Light emitting element and display device including the same

Abstract

A light emitting element and a display apparatus including the same are disclosed, in which a hole generation layer is provided between a hole transport layer and an emission layer of the light emitting element in addition to an electron blocking layer, so as to control the speed of electrons and holes introduced into the emission layer, whereby accumulation of carriers at the electron blocking layer or the hole transport layer can be prevented, and thus the turn-on voltage can be reduced, uniform efficiency can be maintained regardless of changes in current density, defects at a certain level can be prevented, and the lifespan can be increased.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2021-0194758, filed on December 31, 2021, which is incorporated herein by reference as fully set forth herein. Technical Field

[0003] This disclosure relates to a light-emitting element, and more particularly to a light-emitting element configured to alter the structure between its emitting layer and hole transport layer, thereby preventing an increase in driving voltage and improving lifetime, and a display device including the light-emitting element. Background Technology

[0004] With the advent of the information age, displays capable of visually expressing electronic information signals have been rapidly developed. Consequently, various display devices with superior performance (such as thinness, light weight, and low power consumption) have been developed and have quickly replaced traditional cathode ray tubes (CRTs).

[0005] Among these display devices, light-emitting display devices with light-emitting elements in the display panel have been considered a competitive application, enabling compact display devices and vivid color display without the need for a separate light source.

[0006] In a structure with multiple stacks, when an inorganic material is primarily used at the interface of one of the stacks (i.e., at the interface between the electrode face and the stack or at the interface between the charge generation layer and the stack), there is electron dominance in the initial state or in a low-level (low current density driven) state. This may result in a difference in mobility between holes and electrons, and thus hole accumulation may occur between the hole transport layer and the emitter layer of the stack.

[0007] In low-level states, the difference in mobility between holes and electrons may be observed as poor low-level visibility, and hole accumulation due to changes in current density may be the main cause of reduced lifespan of light-emitting display devices. Summary of the Invention

[0008] Therefore, this disclosure relates to a light-emitting element and a display device including the light-emitting element, which substantially avoids one or more problems caused by the limitations and disadvantages of related technologies.

[0009] The purpose of this disclosure is to provide a light-emitting element that reduces the on-state voltage, maintains uniform efficiency regardless of changes in current density, prevents defects at a specific level, and increases lifespan, and to provide a display device including the light-emitting element.

[0010] In the light-emitting element and display device including the light-emitting element according to the present disclosure, in addition to the electron blocking layer, a hole generating layer is provided between the hole transport layer and the emitter layer in order to control the speed of electrons and holes introduced into the emitter layer. This prevents the accumulation of charge carriers at the electron blocking layer or the hole transport layer, and thus reduces the on-state voltage, maintains uniform efficiency regardless of changes in current density, prevents defects at a certain level, and increases lifespan.

[0011] To achieve these and other advantages, and according to the purposes of the invention, as implemented and broadly described herein, a light-emitting element includes a first electrode and a second electrode opposite to each other, at least one charge-generating layer disposed between the first electrode and the second electrode, and a first stack disposed between the first electrode and the first charge-generating layer in the at least one charge-generating layer, and including a first emitting layer, a hole transport layer including a hole transport layer, a hole generation layer and an electron blocking layer disposed sequentially between the first electrode and the first emitting layer, and an electron blocking layer disposed between the first emitting layer and the first charge-generating layer, wherein the hole generation layer includes an organic host and a p-type dopant, the LUMO level and HOMO level of the organic host differing from the LUMO level and HOMO level of the electron blocking layer by 1 eV or less, respectively, and the HOMO level of the p-type dopant is -9.0 eV or less.

[0012] In another aspect of this disclosure, a display device includes: a substrate having a plurality of sub-pixels, a transistor disposed at each sub-pixel, and a light-emitting element. The light-emitting element includes a first electrode connected to the transistor at each sub-pixel, a second electrode opposite to the first electrode, and a plurality of stacked bodies separated by at least one charge-generating layer disposed between the first electrode and the second electrode. The first stacked body of the plurality of stacked bodies is disposed between the first electrode and the first charge-generating layer in the at least one charge-generating layer, and includes a first emitting layer, a hole transport layer including a hole transport layer, a hole generation layer, and an electron blocking layer disposed sequentially between the first electrode and the first emitting layer, and an electron transport layer disposed between the first emitting layer and the first charge-generating layer. The hole generation layer includes an organic host and a p-type dopant. The LUMO and HOMO energy levels of the organic host are 1 eV or less different from the LUMO and HOMO energy levels of the electron blocking layer, respectively, and the HOMO energy level of the p-type dopant is -9.0 eV or less.

[0013] In another aspect of this disclosure, a light-emitting element includes: a first electrode; a hole transport layer on the first electrode; a hole generation layer directly disposed on the hole transport layer; an electron blocking layer directly disposed on the hole generation layer; an emission layer on the electron blocking layer; an electron transport layer on the emission layer; and a second electrode on the electron transport layer, wherein the hole generation layer includes an organic host and a p-type dopant, the LUMO and HOMO energy levels of the organic host differ from the LUMO and HOMO energy levels of the electron blocking layer by 1 eV or less, respectively, and the LUMO energy level of the p-type dopant differs from the HOMO energy level of the electron blocking layer by 1 eV or less.

[0014] It should be understood that the foregoing overview and the following detailed description of this disclosure are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed. Attached Figure Description

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

[0016] Figure 1 This is a schematic cross-sectional view of a light-emitting element according to an embodiment of the present disclosure;

[0017] Figure 2 It is shown that... Figure 1 A view of the energy band diagram of the hole transport cells adjacent to the emitter layer of the first stack;

[0018] Figure 3A and Figure 3B This is a view showing the band diagram of the hole transport unit in the first experimental example and the first experimental modification;

[0019] Figure 4A and 4B It is a schematic cross-sectional view of the light-emitting element according to the first and second experimental examples;

[0020] Figure 5 It is a graph showing the change in external quantum efficiency based on current density from the first experimental example to the third experimental example;

[0021] Figure 6 It is a graph showing the changes in driving voltage and lifetime from the first experimental example to the third experimental example;

[0022] Figure 7 This is a schematic cross-sectional view of the light-emitting element according to the fourth experimental example;

[0023] Figure 8It is a graph showing the JV characteristics in the first, third, and fourth experimental examples;

[0024] Figure 9 It is a graph showing the conduction voltage characteristics in the first, third, and fourth experimental examples;

[0025] Figure 10 This is a schematic cross-sectional view of a light-emitting element according to a first embodiment of the present disclosure;

[0026] Figure 11 This is a schematic cross-sectional view of a light-emitting element according to a second embodiment of the present disclosure;

[0027] Figures 12A to 12C This is a schematic cross-sectional view of a light-emitting element according to the third to fifth embodiments of the present disclosure;

[0028] Figure 13 This is a schematic cross-sectional view of a light-emitting element according to a sixth embodiment of the present disclosure; and

[0029] Figure 14 This is a schematic cross-sectional view of a display device according to the present disclosure. Detailed Implementation

[0030] Preferred embodiments of the invention will now be described in detail, examples of which are illustrated in the accompanying drawings. Where possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts. In the following description of the invention, detailed descriptions of known functions and configurations included herein may obscure the subject matter of the invention, and will be omitted. Furthermore, the component names used in the following description have been chosen with regard to the clarity of the description in the specification and may differ from the component names in actual products.

[0031] The shapes, dimensions, ratios, angles, quantities, etc., shown in the accompanying drawings to illustrate various embodiments of the invention are merely illustrative, and the invention is not limited to what is shown in the drawings. Where possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts. In the following description, detailed descriptions of techniques or configurations related to the invention may be omitted to avoid unnecessarily obscuring the subject matter of the invention. When terms such as "comprising," "having," and "including" are used throughout the specification, additional parts may be present unless "only" is used. Unless otherwise specifically stated, parts described in the singular encompass multiple parts.

[0032] The components included in the embodiments of the present invention should be interpreted as including a range of error, even without additional specific description.

[0033] When describing various embodiments of the present invention, when using terms describing positional relationships such as “on,” “above,” “below,” and “beside,” there may be at least one intermediate element between two elements, unless “immediately following” or “directly” is used.

[0034] When describing various embodiments of the invention, the use of time-related terms such as “after,” “following,” “after,” and “before” may include non-continuous cases, unless “immediately after” or “directly” is used.

[0035] In describing various embodiments of the invention, terms such as "first" and "second" may be used to describe various components, but the purpose of these terms is merely to distinguish identical or similar components from one another. Therefore, throughout the specification, a "first" component may be the same as a "second" component in the inventive concept unless otherwise specifically mentioned.

[0036] The features of the various embodiments of this disclosure may be partially or completely linked or combined with each other, and may interoperate and be technically driven in various ways. The embodiments of this disclosure may be performed independently of each other, or may be performed together in an interrelated manner.

[0037] As used herein, the term "doped" means that a material with different physical properties (e.g., N-type and P-type materials, or organic and inorganic substances) is added at a weight of less than 30% to the material constituting the majority of the weight of a layer. In other words, a "doped" layer is a layer used to distinguish the host material from the dopant material, taking into account weight ratios. Furthermore, the term "undoped" refers to any situation other than "doped." For example, a layer is included in an "undoped" layer when it contains a single material or a mixture of materials having the same properties as each other. For example, a layer is included in an "undoped" layer if at least one of the materials constituting a layer is p-type, and not all the materials constituting the layer are n-type. For example, a layer is included in an "undoped" layer if at least one of the materials constituting a layer is organic, and not all the materials constituting the layer are inorganic. For example, when all the materials constituting a layer are organic materials, and at least one of the materials constituting the layer is n-type and the other is p-type, the layer is included in the "doped" layer when the n-type material is present in an amount of less than 30 wt% or when the p-type material is present in an amount of less than 30 wt%.

[0038] The light-emitting element and the light-emitting display device including the light-emitting element according to the present disclosure will now be described with reference to the accompanying drawings.

[0039] Figure 1 This is a schematic cross-sectional view of a light-emitting element according to an embodiment of the present disclosure, and Figure 2 It shows the neighbors Figure 1 A view of the band structure of the hole transport unit of the emitter layer of the first stack.

[0040] like Figure 1 As shown, the light-emitting element according to an embodiment of the present disclosure includes a first electrode 110 and a second electrode 200 opposite to each other, and at least one charge generation layer (CGL) disposed between the first electrode 110 and the second electrode 200 (e.g., CGL1, ..., CGL2). n-1 )170 and n stacks separated by at least one charge-generating layer between the first electrode 110 and the second electrode 200. Here, n is a number equal to or greater than 2. The number of stacks is one greater than the number of at least one charge-generating layer.

[0041] Furthermore, the first stack S1 near the first electrode 110 includes a first emitter layer (EML 1) 350_1 disposed between the first electrode 110 and a first charge generation layer (CGL1) in at least one charge generation layer, a hole transport unit 1200 comprising a hole transport layer (HTL) 122, a hole generation layer (HGL) 130 and an electron blocking layer (EBL) 140 disposed sequentially between the first electrode 110 and the first emitter layer 350_1, and an electron transport layer (ETL) 160 disposed between the first emitter layer 350_1 and the first charge generation layer 170.

[0042] like Figure 2 As shown, the hole transport unit 1200 according to this disclosure includes a hole transport layer 122 configured to transport holes injected from a hole injection layer (HIL) 121 to a first emitter layer 350_1, an electron blocking layer 140 configured to prevent excitons generated from the first emitter layer 350_1 or electrons transported to the first emitter layer 350_1 from being transported to the hole transport layer 122, and a hole generation layer 130 disposed between the hole transport layer 122 and the electron blocking layer 140. The hole generation layer 130 is configured to attract or pull some electrons or excitons discharged through the electron blocking layer 140, thereby providing a hole generation effect. The hole generation layer 130 includes a material constituting the electron blocking layer 140 or an organic material having a band gap similar to that of the material constituting the electron blocking layer 140 as the main body, and also includes a p-type dopant pd.

[0043] like Figure 2As shown, the host constituting the hole generation layer 130 may have a LUMO (lowest unoccupied molecular orbital) energy level and a HOMO (highest occupied molecular orbital) energy level that differ from the electron blocking layer 140 by 1 eV (electron volts) or less. To prevent electrons or excitons from being transported to the hole transport layer 122 when electrons or excitons are primarily emitted from the first emitter layer 350_1, the LUMO energy level of the host is not lower than the LUMO energy level of the first emitter layer 350_1. Furthermore, to ensure that holes transported from the hole transport layer 122 to the first emitter layer 350_1 are transported without internal accumulation, the host has a HOMO energy level equal to or lower than the HOMO energy level of the hole transport layer 122 and a HOMO energy level higher than the HOMO energy level of the first emitter layer 350_1.

[0044] Furthermore, the p-type dopant pd included in the hole generation layer 130 has a very low HOMO energy level of -9.0 eV or less, so as to absorb or pull some electrons or excitons discharged from the electron blocking layer 140, generate holes in vacancies, and interact with the hole transport material (which is the host) in the surrounding hole generation layer 130, thereby enhancing the hole generation and transport functions.

[0045] p-type dopant pd includes substituents at the terminal groups, such as cyanide (CN) groups or fluorine (F) groups, thereby enhancing electron extraction capabilities. p-type dopant pd not only traps electrons but also attracts or pulls electrons, generating holes in electron vacancies to increase hole generation in hole transport unit 1200 and improve hole transport capability. Therefore, it can prevent the accumulation of hole carriers that may occur in hole transport layer 122 and electron blocking layer 140 during driving, increase the migration speed of holes ultimately transported to the first emitter layer 350_1, and increase the number of holes.

[0046] Therefore, through the above functions, the hole generation layer 130 can reduce the resistance of hole transport in the initial state or low current density state, thereby reducing the on-state voltage when the light-emitting element is driven, and can prevent efficiency changes at low current density due to the difference in intermaterial mobility between the electron transport layer 160 and the hole transport layer 122.

[0047] The difference between the LUMO level of the p-type dopant pd and the HOMO level of the electron blocking layer 140 is 1 eV or less, and the p-type dopant pd can absorb or pull electrons located at the HOMO level of the electron blocking layer 140 to generate holes.

[0048] p-type dopants (pd) include electron-withdrawing substituents at terminal groups, and as an example, can be organic materials represented by chemical formula 1.

[0049] [Chemical Formula 1]

[0050]

[0051] Alternatively, p-type dopant (pd) can comprise a radialene forming a triangular ring as its core, and can have two different types of substituents at the terminal groups that either attract or pull electrons. For example, p-type dopant (pd) can be an organic material represented by chemical formula 2. Due to the ring strain of the triangular ring, the radialene has low molecular stability, thereby predominantly leading to the generation of hole radicals. Through interaction with the surrounding transport material, the p-type transport properties are enhanced, and due to the low resistance, holes can be generated even without an applied bias voltage.

[0052] [Chemical Formula 2]

[0053]

[0054] Meanwhile, in the hole generation layer 130 of the light-emitting element according to this disclosure, the p-type dopant pd has a LUMO energy level, which is similar to or lower than the HOMO energy level of the host with a low HOMO energy level, thereby having the effect of attracting electrons and generating holes. Specifically, when the core of the axial ene has a substituent with high electronegativity at the terminal group, as represented by Chemical Formula 2, the p-type dopant pd has a lower band gap than a typical p-type dopant, and therefore the host of the hole generation layer 130, which has a lower HOMO energy level than the hole transport layer 122, is easily doped with the p-type dopant pd.

[0055] A p-type dopant, pd, is included in the hole generation layer 130 to account for 1 vol% to 10 vol% of the total volume of the hole generation layer 130. The p-type dopant pd content in the hole generation layer 130 must account for 1 vol% or more of the total volume of the hole generation layer 130 because the hole generation layer 130 must have a significant p-type dopant pd content to effectively generate holes. The p-type dopant pd content in the hole generation layer 130 must account for 10 vol% or less of the total volume of the hole generation layer 130 because a balance must be achieved between holes generated from the hole generation layer 130 and introduced into the first emitter layer 350_1, and electrons introduced from the electron transport layer 160. For example, if the p-type dopant pd content in the hole generation layer 130 exceeds 10 vol% of the total volume of the hole generation layer 130, the number of holes generated from the hole generation layer 130 and injected into the first emitter layer 350_1 may be greater than the number of electrons introduced from the electron transport layer 160 into the first emitter layer 350_1.

[0056] The hole generation layer 130 may be adjacent to the electron blocking layer 140, and the thickness ratio of the hole generation layer 130 to the electron blocking layer 140 may be 1:4 to 1:1. That is, the thickness of the hole generation layer 130 is no greater than the thickness of the electron blocking layer 140. This is because the hole generation layer 130 must generate holes while simultaneously hindering the function of the electron blocking layer 140. Furthermore, the thickness of the hole generation layer 130 is 1 / 4 or more of the thickness of the electron blocking layer 140. This is because the hole generation layer 130 must have a meaningful thickness to absorb electrons in the overlapping state of the first emitter layer 350_1, while also being processable to generate holes. For example, when the total thickness of the hole generation layer 130 and the electron blocking layer 140 is... At that time, the hole generation layer 130 can have the following properties: arrive The thickness, while the electron blocking layer 140 can have a thickness from arrive The thickness of the hole generation layer 130 and the electron blocking layer 140. If the total thickness of the hole generation layer 130 and the electron blocking layer 140 increases or decreases, the thickness of the hole generation layer 130 and the electron blocking layer 140 can be increased or decreased accordingly, such that the thickness ratio of the hole generation layer 130 to the electron blocking layer 140 corresponds to 1:4 to 1:1. To ensure a sufficient emission area in the first emission layer 350_1, the total thickness of the hole generation layer 130 and the electron blocking layer 140 preferably exceeds [a certain value].

[0057] Meanwhile, the main body of the hole generation layer 130 can be the same as the organic material constituting the electron blocking layer 140.

[0058] Meanwhile, in the light-emitting element according to the present disclosure, the first stack body S1 may also include a hole injection layer 121, which includes a metal fluoride and is disposed between the first electrode 110 and the hole transport layer 122.

[0059] The hole injection layer 121 is adjacent to the first electrode 110 (which is a transparent electrode made of a metal fluoride such as MgF2 or including a metallic component) and the hole transport layer 122 (which includes an organic component) at the two interfaces. It is stable at the interface when holes are injected and has a low interfacial resistance equal to the work function of the first electrode 110.

[0060] Furthermore, the first charge generation layer 170 connecting the first stack S1 to the next stack includes an n-type charge generation layer (N-CGL) 170a that participates in the generation and transport of electrons and a p-type charge generation layer (P-CGL) 170b that participates in the generation and transport of holes. That is, the electron transport layer 160 of the first stack S1 is adjacent to the n-type charge generation layer 170a.

[0061] In the light-emitting element according to the present disclosure, a hole generation layer is disposed between a hole transport layer and an electron blocking layer in a hole transport unit of at least a first stack S1 disposed between a first electrode 110 and a first charge generation layer 170, and compensates for the velocity difference between electrons and holes transported to the emission layer in terms of material or structure. This can improve the transport speed and number of holes transported to the emission layer without accumulating carriers, such as holes, in the hole transport unit at low current densities, and thus prevent changes in color efficiency when the current density changes, while maintaining the balance in recombination between holes and electrons in the emission layer.

[0062] In addition, in order to illustrate the importance of the hole generation layer according to this disclosure, hole transport in a hole transport unit without a hole generation layer (which is different from the hole transport unit of the light-emitting element according to this disclosure) will be described.

[0063] exist Figure 3A and Figure 3B The difference in the experiment is that, although it used Figure 1 The structure is similar, but no hole generation layer is set in the first stack.

[0064] Figure 3A and Figure 3B These are views showing the band diagrams of the hole transport units in the first experimental example (Ex1) and the first experimental modification (Ex1a), respectively. Figure 3A and Figure 3B The diagram shows carrier accumulation due to the HOMO energy level of the electron blocking layer between the hole transport layer and the emitter layer.

[0065] like Figure 3A and Figure 3B As shown, in the first experimental example (Ex1) or the first experimental modification (Ex1a), the hole transport unit disposed on one side of the emission layer 50 includes a hole transport layer 22 and an electron blocking layer 25 or 30, respectively.

[0066] exist Figure 3A In the structure of the first experimental example (Ex1) shown, a material with a low HOMO energy level is used as the electron blocking layer 25. Figure 3B In the structure of the first experimental modification (Ex1a) shown, a material with a low HOMO energy level is used as the electron blocking layer 30.

[0067] For example, in the first stack S1, a metal fluoride is used as a hole injection layer 121 adjacent to the first electrode 110, and an electron transport layer 160 and an n-type charge generation layer 170a (which is doped with a metal, such as lithium) are provided.

[0068] In this configuration, each of the two interfaces of the first stack S1 is made of an inorganic material including metals, or has a structure adjacent to an inorganic material including metals. Therefore, the flow of holes is structurally slow, while the flow of electrons is structurally fast. That is, electron dominance exists.

[0069] Therefore, in the first stack S1, electrons are introduced from the electron transport layer 160 into the emitter layer 50 at high speed, while holes injected from the first electrode 110 are injected at low speed. Furthermore, when an electron blocking layer 25 with a low HOMO energy level is applied, hole accumulation occurs at the interface between the hole transport layer 21 and the electron blocking layer 25, where there is a large HOMO energy level difference between adjacent layers. Figure 3A In the first experimental example (Ex1). Furthermore, in the structure in which an electron blocking layer 30 with a low HOMO energy level is set, such as... Figure 3B In the first experimental modification (Ex1a), there is a large HOMO energy level difference between the electron blocking layer 30 and the emission layer 50, which leads to hole accumulation between the electron blocking layer 30 and the emission layer 50.

[0070] Hole accumulation is caused by the physical properties of the layers constituting the stack. During high-level driving, holes and electrons exhibit high mobility due to high current density. However, during low-level driving, holes are easily affected by the physical properties of each layer. Meanwhile, Figure 3A and Figure 3B Comparative experiments show that during low current density driving, it is difficult to avoid hole accumulation simply by changing the material of the electron blocking layer between the hole transport layer and the emitter layer.

[0071] According to the present disclosure, a structure is proposed for the light-emitting element and display device, wherein, in a stack having electronic advantage due to the provision of inorganic materials at the interface of the stack during low-level driving, a hole generation layer is further provided between the hole transport layer and the electron blocking layer, thereby avoiding hole accumulation during low-level driving, and thus the emitting layer has uniform efficiency regardless of current density.

[0072] The following describes second to fourth experimental examples, each having a hole generation layer, in a light-emitting element according to the present disclosure, for comparison with the first experimental example.

[0073] Figure 4A and Figure 4B It schematically shows a cross-sectional view of the light-emitting element according to the first experimental example and the second experimental example, and Figure 5 It is a graph showing the change in external quantum efficiency based on current density from the first experimental example to the third experimental example. Figure 6 It is a graph showing the changes in driving voltage and lifetime from the first experimental example to the third experimental example.

[0074] In the light-emitting element according to the first experimental example, such as Figure 4A As shown, a thickness of [missing information] is sequentially formed on the first electrode 10 made of ITO. Hole injection layer 21, thickness is Hole transport layer 22, thickness is The electron blocking layer 25 has a thickness of Blue emitting layer (BEML) 50, thickness is The electron transport layer 60 has a thickness of The charge generation layer 70a and the second electrode 20 made of aluminum.

[0075] Hole injection layer 21 can be made of metal fluoride, such as MgF2, and hole transport layer 22 can be made of NPB (N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'diamine, N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-diphenyl-4,4'diamine), CBP (4,4'-bis(carbazol-9-yl, 4,4'-bis(carbazol-9-yl)), TPD (N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-benzidine, N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-benzidine), Spiro-TAD (2,2',7,7'-tetrakis(N,N-diphenylamino-9,9'-spirobifluorene, 2,2'... ,7,7'-tetra(N,N-diphenylamino-9,9'-spirobisfluorene) or MTDATA (4,4',4”-tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine, 4,4',4”-tris(N-3-methylphenyl-N-phenylamino)-triphenylamine). The electron blocking layer 25 can be made of a material having a lower HOMO level than the hole transport layer 22 and a higher LUMO level than the blue emitter layer 50. The electron blocking layer 25 can be made of materials such as TAPC or TCTA. However, this disclosure is not limited thereto. The electron blocking layer 25 can be made of a material similar to the hole transport layer 22, but with a lower HOMO level than the hole transport layer 22 and a higher LUMO level than the core of the blue emitter layer 50 by changing the substituents. As an example, the electron transport layer 60 can be made of a compound having anthracene as a core.

[0076] The material of the blue emitting layer 50 may include at least one blue host and at least one blue dopant. Specifically, the blue emitting layer 50 may be formed by doping at least one host material selected from the group consisting of anthracene derivatives, pyrene derivatives and perylene derivatives with a pyrene-based or boron-based blue dopant.

[0077] Meanwhile, the material for the layer specified in the first experimental example (Ex1) is provided as an example. It makes sense to use the same material for the same layer in the first to fourth experimental examples, and other materials may also be used as long as they can provide the same or similar functionality.

[0078] In the light-emitting element according to the second experimental example (Ex2), such as Figure 4B As shown, a thickness of [thickness value missing] is sequentially formed on the first electrode 110 made of ITO. Hole injection layer 121, thickness is Hole transport layer 122, thickness is Hole generation layer 130, thickness is The electron blocking layer 140 has a thickness of The blue emitting layer is 150, and its thickness is The electron transport layer 160 has a thickness of The n-type charge generation layer 170a and the second electrode 200 made of aluminum.

[0079] In the second experimental example (Ex2), the hole generation layer 130 has the same material as the electron blocking layer 140 as its host material, and has a material represented by the above-described chemical formula 2 as a p-type dopant. The p-type dopant is included so that it accounts for 5 vol% of the hole generation layer 130. The sum of the thicknesses of the hole generation layer 130 and the electron blocking layer 140 in the second experimental example is... It is equal to the thickness of the electron blocking layer 25 in the first experimental example.

[0080] In the third experimental example (Ex3), it is provided Figure 4B The structure is the same as in the second experimental example (Ex2), and the materials and doping amounts of each layer are the same, but the difference is that the thicknesses of the hole generation layer 130 and the electron blocking layer 140 are respectively... and

[0081] [Table 1]

[0082]

[0083] ΔEQE, which is the change in external quantum efficiency based on the change in current density in each experiment, is at a current density of 0.1 mA / cm². 2 The external quantum efficiency during the driving period is the same as that at a current density of 10 mA / cm². 2 The ratio of external quantum efficiency during the driving period.

[0084] Vc, which is the driving voltage in each of the first to third experimental examples compared to the driving voltage in the first experimental example, at a current density of 10 mA / cm². 2 The initial state represents the fluctuation value of the driving voltage over time. When the hole generation layer is set, compared with the first experimental example (reference), the value of Vc represents the voltage drop due to the increase in current density.

[0085] Furthermore, Δ lifetime (T95) is the lifetime until the efficiency degrades to 95% of the initial efficiency, compared to the first experimental example.

[0086] From Table 1 and Figure 5 It can be seen that in the first experimental example (Ex1), assuming a current density of 10 mA / cm² 2 If the external quantum efficiency during the driving period is 1, then at a current density of 0.1 mA / cm², the quantum efficiency is 1. 2 During the driving period, the external quantum efficiency drops to 0.56, resulting in a sudden change in external quantum efficiency between high and low levels. In the first to third experimental examples, a blue emission layer was used as the emission layer of the first stack. That is, in the blue stack, there is a sudden difference in color efficiency during low-level driving. In a structure with multiple stacks, white light is implemented in a state where the efficiency of blue light is relatively low at low levels, and the efficiency of blue light is lower than that of other colors, as in the structure of the first experimental example.

[0087] In contrast, in the second experimental example (Ex2), a hole generation layer was placed between the hole transport layer and the electron blocking layer, assuming that in the first experimental example (Ex1) the current density was 10 mA / cm². 2 If the external quantum efficiency during the driving period is 1, then at a current density of 0.1 mA / cm², the quantum efficiency is 1. 2 The external quantum efficiency during the driving period is 0.85, indicating that the change in external quantum efficiency between high and low levels is significantly reduced compared to the first experimental example. Furthermore, the change in external quantum efficiency between high and low levels is 15% or less, demonstrating that the visibility of color efficiency changes is greatly reduced during low-level driving.

[0088] Meanwhile, in the third experimental example (Ex3), a hole generation layer was set between the hole transport layer and the electron blocking layer, and the thickness of the hole generation layer was increased. It is assumed that in the first experimental example (Ex1), the current density was 10 mA / cm². 2 If the external quantum efficiency during the driving period is 1, then at a current density of 0.1 mA / cm², the quantum efficiency is 1. 2 The external quantum efficiency during the driving period is 0.89, indicating that the variation in external quantum efficiency between the high and low levels is further reduced compared to the second experimental example. Furthermore, the variation in external quantum efficiency between the high and low levels is 11% or less, thus virtually eliminating the visibility of color efficiency variations during the low-level driving period.

[0089] Furthermore, as shown in Table 1, it can be seen that the driving voltage of the second and third experimental examples (Ex2 and Ex3) is 0.1V and 0.3V lower than that of the first experimental example, respectively. Thus, the driving voltage is reduced in both the second and third experimental examples (Ex2 and Ex3) in which the hole generation layer is set.

[0090] exist Figure 6 In the experiment, the temperature was 40℃ and the current density was 22.5 mA / cm². 2 In this case, the lifetime and the change in drive voltage based on the initial state were measured.

[0091] like Figure 6 As shown, in the first experimental example, the driving voltage changes significantly over time, while in the second and third experimental examples, the change in driving voltage over time is significantly reduced. In the first experimental example, the large change in driving voltage over time makes it difficult to drive the light-emitting element at the initial driving voltage after a predetermined time. In contrast, in the second and third experimental examples, the smaller change in driving voltage over time allows for stable driving of the light-emitting element under conditions similar to the initial state for a longer period.

[0092] In addition, such as Figure 6 As shown, in the second and third experimental examples where a hole generation layer was provided, the 95 lifetime (T95) was twice or more than that of the first experimental example where no hole generation layer was provided. This is because, as previously mentioned, hole accumulation occurred at the interface of the hole transport layer in the first experimental example, while in the second and third experimental examples, by providing a hole generation layer, some electrons or excitons emitted from the emitter layer were absorbed to generate holes, thereby increasing the number of generated holes and thus stably maintaining the balance of holes and electrons at the emitter layer.

[0093] The JV (current density and voltage) characteristics of the hole generation layer-based material will now be described with further reference to the fourth experimental example.

[0094] Figure 7 It schematically shows a cross-sectional view of the light-emitting element according to the fourth experimental example (Ex4), and Figure 8 It is a graph showing the JV characteristics in the first, third, and fourth experimental examples. Figure 9 It is a graph showing the conduction voltage characteristics in the first, third, and fourth experimental examples.

[0095] like Figure 7 As shown, in the light-emitting element according to the fourth experimental example, the hole generation layer 130c is formed using only a single p-type dopant. In this case, in the fourth experimental example, the hole generation layer is formed using only a p-type dopant in order to have… The thickness of the layers was such that the other layers had the same structure as in the third experimental example, so that the JV properties could be compared based on the differences in material composition compared to the third experimental example. Meanwhile, the material represented by the aforementioned chemical formula 1 was used as the p-type dopant in the fourth experimental example.

[0096] In both the third and fourth experimental examples, when the voltage value increases, as... Figure 8 As shown, it can be seen that the current density increases when a drive voltage of 4V or greater is applied, and 15mA / cm is obtained when the drive voltage is 6V or greater. 2 The current density was significantly higher. In contrast, in the first experimental example, without a hole generation layer, the current density was less than 5 mA / cm² even when a drive voltage of 6V or higher was applied. 2 Therefore, it can be seen that when a hole generation layer is set, the driving voltage required to achieve a given current density can be reduced.

[0097] At the same time, such as Figure 9 As shown, it can be seen that in both the third and fourth experimental examples, 0.001 mA / cm was obtained. 2 The required driving voltage for the current density is reduced. In the fourth experimental example, where the hole generation layer consists of only a single p-type dopant, the turn-on driving voltage is increased, similar to the first experimental example. This means that when the hole generation layer is composed only of p-type dopant, there are limitations in reducing the initial turn-on voltage, and it can be seen that the hole generation layer requires an organic host capable of performing electron blocking functions.

[0098] Meanwhile, in Formula 2, which was used as a p-type dopant in the third experimental example, the axialene core has substituents with high electronegativity. Therefore, the p-type dopant has a lower band gap than known p-type dopants (e.g., TCNQ or F4TCNQ), and thus can be used to dop organic hosts with HOMO energy levels lower than the hole transport layer.

[0099] The following will describe embodiments of the light-emitting element according to the present disclosure and a display device having the light-emitting element applied thereto.

[0100] Figure 10 This is a schematic cross-sectional view of a light-emitting element according to a first embodiment of the present disclosure.

[0101] like Figure 10 As shown, the light-emitting element OLED according to the first embodiment of the present disclosure is configured such that two stacks (first stack S1 and second stack S2) are separated by a charge generation layer 170 located between a first electrode 110 and a second electrode 200 that are opposite to each other on the substrate 100.

[0102] For reference Figure 1 The description and such Figure 10 As shown, the first stack S1 includes a stack formed by a hole injection layer 121, a hole transport unit 1200 consisting of a hole transport layer (HTL1) 122, a hole generation layer 130, and an electron blocking layer 140, which are sequentially disposed on the first electrode 110; a blue emission layer (BEML1) 150; and an electron transport layer (ETL1) 160. That is, the hole generation layer 130 of the first stack S1 can attract or pull some electrons or excitons emitted from the blue emission layer 150 to generate holes, thereby increasing the injection rate and the number of holes reaching the blue emission layer 150, and maintaining the balance of holes and electrons at the blue emission layer 150, regardless of current density.

[0103] The second stack S2 may include an emitting layer capable of emitting white light together with the blue emitting layer 150, so as to emit white light according to the combination of light emitted from the first stack S1 and the second stack S2. As an example, Figure 10 As shown, the emitting portion 190 of the second stack S2 includes multiple emitting layers with different wavelengths longer than that of blue light. The emitting portion 190 is disposed between the hole transport layer (HTL2) 180 and the electron transport layer (ETL2) 185, and includes a red emitting layer (REML) 191, a yellow-green emitting layer (YG EML) 192, and a green emitting layer (G EML) 193.

[0104] Depending on the circumstances, the emitting section 190 may have a two-layer structure, including a red emitting layer 191 and a yellow-green emitting layer 192.

[0105] When the blue emitting layer 150 of the first stack S1 is a fluorescent emitting layer, each of the emitting layers 191, 192, and 193 disposed in the emitting portion 190 of the second stack S2 can be a phosphorescent emitting layer. However, this is only an example, and the emitting layers of the first stack S1 and the second stack S2 can both be fluorescent or phosphorescent emitting layers. Depending on the situation, when the blue emitting layer 150 of the first stack S1 is a fluorescent emitting layer, any one of the plurality of emitting layers disposed in the second stack S2 can be a fluorescent emitting layer, while the other emitting layers can be phosphorescent emitting layers. Alternatively, each emitting layer can include both a fluorescent dopant and a phosphorescent dopant, thereby the emitting layer can have both fluorescent and phosphorescent properties.

[0106] Figure 11 This is a schematic cross-sectional view of a light-emitting element according to a second embodiment of the present disclosure.

[0107] like Figure 11 As shown, the light-emitting element according to the second embodiment of this disclosure is configured such that a second charge-generating layer 270 and a third stack S3 are further disposed on the second stack in the light-emitting element according to the first embodiment, and the third stack S3 is a blue emitting stack. In this case, the second charge-generating layer 270 may be composed of a stack formed of an n-type charge-generating layer (N-CGL2) 270a and a p-type charge-generating layer (P-CGL2) 270b, as in the first charge-generating layer 170 disposed between the first stack S1 and the second stack S2.

[0108] The third stack S3 includes [a structure] with [a structure] Figure 1 The same arrangement is used in the third stack S3, where a hole transport unit 1250, a second blue emission layer (BEML2) 250, and an electron transport layer (ETL3) 260 are sequentially arranged on the p-type charge generation layer 270b, consisting of a hole transport layer (HTL3) 222, a hole generation layer 230, and an electron blocking layer 240. As previously described, even in the third stack S3, the hole generation layer 230 in the hole transport unit 1250 can attract or pull some electrons or excitons discharged from the second blue emission layer 250 to generate holes, thereby increasing the injection rate and the number of holes reaching the second blue emission layer 250 and maintaining the balance of holes and electrons at the second blue emission layer 250, regardless of current density.

[0109] Depending on the circumstances, the hole generation layer may be provided only in the first stack S1, and the hole generation layer may be omitted from the third stack S3. In the first stack S1, the hole injection layer 121 made of metal fluoride and the n-type charge generation layer 170a doped with metal ions (e.g., lithium) are located at their two interfaces. Therefore, due to the physical characteristics of the layers in the first stack, the initial resistance may be high, and thus, during low-level driving, a difference in the migration velocity between holes and electrons may easily occur. To compensate for this, a hole generation layer is provided in the first stack S1.

[0110] Figures 12A to 12C This is a schematic cross-sectional view of a light-emitting element according to the third to fifth embodiments of the present disclosure.

[0111] refer to Figures 12A to 12C According to the third to fifth embodiments of this disclosure, the light-emitting elements are configured to further improve blue efficiency. Each light-emitting element includes four stacks disposed between the first electrode 110 and the second electrode 200, and the phosphorescent stack PS includes an emitting layer having a color other than blue, while the other stacks are composed of blue stacks BS1, BS2 and BS3.

[0112] Furthermore, the light-emitting elements according to the third to fifth embodiments of this disclosure can be distinguished from each other based on the position of the phosphorescent stack PS. Figure 12A In the light-emitting element of the third embodiment shown, the second stack starting from the first electrode 110 is a phosphorescent stack (PS). According to... Figure 12B In the light-emitting element of the fourth embodiment shown, the third stack starting from the first electrode 110 is a phosphorescent stack PS. According to... Figure 12C In the light-emitting element of the fifth embodiment shown, the fourth stack starting from the first electrode 110 is a phosphorescent stack PS.

[0113] In each of the blue stacks BS1, BS2, and BS3, a hole transport unit 1200, consisting of a stack formed by a hole transport layer 122, a hole generation layer 130, and an electron blocking layer 140, may be disposed adjacent to the blue emission layer, as shown in the reference. Figure 1 As mentioned above.

[0114] Even in the light-emitting elements according to the third to fifth embodiments, the same effect can be obtained due to the hole generation layer.

[0115] Figure 13 This is a schematic cross-sectional view of a light-emitting element according to a sixth embodiment of the present disclosure.

[0116] Figure 13The light-emitting element shown according to the sixth embodiment of the present disclosure is configured such that a single stack including a single emitting layer 1500 is disposed between the first electrode 110 and the second electrode 200.

[0117] Compared to the above embodiments, the emitting layer 1500 can be an emitting layer configured to emit light of a color different from blue light. Therefore, the emitting layer 1500 can be a green emitting layer, a red emitting layer, or an emitting layer that emits light of another color.

[0118] like Figure 13 As shown, the light-emitting element according to the sixth embodiment includes an emitting layer 1500 disposed between a first electrode 110 and a second electrode 200, a hole transport unit 1200 comprising a hole transport layer 1220, a hole generation layer 1300 and an electron blocking layer 1400 sequentially disposed between the first electrode 110 and the emitting layer 1500, and an electron transport layer 1600 disposed between the emitting layer 1500 and the second electrode 200. An electron injection layer may be further disposed between the electron transport layer 1600 and the second electrode 200.

[0119] The hole transport unit 1200 according to this disclosure includes a hole transport layer 1220 configured to transport holes injected from a hole injection layer 1210 to an emitter layer 1500, an electron blocking layer 1400 configured to prevent excitons generated in the emitter layer 1500 or electrons transported to the emitter layer 1500 from being transported to the hole transport layer 1220, and a hole generation layer 1300 disposed between the hole transport layer 1220 and the electron blocking layer 1400. The hole generation layer 1300 is configured to attract or pull some electrons or excitons discharged through the electron blocking layer 1400, thereby providing a hole generation effect. The hole generation layer 1300 includes a material constituting the electron blocking layer 1400 or an organic material having a band gap similar to that of the material constituting the electron blocking layer 1400 as a main body, and also includes a p-type dopant pd.

[0120] The body constituting the hole generation layer 1300 may have LUMO and HOMO energy levels that differ from the LUMO and HOMO energy levels of the electron blocking layer 1400 by 1 eV or less. To prevent electrons or excitons from being transported to the hole transport layer when electrons or excitons are primarily emitted from the emitter layer 1500, the body has LUMO energy levels not lower than the LUMO energy level of the emitter layer 1500. Furthermore, to transport holes transported from the hole transport layer 1220 to the emitter layer 1500 without internal accumulation, the body has HOMO energy levels equal to or lower than the HOMO energy level of the hole transport layer 1220 and HOMO energy levels higher than the HOMO energy level of the emitter layer 1500.

[0121] Furthermore, the p-type dopant included in the hole generation layer 1300 has a very low HOMO energy level of -9.0 eV or less, so as to absorb or pull some electrons or excitons discharged from the electron blocking layer 1400, generate holes in vacancies, and interact with the hole transport material (which is the host) in the surrounding hole generation layer, thereby enhancing the hole generation and transport functions.

[0122] p-type dopant pd includes substituents located at the terminal groups, such as cyanide (CN) groups or fluorine (F) groups, thereby enhancing electron extraction capabilities. p-type dopant pd not only traps electrons but also attracts or pulls electrons, generating holes in electron vacancies to increase hole generation in hole transport unit 1200 and improve hole transport capability. Therefore, it can prevent the accumulation of hole carriers that may occur in hole transport layer 1220 and electron blocking layer 1400 during driving, increase the migration speed of holes ultimately transported to the emitter layer, and increase the number of holes.

[0123] according to Figure 13 The light-emitting element of the sixth embodiment shown is structurally similar to... Figure 1 The first stack is similar, which means that even a single emitting stack that emits light of colors other than blue has the effect of setting up a hole generation layer.

[0124] Figure 14 This is a cross-sectional view showing a display device according to the present disclosure.

[0125] At the same time, the light-emitting element can be applied to multiple sub-pixels to emit white light through the electrode on the exit side.

[0126] like Figure 14 As shown, the display device according to this disclosure may include a substrate 100 having a plurality of sub-pixels R_SP, G_SP, B_SP and W_SP; a white light emitting element OLED commonly disposed on the substrate 100; a thin film transistor TFT disposed at each sub-pixel, the thin film transistor being connected to a first electrode 110 of the white light emitting element OLED; and color filter layers 109R, 109G and 109B disposed under the first electrode 110 of at least one of the sub-pixels.

[0127] In the example shown, a white subpixel W_SP is included; however, this disclosure is not limited thereto. The white subpixel W_SP may be omitted, and only the red subpixel R_SP, green subpixel G_SP, and blue subpixel B_SP may be set. Depending on the situation, a combination of cyan, magenta, and yellow subpixels capable of representing white may be used instead of the red, green, and blue subpixels.

[0128] 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. A channel passivation layer 105 configured to prevent direct connection between the source electrode 106a and the drain electrode 106b and the semiconductor layer 104 may be further provided on the portion of the semiconductor layer 104 where the channel is located.

[0129] A gate insulating film 103 is disposed between the gate electrode 102 and the semiconductor layer 104.

[0130] For example, the semiconductor layer 104 can be made of any one or a combination of two or more of oxide semiconductors, amorphous silicon, and polycrystalline silicon. For example, when the semiconductor layer 104 is made of oxide semiconductors, the heating temperature required to form thin-film transistors can be reduced, and therefore the degree of freedom in using the substrate 100 is greater, which is advantageous when applied to flexible display devices.

[0131] Furthermore, the drain electrode 106b of the thin-film transistor TFT can be connected to the first electrode 110 in the contact hole CT disposed in the first passivation film 107 and the second passivation film 108.

[0132] The first passivation film 107 is configured to primarily protect the thin-film transistor TFT, and color filter layers 109R, 109G and 109B may be disposed thereon.

[0133] When multiple sub-pixels include 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, color filter layers can be provided at sub-pixels excluding the white sub-pixel W_SP as first to third color filter layers 109R, 109G, and 109B to transmit white light passing through the first electrode 110 based on its wavelength. Furthermore, a second passivation film 109 is formed under the first electrode 110 to cover the first to third color filter layers 109R, 109G, and 109B. The first electrode 110 is formed on the surface of the second passivation film 109 excluding the contact hole CT.

[0134] Here, the light-emitting element OLED includes: a first electrode 110, which is transparent; a second electrode 200 opposite to the first electrode, the second electrode being reflective; and a hole transport unit 1200 composed of a hole transport layer, a hole generation layer, and an electron blocking layer disposed in any one of a stack separated by a charge generation layer located between the first electrode 110 and the second electrode 200, as shown below. Figures 10 to 12C As shown.

[0135] The first electrode 110 is divided for each sub-pixel, while the other layers of the white light-emitting element OLED are disposed as a whole on the display area without any sub-pixel-specific division.

[0136] Here, reference numeral 119 indicates a dam, and BH between the dams indicates a dam aperture. Light is emitted from the area open through the dam aperture, and the dam aperture defines the emission portion of each sub-pixel.

[0137] Meanwhile, as a structure below the first electrode 110, the substrate 100, the thin-film transistor TFT, the color filter layers 109R, 109G and 109B, and the insulating film on which these components are disposed are referred to as the thin-film transistor array substrate.

[0138] In the light-emitting element and the display device including the light-emitting element according to the present disclosure, an electron blocking layer configured to primarily block electrons or excitons emitted from the emission layer from reaching the hole transport layer is provided between the emission layer and the hole transport layer, and a hole generating layer configured to receive some of the emitted electrons or excitons to generate holes is further provided between the hole transport layer and the electron blocking layer, thereby increasing the number and speed of holes reaching the emission layer and preventing hole accumulation between the hole transport layer and the emission layer.

[0139] Furthermore, the hole generation layer is formed by doping an organic material (as the host) capable of performing electron blocking functions with a p-type organic dopant having a LUMO energy level similar to the HOMO energy level of the electron blocking layer. This allows electrons located at the HOMO energy level of the electron blocking layer to be easily absorbed, and thus allows the generated holes to be easily transported through the hole generation layer and the electron blocking layer.

[0140] Furthermore, the p-type organic dopants in the hole generation layer include substituents that absorb or pull electrons at the terminal groups, thereby ensuring low resistance in the current path caused by holes even in the initial state without applied bias and in the low current density drive state, and thus reducing the initial turn-on voltage.

[0141] Furthermore, in a structure comprising multiple stacks, where a high-mobility electron transport layer is required for the blue stack due to its lower efficiency compared to stacks with other color emission layers, a hole generation layer is provided to reduce the resistance in hole transport. This prevents carrier accumulation even during low current density driving and maintains a balance in the recombination between holes and electrons in the emission layer, thus preventing poor visibility at low levels.

[0142] A light-emitting element according to an embodiment of the present disclosure may include a first electrode and a second electrode opposite to each other, at least one charge-generating layer disposed between the first electrode and the second electrode, and a first stack. The first stack is disposed between the first electrode and the first charge-generating layer in the at least one charge-generating layer, and includes a first emitting layer, a hole transport layer including a hole transport layer, a hole generation layer and an electron blocking layer disposed sequentially between the first electrode and the first emitting layer, and an electron transport layer disposed between the first emitting layer and the first charge-generating layer. The hole generation layer may include an organic host and a p-type dopant. The LUMO and HOMO energy levels of the organic host differ from the LUMO and HOMO energy levels of the electron blocking layer by 1 eV or less, respectively. The p-type dopant may have a HOMO energy level of -9.0 eV or less.

[0143] In a light-emitting element according to an embodiment of the present disclosure, the p-type dopant has a LUMO level that differs from the HOMO level of the electron blocking layer by 1 eV or less.

[0144] In a light-emitting element according to an embodiment of the present disclosure, the p-type dopant may be an organic material comprising an electron-withdrawing substituent at a terminal group.

[0145] In a light-emitting element according to an embodiment of the present disclosure, the p-type dopant may have an axylene as the core and include one or more different kinds of substituents that draw electrons at the terminal groups.

[0146] In a light-emitting element according to an embodiment of the present disclosure, the first stack may further include a hole injection layer comprising a metal fluoride and disposed between the first electrode and the hole transport layer.

[0147] In a light-emitting element according to an embodiment of the present disclosure, the first charge generation layer includes an n-type charge generation layer and a p-type charge generation layer. The electron transport layer of the first stack may be adjacent to the n-type charge generation layer.

[0148] In a light-emitting element according to an embodiment of the present disclosure, the hole-generating layer may be adjacent to the electron-blocking layer, and the thickness ratio of the hole-generating layer to the electron-blocking layer may be 1:4 to 1:1.

[0149] In a light-emitting element according to an embodiment of the present disclosure, the organic host of the hole generation layer may be the same as the organic material constituting the electron blocking layer.

[0150] In a light-emitting element according to an embodiment of the present disclosure, at least one charge-generating layer may include a first charge-generating layer and a second charge-generating layer spaced apart from each other. The light-emitting element may also include a second stack disposed between the first charge-generating layer and the second charge-generating layer, and a third stack disposed between the second charge-generating layer and a second electrode. Furthermore, the second stack may include a second emitting layer and another hole transport unit disposed between the first charge-generating layer and the second emitting layer, the other hole transport unit of the second stack being identical to the hole transport unit of the first stack.

[0151] A display device according to an embodiment of the present disclosure may include a substrate having a plurality of sub-pixels, a transistor at each sub-pixel, and a light-emitting element. The light-emitting element includes a first electrode connected to the transistor at each sub-pixel, a second electrode opposite to the first electrode, and a plurality of stacked bodies separated by at least one charge-generating layer located between the first electrode and the second electrode. The first stacked body of the plurality of stacked bodies may be disposed between the first electrode and the first charge-generating layer, and includes a first emitting layer, a hole transport layer including a hole transport layer, a hole generation layer, and an electron blocking layer sequentially disposed between the first electrode and the first emitting layer, and an electron transport layer disposed between the first emitting layer and the first charge-generating layer. The hole generation layer may include an organic host and a p-type dopant. The organic host may have a LUMO level and a HOMO level that differ from the LUMO level and HOMO level of the electron blocking layer by 1 eV or less, respectively, and the p-type dopant may have a HOMO level of -9.0 eV or less.

[0152] In a display device according to an embodiment of the present disclosure, the p-type dopant may be an organic material comprising an electron-withdrawing substituent at a terminal group.

[0153] In a display device according to an embodiment of the present disclosure, the p-type dopant may have an axial ene as a core and may include two or more different kinds of substituents that draw electrons at the terminal groups.

[0154] In a display device according to an embodiment of the present disclosure, the first stack may further include a hole injection layer comprising a metal fluoride and disposed between the first electrode and the hole transport layer.

[0155] In a display device according to an embodiment of the present disclosure, the first charge generation layer may include an n-type charge generation layer and a p-type charge generation layer, and the electron transport layer of the first stack may be adjacent to the n-type charge generation layer.

[0156] In a display device according to an embodiment of the present disclosure, the hole generation layer may be adjacent to the electron blocking layer, and the thickness ratio of the hole generation layer to the electron blocking layer may be from 1:4 to 1:1.

[0157] In a display device according to an embodiment of the present disclosure, the organic host of the hole generation layer may be the same as the organic material constituting the electron blocking layer.

[0158] In a display device according to an embodiment of the present disclosure, at least one charge generation layer may include a first charge generation layer and a second charge generation layer spaced apart from each other. A plurality of stacks may also include a second stack disposed between the first and second charge generation layers and a third stack disposed between the second charge generation layer and a second electrode. Furthermore, the second or third stack may include a second emitter layer and another hole transport unit disposed between the first and second charge generation layers, the other hole transport unit of the second or third stack being identical to the hole transport unit of the first stack.

[0159] In a display device according to an embodiment of the present disclosure, a second emitting layer of a second stack or a third stack including another hole transport unit can emit light of the same color as the first emitting layer.

[0160] In a display device according to an embodiment of the present disclosure, the at least one charge generation layer may further include a third charge generation layer, and the plurality of stacks may further include a fourth stack located between the third charge generation layer and the second electrode, and the fourth stack may include an emitting layer configured to emit light of a different color than the first emitting layer.

[0161] In another embodiment of this disclosure, a light-emitting element includes a first electrode; a hole transport layer on the first electrode; a hole generation layer directly disposed on the hole transport layer; an electron blocking layer directly disposed on the hole generation layer; an emission layer on the electron blocking layer; an electron transport layer on the emission layer; and a second electrode on the electron transport layer, wherein the hole generation layer includes an organic host and a p-type dopant, the organic host having a LUMO level and a HOMO level that differ from the LUMO level and HOMO level of the electron blocking layer by 1 eV or less, respectively, and the LUMO level of the p-type dopant differs from the HOMO level of the electron blocking layer by 1 eV or less.

[0162] In another embodiment of the light-emitting element according to this disclosure, the p-type dopant may have a HOMO level of -9.0 eV or less.

[0163] In another embodiment of the light-emitting element according to the present disclosure, the p-type dopant may be an organic material comprising an electron-withdrawing substituent at the terminal group.

[0164] In another embodiment of the light-emitting element according to the present disclosure, the p-type dopant may have an axylene as the core and include one or more different kinds of substituents that draw electrons at the terminal groups.

[0165] In another embodiment of the light-emitting element according to the present disclosure, the thickness ratio of the hole-generating layer to the electron-blocking layer may be from 1:4 to 1:1.

[0166] In another embodiment of the light-emitting element according to the present disclosure, the organic host of the hole generation layer may be the same as the organic material constituting the electron blocking layer.

[0167] Based on the above description, it is clear that the light-emitting element according to this disclosure and the display device including the light-emitting element have the following effects.

[0168] First, an electron blocking layer configured to primarily block electrons or excitons emitted from the emitter layer from reaching the hole transport layer is provided between the emitter layer and the hole transport layer. Furthermore, a hole generating layer configured to receive some emitted electrons or excitons to generate holes is provided between the hole transport layer and the electron blocking layer. This increases the number and speed of holes reaching the emitter layer and prevents hole accumulation between the hole transport layer and the emitter layer.

[0169] Second, the hole generation layer is formed by doping an organic material (as the host) capable of performing electron blocking function with a p-type organic dopant having a LUMO energy level similar to the HOMO energy level of the electron blocking layer. This allows electrons located at the HOMO energy level of the electron blocking layer to be easily absorbed, and thus allows the generated holes to be easily transported through the hole generation layer and the electron blocking layer.

[0170] Third, the p-type organic dopant of the hole generation layer includes electron-withdrawing substituents at the terminal groups, thereby ensuring low resistance in the current path caused by holes even in the initial state without applied bias and in the low current density driving state, and thus reducing the initial turn-on voltage.

[0171] Fourth, in a structure comprising multiple stacks, where a high-mobility electron transport layer is required for the blue stack due to its lower efficiency compared to stacks with other color emission layers, a hole generation layer is provided to reduce the resistance in hole transport. This prevents carrier accumulation even during low current density driving and maintains a balance in the recombination between holes and electrons in the emission layer, thus preventing poor visibility at low levels.

[0172] While embodiments of the present disclosure have been described with reference to the accompanying drawings, the present disclosure is not limited to these embodiments and can be implemented in a variety of different forms. Those skilled in the art will understand that the present disclosure can be implemented in specific forms other than those described herein without departing from the technical spirit and essential characteristics of the present disclosure. Therefore, the disclosed embodiments should be interpreted in all respects as illustrative and not restrictive.

Claims

1. A light-emitting element, comprising: The first and second electrodes are opposite to each other; At least one charge generation layer disposed between the first electrode and the second electrode; as well as A first stack, disposed between the first electrode and a first charge generation layer in the at least one charge generation layer, includes a first emitter layer, a hole transport layer comprising a hole transport layer, a hole generation layer, and an electron blocking layer sequentially disposed between the first electrode and the first emitter layer, and an electron transport layer disposed between the first emitter layer and the first charge generation layer, wherein... The hole generation layer comprises an organic host and a p-type dopant. The LUMO and HOMO energy levels of the organic host differ from the LUMO and HOMO energy levels of the electron blocking layer by 1 eV or less, respectively. The HOMO level of the p-type dopant is -9.0 eV or less.

2. The light-emitting element according to claim 1, wherein, The LUMO level of the p-type dopant differs from the HOMO level of the electron blocking layer by 1 eV or less.

3. The light-emitting element according to claim 1, wherein, The p-type dopant is an organic material that includes an electron-withdrawing substituent at the terminal group.

4. The light-emitting element according to claim 1, wherein, The p-type dopant has an axial alkene as its core and includes one or more different kinds of substituents that extract electrons at the terminal groups.

5. The light-emitting element according to claim 1, wherein, The first stack also includes a hole injection layer comprising a metal fluoride and disposed between the first electrode and the hole transport layer.

6. The light-emitting element according to claim 1, wherein, The first charge generation layer includes an n-type charge generation layer and a p-type charge generation layer, and The electron transport layer of the first stack is adjacent to the n-type charge generation layer.

7. The light-emitting element according to claim 1, wherein, The hole-generating layer is adjacent to the electron-blocking layer, and The thickness ratio of the hole-generating layer to the electron-blocking layer is 1:4 to 1:

1.

8. The light-emitting element according to claim 7, wherein, The organic host of the hole-generating layer is the same as the organic material constituting the electron-blocking layer.

9. The light-emitting element according to claim 1, wherein, The at least one charge generation layer further includes a second charge generation layer spaced apart from each other. The light-emitting element further includes a second stack disposed between the first charge-generating layer and the second charge-generating layer, and a third stack disposed between the second charge-generating layer and the second electrode. The second stack includes a second emitter layer and another hole transport unit disposed between the first charge generation layer and the second emitter layer, wherein the other hole transport unit of the second stack is the same as the hole transport unit of the first stack.

10. A display device, comprising: A substrate with multiple sub-pixels; The transistor is located at each sub-pixel; as well as A light-emitting element includes a first electrode connected to the transistor located at each sub-pixel, a second electrode opposite to the first electrode, and a plurality of stacked bodies separated by at least one charge-generating layer disposed between the first electrode and the second electrode, wherein... The first stack of the plurality of stacks is disposed between the first electrode and the first charge generation layer of the at least one charge generation layer, and includes a first emitter layer, a hole transport layer including a hole transport layer, a hole generation layer and an electron blocking layer disposed sequentially between the first electrode and the first emitter layer, and an electron transport layer disposed between the first emitter layer and the first charge generation layer. The hole generation layer comprises an organic host and a p-type dopant. The LUMO and HOMO energy levels of the organic host differ from the LUMO and HOMO energy levels of the electron blocking layer by 1 eV or less, respectively. The HOMO level of the p-type dopant is -9.0 eV or less.

11. The display device according to claim 10, wherein, The p-type dopant is an organic material that includes an electron-withdrawing substituent at the terminal group.

12. The display device according to claim 10, wherein, The p-type dopant has an axial alkene as its core and includes two or more different types of substituents that draw electrons from end groups.

13. The display device according to claim 10, wherein, The first stack also includes a hole injection layer comprising a metal fluoride and disposed between the first electrode and the hole transport layer.

14. The display device according to claim 10, wherein, The first charge generation layer includes an n-type charge generation layer and a p-type charge generation layer, and The electron transport layer of the first stack is adjacent to the n-type charge generation layer.

15. The display device according to claim 10, wherein, The hole-generating layer is adjacent to the electron-blocking layer, and The thickness ratio of the hole-generating layer to the electron-blocking layer is 1:4 to 1:

1.

16. The display device according to claim 15, wherein, The organic host of the hole-generating layer is the same as the organic material constituting the electron-blocking layer.

17. The display device according to claim 10, wherein, The at least one charge generation layer includes a first charge generation layer and a second charge generation layer spaced apart from each other. The plurality of stacks further includes a second stack disposed between the first charge generation layer and the second charge generation layer, and a third stack disposed between the second charge generation layer and the second electrode. The second stack or the third stack includes a second emitter layer and another hole transport unit disposed between the first charge generation layer and the second emitter layer, wherein the other hole transport unit of the second stack or the third stack is the same as the hole transport unit of the first stack.

18. The display device according to claim 17, wherein, The second emission layer of the second stack, which includes the other hole transmission unit, or the third stack, emits light of the same color as the first emission layer.

19. The display device according to claim 17, wherein, The at least one charge generation layer further includes a third charge generation layer, and the plurality of stacks further include a fourth stack disposed between the third charge generation layer and the second electrode. The fourth stack includes a fourth emitting layer configured to emit light of a different color than the first emitting layer.

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