JP2003272855A - Organic el element and organic el panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element capable of improving contrast and external quantum efficiency without deterioration of brightness, and to provide an organic EL panel using the same. <P>SOLUTION: A transparent conductive film made of either In<SB>2</SB>O<SB>3</SB>-ZnO, In<SB>2</SB>O<SB>3</SB>- SnO<SB>2</SB>, ZnO, or SnO<SB>2</SB>is formed on the light emitting layer side surface of a metal electrode of the organic EL element. It is made so that the light reflected at the metal electrode is strengthened by interfering between each other in the element by setting the film thickness of the transparent conductive film so as to fulfill the formula on condition that L is an optical length between the organic light emitting layer and the metal electrode, λ is the wavelength of emitted light. By the above, the organic EL element, capable of improving contrast and external quantum efficiency without deterioration of brightness, is provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL element and an organic EL panel, and more specifically, it is possible to improve external quantum efficiency without deterioration of brightness.
Also, the present invention relates to an organic EL element capable of improving contrast and an organic EL panel using the same.

[0002]

2. Description of the Related Art Since a highly efficient organic EL device was announced by Tang in 1987 as a device having a two-layer laminated structure (CW Tang et al., Appl. Ph.
ys. Lett. 51, 913 (1987)), various organic EL devices have been developed so far, and some of them have already been put to practical use.

FIG. 4 is a diagram for explaining the structure of a conventional organic EL device, in which a hole transport layer 42, a hole injection layer 43, a light emitting layer 44, and a transparent electrode 41 as an anode are provided. An electron transport layer 45 and an electron injection layer 46 are sequentially stacked, and a metal electrode 47 serving as a cathode is provided on the electron injection layer 46 to form an element.

The quantum efficiency of the organic EL having the structure shown in FIG. 4 is considered as follows. First, the holes and the electrons arriving from the anode and the cathode form electron-hole pairs in the light-emitting layer to become luminescent excitons, and the probability of generating these luminescent excitons is about 25%. . On the other hand, the efficiency of extracting the light generated in the light emitting layer to the outside of the device is given by the following equation, where n is the refractive index of the light emitting layer.

[0005]

[Equation 3]

Since the refractive index of a general light emitting layer is 1.6, this external extraction efficiency is about 20%. Therefore, the theoretical limit of the external quantum efficiency is about 5% given by the product of the generation probability of the luminescent excitons (about 25%) and the external extraction efficiency (about 20%).

[0007]

However, the external quantum efficiency of an actual organic EL element is as low as about 3%, which is about 60% of this theoretical value, and therefore, in order to take out light of a certain brightness to the outside. When the current passed through the element is increased, the deterioration of the brightness is promoted and the power consumption is increased.

Further, in an actual panel, the problem of contrast, which makes it difficult to see the display due to external light, has been a practical problem. One reason for such a decrease in contrast is that the metal electrode reflects external light.

The present invention has been made in view of this problem, and it is an object of the present invention to improve the external quantum efficiency without deterioration of luminance and to improve the contrast of an organic EL. An object is to provide an element and an organic EL panel using the element.

[0010]

In order to solve this problem, the present invention provides an organic EL light emitting portion including an organic light emitting layer between a metal electrode and a transparent electrode. An organic EL element comprising: a transparent conductive film provided on the surface of the metal electrode on the organic EL light emitting portion side, wherein the thickness of the transparent conductive film is L from the organic light emitting layer to the metal electrode. Optical distance of λ, λ is the emission wavelength of the organic light emitting layer,
It is characterized in that it is set so as to satisfy the following equation.

[0011]

[Equation 4]

The invention according to claim 2 is an organic EL element comprising an organic EL light emitting portion including an organic light emitting layer between a metal electrode and a transparent electrode, wherein the organic E of the metal electrode is
A transparent conductive film is provided on the surface on the L light emitting portion side, and the metal electrode and / or the transparent conductive film absorbs light having a wavelength different from the emission wavelength of the organic EL light emitting layer, Only the light of the wavelength emitted from the light emitting layer is emitted from the transparent electrode.

Further, the invention according to claim 3 is an organic EL element comprising an organic EL light emitting part including an organic light emitting layer between a metal electrode and a transparent electrode, wherein the organic E of the metal electrode is
A transparent conductive film is provided on the surface on the L light emitting portion side, the thickness of the transparent conductive film is L, the optical distance from the organic light emitting layer to the metal electrode, and λ the emission wavelength of the organic light emitting layer. Is set to satisfy the following equation,

[0014]

[Equation 5]

Light having a wavelength different from the emission wavelength of the organic EL light emitting layer is absorbed by the metal electrode and / or the transparent conductive film, and only light having a wavelength emitted from the organic EL light emitting layer is transparent. It is characterized in that it is emitted from an electrode.

The invention according to claim 4 is the same as claim 1
In the organic EL element according to any one of 3 to 3, the material of the transparent conductive film is In ₂ O ₃ —ZnO, In ₂ O ₃
It is characterized by being any one of —SnO ₂ , ZnO, and SnO ₂ .

The invention according to claim 5 is the same as claim 2
Alternatively, in the organic EL element described in the item 3, the transparent conductive film is doped with impurities and colored in the same color as the color of light emitted from the organic EL light emitting layer.

The invention described in claim 6 is the same as claim 5
In the organic EL element described in the paragraph 1, the organic EL light emitting layer emits blue light, and the transparent conductive film is CuO, Co,
Or, at a concentration of less than 1% of any impurity _{Ti, In 2 O 3 -ZnO,} In 2 O 3 -SnO 2,
It is made of either ZnO or SnO ₂ ,
The transparent conductive film absorbs blue light.

The invention according to claim 7 is the organic EL element according to any one of claims 2, 3, and 6, wherein
The organic EL light emitting layer emits blue light, the metal electrode is made of Zn, Mo, Cr, or an alloy of these metals, and the metal electrode absorbs blue light.

The invention according to claim 8 is a monochrome panel or an area color panel, which is characterized by including the organic EL element according to any one of claims 1 to 5.

The invention according to a ninth aspect is a color conversion type color panel, comprising the organic EL element according to the sixth aspect, a monochromatic blue backlight, and a color conversion filter. It is characterized in that the transparent conductive film of the EL element absorbs light other than blue light, and the metal electrode reflects only blue monochromatic light from the backlight.

Further, the invention according to claim 10 is a color conversion type color panel, which is the organic E according to claim 7.
An L element, a monochromatic blue backlight, and a color conversion filter are provided, and the metal electrode absorbs light other than blue light and reflects only monochromatic blue light from the backlight.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a view for explaining a constitutional example of the organic EL element of the present invention formed on a substrate.
The device includes an organic EL light emitting unit including a plurality of organic layers including an organic light emitting layer, and specifically, the transparent electrode 11 of the anode.
A hole-transporting layer 12, a hole-injecting layer 13, a light-emitting layer 14, an electron-transporting layer 15, and an electron-injecting layer 16 are sequentially stacked on top of each other, and a transparent conductive film is formed on the electron-injecting layer 16. 17 is provided, and a metal electrode 18 which is a metal layer of the cathode is provided on the transparent conductive film 17. In addition,
In constructing the organic EL device of the present invention, the glass substrate may be provided either on the transparent electrode 11 of the anode or on the metal electrode 18 which is the metal layer of the cathode.

Of the light emitted from the light emitting layer 14, the light emitted to the hole injection layer 13 side passes through the hole injection layer 13 and the hole transport layer 12 and is extracted from the transparent electrode 11 to the outside. The light emitted to the electron transport layer 15 side is
The light passes through the electron transport layer 15, the electron injection layer 16, and the transparent conductive film 17, is reflected by the metal electrode 18, and returns to the inside of the element. Therefore, if the reflected light can be extracted to the outside without being attenuated inside the element, the external quantum efficiency can be improved.

That is, the electron transport layer 1 constituting the device
5, the thickness of each layer of the electron injection layer 16 and the transparent conductive film 17 is d _i (i = 1, 2, 3), and the refractive index is n _i (i =
1, 2, 3), the optical distance L from the light emitting layer 14 to the metal electrode 18 is given by the following equation which is the sum of the optical distances of these layers.

[0027]

[Equation 6]

When the light is reflected at the interface between the metal electrode 18 and the transparent conductive film 17, the phase of the light is inverted, so that the conditions for the lights to reinforce each other within the element are:

[0029]

[Equation 7]

It becomes

The metal electrode 18 is used as a cathode, and the electron transport layer 15, the electron injection layer 16 and the transparent conductive film 17 are interposed between the metal electrode 18 and the light emitting layer 14. If the design is made to satisfy (3), the external quantum efficiency can be improved.

However, the thickness of the electron injection layer 16 is 0.5 to
In addition to the need to reduce the thickness to about 1 nm, increasing the thickness of the electron transport layer 15 causes a problem that the luminance deterioration of the element becomes noticeable. Therefore, in the organic EL element of the present invention,
A transparent conductive film 17 is provided between the electron injection layer 16 and the metal electrode 18.
By setting the film thickness of the transparent conductive film 17 so that the light reflected by the metal electrode 18 satisfies the above interference condition, the light is extracted to the outside without the light intensity being attenuated inside the element. It is supposed to improve the external quantum efficiency.

As described above, the method of setting the optical distance by adjusting the film thickness of the transparent conductive film 17 so that the external quantum efficiency is maximized is a monochrome panel or area color in which light is emitted using a monochromatic backlight. It is particularly useful not only for a panel but also for a color panel that adopts a color conversion method in which light emitted from a monochromatic backlight is received by a color conversion layer and converted into RGB luminescence.

Further, one of the practical problems of the organic EL panel is that the contrast is deteriorated by external light, and it is known that the external light is directly reflected by the metal layer. According to the formula (3), the light of the wavelength enhanced by the interference is limited, and only the light of the specific wavelength is reflected. Therefore, the reflection intensity of the light of the wavelength not satisfying the formula (3) decreases, It can be seen that the organic EL element of the present invention also contributes to the improvement of the contrast of the organic EL panel.

To further improve the contrast,
A transparent electrode and a metal layer are laminated to form a reflective layer, and the transparent electrode layer of the reflective layer is colored with a luminescent color so that the structure other than the luminescent color cannot be reflected, or the material of the metal layer emits light. It is effective to use a material that has the property of absorbing other than color. For this purpose, a method of absorbing light having a wavelength that does not need to be extracted to the outside of the transparent electrode in the laminated portion of the transparent electrode and the metal layer and a method of absorbing it in the metal layer material can be considered. In this case, it is desirable to configure each layer such that the optical distance of the layer interposed between the metal electrode and the light emitting layer satisfies the expression (3), but the present invention is not limited to this.

In particular, in the color panel of the color conversion system, since the backlight is blue, it is effective to use a metal having a larger blue reflection coefficient than red as the reflective metal. , Mo, Cr may be used. Further, the blueing method of the transparent electrode can be achieved by adding CuO, Co, or Ti in an amount of 1% or less to the oxide layer forming the transparent electrode.

The structure of the organic EL element of the present invention may be the structure shown in FIG. 2 in addition to the structure shown in FIG.

FIG. 2 is a diagram for explaining the structure in which the lower electrode of the organic EL element is used as an anode.
Metal electrode 28, anode transparent conductive film 27, and hole injection layer 23
The hole transport layer 22, the light emitting layer 24, the electron transport layer 25, the electron injection layer 26, and the transparent electrode 21 of the cathode are laminated in this order. Here, the electron injection layer 26 and the transparent electrode 21 portion of the cathode are formed by forming the electron injection layer 26 with an ultrathin film of an oxide, a fluoride, a boride or a chloride of an alkali or an alkaline earth metal. An ultrathin film of a metal such as Al is deposited on the above, and an In ₂ O ₃ —ZnO oxide layer (I
ZO) may be provided, or the transparent electrode 21 made of a transparent oxide such as IZO may be directly deposited on the electron injection layer 26.

In addition to the organic EL device having the layer structure shown in FIGS. 1 and 2, the present invention has been proposed as a conventional organic EL device structure having no hole transport layer. It can be applied to the organic EL device of.

Example 1 FIG. 3 is a sectional view of a color conversion type color panel constructed by using the organic EL device of the present invention. On the substrate 301 having the TFT 302, Cr (5 nm) / Pt as a metal electrode 303 as a reflective metal
(100 nm) is deposited, and an In ₂ O ₃ —ZnO oxide layer (I
ZO: refractive index 2.2 nm) was deposited. The metal electrode 303 as the reflective metal used here has an unevenness of 4n.
It is not limited to the Cr / Pt laminated body as long as it is a metal or alloy that is a conductor of m or less. The IZO film is formed by the sputtering method, but other film forming methods such as an electron beam evaporation method and a resistance heating evaporation method may be used.

The hole injection layer 3 is formed on the transparent conductive film 304.
05, a hole transport layer 306, and a light emitting layer 307 are sequentially deposited by a resistance heating vapor deposition method, and an 8-hydroxyquinoline Al complex (Alq ₃ ) is used as an electron transport layer 308 in an amount of 20.
nm stacked.

Laminate 309 of electron injection layer and upper transparent electrode
After depositing 0.5 nm of LiF as an electron injection layer, 1 nm of Al and 220 nm of IZO are formed on the upper transparent electrode.
Is deposited, and finally SiON of 300 n is used as a protective film.
m are deposited.

The optical distance of the organic EL device having this structure is as follows: the transparent conductive film 304 of IZO which is the lower electrode of the anode, the hole injection layer 305, the hole transport layer 306 and the Pt film which constitutes the metal electrode 303. It was adjusted. The wavelength of the light of the color conversion type backlight is 470 nm, and the hole injection layer 305 has a wavelength of 80 n.
m and the hole transport layer 306 were deposited to a thickness of 20 nm, the refractive index of the organic substance was set to 1.85, and I was calculated from the interference condition of formula (3).
The ZO film thickness was 183 nm. Further, the IZO film, which is the transparent conductive film 304 that constitutes the lower electrode, contains 0.6% Cu.
O was added and colored blue.

A protective layer 316 is provided on the substrate 301 thus formed with elements, and RGB color conversion filters 311 and
The substrate 310 on which 312 and 313 were manufactured was faced to each other, and the outer periphery of the element was sealed with the outer peripheral sealant 315 in a state where the void was filled with the gel body 314 to complete the panel. Here, the color conversion filter is a filter provided with a color filter and / or a fluorescence filter.

As a result of comparing the characteristics of the panel having the structure shown in this embodiment with the characteristics of the panel having the conventional structure, it is possible to improve the external extraction efficiency from 2.0% to 3.0%, and at the same brightness. It has become possible to reduce the current flow to 2/3. Furthermore, the contrast ratio is 1000 Lx, 10
200: 1 was obtained at 0 cd / m ² . Moreover, the same result was obtained when the same comparative experiment was performed with a monochrome panel and area color.

[Example 2] In as a transparent conductive film film material
_TwoO_Three-Indium with a film thickness of 201 nm instead of ZnO _TwoO_Three
-SnO_TwoExample using (ITO) (refractive index 2.0)
Even when the same comparison as in Example 1 was performed, the same results as in Example 1 were obtained.
The effect was obtained. This ITO film is formed by sputtering, vapor deposition
The film can be formed by a method such as a CVD method or a CVD method. Well
In addition, the transparent conductive film material is ZnO or SnO._TwoAs optics
Similar results were obtained when the distances were matched.

[0047]

As described above, according to the present invention,
Since a transparent conductive film is provided on the surface of the metal electrode of the organic EL element on the light emitting layer side, the film thickness of this transparent conductive film is adjusted so that the light reflected by the metal electrode interferes with each other in the element to strengthen each other. It is possible to improve the external quantum efficiency without deterioration, and the metal electrode and the transparent conductive film absorb light of a specific wavelength to improve the contrast. It is possible to provide an organic EL element that can improve the external quantum efficiency without being accompanied and can improve the contrast, and an organic EL panel using the same.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a configuration example of an organic EL element of the present invention.

FIG. 2 is a diagram for explaining a second configuration example of the organic EL element of the present invention.

FIG. 3 is a cross-sectional view of a color conversion type color panel configured by using the organic EL element of the present invention.

FIG. 4 is a diagram for explaining the structure of a conventional organic EL element.

[Explanation of symbols]

11, 21, 41 Transparent electrodes 12, 22, 42, 306 Hole transport layer 13, 23, 43, 305 Hole injection layer 14, 24, 44, 307 Light emitting layer 15, 25, 45, 308 Electron transport layer 16, 26, 46 Electron injection layer 17, 27, 304 Transparent conductive film 18, 28, 47, 303 Metal electrode 29, 301, 310 substrate 302 TFT 309 Laminated part 311, 312, 313 color conversion filter 314 gel 315 Peripheral sealant

Claims (10)

[Claims] 1. An organic EL device comprising an organic EL light emitting part including an organic light emitting layer between a metal electrode and a transparent electrode, wherein a transparent conductive film is provided on a surface of the metal electrode on the organic EL light emitting part side. The thickness of the transparent conductive film is set so as to satisfy the following expression, where L is an optical distance from the organic light emitting layer to the metal electrode, and λ is an emission wavelength of the organic light emitting layer. An organic EL device characterized in that [Equation 1] 2. An organic EL element comprising an organic EL light emitting part including an organic light emitting layer between a metal electrode and a transparent electrode, wherein a transparent conductive film is provided on a surface of the metal electrode on the organic EL light emitting part side. Provided, the light having a wavelength different from the emission wavelength of the organic EL light emitting layer, the metal electrode, and / or, the transparent conductive film is absorbed,
An organic EL device characterized in that only light having a wavelength emitted from the organic EL light emitting layer is emitted from the transparent electrode. 3. An organic EL element comprising an organic EL light emitting part including an organic light emitting layer between a metal electrode and a transparent electrode, wherein a transparent conductive film is provided on the surface of the metal electrode on the organic EL light emitting part side. The thickness of the transparent conductive film is set so as to satisfy the following expression, where L is an optical distance from the organic light emitting layer to the metal electrode, and λ is an emission wavelength of the organic light emitting layer. , And [Formula 2] Light having a wavelength different from the emission wavelength of the organic EL light-emitting layer is absorbed by the metal electrode and / or the transparent conductive film,
An organic EL device characterized in that only light having a wavelength emitted from the organic EL light emitting layer is emitted from the transparent electrode. 4. The material of the transparent conductive film is In ₂ O ₃ −.
The organic EL element according to claim 1, wherein the organic EL element is any one of ZnO, In ₂ O ₃ —SnO ₂ , ZnO, and SnO ₂ . 5. The organic film according to claim 2, wherein the transparent conductive film is doped with impurities and colored in the same color as the light emitted from the organic EL light emitting layer. EL element. 6. The organic EL light emitting layer emits blue light, and the transparent conductive film contains In ₂ O ₃ containing impurities of CuO, Co or Ti at a concentration of 1% or less.
The organic EL device according to claim 5, wherein the transparent conductive film is made of any one of —ZnO, In ₂ O ₃ —SnO ₂ , ZnO, and SnO ₂ , and absorbs blue light. element. 7. The organic EL light emitting layer emits blue light, the metal electrode is made of Zn, Mo, Cr, or an alloy of these metals, and the metal electrode absorbs blue light. 7. The organic EL element according to claim 2, 3, or 6. 8. The organic E according to claim 1.
A monochrome panel or an area color panel comprising an L element. 9. The organic EL element according to claim 6, a monochromatic blue backlight, and a color conversion filter, wherein the transparent conductive film of the organic EL element absorbs light other than blue, A color panel of a color conversion system, characterized in that electrodes reflect only blue monochromatic light from the backlight. 10. The organic EL element according to claim 7, a monochromatic blue backlight, and a color conversion filter, wherein the metal electrode absorbs light other than blue light, and monochromatic blue light from the backlight. Color conversion type color panel characterized by reflecting only light.