Organic electroluminescent device

Abstract

The present invention provides an organic electroluminescent device having at least two electron transport layers controlled to have a predetermined refractive index difference between the light emitting layer and the electrode, thereby optimizing efficiency by maximizing light extraction.

Description

[Technical Field]

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

[0002] In 1965, research on organic electroluminescent (EL) elements (hereafter simply referred to as "OLEDs") using anthracene single crystals led to blue electroluminescence. In 1987, Tang proposed an OLED element with a two-layer structure consisting of a hole layer (NPB) and an emissive layer (Alq3). Subsequently, to achieve the high efficiency and long life required for commercialization, a multilayer structure was proposed, with each layer having its own distinctive and specialized functions: an organic layer responsible for hole injection and transport, an organic layer responsible for electron injection and transport, and an organic layer responsible for inducing electroluminescence through the recombination of holes and electrons. The introduction of the multilayer structure improved the performance of OLEDs to a level that allowed them to be commercially viable, and their range of applications has expanded, from in-car radio display products in 1997 to portable information displays and television display elements.

[0003] The demand for larger displays and higher resolutions poses the challenge of improving the efficiency and lifespan of organic EL elements. In particular, when higher resolution is achieved by forming more pixels in the same area, this results in a reduction in the light-emitting area of ​​the organic EL pixel, which inevitably shortens its lifespan. This is the most important technical challenge that organic EL elements must overcome.

[0004] When a current or voltage is applied to two electrodes in an organic EL element, holes are injected into the organic layer from the anode, and electrons are injected into the organic layer from the cathode. The injected holes and electrons combine to form excitons, which emit light when they return to their ground state. Depending on the type of electron spin of the excitons formed, organic EL elements can be divided into fluorescent EL elements, in which singlet excitons contribute to light emission, and phosphorescent EL elements, in which triplet excitons contribute to light emission.

[0005] The electron spin of excitons formed by the recombination of electrons and holes is generated at a rate of 25% as singlet excitons and 75% as triplet excitons. Fluorescent EL elements that emit light from singlet excitons theoretically cannot exceed an internal quantum efficiency of 25% due to the generation rate, and their external quantum efficiency is said to be limited to 5%. Phosphorescent EL elements that emit light from triplet excitons can improve their luminous efficiency by up to four times compared to fluorescence when using a metal complex compound containing heavy atoms of transition metals such as Ir or Pt as a phosphorescent dopant.

[0006] As described above, based on theoretical facts, phosphorescent EL devices exhibit higher luminous efficiency than fluorescent devices. However, in the case of blue phosphorescent devices (excluding green and red), the color purity of deep blue, the development level of highly efficient phosphorescent dopants, and hosts with wide energy gaps to satisfy the dopants are insufficient. As a result, blue phosphorescent devices have not yet been commercialized, and blue fluorescent devices are still used in products.

[0007] In order to improve the characteristics of the organic EL device, research results have been reported to prevent holes from diffusing into the electron transport layer and increase the stability of the device, but satisfactory results have not been obtained to date. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide an organic EL device that has at least two electron transport layers between an emitting layer and an electrode, and in which the difference in refractive index between the first electron transport layer adjacent to the emitting layer and the second electron transport layer adjacent to the electrode is controlled within a predetermined range, thereby maximizing light extraction through the micro-cavity effect and achieving high efficiency.

[0009] Other objects and advantages of the present invention will be more clearly explained from the detailed description and claims that follow. [Means for solving the problem]

[0010] In order to achieve the above technical object, the present invention provides 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, and the electron transport region includes at least two layers, and the at least two layers are: 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; The organic electroluminescent device is provided, wherein the refractive index (n1) of the first electron transport layer is higher than the refractive index (n2) of the second electron transport layer in the blue wavelength region of 460±20 nm.

[0011] According to one embodiment of the present invention, the difference in refractive index (n1-n2) between the first electron transport layer and the second electron transport layer may be greater than 0 and less than 1.0 in the wavelength region of 460±20 nm.

[0012] According to one embodiment of the present invention, the refractive index (n1) of each of the first electron transport layer and the second electron transport layer may be 1.45 to 3.0 in the wavelength range of 460±20 nm.

[0013] According to one embodiment of the present invention, the difference in absolute value of the refractive index between the first electron transport layer and the light emitting layer may be 0 to 1.5 in the wavelength region of 460±20 nm.

[0014] According to one embodiment of the present invention, the difference in absolute value of the refractive index between the second electron transport layer and the light emitting layer may be 0 to 1.5 in the wavelength region of 460±20 nm.

[0015] According to one 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.

[0016] According to one 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.

[0017] According to one embodiment of the present invention, the difference in absolute value 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.

[0018] According to one embodiment of the present invention, the difference in absolute value 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.

[0019] According to one embodiment of the present invention, the difference in absolute value between the LUMO energy level 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.

[0020] According to one embodiment of the present invention, the difference in absolute value between the LUMO energy level 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.

[0021] According to one embodiment of the present invention, the difference in absolute value of the molecular weight (MW) between the first electron transport layer and the second electron transport layer may be 0 to 600 g / mol.

[0022] According to one 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.

[0023] According to one 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.

[0024] According to an embodiment of the present invention, the lowest energy level of ground state bond dissociation energies (BDEs) of the first electron transport layer and the second electron transport layer may be 0.5 eV or more.

[0025] According to one embodiment of the present invention, the first electron transport layer and the second electron transport layer may each have a dipole moment greater than zero.

[0026] According to one embodiment of the present invention, the first electron transport layer and the second electron transport layer may each have an electron affinity (EA) of 0.1 eV or more.

[0027] According to one embodiment of the present invention, at least 1×10 -8 cm 2 The electron mobility (μ) may be equal to or greater than 1 / Vs.

[0028] 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 assisting layer, and an electron injection layer.

[0029] According to one embodiment of the present invention, the light-emitting layer includes a host and a dopant, and the mixing ratio of the host to the dopant may be 70 to 99.5:0.5 to 30 by weight.

[0030] According to one embodiment of the present invention, the organic electroluminescent device may include a multi-emissive layer stack including at least one emissive layer. [Effects of the Invention]

[0031] According to one embodiment of the present invention, at least two electron transport layers controlled to have a predetermined refractive index difference between the light emitting layer and the electrode are provided, thereby maximizing light extraction and optimizing the luminous efficiency of the organic electroluminescent device.

[0032] The effects of the present invention are not limited to the above-mentioned examples, and various other effects are included in this specification. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a cross-sectional view showing a structure of an organic electroluminescent device according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view illustrating a structure of an organic electroluminescent device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] The advantages and features of the present invention, as well as methods for achieving them, will become more apparent from the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various different forms. The present embodiments are provided solely to ensure that the disclosure of the present invention is complete and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains. The present invention is defined solely by the scope of the claims. Therefore, in some embodiments, well-known process steps, well-known device structures, and well-known techniques are not specifically described to avoid ambiguous interpretation of the present invention. The same reference numerals refer to the same elements throughout the specification.

[0035] Unless otherwise defined, all terms (including technical and scientific terms) used in this specification can be used in a manner commonly understood by a person of ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries should not be interpreted ideally or excessively unless explicitly defined otherwise.

[0036] Furthermore, throughout the specification, when a part "comprises" a certain element, it does not mean excluding other elements, but may further include other elements, unless otherwise specified. Furthermore, throughout the specification, "above" or "on top" means not only being located above or below the part in question, but also including cases where there are other elements therebetween, and does not necessarily mean being located on the upper side based on the direction of gravity. Furthermore, throughout the specification, terms such as "first" and "second" do not indicate any order or importance, but are used to distinguish elements from each other.

[0037] <Organic electroluminescent device> Hereinafter, preferred embodiments of the organic electroluminescent device according to the present invention will be described with reference to the accompanying drawings. However, the present invention may be modified into various different forms, and the scope of the present invention is not limited to the following embodiments.

[0038] FIG. 1 is a cross-sectional view schematically illustrating the structure of an organic electroluminescent device 100 according to one embodiment of the present invention.

[0039] 1, the organic electroluminescent device 100 includes a first electrode 10; a second electrode 20; an emitting layer 40 disposed between the first electrode 10 and the second electrode 20; a hole transport region 30 disposed between the first electrode 10 and the emitting layer 40; and an electron transport region 50 disposed between the emitting layer 40 and the second electrode 20. The electron transport region 50 includes at least two layers, a first electron transport layer 51 disposed adjacent to the 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.

[0040] The light efficiency of an organic electroluminescent device (OLED) can be broadly divided into external quantum efficiency (EQE) and internal quantum efficiency (IQE). Even if the internal quantum efficiency of an OLED is 100%, there is a problem in that only about 20-30% of the light is extracted externally. In addition, at the interface of the organic layer adjacent to the electrode (metal), the surface plasmon polarization (SPP) phenomenon causes light to move along the surface of the electrode and / or causes heat loss. As a result, a significant amount of light generated inside the OLED is waveguided, and ultimately only about 20-30% of the light is extracted externally.

[0041] In contrast, the present invention is differentiated from conventional organic electroluminescent devices in that at least two electron transport layers 50 are provided between the light-emitting layer 40 and the second electrode (e.g., the cathode 20), and the refractive index of the first electron transport layer 51 arranged adjacent to the light-emitting layer 40 and the refractive index of the second electron transport layer 52 arranged adjacent to the second electrode 20 are precisely controlled within predetermined ranges.

[0042] 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 at least a predetermined range. In this case, light emitted from the light-emitting layer 40 is emitted toward the top (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, thereby increasing the primary efficiency of light extraction due to the micro-cavity effect. The micro-cavity effect increases the light emission speed using a micro-oscillating effect (constructive interference of waves). When even micro-oscillating waves have the same period and phase, their energy is amplified, generating the micro-cavity effect, which can be adjusted to efficiently emit emitted light 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 a low value within a predetermined range, the surface plasmon loss phenomenon occurring in the metal of the second electrode 20 can be significantly reduced by total reflection, and an increase in secondary efficiency due to light extraction can also be expected.

[0043] As described above, in the present invention, the microcavity effect and surface plasmon loss are minimized by adjusting the arrangement structure between the first electron transport layer 51 and the second electron transport layer 52 and the refractive index difference therebetween, thereby maximizing light extraction and achieving an increase in the efficiency of the device.

[0044] According to one specific example, the electron transport region 50 includes at least two layers with different refractive indices. The electron transport region 50 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, may be 0.05 or higher.

[0045] Here, the refractive index is based on the refractive index calculated using the Lorenz-Lorenz formula and the quantum mechanical method of CAM-B3LYP / 6-31G*, but is not limited thereto, and it is also within the scope of the present invention to use a refractive index measured or calculated by a method known in the art.

[0046] In addition, since the refractive index of a material varies depending on the wavelength, the refractive index of the present invention is based on that measured in the blue wavelength range of 460±20 nm. However, when the green or red wavelength range is used as the reference, the refractive index can be changed to that measured in the wavelength range of about 520±20 nm or 630±20 nm.

[0047] According to one 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 are each 1.45 to 3.0 at a wavelength of 460±20 nm, and may be specifically 1.45 to 2.8.

[0048] According to another specific example, in the blue wavelength region of 460±20 nm, the difference in refractive index (n1−n2) between the first electron transport layer 51 and the second electron transport layer 52 is greater than 0 and less than 1.0, and specifically may be in the range of 0.1 to 0.8.

[0049] According to another specific example, in the wavelength region of 460±20 nm, the difference in absolute value of the refractive index between the first electron transport layer 51 and the light-emitting layer 40 may be 0 to 1.5, specifically 0.05 to 1. Here, the light-emitting layer 40 may refer to the light-emitting layer itself or the host contained in the light-emitting layer 40.

[0050] In order to maximize light extraction by adjusting the arrangement structure of the first electron transport layer 51 and the second electron transport layer 52 and the refractive index difference therebetween, as well as to achieve low driving voltage and high efficiency, it is preferable that the organic electroluminescent device 100 according to the present invention further satisfies at least one of the following physical properties:

[0051] According to one specific example, the absolute value of the HOMO energy of each of the first electron transport layer 51 and the second electron transport layer 52 may be 4.0 eV or more, specifically 4.0 to 7.0 eV, more specifically 4.0 to 6.5 eV. Such HOMO energy values ​​can prevent holes transferred to the light-emitting layer 40 from diffusing or migrating to other electron transport regions, such as the electron transport layers 51 and 52. This increases the probability of hole-electron recombination within the light-emitting layer 40, thereby further improving the luminous efficiency of the organic electroluminescent device. Furthermore, irreversible decomposition reactions due to oxidation that occur when holes diffuse or migrate beyond the light-emitting layer 40 to the electron transport layers 51 and 52, and the resulting reduction in the lifespan of the organic electroluminescent device, can be prevented, thereby improving the lifespan of the device.

[0052] According to another specific example, the absolute value of the LUMO energy of each of the first electron transport layer 51 and the second electron transport layer 52 may be 1.60 eV or more, specifically 1.60 to 3.50 eV, and more specifically 1.80 to 3.0 eV. For efficient and high-efficiency generation, the band gap energy of each of the first electron transport layer 51 and the second electron transport layer 52 may be 2.0 eV or more, specifically 2.0 to 4.5 eV.

[0053] According to another specific example, the difference in absolute value between the HOMO (Highest Occupied Molecular Orbital) energy level of the first electron transport layer 51 and the HOMO energy level of the second electron transport layer 52 may be in the range of 0 to 2.5 eV, specifically 0.05 to 2.0 eV.

[0054] According to another specific example, the difference in absolute value between the LUMO (Lowest Unoccupied Molecular Orbital) energy level of the first electron transport layer 51 and the LUMO energy level of the second electron transport layer 51 may be in the range of 0 to 2.5 eV, specifically 0.05 to 1.5 eV.

[0055] According to another specific example, the difference in absolute value between the LUMO energy of the light-emitting layer 40 and the LUMO energy level of the first electron transport layer (ET1) 51 may be in the range of 0 to 1.5 eV, specifically 0.05 to 1.0 eV.

[0056] According to another specific example, the difference in absolute value between the LUMO energy of the light-emitting layer 40 and the LUMO energy level of the second electron transport layer (ET2) 52 may be in the range of 0 to 1.5 eV, specifically 0.1 to 0.8 eV.

[0057] According to another specific example, the difference in absolute value of the molecular weight (MW) between the first electron transport layer 51 and the second electron transport layer 52 may be 0 to 600 g / mol, specifically 0 to 400 g / mol.

[0058] According to another specific example, the singlet energy (S1) of each of the first electron transport layer 51 and the second electron transport layer 52 may be 1.8 eV or more, specifically 1.8 eV to 4.5 eV, and more specifically 2.0 to 4.0 eV. This prevents singlet excitons from diffusing to adjacent interfaces and / or other layers, or from emitting light at the interfaces, thereby efficiently binding the singlet excitons. This increases the number of excitons and improves the luminous efficiency of the organic electroluminescent device. As a result, spectral color mixing of the organic electroluminescent device is prevented, stability is improved, and the efficiency and lifetime of the organic electroluminescent device are improved.

[0059] According to another specific example, the triplet energy (T1) of each of the first electron transport layer 51 and the second electron transport layer 52 may be 1.6 eV or more, specifically 1.6 to 4.5 eV, more specifically 1.6 to 4.0 eV, which prevents excitons from migrating to other layers, thereby achieving the effect of significantly increasing the efficiency of the organic electroluminescent device.

[0060] According to another specific example, the lowest energy level of the bond dissociation energies (BDE) of the ground states of the first electron transport layer 51 and the second electron transport layer 52 may be 0.5 eV or higher, specifically 0.5 to 6.5 eV, and more specifically 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, the stronger the bond, the more closely the bond dissociation energy (BDE) is related to molecular stability, and therefore may act as a factor affecting the lifetime.

[0061] According to another specific example, the dipole moment of each of the first electron transport layer 51 and the second electron transport layer 52 may be greater than 0, specifically, 0-10.

[0062] According to another specific example, the electron affinity (EA) of each of the first electron transport layer 51 and the second electron transport layer 52 is 0.1 eV or more, specifically 0.1 to 3.0 eV, more specifically 0.1 to 2.5 eV. When the layer has the above-mentioned electron affinity, high electron injection efficiency can be obtained.

[0063] Meanwhile, if the balance between electrons and holes is not achieved 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 cannot recombine to form excitons will accumulate in the light-emitting layer 40. The electrons or holes accumulated in the light-emitting layer 40 may hinder smooth oxidation and reduction in the light-emitting layer 40 or may affect adjacent layers, thereby reducing the lifespan of the organic electroluminescent device. In contrast, the first electron transport layer 51 and the second electron transport layer 52 each have a density of at least 1×10 in a zero-field. -8 cm 2By having an electron mobility (μ) of 1 / Vs or more, the injection of electrons is prevented from becoming slow compared to the number of holes injected from the first electrode 10, and electron injection into the light-emitting layer 40 is carried out smoothly, thereby increasing the efficiency of exciton formation in the light-emitting layer 40 and improving the life of the organic electroluminescent device.

[0064] Hereinafter, the structure of the organic electroluminescent device 100 according to an embodiment of the present invention, which includes at least two electron transport layers whose refractive index difference is adjusted to fall within a predetermined range, will be described in more detail.

[0065] substrate In the organic light-emitting device of the present invention, any substrate commonly used in the field of organic light-emitting devices can be used without limitation as the substrate 110. In consideration of the mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, waterproofness, etc. of the organic light-emitting device, a glass substrate or a transparent plastic substrate is preferred.

[0066] 1st electrode In the organic electroluminescent device 100 according to the present invention, the first electrode 10 is disposed on the substrate and serves as an anode that injects holes into the organic layer (A).

[0067] The first electrode 10 may be made of a material with a relatively high work function, and therefore serves as an anode that injects holes into the adjacent hole transport region 30. In this case, the second electrode 20 disposed opposite the first electrode 10 serves as a cathode that injects electrons into the adjacent electron transport region 50. However, the present invention is not limited thereto, and in some cases, the first electrode 10 may serve as a cathode and the second electrode 20 may serve as an anode.

[0068] The material for the first electrode 10 is not particularly limited, and may be any material known in the art, including, but not limited to, metals such as vanadium, chromium, copper, zinc, and gold; alloys thereof; 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 SnO:Sb; conductive polymers such as polythiophene, poly(3-methylthiophene), poly[3,4-(ethylene-1,2-dioxy)thiophene] (PEDT), polypyrrole, and polyaniline; and carbon black.

[0069] The method for manufacturing the first electrode 10 is not particularly limited, and may be a conventional method well known in the art, such as coating an anode material onto a substrate made of a silicon wafer, quartz, glass plate, metal plate, or plastic film.

[0070] 2nd electrode In the organic electroluminescent device 100 according to the present invention, the second electrode 20 is a portion disposed opposite the first electrode 10 described above, and specifically, is disposed on the electron transport region 50 and serves as a cathode that injects electrons into the organic layer (A).

[0071] The material for the second electrode 20 is not particularly limited, and may be any material known in the art, such as, but not limited to, metals such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, and lead; alloys thereof; and multilayer structures such as LiF / Al and LiO / Al.

[0072] In this case, the second electrode 20 may be a (semi-)transmissive electrode, and the organic electroluminescent device including the second electrode 20 may have a top-emission structure. In this case, the light generated in the light-emitting layer 40 may be transmitted through the second electrode 20, but may also be reflected by the lower surface of the second electrode 20, and thus may be repeatedly reflected between the upper surface of the first electrode 10 and the lower surface of the second electrode 20.

[0073] The method for manufacturing the second electrode 20 is not particularly limited, and the second electrode 20 may be manufactured by a method known in the art.

[0074] organic layer The organic layer (A) included in the organic electroluminescent device according to the present invention can be any ordinary structure used as an organic layer in a conventional organic EL device, and may include, for example, 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. In this case, in consideration of the properties of the organic electroluminescent device, it is preferable that the organic layer (A) include all of the above-mentioned organic layers.

[0075] hole transport region The hole transport region 30 contained in the organic layer (A) of the present invention plays a role in transferring holes injected from the first electrode 10 to the light-emitting layer 40. Such a hole transport region 30 may include one or more layers selected from the group consisting of a hole injection layer 31 and a hole transport layer 32. In this case, in consideration of the properties of the organic electroluminescent device, it is preferable to include both the hole injection layer 31 and the hole transport layer 32.

[0076] The materials forming 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 high hole mobility, and any hole injection layer / transport layer materials commonly used in the art can be used without limitation. In this case, the materials forming the hole injection layer 31 and the hole transport layer 32 may be the same or different.

[0077] The hole injection material may be any hole injection material known in the art, without limitation. Examples of usable hole injection materials include phthalocyanine compounds such as copper phthalocyanine; DNTPD (N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4'-diamine), m-MTDATA (4,4',4''-tris(3-methylphenylphenylamino)triphenylamine), TDATA (4,4',4''-tris(N,N-diphenylamino)triphenylamine), 2TNATA (4,4',4''-tris{N,-( Examples of suitable polymers include, but are not limited to, PEDOT / PSS (poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate), PANI / DBSA (polyaniline / dodecylbenzenesulfonic acid), PANI / CSA (polyaniline / camphorsulfonic acid), and PANI / PSS (polyaniline) / poly(4-styrenesulfonate). These may be used alone or in combination of two or more.

[0078] The hole transport material may be any hole transport material known in the art. Examples of usable hole transport materials include, but are not limited to, carbazole derivatives such as phenylcarbazole and polyvinylcarbazole, fluorene derivatives, triphenylamine derivatives such as TPD (N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1-biphenyl]-4,4'-diamine) and TCTA (4,4',4''-tris(N-carbazolyl)triphenylamine), NPB (N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine), and TAPC (4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine]). These may be used alone or in combination.

[0079] The hole transport region 30 may be fabricated by a conventional method known in the art, such as, but not limited to, vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) printing, inkjet printing, laser printing, and laser induced thermal imaging (LITI).

[0080] Light-emitting layer The light-emitting layer 40 included in the organic material layer (A) of the present invention is a layer in which holes and electrons combine to form excitons, and the color of light emitted by the organic electroluminescent device may vary depending on the material forming the light-emitting layer 40.

[0081] The light-emitting layer 40 may include a host and a dopant, and the mixing ratio thereof can be appropriately adjusted within a range known in the art. For 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, when the light-emitting layer 40 is blue fluorescent, green fluorescent, or red fluorescent, it may include 80 to 99.9 parts by weight of the host and 0.1 to 20 parts by weight of the dopant. When the light-emitting layer 40 is blue fluorescent, green fluorescent, or red phosphorescent, it may include 70 to 99 parts by weight of the host and 1 to 30 parts by weight of the dopant.

[0082] The host contained in the light-emitting layer 40 of the present invention is not particularly limited as long as it is known in the art, and examples thereof include, but are not limited to, alkali metal complex compounds; alkaline earth metal complex compounds; and fused aromatic ring derivatives.

[0083] More specifically, it is preferable to use, as the host material, an aluminum complex compound, a beryllium complex compound, 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 these, which can improve the luminous efficiency and lifespan of the organic electroluminescent device.

[0084] Furthermore, the dopant contained in the light-emitting layer 40 of the present invention is not particularly limited as long as it is known in the art, and examples thereof include, but are not limited to, anthracene derivatives, pyrene derivatives, arylamine derivatives, and metal complex compounds containing iridium (Ir) or platinum (Pt).

[0085] The dopants can be classified into red dopants, green dopants, and blue dopants, and any red dopants, green dopants, and blue dopants known in the art can be used without any particular limitation.

[0086] Specific examples of red dopants include, but are not limited to, PtOEP (Pt(II) octaethylporphine), Ir(piq) (tris(2-phenylisoquinoline)iridium), BtpIr(acac) (bis(2-(2'-benzothienyl)-pyridinato-N,C3')iridium(acetylacetonate)), or mixtures of two or more thereof.

[0087] Examples of green dopants include Ir(ppy)3 (tris(2-phenylpridine)iridium), Ir(ppy)2(acac) (bis(2-phenylpyridine)(acetylacetonato)iridium(III)), and Ir(mppy)3 (tris(2-(4-tolyl)phenylpridine)iridium). idium), 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 thereof.

[0088] Examples of blue dopants include 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-butylperylene), and the like. perylene), or a mixture of two or more thereof, but are not limited thereto.

[0089] The light-emitting layer 40 according to 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 material. Preferably, the light-emitting layer 40 may be a light-emitting layer containing a blue fluorescent material.

[0090] The light-emitting layer 40 may be a single layer made of one material, a single layer made of multiple different materials, or a multi-layer structure consisting of two or more layers, each made of a different material. When the light-emitting layer 40 is a multi-layer structure, the organic electroluminescent device can emit light of various colors. Specifically, the present invention provides an organic electroluminescent device that includes multiple light-emitting layers made of different materials in series, thereby exhibiting a mixed color. Furthermore, when multiple light-emitting layers are included, the device's driving voltage increases, but the current value within the organic electroluminescent device remains constant, thereby improving the luminous efficiency by the number of light-emitting layers.

[0091] Although not shown, the organic electroluminescent device 100 may include a plurality of light-emitting stacks (not shown), each including at least one light-emitting layer.

[0092] The plurality of light-emitting layers included in such a light-emitting stack may emit light of different colors or may emit light of the same color. That is, the emitted color may vary depending on the material constituting the light-emitting layer. For example, the plurality of light-emitting stacks may include materials that emit blue, green, red, yellow, white, etc., and may be formed using phosphorescent or fluorescent materials. In this case, the colors emitted by each light-emitting layer may be complementary to each other. Alternatively, a hue may be selected as a color combination that can emit white light. Each of such light-emitting layers may include a phosphorescent or fluorescent dopant corresponding to the selected hue.

[0093] Although not shown, the organic electroluminescent device 100 may further include a charge generation layer (not shown) disposed between and connecting adjacent stacks among the plurality of light-emitting stacks.

[0094] A charge generation layer (CGL) is a layer that does not directly contact both electrodes (e.g., anode and cathode) in an organic light-emitting device having multiple light-emitting stacks and separates adjacent light-emitting stacks. Such a charge generation layer is disposed between two adjacent light-emitting stacks and serves as a cathode by generating electrons for one light-emitting stack and an anode by generating holes for the other light-emitting stack. Materials known in the art that can be used as charge generation layers (CGLs) can be used without limitation for such a charge generation layer. Materials used for charge generation layers may also be doped with conventional n-type and / or p-type materials known in the art.

[0095] electron transport area In the organic electroluminescent device 100 according to the present invention, the electron transport region 50 included in the organic layer (A) plays a role in transferring electrons injected from the second electrode 20 to the light-emitting layer 40 .

[0096] 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 indices, 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 necessary.

[0097] The electron transport region 50 may have a structure in which a first electron transport layer 51 and a second electron transport layer 52 are arranged based on the light-emitting layer, 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. In consideration of the properties of the organic electroluminescent device, it is preferable that the electron transport region 50 includes all of the first electron transport layer 51, the second electron transport layer 52, and the electron injection layer 53.

[0098] As long as the difference in refractive index between the first electron transport layer 51 and the second electron transport layer 52 is controlled within the above-mentioned specific range, any material known in the art having normal electron transport properties can be used without limitation. Examples of the material include oxadiazole derivatives, triazole derivatives, phenanthroline derivatives (e.g., BCP), and nitrogen-containing heterocyclic derivatives.

[0099] According to one specific example, the first compound used as a material for the first electron transport layer 51 and the second compound used as a material for the second electron transport layer 52 may be different from each other, and each may be a compound to which at least one moiety having electron-withdrawing group (EWG) characteristics with high electron absorption properties, as known in the art, is bonded. As an example, they may be bipolar compounds that simultaneously contain a moiety having electron-withdrawing group (EWG) characteristics with high electron absorption properties and a moiety having electron-donating group (EDG) characteristics with high electron donating properties.

[0100] More specifically, the first compound (material) constituting the first electron transport layer 51 and the second compound used as a material for the second electron transport layer 52 may contain at least one electron-withdrawing group (EWG) moiety selected from the group consisting of a 6-membered moiety represented by the following chemical formula 1; a 5-membered moiety represented by the following chemical formula 2; and a polycyclic moiety formed by condensing the 6-membered moiety and the 5-membered moiety.

[0101] [ka]

[0102] [ka] In the above Chemical Formula 1 or 2, X1 to X6 and Y1 to Y5 are the same or different and each independently represent N or C(R), provided that at least one of X1 to X6 and Y1 to Y5 is N; When there are a plurality of C(R), the Rs may be the same or different and each independently represent hydrogen, deuterium, a halogen group, a cyano group, a nitro group, an amino group, a C1 to C 40 Alkyl groups of C2 to C 40 Alkenyl groups, C2-C 40 Alkynyl groups, C3-C 40 Cycloalkyl groups having 3 to 40 ring atoms, heterocycloalkyl groups having 6 to 40 ring atoms, 60 aryl groups, heteroaryl groups with 5 to 60 ring atoms, C1 to C 40 Alkyloxy groups, C6-C 60 Aryloxy groups, C1-C 40 Alkylsilyl groups, C6-C 60 Arylsilyl groups, C1-C 40 Alkylboron groups, C6-C 60 Arylboron groups, C6-C 60 Arylphosphine groups, C6-C 60 arylphosphine oxide groups, and C6-C 60 or which may be joined to adjacent groups to form a fused ring, The alkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, aryloxy group, alkyloxy group, cycloalkyl group, heterocycloalkyl group, arylamine group, alkylsilyl group, alkylboron group, arylboron group, arylphosphine group, arylphosphine oxide group, and arylamine group represented by R each independently represent hydrogen, deuterium (D), halogen, cyano group, nitro group, C1 to C6 40 Alkyl groups of C2 to C 40 Alkenyl groups, C2-C 40 Alkynyl groups, C3-C 40 Cycloalkyl groups having 3 to 40 ring atoms, heterocycloalkyl groups having 6 to 40 ring atoms, 60 aryl groups, heteroaryl groups with 5 to 60 ring atoms, C1 to C 40 Alkyloxy groups, C6-C 60 Aryloxy groups, C1-C 40 Alkylsilyl groups, C6-C 60Arylsilyl groups, C1-C 40 Alkylboron groups, C6-C 60 Arylboron groups, C6-C 60 Arylphosphine groups, C6-C 60 arylphosphine oxide groups, and C6-C 60 In this case, when there are a plurality of the substituents, they may be the same or different.

[0103] The first compound (material) constituting the first electron transport layer 51 and the second compound (material) constituting the second electron transport layer 52 contain at least one nitrogen-containing heteroaromatic ring, i.e., one or more electron-withdrawing groups (EWGs), and thus exhibit excellent electronic properties. Therefore, when a compound having a 6- or 5-membered moiety represented by the above-mentioned Chemical Formula 1 or 2 or a polycyclic moiety formed by condensing these moieties is used as the material for the first electron transport layer 51 and the second electron transport layer 52, the compound can efficiently accommodate electrons from the cathode 20 and smoothly transfer the electrons to the light-emitting layer 40, thereby reducing the driving voltage of the device 100 and achieving high efficiency and a long life.

[0104] Furthermore, the materials for the first electron transport layer 51 and the second electron transport layer 52 not only have high triplet energy, but also have improved glass transition temperatures and thermal stability due to the significant increase in molecular weight of the compound by controlling the types and positions of various substituents introduced into the mother nucleus. Furthermore, since they are effective in suppressing crystallization of the organic material layer, the durability and lifespan of the organic electroluminescent device 100 including them can be significantly improved.

[0105] In one embodiment of the present invention, the electron-withdrawing group (EWG) moiety contained in each compound constituting the first electron-transporting layer 51 and the second electron-transporting layer 52 may be further embodied as any one selected from the following structural formula group, but is not limited thereto.

[0106] [ka]

[0107] In the above formula, * indicates the portion where bonding occurs with the compounds that constitute the first electron transport layer and the second electron transport layer.

[0108] Although not specifically shown in the structural formula, the compound may be substituted with at least one substituent known in the art (for example, the same as the definition of R). In addition, although the structural formula shows only one moiety (*) connecting to the compound constituting the hole-leakage suppression layer 53, the case where two moieties are included also falls within the scope of the present invention.

[0109] According to one embodiment of the present invention, each of the compounds constituting the first electron transport layer 51 and the second electron transport layer 52 may contain at least one moiety of a conventional electron donating group (EDG) known in the art, which is different from the electron withdrawing group (EWG) described above and has a higher electron donating ability than the electron withdrawing group (EWG).

[0110] The first compound and the second compound usable as materials for the first electron transport layer 51 and the second electron transport layer 52 according to the present invention described above may be further embodied as the exemplified compounds described below. However, the first compound and the second compound constituting the first electron transport layer 51 and the second electron transport layer 52 according to the present invention are not limited to the exemplified compounds described below. In particular, as long as the physical properties such as the arrangement structure of the first electron transport layer 51 and the second electron transport layer 52 and the difference in refractive index between the layers are satisfied, the type of moiety (e.g., EDG group, EWG group), its bonding position, and the position at which the linker is introduced are not particularly limited. Compounds with various modifications of their chemical structures also fall within the scope of the present invention.

[0111] The electron transport region 50 according to the present invention, specifically the first electron transport layer 51 and the second electron transport layer 52, may be co-deposited with an n-type dopant to facilitate injection of electrons from the cathode 20. In this case, any alkali metal complex compound known in the art can be used as the n-type dopant without limitation, and examples thereof include alkali metals, alkaline earth metals, and rare earth metals.

[0112] The electron transport region 50 of the present invention may be formed by a method well known in the art, such as vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) method, inkjet printing, laser printing, or laser induced thermal imaging (LITI), but is not limited to these.

[0113] Light-emitting auxiliary layer Optionally, the organic light emitting device 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 .

[0114] The light-emitting auxiliary layer serves to transport holes moving from the hole transport region 30 to the light-emitting layer 40 and to adjust the thickness of the organic layer (A). Such a light-emitting auxiliary layer has a high LUMO value, thereby preventing electrons from moving to the hole transport layer 32, and has high triplet energy, thereby preventing excitons in the light-emitting layer 40 from diffusing to the hole transport layer 32.

[0115] The light-emitting auxiliary layer may include a hole-transporting material and may be made of the same material as the hole-transporting region. Also, the light-emitting auxiliary layers of the red, green, and blue organic light-emitting devices may be made of the same material.

[0116] The light-emitting auxiliary layer material is not particularly limited, and examples thereof include carbazole derivatives and arylamine derivatives. Usable light-emitting auxiliary layer materials include, but are not limited to, NPD (N,N-dinaphthyl-N,N'-diphenylbenzidine), TPD (N,N'-bis-(3-methylphenyl)-N,N'-bis(phenyl)-benzidine), s-TAD, and MTDATA (4,4,'4''-tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine). These materials may be used alone or in combination of two or more. The light-emitting auxiliary layer may also contain a p-type dopant in addition to the above-mentioned materials. The p-type dopant may be a p-type dopant known in the art.

[0117] Capping Layer Optionally, the organic electroluminescent device 100 of the present invention may further include a capping layer (not shown) disposed on the second electrode 20. The capping layer protects the organic electroluminescent device and helps the light generated from the organic material layer to be efficiently emitted to the outside.

[0118] The capping layer may include 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). Such materials for forming the capping layer are inexpensive compared to the materials for other layers of the organic light-emitting device.

[0119] Such a capping layer may be a single layer, or may include two or more layers having different refractive indices so that the refractive index gradually changes as the light passes through the two or more layers.

[0120] The capping layer may be manufactured by a conventional method known in the art, for example, a vacuum deposition method, a spin coating method, a casting method, or a Langmuir-Blodgett (LB) method.

[0121] The organic electroluminescent device of the present invention having the above-described configuration may be fabricated by a conventional method well known in the art. For example, an organic electroluminescent device can be fabricated by vacuum-depositing an anode material on a substrate, and then vacuum-depositing materials for a hole transport region, a light-emitting layer, an electron transport region, and a cathode on the anode.

[0122] 2 is a cross-sectional view showing the structure of an organic electroluminescent device 200 according to another embodiment of the present invention. In FIG. 2, the same reference numerals as in FIG. 1 denote the same components.

[0123] 2, only the differences will be described without repeating the same content as in FIG. 1. Referring to FIG. 2, an organic electroluminescent device 200 according to the second embodiment of the present invention includes an electron transport region 50 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, unlike the embodiment of FIG. 1 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.

[0124] 2 is disposed between the light-emitting layer 40 and the second electrode 20, and has a structure in which a first electron transport layer 51, a second electron transport layer 52, and an electron injection layer 53 are disposed relative to the light-emitting layer 40. If necessary, a hole leakage suppression layer (not shown) and / or an electron transport auxiliary layer (not shown) may be further included.

[0125] The electron injection layer 53 is not particularly limited as long as it is a material that easily injects electrons and has high electron mobility, and any material commonly used in the art for electron injection layers can be used without limitation. In this case, the materials forming the second electron transport layer 52 and the electron injection layer 53 may be the same or different.

[0126] Usable electron injection materials include, but are not limited to, anthracene derivatives, heteroaromatic compounds, and alkali metal complex compounds. Specific examples include LiF, LiO, BaO, NaCl, and CsF; lanthanide metals such as Yb; and metal halides such as RbCl and RbI. These may be used alone or in combination of two or more.

[0127] The electron injection layer 53 according to the present invention may be co-deposited with an n-type dopant to facilitate injection of electrons from the cathode 20. In this case, any alkali metal complex compound known in the art can be used as the n-type dopant without limitation, and examples thereof include alkali metals, alkaline earth metals, and rare earth metals.

[0128] The electron injection layer 53 may be formed by a method known in the art, such as vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) method, inkjet printing, laser printing, or laser induced thermal imaging (LITI), but is not limited to these.

[0129] As for the materials and structures of the components in the embodiment of FIG. 2, the description of the organic electroluminescent device 100 according to the first embodiment of FIG. 1 can be applied as is, and therefore individual descriptions thereof will be omitted.

[0130] The organic electroluminescent device 100 according to the present invention has a structure in which a first electrode 10, an organic material layer (A), and a second electrode 20 are sequentially laminated, and may further include an insulating layer or an adhesive layer between the first electrode 10 and the organic material layer (A) or between the second electrode 20 and the organic material layer (A). When a voltage, a current, or both are applied, the organic electroluminescent device according to the present invention maintains maximum luminous efficiency and has an increased half-life time of the initial brightness, thereby achieving excellent life characteristics. [Example]

[0131] The present invention will be described in detail below with reference to examples. However, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0132] [Preparation (calculation) example] The compounds according to the present invention were prepared as follows, and their physical properties were measured by methods known in the art. The results are shown in Table 1 below.

[0133] Schroedinger software release 2021-4 was used to calculate the HOMO, LUMO, singlet (S1), and triplet (T1) energies of the materials used in the present invention. Specifically, the basic calculation method for each physical property was the B3LYP (Becke, 3-parameter, Lee-Yang-Parr) functional calculation method in density functional theory (DFT), and the molecular structure was optimized using 6-31G* as the basis set.

[0134] The HOMO and LUMO energies of each compound were calculated in the optimized ground state (S0), and the singlet (S1) and triplet (T1) energies were calculated using the optimized energy differences between the ground state (S0) / singlet (S1) and ground state (S0) / triplet (T1), respectively.

[0135] The refractive index was calculated using the Lorenz-Lorenz formula and the quantum mechanical method of Cam-B3LYP / 6-31G*.

[0136] The bond dissociation energy (BDE) and dipole moment were calculated using the quantum mechanical method B3LYP / 6-31G*, as described above. In particular, the bond dissociation energy was calculated by calculating the energy required to break a specific chemical bond in the molecule, and the smallest value was selected as the BDE.

[0137] [Table 1]

[0138] The structures of the compounds used in Table 1 above are as follows:

[0139] [ka]

[0140] [ka]

[0141] [Examples 1 to 8] Preparation of blue organic electroluminescent devices Each compound was purified to a high purity by sublimation using a conventional method, and then a blue organic electroluminescent device was fabricated by the following process.

[0142] First, a glass substrate coated with a 1500 Å thick indium tin oxide (ITO) thin film was ultrasonically cleaned in distilled water. After the distilled water cleaning, the substrate was ultrasonically cleaned with solvents such as isopropyl alcohol, acetone, and methanol, dried, and then transferred to a UV ozone cleaner (Powersonic 405, manufactured by HWASHIN TECH Co., Ltd.) and cleaned using UV for 5 minutes before being transferred to a vacuum deposition machine.

[0143] On the ITO transparent glass substrate (electrode) prepared as described above, HI+2wt% HD(100Å) / HI(1400Å) / HT(50Å) / BH+2wt% BD(200Å) / EA(50Å) / ET+Liq(300Å_1:1) / LiF(10Å) / Al(1000Å) were laminated in this order to prepare the organic EL devices shown in Table 2 below.

[0144] [Table 2]

[0145] The structures of the compounds used here, HI, HD, HT, BH, BD, EA, and ET, are as follows:

[0146] [ka]

[0147] [Comparative Example 1] An organic electroluminescent device of Comparative Example 1 was fabricated in the same manner as in Example 1, except that 1_H and 2_H, which have the same refractive index, were used as materials for the first electron transport layer and the second electron transport layer.

[0148] Comparative Example 2 An organic electroluminescent device of Comparative Example 2 was fabricated in the same manner as in Example 1, except that compounds AE and ET were used as materials for the first electron transport layer and the second electron transport layer.

[0149] [Evaluation example 1] For the organic electroluminescent devices manufactured in Examples 1 to 8 and Comparative Examples 1 and 2, a current density of 10 mA / cm 2 The driving voltage and current efficiency were measured, and the results are shown in Table 3 below.

[0150] [Table 3]

[0151] As shown in Table 3, the organic electroluminescent devices of Examples 1 to 8, which have two electron transport layers with different refractive indices and in which the refractive index of the first electron transport layer adjacent to the light-emitting layer is adjusted to be higher, are superior to those of Comparative Examples 1 to 3 in terms of device driving voltage and current efficiency characteristics.

[0152] Specifically, the organic electroluminescent devices of Comparative Example 1, in which the first electron transport layer and the second electron transport layer had the same refractive index, and Comparative Example 2, in which the first electron transport layer had a lower refractive index than the second electron transport layer, exhibited poor physical properties in terms of device driving voltage and current efficiency. Furthermore, the device of Example 8, in which the difference in refractive index between the first electron transport layer and the second electron transport layer was somewhat large, also exhibited relatively poor performance. In contrast, the organic electroluminescent devices of Examples 1 to 7, in which the difference in refractive index between the first electron transport layer and the second electron transport layer was controlled within a predetermined range, were confirmed to have significantly superior device driving voltage and current efficiency characteristics. [Explanation of symbols]

[0153] 100 Organic electroluminescent device A...Organic layer 10...1st electrode 20...Second electrode 30 ···Hole transport region 31 Hole injection layer 32 Hole transport layer 40 Emitting layer 50...electron transport region 51...first electron transport layer 52...Second electron transport layer 53...electron injection layer

Claims

1. a first electrode, a hole transport region, a light-emitting layer, an electron transport region, and a second electrode stacked in this order; the electron transport region comprises at least two layers; The at least two layers are 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; The refractive index (n １ ) is the refractive index (n ２ ) higher than the organic electroluminescent element.

2. The difference in refractive index between the first electron transport layer and the second electron transport layer in the wavelength region of 460±20 nm (n １ -n ２ 2. The organic electroluminescent device according to claim 1, wherein .gamma..times ...

3. In the wavelength region of 460±20 nm, the refractive index (n １ 2. The organic electroluminescent device according to claim 1, wherein each of the above is 1.45 to 3.

0.

4. 2. The organic electroluminescent device according to claim 1, wherein a difference in absolute value of refractive index between the first electron transport layer and the light emitting layer is 0 to 1.5 in a wavelength region of 460±20 nm.

5. 2. The organic electroluminescent device according to claim 1, wherein a difference in absolute value of refractive index between the second electron transport layer and the light emitting layer is 0 to 1.5 in a wavelength region of 460±20 nm.

6. The organic electroluminescent device according to claim 1 , wherein the absolute values ​​of the HOMO energies of the first electron transport layer and the second electron transport layer are each 4.0 eV or more.

7. The organic electroluminescent device according to claim 1 , wherein the absolute values ​​of the LUMO energies of the first electron transport layer and the second electron transport layer are each 1.60 eV or more.

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

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

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

11. 2. The organic electroluminescent device according to claim 1, wherein a difference in absolute value between the LUMO energy level of the light-emitting layer and the LUMO energy level of the second electron transport layer (ET2) is 0 to 1.5 eV.

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

13. The organic electroluminescent device according to claim 1 , wherein 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 device according to claim 1 , wherein the triplet energy (T1) of the first electron transport layer and the second electron transport layer is 1.6 eV or more.

15. The organic electroluminescent device of claim 1 , wherein the lowest energy level of ground state bond dissociation energies (BDEs) of the first electron transport layer and the second electron transport layer is 0.5 eV or more.

16. The organic electroluminescent device of claim 1 , wherein the first electron transport layer and the second electron transport layer each have a dipole moment greater than zero.

17. The organic electroluminescent device of claim 1 , wherein the first electron transport layer and the second electron transport layer each have an electron affinity (EA) of 0.1 eV or more.

18. The electron mobility (μ) of the first electron transport layer and the second electron transport layer is at least 1×10 in zero-field. －８ cm ２ The organic electroluminescent device according to claim 1 , wherein the dc voltage Vdc is 0.1 V or more.

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

20. the light-emitting layer comprises a host and a dopant; 2. The organic electroluminescent device according to claim 1, wherein the mixing ratio of the host to the dopant is 70 to 99.5:0.5 to 30 by weight.

21. The organic electroluminescent device of claim 1 , wherein the organic electroluminescent device comprises a plurality of light-emitting layer stacks including at least one light-emitting layer.

Images