JP2007243044A - Method for manufacturing organic electroluminescent (el) element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent (EL) element that can lower driving voltage, control occurrence of leakage, and maintain high reverse breakdown voltage. <P>SOLUTION: The organic EL element includes a primary electrode, an organic EL layer, and a secondary electrode on a substrate, wherein the organic EL layer includes a primary and a secondary doping layer arranged adjacently, the primary and the secondary doping layer include an organic host material and dopant, and the doping concentration of the dopant in the primary doping layer is different than that of the dopant in the secondary doping layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic EL element, and particularly relates to an organic EL element having a low driving voltage and a high reverse breakdown voltage and having no leakage.

  As an example of a light-emitting element applied to a display device, an organic electroluminescence element (hereinafter referred to as an “organic EL element”) having a thin film laminated structure of an organic compound is known. The organic EL element has a structure in which an organic EL layer composed of one or more constituent layers is sandwiched between two electrodes (anode and cathode), injects holes from the anode, injects electrons from the cathode, This is based on the principle that the organic dye is excited using the energy when these carriers are recombined to generate excitons, and the light emitted when the excitons relax to the ground level is extracted to the outside.

  Then, depending on which of the electrode in contact with the element substrate and the organic EL layer and the electrode in contact with the organic EL layer is a transparent electrode, it is opposite to the bottom emission method in which light is emitted to the element substrate side, or opposite to the element substrate An organic EL element such as a top emission type that emits light to the side can be obtained. In addition, application to display applications such as passive matrix driving by forming two electrodes from a plurality of striped partial electrodes or active matrix driving using a switching element (TFT or the like) has been made. Furthermore, application to a multicolor display by combining such an organic EL element with a color filter layer or the like has been studied.

  In such an organic EL element, the smooth carrier injection from the anode and the cathode is an important factor for reducing the driving voltage of the element and, in turn, extending the life of the element accompanying the reduction of the driving voltage.

  In the injection of holes, which are one of carriers, into the organic EL layer, it is necessary to consider mainly two conditions. One condition is that the energy barrier between the anode and the organic EL layer is small. To satisfy this condition, it is important that the ionization potential of the material constituting the anode is sufficiently large. Another condition is that the state density of carriers in the organic EL layer (or its constituent layer) in contact with the anode is high.

  At present, a single layer film of material is generally used as the hole injection layer in contact with the anode of the organic EL layer. Recently, research on techniques for adding various dopants to a single layer film of a hole injection layer has been actively conducted, and this technique is one technique for lowering the driving voltage of an organic EL element. Has attracted attention. For example, although it is an example using an inorganic material, a laminated body of a metal layer and an insulating layer or a resistance layer made of silicon oxide, germanium oxide, or the like is inserted between the anode and the organic EL layer to reduce driving Attempts have been made to achieve both voltage and leakage prevention (see Patent Document 1).

JP-A-8-279394 JP-A-6-25659 JP-A-6-203963 JP-A-6-215874 JP 7-145116 A JP-A-7-224012 JP-A-7-157473 JP-A-8-48656 JP 7-126226 A JP 7-188130 A JP-A-8-40995 JP-A-8-40996 JP-A-8-40997 JP 7-126225 A JP-A-7-101911 JP-A-7-97355

  In the organic EL element, it is important to reduce the driving voltage and prevent the occurrence of a failure such as leakage (short-circuit between the cathode and the anode due to insufficient formation of the organic EL layer). Leakage is considered to be due to electric field concentration caused by particles (microparticles) or irregularities present on the surface of the electrode serving as a base when forming the organic EL layer. In addition, when the inorganic material laminate is inserted, particles may be generated in the process of forming the insulating layer or the resistance layer from silicon oxide, germanium oxide, or the like, and the insulating layer or the resistance layer may cause carrier movement. In order to inhibit, these layers cannot be thickened to suppress the influence of particles and irregularities on the electrode surface. In view of such a situation, it is desired to provide a smooth electrode surface by eliminating particles and irregularities on the electrode surface.

  However, when increasing the area of the light emitting portion of the organic EL element, it is practically difficult to eliminate particles and irregularities on the electrode surface over the entire surface. Therefore, it has been desired to provide an organic EL layer having a structure that is not sensitive to the presence of particles and irregularities on the electrode surface.

  For example, by increasing the thickness of the hole injection layer or electron injection layer that is a constituent layer in contact with the electrode in the organic EL layer, the influence of particles and irregularities on the electrode surface is alleviated, and leakage due to electric field concentration occurs. Can be prevented. However, when these layers are made thicker, the distance that the carrier should move becomes longer, the carrier movement resistance increases, and the drive voltage of the organic EL element rises.

  Furthermore, rather than forming the hole injection layer or the electron injection layer from a single material, doping with a dopant reduces the resistance of carrier movement and suppresses the occurrence of leakage at the same time as the drive voltage decreases. Conceivable. However, simply doping with the necessary amount of dopant to achieve the desired reduction in carrier transfer resistance reduces the ability to stop charge carriers (electrons in the hole injection layer or holes in the electron injection layer). It has been found that there arises a new problem that the reverse breakdown voltage as a whole of the blocking is lowered.

  Accordingly, an object of the present invention is to provide an organic EL layer that can reduce a drive voltage, suppress occurrence of leakage, and maintain a high reverse breakdown voltage, and an organic EL element using the organic EL layer.

  In order to solve the above-described problem, the organic EL element of the present invention includes an organic EL layer having first and second doping layers disposed adjacent to each other. The first and second doping layers arranged adjacent to each other are layers containing an organic host material and a dopant, and function as a hole injection layer in contact with the anode or an electron injection layer functioning as a cathode. The first doping layer is a layer that is in direct contact with the electrode, and has a high doping concentration and a film thickness sufficient to alleviate the influence of particles and unevenness. On the other hand, the second doping layer is in contact with the surface of the first doping layer opposite to the electrode and has a lower doping concentration than the first doping layer, and has a function of maintaining the reverse breakdown voltage of the device.

  The organic EL element of the present invention having the organic EL layer configured as described above has a reduction in driving voltage by making the constituent layers in contact with the electrodes in the organic EL layer into two layers with functional separation. This has the special effect of suppressing the occurrence of a failure such as a leak and maintaining the reverse breakdown voltage at the same time.

  As shown in FIG. 1, the organic EL element of the present invention includes a first electrode 20, an organic EL layer 30, and a second electrode 40 on a substrate 10, and the organic EL layer 30 is disposed adjacent to the first electrode 20. First and second doping layers, wherein the first and second doping layers include an organic host material and a dopant, and the doping concentration of the dopant in the first doping layer is the doping concentration of the dopant in the second doping layer. It is characterized by being different.

  The substrate 10 may be transparent or opaque, should be able to withstand the conditions (solvent, temperature, etc.) used to form the layer to be laminated, and has excellent dimensional stability. Is preferred. As will be described later, when a bottom emission type organic EL element is formed using the first electrode 20 as a transparent electrode, the substrate 10 should also be transparent. When it is required to be transparent, the substrate 10 preferably has a transmittance of 80% or more with respect to visible light, and more preferably has a transmittance of 86% or more. Transparent materials that can be used to form the substrate 10 are glass, diacetyl cellulose, triacetyl cellulose (TAC), cellulose esters such as propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose, nitrocellulose; polyamides; polycarbonates; polyethylenes Polyester such as terephthalate, polyethylene naphthalate, polybutylene terephthalate, poly-1,4-cyclohexanedimethylene terephthalate, polyethylene-1,2-diphenoxyethane-4,4′-dicarboxylate, polybutylene terephthalate; polystyrene; polyethylene Polyolefins such as polypropylene and polymethylpentene; acrylic resins such as polymethyl methacrylate; polycarbonate; Emissions; polyether sulfone; polyether ketone; polyetherimides; may be a polymer material such as norbornene resins; polyoxyethylene. When a polymer material is used, the transparent substrate 10 may be rigid or flexible. Alternatively, if the substrate 10 is not required to be transparent, the substrate 10 may be formed using metal or ceramic.

  The first electrode 20 and the second electrode 40 may be transparent electrodes or reflective electrodes. Either the first electrode 20 or the second electrode 40 is a transparent electrode. When the bottom emission method is adopted, the first electrode 20 is a transparent electrode, and when the top emission method is adopted, the second electrode is a transparent electrode. The other of the first electrode 20 or the second electrode 40 may be a transparent electrode or a reflective electrode, but is preferably a reflective electrode.

  The transparent electrode desirably has a transmittance of 80% or more at a wavelength of 380 to 780 nm, which is a visible light region, in order to be a light extraction side. The transparent electrode is made of IZO (In—Zn oxide), ITO (In—Sn oxide), Sn oxide, In oxide, Zn oxide, Zn—Al oxide, Zn—Ga oxide, or oxidation thereof. It can be formed using a conductive transparent metal oxide in which a dopant such as F or Sb is added to an object. The transparent electrode is formed using a vapor deposition method (resistance heating or electron beam heating), a sputtering method, or a chemical vapor deposition (CVD) method, and preferably formed using a sputtering method. The transparent electrode may be used as an anode or a cathode. When using a transparent electrode as a cathode, it is desirable to provide a buffer layer at the interface with the organic EL layer 30 to improve electron injection efficiency. As the material of the buffer layer, alkali metals such as Li, Na, K, or Cs, alkaline earth metals such as Ba and Sr, alloys containing them, rare earth metals, or fluorides of these metals can be used. However, it is not limited to them. The film thickness of the buffer layer can be appropriately selected in consideration of the driving voltage, transparency, and the like, but in a normal case, it is preferably 10 nm or less.

  On the other hand, the reflective electrode can be formed using a highly reflective metal, amorphous alloy, or microcrystalline alloy. High reflectivity metals include Al, Ag, Mo, W, Ni, Cr, and the like. High reflectivity amorphous alloys include NiP, NiB, CrP, CrB, and the like. The highly reflective microcrystalline alloy includes NiAl and the like. The reflective electrode may be used as an anode or a cathode. When the reflective electrode is used as a cathode, the aforementioned buffer layer may be provided at the interface between the reflective electrode and the organic EL layer 30 to improve the efficiency of electron injection into the organic EL layer 30. Alternatively, an alkali metal such as lithium, sodium or potassium, or an alkaline earth metal such as calcium, magnesium or strontium, which is a material having a low work function, compared to the aforementioned high reflectivity metal, amorphous alloy or microcrystalline alloy. Addition and alloying can improve electron injection efficiency. On the other hand, when the reflective electrode is used as an anode, the conductive transparent metal oxide layer described above is provided at the interface between the reflective electrode and the organic EL layer 30 to improve the efficiency of hole injection into the organic EL layer 30. May be. The reflective electrode can be formed using any means known in the art such as vapor deposition, sputtering, ion plating, and laser ablation, depending on the material used.

  The organic EL device of the present invention is applied to display applications by dividing one or both of the first electrode 20 and / or the second electrode 40 into a plurality of partial electrodes to form a plurality of independent light emitting portions. Is possible. One method for forming a plurality of independent light emitting portions is to form the first electrode 20 from a plurality of stripe-shaped partial electrodes extending in the first direction and the second electrode 40 to a plurality of stripes extending in the second direction. It is formed from a partial electrode having a shape, and the first direction and the second direction intersect, preferably orthogonally. In such a structure, when a voltage is applied to specific partial electrodes of the first electrode 20 and the second electrode 40, light emission occurs at a position where the partial electrodes intersect, and so-called passive matrix driving is possible. Alternatively, one of the first electrode 20 and the second electrode 40 is formed from a plurality of partial electrodes, and each of the plurality of partial electrodes is connected to a switching element (for example, TFT) in a one-to-one relationship. By making the other of the second electrodes 40 an integrated common electrode, so-called active matrix driving is possible.

  When forming the first electrode 20 composed of a plurality of partial electrodes, a film of a material for forming the first electrode is uniformly formed over the entire surface, and thereafter, etching is performed so as to give a desired pattern. The first electrode 20 made of a partial electrode may be formed. Or you may form the 1st electrode 20 which consists of a some partial electrode by the formation method using the mask which gives a desired shape. Alternatively, patterning can be performed by applying a lift-off method.

  On the other hand, when forming the 2nd electrode 40 consisting of a plurality of partial electrodes, the 2nd electrode 40 consisting of a plurality of partial electrodes may be formed by the formation method using the mask which gives a desired shape. Alternatively, a second electrode separation partition having an inversely tapered cross section is provided before the organic EL layer 30 is formed, then the organic EL layer 30 and the second electrode are formed, and a second electrode composed of a plurality of partial electrodes is formed. The electrode 40 may be formed.

  The organic EL layer 30 includes first and second doping layers disposed adjacent to each other. The organic EL layer 30 includes a light emitting layer and one or both of a hole injection layer and an electron injection layer, and may include a hole transport layer and / or an electron transport layer as necessary. The first and second doping layers disposed adjacent to each other function as a hole injection layer or an electron injection layer.

In FIG. 2, the structural example of the organic EL layer 30 of the organic EL element of this invention is shown. FIG. 2A shows an organic EL layer 30 having a six-layer structure including a first doping layer 36a / second doping layer 36b / hole transport layer 32 / light emitting layer 33 / electron transport layer 34 / electron injection layer 35. . In this example, the first doping layer 36a / second doping layer 36b function as a hole injection layer. FIG. 2B shows a six-layer organic EL layer 30 comprising a hole injection layer 31 / hole transport layer 32 / light emitting layer 33 / electron transport layer 34 / second doping layer 37b / first doping layer 37a. Show. In this example, the second doping layer 37b / first doping layer 37a functions as an electron injection layer. In addition to the configuration shown in FIG. 2, the organic EL layer 30 can have the following configuration, for example.
(1) Anode / organic light emitting layer / electron injection layer / cathode (2) Anode / hole injection layer / light emitting layer / cathode (3) Anode / hole injection layer / light emitting layer / electron injection layer / cathode (4) Anode / Hole injection layer / hole transport layer / light emitting layer / electron injection layer / cathode (5) Anode / hole injection layer / light emitting layer / electron transport layer / electron injection layer / cathode (where hole injection layer or (At least one of the electron injection layers is formed of the first and second doping layers, and the anode and the cathode may be any of the first and second electrodes.)

  Below, each layer which comprises the organic EL layer 30 is described. The first doping layer and the second doping layer are layers including an organic host material and a dopant, and desirably both layers include the same organic host material and dopant. The dopant concentration in the first doping layer is different from the dopant concentration in the second doping layer, and the first doping layer doping concentration is set higher than the second doping layer doping concentration. In the present invention, the first doping layer is a layer in contact with either the first electrode or the second electrode, while the second doping layer is the opposite side of the first doping layer from the first electrode or the second electrode. This layer is in contact with the surface of the film.

  Organic host materials used when forming the first doping layer 36a and the second doping layer 36b used as the hole injection layer are metal phthalocyanines (such as copper phthalocyanine (CuPc)), indanthrene compounds, or aryls. It can be formed using an amine compound. The arylamine compounds that can be used are N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl, N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4'-diaminophenyl, 2,2-bis (4-di-p-tolylaminophenyl) propane, N, N, N ', N'-tetra-p-tolyl-4,4'-diaminobiphenyl Bis (4-di-p-tolylaminophenyl) 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) -p-quaterphenyl, 4-N, N-diphenylamino- (2-diphenylvinyl) benzene, 3, Methoxy-4 ′-(diphenylaminostyryl) benzene, N-phenylcarbazole, 1,1-bis [4-di-p-tolylaminophenyl] cyclohexane, 1,1-bis [4-di- (p-tolylamino) Phenyl] -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'-diamino-biphenyl-N-phenylcarbazole, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl, 4,4 "-bis [N- (1-naphthyl) -N-phenylamino] -p-terphenyl, 4,4′-bis [N- (2-naphthyl) -N-phenylamino] biphenyl, 4,4′-bis [N -(3-Acenaphthenyl) -N-phenylamino] biphenyl, 1,5-bis [N- (1-naphthyl) -N-phenylamino] naphthalene, 4,4'-bis [N- (9-anthryl)- N-phenylamino] biphenyl, 4,4 ″ -bis [N- (1-anthryl) -N-phenyl-amino] -p-terphenyl, 4,4′-bis [N- (2-phenanthryl) -N -Phenylamino] biphenyl, 4,4'-bis [N- (8-fluoranthenyl) -N-phenylamino] biphenyl, 4,4'-bis [N- (2-bienyl) -N-phenylamino] Biphenyl, 4,4'- [N- (2-perylenyl) -N-phenylamino] biphenyl, 4,4′-bis [N- (1-coronenyl) -N-phenylamino] biphenyl, 2,6- (di-p-tolylamino) Naphthalene, 2,6-bis [di- (1-naphthyl) amino] naphthalene, 2,6-bis [N- (1-naphthyl) -N- (2-naphthyl) amino] naphthalene, 4,4 "-bis [N, N-di (2-naphthyl) amino] -p-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) -p-terphenyl, bis ( , Including N-1- naphthyl) -2-naphthylamine (see Patent Document 2 to 16).

The dopant material used when forming the first doping layer 36a and the second doping layer 36b used as the hole injection layer is an acceptor material, for example, F ₄ -TCNQ (2,3,5,6-tetrafluoro- 7,7,8,8-tetracyanoquinodimethane), F ₄ DCNQI (N, N′-dicyano-2,3,5,6-tetrafluoro-1,4-quinonediimine), Cl ₂ DCNQI (N, N′-dicyano-2,5-dichloro-1,4-quinonediimine), Cl ₂ F ₂ DCNQI (N, N′-dicyano-2,5-dichloro-3,6-difluoro-1,4-quinonediimine), F ₆ DCNNQI (N, N'- dicyano-2,3,5,6,7,8-hexafluoro-1,4-naphthoquinone _imines), CN 4 TTAQ (1,4,5,8- Torahidoro 1,4,5,8 Tetorachia 2,3,6,7-tetra-cyano-anthraquinone) and the like.

  The first doping layer 36a forming a part of the hole injection layer has a high doping concentration while preventing the occurrence of leakage due to electric field concentration due to particles or unevenness at the interface of the first electrode 20 / organic EL layer 30. This is a layer for preventing an increase in driving voltage due to thickening. The first doping layer 36a has a thickness of 100 nm or more, preferably 100 to 400 nm. The doping concentration of the first doping layer 36a is 1 to 5%, preferably 2 to 4%, based on the volume of the organic host material. By using a film thickness and doping concentration within this range, it is possible to prevent the occurrence of leakage without increasing the drive voltage.

  The second doping layer 36b that forms part of the hole injection layer is a layer that has a low doping concentration and prevents a decrease in reverse breakdown voltage due to a thick film. The second doping layer 36b has a thickness of 10 to 100 nm, preferably 20 to 80 nm. The doping concentration of the second doping layer 36b is ½ or less, preferably １ ／ or less of the doping concentration of the first doping layer 36a. By using a film thickness and a doping concentration within this range, it is possible to prevent the drive voltage from rising without reducing the reverse breakdown voltage.

The organic host material used when forming the first doping layer 37a and the second doping layer 37b used as the electron injection layer is 2- (4-biphenyl) -5- (pt-butylphenyl) -1, Oxadiazole derivatives such as 3,4-oxadiazole (PBD), triazole derivatives, triazine derivatives, phenylquinoxalines, aluminum quinolinol complexes (eg, Alq ₃ ), and the like.

  The dopant material used when forming the first doping layer 37a and the second doping layer 37b used as the electron injection layer is a donor material, and includes, for example, an alkali metal such as Li, Na, and Ka.

  The first doping layer 37a, which forms part of the electron injection layer, has a high doping concentration while preventing leakage due to electric field concentration due to particles or unevenness at the interface of the organic EL layer 30 / second electrode 40. This is a layer for preventing an increase in driving voltage due to thickening. The first doping layer 37a has a thickness of 100 nm or more, preferably 100 to 400 nm. The doping concentration of the first doping layer 37a is 1 to 5%, preferably 2 to 4% based on the volume of the organic host material. By using a film thickness and doping concentration within this range, it is possible to prevent the occurrence of leakage without increasing the drive voltage.

  The second doping layer 37b that forms part of the electron injection layer is a layer that has a low doping concentration and prevents a reduction in reverse breakdown voltage due to a thick film. The second doping layer 37b has a thickness of 10 to 100 nm, preferably 20 to 80 nm. The doping concentration of the second doping layer 37b is ½ or less, preferably １ ／ or less of the doping concentration of the first doping layer 37a. By using a film thickness and a doping concentration within this range, it is possible to prevent the drive voltage from rising without reducing the reverse breakdown voltage.

The light emitting layer 33 is a layer that emits light by recombination of carriers (holes and electrons) injected by applying a voltage to the first electrode 20 and the second electrode 40. The material of the light emitting layer 33 can be selected according to a desired color tone. For example, in order to obtain blue to blue-green light emission, fluorescent whitening agents such as benzothiazole, benzimidazole, and benzoxazole, metal chelated oxonium compounds, styrylbenzene compounds, aromatic dimethylidin compounds, etc. Can be used. More specifically, 4,4′-bis (2,2-diphenylvinyl) biphenyl (DPVBi) can be mentioned. In addition, in order to obtain light emission in various wavelength ranges, a host compound (distyrylarylene compound, 4,4′-bis [N- (3-tolyl) -N-phenylamino] biphenyl (TPD), aluminum complex (for example, Tris (8-hydroxyquinolinato) aluminum complex (Alq ₃ , etc.) added with a dopant (perylene, quinacridones, rubrene, etc.) can also be used.

  The materials of the hole transport layer 32 and the hole injection layer 31 (when the stacked body of the first and second doping layers is not used) are not particularly limited, and these hole injection layers 31 and The hole transport layer 32 can be formed. For example, the hole injection layer 31 can be formed using phthalocyanines (such as copper phthalocyanine (CuPc)) or indanthrene compounds. The hole transport layer 32 can be formed using, for example, the above-described arylamine compound.

In the case of the electron transport layer 34 and the electron injection layer 35 (when the stacked body of the first and second doping layers is not used), the material is not particularly limited, and these layers are formed using a known material. Can do. For example, oxadiazole derivatives such as 2- (4-biphenyl) -5- (pt-butylphenyl) -1,3,4-oxadiazole (PBD), triazole derivatives, triazine derivatives, phenylquinoxalines The electron transport layer 34 and the electron transport layer 35 can be formed using a quinolinol complex of aluminum (for example, Alq ₃ ).

  The organic EL layer 30 is implemented by depositing the material of each constituent layer by an evaporation method or a co-evaporation method according to a desired configuration. Either resistance heating evaporation method or electron beam heating evaporation method may be used. When the co-evaporation method is used, a mixture obtained by mixing two or more film forming materials in a predetermined ratio in advance may be used as a heating evaporation source, or alternatively, each of two or more independent heating evaporation sources may be formed. A film material may be deposited.

  Furthermore, when an organic EL device having a plurality of independent light emitting portions is applied to a display application, one or more color filter layers that transmit light in a specific wavelength range, and absorb light in a specific wavelength range. One or more color conversion layers that emit light of longer wavelengths, a flattening layer for eliminating the steps caused by the plurality of color filter layers / color conversion layers, and organic by blocking the transmission of moisture or oxygen A layer such as a passivation layer for preventing deterioration of the EL element can be provided as necessary. For example, a laminated structure of color filter layer (and / or color conversion layer) / planarization layer / passivation layer may be provided between the transparent substrate 10 and the first electrode 20. Or you may provide a color filter layer and / or a color conversion layer on the surface on the opposite side to the 1st electrode 20 of the board | substrate 10 which is transparent. Alternatively, a filter substrate in which a laminate of a color filter layer (and / or color conversion layer) / passivation layer is provided on a transparent substrate different from the substrate 10 of the organic EL element is manufactured. A display may be formed by bonding. The color filter layer, color conversion layer, planarization layer, and passivation layer may be formed using any known material.

[Example 1]
An F ₄ -TCNQ / CuPc film (thickness: 200 nm) with a doping concentration of 0%, 1% and 2% was formed on the substrate, and the specific resistance was measured. The doping concentration is indicated by volume% based on the volume of CuPc. The results are shown in Table 1.

From this measurement result, it is understood that the F ₄ -TCNQ / CuPc film having a doping concentration of 2% has a sufficiently low specific resistance that can be increased without increasing the driving voltage. It can also be seen that the F ₄ -TCNQ / CuPc film with a doping concentration of 1% has a high specific resistance sufficient to improve the reverse breakdown voltage.

[Example 2]
In this example, a bottom emission type organic EL element having an organic EL layer 30 having a five-layer structure of a hole injection layer (first and second doping layers) / hole transport layer / light emitting layer / electron injection layer is fabricated. did.

A 200 nm-thick amorphous IZO film (In ₂ O ₃ : ZnO, ZnO in a molar ratio of 5%) was formed over the entire surface of the cleaned transparent glass substrate by sputtering. Next, patterning was performed by photolithography to form a plurality of stripe-shaped partial electrodes extending in the first direction having a width of 2 mm, a gap of 0.5 mm, and a film thickness of 100 nm. A plurality of partial electrodes were cleaned with oxygen plasma at room temperature to obtain a transparent electrode (first electrode, anode).

Next, the substrate on which the transparent electrode was formed was mounted in a resistance heating vapor deposition apparatus, and the organic EL layer 30 composed of a hole injection layer, a hole transport layer, a light emitting layer, and an electron injection layer was sequentially formed without breaking the vacuum. . A CuPc film doped with 2 volume% F ₄ -TCNQ having a thickness of 100 nm is formed as a first doping layer, and a CuPc film doped with 1 volume% F ₄ -TCNQ having a thickness of 50 nm is formed as a second doping layer. A hole injection layer was formed by forming a film. As the hole transport layer, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (α-NPD) having a thickness of 20 nm was stacked. As the light emitting layer, DPVBi with a thickness of 30 nm was stacked. Alq ₃ having a film thickness of 20 nm was stacked as the electron injection layer.

  Here, a master curve was created in advance to summarize the relationship between the output of the crystal oscillator film thickness monitor and the actual film thickness obtained with the stylus type surface shape measuring device (DEKTAK) and atomic force microscope (AFM). Based on the master curve, the vapor deposition rate of the vapor deposition material for each layer was determined. The doping concentrations of the first and second doping layers are indicated by volume% based on the volume of CuPc, which is an organic host material.

  A buffer layer made of LiF with a film thickness of 0.5 nm is formed on the organic EL layer obtained as described above using a mask capable of obtaining a stripe shape extending in the second direction orthogonal to the first direction. Further, Al having a thickness of 200 nm was laminated to obtain a reflective electrode (second electrode, cathode) composed of a plurality of stripe-shaped partial electrodes extending in the second direction with a width of 2 mm and a gap of 0.5 mm.

  With respect to the organic EL element obtained by the above procedure, the drive voltage, reverse breakdown voltage, and leak generation density were evaluated. The results are shown in Table 2.

[Comparative Example 1]
Instead of the hole injection layer composed of the first and second doping layers, the procedure of Example 2 was repeated except that a non-doped CuPc film having a thickness of 50 nm was laminated to form a hole injection layer, An EL element was obtained. The evaluation results of the obtained organic EL element are shown in Table 2.

[Comparative Example 2]
An organic EL device was obtained by repeating the procedure of Comparative Example 1 except that the thickness of the undoped CuPc film was changed to 200 nm. The evaluation results of the obtained organic EL element are shown in Table 2.

[Comparative Example 3]
The procedure of Example 2 was repeated to obtain an organic EL device, except that the second doping layer was not formed and the hole injection layer was formed only from the first doping layer. The evaluation results of the obtained organic EL element are shown in Table 2.

[Evaluation]
For the organic EL elements obtained in Example 2 and Comparative Examples 1 to 3, the drive voltage (voltage required to obtain a luminance of 100 cd / m ² ), reverse breakdown voltage (voltage in the reverse direction with respect to the organic EL element) The voltage at which the device was destroyed when applied) and the density of leak generation (number of leaks per unit area (1 cm ² )) were evaluated.

As can be seen from Table 2, in Comparative Example 1 in which 50 nm-thick undoped CuPc was used as the hole injection layer, a sufficiently low driving voltage and a sufficiently high reverse breakdown voltage were obtained, but the leak generation density was high. I understand. In addition, in Comparative Example 2 having an undoped CuPc hole injection layer whose film thickness was increased to 200 nm, it was found that although the occurrence of leakage could be suppressed, the drive voltage increased. Furthermore, in Comparative Example 3 in which a single layer of F4-TCNQ / CuPc having a thickness of 200 nm and a doping concentration of 2% was used as a hole injection layer, although leakage suppression and drive voltage reduction were realized, the reverse breakdown voltage was low. You can see that it has dropped. As described above, it can be seen that some characteristic problems occur in the devices of Comparative Examples 1 to 3 in which the two adjacent dopant layers of the present invention are not used as the hole injection layer. On the other hand, in Example 2 according to the present invention, no problem in characteristics occurs, a low driving voltage, a sufficiently high reverse breakdown voltage are obtained, and almost no leakage occurs (1 piece / It can be seen that this is less than cm ² .

[Example 3]
In this example, a top emission type organic EL element having an organic EL layer 30 having a five-layer structure of an electron injection layer (first and second doping layers) / a light emitting layer / a hole transport layer / a hole injection layer is manufactured. did.

  A substrate on which a plurality of TFTs are arranged as a switching element is subjected to a cleaning process, and Al is laminated on the upper surface of the substrate by a vapor deposition method using a mask to have a size of 2 × 2 mm, a gap of 0.5 mm, and a film thickness of 200 nm. A reflective electrode (second electrode, cathode) composed of a plurality of partial electrodes was formed. Furthermore, using the same mask, a 0.5 nm-thick LiF film was laminated, and a buffer layer was formed on a plurality of partial electrodes constituting the reflective electrode.

Next, the substrate on which the reflective electrode was formed was mounted in a resistance heating vapor deposition apparatus, and the organic EL layer 30 composed of an electron injection layer, a light emitting layer, a hole transport layer, and a hole injection layer was sequentially formed without breaking the vacuum. . The Alq ₃ film doped with 5% by volume of the Li thickness 200nm as a first doping layer is formed, by forming a Alq ₃ film doped with 1% by volume of the Li thickness 50nm as a second doped layer An electron injection layer was formed. As the light emitting layer, DPVBi with a thickness of 30 nm was stacked. As the hole transport layer, α-NPD having a thickness of 20 nm was stacked. CuPc with a film thickness of 200 nm was laminated as a hole injection layer.

  Finally, a uniform amorphous IZO film having a film thickness of 100 nm was laminated over the entire upper surface of the obtained organic EL layer to obtain a transparent electrode (first electrode, anode).

The organic EL device obtained as described above had a drive voltage (@ 100 cd / m ² ) of 12 V, a reverse breakdown voltage of ˜20 V, and a leak generation density of less than 1 / cm ² .

It is typical sectional drawing which shows an example of the organic EL element of this invention. It is typical sectional drawing which shows an example of a structure of the organic electroluminescent layer of this invention, (a) shows the case where the 1st and 2nd doping layer is used as a hole injection layer, (b) shows 1st and 2nd It is a figure which shows the case where a 2 doping layer is used as an electron injection layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 20 1st electrode 30 Organic EL layer 31 Hole injection layer 32 Hole transport layer 33 Light emitting layer 34 Electron transport layer 35 Electron injection layer 36a, 37a First doping layer 36b, 37b Second doping layer 40 Second electrode

Claims (9)

  An organic EL device including a first electrode, an organic EL layer, and a second electrode on a substrate, the first and second doping layers including the first and second doping layers disposed adjacent to each other. The doping layer includes an organic host material and a dopant, and the doping concentration of the dopant in the first doping layer is different from the doping concentration of the dopant in the second doping layer.   The first doping layer is disposed in contact with either the first electrode or the second electrode, and the doping concentration of the dopant in the first doping layer is higher than the doping concentration of the dopant in the second doping layer. The organic EL element according to claim 1, wherein the organic EL element is also large.   The organic EL device according to claim 2, wherein the dopant is an acceptor material, and the first and second doping layers are hole injection layers.   The organic EL device according to claim 2, wherein the dopant is a donor material, and the first and second doping layers are electron injection layers.   5. The organic EL element according to claim 1, wherein the substrate is a transparent substrate, the first electrode is a transparent electrode, and the second electrode is a reflective electrode.   5. The organic EL element according to claim 1, wherein the first electrode is a reflective electrode, and the second electrode is a transparent electrode.   The organic EL element according to claim 5 or 6, wherein each of the first electrode and the second electrode is an integrally formed electrode.   The first electrode is composed of a plurality of stripe-shaped partial electrodes extending in a first direction, the second electrode is composed of a plurality of stripe-shaped partial electrodes extending in a second direction, and the first direction The organic EL element according to claim 5, wherein the second direction is a crossing direction. The first electrode is composed of a plurality of partial electrodes, and each of the plurality of partial electrodes of the first electrode is connected to a plurality of switching elements on a one-to-one basis, and the second electrode is uniformly formed. The organic EL device according to claim 5, wherein the organic EL device is a body electrode.

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