Abstract:
An organic light-emitting display device and a method of manufacturing the organic light-emitting display device. The organic light-emitting display device is a dual emission display capable of displaying differing images on either side of the display, and includes a facing electrode that is selectively deposited in the first area but not in the second area, the selectivity being brought about by a varying an underlying material having differing adhesive forces with the material of the facing electrode. In addition, the underlying materials of the facing electrode and other intermediate layers of the organic light emitting diode device provide extra distance between the organic light emitting layer and a reflective electrode, so that exciton quenching is reduced, resulting in improved light emitting efficiency.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates into this specification the entire contents of, and claims all benefits accruing under 35 U.S.C. §119 from an application earlier filed in the Korean Intellectual Property Office filed on Sep. 13, 2013 and there duly assigned Serial No. 10-2013-0110626 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     One or more embodiments of the present invention relate to an organic light-emitting display device and a method of manufacturing the organic light-emitting display device. 
     2. Description of the Related Art 
     An organic light emitting display device is a self-emissive display including an organic compound that is electrically exited to emit light. The organic light emitting display device is driven via a low voltage, is thin, has a wide view angle, and a fast response speed. Thus, the organic light emitting display device has been regarded as a next-generation display that does not have the defects of a liquid crystal display (LCD) device or the like. 
     Compared to the LCD device, the organic light emitting display device can emit light on two sides. In order to implement top and bottom emissions at the same time, a cathode electrode of a bottom emission unit is necessarily patterned. However, it is difficult to use a fine metal mask that is typically used in the art, in a patterning operation of a cathode reflective electrode formed on an organic emitting layer 
     SUMMARY OF THE INVENTION 
     One or more embodiments of the present invention include an organic light-emitting display device, in which a pattern of a cathode, which is a top electrode, may be easily formed, and a method of manufacturing the organic light-emitting display device. 
     One or more embodiments of the present invention include an organic light-emitting display device having a dual emission structure wherein a top electrode thereof is produced by selective deposition of a conductor where an open mask is used in the production of a pattern. 
     One or more embodiments of the present invention may include a design for an organic light-emitting display device that reduces exciton quenching, to provide for improved luminance efficiency. 
     One or more embodiments of the present invention include a dual emitting organic light-emitting display device capable of producing differing images on opposite sides of the display panel. 
     One or more embodiments of the present invention include dual emitting organic light-emitting display device that is also transparent to external light. 
     According to one aspect of the present invention, there is provided an organic light-emitting display (OLED) device that includes a plurality of pixels, each of the pixels including a first area in which light is emitted from the display device in a first direction and not in a second direction opposite to the first direction, a second area in which light is emitted from the display device in the second direction and not in the first direction and a third area that is transparent to external light, a plurality of first electrodes arranged within the first area of each of the plurality of pixels, a plurality of second electrodes arranged within the second area of each of the plurality of pixels, an intermediate layer arranged on the plurality of first electrodes and the plurality of second electrodes, the intermediate layer including an organic emitting layer, a third electrode arranged on the intermediate layer and within both the first area and the second area, a first auxiliary layer arranged on the third electrode within the first area, a second auxiliary layer arranged on the third electrode within the second area and a fourth electrode arranged on the first auxiliary layer within the first area. 
     The fourth electrode may be absent from the second area and the third area. A portion of the fourth electrode may be arranged within the second area and the third area, and a thickness of the portion of the fourth electrode arranged within the second area and the third area may be less than a thickness of a portion of the fourth electrode arranged within the first area. The portion of the fourth electrode arranged within the second area may be arranged on the second auxiliary layer. The first auxiliary layer may be absent from the second area and the third area. The second auxiliary layer bay be absent from the first area. A portion of the second auxiliary layer may be arranged within the first area, and the first auxiliary layer may be arranged on the portion of the second auxiliary layer arranged within the first area. A portion of the first auxiliary layer may be arranged within the second area, and the second auxiliary layer may be arranged on the portion of the first auxiliary layer arranged within the second area. A thickness of the fourth electrode may be greater than a thickness of the third electrode. An adhesive force of the fourth electrode with respect to the first auxiliary layer may be greater than an adhesive force of the fourth electrode with respect to the second auxiliary layer. The first auxiliary layer may include one of tris(8-hydroxy-quinolinato)aluminum (Alq3), di-tungsten tetra(hexahydropyrimidopyrimidine)), fullerene, lithium fluoride (LiF), ADN [9,10-di(2-naphthyl)anthracene] and Liq: 8-hydroxyquinolinolato-lithium. The second auxiliary layer may include one of N,N′-diphenyl-N,N′-bis(9-phenyl-9H-carbazol-3-yl)biphenyl-4,4′-diamine, N(diphenyl-4-yl)9,9-dimethyl-N-(4(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluorene-2-amine, 2-(4-(9,10-di(naphthalene-2-yl)anthracene-2-yl)phenyl)-1-phenyl-1H-benzo-[D]imidazole, m-MTDATA [4,4,4-tris(3-methylphenylphenylamino)triphenylamine], α-NPD (N,N′-bis(1-naphthyl)-N,N′-diphenyl[1,1′-biphenyl]-4,4′-diamine) and TPD [4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl]. The intermediate layer may include a first intermediate layer interposed between the organic emitting layer and the first and second electrodes and including at least one of a hole injection layer and a hole transport layer; and a second intermediate layer interposed between the organic light emitting layer and the third electrode, the second intermediate layer including at least one of an electron injection layer and an electron transport layer, wherein the first intermediate layer is thicker than the second intermediate layer. 
     According to another aspect of the present invention, there is provided a method of manufacturing an organic light-emitting display device that includes defining a plurality of pixels, each of the pixels including a first area in which light is emitted from the display device in a first direction and not in a second direction that is opposite to the first direction, a second area in which light is emitted from the display device in the second direction and not in the first direction and a third area that is transparent to external light, forming a plurality of first electrodes within the first area of each of the plurality of pixels, forming a plurality of second electrodes within the second area of each of the plurality of pixels, forming an intermediate layer on the plurality of first electrodes and on the plurality of second electrodes, the intermediate layer including an organic emitting layer, forming a third electrode on the intermediate layer within both the first area and the second area by depositing a metal for forming the third electrode, forming a first auxiliary layer on the third electrode within the first area, forming a second auxiliary layer on the third electrode within the second area and forming a fourth electrode within the first area via a vacuum deposition technique by applying a vapor that includes a metal for forming the fourth electrode to a top surface of the first auxiliary layer within the first area and a top surface of the second auxiliary layer within the second area of each pixel. 
     In the forming of a fourth electrode, the vapor that includes the metal for forming the fourth electrode may be applied to the first area, the second area and the third area simultaneously, the fourth electrode may be absent from and does not form within the second area or the third area. In the forming of a fourth electrode, the metal for forming the fourth electrode may be applied to the first area, the second area and the third area simultaneously, wherein a portion of the fourth electrode is formed within the second area and the third area, and a thickness of the portion of the fourth electrode formed within the second area and the third area may be less than a thickness of a portion of the fourth electrode formed within the first area. In the forming of a fourth electrode, the portion of the fourth electrode formed within the second area and the third area may be formed on the second auxiliary layer. The first auxiliary layer may be absent from the second area and the third area. The second auxiliary layer may be absent from the first area and the third area. A portion of the second auxiliary layer may be formed within the first area, and the first auxiliary layer may be formed on the portion of the second auxiliary layer formed within the first area. A portion of the first auxiliary layer may be formed within the second area and the third area, and the second auxiliary layer may be formed on the portion of the first auxiliary layer formed within the second area and the third area. A thickness of the fourth electrode may be greater than a thickness of the third electrode. An adhesive force of the metal for forming the fourth electrode with respect to the first auxiliary layer may be greater than an adhesive force of the metal for forming the fourth electrode with respect to the second auxiliary layer. The first auxiliary layer may include one of tris(8-hydroxy-quinolinato)aluminum (Alq3), di-tungsten tetra(hexahydropyrimidopyrimidine)), fullerene, lithium fluoride (LiF), ADN [9,10-di(2-naphthyl)anthracene] and Liq: 8-hydroxyquinolinolato-lithium. The second auxiliary layer may include one of N,N′-diphenyl-N,N′-bis(9-phenyl-9H-carbazol-3-yl)biphenyl-4,4′-diamine, N(diphenyl-4-yl)9,9-dimethyl-N-(4(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluorene-2-amine, 2-(4-(9,10-di(naphthalene-2-yl)anthracene-2-yl)phenyl)-1-phenyl-1H-benzo-[D]imidazole, m-MTDATA[4,4,4-tris(3-methylphenylphenylamino)triphenylamine], α-NPD (N,N′-bis(1-naphthyl)-N,N′-diphenyl[1,1′-biphenyl]-4,4′-diamine), and TPD [4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl]. The forming of the intermediate layer may include forming a first intermediate layer on the first and second electrodes and including at least one of a hole injection layer and a hole transport layer, forming the organic light emitting layer on the first intermediate layer and forming a second intermediate layer on the organic light emitting layer, the second intermediate layer including at least one of an electron injection layer and an electron transport layer, wherein the first intermediate layer is thicker than the second intermediate layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is a schematic cross-sectional view illustrating an organic light-emitting display device according to an embodiment of the present invention; 
         FIG. 2  is a schematic cross-sectional view illustrating an organic light-emitting display device according to another embodiment of the present invention; 
         FIG. 3  is a plan view illustrating a pixel of an organic light-emitting unit illustrated in  FIGS. 1 and 2  according to an embodiment of the present invention; 
         FIG. 4  is a cross-sectional view illustrating the pixel cut along line I-I of  FIG. 3  according to an embodiment of the present invention; 
         FIG. 5  is a circuit diagram illustrating a pixel circuit unit according to an embodiment of the present invention; 
         FIG. 6  is a cross-sectional view to specifically explain organic light-emitting devices of  FIG. 4 ; 
         FIG. 7  is a cross-sectional view of the pixel of  FIG. 3 , cut along line I-I, according to an embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of the pixel of  FIG. 3 , cut along line I-I, according to another embodiment of the present invention; 
         FIG. 9  is a cross-sectional view to specifically explain organic light-emitting devices of  FIG. 8 ; 
         FIG. 10  is a cross-sectional view of the pixel of  FIG. 3 , cut along line I-I, according to another embodiment of the present invention; 
         FIG. 11  is a cross-sectional view of the pixel of  FIG. 3 , cut along line I-I, according to another embodiment of the present invention; 
         FIG. 12  is a cross-sectional view to specifically explain organic light-emitting devices of  FIG. 11 ; 
         FIG. 13  is a cross-sectional view of the pixel of  FIG. 3 , cut along line I-I, according to another embodiment of the present invention; 
         FIG. 14  is a plan view illustrating a pixel of an organic light-emitting unit of  FIGS. 1 and 2 , according to an embodiment of the present invention; 
         FIG. 15  is a cross-sectional view illustrating the pixel cut along line II-II of  FIG. 14 , according to an embodiment of the present invention; 
         FIG. 16  is a cross-sectional view illustrating the pixel cut along line II-II of  FIG. 14 , according to another embodiment of the present invention; and 
         FIG. 17  is a cross-sectional view illustrating the pixel cut along line II-II of  FIG. 14 , according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. 
     It will be understood that although the terms “first”, “second”, etc. may be used herein to describe various components, these components should not be limited by these terms. These components are only used to distinguish one component from another. 
     As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     It will be further understood that the terms “comprises” and/or “comprising” used herein specify the presence of stated features or components, but do not preclude the presence or addition of one or more other features or components. 
     It will be understood that when a layer, region, or component is referred to as being “formed on,” another layer, region, or component, it can be directly or indirectly formed on the other layer, region, or component. That is, for example, intervening layers, regions, or components may be present. 
     Sizes of elements in the drawings may be exaggerated for convenience of explanation. In other words, since sizes and thicknesses of components in the drawings are arbitrarily illustrated for convenience of explanation, the following embodiments are not limited thereto. 
     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. 
     Turning now to  FIG. 1 ,  FIG. 1  is a schematic cross-sectional view illustrating an organic light-emitting display device according to an embodiment of the present invention. Referring to  FIG. 1 , the organic light-emitting display device includes a display unit  2  formed on a substrate  1 . 
     The display unit  2  may include an organic light-emitting unit  21  formed on the substrate  1  and an encapsulation substrate  23  encapsulating the organic light-emitting unit  21 . 
     The encapsulation substrate  23  prevents penetration of an external air or moisture into the organic light-emitting unit  21 . The encapsulation substrate  23  is made out of a transparent member so that an image formed by using the organic light-emitting unit  21  may be transmitted through the encapsulation substrate  23 . 
     Edges of the substrate  1  and the encapsulation substrate  23  are coupled to each other by using an encapsulation member  24  so that space  25  between the substrate  1  and the encapsulation substrate  23  is encapsulated. The space  25  may include a moisture absorbing material, a filling material or the like. 
       FIG. 2  is a schematic cross-sectional view illustrating an organic light-emitting display device according to another embodiment of the present invention. As illustrated in  FIG. 2 , instead of the encapsulation substrate  23 , a thin film encapsulation layer  26  may be formed on the organic light-emitting unit  21  to protect the organic light-emitting unit  21  from penetration of the external air and moisture. The thin film encapsulation layer  26  may be made out of a plurality of inorganic layers or a combination of an inorganic layer and an organic layer. 
     The organic layer of the thin film encapsulation layer  26  may be made out of a polymer, and in detail, the organic layer may be a single layer or a stacked layer made out of one of polyethylene terephthalate, polyimide, polycarbonate, epoxy, polyethylene, and polyacrylate. For example, the organic layer may be made out of polyacrylate, and in detail, the organic layer may include a polymerized monomer composition including a diacrylate-based monomer and triacrylate-based monomer. Also, a photo-initiator such as trimethyl benzoyl diphenyl phosphine oxide (TPO) that is well-known in the art may be further included in the monomer composition, but the embodiments of the present invention are not limited thereto. 
     The inorganic layer of the thin film encapsulation layer  26  may be a single layer or a stacked layer including a metal oxide or a metal nitride. In detail, the inorganic layer may include one of SiN x , Al 2 O 3 , SiO 2 , and TiO 2 . An exposed uppermost layer of the thin film encapsulation layer  26  may be made out of an inorganic layer in order to prevent moisture penetration with respect to the organic light-emitting unit  21 . 
     The thin film encapsulation layer  26  may include at least one sandwich structure in which at least one organic layer is inserted between at least two inorganic layers. Alternatively, the thin film encapsulation layer  26  may include at least one sandwich structure in which at least one inorganic layer is inserted between at least two organic layers. Alternatively, the thin film encapsulation layer  26  may include a sandwich structure in which at least one organic layer is inserted between at least two inorganic layers, or a sandwich structure in which at least one inorganic layer is inserted between at least two organic layers. 
     The thin film encapsulation layer  26  may sequentially include a first inorganic layer, a first organic layer, and a second inorganic layer sequentially stacked on a top portion of the organic light-emitting unit  21 . Alternatively, the thin film encapsulation layer  26  may sequentially include a first inorganic layer, a first organic layer, a second inorganic layer, a second organic layer, and a third inorganic layer stacked on a top portion of the organic light-emitting unit  21 . 
     Alternatively, the thin film encapsulation layer  26  may sequentially include a first inorganic layer, a first organic layer, a second inorganic layer, a second organic layer, a third inorganic layer, a third organic layer, and a fourth inorganic layer stacked on a top portion of the organic light-emitting unit  21 . 
     A halogenated metal layer including LiF may be further included between the organic light-emitting unit  21  and the first inorganic layer. The halogenated metal layer may prevent damage of the organic light-emitting unit  21  when forming the first inorganic layer by using a sputtering method or a plasma deposition method. 
     The first organic layer may have a smaller surface area than the second inorganic layer, and the second organic layer may have a smaller surface area than the third inorganic layer. 
     Alternatively, the first organic layer may be completely covered by the second inorganic layer, and the second organic layer may be completely covered by the third inorganic layer. 
     The organic light-emitting unit  21  of  FIGS. 1 and 2  may include a plurality of pixels.  FIG. 3  is a plan view illustrating a pixel P of the organic light-emitting unit  21  illustrated in  FIGS. 1 and 2  according to embodiments of the present invention. 
     The pixel P may include a first area  31  and a second area  32  that are arranged adjacent to each other. The first area  31  may be a bottom emission area, and the second area  32  may be a top emission area. 
     The pixel P illustrated in  FIG. 3  may be a single sub-pixel in which the first area  31  and the second area  32  emit single-colored light, however the pixel P is not limited thereto, and may also be a single sub-pixel where the first area  31  and the second area  32  emit light of different colors. Pixel P of  FIG. 3  is used to describe the different embodiments of  FIGS. 4 to 13  to be described later. Hereinafter, the case where the pixel P is a single sub-pixel in which the first area  31  and the second area  32  emit single-colored light will be described. 
     The pixel P may be a sub-pixel that emits light of red, green, or blue color. In addition to the pixel P illustrated in  FIG. 3 , the organic light-emitting unit  21  of  FIGS. 1 and 2  further include a plurality of sub-pixels that emit light of another color from among red, green, and blue colors. 
     Alternatively, the pixel P may be a sub-pixel that emits red, green, or blue light. In addition to the pixel P illustrated in  FIG. 3 , the organic light-emitting unit  21  of  FIGS. 1 and 2  further includes a plurality of sub-pixels that emit light of another color from among red, green, and blue colors. 
     Alternatively, sub-pixels that emit light of the red, green, and blue colors and/or white light may form a single pixel that emits white light as the colors of light of the sub-pixels are mixed. In this case, a color converting layer that converts white light of each pixel to a predetermined color or a color filter may be applied. 
     The red, green, blue, and/or white colors are exemplary, and the embodiments of the present invention are not limited thereto. In other words, as long as white light is emitted, combination of various colors besides the combination of the red, green, blue, and/or white light may also be used. 
       FIG. 4  is a cross-sectional view of a display unit  104  which is a cross-section of a variation of pixel P of  FIG. 3  cut along a line I-I of  FIG. 3  according to an embodiment of the present invention. Referring to  FIG. 4 , the first area  31  emits a first image in a first direction toward the substrate  1 , and the second area  32  emits a second image in a second direction which is opposite the first direction. Preferably, the first area  31  emits light only in the first direction and not the second direction, while the second area  32  emits light only in the second direction and not the first direction. To this end, organic light-emitting devices are arranged in the first area  31  and the second area  32 . The organic light-emitting devices are electrically connected to the first area  31  and the second area  32 . A first pixel circuit unit of the first area  31  is not arranged on an emission path by being arranged within the second area  32 , thereby preventing a decrease in a light-emitting efficiency and luminance of the first image. As a second image is emitted from the second area  32  in the opposite direction from the substrate  1 , the first pixel circuit unit that is electrically connected to the organic light-emitting device of the first area  31  and the second pixel circuit unit that is electrically connected to the organic light-emitting device of the second area  32  may both be arranged in the second area  32 . The first pixel circuit unit and the second pixel circuit unit may be each an independent pixel circuit unit, and accordingly, the first image and the second image may not be identical images but different images. 
     However, the embodiments of the present invention are not limited thereto; a single pixel circuit unit that is electrically connected to each of the organic light-emitting device of the first area and the organic light-emitting device of the second area  32  may also be included. The pixel circuit unit may be located in the second area  32  to prevent a decrease in a light-emitting efficiency and luminance of the first image. 
       FIG. 5  is a circuit diagram illustrating a pixel circuit unit PC, which is a single pixel circuit unit, according to an embodiment of the present invention. Referring to  FIG. 5 , a scan line S, a data line D, and a Vdd line V, which is a driving power supply, are electrically connected to the pixel circuit unit PC. Although not shown in  FIG. 5 , according to a structure of the pixel circuit unit PC, other various conductive lines may be further included in addition to the scan line S, the data line D, and the Vdd line V. 
     The pixel circuit unit PC includes a switching thin film transistor T 1  that is connected to the scan line S and the data line D, a driving thin film transistor T 2  that is connected to the switching thin film transistor T 1  and the Vdd line V, and a capacitor Cst that is connected to the switching thin film transistor T 1  and the driving thin film transistor T 2 . 
     A gate electrode of the switching thin film transistor T 1  is connected to the scan line S to receive a scan signal, and a first electrode (i.e. one of the source and drain electrodes) is connected to the data line D, a second electrode (i.e. another of the source and drain electrodes) is connected to a capacitor Cst and a gate electrode of the driving thin film transistor T 2 . 
     A first electrode of the driving thin film transistor T 2  is connected to the Vdd line V and the capacitor Cst, and a second electrode of the driving thin film transistor T 2  is connected to a first electrode of a first emission control thin film transistor T 3  and a first electrode of a second emission control thin film transistor T 4 . 
     A second electrode of the first emission control thin film transistor T 3  may be electrically connected to a first organic light-emitting device E 1  located in the first area  31 , and a second electrode of the second emission control thin film transistor T 4  may be electrically connected to a second organic light-emitting device E 2  located in the second area  32 . Gate electrodes of the first emission control thin film transistor T 3  and the second emission control thin film transistor T 4  are electrically connected to additional emission signal lines. 
     While the switching thin film transistor T 1 , the driving thin film transistor T 2 , and the first and second emission control thin film transistors T 3  and T 4  of  FIG. 5  are all P-type transistors, they are not limited thereto, and at least one of the thin film transistors may be an N-type transistor. Also, the number of thin film transistors and capacitors is not limited to those in the illustrated embodiment. Thus, at least two thin film transistors and at least one capacitor may be further included according to the pixel circuit unit PC. 
     According to the structure of the pixel circuit unit PC as described above, image information input through the data line D may be used to form an image by using the first organic light-emitting device E 1  when the first emission control thin film transistor T 3  is opened. Also, the image information input may be used to form an image by using the second organic light-emitting device E 2  when the second emission control thin film transistor T 4  is opened. Thus, the first organic light-emitting device E 1  and the second organic light-emitting device E 2  may form different images. Thus, dual emission may be achieved through time division driving so that an image on a top emission surface and an image on a bottom emission surface are not limited to reversed mirror images of each other. Nevertheless, when the same switching signal is applied to the first emitting thin film transistor T 3  and the second emitting thin film transistor T 4  in a state where the same data signal is applied to the pixel circuit unit PC, a reversed mirror image may be displayed on top and bottom surfaces. As described above, the pixel circuit unit PC may allow various screen configurations while the basic structure of the pixel circuit unit PC is shared by the first organic light-emitting device E 1  and the second organic light-emitting device E 2 . 
     Referring to  FIG. 4  again, a first thin film transistor TR 1  and a second thin film transistor TR 2  are located on the substrate  1  and are respectively electrically connected to a first electrode  221  included in the first area  31  and a second electrode  222  included in the second area  32 . The first thin film transistor TR 1  and the second thin film transistor TR 2  may be driving thin film transistors of the first pixel circuit unit and the second pixel circuit unit described above. Alternatively, the first thin film transistor TR 1  and the second thin film transistor TR 2  may be respectively the first emission control thin film transistor T 3  and the second emission control thin film transistor T 4  illustrated in  FIG. 5 . 
     In detail, as illustrated in  FIG. 4 , a buffer layer  211  is formed on the substrate  1 , semiconductor active layers  2121  and  2122  and a pixel circuit unit including the first and second thin film transistors T 1  and T 2  are formed on the buffer layer  211 . 
     The buffer layer  211  is made out of a transparent insulating material and prevents penetration of impurity elements into the semiconductor active layers  2121  and  2122 . Also, the buffer layer  211  planarizes a surface of the substrate  1 . Thus, the buffer layer  211  may be made out of various materials that are capable of performing these functions. For example, the buffer layer  211  may be made out of an inorganic material such as 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 such as polyimide, polyester, or an acryl; or a stack structure including the inorganic and organic materials. The buffer layer  211  is not an essential element and may be omitted according to necessity. 
     The semiconductor active layers  2121  and  2122  may be made out of polycrystalline silicon, but are not limited thereto, and may also be made out of an oxide semiconductor. For example, the semiconductor active layers  2121  and  2122  may be a G-I—Z—O layer [(In 2 O 3 ) a (Ga 2 O 3 ) b (ZnO) c  layer](where a, b, and c are real numbers that respectively satisfy the conditions of a≧0, b≧0, and c&gt;0). 
     A gate insulating layer  213  is formed on the buffer layer  211  to cover the semiconductor active layers  2121  and  2122 , and gate electrodes  2141  and  2142  are formed on the gate insulating layer  213 . 
     An interlayer insulating layer  215  is formed on the gate insulating layer  213  to cover the gate electrodes  2141  and  2142 , and source electrodes  2161  and  2162  and drain electrodes  2171  and  2172  are formed on the interlayer insulating layer  215  so that the source electrodes  2161  and  2162  and the drain electrodes  2171  and  2172  respectively contact the semiconductor active layers  2121  and  2122  through contact holes. 
     Structures of the first and second thin film transistors TR 1  and TR 2  as described above are not limited thereto, and various other structures of thin film transistors are also available. 
     A first insulating layer  218  is formed to cover the first and second thin film transistors TR 1  and TR 2 . The first insulating layer  218  may be a single insulating layer or a plurality of insulating layers whose top surface is planarized. The first insulating layer  218  may be made out of an inorganic material and/or an organic material. 
     As illustrated in  FIG. 4 , the first electrode  221  of the first organic light-emitting device that is electrically connected to the first thin film transistor TR 1  and the second electrode  222  of the second organic light-emitting device that is electrically connected to the second thin film transistor TR 2  are formed on the first insulating layer  218 . The first electrode  221  and the second electrode  222  are formed as an island. 
     A second insulating layer  219  is formed on the first insulating layer  218  to cover edges of the first electrode  221  and the second electrode  222 . The second insulating layer  219  may be made out of an organic material such as acryl or polyimide. 
     An intermediate layer  220  including an organic emitting layer is formed on the first electrode  221  and the second electrode  222 . The intermediate layer  220  may be made out of a low-molecular or polymer organic layer. A third electrode  223  is formed to cover the intermediate layer  220 , thereby completing the organic light-emitting devices. 
       FIG. 6  is a cross-sectional view to specifically explain organic light-emitting devices of  FIG. 4 . As illustrated in  FIG. 6 , the intermediate layer  220  may include a first intermediate layer  2201 , a second intermediate layer  2202 , and an organic emitting layer  2203  interposed between the first and second intermediate layers  2201  and  2202 . The first intermediate layer  2201  is interposed between the organic emitting layer  2203  and the first and second electrodes  221  and  222 , and may include a hole injection layer (HIL) and/or a hole transport layer (HTL). The second intermediate layer  2202  is interposed between the organic emitting layer  2203  and a third electrode  223 , and may include an electron transport layer (ETL) and/or an electron injection layer (EIL). 
     The organic emitting layer  2203  may be formed for each of red, green, and blue sub-pixels, and the first and second intermediate layers  2201  and  2202  are common layers for the respective sub-pixels. Referring to  FIG. 4 , the first area  31  and the second area  32  are included in a pixel P that forms a sub-pixel, and thus, a single-color organic emitting layer  2203  may be deposited in the first area  31  and the second area  32 , however the embodiments of the present invention are not limited thereto, and the organic emitting layer  2203  may be in different colors in the first area  31  and the second area  32 . 
     The HIL may include a phthalocyanine compound such as copper phthalocyanine or a Starburst type amine such as TCTA, m-MTDATA, or m-MTDAPB. The HTL may include N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1-biphenyl]-4,4′-diamine (TPD), or N,N′-di(naphthalene-1-yl)-N,N′-diphenyl benzidine (α-NPD). 
     The ETL may include tris(8-hydroxy-quinolinato)aluminum (Alq3). The EIL may include LiF, NaCl, CsF, Li 2 O, BaO, or Liq. 
     The organic emitting layer  2203  may include a host material and a dopant material. The host material may include Alq3, 9,10-di(naphth-2-yl)anthracene (ADN), 2-Tert-butyl-9,10-di(naphth-2-yl)anthracene (TBADN), 4,4′-bis(2,2-diphenyl-ethene-1-yl)biphenyl (DPVBi), or 4,4′-bis(2,2-di(4-methylphenyl)-ethene-1-yl)biphenyl (p-DMDPVBi). The dopant material may include DPAVBi (4,4′-bis[4-(di-p-tolylamino) styril]biphenyl), ADN (9,10-di(naph-2-tyl)anthracene), or TBADN (2-tert-butyl-9,10-di(naphth-2-yl)anthracene). 
     The first electrode  221  and the second electrode  222  may function as anode electrodes, and the third electrode may function as a cathode electrode, however the polarities of the first and second electrode  221  and  222  and the third electrode  223  may instead be exchanged. 
     When the first electrode  221  and the second electrode  222  function as anode electrodes, the first electrode  221  and the second electrode  222  may include ITO, IZO, ZnO, or In 2 O 3 , which have high work functions. The second electrode  222  included in the second area  32  in which an image is formed in a direction away from the substrate  1  may further include a reflective layer (not shown) that includes at least one of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Yb, Co, Sm, and Ca. 
     When the third electrode  223  functions as a cathode electrode, the third electrode  223  may be made out of a metal such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Yb, Co, Sm or Ca. In order that a second image may be easily formed, light from an emitting layer may have to be transmitted through the third electrode  223 . To this end, the third electrode  223  may be a thin film made out of Mg and/or Mg alloy. The third electrode  223  may also be made out of a thin film made out of Ag and/or Ag alloy which has a relatively high light transmissivity. The third electrode  223  may also be formed by co-depositing or stacking Mg and/or Mg alloy and Ag and/or Ag alloy. 
     Unlike the first electrode  221  and the second electrode  222 , the third electrode  223  is formed as a common electrode. Thus, a common voltage is applied to all pixels. Also, the third electrode  223  may be formed by commonly depositing the metal using an open mask without patterning the third electrode  223  for each pixel. Accordingly, the third electrode  223  may be located both in the first area  31  and the second area  32 . 
     On the third electrode  223 , a first auxiliary layer  231  is formed in the first area  31 , and a second auxiliary layer  232  is formed in the second area  32 . According to the embodiment illustrated in  FIG. 4 , the first auxiliary layer  231  may be patterned to be formed not in the second area  32  but only in the first area  31 , and the second auxiliary layer  232  may be patterned to be formed in the second area  32  but not in the first area  31 . 
     The first auxiliary layer  231  may be made out of a metal that is used to produce the fourth electrode  224 , particularly, of a material that Mg and/or Mg alloy easily bonds thereto. Likewise, the second auxiliary layer  232  may be made out of a metal that is used to produce the fourth electrode  224 , particularly, of a material that Mg and/or Mg alloy easily bonds thereto. 
     For example, the first auxiliary layer  231  may be made out of a material including [9,10-di(2-naphthyl)anthracene], or Liq: 8-hydroxyquinolinolato-lithium, and the second auxiliary layer  232  may be made out of a material including N,N′-diphenyl-N,N′-bis(9-phenyl-9H-carbozole-3-yl)biphenyl-4,4′-diamine, N(diphenyl-4-yl)9,9-dimethyl-N-(4(9-phenyl-9H-carbazole-3-yl)phenyl)-9H-fluorene-2-amine, 2-(4-(9,10-di(naphthalene-2-yl)anthracene-2-yl)phenyl)-1-phenyl-1H-benzo-[D]imidazole, m-MTDATA [4,4,4-tris(3-methylphenylphenylamino)triphenylamine], α-NPD (N,N′-bis(1-naphthyl)-N,N′-diphenyl[1,1′-biphenyl]-4,4′-diamine), or TPD [4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl]. 
     After forming the first auxiliary layer  231  and the second auxiliary layer  232  on the third electrode  223 , the fourth electrode  224  is formed. The fourth electrode  224  may be formed by attempting to commonly deposit, using for example a vapor or vacuum deposition technique, a metal for forming the fourth electrode over all pixels that include the first area  31  and the second area  32  by using an open mask. 
     When a metal for forming the fourth electrode  224  is attempted to be commonly deposited over all pixels by using an open mask, the metal for forming the fourth electrode  224  selectively deposits (i.e. is easily formed) on the first auxiliary layer  231 , but does not form or accumulate on the second auxiliary layer  232 . This is because an adhesive force of the fourth electrode  224  with respect to the first auxiliary layer  231  is greater than an adhesive force of the fourth electrode  224  with respect to the second auxiliary layer  232 . 
     Accordingly, the fourth electrode  224  may be automatically patterned such that it is located within the first area  31 , but not within the second area  32 . Thus, without using an additional patterning mask, the fourth electrode  224  may be easily patterned by the above selective deposition technique. 
     The metal for forming the fourth electrode may be Mg and/or Mg alloy that easily forms (i.e. selectively deposits) on the first auxiliary layer  231  but not on the second auxiliary layer  232 . However, the metal for forming the fourth electrode is not limited thereto, and any metal that has a greater adhesive force with respect to the first auxiliary layer  231  than with respect to the second auxiliary force  232  may be selected from the group consisting of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Yb, Co, Sm, and Ca to be used as a metal for forming the fourth electrode. 
     While not shown in the drawings, the fourth electrode  224  may be formed to contact the third electrode  223  in an area outside the first area  31  and the second area  32 . The first auxiliary layer  231  and the second auxiliary layer  232  may not be present in an area where the fourth electrode  224  contacts the third electrode  223 . 
     As described above, the third electrode  223  is made out of a thin film and functions as a common electrode through which a common voltage is applied to all pixels, and thus, if surface resistance increases, a voltage drop may occur. As the fourth electrode  224  contacts the third electrode  223 , a voltage drop of the third electrode  223  may be reduced. To this end, the fourth electrode  224  may be thicker than the third electrode  223 . 
     The fourth electrode  224  is formed in the first area  31 , and when the organic light-emitting device of the first area  31  emits a first image, the fourth electrode  224  may function as a reflection plate, and thus, image quality of the first image may be further improved, accordingly. 
     The first intermediate layer  2201  may be thicker than the second intermediate layer  2202 . In this case, as a sufficient distance between the organic emitting layer  2203  and the second electrode  222  may be provided in the second area  32  which is a top emission area, exciton quenching may be prevented, thereby also increasing light-emitting efficiency. 
     In the first area  31  which forms a bottom emission type organic light-emitting device, the second intermediate layer  2202  may be thinner than the first intermediate layer  2201 , and in this case, a distance between the organic emitting layer  2203  from which light is emitted and the fourth electrode  224  which is a reflection plate is relatively short, and thus, exciton quenching may occur, which may decrease light-emitting efficiency. According to the current embodiment of the present invention, as illustrated in  FIG. 6 , as the first auxiliary layer  231  is interposed between the organic emitting layer  2203  and the fourth electrode  224  in the first area  31 , a distance d 1  between the organic emitting layer  2203  and the fourth electrode  224  may be increased by a thickness of the first auxiliary layer  231  in the first area  31 , and an influence of exciton quenching described above may be reduced, thereby increasing light-emitting efficiency. 
       FIG. 7  is a cross-sectional view of a display unit  107 , which is a cross-section of a variation of pixel P of  FIG. 3 , cut along a line I-I of  FIG. 3  according to another embodiment of the present invention. As described above, even a metal for forming the fourth electrode  224 , in detail, Mg and/or Mg alloy, is not easily bonded on the second auxiliary layer  232 , however in the embodiment of  FIG. 7 , a relatively small amount of metal for forming the fourth electrode  224  may nevertheless be deposited on the second auxiliary layer  232 . 
     Thus, while the second auxiliary layer  232  is formed in the second area  32 , when a metal for forming the fourth electrode  224  is applied to the first area  31  and the second area  32 , the fourth electrode  224  may be formed both in the first area  31  and the second area  32  as illustrated in  FIG. 7 . 
     In  FIG. 7  however, although the metal for forming the fourth electrode  224  is partially deposited on the second auxiliary layer  232 , an amount of the metal is small, and thus, a thickness t 2  of a portion  224   b  of the fourth electrode  224  that forms within the second area  32  is much less than a thickness t 1  of a portion  224   a  of the fourth electrode  224  that is located in the first area  31 . Thus, the transmissivity of the second image may not remarkably decrease due to the portion  224   b  of the fourth electrode  224  arranged within the second area  32 . 
     Turning now to  FIGS. 8 and 9 ,  FIG. 8  is a cross-sectional view of a display unit  108 , which is a cross-section of a variation of pixel P of  FIG. 3 , cut along a line I-I of  FIG. 3  according to another embodiment of the present invention, and  FIG. 9  is a cross-sectional view to specifically explain organic light-emitting devices of  FIG. 8 . 
     Unlike the embodiments illustrated in  FIGS. 4 and 6 , according to the embodiment of  FIGS. 8 and 9 , the second auxiliary layer  232  is formed in both the first area  31  and the second area  32 , and the first auxiliary layer  231  is formed only in the first area  31 . The first auxiliary layer  231  may be formed on the second auxiliary layer  232  in the first area  31 . 
     In this state, a metal for forming the vapor of the material that constitutes the fourth electrode is applied to both the first area  31  and the second area  32 , and the fourth electrode  224  is selectively formed only on the first auxiliary layer  231  in the first area  31 , but is not formed on the second auxiliary layer  232  of the second area  32 . Accordingly, the fourth electrode  224  may be easily patterned without using an additional patterning mask. 
     Also, as the second auxiliary layer  232  and the first auxiliary layer  231  are interposed between the organic emitting layer  2203  and the fourth electrode  224  in the first area  31 , a distance d 2  between the organic emitting layer  2203  and the fourth electrode  224  in the first area  31  may be increased by thicknesses of the first auxiliary layer  231  and the second auxiliary layer  232 , and the influence of exciton quenching described above may be reduced, thereby increasing light-emitting efficiency. 
       FIG. 10  is a cross-sectional view of a display unit  1010 , which is a cross-section of a variation of pixel P of  FIG. 3 , cut along a line I-I of  FIG. 3  according to another embodiment of the present invention. Unlike the embodiment illustrated in  FIG. 8 , according to the embodiment of  FIG. 10 , the fourth electrode  224  is formed not only in the first area  31 , but also in the second area  32 . 
     Even if the metal for forming the fourth electrode is partially deposited on the auxiliary layer  232 , the amount of such metal is small, and thus a thickness t 2  of a portion  224   b  of the fourth electrode  224  that is located within the second area  32  is far thinner than a thickness t 1  of a portion  224   a  of the fourth electrode  224  that is located in the first area  31 . Thus, the transmissivity of the second image may not remarkably decrease due to the portion  224   b  of the fourth electrode  224  that is located in the second area  32 . 
     Turning now to  FIGS. 11 and 12 ,  FIG. 11  is a cross-sectional view of a display unit  1011 , which is a cross-section of a variation of pixel P of  FIG. 3 , cut along a line I-I of  FIG. 3  according to another embodiment of the present invention, and  FIG. 12  is a cross-sectional view to specifically explain organic light-emitting devices of  FIG. 11 . 
     Unlike the embodiment illustrated in  FIGS. 4 and 6 , according to the embodiment of  FIGS. 11 and 12 , the first auxiliary layer  231  is formed both in the first area  31  and the second area  32 , and the second auxiliary layer  232  is formed on the first auxiliary layer  231  and only in the second area  32 . 
     In this embodiment of  FIGS. 11 and 12 , a metal for forming the fourth electrode  224  is applied to the first area  31  and the second area  32 , and the fourth electrode  224  is selectively deposited only on the first auxiliary layer  231  in the first area  31  and not on the second auxiliary layer  232  of the second area  32 . Accordingly, the fourth electrode  224  may be easily patterned without using an additional patterning mask. 
     Also, as the first auxiliary layer  231  is interposed between the organic emitting layer  2203  and the fourth electrode  224  in the first area  31 , a distance d 3  between the organic emitting layer  2203  and the fourth electrode  224  in the first area  31  may be increased by a thickness of the first auxiliary layer  231 , and the influence of exciton quenching described above may be reduced, thereby increasing light-emitting efficiency. 
       FIG. 13  is a cross-sectional view of a display unit  1013 , which is a cross-section of a variation of pixel P of  FIG. 3 , cut along a line I-I of  FIG. 3  according to another embodiment of the present invention. Unlike the embodiment illustrated in  FIG. 11 , according to the embodiment of  FIG. 13 , the fourth electrode  224  is formed not only in the first area  31  but also in the second area  32 . 
     Even if the metal for forming the fourth electrode  224  is partially deposited on second auxiliary layer  232 , an amount of said metal is small, and thus a thickness t 2  of a portion  224   b  of the fourth electrode  224  that is located within the second area  32  is much smaller than a thickness t 1  of a portion  224   a  of the fourth electrode  224  that is located in the first area  31 . Thus, the transmissivity of the second image may not remarkably decrease due to the portion  224   b  of the fourth electrode  224  that is arranged within the second area  32 . 
       FIG. 14  is a plan view illustrating a pixel P′ of the organic light-emitting unit  21  illustrated in  FIGS. 1 and 2 , according to another embodiment of the present invention. The pixel P′ of  FIG. 14  is used to describe the designs of  FIGS. 15 to 17  to be described later. Pixel P′ of  FIG. 14  includes a first area  31 , a second area  32 , and a third area  33  that are adjacent to one another. The first area  31  may be a bottom emission area, the second area  32  may be a top emission area, and the third area  33  may be an external light transmission area through which external light is transmitted in a thickness direction of an organic light-emitting device. While the first area  31 , the second area  32 , and the third area  33  are sequentially arranged in a vertical direction in  FIG. 14 , the embodiments of the present invention are not limited thereto. For example, the third area  33 , the first area  31 , and the second area  32  may instead be sequentially arranged, or the first area  31 , the third area  33 , and the second area  32  may instead be sequentially arranged. 
     In addition, as illustrated in  FIG. 14 , the third area  33  may be included for each pixel P′, but the embodiments of the present invention are not limited thereto. For example, the third area  33  may be included only in a predetermined number of pixels. Alternatively, the third area  33  may be included for sub-pixels that form a single pixel, for example, for each of red, green, and blue sub-pixels or for each of red, green, blue, and white sub-pixels. 
       FIG. 15  is a cross-sectional view illustrating a display unit  1015 , which is a variation of a cross section of pixel P′ of  FIG. 14  cut along line II-II of  FIG. 14 , according to an embodiment of the present invention. In the embodiment of  FIG. 15 , the first auxiliary layer  231  is formed only in the first area  31 , and the second auxiliary layer  232  is formed only in the second area  32  and the third area  33 . Thus, the fourth electrode  224  may be selectively deposited only within the first area  31  but not within the second area  32  or the third area  33 . 
     Accordingly, a decrease in transmissivity of external light in the third area  33 , through which external light is transmitted, due to the fourth electrode  224 , may be prevented, and a transparent dual emission display including an organic emitting unit having an increased external light transmissivity may be realized. 
       FIG. 16  is a cross-sectional view illustrating the display unit  1016 , which is a variation of a cross section of a variation of pixel P′ of  FIG. 14  cut along line II-II of  FIG. 14 , according to another embodiment of the present invention. Unlike the embodiment illustrated in  FIG. 15 , according to the embodiment of  FIG. 16 , the fourth electrode  224 , which is a thin film, is also formed on the second auxiliary layer  232 . Thus, the fourth electrode  224  is formed in the first area  31 , the second area  32 , and the third area  33 . 
     Even if the metal for forming the fourth electrode is partially deposited on the second auxiliary layer  232 , an amount of the metal is small, and thus, thicknesses t 2  and t 3  of portions  224   b  and  224   c  of the fourth electrode  224  that are located in the second area  32  and the third area  33  respectively are much less than a thickness t 1  of a portion  224   a  of the fourth electrode  224  that is located in the first area  31 . Thus, the transmissivity of the second image may not remarkably decrease due to the portion  224   b  of the fourth electrode  224  that is located within the second area  32 , and also the transmissivity of external light may not remarkably decrease due to the portion  224   c  of the fourth electrode  224  that is located within the third area  33 . 
     A structure of the third area  33  as described above may also be applied to the embodiment of  FIG. 7 ,  8 ,  10 , or  11 . In these scenarios, a stack structure of the first auxiliary layer  231  and/or the second auxiliary layer  232  within the third area  33  may have the same stack structure as that of the first auxiliary layer  231  and/or the second auxiliary layer  232  within the first area  31 . 
       FIG. 17  is a cross-sectional view illustrating a display unit  1017  which is a variation of a cross section of the pixel P′ of  FIG. 14  cut along line II-II of  FIG. 14 , according to another embodiment of the present invention. Unlike the display unit  25  of  FIG. 15 , in the display unit  27  of  FIG. 17 , the second insulating layer  219  further includes a transmission window  241  within the third area  33 . The transmission window  241  is formed by removing a portion of the second insulating layer  219 . As the transmission window  241  is formed within the third area  33 , external light transmissivity within the third area  33  may be increased. While the transmission window  241  is illustrated as being formed only in the second insulating layer  219  of  FIG. 17 , the embodiments of the present invention are not limited thereto, as a transmission window connected to the transmission window  241  may also be further formed in at least one of the first insulating layer  218 , the interlayer insulating layer  215 , the gate insulating layer  213 , and the buffer layer  211 . Also, a transmission window that is connected to the transmission window  241  may be further formed in the third electrode  223 . 
     It is also possible that the transmission window  241  having a structure as illustrated in the display unit  27  of  FIG. 17  may also be applied to the display unit  26  of  FIG. 16 . Also, the transmission window  241  having the structure as illustrated in  FIG. 17  may also be applied in the pixels as illustrated in  FIG. 7 ,  8 ,  10 , or  11  in which the third area  33  is formed. 
     As described above, according to the one or more of the above embodiments of the present invention, a fourth electrode made out of a metal may be formed by patterning the metal without using an additional patterning mask, thereby providing an advantage in the manufacturing process. 
     Also, a distance between an organic emitting layer and a fourth electrode in the bottom emission area may be increased to reduce exciton quenching, thereby increasing light-emitting efficiency. 
     The fourth electrode may not be formed in a third area through which external light is transmitted or the fourth electrode may be formed to have a thickness that is as small as possible, thereby increasing the total transmissivity of a the organic light-emitting display device. 
     Furthermore, wiring resistance of the third electrode may be reduced by the fourth electrode. 
     The organic light-emitting display device according to the embodiments of the present invention may be easily applied to a large display device. 
     According to the principles of the present invention, a dual emission display is realized by having each pixel comprised of a first sub-pixel that displays on the front side of the display only and a second sub-pixel that displays on a rear side of the display only. The pixel can further include a third sub-pixel which is transparent to allow external light to pass there through. 
     In the method of making the display device, the fourth or facing electrode is deposited selectively, by a vacuum deposition technique, on auxiliary layers on the display device. This is achieved by forming a first auxiliary layer in the first sub-pixel and a second auxiliary layer and a second sub-pixel, the first auxiliary layer having a greater bonding force or adhesive force to the material of the facing electrode than the second auxiliary layer. Consequently, on open mask can be used, and no patterning step is required. 
     Numerous embodiments have been disclosed, in which the first auxiliary layer is formed in both the first and second sub-pixels, in which the second auxiliary layer can be formed in the first and second sub-pixels, and in which the facing electrode can be formed in the second sub-pixel. When the facing electrode is formed in the second sub-pixel, as with the third electrode, it is formed to be very thin so that light may pass therethrough. When either of the first or second auxiliary layers are formed in both sub-pixels, the other of the auxiliary layer may be formed on or underneath the common auxiliary layer. By including the auxiliary layers along with intermediate layers in the diode display device, the organic emission layer can be spaced further apart from a reflecting electrode, thereby reducing the quenching of excitons. Consequently, the luminance can be improved while a dual display device can be realized, wherein an image displayed on the front side can be the same or different from the image on the backside. Furthermore, an easy method of manufacturing can be realized whereby a selective deposition of an electrode metal can be performed. 
     It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. 
     While one or more embodiments of the present invention have been described with reference to the figures, 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.