Abstract:
An organic light emitting diode display panel includes a transparent substrate on which a matrix array of pixels is formed with each pixel including an organic light emitting diode (OLED). The OLEDS include light emitting regions sandwiched between pixel electrodes or anodes made of transparent conductive material and a common electrode made of a conductive material. The refractive index of the pixel electrodes is higher than the refractive index of the insulating layer on which the pixel electrodes are disposed so that light undergoes multiple reflections at the interface between the pixel electrodes and the insulating layer and also at the interface between the light emitting regions and the common electrode. The thickness of the pixel electrodes is chosen so that light that eventually exits the pixel electrodes after multiple reflections contains a relatively strong component of a chosen primary color.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority of Korean Patent Application No. 10-2008-0085859 filed in the Korean Intellectual Property Office on Sep. 1, 2008, the contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to an organic light emitting device and a manufacturing method thereof. 
         [0004]    (b) Description of the Related Art 
         [0005]    Since an organic light emitting display (OLED) is a self emissive display, it does not require a light source. Therefore, the OLED consumes relatively less power than other displays. Also, the OLED has a fast response speed, a wide viewing angle, and an excellent contrast ratio. 
         [0006]    The OLED includes a plurality of primary color pixels such as red pixels, blue pixels, and green pixels, and displays a full range of colors composed of the spatial sum of primary colors emitted through a combination of these pixels. 
         [0007]    Each pixel of the OLED includes an organic light emitting element and a plurality of thin film transistors for driving the organic light emitting element. 
         [0008]    The organic light emitting element includes an anode, a cathode, and an organic light emitting member interposed between the anode and the cathode. The organic light emitting member emits light of one of three primary colors, for example, red, green, and blue, or emits white light. A material of the organic light member may vary according to the color emitted from the organic light emitting member. In the case of white light, materials each emitting one of the colors, red, green, and blue are stacked, and the white light is the sum of the red, green, and blue light emitted from the stacked materials. Also, when using an organic light emitting member that emits white light, color filters may be used to obtain light of a desired color. 
         [0009]    However, after passing through the color filters, color purity of light deteriorates due to a limitation in color reproducibility of the color filters. 
         [0010]    The above information, disclosed in this Background section, is provided only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form part of the prior art. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention has been made in an effort to provide an organic light emitting device having advantages of improved color reproducibility and improved range of viewing angle. 
         [0012]    The present invention provides an organic light emitting display comprising: a substrate comprising a first region, a second region, a third region, and a fourth region respectively corresponding to a red pixel, a green pixel, a blue pixel, and a white pixel; a thin film transistor array disposed on the substrate and comprising a first driving transistor disposed on the first region, a second driving transistor disposed on the second region, a third driving transistor disposed on the third region and a fourth driving transistor disposed on the fourth region; an overcoat disposed on the thin film transistor array; first, second, third, and fourth pixel electrodes disposed on and contacting the overcoat, the first pixel electrode disposed at the first region, the second pixel electrode disposed on the second region, the third pixel electrode disposed on the third region, and the fourth pixel electrode disposed on the fourth region, respectively; an organic light emitter disposed on the first, second, third, and fourth pixel electrodes; and a common electrode disposed on the organic light emitter. Thicknesses of the first, third, and fourth pixel electrodes are substantially equal to each other and different from the thickness of the second pixel electrode. 
         [0013]    A refractive index difference between the overcoat and the first to fourth pixel electrodes may be 0.2 or greater. 
         [0014]    The first, second, third, and fourth pixel electrodes may comprise ITO or IZO. 
         [0015]    The overcoat may comprise an organic material. 
         [0016]    The second pixel electrode may be thicker than the first, third, and fourth pixel electrodes. 
         [0017]    The second pixel electrode may comprise a lower transparent electrode and an upper transparent electrode. 
         [0018]    First, second, third, and fourth contact holes formed in the overcoat extend to portions of the first, third, and fourth driving transistors respectively; the first, third, and fourth pixel electrodes comprise a transparent conductor which is disposed in the first, third, and fourth contact holes and contacts the portions of the first, third, and fourth driving transistors respectively; and lower first transparent electrode of the second pixel electrode is disposed on the overcoat and contacts the second driving transistor through the second contact hole. 
         [0019]    The first, second, third, and fourth pixel electrodes may comprise ITO or IZO. 
         [0020]    The overcoat may comprise an organic material. 
         [0021]    First, second, third, and fourth contact holes formed in the overcoat extend to portions of the first, second, third, and fourth driving transistors respectively; the first, third, and fourth pixel electrodes contact the portions of the first, third, and fourth driving transistors through the first, third, and fourth contact holes; and the upper transparent electrode of the second pixel electrode contacts the second driving transistor through the second contact hole. 
         [0022]    The second contact hole may penetrate the lower transparent electrode of the second pixel electrode. 
         [0023]    The first, second, third, and fourth pixel electrodes may comprise ITO or IZO. 
         [0024]    The overcoat may comprise an organic material. 
         [0025]    The thickness of the second pixel electrode may be between about 1400 Å and about 1600 Å, and the thickness of the first, third, and fourth pixel electrodes may be between about 800 Å and about 1000 Å. 
         [0026]    The second pixel electrode may be thinner than the first, third, and fourth pixel electrodes. 
         [0027]    Each of the first, third, and fourth pixel electrodes may comprise a lower transparent electrode and an upper transparent electrode. 
         [0028]    The thickness of the second pixel electrode may be between about 300 Å and about 500 Å, and the thickness of the first, third, and fourth pixel electrodes may be between about 800 Å and about 1000 Å. 
         [0029]    The organic light emitting device may further comprise first, second, and third color filters disposed on the thin film transistor array and disposed at the first, second, and third regions, respectively. 
         [0030]    The organic light emitting device may further comprise a fourth color filter disposed on the thin film transistor array and disposed at the fourth region. 
         [0031]    The organic light emitter may be a white organic light emitting member. 
         [0032]    The organic light emitter may comprise first, second, third, and fourth organic light emitting members disposed at the first, second, third, and fourth regions, respectively. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  is an equivalent circuit diagram of an organic light emitting device according to an exemplary embodiment of the present invention. 
           [0034]      FIG. 2  is a plan view illustrating a plurality of pixels in an organic light emitting device according to an exemplary embodiment of the present invention. 
           [0035]      FIG. 3  is a cross-sectional view of an organic light emitting device according to an exemplary embodiment of the present invention. 
           [0036]      FIG. 4  to  FIG. 12  are cross-sectional views of an organic light emitting device of  FIG. 3  at intermediate steps of a manufacturing method of an organic light emitting device according to an exemplary embodiment of the present invention. 
           [0037]      FIG. 13  is a cross-sectional view of an organic light emitting device according to another exemplary embodiment of the present invention. 
           [0038]      FIG. 14  to  FIG. 18  are cross-sectional views of an organic light emitting device of  FIG. 13  at intermediate steps of a manufacturing method of an organic light emitting device according to an exemplary embodiment of the present invention. 
           [0039]      FIG. 19  and  FIG. 20  are cross-sectional views of organic light emitting devices according to exemplary embodiments of the present invention. 
           [0040]      FIG. 21  is a plan view illustrating a plurality of pixels disposed in an organic light emitting device according to another exemplary embodiment of the present invention. 
           [0041]      FIG. 22  is a cross-sectional view of the organic light emitting device of  FIG. 21  according to another exemplary embodiment of the present invention. 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THE DRAWINGS 
       [0042]      
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 110: insulation substrate 
                 112: insulating layer 
               
               
                 121: gate line 
                 171: data line 
               
               
                 172: driving voltage line 
                 180: overcoat 
               
               
                 185R, 185G, 185B, 185W: contact hole 
               
               
                 191R, 191G, 191B, 191W: pixel electrode 
               
               
                 230R, 230G, 230B, 230W: color filter 
               
               
                 270: common electrode 
                 361: insulating member 
               
               
                 370, 370R, 370G, 370B, 370W: 
               
               
                 organic light emitting member 
               
               
                 Cst: storage capacitor 
                 I LD : driving current 
               
               
                 LD: organic light emitting element 
                 PX, R, G, B, W: pixel 
               
               
                 Qs, QsR, QsG, QsB, QsW: switching transistor 
               
               
                 Qd, QdR, QdG, QdB, QdW: driving transistor 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0043]    The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
         [0044]    In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
         [0045]    First, an organic light emitting device according to an exemplary embodiment of the present invention will be described in detail with reference to  FIG. 1 . 
         [0046]      FIG. 1  is an equivalent circuit diagram of an organic light emitting device according to an exemplary embodiment of the present invention. 
         [0047]    Referring to  FIG. 1 , the organic light emitting device according to the present exemplary embodiment includes a plurality of pixels PX that are arranged in a matrix array and connected to a plurality of signal lines  121 ,  171 , and  172 . 
         [0048]    The signal lines include a plurality of gate lines  121  for transferring a gate signal (or scanning signal), a plurality of data lines  171  for transferring a data signal, and a plurality of driving voltage lines  172  for transferring a driving voltage. The gate lines  121  extend in a row direction parallel to each other, and the data lines  171  extend in a column direction parallel to each other. Although the driving voltage lines  172  extend in a column direction in  FIG. 1 , they may extend in a row direction or a column direction, or may be formed in a mesh style. 
         [0049]    Each pixel PX includes a switching transistor Qs, a driving transistor Qd, a storage capacitor Cst, and an organic light emitting element LD. 
         [0050]    The switching transistor Qs includes a control terminal, an input terminal and an output terminal. The control terminal is connected to the gate line  121 , the input terminal is connected to the data line  171 , and the output terminal is connected to the driving transistor Qd. The switching transistor Qs transfers a data signal received from the data line  171  to the driving transistor Qd in response to a scanning signal from the gate line  121 . 
         [0051]    The driving transistor Qd also includes a control terminal, an input terminal, and an output terminal. The control terminal of the driving transistor Qd is connected to the output terminal of the switching transistor Qs, the input terminal of the driving transistor Qd is connected to the driving voltage line  172 , and the output terminal of the driving transistor Qd is connected to the organic light emitting element LD. The driving transistor Qd provides an output current I LD , the magnitude of which is controlled by a voltage applied between the control terminal of the driving transistor Qd and the input terminal of the driving transistor Qd. 
         [0052]    The capacitor Cst is connected between the control terminal and the input terminal of the driving transistor Qd. The capacitor Cst stores a data voltage that is applied between the control terminal and the input terminal of the driving transistor Qd and maintains the stored data voltage even after the switching transistor Qs is turned off. 
         [0053]    The organic light emitting element LD, for example an organic light emitting diode, includes an anode connected to the output terminal of the driving transistor Qd and a cathode connected to a common voltage Vss. The output current I LD  passes through the light emitting element LD. The organic light emitting element LD displays images by emitting light with an intensity that is related to the magnitude of output current I LD  of the driving transistor Qd. The organic light emitting element LD may include an organic material that uniquely emits light of at least one of a set of primary colors such as red, green, and blue, or may include an organic material that emits white light. The organic light emitting device displays images that include desired colors, the desired colors being a spatial sum of these primary colors. 
         [0054]    Although the switching transistor Qs and the driving transistor Qd are n-channel field effect transistors (FET), at least one of them may be a p-channel field effect transistor. Also, connection relationships among the transistors Qs, and Qd, the capacitor Cst, and the organic light emitting element LD may be modified. 
         [0055]    Hereinafter, a pixel layout of the organic light emitting device of  FIG. 1  will be described with reference to  FIG. 2 . 
         [0056]      FIG. 2  is a plan view illustrating a plurality of pixels disposed in an organic light emitting device according to an exemplary embodiment of the present invention. 
         [0057]    Referring to  FIG. 2 , an organic light emitting device according to an exemplary embodiment of the present invention includes red pixels R for displaying red, green pixels G for displaying green, blue pixels B for displaying blue and white pixels W for displaying no specific color but for emitting white light, these pixels being alternately arranged on a substrate. The red pixels R, the green pixels G, and the blue pixels B are basic pixels which are used together for displaying a full range of colors. Instead of the three primary colors red, green, and blue, the organic light emitting device may include pixels that emit a different set of three primary colors. The white pixel W is used for enhancing luminance and may be omitted. 
         [0058]    Four pixels including a red pixel R, a green pixel G, a blue pixel B, and a white pixel W can be arranged to form one group such as the group of pixels enclosed by the dashed line in  FIG. 2 . Such groups of four pixels may be arranged in columns and rows. However, the pixel layout may be modified in various ways. 
         [0059]    Hereinafter, details of a structure of the organic light emitting device shown in  FIG. 1  and  FIG. 2  will be described with reference to  FIG. 3 . 
         [0060]      FIG. 3  is a cross-sectional view including a composite of four cross-sections including a cross-section of a red pixel R, a cross-section of a green pixel G, a cross-section of a blue pixel B, and a cross-section of a white pixel W of an organic light emitting device according to an exemplary embodiment of the present invention. 
         [0061]    The organic light emitting device includes an insulating substrate  110  that may be made of transparent glass or plastic. The insulating substrate  110  includes first regions  110 R, second regions  110 G, third regions  110 B and fourth regions  110 W. A red pixel R is disposed on each first region  110 R, a green pixel G is disposed on each second region  110 G, a blue pixel B is disposed on each third region  110 B, and a white pixel W is disposed on each fourth region  110 W. A thin film transistor array including a plurality of switching transistors QsR, QsG, QsB, and QsW and a plurality of driving transistors QdR, QdG, QdB, and QdW are disposed on the insulating substrate  110 . The red pixel R includes a first switching transistor QsR and a first driving transistor QdR. The green pixel G includes a second switching transistor QsG and a second driving transistor QdG. The blue pixel B includes a third switching transistor QsB and a third driving transistor QdB. The white pixel W includes a fourth switching transistor QsW and a fourth driving transistor QdW. Although not shown in  FIG. 3 , the first switching transistor QsR and the first driving transistor QdR are electrically connected to each other. The first switching transistor QsR and the first driving transistor QdR may be connected together as previously described and_further description is omitted here. Likewise the switching transistors QsG, QsB and QSW are connected to the driving transistors QdG, QdB and QdW, respectively. 
         [0062]    An insulating layer  112  is disposed on the thin film transistor array including the switching transistors QsR, QsG, QsB, and QsW and the driving transistors QdR, QdG, QdB, and QdW. 
         [0063]    On the insulating layer  112 , the red pixel R includes a red color filter  230 R also referred to as a first color filter, the green pixel G includes a green color filter  230 G also referred to as a second color filter, the blue pixel B includes a blue color filter  230 B also referred to as a third color filter, and the white pixel W includes a transparent white color filter  230 W also referred to as a fourth color filter. The white color filter  230 W of the white pixel W may be omitted. 
         [0064]    An overcoat  180  is disposed on the color filters  230 R,  230 G,  230 B, and  230 W, and on the insulating layer  112 . The overcoat  180  may be made of an organic material and may have a flat surface. 
         [0065]    A plurality of contact holes including a first contact hole  185 R, a second contact hole  185 G, a third contact hole  185 B, and a fourth contact hole  185 W are formed in the overcoat  180  and the insulating layer  112 , and extend to a portion of the output terminal (not shown) of the driving transistors QdR, QdG, QdB and QdW, respectively. 
         [0066]    Pixel electrodes, including a first pixel electrode  191 R, a second pixel electrode  191 G, a third pixel electrode  191 B, and a fourth pixel electrode  191 W are disposed on the overcoat  180 , and are located above the color filters  230 R,  230 G,  230 B, and  230 W, respectively. 
         [0067]    Each of the pixel electrodes  191 R,  191 B, and  191 W of the red, blue, and white pixels R, B, and W includes a lower transparent electrode and an upper transparent electrode. The pixel electrodes  191 R,  191 B, and  191 W include a first lower transparent electrode  192 R, a third lower transparent electrode 192 B, and a fourth lower transparent electrode  192 W, respectively at the bottom thereof and a first upper transparent electrode  193 R, a third upper transparent electrode  193 B, and a fourth upper transparent electrode  193 W at the top thereof. 
         [0068]    The second pixel electrode  191 G of the green pixel G includes a transparent electrode  193 G formed of a single layer and a transparent conductor  192 G disposed in the contact hole  185 G. 
         [0069]    The lower transparent electrodes  192 R,  192 B, and  192 W of the red, blue, and white pixels R, B, and W are disposed on the overcoat  180  and in the contact holes  185 R,  185 B, and  185 W, and are electrically connected to the driving transistors QdR, QdB and QdW through the contact holes  185 R,  185 B, and  185 W, respectively. The upper transparent electrodes  193 R,  193 B, and  193 W are respectively disposed on the lower transparent electrodes  192 R,  192 B, and  192 W, and also may in part be disposed on the overcoat  180 . 
         [0070]    The transparent conductor  192 G of the green pixel G is not present on the overcoat  180  but is disposed only in the second contact hole  185 G. The transparent electrode  193 G is disposed on the transparent conductor  192 G and on the overcoat  180 , and is electrically connected to the driving transistor QdG via the transparent conductor  192 G. 
         [0071]    The lower transparent electrodes  192 R,  192 B,  192 W, and the transparent conductor  192 G may be formed in a first layer of transparent conductive material, the upper transparent electrodes  193 R,  193 B, and  193 W, and the transparent electrode  193 G may be formed in a second layer of transparent conductive material. The first layer and the second layer of transparent conductive material may be made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). 
         [0072]    As shown in  FIG. 3 , a thickness Dg of the pixel electrode  191 G of the green pixel G is less than that of the pixel electrodes  191 R,  191 B, and  191 W of the red, blue, and white pixels R, B, and W. The thickness Dg of the pixel electrode  191 G may be between about 300 Å and about 500 Å, and the thicknesses Dr, Db, and Dw of the pixel electrodes  191 R,  191 B, and  191 W may be between about 800 Å and about 1000 Å. The thicknesses Dr, Db, and Dw are substantially equal. 
         [0073]    Alternatively, each of the pixel electrodes  191 R,  191 G,  191 B, and  191 W may be formed of a single layer including ITO or IZO. In this case, the thickness Dg of the pixel electrode  191 G may be also thinner than the thicknesses Dr, Db, and Dw of the pixel electrodes  191 R,  191 B, and  191 W. 
         [0074]    The pixel electrodes  191 R,  191 G,  191 B, and  191 W have a refractive index that is greater than the refractive index of the overcoat  180 . The refractive index difference therebetween may be 0.2 or greater. For example, when a refractive index of the overcoat  180  made of an organic layer is between about 1.5 and about 1.7, a refractive index of the pixel electrodes  191 R,  191 G,  191 B, and  191 W made of ITO or IZO may be between about 1.8 and about 2.3. Due to the refractive index difference between the overcoat  180  and the pixel electrodes  191 R,  191 G,  191 B, and  191 W, at least a portion of incident light entering the pixel electrodes  191 R,  191 G,  191 B, and  191 W from above is reflected at the interface or boundary between the pixel electrodes  191 R,  191 G,  191 B and  191 W and the overcoat  180 . 
         [0075]    A plurality of insulating members  361  are disposed on the overcoat  180  between the adjacent pixel electrodes  191 R,  191 G,  191 B, and  191 W to provide insulation between the pixel electrodes  191 R,  191 B,  191 G, and  191 W. The insulating members  361  may be omitted. 
         [0076]    A light emitter is disposed on the insulating members  361  and the pixel electrodes  191 R,  191 G,  191 B, and  191 W. The light emitter may be an organic light emitter, which in this embodiment is a white organic light emitting member  370 . A common electrode  270 , to which a common voltage Vss may be applied, is disposed on the white organic light emitting member  370 . 
         [0077]    The white organic light emitting member  370  may have a stacked structure that includes a plurality of organic material layers each emitting a different color from a set of primary colors. The common electrode  270  may be made of a reflective metal including calcium (Ca), barium (Ba), magnesium (Mg), aluminum (Al), or silver (Ag). 
         [0078]    Alternatively, the organic light emitter may include organic light emitting members (not shown) including red, green and blue light emitting members, and a white organic light emitting member, that may be disposed in the red, green, blue, and white pixels R, G, B, and W, respectively. In this case, the red, green, and blue color filters  230 R,  230 G, and  230 B, and the white color filter  230 W, may be omitted. 
         [0079]    In the organic light emitting device shown in  FIG. 3 , the pixel electrodes  191 R,  191 G,  191 B, and  191 W, the organic light emitting member  370 , and the common electrode  270  form organic light emitting elements LD, wherein the pixel electrodes  191 R,  191 G,  191 B, and  191 W are anodes. Also, the common electrode  270  is a common cathode that is shared by the light emitting elements LD. 
         [0080]    Such an organic light emitting device emits light in a downward direction through the insulating substrate  110 , thereby displaying images. The light emitted from the organic light emitting member  370  toward the substrate  110  passes through the pixel electrodes  191 R,  191 G,  191 B, and  191 W and reaches a boundary between the pixel electrodes  191 R,  191 G,  191 B, and  191 W and the overcoat  180 . At the boundary, light is reflected toward the common electrode  270 , and at the common electrode  270  this light is reflected again so that the light again reaches the boundary between the pixel electrodes  191 R,  191 G,  191 B, and  191 W and the overcoat  180 . In this way, light that is repeatedly reflected at the common electrode  270  and at the boundary between the pixel electrodes  191 R,  191 G,  191 B, and  191 W and the overcoat  180 , as described above, undergoes an optical process such as interference, and as a result, a predetermined wavelength of light may be intensified. Light with an intensified predetermined wavelength is emitted after passing out of the overcoat  180  and this modified light then passes through the color filters  230 R,  230 G,  230 B, and  230 W. 
         [0081]    The optical path lengths are dependent on thicknesses and refractive indexes of the thin films disposed between the overcoat  180  and the common electrode  270 . It is possible to obtain desired optical characteristics, for example, a desired range of wavelengths and a desired color purity for respective wavelengths, by properly controlling the thicknesses Dr, Dg, Db, and Dw of the pixel electrodes  191 R,  191 G,  191 B, and  191 W as well as the thickness of the organic light emitting member  370  while particularly controlling the thickness Dg of the pixel electrode  191 G of the green pixel G to be different from the thicknesses Dr, Db, and Dw of the pixel electrodes  191 R,  191 B, and  191 W of the other pixels R, B, and W. Also, light transmittance of a desired range of wavelengths for each of the primary colors including green may be increased, and color variation at side viewing angles may be reduced. 
         [0082]    In particular, as the refractive index difference between the overcoat  180  and the pixel electrodes  191 R,  191 G,  191 B, and  191 W is made greater, it is possible to further increase the reflectance at the boundary between the overcoat  180  and the pixel electrodes  191 R,  191 G,  191 B, and  191 W and thus further improve the color purity. 
         [0083]    Hereinafter, a manufacturing method of manufacturing the organic light emitting device of  FIG. 3  will be described with reference to  FIG. 4  to  FIG. 12 . 
         [0084]      FIG. 4  to  FIG. 12  are cross-sectional views of an organic light emitting device of  FIG. 3  in intermediate steps of a manufacturing method of an organic light emitting device according to an exemplary embodiment of the present invention. 
         [0085]    Referring  FIG. 4 , a thin film transistor array including a plurality of switching transistors QsR, QsG, QsB and QsW and a plurality of driving transistors QdR, QdG, QdB, and QdW is formed on a substrate  110 . 
         [0086]    Referring to  FIG. 5 , an insulating layer  112  is deposited on the thin film transistor array and a plurality of color filters  230 R,  230 G,  230 B, and  230 W are formed on the insulating layer  112 . 
         [0087]    Referring to  FIG. 6  and  FIG. 7 , an overcoat  180  is formed on the insulating layer  112  and on the color filters  230 R,  230 G,  230 B, and  230 W. Then, a plurality of contact holes  185 R,  185 G,  185 B, and  185 W are formed by patterning the insulating layer  112  and the overcoat  180 . The contact holes  185 R,  185 G,  185 B, and  185 W extend through the overcoat  180  and the insulating layer  112  to the output terminals (not shown) of the driving transistors QdR, QdG, QdB, and QdW, respectively. 
         [0088]    Referring to  FIG. 8 , a first transparent conductive layer  190   p  made of ITO or IZO is formed on the overcoat  180  by, for example, a sputter deposition process. 
         [0089]    Then, a first photosensitive film is coated on the first transparent conductive layer  190   p , and a first photoresist pattern  40   a  is formed by patterning the first photosensitive film. 
         [0090]    Referring to  FIG. 9 , a plurality of lower transparent electrodes  192 R,  192 B, and  192 W and transparent conductors  192 G are formed by etching the first transparent conductive layer  190   p  while using the first photoresist pattern  40   a  as a mask. Here, the transparent conductor  192 G of the green pixel G is left in the contact hole  185 G by terminating the etching process when the etching process penetrates to the overcoat  180 . 
         [0091]    Referring to  FIG. 10 , a second transparent conductive layer  190   q  made of ITO or IZO is deposited on the lower transparent electrodes  192 R,  192 B, and  192 W, the transparent conductor  192 G, and the overcoat  180 , for example by sputtering. Then, a second photoresist pattern  50   a  is formed on the second transparent conductive layer  190   q  by coating and patterning a second photosensitive film on the second transparent conductive layer  190   q.    
         [0092]    Referring to  FIG. 11 , a plurality of the upper transparent electrodes  193 R,  193 B, and  193 W and transparent electrodes  193 G are formed by etching the second transparent conductive layer  190   q  using the second photoresist pattern  50   a  as a mask, thereby completely forming pixel electrodes  191 R,  191 G,  191 B, and  191 W of pixels R, G, B, and W, respectively. 
         [0093]    Referring to  FIG. 12 , an insulating layer is coated on the pixel electrodes  191 R,  191 G,  191 B, and  191 W, and the overcoat  180 , and a plurality of insulating members  361  are formed by patterning the insulating layer. The insulating members  361  extend between adjacent pixel electrodes and around the perimeter of each pixel electrode. 
         [0094]    Finally, as shown in  FIG. 3 , an organic light emitter including a white organic light emitting member  370  and a common electrode  270  are sequentially formed on the pixel electrodes  191 R,  191 G,  191 B, and  191 W, and on insulating members  361 . 
         [0095]    As described above, the transparent conductor  192 G is left in the contact hole  185 G of the green pixel G when the lower transparent electrodes  192 R,  192 B, and  192 W are formed. Therefore, the output terminal of the driving transistor QdG is protected from being exposed to an etchant used for etching the first transparent conductive layer  190   p  and is thus protected from being damaged by the etchant. 
         [0096]    An organic light emitting device according to another exemplary embodiment of the present invention will be described with reference to  FIG. 1 ,  FIG. 2  and  FIG. 13 . 
         [0097]      FIG. 13  is a cross-sectional view of an organic light emitting device according to another exemplary embodiment of the present invention. 
         [0098]    The descriptions already provided of like elements in the previous embodiment are omitted here, and like reference numerals are designated to like constituent elements. 
         [0099]    A thin film transistor array, an insulating layer  112 , a plurality of color filters  230 R,  230 G, and  230 B, an overcoat  180 , pixel electrodes  191 R,  191 G,  191 B, and  191 W, insulating members  361 , an organic light emitter including a white organic light emitting member  370 , and a common electrode  270  are sequentially disposed on an insulating substrate  110 . 
         [0100]    In the organic light emitting device according to the present exemplary embodiment, red color filters  230 R, green color filters  230 G, and blue color filters  230 B are disposed on the insulating layer  112 . However, no color filter is provided in the white pixel W. Alternatively, a white color filter may be provided in the white pixel W. 
         [0101]    Also, structures of the contact holes  185 R,  185 G,  185 B, and  185 W and the pixel electrodes  191 R,  191 G,  191 B, and  191 W in the present embodiment are different from those in the previously described exemplary embodiment shown in  FIG. 3 . 
         [0102]    Although the pixel electrodes  191 R,  191 B, and  191 W of the red, blue, and white pixels R, B, and W respectively include a lower transparent electrode  192 R,  192 B and  192 W and an upper transparent electrode  193 R,  193 B and  193 W, the pixel electrode  191 G of the green pixel G is made of a single layer of a transparent conductive material. 
         [0103]    Although the contact holes  185 R,  185 B, and  185 W of the red, blue and white pixels R, B and W penetrate the insulating layer  112 , the overcoat  180 , and the first transparent electrodes  192 R,  192 B, and  192 W, the contact hole  185 G of the green pixel G penetrates only the insulating layer  112  and the overcoat  180 . The upper transparent electrodes  193 R,  193 B, and  193 W of the red, blue, and white pixels R, B, and W are electrically connected to the driving transistors QdR, QdB, and QdW through the contact holes  185 R,  185 B, and  185 W, respectively, and the pixel electrode  191 G of the green pixel G is electrically connected to the driving transistor QdG through the contact hole  185 G. 
         [0104]    The thicknesses Dr, Dg, Db, and Dw of the pixel electrodes  191 R,  191 G,  191 B, and  191 W are similar to those of the previous exemplary embodiment shown in  FIG. 3 . 
         [0105]    Now, a manufacturing method of the organic light emitting device of  FIG. 13  will be described with reference to  FIG. 14  to  FIG. 18 . 
         [0106]      FIG. 14  to  FIG. 18  are cross-sectional views of the organic light emitting device of  FIG. 13  at intermediate steps of a manufacturing method of an organic light emitting device according to an exemplary embodiment of the present invention. 
         [0107]    Referring to  FIG. 14 , as in the previous exemplary embodiment, a thin film transistor array is formed on an insulating substrate  110 . Then, an insulating layer  112 , a plurality of color filters  230 R,  230 G, and  230 B, and an overcoat  180  are sequentially formed. 
         [0108]    The first transparent conductive layer  190   r  is deposited on the overcoat  180 , and a first photoresist pattern  40   b  is formed by coating a first photosensitive film on the first transparent conductive layer  190   r  and patterning the first photosensitive film. 
         [0109]    Referring to  FIG. 15 , a plurality of lower transparent electrodes  192 R,  192 B, and  192 W are formed at the red, blue, and white pixels R, B, and W by etching the first transparent conductive layer  190   r  while using the first photoresist pattern  40   b  as a mask. 
         [0110]    Referring to  FIG. 16  and  FIG. 17 , a second photoresist pattern  45   a  is formed by coating a second photosensitive film on the lower transparent electrodes  192 R,  192 B, and  192 W, and on the overcoat  180 , and patterning the second photosensitive film. 
         [0111]    Then, a plurality of contact holes  185 R,  185 G,  185 B, and  185 W are formed in the lower transparent electrodes  192 R,  192 B, and  192 W, the overcoat  180 , and the insulating layer  112  by etching while using the second photoresist pattern  45   a  as a mask. Since the contact holes  195 R,  185 G,  185 B, and  185 W are formed after the lower transparent electrodes  192 R,  192 B, and  192 W are formed, the driving transistors QdR, QdB, and QdW are prevented from being damaged by an etchant that is used for patterning the lower transparent electrodes  192 R,  192 B, and  192 W. 
         [0112]    Referring to  FIG. 18 , a second transparent conductive layer made of ITO or IZO is deposited on the lower transparent electrodes  192 R,  192 B, and  192 W, and the overcoat  180 , and a photoresist pattern (not shown) is formed thereon. Then, a plurality of upper transparent electrodes  193 R,  193 B, and  193 W and pixel electrodes  191 G of the green pixel G are formed by etching the second transparent conductive layer using the photoresist pattern (not shown) as a mask. The lower transparent electrodes  192 R,  192 B, and  192 W and the upper transparent electrodes  193 R,  193 B, and  193 W of the red, blue, and white pixels R, B, and W form the pixel electrodes  191 R,  191 B, and  191 W, respectively. 
         [0113]    Finally, as shown in  FIG. 13 , a plurality of insulating members  361 , a white organic light emitting member  370 , and a common electrode  270  are sequentially formed on the pixel electrodes  191 R,  191 G,  191 B, and  191 W and the overcoat  180 . 
         [0114]    An organic light emitting device according to two other exemplary embodiments will be described with reference to  FIG. 19  and  FIG. 20  as well as  FIG. 1  and  FIG. 2 . 
         [0115]      FIG. 19  and  FIG. 20  are cross-sectional views of organic light emitting devices according to exemplary embodiments of the present invention. 
         [0116]    The descriptions of like elements previously described are here omitted, and like reference numerals are designated to like constituent elements. 
         [0117]    Referring to  FIG. 19 , an organic light emitting device according to the present exemplary embodiment has a structure that is similar to that shown in  FIG. 3  except for the pixel electrodes  191 R,  191 G,  191 B, and  191 W. 
         [0118]    Unlike the organic light emitting device shown in  FIG. 3 , the pixel electrode  191 G of the green pixel G includes a lower transparent electrode  194 G and an upper transparent electrode  195 G, and the pixel electrodes  191 R,  191 B, and  191 W of the red, blue, and white pixels R, B, and W respectively include transparent electrodes  195 R,  195 B, and  195 W made of a single second transparent conductive layer and transparent conductors  194 R,  194 B, and  194 W made from a first transparent conductive layer and disposed in the respective contact holes  185 R,  185 B, and  185 W. 
         [0119]    In the present exemplary embodiment, a thickness Dg of the pixel electrode  191 G of the green pixel G is greater than that of the pixel electrodes  191 R,  191 B, and  191 W of the red, blue, and white pixels R, B, and W. The thickness Dg of the pixel electrode  191 G may be between about 1400 Å and about 1600 Å, and the thicknesses Dr, Db, and Dw of the red, blue, and white pixels R, B, and W may be between about 800 Å and about 1000 Å. The thicknesses Dr, Db, and Dw are substantially equal. 
         [0120]    In the previous exemplary embodiments shown in  FIGS. 3 and 13 , light that is reflected repeatedly at a boundary between the green pixel electrode  191 G and the overcoat  180  and at the common electrode  270  is finally emitted as light that contains a strong green component which is then separated by a green filter. In the previous exemplary embodiments the green pixel electrode is between about 300 Å and about 500| thick and has an index of refraction between 1.5 and 1.7. 
         [0121]    In the present embodiment, the green pixel G has a different optical path length from the previous embodiments. The thickness of the green pixel electrode is increased to between about 1400 Å and about 1600 Å while the index of refraction is again between about 1.5 and about 1.7, and light experiences an optical process such as constructive interference under different conditions to again be emitted from the green pixel electrode  191 G as light that contains a strong green component. Therefore, it is possible to obtain light having a desired range of wavelength and desired color purity for respective primary colors including green. Also, it is possible to reduce color variation and to improve transmittance. 
         [0122]    Also, in the present exemplary embodiment, color filters are omitted in the white pixel W although red color filters  230 R, green color filters  230 G, and blue color filters  230 B are disposed on the insulating layer  112 . 
         [0123]    Next, referring to  FIG. 20 , an organic light emitting device according to another exemplary embodiment that is similar to the organic light emitting device of  FIG. 19  except for the color filters  230 R,  230 G,  230 B, and  230 W, the pixel electrodes  191 R,  191 G,  191 B, and  191 W, the insulating members  361 , and the organic light emitting members  370 R,  370 G,  370 B, and  370 W. 
         [0124]    In the organic light emitting device according to the present exemplary embodiment as shown in  FIG. 20 , color filters including red color filters  230 R, green color filters  230 G, blue color filters  230 B, and white color filters  230 W are disposed on the insulating layer  112 . 
         [0125]    The pixel electrode  191 G of the green pixel G includes a lower transparent electrode  194 G formed in a first layer of transparent conductive material at a lower side and an upper transparent electrode  195 G formed in a second layer of transparent conductive material at an upper side. The pixel electrodes  191 R,  191 B, and  191 W of red, blue, and white pixels R, B, and W are made of a single layer of a transparent conductive material, which layer may be the second layer. 
         [0126]    Also, while the contact holes  185 R,  185 B, and  185 W of the red pixel R, the blue pixel B, and the white pixel B penetrate the insulating layer  112  and the overcoat  180 , the contact hole  185 G of the green pixel G penetrates the insulating layer  112 , the overcoat  180 , and the lower transparent electrode  194 G. The upper transparent electrode  195 G of the green pixel G is connected to the driving transistor QdG through the contact hole  185 G, and the pixel electrodes  191 R,  191 B, and  191 W of the red pixel R, the blue pixel B, and the white pixel W are electrically connected to driving transistors QdR, QdB, and QdW through the contact holes  185 R,  185 B, and  185 W, respectively. 
         [0127]    The thicknesses Dr, Dg, Db, and Dw of the pixel electrodes  191 R,  191 G,  191 B, and  191 W may be substantially the same as those of the organic light emitting device of  FIG. 19 . 
         [0128]    A plurality of insulating members  361  is disposed on the overcoat  180  between adjacent pixel electrodes  191 R,  191 G,  191 B, and  191 W. Each insulating member  361  defines an opening by surrounding the edges of the pixel electrodes  191 R,  191 G,  191 B, and  191 W, and may be made of an organic insulator or an inorganic insulator. 
         [0129]    In this embodiment, the organic light emitter includes red, green, blue, and white organic light emitting members  370 R,  370 G,  370 B, and  370 W disposed in the openings that are surrounded by the insulating members  361  at the red pixel R, the green pixel G, the blue pixel B, and the white pixel W, respectively. The red, green, blue, and white organic light emitting members  370 R,  370 G,  370 B, and  370 W are made of organic materials each uniquely emitting one of red, green, blue, and white light. The white organic light emitting member  370 W may have a stacked structure of a plurality of organic material layers each emitting a different color of light. 
         [0130]    In such a way, organic light emitting members  370 R,  370 G,  370 B, and  370 W each of which uniquely emits one of red, green, blue, and white light are disposed at pixels R, G, B, and W, respectively. Therefore, color reproducibility may be further improved. 
         [0131]    The white color filters  230 W of the white pixels W may be omitted. 
         [0132]    Alternatively, the red, green, blue, and white color filters  230 R,  230 G,  230 B, and  230 W may be omitted. 
         [0133]    With reference to  FIG. 21  and  FIG. 22 , an organic light emitting device according to another exemplary embodiment of the present invention will be described in detail. 
         [0134]      FIG. 21  is a plan view illustrating a plurality of pixels disposed in an organic light emitting device according to another exemplary embodiment of the present invention, and  FIG. 22  is a cross-sectional view of the organic light emitting device according to this exemplary embodiment of the present invention. 
         [0135]    Referring to  FIG. 21 , an organic light emitting device includes red pixels R, green pixels G, and blue pixels B, which are disposed in that order in rows of pixels. 
         [0136]    The three pixels including a red pixel R, a green pixel G, and a blue pixel B form one group, and the group of pixels R, G and B is disposed repeatedly along the rows and columns. Adjacent rows are offset so that columns include groups of pixels R, G, and B. However, the pixel layout and the pixel shape may be modified in various ways. 
         [0137]    Referring to  FIG. 22 , an organic light emitting device according to the present exemplary embodiment has a stacked structure that is similar to that of the organic light emitting device of  FIG. 20 . 
         [0138]    However, the organic light emitting device according to the present exemplary embodiment includes only pixels of three colors, red, green, and blue pixels R, G, and B. Since the pixel electrodes  191 R,  191 G, and  191 B and the organic light emitting members  370 R,  370 G, and  370 B are the same as those of the organic light emitting device shown in  FIG. 20 , further descriptions thereof are omitted. 
         [0139]    Various features of the organic light emitting device of  FIG. 20  may be applied to the organic light emitting device of the present exemplary embodiment. 
         [0140]    Various features of the organic light emitting device and the manufacturing method thereof shown in  FIG. 1  to  FIG. 18  may be applied to the organic light emitting devices shown in  FIG. 19  to  FIG. 22 . Also, color filters of the organic light emitting device and the structure and arrangement of the organic light emitting members according to various exemplary embodiments of the present invention may be modified in various ways. 
         [0141]    In this way, display characteristics such as color reproducibility and viewing angle characteristics of an organic light emitting device may be improved. Also, during a manufacturing process of an organic light emitting device, thin film transistors may be prevented from being damaged. 
         [0142]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.