Patent Publication Number: US-2021183986-A1

Title: Transparent display panel and transparent display device including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2019-0166513 filed on Dec. 13, 2019, in the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a transparent display panel in which an area of a transmissive region of a GIP (gate in panel) region is increased or maximized, and a transparent display device including the panel. 
     Description of the Related Art 
     A display device that displays various information using an image includes a liquid crystal display device (LCD), and an organic light emitting diode based display device (OLED). 
     As an image implementation skill is advanced, in recent years, a demand for a transparent display device in which at least a partial region on which information is displayed is transparent to transmits light so that an object or a background behind the display device is visible to a user in front of the device has increased. 
     The transparent display device transmits light in front and rear directions. Thus, the device may display information in the front and rear directions of the display device, such that front and rear users in front and rear of the display device may see objects or backgrounds opposite thereto respectively. 
     For example, the transparent display device implemented as an organic light-emitting display device may include a transparent region that transmits incident light as it is and a light-emitting region that emits light. 
     BRIEF SUMMARY 
     The transparent display device requires various lines that supply data voltage or power voltage, etc. In general, the lines are non-transparent and thick in consideration of electrical resistance. 
     In particular, when the non-transparent and thick lines as described above are disposed in a bezel of the transparent display device, the transparent region decreases due to presence of the non-transparent lines. Thus, it is difficult to slim down the bezel. 
     When a gate driver is placed in the bezel in a form of GIP (gate in panel), a GIP transistor circuit constituting a GIP region and signal lines extending in a vertical direction are arranged in a compact manner as much as possible for slimness of the bezel. 
     When the GIP transistor circuit and the signal lines are arranged as closely as possible, this may be helpful to slim the bezel, but the transmissive region may hardly be secured in a region where the GIP is disposed. 
     In addition, when a non-transparent thick line for applying a VSS voltage is formed in the bezel and covers an upper portion of the GIP region, a transmission area may not be secured in the GIP region. 
     Accordingly, inventors of the present application have invented a transparent display panel in which the GIP region may be used as a transmissive region, and an area of the transmissive region may be increased or maximized in the GIP region, and a transparent display device including the same. 
     One or more embodiments of the present disclosure provides a transparent display panel in which a GIP region may be used as a transmissive region, and a transparent display device including the same. 
     Further, one or more embodiments of the present disclosure provides a transparent display panel in which an area of a transmissive region may be increased or maximized in a GIP region, and a transparent display device including the same. 
     Furthermore, one or more embodiments of the present disclosure provides a transparent display panel in which yellowish phenomenon may be reduced or minimized while improving a transmittance in a GIP region, and a transparent display device including the same. 
     The technical benefits of the present disclosure are not limited to the above-mentioned benefits. Other benefits and advantages of the present disclosure, as not mentioned above, may be understood from the following descriptions, and more clearly understood from the embodiments of the present disclosure. Further, it will be readily appreciated that advantages of the present disclosure may be realized by features and combinations thereof as disclosed. 
     A transparent display panel according to an embodiment of the present disclosure includes a substrate including a display region and a non-display region surrounding the display region; and a GIP (gate in panel) circuit region disposed on substrate and disposed in the non-display region thereof, wherein the GIP circuit region includes: at least one GIP block; at least one GIP input signal line region; at least one GIP output signal line region; and at least one GIP input signal connection line for electrically connecting the GIP input signal line region and the GIP block to each other. 
     In this case, the GIP input signal line region and the GIP output signal line region constitute different layers (e.g., the GIP input signal line region and the GIP output signal line region are arranged at different layers), respectively. 
     The GIP input signal line region may transmit a gate control signal to the GIP block. The GIP output signal line region may transmit the gate control signal from the GIP block to the display region. 
     A layer of the GIP input signal connection line may be different from the layer of the GIP input signal line region and the layer of the GIP output signal line region. 
     Further, a bank layer may not be formed on the GIP circuit region, thereby improving the transmittance of the GIP circuit region, and reducing the yellowish phenomenon. In addition, a spacing between adjacent GIP input signal lines may be larger from a width of one GIP input signal line, such that the GIP input signal lines may not be arranged in a dense manner. 
     According to the present disclosure, the line for VSS voltage application may be disposed in the display region. Thus, it is not necessary to place the non-transparent thick line for VSS voltage application in an upper portion of the GIP circuit region. Thus a transparent bezel in which a GIP region acts as a transmissive region may be implemented. 
     Further, according to the present disclosure, the GIP input signal line region and the GIP output signal line region may constitute different layers so that a spacing between the GIP input signal lines is large. Thus, the transmissive region in the GIP circuit region may be increased or maximized. 
     In particular, there is no need to place the non-transparent and thick lines for VSS voltage application in the bezel region. Thus, the GIP circuit region may further include the region where the lines are not disposed. Thus, a spacing between the GIP input signal lines may be increased or maximized, thereby to increase or maximize the transmissive region. 
     Further, according to the present disclosure, it is not necessary to form the bank layer on the GIP circuit region, thereby to improve the transmittance in the GIP region. Due to the material characteristic of the bank layer, the yellowish phenomenon in which the yellowish color is displayed may be reduced or minimized. 
     Further specific effects of the present disclosure as well as the effects as described above will be described in connection with illustrations of specific details for carrying out the present disclosure. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a block diagram schematically illustrating a system of a transparent display device. 
       FIG. 2  is a plan view for schematically illustrating connection and arrangement relationships of components constituting a transparent display device. 
       FIG. 3  is a schematic cross-sectional view of light-emitting and transmissive regions of a pixel in an organic light-emitting display panel. 
       FIG. 4  shows a connection relationship of line connection pads disposed on a first substrate in a transparent display panel according to an embodiment of the present disclosure. 
       FIG. 5  to  FIG. 9  are plan views showing, based on an interlayer stacking structure, a connection relationship between lines of  FIG. 4  in the transparent display panel according to an embodiment of the present disclosure. 
       FIG. 10  is an enlarged plan view of a A-A′ region in  FIG. 7 . 
       FIG. 11  is an enlarged plan view of a B-B′ region of  FIG. 10 . 
       FIG. 12  is an enlarged plan view of a C-C′ region of  FIG. 10 . 
       FIG. 13  is an enlarged plan view of a D-D′ region of  FIG. 8 . 
       FIG. 14  is an enlarged plan view of a E-E′ region of  FIG. 9 . 
       FIG. 15  is an enlarged cross-sectional view of a F-F′ region in  FIG. 9 . 
       FIG. 16  is an enlarged plan view of a G-G′ region of  FIG. 9 . 
       FIG. 17  is an enlarged cross-sectional view of a H-H′ region of  FIG. 16 . 
       FIG. 18  is an embodiment of a transparent display device used as a head-up-display. 
       FIG. 19A  shows a long-distance diffraction pattern by a single slit. 
       FIG. 19B  is an illustration of a diffraction effect in a single slit. 
       FIG. 20A  to  FIG. 20D  show results of a double slit test for a particle, a wave, light and an electron, respectively. 
       FIG. 21  shows an arrangement of typical quadrangle shaped transmissive regions in a transparent display device. 
       FIG. 22  shows diffraction phenomenon of light generated when light is incident onto a central region of a transparent display device having the transmissive region shape as shown in  FIG. 21 . 
       FIG. 23  to  FIG. 25  show embodiments of the present disclosure in which a transmissive region in a transparent display device has a curved shape. 
       FIG. 26  shows diffraction phenomenon of light generated when light is incident onto a central region of a transparent display device having a circular transmissive region shape as shown in  FIG. 25 . 
       FIG. 27  and  FIG. 28  show embodiments of the present disclosure in which a transmissive region in a transparent display device has a polygonal shape whose all internal angles are obtuse. 
       FIG. 29  shows a configuration in which transmissive regions and light-emitting regions of a transparent display device according to an embodiment of the present disclosure are arranged. 
       FIG. 30A  to  FIG. 30C  show haze value measurements based on transmissive region shape. 
       FIG. 31  shows haze value measurements based on transmissive region shapes and based on different ppi. 
       FIG. 32  shows a configuration in which transmissive regions and light-emitting regions of a transparent display device according to another embodiment of the present disclosure are arranged. 
       FIG. 33  and  FIG. 34  show cross-sections of a I-I′ region and a J-J′ region in  FIG. 29 , respectively. 
       FIG. 35  and  FIG. 36  show a dummy pixel pattern region surrounding the outermost portion of a display region. 
       FIG. 37  specifically shows an arrangement relationship between a line region and a pixel circuit region in a display region according to an embodiment of the present disclosure. 
       FIG. 38  shows a cross-sectional view of  0 - 0 ′ and P-P′ regions in  FIG. 37 . 
       FIG. 39  shows a top view of a GIP circuit region according to an embodiment of the present disclosure, and is related to a Q-Q′ region in  FIG. 10 . 
       FIG. 40  shows a top view of a GIP circuit region according to another embodiment according to the present disclosure. 
       FIG. 41  to  FIG. 43  are cross-sectional views of R-R′, S-S′, and T-T′ regions in  FIG. 40 , respectively. 
    
    
     DETAILED DESCRIPTIONS 
     For simplicity and clarity of illustration, elements in the figures are not necessarily drawn to scale. The same reference numbers in different figures represent the same or similar elements, and as such perform similar functionality. Further, descriptions and details of well-known steps and elements are omitted for simplicity of the description. Furthermore, in the following detailed description of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be understood that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present disclosure. 
     Examples of various embodiments are illustrated and described further below. It will be understood that the description herein is not intended to limit the claims to the specific embodiments described. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the present disclosure. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and “including” when used in this specification, specify the presence of the stated features, integers, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, operations, elements, components, and/or portions thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expression such as “at least one of” when preceding a list of elements may modify the entire list of elements and may not modify the individual elements of the list. 
     It will be understood that, although the terms “first”, “second”, “third”, and so on may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section described below could be termed a second element, component, region, layer or section, without departing from the spirit and scope of the present disclosure. 
     In addition, it will also be understood that when a first element or layer is referred to as being present “on” or “beneath” a second element or layer, the first element may be disposed directly on or beneath the second element or may be disposed indirectly on or beneath the second element with a third element or layer being disposed between the first and second elements or layers. 
     It will be understood that when an element or layer is referred to as being “connected to”, or “coupled to” another element or layer, it may be directly on, connected to, or coupled to the other element or layer, or one or more intervening elements or layers may be present. In addition, it will also be understood that when an element or layer is referred to as being “between” two elements or layers, it may be the only element or layer between the two elements or layers, or one or more intervening elements or layers may also be present. 
     Further, as used herein, when a layer, film, region, plate, or the like is disposed “on” or “on a top” of another layer, film, region, plate, or the like, the former may directly contact the latter or still another layer, film, region, plate, or the like may be disposed between the former and the latter. As used herein, when a layer, film, region, plate, or the like is directly disposed “on” or “on a top” of another layer, film, region, plate, or the like, the former directly contacts the latter and still another layer, film, region, plate, or the like is not disposed between the former and the latter. Further, as used herein, when a layer, film, region, plate, or the like is disposed “below” or “under” another layer, film, region, plate, or the like, the former may directly contact the latter or still another layer, film, region, plate, or the like may be disposed between the former and the latter. As used herein, when a layer, film, region, plate, or the like is directly disposed “below” or “under” another layer, film, region, plate, or the like, the former directly contacts the latter and still another layer, film, region, plate, or the like is not disposed between the former and the latter. 
     Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Hereinafter, a transparent display panel according to some embodiments of the present disclosure and a transparent display device including the same will be exemplified. 
       FIG. 1  is a block diagram for schematically illustrating a transparent display device according to an embodiment of the present disclosure.  FIG. 2  is a plan view for schematically illustrating connection and arrangement relationships of components constituting a transparent display device. 
     However, each of  FIG. 1  and  FIG. 2  is one embodiment according to the present disclosure. Thus, the connection and arrangement relationships of the components of the transparent display device  100  according to the present disclosure are not limited thereto. 
     The transparent display device  100  may include a transparent display panel  110 , a timing controller  140 , a data driver  120 , and a gate driver  130 . 
     The transparent display panel  110  may include a display region DA containing at least one pixel P to display an image, and a non-display region NDA in which an image is not displayed. 
     The non-display region NDA may be disposed to surround the display region DA. 
     In the non-display region NDA, the gate driver  130 , a data drive IC pad DDPA, and various lines may be disposed. The non-display region NDA may correspond to a bezel. 
     The transparent region of the transparent display panel  110  may be contained in both the display region DA and the non-display region NDA. The transparent display panel  110  may include a plurality of pixel regions defined by a plurality of gate lines GL extending in a first direction, and a plurality of data lines DL extending in a second direction orthogonal to the gate lines GL. 
     The pixel regions may be arranged in a matrix form. Each pixel region may include a pixel P composed of at least one sub-pixel SP. 
     The gate driver  130  is directly stacked on the transparent display panel  110  in a form of GIP (Gate In Panel). 
     A plurality of GIP circuit regions may be arranged in the GIP form and may be disposed in left and right portions of the non-display region NDA respectively adjacent to left and right outer peripheral portions of the display region DA while the display region DA is interposed between the left and right portions of the non-display region NDA. 
     The data driver  120  may include at least one source driver integrated circuit  121  (source driver IC) to drive a plurality of data lines DL. 
     For example, a source driving chip corresponding to each source driver integrated circuit  121  may be mounted on a flexible film  123 . One end of the flexible film  123  may be bonded to at least one control printed circuit board  150 , while the other end thereof may be bonded to a data drive IC pad (DDPA) of the transparent display panel  110 . 
     The timing controller  140  may be disposed on the control printed circuit board  150 . Further, a power controller may be further disposed on the control printed circuit board  150 . 
     In addition, a source printed circuit board may be disposed between the flexible film  123  and the control printed circuit board  150  while the source printed circuit board is connected thereto via a connection medium such as a flexible flat cable (FFC) or a flexible printed circuit (FPC). 
     In one example, the transparent display device  100  may be embodied as a liquid crystal display device, an organic light-emitting display device, etc. However, the present disclosure is not limited thereto. Hereinafter, in accordance with an embodiment of the present disclosure, an example in which the transparent display device  100  may be embodied as an organic light-emitting display device will be described with reference to  FIG. 3  and  FIG. 4 . 
     The transparent display panel may include a first substrate  200  and a second substrate  270 . 
     The first substrate  200  may act as a base substrate including a display region DA in which pixels are disposed, and a non-display region NDA. 
     The second substrate  270  may be opposite to the first substrate  200  and may act as an encapsulating substrate. 
     Each of the first substrate  200  and the second substrate  270  may be embodied as a plastic substrate or a glass substrate. 
     The display region DA of the first substrate  200  includes a light-emitting region EA and a transmissive region TA. 
     A plurality of sub-pixels may be arranged in the light-emitting region EA. 
     Each sub-pixel may be a red sub-pixel emitting red light, or may be a green sub-pixel emitting green light, or may be a blue sub-pixel emitting blue light, or may be a sub-pixel emitting light, for example, white light other than the red, green, or blue light. 
     Each sub-pixel may include a light-emitting region EA for emitting light of a corresponding color, and a circuit region electrically connected to the light-emitting region EA to control light-emission from the light-emitting region EA. 
     The light-emitting region of the sub-pixel EA may refer to a region in which light of a corresponding color to each sub-pixel is emitted or may refer to a pixel electrode such as an anode electrode that exists in each sub-pixel, or may mean a region where the pixel electrode is disposed. 
     The light-emitting region EA includes an organic light-emitting element  220  including an anode electrode as a first electrode  221 , an organic light-emitting layer  223 , and a cathode electrode as a second electrode  225 . The organic light-emitting element  220  emits light at a predefined brightness using a voltage supplied to the first electrode  221  and a voltage supplied to the second electrode  225 . 
     In this case, the second electrode  225  as a transparent electrode may extend across both the light-emitting region EA and the transmissive region TA. 
     The circuit region of the sub-pixel means a circuit region including the driving thin-film transistor  210  that supplies a voltage or a current to the pixel electrode of each sub-pixel to control light emission from the light-emitting region EA or may mean a region in which the circuit region is disposed. 
     The driving thin-film transistor  210  includes a gate electrode  214 , a source electrode  217   a , a drain electrode  217   b  and an active layer  212 . 
     When the circuit region receives a gate signal from the gate line GL using the thin-film transistors, the circuit region may supply a predefined voltage to the first electrode  221  of the organic light-emitting element  220  of the light-emitting region EA based on a data voltage of the data line DL. 
     The circuit region may vertically at least partially overlap with the light-emitting region EA, but may be disposed at an opposite side to a side from which light is emitted so as not to interfere with the light emission. 
     An encapsulating layer  250  is formed on the organic light-emitting element  220 , specifically, the second electrode  225  thereof. A color filter  260  corresponding to the organic light-emitting element  220  may be formed on the encapsulating layer  250 . 
     The color filter  260  may have the same color as or a different color from that of a corresponding sub-pixel. 
     The transmissive region TA refers to a region that transmits incident light, and may be a region excluding the circuit region. A transmittance of the transparent display device depends on an area of the transmissive region TA. 
       FIG. 3  shows one embodiment of the present disclosure in which the light-emitting region EA and the transmissive region TA corresponds to one sub-pixel. However, the present disclosure is not limited thereto. The arrangement form of the light-emitting region EA and the transmissive region TA of the transparent display device according to the present disclosure is not limited thereto. 
       FIG. 4  shows a connection relationship of line connection pads disposed on the first substrate  301  in the transparent display panel  300  according to an embodiment of the present disclosure. 
     The first substrate  301  includes a display region DA and a non-display region NDA disposed to surround the display region DA. The non-display region NDA may surround top, bottom, left, and right sides of the display region DA. A vertical or up-down direction of the display region DA refers to a Y-axis direction, while a horizontal or left-right direction of the display region DA refers to a X-axis direction. 
     The display region DA may have a rectangular shape including long sides and short sides. 
     In this case, the long side is relatively longer than the short side. 
     Further, the long side means a side parallel to the X-axis direction as the left and right direction of the display region DA. 
     The short side means a side parallel to the Y-axis direction as the vertical or up-down direction of the display region DA. 
     The gate driver  130  may be disposed in a form of GIP (gate in panel) and on at least one side to the display region DA. 
     In other words, a pair of GIP circuit regions  360  are disposed in portions of the non-display region NDA located on the left and right sides to the display region DA, respectively. 
     For example, the GIP circuit region  360  is disposed along the short side of the display region DA. A first VSS voltage line  321  and a second VSS voltage line  322  may be disposed along the long side of the display region DA. 
     On one portion of the non-display region NDA where the GIP circuit region  360  is disposed, a GIP ESD (electro-static discharge) protection circuit region  369  that operates when static electricity is introduced into the GIP circuit region  360  to reduce or minimize static electricity inflow may be disposed. 
     At least one data drive IC pad  310  may be disposed on one side to the display region DA where the GIP circuit region  360  is not disposed, for example, at a portion of the non-display region NDA above a top long side of the display region DA. 
     The data drive IC pad  310  is connected to various lines necessary for driving the transparent display panel  300  such as the power line and the data line. 
     Between the data drive IC pad  310  and the display region DA, a data line connection pad  311 , a reference voltage line connection pad  340 , a VSS voltage line connection pad  320 , and a VDD voltage line connection pad  330  are disposed to be connected to each other via the data drive IC pad  310  and various lines. 
     Specifically, each of right and left reference voltage line connection pads  340 , each of right and left VDD voltage line connection pads  330 , and each of right and left VSS voltage line connection pads  320  may be disposed adjacent to each of right and left portions of the data drive IC pad  310 . A spacing between each of right and left reference voltage line connection pads  340  and a length direction center of the data drive IC pad  310  is smaller than a spacing between each of right and left VDD voltage line connection pads  330  and the length direction center of the data drive IC pad  310  which is smaller than a spacing between each of right and left VSS voltage line connection pads  320  and the length direction center of the data drive IC pad  310 . 
     That is, the both reference voltage line connection pads  340 , the both VDD voltage line connection pads  330 , and the both VSS voltage line connection pads  320  may be arranged symmetrically to each other around a center of the data line connection pad  311 . In one or more embodiments, the term “symmetrically” used throughout in the specification is used to include the meaning of both symmetrically and substantially symmetrically. 
     The reference voltage line connection pad  340 , the VDD voltage line connection pad  330 , and the VSS voltage line connection pad  320  are arranged to be spaced apart from each other. 
     The VDD voltage line connection pad  330  may act as a high-level voltage power line connection pad that supplies high-level voltage power to a pixel for driving the pixel, while the VSS voltage line connection pad  320  may act as a low-level voltage power line connection pad that applies low-level voltage power to the pixel for driving the pixel. 
     The reference voltage line connection pad  340  may supply a reference voltage Vref to a pixel. 
     A reference voltage line  341  electrically connected to the reference voltage line connection pad  340 , a first VDD voltage line  331  electrically connected to the VDD voltage line connection pad  330 , and a first VSS voltage line  321  electrically connected to the VSS voltage line connection pad  320  may be disposed between the reference voltage line connection pad  340  and the display region DA, between the VDD voltage line connection pad  330  and the display region DA, and between the VSS voltage line connection pad  320  and the display region DA, respectively. 
     In one embodiment of the present disclosure, the VDD voltage line connection pad  330  and the first VDD voltage line  331  are integrally formed with each other, the reference voltage line connection pad  340  and the reference voltage line  341  are formed to be spaced apart from each other and electrically connected to each other via a separate connection electrode, and the VSS voltage line connection pad  320  and the first VSS voltage line  321  are formed to be spaced apart from each other and electrically connected to each other via a separate connection electrode. However, the present disclosure is not limited thereto. 
     The first VDD voltage line  331  may be formed to have a bar shape, and may extend parallel to one side face of the display region DA, specifically, along the long side of the display region DA and may be integrally formed with the VDD voltage line connection pad  330 . In one or more embodiments, a bar shape may include a rectangular bar shape, an elongated bar shape or even a bar shape closer to a square bar shape, or any other suitable shape for being implemented in a display device. 
     Further, the first VDD voltage line  331  may be formed integrally with a plurality of VDD voltage line connection pads  330  corresponding to each data drive IC pad  310  to electrically connect the plurality of VDD voltage line connection pads  330  to each other. 
     The reference voltage line  341  may be disposed between the first VDD voltage line  331  and the display region DA. In one embodiment of the present disclosure, an example in which the reference voltage line may act as the initial voltage line will be described. However, the present disclosure is not limited thereto. Depending on a compensation circuit region, the reference voltage line  341  may act as a separate line from the initial voltage line. 
     Thus, the reference voltage line connection pad  340  may be disposed to be spaced apart from the reference voltage line  341  in the Y direction while a spacing between the former and the display region DA is larger than a spacing between the latter and the display region DA. 
     The reference voltage line  341  may be formed to have a bar shape, and may extend parallel to the first VDD voltage line  331 . 
     In order to apply the reference voltage to the reference voltage line  341 , the reference voltage line connection pad  340  and the reference voltage line  341  may be electrically connected to each other via a second connection electrode  352  as a separate connection electrode. 
     The first VSS voltage line  321  may be disposed between the reference voltage line  341  and the display region DA. 
     Thus, the VSS voltage line connection pad  320  may be disposed to be spaced apart from the first VSS voltage line  321  in the Y direction while a spacing between the VSS voltage line connection pad  320  and the display region DA is larger than a spacing between the first VSS voltage line  321  and the display region DA. 
     The first VSS voltage line  321  may be formed to have a bar shape and may extend in parallel with the first VDD voltage line  331  and the reference voltage line  341 . 
     In order to apply the VSS voltage to the first VSS voltage line  321 , the VSS voltage line connection pad  320  and the first VSS voltage line  321  may be electrically connected to each other via a first connection electrode  351  as a separate connection electrode. 
     Further, a VSS voltage auxiliary line connection pad  326  as a separate portion from the VSS voltage line connection pad  320  may be disposed between the left and right reference voltage line connection pads  340 . 
     Specifically, the VSS voltage auxiliary line connection pad  326  may have a form of an island spaced from and disposed between the left and right reference voltage line connection pads  340  and spaced from and disposed between the data line connection pad  311  and the VDD voltage line. 
     The VSS voltage auxiliary line connection pad  326  may be electrically connected to the first VSS voltage line  321  via the first connection electrode  351 . 
     In this way, when the VSS voltage auxiliary line connection pad  326  is electrically connected to the first VSS voltage line  321  via the first connection electrode  351 , an entire contact area of the first VSS voltage line  321  is enlarged, thereby to keep a resistance distribution of the first VSS voltage line  321  uniform while lowering an overall resistance thereof. 
     An ESD protection circuit region  371  may be disposed between the reference voltage line  341  and the display region DA. A multiplexer (MUX) circuit region  373  may be disposed between the first VSS voltage line  321  and the display region DA. However, the present disclosure is not limited thereto. The positions of ESD protection circuit region  371  and MUX circuit region  373  may vary based on a design scheme of the transparent display panel  300 . Further, in some embodiments, the MUX circuit region  373  may be disposed between the first VSS voltage line  321  and a dummy pixel pattern region DPA that is adjacent to the display region DA (see  FIG. 35 ). 
     The ESD protection circuit region  371  may include a plurality of thin-film transistors constituting an ESD protection circuit. When static electricity is generated from the transparent display panel  300 , the ESD protection circuit region operates to take out static electricity to an outside. 
     The MUX circuit region  373  may be configured to include a plurality of thin-film transistors constituting a MUX circuit. 
     When using the MUX circuit region  373 , one channel of a driver IC output may supply a signal to two or more data lines  313 . This has an advantage of reducing the number of driver ICs as used. 
     Each of the ESD protection circuit region  371  and the MUX circuit region  373  may be formed in a bar shape extending parallel to the reference voltage line  341  and the like. However, the present disclosure is not limited thereto. 
     The first VDD voltage line  331  and the first VSS voltage line  321  may be disposed in an upper portion of the non-display region NDA adjacent to an upper side of the display region DA, while a second VDD voltage line  332  and a second VSS voltage line  322  may be disposed in a lower portion of the non-display region NDA adjacent to a lower side of the display region DA. 
     The second VDD voltage line  332  and the second VSS voltage line  322  may be spaced from each other while a spacing between the second VDD voltage line  332  and the display region DA is smaller than a spacing between the second VSS voltage line  322  and the display region DA. 
     The second VDD voltage line  332  may be formed to have a bar shape, and may extend in parallel along one side face of the display region DA, specifically, along the long side of the display region DA. 
     In order to apply the VDD voltage to the second VDD voltage line  332 , the first VDD voltage line  331  and the second VDD voltage line  332  may be electrically connected to each other via a separate connection electrode as a VDD voltage connection line  333 . 
     Therefore, using the connection structure as described above, the VDD voltage supplied via the VDD voltage line connection pad  330  may be applied to the second VDD voltage line  332  via the first VDD voltage line  331  and the VDD voltage connection line  333 . 
     In this case, at least one VDD voltage connection line  333  is disposed in the display region DA to extend across the display region DA and thus electrically connects the first VDD voltage line  331  and the second VDD voltage line  332  to each other. 
     In one example, the second VSS voltage line  322  may be formed to have a bar shape, and may extend in parallel along one side face of the display region DA, specifically, along the long side of the display region DA. 
     A width WW 2  of the second VSS voltage line  322  may be smaller than a width WW 1  of the first VSS voltage line  321 , such that the second VSS voltage line  322  is thinner than the first VSS voltage line  321 . 
     In order to apply the VSS voltage to the second VSS voltage line  322 , the first VSS voltage line  321  and the second VSS voltage line  322  may be electrically connected to each other via a separate connection electrode as a VSS voltage connection line  323 . 
     Therefore, using the connection structure as described above, the VSS voltage supplied via the VSS voltage line connection pad  320  may be applied to the second VSS voltage line  322  via the first VSS voltage line  321  and the VSS voltage connection line  323 . 
     In this case, at least one VSS voltage connection line  323  may be disposed in the display region DA to extend across the display region DA and thus electrically connects the first VSS voltage line  321  and the second VSS voltage line  322  to each other. 
     As in one embodiment of the present disclosure, the first VSS voltage line  321  and the second VSS voltage line  322  disposed above and below the display region DA may be electrically connected to each other via at least one VSS voltage connection line  323  extending across the display region DA. Thus, following effects may be realized. 
     First, non-transparent VSS voltage lines located at left and right portions of the non-display region on the left and right sides to the display region DA may be omitted. Thus, the transparent region of the bezel may be enlarged, so that the transparent region in the bezel may be increased or maximized. 
     Further, non-transparent VSS voltage lines located at left and right portions of the non-display region on the left and right sides to the display region DA may be omitted. Thus, the VSS voltage line-connection regions required to allow the VSS voltage lines to be placed on bezel portions left and right to the display region DA are not needed. Thus, the bezel may be slim. 
     For example, when the VSS voltage connection line  323  is disposed in each of left and right portions of the non-display region NDA left and right to the display region DA, the VSS voltage line is disposed to surround the display region DA and extends along an outer periphery of the display region DA. In this case, a size of the transparent region of the bezel is reduced because the non-transparent VSS voltage line is formed in the non-display region NDA out of the outer periphery of the display region DA, thereby to disallow reduction of the bezel area. 
     However, in the VSS voltage line arrangement structure according to an embodiment of the present disclosure, the VSS voltage lines are not disposed on the top, bottom, left, and right sides to the display region DA, that is, on four side portions of the bezel. Rather, it may suffice that the VSS voltage lines are disposed only on top and bottom side portions of the bezel up and down to the display region DA. 
     Therefore, according to an embodiment of the present disclosure, a maximum of a transparent region of a bezel where the non-transparent VSS voltage line is not disposed may be secured. When necessary, a size of the bezel may be reduced, so that the bezel may be slimmer. 
     Further, when the VSS voltage line surrounds the outer periphery of the display region DA, the VSS voltage flows around the outer periphery of the display region DA and flows into the display region DA and then is supplied to the pixels in the display region DA. Thus, the VSS voltage line which serves as a current path must be thick in order to function as the current path in a reliable manner in terms of the electrical resistance. 
     However, in one embodiment of the present disclosure, while the VSS voltage connection line  323  passes across the display region DA, the VSS voltage connection line may directly supply the VSS voltage to the pixel. Thus, the second VSS voltage line  322  may not serve as a current path. 
     In this way, when the second VSS voltage line  322  does not serve as the current path, the second VSS voltage line  322  does not need to be formed to be thick in consideration of the electrical resistance and thus be as thin as possible. 
     Therefore, according to an embodiment of the present disclosure, the second VSS voltage line  322  may have a width smaller than that of the first VSS voltage line  321 . Thus, as the width of the second VSS voltage line  322  decreases, a size of a transparent region in a lower bezel portion below the display region DA may be increased. When necessary, the bezel may be made slimmer. 
     A lighting tester  375  may be disposed in the non-display region NDA and be spaced apart from the second VSS voltage line  322  while a spacing between the former and the display region DA is larger than a spacing between the latter and the display region DA. 
     The lighting tester  375  may be formed in a bar shape extending parallel to the second VSS voltage line  322 , and may further extend along both left and right sides of the display region DA, thereby to surround three sides of the display region DA. 
     The lighting tester  375  may supply a lighting test signal to a plurality of data lines  313  before a module process after the transparent display panel  300  is manufactured and may inspect a defect of the transparent display panel  300 . 
     The lighting tester  375  includes a plurality of inspection switching elements connected to the plurality of data lines  313 , respectively. 
     Therefore, the plurality of data lines  313  branched from the data line connection pad  311  extend across the display region DA and then are electrically connected to the lighting tester  375 . 
     A lighting test signal applicator  376  may be formed on a partial region of each of the reference voltage line connection pad  340 , the VDD voltage line connection pad  330 , and the VSS voltage line connection pad  320  to supply the lighting test signal to the lighting tester  375 . 
       FIG. 5  to  FIG. 9  are plan views showing, based on an interlayer stacking structure, a connection relationship between the lines of  FIG. 4  in the transparent display panel  300  according to an embodiment of the present disclosure. 
     As shown in FIG. 5 , the reference voltage line connection pad  340 , the VDD voltage line connection pad  330 , the VSS voltage line connection pad  320 , the VSS voltage auxiliary line connection pad  326 , the reference voltage line  341 , the first VDD voltage line  331 , the second VDD voltage line  332 , the first VSS voltage line  321  and the second VSS voltage line  322  of the transparent display panel  300  according to an embodiment of the present disclosure may constitute the same layer and may be spaced apart from each other. In some embodiments where appropriate, constitute the same layer means that the elements (or components) are formed of the same layer (or in some cases are formed on the same layer). 
     The reference voltage line connection pad  340 , the VDD voltage line connection pad  330 , the VSS voltage line connection pad  320 , the VSS voltage auxiliary line connection pad  326 , the reference voltage line  341 , the first VDD voltage line  331 , the second VDD voltage line  332 , the first VSS voltage line  321 , the second VSS voltage line  322 , the source electrode  217   a , and the drain electrode  217   b  of the driving thin-film transistor  210  of a pixel may be made of the same material and may constitute the same layer. 
     However, as illustrated above, the VDD voltage line connection pad  330  and the first VDD voltage line  331  may be integrally formed with each other without being separated from each other. 
     Thus, the line connection pads and the lines constitute the same layer. Thus, the connection electrodes that electrically connect the line connection pads and the lines to each other should not form a short-circuit with other lines between the line connection pad and the line to be connected to each other, or between the lines. 
     For example, in order to connect the data lines  313  branched from the data line connection pad  311  to the lighting tester  375 , the data line  313  may be composed of a first data line  314  and a second data line  315  which constitute different layers and are electrically connected to each other. 
     In this case, the first data line  314 , the source electrode  217   a , and drain electrode  217   b  of the driving thin-film transistor  210  of the pixel may constitute the same layer and may be made of the same material. The second data line  315 , and the gate electrode  214  of the driving thin-film transistor  210  of the pixel may constitute the same layer and may be made of the same material. 
     The data line  313  applies a data signal to pixels in the display region DA. Thus, the first and second data lines  314  and  315  of the data line  313  branched from the data line connection pad  311  may constitute different layers so as not to form a short-circuit with various line connection pads and lines disposed in a region between the display region DA and the data line connection pad  311 . 
     Thus, the second data line  315  may act as the data line  313  in a region between the display region DA and the data line connection pad  311 . The first data line  314  constituting a different layer from a layer of the second data line  315  may act as the data line  313  in the display region. 
     Then, the second data line  315  may act as the data line  313  in a region between the display region DA and the lighting tester  375 . Then, the first data line  314  as the data line  313  may be connected to the lighting tester  375 . 
     However, the first data line  314  and the second data line  315  may act as the data line  313  in a repeatedly alternate manner such that the data line  313  does not form a short-circuit with the second VDD voltage line  332  and the second VSS voltage line  322  in regions in which the data line  313  overlaps with the second VDD voltage line  332  and the second VSS voltage line  322  in a region between the display region DA and the lighting tester  375 . 
     The data line  313  may change from the first data line  314  to the second data line  315  in a region where the data line  313  does not overlap with the second VDD voltage line  332 , such that the data line  313  does not form a short-circuit with the second VDD voltage line  332  while extending across the second VDD voltage line  332 . In this way, the second data line  315  and the second VDD voltage line  332  do not constitute the same layer, thereby preventing the short circuit therebetween. 
     In the connection, the data line  313  changing from the first data line  314  to the second data line  315  may mean that, as shown in  FIG. 11 , the first data line  314  is connected to the second data line  315  via at least one contact-hole such that electrical connection therebetween is maintained, but the first data line  314  and the second data line  315  constitute different layers and are made of the different materials. This principle may be equally applied to other lines as exemplified below. 
     After the second data line  315  extends across the second VDD voltage line  332 , the second data line may be changed back to the first data line  314  in a region where the data line  313  does not overlap with the second VDD voltage line  332 . 
     That is, the first data line  314  and the second data line  315  may constitute different layers and are electrically connected to each other via at least one second data line contact-hole  315   h.    
     In the same manner, the reference voltage connection line  343  may be composed of a first reference voltage connection line  344  and a second reference voltage connection line  345  which constitute different layers and are electrically connected to each other. 
     In this case, the first reference voltage connection line  344 , the source electrode  217   a  and the drain electrode  217   b  may constitute the same layer and may be made of the same material. The second reference voltage connection line  345  and the gate electrode  214  may constitute the same layer and may be made of the same material. 
     For example, the reference voltage connection line  343  extends to a lower end of the display region DA. The reference voltage connection line  343  may be composed of the first reference voltage connection line  344  and the second reference voltage connection line  345  which constitute different layers and are electrically connected to each other. The reference voltage connection line  343  extends across the display region DA. A distal end of the reference voltage connection line  343  need not contact a separate line. 
     Because the reference voltage connection line  343  applies a reference voltage to pixels in the display region DA, the reference voltage connection line  343  is composed of different reference voltage connection lines constituting different layers such that the reference voltage connection line  343  does not form a short-circuit with various line connection pads and lines in a region between the display region DA and the reference voltage line  341 . 
     Thus, the reference voltage connection line  343  is embodied as the second reference voltage connection line  345  in a region between the display region DA and the reference voltage line  341 . In the display region DA, the reference voltage connection line  343  is embodied as the first reference voltage connection line  344  which constitutes a different layer from that of the second reference voltage connection line  345 . 
     The first reference voltage connection line  344  and the second reference voltage connection line  345  may constitute different layers and may be electrically connected to each other via at least one contact-hole. Further, the VSS voltage connection line  323  may be composed of a first VSS voltage connection line  324  and a second VSS voltage connection line  325  constituting different layers and being electrically connected to each other. 
     In this case, the first VSS voltage connection line  324 , the source electrode  217   a  and drain electrode  217   b  may constitute the same layer and may be made of the same material. The second VSS voltage connection line  325  and the gate electrode  214  may constitute the same layer and may be made of the same material. 
     For example, in order to connect the VSS voltage connection line  323  to the second VSS voltage line  322 , the first VSS voltage connection line  324  and the second VSS voltage connection line  325  constituting different layers are electrically connected to each other. 
     Since the VSS voltage connection line  323  electrically connects the first VSS voltage line  321  and the second VSS voltage line  322  sandwiching the display regions DA therebetween to each other, the first VSS voltage connection line  324  and the second VSS voltage connection line  325  of the VSS voltage connection line may constitute different layers such that the VSS voltage connection line does not form a short-circuit with various line connection pads and lines in a region between the first VSS voltage line  321  and the second VSS voltage line  322 . 
     In one embodiment of the present disclosure, no other line is disposed between the display region DA and the first VSS voltage line  321 . Thus, the VSS voltage connection line  323  extending from the first VSS voltage line  321  may be embodied as the first VSS voltage connection line  324  integrally formed with the first VSS voltage line  321  and made of the same material as that of the first VSS voltage line  321  and constituting the same layer with the first VSS voltage line  321 . 
     The first VSS voltage connection line  324  branched from the first VSS voltage line  321  may extend across the display region DA. Then, when the VSS voltage connection line  323  extends across the second VDD voltage line  332 , the first VSS voltage connection line  324  and the second VSS voltage connection line  325  may act as the VSS voltage connection line  323  in a repeatedly alternate manner such that the VSS voltage connection line  323  does not form a short-circuit with the second VDD voltage line  332  in a region where the VSS voltage connection line  323  overlaps with the second VDD voltage line  332 . 
     When the VSS voltage connection line  323  extends across the second VDD voltage line  332 , the VSS voltage connection line  323  may change from the first VSS voltage connection line  324  to the second VSS voltage connection line  325  in a region where the VSS voltage connection line  323  does not overlap with the second VDD voltage line  332 . Thus, when the VSS voltage connection line  323  extends across the second VDD voltage line  332 , the VSS voltage connection line  323  does not form a short-circuit with the second VDD voltage line  332 . 
     That is, the first VSS voltage connection line  324  and the second VSS voltage connection line  325  constitute different layers and are electrically connected to each other via at least one second VSS voltage connection line contact-hole  325   h.    
     After the VSS voltage connection line  323  has extended across the second VDD voltage line  332 , the first VSS voltage connection line  324  may be connected to the second 
     VSS voltage line  322 , as shown in  FIG. 12 . In this case, the first VSS voltage connection line  324  and the second VSS voltage line  322  may be electrically connected to each other via a second VSS voltage connection line  325  connected to the first VSS voltage connection line  324  via at least one second VSS voltage connection line contact-hole  325   h.    
     In addition, in a region where the second VSS voltage line  322  does not overlap with the data line  313 , auxiliary lines  327  connected to the second VSS voltage line  322  via at least one auxiliary line contact-hole  327 h are disposed below the second VSS voltage line  322 . 
     The auxiliary line  327  and the gate electrode  214  may be made of the same material and may constitute the same layer. 
     The auxiliary line  327  may be connected to a rear face of the second VSS voltage line  322 , thereby reducing an overall resistance of the second VSS voltage line  322 . 
     Further, the VDD voltage connection line  333  may be composed of a first VDD voltage connection line  334  and a second VDD voltage connection line  335  constituting different layers and being electrically connected to each other. 
     In this case, the first VDD voltage connection line  334 , the source electrode  217   a  and drain electrode  217   b  of the driving thin-film transistor  210  of the pixel may be made of the same material and may constitute the same layer. The second VDD voltage connection line  335  and the gate electrode  214  of the driving thin-film transistor  210  of the pixel may be made of the same material and may constitute the same layer. 
     For example, in order to connect the VDD voltage connection line  333  to the second VDD voltage line  332 , the first VDD voltage connection line  334  and the second VDD voltage connection line  335  constitute different layers and are electrically connected to each other. 
     The VDD voltage connection line  333  electrically connects the first VDD voltage line  331  and the second VDD voltage line  332  sandwiching the display regions DA therebetween to each other. Thus, the first VDD voltage connection line  334  and the second VDD voltage connection line  335  constitute different layers so that the VDD voltage connection line  333  does not form a short-circuit with various line connection pads and lines in a region between the first and second VDD voltage lines  331  and  332 . 
     Thus, the VDD voltage connection line  333  may be embodied as the first VDD voltage connection line  334  in a region between the first VDD voltage line  331  and the display region DA. When the VDD voltage connection line  333  extends across the display region DA, the VDD voltage connection line  333  may be embodied as the second VDD voltage connection line  335 . That is, the VDD voltage connection line  333  changes from the first VDD voltage connection line  334  to the second VDD voltage connection line  335 . 
     That is, the first VDD voltage connection line  334  and the second VDD voltage connection line  335  constitute different layers and are electrically connected to each other via at least one contact-hole. 
     Then, the VDD voltage connection line  333  may be embodied as the first VDD voltage connection line  334  which may be connected to the second VDD voltage line  332 , as shown in  FIG. 12 , in a region between the display region DA and the second VDD voltage line  332 . 
     In this case, the first VDD voltage connection line  334  and the second VDD voltage line  332  may be electrically connected to each other via the second VDD voltage connection line  335  connected to the first VDD voltage connection line  334  via at least one second VDD voltage connection line contact-hole  335   h.    
     In addition, auxiliary lines  327  connected to the second VDD voltage line  332  via at least one contact-hole may be disposed in a region where the second VDD voltage line  332  does not overlap with the data line  313  and VSS voltage connection line  323 . 
     The auxiliary line  327  and the gate electrode  214  may be made of the same material and may constitute the same layer. 
     The VDD voltage auxiliary line  327  may be connected to a rear face of the second VDD voltage line  332  to reduce an overall resistance of the second VDD voltage line  332 . 
       FIG. 6  additionally shows a passivation-hole formed in the passivation layer  218 .  FIG. 7  further shows a first connection electrode  351  connecting the VSS voltage line connection pad  320  and the first VSS voltage line  321  to each other, and a second connection electrode  352  connecting the reference voltage line connection pad  340  and the reference voltage line  341  to each other. 
     The passivation layer  218  may be formed on the reference voltage line connection pad  340 , the VDD voltage line connection pad  330 , the VSS voltage line connection pad  320 , the reference voltage line  341 , the first VSS voltage line  321 , the second VSS voltage line  322 , the first VDD voltage line  331 , and the second VDD voltage line  332 . The passivation layer  218  may act as a planarization layer made of an organic material layer such as PAC. 
     Further, the passivation layer  218  serves as an insulating layer. Thus, for electrical connection between the line connection pads and the lines, a passivation-hole, that is, a planarization-hole may be formed in portions of each line connection pad and each line. 
     The passivation-hole means not only a contact-hole, but also an open hole formed by partially removing the passivation layer  218  to secure a contact area as much as possible. Each line connection pad and each line may be electrically connected to each other via the connection electrodes connected to each other via the passivation-hole. 
     In  FIG. 6 , in order to clarify distinction between the layers, the passivation layer  218  is not shown separately, but only a region where the passivation-hole is formed is shown in an emphasis manner. 
     A first passivation-hole  218   a  is formed on the VSS voltage line connection pad  320  and the first VSS voltage line  321 . The first connection electrode  351  electrically connects the VSS voltage line connection pad  320  and the first VSS voltage line  321  to each other via the first passivation-hole  218   a , as shown in  FIG. 7  and  FIG. 13 . 
     In other words, in order to prevent a short circuit between the VSS voltage line connection pad  320  and the first VSS voltage line  321  and the first VDD voltage line  331  and the reference voltage line  341  disposed between the VSS voltage line connection pad  320  and the first VSS voltage line  321 , a jumping connection structure of an electrode to connect the VSS voltage line connection pad  320  and the first VSS voltage line  321  to each other may be beneficial. 
     Therefore, according to an embodiment of the present disclosure, the passivation layer  218  is formed on the first VDD voltage line  331  and the reference voltage line  341 . The first passivation-hole  218   a  is formed on the VSS voltage line connection pad  320  and the first VSS voltage line  321 . 
     Thus, the jumping connection structure of the electrode may be formed using the first connection electrode  351  which is formed on the passivation layer  218  and whose one portion is connected to the VSS voltage line connection pad  320  via one first passivation-hole  218   a  and whose an opposite portion is connected to the first VSS voltage line  321  via an opposite first passivation-hole  218   a.    
     The first connection electrode  351  and the anode electrode as the first electrode  221  constituting the organic light-emitting element  220  may be made of the same material and may constitute the same layer. 
     The first connection electrode  351  electrically connects the VSS voltage line connection pad  320  and the first VSS voltage line  321  to each other and, to this end, is preferably formed to have a large area as much as possible in order to reduce or minimize electrical resistance and to increase or maximize uniformity of the resistance distribution. 
     Therefore, the first connection electrode  351  may be formed to extend over the first VDD voltage line  331 , the reference voltage line  341 , and the first VSS voltage line  321 , and thus may be formed to have an increased area or a maximum area. 
     However, the first connection electrode  351  does not extend over all regions of the first VDD voltage line  331  and the reference voltage line  341  and the first VSS voltage line  321 . The first connection electrode  351  does not extend over a partial region such as a region of the second connection electrode  352  as described later or a spacing region between the first and second connection electrodes  351  and  352 . 
     Further, in ordered to increase or maximize a contact area of the first passivation-hole  218   a  with the VSS voltage line connection pad  320  and the first VSS voltage line  321 , the first passivation-hole  218   a  may have a shape corresponding to the first VSS voltage line  321 , that is, a long bar shape. 
     Further, at least one gas exhaust hole  355  may be formed in at least a partial region of the first connection electrode  351  as shown in  FIG. 13 . 
     The gas exhaust hole  355  serves to discharge unnecessary gases that may be generated during a process of forming the transparent display panel  300 . Thus, when forming the gas exhaust hole  355  in the first connection electrode  351  having a large area, reliability of the transparent display panel  300  may be further enhanced. 
     The bank layer  231  formed on the first connection electrode  351  has open regions defined therein corresponding to the gas exhaust holes  355  to secure a passage of the gas exhaust hole  355 . Each bank layer  231  may define a boundary between adjacent gas exhaust holes  355 . 
     Further, a VSS voltage auxiliary line connection pad  326  may be additionally disposed and may be electrically connected to the first VSS voltage line  321  via the first connection electrode  351 . 
     The VSS voltage auxiliary line connection pad  326  and the VSS voltage line connection pad  320  may be made of the same material and constitute the same layer. However, the VSS voltage auxiliary line connection pad  326  has an island form separated from the VSS voltage line connection pad  320  and not connected to a separate line. 
     The first passivation-hole  218   a  is formed on the VSS voltage auxiliary line connection pad  326  such that the VSS voltage auxiliary line connection pad  326  is connected to the first connection electrode  351  via the first passivation-hole  218   a , thereby increasing a total area of the first connection electrode  351 , thereby reducing the overall resistance and making the resistance distribution more uniform. 
     In one example, the passivation layer  218  is formed on the reference voltage line connection pad  340  and the reference voltage line  341 . The second connection electrode  352  electrically connects the reference voltage line connection pad  340  and the reference voltage line  341  to each other via a second passivation-hole  218   b  as shown in  FIG. 7  and  FIG. 13 . 
     In order to prevent a short circuit between the reference voltage line connection pad  340  and the reference voltage line  341  and the first VDD voltage line  331  between the reference voltage line connection pad  340  and the reference voltage line  341 , a jumping structure of an electrode for connecting the reference voltage line connection pad  340  and the reference voltage line  341  to each other is required. 
     Therefore, according to an embodiment of the present disclosure, the passivation layer  218  is formed on the first VDD voltage line  331 , and the second passivation-hole  218   b  is formed on each of the reference voltage line connection pad  340  and the reference voltage line  341 , as shown in  FIG. 6 . 
     Thus, the jumping connection structure of an electrode may be formed using the second connection electrode  352  which is formed on the passivation layer  218  and whose one portion is connected to the reference voltage line connection pad  340  via one second passivation-hole  218   b  and whose an opposite portion is connects to the reference voltage line  341  via an opposite second passivation-hole  218   b.    
     The second connection electrode  352  and the first connection electrode  351  may be made of the same material and may constitute the same layer but may be spaced apart from each other. Thus, the second connection electrode  352  may have an island shape. 
     Therefore, the second connection electrode  352  and the anode electrode as the first electrode  221  constituting the organic light-emitting element  220  of the pixel may be made of the same material and may constitute the same layer. 
     The second connection electrode  352  electrically connects the reference voltage line connection pad  340  and the reference voltage line  341  to each other and, to this end, is preferably formed to have a large area as much as possible in order to reduce or minimize resistance thereof and increase or maximize uniformity of resistance distribution thereof. Further, the second passivation-hole  218   b  is formed to have a large area as much as possible to increase or maximize a contact area thereof with the reference voltage line connection pad  340  and the reference voltage line  341 . 
     Further, at least one gas exhaust hole  355  may be formed in a partial region of the second connection electrode  352  as in the first connection electrode  351 . 
     In one example, a third passivation-hole  218   c  may be formed on the second VSS voltage line  322 , as shown in  FIG. 6 . As shown in  FIG. 7 , a third connection electrode  353  may be formed on the third passivation-hole  218   c.    
     The third passivation-hole  218   c  formed on the second VSS voltage line  322  is intended for connecting the second VSS voltage line  322  and the third connection electrode  353  to each other. The third connection electrode  353  is electrically connected to the second VSS voltage line  322  via the third passivation-hole  218   c.    
     In order to reduce the resistance by increasing or maximizing the contact area between the second VSS voltage line  322  and the third connection electrode  353 , the third passivation-hole  218   c  may have a bar shape corresponding to the second VSS voltage line  322 . 
     Further, when forming the third connection electrode  353  at a lower end portion of the transparent display panel  300 , an effect may occur that a difference between vertical levels of the lower end portion of the transparent display panel  300  and an upper end portion of the transparent display panel  300  in which the first connection electrode  351  and the second connection electrode  352  formed may be removed. 
     The third connection electrode  353 , the first connection electrode  351  and the second connection electrode may be made of the same material and may constitute the same layer but may be spaced apart from each other. Thus, the third connection electrode  353  is formed to have an island shape. 
     Accordingly, the third connection electrode  353  and the anode electrode as the first electrode  221  constituting the organic light-emitting element  220  of the pixel may be made of the same material and may constitute the same layer. 
     The bank layer  231  may be formed on the first connection electrode  351 , the second connection electrode  352  and the third connection electrode  353 . As shown in  FIG. 8 , the bank layer  231  may form a dam  380  disposed in the non-display region NDA to surround the display region DA. The dam  380  may include at least one dam  380  as patterned. When the dam  380  is formed on the first substrate  200 , the dam  380  may serve to prevent an encapsulating material used to form the encapsulating layer  250  from flowing to an outside. 
     The dam  380  may be disposed in the non-display region NDA, and may be disposed to surround the lighting tester  375  and the first VDD voltage line  331  disposed in the non-display region NDA. 
     In one example, a fourth connection electrode  354  is formed on the bank layer  231 , and is connected to the cathode electrode as the second electrode  225  of the pixel. The fourth connection electrode  354  is electrically connected to the VSS voltage line to apply a VSS voltage to the cathode electrode of the pixel. In this case, the cathode electrode and the fourth connection electrode  354  may be formed integrally with each other. 
     One end of the fourth connection electrode  354  is electrically connected to the first connection electrode  351  to which the VSS voltage is applied, while the other end of the fourth connection electrode  354  is electrically connected to the third connection electrode  353 , thereby to apply the VSS voltage to the cathode electrode. 
     As shown in  FIG. 8 ,  FIG. 9  and  FIG. 15 , the bank layer  231  is formed on the first connection electrode  351 . A first bank-hole  231   a  is formed on the first connection electrode  351  and is formed by removing a partial region of the bank layer  231 , thereby to expose the first connection electrode  351  to an outside. Thus, the first connection electrode  351  may be electrically connected to one end of the fourth connection electrode  354  via the first bank-hole  231   a.    
     When the VSS voltage is applied to the fourth connection electrode  354 , the fourth connection electrode  354  is not directly connected to the first VSS voltage line  321 , but the fourth connection electrode  354  is connected thereto via the first connection electrode  351  made of a same material as an anode electrode, thereby to reduce an electrical resistance. 
     To increase or maximize the contact area between the first connection electrode  351  and the fourth connection electrode  354 , the first bank-hole  231   a  of the bank layer  231  on the first connection electrode  351  may be formed in a bar shape as in the reference voltage line  341 . 
     Further, the first bank-hole  231   a  may be formed in a corresponding manner to the reference voltage line  341  or the first VSS voltage line  321 . For example, in some cases, the first bank-hole  231   a  may overlap with either the reference voltage line  341  or the first VSS voltage line  321 . 
     For example, when the first bank-hole  231   a  is formed on a separate circuit region such as an ESD protection circuit region  371 , there may be a problem that the bank-hole is formed in a region where a flatness is poor. 
     Further, when the first bank-hole  231   a  is formed on a line far away from the first VSS voltage line  321  such as the first VDD voltage line  331 , a current path of the fourth connection electrode  354  which is electrically connected to the first VSS voltage line  321  via the first bank-hole  231   a  becomes longer. Thus, the resistance increases correspondingly. 
     For example, when a length of a connection to the fourth connection electrode  354  as the cathode electrode of the high resistance rather than the anode electrode of the low resistance is larger, the overall resistance may be greater. 
     Thus, according to an embodiment of the present disclosure, the first bank-hole  231   a  is preferably formed on the reference voltage line  341  or the first VSS voltage line  321 . 
     When the first bank-hole  231   a  is formed on the reference voltage line  341 , an inclined face of the hole may be removed to obtain a high flatness, thereby to reduce resistance variation than when a bank-hole is formed in a portion of the bank layer  231  on which no line is formed. 
     Further, when the first bank-hole  231   a  is formed on the first VSS voltage line  321 , a length of a connection between the fourth connection electrode  354  and the first VSS voltage line  321  becomes smaller, thereby reducing the resistance. 
     As shown in  FIG. 8  and  FIG. 9 , a second bank-hole  231   b  formed by removing a partial region of bank layer  231  is formed in a portion of the bank layer  231  on the third connection electrode  353  electrically connected to the second VSS voltage line  322 , thereby to electrically connect an opposite portion of the fourth connection electrode  354  to the third connection electrode  353 . 
     In this case, the second bank-hole  231   b  is formed to correspond to a third passivation-hole  218   c  on the second VSS voltage line  322 . Thus, while the second VSS voltage line  322 , the third connection electrode  353  and the fourth connection electrode  354  are in a stacked state, they electrically contact each other at the same position. For example, in some cases, the second bank-hole  231   b  overlaps with a third passivation-hole  218   c  on the second VSS voltage line  322 . 
     In addition, the second VSS voltage line  322  is not directly connected to the cathode electrode, but is connected thereto via the third connection electrode  353  as a low-resistance anode electrode, thereby to reduce resistance. 
     Due to the connection structure of the fourth connection electrode  354 , the VSS voltage may be applied to the fourth connection electrode  354 . Thus, the VSS voltage may be applied to the cathode electrode of the organic light-emitting element  220 . That is, the VSS voltage applied from the VSS voltage line connection pad  320  may be applied to the fourth connection electrode  354  via the first VSS voltage line  321  and the first connection electrode  351 . 
     In some embodiments, the fourth connection electrode  354  may extend across an entirety of the display region DA including the first VDD voltage line  331 , the reference voltage line  341 , the first VSS voltage line  321 , the second VDD voltage line  332  and the second VSS voltage line  322 . 
     For example, as shown in  FIG. 14 , the cathode electrode may extend across an entirety of the display region DA including the second VDD voltage line  332  and the second VSS voltage line  322 , and may be surrounded with the dam  380 . 
     In one example, the GIP circuit region  360  includes a GIP block  361  and a clock signal line region  363 , as shown in  FIG. 16 . 
     The GIP block  361  includes at least one GIP block that divides the gate lines GL into multiple blocks and drives each of the multiple blocks in each of multiple display driving periods. The clock signal line region  363  may include at least one clock signal lines to control nodes of the GIP circuit region  360 . 
     The GIP block  361  and the clock signal line region  363  may be alternately arranged in a direction away from the display region DA. 
     Specifically, non-transparent and thick VSS voltage lines may be omitted in left and right portions of the non-display region NDA left and right to the display region DA. Thus, the GIP circuit region  360  may occupy a region increased by the omitted area. 
     Therefore, the GIP block  361  and the clock signal line region  363  constituting the GIP circuit region  360  may be arranged in a non-compacted manner. Thus, a transparent region may be secured even in the GIP circuit region  360 . 
     For example, in a case where a space of the GIP circuit region  360  is narrow, the GIP block  361  and the clock signal line region  363  must be arranged in a very dense manner to increase or maximize space utilization. Thus, it is difficult to secure a separate transparent region in the GIP circuit region  360 . 
     To the contrary, when the space of the GIP circuit region  360  increases as in one embodiment of the present disclosure, the GIP block  361  having a non-transparent region at a larger amount and the clock signal line region  363  having a transparent region at a larger amount may be alternately arranged in the GIP circuit region  360  in a distinguished manner. Thus, the transparent region may be secured to the maximum even in the GIP circuit region  360 . 
     In other words, according to one embodiment of the present disclosure, the VSS voltage line is omitted in one side region of the non-display region NDA out of the display region DA where the GIP circuit region  360  is disposed, as shown in  FIG. 16  and  FIG. 17 . Thus, reduction of a transparent region due to the non-transparent VSS voltage line may be reduced or minimized. 
     Therefore, the lighting tester  375  may be disposed between the dam  380  and the GIP circuit region  360 , but the VSS voltage line may not be disposed between the dam  380  and the GIP circuit region  360 . 
     A transparent display device should be capable of displaying image information to be displayed while having the same properties as those of a transparent glass substrate. A transparent display device having such characteristics may be configured as a complex transparent display device in which the display information and a spatial situation behind the transparent display device overlap with each other. Representative examples thereof include a head-up-display (HUD) used in airplanes and automobiles. 
     The head-up-display used in a vehicle as shown in  FIG. 18  is mounted on a windshield of the vehicle to display various driving information to a driver while allowing the driver&#39;s front view to be secured. 
     Therefore, in the head-up-display, high visibility of display information is required. When a haze value is high, visibility of display information is not good. Thus, it is important to make the haze value as low as possible. 
     The haze is related to clarity of an object (or objects) seen through the transparent display device. Therefore, in a transparent display device having a high transmittance but a high haze value, there is a problem in that a driver sees the object in a blurry manner, and thus visibility of display information is deteriorated. Occurrence of the haze in the transparent display device may be attributed to the following light characteristics. 
       FIG. 19A  shows a long-distance diffraction pattern by a single slit.  FIG. 19B  is an illustration of a diffraction effect in a single slit. 
     Diffraction of a wave refers to a phenomenon in which a wave front is bent when the wave encounters an obstacle or a slit. In diffraction using a single slit, a surface wave of a certain wavelength having exited the slit forms a myriad of spherical waves. 
     In this regard, light may be treated as a wave in that a diffraction phenomenon occurs in a slit experiment using light as shown in  FIG. 19A . As the light passes through the slit, diffraction appears in the same way as the surface wave. However, a myriad of new spherical waves interfere with each other, resulting in occurrence of contrasting diffraction patterns. 
       FIG. 19B  shows Fraunhoffer diffraction in which a diffraction pattern is viewed at a long distance from an diffracting object. The Fraunhoffer diffraction occurs when all rays are considered as parallel rays, and the diffraction pattern is the same regardless of the distance. 
     A condition under which the Fraunhoffer diffraction occurs in a single slit may be calculated as follows. 
     When a difference between paths of two light beams traveling at an edge and a center of the slit respectively is r1−r2, r1−r2=a/2 sin θ. In this connection, a m-th offset interference condition in which an offset interference occurs is a/2 sin θ=±mλ/2. Since θ is usually much smaller than 1, a darkened point corresponds to a point away θ=±mλ/a or ym=±mλ/a R from the center. 
       FIG. 20A  to  FIG. 20D  shows results of a double slit experiment for a particle, a wave, light, and an electron, respectively. 
     When particles pass through a double slit, a distribution of particles hitting a screen appears as a simple sum of single distributions of the particles passing through a single slit as shown in  FIG. 20A . 
     That is, in this case, a bright band appears on a portion of the screen corresponding not to a center of the screen but to a slit position. When the wave passes through the double slit, the brightest band appears at the center of the screen, as shown in  FIG. 20B . This allow knowing whether interference occurs. Since the particles do not interfere with each other, a distribution of particles is strong at a position where they may pass through the slit in a best manner. 
     In one example, when the light passes through the double slit as shown in  FIG. 20C , an interference pattern resulting from a fact that the particle property thereof disappears and the wave passes therethrough occurs. Electron is generally considered to be a particle. However, when an electron accelerated at a high speed passes through a double slit as shown in  FIG. 20D , a result appears as the same result as that of a double slit experiment of the wave. 
     That is, it may be seen that even when the particles pass through the double slit at a sufficiently high speed, the same interference as that occurring in the wave occurs. As a result, it may be seen that light has the wave-particle duality in that light is a wave generated by particles as photons that is sufficiently fast. 
     In this way, light has the properties of waves and particles at the same time. Thus, when the light encounters a slit having a periodic pattern, overlapping and offsetting occur, resulting in periodic diffraction. Consequently, the diffraction phenomenon due to the wave-particle duality of light may vary depending on a shape of the transmissive region which acts as a slit in the transparent display device. 
     For example,  FIG. 21  shows an arrangement of transmissive regions having a typical quadrangle shape in a transparent display device. 
     Multiple transmissive regions TAij in which i is a row number, and j is a column number (i and j are natural numbers) are arranged in a matrix type. Thus, the transmissive regions in a first row include TA 11 , TA 12 , TA 13  . . . , the transmissive regions in a second row include TA 21 , TA 22 , TA 23  . . . , and the transmissive regions in a third row include TA 31 , TA 32 , TA 33  . . . . Similarly, the transmissive regions in a first column are TA 11 , TA 21 , TA 31  . . . , the transmissive regions in a second column are TA 12 , TA 22 , TA 32  . . . , and the transmissive regions in a third column are TA 13 , TA 23 , TA 33  . . . . 
     In this case, each transmissive region has a rectangular shape having all internal angles of  90  degrees. As a result, each of the transmissive regions TA 21  and TA 23  adjacent to the transmissive region TA 22  to the same row has a vertical side facing and parallel to a vertical side of the transmissive region TA 22 . 
     Further, each of the transmissive regions TA 12  and TA 32  adjacent to the transmissive region TA 22  in the same column has a horizontal face facing and parallel to a horizontal side of the transmissive region TA 22 . That is, each of all sides of the transmissive region TA 22  faces and is parallel to a corresponding side of each of adjacent transmissive regions. The same principle may be equally applied to other transmissive regions. 
     Since light transmits the transmissive regions, they may play the same role as the slit illustrated in the double slit experiment above. Therefore, occurrence or non-occurrence, and an intensity of diffraction of light may vary depending on shapes and an arrangement structure of the transmissive regions. 
     Diffraction of light is caused by periodic repetition of lines constituting the slit, and may be more clearly generated when adjacent lines constituting the slit have a periodicity in a parallel manner to each other or when the slits are periodically arranged. 
     Therefore, in the transparent display device, when the transmissive regions, each having the rectangular shape are arranged in a matrix type having regularity and periodicity in a parallel manner as shown in  FIG. 21 , the diffraction phenomenon of light may be clearly observed. 
       FIG. 22  shows the diffraction phenomenon of light generated when light is incident onto a central region of a transparent display device having the transmissive region shape and the arrangement structure of the transmissive regions as shown in  FIG. 21 . 
     As may be seen in  FIG. 22 , it may be seen that the diffraction phenomenon of light appears very clearly around the central region where the light is incident. As the diffraction phenomenon of light becomes more apparent in the transparent display device, the haze also increases. As a result, the clarity or visibility of the transparent display device is reduced. 
     Therefore, there is a need for a new pixel structure having a shape of a transmissive region that may reduce or minimize the diffraction of light caused by periodic repetition of lines in the transmissive regions. Thus, the present disclosure provides a new pixel structure including transmissive regions having a new transmissive region shape as follows. 
     A transparent display panel according to another embodiment according to the present disclosure includes a substrate having a display region including a plurality of light-emitting regions and a plurality of transmissive regions, and a plurality of line regions disposed on the substrate and extending across the display region, wherein an outer contour of each of the transmissive regions is at least partially curved. 
     For example, in an embodiment of the present disclosure shown in  FIG. 23 , an outer contour of each of the transmissive regions may be partially curved. Specifically, the transmissive region TA 22  has four outwardly convex sides corresponding to four sides of a dotted virtual rectangle drawn inside the transmissive region. The same feature may be applied to other transmissive regions. 
     Thus, mutually facing sides of the transmissive region TA 22  and each of transmissive regions TA 21  and TA 23  adjacent to the transmissive region TA 22  may not be parallel to each other. Further, mutually facing sides of the transmissive region TA 22  and each of transmissive regions TA 12  and TA 32  adjacent to the transmissive region TA 22  in the same column may not be parallel to each other. 
     In another embodiment according to the present disclosure shown in  FIG. 24 , an outer contour of each of transmissive regions may be partially curved. Specifically, the transmissive region TA 22  has six outwardly convex sides corresponding to six sides of a dotted virtual hexagon drawn inside the transmissive region. The same feature may be applied to other transmissive regions. 
     Thus, mutually facing sides of the transmissive region TA 22  and each of transmissive regions TA 21  and TA 23  adjacent to the transmissive region TA 22  may not be parallel to each other. Further, mutually facing sides of the transmissive region TA 22  and each of transmissive regions TA 12  and TA 32  adjacent to the transmissive region TA 22  in the same column may not be parallel to each other. 
     In still another embodiment according to the present disclosure shown in  FIG. 25 , an outer contour of each of transmissive regions has a circular shape. Specifically, the transmissive region TA 22  is formed to have a circular shape. The same feature may be applied to other transmissive regions. 
     Thus, mutually facing sides of the transmissive region TA 22  and each of transmissive regions TA 21  and TA 23  adjacent to the transmissive region TA 22  may not be parallel to each other. Further, mutually facing sides of the transmissive region TA 22  and each of transmissive regions TA 12  and TA 32  adjacent to the transmissive region TA 22  in the same column may not be parallel to each other. 
     In other words, all sides of the transmissive region TA 22  in  FIG. 23  to  FIG. 25  may not be parallel to all sides of each of adjacent transmissive regions thereto. The same features may be applied to other transmissive regions. 
     Therefore, even when the transmissive regions, each having the shape shown in  FIG. 23  to  FIG. 25 , are arranged in a matrix type, parallel regularity and periodicity of the transmissive regions acting as slits are avoided, thereby reducing or minimizing the diffraction of light. 
     Further, in another embodiment according to the present disclosure, each of transmissive regions may be formed in an elliptical shape. Due to this elliptical shape, the parallel regularity and periodicity of the transmissive regions that act as the slit as illustrated above may be avoided, thereby reducing or minimizing the diffraction of light as much as possible. 
     Although  FIG. 23  to  FIG. 25  show that an entirety of the outer contour of each of the transmissive regions is curved by way of example, the present disclosure is not limited thereto. Even when only a portion of the contour of the transmissive region is curved, the parallel regularity and periodicity of the transmissive regions may be avoided, thereby reducing or minimizing the diffraction of light. 
     Therefore, in the transparent display panel including transmissive regions, each having the outer contour being at least partially curved, diffraction of light may be reduced or minimized, thereby to reduce the haze level. As a result, the clarity or visibility of the transparent display device may be improved. 
       FIG. 26  shows the diffraction phenomenon of light generated when light is shot onto a central region of a transparent display device having a transmissive region of a circular shape and an arrangement structure of the transmissive regions as shown in  FIG. 25 . As may be seen in  FIG. 26 , substantially no diffraction of light is generated around the central region where light is incident. 
     Thus, non-occurrence of the diffraction of light in a transparent display device having a transmissive region of a circular shape and an arrangement structure of the transmissive regions as shown in  FIG. 25  is clearer, compared to  FIG. 22  which shows the result when light is incident onto the central region of the transparent display device having a conventional quadrangle transmissive region shape. 
     The diffraction of light is reduced or minimized, especially when the transmissive region has a circular shape. Thus, in order to reduce or minimize the diffraction interference of light, it is desirable to form the transmissive region to have a shape approximate to a circle as much as possible. However, when the outer contour of the transmissive region is at least partially curved, as in the circular transmissive region, an area of the transmissive region may be reduced. Thus, it may be difficult to design a pixel including the light-emitting region and the line region. 
     Therefore, hereinafter, another embodiment according to the present disclosure capable of designing an optimized transmissive region and an optimized light-emitting region while reducing or minimizing diffraction interference of light is illustrated. 
     A transparent display panel according to another embodiment of the present disclosure includes a substrate including a display region including a plurality of light-emitting regions and a plurality of transmissive regions, and a plurality of line regions disposed on the substrate and extending across the display region, wherein each of the transmissive region has a polygonal shape, and all internal angles of the polygon are obtuse. 
     For example, as shown in  FIG. 27 , each of transmissive regions has a polygonal shape whose all internal angles are obtuse. That is, the polygon having all internal angles being an obtuse angle include all of polygons having at least 5 sides. The polygon may include all of the sides of lengths equal to each other. 
     Specifically, in  FIG. 27 , the transmissive region has a hexagon shape, and more specifically, a regular hexagon shape. This is one example. As shown in  FIG. 27 , mutually facing sides of the transmissive region TA 22  and each of transmissive regions TA 21  and TA 23  adjacent to the transmissive region TA 22  may not be parallel to each other. However, mutually facing sides of the transmissive region TA 22  and each of transmissive regions TA 12  and TA 32  adjacent to the transmissive region TA 22  in the same column may be parallel to each other. 
     Thus, when transmissive regions with hexagonal shapes are arranged as shown in  FIG. 26 , mutually facing sides of transmissive regions adjacent to each other in the same row may not be parallel to each other. Thus, the parallel regularity and periodicity of the transmissive regions are avoided, such that diffraction of light may be reduced or minimized as much as possible. 
     In other words, when mutually facing sides of transmissive regions adjacent to each other in the same row and/or column are not parallel to each other, diffraction of light may be reduced or minimized, compared to when mutually facing sides of transmissive regions adjacent to each other in the same row and/or column are parallel to each other. 
     In the hexagonal transmissive region shape shown in  FIG. 27 , a length of each of mutually facing sides of transmissive regions adjacent to each other in the same column is small. Thus, even when mutually facing sides of transmissive regions adjacent to each other in the same column are parallel to each other, the diffraction phenomenon of light may be reduced. 
     Therefore, even when transmissive regions, each having the shape shown in  FIG. 27 , are arranged in a matrix type in a transparent display device, the parallel regularity and periodicity of the transmissive regions acting as slits are avoided, such that diffraction of light may be reduced or minimized as much as possible. 
     In another embodiment according to the present disclosure, as shown in  FIG. 28 , each of the transmissive regions has an octagon shape, especially, a regular octagon shape having all internal angles being an obtuse angle. This is one example. The octagon as shown in  FIG. 28  is more approximate to a circle than the hexagon is, such that an effect similar to that as achieved by the transmissive region having a circular shape that reduces or minimizes diffraction of light may be obtained by the shape of  FIG. 28 . 
     In the octagonal transmissive region shape shown in  FIG. 28 , a length of each of mutually facing sides of transmissive regions adjacent to each other in the same column is small. Thus, even when mutually facing sides of transmissive regions adjacent to each other in the same column are parallel to each other, the diffraction phenomenon of light may be reduced. 
     Therefore, even when transmissive regions, each having the shape shown in  FIG. 28 , are arranged in a matrix type in a transparent display device, the parallel regularity and periodicity of the transmissive regions acting as slits are avoided, such that diffraction of light may be reduced or minimized as much as possible. 
     That is, a transmissive region of a polygonal shape in which all internal angles are obtuse, in particular, a transmissive region having a regular polygonal shape in which all internal angles are obtuse has a shape more approximate to a circle, thereby reducing or minimizing diffraction of light. 
     Further, an area of a transmissive region of a polygonal shape in which all internal angles are obtuse may be larger than an area of the curved or circular shaped transmissive region. Thus, when using a transmissive region of a polygonal shape in which all internal angles are obtuse, the pixel design and the line region design may be easier than that when using the curved or circular shaped transmissive region. 
     Therefore, a transparent display panel including a transmissive region having a polygonal shape in which all internal angles are obtuse may secure a maximum transmissive region with the reduced haze level and may facilitate the design of the pixel and the line region. 
     Hereinafter, the arrangement shape of the light-emitting regions and the transmissive regions according to an embodiment of the present disclosure will be described in more detail, based on the embodiment in which the transmissive region has an octagon among the various embodiments of the transmissive region shapes as exemplified above. 
     As shown in  FIG. 29 , a transparent display panel according to an embodiment of the present disclosure includes a substrate having a display region including a plurality of light-emitting regions and a plurality of transmissive regions, and line regions disposed on the substrate while extending across the display region. In this case, the transmissive region has a polygonal shape whose all internal angles are obtuse. 
     The transparent display panel may be composed of a transmissive region including a plurality of transmissive regions TA through which light is transmitted, and a non-transmissive region NTA through which light is not transmitted. In the transmissive region, a plurality of transmissive regions TA are arranged in a matrix composed of a plurality of rows of transmissive regions and a plurality of columns of transmissive regions. 
     In this case, a plurality of transmissive regions TA arranged in the same row may be referred to as one transmissive region row. For example, one transmissive region row may indicate the transmissive regions running horizontally (e.g., along the x-axis). A plurality of transmissive regions TA arranged in the same column may be referred to as one transmissive region column. For example, one transmissive region column may indicate the transmissive regions running vertically (e.g., up and down or along the y-axis). In the connection, the row direction refers to a horizontal direction of the substrate and coincides with the X-axis direction. The column direction is defined as the vertical direction of the substrate coinciding with the Y-axis direction. 
     The non-transmissive region NTA may include a light-emitting region in which light is emitted and a non-light-emitting region in which light is not emitted. The light-emitting region refers to a region in which a light-emitting region EA of a sub-pixel is disposed. The non-light-emitting region may contain a plurality of line regions CLA, each extending in the vertical direction of the substrate. 
     In this case, the plurality of line regions are column line regions CLA 1 , CLA 2 , CLA 3 , CLA 4  . . . , each extending in a column direction. The plurality of line regions contains data lines and various voltage lines extending in the column direction. Further, a pixel circuit region PCA connected to the light-emitting region of each sub-pixel may be disposed in the non-light-emitting region. 
     The pixel circuit region PCA may be disposed under the light-emitting region EA and may be aligned with the light-emitting region EA. The PCA partially overlaps with the light-emitting region EA and the non-overlapping region of the PCA region may be contained in the non-light-emitting region. 
     In addition, the line region CLA is placed in a non-light-emitting region. However, when the light-emitting region EA partially overlaps with the line region CLA, a portion of the region CLA overlapping with the light-emitting region EA may act as a light-emitting region. A plurality of transmissive regions (TAij, where i is the row number, and j is the column number, i and j are natural numbers) may be arranged in matrix type. 
     The transparent display panel of  FIG. 29  is one example having a sub-pixel arrangement structure of RG-BG, but the present disclosure is not limited thereto. For example, a first color sub-pixel may be a red sub-pixel including a first color light-emitting region emitting red light. A second color sub-pixel may be a green sub-pixel including a second color light-emitting region emitting green light. A third color sub-pixel may be a blue sub-pixel including a third color light-emitting region emitting blue light. However, the present disclosure is not limited thereto. 
     The first color sub-pixel Rij_SP includes a first color light-emitting region Rij and a first color pixel circuit region Rij_PCA that is electrically connected to the first color light-emitting region Rij to control light emission from the first color light-emitting region Rij. The first color pixel circuit region Rij_PCA may be disposed under the first color light-emitting region Rij while partially overlapping therewith. Thus, at least a partial region of the first color pixel circuit region Rij_PCA does not overlap with the first color light-emitting region Rij, and thus may be exposed to an outside. 
     In this case, a portion of the first color pixel circuit region Rij_PCA as exposed to the outside may be positionally biased relative to the first color light-emitting region Rij, for example, may be biased to a right side to the first color light-emitting region Rij. Thus, it is possible to more efficiently arrange the emitting region and the pixel circuit region in an entire pixel arrangement structure. 
     In the partial region of the first color pixel circuit region Rij_PCA as exposed to the outside, a first color sub-pixel contact-hole Rij_H that electrically connects the first color light-emitting region Rij and the first color pixel circuit region Rij_PCA to each other may be formed. 
     Further, each of the second color sub-pixel Gij_SP and the third color sub-pixel Bij_SP may be configured in the same manner as the first color sub-pixel Rij_SP as exemplified above in terms of the light-emitting region, the pixel circuit region, the sub-pixel contact-hole, etc. Thus, additional overlapping descriptions thereof will be omitted. 
     The first color sub-pixel is placed between adjacent rows of the transmissive regions. For example, first color sub-pixels R 11 _SP, R 12 _SP, and R 13 _SP are disposed between the transmissive regions TA 11 , TA 12 , and TA 13  in the first row and the transmissive regions TA 21 , TA 22 , and TA 23  in the second row, respectively. Thus, the first color light-emitting regions R 11 , R 12 , and R 13  may be disposed between the transmissive regions TA 11 , TA 12 , and TA 13  in the first row and the transmissive regions TA 21 , TA 22 , and TA 23  in the second row, respectively. 
     The first color sub-pixel is disposed between the second color sub-pixel and the third color sub-pixel. Thus, the first color light-emitting region is disposed between the second color light-emitting region and the third color light-emitting region. 
     Further, the first color sub-pixel is disposed between adjacent line region CLAs among the plurality of line regions CLA arranged in the vertical direction of the substrate and does not overlap with the line regions CLA. The second color sub-pixel and the third color sub-pixel are disposed on the line region CLA and partially overlap with the line region CLA. 
     For example, the second color sub-pixels G 12 _SP and G 14 _SP in the same row as the first color sub-pixels R 11 _SP, R 12 _SP, and R 13 _SP among the second color sub-pixels at least partially overlap with the second column line region CLA 2  and the fourth column line region CLA 4 , respectively. The second color sub-pixels G 21 _SP and G 23 _SP in the same row as the first color sub-pixels R 21 _SP, R 22 _SP, and R 23 _SP at least partially overlap with the first column line region CLA 1  and the third column line region CLA 3 , respectively. 
     The third color sub-pixels B 11 _SP and B 13 _SP in the same row as the first color sub-pixels R 11 _SP, R 12 _SP, and R 13 _SP among the third color sub-pixels at least partially overlap with the first column line region CLA 1  and the third column line region CLA 3 , respectively. The third color sub-pixels B 22 _SP and B 24 _SP in the same row as the first color sub-pixels R 21 _SP, R 22 _SP, and R 23 _SP at least partially overlap with the second column line region CLA 2  and the fourth column line region CLA 4 , respectively. 
     In other words, as in a configuration in which the second color sub-pixel B 11 _SP and the third color sub-pixel G 21 _SP are spaced apart in the column direction and disposed on the first column line region CLA 1 , the second color sub-pixel and the third color sub-pixel are disposed on one column line region and are alternately arranged in the column direction. 
     Further, as in a configuration in which the second color sub-pixel B 11 _SP and the third color sub-pixel G 12 _SP in the same row are disposed on the first column line region CLA 1  and the second column line region CLA 2  adjacent thereto respectively, the second color sub-pixel and the third color sub-pixel are alternately arranged in the row direction and are disposed on column line regions adjacent to each other in the row direction respectively. 
     Therefore, the first color sub-pixel R 11 _SP, the second color sub-pixel G 12 _SP, the first color sub-pixel R 12 _SP, and the third color sub-pixel B 13 _SP are sequentially arranged in the first row. In the second row adjacent to the first row, the first color sub-pixel R 21 _SP, the third color sub-pixel B 22 _SP, the first color sub-pixel R 22 _SP, and the second color sub-pixel G 23 _SP are sequentially arranged to correspond to the above pattern. 
     Therefore, the second color sub-pixel G 12 _SP, the first color sub-pixel R 12 _SP, and the third color sub-pixel B 13 _SP consecutively arranged in the first row, and the third color sub-pixel B 22 _SP, the first color sub-pixel R 22 _SP, and the second color sub-pixel G 23 _SP arranged in the second row surround the transmissive region TA 22 . When using this arrangement shape as a basic unit, a plurality of units are arranged in a matrix manner in the display region. 
     That is, in the transmissive region according to an embodiment of the present disclosure, when the above-described basic unit is defined as one pixel, a single transmissive region is not divided into two or more in a single pixel, thereby to effectively suppress increase in the haze. 
     In this regard, the variation in the haze value based on the shape of the transmissive region and based on the division or non-division of the transmissive region may be identified based on  FIG. 30  and  FIG. 31 . Specifically,  FIG. 30A  shows a configuration in which the transmissive region has a quadrangle shape, and three transmissive regions correspond to one pixel.  FIG. 30B  shows a configuration in which the transmissive region has a quadrangle shape, and two transmissive regions correspond to one pixel.  FIG. 30C  shows a configuration in which one transmissive region corresponds to one pixel while the transmissive region has a circular shape as in one embodiment of the present disclosure. 
     All of  FIG. 30A  to  FIG. 30C  are experiment results based on 145 ppi (pixels per inch). In  FIG. 30A , a haze value of 2.76% was measured. In  FIG. 30B , a haze value of 2.03% was measured. Therefore, it may be seen that the haze value decreases by 26.4% as the number of transmissive regions corresponding to one pixel decreases from three to two. 
     In  FIG. 30C , a haze value of 1.33% was measured. Therefore, in  FIG. 30C , the haze value decreased by 34.5% compared to that of  FIG. 30B . Thus, it may be clearly seen that as the number of transmissive regions decreased from 2 to 1, and the transmissive region has the circular shape, the haze value further decreases. 
       FIG. 31  shows a graph of the haze value when ppi is 200 ppi, 100 ppi, and 145 ppi respectively, and when the transmissive region has a quadrangle shape, and the number of transmissive regions corresponding to one pixel is 3 (A), when the transmissive region has a quadrangle shape, and the number of transmissive regions corresponding to one pixel is 2 (B), and when a circular transmissive region is provided, and the number of transmissive regions corresponding to one pixel is 1 (C). 
     As may be seen from the graph result value in  FIG. 31  that in the configuration C in which a circular transmissive region is disposed, but the number of transmissive regions corresponding to one pixel is 1, the haze value is reduced or minimized for all ppi. 
     The first color light-emitting region, the second color light-emitting region and the third color light-emitting region are arranged to correspond to the first color sub-pixel, the second color sub-pixel and the third color sub-pixel, respectively. Thus, the light-emitting regions are arranged in the same manner as the arrangement structure of the sub-pixels as illustrated above. 
     As shown in  FIG. 29 , the transmissive region has an octagonal shape. The first color light-emitting region has a rectangular shape. In this case, the shape of the first color light-emitting region is formed so as be surrounded by the bank layer  231  as shown in  FIG. 33 . Specifically, in the first color light-emitting region, the bank layer  231  may be removed to be opened. 
     Further, each of the second color light-emitting region and the third color light-emitting region may have a polygonal shape, for example, a hexagon. A shape of each of the second color light-emitting region and the third color light-emitting region is formed so as be surrounded by the bank layer  231 . Specifically, in each of the second and third color light-emitting regions, the bank layer  231  may be removed to be opened. 
     An area of one first color light-emitting region may be smaller than an area of each of one second color light-emitting region and one third color light-emitting region. Specifically, since the red light-emitting region has a longer lifespan than that of each of the green and blue light-emitting regions, the former has better lifespan reliability and light-emitting efficiency. Therefore, it is desirable to form the red light-emitting region to have a smaller area than that of each of the green and blue light-emitting regions. For example, the first color light-emitting region, the second color light-emitting region, and the third color light-emitting region may be formed at an area ratio of approximately 1:1.8:1.8. 
     Each of the second color light-emitting region and the third color light-emitting region may be disposed on the corresponding line region and may at least partially overlap therewith. In this case, each of the second color light-emitting region and the third color light-emitting region may be arranged to be symmetrical around each corresponding line region. Due to this arrangement structure, the transparent display panel according to an embodiment of the present disclosure may have a pixel arrangement structure that may make the most of a light-emitting area efficiently. 
     In another embodiment of the present disclosure, as shown in  FIG. 32 , each of the second color sub-pixel and the third color sub-pixel may include a light-emitting region further extending along the line region in the column direction of the line region. 
     In order to secure the light-emitting region as much as possible, as shown in  FIG. 32 , for example, the third color sub-pixel B 11 _SP and the second color sub-pixel G 21 _SP arranged in the column direction of the first line region CLA 1  expand such that a spacing therebetween is larger. 
     Preferably, the third color sub-pixel B 11 _SP and the second color sub-pixel G 21 _SP arranged in the column direction of the first line region CLA 1  may be further extended to an extent such that distal ends of the two sub-pixels abut each other. However, the distal ends thereof may have a predefined separation space therebetween considering a process margin. 
     In particular, when the second electrode of the organic light-emitting diode, for example, the cathode electrode is made of a metal such as Ag having a low sheet resistance, a separate contact structure is not required to lower the resistance of the cathode electrode. Thus, as shown in  FIG. 32 , the area of each of the color sub-pixels may be expanded as much as possible on the line region. 
       FIG. 33  and  FIG. 34  show cross-sections of a I-I′ region and a J-J′ region in  FIG. 29 , respectively.  FIG. 33  is a cross-sectional view of a first color sub-pixel region. 
     Specifically, the passivation layer  218  as a planarization layer is disposed on the first color pixel circuit region R PCA. The first electrode  221  of the organic light-emitting diode  220 , for example, an anode electrode, is formed on the passivation layer  218 . 
     The bank layer  231  is formed on the first electrode  221 . In order to expose a portion of the first electrode  221  corresponding to the light-emitting region to the outside, a portion of the bank layer  231  corresponding to the light-emitting region is removed and thus the bank layer is patterned. That is, the bank layer  231  may serve as a boundary that defines the light-emitting region, thereby determining a shape of the light-emitting region, and may also serve as a boundary between the sub-pixel and the transmissive region. 
     The shape of the first electrode  221  is determined based on the shape into which the bank layer  231  is patterned. In order to increase or maximize the transmittance and the light-emitting region, it is desirable to form the bank layer to have a minimum width allowable in a mask process for forming the bank layer  231 . 
     On and over the first electrode  221 , the organic light-emitting layer  223  is formed to cover the bank layer  231 . The second electrode  225 , for example, a cathode electrode, is formed on the organic light-emitting layer  223 . As the organic light-emitting layer  223  and the second electrode  225  are stacked on the first electrode  221  in an overlapping manner to form the organic light-emitting diode  220 , a region of the first electrode  221  exposed to an outside through an open region in the bank layer  231  may act as the light-emitting region. 
     The encapsulating layer  250  may be formed on the second electrode  225 . A color filter CF may be formed on the encapsulating layer  250 . The color filter CF may have the same color as a corresponding light-emitting region. A first color filter R_CF corresponding to the first color sub-pixel R_SP may have the same color as the first color. 
     When using the color filter CF, it is possible to reduce reflectance and increase the color purity of RGB color. The color filter CF may extend to a boundary between the transmissive region TA and the light-emitting region EA and thus may be formed in the non-transmissive region NTA. Therefore, a region where the color filter CF is formed may be defined as the light-emitting region. 
     The top substrate as the second substrate  270  may be adhered onto the color filter CF. Further, to prevent damage to the organic film layer which is vulnerable to high temperatures, the top substrate may be disposed on the color filter CF using a COE (color-filter on encap) approach in which a low-temperature color filter process is performed on the substrate without a bonding process. 
     In one example,  FIG. 34  is a cross-sectional view of a border region between the first color sub-pixel R_SP and the second color sub-pixel G_SP. 
     The passivation layer  218  as the planarization layer is disposed on the pixel circuit region PCA, specifically, the first color pixel circuit region R_PCA and the second color pixel circuit region G_PCA. The first electrode  221  of the organic light-emitting diode  220 , for example, an anode electrode is formed on the passivation layer  218 . 
     The first electrodes  221  spaced apart from each other are respectively formed in the first color sub-pixel region and the second color sub-pixel region. The bank layer  231  is formed on the first electrode  221 . In order to expose a portion of the first electrode  221  corresponding to the light-emitting region to the outside, a portion of the bank layer  231  corresponding to the light-emitting region is removed and then the bank layer is patterned. 
     That is, the bank layer  231  may serve as a boundary between sub-pixels adjacent to each other. The region corresponding to the bank layer  231  may be a non-transmissive region NTA. On and over the first electrode  221 , the organic light-emitting layer  223  is formed to cover the bank layer  231 . The second electrode  225  is formed on the organic light-emitting layer  223 . 
     As the organic light-emitting layer  223  and the second electrode  225  are stacked on the first electrode  221  in an overlapping manner to form the organic light-emitting diode  220 , the region of the first electrode  221  exposed to the outside through the open region of the bank layer  231  may be a light-emitting region. 
     The encapsulating layer  250  may be formed on the second electrode  225 . The color filter CF may be formed on the encapsulating layer  250 . 
     The first color filter R_CF corresponding to the first color sub-pixel R_SP may have the first color. The second color filter G_F corresponding to the second color sub-pixel G_SP may have the second color. That is, a color filter corresponding to a color of a corresponding light emitting region may be disposed on the light emitting region of each color. 
     Both of the first color filter R_CF and the second color filter G_F may be formed to be as wide as possible so that at least a partial region thereof overlaps with the bank layer  231 . 
     In one example, the first color sub-pixel R_SP and the second color sub-pixel G_SP are adjacent to each other. Thus, in order to reduce or minimize mixing of light beams of different colors adjacent to each other and to clarify a boundary between different color light-emitting regions, a non-transparent black matrix may be disposed between the first color filter R_CF and the second color filter G_F. 
     Likewise, a non-transparent black matrix BM may be disposed between the second color sub-pixel G_SP and the third color sub-pixel B_SP arranged vertically on the same line region, such that mixing of light beams of different colors is reduced or minimized, and a boundary of each light-emitting region is clear. Specifically, a non-transparent black matrix BM may be disposed between the second color filter G_F and the third color filter B_F. For example, as shown in  FIG. 29 , a black matrix may be disposed between the second color sub-pixel G 12 _P and the third color sub-pixel B 22 _P on the second column line region CLA 2 . Thus, the black matrix may partially overlap with the second column line region CLA 2 . 
     Further, the transmissive regions TA 21  and TA 22  are respectively disposed on both sides to the second column line region CLA 2  partially overlapping with the black matrix. A line region between one transmissive region and another transmissive region adjacent thereto may partially overlap with the black matrix. That is, the black matrix may partially overlap with the line region disposed between adjacent transmissive regions. 
     The black matrix may be formed in a pattern corresponding to the bank layer  231  forming the boundary, and may be formed to be narrower than the bank layer  231  and may be disposed inwardly of the region of the bank layer  231 . 
     In one example, as shown in  FIG. 35 , the substrate has a non-display region surrounding the display region. The non-display region may include a dummy pixel pattern region DPA arranged to surround the outermost portion of the display region. Specifically, the display region DA includes a plurality of sub-pixels SP. The dummy pixel pattern region DPA may include a plurality of dummy pixels or dummy sub-pixels DSP (see  FIG. 36 ). 
     The dummy pixel or dummy sub-pixel DSP is formed to reduce or minimize a process deviation and a side effect such as a loading effect that may occur during a manufacturing process of the transparent display device. The dummy pixel DSP may surround the sub-pixel to serve as a kind of a buffer area. 
     The dummy pixel DSP may have an organic light-emitting element layer and a circuit region such as a driving thin-film transistor as in the sub-pixel. However, a signal is not applied to each element layer and the circuit region of the dummy pixel. Thus, a separate pixel contact-hole SP_H that electrically connect the components thereof to each other is not required. As a result, the organic light-emitting element layer in the dummy pixel pattern region DPA does not emit light. For example, the circuit region such as the driving thin-film transistor of the dummy pixel may not work or operate to emit light. 
     The dummy pixel pattern region DPA surrounding the outermost portion of the display region DA may include a top row direction region and a bottom row direction region above and below the display region DA, as shown in  FIG. 36 . The dummy pixel pattern region DPA surrounding the outermost portion of the display region DA may include a left column direction region and a right column direction region left and right to the display region DA as shown in  FIG. 36 . The static electricity may invade the GIP regions left and right to the display region DA through the gate line. Thus, a left column direction region and a right column direction region of the dummy pixel pattern region DPA may be thicker than a top row direction region and a bottom row direction region thereof. For example, as shown in  FIG. 36 , the left column direction region may have a width WW 3  and the bottom row direction region may have a width WW 4 . In some embodiments, width WW 3  may be thicker than width WW 4 . However, other dimensions may be used in other embodiments according to the display design. 
     Hereinafter, another embodiment according to the present disclosure in which an area of the transmissive region may be increased or maximized by reducing or minimizing an area of the line region in the display region, while the occurrence of luminance non-uniformity may be reduced or minimized by reducing or minimizing the occurrence of the high-level voltage drop (VDD drop) or low-level voltage rise (VSS rise) will be described. 
     As shown in  FIG. 37  and  FIG. 38 , a transparent display panel includes a substrate having a display region including a plurality of light-emitting regions and a plurality of transmissive regions, and a plurality of display line regions disposed on the substrate and extending across the display region. Alternatively-arranged adjacent line regions include alternatively-arranged adjacent VSS voltage connection line  323  and VDD voltage connection line  333 , respectively. Each line region including at least one data line  313  and at least one reference voltage connection line  343 . 
     In this case, a layer composed of the VSS voltage connection line  323  and the VDD voltage connection line  333  may be different from a layer composed of the data line  313  and the reference voltage connection line  343 . For example, the line region CLA extends in the vertical direction of the display region. Alternatively-arranged adjacent line regions include alternatively-arranged adjacent VSS voltage connection line  323  and VDD voltage connection line  333 , respectively. Specifically, the VSS voltage connection line  323  and VDD voltage connection line  333  are alternately arranged with each other while the transmissive region are interposed therebetween. 
     The line region CLA including the VSS voltage connection line  323  may include a plurality of reference voltage connection lines  343  (Vref) arranged in a symmetrical manner around the VSS voltage connection line  323 , and a plurality of data lines  313  (Vdata) arranged in a symmetrical manner around the VSS voltage connection line  323 . In some embodiments, a plurality of reference voltage (Vref) connection lines  343  are adjacently arranged around the VSS voltage connection line  323 , and a plurality of data (Vdata) lines  313  are also adjacently arranged around the VSS voltage connection line  323 . Here, the plurality of data (Vdata) lines  313  may be arranged adjacent to the outer side of the plurality of reference voltage (Vref) connection lines  343 . 
     In this case, the VSS voltage connection line  323  is disposed above the at least one data line  313  and above the at least one reference voltage connection line  343 . That is, a layer composed of the VSS voltage connection line  323  is different from a layer composed of the at least one data line  313  and the at least one reference voltage connection line  343 . Thus, in this case, a width of the line region may be significantly reduced compared to a case when the VSS voltage connection line  323 , the data line  313 , and the reference voltage connection line constitute the same layer. 
     In particular, the VSS voltage connection line  323  may at least partially overlap with at least two of the at least one data line  313  and the at least one reference voltage connection line  343 , and may not extend beyond a boundary of the outermost data line  313 . Thus, a width of the entire line region may be greatly reduced. 
     Further, the line region CLA including the VDD voltage connection line  333  includes a plurality of reference voltage connection lines  343  (Vref) arranged symmetrically around the VDD voltage connection line  333 , and a plurality of data lines  313  (Vdata) arranged symmetrically around the VDD voltage connection line  333 . In some embodiments, a plurality of reference voltage connection lines  343  are adjacently arranged around the VDD voltage connection line  333 , and a plurality of data lines  313  are also adjacently arranged around the VDD voltage connection line  333 . Here, the plurality of data lines  313  may be arranged adjacent to the outer side of the plurality of reference voltage connection lines  343 . 
     In this case, a layer composed of the VDD voltage connection line  333  is different from a layer composed of the data line  313  and the reference voltage connection line  343 . Thus, in this case, a width of the line region may be significantly reduced compared to that when the VDD voltage connection line  333 , the data line  313 , and the reference voltage connection line  343  constitute the same layer. 
     In particular, the VDD voltage connection line  333  may at least partially overlap with at least two of the at least one data line  313  and the at least one reference voltage connection line  343  and may not extend beyond a boundary of the outermost data line  313 . Thus, a width of the entire line region may be greatly reduced. 
     Therefore, a width W of each line region may be a sum of a width of the at least one data line  313  and a width of the at least one reference voltage connection line  343  and spacings between the lines (see  FIG. 37 ). For example, when the line region including the VDD voltage connection line  333  is a first column line region CLA 1 , the first column line region CLA 1  may include the VDD voltage connection line  333 , two reference voltage connection lines  343  arranged symmetrically around the VDD voltage connection line  333  and disposed under the VDD voltage connection line  333 , and two data lines  313  arranged symmetrically around the VDD voltage connection line  333  and disposed under the VDD voltage connection line  333 . 
     A second column line region CLA 2  immediately adjacent to the first column line region CLA 1  includes the VSS voltage connection line  323 , two reference voltage connection lines  343  arranged symmetrically around the VSS voltage connection line  323  and disposed under the VSS voltage connection line  323 , and two data lines  313  arranged symmetrically around the VSS voltage connection line  323  and disposed under the VSS voltage connection line  323 . In this way, a third column line region CLA 3  includes the VDD voltage connection line  333 . A fourth column line region CLA 4  includes the VSS voltage connection line  323 . 
     Further, in accordance with the present disclosure, the width of the entire line region may be reduced or minimized due to the configuration that the non-transparent lines extending across the display region in the same line region may constitute different layers. Thus, an area occupied by the line region in the display region may be reduced. 
     When the area of the line region is reduced, the area of the pixel circuit region corresponding to each sub-pixel is reduced. Thus, an area of the transmissive region increases, such that an overall transmittance of the transparent display device may increase. 
     In one example, according to the present disclosure, each of the VSS voltage connection line  323  and the VDD voltage connection line  333  may have a width greater than that of each of the data line  313  and the reference voltage connection line  343 . 
     When a layer composed of each of the VSS voltage connection line  323  and the VDD voltage connection line  333  is different from a layer composed of the data line  313  and the reference voltage connection line  343 , it is not necessary to reduce the width of the VSS voltage connection line  323  and the width of the VDD voltage connection line  333  to reduce the width of the entire line region. 
     That is, although a width of each of the VSS voltage connection line  323  and the VDD voltage connection line  333  is larger than that of each of the data line  313  and the reference voltage connection line  343 , an overall width of the non-transparent line region is not increased. 
     For example, as shown in  FIG. 37 , each of the VSS voltage connection line  323  and the VDD voltage connection line  333  at least partially overlaps with the two data lines  313  and the two reference voltage connection lines  343  disposed under each of the VSS voltage connection line  323  and the VDD voltage connection line  333 . 
     In this case, each of the VSS voltage connection line  323  and the VDD voltage connection line  333  may extend to an outer boundary of the outermost data line  313 , thereby forming a relatively thick power line. 
     When the width of each of the power lines such as the VSS voltage connection line and the VDD voltage connection line is reduced to ensure a maximum area of the transmissive region, occurrence of the high-level voltage drop (VDD drop) or the low-level voltage rise (VSS rise) may increase. 
     However, when the width of each of the power lines such as the VSS voltage connection line and the VDD voltage connection line is large as in one embodiment of the present disclosure, occurrence of the high-level voltage drop (VDD drop) or the low-level voltage rise (VSS rise) may be reduced or minimized. Accordingly, occurrence of the luminance non-uniformity of the transparent display device may be reduced or minimized without increasing a driving voltage and power consumption. 
     Thus, when the lines of the line region constitute different layers but at least partially overlap with each other in accordance with one embodiment of the present disclosure, the area of the line region in the display region may be reduced or minimized such that the area of the pixel circuit region may be reduced or minimized. Thus, the area of the transmissive region increases, thereby to increase the overall transmittance of the transparent display device. 
     Further, the width of each of the power lines such as the VSS voltage connection line and the VDD voltage connection line may be large, thereby reducing or minimizing the occurrence of the high-level voltage drop (VDD drop) or the low-level voltage rise (VSS rise), thereby to reduce or minimize the occurrence of the luminance-uniformity. 
     In other words, in general, the increase in the width of the line region within the display region, especially, the increase in the width of the power line has a trade-off relationship with the increase in the transmittance. However, according to an embodiment of the present disclosure, there is an advantage of increasing the transmittance of the transparent display device while increasing the width of the power line region. 
     The plurality of light-emitting regions may include a first color light-emitting region Rij, a second color light-emitting region Gij, and a third color light-emitting region Bij. Each of the second color light-emitting region and the third color light-emitting region may at least partially overlap with the line region. Thus, the first color light-emitting region may be placed between the line regions adjacent to each other. Each of the second color light-emitting region and the third color light-emitting region may be arranged symmetrically around a corresponding line region. 
     Specifically, each of the VSS voltage connection line and the VDD voltage connection line at least partially overlaps with the second color light-emitting region or the third color light-emitting region. Colors of the light-emitting regions arranged in the same row and partially overlapping with the VSS voltage connection line and the VDD voltage connection line respectively may be different from each other. 
     In one example, the first color sub-pixel Rij_SP may include the first color light-emitting region Rij, and the first color pixel circuit region Rij_PCA electrically connected to the first color light-emitting region Rij to drive the first color light-emitting region Rij to emit light. The first color light-emitting region Rij and the first color pixel circuit region Rij_PCA may be electrically connected to each other via the first color sub-pixel contact-hole Rij_H. 
     Further, each of the second color sub-pixel Gij_SP and the third color sub-pixel Bij_SP may be configured in the same way as the first color sub-pixel Rij_SP in terms of the light-emitting region, the pixel circuit region, the sub-pixel contact-hole, etc. 
     Therefore, a plurality of pixel circuit regions are arranged over the substrate and are electrically connected to the light-emitting regions respectively to drive the light-emitting regions. The pixel circuit regions may include the first color pixel circuit region electrically connected to the first color light-emitting region, the second color pixel circuit region electrically connected to the second color light-emitting region, and the third color pixel circuit region electrically connected to the third color light-emitting region. 
     In this case, each of the plurality of pixel circuit regions may be arranged symmetrically with respect to each line region. Further, each pixel circuit region may have a narrower shape as the pixel circuit region extends away from a center of each line region. Specifically, the first color pixel circuit region is arranged symmetrically to the second color pixel circuit region or the third color pixel circuit region around the line region interposed therebetween. 
     For example, the second color light-emitting region G 12  may be arranged symmetrically around the second column line region CLA 2 . Further, the first color pixel circuit region R 11 _PCA and the second color pixel circuit region G 12 _PCA may be arranged symmetrically to each other around the second column line region CLA 2 . 
     Specifically, the first color pixel circuit region R 11 _PCA has a shape that becomes narrower as the first color pixel circuit region R 11 _PCA extends away from a center of the second column line region CLA 2  in the left direction. The second color pixel circuit region G 12 _PCA may have a shape that becomes narrower as the second color pixel circuit region extends away from a center of the second column line region CLA 2  in the right direction. 
     In this way, the first color pixel circuit region R 12 _PCA and the third color pixel circuit region B 13 _PCA may be arranged symmetrically to each other around the third column line region CLA 3 . 
     Further, the first color pixel circuit region may overlap with at least partial regions of the first color light-emitting region and the second color light-emitting region, and may overlap at least partial regions of the first color light-emitting region and the third color light-emitting region. 
     The second color pixel circuit region may overlap with at least partial regions of the first color light-emitting region and the second color light-emitting region. The third color pixel circuit region may overlap with at least partial regions of the first color light-emitting region and the third color light-emitting region. 
     The arrangement form of the pixel circuit region is due to the arrangement form of the light-emitting region and the transmissive region. The light-emitting region become narrower as the region extends away from a center of a corresponding line region. Thus, the pixel circuit region is disposed within the light-emitting region so as not to overlap with the transmissive region, thereby not to lower the transmittance of the display region. 
     Therefore, according to the present disclosure, the VSS voltage connection line and the VDD voltage connection line are alternately arranged in the adjacent line regions within the display region. Each pixel circuit region connected to each light-emitting region corresponding to each color has a symmetrical structure. Thus, a new pixel arrangement structure capable of increasing or maximizing an area of the transparent region of the bezel and reducing or minimizing the haze value without reducing the transmittance of the display region may be realized. 
     In one example, the pixel circuit region may include a driving thin-film transistor, a capacitor, and a plurality of switching thin-film transistors. That is, each of the first color pixel circuit region, the second color pixel circuit region, and the third color pixel circuit region may include a driving thin-film transistor, a capacitor, and a plurality of switching thin-film transistors. 
     In one example, the driving thin-film transistor DR included in the pixel circuit region connected to the first color sub-pixel may at least partially overlap the second color light-emitting region of the second color sub-pixel or the third color light-emitting region of the third color sub-pixel. Specifically, the driving thin-film transistor DR included in the first color pixel circuit region may at least partially overlap the first electrode as the pixel electrode of the second color light-emitting region, or the first electrode as the pixel electrode of the third color light-emitting region. 
     For example, as shown in  FIG. 37 , the first color pixel circuit region R 11 _PCA connected to the first color sub-pixel R 11 _SP may at least partially overlap the second color light-emitting region G 12  of the second color sub-pixel G 12 _SP disposed on a right side to the first color sub-pixel R 11 _SP. Specifically, the driving thin-film transistor DR included in the first color pixel circuit region R 11 _PCA may at least partially overlap the first electrode  221  of the second color light-emitting region G 12 . 
     Likewise, the first color pixel circuit region R 12 _PCA connected to the first color sub-pixel R 12 _SP may at least partially overlap the third color light-emitting region B 13  of the third color sub-pixel B 13 _SP disposed on a right side to the first color sub-pixel R 12 _SP. Specifically, the driving thin-film transistor DR included in the first color pixel circuit region R 12 _PCA may at least partially overlap with the first electrode  221  of the third color light-emitting region B 13 . 
     Further, the second color pixel circuit region connected to the second color sub-pixel may at least partially overlap with the second color light-emitting region. Specifically, the driving thin-film transistor DR of the second color pixel circuit region may at least partially overlap with the first electrode  221  as the pixel electrode of the second color light-emitting region. 
     Likewise, the third color pixel circuit region connected to the third color sub-pixel may at least partially overlaps with the third color light-emitting region. Specifically, the driving thin-film transistor DR of the third color pixel circuit region may at least partially overlap with the first electrode  221  as the pixel electrode of the third color light-emitting region. 
     Further, the pixel circuit regions may be arranged symmetrically to each other around one line region. In this case, one pixel circuit region including a driving thin-film transistor DR driving a light-emitting region partially overlapping with the line region may be disposed on one side to the line region. The other pixel circuit region related to a different color from that of one pixel circuit region and including a driving thin-film transistor DR driving a light-emitting region between the corresponding line region and a neighboring line region thereto may be disposed on the other side to the line region. 
     That is, a driving thin-film transistor driving a light-emitting region at least partially overlapping with the line region may be disposed on one side to the line region, while a driving thin-film transistor driving a light-emitting region between the line region and a neighboring line region thereto may be disposed on the other side to the line region. 
     For example, the line region CLA 2  at least partially overlaps with the second color light-emitting region G 12 . The first color pixel circuit region R 11 _PCA and the second color pixel circuit region G 12 _PCA may be symmetrically arranged to each other on one side to the line region CLA 2 . 
     Thus, a driving thin-film transistor driving the light-emitting region G 12  at least partially overlapping with the line region CLA 2  may be disposed on one side to the line region CLA 2 . A driving thin-film transistor driving the light-emitting region R 11  between the line region CLA 2  and the neighboring line region CLA 1  thereto may be disposed on the other side to the line region CLA 2 . 
       FIG. 38  is a cross-sectional view of O-O′ and P-P′ regions in  FIG. 37 . As shown in  FIG. 38 , a buffer layer  201  may be formed on an entire face of the first substrate  200 . On the buffer layer  201 , a driving thin-film transistor  210  including an active layer  212 , a source electrode  217   a , a drain electrode  217   b , and a gate electrode  214 , and a capacitor Cst including a first capacitor electrode  204  and a second capacitor electrode  206  may be formed. 
     A gate insulating layer  213  may be formed between the active layer  212  and the gate electrode  214  and the first capacitor electrode  204 . A first interlayer insulating layer  215  may be formed on the gate electrode  214  and the first capacitor electrode  204 . A second capacitor electrode  206  may be formed on the first interlayer insulating layer  215 . A second interlayer insulating layer  216  may be formed on the second capacitor electrode  206 . The source electrode  217   a  and the drain electrode  217   b  may be formed on the second interlayer insulating layer  216 . 
     Further, on the second interlayer insulating layer  216 , the data line  313  and the reference voltage connection line  343  may be formed to constitute the same layer. In this case, the data line  313  and the reference voltage connection line  343  may be made of the same material as the source electrode  217   a  and the drain electrode  217   b . The data line  313  and the reference voltage connection line  343  may be spaced apart from each other. 
     The passivation layer  218  and the first planarization layer  219   a  may be formed on the data line  313 , the reference voltage connection line  343 , the source electrode  217   a , and the drain electrode  217   b . When forming the first planarization layer  219   a , the VSS voltage connection line  323  or the VDD voltage connection line  333  may be formed on the first planarization layer  219   a.    
     As shown in  FIG. 38 , the VSS voltage connection line  323  may be formed on the first planarization layer  219   a . Specifically, the VSS voltage connection line  323  may at least partially overlap with the plurality of data lines  313  and the plurality of reference voltage connection lines  343 . 
     In this case, a width W 1  of the VSS voltage connection line  323  may be much larger than each of a width W 3  of the data line  313  and a width W 2  of the reference voltage connection line  343 , resulting in reducing the occurrence of the low-level voltage rise (VSS rise). Further, a width (not shown) of the VDD voltage connection line  333  may be much larger than each of a width W 3  of the data line  313  and a width W 2  of the reference voltage connection line  343 , resulting in reducing the occurrence of the high-level voltage drop (VDD drop). In this case, the width of each of the VSS voltage connection line and the width of the VDD voltage connection line may be same. 
     A width of one line region may be sized such that each of the VSS voltage connection line and the VDD voltage connection line may extend to the outer boundary of the data line  313  disposed outside of the reference voltage connection line  343 . Therefore, when the VSS voltage connection line  323  constitutes the same layer with the reference voltage connection line  343  and the data line  313 , the width of the line region may be a sum of widths of the VSS voltage connection line  323 , the reference voltage connection line  343  and the data line  313 . However, according to the present disclosure, the width of the line region may be reduced by the width of the VSS voltage connection line  323 , so that the width of the entire line region may be reduced. 
     In addition, the width of the VSS voltage connection line  323  may be sized that the VSS voltage connection line  323  may extend to the outer boundary of the data line  313  disposed outside the reference voltage connection line  343 , thereby reducing or minimizing the transmittance reduction resulting from the increase in the width of the power line while increasing the width of the power line. 
     A second planarization layer  219   b  may be formed on the VSS voltage connection line and the VDD voltage connection line. The organic light-emitting element  220  including the first electrode  221 , the organic light-emitting layer  223  and the second electrode  225  may be disposed on the second planarization layer  219   b.    
     In this case, the bank layer  231  is formed between the first electrode  221  and the organic light-emitting layer  223 . The bank layer  231  may serve as a boundary defining a region of a light-emitting region and may act as a boundary between the sub-pixel and the transmissive region. The bank layer  231  may have a bank-hole defined therein positionally corresponding to the sub-pixel region, thereby to partially expose the first electrode  221 . 
     The organic light-emitting layer  223  is formed on a top face of the bank layer  231  and a portion of the first electrode  221  as exposed through the bank-hole. A region in which the organic light-emitting layer  223  contacts the first electrode  221  may correspond to a sub-pixel region, more specifically, a light-emitting region EA. 
     In some embodiments, the second electrode  225  is formed over the entirety of the first substrate  200  and on the organic light-emitting layer  223 . An encapsulating layer  250 , an adhesive layer  251 , a color filter CF, and a second substrate  270  may be formed on the second electrode  225 . 
     Hereinafter, a transparent display panel of another embodiment according to the present disclosure that may uses a GIP region as a transmissive region to increase or maximize a transmissive region in the GIP region, and a transparent display device including the same will be described. 
     As shown in  FIG. 39 , a transparent display panel includes a substrate including a display region and a non-display region surrounding the display region, and a GIP circuit region disposed in the non-display region of the substrate, wherein the GIP circuit region includes at least one GIP (Gate-In Panel) block, at least one GIP input signal line region, at least one GIP output signal line region, and at least one GIP input signal connection line electrically connecting the GIP block with the GIP input signal line region to each other. 
     The GIP block  361  supplies a gate signal such as a scan signal and a light-emitting EM signal to pixel circuits of a display region. 
     Specifically, the GIP block  361  may include at least one GIP block to divide a gate line GL into a plurality of blocks, and to drive the plurality of blocks for a plurality of display driving periods, respectively. For example, the GIP block may include a GIP transistor circuit such as a shift register. 
     In one example, the timing controller provides timing signals and control signals so that the GIP block and the data driver may generate control signals at an appropriate timing. 
     The timing controller may generate and supply signals for controlling operation timings of the GIP block and the data driver based on timing signals such as a vertical synchronization signal, a horizontal synchronization signal, a clock signal, and a data enable signal. 
     The GIP input signal line region  365  may include at least one signal line that transmits a gate control signal applied from the timing controller to a GIP block  361  via a gate pad. The at least one signal line may include at least one GIP input signal line  365   a  extending in the vertical direction of the display region. 
     In this case, the GIP input signal line region  365  may be embodied as a clock signal line region that controls nodes of the GIP circuit region  360 . 
     The GIP input signal line region  365 , and the source electrode and the drain electrode constituting the driving thin-film transistor of the display region may be made of the same material and may constitute the same layer. 
     The GIP output signal line region  367  may include a signal line that delivers the gate signal of the GIP block  361  to the display region. Such a signal line may include at least one GIP output signal line  367   a ,  367   b , and  367   c  extending in a horizontal direction of the display region, that is, a direction perpendicular to the length direction of the GIP input signal line region  365 . 
     The GIP output signal line region  367  may include a gate line GL. For example, the GIP output signal line region  367  may include a signal line electrically connected to separate gate lines GL 1 , GL 2 , and GL 3  as shown in  FIG. 40 . 
     First, in one embodiment of the present disclosure, a line for applying the VSS voltage is disposed in the display region as in the other embodiment as illustrated above. Thus, the non-transparent thick line for applying the VSS voltage does not need to be disposed in an upper portion of the GIP circuit region. Thus, the transparent bezel in which the GIP region is used as the transmissive region may be implemented. 
     Specifically, the first VSS voltage line  321  and the second VSS voltage line  322  may be disposed in the non-display region while the display region is interposed therebetween. The VSS voltage connection line  323  may electrically connect the first VSS voltage line  321  and the second VSS voltage line  322  to each other. 
     Further, the first VDD voltage line  331  and the second VDD voltage line  332  may be disposed in the non-display region while the display region is interposed therebetween. The VDD voltage connection line  333  may electrically connect the first VDD voltage line  331  and the second VDD voltage line  332  to each other. 
     That is, each of the VSS voltage connection line  323  and the VDD voltage connection line  333  extends across the display region. Thus, the thick connection line covering the GIP circuit region, in particular, the VSS voltage connection line may be removed from the bezel, such that the GIP circuit region may act as a transmissive region. 
     Further, a region occupied by the GIP circuit region  360  may be further expanded as much as an area where the VSS voltage lines are omitted in the bezel. Thus, the GIP block  361  and the GIP input signal line regions  365  constituting the GIP circuit region  360  may not be arranged densely. Thus, the transmissive region in the GIP circuit region  360  may be secured as much as possible. 
     In an embodiment of the present disclosure, the GIP input signal line region  365  and the GIP output signal line region  367  may constitute different layers in order to secure the transmissive region in the GIP circuit region  360  as much as possible. 
     In order to secure the transmissive region in the GIP circuit region  360  as much as possible, the components such as the GIP block  361  and the GIP input signal line regions  365  may not be arranged as closely as possible. Thus, the transmissive region may be further secured when the GIP output signal line region  367  and the GIP input signal line region  365  constitute different layers. 
     Specifically, the GIP output signal line region  367  is formed in a different layer from a layer of the GIP input signal line region  365 . Thus, the GIP output signal line region  367  and the GIP input signal line region  365  may at least partially overlap with each other. 
     In this way, a region in which the GIP output signal line region  367  and the GIP input signal line region  365  partially at least overlap with each other may be present. Thus, the transmissive region may be larger than when the GIP output signal line region  367  and the GIP input signal line region  365  constitute the same layer. 
     In one example, the GIP block  361  and the GIP input signal line region  365  may be alternately arranged with each other. 
     A plurality of GIP blocks  361  may include a first GIP block  361   a , a second GIP block  361   b , and a third GIP block  361   c . The first GIP block  361   a , the second GIP block  361   b  and the third GIP block  361   c  are spaced apart from each other. The GIP input signal line region  365  may be disposed between the first GIP block  361   a  and the second GIP block  361   b  and between the second GIP block  361   b  and the third GIP block  361   c.    
     The first GIP block  361   a  may be a first scan signal circuit that applies a first scan signal. The second GIP block  361   b  may be a light-emitting circuit that applies a light-emitting EM signal. The third GIP block  361   c  may be a second scan signal circuit that applies a second scan signal. 
     In one embodiment of the present disclosure, the GIP output signal line region  367  and the GIP block  361  may constitute different layers respectively and may at least partially overlap with each other. 
     For example, the GIP output signal line region  367  may include a first GIP output signal line  367   a , a second GIP output signal line  367   b  and a third GIP output signal line  367   c.    
     The first GIP output signal line  367   a  may connect the first GIP block  361   a  and the display region DA with each other. The second GIP output signal line  367   b  may connect the second GIP block  361   b  and the display region DA with each other. The third GIP output signal line  367   c  may connect the third GIP block  361   c  and the display region DA with each other. 
     Further, in another embodiment of the present disclosure, as shown in  FIG. 40 , the first GIP output signal line  367   a  and the display region DA may be electrically connected to each other via a first gate line GL 1 . The second GIP output signal line  367   b  and the display region DA may be electrically connected to each other via a second gate line GL 2 . The third GIP output signal line  367   c  and the display region DA may be electrically connected to each other via a third gate line GL 3 . 
     Specifically, as shown in  FIG. 39 , the first GIP output signal line  367   a  may at least partially overlap with the second GIP block  361   b  and the third GIP block  361   c.    
     Further, the second GIP output signal line  367   b  may at least partially overlap with the third GIP block  361   c.    
     The GIP output signal line region  367  is disposed in a different layer from a layer of the GIP block  361  and at least partially overlaps with the GIP block  361 . Thus, a larger transmissive region may be secured compared to a case when the GIP output signal line region  367  and the GIP block  361  constitute the same layer, that is, are formed in the same layer. 
     Between the GIP input signal line region  365  and the GIP block  361 , at least one GIP input signal connection line  366  may be disposed to electrically connect the GIP input signal line region  365  and the GIP block  361  with each other. 
     In this case, the GIP input signal connection line  366  may be formed in a different layer from a layer of the GIP input signal line region  365  and a layer of the GIP output signal line region  367 . 
     Specifically, the GIP input signal connection line  366  may be made of the same material as the gate electrode constituting the driving thin-film transistor of the display region DA. The GIP input signal connection line  366  may be formed in the same layer as a layer of the gate electrode constituting the driving thin-film transistor of the display region DA. 
     The GIP input signal connection line  366  may extend in the horizontal direction of the display region DA, and in parallel to the GIP output signal line. 
     At least one first test line  375   a  may be disposed outside the first GIP block  361   a . At least one second test line  375   b  may be disposed between the third GIP block  361   c  and the display region DA. 
     For example, the first test line  375   a  may act as a lighting test line that inspects defects in the transparent display panel by supplying a lighting test signal to multiple data lines before a module process after the transparent display panel is manufactured. 
     The second test line  375   b  may act as a gate output test line capable of monitoring whether the gate output is properly output. 
     On at least a partial region of the second test line  375   b , the bank layer  231  may be formed. The bank layer  231  may be absent on the GIP circuit region. 
     According to the present disclosure, there is no need to place the non-transparent thick line for the application of VSS voltage in the bezel region, such that the bank layer  231  is not formed on the GIP circuit region. 
     When the bank layer  231  is not formed on the GIP circuit region, transmittance in the GIP region may be improved. 
     Further, due to material characteristic of the bank layer  231 , a yellowish phenomenon in which a yellowish color is displayed may be reduced or minimized. 
     However, the bank layer  231  may cover a partial region of the second test line  375   b . When the bank layer  231  is formed in the display region DA, this may be intended due to a process margin. In this connection, the bank layer  231  may be formed to cover a partial region of the second test line  375   b.    
     Therefore, the bank layer  231  may cover at least a partial region of the second test line  375   b . However, the bank layer  231  may not be formed on the GIP circuit region. 
     As described above, the GIP block of the transparent display panel according to an embodiment of the present disclosure may have a transmissive region TA of at least 40% or more. The GIP input signal line region may have a transmissive region TA of at least 50% or more. Thus, the bezel may have a transmissive region of a certain percentage or more. Thus, a transparent bezel may be implemented. 
     In this case, the transmissive region TA in the GIP block  361  may mean a region in which the GIP blocks  361   a ,  361   b , and  361   c  are not disposed. However, the present disclosure is not limited thereto. The transmissive region TA may be present in the GIP blocks  361   a ,  361   b , and  361   c.    
     However, in an embodiment of the present disclosure, a maximum transmissive region TA may be secured via arrangement of the GIP blocks  361   a ,  361   b , and  361   c  such that each of the GIP blocks  361   a ,  361   b , and  361   c  defines only a single block. 
     In one example, the transmissive region TA in the GIP input signal line region  365  may mean a region in which a plurality of GIP input signal lines  365   a  are not disposed.  FIG. 41  to  FIG. 43  show cross-sectional views of R-R′, S-S′, and T-T′ regions in  FIG. 40 , respectively. 
     Specifically,  FIG. 41  shows connection between the first GIP block and the first GIP output signal line.  FIG. 42  shows connection between the second GIP block and the second GIP output signal line.  FIG. 43  shows connection between the third GIP block and the third GIP output signal line. 
     The buffer layer  201  may be formed on the first substrate  200 . On the buffer layer  201 , the first GIP block  361   a , the second GIP block  361   b , and the third GIP block  361   c  may be arranged and may be spaced apart from each other and may be formed in the non-display region. 
     Further, the gate insulating layer  213 , the first interlayer insulating layer  215  and the second interlayer insulating layer  216  may be sequentially stacked on the buffer layer  201  in their order. The gate insulating layer  213 , the first interlayer insulating layer  215  and the second interlayer insulating layer  216  may be disposed between transistors included in the first GIP block  361   a , the second GIP block  361   b  and the third GIP block  361   c , respectively. 
     At least one first test line  375   a , at least one GIP input signal line  365   a  and at least one second test line  375   b  may be formed on the second interlayer insulating layer  216 . 
     The first test line  375   a , the GIP input signal line  365   a , and the second test line  375   b  may be made of the same material as the source electrode and the drain electrode of the display region DA and may be formed in the same layer as a layer of the source electrode and the drain electrode of the display region DA. 
     The GIP input signal line region  365  including one or more GIP input signal lines  365   a  may be disposed between the GIP blocks  361   a  and  361   b , and between the GIP blocks  361   b  and  361   c.    
     A spacing d between adjacent GIP input signal lines  365   a  among the GIP input signal lines  365   a  constituting one GIP input signal line region  365  may be larger than a width W 4  of one GIP input signal line  365   a.    
     When the spacing d between the adjacent GIP input signal lines is larger than the width W 4  of one GIP input signal line  365   a , the GIP input signal lines  365   a  may not be densely arranged with each other. Thus, a transmissive region in the GIP input signal line region  360  may be further secured. 
     A first planarization layer  219   a  may be formed on the first test line  375   a , the GIP input signal line  365   a , the second test line  375   b , and the GIP blocks  361   a ,  361   b , and  361   c . Thus, the GIP output signal lines  367   a ,  367   b , and  367   c  may be formed on the first planarization layer  219   a.    
     A second planarization layer  219   b  may be formed on the GIP output signal lines  367   a ,  367   b , and  367   c . That is, the first planarization layer  219   a  may be disposed between the GIP input signal line region  365  and the GIP output signal line region  367 . The second planarization layer  219   b  may be disposed on the GIP output signal line region  367 . Thus, the GIP input signal line  365   a  and the GIP output signal lines  367   a ,  367   b , and  367   c  may constitute different layers. 
     On the second planarization layer  219   b , the organic light-emitting element  220  including the first electrode  221 , the organic light-emitting layer  223 , and the second electrode  225  may be disposed. 
     In this case, in a boundary region of the display region DA, the bank layer  231 , the organic light-emitting layer  223  and the second electrode  225  may cover at least a partial region of the second test line  375   b  in consideration of a process margin. 
     On the second electrode  225 , the encapsulating layer  250  may be formed. The adhesive layer  251  such as OCA (optical clear adhesive) may be formed on the encapsulating layer  250 . Onto the adhesive layer  251 , the second substrate  270  as a top substrate may be bonded. 
     The present disclosure may provide following aspects and implementations thereof. 
     A first aspect of the present disclosure provides a transparent display panel comprising: a substrate including a display region and a non-display region surrounding the display region; and a GIP (gate in panel) circuit region disposed on substrate and disposed in the non-display region thereof, wherein the GIP circuit region includes: at least one GIP block; at least one GIP input signal line region; at least one GIP output signal line region; and at least one GIP input signal connection line for electrically connecting the GIP input signal line region and the GIP block to each other, wherein the GIP input signal line region and the GIP output signal line region constitute different layers, respectively. 
     In one implementation of the first aspect, the GIP input signal line region transmits a gate control signal to the GIP block, wherein the GIP output signal line region transmits the gate control signal from the GIP block to the display region. 
     In one implementation of the first aspect, a layer of the GIP input signal connection line is different from the layer of the GIP input signal line region and the layer of the GIP output signal line region. 
     In one implementation of the first aspect, a first planarization layer is disposed between the GIP input signal line region and the GIP output signal line region, wherein a second planarization layer is disposed on the GIP output signal line region. 
     In one implementation of the first aspect, the GIP input signal line region includes at least one GIP input signal line extending in a vertical direction of the display region, wherein the GIP output signal line region includes at least one GIP output signal line extending in a horizontal direction of the display region, wherein the GIP input signal connection line extends in a parallel manner to a length direction of the GIP output signal line. 
     In one implementation of the first aspect, the GIP block and the GIP input signal line region are alternately arranged with each other. 
     In one implementation of the first aspect, the GIP block includes a first GIP block, a second GIP block, and a third GIP block, wherein the first GIP block, the second GIP block and the third GIP block are arranged and are spaced apart from each other, wherein the GIP input signal line region is disposed between the first GIP block and the second GIP block, and between the second GIP block and the third GIP block. 
     In one implementation of the first aspect, the first GIP block applies the first scan signal, wherein the second GIP block applies a light-emitting signal, and wherein the third GIP block applies a second scan signal. 
     In one implementation of the first aspect, at least one first test line is disposed outside of the first GIP block, wherein at least one second test line is disposed between the third GIP block and the display region. 
     In one implementation of the first aspect, the first test line is embodied as a lighting test line, wherein the second test line is embodied as a gate output test line. 
     In one implementation of the first aspect, a bank layer is disposed on at least a partial region of the second test pattern, wherein the bank layer is absent on the GIP circuit region. 
     In one implementation of the first aspect, the GIP output signal line region includes a first GIP output signal line, a second GIP output signal line, and a third GIP output signal line, wherein the first GIP output signal line connects the first GIP block and the display region to each other, wherein the second GIP output signal line connects the second GIP block and the display region to each other, wherein the third GIP output signal line connects the third GIP block to the display region to each other. 
     In one implementation of the first aspect, the first GIP output signal line and the display region are electrically connected to each other via a first gate line, wherein the second GIP output signal line and the display region are electrically connected to each other via a second gate line, wherein the third GIP output signal line and the display region are electrically connected to each other via a third gate line. 
     In one implementation of the first aspect, a spacing between adjacent the GIP input signal lines is larger than a width of one of the GIP input signal lines. 
     In one implementation of the first aspect, a percentage of a transmission area of the GIP block relative to a total area thereof is at least 40%. 
     In one implementation of the first aspect, a percentage of a transmission area of the GIP input signal line region relative to a total area thereof is at least 50%. 
     In one implementation of the first aspect, the display region includes a plurality of light-emitting regions and a plurality of transmissive regions, wherein a plurality of line regions are disposed on the substrate and extend across the display region, wherein at least one of the line regions includes a VSS voltage connection line. 
     In one implementation of the first aspect, each of the line regions includes at least one data line and at least one reference voltage connection line, wherein a layer of the VSS voltage connection line is different from a layer of the data line and the reference voltage connection line. 
     In one implementation of the first aspect, the VSS voltage connection line at least partially overlaps at least two of the at least one data line and the at least one reference voltage connection line. 
     In one implementation of the first aspect, a first driving thin-film transistor is disposed on one side to a single line region and is configured to drive a first light-emitting region disposed on one side to the single line region and at least partially overlapping the single line region, wherein a second driving thin-film transistor is disposed on the other side to the single line region and is configured to drive a second light-emitting region disposed between the single line region and a further line region adjacent thereto. For example, the first driving thin-film transistor is disposed adjacent to a first side of a first line region and the second thin-film transistor is disposed adjacent to a second side of the first line region that is opposite the first side. 
     In one implementation of the first aspect, alternately-arranged adjacent line regions include alternately-arranged adjacent VSS and VDD voltage connection lines, respectively, wherein the VSS voltage connection line and the VDD voltage connection line are alternately arranged with each other while the transmissive region is interposed therebetween. 
     In one implementation of the first aspect, the light-emitting regions includes a first color light-emitting region, a second color light-emitting region, and a third color light-emitting region, wherein each of the second color light-emitting region and the third color light-emitting region is disposed on a corresponding line region, wherein the first color light-emitting region is disposed between the second color light-emitting region and the third color light-emitting region, wherein each of the VSS voltage connection line and the VDD voltage connection line at least partially overlaps the second color light-emitting region or the third color light-emitting region, wherein colors of two light-emitting regions arranged in the same row and at least partially overlapping the VSS voltage connection line and the VDD voltage connection line respectively are different from each other. 
     In one implementation of the first aspect, a plurality of pixel circuit regions are disposed on the substrate, and are electrically connected to the light-emitting regions respectively to drive the light-emitting regions, wherein the pixel circuit regions includes a first color pixel circuit region electrically connected to the first color light-emitting region, a second color pixel circuit region electrically connected to the second color light-emitting region, and a third color pixel circuit region electrically connected to the third color light-emitting region, wherein the first color pixel circuit region is arranged symmetrically to the second color pixel circuit region or the third color pixel circuit region around the line region interposed therebetween. 
     In one implementation of the first aspect, a driving thin-film transistor of the first color pixel circuit region at least partially overlaps a pixel electrode of the second or third color light-emitting region disposed on a right side to the first color pixel circuit region, wherein a driving thin-film transistor of the second color pixel circuit region at least partially overlaps the pixel electrode of the second color light-emitting region, wherein a driving thin-film transistor of the third color pixel circuit region at least partially overlaps the pixel electrode of the third color light-emitting region. 
     In one implementation of the first aspect, the light-emitting regions include a first color light-emitting region, a second color light-emitting region, and a third color light-emitting region, wherein each of the second color light-emitting region and the third color light-emitting region is disposed on a corresponding line region, wherein the first color light-emitting region is disposed between the second color light-emitting region and the third color light-emitting region, wherein each color filter corresponding to a color of each light-emitting region color is disposed on each light-emitting region, wherein a black matrix is placed between adjacent color filters. 
     In one implementation of the first aspect, the black matrix at least partially overlaps the line region placed between two transmissive regions adjacent to each other. 
     A second aspect of the present disclosure provides a transparent display device including the transparent display panel as defined above, a data driver supplying a data voltage to the transparent display panel, a gate driver supplying a scan signal to the transparent display panel, and a timing controller that controls the gate driver and the data driver. 
     As described above, the present disclosure is described with reference to the drawings. However, the present disclosure is not limited by the embodiments and drawings disclosed in the present specification. It will be apparent that various modifications may be made thereto by those skilled in the art within the scope of the present disclosure. Furthermore, although the effect resulting from the features of the present disclosure has not been explicitly described in the description of the embodiments of the present disclosure, it is obvious that a predictable effect resulting from the features of the present disclosure should be recognized. 
     The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.