Patent Publication Number: US-2007120467-A1

Title: Full-color organic electroluminescence display and its manufacturing method

Description:
RELATED APPLICATIONS  
      The present application is based on, and claims priority from, Taiwan Application Serial Number 94141762, filed Nov. 28, 2005, the disclosure of which is hereby incorporated by reference herein in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The invention relates to an organic electroluminescence display (OELD) and, in particular, to a full-color organic electroluminescence display and the method of making the same.  
      2. Related Art  
      Generally speaking, the OELD has the advantages of self-illuminating, light-weight, wide-angle, high contrast, low power consumption, and high response speed. The structure of an OELD includes an anode on the substrate, an organic light-emitting layer (OLEL) on the anode, and a cathode on the organic light-emitting layer. When a voltage is imposed between the anode and the cathode, electrons and holes are driven into the OLEL, making the OLEL generate electroluminescence (EL).  
      The prior art provides many method of making full-color OELD, such as U.S. Pat. No. 6,515,428 with the title “Pixel structure an organic light-emitting diode display device and its manufacturing method.” First, the OLEL emits white light. The white then passes through color filters of different colors, thereby obtaining red, green, and blue light to achieve full colors. However, the technology of using the white light to pass color filters renders a penetration rate of a single color lower than 25% and bad color saturation. Moreover, using the photolithography process to prepare these color filters usually requires complicated steps and consumes a lot of time.  
      Another conventional technology, as in U.S. Pat. No. 6,522,066 with the title “Pixel structure of an organic light-emitting diode display device and its fabrication method,” uses different color conversion medium (CCM) layers to convert the blue light emitted by the OLEL and obtain red, green, and blue light, thereby achieving full-color effects. However, using the photolithography process to prepare the CCM layers also involves complicated steps and long time.  
      “OELD with color filters or color conversion media” disclosed in Korea Pat. App. 2001-0000943 uses a different single mask to form OLELs of different colors. However, since the opening of the mask of each pixel is tens of micrometers, therefore the alignment precision of the mask and the substrate is required to be very high. This increases the difficulty in the manufacturing process. Moreover, the OLELs of different colors use the side by side coating technique, which increases the production cost and time.  
      To achieve full-color effects, using different color filters on the white light produced by the white-light OLEL reduces the usage efficiency of the light and has worse color saturation. On the other hand, using the technology of separate coating involves a more complicated process and higher production cost. The process requires a high alignment precision, inevitably increasing the difficulty in production. Therefore, it is necessary to improve the structure of the OELD and solve the problem in the alignment precision of the mask, thereby enhancing the penetration rate, color saturation, brightness, and yield of the OELD.  
     SUMMARY OF THE INVENTION  
      An objective of the invention is to provide an OELD that has enhanced brightness, penetration rate, and color saturation, achieving full colors in the OELD. A lower driving voltage is required in practice. Therefore, it has a longer lifetime.  
      According to a preferred embodiment of the invention, the structure of the OELD includes a plurality of pixel units. Each pixel unit includes a first electrode, a first OLEL, a second OLEL, a third OLEL, and a second electrode. The first electrode is disposed over a transparent substrate and has a first sub-pixel electrode region, a second sub-pixel electrode region, and a third sub-pixel electrode region. The first OLEL is disposed on the first sub-pixel electrode region. The second OLEL is disposed on the second sub-pixel electrode region. The third OLEL is disposed on the third sub-pixel electrode region, overlaying the first OLEL and the second OLEL. The OLELs have different light-emitting spectra. The second electrode is disposed on the third OLEL.  
      Another objective of the invention is to provide a method of making an OELD. A wide open mask alignment procedure is introduced to increase the alignment error tolerance, thereby decreasing the difficulty in production while enhancing the yield.  
      According to a preferred embodiment of the invention, a first electrode is first formed on a transparent substrate. Afterwards, a first sub-pixel region, a second sub-pixel region, and a third sub-pixel region are defined on the first electrode. A first mask is used to cover the second sub-pixel region and the third sub-pixel region, and a first OLEL is formed on the first sub-pixel region. A second mask is used to cover the first sub-pixel region and the third sub-pixel region, and a second OLEL is formed on the second sub-pixel region. A third OLEL is formed on the third sub-pixel region, covering the first OLEL and the second OLEL. The OLELs have different light-emitting spectra. Finally, a second electrode is formed on the third OLEL. The light emitted by the first OLEL and the second OLEL can be any two of red, green, and blue light. The light emitted by the third OLEL can be the other color of the three or white light.  
      In summary, the disclosed OELD uses an open mask to replace the conventional mask in the step of coating the OLEL through vaporization. Color filters or CCM layers are selectively used for filtering or modifying light. The allowed error in the mask alignment is thus increased. This can reduce the difficulty in production and increase the yield.  
      If each color filter is provided with an OLEL with the corresponding color, the brightness and color saturation and penetration rate of the OELD can be enhanced. If the absorption spectrum of each CCM corresponds to the light-emitting spectrum of the OLEL thereon, the brightness and color saturation can be enhanced too. Therefore, the disclosed OELD has a better light-emitting efficiency. It only needs a lower driving voltage, thus reducing its power consumption and elongating its lifetime. The invention thus achieves full colors of the OELD for applications in larger displays. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features, aspects and advantages of the invention will become apparent by reference to the following description and accompanying drawings which are given by way of illustration only, and thus are not limitative of the invention, and wherein:  
       FIG. 1  shows a cross-sectional view of the OELD in accord with a preferred embodiment of the invention;  
       FIG. 2  is a cross-sectional view of the OELD in accord with another embodiment of the invention;  
       FIG. 3  is a cross-sectional view of the OELD with an alignment error in yet another embodiment;  
       FIG. 4  is a flowchart showing the manufacturing method of the disclosed OELD in accord with a preferred embodiment of the invention; and  
       FIG. 5  is a flowchart showing the manufacturing method of the disclosed OELD in accord with another embodiment of the invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.  
      The invention provides an OELD. After forming a first OLEL and a second OLEL, an open mask is used to form a third OLEL on the first OLEL and the second OLEL, thereby improving the mask alignment in the conventional process. Moreover, color filters or CCM layers of the corresponding colors can be used to filter or modify the colors. Therefore, even if the mask alignment exceeds the allowed error, the invention can still achieve full-color effects.  
       FIG. 1  shows a cross-sectional view of the OELD in accord a preferred embodiment of the invention. To clearly elucidate the preferred embodiment, a single pixel unit is used in the following drawings for the explanation. The pixel unit of the OELD includes transparent substrate  100 , a first electrode  102 , a first OLEL  110 , a second OLEL  112 , a third OLEL  114 , and a second electrode  116 .  
      The first electrode  102  is disposed on the transparent substrate  100 . The first electrode  102  is defined with a first sub-pixel region  104 , a second sub-pixel region  106 , and a third sub-pixel region  108 . The first OLEL  110  is formed on the first sub-pixel region  104 . The second OLEL  112  is formed on the second sub-pixel region  106 . The third OLEL  114  is formed on the third sub-pixel region  108  and covers the first OLEL  110  and the second OLEL  112 . The OLELs  110 ,  112 ,  114  have different light-emitting spectra. The second electrode  116  is disposed on the third OLEL  114 .  
      In this embodiment, the light-emitting spectra of the first OLEL  110 , the second OLEL  112 , and the third OLEL  114  are essentially the three primitive colors. For example, the light-emitting spectrum of the first OLEL  110  is red (R), with a wavelength in the range of 585-780 nm. The light-emitting spectrum of the second OLEL  112  is green (G), with a wavelength in the range of 485-585 nm. The light-emitting spectrum of the third OLEL  114  is blue (B), with a wavelength in the range of 380-485 nm.  
      In the above-mentioned structure, the light (e.g., blue) emitted by the third OLEL  114  on the top overlaps with the light (e.g., red, green) emitted by the first and second OLELs  110 ,  112  below it. However, experimental results show that the light emitted by the third OLEL  114  does not have much influence on the visual perception of the viewer. Therefore, using this structure, a desired color (e.g. red, green, and blue) can be obtained from the first color range  134 , the second color range  136 , and the third color range  138 . That is, this preferred embodiment can use a simple structure to achieve the full-color effects of the OELD without the use of color filters.  
      As shown in  FIG. 1 , each of the three OLELs emits one of the three primitive colors, and experimental results indicate that full-color effects can be achieved without the use of color filters. Of course, the disclosed OELD can be provided with color filters or CCM layers to filter or convert the colors to other colors similar with the three primitive colors.  
       FIG. 2  shows the cross-sectional view of the OELD in accord with another preferred embodiment of the invention. The first color filter  218  is disposed between the first sub-pixel region  204  and the transparent substrate  200 . The second color filter  220  is disposed between the second sub-pixel region  206  and the transparent substrate  200 . The third color filter  222  is disposed between the third sub-pixel region  208  and the transparent substrate  200 . The spectrum of each of the color filters  218 ,  220 ,  222  corresponds to the light-emitting spectrum of the OLEL  210 ,  212 ,  214  above it.  
      For example, suppose the first color region  234 , the second color region  236 , and third color region  238  are required to emit red, green, and blue light, respectively. The red spectrum of the first color filter  218  corresponds to the red light-emitting spectrum of the first OLEL  210  and filters the non-red spectrum emitted by the third OLEL  214  above the first color filter  218 . The green spectrum of the second color filter  220  corresponds to the green light-emitting spectrum of the second OLEL  212  and filters the non-green spectrum emitted by the third OLEL  214  on the second OLEL  212 .  
      However, only the third OLEL  214  is disposed above the third color filter  222  with the same spectrum. If the third OLEL  214  already emits an ideal spectrum (e.g., blue), then the third color filter  222  of the same blue can be selectively disposed below it. If the third OLEL  214  emits a white spectrum, then the third color filter  222  has to be used in order to produce blue light in the third color region  238 . A person skilled in the art can select appropriate materials and tune the production parameters so that the light-emitting spectra of the OLELs  210 ,  212 ,  214  directly match with the required colors. Alternatively, a third color filter  222  with a specific spectrum can be used so that the color emitted by the third OLEL  214  is close to the desired one, further enhancing the color saturation of the OELD. Of course, the first color region  234 , the second color region  236 , and the third color region  238  are not limited to the above-mentioned case to emit R, G, and B light respectively. Each color region can be any one of the three primitive colors.  
      According to another embodiment of the invention, when the light-emitting spectrum of the third OLEL  214  is the one required by the third sub-pixel region  208 , the third color filter  222  below the third OLEL  214  can be omitted. Only the first color filter  218  and the second color filter  220  are disposed below the first OLEL  210  and the second OLEL  212 , respectively. It should be noted that this embodiment can still include the third color filter  222  to filter out any possibly non-primitive spectrum emitted by the third OLEL  214 .  
      On the other hand, in yet another embodiment of the invention, each of the first OLEL  210  and the second OLEL  212  emit one of the three primitive colors, and the third OLEL  214  emits a spectrum containing the third primitive color, such as white or blue light. In this case, three color filters can be used to filter out the light-emitting spectra of the three primitive colors. More explicitly, the light-emitting spectra of the first OLEL  210  and the second OLEL  212  substantially contain two of the three primitive colors. The light-emitting spectrum of the third OLEL  214  is the white light. For example, the light-emitting spectrum of the first OLEL  210  is red, that of the second OLEL  212  is green, and that of the third OLEL  214  is white.  
      Therefore, this embodiment uses three color filters to filter out the non-primitive color spectra. For example, the red spectrum of the first color filter  218  is used to filter out non-red spectrum emitted by the third OLEL  214 . The green spectrum of the second color filter  220  is used to filter out the non-green spectrum emitted by the third OLEL  214 . The blue spectrum of the third color filter  222  is used to filter out the non-blue spectrum emitted by the third OLEL  214 . Consequently, the three primitive colors can be obtained using this combination.  
      The color filters used in the above-mentioned embodiments can be partially or completely replaced by CCM layers in another embodiment of the invention. Suppose that in this embodiment the first color region  234 , the second color region  236 , and the third color region  238  are required to emit red, green, and blue light, respectively. The first color filter  218 , the second color filter  220 , and the third color filter  222  in  FIG. 2  are replaced respectively by a first CCM layer, a second CCM layer, and a third CCM layer. In other words, the first CCM layer is disposed between the first sub-pixel region  204  and the transparent substrate  200 . The second CCM layer is disposed between the second sub-pixel region  206  and the transparent substrate  200 . The third CCM layer is disposed between the third sub-pixel region  208  and the transparent substrate  200 .  
      The absorptive spectrum of each CCM layer corresponds to the light-emitting spectrum of the OLEL  210 ,  212 ,  214  above it. When the OLELs  210 ,  212 ,  214  emit non-primitive colors, the CCM layers can appropriately convert the spectra emitted by the OLELs  210 ,  212 ,  214 , releasing ideal primitive colors. This can enhance the light-emitting efficiency and color saturation. The disclosed OELD thus achieves full-color effects.  
      As described above, each of the three color regions  234 ,  236 , and  238  emits one of the three primitive colors. Two CCM layers can be disposed under the sub-pixel regions  204 ,  206 , and a CCM layer may be disposed under the OLEL  214  of the sub-pixel region  208  too, modifying the non-primitive spectra emitted by the OLELs  210 ,  212 ,  214 . Likewise, there is no need for the third CCM layer in the third color region  238  if the third OLEL  214  already emits an ideal blue spectrum. Alternatively, if the first OLEL  210  and the second OLEL  212  emit two of the three primitive colors and the third OLEL  214  emits a spectrum containing the third primitive color, then three CCM layers are required to filter out the emitted non-primitive spectra.  
      In the above-mentioned embodiment, a planarized barrier layer  224  is disposed between the first electrode  202  and the transparent substrate  200 . In a preferred embodiment of the invention, the planarized barrier layer  224  can be a transparent layer made of acryl resins or dix. The regions of the first OLEL  210 , the second OLEL  212 , and the third OLEL  214  correspond respectively to the sizes of the first color region  234 , the second color region  236 , and the third color region  238 .  
       FIG. 3  is a cross-sectional view of the disclosed OELD in  FIG. 2  with an alignment error. The same components in  FIG. 3  use the same numeral references as in  FIG. 2 . With reference to  FIG. 2 , the vaporization of the organic light-emitting materials (not shown) in the OLELs  210 ,  212  requires the use of masks to avoid regions that do not need coating. Therefore, there is a mask alignment problem during the production. If there is an error in the mask alignment, the OLEL  312  may deviate from the second color region  236 , as shown in  FIG. 3 . In this case, the light-emitting area of the second color region  236  is greatly reduced.  
      In this embodiment, the light-emitting area of the second color region  236  does not reduce much. When the light-emitting spectrum of the third OLEL  214  is white, the color  314  emitted by the third OLEL  214  can be used to compensate for the light-emitting area loss in the position-deviated second OLEL  312 . The color  314  is filtered by the second color filter  220  and becomes the desired color in the second color region  236 . Likewise, if the deviation occurs in the first OLEL  210  or the two OLELs  210 ,  212  below the third OLEL  214 , the third OLEL  214  can compensate for the light-emitting area due to these deviations, increasing the light-emitting efficiency and color saturation.  
      In accord with the above description, the color filters can be replaced by CCM layers for converting the light-emitting spectra of the OLELs thereon into ideal primitive colors. When the wavelengths of the light-emitting spectrum of the third OLEL  214  are shorter (e.g., blue light), the colored light  314  emitted by the third OLEL  214  can be used to compensate for the light-emitting area loss in the position-deviated second OLEL  312 . The second CCM layer converts it into light in the second color region  236 . Likewise, if the deviation occurs in the first OLEL  210  or the two OLELs  210 ,  212  below the third OLEL  214 , the third OLEL  214  can compensate the light-emitting area for these deviations, increasing the light-emitting efficiency and color saturation.  
      Therefore, if the second OLEL  312  has an alignment error in the production process, the light emitted by the third OLEL  214  is filtered or converted by the second color filter  220  or second CCM layer (not shown) into one of the three primitive colors. This then compensate for the light-emitting area loss due to the deviation in the second OLEL  312 . Moreover, the second color filter  220  or second CCM layer can filter or convert the spectrum emitted by the third OLEL  214  into a more ideal primitive color. For the mask alignment precision problem, another embodiment of the invention provides an effective solution. Even if the mask alignment exceeds the desired precision, the invention can still implement the full-color OELD.  
      An embodiment is shown in  FIG. 2 . Each of the first and second OLELs  210 ,  212  has its own hole injection layer, hole transmission layer, and organic light-emitting material layer (not shown). The third OLEL  214  above the third sub-pixel region  208  has in sequence a hole injection layer, a hole transmission layer, an organic light-emitting material layer, an electron transmission layer, and an electron injection layer (not shown). Furthermore, the third OLEL  214  is above the first and second OLELs  210 ,  212 , and includes in sequence an organic light-emitting material layer, an electron transmission layer, and an electron injection layer (not shown). The organic light-emitting material in the first, second, and third OLELs  210 ,  212 ,  214  can be a single light-emitting material or some a co-host/co-dopant material. When the OELD is in the form of bottom emission, the first electrode  202  is a transparent electrode. In this case, the material of the first electrode  202  can be ITO, IZO, IWO, or AZO. The material of the second electrode  216  can be any metal, alloy, or transparent conductive material. The transparent substrate  200  can be a glass substrate, a flexible substrate, a rigid substrate, or a plastic substrate. As illustrated in  FIG. 1 , a transparent substrate without any color filter can even be used for the disclosed OELD when no color filter is required.  
      In accord with the above embodiment, since each color filter corresponds to the spectrum of the OLEL above it, the penetration rate can optimally reach over 70%. Therefore, the invention has a good light usage rate. It improves the low penetration rate of smaller than 25% as white light penetrates through a color filter in the prior art. Besides, due to its good light usage rate, only a low driving voltage is required. This helps elongate the lifetime of the disclosed OELD.  
      Furthermore, using the color filters or CCM layers of the corresponding colors to filter or convert light can achieve better color saturation. This improves the full-color effects. Experimental results show that the color saturation can reach above 100%, largely improving the color saturation problem of white light with color filters in the prior art.  
      Please refer to  FIG. 4  for the flowchart of the method of making the disclosed OELD according to a preferred embodiment of the invention. Please also refer to  FIG. 1  simultaneously for the following explanation. In step  410 , a first electrode  102  is formed on the transparent substrate  100 . In step  420 , a first sub-pixel region  104 , a second sub-pixel region  106 , and a third sub-pixel region  108  are defined on the first electrode  102 . In step  422 , the hole injection layers and the hole transmission layers (not shown in  FIG. 1 ) of the first, second, and third OLELs  110 ,  112 ,  114  are formed respectively on the first, second, and third sub-pixel regions  104 ,  106 ,  108 .  
      In step  430 , a first mask is used to cover the second sub-pixel region  106  and the third sub-pixel region  108 . A first organic light-emitting material layer of the first OLEL  110  is coated above the hole injection layer and the hole transmission layer of the first sub-pixel region  104 . In step  440 , a second mask is used to cover the first sub-pixel region  104  and the third sub-pixel region  108 . A second organic light-emitting material layer of the second OLEL  112  is coated above the hole injection layer and the hole transmission layer of the second sub-pixel region  106 . Afterwards, in step  450  an open mask is used to form a third organic light-emitting material layer of the third OLEL  114  on the hole injection layer and the hole transmission layer of the third sub-pixel region  108 , also covering the organic light-emitting material layers of the first OLEL  110  and the second OLEL  112 . The organic light-emitting material layers of the OLELs  110 ,  112 ,  114  emit different spectra. In step  452 , the organic light-emitting layer of the third OLEL  114  is formed with an electron transmission layer and an electron injection layer (not shown in  FIG. 1 ). In step  460 , the second electrode  116  is formed on the electron transmission layer and the electron injection layer of the third OLEL  114 .  
      More explicitly, the above embodiment employs an open mask to form the third OLEL  114 , so that the third OLEL  114  covers the first OLEL  110  and the second OLEL  112 . Therefore, it is possible to solve the mask alignment problem in the conventional evaporation process when forming the OLELs  110 ,  112 ,  114  that emit different colors of light. The tolerance in the mask alignment error becomes better, reducing difficulty in production.  
       FIG. 5  gives the flowchart of another embodiment method of making the disclosed OELD. Please refer simultaneously to  FIG. 2  in the following explanation. When each of the above-mentioned OLELs emits a primitive color, three or two color filters can be disposed to filter the spectra of the emitted light. In this embodiment, step  502  starts first to form a first color filter  218  and a second color filter  220 . On the other hand, when the first OLEL  210  and the second OLEL  212  emit different primitive colors and the third OLEL  214  emits white light, three color filters  218 ,  220  and  222  can be used to filter and obtain the spectra of the three primitive colors.  
      More explicitly, the spectrum of each of the first OLEL  210  and the second OLEL  212  is essentially only one of the three primitive colors. Moreover, the spectrum of the third OLEL  214  is either white or contains the third primitive color. In this case, in addition to forming the first color filter  218  and the second color filter  220 , a third color filter  222  is formed between the third sub-pixel region  208  and the transparent substrate  200 , thereby filtering out the non-primitive spectrum emitted by the third OLEL  214 . Therefore, this embodiment can render all the three primitive colors.  
      Each of the color filters in the above-mentioned embodiments can be replaced partially or completely by CCM layers in other embodiments. For example, a first CCM layer may be disposed between the first sub-pixel region  204  and the transparent substrate  200  (i.e., at the position of the above-mentioned first color filter  218 ). A second CCM layer may be disposed between the second sub-pixel region  206  and the transparent substrate  200  (i.e., at the position of the above-mentioned second color filter  220 ). Finally, a third CCM layer may be disposed between the third sub-pixel region  208  and the transparent substrate  200  (i.e., at the position of the above-mentioned third color filter  222 ).  
      Afterwards, step  504  is performed to planarized the color filters  218 ,  220 ,  222  or the CCM layers, forming a planarized barrier layer  224 . The planarized barrier layer  224  can be a transparent layer and is preferably made of acrylic resins and dix.  
      In step  510 , a first electrode  202  is formed above the planarized barrier layer  224 . In step  520 , a first sub-pixel region  204 , a second sub-pixel region  206 , and a third sub-pixel region  208  are defined on the first electrode  202 . In step  522 , the hole injection layers and hole transmission layers of the first, second, and third OLELs  210 ,  212 ,  214  are formed on the first, second, and third sub-pixel regions  204 ,  206 ,  208 .  
      In step  530 , a first mask is used to cover the second sub-pixel region  206  and the third sub-pixel region  208 , forming the first organic light-emitting material layer of the first OLEL  210  on the hole injection layer and the hole transmission layer of the first sub-pixel region  204 . In step  540 , a second mask is used to cover the first sub-pixel region  204  and the third sub-pixel region  208 , also forming the second organic light-emitting material layer of the second OLEL  212  on the hole injection layer and the hole transmission layer of the second sub-pixel region  206 .  
      In step  550 , an open mask is used to form the third organic light-emitting material layer of the third OLEL  214  on the hole injection layer and the hole transmission layer of the third sub-pixel region  208 , covering the organic light-emitting layers of the first OLEL  210  and the second OLEL  212 . The organic light-emitting material layers of the OLELs  210 ,  212 ,  214  have different spectra. In step  552 , an electron transmission layer and an electron injection layer are formed on the organic light-emitting material layer of the third OLEL  214  (not shown in  FIG. 2 ). In step  560 , a second electrode  216  is formed on the electron transmission layer and the electron injection layer of the third OLEL  214 . The above embodiment uses thermal evaporation to form the organic light-emitting material layers of the OLELs  210 ,  212 ,  214 . The organic light-emitting material in the first, second, and third OLELs  210 ,  212 ,  214  can be a single light-emitting material or some a co-host/co-dopant material. When the OELD is in the form of bottom emission, the first electrode  202  is a transparent electrode. In this case, the material of the first electrode  202  can be ITO, IZO, IWO, or AZO. The material of the second electrode  216  can be any metal, alloy, or transparent conductive material. The transparent substrate  200  can be a glass substrate, a flexible substrate, a rigid substrate, or a plastic substrate.  
      In summary, the preferred embodiment of the invention uses an open mask to improve the conventional mask alignment problem during the manufacturing process of the OLELs with different colors. This solves the precision alignment problem of the mask and the substrate. The tolerance of the alignment error is better. Therefore, the invention can reduce the production difficulty and increase the yield.  
      Moreover, if an OLEL is disposed on each color filter of the corresponding color, then the penetration rate and color saturation of the colored light emitted by the OLELs can be increased. The color filters can be replaced by CCM layers. The light-emitting efficiency and color saturation of the disclosed OELD is enhanced by the color filters and/or CCM layers. Therefore, the disclosed OELD has a better light usage rate. In practice, only a low driving voltage is required. Therefore, the power consumption of the disclosed OELD can be reduced, while its lifetime is extended. The disclosed OELD also achieves full-color effects that may have applications in large displays.  
      The embodiments of the invention disclosed herein should not be used to limit other variations and applications of the invention. For example, the OELD can be used for both top emission and bottom emission. The invention can be applied to both passive and active OELDs. The color filters used herein can be in the form of color filters on transparent substrate, color filters on encap. glass, color filters on array (COA), or array on color filters (AOC). Likewise, the CCM layers disclosed herein can be in the form of CCM layers on transparent substrate, CCM layers on encap. glass, CCM layers on array, or array on CCM layers.  
      The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.