Abstract:
A pixel structure for use in a white light emitting organic electroluminescent device therein comprises a first sub-pixel, a second sub-pixel, a third sub-pixel, and a fourth sub-pixel. The first sub-pixel has a first color filter and a first color change medium. The second sub-pixel has a second color filter and a second color change medium. The third sub-pixel has only a third color filter. The fourth sub-pixel does not have any color filter or color change medium so that the white light emitted from the white light emitting organic electroluminescent device can pass through the fourth sub-pixel directly. Thereby, the white light can be transformed into the color corresponding to each color change medium. Besides, the color shown from the pixel structure can be modulated by the white light from the fourth sub-pixel.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (1) Field of the Invention  
         [0002]     The invention provides a pixel structure, especially related to the pixel structure used in an organic electroluminescent device.  
         [0003]     (2) Description of the Prior Art  
         [0004]     Referring to  FIG. 1 , a diagram of a pixel structure of a full color organic electroluminescent (EL) devices is shown.  
         [0005]     The white color EL device  10  is disposed on a substrate  11 . A red color filter  13 , a green color filter  14 , and a blue color filter  15  are disposed under another substrate  12  above the previous substrate  11 . As  FIG. 1  shows, the substrate  11  and the substrate  12  are sealed face to face (though not shown in the figure), wherein the light emitted from the top of the white organic EL device  10  passes through the three color filters  13 - 15  in order to get a predetermined mixed color that image needs.  
         [0006]     In the aforesaid design, the white sub pixel area is left unfiltered. This design has the advantage of lower power consumption and current density, by compared to a three-color filtered white-emitting organic EL device that is frequently used with apparatuses having white backgrounds such as the typical personal digital assistant or computer display.  
         [0007]     However, the device described above has a disadvantage that the luminous intensity of the emitted light would decrease after passing through the filters. Also, the luminous efficacy of the blue light and the red light are worse than that of the green light.  
       SUMMARY OF THE INVENTION  
       [0008]     It is an object of the present invention to provide a pixel structure, which may lower the power consumption and enhance the luminous utility rate.  
         [0009]     In the present invention, the pixel structure for use in a white light emitting organic electroluminescent device therein comprises a first sub-pixel, a second sub-pixel, a third sub-pixel, and a fourth sub-pixel. The first sub-pixel has a first color filter and a first color change medium. The second sub-pixel has a second color filter and a second color change medium. The third sub-pixel has a third color filter. However, the fourth sub-pixel does not have any color filter or color change medium so as to have the white light emitted from the white light emitting organic electroluminescent device able to pass through the fourth sub-pixel directly. Thereby, the white light can be transformed into the color corresponding to each color change medium. Besides, the color shown from the pixel structure can be modulated by the white light from the fourth sub-pixel.  
         [0010]     To sum up, the present invention provides a pixel structure that can enhance the luminous utility rate by pre-changing the white light into corresponding red and green lights, and also can provide a transparent sub-pixel to allow the white light to pass there through directly. Comparing to the related art with the same brightness, the power consumption of the present invention is only 30% of that of the related art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will now be specified with reference to its preferred embodiment illustrated in the drawings, in which  
         [0012]      FIG. 1  shows a pixel structure of a related art;  
         [0013]      FIG. 2  shows a diagram of an embodiment of the present invention;  
         [0014]      FIG. 3  shows a diagram of another embodiment of the present invention;  
         [0015]      FIG. 4A  shows perspective an embodiment of the organic EL device of the present invention;  
         [0016]      FIG. 4B  shows the cross-section diagram of the organic EL device in  FIG. 4A ;  
         [0017]      FIG. 5  shows perspective another embodiment of the organic EL device of the present invention; and  
         [0018]      FIG. 6  shows a further embodiment of the organic EL device of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]      FIG. 2  shows one embodiment of the present invention, as a top-emitted pixel structure.  
         [0020]     The light source of the pixel structure  2  is a white organic EL device  20 , and the pixel structure  2  comprises a first sub-pixel  21 , a second sub-pixel  22 , a third sub-pixel  23 , and a fourth sub-pixel  24 . The first sub-pixel  21  includes a first color filter  211  and a first color change medium  212 . The second sub-pixel  22  includes a second color filter  221  and a second color change medium  222 . The third sub-pixel  23  includes a third color filter  231  but no change medium. The white organic EL device  20  emits white light passing through the first, second, third and fourth sub-pixels. The fourth sub-pixel  24  has neither the color filter nor the color change medium, and hence the white light can pass through the fourth sub-pixel  24  directly.  
         [0021]     In the present embodiment, the first color filter  211  is a red color filter, and the first color change medium  212  is a red color change medium. The red color change medium can absorb the light with a particular wavelength of the white light emitted from the white organic EL device  20  (i.e., blue and green light) and further change these absorbed lights into a red light, and then the red light is released to pass through the red color filter  211 . Thus, the utility rate of the emitted white light in red lighting is enhanced.  
         [0022]     In the present embodiment, the second color filter  221  is a green color filter, and the second color change medium  222  is a green color change medium. The green color change medium can absorb the light with a particular wavelength of the white light emitted from the white organic EL device  20  (i.e., blue and red light) and further change these absorbed lights into a green light, and then the green light is released to pass through the green color filter  221 . Thus, the utility rate of the emitted white light in green lighting is enhanced.  
         [0023]     Also, the third color filter  231  of the present invention can be a blue color filter. Similarly, after the white light emitted from the white organic EL device  20  passes through the third filter  231 , only the blue light can pass through.  
         [0024]     In addition, for the fourth sub-pixel is absent of any color filter and color change medium, hence the white light from the white organic EL device  20  may pass through the fourth sub-pixel directly. The white light from the fourth sub-pixel  24  mixes with the RGB lights from the first sub-pixel, the second sub-pixel, and the third sub-pixel to form the display color of the pixel structure.  
         [0025]     For instance, while in displaying a particular color, the brightness of red light contributed by the first sub-pixel  21  is R 1 , the brightness of green light contributed by the second sub-pixel  22  is G 1 , the brightness of blue light contributed by the third sub-pixel  23  is B 1 , and the brightness of white light from the fourth sub-pixel  24  is W 1 . For the existence of the white light from the fourth sub-pixel  24 , so, by compared to the related art, the required brightness R 1 , B 1 , and G 1  can be reduced and thus the goal in power saving of the first, second, and third sub-pixels  21 - 23  can be achieved.  
         [0026]     In the present embodiment, the three color filters  211 ,  221 , and  231  of the corresponding sub-pixels  21 ,  22 , and  23  are disposed on the top surface of the white organic EL device  20 . However, in other embodiments of the present invention, a protect layer (not shown in the figure) may be sandwiched between the three color filters  211 ,  221 ,  231  and the white organic EL device  20 , and the first color change medium  212  can be disposed upon the first color filter  211  and the second color change medium  222  can be disposed upon the second color filter  221 . The fourth sub-pixel  24  has neither color filter nor color change medium, hence the white light can pass through the fourth sub-pixel  24  without any filtering and color changing.  
         [0027]      FIG. 3  shows another embodiment of the present invention, wherein the color filters  211 ,  221 , and  231  and the color change mediums  212  and  222  are disposed on the bottom surface of a filter substrate  25 , which is disposed on the light emitted potion of the white organic EL device  20 .  
         [0028]      FIG. 4A  and  FIG. 4B  show another embodiment of the present invention. An organic EL device  3  in  FIG. 4A  is a top-type emitting device driven by active matrix circuitry, wherein the pixel structure within the organic EL  3  is the same as the pixel structure in  FIG. 3 .  FIG. 4B  shows a typical the pixel structure of  FIG. 4A .  
         [0029]     The organic EL device  3  comprises an array substrate  31 , a white organic EL device  32 , and a filter substrate  33 . The array substrate  31  is a glass substrate having a plurality of data lines and scan lines. The top surface of the glass substrate is divided into a plurality of array units, so formed as an array area. A plurality of transistors are disposed on every array unit individually to connect the data lines and the scan lines.  
         [0030]     The white organic EL device  32  is composed of a first electrode layer on top, a second electrode layer at the bottom, and a middle emitting layer sandwiched in between. The white organic EL device  32  is disposed on the array substrate  31 .  
         [0031]     The second electrode layer described above is patterned on the array substrate and electrically connects to the transistors, the emitting layer (i.e., an electron transparent layer, an electric hole transparent layer, or a material layer) is formed upon the second electrode layer, and the first electrode layer is formed upon the emitting layer. Every transistor is used to control the power of the white organic EL device at the corresponding array unit.  
         [0032]     The filter substrate  33  includes a plurality of filter areas  34  on the bottom surface facing the array substrate  31 . One array unit, the white organic EL device and the filter area disposed to said array unit is called a pixel unit, like the pixel structure  2  we described in  FIG. 3 .  
         [0033]     Every filter area  34  is composed of a first area  341 , a second area  342 , a third area  343 , and a fourth area  344 .  
         [0034]     The first area  341  further includes a first color filter  3411  and a first color change medium  3412 , wherein the first color filter  3411  is sandwiched between the first color change medium  3412  and the filter substrate  33 .  
         [0035]     The second area  342  further includes a second color filter  3421  and a second color change medium  3422 , wherein the second color filter  3421  is sandwiched between the second color change medium  3422  and the filter substrate  33 .  
         [0036]     The second area  343  further includes a third color filter  3431  and no color change medium is present in the third area  343 .  
         [0037]     The white organic EL device  32  emits white light passing through the first, second, third and fourth areas. The fourth area  344  is transparent to the white organic EL device  32 , and thus the white light may pass through the fourth area directly. Of course, a transparent flat layer could be disposed within the fourth area  344 , but in this preferred embodiment of the present invention, there&#39;s nothing within the fourth area  344 .  
         [0038]     While the transistors power the electric current, the white organic EL device  32  emits white light. The emitted white light passing through the first area  341  and the second area  342  is changed to lights corresponding to different color filters; hence the luminous utility rate of the emitted white light can be increased. Meanwhile, the white light passing through the fourth area  344  can regulate the final color that the pixel structures  2  displays, and thus the goal of power saving can be achieved.  
         [0039]     Though the embodiment described above is driven by the active matrix circuitry, however the driving mode of the present invention is not restricted. For example, a passive matrix circuitry can also work for the present invention.  
         [0040]     In addition, a bottom emission can also work for the present invention.  FIG. 5  shows a cross-section diagram of another embodiment of the present invention, wherein a bottom emission is used in this embodiment. The white organic EL device of this embodiment is disposed on the filter areas, which is the same side with the array substrate.  
         [0041]     The organic EL device in  FIG. 5  comprises an array substrate  41 , a plurality of filter areas  42 , a white organic EL device  43 , and a sealing top  44  which sealed with the array substrate  41 .  
         [0042]     A plurality of filter areas  42  are formed on the surface of the array substrate  41 . Every filter area  42  is composed of a first area  421 , a second area  422 , a third area  423  and a fourth area  424 . The light emitted from the white organic EL device  43  passes through the filter areas  42  as the arrows show.  
         [0043]     The first area  421  further includes a first color filter  4211  and a first color change medium  4212 . The second area  422  further includes a second color filter  4221  and a second color change medium  4222 . The third area  423  further comprises a third color filter  4231 , and the fourth area  424  further comprises a transparent flat layer  4241 .  
         [0044]     The transparent flat layer  4241  shall keep the same thickness with the whole filter areas  42  so as to evenly mount the white organic EL devices upon the filter areas  42 .  
         [0045]      FIG. 6  shows another embodiment of the present invention. The white organic EL device  53  herein is disposed on the opposite side of the array substrate  51  to the filter areas  52 .  
         [0046]     The organic EL device  5  comprises a array substrate  51 , a plurality of filter areas  52 , a white organic EL device  53 , a sealing top  54  which sealed with the array substrate  51 .  
         [0047]     The white organic EL device  53  is disposed on one side surface of the array substrate  51 , while the plurality of filter areas  52  is disposed on the other surface of the array substrate  51 . Alike embodiments described above, every filter area  52  further comprises a first area having a first color filter  5211  and a first color change medium  5212 , a second area  522  having a second color filter  5212  and a second color change medium  5222 , a third area  523  having a third color filter  5231 , and a transparent fourth area  521 .  
         [0048]     To sum up, the present invention provides a pixel structure that can not only enhance the luminous utility rate by pre-changing the white light into respective red and green lights, but can also provide a transparent sub-pixel to allow the white light to pass through directly. Comparing to the related art, on the basis of the same brightness, the power consumption of the present invention can be only 30% of the related art.  
         [0049]     While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the present invention.