Light-emitting element and light-emitting display device including the light-emitting element.

Abstract

The holes transmitted to the green light-emitting layer are not trapped by the green dopant, and hole transfer is also generated in the hole-transporting and electron-transporting hosts within the green light-emitting layer, thereby preventing the accumulation of charge within the green light-emitting layer. [Solution] A light-emitting element comprising a first electrode and a second electrode facing each other, and a green light-emitting stack comprising a hole transport layer HTL, a capacitance relaxation layer CRL, a green light-emitting layer GEML, and an electron transport layer ETL disposed between the first and second electrodes, wherein the capacitance relaxation layer comprises an auxiliary dopant with a HOMO energy level lower than that of the green dopant of the green light-emitting layer.

Description

Technical Field

[0001] This specification relates to an invention of a light-emitting device with improved image quality and efficiency and a light-emitting display device including the light-emitting device.

Background Art

[0002] With the advent of the full-fledged information age, the field of displays that visually represent electrical information signals has been rapidly developing. Accordingly, many diverse display devices having excellent performance in terms of thinning, lightening, and low power consumption have been developed.

[0003] Among these, a light-emitting display device that does not require a separate light source, does not have a separate light source for compactification of the device and vivid color display, and has a light-emitting device in the display panel is considered as a competitive application.

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

[0005] On the other hand, the light-emitting device may include various functional layers in the common layer, for example, for various functions. Among many functional layers, a hole transport layer that transmits holes to the light-emitting layer and an electron transport layer that transmits electrons to the light-emitting layer are included.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The light-emitting device may include light-emitting layers that emit different colors from each other in order to represent various colors.

[0007] In recent years, in a light-emitting display device including different light-emitting layers, when converting from a black state to a low-gray state, a flashing phenomenon in which a specific color is significantly visible has been a problem.

[0008] The light-emitting element according to the embodiments of this specification has a structure that includes light-emitting layers of different colors, and the objective is to improve the image quality defects in which a particular color is prominent when switching from an off state (black state) to a low-gradation gray state.

[0009] The light-emitting display device according to the embodiments of this specification aims to reduce the driving voltage of the green light-emitting stack, which has a high specificity in color representation. [Means for solving the problem]

[0010] A light-emitting element according to one embodiment of this specification includes a first electrode and a second electrode facing each other, and a green light-emitting stack disposed between the first and second electrodes, the stack including a hole transport layer, a capacitance relaxation layer, a green light-emitting layer, and an electron transport layer, wherein the capacitance relaxation layer may include an auxiliary dopant with a HOMO energy level lower than that of the green dopant of the green light-emitting layer.

[0011] The light-emitting element according to the embodiments of this specification and the light-emitting device including the same include a capacitance-relieving layer containing an auxiliary dopant between the hole-transporting common layer and the green light-emitting layer. The auxiliary dopant is either a green dopant in the green light-emitting layer or has a low HOMO energy level. When holes are injected from the hole-transporting common layer into the green light-emitting layer, the holes are not immediately trapped by the green dopant but can be sequentially transferred to the green dopant in the green light-emitting layer via the auxiliary dopant in the capacitance-relieving layer. Therefore, holes transferred from the hole-transporting common layer to the green light-emitting layer via the capacitance-relieving layer are not trapped by the green dopant, and hole transfer passage is generated in the hole-transporting host and electron-transporting host in the green light-emitting layer, thereby preventing the accumulation of charge in the green light-emitting layer.

[0012] Since holes and electrons are not trapped by the green dopant and can contribute to exciton formation in their respective hosts and dopants, the problem of image quality degradation caused by the accumulation of residual carriers in the green light-emitting layer can be prevented. In other words, the flashing phenomenon in which a significant green color is observed when transitioning from the off state to a low-gradation gray state, caused by residual carriers in the green light-emitting layer, can be prevented or reduced.

[0013] A capacitance relaxation layer, provided between the hole transport common layer and the green light-emitting layer, prevents residual carriers from accumulating within the green light-emitting layer. This facilitates carrier release when transitioning from the turn-on state to the turn-off (black state), and facilitates carrier transfer between the auxiliary dopant and the various materials within the green light-emitting layer when transitioning from the turn-off (black state) to the turn-on state. As a result, rapid carrier accumulation is possible in the turn-on state, and the drive voltage during turn-on can be reduced. Therefore, by providing the green light-emitting layer with CV (Capacitance-Voltage) characteristics that facilitate carrier accumulation / release during turn-on / turn-off, the degradation of image quality that occurs during the on / off transition of the green light-emitting layer can be resolved.

[0014] The light-emitting element and light-emitting display device according to the embodiments of this specification have the advantage of preventing residual carriers generated by trapped holes in specific materials within the light-emitting layer, improving the accumulation / emission characteristics during turn-on / turn-off, resolving the flashing issue, and lowering the drive voltage, making them highly applicable for sustained use. Therefore, they can embody ESG (Environment / Social / Governance) principles. [Brief explanation of the drawing]

[0015] [Figure 1] This is a cross-sectional view showing a light-emitting element according to one embodiment of the foregoing. [Figure 2] As an example, Figure 1 shows the energy band diagram of the third stack. [Figure 3a]It is an energy band diagram of an auxiliary dopant in a capacitance relaxation layer and a green dopant in a green light-emitting layer. [Figure 3b] It is a diagram showing the HOMO energy levels and LUMO energy levels for each material of the capacitance relaxation layer and the green light-emitting layer in FIG. 2. [Figure 4] It is a diagram showing the triplet energy level relationship between the auxiliary dopant and the green dopant. [Figure 5] It is a graph showing the luminescence characteristics of the auxiliary dopant and the green dopant. [Figure 6] It is a graph showing the JV characteristics of the auxiliary dopant and the green dopant in a HOD device. [Figure 7] It is a graph showing the JV characteristics of the auxiliary dopant and the green dopant in an EOD device. [Figure 8a] It is a cross-sectional view showing a light-emitting device applied to the first experimental example. [Figure 8b] It is a cross-sectional view showing a light-emitting device applied to the second experimental example. <s [Figure 9] It is a graph showing the JV characteristics of the first experimental example and the second experimental example at a current density of 10 mA / cm2 or less. [Figure 10] It is a graph showing the JV characteristics of the first experimental example and the second experimental example at a current density of 100 mA / cm2 or less. [Figure 11] It is a graph showing the change in luminance efficiency with respect to the current density of the first experimental example and the second experimental example. [[ID=3|1]] [Figure 12] It is a graph showing the intensity with respect to the wavelength of the first experimental example and the second experimental example. [Figure 13] It is a graph showing the CV characteristics from the first experimental example to the third experimental example. [Figure 14] It is a graph showing together the JV and CV characteristics of the first experimental example and the second experimental example. [Figure 15] It is a graph showing the luminance change when converting from a black state to a low-tone gray state in the fourth experimental example and the fifth experimental example. [Figure 16]In the 6th, 8th, and 9th experimental examples, when converting from the black state to the low-tone gray state, it is a graph showing the luminance change. [Figure 17] It is a cross-sectional view showing a light-emitting display device according to an embodiment of the present specification. [Figure 18] It is a cross-sectional view showing a light-emitting display device according to another embodiment of the present specification.

Mode for Carrying Out the Invention

[0016] [[ID=J14]]Hereinafter, with reference to the accompanying drawings, desirable embodiments of the present invention will be described. The same reference numerals throughout the specification mean substantially the same components. In the following description, when it is determined that a specific description of the technology or configuration related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Also, the component names used in the following description are selected in consideration of the ease of preparing the specification, and may be different from the part names of actual products.

[0017] The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining various embodiments of the present invention are illustrative, and the present invention is not limited to the matters illustrated in the drawings. The same drawing reference numerals throughout the specification refer to the same components. Also, in describing the present invention, when it is determined that a specific description of related known technologies may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. When terms such as "including", "having", and "comprising" mentioned in this specification are used, unless "only" is used, other parts may be added. When a component is expressed in the singular, it includes the case of including a plurality unless there is a particularly explicit description.

[0018] When interpreting the components included in various embodiments of the present invention, it is interpreted as including an error range even without a separate explicit description.

[0019] When describing various embodiments of the present invention, if the positional relationship between two parts is described using phrases such as "above," "below," or "next to," then unless "immediately" or "directly" is used, there may be one or more different parts located between the two parts.

[0020] When describing various embodiments of the present invention, if temporal relationships are described using phrases such as "after," "following," "next," or "before," then, unless "immediately" or "directly" is used, it may include cases that are not continuous.

[0021] In describing the various embodiments of the present invention, terms such as "First," "Second," etc., may be used to describe various components, but such terms are used only to distinguish between identical and similar components. Therefore, components modified as "First," etc. in this specification may be identical to components modified as "Second," etc., within the technical concept of the present invention, unless otherwise mentioned.

[0022] The features of each of the various embodiments of the present invention can be partially or entirely combined or combined with one another, enabling a variety of technical interdependencies and drives, and each of the various embodiments may be implemented independently of one another or together in relation to one another.

[0023] In this specification, the LUMO (Lowest Unoccupied Molecular Orbitals Level) energy level and HOMO (Highest Occupied Molecular Orbitals Level) energy level of a given layer refer to the LUMO energy level and HOMO energy level of the dopant substance doped into that layer.

[0024] In this specification, the HOMO energy level may be the energy level measured by Cyclic Voltammetry (CV), a current-voltage measurement method that determines the energy level from the relative potential value with respect to a reference electrode or reference substance whose electrode potential value is known. For example, the HOMO energy level of one substance may be measured using a substance whose oxidation potential and reduction potential values ​​are known as a reference.

[0025] In this specification, "doped" means that a substance that makes up the majority of a layer by weight is mixed with a substance that has different physical properties from the majority of the layer by weight. For example, substances with N-type and P-type properties, or organic and inorganic properties, are added in a weight ratio of 20% or less. In other words, a "doped" layer is one in which the host substance and dopant substance can be separated by weight ratio and specific gravity. "Undoped" refers to all cases other than those that fall under "doped." For example, if a layer is composed of a single substance or a mixture of substances with identical or similar properties, that layer is considered "undoped." For example, if at least one of the substances in a layer is P-type and none of the substances in that layer are N-type, that layer is considered "undoped." For example, if at least one of the substances in a layer is organic and none of the substances in that layer are inorganic, that layer is considered "undoped." For example, if all the materials that make up a layer are organic, but at least one of the materials in that layer is N-type and at least one other is P-type, then the layer is considered "doped" if the N-type material accounts for less than 20% by weight, or the P-type material accounts for less than 30% by weight.

[0026] On the other hand, in this specification, the EL (electroluminescence) spectrum is calculated by the product of 1) the PL (photoluminescence) spectrum, which reflects the intrinsic properties of the luminescent material, such as the dopant or host material contained in the organic light-emitting layer, and 2) the out-coupling emittance spectral curve, which is determined by the structure and optical properties of the organic light-emitting element, including the thickness of the organic layer such as the electron transport layer.

[0027] The light-emitting element and light-emitting display device of the present invention will be described below with reference to the attached drawings.

[0028] Figure 1 is a cross-sectional view showing a light-emitting element according to one embodiment of this specification. Figure 2 is a diagram showing the energy band diagram of the third stack in Figure 1 as an example. Figure 3a is an energy band diagram of the auxiliary dopant in the capacitance relaxation layer and the green dopant in the green light-emitting layer. Figure 3b is a diagram showing the HOMO energy levels and LUMO energy levels of the capacitance relaxation layer and green light-emitting layer in Figure 2 by material.

[0029] A light-emitting element according to one embodiment of this specification is provided in at least one subpixel of a light-emitting display device.

[0030] As shown in Figure 1, a light-emitting element ED according to one embodiment of this specification includes a first electrode AND and a second electrode CAT facing each other, and a plurality of light-emitting stacks S1, S2, S3, S4 between the first and second electrodes AND and CAT. Among the plurality of light-emitting stacks S1, S2, S3, S4, charge generation layers CGL1, CGL2, CGL3 are included between adjacent light-emitting stacks.

[0031] The first electrode AND can function as the anode, and the second electrode CAT can function as the cathode.

[0032] At least one of the first electrode AND and the second electrode CAT is transparent or semi-transparent, and light generated within the light-emitting element can be transmitted through the transparent or semi-transparent electrode side. For example, when the first electrode AND includes a reflective electrode and the second electrode CAT includes a semi-transparent or transparent electrode, the light-emitting element can emit light through the second electrode CAT. As another example, when the first electrode AND includes a transmissive electrode and the second electrode CAT includes a reflective electrode, the light-emitting element can emit light through the first electrode AND. As yet another example, each of the first electrode AND and the second electrode CAT can be a transparent or semi-transparent electrode, so that the light-emitting element ED1 emits light through both sides of the first and second electrodes AND and CAT.

[0033] The first electrode AND may be connected to any one of the thin-film transistors in the pixel circuitry provided at each subpixel on the substrate. The second electrode CAT is provided in common to each subpixel, and a common voltage signal may be applied from outside the non-display region surrounding at least several subpixels.

[0034] Each charge generation layer CGL1, CGL2, and CGL3 may include an n-type charge generation layer NCGL and a p-type charge generation layer PCGL. The n-type charge generation layer NCGL generates electrons and supplies them to adjacent light-emitting stacks, while the p-type charge generation layer PCGL generates holes and supplies them to adjacent light-emitting stacks.

[0035] The example shown in Figure 1 illustrates a configuration in which four light-emitting stacks S1, S2, S3, and S4 are arranged between the first electrode AND and the second electrode CAT, but the embodiments of this specification are not limited thereto. That is, the light-emitting devices of the embodiments of this specification may include two light-emitting stacks, three or more light-emitting stacks, or five or more light-emitting stacks between the first electrode AND and the second electrode CAT. When the light-emitting devices of the embodiments of this specification include two or more light-emitting stacks, any one of the light-emitting stacks may include a green light-emitting layer GEML that emits green light.

[0036] The light-emitting device shown in Figure 1 is an example in which the first light-emitting stack S1 includes a red light-emitting layer REML, the second light-emitting stack S2 includes a first blue light-emitting layer BEML1, the third light-emitting stack S3 includes a green light-emitting layer GEML, and the fourth light-emitting stack S4 includes a second blue light-emitting layer BEML2.

[0037] Thus, a light-emitting element ED including light-emitting stacks S1, S2, S3, and S4 that emit light of different colors from each other can emit white light through at least one of the first electrode AND and the second electrode CAT.

[0038] Each of the first to fourth light-emitting stacks S1, S2, S3, and S4 is equipped with hole-transporting common layers CML11, CML12, CML13, and CML14 below the light-emitting layers REML, BEML1, GEML, and BEML2, and electron-transporting common layers CML21, CML22, CML23, and CML24 above the light-emitting layers REML, BEML1, GEML, and BEML2.

[0039] The hole-transporting common layers CML11, CML12, CML13, and CML14 may include hole injection layers, hole transport layers (see HTL in Figure 2), electron blocking layers, etc. The hole injection layer may be selectively provided in the first light-emitting stack S1 in contact with the first electrode AND. In this case, the hole injection layer can perform the function of transferring from the first electrode AND to the red light-emitting layer REML. The hole transport layer can transfer holes supplied from the first electrode AND or charge generation layers CGL1, CGL2, and CGL3 to the respective light-emitting layers REML, BEML1, GEML, and BEML2. The electron blocking layer can perform the function of preventing electrons from crossing from the light-emitting layers REML, BEML1, GEML, and BEML2 to the hole-transporting common layers CML11, CML12, CML13, and CML14.

[0040] The electron blocking layer may or may not be selectively provided in each of the light-emitting stacks S1, S2, S3, and S4.

[0041] Depending on the circumstances, in addition to hole transport layers and electron blocking layers, a separate optical compensation layer or hole transport auxiliary layer may be further provided between the first electrode AND or charge generation layers CGL1, CGL2, CGL3 and each light-emitting layer REML, BEML1, GEML, BEML2.

[0042] The hole-transporting common layers CML11, CML12, CML13, and CML14 may contain hole-transporting materials. At least one of the hole-transporting common layers CML11, CML12, CML13, and CML14 may consist of multiple layers containing different materials.

[0043] The electron-transporting common layers CML21, CML22, CML23, and CML24 may include a hole-blocking layer, an electron-transporting layer (see ETL in Figure 2), and an electron-injection layer. The electron-injection layer may be selectively provided in the fourth light-emitting stack S4 in contact with the second electrode CAT. In this case, the electron-injection layer functions to inject electrons from the second electrode CAT towards the second blue light-emitting layer BEML2. The electron-transporting layer ETL functions to transfer electrons from the second electrode CAT towards each light-emitting layer in each light-emitting stack. The hole-blocking layer functions to restrict holes injected into the light-emitting layer from escaping towards the electron-transporting layer.

[0044] The hole blocking layer may or may not be selectively provided in each light-emitting stack.

[0045] The electron-transporting common layers CML21, CML22, CML23, and CML24 may contain electron-transporting materials. At least one of the electron-transporting common layers CML21, CML22, CML23, and CML24 may contain different materials and be provided in multiple layers.

[0046] The light-emitting element in Figure 1 is an example embodied by a red light-emitting stack in which the first light-emitting stack emits red light, a first blue light-emitting stack in which the second light-emitting stack emits blue light, a green light-emitting stack in which the third light-emitting stack emits green light, and a second blue light-emitting stack in which the fourth light-emitting stack emits blue light. In other words, it shows a stacked arrangement of light-emitting stacks of R / B1 / G / B2 stacks in the direction from the first electrode AND to the second electrode CAT, but the light-emitting elements in the embodiments described herein are not limited to this. For example, when multiple light-emitting stacks are placed between the first and second electrodes, unlike the example shown in Figure 1 where they are arranged by color, they may be arranged in the following order between the first and second electrodes: red light-emitting stack, green light-emitting stack, first and second blue light-emitting stacks (R / G / B1 / B2); green light-emitting stack, red light-emitting stack, first and second blue light-emitting stacks (G / R / B1 / B2); first blue light-emitting stack, red light-emitting stack, green light-emitting stack, second blue light-emitting stack (B1 / R / G / B2); or in any other order.

[0047] The reason why two blue light-emitting stacks are placed in the light-emitting element is to compensate for the relatively lower efficiency of blue light compared to other colors. When two blue light-emitting stacks are provided between the first and second electrodes AND and CAT, the second blue light-emitting layer BEML2, which is closer to the second electrode CAT, may be thicker than the first blue light-emitting layer BEML1, which is closer to the first electrode AND. This is to compensate for the efficiency of the second blue light-emitting layer BEML2, which is located relatively behind the first electrode AND (Figure 1).

[0048] The light-emitting element, including the first to fourth light-emitting stacks S1, S2, S3, and S4 described above, can emit white light when a voltage of a certain level or higher is applied between the first electrode AND and the second electrode CAT. Each subpixel can be further provided with a color filter outside the light-emitting first electrode AND or second electrode CAT to allow for different color representation in each subpixel.

[0049] On the other hand, green has the best visibility and is responsible for the highest brightness when representing white. Therefore, among the different light-emitting stacks, the green light-emitting stack requires a higher brightness efficiency than the light-emitting stacks of other colors. Accordingly, the green light-emitting layer GEML of the green light-emitting stack is thicker than the light-emitting layers REML, BEML1, and BEML2 of the light-emitting stacks of other colors, allowing for a larger amount of doping.

[0050] Furthermore, the green light-emitting layer (GEML) may contain phosphorescent material to increase efficiency.

[0051] Referring to Figures 2 to 3b, we examine the green light-emitting stack of the light-emitting element in the embodiment described herein.

[0052] As shown in Figure 2, the green light-emitting stack may sequentially include a hole transport layer (HTL), a capacity relaxation layer (CRL), a green light-emitting layer (GEML), and an electron transport layer (ETL).

[0053] The capacity-relieving layer (CRL) precedes the green light-emitting layer (GEML) and is located adjacent to the hole transport layer (HTL).

[0054] The capacity relaxation layer CRL includes the auxiliary dopant CRD and host GH:GHH, GEH.

[0055] The green light-emitting layer GEML contains the green dopant GD and the host GH:GHH, GEH.

[0056] The host GHH and GEH contained in the capacity relaxation layer CRL and the green light-emitting layer GEML are hole-transporting host GHH and electron-transporting host GEH, and are hosts commonly included. The capacity relaxation layer CRL and the green light-emitting layer GEML can be composed of the same host GH:GHH and GEH, with only the components of the auxiliary dopant CRD and green dopant GD differing.

[0057] As shown in Figure 3a, the HOMO energy level of the auxiliary dopant CRD is lower than that of the green dopant GD, and the LUMO energy level of the auxiliary dopant CRD is higher than that of the green dopant GD. Therefore, the auxiliary dopant CRD has a larger energy band gap than the green dopant GD.

[0058] The auxiliary dopant CRD has an emission peak at a relatively lower wavelength than the green dopant GD and can be considered a type of green-emitting dopant. Because the auxiliary dopant CRD has a low HOMO energy level between the hole transport layer HTL and the green-emitting layer GEML, it functions more as a hole transfer agent to the green dopant GD, host GHH, and GEH, thereby increasing the efficiency of exciton generation in the green-emitting layer GEML, rather than functioning as a direct-emitting dopant. Therefore, its main feature is its hole transfer function to the green-emitting layer GEML, rather than the direct emission of the capacity relaxation layer CRL containing the auxiliary dopant CRD.

[0059] Furthermore, the auxiliary dopant CRD has a lower HOMO energy level than the green dopant GD and is positioned adjacent to the hole transport layer HTL. Therefore, holes do not accumulate and are smoothly transferred from the hole transport layer HTL to the green light-emitting layer GEML. This prevents or reduces carrier accumulation caused by hole accumulation, thereby improving green flashing. Note that in a light-emitting element, carriers refer to holes and / or electrons, and are also called electric charge.

[0060] In the volume relaxation layer (CRL) and the green light-emitting layer (GEML), host GHH and GEH are present as primary components, respectively, more so than auxiliary dopant CRD and green dopant GD. Auxiliary dopant CRD in the volume relaxation layer (CRL) and green dopant GD in the green light-emitting layer (GEML) are present in concentrations ranging from 5 wt% to 25 wt% in their respective layers.

[0061] The HOMO energy level of the auxiliary dopant CRD (HOMO_CRD) is lower than that of the green dopant GD (HOMO_GD), and the capacity relaxation layer CRL containing the auxiliary dopant CRD is positioned adjacent to the hole transport layer HTL. In this case, holes crossing from the hole transport layer HTL towards the green light-emitting layer GEML are transferred sequentially through the auxiliary dopant CRD and then the green dopant GD. Because a hole transfer pathway is generated not only from the auxiliary dopant CRD to the green dopant GD but also through the hole-transporting host GHH and the electron-transporting host GEH, holes are not trapped in the green dopant GD. Therefore, holes crossing from the hole transport layer HTL can be fully utilized for exciton production, preventing or reducing the accumulation of holes trapped near the HOMO energy level in the green dopant GD that are not used for exciton generation. Furthermore, since the hole-transporting host GHH and the electron-transporting host GEH are both continuous in the capacity relaxation layer CRL and the green light-emitting layer GEML, the hole flow can be continuous in both layers.

[0062] If a green light-emitting layer containing a green dopant GD with a higher HOMO energy level than the host GH:GHH,GEH is placed directly adjacent to the hole transport layer, holes will be trapped in the relatively shallow HOMO energy level of the green dopant GD and will not be available for exciton generation. Furthermore, since trapped holes are not easily released, charge accumulation can become severe in a structure where light-emitting stacks of different colors within a subpixel are accumulated, especially in the green light-emitting stack that emits green light, when a voltage below the threshold voltage of the light-emitting element is applied. Therefore, when the light-emitting element transitions from a black state to a low-gradation gray, a green flashing phenomenon may occur where green is prominently displayed.

[0063] In contrast, the light-emitting element of the embodiment described herein can resolve the charge accumulation and green flashing phenomenon by placing a capacitance relaxation layer CRL between the hole transport layer HTL and the green light-emitting layer GEML, which can mitigate the phenomenon of charge exceeding the green light-emitting layer not being used for exciton generation and instead accumulating.

[0064] The capacitance relaxation layer (CRL) is thinner than the green light-emitting layer (GEML). Furthermore, the auxiliary dopant CRD contained in the CRL has a lower HOMO energy level than the green dopant GD. Therefore, energy transfer to the green dopant GD is spontaneous, and because its triplet energy level is higher than that of the green dopant GD, a reverse energy transfer (bank energy transfer) from the green dopant GD to the auxiliary dopant CRD does not occur, thus not reducing the exciton generation efficiency of the green dopant GD within the GEML. Consequently, light emission within the green light-emitting stack primarily occurs within the GEML, and the capacitance relaxation layer primarily functions to prevent hole transfer and hole trapping to the green dopant. It either does not emit light, or emits light to an extent that does not reduce the efficiency of the GEML. In some cases, the triplet energy level T1_CRD of the auxiliary dopant CRD may be the same as the triplet energy level T1_GD of the green dopant GD.

[0065] Furthermore, the auxiliary dopant CRD has a higher LUMO energy level than the green dopant GD (LUMO_CRD > LUMO_GD), allowing for smoother electron transfer when electrons cross from the electron transport layer ETL to the green light-emitting layer GEML. This enables faster carrier emission when the light-emitting element switches from the turn-on state to the turn-off state, preventing or reducing defects such as afterimages.

[0066] The aforementioned auxiliary dopant CRD may, for example, include electron-withdrawing groups in the iridium phosphor dopant matrix. The auxiliary dopant CRD may further include electron-withdrawing groups to have lower HOMO energy levels. Furthermore, the auxiliary dopant CRD can have a hole mobility greater than that of the green dopant GD.

[0067] As an example of a green dopant GD, phenylpyridine ligands can be used among iridium (Ir)-based complex compounds.

[0068] For example, the phosphorescent dopant matrix used in the green dopant GD may contain iridium compounds such as Ir(ppy)3(Tris(2-phenylpyridine)iridium(III)) or Ir(ppy)2(acac).

[0069] The auxiliary dopant CRDs according to the examples herein have higher hole mobility and electron mobility than the green dopant GD. For this reason, the auxiliary dopant CRDs may contain more electron-withdrawing groups than the green dopant GD. The green dopant GDs according to the examples herein can have lower HOMO energy levels and higher mobility by further including electron-withdrawing groups along with cyanide groups (-CN) or fluorine groups (-F) in the iridium phosphorescent dopant matrix.

[0070] Based on experiments described later, the auxiliary dopants and green dopants of the examples in this specification will be specifically compared and explained.

[0071] The green light-emitting layer (GEML) and the capacity relaxation layer (CRL), as shown in Figure 3b, each contain a mixed host comprising a hole-transporting host (GHH) and an electron-transporting host (GEH) to facilitate the injection and transfer of holes and electrons. These mixed hosts also contain a green dopant (GD) and an auxiliary dopant (CRD), respectively.

[0072] Figure 3b shows the hole-transporting host GHH and the electron-transporting host GEH separately. This is to illustrate the energy band diagrams of both materials, but in substance, the hole-transporting host GHH and the electron-transporting host GEH are not separated within the capacity relaxation layer CRL and the green light-emitting layer GEML, but are mixed in a constant ratio. Here, the ratio of hole-transporting host GHH to electron-transporting host GEH refers to the volume ratio.

[0073] Furthermore, in the capacity relaxation layer (CRL), the content of the auxiliary dopant CRD and the green dopant GD in the green light-emitting layer (GEML) are each present in amounts less than the total content of the hole-transporting host GHH and the electron-transporting host GEH. For example, the green dopant GD in the green light-emitting layer (GEML) may be present in amounts of 5 wt% to 25 wt% relative to the entire green light-emitting layer (GEML). Similarly, the auxiliary dopant CRD in the capacity relaxation layer (CRL) may be present in amounts of 5 wt% to 25 wt% relative to the entire capacity relaxation layer (CRL).

[0074] Between the hole transport layer (HTL) and the green light-emitting layer (GEML), the capacity relaxation layer (CRL) allows for spontaneous energy transfer from the auxiliary dopant CRD to the green dopant GD when holes are injected from the HTL towards the GEML. This is because the auxiliary dopant CRD has a lower HOMO energy level than the green dopant GD. Furthermore, since the auxiliary dopant CRD has a higher triplet energy level and greater mobility than the green dopant GD, energy transfer does not occur in the direction of conversion from the green dopant GD to the auxiliary dopant CRD, thus preventing a decrease in the efficiency of the green light-emitting layer (GEML). Although the capacity relaxation layer (CRL) contains a light-emitting dopant, most of it is transferred to the green light-emitting layer and performs the function of hole transport, so there is almost no direct emission in the capacity relaxation layer (CRL).

[0075] The HOMO and LUMO energy levels described herein are evaluated with the energy level of a vacuum state set to 0.0 eV, and since both are below 0.0 eV, they show negative values. In a comparison between the two materials, a deeper energy level in one material means that it has energy levels on the lower side of the energy diagram and has a larger absolute value.

[0076] Therefore, in the examples described herein, the HOMO energy level of the auxiliary dopant CRD is lower than the HOMO energy level of the green dopant GD of the green luminescent layer GEML, and has a larger absolute value.

[0077] In the following section, with reference to Figure 3b, we will compare and explain the characteristics of the HOMO and LUMO energy levels of the auxiliary dopant CRD, the hole-transporting host GHH, and the electron-transporting host GEH.

[0078] The HOMO energy level of the auxiliary dopant CRD, HOMO_CRD, is lower than the HOMO energy level of the hole-transporting host GHH, HOMO_GHH (HOMO_CRD <HOMO_GHH)。

[0079] Furthermore, the HOMO energy level of the auxiliary dopant CRD, HOMO_CRD, is higher than the HOMO energy level of the electron-transporting host GEH, HOMO_GEH (HOMO_CRD > HOMO_GEH).

[0080] The LUMO energy level LUMO_CRD of the auxiliary dopant CRD may be lower than the LUMO energy level LUMO_GEH of the electron-transporting host GEH (LUMO_GEH > LUMO_CRD).

[0081] The HOMO energy level HOMO_GD of the green dopant GD is higher than the HOMO energy level HOMO_GHH of the hole-transporting host GHH (HOMO_GD > HOMO_GHH).

[0082] Furthermore, the HOMO energy level HOMO_GD of the green dopant GD is higher than the HOMO energy level HOMO_GEH of the electron-transporting host GEH (HOMO_GD > HOMO_GEH).

[0083] The LUMO energy level LUMO_GD of the green dopant GD may be lower than the LUMO energy level LUMO_GEH of the electron-transporting host GEH (LUMO_GEH > LUMO_GD).

[0084] In the volume relaxation layer (CRL), the auxiliary dopant CRD is doped at a concentration of 5 wt% to 25 wt%. In the green luminescence layer (GEML), the green dopant GD is doped at a concentration of 5 wt% to 25 wt%.

[0085] Referring to Figure 3b, the HOMO energy levels gradually decrease in the order of green dopant GD, hole-transporting host GHH, and auxiliary dopant CRD. Furthermore, the HOMO energy difference between green dopant GD and auxiliary dopant CRD may be less than 0.25 eV.

[0086] The HOMO energy level HOMO_CRD of the auxiliary dopant CRD has a difference of 0.15 eV or less from the HOMO energy level HOMO_GHH of the hole-transporting host. The HOMO energy level HOMO_CRD of the auxiliary dopant CRD lies between the HOMO energy level HOMO_GHH of the hole-transporting host GHH and the HOMO energy level HOMO_GEH of the electron-transporting host GEH, and is closer to the HOMO energy level HOMO_GHH of the hole-transporting host GHH than to the HOMO energy level HOMO_GHH of the electron-transporting host GEH.

[0087] Even if the auxiliary dopant CRD has a small difference in HOMO energy level from the hole-transporting host GHH, if it has a lower HOMO energy level than the green dopant GD, it can prevent or reduce the phenomenon of holes being trapped in the green dopant GD due to the physical differences between the auxiliary dopant CRD and the green dopant GD.

[0088] The following examines the physical differences between the auxiliary dopant CRD and the green dopant GD.

[0089] Figure 4 shows the relationship between the triplet energy levels of the auxiliary dopant and the green dopant. Figure 5 is a graph showing the luminescence characteristics of the auxiliary dopant and the green dopant. Figure 6 is a graph showing the JV characteristics of the auxiliary dopant and the green dopant of the HOD device. Figure 7 is a graph showing the JV characteristics of the auxiliary dopant and the green dopant of the EOD device.

[0090] As shown in Figure 4, the auxiliary dopant CRD has a higher triplet energy level than the green dopant GD (T1_CRD>T1_GD).

[0091] In the following experiment, the triplet energy level T1_CRD of the auxiliary dopant CRD was 2.43 eV, and the triplet energy level T1_GD of the green dopant GD was 2.39 eV. Here, since the auxiliary dopant CRD contained in the capacity relaxation layer CRL has a lower HOMO energy level than the green dopant GD, not only is energy transfer to the green dopant GD spontaneous, but because its triplet energy level is higher than that of the green dopant GD (T1_CRD > T1_GD), no bank energy transfer occurs from the green dopant GD to the auxiliary dopant CRD. Therefore, excitons generated in the green dopant GD within the green emission layer GEML fall to the ground state (S0) and can be used for emission. Thus, emission within the green emission stack mainly occurs within the green emission layer GEML, to the extent that it does not reduce the efficiency of the green emission layer GEML.

[0092] As shown in Figure 5, the auxiliary dopant CRD has an emission peak at short wavelengths. The emission peak of the auxiliary dopant CRD has a wavelength difference Wx of approximately 10 nm or less from the emission peak of the green dopant GD.

[0093] In the embodiments described herein, the capacity relaxation layer CRL contains a hole-transporting host GHH and an electron-transporting host GEH, but the auxiliary dopant CRD is not primarily used for luminescence because it is designed to have the function of transferring holes and energy in terms of mobility, triplet energy, and HOMO energy levels to the green dopant GD of the adjacent green luminescence layer GEML, and is designed so that the hole-transporting host GHH and electron-transporting host GEH emit light optimally with the green dopant GD.

[0094] Figures 6 and 7 show the hole mobility investigated via a HOD device for the case where the active layer contains only host (Host Only), the case where it contains the green dopant GD, and the case where it contains the auxiliary dopant CRD, and the electron mobility investigated via an EOD device for each case.

[0095] The HOD (Hole Only Device) element evaluated in Figure 6 includes a hole injection layer, a first hole transport layer, an emissive layer, and a second hole transport layer between the first and second electrodes, and the hole-related electrical characteristics of the active layer were investigated. Here, the electrical mobility of the emissive layer was evaluated, and actual luminescence was not evaluated as a primary item.

[0096] As shown in Figure 6, when the HOD element contains only the hole-transporting host GHH and when the HOD element active layer contains the auxiliary dopant CRD of the embodiments herein, the current density characteristics with respect to the drive voltage show similar trends. However, when the HOD element active layer contains the green dopant GD, the current density value becomes considerably lower for the same drive voltage, and the drive voltage value required to achieve the same current density becomes larger.

[0097] In other words, the hole mobility of the auxiliary dopant CRD in the embodiments of this specification is greater than that of the green dopant GD. For example, when the driving voltage is 5V, it can be seen that the current density of the auxiliary dopant CRD is 10 times or more that of the green dopant GD.

[0098] The EOD device has a structure that includes a first electron injection layer, a first electron transport layer, an active layer, a second electron transport layer, and a second electron injection layer between the first and second electrodes, and the electron-related electrical properties of the active layer were investigated.

[0099] As shown in Figure 7, when the active layer of an EOD (Electron Only Device) element contains only the electron-transporting host GEH and when the active layer of a HOD element contains the auxiliary dopant CRD of the embodiment described herein, the current density characteristics with respect to the drive voltage show a similar trend. However, when the active layer of the EOD element contains the green dopant GD, the current density value for the same drive voltage is considerably lower. In other words, the electron mobility of the auxiliary dopant CRD of the embodiment described herein is greater than that of the green dopant GD. For example, when the drive voltage is 5V, the current density of the auxiliary dopant CRD is more than three times that of the green dopant GD.

[0100] Thus, in the embodiments described herein, the auxiliary dopant CRD exhibits higher hole mobility and electron mobility under the same conditions compared to the green dopant GD. Therefore, the auxiliary dopant CRD readily functions to transfer holes to the green dopant GD and spontaneously transfer energy when contained in the capacitance relaxation layer CRL adjacent to the green light-emitting layer GEML.

[0101] Thus, the green dopants according to the examples of this specification have low HOMO energy levels, hole mobility similar to that of hole-transporting hosts, and electron mobility similar to that of electron-transporting hosts.

[0102] When an auxiliary dopant according to the embodiments of this specification is included in the capacitance relaxation layer, the charge mobility increases, enabling rapid carrier emission in the green light-emitting layer when the light-emitting element is turned off. The inclusion of the capacitance relaxation layer also solves the problem of increased capacitance in the off state caused by the accumulation of carriers in the green light-emitting layer. Furthermore, if carrier emission is completed quickly in the green light-emitting layer in the off state, rapid carrier accumulation is possible when the element is subsequently turned on, eliminating the flashing phenomenon caused by residual carriers within the light-emitting element.

[0103] The significance of the capacitance relaxation layer will be investigated below, based on the structure of the first experimental example EX1 in Figure 8a, which includes a green light-emitting stack between the first and second electrodes, and the structure of the second experimental example EX2 in Figure 8b, which includes a capacitance relaxation layer.

[0104] Figures 8a and 8b are cross-sectional views showing the light-emitting elements applied to the first and second experimental examples.

[0105] As shown in Figure 8a, the light-emitting element of the first experimental example EX1 comprises a hole injection layer HIL, a hole transport layer HTL, a green light-emitting layer GEML, an electron transport layer ETL, an electron injection layer EIL, and a second electrode CAT on a first electrode AND.

[0106] Here, the green light-emitting layer GEML includes a hole-transporting host GHH, an electron-transporting host GEH, and a green dopant GD, as shown in Figures 2 and 3b.

[0107] The thickness of the green luminescent layer GEML was set to 350 Å, and the volume ratio of the hole-transporting host GHH to the electron-transporting host GEH was set to 7:3. The green dopant GD was included at a content of 8 wt% relative to the mixed host GH of the hole-transporting host GHH and electron-transporting host GEH.

[0108] As shown in Figure 8b, the light-emitting element of the second experimental example EX2 comprises a hole injection layer HIL, a hole transport layer HTL, a capacitance relaxation layer CRL, a green light-emitting layer GEML, an electron transport layer ETL, an electron injection layer EIL, and a second electrode CAT on a first electrode AND.

[0109] In the second experimental example, EX2, the total thickness of the volume relaxation layer (CRL) and the green light-emitting layer (GEML) was set to 350 Å, the same thickness as the green light-emitting layer (GEML) in the first experimental example, EX1. The volume relaxation layer (CRL) was set to a thickness of 150 Å, and the green light-emitting layer (GEML) was set to a thickness of 200 Å.

[0110] Furthermore, in the second experimental example EX2, the components and content ratios of the hole-transporting host GHH, electron-transporting host GEH, and green dopant GD in the green light-emitting layer GEML were the same as in the first experimental example EX1. The difference between the volume relaxation layer CRL and the adjacent green light-emitting layer GEML is that, in addition to the hole-transporting host GHH and electron-transporting host GEH, it also contains the auxiliary dopant CRD.

[0111] On the other hand, the third experimental example, EX3, is the same as the second experimental example, EX2, but with the positions of the green light-emitting layer (GEML) and the volume relaxation layer (CRL) reversed. The same materials and thicknesses were used for the volume relaxation layer (CRL) and the green light-emitting layer (GEML).

[0112] The HOMO, LUMO, and triplet energy levels of the green dopant GD and auxiliary dopant CRD used in the following experiments are shown in Table 1.

[0113] [Table 1]

[0114] Figure 9 is a graph showing the JV characteristics of the first and second experimental examples at a current density of 10 mA / cm² or less. Figure 10 is a graph showing the JV characteristics of the first and second experimental examples at a current density of 100 mA / cm² or less. Figure 11 is a graph showing the change in luminance efficiency with respect to current density for the first and second experimental examples. Figure 12 is a graph showing the intensity with respect to wavelength for the first and second experimental examples. Figure 13 is a graph showing the CV characteristics of the first to third experimental examples. Figure 14 is a graph showing the JV and CV characteristics of the first and second experimental examples together.

[0115] [Table 2]

[0116] As shown in Table 2 and Figure 10, the first experimental example EX1 was compared with the second experimental example EX2 and the third experimental example EX3, using a current density of 100 mA / cm2 and a driving voltage set to the first reference voltage Vr1. When the capacitance relaxation layer CRL was placed between the hole transport layer HTL and the green light-emitting layer GEML, it was confirmed that the driving voltage decreased by 0.23 V compared to the first experimental example EX1. On the other hand, in the third experimental example EX3, where the capacitance relaxation layer CRL was placed between the green light-emitting layer GEML and the electron transport layer ETL, the driving voltage increased by 0.05 V compared to the first experimental example EX1.

[0117] Furthermore, as shown in Table 2 and Figure 9, the driving voltage was set to the second reference voltage Vr2 at a current density of 10 mA / cm2 in the first experimental example EX1, and this was compared with the second experimental example EX2 and the third experimental example EX3. When the capacitance relaxation layer CRL was placed between the hole transport layer HTL and the green light-emitting layer GEML, it was confirmed that the driving voltage decreased by 0.15 V compared to the first experimental example EX1. On the other hand, when the capacitance relaxation layer CRL was placed between the green light-emitting layer GEML and the electron transport layer ETL (EX3), the driving voltage increased by 0.04 V compared to the first experimental example EX1.

[0118] Referring to Table 2 and Figure 11, it can be seen that the luminous efficiency (Cd / A) and quantum efficiency (QE) of the first and second experimental examples EX1 and EX2 are almost similar, or that the second experimental example EX2 shows further improvement.

[0119] Furthermore, referring to Table 2 and Figure 12, it can be seen that although the CIEx and CIEy values ​​for the first and second experimental examples EX1 and EX2 are slightly different, the emission spectra show almost similar trends.

[0120] Referring to Table 2 and Figure 13, it can be seen that the capacitance value accumulated at voltage values ​​below the threshold voltage Vth decreased in the second and third experimental examples EX2 and EX3 compared to the first experimental example EX1. This occurs due to the use of auxiliary dopants.

[0121] Relatively speaking, in the second experimental example EX2, the drive voltage is lower compared to the first experimental example EX1, the efficiency is at or above the same level, and the capacitance value before the threshold voltage is reduced to 6% or less, confirming that the flushing issue due to charge accumulation is prevented or reduced. On the other hand, in the third experimental example EX3, the drive voltage is higher and the efficiency is lower compared to the first experimental example EX1.

[0122] In other words, by providing a capacitance relaxation layer adjacent to the green light-emitting layer, the problem of charge accumulating in the capacitance before reaching the threshold voltage can be solved. Furthermore, by positioning the capacitance relaxation layer between the hole transport layer and the light-emitting layer, it can be confirmed that it is more effective than the first experimental example EX1, which has a single green light-emitting layer, in terms of efficiency, driving voltage, and ensuring color characteristics.

[0123] Furthermore, as shown in Figure 14, it can be confirmed that the width of the CV graph decreases in the second experimental example EX2 compared to the first experimental example EX1. The width of the CV graph is related to the capacitance at which charge accumulates in the green light-emitting layer. When an auxiliary dopant CRD is included, the high mobility and low HOMO energy level characteristics of the auxiliary dopant CRD reduce the capacitance area and the amount of charge accumulated, and also provide advantages in charge release in the off state compared to a structure using a single green light-emitting layer.

[0124] In the second experimental example, EX2, the width of the CV graph is reduced compared to the first experimental example, EX1, thereby reducing the amount of charge accumulation. This reduces the accumulation of residual carriers in the green light-emitting layer and simultaneously facilitates rapid charge release when switching from the ON state to the OFF state.

[0125] In the following, referring to the stack structures including the different colored light-emitting stacks in Figure 1, we investigate the change in luminance when transitioning from a black state to a low-gradation gray state in Experiment 4 EX4, where the dopant of the green light-emitting layer is the aforementioned green dopant GD, and in Experiment 5 EX5, where it is replaced with the auxiliary dopant CRD, without a separate capacitance relaxation layer in the green light-emitting stack.

[0126] Figure 15 is a graph showing the change in brightness when transitioning from a black state to a low-gradation gray state in the fourth and fifth experimental examples.

[0127] In the black state, the drive voltage of the light-emitting element was set to 0V, and in the low-gradation gray state, the drive current was set to generate a current of 0.5μA.

[0128] On the other hand, the fourth experimental example EX4 and the fifth experimental example EX5, shown in Figure 15, differ in whether the dopant in the green light-emitting layer is the green dopant GD or the auxiliary dopant CRD shown in Table 1.

[0129] As shown in Figure 15, in the fourth experimental example, EX4, when transitioning from a black state to a low-gradation gray state, the luminance intensity tends to increase sharply before decreasing to a constant value.

[0130] In Experimental Example 5 (EX5), compared to Experimental Example 4 (EX4), the luminance intensity that temporarily changed abruptly when transitioning from a black state to a low-gradation gray state was reduced. Furthermore, in Experimental Example 5 (EX5), the saturated luminance intensity in the stabilized low-gradation state was greater than in Experimental Example 4 (EX4). This reduced the difference between the temporarily changed luminance intensity and the saturated luminance intensity, resulting in a decrease in the visibility of flashing.

[0131] Therefore, according to the experimental results described above, by including an auxiliary dopant in the volume relaxation layer, it is possible to prevent or make the flashing phenomenon invisible when transitioning from a black state to a low-gradation gray state.

[0132] Furthermore, in the light-emitting devices according to the embodiments of this specification, when a capacitance relaxation layer is provided between the hole transport layer and the green light-emitting layer of the green light-emitting stack, the high mobility and low HOMO energy level of the auxiliary dopant prevent holes from being trapped in the green dopant of the green light-emitting layer, allowing holes to be smoothly transmitted to the green light-emitting layer. In addition, due to the high triplet energy level characteristics of the auxiliary dopant, spontaneous energy transfer to the green dopant of the adjacent green light-emitting layer contributes to exciton generation, and it can be expected that sufficient exciton generation efficiency will be achieved even with a thinner green light-emitting layer.

[0133] On the other hand, the light-emitting element in the embodiment of this specification does not use the dopant of the green light-emitting layer as the auxiliary dopant, and is designed by separating the capacitance relaxation layer containing the auxiliary dopant from the green light-emitting layer. Below, we will examine the meaning of the thickness of the capacitance relaxation layer between the hole transport layer and the green light-emitting layer in relation to the lifetime of the light-emitting element.

[0134] In the following experiment, the structure of the light-emitting element was modified by omitting the red light-emitting stack in contact with the first electrode AND in Figure 1, and instead stacking the first blue light-emitting stack B1, the green light-emitting stack G, and the second blue light-emitting stack B2 in that order between the first electrode AND and the second electrode CAT. Each of the light-emitting stacks B1, G, and B2 included a hole-transporting common layer, a light-emitting layer, and an electron-transporting common layer.

[0135] In this configuration, the green light-emitting stack consists of a stacked structure of a hole-transporting common layer, a green light-emitting layer, and an electron-transporting common layer.

[0136] Furthermore, in Experimental Example 6 EX6, a single green light-emitting layer GEML was constructed at the position of the green light-emitting layer; in Experimental Example 7 EX7, a single capacitance relaxation layer CRL was constructed; and in Experimental Examples 8 EX8 to 10 EX10, the capacitance relaxation layer CRL was placed at the front end and the green light-emitting layer GEML was placed at the rear end, with varying thicknesses.

[0137] In experimental examples EX6, EX7, EX8, EX9, and EX10 (6th to 10th experiments), the combined thickness of the green light-emitting layer (GEML) and the volume relaxation layer (CRL) was set to 350 Å. In experimental examples EX8 (8th) through EX10 (10th experiment), the thickness of the volume relaxation layer (CRL) was gradually increased to 50 Å, 100 Å, and 150 Å, respectively.

[0138] [Table 3]

[0139] As shown in Table 3, when the capacitance relaxation layer CRL is configured as a single unit, as in Experimental Example EX7, the effect of reducing the drive voltage is excellent, but the tendency to decrease the green life is significant.

[0140] In the case of experimental examples EX8, EX9, and EX10 (8th to 10th), the green lifetime was secured to be 80% or more compared to experimental example EX6 (6th) which had a single green light-emitting layer (GEML), demonstrating equivalent or better characteristics in terms of green efficiency, and confirming that the effect of reducing the driving voltage was also secured.

[0141] Figure 16 is a graph showing the change in brightness when transitioning from a black state to a low-gradation gray state in experimental examples 6, 8, and 9.

[0142] As shown in Figure 16, in the experimental example comparing the low-gradation flashing characteristics, it can be seen that, compared to the 6th experimental example EX6, the 8th experimental example EX8 and the 9th experimental example EX9 were able to reduce the abrupt change in brightness when transitioning from the black state to low-gradation gray, and that the degree of low-gradation flashing visibility could be reduced as the thickness of the capacitance relaxation layer was increased.

[0143] In other words, according to the experiments in Table 3 and Figure 16, it can be predicted that when the thickness of the capacitance relaxation layer is made thinner than the thickness of the green light-emitting layer, to approximately 1 / 6 to 3 / 4 of the thickness of the green light-emitting layer, the loss of green light lifetime will be reduced, and at the same time, the decrease in drive voltage and the visibility of low gradation will be prevented or reduced.

[0144] The following describes an embodiment of a light-emitting device according to this specification, to which the above-described light-emitting element is applied.

[0145] Figure 17 is a cross-sectional view showing a light-emitting device according to one embodiment of this specification.

[0146] As shown in Figure 17, in one embodiment of the present invention, the light-emitting display device can, for example, apply the light-emitting element of Figure 1 to at least one of a plurality of sub-pixels R_SP, G_SP, B_SP, and W_SP, and emit light through the first electrode AND on the output side.

[0147] Each subpixel's light-emitting element ED may consist of a first electrode AND, a second electrode CAT, and an intermediate layer OS. The intermediate layer OS includes multiple stacks, and multiple subpixels R_SP, G_SP, B_SP, and W_SP may have the same configuration. Furthermore, the intermediate layer OS may include a configuration in which at least the green light-emitting stack has a stacked structure of a hole transport layer, a capacitance relaxation layer, a green light-emitting layer, and an electron transport layer.

[0148] As shown in Figure 17, a light-emitting display device 1000 according to one embodiment of the present invention may include a substrate 100 having a plurality of subpixels R_SP, G_SP, B_SP, and W_SP; a light-emitting element ED provided in common to the substrate 100; thin-film transistors TFTs provided in each of the subpixels R_SP, G_SP, B_SP, and W_SP and connected to the first electrode AND of the light-emitting element ED; and color filter layers 109R, 109G, and 109B provided below at least one of the first electrode ANDs among the subpixels.

[0149] Figure 17 illustrates an example in which a white subpixel W_SP is included in the light-emitting device, but it is not limited to this. It is also possible to omit the white subpixel W_SP and have a structure that only includes red, green, and blue subpixels R_SP, G_SP, and B_SP. Depending on the case, it is also possible to replace the red, green, and blue subpixels with a combination of cyan, magenta, and yellow subpixels that can represent white.

[0150] The thin-film transistor TFT includes, as an example, a gate electrode 102, a semiconductor layer 104, and source electrodes 106a and drain electrodes 106b connected to both sides of the semiconductor layer 104. Furthermore, a channel protection layer may be provided above the portion of the semiconductor layer 104 where the channel is located, to prevent direct connection between the source / drain electrodes 106a, 106b and the semiconductor layer 104. The thin-film transistor TFT may be located on a buffer layer 101 on a substrate 100.

[0151] A gate insulating film 103 is provided between the gate electrode 102 and the semiconductor layer 104.

[0152] The semiconductor layer 104 may be, for example, one of oxide semiconductors, amorphous silicon, and polycrystalline silicon, or a combination of two or more of the above. For example, if the semiconductor layer 104 is an oxide semiconductor, the heating temperature required for forming the thin-film transistor can be lowered, which provides greater flexibility in the use of the substrate 100 and makes it advantageous for use in flexible display devices.

[0153] A gate electrode 102 is provided on a gate insulating film 103, and an interlayer insulating film 105 may be further provided between the gate electrode 102 and the source electrode 106a / drain electrode 106b.

[0154] Furthermore, the drain electrode 106b of the thin-film transistor TFT can be connected to the first electrode AND in the contact hole CT region provided within the first and second protective films 107 and 108.

[0155] The first protective film 107 is provided to temporarily protect the thin-film transistor TFT, and color filters 109R, 109G, and 109B may be provided on top of the first protective film 107.

[0156] A second protective film 108 is provided on a first protective film 107 which includes color filters 109R, 109G, and 109B.

[0157] When multiple subpixels include a red subpixel R_SP, a green subpixel G_SP, a blue subpixel B_SP, and a white subpixel W_SP, as shown in Figure 17, the color filter is provided with first to third color filters 109R, 109G, and 109B on the remaining subpixels R_SP, G_SP, and B_SP, excluding the white subpixel W_SP, allowing white light emitted after passing through the first electrode AND to pass through at each wavelength. A second protective film 108 is formed on the underside of the first electrode AND so as to cover the first to third color filters 109R, 109G, and 109B. The first electrode AND is formed on the surface of the second protective film 108, except for the contact hole CT, and is connected to either the drain electrode 106b or the source electrode 106a of the thin-film transistor TFT, and an electrical signal is applied by the thin-film transistor TFT.

[0158] Here, the substrate 100, including the thin-film transistor TFT, color filters 109R, 109G, 109B, and the first and second protective films 107 and 108, can be called a thin-film transistor array substrate TFA.

[0159] The light-emitting element ED is formed on a thin-film transistor array substrate TFA which includes a bank 119 that defines the light-emitting portion BH. The light-emitting element ED includes a transparent first electrode AND, a reflective second electrode CAT facing the first electrode AND and the second electrode CAT, and as an intermediate layer OS configured between the first electrode AND and the second electrode CAT, a plurality of light-emitting stacks S1, S2, S3, S4 and first to third charge generation layers CGL1, CGL2, CGL3 as shown in Figure 1. At least one of the plurality of light-emitting stacks S1, S2, S3, S4 that emits green light can be configured to include a stacked configuration of a capacitance relaxation layer CRL and a green light-emitting layer GEML, which both contain a hole-transporting host GHH and an electron-transporting host GEH between the hole transport layer and the electron transport layer, as shown in Figures 2 to 3b, with the difference being that the capacitance relaxation layer CRL includes an auxiliary dopant CRD and the green light-emitting layer GEML includes a green dopant GD.

[0160] Here, the HOMO energy level of the auxiliary dopant CRD may be lower than the HOMO energy level of the green dopant GD.

[0161] Furthermore, the HOMO energy level of the auxiliary dopant CRD may be lower than the HOMO energy level of the hole-transporting host GHH and higher than the HOMO energy level of the electron-transporting host GEH, and the LUMO energy level of the auxiliary dopant CRD may be lower than the LUMO energy level of the electron-transporting host GEH.

[0162] Furthermore, the HOMO energy level of the green dopant GD may be higher than the HOMO energy level of the hole-transporting host GHH.

[0163] The HOMO energy level of the auxiliary dopant CRD may have a difference of 0.15 eV or less from the HOMO energy level of the hole-transporting host GHH.

[0164] The auxiliary dopant CRD may contain electron-withdrawing groups in the iridium phosphor dopant matrix.

[0165] The hole-transporting host GHH and the electron-transporting host GEH, which are commonly included in the green light-emitting layer GEML and the charge relaxation layer CRL, have the following relationship of energy band gaps.

[0166] That is, the electron-transporting host GEH has a LUMO energy level lower than the LUMO energy level of the hole-transporting host GHH (LUMO_GEH < LUMO_GHH), has a HOMO energy level lower than the HOMO energy level of the hole-transporting host GHH (HOMO_GEH < HOMO_GHH), and the HOMO energy level HOMO_CRD of the auxiliary dopant CRD may be lower than the HOMO energy level HOMO_GHH of the hole-transporting host (HOMO_CRD < HOMO_GHH).

[0167] The HOMO energy level HOMO_CRD of the auxiliary dopant CRD may be closer to the HOMO energy level HOMO_GHH of the hole-transporting host than the HOMO energy level HOMO_GEH of the electron-transporting host (|HOMO_CRD - HOMO_GEH| > |HOMO_CRD - HOMO_GHH|).

[0168] The HOMO energy level HOMO_GEH of the electron-transporting host GEH may be 0.25 eV to 0.55 eV lower than the HOMO energy level HOMO_CRD of the auxiliary dopant CRD.

[0169] The thickness of the charge relaxation layer CRL may be thinner than the thickness of the green light-emitting layer GEML.

[0170] The auxiliary dopant CRD is contained in the charge relaxation layer CRL at 5 wt% to 25 wt%, and the green dopant GD may be contained in the green light-emitting layer GEML at 5 wt% to 25 wt%.

[0171] The HOMO energy decreases in the order of the green dopant GD, the hole-transporting host GHH, and the auxiliary dopant CRD, and the HOMO energy difference between the green dopant GD and the auxiliary dopant CRD may be 0.25 eV or less.

[0172] The auxiliary dopant CRD may have shorter wavelength emission peaks than the green dopant GD.

[0173] The emission peak of the auxiliary dopant CRD may have an emission peak in a different green wavelength band than the emission peak of the green dopant GD.

[0174] The emission peak of the auxiliary dopant CRD may have a difference of less than 10 nm from the emission peak of the green dopant GD.

[0175] As a result, the light-emitting element ED in Figure 17 maintains high green light emission efficiency, while simultaneously reducing the driving voltage and improving the carrier storage and emission characteristics of the light-emitting element. This prevents or reduces the flashing phenomenon in which green light is observed when switching from the off state to the on state.

[0176] The first electrode AND is separated for each subpixel, and the remaining layers of the light-emitting element ED, excluding the first electrode AND, can be integrated into the entire display area without subpixel separation.

[0177] Either the first electrode AND or the second electrode CAT can be connected to a thin-film transistor TFT.

[0178] On the other hand, although the light-emitting display device 1000 in Figure 17 described above is shown as having a structure that emits light downwards, the present invention is not limited to this. For example, by including a reflective electrode in the first electrode AND and a transparent electrode or a reflective-transmitting electrode in the second electrode CAT, and positioning the color filter above the second electrode CAT, the light-emitting display device can be applied in an upward-emitting manner.

[0179] The structure described above shows a configuration in which the intermediate layer OS of the light-emitting element ED is common to each subpixel, but the light-emitting devices of the embodiments described herein are not limited to this.

[0180] Figure 18 is a cross-sectional view showing a light-emitting device 2000 according to another embodiment of this specification.

[0181] As shown in Figure 18, a light-emitting display device according to another embodiment of the present invention includes a first electrode AND and a second electrode CAT facing each of a red subpixel R_SP, a green subpixel G_SP, and a blue subpixel B_SP, and a plurality of light-emitting stacks provided between the first electrode AND and the second electrode CAT, wherein the plurality of light-emitting stacks may include superimposed light-emitting layers that emit the same color. That is, the red subpixel R_SP may have red light-emitting layers REML1 and REML2 in stacks separated from each other by a charge generation layer CGL, the green subpixel G_SP may have green light-emitting layers GEML1 and GEML2 in stacks separated from each other by a charge generation layer CGL, and the blue subpixel B_SP may have blue light-emitting layers BEML1 and BEML2 in stacks separated from each other by a charge generation layer CGL.

[0182] Here, a common layer CML11 related to hole injection and hole transport is provided between the first electrode AND and the first red light-emitting layer REML1, the first green light-emitting layer GEML1, and the first blue light-emitting layer BEML1, and a common layer CML21 related to electron transport may be provided between the first red light-emitting layer REML1, the first green light-emitting layer GEML1, the first blue light-emitting layer BEML1 and the charge generation layer CGL.

[0183] The charge generation layer CGL may be provided by stacking an n-type charge generation layer NCGL and a p-type charge generation layer PCGL on top of each other.

[0184] Furthermore, a common layer CML12 related to hole injection and hole transport is provided between the charge generation layer CGL and the second red light-emitting layer REML2, the second green light-emitting layer GEML2, and the second blue light-emitting layer BEML2, and a common layer CML22 including an electron transport layer and an electron injection layer may be provided between the second red light-emitting layer REML2, the second green light-emitting layer GEML2, the second blue light-emitting layer BEML2 and the second electrode CAT.

[0185] Common layers CML11 and CML12 related to hole injection and transport include at least one of a hole injection layer, a hole transport layer, and an electron blocking layer, while common layers CML21 and CML22 related to electron transport and injection may include at least one of a hole blocking layer, an electron transport layer, and an electron injection layer.

[0186] Here, at least one of the first green light-emitting stacks positioned below and above the charge generation layer CGL between the green subpixels G_SP can include the capacitance relaxation layers CRL1 and CRL2 and the green light-emitting layers GEML1 and GEML2 as described in Figures 2 to 3b. A detailed explanation of the same content is omitted.

[0187] The green light-emitting element of the green subpixel G_SP has a predetermined improved luminous efficiency of the green light-emitting layer, can reduce the driving voltage, ensures a lifespan above a certain level, and improves the carrier storage and emission characteristics of the green light-emitting element, thereby preventing the flashing phenomenon in which green light is observed when switching from the off state to the on state.

[0188] The light-emitting element according to the embodiments of this specification and the light-emitting device including the same are provided with a capacitance relaxation layer CRL having an auxiliary dopant CRD having a lower HOMO energy level than the green dopant GD at the leading end of the green light-emitting layer. This prevents the phenomenon of holes being trapped in the green dopant in the green light-emitting layer during hole movement when holes are injected from the hole transport layer into the green light-emitting layer, and allows for the formation of multiple paths between the green dopant, the hole-transporting host and the electron-transporting host via the auxiliary dopant.

[0189] Since holes and electrons are not trapped in the green dopant and can contribute to exciton formation in both the host and the dopant, the problem of image degradation caused by the accumulation of residual carriers in the green light-emitting layer can be prevented or reduced.

[0190] Since an auxiliary dopant with a low HOMO energy level is provided between the hole transport layer and the green light-emitting layer, the green light-emitting layer has CV characteristics that facilitate carrier accumulation / release, thus resolving the image quality degradation that occurs when the green light-emitting layer is switched on or off.

[0191] The light-emitting element and light-emitting device according to the embodiments of this specification have the advantage of preventing residual carriers generated by trapped holes in specific materials within the light-emitting layer, improving carrier accumulation / emission characteristics during turn-on / turn-off, resolving the flashing issue, and lowering the drive voltage, making them highly applicable for sustained use. Therefore, they can embody ESG (Environment / Social / Governance) principles.

[0192] A light-emitting device according to one embodiment of this specification includes a first electrode and a second electrode facing each other, and a green light-emitting stack disposed between the first and second electrodes, the stack including a hole transport layer, a capacitance relaxation layer, a green light-emitting layer, and an electron transport layer, wherein the capacitance relaxation layer may include an auxiliary dopant with a lower HOMO energy level than the green dopant of the green light-emitting layer.

[0193] The capacitance relaxation layer is in contact with the green light-emitting layer and may contain the same host as the green light-emitting layer.

[0194] The hole mobility of the auxiliary dopant may be greater than that of the green dopant.

[0195] The triplet energy level of the auxiliary dopant may be the same as or higher than the triplet energy level of the green dopant.

[0196] Each of the green light-emitting layer and the capacity relaxation layer includes a hole-transporting host and an electron-transporting host, wherein the HOMO energy level of the auxiliary dopant is lower than the HOMO energy level of the hole-transporting host but higher than the HOMO energy level of the electron-transporting host, and the LUMO energy level of the auxiliary dopant may be lower than the LUMO energy level of the electron-transporting host.

[0197] The HOMO energy level of the green dopant may be higher than that of the hole-transporting host.

[0198] The HOMO energy level of the auxiliary dopant may have a difference of 0.15 eV or less from the HOMO energy level of the hole-transporting host.

[0199] The aforementioned auxiliary dopant may contain an electron-withdrawing group in the iridium phosphor dopant matrix.

[0200] Each of the green light-emitting layer and the capacity relaxation layer includes a hole-transporting host and an electron-transporting host, wherein the electron-transporting host has a LUMO energy level lower than the LUMO energy level of the hole-transporting host and a HOMO energy level lower than the HOMO energy level of the hole-transporting host, and the HOMO energy level of the auxiliary dopant may be lower than the HOMO energy level of the hole-transporting host.

[0201] The HOMO energy level of the auxiliary dopant may be closer to the HOMO energy level of the hole-transporting host than to the HOMO energy level of the electron-transporting host.

[0202] The HOMO energy level of the electron-transporting host may be 0.25 eV to 0.55 eV lower than the HOMO energy level of the auxiliary dopant.

[0203] The thickness of the capacitance relaxation layer may be thinner than the thickness of the green light-emitting layer.

[0204] The auxiliary dopant may be present in the volume relaxation layer in an amount of 5 wt% to 25 wt%, and the green dopant may be present in the green light-emitting layer in an amount of 5 wt% to 25 wt%.

[0205] The HOMO energy levels decrease in the order of the green dopant, the hole-transporting host, and the auxiliary dopant, and the difference in HOMO energy levels between the green dopant and the auxiliary dopant may be 0.25 eV or less.

[0206] The auxiliary dopant may have an emission peak with a shorter wavelength than the green dopant.

[0207] The emission peak of the auxiliary dopant may have an emission peak in a different green wavelength band than the emission peak of the green dopant.

[0208] The emission peak of the auxiliary dopant may have a difference of 10 nm or less from the emission peak of the green dopant.

[0209] The first electrode and the hole transport layer of the green light-emitting stack may include a red light-emitting stack containing a red light-emitting layer, a first charge generation layer, a first blue light-emitting stack containing a first blue light-emitting layer, and a second charge generation layer. The electron transport layer of the green light-emitting stack and the second electrode may include a third charge generation layer and a second blue light-emitting stack containing a second blue light-emitting layer.

[0210] The thickness of the green light-emitting layer may be greater than that of the red light-emitting layer, the first blue light-emitting layer, and the second blue light-emitting layer.

[0211] The content of the green dopant in the green light-emitting layer may be greater than the content of the dopant in the red light-emitting layer, the first blue light-emitting layer, and the second blue light-emitting layer, respectively.

[0212] Each of the first to third charge generation layers includes an n-type charge generation layer and a p-type charge generation layer, the hole transport layer is in contact with the p-type charge generation layer of the second charge generation layer, and the electron transport layer may be in contact with the n-type charge generation layer of the third charge generation layer.

[0213] The second blue light-emitting layer may be thicker than the first blue light-emitting layer.

[0214] The aforementioned green light-emitting stacks can be stacked in pairs or more, with a charge generation layer in between.

[0215] A light-emitting display device according to one embodiment of this specification may include a substrate having a plurality of subpixels, a pixel circuit provided in each of the plurality of subpixels and including at least one transistor, and a light-emitting element connected to at least one of the pixel circuits among the plurality of subpixels.

[0216] On the other hand, the present invention described above is not limited to the embodiments and accompanying drawings, and it will be obvious to those with ordinary skill in the art to which the present invention belongs that various substitutions, modifications, and changes are possible without departing from the technical spirit of the present invention. [Explanation of Symbols]

[0217] AND: 1st electrode CAT: 2nd electrode CML11, CML12, CML13, CML14: 1st common layer CML21, CML22, CML23, CML24: 2nd common layer HTL: Hole Transport Layer ETL: Electron transport layer CRL: Capacitive Relaxation Layer GEML: Green light-emitting layer CRD: Auxiliary Dopant GD: Green Dopant GHH: Hole-transporting host GEH: Electron Transport Host

Claims

1. A first electrode and a second electrode facing each other, The present invention includes a green light-emitting stack disposed between the first electrode and the second electrode, which includes a hole transport layer, a capacitance relaxation layer, a green light-emitting layer, and an electron transport layer, The capacitance relaxation layer includes an auxiliary dopant with a lower HOMO energy level than the green dopant of the green light-emitting layer, wherein the light-emitting element is a light-emitting element.

2. The light-emitting element according to claim 1, wherein the capacitance relaxation layer is in contact with the green light-emitting layer and contains the same host as the host of the green light-emitting layer.

3. The light-emitting element according to claim 1, wherein the hole mobility of the auxiliary dopant is greater than the hole mobility of the green dopant.

4. The light-emitting element according to claim 1, wherein the triplet energy level of the auxiliary dopant is the same as or higher than the triplet energy level of the green dopant.

5. Each of the green light-emitting layer and the capacity relaxation layer includes a hole-transporting host and an electron-transporting host, The HOMO energy level of the auxiliary dopant is lower than the HOMO energy level of the hole-transporting host, but higher than the HOMO energy level of the electron-transporting host. The light-emitting element according to claim 1, wherein the LUMO energy level of the auxiliary dopant is lower than the LUMO energy level of the electron-transporting host.

6. The light-emitting element according to claim 5, wherein the HOMO energy level of the green dopant is higher than the HOMO energy level of the hole-transporting host.

7. The light-emitting element according to claim 5, wherein the HOMO energy level of the auxiliary dopant has a difference of 0.15 eV or less from the HOMO energy level of the hole-transporting host.

8. The light-emitting element according to claim 1, wherein the auxiliary dopant comprises an electron-withdrawing group in the iridium phosphor dopant matrix.

9. Each of the green light-emitting layer and the capacity relaxation layer includes a hole-transporting host and an electron-transporting host, The electron-transporting host has a LUMO energy level lower than the LUMO energy level of the hole-transporting host, and a HOMO energy level lower than the HOMO energy level of the hole-transporting host. The light-emitting element according to claim 1, wherein the HOMO energy level of the auxiliary dopant is lower than the HOMO energy level of the hole-transporting host.

10. The light-emitting element according to claim 9, wherein the HOMO energy level of the auxiliary dopant is closer to the HOMO energy level of the hole-transporting host than the HOMO energy level of the electron-transporting host.

11. The light-emitting element according to claim 5, wherein the HOMO energy level of the electron-transporting host is 0.25 eV to 0.55 eV lower than the HOMO energy level of the auxiliary dopant.

12. The light-emitting element according to claim 1, wherein the thickness of the capacitance relaxation layer is thinner than the thickness of the green light-emitting layer.

13. The auxiliary dopant is contained in the volume relaxation layer in an amount of 5 wt% to 25 wt%, The light-emitting element according to claim 1, wherein the green dopant is contained in the green light-emitting layer in an amount of 5 wt% to 25 wt%.

14. The HOMO energy levels decrease in the order of the green dopant, the hole-transporting host, and the auxiliary dopant. The light-emitting element according to claim 5, wherein the difference in HOMO energy levels between the green dopant and the auxiliary dopant is 0.25 eV or less.

15. The light-emitting element according to claim 1, wherein the auxiliary dopant has an emission peak with a shorter wavelength than the green dopant.

16. The light-emitting element according to claim 15, wherein the wavelength of the emission peak of the auxiliary dopant has a difference of 10 nm or less from the wavelength of the emission peak of the green dopant.

17. The light-emitting element according to claim 1, wherein the emission peak of the auxiliary dopant has an emission peak in a different green wavelength band from the emission peak of the green dopant.

18. Between the first electrode and the hole transport layer of the green light-emitting stack, there is a red light-emitting stack including a red light-emitting layer, a first charge generation layer, a first blue light-emitting stack including a first blue light-emitting layer, and a second charge generation layer. The light-emitting element according to claim 1, further comprising a third charge generation layer and a second blue light-emitting stack including a second blue light-emitting layer between the electron transport layer and the second electrode of the green light-emitting stack.

19. The light-emitting element according to claim 18, wherein the thickness of the green light-emitting layer is greater than that of the red light-emitting layer, the first blue light-emitting layer, and the second blue light-emitting layer.

20. The light-emitting element according to claim 18, wherein the content of the green dopant contained in the green light-emitting layer is greater than the content of the dopant contained in the red light-emitting layer, the first blue light-emitting layer, and the second blue light-emitting layer, respectively.

21. Each of the first to third charge generation layers includes an n-type charge generation layer and a p-type charge generation layer. The hole transport layer is in contact with the p-type charge generation layer of the second charge generation layer, The light-emitting element according to claim 18, wherein the electron transport layer is in contact with the n-type charge generation layer of the third charge generation layer.

22. The light-emitting element according to claim 18, wherein the second blue light-emitting layer is thicker than the first blue light-emitting layer.

23. The light-emitting element according to claim 1, wherein two or more green light-emitting stacks are stacked with a charge generation layer in between.

24. A substrate containing multiple subpixels, Each of the aforementioned subpixels is provided with a pixel circuit including at least one transistor, A light-emitting device comprising: a light-emitting element according to claim 1, which is connected to at least one of the plurality of subpixels in the pixel circuit.

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