JPH08279626A - Electroluminescent element and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide an electroluminescent element large in emitted light quantity per area. CONSTITUTION: A large number of spring coil-like conductive projections 13 of polythiophene are made to grow on a transparent electrode (ITO) 12 by electrolytic composition, a hole transfer layer 14 is formed so as to seal up the spring coil-like conductive projections 13, and an electron transfer layer 15 and a back electrode 16 are successively formed on the hole transfer layer 14 for the formation of an electroluminescent element, wherein holes injected into the hole transfer layer 14 can be enhanced in amount to improve the electroluminescent element in brightness.

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 a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as an electroluminescent device of this type,
A light emitting diode (LED) having a structure as shown in FIG. 4 is known. As shown in the figure, in this light emitting diode, a transparent electrode (anode electrode) 2 is formed on a transparent substrate 1 made of glass or the like, and a hole transport layer (P-type semiconductor layer) made of an organic material is formed on the transparent electrode 2. ) 3 is formed. The hole transport layer 3 is composed of a first hole transport layer 3a having a high work function and a second hole transport layer 3b having a low work function. Then, on the hole transport layer 3, an electron transport layer (N
Type semiconductor layer) 4 is joined, and a back electron (cathode electrode) 5 made of aluminum or the like is formed on the electron transport layer 4 to form a light emitting diode. In addition, ITO (Indium Tin Oxide) is used for the above-mentioned transparent electrode 2 mainly because of its transparency and the value of its work function.

In such a structure, when a predetermined voltage is applied between the electrodes 2 and 5, holes are injected from the transparent electrode 2 into the first hole transport layer 3a through the interface, and the first hole transport layer is formed. The holes injected into the layer 3a move to the second hole transporting layer 3b having a low work function, and the electron transporting layer 4 of the second hole transporting layer 3b.
Move to near the interface with. The electrons injected into the electron transport layer 4 move to the vicinity of the interface of the electron transport layer with the second hole transport layer 3b. Here, the holes and electrons are the second hole transport layer 3
Recombination occurs in the vicinity of the interface between b and the electron transport layer 4, and luminescence is generated accordingly.

[0004]

In such an electroluminescent device, the hole injection efficiency is preferably such that the injection interface area per unit light emitting area is large, but the transparent electrode (I
Since (TO) 2 is generally formed on the flat surface of the transparent substrate 1 by means such as vapor deposition and sputtering, the surface of the formed transparent electrode is also flat, and holes are injected per unit light emitting area. It was difficult to improve the interface area. For the first hole transport layer, the second hole transport layer and the electron transport layer, the material of the hole transport layer or the electron transport layer is dissolved in a solvent in a vacuum deposition method or a solvent, and spin coating, casting, dipping There is a problem that the throughput is low because the layers are layered one by one by the method, dried and then patterned.

An object of the present invention is to provide a high-brightness electroluminescent device having a large hole injection interface area and an efficient manufacturing method thereof.

[0006]

According to the first aspect of the present invention,
In an electroluminescent device having a hole transport layer and an electron transport layer formed between an anode electrode and a cathode electrode, a plurality of conductive protrusions are formed on the electrode surface, and a transport layer is formed so as to cover the conductive protrusions. It is characterized by being. The invention according to claim 2 is characterized in that the conductive protrusion contains a polymer having a work function between the work function of the electrode and the work function of the transport layer. The invention according to claim 3 is characterized in that the polymer has a conjugated double bond. According to a fourth aspect of the present invention, the conductive protrusion is formed in a spiral shape with its end contacting the anode electrode. In the invention according to claim 5, the work function is between the work function of the anode electrode and the work function of the hole transport layer, or between the work function of the cathode electrode and the work function of the electron transport layer. The anode electrode or the cathode electrode is dipped in a mixed solution in which a polymer material for polymerizing the binding polymer and a transport layer material for forming the hole transport layer or the electron transport layer are dipped to form an electric field on the electrode. In addition, the conjugated double bond polymer is polymerized on the electrode, and the transport layer material is deposited on the conjugated double bond polymer.

[0007]

According to the first aspect of the invention, holes or electrons can be efficiently injected from the electrode to the hole transport layer or the electron transport layer through the plurality of conductive protrusions having a large surface area, so that the emission characteristics are improved. Get better In the invention according to claim 2, since the conductive protrusion includes a polymer having a work function between the work function of the electrode and the work function of the transport layer,
Since holes or electrons are injected from the electrode to the transport layer, power consumption applied to the electrode can be suppressed. In the invention according to claim 3, since the polymer has a conjugated double bond, the area of the site where holes or electrons are injected can be increased. In the invention according to claim 4, since the conductive protrusion is formed in a spiral shape with its end being in contact with the anode electrode, the area of the conductive protrusion per unit area on the electrode and the conductivity The amount of light emission can be increased because the area of the transport layer in contact with the protrusions is significantly increased. In the invention according to claim 5, the anode electrode or the cathode electrode is added to a mixed solution in which a polymer material for polymerizing a conjugated double bond polymer and a transport layer material for forming a hole transport layer or an electron transport layer are mixed. So as to form an electric field on the electrode, polymerize the conjugated double bond polymer on the electrode, and deposit the transport layer material on the conjugated double bond polymer. The molecule and transport layer can be formed together.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the electroluminescent device according to the present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 is a cross-sectional view showing an electroluminescent device 10 of this example. In this embodiment, the transparent electrode 12 made of ITO is formed on the transparent substrate 11 made of glass or the like by, for example, the sputtering method. A large number of conductive protrusions 13 made of an organic material are provided on the surface of the transparent electrode 12. A hole transport layer 14 is formed on the transparent electrode 12 so as to cover the conductive protrusions 13 in a protruding state.
The thickness of the hole transport layer 14 is set so that the lower portion covers the conductive protrusions 13 and the upper portion is composed of only the hole transport layer 14 as described above. Then, the hole transport layer 14
An electron transport layer 15 is formed on the top. Further, a back electrode 16 made of aluminum or the like is provided on the electron transport layer 15 as a cathode electrode.

In this embodiment, the conductive protrusion 13 is grown on the transparent electrode 12 by using an electrolytic synthesizing apparatus as shown in FIG. Hereinafter, this electrolytic synthesizing apparatus and a method for manufacturing an electroluminescent device using the same will be described. This electrolytic synthesizer
It also has the function of a dip coater.
That is, this device has an electrolytic bath 17 and a standard electrode bath 18. In the electrolytic bath 17, a monomer or oligomer of an organic material to be the conductive protrusions 13 and the hole transport layer 14 are provided.
A mixed solution 19 of an organic material having a hole-transporting property, a solvent that dissolves these organic materials, and an electrolyte is placed therein. In this mixed solution 19, a transparent substrate 11 as a working electrode is provided. The upper transparent electrode 12 and the counter electrode 20 that supplies electric charge are immersed. On the other hand, the standard electrolytic cell 18 contains an electrolyte solution 21.
A standard electrode 22 for knowing the potential of the solution on the surface of the working electrode
Is soaked. Furthermore, the electrolytic cell 17 and the standard electrode cell 1
8 has a salt bridge 23 disposed so as to straddle both tanks, and both ends of the salt bridge 23 are immersed in both liquids. The transparent electrode 12 as a working electrode and the counter electrode 20 are connected in series to the variable resistor 24 and the DC power supply 25. The counter electrode 20 and the standard electrode 22 are connected via a voltmeter 26.

When electrolytic synthesis is performed using the electrolytic synthesizer having such a structure, as shown in FIG. 2, a large number of spring coil-shaped conductive projections (polymers) 13 are formed on the transparent electrode 12 made of ITO. grow up. At this time, the transparent electrode 12
Hold a positive potential sufficient to synthesize the polymer by electrolytic oxidation of the monomers. In this embodiment, thiophene is used as a monomer of the organic material forming the conductive protrusions 13, and a polymerization reaction represented by the following chemical reaction formula 1 occurs to generate polythiophene having a chain structure.

Embedded image In addition to this polythiophene, as a conductive polymer that can be used for the conductive protrusion 13, polyaniline,
There are polymers having conjugated double bonds such as polythiazyl, polyacetylene, polydiacetylene, polypyrrole, polyparaphenylene, and polyparaphenylene sulfide.

Since such electrolytic synthesis is carried out in an organic material having a hole transporting property, when the transparent substrate 11 is pulled up from the mixed liquid 19, the conductive projections 13 are formed on the hole transporting layer 14 as shown in FIG. It is covered by. After the hole transport layer 14 is solidified, an electron transporting organic material is stacked on the hole transport layer 14 to form the electron transport layer 1.
5 can be formed. After that, a conductive material such as aluminum is sputtered on the electron transport layer 15 to form the back electrode 16 as a cathode electrode, whereby the electroluminescent element of the present embodiment can be manufactured. As described above, by performing the electric field polymerization and the dipping method at the same time, the step of forming the conductive protrusion 13 on the transparent electrode 12 and the step of forming the hole transport layer 14 covering the conductive protrusion 13 are collectively performed. Therefore, productivity is good.

In the electroluminescent device having such a structure, at the interface between the hole transport layer 14 and the electron transport layer 15, a large amount of energy for preventing the electrons from moving toward the transparent electrode (anode electrode) 12 side. A barrier is generated, and as a result, recombination of holes and electrons occurs on the hole transport layer 14 side of the interface between the hole transport layer 14 and the electron transport layer 15, and the excitation energy generated by this causes the excitation energy in FIG. Light emission occurs as shown by a thick arrow.

The solid and dashed arrows in FIG. 2 conceptually indicate the paths through which holes are injected into the hole transport layer 14. A broken line shown in the figure shows a path in which holes are directly injected from the transparent electrode 12 into the hole transport layer 14 as in the conventional electroluminescent device, and the first oxidation of the conductive protrusions 13 (takes electrons). Energy required for the transparent electrode (IT
There is a new path indicated by the solid arrow because it is located between the work function of O) 12 and the energy required for the first oxidation of the hole transport layer 14. Since the energy required for this new route is smaller than the energy of the route indicated by the broken line arrow, the number of hole injections is relatively larger in the route indicated by the solid line. Since many conductive protrusions 13 are present on the transparent electrode 12, the area of the hole injection interface from the transparent electrode 12 to the hole transport layer 14 is significantly increased. In addition, the conductive protrusion 13 is formed in a coil shape on the transparent electrode 12, and almost the entire surface thereof is covered with the hole transport layer 1.
Since it is covered with 4, the number of holes injected from the surface of the conductive protrusion 13 into the hole transport layer 14 increases dramatically. Many holes injected into the hole transport layer 14 in this manner move to the vicinity of the interface between the hole transport layer 14 and the electron transport layer 15, so that the amount of light emission per unit light emitting area becomes large. In this embodiment, since the amount of light emission per unit area is increased as described above, it is possible to achieve high brightness of the electroluminescent device. In addition, the coil-like structure improves the injection efficiency of holes due to the presence of the conductive protrusions 13 having an increased surface area with the hole transport layer 14, so that driving at a lower voltage can be performed to obtain desired brightness. It will be possible. Furthermore, since the conductive protrusions 13 scatter and absorb the incident external light, it reduces the reflection of external light when the device is not biased. For example, if a display is configured with such an electroluminescent device, the quality will be improved. Can be displayed well. Further, normally, the polymer material used for the conductive protrusions 13 is easily oxidized by being exposed to the air and loses its function, but the conductive protrusions 13 are sealed as in the present embodiment. If formed together with the organic material (hole transport layer 14),
The conductive protrusion 13 is not exposed to the atmosphere, and the device life can be extended.

Although the embodiment has been described above, the present invention is not limited to this, and various design changes and material changes accompanying the gist of the configuration can be made. For example, in the above embodiment, the conductive protrusion 13 was formed of a conductive polymer material by electrolytic synthesis, but the hole transport layer 14 was used.
Other materials may be used as long as they are fine conductive protrusions having a surface area that substantially increases the amount of holes injected into the side, and the formation method thereof is not limited. Further, various materials can be selected as a constituent material of the hole transport layer 14 and the electron transport layer 15. In the above examples, the conductive protrusion and the hole transport layer were formed on the transparent electrode, but a polymer material for polymerizing the conjugated double bond polymer between the work function of the back electrode and the work function of the electron transport layer. The back electrode is immersed in a mixed solution in which the transport layer material forming the electron transport layer is mixed with the back electrode, and an electric field is formed on the back electrode.
The conjugated double bond polymer may be polymerized on the back electrode and the electron transport layer material may be deposited on the conjugated double bond.

[0015]

As is apparent from the above description, according to the present invention, the amount of light emission per unit area of the electroluminescent element is increased, and the effect of achieving high brightness can be obtained. Also,
The electroluminescent device has an effect of enabling driving at a lower voltage in order to obtain a desired brightness.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of an electroluminescent device of the present invention.

FIG. 2 is an enlarged sectional view of an essential part showing an embodiment of the electroluminescent device of the present invention.

FIG. 3 is an explanatory diagram of an electrolytic synthesis apparatus used in an example of the present invention.

FIG. 4 is a sectional view of a conventional electroluminescent device.

[Explanation of symbols]

 12 Transparent Electrode 13 Conductive Protrusion 14 Hole Transport Layer 15 Electron Transport Layer 16 Back Electrode 17 Electrolyzer 19 Mixed Liquid

Claims (5)

[Claims] 1. An electroluminescent device comprising a hole transport layer and an electron transport layer formed between an anode electrode and a cathode electrode, wherein a plurality of conductive protrusions are formed on an electrode surface to cover the conductive protrusions. An electroluminescent device having a transport layer formed on a surface thereof. 2. The electroluminescent device according to claim 1, wherein the conductive protrusion comprises a polymer having a work function between the work function of the electrode and the work function of the transport layer. 3. The electroluminescent device according to claim 2, wherein the polymer has a conjugated double bond. 4. The electroluminescent device according to claim 1, wherein the conductive protrusion is formed in a spiral shape having an end contacting the anode electrode. 5. A conjugated double bond polymer in which the work function is between the work function of the anode electrode and the work function of the hole transport layer, or between the work function of the cathode electrode and the work function of the electron transport layer. By immersing the anode electrode or the cathode electrode in a mixed solution in which a polymerizing material for polymerizing the above and a transporting layer material forming the hole transporting layer or the electron transporting layer are formed to form an electric field on the electrode. A method of manufacturing an electroluminescence device, comprising polymerizing a conjugated double bond polymer on the polymer and depositing the transport layer material on the conjugated double bond polymer.