Abstract:
An organic light emitting display device including: a first emission area including a first organic light emitting diode; a second emission area arranged adjacent to the first emission area and not overlapping with the first emission area, the second emission area including a second organic light emitting diode; a pixel circuit unit electrically connected to the first organic light emitting diode and the second organic light emitting diode; and a transmissive area adjacent to the first and second emission areas and not overlapping with the first and second emission areas, the transmissive area configured to transmit external light therethrough.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0006809, filed on Jan. 20, 2012 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of embodiments of the present invention relate to organic light emitting display devices. 
     2. Description of the Related Art 
     Organic light emitting display devices generally have wide viewing angles, high contrast ratios, short response times, and reduced power consumption, and thus may be used across a variety of applications, such as personal portable devices (e.g., MP3 players and mobile phones), or large-screen displays (e.g., television sets). 
     An organic light emitting display device has self-emitting characteristics, and weight and thickness of the organic light emitting display device can be reduced since the organic light emitting display device does not require an additional light source, unlike a liquid crystal display (LCD) device. 
     Also, an organic light emitting display device can be manufactured as a transparent display device by including transparent thin-film transistors ( TFTs) and transparent organic light emitting diodes. 
     In a transparent display device, when the device is in an off-state, an image of an object or an image positioned at a side of the device opposite to a user is transmitted to the user through not only patterns of organic light emitting diodes, TFTs and various wires but also through spaces between the patterns. However, the patterns of organic light emitting diodes, TFTs, and wires do not have a high transmissivity, and the spaces between the patterns are not very high. Thus, the transmissivity of the entire transparent display device is typically not great. 
     Therefore, a distorted image may be transmitted to the user due to the patterns of organic light emitting diodes, TFTs, and wires. The reason for this is because gaps between the patterns are typically merely a few hundred nanometers, that is, almost equal to the wavelengths of visible light, thus causing light to scatter as it passes through the patterns. 
     An organic light emitting display device may be produced to be a dual-sided light emitting display device, compared to an LCD device. However, in the existing dual-sided light emitting display device, the same image is displayed on both surfaces thereof. Thus, the left and right sides of the image displayed on one of the surfaces are reversed relative to those of the image displayed on the other surface. 
     In addition, a dual-sided light emitting display device may be manufactured by separately manufacturing two organic light emitting display devices and binding them together. However, in this case, the dual-sided light emitting display device cannot be embodied as a transparent display device. 
     SUMMARY 
     According to an aspect of embodiments of the present invention, in an organic light emitting display device, transparent transmissive areas are formed by improving the transmissivity of the transmissive areas, and dual emission occurs. 
     According to another aspect of embodiments of the present invention, a transparent organic light emitting display device prevents or reduces distortion of an image transmitted therethrough by preventing or substantially preventing light from scattering during image display. 
     According to an embodiment of the present invention, an organic light emitting display device includes: a first emission area including a first organic light emitting diode; a second emission area arranged adjacent to the first emission area and not overlapping with the first emission area, the second emission area including a second organic light emitting diode; a pixel circuit unit electrically connected to the first organic light emitting diode and the second organic light emitting diode; and a transmissive area adjacent to the first and second emission areas and not overlapping with the first and second emission areas, the transmissive area configured to transmit external light therethrough. 
     The pixel circuit unit may be arranged to overlap with the first emission area and not to overlap with the second emission area. 
     The first organic light emitting diode may include a first pixel electrode configured to reflect light. 
     The second organic light emitting diode may include a second pixel electrode configured to transmit light therethrough. 
     The pixel circuit unit may individually drive the first organic light emitting diode and the second organic light emitting diode. 
     The pixel circuit unit may include a first light emitting thin film transistor (TFT) electrically connected to the first organic light emitting diode; and a second light emitting TFT electrically connected to the second organic light emitting diode. 
     The organic light emitting display device may further include a data line, a scan line, and a power supply source line for supplying a data signal, a scan signal, and power to the pixel circuit unit, respectively. The pixel circuit unit may include a first TFT, a second TFT, and a capacitor. In the first TFT, a gate electrode may be electrically connected to the scan line, a first electrode may be electrically connected to the data line, and a second electrode may be electrically connected to a gate electrode of the second TFT and the capacitor. In the second TFT, a first electrode may be electrically connected to the power supply source line and the capacitor, and a second electrode may be electrically connected to the first and second light emitting TFTs. 
     In the first light emitting TFT, a first electrode may be electrically connected to the second TFT, and a second electrode may be electrically connected to the first organic light emitting diode. In the second light emitting TFT, a first electrode may be electrically connected to the second TFT, and a second electrode may be electrically connected to the second organic light emitting diode. 
     The first organic light emitting diode and the second organic light emitting diode may emit a same color of light. 
     The organic light emitting display device may further include a transparent window arranged in the transmissive area. 
     According to another embodiment of the present invention, an organic light emitting display device includes: a substrate; a plurality of pixels formed on the substrate, each of the plurality of pixels including a first emission area, a second emission area, a transmissive area configured to transmit external light therethrough, and a pixel circuit unit; a plurality of first pixel electrodes, each being arranged in the first emission area of one of the plurality of pixels and electrically connected to the pixel circuit unit of the one of the plurality of pixels, each of the plurality of first pixel electrodes including a transparent conductive film and a reflective layer; a plurality of second pixel electrodes, each being arranged in the second emission area of a respective one of the plurality of pixels, electrically connected to the pixel circuit unit of the respective one of the plurality of pixels, and arranged apart from the plurality of first pixel electrodes, each of the plurality of second pixel electrodes including a transparent conductive film or a semi-transmissive layer; a first opposite electrode facing the plurality of first pixel electrodes; a second opposite electrode facing the plurality of second pixel electrodes; a first organic layer between the plurality of first pixel electrodes and the first opposite electrode, the first organic layer including a first emission layer; and a second organic layer between the plurality of second pixel electrodes and the second opposite electrode, the second organic layer including a second emission layer. 
     The first and second opposite electrodes may be electrically connected to each other. 
     The first opposite electrode may be configured to transmit light therethrough. 
     The first opposite electrode may be a reflective electrode. 
     The first opposite electrode and the second opposite electrode may each include at least one metal selected from the group consisting of silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), and ytterbium (Yb). 
     Each of the pixel circuit units may be arranged to overlap with one of the plurality of first pixel electrodes and not to overlap with any of the plurality of second pixel electrodes. 
     Each of the pixel circuit units may include a first light emitting thin film transistor (TFT) electrically connected to one of the plurality of first pixel electrodes; and a second light emitting TFT electrically connected to one of the plurality of second pixel electrodes. 
     The organic light emitting display device may further include a data line, a scan line, and a power supply source line for supplying a data signal, a scan signal, and power to the pixel circuit unit, respectively. The pixel circuit unit may include a first TFT, a second TFT, and a capacitor. I the first TFT, a gate electrode may be electrically connected to the scan line, a first electrode may be electrically connected to the data line, and a second electrode may be electrically connected to a gate electrode of the second TFT and the capacitor. In the second TFT, a first electrode may be electrically connected to the power supply source line and the capacitor, and a second electrode may be electrically connected to the first and second light emitting TFTs. 
     In the first light emitting TFT, a first electrode may be electrically connected to the second TFT and a second electrode may be electrically connected to a first organic light emitting diode of a pixel of the plurality of pixels, and, in the second light emitting TFT, a first electrode may be electrically connected to the second TFT and a second electrode may be electrically connected to a second organic light emitting diode of the pixel of the plurality of pixels. 
     Each of the pixel circuit units may include a first pixel circuit unit electrically connected to one of the plurality of first pixel electrodes; and a second pixel circuit unit electrically connected to one of the plurality of second pixel electrodes, and being operated independently with the first pixel circuit unit. 
     The first pixel circuit unit and the second pixel circuit unit may be arranged to overlap with the first emission area and not to overlap with the second emission area. 
     The transmissive areas of at least two adjacent pixels from among the plurality of pixels may be integrally formed. 
     The organic light emitting display device may further include a plurality of transparent windows arranged in the transmissive areas. 
     The transparent windows of at least two adjacent pixels from among the plurality of pixels may be integrally formed. 
     The second opposite electrode may include a reflective metal film, and the reflective metal film may include a plurality of apertures, each corresponding to one of the first emission areas and one of the plurality of the transparent windows. 
     According to an aspect of embodiments of the present invention, a transparent organic light emitting display device may be manufactured by improving the transmissivity of external light and to allow dual emission to occur in the transparent organic light emitting display device. 
     According to another aspect of embodiments of the present invention, a transparent organic light emitting display device is capable of preventing or reducing distortion of an image transmitted therethrough by eliminating or substantially eliminating light-scattering during image display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and aspects of the present invention will become more apparent by describing in further detail some exemplary embodiments thereof with reference to the attached drawings, in which: 
         FIG. 1  is a cross-sectional view of an organic light emitting display device according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of an organic light emitting display device according to another embodiment of the present invention; 
         FIG. 3  is a schematic plan view of an organic emission unit according to an embodiment of the present invention; 
         FIG. 4  is a circuit diagram of a pixel circuit unit of the organic emission unit of  FIG. 3 , according to an embodiment of the present invention; 
         FIG. 5  is a schematic plan view of an organic emission unit according to another embodiment of the present invention; 
         FIG. 6  is a schematic plan view of an organic emission unit according to another embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of the organic emission unit of  FIG. 3 , according to an embodiment of the present invention; 
         FIG. 8A  is a schematic cross-sectional view of a first organic light emitting diode in a first emission area of the organic emission unit of  FIG. 7 , according to an embodiment of the present invention; 
         FIG. 8B  is a schematic cross-sectional view of a second organic light emitting diode in a second emission area of the organic emission unit of  FIG. 7 , according to an embodiment of the present invention; 
         FIG. 8C  is a schematic cross-sectional view of a second organic light emitting diode in a second emission area of an organic emission unit, according to another embodiment of the present invention; 
         FIG. 8D  is a schematic cross-sectional view of a second organic light emitting diode in a second emission area of an organic emission unit, according to another embodiment of the present invention; 
         FIG. 8E  is a schematic cross-sectional view of a second organic light emitting diode in a second emission area of an organic emission unit, according to another embodiment of the present invention; 
         FIG. 9  is a cross-sectional view of an organic emission unit according to another embodiment of the present invention; and 
         FIG. 10  is a cross-sectional view of an organic emission unit according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, some exemplary embodiments of the present invention are shown and described, by way of illustration. 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. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
       FIG. 1  is a cross-sectional view of an organic light emitting display device  2  according to an embodiment of the present invention. Referring to  FIG. 1 , the organic light emitting display device  2  includes an organic emission unit  21  formed on a first surface  11  of a substrate  1 , and a sealing substrate  23  for sealing the organic emission unit  21 . 
     The sealing substrate  23  may be formed of a transparent material to display an image generated by the organic emission unit  21 , and to prevent or substantially prevent external air and moisture from penetrating into the organic emission unit  21 . 
     A space  25  between the substrate  1  and the sealing substrate  23  is sealed by coupling edges of the substrate  1  and the sealing substrate  23  with sealing materials  24 . The space  25  may be filled with an absorbent or a filler, as will be described later. 
     As illustrated in  FIG. 2 , in an organic light emitting display device  2 ′ according to another embodiment of the present invention, a thin sealing film  26  instead of the sealing substrate  23  may be formed on the organic emission unit  21  to protect the organic emission unit  21  from external air and moisture. In one embodiment, the thin sealing film  26  may have a structure in which a film formed of an inorganic material (e.g., a silicon oxide or a silicon nitride), and a film formed of an organic material (e.g., epoxy or polyimide) are alternately stacked, but the present invention is not limited thereto. That is, in other embodiments, the thin sealing film  26  may include any thin film type sealing structure. 
       FIG. 3  is a schematic plan view of an example of the organic emission unit  21  of  FIG. 1  or  FIG. 2 , according to an embodiment of the present invention. Referring to  FIG. 3 , a red pixel Pr, a green pixel Pg, and a blue pixel Pb are arranged to be adjacent to one another in the organic emission unit  21 . 
     Each of the red pixel Pr, the green pixel Pg, and the blue pixel Pb includes a first emission area PA 1 , a second emission area PA 2 , and a transmissive area TA. 
     In one embodiment, in each of the red pixel Pr, the green pixel Pg, and the blue pixel Pb, the first emission area PA 1 , the second emission area PA 2 , and the transmissive area TA are sequentially arranged to be adjacent to each other in a vertical direction, as illustrated in  FIG. 3 , but the present invention is not limited thereto. For example, in another embodiment, the transmissive area TA may be disposed above or between the first and second emission areas PA 1  and PA 2 . 
     Referring to  FIG. 3 , each of the first emission areas PA 1  includes a pixel circuit unit PC. Although not shown in  FIG. 3 , various wires connected to the pixel circuit unit PC may be disposed to pass through the first emission area PA 1  or near the first emission area PA 1 . 
       FIG. 4  is a circuit diagram of the pixel circuit unit PC of  FIG. 3 , according to an embodiment of the present invention. Referring to  FIG. 4 , conductive lines (e.g., a scan line S, a data line D, and a Vdd line V which is a power supply voltage line) are electrically connected to the pixel circuit unit PC. Although not shown, various other conductive lines may further be connected to the pixel circuit unit PC according to a structure of the pixel circuit unit PC. 
     The pixel circuit unit PC, in one embodiment, includes a first thin-film transistor (TFT) T 1  connected to the scan line S and the data line D, a second TFT T 2  connected to the first TFT T 1  and the Vdd line V, and a capacitor Cst connected to the first and second TFTs T 1  and T 2 . 
     In the first TFT T 1 , a gate electrode is connected to the scan line S to receive a scan signal, a first electrode is connected to the data line D, and a second electrode is connected to the capacitor Cst, and a gate electrode of the second TFT T 2 . 
     In the second TFT T 2 , a first electrode is connected to the Vdd line V and the capacitor Cst, and a second electrode is connected to first electrodes of a first light emitting TFT T 3  and a second light emitting TFT T 4 . 
     In one embodiment, the first TFT T 1  may act as a switching transistor, and the second TFT T 2  may act as a driving transistor. 
     In one embodiment, a second electrode of the first light emitting TFT T 3  is electrically connected to a first organic light emitting diode E 1 , and a second electrode of the second light emitting TFT T 4  is electrically connected to a second organic light emitting diode E 2 . Thus, referring to  FIGS. 3 and 4 , the second electrode of the first light emitting TFT T 3  and the second electrode of the second light emitting TFT T 4  are electrically connected to a first pixel electrode  221  and a second pixel electrode  222  of the organic emission unit  21 , respectively. 
     Gate electrodes of the first light emitting TFT T 3  and the second light emitting TFT T 4  are electrically connected to additional emission signal lines (not shown), respectively. 
     In one embodiment, the TFTs T 1  to T 4  are P-type transistors, but the present invention is not limited thereto, and, in another embodiment, at least one of the TFTs T 1  to T 4  may be an N-type transistor. Although four TFTs and one capacitor are included in the pixel circuit unit PC according to one embodiment, the present invention is not limited thereto, and, in another embodiment, a combination of at least two TFTs and at least one capacitor may further be used according to a structure of the pixel circuit unit PC. 
     According to an embodiment of the present invention, the pixel circuit unit PC is disposed to overlap with the first emission area PA 1  and not to overlap with the second emission area PA 2 . 
     As will be described below, top emission of each subpixel occurs in each of the first emission areas PA 1 . Since the pixel circuit unit PC is disposed in each of the first emission areas PA 1  where top emission occurs, and a conductive pattern of the pixel circuit unit PC, which is an important factor that can degrade transmissivity, is not disposed in the transmissive area TA, the transmission of the transmissive area TA is greatly improved. 
     In other words, the pixel circuit unit PC overlaps with the first pixel electrode  221  to be hidden by the first pixel electrode  221 , but does not overlap with the second pixel electrode  222 . 
     In one embodiment, at least one of the conductive lines including the scan line S, the data line D, and the Vdd line V may be disposed to cross the first pixel electrode  221 . Since transmissivity is decreased less by the conductive lines than by the pixel circuit unit PC, according to one embodiment, all of the conductive lines may be arranged adjacent to the first pixel electrode  221 . The first pixel electrode  221  may include a reflective layer formed of conductive metal that reflects light, as described later herein, and the pixel circuit unit PC hidden by the first pixel electrode  221  may be screened by the first pixel electrode  221 . 
     In each of the second emission areas PA 2 , bottom emission of each subpixel occurs. Since the pixel circuit unit PC is not disposed in each of the second emission areas PA 2  where bottom emission occurs, the efficiency of bottom emission is not degraded. 
     According to the above-described structure of the pixel circuit unit PC, image information received via the data line D is displayed on the first organic light emitting diode E 1  when the first light emitting TFT T 3  is “off,” and is displayed on the second organic light emitting diode E 2  when the second light emitting TFT T 4  is “off.” Thus, different images may be displayed on the first organic light emitting diode E 1  and the second organic light emitting diode E 2 . Accordingly, dual emission may be performed based on time-division driving in such a manner that the left and right sides of an image displayed on a surface on which top emission occurs without being reversed relative to those of an image displayed on a surface on which bottom emission occurs. However, if the same switching signal is supplied to the first light emitting TFT T 3  and the second light emitting TFT T 4  to which the same data signal is input, then the left and right sides of an image displayed on a front surface are reversed relative to those of an image displayed on a bottom surface. As described above, it is possible to display an image on the first organic light emitting diode E 1  and the second organic light emitting diode E 2  that share the basic structure of the pixel circuit unit PC, in various manners. 
     Referring to  FIG. 5 , according to another embodiment of the present invention, the pixel circuit unit PC may include a first pixel circuit unit PC 1  being electrically connected to the first pixel electrode  221 , and a second pixel circuit unit PC 2  being electrically connected to the second pixel electrode  222 . The first pixel circuit unit PC 1  and the second pixel circuit unit PC 2  may be individually operated. The first pixel circuit unit PC 1  and the second pixel circuit unit PC 2  may have a structure of a general pixel circuit unit. 
     Referring to  FIG. 3  or  FIG. 5 , a plurality of separate transmissive areas TA may be formed to correspond to a red pixel Pr, a green pixel Pg, and a blue pixel Pb, respectively, but the present invention is not limited thereto. For example, referring to  FIG. 6 , in another embodiment, a single transmissive area TA may be formed to correspond to all of the red pixel Pr, the green pixel Pg, and the blue pixel Pb. In this case, the area of the single transmissive area TA is greater than the sum of the areas of the separate transmissive areas TA of the previously described embodiments, thereby increasing the transmissivity of external light. 
       FIG. 7  is a cross-sectional view of a pixel of the organic emission unit  21 , according to an embodiment of the present invention. In the organic emission unit  21 , according to an embodiment of the present invention, a buffer film  211  is formed on the first surface  11  of the substrate  1 , and the first light emitting TFT T 3  and the second light emitting TFT T 4  are formed on the buffer film  211 . Although  FIG. 7  illustrates only the first light emitting TFT T 3  and the second light emitting TFT T 4  for reasons of clarity, all the elements of the pixel circuit unit PC illustrated in  FIG. 4  may be formed on the buffer film  211 . 
     In one embodiment, a first semiconductor active layer  212   a  and a second semiconductor active layer  212   b  are formed on the buffer film  211 . 
     The buffer film  211  prevents or substantially prevents impurity elements from penetrating into the organic emission unit  21  and planarizes a surface of the organic emission unit  21 . The buffer film  211  may be formed of any of various materials to perform the functions described above. For example, the buffer film  211  may be formed of an inorganic material (e.g., a silicon oxide, a silicon nitride, a silicon oxynitride, an aluminum oxide, an aluminum nitride, a titanium oxide, or a titanium nitride), an organic material (e.g., polyimide, polyester, or acryl), or a stack of these materials. In another embodiment, the buffer film  211  may be omitted. 
     The first and second semiconductor active layers  212   a  and  212   b,  in one embodiment, may be formed of polycrystal silicon, but are not limited thereto, and, in another embodiment, for example, may be formed of an oxide semiconductor. For example, the first and second semiconductor active layers  212   a  and  212   b  may be G-I-Z-O layers [(In 2 O 3 )a(Ga 2 O 3 )b(ZnO)c layer], wherein a, b, and c are integers that respectively satisfy a≧0, b≧0, and c≧0. 
     In one embodiment, a gate insulating film  213  covering the first and second semiconductor active layers  212   a  and  212   b  is formed on the buffer film  211 , and first and second gate electrodes  214   a  and  214   b  are formed on the gate insulating film  213 . 
     In one embodiment, an interlayer insulating film  215  is formed on the gate insulating film  213  to cover the first and second gate electrodes  214   a  and  214   b.  A first source electrode  216   a  and a first drain electrode  217   a,  and a second source electrode  216   b  and a second drain electrode  217   b  are formed on the interlayer insulating film  215  to be connected to the first semiconductor active layer  212   a  and the second semiconductor active layer  212   b  through contact holes, respectively. 
     The scan line S, in one embodiment, may be concurrently or simultaneously formed with the first and second gate electrodes  214   a  and  214   b.  The data line D and the Vdd line V, in one embodiment, may be concurrently or simultaneously formed with the first source electrode  216   a  and the second source electrode  216   b.    
     However, the structures of the first and second light emitting TFTs TR3 and TR4 are not limited thereto, and any of various types of TFT structures may be employed. 
     In one embodiment, a passivation film  218  is formed to cover the first and second light emitting TFTs T 3  and T 4 . The passivation film  218  may be a single layer or multiple layers of insulating film. The passivation film  218  may be formed of an inorganic material and/or an organic material. 
     Referring to  FIG. 7 , the first pixel electrode  221  covering the first and second light emitting TFTs T 3  and T 4  may be formed on the passivation film  218 . The first pixel electrode  221  is connected to the first drain electrode  217   a  of the first light emitting TFT T 3  through a via hole formed in the passivation film  218 . 
     The second pixel electrode  222 , in one embodiment, is formed on the passivation film  218  adjacent to the first pixel electrode  221 . The first pixel electrode  221  and the second pixel electrode  222  are separated from each other. The second pixel electrode  222  is connected to the second drain electrode  217   b  of the second light emitting TFT T 4  through a via hole formed in the passivation film  218 . 
     In one embodiment, a pixel defining film  219  covering edges of the first pixel electrode  221  and the second pixel electrode  222  is formed on the passivation film  218 . 
     A first organic layer  223  is formed on the first pixel electrode  221 , and a first opposite electrode  224  is formed to cover the first organic layer  223 . 
     A second organic layer  223 ′ is formed on the second pixel electrode  222 , and a second opposite electrode  225  is formed to cover the second organic layer  223 ′. 
     The first opposite electrode  224  and the second opposite electrode  225  may be electrically connected to each other, as illustrated in  FIG. 7 . 
     The same material may be used to form the first organic layer  223  and the second organic layer  223 ′. The first organic layer  223  and the second organic layer  223 ′ may each be a low-molecular weight organic layer or a polymer organic layer having a high molecular weight. In one embodiment, the first organic layer  223  and the second organic layer  223 ′ are each a low-molecular weight organic film, and may be formed by stacking a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL) in a single structure or a composite structure, and may be formed of any of various materials, such as copper phthalocyanine (CuPc), N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), or tris-8-hydroxyquinoline aluminum (Alq3). The low-molecular weight organic layer may be formed by vacuum deposition. In this regard, the EML may be individually formed for each pixel, and the HIL, the HTL, the ETL, and the EIL may be common layers that are used in the pixels. 
     The first pixel electrode  221  and the second pixel electrode  222  may function as anode electrodes, and the first opposite electrode  224  and the second opposite electrode  225  may function as cathode electrodes, or vice versa. 
     In one embodiment, the first pixel electrode  221  may have a size corresponding to that of the first emission area PA 1  of each pixel, and the second pixel electrode  222  may have a size corresponding to that of the second emission area PA 2  of each pixel. 
     A common voltage may be applied to the first and second opposite electrodes  224  and  225  of all of the pixels of the organic emission layer  21 . 
     The passivation film  218 , the gate insulating film  213 , the interlayer insulating film  215 , and the pixel defining film  219  may be formed as transparent insulating films, but the present invention is not limited thereto. In one embodiment, the substrate  1  may have a transmissivity less than or equal to a total transmissivity of the transparent insulating films. 
       FIG. 8A  is a schematic cross-sectional view of a first organic light emitting diode in the first emission area PA 1  of  FIG. 7 , according to an embodiment of the present invention.  FIG. 8B  is a schematic cross-sectional view of a second organic light emitting diode in the second emission area PA 2  of  FIG. 7 , according to an embodiment of the present invention. 
     According to an embodiment of the present invention, the first pixel electrode  221  may be an electrode including a reflective layer, and the first opposite electrode  224  may be a semi-transparent and semi-reflective electrode. Accordingly, the first emission area PA 1  may be a top emission type area in which an image is displayed toward the first opposite electrode  224 . 
     In one embodiment, the first pixel electrode  221  is a reflective electrode, and the pixel circuit unit PC disposed under the first pixel electrode  221  is covered by the first pixel electrode  221 . Thus, referring to  FIG. 7 , patterns of the first light emitting TFT T 3  and the second light emitting TFT T 4  under the first pixel electrode  221  are not visible at an outer side above the first opposite electrode  224 . 
     As the first pixel electrode  221  is a reflective electrode, light is emitted only toward a user, thereby preventing or reducing optical loss in a direction opposite to the user. 
     In one embodiment, the second pixel electrode  222  is a transparent electrode, and the second opposite electrode  225  is a reflective electrode. In this case, the second emission area PA 2  is a bottom emission type area in which an image is displayed toward the second pixel electrode  222 . 
     The first pixel electrode  221 , in one embodiment, may be a stacked structure of a first transparent conductive film  221   a,  a reflective layer  221   b,  and a second transparent conductive film  221   c.  The first transparent conductive film  221   a  and the second transparent conductive film  221   c  may each include an oxide having a high work function, such as ITO, IZO, ZnO, or In 2 O 3 . The reflective layer  221   b  may be formed of a metal having a low work function, such as silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), ytterbium (Yb), or an alloy thereof, as described above. 
     The first organic layer  223 , in one embodiment, is a stacked structure of a first functional layer  223   a,  a first emission layer  223   b,  and a second functional layer  223   c  formed on the first pixel electrode  221 . The first opposite electrode  224  is formed on the first organic layer  223 . 
     The first functional layer  223   a  may include an HIL and a HTL, and the second functional layer  223   c  may include an EIL and an ETL. 
     The first opposite electrode  224  may be formed of a metal having a low work function, such as silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), ytterbium (Yb), or an alloy thereof. The first opposite electrode  224  may be a thin film having a high transmissivity, and may be formed having a thickness of about 100 to 300 Å. 
     A distance between a surface of the reflective layer  221   b  and the first opposite electrode  224  may be adjusted to cause optical resonance to occur, based on a wavelength of light emitted from the first emission layer  223   b.  The distance may be different for red, green, and blue pixels. For optical resonance, the distance may be adjusted by further forming an auxiliary layer on the first functional layer  223   a  and/or the second functional layer  223   c  to a thickness according to the color of a pixel. 
     The first emission area PA 1  having the above-described structure is a top emission type area in which an image is displayed toward the opposite electrode  224 , and light extraction efficiency may be increased or maximized by adjusting the distance between a surface of the reflective layer  221   b  and the first opposite electrode  224 . 
     As described above, the second pixel electrode  222  is formed of a transparent conductive material having a low reflectivity. Thus, the second pixel electrode  222  may be formed concurrently or simultaneously with at least one of the first transparent conductive film  221   a  and the second transparent conductive film  221   c  included in the first pixel electrode  221 . However, the present invention is not limited thereto, and a second pixel electrode  222 ′ according to another embodiment of the present invention may be a stacked structure of a first transparent conductive film  222   a,  a reflective layer  222   b,  and a second transparent conductive film  222   c,  as shown in  FIG. 8C . The first transparent conductive film  222   a  and the second transparent conductive film  222   c  may include an oxide having a high work function, such as ITO, IZO, ZnO, or In 2 O 3 . The reflective layer  222   b  may have a semi-transparent characteristic by being formed of a thin film metal, such as silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), ytterbium (Yb), or an alloy thereof. In one embodiment, the first transparent conductive film  222   a,  the reflective layer  222   b,  and the second transparent conductive film  222   c  of the second pixel electrode  222 ′ may be formed concurrently or simultaneously with the first transparent conductive film  221   a,  the reflective layer  221   b,  and the second transparent conductive film  221   c  of the first pixel electrode  221 , respectively. 
     The second organic layer  223 ′, in one embodiment, is a stacked structure including a third functional layer  223   a ′, a second emission layer  223   b ′, and a fourth functional layer  223   c ′ formed on the second pixel electrode  222 . The second opposite electrode  225  is formed on the second organic layer  223 ′. The third functional layer  223   a ′ and the fourth functional layer  223   c ′ may extend from the first functional layer  223   a  and the second functional layer  223   c,  respectively. In an embodiment where the second emission layer  223   b ′ has the same color as that of the first emission layer  223   b,  the second emission layer  223   b ′ may extend from the first emission layer  223   b.    
     In one embodiment, the second emission area PA 2  is a bottom emission type area in which an image is displayed toward the second pixel electrode  222 , and the second opposite electrode  225  may include a semi-transmissive film  225   a  and a metal film  225   b.  The semi-transmissive film  225   a  may be formed of a material used to form the first opposite electrode  224 , and may extend from the first opposite electrode  224 . The metal film  225   b  may be stacked on the semi-transmissive film  225   a  and may function as a reflective layer. The metal film  225   b  may be formed of a metal having a low work function, such as silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), ytterbium (Yb), or an alloy thereof. The metal film  225   b,  in one embodiment, may be formed to be thicker than the semi-transmissive film  225   a  so as to increase the reflectivity of light emitted from the second organic layer  223 ′ and reduce a voltage drop in the second opposite electrode  225 . With reference to  FIG. 8D , in a second opposite electrode  225 ′ according to another embodiment of the present invention, the metal film  225   b  may be formed before the semi-transmissive film  225   a  is formed. In this case, the second opposite electrode  225 ′ has a structure in which the metal film  225   b  and the semi-transmissive film  225   a  are sequentially stacked. 
     In one embodiment, the semi-transmissive film  225   a  of the second opposite electrode  225  may be integrally formed with the first opposite electrode  224 . 
     However, the present invention is not limited thereto, and a second opposite electrode  225 ″ according to another embodiment of the present invention may include only the metal film  225   b  if needed, as illustrated in  FIG. 8E . 
     Similarly, the above various embodiments of the structure of the second opposite electrode  225 ′ and  225 ″ may also be applied with the structure of the second pixel electrode  222 ′ illustrated in  FIG. 8C . 
     Although  FIG. 7  illustrates that the second opposite electrode  225  is a stacked structure of the semi-transmissive film  225   a  and the metal film  225   b  as illustrated in  FIG. 8B , the present invention is not limited thereto, and, in other embodiments, the second emission area PA 2  shown in  FIG. 7  may include the second opposite electrode  225 ′ that is a stacked structure of the metal film  225   b  and the semi-transmissive film  225   a,  as illustrated in  FIG. 8D , or may include the second opposite electrode  225 ″ that is only the metal film  225   b,  as illustrated in  FIG. 8E . 
     The metal film  225   b,  in one embodiment, may be formed not to extend at least to the transmissive area TA, as illustrated in  FIG. 7 . 
     According to an embodiment of the present invention, a transparent window  230  may be formed in the transmissive area TA to greatly increase the transmittance of external light through the transmissive area TA, as illustrated in  FIG. 7 . 
     The transparent window  230  may have an area corresponding to the transmissive area TA. Referring to  FIG. 7 , a first transparent window  231  may be formed by forming an aperture in the first opposite electrode  224  and the second opposite electrode  225  at a location corresponding to the transmissive area TA such that the first opposite electrode  224  and the second opposite electrode  225  are not formed in the transmissive area TA. In one embodiment, the first transparent window  231  improves the transmittance of external light through the transmissive area TA. 
     However, the present invention is not limited thereto, and, in another embodiment, an extended opposite electrode  226  may be formed in the transmissive area TA, as illustrated in  FIG. 9 . The extended opposite electrode  226  may be formed of a material used to form the first opposite electrode  224  and the semi-transmissive film  225   a,  and may extend from the semi-transmissive film  225   a.  By forming the extended opposite electrode  226  in the transmissive area TA, it is not needed to pattern a semi-transmissive film extending from the first opposite electrode  224  and the semi-transmissive film  225   a,  thereby facilitating the manufacture of an organic light emitting display device. 
     When the second opposite electrode  225 ,  225 ′,  225 ″ includes the metal film  225   b  as illustrated in  FIG. 8B ,  8 D, or  8 E, the metal film  225   b  may have apertures corresponding to the first emission area PA 1  and the transmissive area TA as illustrated in  FIG. 7  or  FIG. 9 . The aperture in the metal film  225   b  corresponding to the transmissive area TA may be formed to correspond to the first transparent window  231 . Thus, it is possible to increase light extraction efficiency of the first emission area PA 1  in which top emission occurs, and the transmittance of external light through the transmissive area TA. 
       FIG. 10  is a cross-sectional view of an organic emission unit according to another embodiment of the present invention. In the organic emission unit of  FIG. 10 , a second transparent window  232  is formed in the pixel defining film  219 . The second transparent window  232  may be connected to the first transparent window  231 , such as that shown in  FIG. 7 , thus forming the transparent window  230 . In  FIG. 10 , the second transparent window  232  is shown formed only in the pixel defining film  219 , but the present invention is not limited thereto, and, in another embodiment, the second transparent window  232  may be formed in at least one of the insulating films formed in the transmissive area TA. 
     The second transparent window  232 , in one embodiment, increases the transmissivity of the transmissive area TA, and may also prevent or reduce optical interference, degradation in color purity, and a change in color, caused by multilayered transparent insulating films. 
     Although not shown, in another embodiment, the transparent window  230  may include only the second transparent window  232 , and a first transparent window which is an aperture may not be formed in the extended opposite electrode  226 . 
     In one embodiment, a plurality of the transparent windows each corresponding to the shape of the transmissive area TA may be formed separately for the red pixel Pr, the green pixel Pg, and the blue pixel Pb, as illustrated in  FIG. 3 . In another embodiment, a single transmissive area TA corresponds to all of the red pixel Pr, the green pixel Pg, and the blue pixel Pb, as illustrated in  FIG. 6 , and a transparent window may be formed for all of the red pixel Pr, the green pixel Pg, and the blue pixel Pb. 
     While the present invention has been particularly shown and described with reference to some exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.