KR100789452B1 - An organic light emitting device having protected transparent electrode - Google Patents

Abstract

In the organic light emitting device of the present invention, a transparent electrode connected to a ground electrode is disposed on a front surface to emit light from the light emitting layer, and a front light emitting organic light emitting diode having a protective means on the front surface of the transparent electrode, wherein the protective means is provided. Is extended to a contact region between the transparent electrode and the ground electrode to block the contact region from the outside. The protective means consists of a protective layer laminated on the transparent electrode or a projection packaging plate attached to the front surface of the transparent electrode.

Organic light emitting diode, top emitting type, IZO, transparent electrode, protective layer, packaging plate

Description

Organic Electroluminescent Device with Transparent Electrode Protection {AN ORGANIC LIGHT EMITTING DEVICE HAVING PROTECTED TRANSPARENT ELECTRODE}

1 is a view illustrating a pixel of a general organic light emitting display device.

Figure 2 (a) is a cross-sectional view showing the structure of the back-emitting organic light emitting device.

Figure 2 (b) is a cross-sectional view showing the structure of a conventional top-emitting organic light emitting display device.

3 is a schematic plan view of a top-emitting organic light emitting display device according to the present invention;

Figure 4 is a cross-sectional view showing the structure of a top-emitting organic light emitting display device according to an embodiment of the present invention.

5 is a cross-sectional view showing the structure of a top-emitting organic light emitting display device according to another embodiment of the present invention.

** Explanation of symbols for main parts of drawings **

121,221: Substrate 122,129,132,222,229,232: Insulation layer

123,223 semiconductor layers 125,225 impurity semiconductor layers

127,227 gate electrodes 130,230 source / drain electrodes

134,234 Anode 135,235 Electron injection layer

136,236 Light emitting layer 137,237 Bulkhead

138,238 Cathode 152,252 Hole                 

154,254: ground electrode 155: protective layer

260: packaging plate 262: adhesive

The present invention relates to an organic light emitting display device, and in particular, a transparent electrode is provided on a transparent electrode on the front surface connected to a ground electrode in a front light emitting organic light emitting display device, the protective means extending to a contact area between the transparent electrode and the ground electrode. The present invention relates to an organic light emitting device that can be prevented from being influenced by external oxygen or moisture.

Recently, since organic electroluminescent devices using poly (p-phenylinvinyline) (PPV), which is one of conjugated polymers, have been developed, research on organic materials such as conductive conjugated polymers has been actively conducted. . Research into applying such organic materials to thin film transistors, sensors, lasers, and optoelectronic devices continues to be conducted, and among them, research into organic electroluminescent devices is being actively conducted.

Electroluminescent devices made of phosphor-based inorganic materials require an operating voltage of 200V or more and the manufacturing process of the device is made by vacuum deposition, which makes it difficult to enlarge the size, in particular, it is difficult to emit blue light and the manufacturing cost is high. have. However, the electroluminescent device made of organic material has the advantages of excellent luminous efficiency, large area, ease of process, especially blue light emission, and it is possible to develop an electroluminescent device that can bend. It is attracting attention as a display device.                         

In particular, active matrix electroluminescent devices having active driving elements in each pixel like the liquid crystal display are being actively researched as flat panel displays.

One pixel 1 of such an active matrix electroluminescent device is shown in FIG. 1. As shown in the figure, the pixel 1 of the organic light emitting diode is defined by a gate line 3 and a data line 5 intersecting vertically and horizontally, and a power line 10 in the pixel 1. ) Is arranged parallel to the data line (5). In the pixel 1, two TFTs 7 and 9 and a light emitting portion 12 are arranged. The two TFTs 7 and 9 each play a different role. One TFT 7 is a switching TFT and is switched by a scanning signal supplied through the gate line 3, and the other TFT 9 is a driving TFT and an excitation signal when the switching TFT 7 is switched. Is supplied to the light emitting unit 12 through the power line 10.

In general, an organic light emitting display device having the above structure can be classified into two methods. The first is a front light emitting organic light emitting device that emits light to the front (top) of the organic light emitting device, and the second is a back light emitting organic light emitting device that emits light to the rear (bottom) of the organic light emitting device.

Hereinafter, specific structures of the top emission type organic light emitting diode and the bottom emission type organic light emitting diode will be described.

FIG. 2A is a cross-sectional view illustrating a pixel structure of the organic light emitting display device illustrated to explain the structure of the back light emitting active matrix electroluminescent device. As shown in the figure, a semiconductor layer 23 and impurity semiconductor layers 25 disposed on both sides thereof are formed on the substrate 21, and a first insulating layer 22 is formed over the entire substrate 21. The semiconductor layer 23 and the impurity semiconductor layer 25 are covered. A gate electrode 27 is formed in the region of the semiconductor layer 23 on the first insulating layer 22, and a second insulating layer 29, which is an interlayer insulating film, is stacked over the entire substrate 21. . A source / drain electrode 30 is formed on the second insulating layer 29 to form an impurity semiconductor layer 25 through contact holes formed in the first insulating layer 22 and the second insulating layer 29. Is electrically connected).

A third insulating layer 32 is formed on the second insulating layer 29 on which the source / drain electrodes 30 are formed to protect the completed thin film transistor. Meanwhile, a contact hole is formed in the third insulating layer 32 on the source / drain electrode 30 so that the source / drain electrode 30 is electrically connected to the anode 34 formed on the third insulating layer 32. Connected. The anode 34 is typically made of indium tin oxide (ITO), which is a transparent metal having a high work function. On the transparent anode 34, a light emitting layer 36 separated from adjacent pixels by a partition wall 37 is formed, and a cathode 38 made of an opaque metal having a low work function is formed thereon.

In the organic light emitting diode configured as described above, when a voltage is applied to the gate electrode 27 and an excitation signal is applied to the anode 34 and the cathode 38 through the source / drain electrode 30, the anode 34 is formed. And holes and electrons are respectively injected from the cathode 38 into the light emitting layer 36 to generate excitons in the light emitting layer 36. As the excitons decay, the LUMO of the light emitting layer 36 is lost. Light is generated by the energy difference between Low Unoccupied Molecular Orbital and High Occupied Molecular Orbital, and emits to the outside (the anode side in the drawing).

However, in the organic light emitting diode having the above structure, the light emitted from the light emitting layer 36 is the anode 34, the third insulating layer 32, the second insulating layer 29, and the first insulating layer 22. And the substrate 21, the light absorption occurs due to the respective layers, thereby lowering the light efficiency of the organic light emitting display device.

In order to solve this problem, the proposed one is a top light emitting organic electroluminescent device shown in Fig. 2 (b). The top emission type organic light emitting diode has a structure substantially similar to the bottom emission type organic light emitting diode shown in FIG. The structural difference between the top emission type organic light emitting diode and the bottom emission type organic light emitting diode is that only the cathode 34 is made of a transparent metal and the anode 38 is made of an opaque metal. That is, as shown in the figure, in the back-emitting organic light emitting device, a transparent anode is formed on the bottom surface (back side) of the light emitting layer and is connected to the source / drain electrode of the thin film transistor, and an opaque cathode is formed on the top surface (front side) of the light emitting layer. In the front emission type organic light emitting diode, an opaque anode 38 is formed on the bottom surface of the light emitting layer, and is connected to the source / drain electrodes of the thin film transistor, and the transparent cathode 34 is formed on the top surface (front surface) of the light emitting layer. ) Is formed and exposed to the outside.

The transparent cathode 34 is made of ITO or IZO (Indium Zinc Oxide). However, since ITO and IZO generally have a low work function, electron injection into the light emitting layer 36 is not sufficient. Therefore, an electron injection layer 35 is provided between the transparent cathode 34 and the light emitting layer 36 to facilitate the injection of electrons into the light emitting layer 36 so that sufficient electrons can be injected into the light emitting layer 36.

On the other hand, the cathode 34 of the top emission type organic light emitting display device is preferably IZO rather than ITO. In general, the specific resistance of ITO formed at room temperature is about 1109-1777 μΩ · cm, whereas the specific resistance of IZO is about 300-400 μΩ · cm, while the transmittance of ITO is about 77-83%, while the transmittance of IZO is about 85%. These characteristics are very important factors that determine the performance of the organic light emitting device, and it is preferable to use IZO having excellent properties as described above, and most of the top-emitting organic light emitting devices employ IZO as a transparent cathode. Doing. In addition, since IZO also has an advantage of better etching characteristics than ITO, the IZO-applied top-emitting organic electroluminescent device may also have advantages in process.

However, the IZO reacts with moisture and oxygen when exposed to the air, thereby increasing the contact resistance and deteriorating the characteristics of the fabricated front light emitting organic light emitting device.

The present invention is to solve the above problems, a protective layer extending to the contact region of the transparent electrode and the ground electrode on the front of the transparent electrode formed on the front surface of the organic light emitting device of the front light emitting type or mounting a transparent packaging plate Accordingly, an object of the present invention is to provide an organic light emitting device capable of preventing an abnormal increase in resistance of a transparent electrode due to a reaction with oxygen and moisture by exposing the transparent electrode and a contact region to the outside.

In order to achieve the above object, an organic light emitting display device according to the present invention includes a substrate consisting of a pixel region and a ground region, a thin film transistor formed in a pixel region of the substrate, a ground electrode formed in a ground region of the substrate, and a pixel. An anode formed in the region and connected to the thin film transistor, a light emitting layer formed in the pixel region and the ground region to emit light, a transparent cathode formed on the light emitting layer and connected to the ground electrode of the ground region, and formed on the transparent metal layer, Protection means extending to the contact area of the ground electrode and the transparent metal layer.

The cathode is composed of ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide), but in order to minimize damage to the lower organic layer during the process, it is advantageous to form at room temperature, and to form IZO having excellent transmittance and resistivity characteristics at room temperature. It is preferable to use. The protective means comprises a protective layer formed on the transparent cathode or a transparent packaging plate attached by an adhesive with a predetermined space in front of the transparent cathode. The protective layer is made of inorganic oxide, nitride, carbide or polymer, and the transparent packaging plate is made of glass or plastic.

An electron injection layer is formed between the light emitting layer and the transparent cathode to facilitate electron injection, and a hole transport layer may be formed between the light emitting layer and the anode. In addition, an electron transport layer for improving electron mobility and a hole transport layer for improving mobility of holes may be formed between the light emitting layer and the cathode and between the light emitting layer and the anode, respectively.

In the present invention, in order to prevent the transparent cathode employed in the front emission type organic light emitting device reacts with external air and moisture, a protective means is provided on the front surface of the transparent cathode to block oxygen and moisture from the outside. Particularly, in the present invention, the protection means extends to the area where the cathode and the ground electrode contact each other, thereby preventing the contact resistance in the contact area between the transparent cathode and the ground electrode from increasing.

The protective means may be formed as a protective film laminated on the transparent cathode to seal the contact region with the ground electrode, or may be configured as a transparent packaging plate containing the contact region of the transparent cathode. ITO or IZO may be used as the transparent cathode, but IZO will be preferable in view of characteristics.

Hereinafter, an organic light emitting display device according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a view showing a panel structure of an organic light emitting display device according to the present invention. Although not shown in detail in the drawing, a plurality of pixels defined by the plurality of gate lines 3 and the data lines 5 are disposed in the emission area. In addition, as shown in the drawing, a gate driver IC 51 for applying a gate signal to the gate line 3 and a data driver IC 52 for applying a data signal to the data line 5 are provided outside the light emitting region. It is arranged. In the drawing, reference numeral 54 denotes a ground electrode, which is connected to the cathode in the light emitting area through a ground pad to ground the voltage applied to the light emitting layer.

4 is a diagram illustrating a structure of an organic light emitting display device according to an embodiment of the present invention, in which the cross section of the pixel region and the ground region along the line AA ′ of FIG. 3 are shown for convenience of description. Divided by.

As shown in the drawing, a semiconductor layer 123 and impurity semiconductor layers 125 disposed on both sides are formed in a pixel region on a substrate 121 made of glass, plastic, or the like, and a ground electrode 154 is formed in a ground region. Is formed. In addition, a first insulating layer 122 is formed over the entire substrate 121 to cover the semiconductor layer 123, the impurity semiconductor layer 125, and the ground electrode 154. A gate electrode 127 is formed in an area of the semiconductor layer 123 on the first insulating layer 122, and a second insulating layer 129 is stacked over the entire substrate 121. A source / drain electrode 30 is formed in the pixel region on the second insulating layer 29 to form an impurity semiconductor layer 125 through contact holes formed in the second insulating layer 122 and the second insulating layer 129. Is electrically connected).

A third insulating layer 132 is formed over the entire substrate 121 on the second insulating layer 129 on which the source / drain electrodes 130 are formed, so that the source / drain electrodes (substantially, the completed thin film transistor) are formed. Protect. Meanwhile, a contact hole is formed in the third insulating layer 132 on the source / drain electrode 130, so that the opaque metal is formed in the pixel area on the third insulating layer 132. It is electrically connected with the anode 134 which consists of.

A light emitting layer 136 is formed on the anode 134 to be isolated from the adjacent pixels by the partition 137, and an electron injection layer 135 is formed thereon. The electron injection layer 135 is used to balance electrons and holes in the light emitting layer 136 by sufficiently injecting electrons into the light emitting layer 136. The electron injection layer 135 is mainly Li, LiF / Al, LiO / Al, Al-Li, MgAg. And so on. A cathode 134 made of a transparent metal such as IZO is formed on the electron injection layer 135. In addition, although not shown in the drawings, a hole injection layer may be formed between the anode 134 and the light emitting layer 136 to inject sufficient holes into the light emitting layer.

As described above, the reason for forming the electron injection layer 135 is that IZO has a higher work function than Ca used as a cathode of the back-emitting organic light emitting diode, and thus, sufficient electron injection into the light emitting layer 136 is not achieved. Do not. Therefore, the electron injection layer 135 is formed as described above to sufficiently supply electrons to the light emitting layer 136.

Holes 152 are formed in the ground region. The hole 152 is formed by processing the first insulating layer 122, the second insulating layer 129, the third insulating layer 130, the light emitting layer 134, and the electron injection layer 135. The ground electrode 152 is exposed to the outside at the bottom of the 152, and an anode 134 formed on the electron injection layer 135 is connected to the ground electrode 154 through the hole 152.

As described above, a protective layer 155 is stacked on the transparent cathode 134 of the configured top emission type organic light emitting diode to prevent oxygen and moisture from penetrating into the cathode 134. The protective layer 155 is stacked over the entirety of the substrate 121 and filled in the hole 152 in which the cathode 134 is formed and extends to the area of the ground electrode 154, so that the cathode 134 and the ground electrode 154 are separated from each other. It is possible to seal the contact area completely.

The protective layer 155 may be formed of any material as long as it can prevent the penetration of oxygen and moisture, but inorganic oxide layers such as SiOx, SiNx, AlOx, SiC, nitride layers, carbide layers, epoxy, Polymer layers excellent in moisture resistance such as polyimide, poly acrylate, poly siloxane, and multilayer films thereof may be used.

The protective layer 155 as described above is formed on the entire surface of the completed top emission type organic light emitting diode to prevent the transparent cathode 134 from reacting with oxygen and moisture. However, the transparent cathode 134 does not react with external oxygen and moisture in the case of the completed organic electroluminescent device but reacts during the manufacturing process. Therefore, in order to solve such a problem, the lamination process of the protective layer 155 is preferably performed in vacuum after the cathode 134 is formed.

5 is a view showing the structure of a top-emitting organic light emitting display device according to another embodiment of the present invention. As shown in the figure, the structure of the organic light emitting device of this embodiment is an organic electric field shown in FIG. 4 except for a protective means for blocking the transparent cathode 234 from the outside to prevent the reaction with oxygen and moisture. It is the same as the structure of the light emitting element. Therefore, the description of the same structure is omitted, and only the difference in the negative electrode protection means will be described.

As shown in the figure, in this embodiment, no layer for protecting the transparent cathode 234 is formed. Instead, in the present invention, the packaging plate 260 made of glass or transparent plastic having high transmittance and excellent mechanical properties is mounted on the front surface (upper surface) of the cathode 234 to prevent oxygen and moisture from penetrating into the cathode 234. prevent. In this case, the packaging plate 260 extends to the contact area between the cathode 234 and the ground electrode 245 and is attached by an adhesive 262 such as a thermosetting resin or a photocurable resin. As the packaging plate 260 is mounted on the front surface of the cathode 234, a space 264 is formed between the cathode 234 and the packaging plate 260, and a transparent inert liquid or an inert gas is formed in the space 264. It is filled to prevent the contact region of the cathode 234 and the cathode 234 and the ground electrode 245 react with oxygen or moisture.

As described above, in this embodiment, not only the front surface of the cathode 234 but also the contact region of the cathode 234 and the ground electrode 254 is packaged by the packaging plate 260. Therefore, it is possible to prevent oxygen penetration or moisture penetration into the cathode 234, thereby preventing the specific resistance of the entire cathode 234 from increasing, as well as contact between the cathode 234 and the ground electrode 254. It is possible to prevent the resistance from increasing.

As described above, in the present invention, the transparent cathode is protected by the protective means in the front emission type organic light emitting diode to prevent oxygen and moisture from penetrating into the transparent cathode, thereby increasing the specific resistance of the cathode. In particular, in the present invention, since the protective means extends to the contact region of the cathode and the ground electrode to protect the contact region, it is possible to effectively prevent the contact resistance of the cathode and the ground electrode from increasing due to oxygen and moisture.

The present invention having such a feature can be applied to a top-emitting organic electroluminescent device of any structure. For example, the present invention may be applied to an organic electroluminescent device of a current driving type driven by two thin film transistors or an organic electroluminescent device driven by four thin film transistors. In addition, it can be applied to an organic light emitting device having an amorphous thin film transistor or a polycrystalline thin film transistor, and an organic electroluminescent device having a hole injection layer, a hole transporting layer and an electron transporting layer, and an organic light emitting layer consisting of a light emitting layer made of various light emitting materials. It may be applied to the device.

Accordingly, the basic features of the present invention, that is, other examples or modifications having a feature in which the protective means extends to the contact region of the cathode and the ground electrode on the transparent cathode front surface, can be used by anyone skilled in the art to which the present invention pertains. It can be easily created by.

As described above, in the present invention, the transparent cathode formed on the front surface of the front emission type organic light emitting diode is protected by a protective layer or a transparent packaging plate, thereby preventing the reaction with external oxygen and moisture. Furthermore, in the present invention, since the protective layer or the packaging plate extends to the area where the cathode and the ground electrode are in contact to protect the contact area, it is possible to effectively prevent the contact resistance from increasing due to the reaction with oxygen and moisture. .

Claims (26)

A substrate comprising a pixel region and a ground region; A thin film transistor formed in the pixel region of the substrate; A ground electrode formed in the ground region of the substrate; An opaque metal layer formed in the pixel region and connected to the thin film transistor; An emission layer formed on the opaque metal layer of the pixel region and the ground electrode of the ground region to emit light; A transparent metal layer formed on the light emitting layer and connected to the ground electrode of the ground region; And An organic light emitting element formed on the transparent metal layer, the protective device extending to a contact region of the ground electrode and the transparent metal layer; The method of claim 1, wherein the thin film transistor, A semiconductor layer and an impurity semiconductor layer formed on the substrate; A first insulating layer formed on the semiconductor layer; A gate electrode formed on the first insulating layer; A second insulating layer stacked on the gate electrode; A source / drain electrode formed on the second insulating layer; And And a third insulating layer formed on the source / drain electrodes. The organic light emitting device of claim 1, wherein the opaque metal layer is an anode. The organic light emitting device of claim 1, wherein the transparent metal layer is a cathode. The organic light emitting device of claim 4, wherein the cathode is made of a material selected from the group consisting of indium tin oxide (ITO) and indium zinc oxide (IZO). The organic light emitting device of claim 1, wherein the protective means is a protective layer. The organic light emitting device of claim 6, wherein the protective layer is formed of at least one layer made of a material selected from the group consisting of inorganic oxides, nitrides, carbide layers, and polymers. The organic light emitting device of claim 7, wherein the inorganic oxide is a material selected from the group consisting of SiOx, SiNx, AlOx, and SiC. The organic electroluminescent device according to claim 7, wherein the polymer is a material selected from the group consisting of epoxy, polyimide, polyacrylate, and polysiloxane. The organic light emitting device of claim 1, wherein the protective means is a transparent packaging plate attached by an adhesive with a predetermined space in front of the transparent metal layer. The organic light emitting device of claim 10, wherein the transparent packaging plate is made of a material selected from the group consisting of glass and plastic. The organic light emitting device of claim 10, wherein the adhesive is a material selected from the group consisting of a thermosetting resin and a photocurable resin. The organic light emitting device of claim 10, wherein the space is filled with a transparent inert liquid or an inert gas. The organic light emitting device of claim 1, further comprising an electron injection layer formed between the light emitting layer and the transparent metal layer. The organic electroluminescent device according to claim 14, wherein the electron injection layer is made of a material selected from the group consisting of Li, LiF / Al, LiO / Al, Al-Li, and MgAg. The organic light emitting device of claim 10, further comprising a hole injection layer formed between the opaque metal layer and the light emitting layer. The method of claim 10, A hole transport layer formed between the opaque metal layer and the light emitting layer; And The organic light emitting device of claim 1, further comprising an electron transport layer formed between the light emitting layer and the transparent metal layer. A thin film transistor and a ground electrode formed on the substrate; An insulating layer formed on the thin film transistor and the ground electrode; An anode formed on at least a portion of the insulating layer; A light emitting layer formed on the anode; A transparent cathode formed on the light emitting layer and connected to the ground electrode; And Stacked on the transparent cathode, the organic light emitting device comprising a protective layer extending to the contact region of the cathode and the ground electrode to seal the transparent cathode and the contact region from the outside. The organic light emitting device of claim 18, wherein the protective layer is formed of at least one layer made of a material selected from the group consisting of inorganic oxides, nitrides, carbide layers, and polymers. A thin film transistor and a ground electrode formed on the substrate; An insulating layer formed on the thin film transistor and the ground electrode; An anode formed on at least a portion of the insulating layer; A light emitting layer formed on the anode; A transparent cathode formed on the light emitting layer and connected to a ground electrode; And An organic electroluminescent device comprising a transparent packaging plate attached to the transparent cathode by an adhesive and extending to the contact region of the cathode and the ground electrode to block the transparent cathode and the contact region from the outside. 21. The organic light emitting device of claim 20, wherein the transparent packaging plate is made of a material selected from the group consisting of glass and plastic. The organic electroluminescent device according to claim 20, wherein the adhesive is a material selected from the group consisting of a thermosetting resin and a photocurable resin. The organic electroluminescent device according to claim 18 or 20, wherein the transparent cathode is indium zinc oxide (IZO). A transparent electrode connected to the ground electrode is disposed on the front surface to emit light from the light emitting layer, and the front surface of the transparent electrode includes a protective means, wherein the protective means is disposed between the transparent electrode and the ground electrode. The organic light emitting device of claim 1, wherein the organic light emitting device is extended to a contact region of the substrate to block the contact region from the outside. The front light emitting organic electroluminescent device according to claim 24, wherein the protective means is a protective layer. 25. The top emission type organic light emitting device of claim 24, wherein the protection means is a transparent packaging plate attached to the front surface of the transparent electrode.

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