JPH08288068A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE: To effectively restrict the deterioration of an organic layer due to heat so as to improve the durability of an organic electroluminescent element. CONSTITUTION: A transparent first electrode 2, a heat radiating layer 3 made of the transparent material, which has a high heat conductivity and to which the P-type conductivity is given, an organic layer 4 made of the organic compound for emitting light with the application of voltage, and a second electrode 5 are laminated on a transparent substrate 1. Since the heat radiating layer 3, which has a high heat conductivity and to which the P-type conductivity is given, directly contacts the organic layer 4, heat can effectively escape from the organic layer 4, and the deterioration of the organic layer 4 due to the heat can be effectively restricted.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an organic electroluminescent device. INDUSTRIAL APPLICABILITY Since the organic electroluminescent element of the present invention is a planar light-emitting body capable of electrically emitting light, it can be used as a display device such as a front display of an automobile and a backlight of a liquid crystal display.

[0002]

2. Description of the Related Art An organic electroluminescence device is a solid organic compound having a strong fluorescence and a pair of electrodes attached thereto, and emits light when a voltage is applied. In general, as shown in FIG. 4, an organic electroluminescent device includes a transparent glass substrate 81, a transparent electrode (ITO) 82, an organic layer 83 made of an organic compound solid having strong fluorescence, and a metal ( Mg) electrode 8
4 has the structure laminated | stacked in order. The principle of light emission of this organic electroluminescent device is as follows. When holes are injected from the anode and electrons are injected from the cathode, the injected holes and electrons move in the solid, collide and recombine, and disappear.
The energy generated by the recombination is used to generate the excited state of the fluorescent molecule and emits fluorescence.

Such an organic electroluminescent device has no limitation on the viewing angle, can be driven at a low voltage, and can respond at high speed.
Compared with other display devices such as liquid crystal, plasma display and inorganic EL display, it has excellent characteristics as a display. However, it has been pointed out that the organic electroluminescent device has a short life. As one of the causes of the short life of the organic electroluminescence device,
Thermal deterioration is considered. That is, the heat generated in the element during driving causes peeling at the junction interface of the element, and the heat of the organic material in the organic layer 83 causes a change in the crystal structure of the organic material or the alteration of the organic material itself, and the organic layer 83 is thermally deteriorated. To do

Therefore, in order to suppress the thermal deterioration of the organic electroluminescence device and prolong the life thereof, as shown in FIG. 5, a diamond is provided between the glass substrate 81 and the transparent electrode 82 or on the metal electrode 84. , A method of releasing heat by suppressing the temperature rise of the element by incorporating a heat dissipation layer 85 made of a material having a large thermal conductivity such as beryllium oxide (BeO) has been proposed (Japanese Patent Laid-Open No. 59-215694, Japanese Patent Laid-Open No. 59-215694). 4-
129194, JP-A-5-101885).

[0005]

However, between the heat dissipation film 85 and the organic layer 83 that generates the most heat,
Since the transparent electrode 82 or the metal electrode 84 is interposed and the heat dissipation layer 85 and the organic layer 83 are not in direct contact with each other,
Due to the thermal resistance between the heat dissipation layer 85 and the organic layer 83, heat could not be efficiently released. For this reason, it has not been possible to efficiently suppress deterioration of the element due to temperature rise of the element.

It is to be noted that direct contact between the heat dissipation layer 85 and the organic layer 83 in order to efficiently dissipate the heat of the organic layer 83 from the heat dissipation layer 85 is achieved by diamond, beryllium oxide (B).
Since eO) and the like are insulating substances, the principle of electroluminescence is impaired, which is not possible. The present invention has been made in view of the above circumstances, and it is a technical problem to be solved that effectively suppresses thermal deterioration of an organic layer and improves durability of the organic electroluminescent element.

[0007]

Means for Solving the Problems The inventors have found that a diamond film or a beryllium film has high transparency, thermal conductivity, and film formability and is suitable for a film element of an organic electroluminescence device.
Focusing on that if it is possible to impart conductivity to this diamond film or the like, it is possible to use itself as an electrode on the light transmitting side, or to sandwich it between an organic layer and a transparent electrode. As a result, they have found that the use of a diamond film or the like, which has been given conductivity by, for example, doping treatment or hydrogen plasma treatment on the surface, as an electrode material is effective in extending the life of the organic electroluminescence device, and completed the present invention. did.

That is, the organic electroluminescent device according to the first aspect of the present invention includes a transparent substrate, a transparent first electrode, and a heat dissipating material formed of a transparent material having high thermal conductivity and P-type conductivity. It is characterized in that a layer, an organic layer made of an organic compound that emits light when a voltage is applied, and a second electrode are sequentially laminated. The transparent substrate is not particularly limited, and a glass substrate, a transparent ceramic substrate, a diamond substrate or the like can be used.

The transparent first electrode is an electrode having high light transmittance and conductivity, and for example, a vapor deposition film of gold, ITO or polyaniline can be used as in the conventional case. The organic layer made of an organic compound that emits light by applying the above voltage is not particularly limited, but is generally composed of an electron transporting agent, a light emitting agent, a hole transporting agent, a binder, or an organic material having these in combination, and is composed of a single layer or multiple layers. A thin film having a uniform thickness of several tens to several hundreds of nm can be formed.

The second electrode may be a transparent electrode or an opaque electrode, and is generally Mg, Ag, Mg-A.
A metal electrode such as g can be used. In the first aspect of the present invention, the heat dissipation layer made of a transparent material having high thermal conductivity and imparting P-type conductivity is interposed between the transparent first electrode and the organic layer. As a preferable embodiment of the transparent material having the high thermal conductivity and the P-type conductivity, diamond having the P-type conductivity by the doping treatment or the hydrogen plasma treatment can be mentioned. That is, the diamond film is entirely or partially doped with an element (for example, boron) capable of imparting P-type conductivity, or the surface or the whole of the diamond film is subjected to hydrogen plasma treatment, so that the diamond film is P-doped. Mold conductivity can be imparted.

The organic electroluminescent device of the second invention comprises a heat-conductive transparent first electrode made of a transparent material having high heat conductivity and P-type conductivity provided on a transparent substrate. An organic layer made of an organic compound that emits light when a voltage is applied, and a second electrode are sequentially stacked. As the transparent substrate, the organic layer and the second electrode constituting the organic electroluminescent device of the second invention, the same ones as those of the organic electroluminescent device of the first invention can be used.

In the second aspect of the present invention, instead of the transparent electrode which is conventionally composed of the ITO electrode or the like, the thermal conductivity which is composed of the transparent material having high thermal conductivity and imparted with P-type conductivity is used. The transparent first electrode is used. As a preferred embodiment of the transparent material having the high thermal conductivity and the P-type conductivity, a diamond having the P-type conductivity by the doping treatment or the hydrogen plasma treatment is provided as in the first invention. Can be mentioned.

[0013]

The organic electroluminescent device of the first invention has a high thermal conductivity between the transparent first electrode and the organic layer and P
A heat radiating layer made of a transparent material provided with mold conductivity is interposed. In addition, the organic electroluminescent element of the second aspect of the present invention is made of a transparent material, which has high thermal conductivity and is imparted with P-type conductivity, instead of the transparent electrode which is conventionally composed of an ITO electrode or the like. Conductive transparent first
It uses electrodes. As described above, in the organic electroluminescent device of the first and second aspects of the present invention, the heat dissipation layer having high thermal conductivity or the heat conductive transparent first electrode is in direct contact with the organic layer. The heat is well radiated to the outside and the temperature of the organic layer is suppressed, so that the thermal deterioration of the organic layer can be effectively suppressed.

Further, in the case of using doped diamond as a transparent material having high thermal conductivity and P-type conductivity, Fermi is used as compared with ITO which has been conventionally used as an electrode material. The energy level of the energy level is as low as 5.2 eV (ITO is 4.8 eV).
V) makes it easier to inject holes into the organic layer. Therefore, organic substances such as PBO (t-butylphenylbiphenyl oxadiazole) and Alq3 (tris (δ-quinolinol) aluminum, which cannot be used as a hole injecting substance because the energy level in the valence band is too low, have been used. ) Can be used as a hole injecting material. Further, the efficiency of hole injection from the electrodes is also improved.

[0015]

【Example】

(Example 1) The organic electroluminescent device of this example shown in FIG. 1 is a transparent material having a transparent first electrode 2 on a transparent substrate 1 and high thermal conductivity and P-type conductivity. That is, the heat dissipation layer 3 made of a diamond film doped with boron, the organic layer 4 made of an organic compound that emits light when a voltage is applied, and the second metal electrode 5 are sequentially laminated.

The structure of the organic electroluminescent device of this example will be described in detail below along with its manufacturing method. Transparent substrate 1
Is made of quartz glass having a thickness of 0.5 mm, and a film thickness of ITO electrode 10 is formed on the transparent substrate 1 by a vacuum deposition method.
The transparent 1st electrode 2 of 0 nm was formed into a film. And the transparent first
A heat dissipation layer 3 made of a diamond film doped with boron was formed on the electrode 2. The heat dissipation layer 3 was manufactured by the microwave plasma CVD method.

That is, hydrogen and methane (CH_Four/ H₂=
1.5%) mixed gas, B₂H₆CH (diborane)
_FourGas mixed with 167 ppm of (methane)
Reaction of setting transparent substrate 1 on which first electrode 2 is formed
It was introduced into the container. And 300W at 40 Torr,
Under the condition that the microwave of 2.45 GHz is irradiated for 2 hours,
A diamond doped with boron on the transparent first electrode 2.
A heat dissipation layer 3 was formed by depositing a Mondo film. This heat dissipation layer
3 has a thickness of 0.9 μm and a boron concentration of 5 × 10 ²⁰cm
^-3, Resistivity is 3 × 10^-3It was Ωcm.

Next, the transparent first electrode 2 and the heat dissipation layer 3 are formed.
The transparent substrate 1 on which the film is formed is washed with acetone and pure water to form an organic layer.
4 was subjected to vapor deposition. First, TPD (tetraphenylben
Dizine) was vacuum-deposited. The pressure during vapor deposition is 1 x 1
0^-FivePa, film thickness 50 nm, film formation speed 5 nm / min
And Subsequently, Alq3 (tris (δ-key
Norinol) aluminum) was vacuum deposited. In addition, steam
The pressure when wearing is 1 x 10 ^-FivePa, film thickness is 50 nm, film formation speed
The degree was 5 nm / min. As a result, on the heat dissipation layer 3
In addition, organic compounds (TPD and
An organic layer 4 made of Alq3) was formed.

Thereafter, a Mg-Ag alloy was co-deposited at a ratio of 10: 1 by a binary vapor deposition method. Deposition pressure is 1 ×
The film thickness was 10 ⁻⁵ Pa and the film thickness was 200 nm. As a result, the second metal electrode 5 made of a Mg—Ag alloy is formed on the organic layer 4.
Was deposited. The organic electroluminescent element of this example manufactured as described above emitted green light when a voltage was applied. The emission luminance at a current density of 50 mA / cm ² is 500 cd /
It was m ² , and sufficient electroluminescence performance was secured. In this embodiment, since the diamond that has been subjected to the doping treatment is used as the transparent material having high thermal conductivity and P-type conductivity, Fermi is used as compared with ITO which has been conventionally used as an electrode material. The energy level of the energy level is as low as 5.2 eV (4.8 e for ITO).
V), since it became easier to inject holes into the organic layer, it is considered that a high emission luminance of 500 cd / m ² was exhibited.

The half-life of the emission brightness was 200 hours. This is because the thermal deterioration of the organic layer 4 is slower than that of the comparative example described later. (Example 2) The organic electroluminescent device of this example has a heat dissipation layer 3
As a transparent material which has a high thermal conductivity and is imparted with P-type conductivity, which constitutes the above, except that a hydrogen plasma-treated diamond film is used instead of the boron-doped diamond film. It is similar to the organic electroluminescent device.

First, the transparent first electrode 2 made of an ITO electrode was formed on the transparent substrate 1 in the same manner as in Example 1 above. Then, a diamond film was formed on the transparent first electrode 2 by the microwave plasma CVD method. That is,
Using a mixed gas of hydrogen and methane (CH ₄ / H ₂ = 1.0%) as a raw material, microwaves of 300 W and 2.45 GHz are irradiated at 40 Torr for 2 hours to deposit a diamond film on the substrate, and subsequently methane gas Was stopped and plasma treatment was performed for 30 minutes in a hydrogen atmosphere. Thus, the heat dissipation layer 3 made of the hydrogen plasma-treated diamond film was formed on the transparent first electrode 2. The heat dissipation layer 3 had a thickness of 1.1 μm and a resistivity of 8 × 10 ⁻² Ωcm.

Then, in the same manner as in the first embodiment, the heat dissipation layer 3 is formed.
The organic layer 4 was formed on the organic layer 4, and the second metal electrode 5 was further formed on the organic layer 4. The organic electroluminescent element of this example manufactured as described above emitted green light when a voltage was applied. The emission brightness at a current density of 50 mA / cm ² is 50.
It was 0 cd / m ² , and sufficient electroluminescence performance was secured. In addition, the half-life of emission brightness was 180 hours.

(Comparative Example 1) The half-life of luminance of the organic electroluminescent element produced in the same manner as in Example 1 was 60 hours, except that the heat dissipation layer 3 was an untreated diamond film. (Embodiment 3) The organic electroluminescence device of this embodiment shown in FIG. 2 has a transparent substrate 1, a transparent material having high thermal conductivity and P-type conductivity, that is, a diamond film doped with boron. The transparent first electrode 6 having high thermal conductivity, the organic layer 4 made of an organic compound that emits light when a voltage is applied, and the second metal electrode 5 are sequentially laminated.

The structure of the organic electroluminescent device of this example will be described in detail below along with its manufacturing method. After polishing the same transparent substrate 1 as in Example 1 with diamond abrasive grains, a highly heat-conductive transparent first electrode 6 made of a diamond film doped with boron was formed on the transparent substrate 1. The film was formed by the microwave plasma CVD method.

That is, hydrogen and methane (CH_Four/ H₂=
1.5%) mixed gas, B₂H₆CH (diborane)
_FourGas mixed with 167 ppm of (methane)
The bright substrate 1 was introduced into the set reaction container. And
Microwave of 2.45 GHz, 300 W at 40 Torr
On the transparent substrate 1 under the condition of irradiating with boron for 4 hours.
High thermal conductivity by depositing doped diamond film
The transparent first electrode 6 was deposited. This high thermal conductivity transparent first
The pole 6 has a thickness of 2.0 μm and a boron concentration of 5 × 10 ²⁰cm
^-3, Resistivity is 3 × 10^-3It was Ωcm.

Then, in the same manner as in Example 1, the organic layer 4 was formed on the high heat conductive transparent first electrode 6, and further the second metal electrode 5 was formed on the organic layer 4. The organic electroluminescent element of this example manufactured as described above emitted green light when a voltage was applied. The emission luminance at a current density of 80 mA / cm ² was 400 cd / m ² , and sufficient electroluminescence performance was secured. In addition, the half-life of emission brightness is 50
It was 0 hours. It should be noted that, compared with the organic electroluminescent elements of Example 1 and Example 2, the half life of the emission luminance was 2.5 to 2.
It is considered that the reason for the increase of about 8 times is that the thickness of the diamond layer is increased and the heat dissipation efficiency is improved.

(Embodiment 4) The organic electroluminescent device of this embodiment shown in FIG. 3 has an auxiliary heat dissipation layer 7 made of a non-doped diamond film on the transparent substrate 1, a high heat conductivity and a P-type conductivity. A transparent material provided with a high heat conductive transparent first electrode 6 made of a diamond film doped with boron, an organic layer 4 made of an organic compound which emits light when a voltage is applied, and a second metal electrode 5 in order. It is made by stacking.

The structure of the organic electroluminescent device of this example will be described in detail below along with its manufacturing method. Thickness 1mm
After the molybdenum substrate of No. 1 was polished with diamond abrasive grains, a heat dissipation layer 7 made of a non-doped diamond film was formed thereon. The film was formed by the microwave plasma CVD method.

That is, hydrogen and methane (CH ₄ / H ₂ =
1.0%) of the mixed gas was introduced into the reaction vessel in which the molybdenum substrate was set. And 3k at 50 Torr
A heat-dissipating layer 7 was formed by depositing a non-doped diamond film on a molybdenum substrate under the condition that W was irradiated with a microwave of 2.45 GHz for 96 hours. The heat dissipation layer 7 had a thickness of 500 μm.

Then, a highly heat-conductive transparent first electrode 6 having a thickness of 2.0 μm was formed on the heat dissipation layer 7 by the same method as in Example 3 above. Then, the molybdenum substrate was dissolved and removed with dilute nitric acid. Then, the organic layer 4 was formed on the transparent first electrode 6 having high thermal conductivity in the same manner as in Example 1 above.
And the 2nd metal electrode 5 was formed into a film. Finally, the transparent substrate 1 was provided below the heat dissipation layer 7.

The organic electroluminescent device of this example manufactured as described above emitted green light when a voltage was applied. The emission brightness at a current density of 80 mA / cm ² is 400 cd /
It was m ² , and sufficient electroluminescence performance was secured. Further, the half-life of luminance was 800 hours, which is further improved in durability as compared with Example 3. It is considered that this is because the heat deterioration of the organic layer 4 was further suppressed by the presence of the heat dissipation layer 7 which was a non-doped diamond film.

Example 5 In the organic electroluminescent device of this example, boron was used as a transparent material having a high thermal conductivity and having a P-type conductivity, which constitutes the highly heat-conductive transparent first electrode. The organic electroluminescence device of Example 4 is the same as the organic electroluminescence device of Example 4 except that a diamond film whose surface is treated by a microwave plasma CVD method to impart P-type conductivity is used instead of the doped diamond film.

The structure of the organic electroluminescent element of this example will be described in detail below along with its manufacturing method. A molybdenum substrate similar to that used in Example 4 was polished with diamond abrasive grains, and a non-doped diamond film was formed on the molybdenum substrate. Microwave plasma C is used to form the film.
It was performed by the VD method.

That is, hydrogen and methane (CH ₄ / H ₂ =
1.0%) of the mixed gas was introduced into the reaction vessel in which the molybdenum substrate was set. And 3k at 50 Torr
A non-doped diamond film was deposited on the molybdenum substrate under the condition of being irradiated with W microwave at 2.45 GHz for 96 hours. The thickness of this diamond film was 500 μm. Then, the molybdenum substrate was dissolved and removed with dilute nitric acid.

Then, the non-doped diamond film was introduced into the reaction vessel, and the pressure was set to 40 Torr in a hydrogen atmosphere for 3 times.
The diamond film surface was treated by irradiating it with a microwave of 00W and 2.45 GHz for 1 hour to impart P-type conductivity. As a result, a highly heat-conductive transparent first electrode made of a diamond film imparted with P-type conductivity was formed. Next, an organic layer and a second metal electrode were formed on the high thermal conductive transparent first electrode by the same method as in Example 1 above. Finally, a high heat conductive transparent first electrode was provided.

The organic electroluminescent device of this example manufactured as described above emitted green light when a voltage was applied. The emission brightness at a current density of 40 mA / cm ² is 250 cd /
It was m ² , and sufficient electroluminescence performance was secured. The half life of luminance was 750 hours. In this example, only the microwave plasma CVD method was shown as the method for producing the diamond film, but the method for producing the diamond film is not particularly limited. For example, hot filament C
VD method, DC plasma jet method, RF thermal plasma method,
A combustion flame method or the like can also be used. Also in the case of doping boron, the source gas and the film forming method are not limited as long as the diamond film can be doped with boron. In addition to diborane (B ₂ H ₆ ) as a doping gas, triethoxyboron (B (OC ₂ H ₅ ) ₃ )
Any raw material containing boron can be used. The doping element is not limited to boron as long as it can impart P-type conductivity, and, for example, aluminum of Group III element in the periodic table can be used.

[0037]

As described in detail above, the organic electroluminescent device of the present invention has a structure in which the heat dissipation layer having high heat conductivity or the heat conductive transparent first electrode is brought into direct contact with the organic layer. The thermal deterioration of the layer can be effectively suppressed, and the durability of the organic electroluminescent element can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing the structure of an organic electroluminescence device of Example 1.

FIG. 2 is a cross-sectional view that schematically shows the configuration of the organic electroluminescent element of Example 3.

FIG. 3 is a cross-sectional view that schematically shows the configuration of the organic electroluminescent element of Example 4.

FIG. 4 is a cross-sectional view schematically showing the structure of a conventional organic electroluminescent device.

FIG. 5 is a cross-sectional view schematically showing the configuration of another conventional organic electroluminescent element.

[Explanation of symbols]

1 is a transparent substrate, 2 is a transparent first electrode, 3 is a heat dissipation layer, 4 is an organic layer, 5 is a second electrode, 6 is a high thermal conductive transparent first electrode, 7
Is a heat dissipation layer of a non-doped diamond film.

Claims (3)

[Claims] 1. A transparent first electrode on a transparent substrate, a heat dissipation layer made of a transparent material having high thermal conductivity and imparting P-type conductivity, and an organic compound which emits light when a voltage is applied. An organic electroluminescent device, comprising: an organic layer made of a metal and a second electrode, which are sequentially stacked. 2. A heat-conductive transparent first electrode made of a transparent material having high heat conductivity and imparted with P-type conductivity on a transparent substrate, and an organic compound which emits light when a voltage is applied. An organic electroluminescent device, comprising: an organic layer having the following structure and a second electrode stacked in this order. 3. The transparent material having high heat conductivity and being imparted with P-type conductivity is diamond having P-type conductivity imparted by doping treatment or hydrogen plasma treatment. Item 3. The organic electroluminescence device according to item 1 or 2.