Organic electroluminescent element

Abstract

Provided is an organic electroluminescent element which has a structure in which a first electrode, a hole transport region, a light-emitting layer, an electron transport region, and a second electrode are laminated in this order, and which is provided with at least two or more electron transport layers controlled so as to have a predetermined refractive index difference between the light-emitting layer and the electrodes. And the difference between the refractive index of the first electron transport layer adjacent to the light emitting layer and the refractive index of the second electron transport layer adjacent to the electrode is controlled within a predetermined range, thereby optimizing efficiency by maximizing light extraction by a micro-cavity effect.

Description

Technical Field

[0001] The present invention relates to an organic electroluminescent element including at least two or more electron transport layers controlled to have a predetermined refractive index difference between a light emitting layer and an electrode, thereby optimizing efficiency by maximizing light extraction. Background Art

[0002] With the research on organic electroluminescent (EL) elements (hereinafter, simply referred to as "organic EL elements") developed from blue electroluminescence using anthracene single crystals in 1965, in 1987, Tang proposed an organic EL element having a two-layer stacked structure composed of a hole layer (NPB) and a light emitting layer (Alq3). Thereafter, in order to achieve the high efficiency and long life characteristics required for organic EL elements for commercialization, a multi-layer stacked structure was proposed in which organic layers having different characteristics and providing detailed functions, such as an organic layer having a hole injection and transport function, an organic layer having an electron injection and transport function, and an organic layer inducing electroluminescence by the combination of holes and electrons, were provided in the element. The introduction of the multi-layer stacked structure has improved the performance of organic EL elements to commercialization characteristics, and starting from automotive radio display products in 1997, attempts are being made to expand its application range to portable information display devices and TV display elements.

[0003] The requirements for the enlargement and high resolution of displays have posed the problems of high efficiency and long life of organic EL elements. In particular, in the case of high resolution achieved by forming more pixels in the same area, the light emitting area of organic EL pixels is reduced, resulting in a shortened life, which has become the most important technical problem that organic EL elements have to overcome.

[0004] When a current or voltage is applied to two electrodes of an organic EL element, holes are injected from the anode into the organic layer, and electrons are injected from the cathode into the organic layer. When the injected holes and electrons meet, excitons are formed, and when these excitons transition to the ground state, light is emitted. At this time, organic EL elements can be classified into fluorescent EL elements in which singlet excitons participate in light emission and phosphorescent EL elements in which triplet excitons participate in light emission according to the electron spin type of the formed excitons.

[0005] The electron spin of excitons formed by the recombination of electrons and holes is generated at a ratio of 25% singlet excitons and 75% triplet excitons. It is considered that for a fluorescent EL element that emits light through singlet excitons, the internal quantum efficiency theoretically does not exceed 25% according to the generation ratio, and the upper limit of the external quantum efficiency is 5%. In the case of a phosphorescent EL element that emits light through triplet excitons, when a metal complex containing heavy atoms such as Ir and Pt is used as a phosphorescent dopant, the luminous efficiency can be increased up to 4 times compared with fluorescence.

[0006] As described above, although phosphorescent EL elements show higher efficiency in terms of luminous efficiency compared with fluorescence based on theoretical facts, for blue phosphorescent elements other than green and red, due to the insufficient development level of phosphorescent dopants with high color purity and high efficiency for dark blue and hosts with a wide energy gap that meet these requirements, blue phosphorescent elements have not been able to be commercialized so far, and blue fluorescent elements are used in products.

[0007] In order to improve the characteristics of the above-mentioned organic EL elements, research results on improving the stability of the elements by preventing the diffusion of holes into the electron transport layer have been reported. However, in reality, satisfactory results have not been obtained so far. Summary of the Invention

[0008] Technical Problem

[0009] The present invention is proposed to solve the above problems, and aims to provide an organic EL element that has at least two or more electron transport layers between the light-emitting layer and the electrode, and controls the refractive index difference between the first electron transport layer adjacent to the light-emitting layer and the second electron transport layer adjacent to the electrode within a predetermined range, thereby achieving high efficiency through maximizing light extraction brought by the micro-cavity effect.

[0010] Other objects and advantages of the present invention can be more clearly described through the following detailed description of the invention and the scope of the claims.

[0011] Method for Solving the Problem

[0012] To achieve the above technical problem, the present invention provides an organic electroluminescent element having a structure in which a first electrode, a hole transport region, a light-emitting layer, an electron transport region, and a second electrode are sequentially stacked, the electron transport region includes at least two layers, and the at least two layers include a first electron transport layer (ET1) disposed adjacent to the light-emitting layer and a second electron transport layer (ET2) disposed adjacent to the second electrode.

[0013] In the blue wavelength region of 460 ± 20 nm, the refractive index (n1) of the first electron transport layer is greater than the refractive index (n2) of the second electron transport layer.

[0014] According to an embodiment of the present invention, in the wavelength region of 460 ± 20 nm, the refractive index difference (n1 - n2) between the first electron transport layer and the second electron transport layer may be greater than 0 and less than 1.0.

[0015] According to an embodiment of the present invention, in the wavelength region of 460 ± 20 nm, the refractive index (n1) of each of the first electron transport layer and the second electron transport layer may be from 1.45 to 3.0.

[0016] According to an embodiment of the present invention, in the wavelength region of 460 ± 20 nm, the absolute value of the refractive index difference between the first electron transport layer and the light-emitting layer may be from 0 to 1.5.

[0017] According to an embodiment of the present invention, in the wavelength region of 460 ± 20 nm, the absolute value of the refractive index difference between the second electron transport layer and the light-emitting layer may be from 0 to 1.5.

[0018] According to an embodiment of the present invention, the absolute value of the HOMO energy of each of the first electron transport layer and the second electron transport layer may be 4.0 eV or more.

[0019] According to an embodiment of the present invention, the absolute value of the LUMO energy of each of the first electron transport layer and the second electron transport layer may be 1.60 eV or more.

[0020] According to an embodiment of the present invention, the absolute value of the difference between the HOMO energy level of the first electron transport layer and the HOMO energy level of the second electron transport layer may be in the range of 0 to 2.5 eV.

[0021] According to an embodiment of the present invention, the absolute value of the difference between the LUMO energy level of the first electron transport layer and the LUMO energy level of the second electron transport layer may be in the range of 0 to 2.5 eV.

[0022] According to an embodiment of the present invention, the absolute value of the difference between the LUMO energy of the light-emitting layer and the LUMO energy level of the first electron transport layer (ET1) may be in the range of 0 to 1.5 eV.

[0023] According to an embodiment of the present invention, the absolute value of the difference between the LUMO energy of the light-emitting layer and the LUMO energy level of the second electron transport layer (ET2) may be in the range of 0 to 1.5 eV.

[0024] According to an embodiment of the present invention, the absolute value difference in molecular weight (MW) between the first electron transport layer and the second electron transport layer may be from 0 to 600 g / mol.

[0025] According to an embodiment of the present invention, the singlet energy (S1) of each of the first electron transport layer and the second electron transport layer may be 1.8 eV or more.

[0026] According to an embodiment of the present invention, the triplet energy (T1) of each of the first electron transport layer and the second electron transport layer may be 1.6 eV or more.

[0027] According to an embodiment of the present invention, the lowest energy level among the bond dissociation energies (BDE) of the ground states of the first electron transport layer and the second electron transport layer may be 0.5 eV or more.

[0028] According to an embodiment of the present invention, the dipole moment of each of the first electron transport layer and the second electron transport layer may be greater than 0.

[0029] According to an embodiment of the present invention, the electron affinity (EA) of each of the first electron transport layer and the second electron transport layer may be 0.1 eV or more.

[0030] According to an embodiment of the present invention, at least in zero - field, the electron mobility (μ) may be 1×10 -8 cm 2 / Vs or more.

[0031] According to an embodiment of the present invention, the electron transport region may further include at least one of a hole leakage suppression layer, an electron transport assist layer, and an electron injection layer.

[0032] According to an embodiment of the present invention, the light - emitting layer includes a host and a dopant, and the mixing ratio of the host and the dopant may be 70 - 99.5:0.5 - 30 by weight.

[0033] According to an embodiment of the present invention, the organic electroluminescent element may include a plurality of light - emitting layer stacks each including at least one light - emitting layer.

[0034] Advantageous Effects of the Invention

[0035] According to an embodiment of the present invention, by providing at least two or more electron transport layers controlled to have a predetermined refractive index difference between the light - emitting layer and the electrode, the light extraction can be maximized to optimize the light - emitting efficiency of the organic electroluminescent element.

[0036] The effects of the present invention are not limited to the above-exemplified contents, and more diverse effects are included in this specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a cross-sectional view showing the structure of an organic electroluminescent element according to an embodiment of the present invention.

[0038] Figure 2 It is a cross-sectional view showing the structure of an organic electroluminescent element according to another embodiment of the present invention.

[0039] <REFERENCE SIGNS>

[0040] 100: Organic electroluminescent element

[0041] A: Organic layer

[0042] 10: First electrode

[0043] 20: Second electrode

[0044] 30: Hole transport region

[0045] 31: Hole injection layer

[0046] 32: Hole transport layer

[0047] 40: Light emitting layer

[0048] 50: Electron transport region

[0049] 51: First electron transport layer

[0050] 52: Second electron transport layer

[0051] 53: Electron injection layer DETAILED DESCRIPTION

[0052] The advantages and features of the present invention and the methods for realizing them will be clear as long as reference is made to the drawings and the embodiments described in detail. However, the present invention is not limited to the embodiments disclosed below and can be presented in various different forms. These embodiments only make the disclosure of the present invention comprehensive and are provided to enable those of ordinary skill in the technical field to which the present invention pertains to fully understand the scope of the invention. The present invention is only defined by the scope of the claims. Therefore, in some embodiments, in order to avoid the present invention being ambiguously interpreted, well-known process steps, well-known element structures, and well-known technologies will not be specifically described. Throughout the specification, the same reference signs refer to the same components.

[0053] Unless otherwise defined, all terms (including technical and scientific terms) used in this specification can be used with the meanings commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Additionally, terms defined in commonly used dictionaries should not be construed ideally or overly unless explicitly defined otherwise.

[0054] In addition, throughout the specification, when it is stated that a certain part "includes" a certain component, unless there is a particularly contrary description, it means that other components can also be included rather than excluding other components. Also, throughout the specification, "above" or "upper" not only includes the case of being above or below the target part, but also includes the case where there are other parts in between, and does not mean that it must be located on the upper side based on the direction of gravity. In this specification, terms such as "first" and "second" do not indicate any order or degree of importance, but are used to distinguish components from each other.

[0055] <Organic electroluminescent element>

[0056] Hereinafter, preferred embodiments of the organic electroluminescent element of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be deformed into various other forms, and the scope of the present invention is not limited by the embodiments described below.

[0057] Figure 1 It is a cross-sectional view schematically showing the structure of an organic electroluminescent element 100 according to an embodiment of the present invention.

[0058] Referring to Figure 1 , the above-mentioned organic electroluminescent element 100 includes a first electrode 10, a second electrode 20, a light-emitting layer 40 located between the first electrode 10 and the second electrode 20, a hole transport region 30 located between the first electrode 10 and the light-emitting layer 40, and an electron transport region 50 located between the light-emitting layer 40 and the second electrode 20. The electron transport region 50 includes at least two layers, including a first electron transport layer 51 disposed adjacent to the light-emitting layer 40 and a second electron transport layer 52 disposed adjacent to the second electrode 20 and having a refractive index different from that of the first electron transport layer 51.

[0059] The light efficiency of an organic light-emitting device (OLED) is generally divided into an external quantum efficiency (EQE) and an internal quantum efficiency (IQE). Even if the internal quantum efficiency of an OLED is 100%, in the process of extracting light to the outside, there is a problem that only about 20-30% of the low-efficiency light is extracted to the outside. In addition, at the interface of the organic layer adjacent to the electrode (metal), due to the surface plasmon polariton (SPP) phenomenon, light moves along the surface of the electrode and / or thermal loss occurs. As a result, a large amount of light generated inside the OLED is guided, and finally only about 20-30% of the light is extracted to the outside.

[0060] In contrast, in the present invention, at least two or more electron transport layers 50 are provided between the light-emitting layer 40 and the second electrode (for example, the cathode) 20, and the refractive index of the first electron transport layer 51 disposed adjacent to the light-emitting layer 40 and the refractive index of the second electron transport layer 52 disposed adjacent to the second electrode 20 are precisely controlled within a predetermined range, which is different from the conventional organic light-emitting device in this regard.

[0061] Specifically, in the present invention, the refractive index of the first electron transport layer 51 disposed adjacent to the light-emitting layer 40 is controlled to be higher than the refractive index of the second electron transport layer 52 disposed adjacent to the cathode 20 by a predetermined range or more. In this case, the light emitted from the light-emitting layer 40 is emitted to the upper part (vertical direction) of the light-emitting layer 40 due to the high refractive index of the adjacent first electron transport layer 51, and then is totally reflected by the low refractive index of the second electron transport layer 52 adjacent to the second electrode 20, so that the primary efficiency of light extraction can be increased by the micro-cavity effect. Such a micro-cavity effect utilizes the micro-vibration effect (enhanced interference of waves) to increase the emission speed of light. Even for a minute fluctuation, if the same period and phase are continuously overlapped, the energy can be amplified to generate a micro-resonance effect, and the emitted light can be adjusted to be well emitted in the vertical direction. In addition, by adjusting the refractive index of the second electron transport layer 52 adjacent to the second electrode 20 to be as low as a predetermined range, the surface plasmon loss phenomenon occurring in the metal of the second electrode 20 can be significantly reduced by total reflection, so that an improvement in the secondary efficiency can also be expected through light extraction.

[0062] As described above, in the present invention, by adjusting the configuration structure between the first electron transport layer 51 and the second electron transport layer 52 and the refractive index difference therebetween, the microresonance effect and the surface plasmon loss are minimized, whereby the light extraction can be maximized to obtain the effect of improving the efficiency of the device.

[0063] According to a specific example, the electron transport region 50 including at least two layers having different refractive indexes includes a first electron transport layer (ET1) 51 disposed adjacent to the light-emitting layer 40 and a second electron transport layer (ET2) 52 disposed adjacent to the second electrode 20 and having a refractive index different from that of the first electron transport layer 51. At a wavelength of 460 ± 20 nm, the refractive index (n1) of the first electron transport layer 51 may be higher than the refractive index (n2) of the second electron transport layer 52, specifically, it may be 0.05 or more.

[0064] Here, the refractive index is based on the refractive index calculated by using the Lorenz-Lorenz formula and the quantum mechanical method of CAM-B3LYP / 6-31G*. However, it is not limited thereto, and the case of measuring or calculating the refractive index using a method well known in the art also belongs to the scope of the present invention.

[0065] In addition, the refractive index of a substance varies depending on the wavelength. Therefore, the refractive index of the present invention is based on the refractive index measured in the blue wavelength region of 460 ± 20 nm. At this time, when based on the green or red wavelength region, it may be changed to the refractive index measured in the wavelength region of approximately 520 ± 20 nm or 630 ± 20 nm.

[0066] According to a specific example, the refractive index (n1) of the first electron transport layer 51 and the refractive index (n2) of the second electron transport layer 52 may each be 1.45 to 3.0 at a wavelength of 460 ± 20 nm, specifically, they may be 1.45 to 2.8.

[0067] According to another specific example, in the blue wavelength region of 460 ± 20 nm, the refractive index difference (n1 - n2) between the first electron transport layer 51 and the second electron transport layer 52 may be greater than 0 and less than 1.0, specifically, it may be in the range of 0.1 to 0.8.

[0068] According to another specific example, in the wavelength region of 460 ± 20 nm, the absolute value of the refractive index difference between the first electron transport layer 51 and the light-emitting layer 40 may be 0 or more and 1.5 or less, specifically, it may be 0.05 or more and 1 or less. Here, the light-emitting layer 40 may refer to the light-emitting layer itself or the host included in the light-emitting layer 40.

[0069] In addition to maximizing light extraction by satisfying the configuration structures of the above-mentioned first electron transport layer 51 and second electron transport layer 52 and adjusting the refractive index difference therebetween, the organic electroluminescent element 100 of the present invention preferably further satisfies at least one of the physical properties described below to exhibit low driving voltage and high efficiency effects.

[0070] According to a specific example, the absolute value of the HOMO energy of the above-mentioned first electron transport layer 51 and second electron transport layer 52 can each be 4.0 eV or more, specifically, it can be 4.0 to 7.0 eV, and more specifically, it can be 4.0 to 6.5 eV. If such a HOMO energy value is provided, the phenomenon that holes transferred to the light-emitting layer 40 diffuse or cross over to other electron transport regions, such as the first electron transport layer 51 and the second electron transport layer 52, can be prevented. Thereby, the probability of encounter and recombination of holes and electrons inside the light-emitting layer 40 can be increased to further improve the light-emitting efficiency of the organic electroluminescent element. In addition, the irreversible decomposition reaction caused by oxidation and the resulting shortening of the lifespan of the organic electroluminescent element when holes cross over the light-emitting layer 40 and diffuse or migrate to the first electron transport layer 51 and the second electron transport layer 52 can be solved, thereby improving the lifespan characteristics of the element.

[0071] According to another specific example, the absolute value of the LUMO energy of the above-mentioned first electron transport layer 51 and second electron transport layer 52 can each be 1.60 eV or more, specifically, it can be 1.60 to 3.50 eV, and more specifically, it can be 1.80 to 3.0 eV. In addition, in order to achieve effective high efficiency, the bandgap energy of the above-mentioned first electron transport layer 51 and second electron transport layer 52 can each be 2.0 eV or more, specifically, it can be 2.0 to 4.5 eV.

[0072] According to another specific example, the absolute value difference between the highest occupied molecular orbital (HOMO) energy level of the above-mentioned first electron transport layer 51 and the HOMO energy level of the second electron transport layer 52 can be in the range of 0 to 2.5 eV, specifically, it can be 0.05 to 2.0 eV.

[0073] According to another specific example, the absolute value difference between the lowest unoccupied molecular orbital (LUMO) energy level of the above-mentioned first electron transport layer 51 and the LUMO energy level of the second electron transport layer 51 can be in the range of 0 to 2.5 eV, specifically, it can be 0.05 to 1.5 eV.

[0074] According to another specific example, the absolute value difference between the LUMO energy of the above-mentioned light-emitting layer 40 and the LUMO energy level of the above-mentioned first electron transport layer (ET1) 51 can be in the range of 0 to 1.5 eV, specifically, it can be 0.05 to 1.0 eV.

[0075] According to another specific example, the absolute value difference between the LUMO energy of the above-mentioned light-emitting layer 40 and the LUMO energy level of the above-mentioned second electron transport layer (ET2) 52 can be in the range of 0 to 1.5 eV, specifically, it can be 0.1 to 0.8 eV.

[0076] According to another specific example, the absolute value difference in molecular weight (MW) between the above-mentioned first electron transport layer 51 and the above-mentioned second electron transport layer 52 can be 0 to 600 g / mol, specifically, it can be 0 to 400 g / mol.

[0077] According to another specific example, the singlet energy (S1) of the above-mentioned first electron transport layer 51 and the second electron transport layer 52 can each be 1.8 eV or more, specifically, it can be 1.8 to 4.5 eV, more specifically, it can be 2.0 to 4.0 eV. This can prevent singlet excitons from diffusing to adjacent interfaces and / or other layers or from emitting light at the interface, and effectively confine singlet excitons. Therefore, the number of excitons increases, and the luminous efficiency of the organic electroluminescent device can be improved. As a result, spectral color mixing of the organic electroluminescent device can be prevented, stability can be improved, and thus the efficiency and lifespan of the organic electroluminescent device can be increased.

[0078] According to another specific example, the triplet energy (T1) of the above-mentioned first electron transport layer 51 and the second electron transport layer 52 can each be 1.6 eV or more, specifically, it can be 1.6 to 4.5 eV, more specifically, it can be 1.6 to 4.0 eV. This can prevent the migration of excitons to other layers, and thus the effect of significantly increasing the efficiency of the organic electroluminescent device can be achieved.

[0079] According to another specific example, the lowest energy level of the bond dissociation energy (BDE, Bond Dissociation Energy) in the ground state of the above-mentioned first electron transport layer 51 and the second electron transport layer 52 can be 0.5 eV or more, specifically, it can be 0.5 to 6.5 eV, more specifically, it can be 0.5 to 6.0 eV. Here, the bond dissociation energy (BDE) can be interpreted as the energy required to break a specific chemical bond. Generally speaking, the stronger the bond, the more the bond dissociation energy (BDE) is related to the stability of the molecule, and thus it also plays a role as a factor affecting the lifespan.

[0080] According to another specific example, the dipole moments of the above-mentioned first electron transport layer 51 and second electron transport layer 52 can each be greater than 0, specifically, they can be from 0 to 10.

[0081] According to another specific example, the electronic affinities (EA) of the above-mentioned first electron transport layer 51 and the above-mentioned second electron transport layer 52 can each be 0.1 eV or more, specifically, they can be from 0.1 to 3.0 eV, and more specifically, they can be from 0.1 to 2.5 eV. When the above-mentioned electronic affinity is provided, high electron injection efficiency can be obtained.

[0082] On the other hand, if the balance between electrons and holes is not met due to the difference between the number of holes injected from the first electrode 10 and the number of electrons injected from the second electrode 20, the electrons or holes that do not form excitons through recombination will accumulate in the light-emitting layer 40. The electrons or holes accumulated in the light-emitting layer 40 will hinder the smooth progress of oxidation and reduction in the light-emitting layer 40 or affect the adjacent layers, thereby shortening the lifespan of the organic electroluminescent element. In contrast, the first electron transport layer 51 and the above-mentioned second electron transport layer 52 each have an electron mobility (μ) of at least 1×10 -8 cm 2 / Vs or more in zero-field, so it is possible to prevent the delay in electron injection compared to the number of holes injected from the first electrode 10, and the injection of electrons into the light-emitting layer 40 is smooth, thus improving the formation efficiency of excitons in the light-emitting layer 40 and improving the lifespan of the organic electroluminescent element.

[0083] Hereinafter, the configuration of an organic electroluminescent element 100 according to an embodiment of the present invention having an electron transport layer with at least two layers whose refractive index difference is adjusted to a predetermined range will be described in more detail.

[0084] substrate

[0085] In the organic light-emitting element of the present invention, the substrate 110 can be used without limitation as a substrate commonly used in the field of organic light-emitting elements in the art. Considering the mechanical strength, thermal stability, transparency, surface smoothness, processability, and waterproofness of the organic light-emitting element, a glass substrate or a transparent plastic substrate is preferred.

[0086] first electrode

[0087] In the organic electroluminescent element 100 of the present invention, the first electrode 10 is disposed on the substrate and functions as an anode for injecting holes into the organic layer A.

[0088] Such a first electrode 10 may be made of a material with a relatively high work function, and thus serves as an anode for injecting holes into the adjacent hole transport region 30. In this case, the second electrode 20 disposed opposite to the first electrode 10 serves as a cathode for injecting electrons into the adjacent electron transport region 50. However, it is not limited thereto. Depending on the situation, the first electrode 10 may serve as a cathode, and the second electrode 20 may serve as an anode.

[0089] The material constituting the first electrode 10 is not particularly limited, and a commonly known material in the art can be used. As non-limiting examples thereof, there are metals such as vanadium, chromium, copper, zinc, and gold; their alloys; metal oxides such as zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); combinations of metals and oxides such as ZnO:Al and SnO2:Sb; conductive polymers such as polythiophene, poly(3-methylthiophene), poly[3,4-(ethylenedioxy)thiophene] (PEDT), polypyrrole, and polyaniline; and carbon black.

[0090] The method for manufacturing the first electrode 10 is not particularly limited, and it can be manufactured according to a commonly known method in the art. As an example, a method of coating an anode material on a substrate made of a silicon wafer, quartz, glass plate, metal plate, or plastic film can be cited.

[0091] second electrode

[0092] In the organic electroluminescent element 100 of the present invention, the second electrode 20 is a part disposed opposite to the first electrode 10. Specifically, it is disposed on the electron transport region 50 to function as a cathode for injecting electrons into the organic layer A.

[0093] The material constituting the second electrode 20 is not particularly limited, and a commonly known material in the art can be used. As non-limiting examples thereof, there can be cited metals such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, and lead; their alloys; and multilayer structure materials such as LiF / Al and LiO2 / Al.

[0094] In this case, the second electrode 20 is a (semi) transmissive electrode, and the organic electroluminescent element including the second electrode 20 may have a front emission type structure. At this time, the light emitted from the light emitting layer 40 can pass through the second electrode 20, but can also be reflected on the lower surface of the second electrode 20, whereby it can be repeatedly reflected between the upper surface of the first electrode 10 and the lower surface of the second electrode 20.

[0095] The method for manufacturing the second electrode 20 is not particularly limited, and it can be manufactured according to methods well-known in the art.

[0096] organic layer

[0097] The organic layer A included in the organic electroluminescent element of the present invention can be used without limitation with the usual constitution of the organic layer used in conventional organic EL elements. As an example, it can include one or more selected from the group consisting of a hole transport region 30, a light-emitting layer 40, and an electron transport region 50. At this time, considering the characteristics of the organic electroluminescent element, it is preferable to include all of the above organic layers.

[0098] hole transport region

[0099] The hole transport region 30 included in the organic layer A of the present invention functions to transfer the holes injected from the first electrode 10 to the light-emitting layer 40. Such a hole transport region 30 can include one or more selected from the group consisting of a hole injection layer 31 and a hole transport layer 32. At this time, considering the characteristics of the organic electroluminescent element, it is preferable to include both the hole injection layer 31 and the hole transport layer 32.

[0100] The materials constituting the hole injection layer 31 and the hole transport layer 32 are not particularly limited as long as they have a low hole injection barrier and a high hole mobility, and hole injection layer / transport layer materials used in the art can be used without limitation. At this time, the materials constituting the hole injection layer 31 and the hole transport layer 32 can be the same or different from each other.

[0101] The above hole injection materials can use hole injection materials well-known in the art without limitation. As non-limiting examples of hole injection materials that can be used, there are phthalocyanine compounds such as copper phthalocyanine; N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4'-diamine (DNTPD), 4,4',4"-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), 4,4'4"-Tris(N,N-diphenylamino)triphenylamine (TDATA), 4,4',4"-tris{N,-(2-naphthyl)-N-phenylamino}-triphenylamine (2TNATA), Poly(3,4-ethylenedioxythiophene) / Poly(4-styrenesulfonate) (PEDOT / PSS), Polyaniline / Dodecylbenzenesulfonic acid (PANI / DBSA), Polyaniline / Camphor sulfonic acid (PANI / CSA), (Polyaniline) / Poly(4-styrenesulfonate) (PANI / PSS), and the like. Each of them can be used alone or in combination of two or more.

[0102] In addition, the above hole transporting material can use hole transporting materials well-known in the art without limitation. As non-limiting examples of hole transporting materials that can be used, there are carbazole-based derivatives such as phenylcarbazole and polyvinylcarbazole; fluorene-based derivatives; triphenylamine-based derivatives such as N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1-biphenyl]-4,4'-diamine (TPD) and 4,4',4"-tris(N-carbazolyl)triphenylamine (TCTA); N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (NPB), 4,4'-Cyclohexylidene bis[N,N-bis(4-methylphenyl)benzenamine] (TAPC), etc. They can be used alone or in combination of two or more kinds.

[0103] The above hole transporting region 30 can be fabricated by conventional methods known in the art. For example, there are vacuum evaporation method, spin coating method, casting method, Langmuir-Blodgett (LB) method, inkjet printing method, laser printing method, Laser Induced Thermal Imaging (LITI) method, etc., but not limited thereto.

[0104] light-emitting layer

[0105] The light emitting layer 40 included in the organic layer A of the present invention is a layer where holes and electrons meet to form excitons, and the color of the light emitted by the organic electroluminescent device can be changed according to the material constituting the light emitting layer 40.

[0106] Such a light-emitting layer 40 may include a host and a dopant, and their mixing ratio may be appropriately adjusted within a range known in the art. As an example, the light-emitting layer 40 may include 70 to 99.9 parts by weight of the host and 0.1 to 30 parts by weight of the dopant based on the total weight of the light-emitting layer 40. More specifically, in the case where the above light-emitting layer 40 is blue fluorescence, green fluorescence, or red fluorescence, it may include 80 to 99.9 parts by weight of the host and 0.1 to 20 parts by weight of the dopant. In addition, in the case where the above light-emitting layer 40 is blue fluorescence, green fluorescence, or red phosphorescence, it may include 70 to 99 parts by weight of the host and 1 to 30 parts by weight of the dopant.

[0107] The host included in the light-emitting layer 40 of the present invention is not particularly limited as long as it is a host known in the art. As non-limiting examples thereof, there are alkali metal complexes; alkaline earth metal complexes; or condensed aromatic ring derivatives, etc.

[0108] More specifically, as the host material, it is preferable to use an aluminum complex, a beryllium complex, an anthracene derivative, a pyrene derivative, a triphenylene derivative, a carbazole derivative, a dibenzofuran derivative, a dibenzothiophene derivative, or a combination of one or more of them, which can improve the luminous efficiency and lifespan of the organic electroluminescent element.

[0109] In addition, the dopant included in the light-emitting layer 40 of the present invention is not particularly limited as long as it is a dopant known in the art. As non-limiting examples thereof, there may be mentioned anthracene derivatives, pyrene derivatives, arylamine derivatives, metal complexes containing iridium (Ir) or platinum (Pt), etc.

[0110] The above dopants can be classified into red dopants, green dopants, and blue dopants, and the red dopants, green dopants, and blue dopants generally known in the art can be used without particular limitation.

[0111] Specifically, as non-limiting examples of the red dopant, there are PtOEP (Pt(II)octaethylporphine), Ir(piq)3 (tris(2-phenylisoquinoline)iridium), Btp2Ir(acac) (bis(2-(2'-benzothienyl)-pyridinato-N,C3')iridium(acetylacetonate)), or a mixture of two or more of them, etc.

[0112] In addition, as non-limiting examples of the green dopant, there are Ir(ppy)3 (tris(2-phenylpyridine)iridium), Ir(ppy)2(acac) (Bis(2-phenylpyridine)(Acetylacetonato)iridium(III)), Ir(mppy)3 (tris(2-(4-tolyl)phenylpiridine)iridium), C545T (10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]-quinolizin-11-one), or a mixture of two or more of them, etc.

[0113] In addition, as non-limiting examples of the blue dopant, there are F2Irpic (Bis[3,5-difluoro-2-(2-pyridyl)phenyl](picolinato)iridium(III)), (F2ppy)2Ir(tmd), Ir(dfppz)3, DPVBi (4,4'-bis(2,2'-diphenylethen-1-yl)biphenyl), DPAVBi (4,4'-Bis[4-(diphenylamino)styryl]biphenyl), TBPe (2,5,8,11-tetra-tert-butyl perylene), or a mixture of two or more of them, etc.

[0114] The light-emitting layer 40 of the present invention may be a red light-emitting layer containing a red phosphorescent material, a green light-emitting layer containing a green phosphorescent material, or a blue light-emitting layer containing a blue phosphorescent material or a blue fluorescent substance. Preferably, it may be a light-emitting layer containing a blue fluorescent material.

[0115] The above-mentioned light-emitting layer 40 can be configured as: a single layer composed of one substance; a single layer composed of a plurality of different substances; or a multi-layer composed of two or more layers each composed of different substances. Among them, when the light-emitting layer 40 is a plurality of layers, the organic electroluminescent element can emit light of multiple colors. Specifically, the present invention can provide an organic electroluminescent element in which a plurality of light-emitting layers composed of different materials are connected in series to present a mixed color. In addition, when a plurality of light-emitting layers are included, the driving voltage of the element will increase, while the current value in the organic electroluminescent element will remain constant. Therefore, an organic electroluminescent element with improved luminous efficiency matching the number of light-emitting layers can be provided.

[0116] Although not illustrated in the drawings, the above-mentioned organic electroluminescent element 100 may include a plurality of light-emitting stacks (not illustrated) each including at least one light-emitting layer.

[0117] The plurality of light-emitting layers included in such a light-emitting stack may be light-emitting layers that emit different colors of light from each other or light-emitting layers that emit the same color of light. That is, the emission color can be changed according to the substances constituting the light-emitting layer. As an example, the plurality of light-emitting stacks may include substances that emit light such as blue, green, red, yellow, white, etc., and can be formed using phosphorescent or fluorescent substances. At this time, the colors displayed by the respective light-emitting layers may be in a complementary color relationship with each other. In addition to this, colors can also be selected according to a color combination capable of emitting white light. Such respective light-emitting layers may each include a phosphorescent dopant or a fluorescent dopant corresponding to the selected color.

[0118] Although not illustrated in the drawings, the above-mentioned organic electroluminescent element 100 may further include a charge generation layer (not illustrated) disposed between adjacent stacks among the plurality of light-emitting stacks to connect them.

[0119] The charge generation layer (CGL) refers to a layer that neither directly contacts two electrodes (for example, an anode and a cathode) nor separates adjacent light-emitting stacks in an organic electroluminescent element having a plurality of light-emitting stacks. Such a charge generation layer is disposed between two adjacent light-emitting stacks, thereby acting as a cathode that generates electrons for one light-emitting stack and acting as an anode that generates holes for the other light-emitting stack. Such a charge generation layer can use without limitation substances known in the art that can be used as materials for a charge generation layer (charge generation layer, CGL). In addition, a commonly known n-type substance and / or p-type substance in the art can be doped into the substances for the above-mentioned charge generation layer use to form it.

[0120] electron transport region

[0121] In the organic electroluminescent element 100 of the present invention, the electron transport region 50 included in the organic layer A functions to migrate electrons injected from the second electrode 20 to the light-emitting layer 40.

[0122] Such an electron transport region 50 may be two or more layers including a first electron transport layer 51 and a second electron transport layer 52 having different refractive indexes, and may further include an electron injection layer 53, a hole-leakage suppression layer (not shown), and / or an electron transport auxiliary layer (not shown) as needed.

[0123] Based on the above light-emitting layer, the electron transport region 50 may have a structure in which the first electron transport layer 51 and the second electron transport layer 52 are arranged, or a structure in which the first electron transport layer 51, the second electron transport layer 52, and the electron injection layer 53 are arranged. Considering the characteristics of the organic electroluminescent element, it is preferable to include the first electron transport layer 51, the second electron transport layer 52, and the electron injection layer 53 at the same time.

[0124] In the present invention, as long as the refractive index difference between the first electron transport layer 51 and the second electron transport layer 52 is controlled within the above specific range, any commonly known substances having electron transport characteristics in the art can be used without limitation. As an example, it may include oxadiazole derivatives, triazole derivatives, phenanthroline derivatives (e.g., BCP), nitrogen-containing heterocyclic derivatives, etc.

[0125] According to a specific example, the first compound used as the material of the first electron transport layer 51 and the second compound used as the material of the second electron transport layer 52 are different from each other, and each may be a compound having at least one part with the characteristics of a strongly electron-withdrawing group (EWG) commonly known in the art. As an example, it may be a bipolar compound containing both a part with the characteristics of a strongly electron-withdrawing group (EWG) and a part with the characteristics of a strongly electron-donating group (EDG).

[0126] More specifically, the first compound (material) constituting the first electron transport layer 51 and the second compound used as the material of the second electron transport layer 52 may include at least one electron-withdrawing group (EWG) part among the 6-membered part represented by the following Chemical Formula 1, the 5-membered part represented by the following Chemical Formula 2, and the polycyclic part condensed from the above 6-membered part and 5-membered part.

[0127] [Chemical Formula 1]

[0128]

[0129] [Chemical Formula 2]

[0130]

[0131] In the above Chemical Formula 1 or 2,

[0132] X1 to X6 and Y1 to Y5 are the same as or different from each other, and each independently is N or C(R), provided that at least one of the above X1 to X6 and Y1 to Y5 is N,

[0133] When there are a plurality of the above C(R), the plurality of Rs are the same as or different from each other, and each independently may be selected from the group consisting of hydrogen, deuterium, a halogen group, a cyano group, a nitro group, an amino group, a C1-C 40 alkyl group, a C2-C 40 alkenyl group, a C2-C 40 alkynyl group, a C3-C 40 cycloalkyl group, a heterocycloalkyl group having 3 to 40 ring atoms, a C6-C 60 aryl group, a heteroaryl group having 5 to 60 ring atoms, a C1-C 40 alkoxy group, a C6-C 60 aryloxy group, a C1-C 40 alkylsilyl group, a C6-C 60 arylsilyl group, a C1-C 40 alkylboron group, a C6-C 60 arylboron group, a C6-C 60 arylphosphino group, a C6-C 60 arylphosphine oxide group, and a C6-C 60 aryl amino group, or they combine with adjacent groups to form a condensed ring,

[0134] The alkyl, alkenyl, alkynyl, aryl, heteroaryl, aryloxy, alkoxy, cycloalkyl, heterocycloalkyl, aryl amino, alkylsilyl, alkylboron, arylboron, arylphosphino, arylphosphine oxide, and aryl amino of the above R may each independently be selected from the group consisting of hydrogen, deuterium (D), a halogen, a cyano group, a nitro group, a C1-C 40 alkyl group, a C2-C 40 alkenyl group, a C2-C 40 alkynyl group, a C3-C 40 cycloalkyl group, a heterocycloalkyl group having 3 to 40 ring atoms, a C6-C 60 aryl group, a heteroaryl group having 5 to 60 ring atoms, a C1-C 40 alkoxy group, a C6-C 60 aryloxy group, a C1-C 40 alkylsilyl group, a C6-C 60 arylsilyl group, a C1-C 40 alkylboron group, a C6-C 60 arylboron group, a C6-C 60 arylphosphino group, a C6-C 60 arylphosphine oxide group, and a C6-C60 is substituted with one or more substituents selected from the group consisting of arylamino groups, and when there are a plurality of the above substituents, they may be the same as or different from each other.

[0135] The first compound (material) constituting the first electron transport layer 51 and the second compound (material) constituting the second electron transport layer 52 exhibit excellent electron characteristics by including one or more nitrogen-containing heteroaromatic rings containing at least one nitrogen (N), that is, electron-withdrawing groups (EWGs). Therefore, when applying a compound having a 6-membered or 5-membered moiety represented by Chemical Formula 1 or 2 above or a polycyclic moiety formed by condensation thereof as the material for the first electron transport layer 51 and the second electron transport layer 52, electrons can be well received from the cathode 20, and thus electrons can be smoothly transferred to the light-emitting layer 40. Thereby, the driving voltage of the element 100 can be reduced, leading to high efficiency and long life.

[0136] In addition, the materials of the first electron transport layer 51 and the second electron transport layer 52 can not only have a high triplet energy, but also by adjusting the types and introduction positions of various substituents introduced into the parent nucleus, the molecular weight of the compound can be significantly increased to have an increased glass transition temperature and high thermal stability. And since it is also effective in suppressing the crystallization of the organic layer, the durability and life characteristics of the organic electroluminescent element 100 containing it can be greatly improved.

[0137] According to an embodiment of the present invention, the electron-withdrawing group (EWG) moiety included in each compound constituting the first electron transport layer 51 and the second electron transport layer 52 can be further specifically exemplified as any one selected from the following structural formula group. However, it is not particularly limited thereto.

[0138]

[0139] In the above formulas,

[0140] The meaning of * is the part that forms a bond with the compound constituting the first electron transport layer and the second electron transport layer.

[0141] Although not specifically shown in the above structural formulas, it may be substituted with at least one or more substituents well known in the art (for example, the same as the definition part of R). In addition, although only one part (*) connected to the compound constituting the hole-leakage suppression layer 53 is shown in the above structural formulas, the case of including two also belongs to the scope of the present invention.

[0142] According to one embodiment of the present invention, each compound constituting the first electron transport layer 51 and the second electron transport layer 52 may include at least one general electron-donating group (EDG) portion known in the art that is different from the above-described electron-withdrawing group (EWG) and has a higher electron-donating property than the above-described electron-withdrawing group (EWG).

[0143] The first compound and the second compound that can be used as the materials of the first electron transport layer 51 and the second electron transport layer 52 of the present invention described above can each be further specifically exemplified by the exemplified compounds described later. However, the first compound and the second compound constituting the first electron transport layer 51 and the second electron transport layer 52 of the present invention are not limited to the compounds exemplified below. In particular, as long as the physical properties such as the configuration structure of the first electron transport layer 51 and the second electron transport layer 52 and the refractive index difference between the layers are satisfied, the types of portions (for example, EDG groups, EWG groups) included in the first compound and the second compound, their bonding positions, and the introduction positions of the linking groups are not particularly limited, and compounds with various deformed chemical structures also belong to the scope of the present invention.

[0144] For the electron transport region 50 of the present invention, specifically, the first electron transport layer 51 and the second electron transport layer 52, each can also use a substance co-evaporated with an n-type dopant to facilitate electron injection from the cathode 20. At this time, the n-type dopant can be an alkali metal complex known in the art without limitation. For example, alkali metals, alkaline earth metals, or rare earth metals can be cited.

[0145] The electron transport region 50 of the present invention can be formed by a vacuum evaporation method, a spin coating method, a casting method, a Langmuir-Blodgett method (LB), an inkjet printing method, a laser printing method, a laser-induced thermal imaging method (LITI), etc., as known in the art, but is not particularly limited thereto.

[0146] light-emission assisting layer

[0147] Optionally, the organic light-emitting element 100 of the present invention may further include a light-emitting auxiliary layer (not shown) disposed between the hole transport region 30 and the light-emitting layer 40 described above.

[0148] The light-emitting auxiliary layer serves to transport the holes migrated from the hole transport region 30 to the light-emitting layer 40 and serves to adjust the thickness of the organic layer A. Such a light-emitting auxiliary layer has a high LUMO value to prevent electrons from migrating to the hole transport layer 32 and has a high triplet energy to prevent excitons in the light-emitting layer 40 from diffusing to the hole transport layer 32.

[0149] Such a light-emission assisting layer may contain a hole-transporting material and may be made of the same material as the hole-transporting region. Additionally, the light-emission assisting layers of the red, green, and blue organic light-emitting elements may be made of the same material as each other.

[0150] There is no particular limitation on the material for the light-emission assisting layer. As an example, carbazole derivatives or arylamine derivatives can be cited. Non-limiting examples of the light-emission assisting layer that can be used include N,N-dinaphthyl-N,N'-diphenyl benzidine (NPD), N,N'-bis-(3-methylphenyl)-N,N'-bis(phenyl)-benzidine (TPD), s-TAD, 4,4',4-Tris(N-3-methylphenyl-Nphenyl-amino)-triphenylamine (MTDATA), and the like. They can be used alone or in combination of two or more. Additionally, in addition to the above substances, the above light-emission assisting layer may further contain a p-type dopant. As the above p-type dopant, known p-type dopants used in the art can be used.

[0151] cover layer

[0152] Optionally, the organic electroluminescent element 100 of the present invention may further include a covering layer (not shown) disposed on the second electrode 20. The above covering layer serves to protect the organic light-emitting element and at the same time helps the light generated in the organic layer to be effectively emitted to the outside.

[0153] The above-mentioned covering layer may contain at least one selected from the group consisting of tris(8-hydroxyquinoline)aluminum (Alq3), ZnSe, 2,5-bis(6′-(2′,2″-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole, 4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD), and 1,1′-bis(di-4-tolylaminophenyl)cyclohexane (TAPC). The material for forming such a covering layer is inexpensive compared to the materials of other layers of the organic light-emitting element.

[0154] Such a covering layer may be a single layer, but may also contain two or more layers having different refractive indices from each other so that the refractive index gradually changes when passing through the two or more layers.

[0155] The above-mentioned covering layer can be manufactured by a conventional method known in the art. As an example, various methods such as vacuum evaporation, spin coating, casting, or Langmuir-Blodgett (LB) method can be used.

[0156] The organic electroluminescent element of the present invention having the above constitution can be manufactured by a conventional method known in the art. As an example, an organic light-emitting element can be manufactured by vacuum-evaporating an anode material on a substrate and then successively vacuum-evaporating materials for a hole transport region material, a light-emitting layer material, an electron transport region material, and a cathode material on the anode.

[0157] Figure 2 FIG. is a cross-sectional view showing the structure of an organic electroluminescent element 200 according to another embodiment of the present invention. Figure 2 in which Figure 1 the same reference numerals denote the same components.

[0158] In the following description of Figure 2 , the content that is the same as Figure 1 will not be described again, and only the differences will be described. Refer to Figure 2, different from the embodiment in which the electron transport region 50 is composed of a first electron transport layer 51 disposed adjacent to the light-emitting layer 40 and a second electron transport layer 52 disposed adjacent to the second electrode Figure 1 The organic electroluminescent element 200 according to the second embodiment of the present invention includes an electron transport region 50 including a first electron transport layer 51, a second electron transport layer 52, and an electron injection layer 53, which is different from the embodiment

[0159] Specifically, Figure 2 The electron transport region 50 is disposed between the light-emitting layer 40 and the second electrode 20, and has a structure in which the first electron transport layer 51, the second electron transport layer 52, and the electron injection layer 53 are disposed based on the light-emitting layer 40. A hole leakage suppression layer (not shown) and / or an electron transport assisting layer (not shown) may be included as needed.

[0160] The above-mentioned electron injection layer 53 is not particularly limited as long as it is a substance that is easy to inject electrons and has a large electron mobility, and the electron injection layer substances commonly used in the art can be used without limitation. At this time, the substances constituting the second electron transport layer 52 and the electron injection layer 53 may be the same or different from each other.

[0161] Non-limiting examples of electron injection substances that can be used include anthracene derivatives, heteroaromatic compounds, alkali metal complexes, etc. Specifically, there are LiF, Li2O, BaO, NaCl, CsF; lanthanide metals such as Yb; or metal halides such as RbCl, RbI, etc., and they can be used alone or in combination of two or more.

[0162] The electron injection layer 53 of the present invention can also use a substance co-evaporated with an n-type dopant to facilitate electron injection from the cathode 20. At this time, the n-type dopant can be an alkali metal complex well-known in the art without limitation, and for example, alkali metals, alkaline earth metals, or rare earth metals can be cited.

[0163] The above-mentioned electron injection layer 53 can be formed by a vacuum evaporation method, a spin coating method, a casting method, a Langmuir-Blodgett (LB) method, an inkjet printing method, a laser printing method, a laser-induced thermal imaging (LITI) method, etc. as known in the art, but is not particularly limited thereto.

[0164] In addition, since Figure 2 the descriptions of the materials and structures of the respective components in the embodiment can be directly applied Figure 1 to the description of the organic electroluminescent element 100 of the first embodiment, the separate description thereof is omitted.

[0165] The organic electroluminescent element 100 of the present invention has a structure in which a first electrode 10, an organic layer A, and a second electrode 20 are laminated in this order, but an insulating layer or an adhesive layer may be further included between the first electrode 10 and the organic layer A or between the second electrode 20 and the organic layer A. Such an organic electroluminescent element of the present invention can increase the half-life (Life time) of the initial brightness while maintaining the maximum luminous efficiency when a voltage, a current, or both are applied, and thus has excellent lifetime characteristics.

[0166] Hereinafter, the present invention will be described in detail by way of examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited by the following examples.

[0167] [Preparation (Calculation) Example]

[0168] The compounds of the present invention were prepared as follows. For their physical properties, they were measured respectively using methods well-known in the art and are shown in Table 1 below.

[0169] The HOMO, LUMO, singlet (S1), triplet (T1) energies, etc. of the materials used in the present invention were calculated using the Schrödinger program (Schrödinger software release software release) 2021-4). Specifically, the basic calculation method for each physical property used the B3LYP (Becke, three-parameter (3-parameter), Lee-Yang-Parr) generalized functional calculation method in density functional theory (DFT), and 6-31G* was used as the basis set to optimize the molecular structure.

[0170] The HOMO and LUMO energies of each compound were calculated in the optimized ground state (Ground state, S0). In addition, the singlet (S1) and triplet (T1) energies were calculated based on the respective optimized energy differences between the ground state (S0) / singlet (S1) and the ground state (S0) / triplet (T1).

[0171] In addition, the refractive index was calculated using the Lorenz-Lorenz formula and the Cam-B3LYP / 6-31G* quantum mechanics method.

[0172] Furthermore, the bond dissociation energy (Bond Dissociation Energy, BDE) and the dipole moment (Dipole Moment) used the same B3LYP / 6-31G* quantum mechanics method as the above method. In particular, the bond dissociation energy was the energy required to break a specific chemical bond of a molecule, and the minimum value among them was selected as the BDE.

[0173] [Table 1]

[0174]

[0175] The structures of the respective compounds used in Table 1 above are as follows.

[0176]

[0177] [Examples 1 to 8] Fabrication of Blue Organic Electroluminescent Element

[0178] After subjecting each compound to high-purity sublimation purification using generally known methods, a blue organic electroluminescent element is fabricated according to the following process.

[0179] First, a glass substrate coated with indium tin oxide (ITO) with a thin film is washed ultrasonically with distilled water. After the distilled water washing is completed, ultrasonic washing and drying are performed using solvents such as isopropyl alcohol, acetone, and methanol, and then the substrate is transferred to an ultraviolet ozone (UV OZONE) cleaner (Power sonic 405, HWASHIN TECH), and the above substrate is cleaned with UV for 5 minutes. After that, the substrate is transferred to a vacuum evaporator.

[0180] On the ITO transparent glass substrate (electrode) prepared as above, lamination is carried out in the order of to fabricate the organic EL element of Table 2 below.

[0181] [Table 2]

[0182] compound thickness (nm) hole injection layer HI 140 hole transport layer HT 5 light-emitting layer BH + 2% BD 20 first electron transport layer each compound in Table 1, first_A to G, I 5 second electron transport layer each compound in Table 1, second_A to G, I 25 electron injection layer LiF 1 cathode (second electrode) Al 100

[0183] At this time, the structures of the compounds HI, HD, HT, BH, BD, EA, and ET used are as follows, respectively.

[0184]

[0185] [Comparative Example 1]

[0186] The first _H and the second _H having the same refractive index as each other are used as the first electron transport layer and the second electron transport layer materials, and in other respects, the organic electroluminescent element of Comparative Example 1 is fabricated in the same manner as in Example 1 above.

[0187] [Comparative Example 2]

[0188] The compounds AE and ET are used as the first electron transport layer and the second electron transport layer materials, and in other respects, the organic electroluminescent element of Comparative Example 2 is fabricated in the same manner as in Example 1 above.

[0189] [Evaluation Example 1]

[0190] For the organic electroluminescent elements respectively fabricated in Examples 1 to 8 and Comparative Examples 1 to 2, the driving voltage and current efficiency at a current density of 10 mA / cm 2 were measured, and the results are shown in Table 3 below.

[0191] [Table 3]

[0192]

[0193]

[0194] As shown in Table 3 above, it can be seen that the organic electroluminescent elements of Examples 1 to 8, which include an electron transport layer having two layers with different refractive indices from each other and in which the refractive index of the first electron transport layer adjacent to the light-emitting layer is adjusted to be higher, are more excellent in terms of the driving voltage and current efficiency characteristics of the elements than Comparative Examples 1 to 3.

[0195] Specifically, the organic electroluminescent elements of Comparative Example 1 in which the refractive indices of the first electron transport layer and the second electron transport layer are the same and Comparative Example 2 in which the refractive index of the first electron transport layer is less than that of the second electron transport layer showed poor physical properties in terms of the driving voltage and current efficiency of the elements. Also, the element of Example 8 in which the refractive index difference between the first electron transport layer and the second electron transport layer is relatively large also showed relatively low performance. In contrast, it was confirmed that the organic electroluminescent elements of Examples 1 to 7 in which the refractive index difference between the first electron transport layer and the second electron transport layer is controlled within a predetermined range are significantly more excellent in terms of the driving voltage and current efficiency characteristics of the elements.

Claims

1. An organic electroluminescent element, characterized in that, It has a structure in which a first electrode, a hole transport region, a light-emitting layer, an electron transport region, and a second electrode are sequentially stacked. The electron transport region includes at least two layers. The at least two layers include a first electron transport layer ET1 disposed adjacent to the light-emitting layer and a second electron transport layer ET2 disposed adjacent to the second electrode. In the wavelength region of 460 ± 20 nm, the refractive index n1 of the first electron transport layer is greater than the refractive index n2 of the second electron transport layer.

2. The organic electroluminescent element according to claim 1, in the wavelength region of 460 ± 20 nm, the refractive index difference between the first electron transport layer and the second electron transport layer, i.e., n1 - n2, is greater than 0 and less than 1.

0.

3. The organic electroluminescent element according to claim 1, in the wavelength region of 460 ± 20 nm, the refractive index n1 of each of the first electron transport layer and the second electron transport layer is from 1.45 to 3.

0.

4. The organic electroluminescent element according to claim 1, in the wavelength region of 460 ± 20 nm, the absolute value of the refractive index difference between the first electron transport layer and the light-emitting layer is from 0 to 1.

5.

5. The organic electroluminescent element according to claim 1, in the wavelength region of 460 ± 20 nm, the absolute value of the refractive index difference between the second electron transport layer and the light-emitting layer is from 0 to 1.

5.

6. The organic electroluminescent element according to claim 1, the absolute value of the HOMO energy of each of the first electron transport layer and the second electron transport layer is 4.0 eV or more.

7. The organic electroluminescent element according to claim 1, the absolute value of the LUMO energy of each of the first electron transport layer and the second electron transport layer is 1.60 eV or more.

8. The organic electroluminescent element according to claim 1, the absolute value of the difference between the HOMO energy level of the first electron transport layer and the HOMO energy level of the second electron transport layer is from 0 to 2.5 eV.

9. The organic electroluminescent element according to claim 1, the absolute value of the difference between the LUMO energy level of the first electron transport layer and the LUMO energy level of the second electron transport layer is from 0 to 2.5 eV.

10. The organic electroluminescent element according to claim 1, the absolute value of the difference between the LUMO energy of the light-emitting layer and the LUMO energy level of the first electron transport layer ET1 is from 0 to 1.5 eV.

11. The organic electroluminescent element according to claim 1, the absolute value of the difference between the LUMO energy of the light-emitting layer and the LUMO energy level of the second electron transport layer ET2 is from 0 to 1.5 eV.

12. The organic electroluminescent element according to claim 1, the absolute value of the difference in molecular weight MW between the first electron transport layer and the second electron transport layer is from 0 to 600 g / mol.

13. The organic electroluminescent element according to claim 1, the singlet energy S1 of each of the first electron transport layer and the second electron transport layer is 1.8 eV or more.

14. The organic electroluminescent element according to claim 1, wherein the triplet energy T1 of each of the first electron transport layer and the second electron transport layer is 1.6 eV or more.

15. The organic electroluminescent element according to claim 1, wherein the lowest energy level of the bond dissociation energy BDE of the ground state of each of the first electron transport layer and the second electron transport layer is 0.5 eV or more.

16. The organic electroluminescent element according to claim 1, wherein the dipole moment of each of the first electron transport layer and the second electron transport layer is greater than 0.

17. The organic electroluminescent element according to claim 1, wherein the electron affinity EA of each of the first electron transport layer and the second electron transport layer is 0.1 eV or more.

18. The organic electroluminescent element according to claim 1, wherein the electron mobility μ of the first electron transport layer and the second electron transport layer is at least 1×10 -8 cm 2 / Vs or more, at least in a zero field.

19. The organic electroluminescent element according to claim 1, wherein the electron transport region further includes at least one of a hole leakage suppression layer, an electron transport auxiliary layer, and an electron injection layer.

20. The organic electroluminescent element according to claim 1, the light-emitting layer includes a host and a dopant, and the mixing ratio of the host to the dopant is 70 - 99.5:0.5 - 30 by weight.

21. The organic electroluminescent element according to claim 1, wherein the organic electroluminescent element includes a plurality of light-emitting layer stacks each including at least one light-emitting layer.

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