JPH10302966A - Organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL element with good adhesivity and electron filling efficiency on an organic layer interface and less dark spots by providing a cathode containing aluminum and at least one type of SC, Y and rare earth metal element so as to be coated therewith in a spattering method. SOLUTION: On a substrate 21, at least a positive hole filling and transportation layer 23 and a luminous layer 24 are provided between an anode 22 and a cathode 25 located thereon and a protecting layer 26 is provided as the uppermost layer. The cathode 25 is coated with metal, compound or alloy with a small work function in a spattering method and the anode 22 is coated with tin doped indium oxide (ITO), zinc doped indiums oxide (IZO). ZnO, SnO2 , In2 O3 in a spattering method. The cathode 22 has a concentration gradient in the direction of a coat thickness so as to provide more rare earth metal element toward the interface side contacting an organic layer and has aluminum laminated on the opposite side of the interface side contacting the organic layer. In this way, an organic EL element with the cathode having less deterioration is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL device using an organic compound (hereinafter referred to as an organic EL device), and more particularly to a negative electrode for supplying electrons to a light emitting layer.

[0002]

2. Description of the Related Art In recent years, organic EL devices have been actively studied. This is because a tetraphenyldiamine (T) is formed on a transparent electrode (positive electrode) such as tin-doped indium oxide (ITO).
Basic structure in which a hole transporting material such as PD) is formed into a thin film by vapor deposition, a fluorescent substance such as an aluminum quinolinol complex (Alq3) is laminated as a light emitting layer, and a metal electrode (negative electrode) such as Mg having a small work function is formed. With several 100 to 1000 cd / c at a voltage around 10 V
very high luminance and m ² are noted by obtained.

As a material used as a negative electrode of such an organic EL device, a material that injects a large amount of electrons into a light emitting layer is considered to be effective. In other words, it can be said that a material having a smaller work function is more suitable for the negative electrode. There are various materials having a small work function. Examples of materials used as a cathode of an EL light emitting element include MgAg described in JP-A-4-233194,
AlLi is common. The reason for this is that the manufacturing process of the organic EL light-emitting element mainly involves evaporation using resistance heating, so that the evaporation source is naturally limited to those having a low temperature and a high vapor pressure. In addition, since an evaporation process using such resistance heating is used, adhesion at a film interface is poor. As a result, a non-image portion called a dark spot on a pixel is generated immediately after manufacturing, and the non-image portion is enlarged according to driving, and this is a factor that determines the element life.

Further, Japanese Patent Application Laid-Open No. 4-233194 describes that a rare earth metal is used for a negative electrode as a metal having a low work function. However, there is no description that this cathode is used in combination with an electron injection layer having a metal having a higher work function than the cap layer containing the rare earth metal element, and is used as an alloy with aluminum. Moreover, the embodiment only describes the electron injection layer made of MgAl and the Al cap layer, and does not describe a method for forming a rare earth metal element specifically. Further, the organic EL element described in this publication has all the constituent films formed by a vapor deposition method, and has not solved the above-mentioned problem.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the adhesion at the interface of the organic layer and the electron injection efficiency, improve the light emission characteristics, reduce the damage to the organic layer, and suppress the generation of dark spots. It is another object of the present invention to realize an organic EL element having a negative electrode with little performance degradation.

[0006]

The above objects are achieved by the following constitutions (1) to (7). (1) An organic EL element formed by a sputtering method and having a negative electrode containing aluminum and at least one of Sc, Y and rare earth metal elements. (2) The organic EL device according to (1), wherein the negative electrode has a concentration gradient in a film thickness direction, and the concentration gradient is a gradient in which a rare earth metal element increases on an interface side in contact with the organic layer. (3) The organic EL device according to (1) or (2), wherein the cathode is further laminated with aluminum on the side opposite to the interface side in contact with the organic layer. (4) The rare earth elements are Sc, Y and Sm, C
e. The organic EL device according to any one of (1) to (3) above, which is any one of lanthanoid elements of Er, Eu, Gd, La, Nd and Yb. (5) The organic sputtering method according to any one of (1) to (4), wherein the negative electrode is formed under film forming conditions in which a product of a film forming gas pressure and a distance between substrate targets satisfies 20 to 65 Pa · cm. EL element. (6) The organic EL device according to any one of (1) to (5), wherein at least one of Ar, Kr, and Xe is used as the film forming gas. (7) The organic EL device according to any one of (1) to (6), wherein the sputtering method is a DC sputtering method.

[0007]

When the negative electrode obtained by the present invention is used, the electron injection efficiency is improved, the initial emission luminance of the organic EL element is high, and the half-life of the luminance is long. Also, no current leakage occurs between the electrodes, the number of initial dark spots is extremely small, and the number of occurrences after driving is also small. As described above, the improvement of the electron injection efficiency and the suppression of the dark spot were important problems of the organic EL element. However, according to the present invention, this is solved and the light emission characteristics are remarkably improved. As will be understood from the examples described later, such an effect does not occur outside the scope of the present invention. This is presumably because a film having good electron injection efficiency and good stability was formed according to the present invention.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific configuration of the present invention will be described in detail.

The organic EL light emitting device of the present invention has a negative electrode formed by sputtering and containing aluminum and one or more rare earth metal elements containing Sc and Y.

[0010] By using the sputtering method, the formed negative electrode film has a relatively high kinetic energy of the sputtered atoms and atomic groups as compared with the case of vapor deposition. Adhesion at the interface of the organic layer is improved. Also, by performing pre-sputtering,
Since the surface oxide layer can be removed in a vacuum or water and oxygen adsorbed at the organic layer interface can be removed by reverse sputtering, a clean electrode-organic layer interface and electrodes can be formed, resulting in a stable organic EL device. it can. Further, even when a mixture of materials having greatly different vapor pressures is used as a target, there is little deviation in composition between a film to be formed and the target, and there is no limitation on a material to be used due to vapor pressure or the like as in a vapor deposition method. Also,
Compared with the vapor deposition method, there is no need to supply a material for a long time, the film thickness and the film quality are excellent in uniformity, and it is advantageous in terms of productivity.

The contents of Sc, Y and the rare earth metal elements (including the lanthanoid element and the actinoid element) constituting the negative electrode may be selected as appropriate depending on the stable metal to be combined. Although not particularly limited, it is preferably 0.1 to 99 at%, particularly 1 to 99 at%.
It is preferably in the range of ６０60 at%. If the amount of the rare earth metal element containing Sc and Y is large, the stability of the formed negative electrode is reduced, and if the amount is too small, the effect of the present invention cannot be obtained. If the negative electrode can be formed only with the rare earth metal, the work function becomes the lowest, but as described above, the rare earth metal element is a material that is very reactive and unstable, and thus a relatively stable metal, for example, Stabilization is achieved by mixing aluminum or the like. The stable metal to be mixed is not limited to aluminum, but may be Au, Ag, Cu, Co, C
r, Fe, Ga, In, Ir, Mo, Ni, Pd, P
t, Rh, Ru, Si, Sn, Ta, Th, W, Zn
Metals with relatively low work function and good electrical conductivity,
And alloys thereof. The mixing ratio when these alloys are used is arbitrary. In addition, electric conductivity,
As long as it is equivalent to a metal, a stable compound may be used. Stable compounds include, for example, IrO ₂ , MoO ₂ , Nb
O, OsO ₂ , ReO ₂ , ReO ₃ , RuO _{2 and the} like can be mentioned.

The formed negative electrode has a concentration gradient in which the concentration of the rare earth metal changes in the film thickness direction so that the rare earth metal element is more at the interface in contact with the organic layer and the stable metal is more at the opposite surface. Is preferred. By having such a concentration gradient, a rare earth metal element having a high concentration and a low work function is present at the interface of the organic layer where the electron injection function is required, and the surface on the opposite side where there is a high possibility of contact with the outside air or the like is provided. A rare earth element having high reaction activity can be present at a low concentration, and a negative electrode with improved stability can be realized while maintaining high electron injection efficiency.

In order to provide a rare earth element concentration gradient in the negative electrode, for example, a mixed sputter target of a stable metal and a rare earth metal element and a stable metal target are used at the same time, and the respective film formation rates are controlled. By doing so, it can be easily realized. In addition, other than having such a continuous concentration gradient, for example, discontinuous (stepwise)
In addition, a film in which the mixing ratio of the rare earth metal element is changed is formed,
A stable metal layer may be formed on the mixed layer. In this case, the thickness of the mixed layer is preferably 5 to 80 nm, and the thickness of the stable metal layer is preferably about 100 to 300 nm. The negative electrode formed discontinuously as described above can easily reduce the electric resistance.

The rare earth element used in the present invention preferably contains Sc, Y and a lanthanoid element, and more preferably has a work function of 4 eV or less.
e, Nd, La, Sm, Eu, Gd, Er and Yb are preferred. The smaller the work function, the more electrons can be injected into the light emitting layer, and the light emitting characteristics are improved. Above all, Sc, Y, Nd, S having a melting point of 1000 ° C. or more
m, Gd and Er are preferred. By using a material having a melting point of 1000 ° C. or more, crystallization of the thin film and abnormal growth are suppressed, smoothness at the organic layer interface of the negative electrode is maintained, and dark spots and leaks can be prevented.

When a negative electrode is formed by a sputtering method,
An electrode is formed by a DC sputtering method using any of Ar, Kr, and Xe or a mixed gas containing at least one of these gases as a sputtering gas. It is preferable that the film formation conditions satisfy the product of 20 to 65 Pa · cm.

The sputtering gas may be an inert gas used in a usual sputtering apparatus, or a reactive gas such as N ₂ , H ₂ , O ₂ , C ₂ H ₄ , NH ₃ or the like in the case of reactive sputtering. Although it can be used, it is preferable to use any of Ar, Kr, and Xe, or a mixed gas containing at least one or more of these gases. These are preferred because they are inert gases and have a relatively large atomic weight. Particularly, Ar, Kr, and Xe alone are preferred. Ar, Kr, Xe
By using a gas, the sputtered atoms repeatedly collide with the gas while reaching the substrate while arriving at the substrate, and reach the substrate with reduced kinetic energy. For this reason, physical damage caused by the kinetic energy of the sputtered atoms to the organic EL structure is reduced. Ar, K
A mixed gas containing at least one gas of r and Xe may be used. When such a mixed gas is used, Ar,
The total partial pressure of Kr and Xe is set to 50% or more and used as a main sputtering gas. By using a mixed gas obtained by combining at least one of Ar, Kr, and Xe with an arbitrary gas, reactive sputtering can be performed while maintaining the above effects.

When any of Ar, Kr, and Xe is used as the main sputtering gas as the sputtering gas, the product of the distance between the substrate targets is preferably 25 to 55 Pa · cm, particularly 30 to 55 Pa · cm, respectively. 5
When 0 Pa · cm and Kr are used: 20 to 50 Pa · cm, especially 25 to 4
When using 5 Pa · cm and Xe: 20 to 50 Pa · cm, especially 20 to 4
A range of 0 Pa · cm 2 is preferable. Under these conditions, a preferable result can be obtained by using any sputtering gas, but it is particularly preferable to use Ar.

As a sputtering method, a high frequency sputtering method using an RF power source or the like is possible, but it is preferable to use a DC sputtering method in order to reduce damage to the organic EL element structure. As the power of the DC sputtering device,
Preferably 0.1 to 4 W / cm ² , especially 0.5 to 1 W / cm ²
Range. The film formation rate is 5 to 100 nm / min.
Particularly, a range of 10 to 50 nm / min is preferable.

The thickness of the negative electrode thin film may be a certain thickness or more for sufficiently injecting electrons, and may be 50 nm or more, preferably 100 nm or more. Although the upper limit is not particularly limited, the film thickness may be usually about 100 to 500 nm.

In the organic EL device of the present invention, one or more oxides, nitrides or carbides of the constituent material of the negative electrode may be provided as a protective film by utilizing the above-mentioned reactive sputtering. In this case, the raw material of the protective film usually has the same composition as the negative electrode material, but may have a different composition ratio from the negative electrode material, or may lack one or more of the material components. In this manner, by using the same material or the like as the negative electrode, continuous film formation with the negative electrode becomes possible.

The O content of such an oxide, the N content of a nitride or the C content of a carbide may deviate from this stoichiometric composition, and may be in the range of 0.5 to 2 times the composition. I just need.

As the target, a sintered body of the same material as that of the negative electrode is preferably used. As the reactive gas, O ₂ , CO or the like is used for forming an oxide, and N ₂ is used for forming a nitride. ₂ , NH ₃ , NO, NO ₂ , N ₂ O and the like. When forming a carbide, CH ₄ , C ₂ H ₂ , C _2
2 H _{4 and the} like. These reactive gases may be used alone or as a mixture of two or more.

The thickness of the protective film may be a certain thickness or more, preferably 50 nm or more, more preferably 100 nm or more, particularly preferably 100 to 1000 nm, in order to prevent moisture, oxygen or an organic solvent from entering.

The total thickness of the negative electrode and the protective film is not particularly limited, but may be generally about 100 to 1000 nm.

By providing such a protective film, oxidation of the negative electrode and the like are further prevented, and the organic EL element can be driven stably for a long period of time.

The organic EL device manufactured according to the present invention comprises:
The substrate has at least one charge transport layer and at least one light emitting layer sandwiched between a positive electrode and a negative electrode on the substrate, and further has a protective layer as the uppermost layer. Note that the charge transport layer can be omitted. As described above, the negative electrode is formed of a metal, compound or alloy having a small work function formed by a sputtering method, and the positive electrode is formed of tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), ZnO, SnO ₂ , In ₂ O ₃
Etc. are formed by sputtering.

FIG. 1 shows an example of the structure of an organic EL device manufactured according to the present invention. The EL device shown in FIG. 1 has a positive electrode 22, a hole injection / transport layer 23, a light emission and electron injection / transport layer 24, a negative electrode 25, and a protective layer 26 in this order on a substrate 21.

The organic EL device of the present invention is not limited to the illustrated example, but may have various structures. For example, a light emitting layer is provided alone, and an electron injection / transport layer is interposed between the light emitting layer and the negative electrode. It is also possible to adopt a structure in which they have been made. Further, if necessary, the hole injection / transport layer 23 and the light emitting layer may be mixed.

The negative electrode can be formed as described above, the organic layer such as the light-emitting layer can be formed by vacuum deposition, and the positive electrode can be formed by vapor deposition or sputtering. Depending on the conditions, patterning can be performed by a method such as etching after mask evaporation or film formation, whereby a desired light emitting pattern can be obtained. Further, the substrate is a thin film transistor (TFT), and by forming each film according to the pattern, a display and drive pattern can be used as it is.

[0030] After the electrode film formation, the protective film or / and Al, a metal material, an inorganic material such as SiO _X, may be formed of other protective film using an organic material such as Teflon or the like.
This protective film may be transparent or opaque. Generally, the thickness of the other protective film is about 50 to 1200 nm.
The protective film may be formed by a general sputtering method, a vapor deposition method, or the like, in addition to the reactive sputtering method described above.

Further, it is preferable to form a sealing layer on the element in order to prevent oxidation of the organic layer and the electrode of the element. The sealing layer is made of an adhesive resin layer such as a commercially available low-moisture-absorbing light-curing adhesive, an epoxy-based adhesive, a silicone-based adhesive, and a cross-linked ethylene-vinyl acetate copolymer adhesive sheet to prevent moisture from entering. Is used to adhere and seal a sealing plate such as a glass plate. Besides a glass plate, a metal plate, a plastic plate or the like can be used.

Next, the organic material layer provided in the EL device of the present invention will be described.

The light emitting layer has a function of injecting holes (holes) and electrons, a function of transporting them, and a function of generating excitons by recombination of holes and electrons. It is preferable to use a relatively electronically neutral compound for the light emitting layer.

The charge transport layer has a function of facilitating the injection of holes from the positive electrode, a function of transporting holes, and a function of blocking electrons, and is also called a hole injection transport layer.

In addition, if necessary, for example, when the electron injecting / transporting function of the compound used in the light emitting layer is not so high, injection of electrons from the negative electrode between the light emitting layer and the negative electrode as described above. May be provided with an electron injecting and transporting layer having a function of facilitating electron transport, a function of transporting electrons, and a function of blocking holes.

The hole injection transport layer and the electron injection transport layer
Increases and confines holes and electrons injected into the light emitting layer,
Optimize the recombination region and improve luminous efficiency.

The hole injecting / transporting layer and the electron injecting / transporting layer may be provided separately for a layer having an injection function and a layer having a transport function.

The thickness of the light emitting layer, the thickness of the hole injecting and transporting layer, and the thickness of the electron injecting and transporting layer are not particularly limited, and vary depending on the forming method.
It is preferable to set it to 300 nm.

The thickness of the hole injecting / transporting layer and the thickness of the electron injecting / transporting layer depend on the setting of the recombination / light emitting region, but may be about the same as the thickness of the light emitting layer or about 1/10 to 10 times. I just need. When the injection layer and the transport layer for electrons or holes are separated from each other, it is preferable that the injection layer has a thickness of 1 nm or more and the transport layer has a thickness of 20 nm or more. At this time, the upper limit of the thickness of the injection layer and the transport layer is usually about 500 nm for the injection layer and 50 nm for the transport layer.
It is about 0 nm. Such a film thickness is the same when two injection / transport layers are provided.

Further, by controlling the film thickness in consideration of the carrier mobility and carrier density (determined by ionization potential and electron affinity) of the light emitting layer, the electron injection / transport layer, and the hole injection / transport layer to be combined, it is possible to reduce the thickness. It is possible to freely design the coupling region and the light emitting region, and it is possible to design the light emission color, control the light emission luminance and light emission spectrum by the interference effect of both electrodes, and control the spatial distribution of light emission.

The light emitting layer of the EL device of the present invention contains a fluorescent substance which is a compound having a light emitting function. Examples of the fluorescent substance include metal complex dyes such as tris (8-quinolinolato) aluminum [Alq3] disclosed in JP-A-63-264692. In addition, in addition or alone, quinacridone, coumarin, rubrene, styryl dyes, other tetraphenylbutadiene, anthracene, berylene,
Coronene, a 12-phthaloberinone derivative, or the like can also be used. The light emitting layer may also serve as the electron injection / transport layer. In such a case, it is preferable to use tris (8-quinolinolato) aluminum or the like. These fluorescent substances may be deposited.

The electron injecting and transporting layer, which is provided as necessary, includes an organometallic complex such as tris (8-quinolinolato) aluminum, an oxadiazole derivative, a berylen derivative, a pyridine derivative, a pyrimidine derivative, a quinoline derivative, and a quinoxaline derivative. , A diphenylquinone derivative,
Nitro-substituted fluorene derivatives and the like can be used.
As described above, the electron injection / transport layer may also have a light emitting layer. In such a case, it is preferable to use tris (8-quinolinolato) aluminum or the like.
The formation of the electron injecting and transporting layer may be performed by vapor deposition or the like, similarly to the light emitting layer.

When the electron injecting and transporting layer is divided into an electron injecting layer and an electron transporting layer, a preferable combination can be selected from the compounds for the electron injecting and transporting layer. At this time, it is preferable to stack the layers of the compound having the higher electron affinity from the cathode side. This stacking order is the same when two or more electron injection / transport layers are provided.

The hole injecting and transporting layer is described, for example, in JP-A-63-295695 and JP-A-2-191694.
JP, JP-A-3-792, JP-A-5-2346
No. 81, JP-A-5-239455, JP-A-5
JP-A-299174, JP-A-7-126225, JP-A-7-126226, JP-A-8-100
Various organic compounds described in JP-A-172, EP0650955A1, and the like can be used. For example, a tetraarylbendicine compound (tetraaryldiamine or tetraphenyldiamine: TPD), an aromatic tertiary amine, a hydrazone derivative, a carbazole derivative, a triazole derivative, an imidazole derivative, an oxadiazil derivative having an amino group, polythiophene, or the like. . Two or more of these compounds may be used in combination, and when they are used in combination, they may be stacked as separate layers or mixed.

When the hole injecting and transporting layer is divided into a hole injecting layer and a hole transporting layer, a preferable combination can be selected from the compounds for the hole injecting and transporting layer. At this time, it is preferable to stack the layers of the compound having the smaller ionization potential in order from the positive electrode (ITO or the like) side. It is preferable to use a compound having a good thin film property on the surface of the positive electrode. Such a stacking order is the same when two or more hole injection / transport layers are provided. With such a stacking order, the driving voltage is reduced, and the occurrence of current leakage and the occurrence and growth of dark spots can be prevented. In the case of forming an element, a thin film of about 1 to 10 nm can be made uniform and pinhole-free because of the use of vapor deposition, so that the hole injection layer has a small ionization potential and has absorption in the visible part. Even when such a compound is used, it is possible to prevent a change in the color tone of the emission color or a decrease in efficiency due to reabsorption.

The above compound may be deposited on the hole injection / transport layer in the same manner as in the light emitting layer.

In the present invention, the material and thickness of the transparent electrode used as the positive electrode are preferably determined so that the transmittance of emitted light is preferably 80% or more. Specifically, for example, tin-doped indium oxide (ITO), zinc-doped indium oxide (IZ)
O), ZnO, SnO ₂ , In ₂ O _{3 and the} like are preferably used for the positive electrode. The thickness of the positive electrode is 10 to 500.
It is preferable to set it to about nm. It is necessary that the driving voltage be low in order to improve the reliability of the device, but it is preferable that the driving voltage be 10 to 30 Ω / □ (film thickness: 50 to 300 nm).
ITO. If you actually use it,
The electrode thickness and optical constants may be set so that the interference effect of O or the like at the positive electrode interface sufficiently satisfies the light extraction efficiency and color purity.

In a large device such as a display, since the resistance of the positive electrode such as ITO is large and a voltage drop occurs, metal wiring such as Al may be provided.

As a substrate material, in the case of a configuration in which light emitted from the substrate side is extracted, a transparent or translucent material such as glass, quartz, or resin is used. Further, the emission color may be controlled by using a color filter film, a color conversion film containing a fluorescent substance, or a dielectric reflection film on the substrate. In the case of the reverse lamination, the substrate may be transparent or opaque, and when opaque, ceramics or the like may be used.

As the color filter film, a color filter used in a liquid crystal display or the like may be used.
The characteristics of the color filter may be adjusted in accordance with the light emitted from the organic EL to optimize the extraction efficiency and the color purity.

When a color filter capable of cutting off short-wavelength external light that is absorbed by the EL element material or the fluorescent conversion layer is used, the light resistance of the element and the display contrast are improved.

Further, an optical thin film such as a dielectric multilayer film may be used instead of the color filter.

The fluorescent conversion filter film absorbs EL light and emits light from the phosphor in the fluorescent conversion film to perform color conversion of the emission color. It is formed from a fluorescent material and a light absorbing material.

As the fluorescent material, basically, a material having a high fluorescence quantum yield may be used, and it is desirable that the material has strong absorption in an EL emission wavelength region. Actually, laser dyes are suitable, and rhodamine compounds, perylene compounds, cyanine compounds, phthalocyanine compounds (including subphthalo, etc.) naphthaloimide compounds, condensed ring hydrocarbon compounds, condensed heterocyclic compounds, A styryl compound, a coumarin compound, or the like may be used.

As the binder, basically, a material which does not quench the fluorescence may be selected, and a binder which can be finely patterned by photolithography, printing or the like is preferable.
Further, a material that does not suffer damage during the deposition of ITO is preferable.

The light absorbing material is used when the light absorption of the fluorescent material is insufficient, but may be omitted when unnecessary. As the light absorbing material, a material that does not quench the fluorescence of the fluorescent material may be selected.

For forming the hole injecting and transporting layer, the light emitting layer and the electron injecting and transporting layer, it is preferable to use a vacuum deposition method since a uniform thin film can be formed. When a vacuum deposition method is used, a homogeneous thin film having an amorphous state or a crystal grain size of 0.1 μm or less can be obtained. If the crystal grain size exceeds 0.1 μm, the light emission becomes non-uniform, the driving voltage of the device must be increased, and the charge injection efficiency is significantly reduced.

The conditions for vacuum deposition are not particularly limited.
The degree of vacuum is 0 ^-4 Pa or less, and the deposition rate is 0.01 to 1 nm /
It is preferable to set it to about sec. Further, it is preferable to form each layer continuously in a vacuum. If they are formed continuously in a vacuum, impurities can be prevented from adsorbing at the interface between the layers, so that high characteristics can be obtained. Further, the driving voltage of the element can be reduced, and the growth and generation of dark spots can be suppressed.

In the case where a plurality of compounds are contained in one layer when a vacuum evaporation method is used for forming each of these layers, it is preferable to co-deposit each boat containing the compounds by individually controlling the temperature.

The organic EL device of the present invention is usually used as a DC drive type EL device, but it can be AC drive or pulse drive. The applied voltage is usually 2 to 2
It is about 0V.

[0061]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention together with comparative examples.

Example 1 A 200-nm-thick ITO was formed as a transparent electrode on a glass substrate by sputtering, followed by patterning, ultrasonic cleaning using a neutral detergent, acetone and ethanol, and then boiling in ethanol. And dried. After cleaning the transparent electrode surface with UV / O ₃ ,
Fix it with the substrate holder of the vacuum evaporation equipment, and
The pressure was reduced to 10 ⁻⁴ Pa or less.

Next, N, N'-
Diphenyl-m-tolyl-4,4'-diamine-1,
1′-biphenyl (TPD) was deposited at a deposition rate of 0.2 nm / sec to a thickness of 55 nm to form a hole injection transport layer.

Further, while maintaining the reduced pressure, Alq3: tris (8-quinolinolato) aluminum was evaporated at a vapor deposition rate of 0.1.
Evaporation was performed at a thickness of 50 nm at 2 nm / sec to form an electron injection / transport / light-emitting layer.

Next, the wafer was transferred from the vacuum evaporation apparatus to a sputtering apparatus, and Al.Sm (Sm: 20 at
%) As a target, and a negative electrode was formed to a thickness of 200 nm. At this time, Ar was used as the sputtering gas, the gas pressure was 4.5 Pa, and the distance between the target and the substrate (Ts) was 9.0 cm.
And The input power was 100W.

Finally, SiO ₂ was sputtered to a thickness of 200 nm to obtain an organic EL device as a protective layer. This organic E
In the L light emitting element, two parallel striped negative electrodes and eight parallel striped positive electrodes are orthogonal to each other, and element elements (pixels) of 2 × 2 mm vertically and horizontally are arranged at an interval of 2 mm from each other. It is an element of × 2 16 pixels.

A DC voltage was applied to this organic thin-film light emitting device in an N ₂ atmosphere, and the device was continuously driven at a constant current density of 10 mA / cm ² . Initially, green light emission (maximum emission wavelength λmax = 520 nm) of 9 V and 350 cd / cm ² was confirmed. The half-life of luminance is 800 hours, during which the drive voltage rises by 2V
Met.

With respect to the obtained organic EL element, the initial luminance of 160 pixels (for 10 elements) was examined, the average luminance was obtained, and the half-life of light emission and the occurrence of dark spots (after 200 hours from the start of light emission). Table 1
It was shown to. The occurrence of dark spots was evaluated according to the following criteria. ◎: No dark spots ○: Two or less spots can be confirmed in a 10 mm square area of the light emitting surface. X: Three or more can be confirmed in a 10 mm square area of the light emitting surface.

Example 2 In forming the organic EL light emitting device of Example 1, a binary sputtering target of the same Al.Sm target and pure Al target as in Example 1 was used, and the input power was set to DC100. ~ 0
A negative electrode having a thickness of 200 nm was formed in the same manner as in Example 1 except that the w, pure Al target was changed from 0 to 500 w with time, and an organic EL device was obtained.

When the composition of the formed negative electrode was examined,
It was confirmed that the amount of Sm was large at the interface in contact with the organic layer, and the concentration of Sm gradually decreased in the thickness direction toward the opposite side. In addition, when this organic EL device was evaluated in the same manner as in Example 1, it was found that the emission half-life increased to 1000 hours, and that the negative electrode could be prevented from deteriorating due to the rare earth metal concentration gradient. Table 1 shows the results.

Example 3 In forming the organic EL device of Example 1, an Al.Sm target and a pure Al target similar to those in Example 1 were used. First, an Al.Sm target was formed in the same manner as in Example 1. Was used to form a 50 nm negative electrode, and an Al thin film was laminated to a thickness of 150 nm using a pure Al target. Otherwise, the procedure of Example 1 was followed to obtain an organic EL device.

When this organic EL device was evaluated in the same manner as in Example 1, it was confirmed that the initial drive voltage was reduced to 8.5 V and the light emission half-life was increased to 1000 hours. Table 1 shows the results.

Example 4 In forming the organic EL device of Example 1, the sputtering gas was changed to Kr, the gas pressure was 3.5 Pa, and the distance between the target and the substrate (Ts) was 9.0 cm.
And Otherwise, an organic EL element was formed in the same manner. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 5 In the formation of the organic EL device of Example 1, the sputtering gas was changed to Xe, the film forming gas pressure was 2.5 Pa, and the distance Ts between the target and the substrate was 9.0 c.
An organic EL element was formed in the same manner except that m was set. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 6 In the formation of the organic EL device of Example 1, the film forming gas pressure was 2.5 Pa and Ts = 9.
An organic EL element was formed in the same manner except that the distance was set to 0 cm. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 7 In the formation of the organic EL device of Example 1, the film forming gas pressure was 6.0 Pa and Ts = 9.
An organic EL element was formed in the same manner except that the distance was set to 0 cm. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 8 In the formation of the organic EL device of Example 1, the film forming gas pressure was 8.0 Pa and Ts = 5.
An organic EL element was formed in the same manner except that the thickness was changed to 0 cm.
The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Embodiment 9 In forming the organic EL light emitting device of Embodiment 1, the film forming gas pressure was 12 Pa and Ts = 5.0 c.
An organic EL element was formed in the same manner except that m was changed. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 10 In forming the organic EL device of Example 1, the film forming gas pressure was 8.0 Pa and Ts =
An organic EL device was formed in the same manner except that the size was changed to 7.5 cm. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

<Embodiment 11> In forming the organic EL device of Embodiment 1, the film forming gas pressure was 2.5 Pa and Ts = 1.
An organic EL element was formed in the same manner except that the size was changed to 5 cm.
The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

<Embodiment 12> In Embodiment 1, instead of Al.Sm (Sm: 20 at%) as the target,
Al. Ce (Ce: 5 at%), Al. Er (Er: 10
at%), Al-Eu (Eu: 10 at%), Al-Gd
(Gd: 10 at%), Al.La (La: 10 at%),
Al.Nd (Nd: 10 at%), Al.Sc (Sc: 1)
0 at%), Al.Y (Y: 10 at%), Al.Yb (Y
b: 5 at%), and the other steps were the same as in Example 1 to produce an organic EL light emitting device.

Example 1 of the obtained organic EL device
As a result, the same results as in Example 1 were obtained for each organic EL element.

Comparative Example 1 In forming the organic EL device of Example 1, pure Al was used instead of the Al.Sm target.
An organic EL device was obtained in the same manner as in Example 1 except that a target was used.

A direct current voltage was applied to the obtained organic EL device in an N ₂ atmosphere, and the device was continuously driven at a constant current density of 10 mA / cm ² . Initially, green light emission (maximum emission wavelength λmax = 520 nm) of 9 V and 200 cd / cm ² was confirmed.
The light emission luminance in the earlier stage was lower. Further, although the occurrence of dark spots was small, the half-time of luminance was 600 hours, during which the drive voltage increased by 2 V, and the half-time of luminance was also reduced.

This organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 2 An organic EL device was formed in the same manner as in Example 1, except that the gas pressure was changed to 1.0 Pa. When the obtained organic EL device was evaluated in the same manner as in Example 1, both the average value of the initial light emission luminance and the light emission half-life decreased. Also,
The occurrence of dark spots was also remarkable. Table 1 shows the results.

Comparative Example 3 An organic EL device was formed in the same manner as in Example 1, except that the gas pressure was changed to 12 Pa. When the obtained organic EL device was evaluated in the same manner as in Example 1, both the average value of the initial light emission luminance and the light emission half-life decreased. The generation of dark spots was also remarkable. Table 1 shows the results.

Comparative Example 4 An organic EL device was formed in the same manner as in Example 1 except that the gas pressure was changed to 1.0 Pa and Ts = 5.0 cm. When the obtained organic EL device was evaluated in the same manner as in Example 1, both the average value of the initial light emission luminance and the light emission half-life decreased. The generation of dark spots was also remarkable. Table 1 shows the results.

[0089]

[Table 1]

[0090]

EFFECTS OF THE INVENTION A negative electrode having good adhesion at the interface of the organic layer, good electron injection efficiency, improved light emission characteristics, little damage to the organic layer, suppressed generation of dark spots, and little performance deterioration. An organic EL element can be realized.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a configuration example of an organic EL element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Substrate 22 Positive electrode 23 Hole injection / transport layer 24 Light emitting layer 25 Negative electrode 26 Protective layer

Claims (7)

[Claims] 1. An organic EL device formed by a sputtering method and having a negative electrode containing aluminum and at least one of Sc, Y and rare earth metal elements. 2. The organic EL device according to claim 1, wherein the cathode has a concentration gradient in a film thickness direction, and the concentration gradient is a gradient in which a rare earth metal element increases on an interface side in contact with the organic layer. 3. The organic EL device according to claim 1, wherein said cathode further comprises aluminum laminated on the side opposite to the interface side in contact with the organic layer. 4. The rare earth element includes Sc, Y and S
The organic EL device according to any one of claims 1 to 3, wherein the organic EL device is any one of lanthanoid elements of m, Ce, Er, Eu, Gd, La, Nd and Yb. 5. The organic EL device according to claim 1, wherein in the sputtering method, the negative electrode is formed under film forming conditions in which a product of a film forming gas pressure and a distance between substrate targets satisfies 20 to 65 Pa · cm. element. 6. The organic EL device according to claim 1, wherein at least one of Ar, Kr and Xe is used as said film forming gas. 7. The organic EL device according to claim 1, wherein said sputtering method is a DC sputtering method.