JP4486713B2 - Organic electroluminescent device - Google Patents

Description

で表されるαNPD を10^-6torr下で、3 Å／秒の蒸着速度で400 Åの厚さに成膜し、正孔輸送層３を形成した。
【００２９】
次に、前記正孔輸送層３の上に、発光層４として緑色発光を有する下記式２：
【化２】

で表されるトリス（８- キノリノラト）アルミニウム錯体層（以下「Alq」という）４を３と同じ条件で600 Åの厚さに真空蒸着して形成した。
次に、前記発光層４の上に金属ドーピング層５として、Alq とLiF をLiF が２重量％となるように各々の蒸着速度を調整して100 Å成膜した。
最後に、前記金属ドーピング層５の上に陰極となる背面電極６としてAlを蒸着速度15Å／秒で1000Å蒸着した。発光領域は縦0.5cm 、横0.5cm の正方形状とした。
前記の有機EL素子において、陽極電極であるITO と陰極電極であるAl６との間に、直流電圧を印加し、発光層Alq4からの緑色発光の輝度を測定した。この素子からは15000cd/m²の高輝度を13V において示した。このときの電流密度は440mA/cm² であった。
【００３０】
比較例１
実施例１と同じく、ITO 上にまず正孔輸送層としてαNPD を400 Åの厚さに成膜し、その上に、発光層としてAlq を３と同じ条件で600 Åの厚さに真空蒸着して形成した。そして、Alq の上から陰極としてAlを2000Å蒸着した。この素子では15V で最高6700cd/m² の輝度しか与えず、輝度の向上と駆動電圧を下げるのに金属ドーピング層５が有効であることがわかる。
【００３１】
比較例２
実施例１と同条件で、ITO 上にまず正孔輸送層としてαNPD を400 Åの厚さに成膜し、その上に、Alq を500 Å蒸着した後に、LiF のみを100 Åの厚さに真空蒸着して形成し、その上から陰極としてAlを2000Å蒸着した。
この素子では電流が全く注入されず、素子からの発光が観測されなかった。これはLiF のみ100 Å挿入したのではLiF 層が完全な絶縁体層であるため、陰極からの電子注入が行われなかったと思われる。したがって、LiF が100 Åの場合には陰極に接する部分には電子注入のために有機分子が必要であることを示している。
【００３２】
実施例２
厚さ１mmの石英ガラス上に、Alq とLiF をLiF が２重量％となるように各々の蒸着速度を調整して1000Å成膜した。また、Alq のみを蒸着して1000Å成膜した試料も作製した。これらの可視紫外吸収スペクトルにおいて、Alq のみを蒸着した膜ではキノリン環による吸収が400nm 付近に見られたが、LiF をドーピングしたAlq 膜ではこのようなキノリン環による強い吸収が375nm に見られた。これはLiF がAlq 分子の近傍に存在することでAlq 分子のエネルギー準位が変化していることを表している。
【００３３】
実施例３
ITO 上に、正孔輸送層３としてαNPD を400 Å、発光層４としてAlq を600 Å真空蒸着した後、Alq と酸化リチウム（Li₂O）を金属ドーピング層５としてLi₂O濃度が３重量％となるよう100 Åの厚みに共蒸着した。その上から、陰極電極６として、Alを1000Å蒸着し素子を作製した。この素子は印加電圧１３Ｖで最高輝度16000cd/m²と電流密度480mA/cm² を与え、実施例１と同じく、低い駆動電圧で高輝度を与えた。
【００３４】
比較例３
実施例１と同条件で、ITO 上にまず正孔輸送層としてαNPD を400 Åの厚さに成膜し、その上に、Alq を600 Å蒸着した後に、Li₂Oのみを100 Åの厚さに真空蒸着して形成し、その上から陰極としてAlを2000Å蒸着した。
この素子では電流が全く注入されず、発光は観測されなかった。これはLi₂Oのみ100 Å挿入したのではLi₂O層が完全な絶縁体層であるため、陰極からの電子注入が行われなかったと思われる。したがって、金属ドーピング層には電子注入のために有機化合物との共蒸着が必要不可欠であることを示している。
【００３５】
実施例４
ITO 上に、正孔輸送層３としてαNPD を400 Å、発光層４としてAlq を500 Å真空蒸着した後、バソフェナントロリンとLi₂Oを金属ドーピング層５としてLi₂Oが３重量％となるように100 Åの厚みに共蒸着した。その上から、陰極電極６としてAlを1000Å蒸着し素子を作製した。この素子は印加電圧13Ｖで最高輝度21000cd/m²、電流密度630mA/cm² を与え、実施例１と同じく、低い駆動電圧で高輝度を与えた。
【００３６】
【発明の効果】
以上の如く、本発明の有機EL素子は、金属酸化物と金属塩の少なくとも一方によってドーピングした有機化合物層（金属ドーピング層）を陰極電極との界面に設けることによって、駆動電圧が低く、高効率、高輝度発光素子の作製を可能にした。したがって、本発明の有機EL素子は、実用性が高く、表示素子や光源としての有効利用を期待できる。
【図面の簡単な説明】
【図１】本発明の有機EL素子の積層構造例を示す模式断面図である。
【図２】本発明の有機EL素子の陰極部分を示す説明図である。
【図３】従来の有機EL素子の陰極部分を示す説明図である。
【符号の説明】
１ 透明基板
２ 陽極透明電極
４ 発光層
５ 金属ドーピング層
６ 陰極電極[0001]
【Technical field】
The present invention relates to an organic electroluminescent element (hereinafter referred to as an organic EL element) used for a planar light source or a display element.
[0002]
[Prior art and its problems]
2. Description of the Related Art An organic electroluminescent element (hereinafter referred to as an organic EL element) in which a light emitting layer is composed of an organic compound has been attracting attention as a device that realizes a large area display element driven at a low voltage. Tang et al. Stacked organic compounds with different carrier transport properties to increase the efficiency of the device, so that holes and electrons were injected in a balanced manner from the anode and cathode, respectively, and the thickness of the organic layer was 2000 mm or less. 1000cd / m at an applied voltage of 10V or less ² And achieved high brightness and high efficiency sufficient for practical use with an external quantum efficiency of 1% (Appl. Phys. Lett., 51, 913 (1987)).
In this high-efficiency device, Tang et al. Have a low work function Mg (magnesium) to reduce the energy barrier that is a problem when injecting electrons from metal electrodes to organic compounds that are basically regarded as insulators. It was used. At that time, Mg is easy to oxidize and is unstable, and it is relatively stable because it has poor adhesion to the organic surface, and it is alloyed by co-evaporation with Ag (silver) which has good adhesion to the organic surface. It was.
[0003]
Toppan Printing Co., Ltd. Group (51th JSAP Scientific Lecture Meeting, Proceedings 28a-PB-4, p.1040) and Pioneer Corporation Group (54th JSAP Meeting, Lecture Proceedings) 29p-ZC-15, p.1127) is a device using Mg alloy by using Li (lithium), which has a lower work function than Mg, and stabilizing it by alloying with Al (aluminum) and using it as a cathode. A lower driving voltage and a higher luminance are achieved. In addition, the present inventors have reported that a two-layer cathode in which Li is deposited on an organic compound layer as thin as about 10 mm alone and silver is laminated thereon is effective in realizing a low driving voltage. (IEEE Trans. Electron Devices., 40, 1342 (1993)).
[0004]
Recently, PEI et al. From UNIAX have succeeded in uniformly doping the entire polymer light-emitting layer with Li salt to lower the driving voltage (Science, 269, 1086 (1995)). In this method, Li salt uniformly dispersed in the polymer light emitting layer is dissociated by applying a voltage, and polymer ions in the vicinity of the electrode are doped in situ by distributing Li ions and counter ions in the vicinity of the cathode and the anode, respectively. In this case, since the polymer in the vicinity of the cathode exists in a radical anion state reduced by Li, which is an electron donating (donor) dopant, the electron injection barrier from the cathode is much lower than that without Li doping (Science, 269, 1086 (1995)).
[0005]
More recently, Hung et al. From Eastman-Kodak Corp. have extremely thin (5-10 mm) dielectrics such as lithium fluoride (LiF) and magnesium oxide (MgO) between the electron-transporting organic compound layer and the cathode. By inserting it into the gate, the barrier for electron injection from the cathode is lowered to realize low voltage driving. In a device having this two-layer cathode, the energy level (band structure) of the organic compound in contact with the dielectric changes due to the presence of the dielectric between the cathode and the organic compound layer, and electron injection from the cathode is prevented. It is interpreted as easy (Appl. Phys. Lett., 70, 152 (1997)).
[0006]
However, elemental deterioration due to electrode oxidation or the like also occurs in an alloy electrode of Mg or Li, and the function as a wiring material must be taken into consideration, so the alloy electrode is limited in electrode material selection. In the two-layer cathode of the present inventors, the cathode does not function when the thickness of the Li layer is 20 mm or more (IEEE Trans. Electron Devices., 40, 1342 (1993)). Control is difficult and there is a problem in reproducibility of device fabrication. In addition, the in situ doping method in which salt is added to the light-emitting layer of Pei et al. And dissociated by an electric field has the disadvantage that the time required for the dissociated ions to move to the vicinity of the electrode is rate-determined and the device response speed is significantly slowed down. Even in the two-layer cathode of Hung et al., The optimum dielectric layer thickness is as thin as 5 mm, so that it is difficult to produce a dielectric ultrathin layer having a uniform thickness on an organic compound.
[0007]
OBJECT OF THE INVENTION
The present invention has been made in view of the above circumstances, and its purpose is to realize a low driving voltage regardless of the work function of the cathode material by lowering the energy barrier in electron injection from the cathode to the organic compound layer. The purpose is to do.
Another object of the present invention is that even when an inexpensive and stable metal that has been generally used as a wiring material from the past, such as Al, is used alone as a cathode material, as in the case where the above alloy is used as an electrode, Or it is providing the element which can express the characteristic beyond it.
[0008]
SUMMARY OF THE INVENTION
The present invention provides an organic compound layer in contact with the cathode. Consists of specific metal salts It has been completed by finding that doping with a dielectric reduces the electron injection barrier from the cathode to the organic compound layer, and can reduce the driving voltage. That is, the organic EL element of the present invention is an EL element having at least one light-emitting layer composed of an organic compound between an opposing anode electrode and cathode electrode, the cathode electrode is made of aluminum, and the interface with the cathode electrode In addition, Made of alkali metal or alkaline earth metal It has an organic compound layer doped with a metal salt.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view showing one embodiment of an organic EL device according to the present invention. On a glass substrate (transparent substrate) 1, a transparent electrode 2 constituting an anode electrode, a hole transport layer 3 having a hole transport property, a light emitting layer 4, a metal doping layer 5 and a back electrode 6 serving as a cathode are sequentially arranged. It is layered. Among these elements (layers), the glass substrate (transparent substrate) 1, the transparent electrode 2, the hole transport layer 3, the light emitting layer 4, and the cathode electrode 6 are well-known elements, and the metal doping layer 5 is the present invention. The proposed element (layer). In addition to this, as a specific laminated structure of the organic EL element, anode / light emitting layer / metal doping layer / cathode, anode / hole transport layer / light emitting layer / metal doping layer / cathode, anode / hole transport layer / light emission Layer / electron transport layer / metal doping layer / cathode, anode / hole injection layer / light emitting layer / metal doping layer / cathode, anode / hole injection layer / hole transport layer / light emitting layer / metal doping layer / cathode, anode / Hole injection layer / hole transport layer / light emitting layer / electron transport layer / metal doping layer / cathode, and the like. The organic EL device according to the present invention has the metal doping layer 5 at the interface with the cathode electrode 6. Any element configuration may be used as long as it has.
[0010]
FIG. 2 shows an example in which an electron transport layer 8 exists between the cathode electrode 6 and the organic light emitting layer 4, and a metal doping layer 5 is provided at the interface between the electron transport layer 8 and the cathode electrode 6. . In the metal doping layer 5, a metal oxide or metal salt that is a dielectric exists in an organic compound as a dopant, and therefore, the band structure of organic molecules in contact with the dopant is changed, and the LUMO level is lowered. As a result, electron injection from the cathode is facilitated.
[0011]
FIG. 3 shows a cathode interface portion of a conventional organic EL device proposed by Hung et al. For comparison. In this example, the dielectric thin film layer 9 is provided at the interface between the cathode electrode 6 and the electron transport layer 8, but in this device, the band structure of the organic compound near the cathode interface in contact with the dielectric changes, and electrons are injected. It has been said that the lowest vacancy level (LUMO) of the organic compound to be reduced is lowered and the electron injection from the cathode is facilitated. However, in the organic EL device according to the present invention, compared with the conventional cathode interface structure of FIG. In addition, it becomes easier to inject electrons from the cathode, and the driving voltage can be lowered.
[0012]
In the organic EL device, the electron injection process from the cathode to the organic compound layer, which is basically an insulator, is reduction of the organic compound on the cathode surface, that is, formation of a radical anion state (Phys. Rev. Lett., 14, 229 (1965)). This is the electron injection into the lowest vacancy level (LUMO) of the organic compound. Therefore, an organic compound having a lower LUMO level is more likely to inject electrons from the cathode. In the device of the present invention, an energy barrier at the time of electron injection from the cathode electrode is obtained by doping the organic compound layer in contact with the cathode with a metal oxide or metal salt that has an effect of reducing the LUMO of the organic compound in advance. Can be reduced. The metal doping layer 5 is an organic compound layer doped with a dopant substance made of a metal oxide or a metal salt in this way. Since the metal-doped organic compound has a low LUMO level as described above, the barrier against electron injection energy from the cathode is small, and the driving voltage can be reduced as compared with a conventional organic EL device. Moreover, a stable metal such as Al that is generally used as a wiring material can be used for the cathode.
[0013]
Dopants can change the electronic energy level of organic compounds that serve as hosts, and can reduce the LUMO level. Metal oxidation of transition metals including alkali metals such as Li, alkaline earth metals such as Mg, or rare earth metals. If it is a metal oxide, there is no particular limitation. ₂ O, Na ₂ OK ₂ O, Rb ₂ O, Cs ₂ LiF, NaF, KF, RbF, CsF, MgF for metal salts such as O, MgO, CaO ₂ , CaF ₂ , SrF ₂ , BaF ₂ , LiCl, NaCl, KCl, RbCl, CsCl, MgCl ₂ , CaCl ₂ , SrCl ₂ , BaCl ₂ Etc. can be used suitably.
[0014]
The dopant concentration of the metal doping layer 5 is not particularly limited, but is preferably 0.1 to 99% by weight. If it is less than 0.1% by weight, the dopant concentration is too low and the effect of doping is small. If it exceeds 99% by weight, the dopant concentration in the film is too high, and the concentration of the organic compound to which electrons should be injected in the vicinity of the cathode is reversed. In other words, the doping effect is reduced. The thickness of the metal doping layer is not particularly limited, but is preferably 10 to 2000 mm. If it is less than 10 mm, the thickness of the metal doping layer is too thin to obtain a uniform film, and the amount of organic molecules lowered to the LUMO level to which electrons are to be injected is too small. On the other hand, if it exceeds 2000 mm, the film thickness of the whole organic layer is too thick, and conversely, the drive voltage increases, which is not preferable.
[0015]
The film forming method of the metal doping layer 5 may be any thin film forming method. For example, a vapor deposition method or a sputtering method can be used. When a thin film can be formed by coating from a solution, a coating method from a solution such as a spin coating method or a dip coating method can be used. In this case, the organic compound to be doped and the dopant may be dispersed in an inert polymer.
[0016]
The organic compound that can be used as the light emitting layer, the electron transport layer, and the metal doping layer is not particularly limited, but polycyclic compounds such as p-terphenyl and quaterphenyl and derivatives thereof, naphthalene, tetracene, pyrene, coronene, Condensed polycyclic hydrocarbon compounds such as chrysene, anthracene, diphenylanthracene, naphthacene, phenanthrene and derivatives thereof, condensed heterocyclic compounds such as phenanthroline, bathophenanthroline, phenanthridine, acridine, quinoline, quinoxaline, phenazine and derivatives thereof; . Fluorescein, perylene, phthaloperylene, naphthaloperylene, perinone, phthaloperinone, naphthaloperinone, diphenylbutadiene, tetraphenylbutadiene, oxadiazole, aldazine, bisbenzoxazoline, bisstyryl, pyrazine, cyclopentadiene, oxine, aminoquinoline, imine, diphenylethylene, Examples thereof include vinyl anthracene, diaminocarbazole, pyran, thiopyran, polymethine, merocyanine, quinacridone, rubrene, and derivatives thereof.
[0017]
Further, metal chelate complexes disclosed in JP-A-63-295695, JP-A-8-22557, JP-A-8-81472, JP-A-5-9470, and JP-A-5-17764 Compounds, especially metal chelated oxanoid compounds, tris (8-quinolinolato) aluminum, bis (8-quinolinolato) magnesium, bis [benzo (f) -8-quinolinolato] zinc, bis (2-methyl-8-quinolinolato) aluminum , Tris (8-quinolinolato) indium, tris (5-methyl-8-quinolinolato) aluminum, 8-quinolinolatolithium, tris (5-chloro-8-quinolinolato) gallium, bis (5-chloro-8-quinolinolato) A metal complex having at least one 8-quinolinolato or a derivative thereof such as calcium as a ligand is preferably used.
[0018]
Oxadiazoles disclosed in JP-A-5-202011, JP-A-7-179394, JP-A-7-278124, JP-A-7-228579, disclosed in JP-A-7-157473 Triazines, stilbene derivatives and distyrylarylene derivatives disclosed in JP-A-6-203963, styryl derivatives disclosed in JP-A-6-132080 and JP-A-6-88072, Diolefin derivatives disclosed in Kaihei 6-100857 and JP-A-6-207170 are also preferred as the light emitting layer, the electron transport layer, and the metal doping layer.
[0019]
Furthermore, fluorescent brighteners such as benzoxazole, benzothiazole, and benzimidazole can also be used, and examples thereof include those disclosed in JP-A-59-194393. Typical examples are 2,5-bis (5,7-di-t-benzyl-2-benzoxazolyl) -1,3,4-thiazole, 4,4'-bis (5,7-t -Pentyl-2-benzoxazolyl) stilbene, 4,4'-bis [5,7-di- (2-methyl-2-butyl) -2-benzoxazolyl] stilbene, 2,5-bis ( 5.7-di-t-pentyl-2-benzoxazolyl) thiophene, 2,5-bis [5- (α, α-dimethylbenzyl) -2-benzoxazolyl] thiophene, 2,5-bis [5 , 7-Di- (2-methyl-2-butyl) -2-benzoxazolyl] -3,4-diphenylthiophene, 2,5-bis (5-methyl-2-benzoxazolyl) thiophene, 4 , 4'-bis (2-benzoxazolyl) biphenyl, 5-methyl-2- {2- [4- (5-methyl-2-benzoxazolyl) phenyl] vinyl} benzoxazole, 2- [2 -(4-Chlorophenyl) vinyl] naphtho (1,2-d) oxazole etc. Benzoxazoles, benzothiazoles such as 2,2 '-(p-phenylenedipinylene) -bisbenzothiazole, 2- {2- [4- (2-benzimidazolyl) phenyl] vinyl} benzimidazole, Examples thereof include fluorescent whitening agents such as benzimidazoles such as [2- (4-carboxyphenyl) vinyl] benzimidazole.
[0020]
As the distyrylbenzene compound, for example, those starting from EP 0373582 can be used. Typical examples are 1,4-bis (2-methylstyryl) benzene, 1,4-bis (3-methylstyryl) benzene, 1,4-bis (4-methylstyryl) benzene, distyrylbenzene, 1 , 4-Bis (2-ethylstyryl) benzene, 1,4-bis (3-ethylstyryl) benzene, 1,4-bis (2-methylstyryl) -2-methylbenzene, 1,4-bis (2- And methyl styryl) -2-ethylbenzene.
[0021]
Further, a distyrylpyrazine derivative disclosed in JP-A-2-252793 can also be used as a light emitting layer, an electron transport layer, and a metal doping layer. Typical examples include 2,5-bis (4-methylstyryl) pyrazine, 2,5-bis (4-ethylstyryl) pyrazine, 2,5-bis [2- (1-naphthyl) vinyl] pyrazine, 2 , 5-bis (4-methoxystyryl) pyrazine, 2,5-bis [2- (4-biphenyl) vinyl] pyrazine, 2,5-bis [2- (1-pyrenyl) vinyl] pyrazine, and the like.
[0022]
In addition, dimethylidin derivatives disclosed in European Patent No. 388768 and JP-A-3-231970 can also be used as materials for the light emitting layer, the electron transport layer, and the metal doping layer. Typical examples include 1,4-phenylene dimethylidin, 4,4'-phenylene dimethylidin, 2,5-xylylene dimethylidin, 2,6-naphthylene dimethylidin, 1,4-biphenylene. Dimethylidin, 1,4-p-terephenylenedimethylidin, 9,10-anthracenediyldimethylidin, 4,4 '-(2,2-di-t-butylphenylvinyl) biphenyl, 4,4' -(2,2-diphenylvinyl) biphenyl, and the like, and derivatives thereof, silanamine derivatives disclosed in JP-A-6-49079, JP-A-6-29378, JP-A-6-279322, Polyfunctional styryl compounds disclosed in JP-A-6-279323, oxadiazole derivatives disclosed in JP-A-6-107648 and JP-A-6-92947, JP-A-6-206865 Disclosed anthracene compound, oxine disclosed in JP-A-6-145146 Derivatives, tetraphenylbutadiene compounds disclosed in JP-A-4-96990, organic trifunctional compounds disclosed in JP-A-3-296595, and further disclosed in JP-A-2-191694. Coumarin derivatives, perylene derivatives disclosed in JP2-196885, naphthalene derivatives disclosed in JP2-255789, JP2-289676 and JP-2-88689. Phthaloperinone derivatives, styrylamine derivatives disclosed in JP-A-2-250292, and the like.
Furthermore, known materials that have been used in the production of conventional organic EL devices can be used as appropriate.
[0023]
The arylamine compounds used as the hole injection layer, the hole transport layer, and the hole transporting light emitting layer are not particularly limited, but are described in JP-A-6-25659 and JP-A-6-203963. JP-A-6-215874, JP-A-7-115116, JP-A-7-224012, JP-A-7-157473, JP-A-8-48656, JP-A-7-126226, JP-A-7 -188130, JP-A-8-40995, JP-A-8-40996, JP-A-8-40997, JP-A-7-12225, JP-A-7-101911, JP-A-7-97355 The arylamine compounds disclosed in Japanese Patent Publication No. H1 are preferred, for example, N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl, N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4'-diaminobiphenyl, 2,2-bis (4-di-p-tolylaminophenyl) propane, N, N, N ', N'-tetra-p-tolyl-4 , 4'-Diaminobiphenyl, bis (4-di-p-tri Aminophenyl) phenylmethane, N, N'-diphenyl-N, N'-di (4-methoxyphenyl) -4,4'-diaminobiphenyl, N, N, N ', N'-tetraphenyl-4,4 '-Diaminodiphenyl ether, 4,4'-bis (diphenylamino) quadriphenyl, 4-N, N-diphenylamino- (2-diphenylvinyl) benzene, 3-methoxy-4'-N, N-diphenylaminostil Benzene, N-phenylcarbazole, 1,1-bis (4-di-p-triaminophenyl) -cyclohexane, 1,1-bis (4-di-p-triaminophenyl) -4-phenylcyclohexane, bis ( 4-dimethylamino-2-methylphenyl) -phenylmethane, N, N, N-tri (p-tolyl) amine, 4- (di-p-tolylamino) -4 '-[4 (di-p-tolylamino) Styryl] stilbene, N, N, N ', N'-tetra-p-tolyl-4,4'-diamino-biphenyl, N, N, N', N'-tetraphenyl-4,4'-di Mino-biphenyl N-phenylcarbazole, 4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl, 4,4 ''-bis [N- (1-naphthyl) -N-phenyl -Amino] p-terphenyl, 4,4'-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl, 4,4'-bis [N- (3-acenaphthenyl) -N-phenyl- Amino] biphenyl, 1,5-bis [N- (1-naphthyl) -N-phenyl-amino] naphthalene, 4,4'-bis [N- (9-anthryl) -N-phenyl-amino] biphenyl, 4 , 4 ''-bis [N- (1-anthryl) -N-phenyl-amino] p-terphenyl, 4,4'-bis [N- (2-phenanthryl) -N-phenyl-amino] biphenyl, 4 , 4'-bis [N- (8-fluoranthenyl) -N-phenyl-amino] biphenyl, 4,4'-bis [N- (2-pyrenyl) -N-phenyl-amino] biphenyl, 4,4 '-Bis [N- (2-perylenyl) -N- Enyl-amino] biphenyl, 4,4'-bis [N- (1-coronenyl) -N-phenyl-amino] biphenyl, 2,6-bis (di-p-tolylamino) naphthalene, 2,6-bis [di -(1-Naphtyl) amino] naphthalene, 2,6-bis [N- (1-naphthyl) -N- (2-naphthyl) amino] naphthalene, 4.4 ″ -bis [N, N-di (2-naphthyl) Amino] terphenyl, 4.4'-bis {N-phenyl-N- [4- (1-naphthyl) phenyl] amino} biphenyl, 4,4'-bis [N-phenyl-N- (2-pyrenyl)- Amino] biphenyl, 2,6-bis [N, N-di (2-naphthyl) amino] fluorene, 4,4 ″ -bis (N, N-di-p-tolylamino) terphenyl, bis (N-1 -Naphthyl) (N-2-naphthyl) amine. Furthermore, known materials that have been used in the production of conventional organic EL devices can be used as appropriate.
[0024]
Furthermore, as the hole injection layer, the hole transport layer, and the hole transport light-emitting layer, those obtained by dispersing the above-described organic compound in a polymer or those polymerized can be used. So-called π-conjugated polymers such as polyparaphenylene vinylene and derivatives thereof, hole-transporting non-conjugated polymers represented by poly (N-vinylcarbazole), and sigma-conjugated polymers of polysilanes can also be used.
[0025]
The hole injection layer formed on the ITO electrode is not particularly limited, and conductive polymers such as metal phthalocyanines such as copper phthalocyanine and metal phthalocyanines, carbon films, and polyaniline can be preferably used. Furthermore, a Lewis acid can be allowed to act on the above-mentioned arylamines as an oxidizing agent to form radical cations and used as a hole injection layer.
[0026]
The cathode electrode is not limited as long as it is a metal that can be used stably in the air, but aluminum which is generally widely used as a wiring electrode is particularly preferable.
[0027]
[Example]
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, the VPC-400 vacuum evaporation machine made from a vacuum machine company was used for vapor deposition of an organic compound and a metal. The film thickness was measured using a Sloan DekTak3ST stylus step meter.
For the device characteristic evaluation, Kikusui PBX 40-2.5 DC power supply, Iwatori VOAC-7510 multimeter, and Topcon BM-8 luminance meter were used. A direct current voltage was applied stepwise at a rate of 0.5 V / 2 seconds or 1 V / 2 seconds with ITO as the anode and Al as the cathode, and the luminance and current value after 1 second of voltage increase were measured. The EL spectrum was measured by driving at constant current using a Hamamatsu Photonics PMA-10 optical multichannel analyzer.
[0028]
Example 1
The present invention is applied to the organic EL element having the laminated structure of FIG. On the glass substrate 1, ITO (indium-tin oxide, electron beam evaporated product manufactured by Asahi Glass Co., Ltd.) having a sheet resistance of 15Ω / □ is coated as the anode transparent electrode 2. The following formula 1: having hole transportability thereon
[Chemical 1]

ΑNPD represented by 10 ^-6 Under torr, the film was formed to a thickness of 400 mm at a deposition rate of 3 mm / second to form the hole transport layer 3.
[0029]
Next, the following formula 2 having green light emission as the light emitting layer 4 on the hole transport layer 3:
[Chemical formula 2]

A tris (8-quinolinolato) aluminum complex layer (hereinafter referred to as “Alq”) 4 represented by the following formula was formed by vacuum deposition to a thickness of 600 mm under the same conditions as 3.
Next, 100 nm of Alq and LiF were deposited on the light-emitting layer 4 while adjusting the deposition rate so that LiF was 2 wt% as a metal doping layer 5.
Finally, Al was vapor deposited on the metal doping layer 5 as a back electrode 6 serving as a cathode at a vapor deposition rate of 15 mm / sec. The light emitting area was a square shape with a length of 0.5 cm and a width of 0.5 cm.
In the organic EL device, a direct current voltage was applied between ITO as the anode electrode and Al6 as the cathode electrode, and the luminance of green light emitted from the light emitting layer Alq4 was measured. 15000cd / m from this device ² The high brightness of was shown at 13V. The current density at this time is 440 mA / cm ² Met.
[0030]
Comparative Example 1
As in Example 1, first, αNPD was deposited as a hole transport layer on ITO to a thickness of 400 mm on ITO, and then Alq was vacuum deposited as a light emitting layer to a thickness of 600 mm on the same conditions as 3. Formed. Then, 2000 liters of Al was deposited as a cathode from above Alq. This device is up to 6700cd / m at 15V ² It can be seen that the metal doping layer 5 is effective in improving the luminance and lowering the driving voltage.
[0031]
Comparative Example 2
Under the same conditions as in Example 1, αNPD was first deposited as a hole transport layer on ITO to a thickness of 400 mm on ITO. After depositing 500 nm of Alq thereon, only LiF was deposited to a thickness of 100 mm. It was formed by vacuum vapor deposition, and Al was deposited as a cathode on top of the cathode.
In this device, no current was injected, and no light emission from the device was observed. It seems that electron injection from the cathode was not performed when only 100% LiF was inserted because the LiF layer was a complete insulator layer. Therefore, it is shown that when LiF is 100 有機, an organic molecule is required for electron injection in the part in contact with the cathode.
[0032]
Example 2
On the quartz glass with a thickness of 1 mm, Alq and LiF were deposited in a thickness of 1000 mm by adjusting the deposition rate so that LiF was 2% by weight. In addition, a sample was formed by depositing only Alq and depositing 1000 mm. In these visible and ultraviolet absorption spectra, absorption by the quinoline ring was observed at around 400 nm in the film deposited with Alq alone, whereas such absorption by the quinoline ring was observed at 375 nm in the Alq film doped with LiF. This indicates that the energy level of the Alq molecule changes due to the presence of LiF in the vicinity of the Alq molecule.
[0033]
Example 3
On the ITO, vacuum deposition of αNPD as the hole transport layer 3 and 400 nm of Alq as the light emitting layer 4 was performed, and then Alq and lithium oxide (Li ₂ O) as the metal doping layer 5 Li ₂ Co-deposited to a thickness of 100 mm so that the O concentration was 3% by weight. On top of that, 1000 elements of Al were vapor-deposited as a cathode electrode 6 to produce a device. This device has a maximum luminance of 16000cd / m at an applied voltage of 13V. ² And current density 480mA / cm ² In the same manner as in Example 1, high luminance was given with a low driving voltage.
[0034]
Comparative Example 3
Under the same conditions as in Example 1, first, αNPD was deposited as a hole transport layer on ITO to a thickness of 400 mm on ITO. ₂ Only O was vacuum-deposited to a thickness of 100 mm, and Al was deposited as a cathode from the thickness of 2000 mm.
In this device, no current was injected and no light emission was observed. This is Li ₂ If only O was inserted 100 Li Li ₂ Since the O layer is a complete insulator layer, it seems that electron injection from the cathode was not performed. Therefore, it is shown that co-evaporation with an organic compound is indispensable for the metal doping layer for electron injection.
[0035]
Example 4
On the ITO, vacuum deposition of αNPD of 400 と し て as the hole transport layer 3 and Alq of 500 と し て as the light emitting layer 4 was performed by vacuum deposition, and then bathophenanthroline and Li ₂ Li as metal doping layer 5 ₂ Co-deposited to a thickness of 100 mm so that O was 3% by weight. From there, 1000 elements of Al were deposited as the cathode electrode 6 to produce a device. This device has a maximum luminance of 21000cd / m at an applied voltage of 13V. ² , Current density 630mA / cm ² In the same manner as in Example 1, high luminance was given with a low driving voltage.
[0036]
【The invention's effect】
As described above, the organic EL device of the present invention has a low driving voltage and high efficiency by providing an organic compound layer (metal doping layer) doped with at least one of a metal oxide and a metal salt at the interface with the cathode electrode. This makes it possible to manufacture a high-luminance light-emitting element. Therefore, the organic EL device of the present invention is highly practical and can be expected to be effectively used as a display device or a light source.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a laminated structure example of an organic EL element of the present invention.
FIG. 2 is an explanatory view showing a cathode portion of the organic EL device of the present invention.
FIG. 3 is an explanatory view showing a cathode portion of a conventional organic EL element.
[Explanation of symbols]
1 Transparent substrate
2 Anode transparent electrode
4 Light emitting layer
5 Metal doping layer
6 Cathode electrode

Claims (2)

In an organic electroluminescent device having at least one light emitting layer composed of an organic compound between an opposing anode electrode and cathode electrode, the cathode electrode is made of aluminum, and an alkali metal is formed at the interface with the cathode electrode. An organic electroluminescent device having an organic compound layer doped with a metal salt made of an alkaline earth metal as a metal doping layer. 2. The organic electroluminescent device according to claim 1, wherein the concentration of the metal salt in the metal doping layer is 0.1 to 99% by weight.

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