Patent Publication Number: US-2012032153-A1

Title: Organic Light-Emitting Diode Device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an organic light-emitting diode (OLED) device, and more particularly to an improved OLED device which employs a third light-emitting material layer disposed between a first light-emitting material layer and a second light-emitting material layer, so as to improve the phenomenon of efficiency roll-off occurring in a high luminance region of the OLED device. 
     2. Description of the Prior Art 
     An organic light emitting diode (OLED) was invented by C. W. Tang and S. A. VanSlyk et al. of Eastman Kodak Company in 1987 and manufactured by a vacuum evaporation method. A hole transporting material and an electron transporting material (such as Alq 3 ) are respectively deposited on a transparent indium tin oxide (abbreviated as ITO) glass, and then a metal electrode is vapor-deposited thereon to form the self-luminescent OLED apparatus. Due to high brightness, fast response speed, light weight, compactness, true color, no difference in viewing angles, no need of liquid crystal display (LCD) type backlight plates as well as a saving in light sources and low power consumption, it has become a new generation display. 
     Besides light-emitting material layers, the conventional OLED device is often added to other intermediate layers, such as an electron transport layer and a hole transport layer, so as to enhance the efficiency of the OLED device. Referring to  FIG. 1 , which is a structural drawing of a conventional OLED device. As shown in  FIG. 1 , the conventional OLED device  1 ′ includes a cathode  11 ′, an electron injection layer  12 ′, an electron transport layer  13 ′, a first light-emitting material layer  14 ′, a second light-emitting material layer  15 ′, a hole transport layer  16 ′, a hole injection layer  17 ′, and an anode  18 ′. 
     The above-mentioned conventional OLED device  1 ′ is an OLED device with high efficiency. However, referring to  FIG. 2 , which is a curve diagram of the luminous efficiency of the conventional OLED device  1 ′. As shown in  FIG. 2 , when the brightness of the conventional OLED device  1 ′ is higher than 3500 cd/m 2 , the luminous efficiency of the conventional OLED device  1 ′ is decreased rapidly. Such a phenomenon is called an Efficiency Roll-Off phenomenon of the conventional OLED device  1 ′. 
     In view of this, it is necessary to provide a novel OLED device to improve the above shortcomings and insufficiencies. 
     SUMMARY OF THE INVENTION 
     The major objective of the present invention is to provide an improved organic light-emitting diode (OLED) device, which adds a mixed emitting layer having a thickness less than 10 nm between two light-emitting material layers, so as to improve the Efficiency Roll-Off phenomenon happened in the high-brightness area of the conventional OLED device. 
     According to the above objective, the present invention provides an improved organic light-emitting diode (OLED) device comprising: a first conductive layer; a first light-emitting material layer being disposed on the first conductive layer; a second light-emitting material layer being disposed on the first light-emitting material layer; a second conductive layer being disposed on the second light-emitting material layer; and at least one third light-emitting material layer being disposed between the first light-emitting material layer and the second light-emitting material layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a complete understanding of the aspects, structures and techniques of the invention, reference should be made to the following detailed description and accompanying drawings wherein: 
         FIG. 1  is a structural drawing of a conventional OLED device; 
         FIG. 2  is a curve diagram of the luminous efficiency of the conventional OLED device; 
         FIG. 3  is a structural drawing of an improved OLED device of the present invention; 
         FIG. 4  is a curve diagram of the luminous efficiency of the improved OLED device of the present invention; and 
         FIG. 5  is a second curve diagram of the luminous efficiency of the improved OLED device of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 3 , which is a structural drawing of an improved OLED device of the present invention. As shown in  FIG. 3 , the improved OLED device  1  includes a first conductive layer  11 , a hole injection layer  12 , a hole transport layer  13 , a first light-emitting material layer  14 , a second light-emitting material layer  15 , an electron transport layer  16 , an electron injection layer  17 , a second conductive layer  18 , and a third light-emitting material layer  19 . The first conductive layer  11  is an anode of the improved OLED device  1 , and the material of the first conductive layer  11  is ITO. The hole injection layer  12 , the hole transport layer  13 , the first light-emitting material layer  14 , the third light-emitting material layer  19 , the second light-emitting material layer  15 , the electron transport layer  16 , the electron injection layer  17 , and the second conductive layer  18  are formed on the ITO sequentially. 
     The hole injection layer  12  is formed on the first conductive layer  11  by a spin-coating process. Preferably, the material of the hole injection layer  12  is PEDOT:PSS (poly(ethylene-dioxythiophene):poly(styrene sulfonic acid)). The hole transport layer  13  is formed of the hole injection layer  12  by an evaporation deposition process, and the material of the hole transport layer  13  is TAPC (1,1-bis {4-[di(p-tolyl)amino]-phenyl}cyclohexane). 
     Continuously referring to  FIG. 3 , the above first light-emitting material layer  14  is formed on the hole transport layer  13  by the evaporation deposition process, and the material of the first light-emitting material layer  14  is TCTA (4,4′,4′-tris (9-carbazolyl) triphenylamine). Further, in order to make the first light-emitting material layer  14  emit a light with a specific color, the first light-emitting material layer  14  can be doped with a dopant, such as Ir(2-phq)3(Tris(2-phenylquinoline) iridium(III)). 
     The third light-emitting material layer  19  is formed on the first light-emitting material layer  14  by the evaporation deposition process, and the second light-emitting material layer  15  is formed on the third light-emitting material layer  19 . The material of the second light-emitting material layer  15  is TPBi (2-2′-2″-(1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole)). In order to make the second light-emitting material layer  15  emit a light with a specific color, the second light-emitting material layer  15  can be doped with a dopant, such as Ir(2-phq)3 (Tris(2-phenylquinoline) iridium(III)). In the present invention, the third light-emitting material layer  19  is formed by mixing part of the first light-emitting material layer  14  and part of the second light-emitting material layer  15 , and the thickness of the third light-emitting material layer  19  should be less than 10 nm. In a preferred embodiment of the present invention, the thickness of the third light-emitting material layer  19  is 5 nm, and the material of the thickness of the third light-emitting material layer  19  includes TCTA, TPBi and Ir(2-phq)3. 
     Continuously referring to  FIG. 3 , the electron transport layer  16  is formed on the second light-emitting material layer  15  by the evaporation deposition process, and the material of the electron transport layer  16  is Bphen (bathophenanthroline). The electron injection layer  17  is formed on the electron transport layer  16  by the evaporation deposition process, and the material of the electron injection layer  17  is LiF. Finally, the second conductive layer  18  is formed on the electron injection layer  17  by the evaporation deposition process, and the material of the second conductive layer  18  is Al. In the improved OLED device of the present invention, the second conductive layer  18  is a cathode. 
     Referring to  FIG. 4 , which is a curve diagram of the luminous efficiency of the improved OLED device of the present invention. As shown in  FIG. 4 , when the brightness of the improved OLED device of the present invention is about 3500 cd/m 2 , the luminous efficiency still remains in 19 lm/W. Referring to  FIG. 5 , which is a second curve diagram of the luminous efficiency of the improved OLED device of the present invention. As shown in  FIG. 5 , the solid curve with solid triangles represents the luminous efficiency of the conventional OLED device; the dashed curve with hollow circles represents the luminous efficiency of the improved OLED device of the present invention. Wherein when the brightness of the OLED devices exceed 3500 cd/m 2 , the solid curve and the dashed curve begin to decline. However, when the brightness is about 10000 cd/m 2 , the hollow circles on the dashed curve are higher than the solid triangles on the solid curve. It can be seen from this that the Efficiency Roll-off phenomenon in the high-brightness area of the improved OLED device  1  of the present invention is improved greatly compared to the conventional OLED device. 
     By the detailed description of the overall structure and technical content of the present invention, the following advantages of the present invention can be derived: 
     1. By adding the third light-emitting material layer between the first light-emitting material layer and the second light-emitting material layer, and adjusting the thickness of the third light-emitting material layer, the Efficiency Roll-off phenomenon in the high-brightness area of the OLED device can be greatly improved. 
     2. The third light-emitting material layer is formed by mixing part of the first light-emitting material layer and part of the second light-emitting material layer, thus the problem of discontinuous interface between different materials is not to be considered when the third light-emitting material layer is formed. 
     3. The present invention applies the first conductive layer as the anode, and the hole injection layer, the hole transport layer, the first light-emitting material layer, the third light-emitting material layer, the second light-emitting material layer, the electron transport layer, the electron injection layer, and the second conductive layer are formed on the anode sequentially by the evaporation deposition process, it does not require other difficult process, so as to contribute to the mass production of the improved OLED device of the present invention. 
     It should be understood that the embodiments of the present invention described herein are merely illustrative of the technical concepts and features of the present invention and are not meant to limit the scope of the invention. Those skilled in the art, after reading the present disclosure, will know how to practice the invention. Various variations or modifications can be made without departing from the spirit of the invention. All such equivalent variations and modifications are intended to be included within the scope of the invention. 
     As a result of continued thinking about the invention and modifications, the inventors finally work out the designs of the present invention that has many advantages as described above. The present invention meets the requirements for an invention patent, and the application for a patent is duly filed accordingly. It is expected that the invention could be examined at an early date and granted so as to protect the rights of the inventors.