Organic electroluminescent element

Abstract

Provided is an organic electroluminescent element having a structure in which an anode, a hole transport region, a light-emitting layer, an electron transport region, and a cathode are laminated in this order, and further comprising an organic functional layer disposed between the light-emitting layer and the electron transport region, the organic functional layer includes a polycyclic aromatic ring portion selected from among specific structural formulae, and is configured from an organic compound satisfying the following conditions: (i) the refractive index (nF) of the organic functional layer is greater than or equal to the refractive index (nEM) of the light-emitting layer; and (ii) has a HOMO energy (EHOMO) of 5.5 eV or more. The organic electroluminescent element according to the present invention simultaneously exhibits the effects of high efficiency, low voltage, long life, and the like.

Description

[0001] This application is a divisional application of Chinese patent application No. 202080047010.4, filed on June 18, 2020, entitled "Organic Electroluminescent Element". Technical Field

[0002] This invention relates to an organic electroluminescent element, which has an organic functional layer with a refractive index greater than or equal to that of the light-emitting layer between the light-emitting layer and the electron transport region, thereby improving characteristics such as low driving voltage, high luminous efficiency and long lifespan. Background Technology

[0003] Following research on organic electroluminescent (EL) devices (hereinafter referred to as "organic EL devices"), which originated from the blue electroluminescence of anthracene single crystals developed in 1965, Tang proposed a two-layer stacked organic EL device in 1987, consisting of a hole layer (NPB) and a light-emitting layer (Alq3). Subsequently, to achieve the high efficiency and long lifespan required for commercialization, multi-layer stacked structures with distinct functions were proposed, such as organic layers for hole injection and transport, organic layers for electron injection and transport, and organic layers that induce electroluminescence through the combination of holes and electrons. The introduction of multi-layer stacked structures improved the performance of organic EL devices to commercialization levels. Starting with vehicle radio displays in 1997, efforts are underway to expand their applications to portable information display devices and TV display elements.

[0004] The demands for larger and higher resolution displays have placed great emphasis on improving the efficiency and extending the lifespan of organic EL (Elastic Optical Array) devices. In particular, achieving higher resolution by forming more pixels within the same area results in a reduction in the light-emitting area of ​​organic EL pixels, which in turn shortens their lifespan. This has become the most important technical challenge that organic EL devices must overcome.

[0005] When a current or voltage is applied to the 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, they form excitons. When these excitons transition to the ground state, they emit light. Based on the type of electron spin of the excitons formed, organic EL elements can be classified into fluorescent EL elements (using singlet excitons for light emission) and phosphorescent EL elements (using triplet excitons for light emission).

[0006] The electron spin of excitons formed by the recombination of electrons and holes is generated at a ratio of 25% for singlet excitons and 75% for triplet excitons. Based on the generation ratio, fluorescent EL devices that achieve light emission using singlet excitons are theoretically considered to have an internal quantum efficiency not exceeding 25%, with an upper limit of 5% for external quantum efficiency. Phosphorescent EL devices that achieve light emission using triplet excitons, when using metal coordination compounds containing heavy atoms of transition metals such as Ir and Pt as phosphorescent dopants, can achieve up to 4 times higher luminous efficiency compared to fluorescence.

[0007] As mentioned above, although phosphorescent EL elements exhibit higher luminous efficiency than fluorescent elements based on theoretical facts, blue phosphorescent elements, other than green and red, have not yet been commercialized due to insufficient development of phosphorescent dopants with high purity and efficiency for deep blue and a broad band gap to meet these requirements. Instead, blue fluorescent elements are used in products.

[0008] To improve the properties of the aforementioned organic EL devices, research results on improving device stability by preventing hole diffusion into the electron transport layer have been reported. However, in reality, satisfactory results have not yet been obtained. Summary of the Invention

[0009] Technical issues

[0010] The present invention is proposed to solve the above-mentioned problems, and its purpose is to provide an organic EL element that simultaneously achieves high efficiency, low voltage and long life by having an organic functional layer with a refractive index greater than or equal to the refractive index of the light-emitting layer material at a position adjacent to the light-emitting layer.

[0011] Methods for solving problems

[0012] To achieve the above objectives, the present invention provides an organic electroluminescent element having a structure in which an anode, a hole transport region, a light-emitting layer, an electron transport region and a cathode are stacked sequentially, and further includes an organic functional layer disposed between the light-emitting layer and the electron transport region, wherein the organic functional layer satisfies the following conditions (i) and (ii).

[0013] (i) Refractive index of organic functional layers (n) F The refractive index (n) of the light-emitting layer is greater than or equal to that of the above-mentioned light-emitting layer. EM );

[0014] (ii) Possessing HOMO energy (E) above 5.5 eV HOMO ).

[0015] According to a specific embodiment of the present invention, the organic functional layer is in direct contact with the light-emitting layer, and the difference in refractive index (Δn) between the organic functional layer and the light-emitting layer is... F -n EM The value can be between 0 and 1.0.

[0016] According to a specific embodiment of the present invention, the refractive index of the above-mentioned organic functional layer may be from 1.5 to 2.5.

[0017] According to a specific embodiment of the present invention, when the light-emitting layer is a blue light-emitting layer containing a fluorescent blue light-emitting material, the refractive index of the organic functional layer can be 1.8 or higher.

[0018] According to a specific embodiment of the present invention, the HOMO energy of the above-mentioned organic functional layer can be 5.5 to 6.5 eV.

[0019] According to a specific embodiment of the present invention, the electron transport region includes an electron transport auxiliary layer, an electron transport layer and an electron injection layer, wherein the organic functional layer can be the electron transport auxiliary layer.

[0020] Invention Effects

[0021] In this invention, by configuring an organic functional layer with a refractive index greater than or equal to that of the light-emitting layer to directly contact the light-emitting layer, an organic electroluminescent element with low driving voltage and high luminous efficiency can be provided. Furthermore, by applying the organic electroluminescent element of this invention to a display panel, a display panel with improved performance and lifespan can be provided.

[0022] The effects of the present invention are not limited to the examples described above, and this specification contains a wider variety of effects. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view showing the structure of an organic electroluminescent element according to an embodiment of the present invention.

[0024]

[0025] 100: Organic electroluminescent element

[0026] A: Organic layer

[0027] 10: Anode

[0028] 20: Cathode

[0029] 30: Hole transport region

[0030] 31: Hole injection layer

[0031] 32: Hole transport layer

[0032] 40: Emissive layer

[0033] 50: Electronic transmission area

[0034] 51: Electron Transport Layer

[0035] 52: Electron Injection Layer

[0036] 53: Organic functional layer (electron transport auxiliary layer) Detailed Implementation

[0037] The advantages and features of the present invention, as well as the methods of implementing them, will become clear upon reference to the accompanying drawings and the detailed description of the embodiments. However, the present invention is not limited to the embodiments disclosed below and can be presented in a variety of different forms. These embodiments are provided merely to make the disclosure of the invention comprehensive, so that those skilled in the art to which this invention pertains can fully understand the scope of the invention, which is defined only by the scope of the claims. Therefore, in some embodiments, to avoid ambiguity in the interpretation of the invention, well-known process steps, well-known component structures, and well-known techniques will not be specifically described. Throughout the specification, the same reference numerals refer to the same constituent elements.

[0038] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) are to be used in the manner commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, terms as defined in commonly used dictionaries should not be interpreted ideally or excessively unless explicitly defined otherwise.

[0039] Organic electroluminescent elements

[0040] An organic electroluminescent element according to one embodiment of the present invention includes an anode; a cathode disposed opposite to the anode; and one or more organic layers disposed between the anode and the cathode, including a hole transport region, a light-emitting layer and an electron transport region, and an organic functional layer with specific physical properties, such as refractive index and HOMO energy, being adjusted to a predetermined range between the light-emitting layer and the electron transport region.

[0041] Hereinafter, preferred embodiments of the organic electroluminescent element of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention can be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0042] Figure 1 This is a diagram illustrating the structure of an organic electroluminescent element according to an embodiment of the present invention.

[0043] Referring to the above Figure 1As explained above, the organic electroluminescent element 100 has the following structure: it includes an anode 10, a cathode 20, a light-emitting layer 40 located between the anode 10 and the cathode 20, a hole transport region 30 located between the anode 10 and the light-emitting layer 40, and an electron transport region 50 located between the light-emitting layer 40 and the cathode 20, and includes an organic functional layer disposed between the light-emitting layer 40 and the electron transport region 50, wherein the refractive index and HOMO energy and other physical properties are adjusted to a predetermined range.

[0044] Here, the electron transport region 50 includes an electron transport auxiliary layer 53, an electron transport layer 51, and an electron injection layer 52. The aforementioned organic functional layer can be the electron transport auxiliary layer 53 disposed between the light-emitting layer 40 and the electron transport layer.

[0045] anode

[0046] In the organic electroluminescent element 100 of the present invention, the anode 10 serves to inject holes into the organic layer A.

[0047] The material constituting the anode 10 is not particularly limited, and commonly known materials in the art can be used. Non-limiting examples include 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-(ethylidene-1,2-dioxothiophene](PEDT), polypyrrole, and polyaniline; and carbon black, etc.

[0048] The method for manufacturing the anode 10 is not particularly limited and can be manufactured according to conventional methods known in the art. For example, a method of coating an anode material onto a substrate made of a silicon wafer, quartz, glass plate, metal plate or plastic film can be cited.

[0049] cathode

[0050] In the organic electroluminescent element 100 of the present invention, the cathode 20 serves to inject electrons into the organic layer A.

[0051] The material constituting the cathode 20 is not particularly limited, and commonly known materials in the art can be used. As non-limiting examples, metals such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, and lead; their alloys; and multilayer materials such as LiF / Al and LiO2 / Al can be cited.

[0052] Furthermore, there are no particular limitations on the method for manufacturing the cathode 20, and it can be manufactured according to methods known in the art.

[0053] Organic layer

[0054] The organic layer A included in the organic electroluminescent element of the present invention can be constructed without limitation using a conventional configuration used as an organic layer in conventional organic EL elements. For example, it can include one or more selected from the group consisting of hole transport region 30, light-emitting layer 40, and electron transport region 50. In this case, considering the characteristics of the organic electroluminescent element, it is preferable to include all of the above-mentioned organic layers.

[0055] Hole transport region

[0056] The hole transport region 30 included in the organic layer A of the present invention serves to move holes injected from the anode 10 to the light-emitting layer 40. Such a hole transport region 30 may include one or more selected from the group consisting of the hole injection layer 31 and the hole transport layer 32. In this case, considering the characteristics of organic electroluminescent devices, it is preferable to include both the hole injection layer 31 and the hole transport layer 32.

[0057] The materials constituting the hole injection layer 31 and hole transport layer 32 described above are not particularly limited as long as they have a low hole injection barrier and high hole mobility; hole injection layer / transport layer materials used in the art can be used without restriction. In this case, the materials constituting the hole injection layer 31 and hole transport layer 32 can be the same as or different from each other.

[0058] The hole injection material described above can be any hole injection material known in the art. Non-limiting examples of usable hole injection materials include 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), and 4,4',4"-tris(N,N-diphenylamino)triphenylamine (m-MTDATA). '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 (Polyaniline / Dodecylbenzenesulfonic acid) Polyaniline / camphor sulfonic acid (PANI / DBSA), polyaniline / camphor sulfonic acid (PANI / CSA), polyaniline / poly(4-styrene sulfonate) (PANI / PSS), etc. These can be used individually or in combination.

[0059] Furthermore, the aforementioned hole transport material can be any hole transport material known in the art without limitation. Non-limiting examples of usable hole transport materials include carbazole derivatives such as phenylcarbazole and polyvinylcarbazole, fluorene derivatives, N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1-biphenyl]-4,4'-diamine (TPD), and 4,4',4"-tris(N-carbazole) Triphenylamine derivatives such as 4,4',4"-tris(N-carbazolyl)triphenylamine (TCTA), N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (NPB), and 4,4'-Cyclohexylidene bis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) are used. They can be used alone or in combination.

[0060] The aforementioned hole transport region 30 can be manufactured using conventional methods known in the art. For example, methods include vacuum evaporation, spin coating, casting, Langmuir-Blodgett (LB), inkjet printing, laser printing, and laser-induced thermal imaging (LITI), but are not limited to these.

[0061] Emissive layer

[0062] The light-emitting layer 40 contained in the organic layer A of the present invention is a layer in which holes and electrons meet to form excitons. Depending on the material constituting the light-emitting layer 40, the color of the light emitted by the organic electroluminescent element can be changed.

[0063] Such a light-emitting layer 40 may comprise a host and dopants, the mixing ratio of which can be suitably adjusted within a range known in the art. As an example, the content of the host may be 70 to 99.9% by weight, and the content of the dopants may be 0.1 to 30% by weight. More specifically, when the light-emitting layer 40 is blue, green, or red fluorescent, it may comprise 80 to 99.9% by weight of the host and 0.1 to 20% by weight of the dopants. Furthermore, when the light-emitting layer 40 is blue, green, or red phosphorescent, it may comprise 70 to 99% by weight of the host and 1 to 30% by weight of the dopants.

[0064] The main body included in the light-emitting layer 40 of the present invention is not particularly limited as long as it is a body known in the art. As non-limiting examples, there are alkali metal coordination compounds, alkaline earth metal coordination compounds, or condensed aromatic ring derivatives, etc.

[0065] More specifically, as the main material, aluminum coordination compounds, beryllium coordination compounds, anthracene derivatives, pyrene derivatives, triphenylene derivatives, carbazole derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, or combinations thereof are preferred, as they can improve the luminous efficiency and lifetime of organic electroluminescent elements.

[0066] Furthermore, the dopant contained 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, anthracene derivatives, pyrene derivatives, arylamine derivatives, metal coordination compounds containing iridium (Ir) or platinum (Pt) can be cited.

[0067] The aforementioned dopants can be classified as red dopants, green dopants, and blue dopants. Red dopants, green dopants, and blue dopants generally known in this art can be used without particular restriction.

[0068] Specifically, non-limiting examples of red dopants include PtOEP (Pt(II)octaethylporphine), Ir(piq)3(tris(2-phenylisoquinoline)iridium), Btp2Ir(acac)(bis(2-(2'-benzothienyl)-pyridinato-N,C3')iridium(acetylacetonate), or mixtures of two or more thereof.

[0069] In addition, non-limiting examples of green dopants include Ir(ppy)3(tris(2-phenylpyridine)iridium:tris(2-phenylpyridine)iridium), Ir(ppy)2(acac)(Bis(2-phenylpyridine)(Acetylacetonato)iridium(III):bis(2-phenylpyridine)(acetylacetonato)iridium(III)), and Ir(mppy)3(tris(2-(4-tolyl)phenylpiridine)iridium:tris(2-(4-tolyl)phenylpiridine)iridium:tris(2-(4-tolyl)phenylpiridine)iridium:tris(2-(4-tolyl)phenylpiridine)iridium:tris(2-(4-tolyl)phenylpiridine)iridium(III)). (1) benzopyrano[6,7,8-ij]-quinolizin-11-one, or mixtures of two or more thereof.

[0070] In addition, non-limiting examples of blue dopants include F2Irpic(Bis[3,5-difluoro-2-(2-pyridyl)phenyl](picolinato)iridium(III): bis[3,5-difluoro-2-(2-pyridyl)phenyl(pyridinyl)iridium(III)], (F2ppy)2Ir(tmd), Ir(dfppz)3, DPVBi(4,4'-bis(2,2'-diphenyl ethen-1-yl)biphenyl: 4,4'-bis(2,2'-diphenylethylene-1-yl)biphenyl), DPAVBi(4,4'-Bis[4-(diphenylamino)styryl]biphenyl: 4,4'-bis(4-diphenylaminostyryl)biphenyl), and TBPe(2,5,8,11-tetra-tert-butyl) perylene (2,5,8,11-tetra-tert-butylperylene), or mixtures of two or more thereof, etc.

[0071] The light-emitting layer 40 of the present invention can be a red light-emitting layer containing red phosphorescent material, a green light-emitting layer containing green phosphorescent material, or a blue light-emitting layer containing blue phosphorescent material or blue fluorescent substance. Preferably, it can be a light-emitting layer containing green phosphorescent material.

[0072] The aforementioned light-emitting layer 40 can be a single layer or composed of two or more layers. When the light-emitting layer 40 comprises multiple layers, the organic electroluminescent element can emit light of various colors. Specifically, the present invention can provide an organic electroluminescent element that exhibits mixed colors by having multiple light-emitting layers made of dissimilar materials connected in series. Furthermore, when multiple light-emitting layers are included, although the driving voltage of the element increases, the current value within the organic electroluminescent element remains constant, thus providing an organic electroluminescent element with significantly improved luminous efficiency of the light-emitting layers.

[0073] Electronic transmission area

[0074] In the organic electroluminescent element 100 of the present invention, the electron transport region 50 included in the organic layer A serves to move electrons injected from the cathode 20 to the light-emitting layer 40.

[0075] Such an electron transport region 50 may include one or more of the electron transport layer 51, electron injection layer 52, and electron transport auxiliary layer 53. In this case, considering the characteristics of organic electroluminescent devices, it is preferable to include all of the aforementioned electron transport auxiliary layer 53, electron transport layer 51, and electron injection layer 52.

[0076] In the electron transport region 50 of the present invention, the electron injection layer 52 can use electron injection materials that are easy to inject and have high electron mobility without limitation. Non-limiting examples of usable electron injection materials include the aforementioned bipolar compounds, anthracene derivatives, heteroaromatic compounds, alkali metal coordination compounds, etc. Specifically, there are lanthanide group metals such as LiF, Li₂O, BaO, NaCl, CsF; or halide metals such as Yb; which can be used alone or in combination of two or more.

[0077] The electron transport region 50, specifically the electron transport layer 51 and / or the electron injection layer 52 of the present invention can also use a material co-deposited with an n-type dopant to facilitate electron injection from the cathode. In this case, the n-type dopant can be any alkali metal coordination compound known in the art, for example, alkali metals, alkaline earth metals or rare earth metals.

[0078] The aforementioned electron transport region 50 can be manufactured using conventional methods known in the art. For example, methods include vacuum evaporation, spin coating, casting, Langmuir-Blodgett (LB), inkjet printing, laser printing, and laser-induced thermal imaging (LITI), but are not limited to these.

[0079] On the other hand, the present invention is characterized by further having an organic functional layer 53, which is disposed between the light-emitting layer 40 and the electron transport region 50, specifically between the light-emitting layer 40 and the electron transport layer 51, and whose physical properties such as refractive index and HOMO energy are adjusted to a predetermined range.

[0080] Such an organic functional layer 53 can be a multilayer structure with one or more layers. In the case where the organic functional layer 53 is a multilayer structure with two or more layers, it is preferable to configure one of the organic functional layers 53 in the multilayer structure, whose refractive index and HOMO energy are adjusted, to be in direct contact with the light-emitting layer 40.

[0081] The aforementioned organic functional layer 53 is disposed between the light-emitting layer 40 and the electron transport layer 51, serving as an electron transport auxiliary layer 53 to prevent holes from diffusing or moving into the electron transport layer 51. In particular, when the organic functional layer 53, with its refractive index and HOMO energy adjusted to a specific range, acts as an electron transport auxiliary layer, holes are blocked by the high energy barrier of the organic functional layer 53 and do not diffuse or move into the electron transport layer 51, remaining in the light-emitting layer 40. This increases the likelihood of holes and electrons meeting in the light-emitting layer 40 to form excitons, thereby improving the luminous efficiency of the organic electroluminescent device and effectively improving its lifetime characteristics.

[0082] Furthermore, when light travels from a material with a low refractive index to a material with a high refractive index, the angle of refraction becomes smaller than the angle of incidence, thus increasing the light's rectilinearity. This increased rectilinearity results in more light being emitted from the device's surface, leading to a significant synergy effect in terms of the device's luminous efficiency.

[0083] According to one embodiment of the present invention, the refractive index of the organic functional layer 53 may be greater than or equal to the refractive index of the light-emitting layer 40.

[0084] Specifically, the organic functional layer 53 and the light-emitting layer 40 are disposed in direct contact, and the difference in refractive index (Δn) between the organic functional layer 53 and the light-emitting layer 40 is... F -n EM The refractive index can be from 0 to 1.0. For example, the refractive index of the organic functional layer 53 can be from 1.5 to 2.5, and the refractive index of the light-emitting layer 40 can be from 1.5 to 1.9. Here, the refractive index is based on the refractive index measured at a wavelength of 460 nm.

[0085] According to a preferred embodiment of the present invention, when the light-emitting layer 40 is a blue light-emitting layer containing a fluorescent blue light-emitting material, the refractive index of the organic functional layer 53 can be 1.8 or higher, specifically 1.8 to 2.5.

[0086] According to another embodiment of the present invention, the HOMO energy of the organic functional layer 53 can be 5.5 to 6.5 eV, specifically 5.5 to 6.2 eV. Thus, when the HOMO energy of the organic functional layer 53 is 5.5 eV or higher, it has a higher HOMO energy value than the HOMO energy of the light-emitting layer 40, thereby preventing holes transferred to the light-emitting layer 40 from diffusing or crossing the electron transport layer 51. This increases the probability of holes and electrons recombinating within the light-emitting layer 40, further improving the luminous efficiency of the organic electroluminescent element. Furthermore, it solves the problem of irreversible decomposition reactions caused by oxidation when holes diffuse or move across the light-emitting layer 40 to the electron transport layer 51, and the resulting reduction in the lifetime of the organic electroluminescent element, thereby improving the lifetime characteristics of the element.

[0087] According to another embodiment of the present invention, the triplet energy (T1) of the organic functional layer 53 can be greater than or less than the triplet energy of the light-emitting layer 40. For example, when the triplet energy of the organic functional layer 53 is greater than the triplet energy of the light-emitting layer 40, the efficiency of the organic electroluminescent element can be effectively increased due to the aforementioned refractive index effect and TTA effect. On the other hand, when the triplet energy of the organic functional layer 53 is less than the triplet energy of the light-emitting layer 40, the reduction in the light efficiency of the element can be offset due to the refractive index effect. According to one embodiment, the triplet energy (T1) of the organic functional layer 53 can be from 1.5 to 3.0 eV.

[0088] The organic functional layer 53 of the present invention can further satisfy at least one of the following physical properties to perform the function of an electron transport auxiliary layer.

[0089] Specifically, for the compounds constituting the aforementioned organic functional layer 53, the difference between the HOMO and LUMO values ​​(EHOMO-ELUMO) of the compounds can be 3.0 eV or more, specifically 3.0 eV or more and 3.5 eV or less. Furthermore, the difference between the singlet energy (S1) and triplet energy (T1) of the compounds (ΔEst) can be less than 0.5 eV, specifically 0.01 eV or more and less than 0.5 eV. When compounds with the above properties are used as the electron transport auxiliary layer 53 material disposed between the light-emitting layer 40 and the electron transport layer 51, it is possible to prevent excitons formed in the light-emitting layer 40 from diffusing into the electron transport layer 51, and also to prevent luminescence at the interface between the light-emitting layer 40 and the electron transport layer 51. This ultimately prevents spectral color mixing in the organic electroluminescent element, improves stability, and increases the lifetime of the organic electroluminescent element.

[0090] The compound included as the organic functional layer 53 material of the present invention can be a bipolar compound that simultaneously includes a portion having electron-withdrawing (EWG) characteristics and a portion having electron-donating (EDG) characteristics.

[0091] Such bipolar compounds retain both EDG and EWG groups, thus exhibiting the characteristic of electron cloud separation in HOMO and LUMO orbitals. Due to this molecular orbital characteristic, the difference between the triplet and singlet energies (ΔEst) of the compound is small, satisfying the relationship ΔEst < 0.5 eV. Therefore, even if the difference between the HOMO and LUMO values ​​(E... HOMO -E LUMO It can have a high triplet energy (T1) of 3.0 eV or higher.

[0092] On the other hand, if the number of electrons and holes is not balanced due to the difference between the number of holes injected from the anode 10 and the number of electrons injected from the cathode 20, 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 will hinder the smooth oxidation and reduction of the light-emitting layer 40, or affect adjacent layers, thus reducing the lifetime of the organic electroluminescent device.

[0093] In contrast, the aforementioned bipolar compound exhibits a strength of 1×10⁻⁶ at room temperature. -6 cm 2 With hole mobility and / or electron mobility exceeding / V·s, when used in the organic functional layer 53, it is possible to prevent a slowdown in electron injection compared to the number of holes injected from the anode 10, thereby improving the lifetime of the organic electroluminescent device. In fact, the bipolar compound contained in the organic functional layer 53 of the present invention exhibits a hole mobility of 1 × 10⁻⁶ at room temperature due to its electron-donating group (EDG). -6 cm 2 The electron mobility is above / V·s, and due to electron-withdrawing groups (EWG), the electron mobility at room temperature is 1×10⁻⁶. -6 cm 2 / V·s or more. Therefore, when an organic functional layer 53 containing such a bipolar compound is provided, electron injection into the light-emitting layer 40 is smooth, thereby increasing the exciton formation efficiency in the light-emitting layer 40 and improving the lifetime of the organic electroluminescent device.

[0094] According to one specific example, the electron-donating group (EDG) portion in the above-mentioned bipolar compound can be an unrestricted use of condensed polycyclic aromatic moieties known in the art. According to one specific example, it may contain at least three, specifically three to six, polycyclic aromatic moieties formed by the condensation of ring portions selected from the six-membered portion represented by Chemical Formula 1 and the five-membered portion represented by Chemical Formula 2.

[0095] [Chemical Formula 1]

[0096]

[0097] [Chemical Formula 2]

[0098]

[0099] In the above chemical formula 1 or 2,

[0100] X1 to X5 and Y1 to Y5 may be the same as or different from each other, and each is independently represented by C(R1).

[0101] Multiple R1 groups are selected from hydrogen, deuterium, halogen group, cyano group, nitro group, amino group, C1-C1 group. 40 Alkyl groups, C2-C 40 alkenyl, C2~C 40 alkynyl group, C3~C 40 Cycloalkyl groups, heterocyclic alkyl groups with 3 to 40 nuclei, C6 to C4 cycloalkyl groups 60 aryl, heteroaryl with 5 to 60 nuclei, C1 to C 40 alkoxy groups, C6-C 60 aryloxy groups, C1-C 40 alkylsilyl, C6-C 60 arylsilyl, C1-C 40 alkylboron group, C6-C 60 arylboryl, C1-C 40 Phosphine group, C1-C 40 Phosphine oxide and C6~C 60 It is a group composed of aryl amino groups, and can combine with adjacent R1 to form a condensation ring.

[0102] The alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkoxy, aryloxy, alkylsilyl, arylsilyl, alkylboryl, arylboryl, phosphinyl, phosphine oxide, and arylamino groups of R1 can each be independently selected from deuterium, halogen, cyano, nitro, amino, C1-C1. 40 Alkyl groups, C2-C 40 alkenyl, C2~C 40 alkynyl group, C3~C 40Cycloalkyl groups, heterocyclic alkyl groups with 3 to 40 nuclei, C6 to C4 cycloalkyl groups 40 aryl, heteroaryl with 5 to 40 nuclei, C1 to C 40 alkoxy groups, C6-C 60 aryloxy groups, C1-C 40 alkylsilyl, C6-C 60 arylsilyl, C1-C 40 alkylboron group, C6-C 60 arylboryl, C1-C 40 Phosphine group, C1-C 40 Phosphine oxide and C6~C 60 One or more of the arylamine groups in the group are substituted or unsubstituted, where, in the case of multiple substituents, they may be the same or different from each other.

[0103] As a non-limiting example of a polycyclic aromatic moiety possessing such electron-donating group (EDG) properties, condensed polycyclic aromatic rings such as triphenylene, fluoranthene, and fluorene can be used. Such condensed polycyclic aromatic moieties not only exhibit the electron-donating group (EDG) properties with high electron-donating activity, but also possess an increased glass transition temperature (Tg) and high thermal stability due to their large molecular weight, resulting in excellent heat resistance and chemical resistance. Therefore, they are highly beneficial for improving the durability and long-lifetime characteristics of organic electroluminescent devices containing them.

[0104] According to one embodiment of the invention, the aforementioned polycyclic aromatic ring portion can be embodied in any of the following structural formulas.

[0105]

[0106] In the above chemical formula,

[0107] When there are multiple Rs, the Rs may be the same or different, and each R is independently selected from hydrogen, deuterium, halogen group, cyano group, nitro group, amino group, C1 to C2. 40 Alkyl groups, C2-C 40 alkenyl, C2~C 40 alkynyl group, C3~C 40 Cycloalkyl groups, heterocyclic alkyl groups with 3 to 40 nuclei, C6 to C4 cycloalkyl groups 60 aryl, heteroaryl with 5 to 60 nuclei, C1 to C 40 alkoxy groups, C6-C 60 aryloxy groups, C1-C 40 alkylsilyl, C6-C 60 arylsilyl, C1-C 40 alkylboron group, C6-C 60 arylboryl, C1-C 40Phosphine group, C1-C 40 Phosphine oxide and C6~C 60 The group consisting of arylamine groups, where a is an integer from 0 to 4.

[0108] Specifically, R can be selected from hydrogen, deuterium, halogen group, cyano group, alkyl group, C6-C6 group, etc. 60 It is a group consisting of aryl groups and heteroaryl groups with 5 to 60 nuclei, where a can be 0 or 1.

[0109] As a preferred embodiment of the present invention, the polycyclic aromatic portion may be selected from any of the following groups of structural formulas.

[0110]

[0111] In the above structural formula, although not specifically indicated, at least one or more substituents known in the art can be substituted (e.g., the same as the definition portion of R1). Furthermore, although the portion (*) connected to the compound constituting the organic functional layer is not separately indicated in the above structural formula, the binding position of the polycyclic aromatic moiety is not particularly limited and can have binding positions known in the art without restriction. For example, the polycyclic aromatic moiety represented by the above structural formula can be connected to the compound constituting the organic functional layer through one or two binding positions.

[0112] Furthermore, the compound contained in the organic functional layer 53 material of the present invention includes a conventional electron-withdrawing group (EWG) moiety known in the art, which has a larger electron-donating capacity than the condensed polycyclic aromatic ring moiety (EDG) described above.

[0113] As a specific example, the electron-withdrawing group (EWG) moiety described above includes at least one condensed polycyclic moiety of the following chemical formulas 3, 4, or combinations thereof.

[0114] [Chemical Formula 3]

[0115]

[0116] [Chemical Formula 4]

[0117]

[0118] In the above chemical formulas 3 or 4,

[0119] Z1 to Z 11 They are the same or different from each other, and each is independently N or C(R2), Z1 to Z above. 11 At least one of them is N. As a specific example, at least one of Z1 to Z6 in the above chemical formula 3 can be N, and Z7 to Z6 in chemical formula 4 can be N. 11 At least one of them can be N.

[0120] At this point, even if multiple R2 groups are represented in the same way, they can be identical or different, and they can form condensation rings with adjacent R2 groups. For example, in Formula 3, multiple Z1 to Z6 groups as C(R2), such as Z1 and Z2, Z2 and Z3, Z3 and Z4, Z4 and Z5, Z5 and Z6, or Z6 and Z1, can combine with each other to form condensation rings. Similarly, in Formula 4, multiple Z7 to Z6 groups as C(R2) can form condensation rings. 11 For example, Z7 and Z8, Z8 and Z9, Z9 and Z 10 , Z 10 With Z 11 , Z 11 Each of the R2 groups can combine with Z7 to form a condensation ring. Furthermore, R2 in both chemical formulas 3 and 4 can combine with each other to form a condensation polycyclic heteroaromatic ring.

[0121] Even if multiple R2 groups are represented in the same way, they may be identical or different from each other, and each can be independently selected from hydrogen, deuterium, halogen group, cyano group, nitro group, amino group, C1-C2. 40 Alkyl groups, C2-C 40 alkenyl, C2~C 40 alkynyl group, C3~C 40 Cycloalkyl groups, heterocyclic alkyl groups with 3 to 40 nuclei, C6 to C4 cycloalkyl groups 60 aryl, heteroaryl with 5 to 60 nuclei, C1 to C 40 alkoxy groups, C6-C 60 aryloxy groups, C1-C 40 alkylsilyl, C6-C 60 arylsilyl, C1-C 40 alkylboron group, C6-C 60 arylboryl, C1-C 40 Phosphine group, C1-C 40 Phosphine oxide and C6~C 60 The group composed of aryl amino groups.

[0122] The alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkoxy, aryloxy, alkylsilyl, arylsilyl, alkylboryl, arylboryl, phosphinyl, phosphine oxide, and arylamino groups of R2 can each be independently selected from deuterium, halogen, cyano, nitro, amino, C1-C1. 40 Alkyl groups, C2-C 40 alkenyl, C2~C 40 alkynyl group, C3~C 40 Cycloalkyl groups, heterocyclic alkyl groups with 3 to 40 nuclei, C6 to C4 cycloalkyl groups 40 aryl, heteroaryl with 5 to 40 nuclei, C1 to C 40alkoxy groups, C6-C 60 aryloxy groups, C1-C 40 alkylsilyl, C6-C 60 arylsilyl, C1-C 40 alkylboron group, C6-C 60 arylboryl, C1-C 40 Phosphine group, C1-C 40 Phosphine oxide and C6~C 60 The arylamine group is substituted with one or more substituents in the group consisting of arylamine groups. In this case, when there are multiple substituents, they may be the same or different from each other.

[0123] Specifically, the aforementioned electron-withdrawing group (EWG) moiety can be a 5- or 6-membered monocyclic / polycyclic nitrogen-containing heteroaromatic hydrocarbon in which one to three carbons are substituted with nitrogen, or formed by their condensation. Such a nitrogen-containing heteroaromatic ring moiety can exist in a form where two or more rings are simply attached to or condensed together, or it can include forms condensed with an aryl group. Non-limiting examples of nitrogen-containing heteroaromatic hydrocarbons with electron-withdrawing group (EWG) characteristics include pyridine, pyrimidine, triazine, pyrazine, etc.

[0124] As a preferred embodiment of the present invention, the electron-withdrawing group (EWG) portion described above can be embodied in any of the following group of structural formulas.

[0125]

[0126] Although not specifically shown in the above structural formula, it can be a configuration in which at least one commonly known substituent, such as R2, is introduced onto the heteroaromatic ring. Furthermore, the position of the heteroatom introduced in the above structural formula is not particularly limited and can be introduced at various positions.

[0127] The compound constituting the organic functional layer 53 of the present invention may have a structure in which the EDG group and the EWG group are directly combined as illustrated in the above structural formula, or a structure formed by connecting them by at least one linker group introduced between them.

[0128] Such a linker can be any divalent linker known in the art, for example, it can be a single bond, or it can be from C6 to C6. 18 It can be selected from arylene groups and heteroarylene groups with 5 to 18 nuclei. As a specific example, it can be selected from the group consisting of free single bonds, phenylene, biphenylene, and triphenylene.

[0129] The compounds that can be used as the organic functional layer 53 material of the present invention described above can be further specified as the exemplary compounds described below, such as those represented by 1 to 20. However, the compounds constituting the organic functional layer 53 of the present invention are not limited to the compounds illustrated below. In particular, as long as the refractive index and HOMO energy properties are satisfied, the bonding positions of the EDG and EWG groups and the introduction positions of the linking groups are not particularly limited, and compounds with various modifications to their chemical structures also fall within the scope of the present invention.

[0130] The organic functional layer 53 of the present invention can be formed using vacuum evaporation, spin coating, casting, Langmuir-Blodgett (LB) process, inkjet printing, laser printing, laser-induced thermal imaging (LITI) and other methods as known in the art, but is not particularly limited thereto.

[0131] Light-emitting auxiliary layer

[0132] 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.

[0133] The luminescent auxiliary layer serves to transport holes that have moved from the hole transport region 30 to the luminescent layer 40, and also serves to adjust the thickness of the organic layer A. This luminescent auxiliary layer, due to its high LUMO value, prevents electrons from moving to the hole transport layer 32, and due to its high triplet energy, prevents excitons from the luminescent layer 40 from diffusing into the hole transport layer 32.

[0134] Such a light-emitting auxiliary layer can contain hole-transporting material and can be made of the same material as the hole-transporting region. Furthermore, the light-emitting auxiliary layers of red, green, and blue organic light-emitting elements can be made of the same material as each other.

[0135] There are no particular limitations on the materials used for the luminescent auxiliary layer; for example, carbazole derivatives or arylamine derivatives can be used. Non-limiting examples of usable luminescent auxiliary layers include N,N-dinaphthyl-N,N'-diphenylbenzidine (NPD), N,N'-bis-(3-methylphenyl)-N,N'-bis(phenyl)-benzidine (TPD), s-TAD, and 4,4',4″-tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine (MTDATA). These can be used alone or in combination. Furthermore, in addition to the above-mentioned substances, the luminescent auxiliary layer may contain p-type dopants. As the aforementioned p-type dopant, well-known p-type dopants used in this technical field can be used.

[0136] Coating layer

[0137] Optionally, the organic electroluminescent element 100 of the present invention may further include a coating layer (not shown) disposed on the cathode 20. The coating layer serves to protect the organic light-emitting element and help the light generated by the organic layer to be emitted to the outside effectively.

[0138] The aforementioned coating layer may contain a material selected from aluminum tri-8-hydroxyquinoline (Alq3), ZnSe, 2,5-bis(6′-(2′,2″-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole, or 4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl. The coating material is at least one of the following: yl, 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 forming such a coating layer is inexpensive compared to the materials used for other layers of the organic light-emitting element.

[0139] Such a coating can be a single layer, or it can contain two or more layers with different refractive indices, thereby allowing the refractive index to gradually change while passing through the two or more layers.

[0140] The aforementioned coating can be manufactured using conventional methods known in the art, such as vacuum evaporation, spin coating, casting, or the Langmuir-Blodgett (LB) process.

[0141] The organic light-emitting element of the present invention, comprising the above-described structure, can be manufactured using conventional methods known in the art. For example, an organic light-emitting element can be manufactured by vacuum evaporating an anode material onto a substrate, followed by sequentially vacuum evaporating a hole transport region material, a light-emitting layer material, an electron transport region material, and a cathode material onto the anode.

[0142] The organic electroluminescent element 100 of the present invention has a structure in which an anode 10, an organic layer A, and a cathode 20 are sequentially stacked. An insulating layer or an adhesive layer may be further included between the anode 10 and the organic layer A, or between the cathode 20 and the organic layer A. Such an organic electroluminescent element of the present invention exhibits excellent lifetime characteristics because it can maintain maximum luminous efficiency while increasing the half-life of initial brightness when voltage, current, or both voltage and current are applied.

[0143] The present invention will be described in detail below through embodiments, but the following embodiments are merely illustrative of the present invention and the present invention is not limited to the following embodiments.

[0144] [Preparation Example] Compounds 1 to 20

[0145] The compounds of the present invention were prepared as follows, and their refractive indices, HOMO values, and triplet energies were determined using methods known in the art, as shown in Table 1 below. Additionally, an ADN compound was used as a control group.

[0146] 1) The HOMO energy can be an energy level determined using cyclic voltammetry (CV). In cyclic voltammetry, the energy level is determined by the relative potential value of the electrode relative to a known reference potential. For example, using ferrocene with known oxidation and reduction potential values ​​as a reference electrode, the HOMO energy level of any substance can be determined. Specifically, after determining the CV value of ferrocene, the CV value of the substance is determined, and the difference between the substance and the ferrocene value is set as the HOMO energy level of that substance.

[0147] 2) The triplet energy was calculated using Gaussian's program and the formula B3LYP / 6-31G*.

[0148] 3) The refractive index was measured at 25°C using a tungsten halogen lamp and an ellipsometer (Ellipsometer, Ellipso Technology). The sample was tested in a high-vacuum chamber (10... -7 The following (the sample) is prepared by vapor deposition on a silicon wafer and then measured at room temperature.

[0149]

[0150] [Table 1]

[0151] compound Refractive index HOMO(eV) 1 1.91 5.76 2 2.04 5.63 3 1.97 5.74 4 1.87 5.82 5 1.94 5.73 6 1.86 5.92 7 1.85 6.07 8 1.92 6.08 9 1.89 6.12 10 1.90 6.10 11 1.84 6.05 12 1.92 6.07 13 1.86 6.11 14 2.01 5.89 15 1.98 5.76 16 1.89 5.87 17 1.92 5.94 18 1.90 5.76 19 1.87 6.13 20 1.88 6.08 ADN 1.82 5.12 A 1.78 5.50

[0152] [Examples 1 to 20] Fabrication of Blue Organic Electroluminescent Element

[0153] After the prepared compounds are purified by high-purity sublimation using commonly known methods, blue organic electroluminescent elements are fabricated according to the following process.

[0154] First, will be Glass substrates coated with a thin film of indium tin oxide (ITO) were ultrasonically cleaned using distilled water. After distilled water washing, they were ultrasonically cleaned and dried using solvents such as isopropanol, acetone, and methanol. Then, they were transferred to a UV ozone cleaner (Power sonic 405, Hwashintech), where they were cleaned with UV light for 5 minutes. Finally, the substrates were transferred to a vacuum evaporation machine.

[0155] Organic electroluminescent elements were fabricated on the ITO transparent electrode prepared above by stacking DS-205 (Doosan Electronics Co., Ltd., 80nm) / NPB (15nm) / ADN+5% DS-405 (Doosan Electronics Co., Ltd., 30nm) / the compound in Table 2 (5nm) / Alq3 (25nm) / LiF (1nm) / Al (200nm) in that order (see Table 2 below).

[0156] [Table 2]

[0157] compound Thickness (nm) Hole injection layer DS-205 80 Hole transport layer NPB 15 Emissive layer ADN + 5% DS-405 30 Electron transport auxiliary layer Compounds 1-20 in Table 1 5 Electron transport layer <![CDATA[Alq3]]> 25 Electron injection layer LiF 1 cathode Al 200

[0158] [Comparative Example 1] Fabrication of a blue organic electroluminescent element

[0159] Without using compound 1 as the electron transport auxiliary layer material, Alq3 as the electron transport layer material was deposited at 30 nm instead of 25 nm. Otherwise, the same procedure as in Example 1 above was followed to fabricate a blue organic electroluminescent element.

[0160] [Comparative Example 2] Fabrication of Blue Organic Electroluminescent Element

[0161] Using substance A instead of compound 1 as the electron transport auxiliary layer material, the same procedure as in Example 1 above was followed to fabricate a blue organic electroluminescent element.

[0162]

[0163] For reference, the structures of NPB, ADN, and Alq3 used in Examples 1 to 20 and Comparative Example 1 of this application are as follows.

[0164]

[0165] [Evaluation Example 1]

[0166] For the organic electroluminescent devices manufactured in Examples 1 to 20 and Comparative Example 1, the current density was measured. The driving voltage, emission wavelength, and current efficiency at that time are shown in Table 3 below.

[0167] [Table 3]

[0168]

[0169] As shown in Table 3 above, it can be seen that the blue organic electroluminescent elements of Examples 1 to 20, which use the compounds of the present invention as electron transport auxiliary layer materials, exhibit superior performance in terms of current efficiency, emission peak and driving voltage compared with the blue organic electroluminescent element of Comparative Example 1, which does not contain an electron transport auxiliary layer, and the blue organic electroluminescent element of Comparative Example 2, which does not contain a polycyclic aromatic moiety.

Claims

1. An organic electroluminescent device comprising a structure in which an anode, a hole transport region, a light-emitting layer, an electron transport region, and a cathode are sequentially stacked, and further comprising an organic functional layer disposed between the light-emitting layer and the electron transport region. The organic functional layer comprises a polycyclic aromatic ring portion selected from the following structural formulas. The organic functional layer is composed of organic compounds that meet the following conditions: (i) Refractive index of organic functional layers (n) F The refractive index (n) of the light-emitting layer is greater than or equal to that of the light-emitting layer. EM ); (ii) Possessing HOMO energy (E) above 5.5 eV HOMO ), In the chemical formula, When there are multiple Rs, the Rs may be the same or different, and each R is independently selected from hydrogen, deuterium, halogen group, cyano group, nitro group, amino group, C1 to C2. 40 Alkyl groups, C2-C 40 alkenyl, C2~C 40 alkynyl group, C3~C 40 Cycloalkyl groups, heterocyclic alkyl groups with 3 to 40 nuclei, C6 to C4 cycloalkyl groups 60 aryl, heteroaryl with 5 to 60 nuclei, C1 to C 40 alkoxy groups, C6-C 60 aryloxy groups, C1-C 40 alkylsilyl, C6-C 60 arylsilyl, C1-C 40 alkylboron group, C6-C 60 arylboryl, C1-C 40 Phosphine group, C1-C 40 Phosphine oxide and C6~C 60 The group composed of aryl amino groups. a is an integer from 0 to 4.

2. The organic electroluminescent element according to claim 1, The organic functional layer is in direct contact with the light-emitting layer. The difference in refractive index between the organic functional layer and the light-emitting layer is 0 to 1.

0.

3. The organic electroluminescent element according to claim 1, wherein the refractive index of the organic functional layer is 1.5 to 2.

5.

4. In the organic electroluminescent element according to claim 1, when the light-emitting layer is a blue light-emitting layer containing a fluorescent blue light-emitting material, the refractive index of the organic functional layer is 1.8 or higher.

5. The organic electroluminescent element according to claim 1, wherein the HOMO energy of the organic functional layer is 5.5 to 6.5 eV.

6. The organic electroluminescent element according to claim 1, wherein the compound constituting the organic functional layer further comprises an electron-withdrawing group (EWG) portion having a greater electron-withdrawing property than the polycyclic aromatic ring portion.

7. The organic electroluminescent element according to claim 6, wherein the electron-withdrawing group (EWG) portion is selected from the following structural formulas:

8. The organic electroluminescent element according to claim 1, wherein the electron transport region comprises an electron transport auxiliary layer, an electron transport layer and an electron injection layer, and the organic functional layer is an electron transport auxiliary layer.

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