KR20090110230A - Top-emitting organic light emitting diode device and producing method thereof - Google Patents

Abstract

PURPOSE: A top emission organic light emitting device and a manufacturing method thereof are provided to improve hole injection efficiency by suppressing the damage to the hole injection layer when forming an upper electrode. CONSTITUTION: A substrate(1) is a glass substrate. A bottom electrode(2) is formed on the substrate. An organic layer is formed on the bottom electrode. The organic layer includes an electron injection layer(3), an electron transport layer(4), a light emitting layer(5), a hole transport layer(6) and a hole injection layer(7). A metal foil layer(8) is formed on the hole injection layer. The metal foil layer is made of transparent conductive oxide. A top transparent electrode(9) is formed on the metal foil layer. The metal foil layer is oxidized when forming the top transparent electrode.

Description

Top-emitting organic light emitting diode and its manufacturing method {TOP-EMITTING ORGANIC LIGHT EMITTING DIODE DEVICE AND PRODUCING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing method for avoiding damage to an organic layer when forming an upper transparent electrode for extracting light in a top-emitting OLED device.

The organic light emitting device has each component in the same configuration as the lower electrode / light emitting layer / upper electrode on an insulating substrate such as a glass substrate, and emits light in the organic EL device by laminating a reflective metal as a lower electrode on the insulating substrate. The so-called "top emission method" in which a light is taken out from the upper electrode formed of a transparent or translucent material on the opposite side to the substrate has been put into practical use. In the case of such a top emission structure, it is usually comprised so that a lower electrode may function as an anode and an upper electrode may function as a transparent cathode (for example, refer patent document 1).

For this reason, how to improve the electron injection characteristic from the transparent electrode which is a cathode was a point. According to the above general configuration, the cathode is a metal such as Al (aluminum) which is a thin layer. For example, since the work function of Al is about 3.8 eV, an appropriate electron injection electrode, that is, a cathode, is realized in the above general configuration. However, in the case where a transparent electrode such as ITO is used as a cathode, for example, the work function of ITO or IZO is about 5 eV, so that the electron injection property is lowered.

In order to avoid such a problem, in recent years, although the lower electrode functions as a cathode and the upper electrode functions as a transparent anode in the front light emitting structure, a few have been proposed (for example, Non-Patent Document 1). Reference).

In the non-Patent Document 1, it has been found that injection of holes from the upper transparent electrode becomes a problem as a problem when the upper electrode is used as the transparent anode. This is considered to be due to the difficulty of injecting holes due to mismatches in the work functions of the anodes.

As a method of reducing the injection barrier of holes, a method of conventionally surface modifying (oxidizing) the surface of the side facing the organic layer of the anode by UV (ultraviolet) or surface treatment using plasma or the like is known. According to this method, the work function of the anode becomes large and the injection barrier of the hole becomes small.

The surface modification method described above was applicable when the lower electrode was used as the anode. However, when the upper transparent electrode is used as the anode as in the front light emitting structure described in Non-Patent Document 1, the above-described surface modification method is the upper transparent as the anode, because the upper transparent electrode is formed directly on the organic film. Since it cannot be used for the electrode, since the injection barrier of the hole of the upper transparent electrode is in a large state, the hole injection efficiency is extremely small. On the other hand, in Non-Patent Document 1, the hole injection efficiency is improved by forming an organic material of very high conductivity called pentacene as a hole injection layer in the base of the upper transparent electrode at about 40 nm. It is.

By the way, in the top light emitting structure described in the non-patent document 1, when forming the upper transparent electrode, that is, when forming a film such as ITO or IZO as the upper electrode, the sputtering method is usually used. In this case, however, the organic film of the base, i.e., pentacene, which is a hole injection layer, is damaged by heat, oxygen radicals or high energy ions during sputtering.

In order to prevent the deterioration of the luminescence properties due to sputter damage when forming the upper electrode, the film thickness of light transmission through an opaque metal thin film such as gold, nickel or aluminum is reduced to 1-20 nm on the organic layer. Laminating (patent document 2), between the hole transport layer and the transparent electrode, to provide a laminated structure consisting of a first metal layer for sputter damage protection or injection barrier adjustment, and a second metal layer such as Cr, Ti, Al for bonding adjustment The thing (patent document 3) is disclosed, respectively.

In order to avoid a decrease in the hole injection efficiency due to sputter damage when forming the upper electrode, after forming the hole transport layer, it is disclosed to form a hole injection layer by directly depositing a metal oxide such as vanadium oxide, molybdenum trioxide, etc. (For example, refer patent document 4, patent document 5, and patent document 6).

[Patent Document 1] Japanese Patent Publication No. 2000-507029

[Patent Document 2] Japanese Patent Laid-Open No. 2003-77651, Claim 3, Paragraph 0040, US Patent Publication No. 2003-45021

[Patent Document 3] Japanese Patent Laid-Open No. 2005-122910, Claim 3, Paragraph 0029, 0034

[Patent Document 4] Japanese Patent Laid-Open No. 2005-32618, paragraph 0042

[Patent Document 5] Japanese Patent Laid-Open No. 2006-324536, Paragraph 0032, 0033, US Patent Publication No. 2006-261333

[Patent Document 6] Japanese Patent Laid-Open No. 2005-259550, Paragraph 0078, 0083, 0094, US Patent Publication No. 2007-170843

[Non-Patent Document 1] T. Dobbertin et Al., "Inverted top-emitting organic Light-emitting diodes using sputter-deposited anodes", APPLIED PHYSICS LETTERS, (USA), Vol. 2, Number 2, p. 284-286

In view of the above phenomena, the present invention preferably includes a light emitting layer made of an organic EL material, a hole injection layer, and an upper electrode functioning as an anode sequentially formed on a lower electrode serving as a cathode. In the EL element, an object of the present invention is to prevent damage to the hole injection layer when forming the upper electrode and to secure high hole injection efficiency.

In the production method of the present invention, in order to achieve the above object, as an organic light emitting device having a light emitting layer between the anode and the cathode, a metal foil layer capable of forming a transparent conductive oxide under the upper transparent electrode for taking out light Inserting and oxidizing the upper transparent electrode.

The oxidized metal foil layer in this case is preferably a semiconductor and an electron acceptor.

The metal used as the semiconductor and the electron acceptor is not particularly limited and depends on the upper transparent electrode material. Examples thereof include indium, tin, tungsten, molybdenum, vanadium and ruthenium. Moreover, it is preferable that the thickness of a metal foil layer is 1-5 nm. When forming the upper transparent electrode, a film production method using plasma generated from a gas mixed with argon and oxygen, for example, plasma CVD or sputtering method can be used. Moreover, the film production method which uses sputtering and an oxygen radical source together can also be used.

By forming the top-emitting organic light emitting device by using the method of the present invention, it is possible to avoid damages such as oxidation of the organic layer generated when the upper transparent electrode is formed by the sputtering method, and to provide highly efficient and reliable organic light emitting device. Can provide.

EMBODIMENT OF THE INVENTION Below, embodiment is described based on sectional drawing of the element which showed this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure of schematic cross section of the organic light emitting element which shows embodiment of this invention.

The board | substrate 1 should just be an insulating flat board | substrate, and should have rigidity which can maintain the shape of an organic light emitting element. Usually, the board | substrate which consists of glass or resin is used. In this example, the substrate 1 is a glass substrate. The lower electrode 2 is formed on the glass substrate 1 as a cathode. In the present invention, a metal co-deposition of Mg and Ag was used. Since the thickness needs the function which can reflect light, it needs to be about 100 nm or more.

When the co-deposition film in which the metal having a low work function is doped is applied as the electron injection layer 3, the material of the lower electrode 2 only needs to be capable of transporting electrons, thereby increasing the range of choice. For example, the metal oxide film, such as Ag single layer, ITO, IZO, is also applicable. On the lower electrode 2, an organic layer including a light emitting layer 5 made of organic electroluminescent (EL) material, that is, an electron injection layer 3, an electron transport layer 4, a light emitting layer 5, a hole transport layer 6, The hole injection layer 7 is formed. As the organic layers 3 to 7 including these light emitting layers 5, hole transporting materials, electron transporting materials, fluorescent dyes and the like which are generally used in organic EL devices can be employed.

In order to obtain blue to cyan light emission, fluorescent brighteners such as benzothiazole series, benzoimidazole series, and benzoxazole series, metal chelated oxonium compounds, styrylbenzene series compounds, and aromatic dimethylide, for example, in the light emitting layer 5 Dean-based compounds and the like are preferably used.

Examples of the electron injection layer 3 include a quinoline derivative (for example, an organometallic complex having 8-quinolinol as a ligand), an oxadiazole derivative, a perylene derivative, a pyridine derivative, a pyrimidine derivative, a quinoxaline derivative, Diphenyl quinone derivative, nitro substituted fluorene derivative, etc. can be used. As the electron injection layer 3, an alkali metal, an alkaline earth metal, and oxides, fluorides, nitrides, borides such as LiF, and the like can be used.

As the electron transport layer 4, metal complex system (Alq3), an oxadiazole, a triazole type compound, etc. can be used. As the hole transport layer 6, a starburst amine, an aromatic diamine, or the like can be used.

As the hole injection layer 7, an aromatic amine compound, a starburst amine, a multimer of benzidine amine, copper phthalocyanine (CuPc), or the like can be used.

The thickness of these layers may be the same as in the prior art. However, in the present invention, since the thickness of the electron injection layer 3 is made of an inorganic material, the thickness is set to 1 nm to 5 nm in order to reduce the electrical resistance. Nm to 2 nm, most preferably 1 nm. For reference, in the case of an organic material, it is 1-20 nm, and 10 nm is preferable. The electron injection layer 3 does not need to have a uniform thickness, for example, may be formed in island shape. When formed in an island shape, the layer thickness refers to the height to the highest point of the island.

As a material of the metal foil layer 8 formed on the hole injection layer 7, the metal which can form a transparent conductive oxide is applicable. As used herein, the term "transparent" oxide refers to an oxide having a film thickness of 100 nm and a visible light transmittance of 90% or more. In addition, in this specification, the "oxide with conductivity" means the oxide whose electrical conductivity in room temperature is 1x10 <^-3> S / m or more.

In addition, it is preferable that the oxide of such a metal is a semiconductor and a metal used as an electron acceptor. As used herein, the term "electron acceptor" refers to a material whose work function is greater than or equal to that of the upper transparent electrode. Although it does not specifically limit as a metal which becomes such a semiconductor and becomes an electron acceptor, For example, indium, tin, tungsten, molybdenum, vanadium, ruthenium, etc. can be mentioned, One or more elements selected from these can be used.

These metals can be formed by the usual vacuum heating vapor deposition or the electron beam vapor deposition method, and the thickness is 1-5 nm is preferable. If it is thinner than this, the damage prevention effect is weakened, and if it is thicker than this, oxidation by the sputtering gas at the time of forming the transparent oxide of the upper anode 9 formed thereon becomes inadequate, and the transmittance | permeability falls. The thickness of the metal foil layer 8 is more preferably less than 2 nm.

When the top-emitting organic light emitting device is constituted in this manner, oxygen radicals, high energy particles, etc. generated when forming a transparent upper electrode functioning as an anode are blocked by the metal foil layer, and the hole injection layer is formed. Damage due to oxidation or decomposition of the organic molecular bonds due to impact by sputter particles is avoided. Also preferably, since the oxidative sputter gas oxidizes the metal foil layer when it comes in contact with the metal foil layer, the metal foil layer is changed to an oxide having a mostly transparent and conductive property in the process of forming the upper transparent electrode.

In addition, when a metal in which an oxide is an electron acceptor is selected as the metal foil layer, the hole injection property is not affected at all, and the effect of improving the hole injection property is imparted, thereby ensuring high hole injection efficiency.

In addition, in the case where the metal foil layer has a certain thickness, the surface on which the upper transparent electrode is stacked is almost oxidized, and as the depth progresses, the structure of the oxide gradually decreases, that is, the metal foil layer is not completely oxidized. Although it is also possible to consider a structure having no structure, by using an electron-accepting material in the hole injection layer 7 or by mixing and doping with an electron-accepting material, the hole injection property is secured with high probability even if the metal foil layer is not completely oxidized. .

The method of using a metal as a target material in the present invention has the advantage that the film forming rate can be increased compared to the method of directly depositing a metal oxide, and the mass productivity is excellent.

The upper transparent electrode 9 on the metal foil layer 8 is not particularly limited as long as it is a transparent electrode. For example, an oxide containing In, Sn, Zn, Sb, or the like, for example, indium tin oxide (ITO) or indium zinc oxide ( IZO) etc. can be used. In the formation step, a film production method using a plasma generated from a gas mixed with argon and oxygen, for example, a plasma CVD method or a sputtering method can be used. Moreover, the film production method which uses sputtering and an oxygen radical source together can also be used.

When using the sputtering method, it is preferable to form into a film in the atmosphere containing oxygen using a predetermined | prescribed target. For example, a mixed gas of oxygen and argon can be used as the discharge gas. Although the ratio of oxygen of discharge gas is not specifically limited, For example, the range of oxygen / discharge gas (molar ratio) = 0.01-0.05 can be employ | adopted. The minimum with more preferable value of oxygen / discharge gas is 0.01, and a more preferable upper limit is 0.05, More preferably, it is 0.02. In the present invention, the ratio of oxygen does not need to be constant through the film forming process, and for example, the oxidation of the metal foil layer 8 is promoted by using a discharge gas having a high oxygen ratio at the beginning of film formation, and the discharge is completed when the oxidation is completed. The remaining transparent electrode may be prepared by lowering the oxygen ratio of the gas.

By depositing the transparent electrode 9 by, for example, a sputtering method using a gas containing oxygen, the metal foil layer 8 is exposed to oxygen activated by plasma, and the metal foil layer 8 is oxidized to have a transparent and conductive property. It is formed as a layer.

For reference, in the above embodiment, the metal foil layer 8 is oxidized in the process of forming the metal foil layer 8 on the hole injection layer 7 and then forming the upper transparent electrode 9 as an anode. In addition, the lower anode, the hole injection layer described above according to the desired, the hole transport layer described above, the light emitting layer, the electron transporting layer if desired, and the electron injection layer if desired, are laminated on the substrate in the order described above. The metal foil layer may be oxidized in the process of forming a metal foil layer having a work function of oxide smaller than or equal to the upper transparent cathode on the electron injection layer, and then forming the upper transparent cathode.

EXAMPLE

(Example 1)

A schematic cross-sectional view schematically showing one embodiment of the configuration according to the present invention is shown in FIG. 1. First, by the conventional method, 20 nm was co-deposited on a board | substrate with Mg and Ag as 9: 1 as a reflective lower cathode. Then, 1 nm of Li was deposited as an electron injection layer by resistance heating deposition. Since the electron injection layer was thin at 1 nm, it was formed not in a film but in an island form. Thereon, 10 nm of tris (8-hydroxyquinoline) aluminum complexes are formed as the electron transporting layer 4, and the light emitting layer (4,4'-bis (2,2'-diphenylvinyl) biphenyl) is sequentially formed. 10 nm of a hole transport layer (4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) and 20 nm of a hole injection layer (copperphthalocyanine) were deposited.

Then, the metal foil layer 8 was formed into a film by thickness of 2 nm by the electron beam vapor deposition method. Mo (work function of about 4.45 eV) was used as the metal foil layer forming material. An element on which the metal foil layer 8 was formed was introduced into a DC sputtering device, and targeted at indium zinc oxide (IZO) (work function of about 4.7 eV), under an oxygen-argon atmosphere [oxygen / (oxygen + argon) (molar ratio). ) = 0.02] to form a 100 nm transparent anode to obtain a top emission organic light emitting device. By the above method, the metal foil layer 8 was completely oxidized to become transparent, conductive, and electron-accepting oxide. The drive voltage of the obtained device was 8V and the luminous efficiency was about 1.5 lm / W.

(Example 2)

A front-emitting device was obtained in the same manner as in Example 1, except that 10 nm of the metal foil layer was formed using Ru (ruthenium) as a material. In the obtained device, it was confirmed by XPS that the metal foil layer had a structure in which the surface of the side in contact with the upper transparent electrode was almost oxidized, and the ratio of oxide gradually decreased in the depth direction, but the driving voltage of the obtained device was 8V. The luminous efficiency was about 1.4 lm / W, indicating no adverse effect on the hole injection properties.

(Example 3)

First, a reflective lower anode (material MgAg) was formed on a substrate by a conventional method. Then, a hole injection layer (copperphthalocyanine) 20 nm, a hole transport layer (4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) 10 nm, a light emitting layer (4,4'- Bis (2,2'-biphenylvinyl) biphenyl) 30 nm and 10 nm of tris (8-hydroxyquinoline) aluminum complexes are formed in order as an electron carrying layer 4, and an electron injection layer is formed on it as a film | membrane. 1 nm was formed into an island shape instead.

Then, the metal foil layer 8 was formed into a film by thickness of 2 nm by the electron beam vapor deposition method. V (vanadium) was used for the metal foil layer. An element on which the metal foil layer 8 was formed was introduced into a DC sputtering device, and an upper transparent cathode was formed to a thickness of 100 nm with indium zinc oxide as a target to obtain a top emission organic light emitting device. The drive voltage of the obtained device was 8V and the luminous efficiency was about 1.6 lm / W.

(Comparative Example 1)

A front-emitting device was formed in the same manner as in Example 1 except that the metal foil layer 8 was not inserted. The obtained device had a low luminous efficiency of about 1/10 of the organic light emitting device obtained in Example 1, and a leakage current also flowed, and the characteristics as the device were not sufficiently obtained.

(Comparative Example 2)

A front-emitting device was obtained in the same manner as in Example 1 except that a metal thin layer of 5 nm was formed using Al as a material. In the obtained device, the transmittance of visible light decreased due to oxidation of the metal foil layer (Al) at the time of forming the transparent anode. The driving voltage was 8V and the luminous efficiency was about 0.8lm / W.

1 is a schematic cross-sectional view of an organic light emitting device manufactured according to an embodiment of the present invention.

* Explanation of symbols on the main parts of the drawings

1 substrate 2 lower electrode

3: electron injection layer 4: electron transport layer

5: organic light emitting layer 6: hole transport layer

7: hole injection layer 8: metal foil layer

9: upper transparent electrode

Claims (7)

A method of manufacturing a top-emitting organic light emitting device comprising at least a lower electrode, an organic layer including a light emitting layer, and an upper transparent electrode, on the substrate, after forming the organic layer, laminating a metal foil layer capable of forming a transparent conductive oxide. And a step of oxidizing the metal thin layer in the process of forming the upper transparent electrode. The method of claim 1, The oxidized metal thin layer is an electron acceptor, the method of manufacturing a top-emitting organic light emitting device. The method of claim 2, The method of manufacturing a top-emitting organic light emitting diode, characterized in that the oxidized metal foil layer comprises at least one element selected from the group consisting of indium, tin, tungsten, molybdenum, vanadium and ruthenium. The method of claim 1, The thickness of the said metal foil layer is 1-5 nm, The manufacturing method of the top emission organic light emitting element characterized by the above-mentioned. The method of claim 1, And the upper transparent electrode is formed by a film production method using a plasma generated from a gas containing argon and oxygen. The method of claim 1, The process of forming the upper transparent electrode, the method of manufacturing a top-emitting organic light emitting device, characterized in that the use of sputtering and oxygen radical generation source in combination. A top-emitting organic light emitting diode in which at least a lower electrode, an organic layer including a light emitting layer, and an upper transparent electrode are formed in this order on a substrate, and after forming the organic layer, a metal foil layer capable of forming a transparent conductive oxide is formed at 1 nm. A top emission organic light emitting device, which is obtained by laminating at ˜5 nm and then oxidizing the metal foil layer in the process of forming the upper transparent electrode.

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