JP2001338771A - Organic electroluminescent element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent(EL) element which is driven by low voltage. SOLUTION: This element has a structure, where a positive electrode 2, a luminescent layer 4, a first negative electrode 5 formed of a material having work function of 3.0 eV or smaller and a second negative electrode 6 having a work function larger than that of the first negative electrode are laminated sequentially on a substrate 1 from the luminescent layer side, and the first and second electrodes having the total thickness of 100 Å or smaller are laminated, and light is emitted to the outside via at least the electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device which is an electric light emitting device used for a display, a display light source and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, as a self-luminous display replacing a liquid crystal display, a light-emitting element (organic electroluminescence element, hereinafter referred to as an organic EL element) having a structure in which an organic light-emitting layer is provided between an anode and a cathode has been developed. Is accelerating. Among them, a highly transmissive EL element in the visible light region, so-called a transparent EL element (TOLED), which allows light to be extracted from both electrode sides, enables overlapping display, such as another display element can be arranged below the element. Therefore, for example, Appl. Phys. Let
t. 68 (19), 6 May 1996, p. 2606, a specific structure is proposed. The document includes:
An aluminum complex Alq3 which is a low molecular material is used as a light emitting layer, and a film is formed by co-evaporation of Mg and Ag as a cathode,
It is disclosed that an element is formed on the upper layer using ITO formed by sputtering or as a supplement to a cathode by sputtering to realize a threshold voltage of about 8V. In this structure, Mg and Al are used as the cathode, and ITO is further used as an upper layer from the viewpoint of the life and the threshold characteristics of the material used for the light emitting layer.

[0003]

In an organic EL device, a light emitting material having a small threshold is used for a light emitting layer, a metal material having a small work function is used as a cathode, and driving with a low threshold voltage can be realized. Proposed. However,
In the structure of the transparent EL element proposed in the above document, Mg and Al are not sufficient in work function, and in order to prevent the deterioration, ITO is further laminated on the metal material by sputtering, so that Mg is oxidized. Therefore, there is a problem that the threshold voltage of the element is eventually increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the problem of low-voltage driving and high efficiency.
An object of the present invention is to provide an organic EL device having high transmittance and a long life and a method for manufacturing the same.

[0005]

According to the present invention, an anode, a light emitting layer made of an organic material, and a work function having a work function of 3.
A structure in which a first cathode made of a material having 0 eV or less and a second cathode made of a material having a work function larger than that of the first cathode are sequentially laminated from the light emitting layer side, and the total thickness of the first and second cathodes is 100 An organic EL device is provided, in which a cathode having a thickness of Å or less is laminated, and light is emitted to the outside through at least the cathode.

Further, according to the present invention, a step of forming an anode on a substrate, a step of forming a light emitting layer made of an organic material above the anode, and a step of forming a work function above the light emitting layer from the side of the light emitting layer. A first cathode made of a material having a work function of 3.0 eV or less and a second cathode made of a material having a work function larger than that of the first cathode are stacked so that the total thickness of the first and second cathodes becomes 100 Å or less. Forming an organic EL element.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the organic EL device of the present invention, a first cathode made of a material having a work function of 3.0 eV or less and a work function made of a material having a work function of 3.0 eV are formed on an anode provided on a substrate and a light emitting layer made of an organic material. A structure in which a second cathode made of a material larger than the first cathode is sequentially laminated from the light emitting layer side, and a cathode having a total thickness of the first and second cathodes of 100 Å or less is provided. This is characteristic in that light is emitted to the outside via.

In a preferred embodiment of the organic EL device,
The following are mentioned. (1) The organic EL device in which the cathode is sealed with a sealing layer made of a transparent material. (2) The organic EL device, wherein the first cathode is made of Ca. (3) The thickness y (angstrom) of the first cathode is 5
The organic EL device described above, wherein 0 ≦ y ≦ 80. (4) The thickness y (angstrom) of the first cathode is set to 5
The organic EL device described above, wherein 5 ≦ y ≦ 65. (5) The organic EL device described above, wherein the second cathode is made of Al. (6) The thickness z (angstrom) of the second cathode is set to 1
The organic EL device described above, wherein 0 ≦ z ≦ 20. (7) The organic EL device, wherein the organic material forming the light emitting layer is a polymer material.

Further, in the method of manufacturing an organic EL device according to the present invention, a step of forming an anode on a substrate, a step of forming a light emitting layer made of an organic material above the anode, and a step of forming a light emitting layer above the light emitting layer From the side, a first cathode made of a material having a work function of 3.0 eV or less and a second cathode made of a material having a work function larger than the first cathode have a total thickness of the first and second cathodes of 100 Å or less. And forming a cathode to form a cathode.

The following are preferred embodiments of the method for producing an organic EL device. (8) In the formation of the anode, after forming the electrode film, oxygen or air plasma treatment is performed, and the current x and time t in the treatment are set to 10 (mA) ≦ x ≦ 15 (mA), 5
(Minute) ≦ t ≦ 7 (minute). (9) In forming the anode, after forming the electrode film, oxygen or air plasma treatment is performed, and the current x and time t in the treatment are set to 10 (mA) ≦ x ≦ 12 (mA), t =
5. The method for producing an organic EL device according to claim 1, wherein the amount is 5 (minutes).

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1C: \ WINDOWS \ Program FilesParus Ater
AtertempA0056072wIMG_1.htm is a cross-sectional view showing a structure of the organic EL device of the present invention.

In the structure shown in FIG. 1, an anode 2, a hole injection / transport layer 3, a light emitting layer 4 made of an organic material,
A first cathode 5 made of a material having a work function of 3.0 eV or less and a second cathode 6 made of a material having a work function larger than the first cathode (the cathode is formed by a laminated structure of the first and second cathodes) ) Are stacked. Then, the above-described laminated structure includes the first sealing layer 7 and the second sealing layer 8, and furthermore, the sealing substrate 9.
Is sealed.

As the substrate 1, a transparent material such as glass or a reflective material can be used. When a transparent material is used, light can be emitted to the outside via the substrate 1.

As a material used for the anode, for example, ITO or IDIXO (made by Idemitsu Kosan Co., Ltd.) is a transparent electrode material. These materials are deposited on a substrate by a sputtering method or the like to form electrodes. Such a transparent electrode is preferably subjected to oxygen plasma treatment or atmospheric plasma treatment after deposition of the material.

In the plasma processing, preferably, the current is 10 mA to 15 mA, the processing time is 5 minutes to 7 minutes,
More preferably, the current is set to 10 mA to 12 mA for 5 minutes. When the processing time is less than 5 minutes, the transmittance, especially for wavelengths from 400 to 550 nm, can be reduced by a maximum of 3 to 5% compared to when the processing time is more than 5 minutes. On the other hand, during the processing for 5 to 10 minutes, no increase in transmittance is observed in this wavelength region. For example,
In the case of the oxygen plasma treatment, it is preferable to carry out the treatment after purging with oxygen two to three times using VPS020 manufactured by Sanyu Electronics.

If the current is less than 10 mA, the uniformity of the surface treatment may be impaired.
When it exceeds, the thickness may be reduced by ashing.

In the above-described processing, the transmittance of a wavelength from 600 to 800 nm is reduced depending on the processing time. Compared to the unprocessed case,
When the processing is performed for 10 minutes, the transmittance is reduced by about 2% at the maximum. It is considered that these causes are caused by the change in the band structure due to the oxidation of the transparent electrode surface and the generation of defects due to the above treatment. Therefore, preferably 10m
A: Oxygen plasma treatment or atmospheric plasma treatment may be performed for about 5 minutes, thereby realizing an increase in transmittance near 500 nm where human sensitivity is higher and an average increase in transmittance in the entire visible region. it can.

When the above-mentioned transparent electrode material is used for the anode 2, light can be emitted to the outside via the substrate 1.

As the anode 2, for example, Pt, Ir,
It is also possible to use a laminated structure of a layer made of a metal such as Ni, Pd, or Au, a transparent material layer such as ITO, and a reflective layer such as Al.

Further, the substrate on which the anode 2 is formed is preferably an active matrix substrate in which a plurality of anodes are arranged and each anode is provided with a switching element such as a thin film transistor.

In this embodiment, a hole injection / transport layer 3 is provided between the electrode 2 and the light emitting layer 4. Here, hole injection /
The transport layer is a layer having a function of injecting and / or transporting holes from the anode to the light emitting layer side. The hole injection / transport layer 3 is preferably made of polyethylene dioxythiophene.

[0023]

Embedded image And polystyrene sulfonic acid

[0024]

Embedded image And copper phthalocyanine.

For the light emitting layer 4, either a low molecular weight organic light emitting material or a high molecular weight organic light emitting material is used, preferably a fluorene type polymer, particularly preferably.

[0026]

Embedded image Further, a high molecular organic material such as PPV (poly p-phenylene vinylene) is used.

Among the cathodes, the first cathode 5 is made of a material having a work function of 3.0 eV or less as described above. As such a cathode material, Ca is particularly preferably used. In particular, Ca is preferable because it can realize a low threshold voltage with a small work function and a high transmittance from a low reflectance with respect to visible light. The thickness of such a first cathode is preferably between 50 and 80 Angstroms, more preferably between 5 and 80 Angstroms.
5 to 65 angstroms. If the thickness is less than 50 angstroms, the work function of the upper second cathode 6 may affect the threshold voltage of the device. If the thickness is 80 Å or more, the transmittance may be significantly reduced. In particular, when Ca is used, Ca has absorption in most of the visible wavelength region, and therefore, if it is excessively thick, blackness is generally conspicuous on the cathode side. In particular, it is considered that the Ca film becomes a continuous film having a thickness such that electrical conduction can be obtained around 80 Å. From this viewpoint as well, it is preferable that the thickness of the second cathode be 80 Å or less. Also, Au can be used as the second cathode 6.

The first cathode is, for example, 1 × 10 ^-6 torr
Vacuum deposition can be performed at the above degree of vacuum.

On the other hand, among the cathodes, the second cathode 6 is made of a material having a higher work function than the first cathode 5 described above. As the material, it is preferable to use a material that does not greatly differ in work function from the material of the first cathode, and is somewhat stable to oxygen and easily forms a continuous film. Specifically, Al and Ag are mentioned.

In particular, when using Ca as the first cathode, it is preferable to use Al or the like as the material of the second cathode. The thickness of such a second cathode is preferably between 10 and 20 angstroms, more preferably 10 angstroms. If the thickness is less than 10 angstroms, electrical continuity cannot be obtained. If the thickness exceeds 20 angstroms, the transmittance of the second cathode material (particularly, the metal material) may be significantly reduced due to the metal reflection of the material itself.

In the present invention, as described above, a layer of a material having a low work function (3.0 eV or less) is provided on the first cathode, and a layer having a larger work function and becoming a continuous layer is provided on the first cathode. Provided as a second cathode, to prevent degradation of the first cathode,
Further, by setting the total thickness of the laminated structure of the first cathode and the second cathode to 100 angstroms or less, light transmittance on the cathode side is ensured.

As a method of forming the cathode laminated structure, preferably, after forming the first cathode by vapor deposition, after confirming that the degree of vacuum is substantially equal to that at the time of the first cathode vapor deposition,
The second cathode is formed under the same conditions as the first cathode.

As the first sealing layer 7, for example, LiF,
SiO and SiO ₂ are used. In particular, since LiF can be easily formed by a vacuum deposition method, as a series of operations under an inert atmosphere from a cathode film formation, it can be made into an element without being exposed to the air, and the material itself has no oxygen atoms. It has the feature that it can be maintained under oxygen-free condition close to zero. Further, the transmittance in the visible light region is high, and the transmittance is not impaired. The film thickness and deposition rate are between 300 and 50
0 angstrom, 8 angstrom / sec or more. If the film thickness is less than 300 angstroms, it is difficult to seal water and oxygen from outside air and water and oxygen from the upper second sealing layer 8 to the lower cathode. On the other hand, if the thickness exceeds 500 angstroms, the element (often a light-emitting layer) may be damaged by heat radiation at the time of vapor deposition, and the original EL light-emitting characteristics may be impaired. Also, the deposition rate is 8 Å / s.
In the case of ec, since the deposition time is long, the device is similarly deteriorated by heat radiation. For this reason, the deposition rate is also limited, and requires 8 Å / sec or more.

As the second sealing layer 8, for example, a transparent thermosetting epoxy resin or a photocurable epoxy resin is used. In particular, a thermosetting epoxy resin is preferred. Specifically, a sealing substrate is obtained by applying a glass substrate as the sealing substrate 9 by applying by dipping and curing the glass substrate in an inert atmosphere. Also, as the epoxy resin,
As a moisture-proof resin, DPpure60 (manufactured by 3M), S
TYCAST1269A (Emeron) and the like.

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 An organic EL device having the structure shown in FIG. 1 was manufactured.

The following operations were all performed in a clean room.

On the cleaned 150 mm square glass substrate 1, a (transparent) electrode (anode) 2 (IDIXO) was formed by sputtering to a thickness of 1000 angstroms. The conditions are as follows: the degree of vacuum is 1 × 10 ⁻⁴ Pa or less;
The flow rate ratio was 1, 320 V, 0.15 mA, and 14 minutes.
Next, an oxygen plasma treatment was performed on the anode film formed on the glass substrate under the conditions of a current of 10 mA for 5 minutes. Specifically, using Sanyu Electronics VPS020,
A post-treatment was performed after purging with oxygen two or three times.

From this, the following processing proceeded in the glove box. The condition of the glove box is that the oxygen concentration is 0.0
The dew point of water was 1 ppm or less and -70 ° C or less.

First, PEDOT (polyethylenedioxythiophene), which is a polythiophene derivative, is used as a hole injecting / transporting material on the plasma-treated electrode 2.
A mixture of SS (polystyrene sulfonic acid) was applied. These mixtures can be purchased from Bayer as Baytron P. Here, Baytron P and PS
S was mixed at 5: 1 and diluted 1.5 times with water to form a film by spin coating. The conditions were as follows: a slope of 1 second and 3,000 rotations for 45 seconds to obtain a film thickness of 600 Å. This was fired at 200 ° C. for 10 minutes to form a film, thereby forming a hole injection / transport layer 3.

Next, a solution obtained by dissolving a fluorene-based polymer having the following structure in a xylene solvent was applied on the hole injecting / transporting layer 3 by spin coating to a thickness of 800 Å to obtain a light emitting layer 4.

[0042]

Embedded image Subsequently, first, Ca was deposited (deposited) on the light emitting layer 4 as the first cathode 5 using a vacuum evaporation apparatus. The vacuum evaporation apparatus used was arranged in a glove box. The degree of vacuum starts from about 1 × 10 ⁻⁶ torr. The deposition rate is 3
Angstrom / sec, and the film thickness was 70 angstrom. Next, after waiting for the degree of vacuum to be about 1 × 10 ⁻⁶ torr again, Al was formed as the second cathode 6 at a deposition rate of 3 Å / sec to a film thickness of 10 Å.

Subsequently, LiF was formed on the second cathode 6 as the first sealing layer 7 to a thickness of 500 Å at a deposition rate of 8 Å / sec.

After cooling, DPpure60 (manufactured by 3M) which is a moisture-proof epoxy resin is applied on the first sealing layer 7 (thickness: 200 μm) to form a second sealing layer 8.
Sealing glass (thickness 0.3 mm) as
Pressing was performed on a hot plate at 50 ° C. for 12 hours to cure. At this time, the above heating was performed under a vacuum of about 0.1 Torr in order to remove bubbles in the epoxy resin. Thus, an organic EL device was obtained.

The transmittance and the threshold voltage of the obtained organic EL device were measured. The transmittance was measured using a spectroscope (manufactured by Hitachi, Ltd.) with a base line of air and a pinhole having a diameter of 3 mm in the light-collecting portion. The threshold voltage is determined using BM-7 (manufactured by Topcon Corporation), and the voltage at which the luminance of 5 Cd / m ² is output is defined as the threshold voltage.

FIG. 2 shows the results.

According to the results shown in the figure, it is found that the transmittance is 50% or more over almost the entire visible light region. The thickness of the glass substrate 1 is 1.1 mm,
Consider that the transmittance is about 75%. This means that a transmittance of 70% or more for glass is achieved. At this time, the threshold voltage was 3V.

(Example 2) In the method shown in Example 1, the oxygen plasma treatment time of the transparent electrode film as the anode was set to 0 to 1
A glass substrate was obtained in which the anodes were changed every minute up to 10 minutes. The transmission spectrum (transmittance for each wavelength) of the glass substrate on which the anodes were laminated for treatment times of 0, 5 (Example), and 10 minutes was measured. FIG. 3 shows the results. In addition, the transmittance at 450 nm, 550 nm, and 700 nm of the glass substrate on which the anode was laminated for a processing time of 0 to 1 minute every 10 minutes was measured. Table 1 shows the results.

[0049]

[Table 1] In the blue region (450 nm), an increase in transmittance was observed up to a processing time of 5 minutes. In the green region (550 nm), no significant change was observed, but the maximum transmittance was exhibited in a processing time of about 5 minutes. In the red region (700 nm), the transmittance decreases, though to a lesser extent, as the processing time increases. These phenomena are considered to be changes in the band structure due to oxidation of the surface layer by the treatment and partial change of the substance. From this, it is considered that the processing time of about 5 minutes is optimal.

Example 3 An organic EL device was obtained in the same manner as in Example 1 except that the thickness of the first cathode was changed to 40, 50, 60, 80, 90, and 100 Å. Threshold voltage and wavelength of each organic EL device 500
The transmittance in nm was measured. Table 2 shows the results of Example 1 (the thickness of the first cathode was 70 Å).
The results of threshold voltage and transmittance (wavelength region of 550 nm) are shown.

[0051]

[Table 2] The threshold voltage was asymptotic when the thickness of the first cathode was around 70 Å. At a film thickness less than this, an increase in the threshold voltage is observed. This is considered to be caused by the influence of the work function of the second cathode or an increase in the resistance value caused by the insufficient thickness of the second cathode.

The transmittance decreases with the thickness of the first cathode, and is within an allowable range up to about 90 Å (the total thickness of the first and second cathodes is about 100 Å). At a level higher than this (a level exceeding 100 Å in total thickness of the first and second cathodes), the transmittance was excessively low. From these results, it is considered that the most preferable thickness of the first cathode is about 70 angstroms.

Example 4 An organic EL device was obtained in the same manner as in Example 1, except that the thickness of the second cathode was changed to 5, 15, 20, 25, and 40 angstroms.
The threshold voltage and the transmittance at 500 nm of each organic EL element were measured. Table 3 shows Example 1 (film thickness 1 of second cathode).
0 Angstrom), the results of the threshold voltage and the transmittance.

[0054]

[Table 3] No change is seen in the threshold voltage if it is 10 Å or more. At 10 Å or less, it is considered that no light is emitted because conduction cannot be obtained. Since it is a constant value, it is considered that there is no influence of the work function of the second cathode. The decrease in transmittance is more pronounced than Ca. This is considered to be due to Al having high conductivity and high reflectance.

[0055]

As described in detail above, according to the present invention,
Organic EL device with improved transmittance in the visible region, improved sealing failure, and the elimination of the influence of outside air such as oxygen and moisture as much as possible. Can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an element structure of an organic EL element according to one embodiment of the present invention.

FIG. 2 is a view showing a transmission spectrum in a visible light region of the organic EL device prepared according to Example 1 of the present invention.

FIG. 3 is a diagram showing a transmission spectrum in which a change in transmittance of an element due to an oxygen plasma treatment according to an embodiment of the present invention is shown as a time dependency thereof.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 glass substrate 2 anode 3 hole injection / transport layer 4 light emitting layer 5 first cathode 6 second cathode 7 first sealing layer 8 second sealing layer 9 sealing substrate

Claims (11)

[Claims] An anode, a light emitting layer made of an organic material, a first cathode made of a material having a work function of 3.0 eV or less, and a second cathode made of a material having a work function larger than the first cathode are formed on a substrate. A structure in which the first and second cathodes have a total thickness of 100 angstroms or less and are stacked, and light is emitted to the outside through at least the cathode. Organic electroluminescent element. 2. The organic electroluminescence device according to claim 1, wherein said cathode side is sealed with a sealing layer made of a light transmitting material. 3. The organic electroluminescence device according to claim 1, wherein said first cathode is made of Ca. 4. The method according to claim 1, wherein the thickness y (angstrom) of the first cathode satisfies 50 ≦ y ≦ 80.
The organic electroluminescent device according to the above. 5. The method according to claim 1, wherein the thickness y (angstrom) of the first cathode is 55 ≦ y ≦ 65.
The organic electroluminescent device according to the above. 6. The organic electroluminescence device according to claim 1, wherein said second cathode is made of Al. 7. The method according to claim 1, wherein the thickness z (angstrom) of the second cathode is 10 ≦ z ≦ 20.
The organic electroluminescent device according to the above. 8. The organic electroluminescence device according to claim 1, wherein the organic material constituting the light emitting layer is made of a polymer material. 9. A step of forming an anode on a substrate; a step of forming a light emitting layer made of an organic material above the anode; and a work function of 3.0 e above the light emitting layer from the light emitting layer side.
V and a second cathode made of a material whose work function is larger than that of the first cathode, and laminated so that the total thickness of the first and second cathodes is 100 angstroms or less. And a method of manufacturing an organic electroluminescent device. 10. In the step of forming an anode, after forming an electrode film, oxygen or atmospheric plasma treatment is performed, and a current x and a time t in the treatment are set to 10 (mA) ≦ x ≦ 15.
10. The method for manufacturing an organic electroluminescent device according to claim 9, wherein (mA), 5 (minutes) ≦ t ≦ 7 (minutes). 11. In the step of forming an anode, after forming an electrode film, oxygen or air plasma treatment is performed, and a current x and a time t in the treatment are set to 10 (mA) ≦ x ≦ 1.
10. The method for manufacturing an organic electroluminescent device according to claim 9, wherein 2 (mA) and t = 5 (minutes).