Abstract:
This invention provides an organic light-emitting diode (OLED) display device, in which a plurality of electro-luminescent units is sandwiched between a light reflective layer with an aperture array and a micro-lens array. A light absorbing layer is adjacent to a surface of the light reflective layer opposite to the electro-luminescent units. The ambient light entering the display can be focused to the apertures and directly projected unto the light absorbing layer to eliminate the ambient light. The contrast of the organic light-emitting diode display device is improved.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an organic light-emitting diode (OLED) display device. 
     2. Description of the Related Art 
     The ambient light is known to have a negative impact on the visual effect of an organic light-emitting diode display device, and the ambient light elimination design of the prior art mainly relies on adding a light absorbing layer to the display device to reduce the reflection of the incident ambient light and increase the contrast of the display device. Though the design can partially reduce the ambient light, some of the light radiated from the organic light-emitting diode device is eliminated as well. Consequently, the contrast of the display device cannot be improved significantly to enhance the visual effect. 
       FIG. 5A  is a schematic cross-sectional view of a conventional organic light-emitting diode display device with a top-emitting surface that comprises, from bottom to top, a bottom substrate  501 , a light absorbing layer  502  located on the bottom substrate  501 , a reflective electrode layer  503  located on the light absorbing layer  502 , an organic luminescent layer  504  located on the reflective electrode layer  503 , a transparent electrode layer  505  and a transparent top substrate  506 . The transparent electrode layer  505  is under the transparent top substrate  506 . As the ambient light enters the display device from the top, some of the ambient light will penetrate the reflective electrode layer  503  and be absorbed by the light absorbing layer  502 , thus the amount of the reflected ambient light will be less than that of the incident ambient light. 
       FIG. 5B  is a schematic cross-sectional view of a conventional organic light-emitting diode display device with a bottom-emitting surface that comprises, from bottom to top, a transparent bottom substrate  511 , a transparent electrode layer  512  located on the transparent bottom substrate  511 , an organic luminescent layer  513  located on the transparent electrode layer  512 , a reflective electrode layer  514  located on the organic luminescent layer  513 , a light absorbing layer  515  and a top substrate  516 . The light absorbing layer  515  is under the top substrate  516 . When the ambient light enters the display device from the bottom, some of ambient light will penetrate the reflective electrode layer  514  and be absorbed by the light absorbing layer  515 , thus the amount of the reflected ambient light will be less than that of the incident ambient light. 
     As described above, the light-absorbing layer  502  or  515  can partially absorb both the incident ambient light and the light radiated from the organic luminescent layer  504  or  513 , thus the luminescent efficiency of the organic luminescent layer  504  or  513  will be lowered. Though the light absorbing layer  502  or  515  can reduce the negative impact caused by the ambient light, it also absorbs some of the light radiated from the organic luminescent layer  504  or  513 . Consequently, the contrast of the display device cannot be significantly increased to improve the visual effect. 
     SUMMARY OF THE INVENTION 
     The present invention aims to provide an organic light-emitting diode display device that controls an incident position of ambient light, allowing the ambient light to be projected to and absorbed substantially by a light absorbing layer inside the display device to increase a contrast of the display device. 
     The present invention provides an organic light-emitting diode display device including a first substrate, a second substrate separated from the first substrate by a gap, a buffer layer filled in the gap between the two substrates, a light absorbing layer adjacent to a surface of the second substrate opposite to the first substrate, a light reflective layer with an aperture array comprising a plurality of apertures located on a surface of the light absorbing layer opposite to the first substrate, a plurality of electro-luminescent units located on a surface of the light reflective layer with an aperture array opposite to the light absorbing layer, an electrode layer with first electrical conductive type located on the electro-luminescent units and a micro-lens array comprising a plurality of micro lenses located on a surface of the second substrate opposite to the first substrate. 
     In one aspect of the present invention, the light reflective layer with an aperture array of the present organic light-emitting diode display device that features an ambient light elimination design has an electrical conductivity opposite to that of the electrode layer. 
     In another aspect of the present invention, the organic light-emitting diode display device of the present invention includes an electrode layer with a second electrical conductive type, which is located between the light reflective layer with an aperture array and the electro-luminescent units, and the electrical conductivity of said electrode layer with said first electrical conductive type is opposite to the electrical conductivity of said electrical layer with said second electrical conductive type. 
     The present invention enables the ambient light entering the display device to be focused to the apertures of the light reflective layer with an aperture array and then projected to the light absorbing layer for absorption. 
     The purposes or features of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. It is to be understood that the accompanying drawings and embodiments are provided so that this disclosure will fully convey the scope of the invention, and this invention should not be construed as limited to the embodiments set forth herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of an image display system of the present invention; 
         FIG. 2A  is a schematic cross-sectional view showing a structure of an organic light-emitting diode display device with a top-emitting surface according to a first embodiment of the present invention, wherein the function of the ambient light emission mechanism is demonstrated; 
         FIG. 2B  is a schematic cross-sectional view showing the structure of the organic light-emitting diode display device with a top-emitting surface according to the first embodiment of the present invention and demonstrates that the micro-lens array can direct the light radiated from the display device to the same direction; 
         FIG. 2C  is a schematic top view of the light reflective layer with an aperture array according to the first embodiment of the present invention. 
         FIG. 3  is a schematic cross-sectional view that shows a structure of an organic light-emitting diode display device with a bottom-emitting surface according to a second embodiment of the present invention and demonstrates the function of the ambient light emission mechanism; 
         FIG. 4  shows the relationship between the contrast and the intensity of the ambient light according to the first embodiment of the present invention and the conventional display device; 
         FIG. 5A  is a schematic cross-sectional view showing a conventional organic light-emitting diode display device with a top-emitting surface; and 
         FIG. 5B  is a schematic cross-sectional view showing a conventional organic light-emitting diode display device with a bottom-emitting surface. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     To address the disadvantages of the prior art, the present invention adds a micro-lens array to an organic light-emitting diode display device and equips a reflective electrode layer with an aperture array to ensure that the incident ambient light can be substantially absorbed by a light absorbing layer in the display device to eradicate the negative impact caused by the ambient light. 
       FIG. 2A  is a schematic cross-sectional view showing a partial structure of an organic light-emitting diode display device with a top-emitting surface  3  according to a first embodiment of the present invention. According to the first embodiment of the present invention, the organic light-emitting diode display device, from top to bottom, includes a top substrate  201 , a micro-lens array  202 , a buffer layer  203 , an electrode layer  204  of a first electrical conductive type, a plurality of electro-luminescent units  205 , an electrode layer  206  with a second electrical conductive type, a light reflective layer  207  with an aperture array, a light absorbing layer  208  and a bottom substrate  209 . There is a gap between the bottom substrate  209  and the top substrate  201 , which could be a glass substrate or a color filter, and the buffer layer  203  filled in the gap could be made of acrylic resin, epoxy resin or silicon. The micro-lens array  202  is located under the top substrate  201 , and each organic light-emitting diode unit includes a plurality of micro lenses. A refractive index of the micro-lens array  20  that ranges from 1.65 to 2.0 is higher than that of the buffer layer  203  that ranges from 1.5 to 1.6. 
     The electrode layer  204  of a first electrical conductive type, which is transparent and is located on the electro-luminescent units  205 , could be a cathode layer or an anode layer. The light absorbing layer  208  is located on the bottom substrate  209  could be made of black resin or molybdenum oxide (MoOx). The light reflective layer  207  with an aperture array located on the light absorbing layer  208  could be a second electrical conductive type or no electrical conductivity, wherein electrical conductive of the first electrical conductive type is opposite to the electrical conductive of the second electrical conductive type. When the light reflective layer  207  with an aperture array is electrical conductive, the electrode layer  206  with a second electrical conductive type could be omitted. Moreover, the apertures of the aperture array are paired with the micro lenses of the micro-lens array  202 , that is, each aperture is aligned with a corresponding micro lens so that the light penetrating the micro lenses can be focused to the apertures. The light reflective layer  207  with an aperture array could be an aluminum (Al) layer or an aluminum-neodymium (AlNd) layer of a second electrical conductive type. 
       FIG. 2C  is a schematic top view of the light reflective layer  207  with an aperture array that comprises a plurality of apertures  207   a . The electrode layer  206  with a second electrical conductive type, which is transparent and located on the light reflective layer  207  with an aperture array, could be an (ITO) electrode layer. The electro-luminescent units  205  are located on the electrode layer  206  with a second electrical conductive type. 
     Referring to  FIG. 2A , when the ambient light enters the display device from the top, it is preferable that each micro lens is 2˜5 μm in diameter and 5˜6 μm in height, each light aperture  207   a  3 μm in diameter and the gap between the top substrate  201  and the bottom substrate  209  7˜10 μm preferably within the focal length of each micro lens so that the ambient light penetrating each micro lens can be focused to its corresponding aperture  207   a . As described above, the incident ambient light penetrating the micro-lens array  203  can be focused to the apertures  207   a  and substantially absorbed by the light absorbing layer  208  to increase the contrast of the display device. 
       FIG. 2B  is used to demonstrate that the micro-lens array  203  installed in the organic light-emitting diode display device, wherein the micro-lens array  203  can also direct the light radiated from the top-emitting surface of the electro-luminescent units  205  to the same direction to increase the luminescent intensity of the electro-luminescent units  205  and improve the contrast of the display device. 
       FIG. 3  is a schematic cross-sectional view of a partial structure of an organic light-emitting diode display device with a bottom-emitting surface according to a second embodiment of the present invention. According to the second embodiment of the present invention, the organic light-emitting diode display device having the ambient light elimination design comprises, from top to bottom, a top substrate  301 , a light absorbing layer  302 , a light reflective layer  303  with an aperture array, a plurality of electro-luminescent units  304 , a transparent electrode layer  305  of a first electrical conductive type, a buffer layer  306 , a micro-lens array  307  and a bottom substrate  308 . There is a gap between the top substrate  301  and the bottom substrate  308  that could be a glass substrate or a color filter, and the buffer layer  306  filled in the gap could be made of acrylic resin, epoxy resin or silicon. The light absorbing layer  302  located under the top substrate  301  could be made of black resin or molybdenum oxide (MoOx). The light reflective layer  303  with an aperture array comprising a plurality of apertures is located under the light absorbing layer  302 , and its apertures are paired with the micro lenses comprised in the micro-lens array  307 , that is, each aperture is aligned with a corresponding micro lens, so that the light penetrating the micro lenses can be focused to the apertures. The electro-luminescent units  304 , such as OLED units, are located under the light reflective layer  303  with an aperture array. The light reflective layer  303  with an aperture array could be made of aluminum (Al) or aluminum-neodymium (AlNd), and it could be an anode layer or a cathode layer. The transparent electrode layer  305  of a first electrical conductive type is located under the electro-luminescent units  304  while the micro-lens array  307  is located on the bottom substrate  308 , and each electro-luminescent unit includes a plurality of micro lenses. The refractive index of the micro-lens array  307  that ranges from 1.65 to 2.0 is higher than that of the buffer layer  306  that ranges from 1.5 to 1.6. 
     When the ambient light enters the display device from the bottom, it is preferable that each micro lens is 2˜5 μm in diameter and 5˜6 μm in height, each aperture is 3 μm in diameter and the gap between the top substrate  301  and bottom substrate  308  preferably is 7˜10 μm within the focal length of each micro lens so that the ambient light penetrating each micro lens can be focused to its corresponding aperture. As described above, the ambient light penetrating the micro-lens array  307  can be focused to the apertures and substantially absorbed by the light absorbing layer  302  to increase the contrast of the display device. As demonstrated in  FIG. 2B , this embodiment also enables the light radiated from the bottom-emitting surface of the electro-luminescent units  304  to be directed to the same direction to increase the luminescent intensity of the electro-luminescent units  304  and improve the contrast of the display device. 
       FIG. 4  shows the relationship between the contrast and the intensity of the ambient light according to the first embodiment of the present invention and the conventional display device. The contrast of the present invention is apparently higher than that of the conventional display device under the same ambient light level. Thus it is clear that the present invention provides a better visual effect than conventional display. 
     As described above, the present invention adopts a micro-lens array and adds an aperture array to the reflective electrode layer to ensure that the incident ambient light can be accurately led to the apertures and absorbed by the light absorbing layer to increase the contrast of the display device. Furthermore, the micro-lens array enables the light radiated from the light-emitting surface of the electro-luminescent units to be directed to the same direction to increase the luminescent intensity of the display device and further improve the contrast. 
       FIG. 1  is a schematic block diagram of an image display system  10 . The image display system  10  comprises a display panel  100  wherein the display panel  100  comprises an organic light-emitting diode display device  200  of the present invention, and the display panel  100  could be an organic light-emitting diode display panel. 
     The image display system  10  generally includes a display panel  100  and an input unit  300  coupled with the display panel  100 . The input unit  300  enables images to be displayed on the display panel  100  by transmitting signals. The image display system comprises a mobile phone, digital camera, PDA, notebook, desktop computer, TV, automotive display, GPS receiver, aerial display, digital photo frame or portable DVD player. 
     While this invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that this invention is not limited hereto, and that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of this invention as defined by the appended claims.