JP2005251587A - Organic el device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL device wherein electron injection efficiency from an electron injection electrode to an organic luminescent layer is fully improved, and which has excellent light emitting efficiency. <P>SOLUTION: This organic EL device is provided with the organic luminescent layer 10 between a hole injection electrode 1 and the electron injection electrode 2 facing each other, a first inorganic layer 12 containing transition metal oxide formed on a surface on the side of the electron injection electrode 2 of the organic luminescent layer 10, and a second inorganic layer 14 containing an alkali metal or an alkaline earth metal formed on a surface on the side of the electron injection electrode 2 of the first inorganic layer 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic EL (electroluminescence, electroluminescence) element.

  An organic EL element used for an organic EL display or the like includes, for example, a light-emitting layer containing a light-emitting organic compound such as a fluorescent organic compound or a phosphorescent organic compound, a hole injection electrode (anode), and an electron injection electrode ( A device sandwiched between cathodes), and an element that excites and emits light by applying an electric field from the electrode to the light-emitting organic compound. Compared to inorganic EL elements, such organic EL elements have a simple driving method and low driving voltage, and are excellent in element characteristics such as luminance and light emission efficiency (quantum yield). It is about to reach the stage of conversion.

In this organic EL element, a functional layer such as an injection layer or a transport layer for efficiently injecting and transporting holes or electrons from the electrode to the light emitting layer is provided between the electrode and the light emitting layer for the purpose of improving the light emission efficiency. Is provided. Various studies for realizing further improvement in the light emission efficiency of the organic EL element have been made on the functional layer for improving the efficiency of injection and transportation of holes or electrons into the light emitting layer. In these studies, as a method for improving the electron injection (transport) efficiency from the electron injection electrode to the light emitting layer, for example, in Patent Document 1, an insulating metal oxide is provided between the light emitting layer and the electron injection electrode. It has been proposed to insert. In Patent Document 2, it is proposed to insert an inorganic electron transport layer between the light emitting layer and the electron injection electrode.
Japanese Patent Laid-Open No. 5-3080 JP-A-11-149985

  However, as in the inventions described in Patent Documents 1 and 2, electrons from the electron injection electrode to the light emitting layer are simply inserted by inserting a metal oxide or an inorganic electron transport layer between the light emitting layer and the electron injection electrode. The present inventor has found that the effect of improving the injection efficiency and the light emission efficiency of the organic EL element is not necessarily sufficient.

  The present invention has been made in view of the above-described problems of the prior art, and provides an organic EL element having an excellent light emission efficiency with sufficiently improved electron injection efficiency from the electron injection electrode to the organic light emitting layer. The purpose is to do.

  As a result of intensive studies to achieve the above object, the present inventor can achieve the above object as long as it is an organic EL element having two inorganic layers between an organic light emitting layer and an electron injection electrode. As a result, the present invention has been completed.

  That is, the present invention includes an organic light emitting layer between an opposing hole injection electrode and an electron injection electrode, and a first inorganic layer containing a transition metal oxide is formed on the surface of the organic light emitting layer on the electron injection electrode side. Provided is an organic EL device characterized in that a second inorganic layer containing an alkali metal or an alkaline earth metal is formed on the surface of the first inorganic layer on the electron injection electrode side.

  Here, the state of the first inorganic layer formed on the surface of the organic light emitting layer on the electron injection electrode side is not particularly limited. For example, it is formed so as to cover the entire surface of the organic light emitting layer on the electron injection electrode side. It may be in a state of being formed, or may be in a state of being formed in an island shape so as to partially cover the surface of the organic light emitting layer on the electron injection electrode side. Further, the state of the second inorganic layer is not particularly limited, and may be, for example, a state formed so as to cover the entire surface of the first inorganic layer on the electron injection electrode side. It may be in an island shape so as to partially cover the surface on the injection electrode side.

  When the first inorganic layer is formed in an island shape, the second inorganic layer covers the entire surface of the first inorganic layer on the electron injection electrode side and is not covered by the first inorganic layer. You may form so that the surface by the side of the electron injection electrode of an organic light emitting layer may be covered. In addition, when the second inorganic layer is formed in an island shape in contact with the electron injection electrode, the first inorganic layer covers the entire surface of the second inorganic layer on the organic light emitting layer side, and the second inorganic layer You may form so that the surface by the side of the organic light emitting layer of the electron injection electrode which is not covered with the layer may be covered. Furthermore, the constituent materials of each layer may be partially mixed at the interface between the first inorganic layer and the second inorganic layer.

  If it is the organic EL element of this invention which has the said structure, by providing a 1st inorganic layer and a 2nd inorganic layer between an electron injection electrode and an organic light emitting layer, it is from an electron injection electrode to an organic light emitting layer. The electron injection efficiency can be sufficiently improved, and excellent luminous efficiency can be obtained.

  Here, since the alkali metal and alkaline earth metal contained in the second inorganic layer are metals having a sufficiently low work function, an electron injection barrier (an energy barrier necessary for injecting electrons into the organic light emitting layer) This is considered to play a role of effectively improving the electron injection efficiency from the electron injection electrode to the organic light emitting layer.

  However, the present inventors have found that when the second inorganic layer is formed alone between the electron injection electrode and the organic light emitting layer, sufficient light emission efficiency cannot always be obtained. This is presumably because deactivation of the luminescence excitons occurs at the interface between the alkali metal or alkaline earth metal and the organic light emitting layer.

  However, by forming the first inorganic layer containing the transition metal oxide between the second inorganic layer and the organic light emitting layer, it is possible to prevent the deactivation of the luminescence excitons, and the organic injection from the electron injection electrode. The present inventor has found that the efficiency of electron injection into the light emitting layer can be effectively improved, and as a result, excellent light emission efficiency can be obtained. In addition, transition metal oxides have a higher specific resistance than alkali metals and alkaline earth metals, so they are considered to play a role of hole (hole) barrier, and enhance recombination between electrons and holes. This can contribute to the improvement of luminous efficiency.

  Furthermore, since transition metal oxides easily change the valence of the transition metal, the bonding state is changed so that electron injection can be performed more stably at the interface with the light emitting layer. It is guessed. As a result, the dipole moment at the interface between the transition metal oxide and the light emitting layer changes in a direction in which the electron injection efficiency is improved, and the transition metal oxide and the organic light emitting layer are caused by the change in the dipole moment. It is presumed that the work function at the interface is smoothed, the electron injection barrier is reduced, sufficient electron injection efficiency is obtained, and excellent light emission efficiency is obtained.

  For the reasons as described above, the inventor presumes that the organic EL device of the present invention has excellent luminous efficiency.

  Moreover, in the said organic EL element, it is preferable that an organic light emitting layer is a layer containing a hydrocarbon compound.

  Thereby, the change of the dipole moment at the interface between the organic light emitting layer and the transition metal oxide is likely to occur, the electron injection efficiency is improved, and the excellent light emission efficiency can be obtained.

  In addition, in the said patent document 2, the organic EL element of the structure which laminated | stacked the fluoride layer, the inorganic electron carrying layer, and the electron injection electrode in order on the organic light emitting layer is also described, and electron injection is carried out by insertion of a fluoride layer. In particular, when the organic light emitting layer is a layer containing a hydrocarbon compound, electrons are not sufficiently injected from the fluoride layer to the organic light emitting layer, and the light emission efficiency is improved. The present inventor has found that the effect cannot be sufficiently obtained.

  On the other hand, with the organic EL device of the present invention, even if the organic light emitting layer is a layer containing a hydrocarbon compound or a layer made of a hydrocarbon compound, excellent light emission efficiency can be obtained as described above. it can.

  Further, in the organic EL element, the transition metal oxide is an oxide of at least one metal selected from the group consisting of Mo, Nb, W, Ta, Y, Cr, Re, Co, V, and Mn. Is preferred.

  In such a transition metal oxide, since the valence of the transition metal changes more easily, the bonding state at the interface with the organic light emitting layer is likely to change, thereby improving the electron injection efficiency of the dipole moment. By changing the direction, excellent luminous efficiency can be obtained.

  In the organic EL device of the present invention, the second inorganic layer is preferably a layer made of an alkali metal or an alkaline earth metal, or a layer further containing a transition metal oxide.

  When the second inorganic layer is a layer made of an alkali metal or an alkaline earth metal, a sufficiently low work function can be obtained, so that excellent electron injection efficiency can be obtained and excellent light emission efficiency can be obtained.

  When the second inorganic layer is a layer further containing a transition metal oxide, the presence of the transition metal oxide can stabilize the alkali metal or alkaline earth metal and improve the hole barrier property. Excellent luminous efficiency can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the electron injection efficiency from an electron injection electrode to an organic light emitting layer is fully improved, and the organic EL element which has the outstanding light emission efficiency can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings depending on cases, but the present invention is not limited to the following embodiments. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  FIG. 1 is a schematic cross-sectional view showing a first embodiment (single-layer organic EL) of an organic EL element according to the present invention. An organic EL element 100 shown in FIG. 1 has a structure in which an organic light emitting layer 10 is sandwiched between a hole injection electrode (anode) 1 and an electron injection electrode (cathode) 2 that are arranged to face each other. The hole injection electrode 1 is formed on the substrate 4. Further, a first inorganic layer 12 containing a transition metal oxide is formed on the organic light emitting layer 10, and a second inorganic layer 14 containing an alkali metal or an alkaline earth metal is formed on the first inorganic layer 12. Is formed.

  The organic EL element of the present embodiment having such a configuration has a configuration in which the organic light emitting layer 10, the first inorganic layer 12, the second inorganic layer 14, and the electron injection electrode 2 are sequentially stacked, so that the electron injection electrode Electron injection from 2 into the organic light emitting layer 10 is performed efficiently, and excellent light emission efficiency can be obtained.

  Hereinafter, each layer which comprises the organic EL element of this embodiment is demonstrated in detail.

(substrate)
The constituent material of the substrate 4 is not particularly limited as long as it is used as a substrate of a conventional organic EL element. Therefore, as such a substrate 4, an amorphous substrate such as glass and quartz, a crystal substrate such as Si, GaAs, ZnSe, ZnS, GaP, and InP, Mo, Al, Pt, Ir, Au, Pd, SUS, etc. The metal substrate etc. can be mentioned. Further, a thin film made of a crystalline or amorphous ceramic, metal, organic substance or the like formed on a predetermined substrate may be used.

  Further, the emission color may be adjusted by using a color filter film, a color conversion film containing a fluorescent substance (fluorescence conversion filter film), or a dielectric reflection film on the substrate 4.

  As the color filter film, a color filter used in a liquid crystal display or the like can be used. By adjusting the characteristics of the color filter according to the emission color of the organic EL element 100, the extraction efficiency or the color purity is optimized. It tends to be possible.

  In addition, by using a color filter capable of cutting short-wavelength external light that is absorbed by a constituent material used in an organic EL element, the light resistance and display contrast of the element tend to be improved. Furthermore, an optical thin film such as a dielectric multilayer film may be used instead of the color filter.

  The fluorescence conversion filter film absorbs light emitted from the organic EL element, and emits light from the phosphor in the filter film, thereby performing color conversion of the emission color. The composition is formed of three of a binder and a fluorescent material, and further a light absorbing material as required.

  Basically, a fluorescent material having a high fluorescence quantum yield may be used as the fluorescent material, but it is preferable that the organic EL element 100 has strong absorption in the emission wavelength region. In practice, laser dyes are suitable. For example, rhodamine compounds, perylene compounds, cyanine compounds, phthalocyanine compounds (including subphthalocyanines), naphthalimide compounds, condensed ring hydrocarbon compounds, condensed complex compounds, and the like. A ring compound, a styryl compound, a coumarin compound, or the like can be used.

  The binder can be used without particular limitation as long as it does not quench the fluorescence, and among them, it can be finely patterned by photolithography or printing. And preferred. Further, it is more preferable that the material is not damaged during the deposition of ITO or IZO.

  The light absorbing material is preferably used when light absorption of the fluorescent material is insufficient. The light absorbing material can be used without any particular limitation as long as it does not quench the fluorescence of the fluorescent material.

(Hole injection electrode)
The constituent material of the hole injection electrode (anode) 1 is not particularly limited as long as it is used in a conventional organic EL element. Among these, a material that can efficiently inject holes into the organic light emitting layer 10 is preferable. From this viewpoint, a material having a work function of 4.5 to 5.5 eV is preferable.

  In this embodiment, since the substrate 4 side is the light extraction side, the transmittance at a wavelength of 400 to 700 nm, which is the emission wavelength region of the organic EL element, particularly the transmittance of the hole injection electrode 1 at the wavelength of each RGB color. Is preferably 50% or more, more preferably 80% or more, and still more preferably 90% or more. When the transmittance of the hole injection electrode 1 is less than 50%, the light emission from the organic light emitting layer 10 tends to be attenuated, making it difficult to obtain the luminance necessary for image display.

The hole injection electrode 1 having a high light transmittance can be configured using a transparent conductive film composed of various oxides. As such a material, indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO) and the like are preferable. It is particularly preferable in that a thin film having a uniform in-plane specific resistance can be easily obtained. The ratio of SnO ₂ to In ₂ O _{3 in} ITO is preferably 1 to 20% by weight, and more preferably 5 to 12% by weight. The ratio of ZnO to In ₂ O ₃ in IZO is preferably 12 to 32% by weight. The said material may be used individually by 1 type, and may be used in combination of 2 or more type. These materials may be crystalline or non-crystalline.

The composition of the oxide constituting the hole injection electrode 1 may be slightly deviated from the stoichiometric composition. Due to this deviation or the like, the carrier density is 1 for electrical evaluation using a Hall coefficient measuring device or the like. It is preferable that 0 × 10 ^{18 to} 1.0 × 10 ²¹ / cm ³ and mobility be about 1 to ²⁰⁰ cm ² / Vs.

  Further, depending on the film forming conditions in the process of forming the transparent electrode such as the ITO electrode or the heat treatment history after the film forming, the transparent electrode itself may become unstable with respect to the drive history or the heat history. As one method for evaluating this instability, there is a method in which the carrier density and mobility are measured before and after heat treatment at about 100 ° C., and the rate of change is examined. As a result, it can be estimated that those having a large change rate before and after the heat treatment have unstable film quality. By such a method, when the transparent electrode material evaluated as a thermally unstable film quality is used as the main component material of the hole injection electrode 1, the effect of the present invention can be further exhibited.

Further, the work function of the hole injection electrode 1 can be adjusted by adding a transparent dielectric such as silicon oxide (SiO ₂ ) to the hole injection electrode 1. For example, the work function of ITO can be increased by adding about 0.5 to 10 mol% of SiO ₂ with respect to ITO, and the work function of hole injection electrode 1 can be within the above-mentioned preferable range.

  The film thickness of the hole injection electrode 1 is preferably determined in consideration of the above light transmittance. For example, when using an oxide transparent conductive film, the film thickness is preferably 50 to 500 nm, more preferably 50 to 300 nm. When the thickness of the hole injection electrode 1 exceeds 500 nm, the light transmittance becomes insufficient and the hole injection electrode 1 may be peeled off from the substrate 4 in some cases. In addition, the light transmission improves as the film thickness decreases. However, when the film thickness is less than 50 nm, the resistance value increases, the hole injection efficiency into the organic light emitting layer 10 and the like decreases, and the film strength decreases. End up.

(Organic light emitting layer)
As the constituent material of the organic light emitting layer 10, an organic compound that excites excitons by recombination of electrons and holes, and emits light when the excitons release energy to return to the ground state, in particular, may be used. It can be used without limitation.

  Specifically, for example, organometallic complex compounds such as aluminum complex, beryllium complex, zinc complex, iridium complex, or rare earth metal complex, anthracene, naphthacene, benzofluoranthene, naphthofluoranthene, styrylamine, tetraaryldiamine, or These derivatives, low molecular organic compounds such as perylene, quinacridone, coumarin, DCM or DCJTB, or π-conjugated polymers such as polyacetylene derivatives, polyphenylene vinylene derivatives, polyfluorene derivatives or polythiophene derivatives, or polyvinyl compounds, polystyrene derivatives, Non-pi-conjugated side chain polymers such as polysilane derivatives, polyacrylate derivatives or polymethacrylate derivatives, or those containing pigments in the main chain polymer, etc. Examples thereof include high molecular organic compounds.

  Among these, from the viewpoint of obtaining an organic EL device having high luminous efficiency and long life, organometallic complex compounds such as aluminum complex, beryllium complex, zinc complex, iridium complex or rare earth metal complex, anthracene, naphthacene, benzofluoranthene , Naphthofluoranthene, styrylamine or tetraaryldiamine or derivatives thereof, and low molecular organic compounds such as perylene, quinacridone, coumarin, DCM, or DCJTB are preferably used.

  Furthermore, in order to obtain light emission with a relatively high red color purity and a relatively high light emission efficiency, it is preferable to use diindenoperylene or a derivative thereof. Further, in order to obtain light having a relatively high blue color purity and relatively high light emission efficiency, it is preferable to use diphenylbenzofluoranthene or a derivative thereof except the above-described preferred compounds for obtaining red light emission. . Further, rubrene or a derivative thereof is preferably used in order to obtain light emission having a relatively high yellow or orange color purity and a relatively high light emission efficiency. In order to obtain light emission having a relatively high green color purity and a relatively high light emission efficiency, it is preferable to use diphenylnaphthacene or a derivative thereof excluding the preferred compounds for obtaining the respective colors.

Moreover, in order to improve the electron injection efficiency from the 1st inorganic layer 12 and to obtain the outstanding luminous efficiency, it is preferable to use a hydrocarbon compound. Examples of the hydrocarbon compound include a compound represented by the following formula (1) and a compound represented by the following formula (2).

  Moreover, the organic light emitting layer 10 is selected from the viewpoints of easiness of film formation, ease of injection of holes and electrons, and exciton mobility of the excitons to a dopant material described later, among the above constituent materials. When a hole material is used as a base material and a dopant material selected from the viewpoint of ease of receiving energy from the hole material and high luminous ability is dispersed in the hole material, a further excellent luminous efficiency can be obtained. Since there exists a tendency which can be obtained, it is more preferable.

  Furthermore, it is preferable that the concentration of the dopant material contained in the organic light emitting layer 10 is substantially constant over the entire thickness direction of the organic light emitting layer 10. Such an organic light emitting layer 10 is preferable because it can realize light emission without unevenness, thereby improving the light emission efficiency and durability.

  The thickness of the organic light emitting layer 10 is preferably 10 to 200 nm, and more preferably 50 to 150 nm, from the viewpoint of obtaining uniform light emission and long life.

(First inorganic layer)
The first inorganic layer 12 is a layer containing a transition metal oxide formed on the organic light emitting layer 10.

  Although it does not specifically limit as a formation method of this 1st inorganic layer 12, For example, it can form by a vapor deposition method, the apply | coating method, etc. Among these forming methods, it is preferable to employ a vapor deposition method because the organic light emitting layer 10 is hardly damaged.

  As the vapor deposition method, for example, physical vapor deposition methods such as resistance heating vapor deposition, electron beam vapor deposition, sputter vapor deposition, and cluster ion beam vapor deposition, and chemical vapor deposition methods such as CVD can be used. Among these, resistance heating vapor deposition is particularly preferable because it can be relatively easily performed and the organic light emitting layer 10 is hardly damaged.

It does not restrict | limit especially as a transition metal oxide which comprises the 1st inorganic layer 12, Regardless of insulation and electroconductivity, it can be used. Further, since the bonding state at the interface with the organic light emitting layer 10 tends to change in a direction in which the electron injection efficiency is further improved, from Mo, Nb, W, Ta, Y, Cr, Re, Co, V, and Mn An oxide of at least one metal selected from the group consisting of is preferred, and molybdenum oxide (MoO ₃ ) is particularly preferred. Molybdenum oxide (MoO ₃ ) is also preferable from the viewpoint of easy vapor deposition and easy handling.

  Note that the composition of these transition metal oxides may deviate somewhat from the stoichiometric composition. Moreover, these transition metal oxides can be used individually or in combination of 2 or more types.

  The film thickness of the first inorganic layer 12 made of such a transition metal oxide is preferably 0.1 to 10 nm, and preferably 0.3 to 5 nm, from the viewpoint of obtaining sufficient electron injection efficiency. More preferred. In addition, when the film thickness of the 1st inorganic layer 12 is less than 0.1 nm, there exists a tendency for control of a film thickness to become difficult, and when a film thickness exceeds 10 nm, there exists a tendency for a drive voltage to rise.

(Second inorganic layer)
The second inorganic layer 14 is a layer containing an alkali metal or an alkaline earth metal formed on the first inorganic layer 12.

  Although the formation method of this 2nd inorganic layer 14 is not specifically limited, It can form by the vapor deposition method, the apply | coating method, etc. similarly to the case where the 1st inorganic layer 12 is formed. Among these formation methods, since the first inorganic layer 12 and the organic light emitting layer 10 are not easily damaged, it is preferable to employ a vapor deposition method as in the case of forming the first inorganic layer 12, and resistance heating. It is particularly preferable to employ vapor deposition.

  The second inorganic layer 14 is not particularly limited as long as it contains an alkali metal or alkaline earth metal as a constituent material, but is a layer made of an alkali metal or alkaline earth metal, or a layer further containing a transition metal oxide. It is preferable that

  When the second inorganic layer is a layer made of an alkali metal or an alkaline earth metal, the second inorganic layer 14 can obtain a sufficiently low work function, so that excellent electron injection efficiency can be obtained and excellent light emission efficiency can be obtained. be able to.

  When the second inorganic layer is a layer further containing a transition metal oxide, the presence of the transition metal oxide can stabilize the alkali metal or alkaline earth metal and improve the hole barrier property. Thus, excellent luminous efficiency can be obtained.

  Here, although it does not restrict | limit especially as an alkali metal or alkaline-earth metal, In order to obtain sufficient electron injection efficiency, it is preferable to use a thing with a work function of 3 eV or less. Specifically, Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba are preferably used, and Li is particularly preferable because stable film formation is easily possible.

Further, the transition metal oxide is not particularly limited, but the same transition metal oxide as that used for the first inorganic layer 12 is preferably used, and molybdenum oxide (MoO ₃ ) is particularly preferably used.

  The film thickness of the second inorganic layer 14 having such a configuration is preferably 0.1 to 10 nm, more preferably 0.3 to 5 nm, from the viewpoint of obtaining more sufficient electron injection efficiency. In addition, when the film thickness of the second inorganic layer 14 is less than 0.1 nm, it tends to be difficult to control the film thickness, and when the film thickness exceeds 10 nm, device (element) characteristics tend to become unstable. There is.

  Furthermore, the ratio of the film thickness of the second inorganic layer 14 to the film thickness of the first inorganic layer 12 (the film thickness of the second inorganic layer 14 / the film thickness of the first inorganic layer 12) ensures the effect of the present invention. From the viewpoint of obtaining, it is preferably 0.1 to 8, and more preferably 0.5 to 4.

  The organic EL element 100 of the present invention sufficiently improves the electron injection efficiency from the electron injection electrode 2 to the organic light emitting layer 10 by simultaneously including the first inorganic layer 12 and the second inorganic layer 14 described above. And excellent luminous efficiency can be obtained.

(Electron injection electrode)
The constituent material of the electron injection electrode (cathode) 2 is not particularly limited as long as it is used for the electron injection electrode in the conventional organic EL element. Therefore, examples of the constituent material include a metal material, an organometallic complex, or a metal salt, and it is preferable to use a material having a relatively low work function so that electrons can be efficiently and reliably injected into the organic light emitting layer 10. .

  Specific examples of the metal material constituting the electron injection electrode 2 include alkali metals such as Li, Na, K, and Cs, or alkaline earth metals such as Mg, Ca, Sr, and Ba. Alternatively, a metal having characteristics close to those of an alkali metal or an alkaline earth metal such as La, Ce, Eu, Sm, Yb, Y, or Zr can be used. Furthermore, in addition to the above metal materials, alkali metal halides such as LiF or CsI can also be used.

  The film thickness of the electron injection electrode 2 is preferably as thin as possible from the viewpoint of the ability to inject electrons into the organic light emitting layer 10 and the like, specifically, 10 nm or less is preferable, and 1 nm or less is more preferable.

  An auxiliary electrode may be provided on the electron injection electrode 2. Thereby, it exists in the tendency which can improve the electron injection efficiency to the organic light emitting layer 10, and it exists in the tendency for the penetration | invasion of the water | moisture content or the organic solvent to the organic light emitting layer 10 exists. As a material for the auxiliary electrode, a general metal can be used because there is no restriction on work function and charge injection capability. However, it is preferable to use a metal having high conductivity and easy handling. In particular, when the electron injection electrode 2 contains an organic material, it is preferable to select appropriately according to the type of organic material, adhesion, and the like.

  Examples of the material used for the auxiliary electrode include Al, Ag, In, Ti, Cu, Au, Mo, W, Pt, Pd, and Ni. Among them, it is more preferable to use a low-resistance metal such as Al or Ag because the electron injection efficiency tends to be further increased. Moreover, higher sealing properties can be obtained by using a metal compound such as TiN. These materials may be used alone or in combination of two or more. Moreover, when using 2 or more types of metals, you may use as an alloy. Such an auxiliary electrode can be formed by, for example, a vacuum deposition method or the like.

  Next, the manufacturing method of the organic EL element 100 of this embodiment is demonstrated in detail.

  First, the hole injection electrode 1 is formed on the prepared substrate 4 by a method such as sputtering or vapor deposition.

  Next, the organic light emitting layer 10 is formed on the hole injection electrode 1. As a method for forming the organic light emitting layer 10, a conventional method can be appropriately selected and employed according to the constituent material of the organic light emitting layer 10. For example, a vacuum deposition method, an ionization deposition method, a coating method, or the like can be used. Can be adopted.

  Then, the first inorganic layer 12 is formed on the organic light emitting layer 10 and the second inorganic layer 14 is further formed. Here, as described above, as a method of forming the first inorganic layer 12 and the second inorganic layer 14, a vapor deposition method, a coating method, or the like can be adopted. Among these formation methods, a vapor deposition method is also possible. Is preferably employed, and resistance heating vapor deposition is particularly preferably employed.

  Then, the organic EL element 100 is completed by forming the electron injection electrode 2 on the second inorganic layer by, for example, a vacuum deposition method or the like.

  In the organic EL device 100 thus obtained, the electron injection efficiency from the electron injection electrode 2 to the organic light emitting layer 10 is sufficiently improved, and excellent light emission efficiency can be obtained.

  As mentioned above, although preferred embodiment of the organic EL element of this invention and its manufacturing method was described, this invention is not limited to the said embodiment. For example, in the organic EL element of the present invention, like the organic EL element 200 of the second embodiment of the present invention shown in FIG. 2, the order of the layers stacked on the substrate 4 of the organic EL element 100 described above is reversed. It may be. That is, the electron injection electrode 2, the second inorganic layer 14, the first inorganic layer 12, the organic light emitting layer 10, and the hole injection electrode 1 may be laminated on the substrate 4 in this order. On the contrary, the light can be easily extracted from the side opposite to the substrate by stacking. In this case, it is preferable that the electron injection electrode 2 satisfies the optical conditions and film thickness conditions of the hole injection electrode 1 described in the first embodiment. In this case, the second inorganic layer 14 is formed on the electron injection electrode 2, and the first inorganic layer 12 is formed on the second inorganic layer 14.

  FIG. 3 is a schematic cross-sectional view showing a third embodiment of the organic EL element according to the present invention. An organic EL element 300 shown in FIG. 3 has a structure in which a hole injection layer 16 is provided between the hole injection electrode 1 and the organic light emitting layer 10 of the organic EL element 100 in FIG.

  The constituent material of the hole injection layer 16 is not particularly limited as long as it is used for the hole injection layer in the conventional organic EL device, and arylamine, phthalocyanine, polyaniline / organic acid, polythiophene / polymer acid, etc. These organic compound materials, or metal or semimetal oxides such as germanium or silicon can be used. These hole injecting materials may be used singly or in combination of two or more.

  By providing the hole injection layer 16, the organic EL element 300 can easily inject holes from the hole injection electrode 1, stably transport holes, and further prevent electrons from the organic light emitting layer 10. . Thereby, the luminous efficiency of the organic EL element 300 is improved and the driving voltage tends to decrease as a whole.

  FIG. 4 is a schematic cross-sectional view showing a fourth embodiment of the organic EL element according to the present invention. An organic EL element 400 shown in FIG. 4 has a structure in which a hole transport layer 18 is provided between the hole injection layer 16 and the organic light emitting layer 10 of the organic EL element 300 in FIG.

  The constituent material of the hole transport layer 18 is not particularly limited as long as it is used for the hole transport layer in the conventional organic EL device, and any hole transport material of a low molecular material or a polymer material may be used. It can be used. Examples of the hole transporting low molecular weight material include pyrazoline derivatives, arylamine derivatives, stilbene derivatives, and triphenyldiamine derivatives. Also, hole transporting polymer materials include polyvinyl carbazole (PVK), polyethylene dioxythiophene (PEDOT), polyethylene dioxythiophene / polystyrene sulfonic acid copolymer (PEDOT / PSS), polyaniline / polystyrene sulfonic acid copolymer. (Pani / PSS). One of these hole transport materials may be used alone, or two or more thereof may be used in combination.

  By having such a structure, the mobility of holes in the organic EL element 300 is improved, the recombination probability of carriers is improved, and the movement of electrons from the organic light emitting layer 10 to the hole transport layer 18 can be suppressed. Therefore, the luminous efficiency tends to be improved.

  Suitable thicknesses of the hole injection layer 16 and the hole transport layer 18 are both 1 to 100 nm.

  Further, although not shown, a plurality of light-emitting layers containing different constituent materials (material types and material content ratios) may be stacked.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Example 1)
First, an ITO film having a thickness of 100 nm was formed as a hole injection electrode on a prepared glass substrate and patterned.

  On the hole injection electrode, the compound represented by the above formula (1) and the compound represented by the above general formula (2) were co-evaporated at a volume ratio of 97: 3 by resistance heating vapor deposition, An organic light emitting layer having a film thickness was formed.

  Next, molybdenum oxide powder was placed on a Ta boat, and this was heated by resistance heating on the organic light-emitting layer to form a first inorganic layer having a thickness of 0.4 nm. At this time, the current passed through the heater was 60 A, and the vapor deposition rate was 0.01 nm / second.

  Next, lithium was placed on a Ta boat with an alumina coat for resistance heating, and this was resistance heating vapor deposited on the first inorganic layer to form a second inorganic layer having a thickness of 1.6 nm. At this time, the current passed through the heater was 12 A, and the vapor deposition rate was 0.05 nm / second.

And aluminum was resistance-heat-deposited on this 2nd inorganic layer, and the electron injection electrode which has a film thickness of 100 nm was formed. This obtained the organic EL element of Example 1. In addition, resistance heating vapor deposition at the time of forming each layer was performed under the conditions where the system internal pressure was 1 × 10 ⁻⁴ Pa.

(Example 2)
An organic EL device of Example 2 was obtained in the same manner as Example 1 except that the thickness of the first inorganic layer was 1.0 nm.

(Example 3)
An organic EL device of Example 3 was obtained in the same manner as in Example 1 except that the second inorganic layer was formed as follows. That is, lithium and molybdenum oxide are placed in a volume ratio of 4: 1 on a Ta boat with an alumina coat for resistance heating, and this is co-evaporated on the first inorganic layer by resistance heating deposition (system pressure: 1 × 10 ^-4 Pa), and the second inorganic layer was formed to a thickness of 2.0 nm.

(Comparative Example 1)
An organic EL device of Comparative Example 1 was obtained in the same manner as in Example 1 except that the first inorganic layer was not formed.

(Comparative Example 2)
An organic EL device of Comparative Example 2 was obtained in the same manner as in Example 1 except that the thickness of the first inorganic layer was 0.5 nm and the second inorganic layer was not formed.

(Comparative Example 3)
An organic EL device of Comparative Example 3 was obtained in the same manner as in Example 1 except that the first inorganic layer and the second inorganic layer were not formed.

<Element characteristic evaluation test>
The organic EL elements of Examples 1 to 3 and Comparative Examples 1 to 3 obtained as described above were stored in an Ar gas atmosphere at 105 ° C. for a predetermined time. Then, the light emission luminance and driving voltage when the organic EL element after storage was driven at a constant current of 10 mA / cm ² were measured. The results are shown in Table 1.

  As is clear from the results shown in Table 1, the organic EL elements (Examples 1 to 3) of the present invention have higher emission luminance than the organic EL elements of Comparative Examples 1 to 3, and are excellent. It was confirmed to have luminous efficiency. Moreover, it was confirmed that the drive voltage of the organic EL element (Examples 1 to 3) of the present invention was sufficiently reduced.

It is a schematic cross section which shows the organic EL element which concerns on 1st Embodiment of this invention. It is a schematic cross section which shows the organic EL element which concerns on 2nd Embodiment of this invention. It is a schematic cross section which shows the organic EL element which concerns on 3rd Embodiment of this invention. It is a schematic cross section which shows the organic EL element which concerns on 4th Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Hole injection electrode (anode), 2 ... Electron injection electrode (cathode), 4 ... Substrate, 10 ... Organic light emitting layer, 12 ... 1st inorganic layer, 14 ... 2nd inorganic layer, 16 ... Hole injection layer, 18 ... Hole transport layer, 100 ... organic EL element according to the first embodiment, 200 ... organic EL element according to the second embodiment, 300 ... organic EL element according to the third embodiment, 400 ... organic EL element according to the fourth embodiment Element, P ... power supply.

Claims (5)

An organic light emitting layer is provided between the hole injection electrode and the electron injection electrode facing each other,
A first inorganic layer containing a transition metal oxide is formed on the surface of the organic light emitting layer on the electron injection electrode side,
An organic EL device, wherein a second inorganic layer containing an alkali metal or an alkaline earth metal is formed on a surface of the first inorganic layer on the electron injection electrode side.   2. The organic EL device according to claim 1, wherein the organic light emitting layer is a layer containing a hydrocarbon compound.   The transition metal oxide is an oxide of at least one metal selected from the group consisting of Mo, Nb, W, Ta, Y, Cr, Re, Co, V, and Mn. Or the organic EL element of 2.   The organic EL element according to claim 1, wherein the second inorganic layer is a layer made of an alkali metal or an alkaline earth metal. The organic EL device according to any one of claims 1 to 3, wherein the second inorganic layer is a layer further containing a transition metal oxide.

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