Patent Publication Number: US-2003230973-A1

Title: [organic electro-luminescence device and fabricating method thereof]

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001] This application claims the priority benefit of Taiwan application serial no. 91112874, filed on Jun. 13, 2002.  
       BACKGROUND OF INVENTION  
       [0002] 1. Field of the Invention  
       [0003] This invention generally relates to an organic electro-luminescence device (“OEL”) and fabricating method thereof, and more particularly to an organic electro-luminescence device (“OEL”) and fabricating method thereof having a low driving voltage.  
       [0004] 2. Description of Related Art  
       [0005] LCD panel has been widely used because of its lightweight and high efficiency. However, there are still some drawbacks of the LCD panel such as limited viewing angle, slow response speed and the need to be illuminated. More important, it is difficult to fabricate big size LCD panels.  
       [0006] A new flat panel technology, organic electro-luminescence technology, has been proposed and developed to solve the above issues. An organic electro-luminescence device uses the self-light-emitting feature of organic light emitting materials to perform the display. An organic electro-luminescence device comprises a pair of electrodes and a light-emitting layer, wherein the light-emitting layer includes light-emitting material. When the current goes through the transparent anode and the metal cathode, the holes and electrons interact to generate excitons so that the light-emitting material emits the light.  
       [0007] There are two types of the organic electro-luminescence device including the organic light emitting diode (“OLED”) device and the polymer light emitting diode (“PLED”) device. These two types operate essentially the same way. The only difference is that OLED uses small molecule organic material to form the light-emitting layer. The polymer material, with its larger molecular structure, is used to form the light-emitting layer for PLED.  
       [0008]FIG. 1 is the cross-sectional view of a conventional organic electro-luminescence device. The conventional organic electro-luminescence device includes a substrate  100 , an anode  102  on the substrate  100 , a, light-emitting layer  104  on the anode  102 , and a cathode  106  on the light-emitting layer  104 . Furthermore, a cap  110  is set above the cathode  106 ; a sealant  108  is set along the surrounding of the cap  110  and the substrate  100  to cover the organic electro-luminescence device.  
       [0009] The widely used material of the cathode  106  is a LiF/Al, Ba/Al, or Mg/Ag double-layer conducting layer, wherein Ba/Al is the most common material for the cathode  106 . The portion of the double-layer conducting layer connecting with the light-emitting layer  104  has to have low work function in order to enhance the efficiency of the injection. For example, the work function of Ba in Ba/Al double-layer conducting layer has a low work function (2.7 eV.) Furthermore, to prevent the cathode from oxidation due to oxygen or H 2 O, the metal of the outer layer of the cathode has to have a high work function characteristic. For example, the work function of Al in Ba/Al double-layer conducting layer has a high work function (4.28 eV.).  
       [0010] In the conventional organic electro-luminescence device, the thickness of low work function Ba must be larger than 50Ã□However, because of the limitation of semiconductor manufacturing process, it has to take at least two plating steps to form a Ba layer of 3000Ã□thickness. Hence, the conventional process for forming the cathode is complicated and expensive. Furthermore, because Ba is very easy to be oxidized, the process is very dangerous and is difficult to control its purity. Hence, this process for forming the cathode is not suitable for PLED device mass production.  
       SUMMARY OF INVENTION  
       [0011] An object of the present invention is to provide an organic electro-luminescence device and fabricating method thereof to avoid the danger of the conventional process for forming the cathode.  
       [0012] Another object of the present invention is to provide an organic electro-luminescence device and fabricating method thereof to simplify the process complexity and save time.  
       [0013] The present invention provides an organic electro-luminescence device, comprising: a substrate; an anode on the substrate; a light-emitting layer on the anode; a cathode on the light-emitting layer; and an ion-doping layer between the cathode and the light-emitting layer, wherein the ion doping layer is Alq3 doped with a material selected from 0.1%-10% of LiClO 4  and other Li-like ion compounds such as Na, K, and Cs ion compounds. The light-emitting layer material can be polymer light-emitting material or organic light-emitting material. The cathode can be a single-layer conducting layer such as Al and Ag having high work function. The cathode also can be a double-layer conducting layer such as LiF/AI, Ba/Al, and Mg/Ag. The ion-doping layer has a thickness of 100 Ã□. 5000 Ã□and preferably 100 Ã□. 2000 Ã□ 
       [0014] The present invention provides a method of fabricating an organic electro-luminescence device, comprising: forming an anode on a substrate; forming a light-emitting layer on the anode; forming an ion-doping layer on the light-emitting layer, wherein the ion doping layer is Alq3 doped with a material selected from 0.1%-10% of LiClO 4  and other Li-like ion compounds such as Na, K, and Cs ion compounds; and forming a cathode on the ion-doping layer. The ion-doping layer has a thickness of 50 Ã□. 5000 Ã□and preferably 50 Ã□. 2000 Ã□ The cathode can be a single-layer conducting layer such as Al and Ag having high work function. The cathode also can be a double-layer conducting layer such as LiF/AI, Ba/Al, and Mg/Ag.  
       [0015] The organic electro-luminescence device and fabricating method thereof of the present invention avoids the danger when using metal having a low work function to form the cathode so that it can improve the mass production process of forming the cathode and save time.  
       [0016] The organic electro-luminescence device and fabricating method thereof of the present invention improves the interface barrier between the metallic cathode and the light-emitting layer to increase the current density of the device.  
       [0017] The organic electro-luminescence device and fabricating method thereof of the present invention enhances the stability of the light-emitting layer of mass production.  
       [0018] The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages and embodiments of the invention will be apparent to those skilled in the art from the following description, accompanying drawings and appended claims. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0019]FIG. 1 is the cross-sectional view of a conventional organic electro-luminescence device.  
     [0020]FIG. 2 is the cross-sectional view of a preferred embodiment of an organic electro-luminescence device in accordance with the present invention.  
     [0021]FIG. 3 is the cross-sectional view of another preferred embodiment of an organic electro-luminescence device in accordance with the present invention.  
     [0022]FIG. 4 is the cross-sectional view of another preferred embodiment of an organic electro-luminescence device in accordance with the present invention.  
     [0023]FIG. 5 is the cross-sectional view of another preferred embodiment of an organic electro-luminescence device in accordance with the present invention.  
     [0024]FIG. 6 is the cross-sectional view of another preferred embodiment of an organic electro-luminescence device in accordance with the present invention.  
     [0025]FIG. 7 is the cross-sectional view of another preferred embodiment of an organic electro-luminescence device in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0026]FIG. 2 is the cross-sectional view of a preferred embodiment of an organic electro-luminescence device in accordance with the present invention.  
     [0027] Referring to FIG. 2, the organic electro-luminescence device is an double-layer structure comprising a transparent substrate  100 , an anode  102 , a light-emitting layer  104 , an ion-doping layer  105 , a cathode  106 , a cap  110 , and a sealant  108 . The method of fabricating the organic electro-luminescence device comprises the steps of: forming the anode  102  on the transparent substrate  100 ; forming the light-emitting layer  104  on the anode  102 ; forming the ion-doping layer  105  on the light-emitting layer  104 ; forming the cathode  106  on the ion-doping layer  105 ; forming the cap  110  above the cathode  106 ; and forming the sealant  108  along the surrounding of the cap  110  and the substrate  100  to cover the organic electro-luminescence device.  
     [0028] The transparent substrate  100  is a glass substrate, a plastic substrate or a flexible substrate.  
     [0029] The anode  102  is set on the transparent substrate  100 , and injects electrons into the light-emitting layer  104 . Hence, the preferred anode the material having a work function higher than 4.5 eV such as ITO, TiO 2 , Au, Ag, Pt, or Cu. The thickness of the anode is about 500 Ã□. 5000 Ã□ 
     [0030] The light-emitting layer  104  is set on the anode  102 , wherein the light-emitting layer can be polymer light-emitting material or organic light-emitting material. Poly phenylene vinylene (PVV) and polyfulerene (PF) are two examples of polymer light-emitting materials. The light-emitting layer is formed by spin-coating. The thickness of the light-emitting layer  104  is about 500 Ã□. 5000 Ã□The color characteristics of the light-emitting material depend on the energy gap between the ground state and the excited state of the material.  
     [0031] The cathode  106  is set on the light-emitting layer  104  to inject the electrons into the light-emitting layer  104 . The cathode  106  can be a single-layer conducting layer such as Al and Ag having high work function. The cathode also can be a double-layer conducting layer such as LiF/AI, Ba/Al, and Mg/Ag. The cathode is formed by evaporation and has a thickness of 500 Ã□. 5000 Ã□ 
     [0032] To make the cathode more efficiently inject the electrons into the light-emitting layer  104  and avoid the danger of the process, the organic electro-luminescence device of present invention has an ion-doping layer  105  between the cathode  106  and the light-emitting layer  104 . The ion-doping layer  105  is Alq3 doped with a material selected from 0.1%-10% of LiClO 4  and other Li-like ion compounds such as Na, K, and Cs ion compounds. The ion-doping layer is formed by evaporation and has a thickness of 500 Ã□. 5000 Ã□and preferably 50 Ã□. 2000 Ã□ 
     [0033] Because the ion-doping layer is a non-hyperresponsive material and has a low work function, if the ion-doping layer is formed on the surface of the metal having a high low function (e.g., Al), it can enhance the efficiency of the electron injection and can avoid the danger in the conventional method of fabricating an organic electro-luminescence device due to the oxidation-reduction reaction between the metal having a low work function (e.g., Ba) and the air. Hence, the present invention can improve the manufacturing process of forming the cathode to avoid the danger when using metal having a low work function, and is suitable for monochromic or full-color ink jet printing processes for the mass production of organic electro-luminescence devices. Furthermore, because the ion-doping layer is thinner, the present invention also reduces the process time.  
     [0034] Moreover, in the present invention, the ion-doping layer  106  can also be formed on the surface of the double-conducting-layer cathode  106  so that the ion-doping layer  105  can cover the metal having a low work function (e.g., Ba). This alternative also avoids the danger in the conventional method of fabricating an organic electro-luminescence device due to the oxidation-reduction reaction between the metal having a low work function (e.g., Ba) and the air.  
     [0035] It should be noted that the ion-doping layer  106  could improve the interface barrier between the metallic cathode  106  and the light-layer  104  in order to increase the current density of the device. Furthermore, the light-emitting layer is more stable after the thermal treatment process or electric burn-in process of the organic electro-luminescence device.  
     [0036] The cap  110  is set above the cathode  106 ; the sealant  108  is set along the surrounding of the substrate  100  and the cap  110  to cover the electro-luminescence device.  
     [0037] In the present invention, the current applied to the electro-luminescence device is usually a DC, but it also can be a pulse current or an AC. Furthermore, electro-luminescence device can emit the light by transmitting from the anode  102  or reflecting from the cathode  106 .  
     [0038] The electro-luminescence device also can be a three-layer structure device as shown in FIG. 3. Compared to FIG. 2, this device further comprises a hole-transmitting layer  112  between the light-emitting layer  104  and the anode  102 .  
     [0039] The electro-luminescence device also can be a four-layer structure device as shown in FIG. 4. Compared to FIG. 2, this device further comprises a hole-transmitting layer  112  between the light-emitting layer  104  and the anode  102  and an electron-transmitting layer  114  between the light-emitting layer  104  and the ion-doping layer  105 . There is also another four-layer structure device, wherein an electron-transmitting layer  114  is between the light-emitting layer  104  and the anode  102  and a hole-injecting layer  112   a  between the light-emitting layer  104  and the anode  102 .  
     [0040] The electro-luminescence device also can be a five-layer structure device as shown in FIG. 5. Compared to FIG. 4, this five-layer structure device further comprises a hole-injecting layer  112   a  between the hole-transmitting layer  112  and the anode  102 .  
     [0041] The electro-luminescence device also can be a six-layer structure device as shown in FIG. 6. Compared to FIG. 5, this five-layer structure device further comprises an electron-injecting layer  114   a  between the electron-transmitting layer  114  and the light-emitting layer  104 .  
     [0042] The hole-transmitting layer  112 , the electron-transmitting layer  114 , the hole-injecting layer  112   a , and the electron-injecting layer  114   a  are formed by spin coating. Furthermore, the material of the hole-transmitting layer  112  can be poly ethylene dioxythisophene (“PEDOT”) or polyaniline (“PANi”). The thickness of the hole-transmitting layer  112  is around 500 Ã□. 2500 Ã□ 
     [0043] Accordingly, the present invention has the following advantages.  
     [0044] 1. The electro-luminescence device of the present invention can improve the manufacturing process of forming the cathode to avoid the danger when using metal having a low work function, and is suitable for monochromic or full-color ink jet printing processes for the mass production of organic electro-luminescence devices.  
     [0045] 2. The electro-luminescence device of the present invention can save the fabrication time.  
     [0046] 3. The electro-luminescence device of the present invention can improve the interface barrier between the metallic cathode and the light-emitting layer in order to increase the current density of the device.  
     [0047] 4. The light-emitting layer is more stable after the thermal treatment process or electric burn-in process of the organic electro-luminescence device of the present invention.  
     [0048] The above description provides a full and complete description of the preferred embodiments of the present invention. Various modifications, alternate construction, and equivalent may be made by those skilled in the art without changing the scope or spirit of the invention. Accordingly, the above description and illustrations should not be construed as limiting the scope of the invention which is defined by the following claims.