JPH09312196A - Electric field-effect light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric field-effect light emitting element with its high light emitting brightness and efficiency capable of preventing a cathode from being degraded. SOLUTION: On a glass substrate 12, an anode electrode 13 made of ITO (indium titanium oxide), a positive hole transport layer 14 mixed with PVCz(polyvinyl calbazole) and TPD(triphenyldiamine derivative), an electronic transport layer 15 made of Alq3, a mixture layer 16 mixed with Mg and Alq3, and a cathode electrode 17 made of Ar are formed in order. By such a constitution, electronic injection property to the electronic transport layer 15 can be improved. Therefore, it is possible to select a cathode electrode material that is hardly oxidized. Consequently, cathode degradation can be prevented, and an electric field light emitting element with its high light emitting efficiency and longer service life can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device, and more particularly to an electroluminescent device that can be used as a display illumination, a signal light generating device or the like.

[0002]

2. Description of the Related Art In recent years, as an electroluminescence device, an electroluminescence device using an organic compound in a light emitting layer (hereinafter referred to as an organic EL device) has been put into practical use. As such an organic EL element, one having a structure as shown in FIG. 7 is known. In the organic EL device shown in the figure, an anode electrode 2 made of an ITO (Indium Tin Oxide) film is formed on a glass substrate 1, and a light emitting layer 3 is formed on the anode electrode 2.
Is formed, and magnesium (M
The cathode electrode 4 of g) is formed. The light emitting layer 3 is formed by joining the hole transporting material layer 5 and the electron transporting material layer 6 so that charges can be easily injected from the electrodes on both sides. The hole transporting material layer 5 is formed on the anode electrode 2 side, and the electron transporting material layer 6 is formed on the cathode electrode 4 side.

[0003]

However, in the conventional organic EL device as described above, the cathode electrode 4 has a low work function such as Mg (in addition to Ca, Li, In, etc.) as described above. Since it is formed of a metal, it is susceptible to oxidation, and there is a problem that the progress of deterioration after forming the element is fast. Further, there is a problem that it is difficult to handle the element when it is manufactured using such a material that is easily oxidized.

The problem to be solved by the present invention is what kind of means should be taken to obtain an electroluminescent device having high luminance and luminous efficiency, and capable of preventing deterioration of the cathode electrode.

[0005]

According to the first aspect of the present invention,
In an electroluminescent device in which an organic EL layer made of an organic compound is interposed between a cathode electrode and an anode electrode facing each other, the cathode electrode is formed of a first material, and the cathode electrode and the organic EL layer are formed. A mixed layer formed by mixing a second material having a work function smaller than that of the first material and an organic compound is interposed between the layer and the layer.

According to the first aspect of the invention, the organic EL is used.
By mixing the organic compound forming the layer and the second material, the electron injection property into the organic EL layer can be improved. Further, since the cathode electrode is made of a material that is less likely to be oxidized than the second material, it is possible to prevent deterioration of device characteristics. Further, since the mixed layer contains an organic compound, the adhesiveness with the organic EL layer is good.

In the invention according to claim 2, the mixed layer comprises:
It is characterized in that the second material and the organic compound are co-deposited. According to the second aspect of the invention, the organic compound and the second material can be uniformly formed in the mixed layer.

According to a third aspect of the present invention, the organic EL layer has at least the electron transport layer disposed on the cathode electrode side and including an electron transport material, and the organic EL layer disposed on the anode electrode side and having the hole transport property. And a hole transporting layer containing a material, wherein the mixed layer is formed by mixing the electron transporting material and the second material.

In the invention according to claim 4, the second material is an alkali metal, an alkaline earth metal, a rare earth metal, magnesium (Mg), indium (In), or a compound containing these metals and a metal boride. It is characterized by being selected from among metal carbides. The invention according to claim 5 is characterized in that the first material contains aluminum (Al) or silver (Ag). According to the inventions of claims 4 and 5, the second material contains a metal and the cathode electrode is also made of a metal, so that the adhesion is good.

According to a sixth aspect of the present invention, the mixed layer has a mixing molar ratio of the second material and the organic compound (the number of moles of the second material / the number of moles of the organic compound) of 6 or more. It is characterized by being.

The invention according to claim 7 is characterized in that the electron transport layer comprises a tris (8-quinolylate) aluminum complex, and the hole transport layer comprises polyvinylcarbazole and a triphenyldiamine derivative. I am trying. In the invention according to claim 8, the thickness of the mixed layer is 2
It is characterized by being less than 00Å.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the electroluminescent device according to the present invention will be described below with reference to the embodiments shown in the drawings. (Embodiment 1) FIG. 1 is a sectional view showing Embodiment 1 of the electroluminescent device according to the present invention. In the figure, reference numeral 11
Indicates an electroluminescent device. This electroluminescent device 11
On the glass substrate 12, the anode electrode 13,
In this structure, the hole transport layer 14, the electron transport layer 15, the mixed layer 16, and the cathode electrode 17 are formed. The organic EL layer in the present embodiment is the hole transport layer 14 and the electron transport layer 1.
5 is comprised.

The above-mentioned members will be described below. The anode electrode 13 is formed of an ITO thin film having a light transmittance of 80% or more and a sheet resistance of 50 ohms or less.
The hole transport layer 14 is made of polyvinylcarbazole (hereinafter, P
VCz) and triphenyldiamine derivative (hereinafter,
And TPD) are mixed at a molar ratio of 1: 1 and the film thickness thereof is set to about 50 nm. PVCz is a hole transporting polymer. The TPD mixed with this PVCz also has a function as a hole transfer material. As a method for forming the hole transport layer 14, PVC is used.
There is a method of co-evaporating z and TPD, a method of mixing PVCz and TPD and spin coating. The structural formulas of PVCz and TPD are shown below.

[0014]

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[0015]

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The electron transport layer 15 is made of tris (8-quinolylate) aluminum complex (hereinafter referred to as Alq3) and has an electron transport property. Further, the electron transport layer 15 is
It substantially functions as a light emitting layer. The thickness of the electron transport layer 15 is set to about 50 nm like the hole transport layer 14. As a method of forming the electron transport layer 15, as in the case of the hole transport layer 14 described above, there are a vapor deposition method and a spin coating method. In this embodiment, a vacuum vapor deposition method is adopted. The structural formula of Alq3 is shown below.

[0017]

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The mixed layer 16 is composed of magnesium (Mg) and A.
1q3 is formed by a co-evaporation method in a vacuum state at a deposition rate ratio of 20: 1 (molar ratio 656: 1).
By co-evaporating the mixed layer 16 in this manner, it becomes possible to continuously form the mixed layer 16 by vacuum evaporation of the electron transport layer 15. The thickness of the mixed layer 16 is 3
It was set to about nm. The cathode electrode 17 is made of silver (Ag). The thickness of the cathode electrode 17 is set to about 300 nm. Ag forming the cathode electrode 17 functions as a first material,
Mg forming the mixed layer 16 has a function as a second material. That is, Ag as the first material has a large work function (4.26 / eV) and has a function of being hardly oxidized. Further, Mg as the second material has a work function smaller than that of the first material (3.66 / eV) and has a function of lowering the electron injection barrier to the electron transport layer 15 to improve the electron injection property. With.

FIG. 2 is a graph showing voltage-luminance-luminance-luminance efficiency characteristics when a DC voltage is applied between the anode electrode 13 and the cathode electrode 17 using the electroluminescent device 11 of this embodiment. is there. From this graph, in the present embodiment, a luminance of 2000 cd / m ² or more can be obtained at an applied voltage of 10 V, and the luminous efficiency at that time is 1.20 l.
It can be seen that a high luminous efficiency of about m / W can be obtained. Also,
It can be seen that when the applied voltage is 14 V, the maximum brightness of about 8000 cd / m ² is obtained and the luminous efficiency of about 0.50 is obtained. Further, when the applied voltage is 12 V, the luminance is 5000 cd / m ² and the luminous efficiency is about 1.00 lm / W. The efficiency lm / W is K luminance (cd / m ² ).
It was calculated from × π ÷ {current density (A / m ² ) × voltage (V)}.

FIG. 3 is a graph showing voltage-luminance-luminance-luminance efficiency characteristics of the electroluminescent device as Comparative Example 1. The configuration of the electroluminescent device of Comparative Example 1 is a configuration in which only the mixed layer 16 is omitted in the electroluminescent device 11 of the present embodiment described above. That is, the cathode electrode 17 (Ag) is directly placed on the electron transport layer 15 made of Alq3. From the graph shown in the figure, in Comparative Example 1, the maximum luminance was about 3000 cd / m ² , the applied voltage at that time was 11.5 V, and the luminous efficiency was about 0.40 lm / W.
As a result, when the graph of FIG. 2 and the graph of FIG. 3 are compared, in the present embodiment, when the applied voltage is between 10V and 15V, 8
While high brightness of 000 cd / m ² can be obtained,
It is understood that in Comparative Example 1, only a low brightness of about 3000 cd / m ² can be obtained. Further, in the present embodiment, the luminous efficiency of 1.00 lm / W or more can be achieved when the applied voltage is between 10 V and 15 V, whereas in Comparative Example 1, the luminous efficiency is 0.50.
It can be seen that only lm / W can be obtained.

FIG. 4 is a graph showing voltage-luminance-luminance-luminance efficiency characteristics of the electroluminescent device as Comparative Example 2. The configuration of the electroluminescent device of Comparative Example 2 is such that Alq3 and Ag are used as the mixed components constituting the mixed layer 16 in the electroluminescent device 11 of the present embodiment described above, and other configurations are the same as those of the first embodiment. And In Comparative Example 2, the maximum brightness is obtained when the applied voltage is 11V. The maximum luminance is approximately 1400cd / m ^2, a significantly lower brightness compared to the highest luminance 8000 cd / m ² of the embodiment 1 described above. Further, the luminous efficiency of Comparative Example 2 is 0.2 at the maximum.
It is about 3 lm / W, and the brightness and efficiency are both high when the applied voltage is 10 V, but the efficiency is 0.20 lm / W.
The brightness is 1000 cd / m ² . On the other hand, in the first embodiment, when the applied voltage is about 10 V, the efficiency is 1.20 lm / W, the brightness is 3000 cd / m ^2, and the efficiency is
It can be seen that the luminance is significantly higher than that of Comparative Example 2.

In this embodiment, with the above-mentioned structure, the electron injection efficiency is improved. In addition, since the cathode electrode 17 is formed of a metal material that is difficult to be oxidized, it is possible to prevent deterioration of device characteristics.

By the way, in the above-described embodiment, the cathode electrode 17 is formed of Ag and Mg is mixed in the mixed layer 16, but the cathode electrode 17 is not limited to this as long as the electrode material is not easily oxidized. The second material mixed in the mixed layer 16 is not limited to Mg as long as it has a work function lower than that of the cathode electrode material. Further, in this embodiment, the organic EL
The layer is composed of the hole transport layer 14 and the electron transport layer 15,
The organic EL layer may be a single layer or a plurality of layers as long as it is an organic EL layer in which electrons and holes are injected and recombined.

(Second Embodiment) FIG. 5 shows a second embodiment of the present invention. In the present embodiment, an address light element composed of an electroluminescent element is used as a signal light generating means, and the address light element and the EL display element are combined. In the figure, 21 is the address light element 31 and the EL display element 4.
1 is a display device.

First, the structure of the address optical element 31 will be described. As shown in the figure, the address optical element 31 includes a plurality of row electrodes 3 as anode electrodes on the rear surface of the address substrate 32 made of glass or a polymer film having flexibility.
3 are arranged in parallel in the row direction. The row electrode 33 may be made of any electrode material that is light-transmissive and has a work function suitable as an anode.
TO or tin oxide can be used. A first hole transport layer 34 formed by mixing PVCz and TPD is formed on the plurality of row electrodes 33 and the address substrate 32 (rear surface). On this first hole transport layer 34 (rear surface)
, A first electron transport layer 35 made of Alq3 is laminated so as to be bonded. The first electron transport layer 35 substantially functions as a light emitting layer. These first hole transport layers 34
And the first electron transporting layer 35 constitute an organic EL layer. Further, on the first electron transport layer 35 (rear surface), A
A mixed layer 36 is formed by co-evaporating 1q3 and Mg at a vapor deposition rate ratio of 1:20. A plurality of column electrodes 37 arranged in parallel to each other are formed on the mixed layer 35 (rear surface) in the column direction orthogonal to the row direction. That is, the row electrode 33 and the column electrode 37 intersect with each other with the organic EL layer and the mixed layer 36 interposed therebetween, and it becomes possible to inject charges into the organic EL layer in the portion where the row electrode 33 and the column electrode 37 overlap. The column electrode 37 functions as a cathode electrode, is formed of an electrode material that has a physical property that has a lower work function than the anode electrode and that is not easily oxidized. In this embodiment, the column electrode 37 is made of Ag. The row electrodes 33 and the column electrodes 37 extend to the edge of the address substrate 32 and are connected to a driving IC (not shown). In this way, the matrix-driven address optical element 31 is configured.

Next, the structure of the EL display element 41 will be described. The EL display element 41 is formed on the front surface side of the address substrate 32, and has a display area having an area approximately the same as the area over the entire light emitting area of the address light element 31 described above. First, on the front surface of the address substrate 32, a plurality of rear drive electrodes 42 as cathode electrodes are formed of a conductive material that is transparent to the light emitted from the address light element 31. After this, the drive electrodes 42 are arranged in the same number as the row electrodes 33 in substantially the same shape so as to face each of the above-mentioned row electrodes 33 and overlap in a plan view. A photoconductive layer 43 is formed on the address substrate 32 and the rear drive electrode 42 so as to cover the entire display area. The photoconductive layer 43 is made of a material that absorbs photons from the address optical element 31 to generate a conductive carrier. In this embodiment, the photoconductive layer 43 is formed using amorphous silicon (a-Si). And this photoconductive layer 4
A dope layer 43A formed by doping an n-type impurity (for example, phosphorus) is formed on the surface layer of No. 3. On the doped layer 43A, a second electron transport layer 44 having an electron transport property and made of Alq3 which is the same material as the first electron transport layer 35 described above.
Are formed on the entire surface. The doped layer 43A has a function of facilitating injection of electrons into the second electron transport layer 44. Then, on the upper surface of the second electron transport layer 44,
A second hole transport layer 45 having a hole transport property is formed. The second hole transport layer 45 is made of PVCz and BND, and corresponds to each dot portion (a portion where the row electrode 33 and the column electrode 37 of the address light element 31 overlap with each other via the organic EL layer (light emitting region)). Part), R (red), G (green), B (blue) to form a predetermined color arrangement.
A light emitting material (not shown) for emitting each of the above is mixed. As a method of forming the second hole transport layer 45, a method of applying a mixed material of PVCz and BND and then impregnating a light emitting material corresponding to each dot portion, or an organic film in which a light emitting material is mixed in advance is used. A method of forming a pattern for each color according to the color arrangement can be used. The second electron transport layer 44 thus formed
The second hole transport layer 45 and the second hole transport layer 45 form a display light generation layer. Further, on the upper surface of the second hole transport layer 45, a transparent front drive electrode 46 as an anode electrode made of ITO is formed over the entire display area. A protective film 47 that is transparent to display light is formed on the front surfaces of the front drive electrode 46 and the second hole transport layer 45.

The operation of the entire display device will be described below. First, in the address light element 31, when a predetermined voltage is applied between the row electrode 33 and the column electrode 37 selected by line-sequential scanning, a green light emission peak of about 505 nm is emitted from the organic EL layer as signal light. Light is emitted toward the photoconductive layer 43. At this time, the address optical element 31
Since the organic EL layer and the photoconductive layer 43 are sufficiently close to each other, the signal light can be incident on the photoconductive layer 43 while maintaining a practically sufficient spatial frequency. Therefore, the signal light emitted from a predetermined address is incident on the photoconductive layer 43 and the doped layer 43A in the adjacent dot regions to enter the photoconductive layer 43.
Does not excite. The photoconductive layer 43 and the doped layer 43A in the portion where the signal light is incident generate electron-hole pairs as described above and show electrical conductivity in the thickness direction. As a result, the voltage applied between the front drive electrode 46 and the rear drive electrode 42 is applied to a predetermined dot portion of the display light generation layer including the second electron transport layer 44 and the second hole transport layer 45. Will be applied. Therefore, electrons are injected into the second electron transport layer 44 together with the generated electrons, and holes are injected into the second hole transport layer 45. Note that a DC drive voltage, a pulse voltage, an AC voltage, or the like can be used between the drive electrodes. As a result, as described above, due to the light emission of the EL display element 41, display light colored by various light emitting materials is generated in the front direction, and at the same time, return light (not shown) is generated in the rear direction. Since this return light is incident on the photoconductive layer 43 and the doped layer 43A, the photoconductive layer 43 and the doped layer 43A are re-excited to newly generate electron-hole pairs. Therefore, the photoconductive layer 43 holds the state in which charges can be injected in the second electron transport layer 44. Therefore, E
In the state where the drive voltage is continuously applied to the display light generating layer of the L display element 41, the charges are continuously injected into the display light generating layer. While in this state, the display light generating layer can be continuously driven for a sufficiently long time for one frame period, so that the row electrode 33 and the column electrode 37 on the address light element 31 side are driven.
Even when and are no longer selected, the display light generation layer maintains light emission. Therefore, the line-sequential scanning maintains the light emission until the next scanning. By canceling the voltage applied to the rear drive electrode 42 immediately before the next scan, the charges accumulated in the photoconductive layer 43 and the doped layer 43A are eliminated, and new display light emission becomes possible.

In the present embodiment, the address optical element 3
The column electrode 37 serving as a cathode and the first electron transport layer 35
By interposing the mixed layer 36 containing Mg having a work function lower than that of Ag, which is a material of the column electrode 37, between the column and the column electrode 37, deterioration of the column electrode 37 can be prevented and the electron injection efficiency can be improved. Therefore, in the present embodiment, the light emission brightness and the light emission efficiency can be improved. in this way,
When the light emission luminance and the light emission efficiency are improved, the applied voltage can be lowered, so that the power consumption can be reduced and the light emission life can be improved.

(Embodiment 3) FIG. 6 is a sectional view of a display device having an electroluminescent element according to the present invention. This embodiment is characterized in that the electroluminescent element is an address light element for generating address light and includes a liquid crystal display element as a display element. In the figure, reference numeral 51 denotes a display device. The display device 51 includes an address optical element 52 and a liquid crystal display element 5.
3 and a backlight system 54.

The structure of the address optical element 52 will be described below. As shown in FIG. 6, the address optical element 52 is
Address substrate 55, row electrode 56, and hole transport layer 57
An electron transport layer 58, a mixed layer 59, a column electrode 60,
Consists of The address substrate 55 is made of glass.

On the rear surface of the address substrate 55, a plurality of row electrodes 56 which are parallel to each other in the row direction are formed. The row electrode 56 functions as an anode electrode, and may be any electrode material having light transmittance and a predetermined work function. In this embodiment, the row electrode 56 is made of ITO. A hole transport layer 57 formed by mixing PVCz and BND is formed on the row electrodes 56 and the address substrate 55 (rear surface). The film thickness of the hole transport layer 57 is set to about 50 nm. Here, PVCz is a hole transporting polymer. This PVC
BND mixed with z also has a function as a hole transport material. As a method of forming the hole transport layer 57, there are a method of co-evaporating PVCz and TPD, a method of mixing PVCz and BND and spin coating as described above. The structural formula of BND is shown below.

[0032]

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The electron transport layer 58 is made of Alq3 and has an electron transport property. The electron transport layer 58 substantially functions as a light emitting layer. The thickness of the electron transport layer 58 is set to about 50 nm like the hole transport layer 57.
As a method of forming the electron transport layer 58, there is a vapor deposition method, a spin coating method, or the like as in the case of the hole transport layer 57 described above, but in the present embodiment, the vacuum vapor deposition method is adopted. The mixed layer 59 includes magnesium (Mg) and Alq3 at a deposition rate ratio of 20: 1.
It is formed by a co-evaporation method in a vacuum state. By co-evaporating the mixed layer 59 in this manner, the electron transport layer 58 can be obtained.
It is possible to continuously form the mixed layer 59 from the vacuum deposition of. The thickness of the mixed layer 59 was set to about 3 nm. Then, the column electrode 60 as the cathode is
It is made of silver (Ag). The thickness of the column electrode 60 is set to about 300 nm. Ag forming the column electrode 60 has a large work function and has a function of being hardly oxidized. Further, Mg has a small work function and has a function of lowering an electron injection barrier to the electron transport layer 58 to improve the electron injection property. Then, a light-transmitting protective film 62 is formed so as to cover the hole transport layer 57, the electron transport layer 58, the mixed layer 59, and the column electrode 60. As the protective film 62, for example, a silicon nitride film can be used. In the address optical element 52 thus configured, when a voltage is applied between the row electrode 56 and the column electrode 60, a signal is output from a portion of the electron transport layer 58 near the interface with the hole transport layer 57. Ultraviolet light is emitted as light. It is desirable that the signal light is set so that ultraviolet light within a wavelength range of 350 to 400 nm is output. The row electrodes 56 and the column electrodes 60 extend to the edge of the address substrate 55 and are connected to a driving IC (not shown). In this way, the matrix-driven address optical element 52 is configured.

The liquid crystal display element 53 combined with the address optical element 52 having such a structure is the address optical element 52.
The display area has an area similar to that of the light emitting area. The configuration of the liquid crystal display element 53 will be described below with reference to FIG. The liquid crystal display element 53 includes a pair of front transparent substrates 63.
And the rear transparent substrate 64 and a sealing material 65 between these transparent substrates.
TN type liquid crystal sealed by the transparent substrate 6
A configuration is provided in which a TN cell having optical rotatory power is provided, which includes a pair of front polarizing plate 67 and rear polarizing plate 68 which are arranged with 3, and 64 interposed therebetween. Further, in the third embodiment, one transparent rear drive electrode 69 made of ITO is formed on the opposite inner side surface of the rear transparent substrate 63 over the entire display area. A photoconductive layer 70 is formed on the front surface of the rear drive electrode 69. Further, a post-alignment film 71 is formed so as to cover the photoconductive layer 70.

The photoconductive layer 70 is made of a material that absorbs photons to generate conductive carriers. Such a photoconductive layer 7
0 is, for example, ZnO, amorphous silicon (a-Si), amorphous selenium (a-Se), Zn
Inorganic semiconductors such as S and SnOx, charge transfer complexes such as polyvinylcarbazole, organic photocarrier generation layers (perylenes, quinones, phthalocyanines, etc.) and organic carrier transport layers (arylamines, hydrazines, oxazoles, etc.) A material such as an organic composite material in which and are stacked can be used. In such a material, when a photon is absorbed, a conductive carrier is generated and its impedance is rapidly reduced, so that the material becomes electrically conductive. In particular, in the third embodiment, the photoconductive layer 70 uses ZnO having a light absorption characteristic of absorbing only signal light (ultraviolet light). ZnO usually has no absorption in the visible light range.

Further, on the inner surface facing the front transparent substrate 64,
A color filter layer 72 having a predetermined color arrangement is formed over the entire display area. Further, a front drive electrode 74 made of ITO is formed on the rear surface of the color filter layer 72 through a transparent protective film 73 over the front surface of the display area. Further, a pre-alignment film 75 is formed so as to cover the pre-driving electrode 74. In the liquid crystal display element 53 having such a configuration, the front drive electrode 74 and the rear drive electrode 69 do not require patterning, and it is sufficient to form a film over the entire display region. The manufacturing cost of the display element can be significantly reduced as compared with the display element. The liquid crystal display element 53 and the address light element 52 described above have a dot arrangement of the address light element 52 (a crossing portion of the row electrode 56 and the column electrode 60) with respect to the color arrangement of the color filter layer 72. The arrangement is such that the signal light is incident on the photoconductive layer 70 while maintaining the spatial frequency. Further, as shown in FIG. 6, a backlight system 54 is arranged behind the address optical element 52. The backlight system 54 includes a light source 76 that emits visible light.
The light guide plate 77 and the reflection plate 78 are included.

Next, in the display device 51 of the present embodiment, when predetermined row electrodes 56 and column electrodes 60 are selected and matrix-driven, signal light is emitted from a predetermined address of the address optical element 52. The action and operation of the photoconductive layer 70 in the case of the above will be described.

First, in a state where an AC drive voltage is applied between the rear drive electrode 69 and the front drive electrode 74, a predetermined row electrode 56 and a column electrode 60 are selected and holes in a portion where both electrodes overlap each other. When charges are injected into the transport layer 57 and the electron transport layer 58, signal light (ultraviolet light) is generated in this portion. Reference numeral s in FIG. 6 indicates signal light. Then, when the signal light s is incident on the photoconductive layer 70, the photoconductive layer 70 in the incident portion is received.
The impedance of the device decreases. Therefore, the drive voltage can be applied only to the liquid crystal 66 in the portion between the photoconductive layer 70 in which the signal light is incident and the front drive electrode 74, and the liquid crystal 66 can be oriented in a predetermined direction. . By orienting the liquid crystal 66 in this manner, it is possible to drive the display by controlling the light from the backlight system 54 via the address light element 31. Since the light source 76 is only in the visible wavelength range, it does not excite the photoconductive layer 70.

Also in the present embodiment described above, the address optical element 51 comprises Mg and an electron transport layer having a work function smaller than that of the cathode electrode material Ag between the column electrode 60 which is a cathode electrode and the electron transport layer 58. Organic compound A
A mixed layer 59 formed by mixing 1q3 is interposed. Therefore, it becomes possible to efficiently inject electrons from the column electrode 60 into the electron transport layer 58 via the mixed layer 59. By providing such a mixed layer 59, Ag which is difficult to be oxidized can be adopted as a material of the column electrode 60. Therefore, the deterioration of the column electrode 60 can be prevented.
Moreover, since the electron injection efficiency can be improved as described above, the light emission brightness and the light emission efficiency of the address light element 51 can be improved. As described above, when the light emission brightness and the light emission efficiency are improved, the applied voltage can be lowered, so that the power consumption can be reduced and the light emission life can be improved.

Although the first to third embodiments have been described above, the present invention is not limited to these.
Various changes accompanying the gist of the configuration are possible. For example, in each of the above-described embodiments, a mixture of Alq3 and Mg is used as the mixed layer, but a metal having a work function smaller than that of the cathode electrode material or a compound containing these metals is contained in the organic EL material. If For example, when the cathode electrode is formed of Ag (work function 4.26 / eV), indium (I
It is also possible to use n), an alkali metal, an alkaline earth metal, a rare earth metal, a compound containing these metals, a metal boride, or a metal carbide. Incidentally, the work function of Li is 2.93 / eV, Ca is 2.9 / eV, and In is 4.0.
The work function of CaO, which is a compound of Ca, is 1.6 to 1.86 / eV. Further, the cathode electrode may be low resistance aluminum (Al) other than Ag.

In the first embodiment, magnesium (M
g) and Alq3 were mixed in a ratio of 20: 1 to form a mixed layer, but by mixing so that the molar ratio of Mg and Alq3 is 6 or more, good electron injection efficiency can be obtained. . Although Ag is used as the cathode electrode material in each of the above-described embodiments, the electrode material is not limited to Ag as long as the electrode material is not easily oxidized. Further, it is desirable that the film thickness of the mixed layer is 200 Å or less.

In each of the above embodiments, the mixed layer is formed by co-evaporation, but a method of ion-implanting a metal or a compound thereof having a small work function into the organic EL material film, organic EL.
It is possible to form the material film by a method of thermally diffusing a metal or a compound thereof having a small work function, a wet film forming method, or the like.

[0043]

As is clear from the above description, according to the present invention, it is possible to realize an electroluminescent device having high luminance and high luminous efficiency, preventing deterioration of the cathode electrode, and having a long light emission life. .

[Brief description of drawings]

FIG. 1 is a sectional view of an electroluminescent device according to a first embodiment of the present invention.

FIG. 2 is a graph showing voltage-luminance-luminance-luminance efficiency characteristics when a DC voltage is applied in the first embodiment.

FIG. 3 is a graph showing voltage-light emission luminance-light emission efficiency characteristics in Comparative Example 1.

FIG. 4 is a graph showing voltage-light emission luminance-light emission efficiency characteristics in Comparative Example 2.

FIG. 5 is a sectional view of a display device according to a second embodiment of the invention.

FIG. 6 is a sectional view of a display device according to a third embodiment of the invention.

FIG. 7 is an explanatory cross-sectional view of a conventional electroluminescent device.

[Explanation of symbols]

 11 Electroluminescent Device 12 Glass Substrate 13 Anode Electrode 14 Hole Transport Layer 15 Electron Transport Layer (Alq3) 16 Mixed Layer (Alq3 + Mg) 17 Cathode Electrode (Ag)

Claims (8)

[Claims] 1. An electroluminescent device in which an organic EL layer made of an organic compound is interposed between a cathode electrode and an anode electrode facing each other, wherein the cathode electrode is formed of a first material, and
The first electrode is provided between the cathode electrode and the organic EL layer.
An electroluminescent device characterized in that a mixed layer formed by mixing a second material having a work function smaller than that of the above material and an organic compound is interposed. 2. The electroluminescent device according to claim 1, wherein the mixed layer is formed by co-evaporating the second material and the organic compound. 3. The organic EL layer comprises at least an electron transport layer arranged on the cathode electrode side and containing an electron transport material, and a hole transport layer arranged on the anode electrode side and containing a hole transport material. 3. The electroluminescent device according to claim 1, further comprising a layer, wherein the mixed layer is formed by mixing the electron transporting material and the second material. 4. The second material is selected from alkali metals, alkaline earth metals, rare earth metals, magnesium (Mg), indium (In), or compounds containing these metals and metal borides and metal carbides. The electroluminescent element according to any one of claims 1 to 3, which is selected. 5. The first material is aluminum (A
1) or silver (Ag) is contained.
~ The electroluminescent device according to claim 4. 6. The mixed layer has a mixed molar ratio of the second material and the organic compound (the number of moles of the second material / the number of moles of the organic compound) of 6 or more. The electroluminescent element according to any one of claims 1 to 5. 7. The electron transport layer comprises a tris (8-quinolylate) aluminum complex, and the hole transport layer comprises polyvinylcarbazole and a triphenyldiamine derivative. Claim 6
The electroluminescent element according to any one of 1. 8. The electroluminescent device according to claim 7, wherein the mixed layer has a thickness of 200 Å or less.