emitting layer EML1, triplet excitons are transferred to the second emitting layer EML2 via Dexter energy transfer, and singlet excitons contribute to lifetime and efficiency through the radiative decay process of the blue dopant BD.

[0097] Reference Figures 1 to 4 The described luminescent structure is applied to Experimental Examples 8 through 11, Ex8 through Ex11.

[0098] In Experiment 8 and Experiment 9, the thickness of the first light-emitting layer EML1 was determined to be as high as In this case, lifespan can be increased without reducing efficiency.

[0099] As can be seen from the third experimental example Ex3, the increase in lifetime caused by the increase in hole current is accompanied by a decrease in efficiency. In the eighth experimental example Ex8 and the ninth experimental example Ex9, the decrease in efficiency caused by hole current is offset by the contribution to the emission in the first light-emitting layer EML1, thereby improving the device lifetime without reducing efficiency.

[0100] In Experimental Example 10 and Experimental Example 11, the thickness of the first emitting layer EML1 is increased. Therefore, the efficiency reduction caused by the increase in hole current outweighs the contribution to the emission in the first emitting layer EML1. Consequently, the emission efficiency is relatively lower compared to Experimental Example 8 and Experimental Example 9.

[0101] As can be seen from Experimental Examples 8 to 11, when the thickness ratio of the first light-emitting layer to the second light-emitting layer is 1:9 to 6:4, the lifetime can be improved without increasing efficiency.

[0102] Meanwhile, in the twelfth experimental example Ex12, two substrates are included between the first emitting layer EML1 and the second emitting layer EML2, which have different substrates BH1 and BH2, and a blue dopant is provided. In this case, compared with the first experimental example Ex1, the concentration of the second substrate BH2 in the emitting unit 130 is reduced, thereby reducing the efficiency. However, the significance of the twelfth experimental example Ex12 is that its lifetime is twice or more than that of the first experimental example Ex1, thereby enabling the emitting device to be driven for a longer period of time.

[0103] Therefore, it can be seen that in order to increase lifetime, the exciton density must be reduced.

[0104] Meanwhile, the first host material BH1 of the first light-emitting layer is a material exhibiting good hole current characteristics. Therefore, for structural simplification, an example with the electron blocking layer removed was evaluated in Experimental Example 13. In Experimental Example 13, the lifetime remained at the level of Experimental Example 11, but the efficiency decreased. This is because the efficiency decreased due to the sudden increase in hole current when the electron blocking layer was removed.

[0105] Therefore, as shown in Table 2 above, it can be seen that each of the eighth to eleventh experimental examples (Ex8 to Ex11) has a basis according to Figure 1 The structure of the present invention is effective in both efficiency and lifespan. Furthermore, as seen in the twelfth experimental example Ex12, where a mixing region comprising the main components in the first and second light-emitting layers is further provided between the first and second light-emitting layers, a significant increase in lifespan can be observed.

[0106] Through the above experiments, it can be confirmed that the effects caused by the different entities of the first and second light-emitting layers according to the present invention have a specific triplet energy level relationship for each material.

[0107] In the light-emitting device according to the present invention, the light-emitting layer configured to emit blue light is formed with a bilayer structure. The triplet energy level of the dopant in the first light-emitting layer adjacent to the hole transport layer is greater than the triplet energy level of the first host in the first light-emitting layer, and the triplet energy level of the first host is greater than the triplet energy level of the second host in the second light-emitting layer. Thus, triplet excitons generated in the first light-emitting layer are recycled to the second light-emitting layer for reuse in light emission. In other words, exciton or electron accumulation at the interface between the hole transport layer or electron blocking layer and the light-emitting layer can be prevented. Therefore, the efficiency of the light-emitting device can be improved and its lifetime significantly increased.

[0108] The first emitting layer adjacent to the hole transport layer includes a host with hole transport properties, thereby pushing holes to the second emitting layer. Therefore, the recycling rate of triplet excitons in the second emitting layer increases, thereby preventing exciton or electron accumulation at the interface between the hole transport layer or electron blocking layer and the first emitting layer, thus increasing the lifetime of the hole transport layer or electron blocking layer.

[0109] Furthermore, continuous recycling from the first light-emitting layer to the second light-emitting layer (the second light-emitting layer and the first light-emitting layer form a multi-layer structure) can maintain high efficiency, thereby increasing the lifespan of the light-emitting device and the display device and stabilizing the device.

[0110] At the same time, Figure 1In the light-emitting device, a blue stack BU comprising a hole transport layer 122, an electron blocking layer 124, a light-emitting unit 130 composed of a stacked first light-emitting layer EML1 and a second light-emitting layer EML2, and an electron transport layer 140 can be coupled to another stack between the first electrode 110 and the second electrode 170 with the charge generation layer CGL inserted between the first electrode 110 and the second electrode 170.

[0111] An example will be described with reference to the accompanying drawings.

[0112] Figure 5A and Figure 5B This is a cross-sectional view illustrating a white organic light-emitting device according to another embodiment of the present invention.

[0113] Figure 5A A white organic light-emitting device according to another embodiment of the present invention is shown. A first blue light-emitting stack BS1, a phosphorescent light-emitting stack PS, and a second blue light-emitting stack BS2 are sequentially disposed between a first electrode 110 and a second electrode 170. Charge-generating layers CGL1 and CGL2, configured to provide holes and electrons to the light-emitting stacks away from the electrodes, may be further disposed between the light-emitting stacks BS1, PS, and BS2.

[0114] The phosphorescent emitting stack PS can include a stack of two or more phosphorescent emitting layers configured to emit different colors, such as a stack of red and green emitting layers or a stack of yellow-green and green emitting layers. In the example shown, the phosphorescent emitting stack PS is configured as an intermediate stack. However, the invention is not limited thereto. The phosphorescent emitting stack PS can be configured to be adjacent to the first electrode 110 or the second electrode 170.

[0115] also, Figure 1 The blue stack shown can be applied to each of the first blue emitting stack BS1 and the second blue emitting stack BS2, thereby improving the efficiency and lifespan of the white emitting device.

[0116] A charge generation layer CGL1, CGL2, and CGL3, configured to provide holes and electrons to the light-emitting stack away from the electrodes, can be further disposed between the light-emitting stacks BS1, PS, BS2, and BS3.

[0117] Reference Figure 5A and Figure 5B The described multi-layered cascaded structure is configured to maximize the efficiency of the white light-emitting device, thus allowing for a more vivid display.

[0118] Furthermore, in a white organic light-emitting device according to another embodiment of the present invention, such as Figure 5BAs shown, a first blue light-emitting stack BS1, a phosphorescent light-emitting stack PS, a second blue light-emitting stack BS2, and a third blue light-emitting stack BS3 are sequentially disposed between the first electrode 110 and the second electrode 170.

[0119] Depending on the situation, the position of the phosphorescent PS stack can be changed.

[0120] Meanwhile, although the above example includes a three-emissive stacked structure or a four-emissive stacked structure between the first electrode 110 and the second electrode 170, in order to further improve the luminous efficiency, a blue luminescent stacked structure and / or a phosphorescent luminescent stacked structure may be further included.

[0121] The following section will describe examples of white organic light-emitting devices being used in display devices.

[0122] Figure 6 This is a cross-sectional view showing a display device including a white organic light-emitting device according to the present invention.

[0123] like Figure 6 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 sub-pixels R_SP, G_SP, B_SP and W_SP typically disposed on the substrate 100. Figure 1 The light-emitting device, a thin-film transistor (TFT) disposed at each sub-pixel (the TFT is connected to the first electrode 110 of the white organic light-emitting device (OLED)), and color filter layers 109R, 109G, and 109B disposed below the first electrode 110 of at least one sub-pixel. Figure 6 In the diagram, R represents red, G represents green, B represents blue, and W represents white.

[0124] In the example shown, a white sub-pixel W_SP is included. However, the invention is not limited to this. Only red sub-pixels R_SP, green sub-pixels G_SP, and blue sub-pixels B_SP may be included, while the white sub-pixel W_SP is omitted. Depending on the situation, a combination of cyan, magenta, and yellow sub-pixels capable of representing white light may be used instead of the red, green, and blue sub-pixels.

[0125] As an example, a thin-film transistor (TFT) includes a gate electrode 102, a semiconductor layer 104, and a source electrode 106a and a drain electrode 106b connected to opposite sides of the semiconductor layer 104.

[0126] A gate dielectric film 103 is disposed between the gate electrode 102 and the semiconductor layer 104.

[0127] The semiconductor layer 104 may be composed of, for example, amorphous silicon, crystalline silicon, oxide semiconductor, or a combination of two or more thereof. For example, if the semiconductor layer 104 is an oxide semiconductor, an etch stop layer 105 may be further provided to directly adjoin the semiconductor layer 104 to prevent damage to the channel region of the semiconductor layer 104.

[0128] Furthermore, the drain electrode 106b of the thin-film transistor TFT can be connected to the first electrode 110 in the contact hole CT region provided in the first passivation film 107 and the second passivation film 108.

[0129] A first passivation film 107 is provided to primarily protect the thin-film transistor TFT, and color filters 109R, 109G and 109B can be provided on the first passivation film.

[0130] When multiple sub-pixels include red, green, blue, and white sub-pixels, color filter layers are formed at the remaining sub-pixels except for the white sub-pixel W_SP, serving as first to third color filters 109R, 109G, and 109B, to allow white light emitted from the first electrode 110 for each wavelength to pass through. A second passivation film 108 is formed below 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 passivation film 108, excluding the contact hole CT.

[0131] Here, a white organic light-emitting device (OLED) may include a first electrode 110 as a transparent electrode, a second electrode 170 as a reflective electrode (the second electrode is opposite to the first electrode), and a dual-layer structure including a blue light-emitting layer and a long-wavelength (red and green or yellow-green) (phosphorescent) light-emitting layer disposed between the first electrode 110 and the second electrode 170, or as... Figure 5A As shown, the structure comprises a three-layer structure consisting of a first blue luminescent stack BS1, a phosphorescent luminescent stack PS, and a second blue luminescent stack BS2 disposed between the first electrode 110 and the second electrode 170. Alternatively, in the organic stack OS, at least one of the blue luminescent stack and the phosphorescent luminescent stack can be provided as multiple stacks, and a charge generation layer can be disposed between the luminescent stacks. In this case, the multiple luminescent stacks can have the same structure.

[0132] Undescribed reference numeral 119 denotes a dam, and BH refers to a dam hole between dams. Light is emitted in the area opened by the dam hole. The dam hole defines the emission portion of each sub-pixel.

[0133] at the same time, Figure 6 The display device is a downward-emitting type display device.

[0134] However, the present invention is not limited thereto. The display device can be implemented as a downward-emitting display device, wherein the color filter layer is located on the second electrode 170, the first electrode 110 includes reflective metal, and the second electrode 170 is made of transparent electrode or semi-transparent metal.

[0135] Alternatively, the color filter layer can be omitted or provided, and both the first electrode 110 and the second electrode 170 can be made of transparent electrodes, thereby realizing a transparent organic light-emitting device.

[0136] A light-emitting device according to an embodiment of the present invention includes an electron blocking layer, a first light-emitting layer, a second light-emitting layer, and an electron transport layer sequentially disposed between a first electrode and a second electrode opposite to each other. The first light-emitting layer includes a first substrate and a first blue dopant. The second light-emitting layer includes a second substrate and a second blue dopant. The triplet energy level of the first substrate may be greater than the triplet energy level of the second substrate. The triplet energy level of the first blue dopant may be greater than the triplet energy level of the first substrate.

[0137] The first and second blue dopants can be made of the same material. The triplet level of the second host can be less than 2.0 eV, and the triplet level of the first host can be greater than 2.0 eV.

[0138] The singlet energy level of the first host can be greater than the singlet energy level of the second host, and the singlet energy level of the second host can be greater than the singlet energy level of the first blue dopant.

[0139] The first entity can be P-type or bipolar, and the hole mobility of the first entity can be greater than that of the second entity.

[0140] The first light-emitting layer and the second light-emitting layer can be adjacent to each other, and the thickness of the second light-emitting layer can be equal to or greater than the thickness of the first light-emitting layer.

[0141] The HOMO level of the first host can be from -6.0 eV to -5.6 eV, the LUMO level of the first host can be higher than -2.6 eV, and the LUMO level of the first blue dopant can be lower than the LUMO level of the first host.

[0142] The triplet energy level of the second blue dopant can be smaller than the triplet energy level of the first host and larger than the triplet energy level of the second host.

[0143] The HOMO level of the first dopant can be greater than -5.3 eV. The emission spectrum of the first blue dopant and the absorption spectrum of the second blue dopant can overlap.

[0144] The first body may include a naphthalene moiety, and the second body may include one of anthracene, pyrene, and phenanthrene.

[0145] The thickness ratio of the first light-emitting layer to the second light-emitting layer can be from 1:9 to 6:4.

[0146] The hybrid layer consisting of the first host, the second host, and the first blue dopant may be further included between the first luminescent layer and the second luminescent layer.

[0147] The display device according to an embodiment of the present invention includes the above-described light-emitting device.

[0148] Furthermore, the display device according to an embodiment of the present invention includes a plurality of sub-pixels, a thin-film transistor disposed for each sub-pixel, and a blue stack connected to the thin-film transistor at each sub-pixel. The blue stack includes a hole transport layer, an electron blocking layer, a first light-emitting layer, a second light-emitting layer, and an electron transport layer sequentially disposed adjacent to each other between a first electrode and a second electrode that are opposite to each other. The first light-emitting layer includes a first body and a first blue dopant, and the second light-emitting layer includes a second body and a second blue dopant. The triplet energy level of the first body may be greater than the triplet energy level of the second body, and the triplet energy level of the first blue dopant may be greater than the triplet energy level of the first body.

[0149] Multiple blue stacks can be configured between the first electrode and the second electrode. At least one of the blue stacks can be configured between the first electrode and the second electrode with a phosphorescent emitting stack and a charge generating layer inserted between the blue stacks, wherein the phosphorescent emitting stack includes two or more phosphorescent emitting layers, each having a longer wavelength than the blue stack.

[0150] A display device according to another embodiment of the present invention may include: a first electrode, a hole transport layer disposed on the first electrode, a first light-emitting layer disposed on the hole transport layer, a second light-emitting layer directly disposed on the first light-emitting layer, an electron transport layer disposed on the second light-emitting layer, and a second electrode disposed on the electron transport layer, wherein the first light-emitting layer includes a first body and a first blue dopant, the second light-emitting layer includes a second body and a second blue dopant, the triplet energy level of the first body is greater than the triplet energy level of the second body, and the triplet energy level of the first blue dopant is greater than the triplet energy level of the first body.

[0151] The first blue dopant and the second blue dopant can be the same material, the triplet energy level of the second host can be less than 2.0 eV, and the triplet energy level of the first host can be greater than 2.0 eV.

[0152] The singlet energy level of the first host can be greater than the singlet energy level of the second host, the singlet energy level of the second host can be greater than the singlet energy level of the first blue dopant, and the multiply energy level of the second blue dopant can be less than the triplet energy level of the first host and greater than the triplet energy level of the second host.

[0153] The thickness of the second light-emitting layer can be equal to or greater than the thickness of the first light-emitting layer.

[0154] It is evident from the above description that the light-emitting device and the display device including the light-emitting device according to the present invention have the following effects.

[0155] First, the light-emitting layer configured to emit blue light is formed with a bilayer structure. The triplet energy level of the dopant in the first light-emitting layer, adjacent to the hole transport layer, is greater than the triplet energy level of the first host in the first light-emitting layer, and the triplet energy level of the first host is greater than the triplet energy level of the second host in the second light-emitting layer. This allows triplet excitons generated in the first light-emitting layer to be recycled to the second light-emitting layer for reuse in emitting light. In other words, it prevents excitons or electrons from accumulating at the interface between the hole transport layer or electron blocking layer and the light-emitting layer. Therefore, the efficiency of the light-emitting device can be improved, and its lifetime can be significantly increased.

[0156] Second, the first emitting layer adjacent to the hole transport layer includes a host with hole transport properties, thereby pushing holes to the second emitting layer. Therefore, the recycling rate of triplet excitons in the second emitting layer increases, which prevents excitons or electrons from accumulating at the interface between the hole transport layer or electron blocking layer and the first emitting layer, thus increasing the lifetime of the hole transport layer or electron blocking layer.

[0157] Third, continuous recycling from the first light-emitting layer to the second light-emitting layer (the second light-emitting layer and the first light-emitting layer form a multi-layer structure) can maintain high efficiency, thereby increasing the lifespan of the light-emitting device and the display device and stabilizing the device.

[0158] It will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its spirit or scope. Therefore, this invention is intended to cover such modifications and variations, provided they fall within the scope of the appended claims and their equivalents.

Claims

1. A light-emitting device, comprising: An electron blocking layer, a first light-emitting layer, a second light-emitting layer, and an electron transport layer are sequentially arranged between a first electrode and a second electrode, with the first electrode and the second electrode facing each other. The first light-emitting layer includes a first host and a first blue dopant. The second light-emitting layer includes a second body and a second blue dopant. The triplet energy level of the first entity is greater than that of the triplet energy level of the second entity. The triplet energy level of the first blue dopant is greater than the triplet energy level of the first host. Wherein, the singlet state energy level of the first entity is greater than that of the singlet state energy level of the second entity, and The singlet energy level of the second host is greater than that of the first blue dopant.

2. The light-emitting device according to claim 1, wherein... The first blue dopant and the second blue dopant are made of the same material. The second host's triplet energy level is less than 2.0 eV, and The triplet energy level of the first host is greater than 2.0 eV.

3. The light-emitting device according to claim 1, wherein... The first body is P-type or bipolar, and The hole mobility of the first entity is greater than that of the second entity.

4. The light-emitting device according to claim 1, wherein, The first light-emitting layer is in contact with the second light-emitting layer, and The thickness of the second light-emitting layer is equal to or greater than the thickness of the first light-emitting layer.

5. The light-emitting device according to claim 1, wherein, The lowest unoccupied molecular orbital (LUMO) energy level of the first blue dopant is lower than the LUMO energy level of the first host.

6. The light-emitting device according to claim 1, wherein, The triplet energy level of the second blue dopant is lower than the triplet energy level of the first host and higher than the triplet energy level of the second host.

7. The light-emitting device according to claim 6, wherein... The highest occupied molecular orbital (HOMO) level of the first blue dopant is greater than -5.3 eV, and The emission spectrum of the first blue dopant and the absorption spectrum of the second blue dopant overlap.

8. The light-emitting device according to claim 1, wherein... The first body comprises a naphthalene portion, and The second component comprises one of anthracene, pyrene, and phenanthrene.

9. The light-emitting device according to claim 1, wherein, The thickness ratio of the first light-emitting layer to the second light-emitting layer is 1:9 to 6:

4.

10. The light-emitting device according to claim 1, further comprising: A hybrid layer disposed between the first light-emitting layer and the second light-emitting layer. The hybrid layer is composed of the first host, the second host, and the first blue dopant.

11. A display device, comprising: Multiple sub-pixels; Thin-film transistors are configured for each sub-pixel; as well as At each sub-pixel, one or more blue stacks are connected to the thin-film transistor. Each of the blue stacks includes a hole transport layer, an electron blocking layer, a first light-emitting layer, a second light-emitting layer, and an electron transport layer arranged sequentially between a first electrode and a second electrode, with the first electrode and the second electrode facing each other. The first light-emitting layer includes a first host and a first blue dopant. The second light-emitting layer includes a second body and a second blue dopant. The triplet energy level of the first entity is greater than that of the triplet energy level of the second entity. The triplet energy level of the first blue dopant is greater than the triplet energy level of the first host. Wherein, the singlet state energy level of the first entity is greater than that of the singlet state energy level of the second entity, and The singlet energy level of the second host is greater than that of the first blue dopant.

12. The display device according to claim 11, wherein The first blue dopant and the second blue dopant are made of the same material. The second host's triplet energy level is less than 2.0 eV, and The triplet energy level of the first host is greater than 2.0 eV.

13. The display device according to claim 11, wherein The first body is P-type or bipolar, and The hole mobility of the first entity is greater than that of the second entity.

14. The display device according to claim 11, wherein, The thickness of the second light-emitting layer is equal to or greater than the thickness of the first light-emitting layer.

15. The display device according to claim 11, further comprising: A phosphorescent stack comprising two or more phosphorescent layers, and a charge generation layer between one or more blue layers and the phosphorescent stack. Each of the two or more phosphorescent emitting layers has a longer wavelength than the first and second emitting layers of the one or more blue stacks.

16. A display device comprising a light-emitting device according to any one of claims 1 to 10.

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