JP2007305769A - Organic el element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element which sufficiently secures electron injectability, and which is capable of maintaining light transmittance. <P>SOLUTION: The organic EL element is constituted of an anode 2, an organic layer 10, and a cathode 3 which are on a substrate 1, while an interlayer 20 with a thickness of 5-50 nm is arranged between the organic layer 10 and the cathode 3. In this case, the interlayer 20 contains metal halide consisting of a metal, selected from alkali metal, alkaline earth metal, and rare earth metal; and a metal selected from alkaline earth metal, rare earth metal, Ag, Al, Cd, Cu, Mn, Ni, Pd, and Zn. The influence on a chelate material in the organic layer 10 due to the metal of the cathode 3 is suppressed by the interlayer 20 to suppress the decomposition of the chelate material, while the electron injection can be improved by semiconductive characteristics which are realized by mixing the alkali metal or the like with the metal halide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic EL element and a method for manufacturing the same.

  The organic EL device includes an anode and a cathode, and an organic layer disposed between them, injecting holes from the anode and electrons from the cathode, and combining the charges of these holes and electrons in the organic layer. Then, the organic molecules in the organic layer are excited to be in a high energy state, and the operation is performed based on the principle that the energy released when the organic molecules return to the base order is extracted as light. The charge injection efficiency from the anode and cathode at this time is an important factor for determining the device voltage of the organic EL element. If the charge injection efficiency is low, the applied voltage must be increased, but the charge injection efficiency is low. If it is high, the applied voltage can be lowered. The structure of such an organic EL element is roughly classified into a bottom emission structure in which light is extracted from the anode and a top emission structure in which light is extracted from the cathode.

  As a conventional structure of the above bottom emission, for example, a transparent anode is disposed on a transparent substrate, and three organic layers including a hole transport layer, a light emitting layer, and an electron transport layer are disposed on the anode, Furthermore, a structure in which a cathode is laminated on this organic layer is known. Among the above structures, the performance required for the interface between the cathode and the electron transport layer is good electron injectability and the ability to efficiently reflect the light emitted to the cathode side of the emitted light to the substrate side. It is desirable to have

  In order to satisfy such performance, for example, a structure using an Mg electrode containing 20% Ag, or LiF of about 1 nm is deposited as an electron injection layer between the cathode and the electron transport layer, and then Al is deposited. A structure (see Patent Document 1 below) and a structure using a chelate material typified by Alq3 as an electron injection layer are also known.

  Patent Document 2 below discloses a structure in which an interface between a cathode and an organic layer is partially covered with an alkali metal compound or an alkaline earth metal compound, and a metal cathode material and an alkali metal are formed on the organic layer. It is described that an alkali metal compound or the like is formed in an island shape on the organic layer when the above compound is vapor-deposited simultaneously.

  On the other hand, as a conventional structure of top emission for extracting light from the cathode, an anode is disposed on the substrate, and an organic layer composed of a hole transport layer, a light emitting layer, and an electron transport layer is disposed on the anode. A structure in which a transparent cathode is laminated on a layer is known. As in the bottom emission structure, a structure in which an electron injection layer is disposed between the cathode and the electron transport layer is often used.

  As the transparent cathode, an oxide (ITO) in which Sn or Zn is doped into In oxide is generally used. When such an oxide is deposited on an organic layer, electrons caused by highly active oxygen are used. Contamination of the injection layer is unavoidable, and fatal damage may be caused to the electron injection property. In addition, the transparent cathode is formed by a sputtering method, an electron beam evaporation method, or the like, but there is a problem of damage to the organic layer due to high energy particles generated during film formation.

Therefore, a structure in which a buffer layer for reducing damage is interposed between the cathode and the electron injection layer is used (see Patent Documents 3 and 4 below). As the buffer layer, an opaque cathode that is made as thin as possible to about 10 nm or less and has light transmittance is generally employed.
Japanese Patent Laid-Open No. 2001-85165 JP 2000-243567 A JP 2000-58265 A JP 2000-68063 A

  The Mg electrode including 20% Ag of the bottom emission structure, the structure in which Al is deposited after depositing about 1 nm of LiF, and the structure using a chelate material such as Alq3 have good electron injection properties as initial characteristics. Although it is obtained, the electron injecting property may be lowered when it is left standing. This is considered to be because the cathode metal (Al or Mg) is adsorbed on the chelate material and as a result, the chelate material is decomposed.

  In addition, in the Al / LiF structure of Patent Document 1, apparently ultra-thin LiF exists between the electron transport layer and the Al electrode, but in fact, as disclosed in Patent Document 2 above. When LiF is deposited on the organic layer, LiF grows in an island shape, and the surface of the electron transport layer is exposed, and the chelate material of the electron transport layer may be contaminated by the cathode metal.

  Furthermore, since the adsorption potential of Al chelate material to the π-electron system is relatively high at about 1.8 eV, once the cathode metal Al is adsorbed to the chelate material, it becomes difficult to desorb Al. In the same manner as above, the subsequent thermal exposure promotes the decomposition of the chelate material and decreases the electron injection property.

  On the other hand, in the case of a top emission structure, when the buffer layer is interposed between the transparent electrode and the electron injection layer, the light transmittance is lost if the thickness of the buffer layer is increased to improve the damage mitigation performance. There was a thing. That is, the light transmittance of Al (5 nm) / LiF (1 nm) is about 40%, but even if it is thicker than that, the damage mitigation performance cannot be sufficiently improved, but almost no light is emitted from the cathode. The current efficiency was reduced to about half.

  In summary, the problems of the bottom emission and top emission structures are that the electron injection properties are not sufficient, and in the case of the top emission structure, the light transmittance is insufficient. .

  Accordingly, an object of the present invention is to provide an organic EL element capable of sufficiently ensuring electron injection and maintaining light transmittance.

  In order to achieve the above object, an organic EL device of the present invention comprises an anode disposed on a substrate, an organic layer disposed on the anode, and a cathode disposed on the organic layer. Between the layer and the cathode, a metal selected from alkali metals, alkaline earth metals, rare earth metals, alkaline earth metals, rare earth metals, Ag, Al, Cd, Cu, Mn, Ni, Pd, Zn An intervening layer containing a metal halide made of a metal selected from the above is formed with a thickness of 5 to 50 nm.

  According to the present invention, between the organic layer and the cathode, a metal selected from an alkali metal, an alkaline earth metal, and a rare earth metal (hereinafter referred to as an alkali metal) and a metal halide made of an alkaline earth metal, and the like Since the intervening layer containing is disposed with a thickness of 5 to 50 nm, the electron injecting property can be sufficiently ensured.

  In addition, the metal halide composing the intervening layer has a strong ionic bond between the constituent element metal and the halogen element, so it does not affect the organic layer and decomposes organic molecules and chelating materials. Can be suppressed.

  In addition, the alkali metal, etc. constituting the intervening layer has a higher adsorption potential for metal halides than the adsorption potential of the chelate material for the π-electron system. Even if it is exposed on the surface, it can be selectively incorporated into the metal halide and the possibility of contamination of the chelating material can be reduced.

  Further, when alkali metal or the like is mixed with a metal halide, semiconducting characteristics appear, so that the electron injecting property can be improved.

  Further, by mixing an alkali metal or the like with a metal halide, a material having excellent light transmittance can be obtained. Therefore, it is also effective in extracting light from the cathode as in the top emission structure. Furthermore, since the resistance is low even if the intervening layer is formed to a thickness of 10 nm or more, it effectively acts as a buffer layer when forming a cathode on the organic layer by sputtering or the like. Damage can be reduced.

  In the organic EL device of the present invention, the intervening layer preferably contains at least two kinds of the metal halides. According to this, since a plurality of metal halides are contained in the intervening layer, the reactivity with an alkali metal or the like that is another component constituting the intervening layer is improved, and a more stable intervening layer is formed. be able to. Therefore, the electron injection property can be more sufficiently ensured, and the decomposition and contamination of the chelate material in the organic layer can be effectively prevented.

  In the organic EL device of the present invention, the cathode may be a transparent electrode made of an oxide. This can be suitably applied to a so-called top emission structure in which light is extracted from the cathode.

  The organic EL device manufacturing method of the present invention is the organic EL device manufacturing method in which an anode is formed on a substrate, an organic layer is formed on the anode, and a cathode is formed on the organic layer. Between a layer and the cathode, a metal selected from alkali metal, alkaline earth metal, rare earth metal, alkaline earth metal, rare earth metal, Ag, Al, Cd, Cu, Mn, Ni, Pd, Zn A metal halide made of a selected metal is alternately formed on the organic layer to form an intervening layer having a thickness of 5 to 50 nm.

  According to the present invention, since the alkali metal or the like and the metal halide are alternately formed on the organic layer to form the intervening layer, it is easy to adjust the film thickness of the intervening layer. An intervening layer having a desired thickness within the range can be easily formed.

  Another method for producing an organic EL device according to the present invention is an organic EL device in which an anode is formed on a substrate, an organic layer is formed on the anode, and a cathode is formed on the organic layer. In the production method, between the organic layer and the cathode, a metal selected from alkali metals, alkaline earth metals, rare earth metals, alkaline earth metals, rare earth metals, Ag, Al, Cd, Cu, Mn, A metal halide made of a metal selected from Ni, Pd, and Zn is simultaneously deposited on the organic layer to form an intervening layer having a thickness of 5 to 50 nm.

  According to the present invention, the alkali metal or the like and the metal halide are vapor-deposited on the organic layer at the same time, so that the intervening layer can be formed quickly and the productivity can be improved.

  According to the organic EL device of the present invention, since the intervening layer containing an alkali metal and a metal halide is disposed between the organic layer and the cathode in a thickness of 5 to 50 nm, the deterioration of the chelate material is prevented. At the same time, the electron injection property can be sufficiently secured, and the light transmission property can also be maintained.

  That is, since there is a strong ionic bond between the metal and the halogen element of the metal halide, the decomposition of the organic molecule and the chelate material is not promoted, and the alkali metal or the like is less than the adsorption potential of the chelate material to the π-electron system. However, since the adsorption potential with respect to the metal halide is higher, even if the chelate material in the organic layer is exposed, the possibility that the chelate material is contaminated by being selectively taken into the metal halide is small.

  Furthermore, when alkali metals are mixed with metal halides, semiconducting properties appear, so that the electron injection property can be improved and the material has excellent light transmission. Can be applied effectively.

  Hereinafter, an embodiment of the organic EL device of the present invention will be described with reference to FIG.

  As shown in FIG. 1, the organic EL element includes a transparent substrate 1, an anode 2 disposed on the transparent substrate 1, an organic layer 10 disposed on the substrate 1, and the organic layer 10 The cathode 3 is disposed above, and the intervening layer 20 is disposed between the organic layer 10 and the cathode 3.

  The substrate 1 has translucency in order to transmit light emitted from the organic layer 10, and glass or a transparent synthetic resin is preferably used as the material.

  A transparent anode 2 is disposed on the substrate 1. The anode 2 is made of a highly transparent material so as to transmit light emitted from the light emitting layer 13 of the organic layer 10 to be described later. For example, the anode 2 has high hole injection efficiency and low surface resistance. An oxide such as ITO is preferably used. The anode 2 can be formed by, for example, forming a film on the substrate 1 by sputtering, vapor deposition, or the like, and then patterning the film by photolithography. In this embodiment, the anode 2 is transparent and the cathode 3 is opaque and light is extracted from the anode 2 side. The so-called bottom emission structure is used, but the anode 2 is opaque and the cathode 3 is transparent from the cathode 3 side. A so-called top emission structure that extracts light can also be used.

  An organic layer 10 is disposed on the anode 2. In this embodiment, the organic layer 10 has a structure in which a hole injection layer 11, a hole transport layer 12, a light emitting layer 13, and an electron transport layer 14 are sequentially stacked.

  The hole injection layer 11 is for maintaining the efficiency of hole injection from the anode 2, and the hole transport layer 12 for smoothly moving holes to the light emitting layer 13 on the hole injection layer 11. Is formed. The hole transport layer 12 is not particularly limited, and examples thereof include tetraarylbenzidine compounds (tetraaryldiamine or tetraphenyldiamine: TPD), aromatic tertiary amines, hydrazone derivatives, carbazole derivatives, triazole derivatives, imidazole derivatives, amino acids. Preferred combinations can be appropriately selected from compounds such as oxadiazole derivatives having a group and polythiophene.

  A light emitting layer 13 is formed on the hole transport layer 12. Although it does not specifically limit as the light emitting layer 13, For example, when obtaining blue or green light emission, for example, fluorescent whitening agents, such as a benzothiazole type, a benzimidazole type, a benzoxazole type, a metal chelating oxinoid compound, styryl Benzene compounds and aromatic dimethylidin compounds are preferably used.

  On the light emitting layer 13, an electron transporting layer 14 for smoothly moving electrons from the cathode 3 to the light emitting layer 13 is formed. Although it does not specifically limit as this electron carrying layer 14, For example, the chelate material which consists of organometallic complexes, such as a tris (8-quinolinolato) aluminum, can be used.

  The hole injection layer 11, the hole transport layer 12, the organic light emitting layer 13, and the electron transport layer 13 can be formed by a known means such as vapor deposition.

  An intervening layer 20 is disposed on the organic layer 10, and the cathode 3 is disposed via the intervening layer 20. Similarly to the anode 2, the cathode 3 is formed by sputtering, vapor deposition, or the like, and is formed by a photolithographic pattern method or the like as necessary. As the cathode 3, a metal film or the like that has high electron injection efficiency and can reflect the light emitted from the light emitting layer 13 in the direction of the substrate 1 is used. For example, Al, Mg—Ag alloy, Al—Li alloy, etc. Preferably used. In addition, as described above, in the case of a so-called top emission structure in which the anode 2 is opaque and the cathode 3 is transparent and light is extracted from the cathode 3, ITO which is an oxide of In and Sn is preferably used.

  And the intervening layer 20 arrange | positioned between the electron carrying layer 14 of the organic layer 10 and the cathode 3 is a metal (alkali metal etc.) chosen from alkali metal, alkaline earth metal, and rare earth metal, and alkaline earth. It contains metal halides composed of metals selected from metals, rare earth metals, Ag, Al, Cd, Cu, Mn, Ni, Pd, and Zn. The intervening layer 20 is disposed on the electron transport layer 14 of the organic layer 10 with a thickness of 5 to 50 nm, preferably 10 to 40 nm.

  Thus, since the intervening layer containing an alkali metal or the like and a metal halide is disposed between the electron transport layer 14 and the cathode 3 with a thickness of 5 to 50 nm, sufficient electron injection property is ensured. can do.

  That is, the metal halide constituting the intervening layer 20 does not promote the decomposition of organic molecules and chelate materials because there is strong ionic bonding between the constituent elements, the metal and the halogen element.

  Alkali metal and alkaline earth metal have an adsorption potential of 0.5 eV for the π-electron system of the chelate material and an adsorption potential of 1.5 eV for the metal halide, and the adsorption potential for the metal halide is higher. Yes. Therefore, even if the chelate material of the electron transport layer 14 is exposed on the surface at the initial stage of film formation of the intervening layer 20, alkali metal or the like is selectively taken into the metal halide, so that the chelate material can be contaminated. The sex can be reduced.

  Thus, since the alkali metal etc. and metal halide which comprise the intervening layer 20 have strong mutual bonding power, they do not affect the chelate material, and the organic layer 10 and the cathode 3 are sufficiently connected. By separating, the influence on the chelate material such as Al as the cathode metal can be reduced. Therefore, the luminous efficiency and durability of the organic layer 10 can be maintained over a long period of time.

  Further, when alkali metal or the like is mixed with a metal halide, semiconducting characteristics appear, so that the electron injecting property can be improved. That is, since the metal halide is close to an insulator, when the alkali metal and the metal halide are mixed to form a mixed layer, the work function is controlled to a value between the alkali metal and the metal halide, The work function can be lowered, and thereby the electron injection property to the electron transport layer 14 can be improved.

  Furthermore, since the metal halide is transparent, when an alkali metal or the like and a metal halide are mixed, a material having excellent light transmission can be obtained, and light is extracted from the cathode as in the top emission structure. It is also effective in some cases. Furthermore, even if the intervening layer 20 is formed to a relatively large thickness of 10 nm or more, it has low resistance, and therefore when the cathode is formed on the organic layer by sputtering or the like, it effectively acts as a buffer layer, and the organic layer Can reduce damage.

  In addition, when the intervening layer 20 is thinner than 5 nm, the separation performance between the organic layer 10 and the cathode 3 cannot be sufficiently exerted, and when it is thicker than 50 nm, it is light transmissive when applied to a top emission structure. Is unfavorable because it decreases.

  In addition, the intervening layer 20 preferably contains at least two kinds of the metal halides. According to this, since the intervening layer 20 contains a plurality of metal halides, the reactivity with an alkali metal or the like which is another component constituting the intervening layer 20 is improved, and the intervening layer is more stable. 20 can be formed. Therefore, the electron injection property can be more sufficiently ensured, and the decomposition and contamination of the organic layer 10 can be effectively prevented.

  In the organic EL element, the organic layer 10 has a four-layer structure, but various layer structures can be employed. For example, the following layer structure may be used.

(1) Anode 2—organic layer 10 (light emitting layer 13 only) —cathode 3
(2) Anode 2—organic layer 10 (hole transport layer 12—light emitting layer 13) —cathode 3
(3) Anode 2—organic layer 10 (hole injection layer 11—hole transport layer 12—light emitting layer 13) —cathode 3
(4) Anode 2—organic layer 10 (light emitting layer 13—electron transport layer 14) —cathode 3
(5) Anode 2—organic layer 10 (hole transport layer 12—light emitting layer 13—electron transport layer 14) —cathode 3
The organic EL element demonstrated above is manufactured as follows, for example.

  That is, first, the anode 2 is formed on the substrate 1 by sputtering or the like, and the hole injection layer 11, the hole transport layer 12, the light emitting layer 13, and the electron transport layer 14 are sequentially formed on the anode 2 by vapor deposition or the like. Then, the organic layer 10 is formed. Then, an intervening layer 20 made of an alkali metal or the like and a metal halide is formed on the organic layer 10.

  As a method for forming the intervening layer 20 at this time, (a) an alkali metal or the like and a metal halide are alternately formed on the organic layer 10 to form the intervening layer 20 having a thickness of 5 to 50 nm. Method (b) A method in which an alkali metal or the like and a metal halide are simultaneously deposited on the organic layer 10 to form the intervening layer 20 having a thickness of 5 to 50 nm is preferably employed.

  In the case of the formation method of (a), it is easy to adjust the thickness of the intervening layer 20, and the intervening layer 20 having a desired thickness can be easily formed in the range of 5 to 50 nm. In the case of the method, the intervening layer 20 can be formed quickly, and the productivity can be improved.

  On the intervening layer 20 thus formed, the cathode 3 is formed by a sputtering method or the like to manufacture an organic EL element.

(1) Production of organic EL elements of Examples and Comparative Examples Example 1
The organic EL element shown in FIG. 1 having a bottom emission structure in which light is extracted from the anode 2 was produced.

  On the glass substrate 1, ITO made of amorphous In 2 O 3: ZnO (ZnO molar ratio 5%) was formed to a thickness of 200 nm by sputtering. On this ITO, patterning for forming the anode 2 was performed by a normal photo process using a mask capable of obtaining a stripe pattern of 2 mm line and 0.5 mm pitch, and the anode 2 was formed. Then, the surface of the anode 2 was cleaned with oxygen plasma at room temperature.

Next, the substrate 1 on which the transparent anode 2 is formed is mounted in a resistance heating vapor deposition apparatus, and the hole injection layer 11, the hole transport layer 12, the light emitting layer 13, and the electron transport layer 14 are sequentially formed without breaking the vacuum. The organic layer 10 was formed by forming a film. During film formation, the internal pressure of the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa. As the hole injection layer 11, 100 nm of copper phthalocyanine (CuPc) was laminated. As the hole transport layer 12, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (α-NPD) was laminated to 20 nm. As the light emitting layer 13, 4,4′-bis (2,2′-diphenylvinyl) biphenyl (DPVBi) was laminated to 30 nm. As the electron transport layer 14, 20 nm of aluminum chelate (Alq) was laminated.

After the organic layer 10 was formed, an intervening layer 20 was formed on the organic layer 10. That is, the intervening layer 20 in which Ca, which is an alkaline earth metal, was selected as the metal and MgF ₂ was selected as the metal halide, was formed by vapor deposition using the resistance heating vapor deposition apparatus. More specifically, a cycle of depositing 1 nm of MgF ₂ on the electron transport layer 14 and depositing 1 nm of Ca on the electron transport layer 14 is repeated 20 times to form an intervening layer 20 having a thickness of 40 nm. Formed.

  Then, a cathode 3 was formed by laminating 200 nm of Al on the intervening layer 20.

Example 2
Except for the configuration of the intervening layer 20, an organic EL element having a bottom emission structure similar to that of Example 1 was produced.

That is, as the metal halide constituting the intervening layer 20, in addition to MgF ₂ , CaF ₂ was further added. Specifically, a fluoride film in which MgF ₂ and CaF ₂ have a molecular ratio of 1: 1 is formed on the electron transport layer 14 at a thickness of 1 nm by a co-evaporation method, and Ca is further evaporated by 1 nm thereon. The cycle of film formation was repeated 20 times to form an intervening layer 20 having a thickness of 40 nm.

Example 3
An organic EL element having a top emission structure in which light is extracted from the cathode 3 was produced. In this case, the configuration is the same as in Example 1 except that the configurations of the anode 2 and the cathode 3 are different.

That is, as the anode 2, CrB was formed to a thickness of 200 nm by sputtering and patterned to form an opaque anode 2. On the other hand, as the cathode 3, a transparent cathode 3 was formed by depositing ITO made of amorphous In ₂ O ₃ : ZnO (5% by ZnO molar ratio) with a thickness of 100 nm by a sputtering method.

Comparative Example 1
An organic EL element having a bottom emission structure similar to that of Example 1 was prepared except that a layer made of LiF was formed instead of the intervening layer 20 being formed.

  That is, a LiF layer having a thickness of 0.5 nm is formed on the electron transport layer 14 by using a mask capable of obtaining a stripe pattern having a 2 mm line and a 0.5 mm pitch perpendicular to the transparent anode 2 line. A film was formed by vapor deposition using a heating vapor deposition apparatus.

Comparative Example 2
An organic EL element having a top emission structure similar to that of Example 3 was fabricated except that a layer made of Mg was formed instead of the intervening layer 20 being formed.

  That is, on the electron transport layer 14, a Mg layer containing 20% by mass of Ag at a thickness of 10 nm using a mask capable of obtaining a stripe pattern having a 2 mm line and a 0.5 mm pitch perpendicular to the line of the anode 2. The film was formed by vapor deposition using the resistance heating vapor deposition apparatus.

(2) Performance Evaluation of Organic EL Elements of Examples and Comparative Examples Next, for Examples 1 to 3 and Comparative Examples 1 and 2, fluctuations in current density when a predetermined voltage is applied, and light emission The current efficiency was evaluated.

Test example 1
The relationship between the current density (A / cm ² ) and the driving voltage (V) of each organic EL element of Example 1 and Comparative Example 1 was measured, and the result is shown in FIG. In addition, the electroluminescence (EL) light output and the drive current were measured to determine the current efficiency (cd / A) during light emission.

  Referring to FIG. 2, it can be seen that Example 1 (indicated by A1 in the figure) and Comparative Example 1 (indicated by B1 in the figure) have substantially the same current density. Moreover, current efficiency was 4.5 cd / A in both Example 1 and Comparative Example 1, and superiority or inferiority was not recognized.

Test example 2
The relationship between the current density (A / cm ² ) and the drive voltage (V) was measured after leaving the organic EL elements of Example 1 and Comparative Example 1 at a temperature of 85 ° C. for 200 hours, and the result Is shown in FIG. In addition, the electroluminescence (EL) light output and the drive current were measured to determine the current efficiency (cd / A) during light emission.

  Referring to FIG. 3, in Comparative Example 1 (B1), the current density is reduced to about 1/8 compared to Test Example 1, whereas in Example 1 (A1), compared to Test Example 1. It can be seen that the decrease in current density remains below 10%. Therefore, the effect of preventing the chelate material from being decomposed and contaminated by the intervening layer 20 was clearly confirmed.

  In addition, the current efficiency of Comparative Example 1 decreases to 0.5 cd / A, whereas the current efficiency of Example 1 clearly remains at a relatively low decrease of 3.5 cd / A. It became. Therefore, it was found that the light emission efficiency of the organic EL element can be maintained by the intervening layer 20.

Test example 3
For Example 2 having the intervening layer 20 containing two kinds of MgF ₂ and CaF ₂ as metal halides, as in Test Example 2, the current density (A / cm ² ) −drive voltage (V) was measured. In addition, the electroluminescence (EL) light output and the drive current were measured to determine the current efficiency (cd / A) during light emission.

  Although illustration is omitted, the current density was able to maintain the same level as Example 1 in Test Example 2. Further, in the case of Example 1 where the metal halide is a kind, the current efficiency after being left at 85 ° C. for 200 hours is slightly decreased (see Test Example 2), whereas the current efficiency of Example 2 is 4.2 cd / Compared with A and Test Example 1, it was found that there was almost no decrease. Thus, it can be understood that if two or more kinds of metal halides are contained, decomposition and contamination of the chelate material are more effectively prevented, and the effect is effective over a long period of time.

In Test Example 2, the reason why the current efficiency of Example 1 decreased to 3.5 cd / A is considered as follows. That is, when MgF ₂ which is a metal halide is deposited on the electron transport layer 14 of the organic layer 10, as shown in Patent Document 2, MgF ₂ grows in an island shape, and the electron transport layer This is because the entire surface 14 is partially exposed without being covered, and therefore, the contamination of the electron transport layer 14 with Ca to be formed thereafter is inevitable to some extent. As the reason why the MgF ₂ grows in an island shape, when comparing the energy state of aggregation and dispersion state, because the energy in the aggregate state very small, MgF ₂ is agglomerated with natural, 4 ( As shown in a), it is presumed to be island-shaped.

  On the other hand, the mechanism for suppressing the decrease in current efficiency when using a plurality of metal halides of Example 2 is presumed as follows.

That is, as described above, in the case of MgF ₂ alone, as shown in FIG. 4 (a), it grows in an island shape (see symbol S in FIG. 4 (a)), but the mixture of MgF ₂ and CaF ₂ In this case, since the energy difference is smaller than that in the case of a single body, it is considered that the growth proceeds as an island W smaller than the single body as shown in FIG.

When a metal such as Ca is formed on the metal halide, the film is formed on a large island S in the case of MgF ₂ alone, so that the contact area with Ca is small and mixing at the molecular level is not so much. Not proceed. On the other hand, in the case of a mixture of MgF ₂ and CaF ₂ , since Ca is formed on a plurality of small islands W, the contact area with Ca increases, and the metal and metal halide are mixed smoothly. It becomes like this. Therefore, since the contamination to the electron carrying layer 14 of the organic layer 10 is prevented more reliably, it is guessed that the reduction in current efficiency could be suppressed.

Test example 4
The relationship between the current density (A / cm ² ) and the drive voltage (V) of each organic EL element having the top emission structure of Example 3 and Comparative Example 2 was measured, and the result is shown in FIG. For comparison, the measurement result of Comparative Example 1 having a bottom emission structure is also shown in FIG. In addition, the electroluminescence (EL) light output and the drive current were measured to determine the current efficiency (cd / A) during light emission.

  Referring to FIG. 5, the comparative example 2 (indicated by B2 in the figure) of the top emission structure has a higher element resistance than the comparative example 1 (B1) of the bottom emission structure, and the current is less likely to flow by one digit or more. I can see that In contrast, in Example 3 (indicated by A3 in the figure) having a top emission structure, it can be understood that the current density is only 40% lower than that in Comparative Example 1 (B1). In addition, it was found that the current efficiency was 1.5 cd / A in the case of Comparative Example 2 and 3.5 cd / A in the case of Example 3. As described above, according to the organic EL element of the present invention, it can be applied not only to the bottom emission structure but also to the top emission structure, and decomposition and contamination of the chelate material can be effectively prevented.

  INDUSTRIAL APPLICABILITY The present invention can be used as an organic EL element that can sufficiently ensure electron injectability and can maintain light transmittance.

It is sectional drawing which shows one Embodiment of the organic EL element of this invention. It is a graph which shows the relationship between the voltage and current density in the bottom emission structure of an organic EL element. 5 is a chart showing the relationship between voltage and current density after holding for a predetermined time at a predetermined temperature in the bottom emission structure of the organic EL element. The growth process of the metal halide of the organic EL element of this invention is shown, (a) is explanatory drawing in case a metal halide is single substance, (b) is explanatory drawing in case there are two or more metal halides. It is a graph which shows the relationship between the voltage and the current density in the top emission structure of an organic EL element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Cathode 10 Organic layer 11 Hole injection layer 12 Hole transport layer 13 Light emitting layer 14 Electron transport layer 20 Intervening layer

Claims (5)

In an organic EL device comprising an anode disposed on a substrate, an organic layer disposed on the anode, and a cathode disposed on the organic layer,
Between the organic layer and the cathode, a metal selected from alkali metals, alkaline earth metals, rare earth metals, alkaline earth metals, rare earth metals, Ag, Al, Cd, Cu, Mn, Ni, Pd An organic EL device, wherein an intervening layer containing a metal halide made of a metal selected from Zn is formed with a thickness of 5 to 50 nm.   The organic EL device according to claim 1, wherein the intervening layer contains at least two kinds of the metal halides.   The organic EL device according to claim 1, wherein the cathode is a transparent electrode made of an oxide. In the method for producing an organic EL device, an anode is formed on a substrate, an organic layer is formed on the anode, and a cathode is formed on the organic layer.
Between the organic layer and the cathode, a metal selected from alkali metals, alkaline earth metals, rare earth metals, alkaline earth metals, rare earth metals, Ag, Al, Cd, Cu, Mn, Ni, Pd, A method for producing an organic EL element, wherein metal halides made of metal selected from Zn are alternately formed on the organic layer to form an intervening layer having a thickness of 5 to 50 nm. In the method for producing an organic EL device, an anode is formed on a substrate, an organic layer is formed on the anode, and a cathode is formed on the organic layer.
Between the organic layer and the cathode, a metal selected from alkali metals, alkaline earth metals, rare earth metals, alkaline earth metals, rare earth metals, Ag, Al, Cd, Cu, Mn, Ni, Pd, A method for producing an organic EL device, wherein a metal halide comprising a metal selected from Zn is vapor-deposited simultaneously on the organic layer to form an intervening layer having a thickness of 5 to 50 nm.

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